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+Project Gutenberg (https://www.gutenberg.org) public repository for
+eBook #64601 (https://www.gutenberg.org/ebooks/64601)
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-The Project Gutenberg eBook of Elementary Botany, by George Francis
-Atkinson
-
-This eBook is for the use of anyone anywhere in the United States and
-most other parts of the world at no cost and with almost no restrictions
-whatsoever. You may copy it, give it away or re-use it under the terms
-of the Project Gutenberg License included with this eBook or online at
-www.gutenberg.org. If you are not located in the United States, you
-will have to check the laws of the country where you are located before
-using this eBook.
-
-Title: Elementary Botany
-
-Author: George Francis Atkinson
-
-Release Date: February 20, 2021 [eBook #64601]
-
-Language: English
-
-Character set encoding: UTF-8
-
-Produced by: Sonya Schermann and the Online Distributed Proofreading Team
-             at https://www.pgdp.net (This file was produced from images
-             generously made available by The Internet Archive)
-
-*** START OF THE PROJECT GUTENBERG EBOOK ELEMENTARY BOTANY ***
-
-
-
-
-Transcriber’s Notes:
-
-  Underscores “_” before and after a word or phrase indicate _italics_
-    in the original text.
-  Equal signs “=” before and after a word or phrase indicate =bold=
-    in the original text.
-  Small capitals have been converted to SOLID capitals.
-  Illustrations have been moved so they do not break up paragraphs.
-  Footnotes have been moved to the end of the chapter in which they
-    occur.
-  Typographical errors have been silently corrected.
-
-
-
-
-[Illustration: CYCAS REVOLUTA (see page 311). (_Frontispiece._)]
-
-
-
-
-                           ELEMENTARY BOTANY
-
-                                  BY
-                    GEORGE FRANCIS ATKINSON, PH.B.
-              _Professor of Botany in Cornell University_
-
-                       _THIRD EDITION, REVISED_
-
-                            [Illustration]
-
-                               NEW YORK
-                        HENRY HOLT AND COMPANY
-                                 1905
-
-                         Copyright, 1898, 1905
-                                  BY
-                        HENRY HOLT AND COMPANY
-
-                  ROBERT DRUMMOND, PRINTER, NEW YORK
-
-
-
-
-PREFACE.
-
-
-The present book is the result of a revision and elaboration of the
-author’s “Elementary Botany,” New York, 1898. The general plan of the
-parts on physiology and general morphology remains unchanged. A number
-of the chapters in the physiological part are practically untouched,
-while others are thoroughly revised and considerable new matter is
-added, especially on the subjects of nutrition and digestion. The
-principal chapters on general morphology are unchanged or only slightly
-modified, the greatest change being in a revision of the subject of
-the morphology of fertilization in the gymnosperms and angiosperms in
-order to bring this subject abreast of the discoveries of the past few
-years. One of the greatest modifications has been in the addition of
-chapters on the classification of the algæ and fungi with studies of
-additional examples for the benefit of those schools where the time
-allowed for the first year’s course makes desirable the examination of
-a broader range of representative plants. The classification is also
-carried out with greater definiteness, so that the regular sequence
-of classes, orders, and families is given at the close of each of the
-subkingdoms. Thus all the classes, all the orders (except a few in the
-algæ), and many of the families, are given for the algæ, fungi, mosses,
-liverworts, pteridophytes, gymnosperms, and angiosperms.
-
-But by far the greatest improvement has been in the complete
-reorganization, rewriting, and elaboration of the part dealing with
-ecology, which has been made possible by studies of the past few years,
-so that the subject can be presented in a more logical and coherent
-form. As a result the subject-matter of the book falls naturally into
-three parts, which may be passed in review as follows:
-
-Part I. _Physiology._ This deals with the life processes of plants,
-as absorption, transpiration, conduction, photosynthesis, nutrition,
-assimilation, digestion, respiration, growth, and irritability. Since
-protoplasm is fundamental to all the life work of the plant, this
-subject is dealt with first, and the student is led through the study
-of, and experimentation with, the simpler as well as some of the higher
-plants, to a general understanding of protoplasm and the special way in
-which it enables the plant to carry on its work and to adjust itself to
-the conditions of its existence. This study also serves the purpose of
-familiarizing the pupil with some of the lower and unfamiliar plants.
-
-Some teachers will prefer to begin the study with general morphology
-and classification, thus studying first the representatives of the
-great groups of plants, and others will prefer to dwell first on the
-ecological aspects of vegetation. This can be done in the use of this
-book by beginning with Part II or with Part III.
-
-But the author believes that morphology can best be comprehended after
-a general study of life processes and functions of the different parts
-of plants, including in this study some of the lower forms of plant
-life where some of these processes can more readily be observed. The
-pupil is then prepared for a more intelligent consideration of general
-and comparative morphology and relationships. Even more important is
-a first study of physiology before taking up the subject of ecology.
-The great value to be derived from a study of plants in their relation
-to environment lies in the ability to interpret the different states,
-conditions, behavior, and associations of the plant, and for this
-physiology is indispensable. It is true that a considerable measure
-of success can be obtained by a good teacher in beginning with either
-subject, but the writer believes that measure of success would be
-greater if the subjects were taken up in the order presented here.
-
-Part II. _Morphology and life history of representative plants._ This
-includes a rather careful study of representative examples among the
-algæ, fungi, liverworts, mosses, ferns and their allies, gymnosperms
-and angiosperms, with especial emphasis on the form of plant parts,
-and a comparison of them in the different groups, with a comparative
-study of development, reproduction, and fertilization, rounding out
-the work with a study of life histories and noting progression and
-retrogression of certain organs and phases in proceeding from the
-lower to the higher plants. Thus, in the algæ a first critical study
-is made of four examples which illustrate in a marked way progressive
-stages of the plant body, sexual organs, and reproduction. Additional
-examples are then studied for the purpose of acquiring a knowledge of
-variations from these types and to give a broader basis for the brief
-consideration of general relationships and classification.
-
-A similar plan is followed in the other great groups. The processes of
-fertilization and reproduction can be most easily observed in the lower
-plants like the algæ and fungi, and this is an additional argument in
-favor of giving emphasis to these forms of plant life as well as the
-advantage of proceeding logically from simpler to more complex forms.
-Having also learned some of these plants in our study of physiology,
-we are following another recognized rule of pedagogy, i.e., proceeding
-from known objects to unknown structures and processes. Through
-the study of the organs of reproduction of the lower plants and by
-general comparative morphology we have come to an understanding of the
-morphology of the parts of the flower, and of the true sexual organs
-of the seed plants, and no student can hope to properly interpret the
-significance of the flower, or the sexual organs of the seed plants who
-neglects a careful study of the general morphology of the lower plants.
-
-Part III. _Plant members in relation to environment._ This part deals
-with the organization of the plant body as a whole in its relation to
-environment, the organization of plant tissues with a discussion of
-the principal tissues and a descriptive synopsis of the same. This is
-followed by a complete study from a biological standpoint of the
-different members of the plant, their special function and their
-special relations to environment. The stem, root, leaf, flower, etc.,
-are carefully examined and their ecological relations pointed out. This
-together with the study of physiology and representatives in the groups
-of plants forms a thorough basis for pure plant ecology, or the special
-study of vegetation in its relation to environment.
-
-There is a study of the factors of environment or ecological factors,
-which in general are grouped under the physical, climatic, and biotic
-factors. This is followed by an analysis of vegetation forms and
-structures, plant formations and societies. Then in order are treated
-briefly forest societies, prairie societies, desert societies, arctic
-and alpine societies, aquatic societies, and the special societies of
-sandy, rocky, and marshy places.
-
-_Acknowledgments._ The author wishes to express his gratefulness to
-all those who have given aid in the preparation of this work, or of
-the earlier editions of Elementary Botany; to his associates, Dr.
-E. J. Durand, Dr. K. M. Wiegand, and Professor W. W. Rowlee, of the
-botanical department, and to Professor B. M. Duggar of the University
-of Missouri, Professor J. C. Arthur of Purdue University, and Professor
-W. F. Ganong of Smith College, for reading one or more portions of the
-text; as well as to all those who have contributed illustrations.
-
-_Illustrations._ The large majority of the illustrations are new
-(or are the same as those used in earlier editions of the author’s
-Elementary Botany) and were made with special reference to the method
-of treatment followed in the text. Many of the photographs were made
-by the author. Others were contributed by Professor Rowlee of Cornell
-University; Mr. John Gifford of New Jersey; Professor B. M. Duggar,
-University of Missouri; Professor C. E. Bessey, University of Nebraska;
-Dr. M. B. Howe, New York Botanical Garden; Mr. Gifford Pinchot, Chief
-of the Bureau of Forestry; Mr. B. T. Galloway, Chief of the Bureau of
-Plant Industry; Professor Tuomey of Yale University; and Mr. E. H.
-Harriman, who through Dr. C. H. Merriam of the National Museum allowed
-the use of several of his copyrighted photographs from Alaska. To those
-who have contributed drawings the author is indebted as follows: to
-Professor Margaret C. Ferguson, Wellesley College; Professor Bertha
-Stoneman of Huguenot College, South Africa; Mr. H. Hasselbring of
-Chicago; Dr. K. Miyake, formerly of Cornell University and now of
-Doshisha College, Japan; and Professors Ikeno and Hirase of the Tokio
-Imperial University. The author is also indebted to Ginn & Co., Boston,
-for the privilege to use from his “First Studies of Plant Life” the
-following figures: 28, 29, 46, 48, 49, 56, 62, 66, 67, 87, 102, 103,
-422-426, 429, 430, 438-440, 443, 444, 448, 449, 452, 472-475. A few
-others are acknowledged in the text.
-
-CORNELL UNIVERSITY, April, 1905.
-
-
-
-
-TABLE OF CONTENTS.
-
-
-    PART I. PHYSIOLOGY.
-
-                           CHAPTER I.                      PAGE
-    PROTOPLASM.                                               1
-
-                           CHAPTER II.
-    ABSORPTION, DIFFUSION, OSMOSE.                           13
-
-                           CHAPTER III.
-    HOW PLANTS OBTAIN WATER.                                 22
-
-                           CHAPTER IV.
-    TRANSPIRATION, OR THE LOSS OF WATER BY PLANTS.           35
-
-                           CHAPTER V.
-    PATH OF MOVEMENT OF WATER IN PLANTS.                     48
-
-                           CHAPTER VI.
-    MECHANICAL USES OF WATER.                                56
-
-                          CHAPTER VII.
-   STARCH AND SUGAR FORMATION.                               60
-      1. The Gases Concerned.                                60
-      2. Where Starch is Formed.                             64
-      3. Chlorophyll and the Formation of Starch.            67
-
-                          CHAPTER VIII.
-   STARCH AND SUGAR CONCLUDED; ANALYSIS OF PLANT SUBSTANCE.  73
-      1. Translocation of Starch.                            73
-      2. Sugar, and Digestion of Starch.                     75
-      3. Rough Analysis of Plant Substance.                  79
-
-                           CHAPTER IX.
-   HOW PLANTS OBTAIN THEIR FOOD, I.                          81
-      1. Sources of Plant Food.                              81
-      2. Parasites and Saprophytes.                          83
-      3. How Fungi Obtain their Food.                        86
-      4. Mycorhiza.                                          91
-      5. Nitrogen gatherers.                                 92
-      6. Lichens.                                            93
-
-                           CHAPTER X.
-   HOW PLANTS OBTAIN THEIR FOOD, II.                         97
-      Seedlings,                                             97
-      Digestion,                                            107
-      Assimilation                                          109
-
-                           CHAPTER XI.
-    RESPIRATION.                                            110
-
-                          CHAPTER XII.
-    GROWTH.                                                 118
-
-                          CHAPTER XIII.
-    IRRITABILITY.                                           125
-
-
-    PART II. MORPHOLOGY AND LIFE HISTORY OF REPRESENTATIVE PLANTS.
-
-                          CHAPTER XIV.
-    SPIROGYRA.                                              136
-
-                           CHAPTER XV.
-    VAUCHERIA.                                              142
-
-                          CHAPTER XVI.
-    ŒDOGONIUM.                                              147
-
-                          CHAPTER XVII.
-    COLEOCHÆTE.                                             153
-
-                         CHAPTER XVIII.
-    CLASSIFICATION AND ADDITIONAL STUDIES OF THE ALGÆ.      158
-
-                          CHAPTER XIX.
-    FUNGI: MUCOR AND SAPROLEGNIA.                           177
-
-                           CHAPTER XX.
-    FUNGI CONTINUED (“Rusts” Uredineæ).                     187
-
-                          CHAPTER XXI.
-    THE HIGHER FUNGI.                                       195
-
-                          CHAPTER XXII.
-    CLASSIFICATION OF THE FUNGI.                            213
-
-                         CHAPTER XXIII.
-    LIVERWORTS (Hepaticæ).                                  222
-      Riccia, 222
-      Marchantia.                                           226
-
-                          CHAPTER XXIV.
-    LIVERWORTS CONTINUED.                                   231
-      Sporogonium of Marchantia.                            231
-      Leafy-stemmed Liverworts.                             236
-      The Horned Liverworts.                                240
-      Classification of the Liverworts.                     242
-
-                          CHAPTER XXV.
-    MOSSES (Musci).                                         243
-      Classification of Mosses.                             248
-
-                          CHAPTER XXVI.
-    FERNS.                                                  251
-
-                         CHAPTER XXVII.
-    FERNS CONTINUED.                                        262
-      Gametophyte of Ferns.                                 262
-      Sporophyte.                                           268
-
-                         CHAPTER XXVIII.
-    DIMORPHISM OF FERNS.                                    273
-
-                          CHAPTER XXIX.
-    HORSETAILS.                                             280
-
-                          CHAPTER XXX.
-    CLUB MOSSES.                                            284
-
-                          CHAPTER XXXI.
-    QUILLWORTS (Isoetes).                                   289
-
-                         CHAPTER XXXII.
-    COMPARISON OF FERNS AND THEIR RELATIVES.                292
-      Classification of the Pteridophytes.                  295
-
-                         CHAPTER XXXIII.
-    GYMNOSPERMS.                                            297
-
-                         CHAPTER XXXIV.
-    FURTHER STUDIES ON GYMNOSPERMS.                         311
-
-                          CHAPTER XXXV.
-    MORPHOLOGY OF THE ANGIOSPERMS: TRILLIUM; DENTARIA.      318
-
-                         CHAPTER XXXVI.
-    GAMETOPHYTE AND SPOROPHYTE OF ANGIOSPERMS.              325
-
-                         CHAPTER XXXVII.
-    MORPHOLOGY OF THE NUCLEUS AND SIGNIFICANCE OF
-     GAMETOPHYTE AND SPOROPHYTE.                            340
-
-
-        PART III. PLANT MEMBERS IN RELATION TO ENVIRONMENT.
-
-                        CHAPTER XXXVIII.
-    THE ORGANIZATION OF THE PLANT.                          349
-        I. Organization of Plant Members.                   349
-       II. Organization of Plant Tissues.                   356
-
-                         CHAPTER XXXIX.
-    THE DIFFERENT TYPES OF STEMS.                           365
-        I. Erect Stems.                                     365
-       II. Creeping, Climbing, and Floating Stems.          369
-      III. Specialized Shoots and Shoots for Storage
-               of Food.                                     372
-       IV. Annual Growth and Winter Protection of
-               Shoots and Buds.                             374
-
-                         CHAPTER XL.
-    FOLIAGE LEAVES.                                         383
-        I. General Form and Arrangement of Leaves.          383
-       II. Protective Modifications of Leaves.              392
-      III. Protective Positions.                            395
-       IV. Relation of Leaves to Light.                     397
-        V. Leaf Patterns.                                   404
-
-                         CHAPTER XLI.
-    THE ROOT.                                               410
-        I. Function of Roots.                               410
-       II. Kinds of Roots.                                  415
-
-                         CHAPTER XLII.
-    THE FLORAL SHOOT.                                       419
-        I. The Parts of the Flower.                         419
-       II. Kinds of Flowers.                                421
-      III. Arrangement of Flowers, or Mode of
-               Inflorescence.                               426
-
-                         CHAPTER XLIII.
-    POLLINATION.                                            433
-
-                         CHAPTER XLIV.
-    THE FRUIT.                                              450
-        I. Parts of the Fruit.                              450
-       II. Indehiscent Fruits.                              451
-      III. Dehiscent Fruits.                                452
-       IV. Fleshy and Juicy Fruits.                         454
-        V. Reinforced, or Accessory, Fruits.                455
-       VI. Fruits of Gymnosperms.                           456
-      VII. “Fruit” of Ferns, Mosses, etc.                   457
-
-                         CHAPTER XLV.
-    SEED DISPERSAL.                                         458
-
-                         CHAPTER XLVI.
-    VEGETATION IN RELATION TO ENVIRONMENT.                  464
-
-                         CHAPTER XLVII.
-    CLASSIFICATION OF ANGIOSPERMS.                          487
-
-    INDEX.                                                  503
-
-
-
-
-PART I.
-
-PHYSIOLOGY.
-
-
-
-
-CHAPTER I.
-
-PROTOPLASM.[1]
-
-
-=1.= In the study of plant life and growth, it will be found
-convenient first to inquire into the nature of the substance which we
-call the living material of plants. For plant growth, as well as some
-of the other processes of plant life, are at bottom dependent on this
-living matter. This living matter is called in general _protoplasm_.
-
-=2.= In most cases protoplasm cannot be seen without the help of
-a microscope, and it will be necessary for us here to employ one if we
-wish to see protoplasm, and to satisfy ourselves by examination that
-the substance we are dealing with _is_ protoplasm.
-
-=3.= We shall find it convenient first to examine protoplasm
-in some of the simpler plants; plants which from their minute size
-and simple structure are so transparent that when examined with the
-microscope the interior can be seen.
-
-For our first study let us take a plant known as _spirogyra_, though
-there are a number of others which would serve the purpose quite as
-well, and may quite as easily be obtained for study.
-
-
-Protoplasm in spirogyra.
-
-=4. The plant spirogyra.=—This plant is found in the water of
-pools, ditches, ponds, or in streams of slow-running water. It is green
-in color, and occurs in loose mats, usually floating near the surface.
-The name “pond-scum” is sometimes given to this plant, along with
-others which are more or less closely related. It is an _alga_, and
-belongs to a group of plants known as _algæ_. If we lift a portion of
-it from the water, we see that the mat is made up of a great tangle of
-green silky threads. Each one of these threads is a plant, so that the
-number contained in one of these floating mats is very great.
-
-Let us place a bit of this thread tangle on a glass slip, and examine
-with the microscope and we will see certain things about the plant
-which are peculiar to it, and which enable us to distinguish it from
-other minute green water plants. We shall also wish to learn what these
-peculiar parts of the plant are, in order to demonstrate the protoplasm
-in the plant.[2]
-
-=5. Chlorophyll bands in spirogyra.=—We first observe the
-presence of bands; green in color, the edges of which are usually
-very irregularly notched. These bands course along in a spiral manner
-near the surface of the thread. There may be one or several of these
-spirals, according to the species which we happen to select for
-study. This green coloring matter of the band is _chlorophyll_, and
-this substance, which also occurs in the higher green plants, will
-be considered in a later chapter. At quite regular intervals in the
-chlorophyll band are small starch grains, grouped in a rounded mass
-enclosing a minute body, the _pyrenoid_, which is peculiar to many algæ.
-
-[Illustration: Fig. 1.
-
-Thread of spirogyra, showing long cells, chlorophyll band, nucleus,
-strands of protoplasm, and the granular wall layer of protoplasm.]
-
-=6. The spirogyra thread consists of cylindrical cells end to
-end.=—Another thing which attracts our attention, as we examine a
-thread of spirogyra under the microscope, is that the thread is made up
-of cylindrical segments or compartments placed end to end. We can see a
-distinct separating line between the ends. Each one of these segments
-or compartments of the thread is a _cell_, and the boundary wall is in
-the form of a cylinder with closed ends.
-
-=7. Protoplasm.=—Having distinguished these parts of the plant
-we can look for the protoplasm. It occurs within the cells. It is
-colorless (i.e., hyaline) and consequently requires close observation.
-Near the center of the cell can be seen a rather dense granular body
-of an elliptical or irregular form, with its long diameter transverse
-to the axis of the cell in some species; or triangular, or quadrate in
-others. This is the _nucleus_. Around the nucleus is a granular layer
-from which delicate threads of a shiny granular substance radiate in a
-starlike manner, and terminate in the chlorophyll band at one of the
-pyrenoids. A granular layer of the same substance lines the inside of
-the cell wall, and can be seen through the microscope if it is properly
-focussed. This granular substance in the cell is _protoplasm_.
-
-=8. Cell-sap in spirogyra.=—The greater part of the interior
-space of the cell, that between the radiating strands of protoplasm, is
-occupied by a watery fluid, the “cell-sap.”
-
-=9. Reaction of protoplasm to certain reagents.=—We can employ
-certain tests to demonstrate that this granular substance which we have
-seen is protoplasm, for it has been found, by repeated experiments with
-a great many kinds of plants, that protoplasm gives a definite reaction
-in response to treatment with certain substances called reagents. Let
-us mount a few threads of the spirogyra in a drop of a solution of
-iodine, and observe the results with the aid of the microscope. The
-iodine gives a yellowish-brown color to the protoplasm, and it can be
-more distinctly seen. The nucleus is also much more prominent since it
-colors deeply, and we can perceive within the nucleus one small rounded
-body, sometimes more, the _nucleolus_. The iodine here kills and stains
-the protoplasm. The protoplasm, however, in a living condition will
-resist for a time some other reagents, as we shall see if we attempt
-to stain it with a one per cent aqueous solution of a dye known as
-_eosin_. Let us mount a few living threads in such a solution of eosin,
-and after a time wash off the stain. The protoplasm remains uncolored.
-Now let us place these threads for a short time, two or three minutes,
-in strong alcohol, which kills the protoplasm. Then mount them in
-the eosin solution. The protoplasm now takes the eosin stain. After
-the protoplasm has been killed we note that the nucleus is no longer
-elliptical or angular in outline, but is rounded. The strands of
-protoplasm are no longer in tension as they were when alive.
-
-[Illustration: Fig. 2. Cell of spirogyra before treatment with iodine.]
-
-[Illustration: Fig. 3. Cell of spirogyra after treatment with alcohol
-and iodine.]
-
-=10.= Let us now take some fresh living threads and mount them in
-water. Place a small drop of dilute glycerine on the slip at one side
-of the cover glass, and with a bit of filter paper at the other side
-draw out the water. The glycerine will flow under the cover glass and
-come in contact with the spirogyra threads. Glycerine absorbs water
-promptly. Being in contact with the threads it draws water out of the
-cell cavity, thus causing the layer of protoplasm which lines the
-inside of the cell wall to collapse, and separate from the wall,
-drawing the chlorophyll band inward toward the center also. The wall
-layer of protoplasm can now be more distinctly seen and its granular
-character observed.
-
-We have thus employed three tests to demonstrate that this substance
-with which we are dealing shows the reactions which we know by
-experience to be given by protoplasm. We therefore conclude that this
-colorless and partly granular, slimy substance in the spirogyra cell
-is protoplasm, and that when we have performed these experiments, and
-noted carefully the results, we have _seen_ protoplasm.
-
-[Illustration: Fig. 4. Cell of spirogyra before treatment with
-glycerine.]
-
-[Illustration: Fig. 5. Cells of spirogyra after treatment with
-glycerine.]
-
-      =11. Earlier use of the term protoplasm.=—Early
-    students of the living matter in the cell considered it
-    to be alike in substance, but differing in density; so
-    the term protoplasm was applied to all of this living
-    matter. The nucleus was looked upon as simply a denser
-    portion of the protoplasm, and the nucleolus as a still
-    denser portion. Now it is believed that the nucleus
-    is a distinct substance, and a permanent organ of the
-    cell. The remaining portion of the protoplasm is now
-    usually spoken of as the _cytoplasm_.
-
-      In spirogyra then the cytoplasm in each cell consists
-    of a layer which lines the inside of the cell wall,
-    a nuclear layer, which surrounds the nucleus, and
-    radiating strands which connect the nucleus and wall
-    layers, thus suspending the nucleus near the center of
-    the cell. But it seems best in this elementary study to
-    use the term protoplasm in its general sense.
-
-
-Protoplasm in mucor.
-
-=12.= Let us now examine in a similar way another of the simple
-plants with the special object in view of demonstrating the protoplasm.
-For this purpose we may take one of the plants belonging to the group
-of _fungi_. These plants possess no chlorophyll. One of several species
-of _mucor_, a common mould, is readily obtainable, and very suitable
-for this study.[3]
-
-=13. Mycelium of mucor.=—A few days after sowing in some
-gelatinous culture medium we find slender, hyaline threads, which are
-very much branched, and, radiating from a central point, form circular
-colonies, if the plant has not been too thickly sown, as shown in
-fig. 6. These threads of the fungus form the _mycelium_. From these
-characters of the plant, which we can readily see without the aid of a
-microscope, we note how different it is from spirogyra.
-
-To examine for protoplasm let us lift carefully a thin block of
-gelatine containing the mucor threads, and mount it in water on a
-glass slip. Under the microscope we see only a small portion of the
-branched threads. In addition to the absence of chlorophyll, which we
-have already noted, we see that the mycelium is not divided at short
-intervals into cells, but appears like a delicate tube with branches,
-which become successively smaller toward the ends.
-
-=14. Appearance of the protoplasm.=—Within the tube-like thread
-now note the protoplasm. It has the same general appearance as that
-which we noted in spirogyra. It is slimy, or semi-fluid, partly
-hyaline, and partly granular, the granules consisting of minute
-particles (the _microsomes_). While in mucor the protoplasm has the
-same general appearance as in spirogyra, its arrangement is very
-different. In the first place it is plainly continuous throughout the
-tube. We do not see the prominent radiations of strands around a large
-nucleus, but still the protoplasm does not fill the interior of the
-threads. Here and there are rounded clear spaces termed _vacuoles_,
-which are filled with the watery fluid, cell-sap. The nuclei in mucor
-are very minute, and cannot be seen except after careful treatment with
-special reagents.
-
-[Illustration: Fig. 6. Colonies of mucor.]
-
-=15. Movement of the protoplasm in mucor.=—While examining the
-protoplasm in mucor we are likely to note streaming movements. Often a
-current is seen flowing slowly down one side of the thread, and another
-flowing back on the other side, or it may all stream along in the same
-direction.
-
-=16. Test for protoplasm.=—Now let us treat the threads with
-a solution of iodine. The yellowish-brown color appears which is
-characteristic of protoplasm when subject to this reagent. If we
-attempt to stain the living protoplasm with a one per cent aqueous
-solution of eosin it resists it for a time, but if we first kill the
-protoplasm with strong alcohol, it reacts quickly to the application of
-the eosin. If we treat the living threads with glycerine the protoplasm
-is contracted away from the wall, as we found to be the case with
-spirogyra. While the color, form and structure of the plant mucor is
-different from spirogyra, and the arrangement of the protoplasm within
-the plant is also quite different, the reactions when treated by
-certain reagents are the same. We are justified then in concluding that
-the two plants possess in common a substance which we call protoplasm.
-
-[Illustration: Fig. 7. Thread of mucor, showing protoplasm and
-vacuoles.]
-
-
-Protoplasm in nitella.
-
-=17.= One of the most interesting plants for the study of one
-remarkable peculiarity of protoplasm is _Nitella_. This plant belongs
-to a small group known as stoneworts. They possess chlorophyll, and,
-while they are still quite simple as compared with the higher plants,
-they are much higher in the scale than spirogyra or mucor.
-
-=18. Form of nitella.=—A common species of nitella is _Nitella
-flexilis_. It grows in quiet pools of water. The plant consists of a
-main axis, in the form of a cylinder. At quite regular intervals are
-whorls of several smaller thread-like outgrowths, which, because of
-their position, are termed “leaves,” though they are not true leaves.
-These are branched in a characteristic fashion at the tip. The main
-axis also branches, these branches arising in the axil of a whorl,
-usually singly. The portions of the axis where the whorls arise are the
-_nodes_. Each node is made up of a number of small cells definitely
-arranged. The portion of the axis between two adjacent whorls is an
-internode. These internodes are peculiar. They consist of but a single
-“cell,” and are cylindrical, with closed ends. They are sometimes 5-10
-cm. long.
-
-[Illustration: Fig. 8. Portion of plant nitella.]
-
-=19. Internode of nitella.=—For the study of an internode of
-nitella, a small one, near the end, or the ends of one of the “leaves”
-is best suited, since it is more transparent. A small portion of the
-plant should be placed on the glass slip in water with the cover glass
-over a tuft of the branches near the growing end. Examined with the
-microscope the green chlorophyll bodies, which form oval or oblong
-discs, are seen to be very numerous. They lie quite closely side by
-side and form in perfect rows along the inner surface of the wall.
-One peculiar feature of the arrangement of the chlorophyll bodies is
-that there are two lines, extending from one end of the internode to
-the other on opposite sides, where the chlorophyll bodies are wanting.
-These are known as neutral lines. They run parallel with the axis of
-the internode, or in a more or less spiral manner as shown in fig. 9.
-
-=20. Cyclosis in nitella.=—The chlorophyll bodies are stationary
-on the inner surface of the wall, but if the microscope be properly
-focussed just beneath this layer we notice a rotary motion of particles
-in the protoplasm. There are small granules and quite large masses of
-granular matter which glide slowly along in one direction on a given
-side of the neutral line. If now we examine the protoplasm on the other
-side of the neutral line, we see that the movement is in the opposite
-direction. If we examine this movement at the end of an internode
-the particles are seen to glide around the end from one side of the
-neutral line to the other. So that when conditions are favorable, such
-as temperature, healthy state of the plant, etc., this gliding of the
-particles or apparent streaming of the protoplasm down one side of
-the “cell,” and back upon the other, continues in an uninterrupted
-rotation, or _cyclosis_. There are many nuclei in an internode of
-nitella, and they move also.
-
-=21. Test for protoplasm.=—If we treat the plant with a solution
-of iodine we get the same reaction as in the case of spirogyra and
-mucor. The protoplasm becomes yellowish-brown.
-
-[Illustration: Fig. 9. Cyclosis in nitella.]
-
-=22. Protoplasm in one of the higher plants.=—We now wish to
-examine, and test for, protoplasm in one of the higher plants. Young
-or growing parts of any one of various plants—the petioles of young
-leaves, or young stems of growing plants—are suitable for study.
-Tissue from the pith of corn (Zea mays) in young shoots just back of
-the growing point or quite near the joints of older but growing corn
-stalks furnishes excellent material.
-
-If we should place part of the stem of this plant under the microscope
-we should find it too opaque for observation of the interior of the
-cells. This is one striking difference which we note as we pass from
-the low and simple plants to the higher and more complex ones; not
-only in general is there an increase of size, but also in general an
-increase in thickness of the parts. The cells, instead of lying end to
-end or side by side, are massed together so that the parts are quite
-opaque. In order to study the interior of the plant we have selected
-it must be cut into such thin layers that the light will pass readily
-through them.
-
-For this purpose we section the tissue selected by making with a razor,
-or other very sharp knife, very thin slices of it. These are mounted in
-water in the usual way for microscopic study. In this section we notice
-that the cells are polygonal in form. This is brought about by mutual
-pressure of all the cells. The granular protoplasm is seen to form a
-layer just inside the wall, which is connected with the nuclear layer
-by radiating strands of the same substance. The nucleus does not always
-lie at the middle of the cell, but often is near one side. If we now
-apply an alcohol solution of iodine the characteristic yellowish-brown
-color appears. So we conclude here also that this substance is
-identical with the living matter in the other very different plants
-which we have studied.
-
-=23. Movement of protoplasm in the higher plants.=—Certain
-parts of the higher plants are suitable objects for the study of the
-so-called streaming movement of protoplasm, especially the delicate
-hairs, or thread-like outgrowths, such as the silk of corn, or the
-delicate staminal hairs of some plants, like those of the common
-spiderwort, tradescantia, or of the tradescantias grown for ornament in
-greenhouses and plant conservatories.
-
-Sometimes even in the living cells of the corn plant which we have just
-studied, slow streaming or gliding movements of the granules are seen
-along the strands of protoplasm where they radiate from the nucleus.
-See note at close of this chapter.
-
-=24. Movement of protoplasm in cells of the staminal hair of
-“spiderwort.”=—A cell of one of these hairs from a stamen of a
-tradescantia grown in glass houses is shown in fig. 10. The nucleus is
-quite prominent, and its location in the cell varies considerably in
-different cells and at different times. There is a layer of protoplasm
-all around the nucleus, and from this the strands of protoplasm extend
-outward to the wall layer. The large spaces between the strands are, as
-we have found in other cases, filled with the cell-sap.
-
-[Illustration: Fig. 10. Cell from stamen hair of tradescantia showing
-movement of the protoplasm.]
-
-      An entire stamen, or a portion of the stamen, having
-    several hairs attached, should be carefully mounted
-    in water. Care should be taken that the room be not
-    cold, and if the weather is cold the water in which
-    the preparation is mounted should be warm. With these
-    precautions there should be little difficulty in
-    observing the streaming movement.
-
-The movement is detected by observing the gliding of the granules.
-These move down one of the strands from the nucleus along the wall
-layer, and in towards the nucleus in another strand. After a little the
-direction of the movement in any one portion may be reversed.
-
-=25. Cold retards the movement.=—While the protoplasm is moving,
-if we rest the glass slip on a block of ice, the movement will become
-slower, or will cease altogether. Then if we warm the slip gently, the
-movement becomes normal again. We may now apply here the usual tests
-for protoplasm. The result is the same as in the former cases.
-
-=26. Protoplasm occurs in the living parts of all plants.=—In
-these plants representing such widely different groups, we find a
-substance which is essentially alike in all. Though its arrangement
-in the cell or plant body may differ in the different plants or in
-different parts of the same plant, its general appearance is the same.
-Though in the different plants it presents, while alive, varying
-phenomena, as regards mobility, yet when killed and subjected to
-well known reagents the reaction is in general identical. Knowing
-by the experience of various investigators that protoplasm exhibits
-these reactions under given conditions, we have demonstrated to
-our satisfaction that we have seen protoplasm in the simple alga,
-spirogyra, in the common mould, mucor, in the more complex stonewort,
-nitella, and in the cells of tissues of the highest plants.
-
-=27.= By this simple process of induction of these facts
-concerning this substance in these different plants, we have learned an
-important method in science study. Though these facts and deductions
-are well known, the repetition of the methods by which they are
-obtained on the part of each student helps to form habits of scientific
-carefulness and patience, and trains the mind to logical processes in
-the search for knowledge.
-
-=28.= While we have by no means exhausted the study of protoplasm,
-we can, from this study, draw certain conclusions as to its occurrence
-and appearance in plants. Protoplasm is found in the living and growing
-parts of all plants. It is a semi-fluid, or slimy, granular, substance;
-in some plants, or parts of plants, the protoplasm exhibits a streaming
-or gliding movement of the granules. It is irritable. In the living
-condition it resists more or less for some time the absorption of
-certain coloring substances. The water may be withdrawn by glycerine.
-The protoplasm may be killed by alcohol. When treated with iodine it
-becomes a yellowish-brown color.
-
-      _Note._ In some plants, like elodea for example, it
-    has been found that the streaming of the protoplasm is
-    often induced by some injury or stimulus, while in the
-    normal condition the protoplasm does not move.
-
-FOOTNOTES:
-
-[1] For apparatus, reagents, collection and preservation of material,
-etc., see Appendix.
-
-[2] If spirogyra is forming fruit some of the threads will be lying
-parallel in pairs, and connected with short tubes. In some of the cells
-there will be found rounded or oval bodies known as _zygospores_. These
-may be seen in fig. 86, and will be described in another part of the
-book.
-
-[3] The most suitable preparations of mucor for study are made by
-growing the plant in a nutrient substance which largely consists of
-gelatine, or, better, agar-agar, a gelatinous preparation of certain
-seaweeds. This, after the plant is sown in it, should be poured into
-sterilised shallow glass plates, called Petrie dishes.
-
-
-
-
-CHAPTER II.
-
-ABSORPTION, DIFFUSION, OSMOSE.
-
-
-=29.= We may next endeavor to learn how plants absorb water or
-nutrient substances in solution. There are several very instructive
-experiments, which can be easily performed, and here again some of the
-lower plants will be found useful.
-
-=30. Osmose in spirogyra.=—Let us mount a few threads of this
-plant in water for microscopic examination, and then draw under the
-cover glass a five per cent solution of ordinary table salt (NaCl)
-with the aid of filter paper. We shall soon see that the result is
-similar to that which was obtained when glycerine was used to extract
-the water from the cell-sap, and to contract the protoplasmic membrane
-from the cell wall. But the process goes on evenly and the plant is not
-injured. The protoplasmic layer contracts slowly from the cell wall,
-and the movement of the membrane can be watched by looking through the
-microscope. The membrane contracts in such a way that all the contents
-of the cell are finally collected into a rounded or oval mass which
-occupies the center of the cell.
-
-If we now add fresh water and draw off the salt solution, we can see
-the protoplasmic membrane expand again, or move out in all directions,
-and occupy its former position against the inner surface of the cell
-wall. This would indicate that there is some pressure from within while
-this process of absorption is going on, which causes the membrane to
-move out against the cell wall.
-
-The salt solution draws water from the cell-sap. There is thus a
-tendency to form a vacuum in the cell, and the pressure on the outside
-of the protoplasmic membrane causes it to move toward the center of the
-cell. When the salt solution is removed and the thread of spirogyra is
-again bathed with water, the movement of the water is _inward_ in the
-cell. This would suggest that there is some substance dissolved in the
-cell-sap which does not readily filter out through the membrane, but
-draws on the water outside. It is this which produces the pressure from
-within and crowds the membrane out against the cell wall again.
-
-[Illustration: Fig. 11. Spirogyra before placing in salt solution.]
-
-[Illustration: Fig. 12. Spirogyra in 5% salt solution.]
-
-[Illustration: Fig. 13. Spirogyra from salt solution into water.]
-
-=31. Turgescence.=—Were it not for the resistance which the cell
-wall offers to the pressure from within, the delicate protoplasmic
-membrane would stretch to such an extent that it would be ruptured, and
-the protoplasm therefore would be killed. If we examine the cells at
-the ends of the threads of spirogyra we shall see in most cases that
-the cell wall at the free end is arched outward. This is brought about
-by the pressure from within upon the protoplasmic membrane which itself
-presses against the cell wall, and causes it to arch outward. This is
-beautifully shown in the case of threads which are recently broken.
-The cell wall is therefore _elastic_; it yields to a certain extent to
-the pressure from within, but a point is soon reached beyond which it
-will not stretch, and an equilibrium then exists between the pressure
-from within on the protoplasmic membrane, and the pressure from without
-by the elastic cell wall. This state of equilibrium in a cell is
-_turgescence_, or such a cell is said to be _turgescent_, or _turgid_.
-
-[Illustration: Fig. 14. Before treatment with salt solution.]
-
-[Illustration: Fig. 15. After treatment with salt solution.]
-
-[Illustration: Fig. 16. From salt solution placed in water.
-
-Figs. 14-16.—Osmosis in threads of mucor.]
-
-=32. Experiment with beet in salt and sugar solutions.=—We may now
-test the effect of a five per cent salt solution on a portion of the
-tissues of a beet or carrot. Let us cut several slices of equal size
-and about 5mm in thickness. Immerse a few slices in water, a few in
-a five per cent salt solution and a few in a strong sugar solution.
-It should be first noted that all the slices are quite rigid when an
-attempt is made to bend them between the fingers. In the course of one
-or two hours or less, if we examine the slices we shall find that those
-in water remain, as at first, quite rigid, while those in the salt and
-sugar solutions are more or less flaccid or limp, and readily bend
-by pressure between the fingers, the specimens in the salt solution,
-perhaps, being more flaccid than those in the sugar solution. The salt
-solution, we judge after our experiment with spirogyra, withdraws some
-of the water from the cell-sap, the cells thus losing their turgidity
-and the tissues becoming limp or flaccid from the loss of water.
-
-[Illustration: Fig. 17. Before treatment with salt solution.]
-
-[Illustration: Fig. 18. After treatment with salt solution.]
-
-[Illustration: Fig. 19. From salt solution into water again.
-
-Figs. 17-19.—Osmosis in cells of Indian corn.]
-
-
-[Illustration: Fig. 20. Rigid condition of fresh beet section.]
-
-[Illustration: Fig. 21. Limp condition after lying in salt solution.]
-
-[Illustration: Fig. 22. Rigid again after lying again in water.
-
-Figs. 20-22.—Turgor and osmosis in slices of beet.]
-
-=33.= Let us now remove some of the slices of the beet from the
-sugar and salt solutions, wash them with water and then immerse them in
-fresh water. In the course of thirty minutes to one hour, if we examine
-them again, we find that they have regained, partly or completely,
-their rigidity. Here again we infer from the former experiment with
-spirogyra that the substances in the cell-sap now draw water inward;
-that is, the diffusion current is inward through the cell walls and the
-protoplasmic membrane, and the tissue becomes turgid again.
-
-[Illustration: Fig. 23. Before treatment with salt solution.]
-
-[Illustration: Fig. 24. After treatment with salt solution.]
-
-[Illustration: Fig. 25. Later stage of the same.
-
-Figs. 23-25.—Cells from beet treated with salt solution to show
-osmosis and movement of the protoplasmic membrane.]
-
-=34. Osmose in the cells of the beet.=—We should now make a
-section of the fresh tissue of a red colored beet for examination with
-the microscope, and treat this section with the salt solution. Here we
-can see that the effect of the salt solution is to draw water out of
-the cell, so that the protoplasmic membrane can be seen to move inward
-from the cell wall just as was observed in the case of spirogyra.[4]
-Now treating the section with water and removing the salt solution, the
-diffusion current is in the opposite direction, that is inward through
-the protoplasmic membrane, so that the latter is pressed outward until
-it comes in contact with the cell wall again, which by its elasticity
-soon resists the pressure and the cells again become turgid.
-
-=35. The coloring matter in the cell-sap does not readily escape
-from the living protoplasm of the beet.=—The red coloring matter,
-as seen in the section under the microscope, does not escape from the
-cell-sap through the protoplasmic membrane. When the slices are placed
-in water, the water is not colored thereby. The same is true when the
-slices are placed in the salt or sugar solutions. Although water is
-withdrawn from the cell-sap, this coloring substance does not escape,
-or if it does it escapes slowly and after a considerable time.
-
-=36. The coloring matter escapes from dead protoplasm.=—If,
-however, we heat the water containing a slice of beet up to a point
-which is sufficient to kill the protoplasm, the red coloring matter
-in the cell-sap filters out through the protoplasmic membrane and
-colors the water. If we heat a preparation made for study under the
-microscope up to the thermal death point we can see here that the red
-coloring matter escapes through the membrane into the water outside.
-This teaches that certain substances cannot readily filter through
-the living membrane of protoplasm, but that they can filter through
-when the protoplasm is dead. A very important condition, then, for
-the successful operation of some of the physical processes connected
-with absorption in plants is that the protoplasm should be in a living
-condition.
-
-=37. Osmose experiments with leaves.=—We may next take the leaves
-of certain plants like the geranium, coleus or other plant, and place
-them in shallow vessels containing water, salt, and sugar solutions
-respectively. The leaves should be immersed, but the petioles should
-project out of the water or solutions. Seedlings of corn or beans,
-especially the latter, may also be placed in these solutions, so that
-the leafy ends are immersed. After one or two hours an examination
-shows that the specimens in the water are still turgid. But if we lift
-a leaf or a bean plant from the salt or sugar solution, we find that
-it is flaccid and limp. The blade, or lamina, of the leaf droops as if
-wilted, though it is still wet. The bean seedling also is flaccid, the
-succulent stem bending nearly double as the lower part of the stem is
-held upright. This loss of turgidity is brought about by the loss of
-water from the tissues, and judging from the experiments on spirogyra
-and the beet, we conclude that the loss of turgidity is caused by the
-withdrawal of some of the water from the cell-sap by the strong salt
-solution.
-
-=38.= Now if we wash carefully these leaves and seedlings, which
-have been in the salt and sugar solutions, with water, and then immerse
-them in fresh water for a few hours, they will regain their turgidity.
-Here again we are led to infer that the diffusion current is now inward
-through the protoplasmic membranes of all the living cells of the leaf,
-and that the resulting turgidity of the individual cells causes the
-turgidity of the leaf or stem.
-
-[Illustration: Fig. 26. Seedling of radish, showing root hairs.]
-
-=39. Absorption by root hairs.=—If we examine seedlings, which
-have been grown in a germinator or in the folds of paper or cloths so
-that the roots will be free from particles of soil, we see near the
-growing point of the roots that the surface is covered with numerous
-slender, delicate, thread-like bodies, the root hairs. Let us place a
-portion of a small root containing some of these root hairs in water on
-a glass slip, and prepare it for examination with the microscope. We
-see that each thread, or root hair, is a continuous tube, or in other
-words it is a single cell which has become very much elongated. The
-protoplasmic membrane lines the wall, and strands of protoplasm extend
-across at irregular intervals, the interspaces being occupied by the
-cell-sap.
-
-[Illustration: Fig. 27. Root hair of corn before and after treatment
-with 5% salt solution.]
-
-We should now draw under the cover glass some of the five per cent salt
-solution. The protoplasmic membrane moves away from the cell wall at
-certain points, showing that _plasmolysis_ is taking place, that is,
-the diffusion current is outward so that the cell-sap loses some of its
-water, and the pressure from the outside moves the membrane inward.
-We should not allow the salt solution to work on the root hairs long.
-It should be very soon removed by drawing in fresh water before the
-protoplasmic membrane has been broken at intervals, as is apt to be the
-case by the strong diffusion current and the consequent strong pressure
-from without. The membrane of protoplasm now moves outward as the
-diffusion current is inward, and soon regains its former position next
-the inner side of the cell wall. The root hairs then, like other parts
-of the plant which we have investigated, have the power of taking up
-water under pressure.
-
-=40. Cell-sap a solution of certain substances.=—From these
-experiments we are led to believe that certain substances reside in the
-cell-sap of plants, which behave very much like the salt solution when
-separated from water by the protoplasmic membrane. Let us attempt to
-interpret these phenomena by recourse to diffusion experiments, where
-an animal membrane separates two liquids of different concentration.
-
-=41. An artificial cell to illustrate turgor.=—Fill a small
-wide-mouthed vial with a _very strong_ sugar solution. Over the mouth
-tie firmly a piece of _bladder_ membrane. Be certain that as the
-membrane is tied over the open end of the vial, the sugar solution
-fills it in order to keep out air bubbles. Sink the vial in a vessel of
-fresh water and leave it there for twenty-four hours. Remove the vial
-and note that the membrane is arched outward. Thrust a sharp needle
-through the membrane when it is arched outward, and quickly pull it
-out. The liquid spurts out because of the inside pressure.
-
-[Illustration: FIG. 28. Puncturing a make-believe cell after
-it has been lying in water.]
-
-[Illustration: FIG. 29. Same as Fig. 28 after needle is removed.]
-
-=42. Diffusion through an animal membrane.=—For this experiment
-we may use a thistle tube, across the larger end of which should be
-stretched and tied tightly a piece of a bladder membrane. A strong
-sugar solution (three parts sugar to one part water) is now placed in
-the tube so that the bulb is filled and the liquid extends part way in
-the neck of the tube. This is immersed in water within a wide-mouth
-bottle, the neck of the tube being supported in a perforated cork in
-such a way that the sugar solution in the tube is on a level with the
-water in the bottle or jar. In a short while the liquid begins to
-rise in the thistle tube, in the course of several hours having risen
-several centimeters. The diffusion current is thus stronger through the
-membrane in the direction of the sugar solution, so that this gains
-more water than it loses.
-
-We have here two liquids separated by an animal membrane, water on
-the one hand which diffuses readily through the membrane, while on
-the other is a solution of sugar which diffuses through the animal
-membrane with difficulty. The water, therefore, not containing any
-solvent, according to a general law which has been found to obtain in
-such cases, diffuses more readily through the membrane into the sugar
-solution, which thus increases in volume, and also becomes more dilute.
-The bladder membrane is what is sometimes called a diffusion membrane,
-since the diffusion currents travel through it.
-
-=43.= In this experiment then the bulk of the sugar solution is
-increased, and the liquid rises in the tube by this pressure above
-the level of the water in the jar outside of the thistle tube. The
-diffusion of liquids through a membrane is _osmosis_.
-
-=44. Importance of these physical processes in plants.=—Now if
-we recur to our experiment with spirogyra we find that exactly the
-same processes take place. The protoplasmic membrane is the diffusion
-membrane, through which the diffusion takes place. The salt solution
-which is first used to bathe the threads of the plant is a stronger
-solution than that of the cell-sap within the cell. Water therefore
-is drawn out of the cell-sap, but the substances in solution in
-the cell-sap do not readily move out. As the bulk of the cell-sap
-diminishes the pressure from the outside pushes the protoplasmic
-membrane away from the wall. Now when we remove the salt solution and
-bathe the thread with water again, the cell-sap, being a solution of
-certain substances, diffuses with more difficulty than the water, and
-the diffusion current is inward, while the protoplasmic membrane moves
-out against the cell wall, and turgidity again results. Also in the
-experiments with salt and sugar solutions on the leaves of geranium,
-on the leaves and stems of the seedlings, on the tissues and cells of
-the beet and carrot, and on the root hairs of the seedlings, the same
-processes take place.
-
-These experiments not only teach us that in the protoplasmic membrane,
-the cell wall, and the cell-sap of plants do we have structures which
-are capable of performing these physical processes, but they also show
-that these processes are of the utmost importance to the plant; not
-only in giving the plant the power to take up solutions of nutriment
-from the soil, but they serve also other purposes, as we shall see
-later.
-
-FOOTNOTE:
-
-[4] We should note that the coloring matter of the beet resides in
-the cell-sap. It is in these colored cells that we can best see the
-movement take place, since the red color serves to differentiate well
-the moving mass from the cell wall. The protoplasmic membrane at
-several points usually clings tenaciously so that at several places the
-membrane is arched strongly away from the cell wall as shown in fig.
-24. While water is removed from the cell-sap, we note that the coloring
-matter does not escape through the protoplasmic membrane.
-
-
-
-
-CHAPTER III.
-
-HOW PLANTS OBTAIN WATER.
-
-
-In connection with the study of the means of absorption from the soil
-or water by plants, it will be found convenient to observe carefully
-the various forms of the plant. Without going into detail here, the
-suggestion is made that simple thread forms like spirogyra, œdogonium,
-and vaucheria; expanded masses of cells as are found in the thalloid
-liverworts, the duckweed, etc., be compared with those liverworts, and
-with the mosses, where leaf-like expansions of a central axis have been
-differentiated. We should then note how this differentiation, from the
-physiological standpoint, has been carried farther in the higher land
-plants.
-
-=45. Absorption by Algæ and Fungi.=—In the simpler forms of
-plant life, as in spirogyra and many of the algæ and fungi, the plant
-body is not differentiated into parts.[5] In many other cases the only
-differentiation is between the growing part and the fruiting part. In
-the algæ and fungi there is no differentiation into stem and leaf,
-though there is an approach to it in some of the higher forms. Where
-this simple plant body is flattened, as in the sea-wrack, or ulva, it
-is a _frond_. The Latin word for frond is _thallus_, and this name is
-applied to the plant body of all the lower plants, the algæ and fungi.
-The algæ and fungi together are sometimes called the _thallophytes_,
-or _thallus plants_. The word thallus is also sometimes applied to the
-flattened body of the liverworts. In the foliose liverworts and mosses
-there is an axis with leaf-like expansions. These are believed by some
-to represent true stems and leaves, by others to represent a flattened
-thallus in which the margins are deeply and regularly divided, or in
-which the expansion has only taken place at regular intervals.
-
-In nearly all of the algæ the plant body is submerged in water. In these
-cases absorption takes place through all portions of the surface in
-contact with the water, as in spirogyra, vaucheria, and all of the
-larger seaweeds. Comparatively few of the algæ grow on the surfaces
-of rocks or trees. In these examples it is likely that at times only
-portions of the plant body serve in the process of absorption of water
-from the substratum. A few of the algæ are parasitic, living in the
-tissues of higher plants, where they are surrounded by the water or
-liquids within the host. Absorption takes place in the same way in many
-of the fungi. The aquatic fungi are immersed in water. In other forms,
-like mucor, a portion of the mycelium is within the substratum, and
-being bathed by the water or watery solutions absorbs the same, while
-the fruiting portion and the aerial mycelium obtain their water and
-food solutions from the mycelium in the substratum. In higher fungi,
-like the mushrooms, the mycelium within the ground or decaying wood
-absorbs the water necessary for the fruiting portion; while in the case
-of the parasitic fungi the mycelium lies in the water or liquid within
-the host.
-
-[Illustration: Fig. 30. Thallus of Riccia lutescens.]
-
-=46. Absorption by liverworts.=—In many of the plants termed
-liverworts the vegetative part of the plant is a thin, flattened, more
-or less elongated green body known as a thallus.
-
-_Riccia._—One of these, belonging to the genus riccia, is shown in
-fig. 30. Its shape is somewhat like that of a minute ribbon which is
-forked at intervals in a dichotomous manner, the characteristic kind of
-branching found in these thalloid liverworts. This riccia (known as R.
-lutescens) occurs on damp soil; long, slender, hair-like processes grow
-out from the under surface of the thallus which resemble root hairs and
-serve the same purpose in the processes of absorption. Another species
-of riccia (R. crystallina) is shown in fig. 252. This plant is quite
-circular in outline and occurs on muddy flats. Some species float on
-the water.
-
-=47. Marchantia.=—One of the larger and coarser liverworts is figured
-at 31. This is a very common liverwort, growing in very damp and muddy
-places and also along the margins of streams, on the mud or upon
-the surfaces of rocks which are bathed with the water. This is known
-as _Marchantia polymorpha_. If we examine the under surface of the
-marchantia we see numerous hair-like processes which attach the plant
-to the soil. Under the microscope we see that some of these are similar
-to the root hairs of the seedlings which we have been studying, and
-they serve the purpose of absorption. Since, however, there are no
-roots on the marchantia plant, these hair-like outgrowths are usually
-termed here _rhizoids_. In marchantia they are of two kinds, one kind
-the simple ones with smooth walls, and the other kind in which the
-inner surfaces of the walls are roughened by processes which extend
-inward in the form of irregular tooth-like points. Besides the hairs on
-the under side of the thallus we note especially near the growing end
-that there are two rows of leaf-like scales, those at the end of the
-thallus curving up over the growing end, thus serving to protect the
-delicate tissues at the growing point.
-
-[Illustration: Fig. 31. Marchantia plant with cupules and gemmæ;
-rhizoids below.]
-
-[Illustration: Fig. 32. Portion of plant of Frullania, a foliose
-liverwort.]
-
-[Illustration: Fig. 33. Portion of same more highly magnified, showing
-overlapping leaves.]
-
-[Illustration: Fig. 34. Under side, showing forked under row of leaves
-and lobes of lateral leaves.]
-
-=48. Frullania.=—In fig. 32 is shown another liverwort, which
-differs greatly in form from the ones we have just been studying in
-that there is a well-defined axis with lateral leaf-like outgrowths.
-Such liverworts are called foliose liverworts. Besides these two quite
-prominent rows of leaves there is a third row of poorly developed
-leaves on the under surface. Also from the under surface of the axis we
-see here and there slender outgrowths, the rhizoids, through which much
-of the water is absorbed.
-
-[Illustration: Fig. 35. Foliose liverwort (bazzania) showing
-dichotomous branching and overlapping leaves.]
-
-=49. Absorption by the mosses.=—Among the mosses, which are
-usually common in moist and shaded situations, examples are abundant
-which are suitable for the study of the organs of absorption. If we
-take for example a plant of mnium (M. affine), which is illustrated in
-fig. 36, we note that it consists of a slender axis with thin flat,
-green, leaf-like expansions, Examining with the microscope the lower
-end of the axis, which is attached to the substratum, there are seen
-numerous brown-colored threads more or less branched.
-
-[Illustration: Fig. 36. Female plant (gametophyte) of a moss (mnium),
-showing rhizoids below, and the tuft of leaves above, which protect the
-archegonia.]
-
-=50. Absorption by the higher aquatic plants.=—Examples of
-the water plants which are entirely submerged in water are the
-water-crowfoots, some of the pondweeds, elodea or water-weeds, the
-tape-grass, vallisneria, etc. In these plants all parts of the body
-being submerged, they absorb water with which they are in contact. In
-other aquatic plants, like the water-lilies, some of the pondweeds, the
-duck-meats, etc., are only partially submerged in the water; the upper
-surface of the leaf or of the leaf-like expansion being exposed to the
-air, while the under surface lies in close contact with the water, and
-the stems and the petioles of the leaves are also immersed in water. In
-these plants absorption takes place through those parts in contact with
-the water.
-
-=51. Absorption by the duck-meats.=—These plants are very curious
-examples of the higher plants.
-
-      _Lemna._—One of these is illustrated in fig. 37.
-    This is the common duckweed, _Lemna trisulca_. It
-    is very peculiar in form and in its mode of growth.
-    Each one of the lateral leaf-like expansions extends
-    outwards by the elongation of the basal part, which
-    becomes long and slender. Next, two new lateral
-    expansions are formed on these by prolification from
-    near the base, and thus the plant continues to extend.
-    The plant occurs in ponds and ditches and is sometimes
-    very common and abundant. It floats on the surface
-    of the water. While the flattened part of the plant
-    resembles a leaf, it is really the stem, no leaves
-    being present. This expanded green body is usually
-    termed a “frond.” A single rootlet grows out from the
-    under side and is destitute of root hairs. Absorption
-    of water therefore takes place through this rootlet and
-    through the under side of the “frond.”
-
-[Illustration: Fig. 37. Fronds of the duckweed (Lemna trisculca).]
-
-[Illustration: Fig. 38. Spirodela polyrhiza.]
-
-=52. Spirodela polyrhiza.=—This is a very curious plant, closely
-related to the lemna and sometimes placed in the same genus. It occurs
-in similar situations, and is very readily grown in aquaria. It reminds
-one of a little insect as seen in fig. 38. There are several rootlets
-on the under side of the frond. Absorption of water takes place here in
-the same way as in lemna.
-
-=53. Absorption in wolffia.=—Perhaps the most curious of these
-modified water plants is the little wolffia, which contains the
-smallest specimens of the flowering plants. Two species of this genus
-are shown in figs. 39-41. The plant body is reduced to nothing but a
-rounded or oval green body, which represents the stem. No leaves or
-roots are present. The plants multiply by “prolification,” the new
-fronds growing out from a depression on the under side of one end.
-Absorption takes place through the under surface.
-
-=54. Absorption by land plants.=—_Water cultures._—In connection
-with our inquiry as to how land plants obtain their water, it will be
-convenient to prepare some water cultures to illustrate this and which
-can also be used later in our study of nutrition (Chapter IX).
-
-[Illustration: Fig. 39. Young frond of wolffia growing out of older
-one.]
-
-[Illustration: Fig. 40. Young frond of wolffia separating from older
-one.]
-
-[Illustration: Fig. 41. Another species of wolffia, the two fronds
-still connected.]
-
-Chemical analysis shows that certain mineral substances are common
-constituents of plants. By growing plants in different solutions of
-these various substances it has been possible to determine what ones
-are necessary constituents of plant food. While the proportion of the
-mineral elements which enter into the composition of plant food may
-vary considerably within certain limits, the concentration of the
-solutions should not exceed certain limits. A very useful solution is
-one recommended by Sachs, and is as follows:
-
-=55. Formula for water cultures=:
-
-    Water                           1000 cc.
-    Potassium nitrate                0.5 gr.
-    Sodium chloride                  0.5 “
-    Calcium sulphate                 0.5 “
-    Magnesium sulphate               0.5 “
-    Calcium phosphate                0.5 “
-
-The calcium phosphate is only partly soluble. The solution which is not
-in use should be kept in a dark cool place to prevent the growth of
-minute algæ.
-
-=56.= Several different plants are useful for experiments in water
-cultures, as peas, corn, beans, buckwheat, etc. The seeds of these
-plants may be germinated, after soaking them for several hours in warm
-water, by placing them between the folds of wet paper on shallow trays,
-or in the folds of wet cloth. The seeds should not be kept immersed in
-water after they have imbibed enough to thoroughly soak and swell them.
-At the same time that the seeds are placed in damp paper or cloth for
-germination, one lot of the soaked seeds should be planted in good soil
-and kept under the same temperature conditions, for control. When the
-plants have germinated one series should be grown in distilled water,
-which possesses no plant food; another in the nutrient solution, and
-still another in the nutrient solution to which has been added a few
-drops of a solution of iron chloride or ferrous sulphate. There would
-then be four series of cultures which should be carried out with the
-same kind of seed in each series so that the comparisons can be made on
-the same species under the different conditions. The series should be
-numbered and recorded as follows:
-
-    No. 1, soil.
-    No. 2, distilled water.
-    No. 3, nutrient solution.
-    No. 4, nutrient solution with a few drops of iron solution added.
-
-[Illustration: Fig. 42. Culture cylinder to show position of
-corn seedling (Hansen).]
-
-=57.= Small jars or wide-mouth bottles, or crockery jars, can be
-used for the water cultures, and the cultures are set up as follows: A
-cork which will just fit in the mouth of the bottle, or which can be
-supported by pins, is perforated so that there is room to insert the
-seedling, with the root projecting below into the liquid. The seed can
-be fastened in position by inserting a pin through one side, if it is a
-large one, or in the case of small seeds a cloth of a coarse mesh can
-be tied over the mouth of the bottle instead of using the cork. After
-properly setting up the experiments the cultures should be arranged
-in a suitable place, and observed from time to time during several
-weeks. In order to obtain more satisfactory results several duplicate
-series should be set up to guard against the error which might arise
-from variation in individual plants and from accident. Where there are
-several students in a class, a single series set up by several will
-act as checks upon one another. If glass jars are used for the liquid
-cultures they should be wrapped with black paper or cloth to exclude
-the light from the liquid, otherwise numerous minute algæ are apt to
-grow and interfere with the experiment. Or the jars may be sunk in pots
-of earth to serve the same purpose. If crockery jars are used they will
-not need covering.
-
-=58.= For some time all the plants grow equally well, until the
-nutriment stored in the seed is exhausted. The numbers 1, 3 and 4, in
-soil and nutrient solutions, should outstrip number 2, the plants in
-the distilled water. No. 4 in the nutrient solution with iron, having a
-perfect food, compares favorably with the plants in the soil.
-
-=59. Plants take liquid food from the soil.=—From these experiments
-then we judge that such plants take up the food they receive from the
-soil in the form of a liquid, the elements being in solution in water.
-
-If we recur now to the experiments which were performed with the salt
-solution in producing plasmolysis in the cells of spirogyra, in the
-cells of the beet or corn, and in the root hairs of the corn and bean
-seedlings, and the way in which these cells become turgid again when
-the salt solution is removed and they are again bathed with water, we
-shall have an explanation of the way in which plants take up nutrient
-solutions of food material through their roots.
-
-[Illustration: Fig. 43. Section of corn root, showing rhizoids formed
-from elongated epidermal cells.]
-
-=60. How food solutions are carried into the plant.=—We can see
-how water and food solutions are carried into the plant, and we must
-next turn our attention to the way in which these solutions are carried
-farther into the plant. We should make a section across the root of a
-seedling in the region of the root hairs and examine it with the aid
-of a microscope. We here see that the root hairs are formed by the
-elongation of certain of the surface cells of the root. These cells
-elongate perpendicularly to the root, and become _3mm_ to _6mm_ long.
-They are flexuous or irregular in outline and cylindrical, as shown in
-fig. 43. The end of the hair next the root fits in between the adjacent
-superficial cells of the root and joins closely to the next deeper
-layer of cells. In studying the section of the young root we see that
-the root is made up of cells which lie closely side by side, each with
-its wall, its protoplasm and cell-sap, the protoplasmic membrane lying
-on the inside of each cell wall.
-
-=61.= In the absorption of the watery solutions of plant food
-by the root hairs, the cell-sap, being a more concentrated solution,
-gains some of the former, since the liquid of less concentration flows
-through the protoplasmic membrane into the more concentrated cell-sap,
-increasing the bulk of the latter. This makes the root hairs turgid,
-and at the same time dilutes the cell-sap so that the concentration is
-not so great. The cells of the root lying inside and close to the base
-of the root hairs have a cell-sap which is now more concentrated than
-the diluted cell-sap of the hairs, and consequently gain some of the
-food solutions from the latter, which tends to lessen the content of
-the root hairs and also to increase the concentration of the cell-sap
-of the same. This makes it possible for the root hairs to draw on
-the soil for more of the food solutions, and thus, by a variation in
-the concentration of the substances in solution in the cell-sap of
-the different cells, the food solutions are carried along until they
-reach the _vascular bundles_, through which the solutions are carried
-to distant parts of the plant. Some believe that there is a rhythmic
-action of the elastic cell walls in these cells between the root hairs
-and the vascular bundles. This occurs in such a way that, after the
-cell becomes turgid, it contracts, thus reducing the size of the cell
-and forcing some of the food solutions into the adjacent cells, when
-by absorption of more food solutions, or water, the cell increases in
-turgidity again. This rhythmic action of the cells, if it does take
-place, would act as a pump to force the solutions along, and would form
-one of the causes of root pressure.
-
-=62. How the root hairs get the watery solutions from the
-soil.=—If we examine the root hairs of a number of seedlings which
-are growing in the soil under normal conditions, we shall see that a
-large quantity of soil readily clings to the roots. We should note also
-that unless the soil has been recently watered there is no free water
-in it; the soil is only moist. We are curious to know how plants can
-obtain water from soil which is not wet. If we attempt to wash off the
-soil from the roots, being careful not to break away the root hairs,
-we find, that small particles cling so tenaciously to the root hairs
-that they are not removed. Placing a few such root hairs under the
-microscope it appears as if here and there the root hairs were glued to
-the minute soil particles.
-
-[Illustration: Fig. 44. Root hairs of corn seedling with soil particles
-adhering closely.]
-
-=63.= If now we take some of the soil which is only moist, weigh
-it, and then permit it to become quite dry on exposure to dry air, and
-weigh again, we find that it loses weight in drying. Moisture has been
-given off. This moisture, it has been found, forms an exceedingly thin
-film on the surface of the minute soil particles. Where these soil
-particles lie closely together, as they usually do when massed together
-in the pot or elsewhere, this thin film of moisture is continuous from
-the surface of one particle to that of another. Thus the soil particles
-which are so closely attached to the root hairs connect the surface
-of the root hairs with this film of moisture. As the cell-sap of the
-root hairs draws on the moisture film with which they are in contact,
-the tension of this film is sufficient to draw moisture from distant
-particles. In this way the roots are supplied with water in soil which
-is only moist.
-
-=64. Plants cannot remove all the moisture from the soil.=—If we
-now take a potted plant, or a pot containing a number of seedlings,
-place it in a moderately dry room, and do not add water to the soil we
-find in a few days that the plant is wilting. The soil if examined will
-appear quite dry to the sense of touch. Let us weigh some of this soil,
-then dry it by artificial heat, and weigh again. It has lost in weight.
-This has been brought about by driving off the moisture which still
-remained in the soil after the plant began to wilt. This teaches that
-while plants can obtain water from soil which is only moist or which is
-even rather dry, they are not able to withdraw all the moisture from
-the soil.
-
-[Illustration: Fig. 45. Experiment to show root pressure (Detmer).]
-
-=65. “Root pressure” or exudation pressure.=—It is a very common
-thing to note, when certain shrubs or vines are pruned in the spring,
-the exudation of a watery fluid from the cut surfaces. In the case of
-the grape vine this has been known to continue for a number of days,
-and in some cases the amount of liquid, called “sap,” which escapes is
-considerable. In many cases it is directly traceable to the activity
-of the roots, or root hairs, in the absorption of water from the soil.
-For this reason the term _root pressure_ has been used to denote the
-force exerted in supplying the water from the soil. But there are some
-who object to the use of this term “root pressure.” The principal
-objection is that the pressure which brings about the phenomenon
-known as “bleeding” by plants is not present in the roots alone. This
-pressure exists under certain conditions in all parts of the plant. The
-term exudation pressure has been proposed in lieu of root pressure. It
-should be remembered that the movement of water in the plant is started
-by the pressure which exists in the root. If the term “root pressure”
-is used, it should be borne clearly in mind that it does not express
-the phenomenon exactly in all cases.
-
-=Root pressure may be measured.=—It is possible to measure
-not only the amount of water which the roots will raise in a given
-time, but also to measure the force exerted by the roots during root
-pressure. It has been found that root pressure in the case of the
-nettle is sufficient to hold a column of water about 4.5 meters (15
-ft.) high (Vines), while the root pressure of the vine (Hales, 1721)
-will hold a column of water about 10 meters (36.5 ft.) high, and the
-birch (Betula lutea) (Clark, 1873) has a root pressure sufficient to
-hold a column of water about 25 meters (84.7 ft.) high.
-
-=66. Experiment to demonstrate root pressure.=—By a very simple
-method this lifting of water by root pressure is shown. During the
-summer season plants in the open may be used if it is preferred, but
-plants grown in pots are also very serviceable, and one may use a
-potted begonia or balsam, the latter being especially useful. The
-plants are usually convenient to obtain from the greenhouses, to
-illustrate this phenomenon. The stem is cut off rather close to the
-soil and a long glass tube is attached to the cut end of the stem,
-still connected with the roots, by the use of rubber tubing, as shown
-in figure 45, and a very small quantity of water may be poured in to
-moisten the cut end of the stem. In a few minutes the water begins to
-rise in the glass tube. In some cases it rises quite rapidly, so that
-the column of water can readily be seen to extend higher and higher up
-in the tube when observed at quite short intervals. (To measure the
-force of root pressure is rather difficult for elementary work. To
-measure it see Ganong, Plant Physiology, pp. 67, 68, or some other book
-for advanced work.)
-
-=67.= In either case where the experiment is continued for
-several days it is noticed that the column of water or of mercury
-rises and falls at different times during the same day, that is, the
-column stands at varying heights; or in other words the root pressure
-varies during the day. With some plants it has been found that the
-pressure is greatest at certain times of the day, or at certain
-seasons of the year. Such variation of root pressure exhibits what
-is termed a periodicity, and in the case of some plants there is a
-daily periodicity; while in others there is in addition an annual
-periodicity. With the grape vine the root pressure is greatest in
-the forenoon, and decreases from 12-6 P.M., while with the
-sunflower it is greatest before 10 A.M., when it begins to
-decrease. Temperature of the soil is one of the most important external
-conditions affecting the activity of root pressure.
-
-FOOTNOTE:
-
-[5] See Chapter 38 for organization of members of the plant body.
-
-
-CHAPTER IV.
-
-TRANSPIRATION, OR THE LOSS OF WATER BY PLANTS.
-
-
-=68.= We should now inquire if all the water which is taken up in
-excess of that which actually suffices for turgidity is used in the
-elaboration of new materials of construction. We notice when a leaf
-or shoot is cut away from a plant, unless it is kept in quite a moist
-condition, or in a damp, cool place, that it becomes flaccid, and
-droops. It wilts, as we say. The leaves and shoot lose their turgidity.
-This fact suggests that there has been a loss of water from the shoot
-or leaf. It can be readily seen that this loss is not in the form of
-drops of water which issue from the cut end of the shoot or petiole.
-What then becomes of the water in the cut leaf or shoot?
-
-=69. Loss of water from excised leaves.=—Let us take a handful of
-fresh, green, rather succulent leaves, which are free from water on
-the surface, and place them under a glass bell jar, which is tightly
-closed below but which contains no water. Now place this in a brightly
-lighted window, or in sunlight. In the course of fifteen to thirty
-minutes we notice that a thin film of moisture is accumulating on the
-inner surface of the glass jar. After an hour or more the moisture has
-accumulated so that it appears in the form of small drops of condensed
-water. We should set up at the same time a bell jar in exactly the same
-way but which contains no leaves. In this jar there is no condensed
-moisture on the inner surface. We thus are justified in concluding that
-the moisture in the former jar comes from the leaves. Since there is no
-visible water on the surfaces of the leaves, or at the cut ends, before
-it may have condensed there, we infer that the water escapes from the
-leaves in the form of _water vapor_, and that this water vapor, when
-it comes in contact with the surface of the cold glass, condenses and
-forms the moisture film, and later the drops of water. The leaves of
-these cut shoots therefore lose water in the form of water vapor, and
-thus a loss of turgidity results.
-
-[Illustration: Fig. 46. To show loss of water from leaves, the leaves
-just covered.]
-
-[Illustration: Fig. 47. After a few hours drops of water have
-accumulated on the inside of the jar covering the leaves.]
-
-=70. Loss of water from growing plants.=—Suppose we now take a
-small and actively growing plant in a pot, and cover the pot and the
-soil with a sheet of rubber cloth or flexible oilcloth which fits
-tightly around the stem of the plant so that the moisture from the soil
-or from the surface of the pot cannot escape. Then place a bell jar
-over the plant, and set in a brightly lighted place, at a temperature
-suitable for growth. In the course of a few minutes on a dry day a
-moisture film forms on the inner surface of the glass, just as it did
-in the case of the glass jar containing the cut shoots and leaves.
-Later the moisture has condensed so that it is in the form of drops. If
-we have the same leaf surface here as we had with the cut shoots, we
-shall probably find that a larger amount of water accumulates on the
-surface of the jar from the plant that is still attached to its roots.
-
-=71. Water escapes from the surfaces of living leaves in the form of
-water vapor.=—This living plant then has lost water, which also
-escapes in the form of water vapor. Since here there are no cut places
-on the shoots or leaves, we infer that the loss of water vapor takes
-place from the surfaces of the leaves and from the shoots. It is also
-to be noted that, while this plant is losing water from the surfaces of
-the leaves, it does not wilt or lose its turgidity. The roots by their
-activity and pressure supply water to take the place of that which is
-given off in the form of water vapor. This loss of water in the form of
-water vapor by plants is _transpiration_.
-
-=72. A test for the escape of water vapor from plants.=—Make
-a solution of cobalt chloride in water. Saturate several pieces of
-filter paper with it. Allow them to dry. The water solution of cobalt
-chloride is red. The paper is also red when it is moist, but when it
-is thoroughly dry it is blue. It is very sensitive to moisture and the
-moisture of the air is often sufficient to redden it. Before using dry
-the paper in an oven or over a flame.
-
-=73.= Take two bell jars, as shown in fig. 49. Under one place a
-potted plant, the pot and earth being covered by oiled paper. Or cover
-the plant with a fruit jar. To a stake in the pot pin a piece of the
-dried cobalt paper, and at the same time pin to a stake, in another
-jar covering no plant, another piece of cobalt paper. They should both
-be put under the jars at the same time. In a few moments the paper in
-the jar with the plant will begin to redden. In a short while, ten or
-fifteen minutes, probably, it will be entirely red, while the paper
-under the other jar will remain blue, or be only slightly reddened. The
-water vapor passing off from the living plant comes in contact with
-the sensitive cobalt chloride in the paper and reddens it before there
-is sufficient vapor present to condense as a film of moisture on the
-surface of the jar.
-
-[Illustration: Fig. 48.]
-
-[Illustration: Fig. 49.
-
-Fig. 48.—Water vapor is given off by the leaves when attached to the
-living plant. It condenses into drops of water on the cool surface of
-the glass covering the plant.
-
-Fig. 49.—A good way to show that the water passes off from the leaves
-in the form of water vapor.]
-
-=74. Experiment to compare loss of water in a dry and a humid
-atmosphere.=—We should now compare the escape of water from the
-leaves of a plant covered by a bell jar, as in the last experiment,
-with that which takes place when the plant is exposed in a normal way
-in the air of the room or in the open. To do this we should select
-two plants of the same kind growing in pots, and of approximately the
-same leaf surface. The potted plants are placed one each on the arms
-of a scale. One of the plants is covered in this position with a bell
-jar. With weights placed on the pan of the other arm the two sides are
-balanced. In the course of an hour, if the air of the room is dry,
-moisture has probably accumulated on the inner surface of the glass jar
-which is used to cover one of the plants. This indicates that there has
-here been a loss of water. But there is no escape of water vapor into
-the surrounding air so that the weight on this arm is practically the
-same as at the beginning of the experiment. We see, however, that the
-other arm of the balance has risen. We infer that this is the result of
-the loss of water vapor from the plant on that arm. Now let us remove
-the bell jar from the other plant, and with a cloth wipe off all the
-moisture from the inner surface, and replace the jar over the plant. We
-note that the end of the scale which holds this plant is still lower
-than the other end.
-
-=75. The loss of water is greater in a dry than in a humid
-atmosphere.=—This teaches us that while water vapor escaped from
-the plant under the bell jar, the air in this receiver soon became
-saturated with the moisture, and thus the farther escape of moisture
-from the leaves was checked. It also teaches us another very important
-fact, viz., that plants lose water more rapidly through their leaves in
-a dry air than in a humid or moist atmosphere. We can now understand
-why it is that during the very hot and dry part of certain days plants
-often wilt, while at nightfall, when the atmosphere is more humid, they
-revive. They lose more water through their leaves during the dry part
-of the day, other things being equal, than at other times.
-
-=76. How transpiration takes place.=—Since the water of transpiration
-passes off in the form of water vapor we are led to inquire if this
-process is simply _evaporation_ of water through the surface of the
-leaves, or whether it is controlled to any appreciable extent by any
-condition of the living plant. An experiment which is instructive in
-this respect we shall find in a comparison between the transpiration of
-water from the leaves of a cut shoot, allowed to lie unprotected in a
-dry room, and a similar cut shoot the leaves of which have been killed.
-
-=77.= Almost any plant will answer for the experiment. For this
-purpose I have used the following method. Small branches of the locust
-(Robinia pseudacacia), of sweet clover (Melilotus alba), and of a
-heliopsis were selected. One set of the shoots was immersed for a
-moment in hot water near the boiling point to kill them. The other set
-was immersed for the same length of time in cold water, so that the
-surfaces of the leaves might be well wetted, and thus the two sets of
-leaves at the beginning of the experiment would be similar, so far as
-the amount of water on their surfaces is concerned. All the shoots were
-then spread out on a table in a dry room, the leaves of the killed
-shoots being separated where they are inclined to cling together. In
-a short while all the water has evaporated from the surface of the
-living leaves, while the leaves of the dead shoots are still wet on
-the surface. In six hours the leaves of the dead shoots from which the
-surface water had now evaporated were beginning to dry up, while the
-leaves of the living plants were only becoming flaccid. In twenty-four
-hours the leaves of the dead shoots were crisp and brittle, while those
-of the living shoots were only wilted. In twenty-four hours more the
-leaves of the sweet clover and of the heliopsis were still soft and
-flexible, showing that they still contained more water than the killed
-shoots which had been crisp for more than a day.
-
-=78.= It must be then that during what is termed transpiration
-the living plant is capable of holding back the water to some extent,
-which in a dead plant would escape more rapidly by evaporation. It is
-also known that a body of water with a surface equal to that of a given
-leaf surface of a plant loses more water by evaporation during the same
-length of time than the plant loses by transpiration.
-
-=79. Structure of a leaf.=—We are now led to inquire why it is
-that a living leaf loses water less rapidly than dead ones, and why
-less water escapes from a given leaf surface than from an equal surface
-of water. To understand this it will be necessary to examine the minute
-structure of a leaf. For this purpose we may select the leaf of an ivy,
-though many other leaves will answer equally well. From a portion of
-the leaf we should make very thin cross-sections with a razor or other
-sharp instrument. These sections should be perpendicular to the surface
-of the leaf and should be then mounted in water for microscopic
-examination.[6]
-
-=80. Epidermis of the leaf.=—In this section we see that the
-green part of the leaf is bordered on what are its upper and lower
-surfaces by a row of cells which possess no green color. The walls of
-the cells of each row have nearly parallel sides, and the cross walls
-are perpendicular. These cells form a single layer over both surfaces
-of the leaf and are termed the _epidermis_. Their walls are quite stout
-and the outer walls are _cuticularized_.
-
-[Illustration: Fig. 50. Section through ivy leaf showing communication
-between stomate and the large intercellular spaces of the leaf, stoma
-closed.]
-
-[Illustration: Fig. 51. Stoma open.]
-
-[Illustration: Fig. 52. Stoma closed.
-
-Figs. 51, 52.—Section through stomata of ivy leaf.]
-
-=81. Soft tissue of the leaf.=—The cells which contain the green
-chlorophyll bodies are arranged in two different ways. Those on the
-upper side of the leaf are usually long and prismatic in form and
-lie closely parallel to each other. Because of this arrangement of
-these cells they are termed the _palisade_ cells, and form what is
-called the _palisade layer_. The other green cells, lying below, vary
-greatly in size in different plants and to some extent also in the same
-plant. Here we notice that they are elongated, or oval, or somewhat
-irregular in form. The most striking peculiarity, however, in their
-arrangement is that they are not usually packed closely together, but
-each cell touches the other adjacent cells only at certain points. This
-arrangement of these cells forms quite large spaces between them, the
-intercellular spaces. If we should examine such a section of a leaf
-before it is mounted in water we would see that the intercellular
-spaces are not filled with water or cell-sap, but are filled with air
-or some gas. Within the cells, on the other hand, we find the cell-sap
-and the protoplasm.
-
-=82. Stomata.=—If we examine carefully the row of epidermal cells
-on the under surface of the leaf, we find here and there a peculiar
-arrangement of cells shown at figs. 51, 52. This opening through the
-epidermal layer is a _stoma_. The cells which immediately surround the
-openings are the _guard cells_. The form of the guard cells can be
-better seen if we tear a leaf in such a way as to strip off a short
-piece of the lower epidermis, and mount this in water. The guard cells
-are nearly crescent-shaped, and the stoma is elliptical in outline. The
-epidermal cells are very irregular in outline in this view. We should
-also note that while the epidermal cells contain no chlorophyll, the
-guard cells do.
-
-[Illustration: Fig. 53. Portion of epidermis of ivy, showing irregular
-epidermal cells, stoma and guard cells.]
-
-=82=_a_. In the ivy leaf the guard cells are quite plain, but in
-most plants the form as seen in cross-section is irregular in outline,
-as shown in fig. 53_a_, which is from a section of a wintergreen leaf.
-This leaf is interesting because it shows the characteristic structure
-of leaves of many plants growing in soil where absorption of water by
-the roots is difficult owing to the cold water, acids, or salts in the
-water or soil, or in dry soil (see Chapters 47, 54, 55). The cuticle
-over the upper epidermis is quite thick. This lessens the loss of water
-by the leaf. The compact palisades of cells are in two to three cell
-layers, also reducing the loss of water.
-
-=83. The living protoplasm retards the evaporation of water from the
-leaf.=—If we now take into consideration a few facts which we have
-learned in a previous chapter, with reference to the physical
-properties of the living cell, we shall be able to give a partial
-explanation of the comparative slowness with which the water escapes
-from the leaves. The inner surfaces of the cell walls are lined with
-the membrane of protoplasm, and within this is the cell-sap. These
-cells have become turgid by the absorption of the water which has
-passed up to them from the roots. While the protoplasmic membrane of
-the cells does not readily permit the water to filter through, yet it
-is saturated with water, and the elastic cell wall with which it is in
-contact is also saturated. From the cell wall the water evaporates into
-the intercellular spaces. But the water is given up slowly through the
-protoplasmic membrane, so that the water vapor cannot be given off as
-rapidly from the cell walls as it could if the protoplasm were dead.
-The living protoplasmic membrane then which is only slowly permeable to
-the water of the cell-sap is here a very important factor in checking
-the too rapid loss of water from the leaves.
-
-[Illustration: Fig. 53_a_.
-
-Cross-section of leaf of wintergreen. _Cu._, cuticle; _Epid._,
-epidermis; _v.d._, vascular duct; _Int. c. sp._, intercellular space;
-_L. ep._, lower epidermis; _St._, stoma.]
-
-By an examination of our leaf section we see that the intercellular
-spaces are all connected, and that the stomata, where they occur, open
-also into intercellular spaces. There is here an opportunity for the
-water vapor in the intercellular spaces to escape when the stomata are
-open.
-
-=84. Action of the stomata.=—The guard cells serve an important
-function in regulating transpiration. During normal transpiration the
-guard cells are turgid and their peculiar form then causes them to arch
-away from each other, allowing the escape of water vapor. When the air
-becomes too dry transpiration is in excess of absorption by the roots.
-The guard cells lose some of their water, and collapse so that their
-inner faces meet in a straight line and close the stoma. Thus the rapid
-transpiration is checked. Some evaporation of water vapor, however,
-takes place through the epidermal cells, and if the air remains too
-dry, the leaves eventually become flaccid and droop. During the day
-the effect of sunlight is to increase certain sugars or salts in the
-guard cells so that they readily become turgid and open the stomates,
-but at night the cell-sap is less concentrated and the stomates are
-usually closed. Light therefore favors transpiration, while in darkness
-transpiration is checked.
-
-=85. Compare transpiration from the two surfaces of the leaf.=—This can
-be done by using the cobalt chloride paper. This paper can be kept from
-year to year and used repeatedly. It is thus a very simple matter to
-make these experiments. Provide two pieces of glass (discarded glass
-negatives, cleaned, are excellent), two pieces of cobalt chloride
-paper, and some geranium leaves entirely free from surface water. Dry
-the paper until it is blue. Place one piece of the paper on a glass
-plate; place the geranium leaf with the under side on the paper. On the
-upper side of the leaf now place the other cobalt paper, and next the
-second piece of glass. On the pile place a light weight to keep the
-parts well in contact. In fifteen or twenty minutes open and examine.
-The paper next the under side of the geranium leaf is red where it lies
-under the leaf. The paper on the upper side is only slightly reddened.
-The greater loss of water, then, is through the under side of the
-geranium leaf. This is true of a great many leaves, but it is not true
-of all.
-
-=86. Negative pressure.=—This is not only indicated by the
-drooping of the leaves, but may be determined in another way. If the
-shoot of such a plant be cut underneath mercury, or underneath a strong
-solution of eosin, it will be found that some of the mercury or eosin,
-as the case may be, will be forcibly drawn up into the stem toward the
-roots. This is seen on quickly splitting the cut end of the stem. When
-plants in the open cannot be obtained in this condition, one may take
-a plant like a balsam plant from the greenhouse, or some other potted
-plant, knock it out of the pot, free the roots from the soil and allow
-to partly wilt. The stem may then be held under the eosin solution and
-cut.
-
-[Illustration: Fig. 54. Experiment to show lifting power of
-transpiration.]
-
-[Illustration: Fig. 55.
-
-Estimation of the amount of transpiration. The tubes are filled with
-water, and as the water transpires from the leaf surface its movement
-in the tube from _a_ to _b_ can be measured. (After Mangin.)]
-
-=87. Lifting power of transpiration.=—Not only does transpiration
-go on quite independently of root pressure, as we have discovered
-from other experiments, but transpiration is capable of exerting a
-lifting power on the water in the plant. This may be demonstrated in
-the following way: Place the cut end of a leafy shoot in one end of a
-U tube and fit it water-tight. Partly fill this arm of the U tube with
-water, and add mercury to the other arm until it stands at a level in
-the two arms as in fig. 54. In a short time we note that the mercury is
-rising in the tube.
-
-=88. Root pressure may exceed transpiration.=—If we cover small
-actively growing plants, such as the pea, corn, wheat, bean, etc.,
-with a bell jar, and place them in the sunlight where the temperature
-is suitable for growth, in a few hours, if conditions are favorable,
-we shall see that there are drops of water standing out on the margins
-of the leaves. These drops of water have exuded through the ordinary
-stomata, or in other cases what are called water stomata, through the
-influence of root pressure. The plant being covered by the glass jar,
-the air soon becomes saturated with moisture and transpiration is
-checked. Root pressure still goes on, however, and the result is shown
-in the exuding drops. Root pressure is here in excess of transpiration.
-This phenomenon is often to be observed during the summer season in the
-case of low-growing plants. During the bright warm day transpiration
-equals, or may be in excess of, root pressure, and the leaves are
-consequently flaccid. As nightfall comes on the air becomes more
-moist, and the conditions of light are such also that transpiration
-is lessened. Root pressure, however, is still active because the soil
-is still warm. In these cases drops of water may be seen exuding from
-the margins of the leaves due to the excess of root pressure over
-transpiration. Were it not for this provision for the escape of the
-excess of water raised by root pressure, serious injury by lesions, as
-a result of the great pressure, might result. The plant is thus to some
-extent a self-regulatory piece of apparatus so far as root pressure and
-transpiration are concerned.
-
-=89. Injuries caused by excessive root pressure.=—Some varieties
-of tomatoes when grown in poorly lighted and poorly ventilated
-greenhouses suffer serious injury through lesions of the tissues.
-This is brought about by the cells at certain parts becoming charged
-so full with water through the activity of root pressure and lessened
-transpiration, assisted also probably by an accumulation of certain
-acids in the cell-sap which cannot be got rid of by transpiration.
-Under these conditions some of the cells here swell out, forming
-extensive cushions, and the cell walls become so weakened that they
-burst. It is possible to imitate the excess of root pressure in the
-case of some plants by connecting the stems with a system of water
-pressure, when very quickly the drops of water will begin to exude from
-the margins of the leaves.
-
-[Illustration: Fig. 56.
-
-The roots are lifting more water into the plant than can be given off
-in the form of water vapor, so it is pressed out in drops. From “First
-Studies Plant Life.”]
-
-=90.= It should be stated that in reality there is no difference
-between transpiration and evaporation, if we bear in mind that
-evaporation takes place more slowly from living plants than from dead
-ones, or from an equal surface of water.
-
-=91.= The escape of water vapor is not the only function of the
-stomata. The exchange of gases takes place through them as we shall
-later see. A large number of experiments show that normally the stomata
-are open when the leaves are turgid. But when plants lose excessive
-quantities of water on dry and hot days, so that the leaves become
-flaccid, the guard cells automatically close the stomata to check the
-escape of water vapor. Some water escapes through the epidermis of many
-plants, though the cuticularized membrane of the epidermis largely
-prevents evaporation. In arid regions plants are usually provided
-with an epidermis of several layers of cells to more securely prevent
-evaporation there. In such cases the guard cells are often protected by
-being sunk deeply in the epidermal layer.
-
-=92. Demonstration of stomates and intercellular air spaces.=—A
-good demonstration of the presence of stomates in leaves, as well as
-the presence and intercommunication of the intercellular spaces, can be
-made by blowing into the cut end of the petiole of the leaf of a calla
-lily, the lamina being immersed in water. The air is forced out
-through the stomata and rises as bubbles to the surface of the water.
-At the close of the experiment some of the air bubbles will still be
-in contact with the leaf surface at the opening of the stomata. The
-pressure of the water gradually forces this back into the leaf. Other
-plants will answer for the experiment, but some are more suitable than
-others.
-
-=92a. Number of stomata.=—The larger number of stomata are on the
-under side of the leaf. (In leaves which float on the surface of the
-water all of the stomata are on the upper side of the leaf, as in the
-water-lily.) It has been estimated by investigation that in general
-there are 40-300 stomata to the square millimeter of surface. In some
-plants this number is exceeded, as in the olive, where there are 625.
-In an entire leaf of Brassica rapa there are about 11,000,000 stomata,
-and in an entire leaf of the sunflower there are about 13,000,000
-stomata.
-
-=92b. Amount of water transpired by plants.=—The amount of water
-transpired by plants is very great. According to careful estimates a
-sunflower 6 feet high transpires on the average about one quart per
-day; an acre of cabbages 2,000,000 quarts in four months; an oak tree
-with 700,000 leaves transpires about 180 gallons of water per day.
-According to von Höhnel, a beech tree 110 years old transpired about
-2250 gallons of water in one summer. A hectare of such trees (about 400
-on 2½ acres) would at the same rate transpire about 900,000 gallons, or
-about 30,000 barrels in one summer.
-
-FOOTNOTE:
-
-[6] Demonstrations may be made with prepared sections of leaves,
-
-
-
-
-CHAPTER V.
-
-PATH OF MOVEMENT OF WATER IN PLANTS.
-
-
-=93.= In our study of root pressure and transpiration we have seen
-that large quantities of water or solutions move upward through the
-stems of plants. We are now led to inquire through what part of the
-stems the liquid passes in this upward movement, or in other words,
-what is the path of the “sap” as it rises in the stem. This we can
-readily see by the following trial.
-
-=94. Place the cut ends of leafy shoots in a solution of some of
-the red dyes.=—We may cut off leafy shoots of various plants and
-insert the cut ends in a vessel of water to which have been added a few
-crystals of the dye known as fuchsin to make a deep red color (other
-red dyes may be used, but this one is especially good). If the study is
-made during the summer, the “touch-me-not” (impatiens) will be found a
-very useful plant, or the garden balsam, which may also be had in the
-winter from conservatories. Almost any plant will do, however, but we
-should also select one like the corn plant (zea mays) if in the summer,
-or the petioles of a plant like caladium, which can be obtained from
-the conservatory. If seedlings of the castor-oil bean are at hand we
-may cut off some shoots which are 8-10 inches high, and place them in
-the solution also.
-
-=95. These solutions color the tracts in the stem and leaves through
-which they flow.=—After a few hours in the case of the impatiens,
-or the more tender plants, we can see through the stem that certain
-tracts are colored red by the solution, and after 12 to 24 hours there
-may be seen a red coloration of the leaves of some of the plants
-used. After the shoots have been standing in the solution for a few
-hours, if we cut them at various places we will note that there are
-several points in the section where the tissues are colored red. In
-the impatiens perhaps from four to five, in the sunflower a larger
-number. In these plants the colored areas on a cross-section of the
-stem are situated in a concentric ring which separates more or less
-completely an outer ring of the stem from the central portion. If we
-now split portions of the stem lengthwise we see that these colored
-areas continue throughout the length of the stem, in some cases even up
-to the leaves and into them.
-
-[Illustration: Fig. 57. Broken corn stalk, showing fibrovascular
-bundles.]
-
-=96.= If we cut across the stem of a corn plant which has been
-in the solution, we see that instead of the colored areas being in
-a concentric ring they are irregularly scattered, and on splitting
-the stem we see here also that these colored areas extend for long
-distances through the stem. If we take a corn stem which is mature, or
-an old and dead one, cut around through the outer hard tissues, and
-then break the stem at this point, from the softer tissue long strings
-of tissue will pull out as shown in fig. 57. These strings of denser
-tissue correspond to the areas which are colored by the dye. They are
-in the form of minute bundles, and are called _vascular bundles_.
-
-=97.= We thus see that instead of the liquids passing through the
-entire stem they are confined to definite courses. Now that we have
-discovered the path of the upward movement of water in the stem, we are
-curious to see what the structure of these definite portions of the
-stem is.
-
-[Illustration: Fig. 58.
-
-Xylem portion of bundle. Cambium portion of bundle. Bast portion of
-bundle.
-
-Section of vascular bundle of sunflower stem.]
-
-=98. Structure of the fibrovascular bundles.=—We should now make
-quite thin cross-sections, either free hand and mount in water for
-microscopic examination, or they may be made with a microtome and
-mounted in Canada balsam, and in this condition will answer for future
-study. To illustrate the structure of the bundle in one type we may
-take the stem of the castor-oil bean. On examining these cross-sections
-we see that there are groups of cells which are denser than the ground
-tissue. These groups correspond to the colored areas in the former
-experiments, and are the vascular bundles cut across. These groups are
-somewhat oval in outline, with the pointed end directed toward the
-center of the stem. If we look at the section as a whole we see that
-there is a narrow continuous ring[7] of small cells situated at the
-same distance from the center of the stem as the middle part of the
-bundles, and that it divides the bundles into two groups of cells.
-
-=99. Woody portion of the bundle.=—In that portion of the bundle
-on the inside of the ring, i.e., toward the “pith,” we note large,
-circular, or angular cavities. The walls of these cells are quite thick
-and woody. They are therefore called wood cells, and because they
-are continuous with cells above and below them in the stem in such a
-way that long tubes are formed, they are called woody vessels. Mixed
-in with these are smaller cells, some of which also have thick walls
-and are wood cells. Some of these cells may have thin walls. This
-is the case with all when they are young, and they are then classed
-with the fundamental tissue or soft tissue (parenchyma). This part of
-the bundle, since it contains woody vessels and fibres, is the _wood
-portion_ of the bundle, or technically the _xylem_.
-
-=100. Bast portion of the bundle.=—If our section is through a
-part of the stem which is not too young, the tissues of the outer part
-of the bundle will show either one or several groups of cells which
-have white and shiny walls, that are thickened as much or more than
-those of the wood vessels. These cells are _bast_ cells, and for this
-reason this part of the bundle is the _bast_ portion, or the _phloem_.
-Intermingled with these, cells may often be found which have thin
-walls, unless the bundle is very old. Nearer the center of the bundle
-and still within the bast portion are cells with thin walls, angular
-and irregularly arranged. This is the softer portion of the bast, and
-some of these cells are what are called _sieve_ tubes, which can be
-better seen and studied in a longitudinal section of the stem.
-
-=101. Cambium region of the bundle.=—Extending across the center
-of the bundle are several rows of small cells, the smallest of the
-bundle, and we can see that they are more regularly arranged, usually
-in quite regular rows, like bricks piled upon one another. These cells
-have thinner walls than any others of the bundle, and they usually take
-a deeper stain when treated with a solution of some of the dyes. This
-is because they are younger, and are therefore richer in protoplasmic
-contents. This zone of young cells across the bundle is the _cambium_.
-Its cells grow and divide, and thus increase the size of the bundle.
-By this increase in the number of the cells of the cambium layer, the
-outermost cells on either side are continually passing over into the
-phloem, on the one hand, and into the wood portion of the bundle, on
-the other hand.
-
-=102. Longitudinal section of the bundle.=—If we make thin
-longisections of the vascular bundle of the castor-oil seedling (or
-other dicotyledon) so that we have thin ones running through a bundle
-radially, as shown in fig. 59, we can see the structure of these parts
-of the bundle in side view. We see here that the form of the cells is
-very different from what is presented in a cross-section of the same.
-The walls of the various ducts have peculiar markings on them. These
-markings are caused by the walls being thicker in some places than in
-others, and this thickening takes place so regularly in some instances
-as to form regular spiral thickenings. Others have the thickenings in
-the form of the rounds of a ladder, while still others have pitted
-walls or the thickenings are in the form of rings.
-
-[Illustration: Fig. 59.
-
-Longitudinal section of vascular bundle of sunflower stem; spiral,
-scalariform and pitted vessels at left; next are wood fibers with
-oblique cross walls; in middle are cambium cells with straight cross
-walls, next two sieve tubes, then phloem or bast cells.]
-
-=103. Vessels or ducts.=—One way in which the cells in side view
-differ greatly from an end view, in a cross-section in the bundle, is
-that they are much longer in the direction of the axis of the stem. The
-cells have become elongated greatly. If we search for the place where
-two of these large cells with spiral, or ladder-like, markings meet end
-to end, we see that the wall which formerly separated the cells has
-nearly or quite disappeared. In other words the two cells have now an
-open communication at the ends. This is so for long distances in the
-stem, so that long columns of these large cells form tubes or vessels
-through which the water rises in the stems of plants.
-
-=104.= In the bast portion of the bundle we detect the cells of
-the bast fibers by their thick walls. They are very much elongated and
-the ends taper out to thin points so that they overlap. In this way
-they serve to strengthen the stem.
-
-=105. Sieve tubes.=—Lying near the bast cells, usually toward
-the cambium, are elongated cells standing end to end, with delicate
-markings on their cross walls which appear like finely punctured plates
-or sieves. The protoplasm in such cells is usually quite distinct, and
-sometimes contracted away from the side walls, but attached to the
-cross walls, and this aids in the detection of the sieve tubes (fig.
-59.) The granular appearance which these plates present is caused by
-minute perforations through the wall so that there is a communication
-between the cells. The tubes thus formed are therefore called sieve
-tubes and they extend for long distances through the tube so that there
-is communication throughout the entire length of the stem. (The
-function of the sieve tubes is supposed to be that for the downward
-transportation of substances elaborated in the leaves.)
-
-=106.= If we section in like manner the stem of the sunflower we
-shall see similar bundles, but the number is greater than eight. In
-the garden balsam the number is from four to six in an ordinary stem
-3-4_mm_ diameter. Here we can see quite well the origin of the vascular
-bundle. Between the larger bundles we can see especially in free-hand
-sections of stems through which a colored solution has been lifted by
-transpiration, as in our former experiments, small groups of the minute
-cells in the cambial ring which are colored. These groups of cells
-which form strands running through the stem are _pro-cambium strands_.
-The cells divide and increase just like the cambium cells, and the
-older ones thrown off on either side change, those toward the center
-of the stem to wood vessels and fibers, and those on the outer side to
-bast cells and sieve tubes.
-
-=107. Fibrovascular bundles in the Indian corn.=—We should now
-make a thin transection of a portion of the center of the stem of
-Indian corn, in order to compare the structure of the bundle with that
-of the plants which we have just examined. In fig. 60 is represented a
-fibrovascular bundle of the stem of the Indian corn. The large cells
-are those of the spiral and reticulated and annular vessels. This is
-the woody portion of the bundle or xylem. Opposite this is the bast
-portion or phloem, marked by the lighter colored tissue at _i_. The
-larger of these cells are the sieve tubes, and intermingled with them
-are smaller cells with thin walls. Surrounding the entire bundle are
-small cells with thick walls. These are elongated and the tapering ends
-overlap. They are thus slender and long and form fibers. In such a
-bundle all of the cambium has passed over into permanent tissue and is
-said to be closed.
-
-[Illustration: Fig. 60.
-
-Transection of fibrovascular bundle of Indian corn. _a_, toward
-periphery of stem; _g_, large pitted vessels; _s_, spiral vessel; _r_,
-annular vessel; _l_, air cavity formed by breaking apart of the cells;
-_i_, soft bast, a form of sieve tissue; _p_, thin-walled parenchyma.
-(Sachs.)]
-
-=108. Rise of water in the vessels.=—During the movement of the
-water or nutrient solutions upward in the stem the vessels of the wood
-portion of the bundle in certain plants are nearly or quite filled,
-if root pressure is active and transpiration is not very rapid. If,
-however, on dry days transpiration is in excess of root pressure, as
-often happens, the vessels are not filled with the water, but are
-partly filled with certain gases because the air or other gases in
-the plant become rarefied as a result of the excessive loss of water.
-There are then successive rows of air or gas bubbles in the vessels
-separated by films of water which also line the walls of the vessels.
-The condition of the vessel is much like that of a glass tube through
-which one might pass the “froth” which is formed on the surface of
-soapy water. This forms a chain of bubbles in the vessels. This chain
-has been called Jamin’s chain because of the discoverer.
-
-=109.= Why water or food solutions can be raised by the plant
-to the height attained by some trees has never been satisfactorily
-explained. There are several theories propounded which cannot be
-discussed here. It is probably a very complex process. Root pressure
-and transpiration both play a part, or at least can be shown, as we
-have seen, to be capable of lifting water to a considerable height. In
-addition to this, the walls of the vessels absorb water by diffusion,
-and in the other elements of the bundle capillarity comes also into
-play, as well as osmosis.
-
-See Organization of Tissues, Chapter 38.
-
-=110. Flow of sap in the spring.=—The cause of the bleeding of
-trees and the flow of sap in the spring is little understood. One of
-the remarkable cases is the flow of sap in maple trees. It begins
-in early spring and ceases as the buds are opening, and seems to be
-initiated by alternation of high and low temperatures of day and night.
-It has been found that the pressures inside of the tree at this time
-are enormously increased during the day, when the temperature rises
-after a cold night. This has led to the belief that the pressure is
-caused by the expansion of the gases in the vascular ducts. The warming
-up of the twigs and branches of the tree would take place rapidly
-during the day, while the interior of the trunk would be only slightly
-affected. The pressures then would cause the sap to flow downward
-during the day, and at night the branches becoming cool, sap would flow
-back again from the roots and trunk.
-
-Recent experiments by Jones _et al._ show that while some of the
-pressure is due to the expansion of gas in the tree by the rise of
-temperature, this cannot account for the enormous pressures which are
-often present, for example, when after a rise in the temperature of 2°
-C. there was an increase of 20 lbs. pressure.
-
-Then again, after the cessation of the flow in late spring there are
-often as great differences between night and day temperatures. It
-therefore seems reasonable to conclude that the expansion of gases by a
-rise in temperature is not the direct cause.
-
-=Activities of the cells.=—It has been suggested by some that
-the rise in temperature exercises an influence on the protoplasts,
-or living cells, so that they are stimulated to a special activity
-resulting in an exudation pressure from the individual cells, which is
-known to take place. With the fall of temperature at night this
-activity would cease and there might result a lessened pressure in
-the cells. Since the specific activities of cells are known to vary
-in different plants, and in the same plant at different seasons, some
-support is gained for this theory, though it is generally believed that
-the activities of the living cells in the stems are not necessary for
-the upward flow of water. It must be admitted, however, that at present
-we know very little about this interesting problem.
-
-FOOTNOTE:
-
-[7] This ring and the bundles separate the stem into two regions,
-an outer one composed of large cells with thin walls, known as the
-cortical cells, or collectively the _cortex_. The inner portion,
-corresponding to what is called the pith, is made up of the same kind
-of cells and is called the _medulla_, or _pith_. When the cells of
-the cortex, as well as of the pith, remain thin walled the tissue is
-called parenchyma. Parenchyma belongs to the group of tissues called
-fundamental.
-
-
-
-
-CHAPTER VI.
-
-MECHANICAL USES OF WATER.
-
-
-=111. Turgidity of plant parts.=—As we have seen by the experiments on
-the leaves, turgescence of the cells is one of the conditions which
-enables the leaves to stand out from the stem, and the lamina of the
-leaves to remain in an expanded position, so that they are better
-exposed to the light, and to the currents of air. Were it not for this
-turgidity the leaves would hang down close against the stem.
-
-[Illustration: Fig. 61. Restoration of turgidity (Sachs).]
-
-=112. Restoration of turgidity in shoots.=—If we cut off a living
-stem of geranium, coleus, tomato, or “balsam,” and allow the leaves
-to partly wilt so that the shoot loses its turgidity, it is possible
-for this shoot to regain turgidity. The end may be freshly cut again,
-placed in a vessel of water, covered with a bell jar and kept in a room
-where the temperature is suitable for the growth of the plant. The
-shoot will usually become turgid again from the water which is absorbed
-through the cut end of the stem and is carried into the leaves where
-the individual cells become turgid, and the leaves are again expanded.
-Such shoots, and the excised leaves also, may often be made turgid
-again by simply immersing them in water, as one of the experiments with
-the salt solution would teach.
-
-=113.= Turgidity may be restored more certainly and quickly in a
-partially wilted shoot in another way. The cut end of the shoot may be
-inserted in a U tube as shown in fig. 61, the end of the tube around
-the stem of the plant being made air-tight. The arm of the tube in
-which the stem is inserted is filled with water and the water is
-allowed to partly fill the other arm. Into this other arm is then
-poured mercury. The greater weight of the mercury causes such pressure
-upon the water that it is pushed into the stem, where it passes up
-through the vessels in the stems and leaves, and is brought more
-quickly and surely to the cells which contain the protoplasm and
-cell-sap, so that turgidity is more quickly and certainly attained.
-
-=114. Tissue tensions.=—Besides the turgescence of the cells
-of the leaves and shoots there are certain tissue tensions without
-which certain tender and succulent shoots, etc., would be limp, and
-would droop. There are a number of plants usually accessible, some at
-one season and some at others, which may be used to illustrate tissue
-tension.
-
-=115. Longitudinal tissue tension.=—For this in early summer one
-may use the young and succulent shoots of the elder (sambucus); or the
-petioles of rhubarb during the summer and early autumn; or the petioles
-of richardia. Petioles of caladium are excellent for this purpose, and
-these may be had at almost any season of the year from the greenhouses,
-and are thus especially advantageous for work during late autumn or
-winter. The tension is so strong that a portion of such a petiole
-10-15_cm_ long is ample to demonstrate it. As we grasp the lower end of
-the petiole of a caladium, or rhubarb leaf, we observe how rigid it is,
-and how well it supports the heavy expanded lamina of the leaf.
-
-=116.= The ends of a portion of such a petiole or other object
-which may be used are cut off squarely. With a knife a strip from
-2-3_mm_ in thickness is removed from one side the full length of the
-object. This strip we now find is shorter than the larger part from
-which it was removed. The outer tissue then exerts a tension upon the
-petiole which tends to shorten it. Let us remove another strip lying
-next this one, and another, and so on until the outer tissues remain
-only upon one side. The object will now bend toward that side. Now
-remove this strip and compare the length of the strips removed with the
-central portion. We find that they are much shorter now. In other words
-there is also a tension in the tissue of the central portion of the
-petiole, the direction of which is opposite to that of the superficial
-tissue. The parts of the petiole now are not rigid, and they easily
-bend. These two longitudinal tissue tensions acting in opposition to
-each other therefore give rigidity to the succulent shoot. It is only
-when the individual cells of such shoots or petioles are turgid that
-these tissue tensions in succulent shoots manifest themselves or are
-prominent.
-
-[Illustration: Fig. 62. Strip from dandelion stem made to imitate a
-plant tendril.]
-
-=117.= To demonstrate the efficiency of this tension in giving
-support, let us take a long petiole of caladium or of rhubarb. Hold it
-by one end in a horizontal position. It is firm and rigid, and does not
-droop, or but little. Remove all of the outer portion of the tissues,
-as described above, leaving only the central portion. Now attempt to
-hold it in a horizontal position by one end. It is flabby and droops
-downward because the longitudinal tension is removed.
-
-=118. Longitudinal tension in dandelion stems.=—Take long
-and fresh dandelion stems. Split them. Note that they coil. The
-longitudinal tension is very great. Place some of these strips in fresh
-water. They coil up into close curls because by the absorption of water
-by the cells the turgescence of the individual cells is increased, and
-this increases the tension in the stem. Now place them in salt water (a
-5 per cent solution). Why do they uncoil?
-
-=119. To imitate the coiling of a tendril.=—Cut out a narrow
-strip from a long dandelion stem. Fasten to a piece of soft wood, with
-the ends close together, as shown in fig. 62. Now place it in fresh
-water and watch it coil. Part of it coils one way and part another way,
-just as a tendril does after the free end has caught hold of some place
-for support.
-
-=120. Transverse tissue tension.=—To illustrate this one may take
-a willow shoot 3-5_cm_ diameter and saw off sections about 2 cm long.
-Cut through the bark on one side and peel it off in a single strip. Now
-attempt to replace it. The bark will not quite cover the wood again,
-since the ends will not meet. It must then have been held in transverse
-tension by the woody part of the shoot.
-
-
-
-
-CHAPTER VII.
-
-STARCH AND SUGAR FORMATION.
-
-
-1. The Gases Concerned.
-
-=121. Gas given off by green plants in the sunlight.=—Let us take
-some green alga, like spirogyra, which is in a fresh condition, and
-place one lot in a beaker or tall glass vessel of water and set this in
-the direct sunlight or in a well lighted place. At the same time cover
-a similar vessel of spirogyra with black cloth so that it will be in
-the dark, or at least in very weak light.
-
-[Illustration: Fig. 63. Oxygen gas given off by spirogyra.]
-
-[Illustration: Fig. 64. Bubbles of oxygen gas given off from elodea in
-presence of sunlight. (Oels.)]
-
-=122.= In a short time we note that in the first vessel small
-bubbles of gas are accumulating on the surface of the threads of the
-spirogyra, and now and then some free themselves and rise to the
-surface of the water. Where there is quite a tangle of the threads the
-gas is apt to become caught and held back in larger bubbles, which on
-agitation of the vessel are freed.
-
-If we now examine the second vessel we see that there are no bubbles,
-or only a very few of them. We are led to believe then that sunlight
-has had something to do with the setting free of this gas from the
-plant.
-
-=123.= We may now take another alga-like vaucheria and perform the
-experiment in the same way, or to save time the two may be set up at
-once. In fact if we take any of the green algæ and treat them as
-described above gas will be given off in a similar manner.
-
-=124.= We may now take one of the higher green plants, an aquatic
-plant like elodea, callitriche, etc. Place the plant in the water with
-the cut end of the stem uppermost, but still immersed, the plant being
-weighted down by a glass rod or other suitable object. If we place the
-vessel of water containing these leafy stems in the bright sunlight,
-in a short time bubbles of gas will pass off quite rapidly from the
-cut end of the stem. If in the same vessel we place another stem, from
-which the leaves have been cut, the number of bubbles of gas given
-off will be very few. This indicates that a large part of the gas is
-furnished by the leaves.
-
-=125.= Another vessel fitted up in the same way should be placed
-in the dark or shaded by covering with a box or black cloth. It will
-be seen here, as in the case of spirogyra, that very few or no bubbles
-of gas will be set free. Sunlight here also is necessary for the rapid
-escape of the gas.
-
-=126.= We may easily compare the rapidity with which light of
-varying intensity effects the setting free of this gas. After cutting
-the end of the stem let us plunge the cut surface several times in
-melted paraffine, or spread over the cut surface a coat of varnish.
-Then prick with a needle a small hole through the paraffine or varnish.
-Immerse the plant in water and place in sunlight as before. The gas now
-comes from the puncture through the coating of the cut end, and the
-number of bubbles given off during a given period can be ascertained by
-counting. If we duplicate this experiment by placing one plant in weak
-light or diffused sunlight, and another in the shade, we can easily
-compare the rapidity of the escape of the gas under the different
-conditions, which represent varying intensities of light. We see then
-that not only is sunlight necessary for the setting free of this gas,
-but that in diffused light or in the shade the activity of the plant in
-this respect is less than in direct sunlight.
-
-=127. What this gas is.=—If we take quite a quantity of the
-plants of elodea and place them under an inverted funnel which is
-immersed in water, the gas will be given off in quite large quantities
-and will rise into the narrow exit of the funnel. The funnel should be
-one with a short tube, or the vessel one which is quite deep so that
-a small test tube which is filled with water may in this condition be
-inverted over the opening of the funnel tube. With this arrangement
-of the experiment the gas will rise in the inverted test tube, slowly
-displace a portion of the water, and become collected in a sufficient
-quantity to afford us a test. When a considerable quantity has
-accumulated in the test tube, we may close the end of the tube in
-the water with the thumb, lift it from the water and invert. The gas
-will rise against the thumb. A dry soft-pine splinter should be then
-lighted, and after it has burned a short time, extinguish the flame by
-blowing upon it, when the still burning end of the splinter should be
-brought to the mouth of the tube as the thumb is quickly moved to one
-side. The glowing of the splinter shows that the gas is _oxygen_.
-
-[Illustration: Fig. 65. Apparatus for collecting quantity of oxygen from
-elodea. (Detmer.)]
-
-[Illustration: Fig. 66. Ready to see what the gas is.]
-
-=128.= It is better to allow the apparatus to stand several days
-in the sunlight in order to catch a full tube of the gas. Or on a sunny
-day carbon dioxide gas can be led into the water in the jar from a
-generator, such an one as is used for the evolution of CO₂. The CO₂
-can be produced by the action of hydrochloric acid on bits of marble.
-The CO₂ should not be run below the funnel. The test tube should be
-fastened so that the light oxygen gas will not raise it off the funnel.
-With the tube full of gas the test for oxygen can be made by lifting
-the tube with one hand and quickly thrusting the glowing end of the
-splinter in with the other hand. If properly handled, the splinter will
-flame again. If it is necessary to keep the apparatus standing for more
-than one day it is well to add fresh water in the place of most of the
-water in the jar. Do not use leaves of land plants in this experiment,
-since the bubbles which rise when these leaves are placed in water are
-not evidence that this process is taking place.
-
-[Illustration: Fig. 67. The splinter lights again in the presence of
-oxygen gas.]
-
-      =129. Oxygen given off by green land plants
-    also.=—If we should extend our experiments to land
-    plants we should find that oxygen is given off by them
-    under these conditions of light. Land plants, however,
-    will not do this when they are immersed in water, but
-    it is necessary to set up rather complicated apparatus
-    and to make analyses of the gases at the beginning and
-    at the close of the experiments. This has been done,
-    however, in a sufficiently large number of cases so
-    that we know that all green plants in the sunlight, if
-    temperature and other conditions are favorable, give
-    off oxygen.
-
-=130. Absorption of carbon dioxide.=—We have next to inquire
-where the oxygen comes from which is given off by green plants when
-exposed to the sunlight, and also to learn something more of the
-conditions necessary for the process. We know that water which has been
-for some time exposed to the air and soil, and has been agitated, like
-running water of streams, or the water of springs, has mixed with it a
-considerable quantity of oxygen and carbon dioxide.
-
-If we boil spring water or hydrant water which comes from a stream
-containing oxygen and carbon dioxide, for about 20 minutes, these
-gases are driven off. We should set this aside where it will not be
-agitated, until it has cooled sufficiently to receive plants without
-injury. Let us now place some spirogyra or vaucheria, and elodea, or
-other green water plant, in this boiled water and set the vessel in the
-bright sunlight under the same conditions which were employed in the
-experiments for the evolution of oxygen. No oxygen is given off.
-
-Can it be that this is because the oxygen was driven from the water in
-boiling? We shall see. Let us take the vessel containing the water,
-or some other boiled water, and agitate it so that the air will be
-thoroughly mixed with it. In this way oxygen is again mixed with the
-water. Now place the plant again in the water, set in the sunlight, and
-in several minutes observe the result. No oxygen or but little is given
-off. There must be then some other requisite for the evolution of the
-oxygen.
-
-=132. The gases are interchanged in the plants.=—We will now
-introduce carbon dioxide again in the water. This can be done by
-leading CO₂ from a gas generator into the water. Broken bits of marble
-are placed in the generator, acted upon by hydrochloric acid, and the
-gas is led over by glass tubing. Now if we place the plant in the water
-and set the vessel in the sunlight, in a few minutes the oxygen is
-given off rapidly.
-
-=133. A chemical change of the gas takes place within the plant
-cell.=—This leads us to believe then that CO₂ is in some way
-necessary for the plant in this process. Since oxygen is given off
-while carbon dioxide, a different gas, is necessary, it would seem that
-a chemical change takes place in the gases within the plant. Since the
-process takes place in such simple plants as spirogyra as well as in
-the more bulky and higher plants, it appears that the changes go on
-within the cell, in fact within the protoplasm.
-
-=134. Gases as well as water can diffuse through the protoplasmic
-membrane.=—Carbon dioxide then is absorbed by the plant while
-oxygen is given off. We see therefore that gases as well as water can
-diffuse through the protoplasmic membrane of plants under certain
-conditions.
-
-
-2. Where Starch is Formed.
-
-We have found by these simple experiments that some chemical change
-takes place within the protoplasm of the green cells of plants during
-the absorption of carbon dioxide and the giving off of oxygen. We
-should examine some of the green parts of those plants used in the
-experiments, or if they are not at hand we should set up others in
-order to make this examination.
-
-=135. Starch formed as a result of this process.=—We may take
-spirogyra which has been standing in water in the bright sunlight for
-several hours. A few of the threads should be placed in alcohol for a
-short time to kill the protoplasm. From the alcohol we transfer the
-threads to a solution of iodine in potassium iodide. We find that
-at certain points in the chlorophyll band a bluish tinge, or color,
-is imparted to the ring or sphere which surrounds the pyrenoid. In
-our first study of the spirogyra cell we noted this sphere as being
-composed of numerous small grains of starch which surround the pyrenoid.
-
-=136. Iodine used as a test for starch.=—This color reaction
-which we have obtained in treating the threads with iodine is the
-well-known reaction, or test, for starch. We have demonstrated then
-that starch is present in spirogyra threads which have stood in the
-sunlight with free access to carbon dioxide.
-
-If we examine in the same way some threads which have stood in the
-dark for a few days we obtain no reaction for starch, or at best only
-a slight reaction. This gives us some evidence that a chemical change
-does take place during this process (absorption of CO₂ and giving off
-of oxygen), and that starch is a product of that chemical change.
-
-=137. Schimper’s method of testing for the presence of starch.=—Another
-convenient and quick method of testing for the presence of starch
-is what is known as Schimper’s method. A strong solution of chloral
-hydrate is made by taking 8 grams of chloral hydrate for every 5_cc_
-of water. To this solution is added a little of an alcoholic tincture
-of iodine. The threads of spirogyra may be placed directly in this
-solution, and in a few moments mounted in water on the glass slip and
-examined with the microscope. The reaction is strong and easily seen.
-
-We should also examine the leaves of elodea, or one of the higher green
-plants which has been for some time in the sunlight. We may use here
-Schimper’s method by placing the leaves directly in the solution of
-chloral hydrate and iodine. The leaves are made transparent by the
-chloral hydrate so that the starch reaction from the iodine is easily
-detected.
-
-The following is a convenient and safe method of extracting chlorophyll
-from leaves. Fill a large pan, preferably a dishpan, half full of
-hot water. This may be kept hot by a small flame. On the water float
-an evaporating dish partly filled with alcohol. The leaves should be
-first immersed in the hot water for several minutes, then placed in the
-alcohol, which will quickly remove the chlorophyll. Now immerse the
-leaves in the iodine solution.
-
-[Illustration: Fig. 68. Leaf of coleus showing green and white areas,
-before treatment with iodine.]
-
-[Illustration: Fig. 69. Similar leaf treated with iodine, the starch
-reaction only showing where the leaf was green.]
-
-=138. Green parts of plants form starch when exposed to light.=—Thus we
-find that in the case of all the green plants we have examined, starch
-is present in the green cells of those which have been standing for
-some time in the sunlight where the process of the absorption of CO₂
-and the giving off of oxygen can go on, and that in the case of plants
-grown in the dark, or in leaves of plants which have stood for some
-time in the dark, starch is absent. We reason from this that starch is
-the product of the chemical change which takes place in the green cells
-under these conditions. The CO₂ which is absorbed by the plant mixes
-with the water (H₂O) in the cell and immediately forms carbonic acid.
-The chlorophyll in the leaf absorbs radiant energy from the sun which
-splits up the carbonic acid, and its elements then are put together
-into a more complex compound, starch. This process of putting together
-the elements of an organic compound is a _synthesis_, or a _synthetic
-assimilation_, since it is done by the living plant. It is therefore a
-synthetic assimilation of carbon dioxide. Since the sunlight supplies
-the energy it is also called _photosynthesis_, or _photosynthetic
-assimilation_. We can also say carbon dioxide assimilation, or CO₂
-assimilation (see paragraph on assimilation at close of Chapter 10).
-
-=139. Starch is formed only in the green parts of variegated
-leaves.=—If we test for starch in variegated leaves like the leaf
-of a coleus plant, we shall have an interesting demonstration of the
-fact that the green parts of plants only form starch. We may take
-a leaf which is partly green and partly white, from a plant which
-has been standing for some time in bright light. Fig. 68 is from a
-photograph of such a leaf. We should first boil it in alcohol to remove
-the green color. Now immerse it in the potassium iodide of iodine
-solution for a short time. The parts which were formerly green are
-now dark blue or nearly black, showing the presence of starch in
-those portions of the leaf, while the white part of the leaf is still
-uncolored. This is well shown in fig. 69, which is from a photograph of
-another coleus leaf treated with the iodine solution.
-
-
-3. Chlorophyll and the Formation of Starch.
-
-=140.= In our experiments thus far in treating of the absorption
-of carbon dioxide and the evolution of oxygen, with the accompanying
-formation of starch, we have used green plants.
-
-=141. Fungi cannot form starch.=—If we should extend our
-experiments to the fungi, which lack the green color so characteristic
-of the majority of plants, we should find that photosynthesis does not
-take place even though the plants are exposed to direct sunlight. These
-plants cannot then form starch, but obtain carbohydrates for food from
-other sources.
-
-=142. Photosynthesis cannot take place in etiolated plants.=—Moreover
-photosynthesis is usually confined to the green plants, and if by any
-means one of the ordinary green plants loses its green color this
-process cannot take place in that plant, even when brought into the
-sunlight, until the green color has appeared under the influence of
-light.
-
-This may be very easily demonstrated by growing seedlings of the
-bean, squash, corn, pea, etc. (pine seedlings are green even when
-grown in the dark), in a dark room, or in a dark receiver of some
-kind which will shut out the rays of light. The room or receiver must
-be quite dark. As the seedlings are “coming up,” and as long as they
-remain in the dark chamber, they will present some other color than
-green; usually they are somewhat yellowed. Such plants are said to be
-_etiolated_. If they are brought into the sunlight now for a few hours
-and then tested for the presence of starch the result will be negative.
-But if the plant is left in the light, in a few days the leaves
-begin to take on a green color, and then we find that carbon dioxide
-assimilation begins.
-
-=143. Chlorophyll and chloroplasts.=—The green substance in
-plants is then one of the important factors in this complicated
-process of forming starch. This green substance is _chlorophyll_,
-and it usually occurs in definite bodies, the chlorophyll bodies, or
-_chloroplasts_.
-
-      The material for new growth of plants grown in the
-    dark is derived from the seed. Plants grown in the dark
-    consist largely of water and protoplasm, the walls
-    being very thin.
-
-=144. Form of the chlorophyll bodies.=—Chlorophyll bodies vary in
-form in some different plants, especially in some of the lower
-plants. This we have already seen in the case of spirogyra, where the
-chlorophyll body is in the form of a very irregular band, which courses
-around the inner side of the cell wall in a spiral manner. In zygnema,
-which is related to spirogyra, the chlorophyll bodies are star-shaped.
-In the desmids the form varies greatly. In œdogonium, another of the
-thread-like algæ, illustrated in fig. 144, the chlorophyll bodies
-are more or less flattened oval disks. In vaucheria, too, a branched
-thread-like alga shown in fig. 138, the chlorophyll bodies are oval in
-outline. These two plants, œdogonium and vaucheria, should be examined
-here if possible, in order to become familiar with their form, since
-they will be studied later under morphology (see chapters on œdogonium
-and vaucheria, for the occurrence and form of these plants). The form
-of the chlorophyll body found in œdogonium and vaucheria is that which
-is common to many of the green algæ, and also occurs in the mosses,
-liverworts, ferns, and the higher plants. It is a more or less rounded,
-oval, flattened body.
-
-[Illustration: Fig. 69_a_.
-
-Section of ivy leaf, palisade cells above, loose parenchyma, with large
-intercellular spaces in center. Epidermal cells on either edge, with no
-chlorophyll bodies.]
-
-=145. Chlorophyll is a pigment which resides in the chloroplast.=—That
-the chlorophyll is a coloring substance which resides in the
-chloroplastid, and does not form the body itself, can be demonstrated
-by dissolving out the chlorophyll when the framework of the
-chloroplastid is apparent. The green parts of plants which have been
-placed for some time in alcohol lose their green color. The alcohol
-at the same time becomes tinged with green. In sectioning such plant
-tissue we find that the chlorophyll bodies, or chloroplastids as they
-are more properly called, are still intact, though the green color is
-absent. From this we know that chlorophyll is a substance distinct from
-that of the chloroplastid.
-
-=146. Chlorophyll absorbs energy from sunlight for photosynthesis.=—It
-has been found by analysis with the spectroscope that chlorophyll
-absorbs certain of the rays of the sunlight. The energy which is thus
-obtained from the sun, called _kinetic_ energy, acts on the molecules
-of CH₂O₃, separating them into molecules of C, H, and O. (When the
-CO₂ from the air enters the plant cell it immediately unites with
-some of the water, forming carbonic acid = CH₂O₃.) After a series of
-complicated chemical changes starch is formed by the union of carbon,
-oxygen, and hydrogen. In this process of the reduction of the CH₂O₃ and
-the formation of starch there is a surplus of oxygen, which accounts
-for the giving off of oxygen during the process.
-
-=147. Rays of light concerned in photosynthesis.=—If a solution
-of chlorophyll be made, and light be passed through it, and this
-light be examined with the spectroscope, there appear what are called
-absorption bands. These are dark bands which lie across certain
-portions of the spectrum. These bands lie in the red, orange, yellow,
-green, blue, and violet, but the bands are stronger in the red, which
-shows that chlorophyll absorbs more of the red rays of light than of
-the other rays. These are the rays of low refrangibility. The kinetic
-energy derived by the absorption of these rays of light is transformed
-into potential energy. That is, the molecule of CH₂O₃ is broken up, and
-then by a different combination of certain elements starch is formed.[8]
-
-[8] In the formation of starch during photosynthesis the separated
-molecules from the carbon dioxide and water unite in such a way that
-carbon, hydrogen, and oxygen are united into a molecule of starch. This
-result is usually represented by the following equation: CO₂ + H₂O =
-CH₂O + O₂. Then by polymerization 6(CH₂O) = C₆H₁₂O₆ = grape sugar.
-Then C₆H₁₂O₆-H₂O = C₆H₁₀O₅ = starch. It is believed, however, that the
-process is much more complicated than this, that several different
-compounds are formed before starch finally appears, and that the
-formula for starch is much higher numerically than is represented by
-C₆H₁₀O₅.
-
-=148. Starch grains formed in the chloroplasts.=—During
-photosynthesis the starch formed is deposited generally in small grains
-within the green chloroplast in the leaf. We can see this easily by
-examining the leaves of some moss-like funaria which has been in the
-light, or in the chloroplasts of the prothallia of ferns, etc. Starch
-grains may also be formed in the chloroplasts from starch which was
-formed in some other part of the plant, but which has passed in
-solution. Thus the functions of the chloroplast are twofold, that of
-photosynthesis and the formation of starch grains.
-
-=149.= In the translocation of starch when it becomes stored up in
-various parts of the plant, it passes from the state of solution into
-starch grains in connection with plastids similar to the chloroplasts,
-but which are not green. The green ones are sometimes called
-_chloroplasts_, while the colorless ones are termed _leucoplasts_, and
-those possessing other colors, as red and yellow, in floral leaves, the
-root of the carrot, etc., are called _chromoplasts_.
-
-=150. Photosynthesis in other than green plants.=—While
-carbohydrates are usually only formed by green plants, there are some
-exceptions. Apparent exceptions are found in the blue-green algæ, like
-oscillatoria, nostoc, or in the brown and red sea weeds like fucus,
-rhabdonia, etc. These plants, however, possess chlorophyll, but it is
-disguised by another pigment or color. There are plants, however, which
-do not have chlorophyll and yet form carbohydrates with evolution of
-oxygen in the presence of light, as for example a purple bacterium,
-in which the purple coloring substance absorbs light, though the rays
-absorbed most energetically are not the red.
-
-[Illustration: Fig. 70.
-
-Cell exposed to weak diffused light showing chlorophyll bodies along
-the horizontal walls.]
-
-[Illustration: Fig. 71.
-
-Same cell exposed to strong light, showing chlorophyll bodies have
-moved to perpendicular walls.
-
-Figs. 70, 71.—Cell of prothallium of fern.]
-
-=151. Influence of light on the movement of chlorophyll
-bodies.=—_In fern prothallia_.—If we place fern prothallia in weak
-light for a few hours, and then examine them under the microscope,
-we find that the most of the chlorophyll bodies in the cells are
-arranged along the inner surface of the horizontal wall. If now the
-same prothallia are placed in a brightly lighted place for a short
-time most of the chlorophyll bodies move so that they are arranged
-along the surfaces of the perpendicular walls, and instead of having
-the flattened surfaces exposed to the light as in the former case, the
-edges of the chlorophyll bodies are now turned toward the light. (See
-figs. 70, 71.) The same phenomenon has been observed in many plants.
-Light then has an influence on chlorophyll bodies, to some extent
-determining their position. In weak light they are arranged so that the
-flattened surfaces are exposed to the incidence of the rays of light,
-so that the chlorophyll will absorb as great an amount as possible
-of kinetic energy; but intense light is stronger than necessary, and
-the chlorophyll bodies move so that their edges are exposed to the
-incidence of the rays. This movement of the chlorophyll bodies is
-different from that which takes place in some water plants like elodea.
-The chlorophyll bodies in elodea are free in the protoplasm. The
-protoplasm in the cells of elodea streams around the inside of the cell
-wall much as it does in nitella and the chlorophyll bodies are carried
-along in the currents, while in nitella they are stationary.
-
-
-
-
-CHAPTER VIII.
-
-STARCH AND SUGAR CONCLUDED. ANALYSIS OF PLANT SUBSTANCE.
-
-
-1. Translocation of Starch.
-
-=152. Translocation of starch.=—It has been found that leaves of
-many plants grown in the sunlight contain starch when examined after
-being in the sunlight for several hours. But when the plants are left
-in the dark for a day or two the leaves contain no starch, or a much
-smaller amount. This suggests that starch after it has been formed may
-be transferred from the leaves, or from those areas of the leaves where
-it has been formed.
-
-[Illustration: Fig. 72.
-
-Leaf of tropæolum with portion covered with corks to prevent the
-formation of starch. (After Detmer.)]
-
-[Illustration: Fig. 73.
-
-Leaf of tropæolum treated with iodine after removal of cork, to show
-that starch is removed from the leaf during the night.]
-
-To test this let us perform an experiment which is often made. We may
-take a plant such as a garden tropæolum or a clover plant, or other
-land plant in which it is easy to test for the presence of starch. Pin
-a piece of circular cork, which is smaller than the area of the leaf,
-on either side of the leaf, as in fig. 72, but allow free circulation
-of air between the cork and the under side of the leaf. Place the plant
-where it will be in the sunlight. On the afternoon of the following
-day, if the sun has been shining, test the entire leaf for starch. The
-part covered by the cork will not give the reaction for starch, as
-shown by the absence of the bluish color, while the other parts of the
-leaf will show it. The starch which was in that part of the leaf the
-day before was dissolved and removed during the night, and then during
-the following day, the parts being covered from the light, no starch
-was formed in them.
-
-=153. Starch in other parts of plants than the leaves.=—We may
-use the iodine test to search for starch in other parts of plants than
-the leaves. If we cut a potato tuber, scrape some of the cut surface
-into a pulp, and apply the iodine test, we obtain a beautiful and
-distinct reaction showing the presence of starch. Now we have learned
-that starch is only formed in the parts containing chlorophyll. We
-have also learned that the starch which has been formed in the leaves
-disappears from the leaf or is transferred from the leaf. We judge
-therefore that the starch which we have found in the tuber of the
-potato was formed first in the green leaves of the plant, as a result
-of photosynthesis. From the leaves it is transferred in solution to
-the underground stems, and stored in the tubers. The starch is stored
-here by the plant to provide food for the growth of new plants from the
-tubers, which are thus much more vigorous than the plants would be if
-grown from the seed.
-
-=154. Form of starch grains.=—Where starch is stored as a reserve
-material it occurs in grains which usually have certain characters
-peculiar to the species of plant in which they are found. They vary
-in size in many different plants, and to some extent in form also.
-If we scrape some of the cut surface of the potato tuber into a pulp
-and mount a small quantity in water, or make a thin section for
-microscopic examination, we find large starch grains of a beautiful
-structure. The grains are oval in form and more or less irregular in
-outline. But the striking peculiarity is the presence of what seem to
-be alternating dark and light lines in the starch grain. We note that
-the lines form irregular rings, which are smaller and smaller until
-we come to the small central spot termed the “hilum” of the starch
-grain. It is supposed that these apparent lines in the starch grain are
-caused by the starch substance being deposited in alternating dense
-and dilute layers, the dilute layers containing more water than the
-dense ones; others think that the successive layers from the hilum
-outward are regularly of diminishing density, and that this gives the
-appearance of alternating lines. The starch formed by plants is one of
-the organic substances which are manufactured by plants, and it (or
-glucose) is the basis for the formation of other organic substances in
-the plant. Without such organic substances green plants cannot make any
-appreciable increase of plant substance, though a considerable increase
-in size of the plant may take place.
-
-NOTE.—The organic compounds resulting from photosynthesis,
-since they are formed by the union of carbon, hydrogen, and oxygen in
-such a way that the hydrogen and oxygen are usually present in the same
-proportion as in water, are called _carbohydrates_. The most common
-carbohydrates are sugars (cane sugar, C₁₂H₂₂O₁₁ for example, in beet
-roots, sugar cane, sugar maple, etc.), starch, and cellulose.
-
-=155. Vaucheria.=—The result of carbon dioxide assimilation in
-the threads of Vaucheria is not clearly understood. Starch is absent or
-difficult to find in all except a few species, while oil globules are
-present in most species. These oil globules are spherical, colorless,
-globose and highly refringent. Often small ones are seen lying against
-chlorophyll bodies. Oil is a _hydrocarbon_ (containing C, H, and O, but
-the H and O are in different proportions from what they are in H₂O)
-and until recently it was supposed that this oil in Vaucheria was the
-direct result of photosynthesis. But the oil does not disappear when
-the plant is kept for a long time in the dark, which seems to show
-that it is not the direct product of carbon dioxide assimilation, and
-indicates that it comes either from a temporary starch body or from
-glucose. Schimper found glucose in several species of Vaucheria, and
-Waltz says that some starch is present in Vaucheria sericea, while
-in V. tuberosa starch is abundant and replaces the oil. To test for
-oil bodies in Vaucheria treat the threads with weak osmic acid, or
-allow them to stand for twenty-four hours in Fleming’s solution (which
-contains osmic acid). Mount some threads and examine with microscope.
-The oil globules are stained black.
-
-
-2. Sugar, and Digestion of Starch.[9]
-
-=156.= It is probable that some form of sugar is always produced
-as the result of photosynthesis. The sugar thus formed may be stored as
-such or changed to starch. In general it may be said that sugar is most
-common in the green parts of monocotyledonous plants, while starch is
-most frequent in dicotyledons. Plant sugars are of three general kinds:
-cane sugar abundant in the sugar cane, sugar beet, sugar maple, etc.;
-glucose and fruit sugar, found in the fruits of a majority of plants,
-and abundant in some, as in apples, pears, grapes, etc.; and maltose, a
-variety produced in germinating seeds, as in malted barley.
-
-=157. Test for sugar.=—A very pretty experiment maybe made by taking
-two test tubes, placing in one a solution of commercial grape sugar
-(glucose), in the other one of granulated cane sugar, and adding to
-each a few drops of Fehling’s solution.[10] After these tubes have
-stood in a warm place for half an hour, it will be found that a bright
-orange brown or cinnabar-colored precipitate of copper and cuprous
-oxide has formed in the tube containing grape sugar, while the other
-solution is unchanged. Grape sugar or glucose, therefore, reduces
-Fehling’s solution, while cane sugar as such has no effect upon it.
-
-Cane sugar may be changed or converted to glucose by being boiled for a
-short time with a dilute acid, or by adding Fehling’s solution to the
-sugar solution and boiling. In the latter case the change is brought
-about by the alkali and the precipitate of copper and cuprous oxide
-forms.
-
-=158. Tests for sugar in plant tissue.=—(_a_) Scrape out a little
-of the tissue from the inside of a ripe apple or pear, place it with a
-little water in a test tube, and add a few drops of Fehling’s solution.
-After standing half an hour the characteristic precipitate of copper
-and cuprous oxide appears, showing that grape sugar is present in
-quantity.
-
-Make thin sections of the apple and mount in a drop of Fehling’s
-solution on a slide. After half an hour examine with the microscope.
-The granules of cuprous oxide are present in the cells of the tissue in
-great abundance.
-
-(_b_) Cut up several leaves of a young vigorous corn seedling,
-cover with water in a test tube and boil for a minute. After the
-decoction has cooled add the Fehling’s solution and allow to stand.
-The precipitate will appear. For comparison take similar corn leaves,
-remove the chlorophyll with alcohol and test with iodine. No starch
-reaction appears. The carbohydrate in corn leaves is therefore glucose
-and not starch. If now the corn seed be examined the cells will be
-found to be full of starch grains which give the beautiful blue
-reaction with iodine. This experiment shows that grape sugar is formed
-in the leaves of the corn plant, but is changed to starch when stored
-in the seed.
-
-(_c_) Take two leaves of bean seedling or coleus, test one for sugar
-and the other for starch. Both are present.
-
-(_d_) Procure some maple sap in the spring, or in the winter months
-make a decoction of the broken tips of young branches of the sugar
-maple by boiling them in water in a test tube. To the sap or cool
-decoction add Fehling’s solution. No precipitate appears after
-standing. Now heat the same solution to the boiling point, and the
-precipitate forms, showing the presence of cane sugar in the maple
-sap which was converted to glucose and fruit sugar by boiling in the
-presence of an alkali.
-
-(_e_) Scrape out some of the tissue from a sugar beet root, cover with
-water in a test tube and add Fehling’s solution. No change takes place
-after standing. Boil the same solution and the precipitate forms,
-showing the presence of cane sugar, inverted to grape sugar and fruit
-sugar by the hot alkali.
-
-=159. How starch is changed to sugar.=—We have seen that in
-many plants the carbohydrate formed as the result of carbon dioxide
-assimilation is stored as starch. This substance being insoluble
-in water must be changed to sugar, which is soluble before it can
-be used as food or transported to other parts of the plant. This
-is accomplished through the action of certain enzymes, principally
-diastase. This substance has the power of acting upon starch under
-proper conditions of temperature and moisture, causing it to take up
-the elements of water, and so to become sugar.
-
-This process takes place commonly in the leaves where starch is formed,
-but especially in seeds, tubers (during the sprouting, etc.), and
-other parts which the plant uses as storehouses for starch food. It is
-probable that the same conditions of temperature and moisture which
-favor germination or active growth are also favorable to the production
-of diastase.
-
-=160. Experiments to show the action of diastase.=—(_a_) Place
-a bit of starch half as large as a pea in a test tube, and cover with
-a weak solution[11] (about ⅕ per cent) of commercial taka diastase.
-After it has stood in a warm place for five or ten minutes test with
-Fehling’s solution. The precipitate of cuprous oxide appears showing
-that some of the starch has been changed to sugar. By using measured
-quantities, and by testing with iodine at frequent intervals, it can
-be determined just how long it takes a given quantity of diastase to
-change a known quantity of starch. In this connection one should first
-test a portion of the same starch with Fehling’s solution to show that
-no sugar is present.
-
-(_b_) Repeat the above experiment using a little tissue from a potato,
-and some from a corn seed.
-
-(_c_) Take 25 germinating barley seeds in which the radicle is just
-appearing. Grind up thoroughly in a mortar with about three parts of
-water. After this has stood for ten or fifteen minutes, filter. Fill a
-test tube one-third full of water, add a piece of starch half the size
-of a pea or less, and boil the mixture to make starch-paste. Add the
-barley extract. Put in a warm place and test from time to time with
-iodine. The first samples so treated will be blue, later ones violet,
-brown, and finally colorless, showing that the starch has all
-disappeared. This is due to the action of the diastase which was
-present in the germinating seeds, and which was dissolved out and added
-to the starch mixture. The office of this diastase is to change the
-starch in the seeds to sugar. Germinating wheat is sweet, and it is a
-matter of common observation that bread made from sprouted wheat is
-sweet.
-
-(_d_) Put a little starch-paste in a test tube and cover it with saliva
-from the mouth. After ten or fifteen minutes test with Fehling’s
-solution. A strong reaction appears showing how quickly and effectively
-saliva acts in converting starch to sugar. Successive tests with iodine
-will show the gradual disappearance of the starch.
-
-=161. These experiments have shown us that diastase= from three
-different sources can act upon starch converting it into sugar. The
-active principle in the saliva is an _animal_ diastase (_ptyalin_),
-which is necessary as one step in the digestion of starch food in
-animals. The _taka_ diastase is derived from a fungus (Eurotium oryzæ)
-which feeds on the starch in rice grains converting it into sugar
-which the fungus absorbs for food. The _malt_ diastase and _leaf_
-diastase are formed by the seed plants. That in seeds converts the
-starch to sugar which is absorbed by the embryo for food. That in the
-leaf converts the starch into sugar so that it can be transported to
-other parts of the plant to be used in building new tissue, or to be
-stored again in the form of starch (example, the potato, in seeds,
-etc.). The starch is formed in the leaf during the daylight. The light
-renders the leaf diastase inactive. But at night the leaf diastase
-becomes active and converts the starch made during the day. Starch is
-not soluble in water, while the sugar is, and the sugar in solution is
-thus easily transported throughout the plant. In those green plants
-which do not form starch in their leaves (sugar beet, corn, and many
-monocotyledons), grape sugar and fruit sugar are formed in the green
-parts as the result of photosynthesis. In some, like the corn, the
-grape sugar formed in the leaves is transported to other parts of the
-plant, and some of it is stored up in the seed as starch. In others
-like the sugar beet the glucose and fruit sugar formed in the leaves
-flow to other parts of the plant, and much of it is stored up as cane
-sugar in the beet root. The process of photosynthesis probably proceeds
-in the same way in all cases up to the formation of the grape sugar and
-fruit sugar in the leaves. In the beet, corn, etc., the process stops
-here, while in the bean, clover, and most dicotyledons the process is
-carried one step farther in the leaf and starch is formed.
-
-
-3. Rough Analysis of Plant Substance.
-
-=162. Some simple experiments to indicate the nature of plant
-substance.=—After these building-up processes of the plant, it is
-instructive to perform some simple experiments which indicate roughly
-the nature of the plant substance, and serve to show how it can be
-separated into other substances, some of them being reduced to the
-form in which they existed when the plant took them as food. For exact
-experiments and results it would be necessary to make chemical analyses.
-
-=163. The water in the plant.=—Take fresh leaves or leafy shoots
-or other fresh plant parts. Weigh. Permit them to remain in a dry room
-until they are what we call “dry.” Now weigh. The plants have lost
-weight, and from what we have learned in studies of transpiration this
-loss in weight we know to result from the loss of water from the plant.
-
-=164. The dry plant material contains water.=—Take air-dry
-leaves, shavings, or other dry parts of plants. Place them in a test
-tube. With a holder rest the tube in a nearly horizontal position,
-with the bottom of the tube in the flame of a Bunsen burner. Very
-soon, before the plant parts begin to “burn,” note that moisture is
-accumulating on the inner surface of the test tube. This is water
-driven off which could not escape by drying in air, without the
-addition of artificial heat, and is called “hygroscopic water.”
-
-=165. Water formed on burning the dry plant material.=—Light a
-soft-pine or basswood splinter. Hold a thistle tube in one hand with the
-bulb downward and above the flame of the splinter. Carbon will be
-deposited over the inner surface of the bulb. After a time hold the
-tube toward the window and look through it above the carbon. Drops of
-water have accumulated on the inside of the tube. This water is formed
-by the rearrangement of some of the hydrogen and oxygen, which is set
-free by the burning of the plant material, where they were combined
-with carbon, as in the cellulose, and with other elements.
-
-=166. Formation of charcoal by burning.=—Take dried leaves, and
-shavings from some soft wood. Place in a porcelain crucible, and cover
-about 3 cm. deep with dry fine earth. Place the crucible in the flame
-of a Bunsen burner and let it remain for about fifteen minutes. Remove
-and empty the contents. If the flame was hot the plant material will be
-reduced to a good quality of charcoal. The charcoal consists largely of
-carbon.
-
-=167. The ash of the plant.=—Place in the porcelain crucible
-dried leaves and shavings as before. Do not cover with earth. Place the
-crucible in the flame of the Bunsen burner, and for a moment place on
-the porcelain cover; then remove the cover, and note the moisture on
-the under surface from the escaping water. Permit the plant material to
-burn; it may even flame for a time. In the course of fifteen minutes it
-is reduced to a whitish powder, much smaller in bulk than the charcoal
-in the former experiment. This is the ash of the plant.
-
-=168. What has become of the carbon?=—In this experiment the air
-was not excluded from the plant material, so that oxygen combined with
-carbon as the water was freed, and formed carbon dioxide, passing off
-into the air in this form. This it will be remembered is the form in
-which the plant took the carbon-food in through the leaves. Here the
-carbon dioxide met the water coming from the soil, and the two united
-to form, ultimately, starch, cellulose, and other compounds of carbon;
-while with the addition of nitrogen, sulphur, etc., coming also from
-the soil, still other plant substances were formed.
-
-=169.= The carbohydrates are classed among the non-nitrogenous
-substances. Other non-nitrogenous plant substances are the organic
-acids like oxalic acid (H₂C₂O₄), malic acid (H₂C₄H₄O₅), etc.; the fats
-and fixed oils, which occur in the seeds and fruits of many plants. Of
-the nitrogenous substances the proteids have a very complex chemical
-formula and contain carbon, hydrogen, oxygen, nitrogen, sulphur, etc.
-(example, _aleuron_, or proteid grains, found in seeds). The proteids
-are the source of nitrogenous food for the seedling during germination.
-Of the amides, _asparagin_ (C₄H₈N₂O₃) is an example of a nitrogenous
-substance; and of the alkaloids, nicotin (C₁₀H₁₄N₂) from tobacco.
-
-All living plants contain a large per cent of water. According to
-Vines “ripe seeds dried in the air contain 12 to 15 per cent of water,
-herbaceous plants 60 to 80 per cent, and many water plants and fungi as
-much as 95 per cent of their weight.” When heated to 100° C. the water
-is driven off. The dry matter remaining is made up partly of organic
-compounds, examples of which are given above, and inorganic compounds.
-By burning this dry residue the organic substances are mostly changed
-into volatile products, principally carbonic acid, water, and nitrogen.
-The inorganic substances as a result of combustion remain as a white or
-gray powder, the _ash_.
-
-The amount of the ash increases with the age of the plant, though the
-percentage of ash may vary at different times in the different members
-of the plant. The following table taken from Vines will give an idea of
-the amount and composition of the ash in the dry solid of a few plants:
-
-                      CONTENT OF 1000 PARTS OF DRY SOLID MATTER.
-
-                     |Clover, in|Wheat,|Wheat,|Potato|Apples|  Peas
-                     | blossom  |grain |straw |tubers|      |(the seed)
-   ------------------+----------+------+------+------+------+----------
-    Ash.             |  68.3    | 19.7 | 53.7 | 37.7 | 14.4 |  27.3
-    Potash.          |  21.96   | 6.14 | 7.33 | 22.76|  5.14|  11.41
-    Soda.            |   1.39   | 0.44 | 0.74 |  0.99|  3.76|   0.26
-    Lime.            |  24.06   | 0.66 | 3.09 |  0.97|  0.59|   1.36
-    Magnesium.       |   7.44   | 2.36 | 1.33 |  1.77|  1.26|   2.17
-    Ferric Oxide.    |   0.72   | 0.26 | 0.33 |  0.45|  0.2 |   0.16
-    Phosphoric Acid. |   6.74   | 9.26 | 2.58 |  6.53|  1.96|   9.95
-    Sulphuric Acid.  |   2.06   | 0.07 | 1.32 |  2.45|  0.88|   0.95
-    Silica.          |   1.62   | 0.42 |36.25 |  0.8 |  0.62|   0.24
-    Chlorine.        |   2.66   | 0.04 |  0.9 |  1.17|  ....|   0.42
-   ------------------+----------+------+------+------+------+----------
-
-FOOTNOTES:
-
-[9] Paragraphs 156-160 were prepared by Dr. E. J. Durand.
-
-[10] Make up three stock solutions as follows:
-   (1) Copper sulphate 9 grams Water 250 cc.
-   (2) Caustic potash 30 grams Water 250 cc.
-   (3) Rochelle salts 49 grams Water 250 cc.
-   For Fehling’s solution take one volume of each of (1), (2), and (3),
-   and to the mixture add two volumes of water.
-
-[11] This solution of taka diastase should be made up cold. If it is
-     heated to 60° C. or over it is destroyed.
-
-
-
-
-CHAPTER IX.
-
-HOW PLANTS OBTAIN THEIR FOOD. I.
-
-
-1. Sources of Plant Food.
-
-=170. The necessary constituents of plant food.=—As indicated in
-Chapter 3, investigation has taught us the principal constituents of
-plant food. Some suggestion as to the food substances is derived by a
-chemical analysis of various plants. In Chapter 8 it was noted that
-there are two principal kinds of compounds in plant substances, the
-organic compounds and the inorganic compounds or mineral substances.
-The principal elements in the organic compounds are _hydrogen_,
-_carbon_, _oxygen_ and _nitrogen_. The elements in the inorganic
-compounds which have been found indispensable to plant growth are
-_calcium_,[12] _potassium_, _magnesium_, _phosphorus_, _sulphur_ and
-_iron_. (See paragraphs 54-58, and complete observations on water
-cultures.) Other elements are found in the ash of plants; and while
-they are not absolutely necessary for growth, some[13] of them are
-beneficial in one way or another.
-
-=171.= The carbohydrates are derived, as we have learned, from
-the CO₂ of the air, and water in the plant tissue drawn from the soil;
-though in the case of aquatic plants entirely submerged, all the
-constituents are absorbed from the surrounding water.
-
-=172. Food substances in the soil.=—Land plants derive their
-mineral food from the soil, the soil received the mineral substances
-from dissolving and disintegrating rocks. Nitrogenous food is chiefly
-derived from the same source, but under a variety of conditions which
-will be discussed in later paragraphs, but the nitrogen comes primarily
-from the air. Some of the mineral substances, those which are soluble
-as well as some of the nitrogenous substances, are found in solution in
-the soil. These are absorbed by the plant, as needed, along with water,
-through the root hairs.
-
-=173. Absorption of soluble substances.=—Since these substances
-are dissolved in the water of the soil, it is not necessary for us
-to dwell on the process of absorption. This in general is dwelt upon
-in Chapter 3. It should be noted, however, that food substances in
-solution, during absorption, diffuse through the protoplasmic membrane
-independently of each other and also independently of the rate of
-movement of the water from the soil into the root hairs and cells of
-the root.
-
-When the cells have absorbed a certain amount of a given substance,
-no more is absorbed until the concentration of the cell-sap in that
-particular substance is reduced. This, however, does not interfere
-with the absorption of water, or of other substances in solution by
-the same cells. Plants have therefore a certain selective power in the
-absorption of food substances.
-
-=174. Action of root hairs on insoluble substances. Acidity of root
-hairs.=—If we take a seedling which has been grown in a germinator,
-or in the folds of cloths or paper, so that the roots are free from the
-soil, and touch the moist root hairs to blue litmus paper, the paper
-becomes red in color where the root hairs have come in contact. This
-is the reaction for the presence of an acid salt, and indicates that
-the root hairs excrete certain acid substances. This acid property of
-the root hairs serves a very important function in the preparation
-of certain of the elements of plant food in the soil. Certain of the
-chemical compounds of potash, phosphoric acid, etc., become deposited
-on the soil particles, and are not soluble in water. The acid of the
-root hairs dissolves some of these compounds where the particles of
-soil are in close contact with them, and the solutions can then be
-taken up by the roots. Carbonic acid and other acids are also formed in
-the soil, and aid in bringing these substances into solution.
-
-=175.= This corrosive action of the roots can be shown by the
-well-known experiment of growing a plant on a marble plate which is
-covered by soil. In lieu of the marble plate, the peas may be planted
-in clam or oyster shells, which are then buried in the soil of the
-pot, so that the roots of the seedlings will come in contact with the
-smooth surface of the shell. After a few weeks, if the soil be washed
-from the marble where the roots have been in close contact, there will
-be an outline of this part of the root system. Several different acid
-substances are excreted from the roots of plants which have been found
-to redden blue litmus paper by contact. Experiments by Czapek show,
-however, that the carbonic acid excreted by the roots has the power of
-directly bringing about these corrosion phenomena. The acid salts are
-the substances which are most actively concerned in reddening the blue
-litmus paper. They do not directly aid in the corrosion phenomena. In
-the soil, however, where these compounds of potash, phosphoric acid,
-etc., are which are not soluble in water, the acid salt (primary acid
-potassium phosphate) which is most actively concerned in reddening
-the blue litmus paper may act indirectly on these mineral substances,
-making them available for plant food. This salt soon unites with
-certain chlorides in the soil, making among other things small
-quantities of hydrochloric acid.
-
-=176.= NOTE.—It is a general rule that plants cannot
-take solid food into their bodies, but obtain all food in either a
-liquid or gaseous state. The only exception to this is in the case of
-the plasmodia of certain _Myxomycetes_ (Slime Moulds), and also perhaps
-some of the Flagellates and other very low forms, which engulf solid
-particles of food. It is uncertain, however, whether these organisms
-belong to the plant or animal kingdom, and they probably occupy a more
-or less intermediate position.
-
-=177. Action of nitrite and nitrate bacteria.=—Many of the
-higher green plants prefer their nitrogenous food in the form of
-nitrates. (Example, nitrate of soda, potassium nitrate, saltpetre.)
-Nitrates are constantly being formed in soil by the action of certain
-bacteria. The nitrite bacteria (Nitromonas) convert ammonia in the
-soil to _nitrous acid_ (a _nitrite_), while at this point the nitrate
-bacteria (Nitrobacter) convert the nitrites into nitrates. The fact
-that this nitrification is going on constantly in soil is of the utmost
-importance, for while commercial nitrates are often applied to the
-soil, the nitrates are easily washed from the soil by heavy rains.
-These nitrite and nitrate bacteria require oxygen for their activity,
-and they are able to obtain their carbohydrates by decomposing organic
-matter in the soil, or directly by assimilating the CO₂ in the soil,
-deriving the energy for the assimilation of the carbon dioxide from
-the chemical process of nitrification. This kind of carbon dioxide
-assimilation is called _chemosynthetic_ assimilation.
-
-
-2. Parasites and Saprophytes.
-
-=178. Parasites among the fungi.=—A parasite is an organism
-which derives all or a part of its food directly from another living
-organism (its host) and at the latter’s expense. The larger number
-of plant parasites are found among the fungi (rusts, smuts, mildews,
-etc.). (See Nutrition of the Fungi, paragraph 185.) Some of these are
-not capable of development unless upon their host, and are called
-_obligate_ parasites. Others can grow not only as parasites but at
-other times can also grow on dead organic matter, and are called
-_facultative_ parasites, i.e. they can choose either a parasitic life
-or a saprophytic one.
-
-=179. Parasites among the seed plants.=—_Cuscuta._—There are,
-however, parasites among the seed plants; for example, the dodder
-(Cuscuta), parasitic on clover, and a great variety of other plants.
-There is food enough in the seed for the young plant to take root and
-develop a slender stem until it takes hold of its host. It then twines
-around the stem of its host sending wedge-shaped haustoria into the
-stem to obtain food. The part then in connection with the ground dies.
-
-The haustoria of the dodder form a complete junction with the vascular
-bundles of its host so that through the vessels water and salts are
-obtained, while through the junction of sieve tubes the elaborated
-organic food is obtained. The union of the dodder with its host is like
-that between a graft and the graft stock. The beech drops (Epiphegus)
-is another example of a parasitic seed plant. It is parasitic on the
-roots of the beech.
-
-[Illustration: Fig. 74. Dodder.]
-
-=180. The mistletoe= (Viscum album), which grows on the branches
-of trees, sends its roots into the branches, and only the vessels
-of the vascular system are fused according to some. If this is true
-then it probably obtains only water and salts from its host. But the
-mistletoe has green leaves and is thus able to assimilate carbon
-dioxide and manufacture its own organic substances. It is claimed by
-some, however, that the host derives some food from the parasite during
-the winter when the host has shed its leaves, and if this is true it
-would seem that organic food could also be derived during the summer
-from the host by the mistletoe.
-
-=181. Saprophytes.=—A saprophyte is a plant which is enabled
-to obtain its food, especially its organic food, directly from dead
-animals or plants or from dead organic substances. Many fungi are
-saprophytes, as the moulds, mushrooms, etc. (See Nutrition of the
-Fungi.)
-
-=182. Humus saprophytes.=—The action of fungi as described in the
-preceding chapter, as well as of certain bacteria, gradually converts
-the dead plants or plant parts into the finely powdered brown substance
-known as _humus_. In general the green plants cannot absorb organic
-food from humus directly. But plants which are devoid of chlorophyll
-can live saprophytically on this humus. They are known as _humus
-saprophytes_. Many of the mushrooms and other fungi, as well as some
-seed plants which lack chlorophyll or possess only a small quantity,
-are able to absorb all their organic food from humus. It is uncertain
-whether any seed plants can obtain all of their organic food directly
-from humus, though it is believed that many can so obtain a portion
-of it. But a number of seed plants, like the Indian-pipe (Monotropa)
-and certain orchids, obtain organic food from humus. These plants lack
-chlorophyll and cannot therefore manufacture their own carbohydrate
-food. Not being parasitic on plants which can, as in the case of the
-dodder and beech drops mentioned above, they undoubtedly derive their
-organic food from the humus. But fungus mycelium growing in the humus
-is attached to their roots, and in some orchids enters the roots and
-forms a nutritive connection. The fungus mycelium can absorb organic
-food from the humus and in some cases at least can transfer it over to
-the roots of the higher plant (see Mycorhiza).
-
-=183. Autotrophic, heterotrophic, and mixotrophic plants.=—An
-_autotrophic_ plant is one which is self-nourishing, i.e. it is
-provided with an abundant chlorophyll apparatus for carbon dioxide
-assimilation and with absorbing organs for obtaining water and salts.
-Heterotrophic plants are not provided with a chlorophyll apparatus
-sufficient to assimilate all the carbon dioxide necessary, so they
-nourish themselves by other means. _Mixotrophic_ plants are those
-which are intermediate between the other two, i.e. they have some
-chlorophyll but not enough to provide all the organic food necessary,
-so they obtain a portion of it by other means. Evidently there are all
-gradations of mixotrophic plants between the two other kinds (example,
-the mistletoe).
-
-=184. Symbiosis.=—Symbiosis means a living with or living
-together, and is said of those organisms which live so closely in
-connection with each other as to be influenced for better or worse,
-especially from a nutrition standpoint. _Conjunctive_ symbiosis has
-reference to those cases where there is a direct interchange of
-food material between the two organisms (lichens, mycorhiza, etc.).
-_Disjunctive_ symbiosis has reference to an inter-life relation without
-any fixed union between them (example, the relations between flowers
-and insects, ants and plants, and even in a broad sense the relation
-between saprophytic plants in reducing organic matter to a condition
-in which it may be used for food by the green plants, and these in
-turn provide organic matter for the saprophytes to feed upon, etc.).
-_Antagonistic_ symbiosis is shown in the relation of parasite to its
-host, _reciprocal_ symbiosis, or _mutualistic_ symbiosis is shown in
-those cases where both symbionts derive food as a result of the union
-(lichens, mycorhiza, etc.).
-
-
-3. How Fungi Obtain their Food.
-
-[Illustration: Fig. 75. Carnation rust on leaf and flower stem. From
-photograph.]
-
-=185. Nutrition of moulds.=—In our study of mucor, as we have
-seen, the growing or vegetative part of the plant, the mycelium, lies
-within the substratum, which contains the food materials in solution,
-and the slender threads are thus bathed on all sides by them. The
-mycelium absorbs the watery solutions throughout the entire system of
-ramifications. When the upright fruiting threads are developed they
-derive the materials for their growth directly from the mycelium with
-which they are in connection. The moulds which grow on decaying fruit
-or on other organic matter derive their nutrient materials in the same
-way. The portion of the mould which we usually see on the surface of
-these substances is in general the fruiting part. The larger part of
-the mycelium lies hidden within the substratum.
-
-=186. Nutrition of parasitic fungi.=—Certain of the fungi grow on
-or within the higher plants and derive their food materials from them
-and at their expense. Such a fungus is called a _parasite_, and there
-are a large number of these plants which are known as _parasitic
-fungi_. The plant at whose expense they grow is called the “_host_.”
-
-One of these parasitic fungi, which it is quite easy to obtain in
-greenhouses or conservatories during the autumn and winter, is the
-carnation rust (_Uromyces caryophyllinus_), since it breaks out in
-rusty dark brown patches on the leaves and stems of the carnation (see
-fig. 75). If we make thin cross-sections through one of these spots
-on a leaf, and place them for a few minutes in a solution of chloral
-hydrate, portions of the tissues of the leaf will be dissolved. After
-a few minutes we wash the sections in water on a glass slip, and stain
-them with a solution of eosin. If the sections were carefully made, and
-thin, the threads of the mycelium will be seen coursing between the
-cells of the leaf as slender threads. Here and there will be seen short
-branches of these threads which penetrate the cell wall of the host and
-project into the interior of the cell in the form of an irregular knob.
-Such a branch is a _haustorium_. By means of this haustorium, which is
-here only a short branch of the mycelium, nutritive substances are
-taken by the fungus from the protoplasm or cell-sap of the carnation.
-From here it passes to the threads of the mycelium. These in turn
-supply food material for the development of the dark brown gonidia,
-which we see form the dark-looking powder on the spots. Many other
-fungi form haustoria, which take up nutrient matters in the way
-described for the carnation rust. In the case of other parasitic fungi
-the threads of the mycelium themselves penetrate the cells of the host,
-while in still others the mycelium courses only between the cells of
-the host (fungus of peach leaf curl for example) and derives food
-materials from the protoplasm or cell-sap of the host by the process of
-osmosis.
-
-[Illustration: Fig. 76. Several teleutospores, showing the variations
-in form.]
-
-[Illustration: Fig. 77. Cells from the stem of a rusted carnation,
-showing the intercellular mycelium and haustoria. Object magnified 30
-times more than the scale.]
-
-[Illustration: Fig. 78. Cell from carnation leaf, showing haustorium of
-rust mycelium grasping the nucleus of the host. _h_, haustorium; _n_,
-nucleus of host.]
-
-[Illustration: Fig. 79. Intercellular mycelium with haustoria entering
-the cells. _A_, of Cystopus candidus (white rust); _B_, of Peronospora
-calotheca. (De Bary.)]
-
-=187. Nutrition of the larger fungi.=—If we select some one of
-the larger fungi, the majority of which belong to the mushroom family
-and its relatives, which is growing on a decaying log or in the soil,
-we shall see on tearing open the log, or on removing the bark or part
-of the soil, as the case may be, that the stem of the plant, if it have
-one, is connected with whitish strands. During the spring, summer, or
-autumn months, examples of the mushrooms connected with these strands
-may usually be found readily in the fields or woods, but during the
-winter and colder parts of the year often they may be seen in forcing
-houses, especially those cellars devoted to the propagation of the
-mushroom of commerce.
-
-=188.= These strands are made up of numerous threads of the
-mycelium which are closely twisted and interwoven into a cord or
-strand, which is called a mycelium strand, or _rhizomorph_. These are
-well shown in fig. 236, which is from a photograph of the mycelium
-strands, or “spawn” as the grower of mushrooms calls it, of Agaricus
-campestris. The little knobs or enlargements on the strands are the
-young fruit bodies, or “buttons.”
-
-[Illustration: Fig. 80. Sterile mycelium on wood props in coal mine, 400
-feet below surface.
-
-(Photographed by the author.)]
-
-=189.= While these threads or strands of the mycelium in the
-decaying wood or in the decaying organic matter of the soil are not
-true roots, they function as roots, or root hairs, in the absorption
-of food materials. In old cellars and on damp soil in moist places we
-sometimes see fine examples of this vegetative part of the fungi, the
-mycelium. But most magnificent examples are to be seen in abandoned
-mines where timber has been taken down into the tunnels far below
-the surface of the ground to support the rock roof above the mining
-operations. I have visited some of the coal mines at Wilkesbarre, Pa.,
-and here on the wood props and doors, several hundred feet below the
-surface, and in blackest darkness, in an atmosphere almost completely
-saturated at all times, the mycelium of some of the wood destroying
-fungi grows in a profusion and magnificence which is almost beyond
-belief. Fig. 80 is from a flash-light photograph of a beautiful example
-400 feet below the surface of the ground. This was growing over the
-surface of a wood prop or post, and the picture is much reduced. On
-the doors in the mine one can see the strands of the mycelium which
-radiate in fan-like figures at certain places near the margin of
-growth, and farther back the delicate tassels of mycelium which hang
-down in fantastic figures, all in spotless white and rivalling the most
-beautiful fabric in the exquisiteness of its construction.
-
-=190. How fungi derive carbohydrate food.=—The fungi being
-devoid of chlorophyll cannot assimilate the CO₂ from the air. They
-are therefore dependent on the green plants for their carbohydrate
-food. Among the saprophytes, the leaf and wood destroying fungi
-excrete certain substances (known as _enzymes_) which dissolve the
-carbohydrates and certain other organic compounds in the woody or
-leafy substratum in which they grow. They thus produce a sort of
-extracellular digestion of carbohydrates, converting them into a
-soluble form which can be absorbed by the mycelium. The parasitic
-fungi also obtain their carbohydrates and other organic food from the
-host. The mycelium of certain parasitic, and of wood destroying fungi,
-excretes enzymes (_cytase_) which dissolve minute perforations in the
-cell walls of the host and thus aid the hypha during its boring action
-in penetrating cell walls.
-
-NOTE.—Certain wood destroying fungi growing in oaks absorb
-tannin directly, i.e. in an unchanged form. One of the pine destroying
-fungi (_Trametes pini_) absorbs the xylogen from the wood cells,
-leaving the pure cellulose in which the xylogen was filtrated; while
-_Polyporus mollis_ absorbs the cellulose, leaving behind only the wood
-element.
-
-
-4. Mycorhiza.
-
-=191.= While such plants as the Indian-pipe (Monotropa), some
-of the orchids, etc., are _humus saprophytes_ and some of them are
-possibly able to absorb organic food from the humus, many of them have
-fungus mycelium in close connection with their roots, and these fungus
-threads aid in the absorption of organic food. The roots of plants
-which have fungus mycelium intimately associated in connection with
-the process of nutrition, are termed _mycorhiza_. There is a mutual
-interchange of food between the fungus and the host, a _reciprocal
-symbiosis_.
-
-=192. Mycorhiza are of two kinds= as regards the relation of
-the fungus to the root; _ectotrophic_ (or _epiphytic_), where the
-mycelium is chiefly on the outside of the root, and _endotrophic_ (or
-_endophytic_) where the mycelium is chiefly within the tissue of the
-root.
-
-=193. Ectotrophic mycorhiza.=—Ectotrophic mycorhiza occur on the
-roots of the oak, beech, hornbean, etc., in forests where there is a
-great deal of humus from decaying leaves and other vegetation. The
-young growing roots of these trees become closely covered with a thick
-felt of the mycelium, so that no root hairs can develop. The terminal
-roots also branch profusely and are considerably thickened. The fungus
-serves here as the absorbent organ for the tree. It also acts on the
-humus, converting some of it into available plant food and transferring
-it over to the tree.
-
-=194. Endotrophic mycorhiza.=—These are found on many of the
-humus saprophytes, which are devoid of chlorophyll, as well as on those
-possessing little or even on some plants possessing an abundance, of
-chlorophyll. Examples are found in many orchids (see the coral root
-orchid, for example), some of the ferns (Botrychium), the pines,
-leguminous plants, etc. In endotrophic mycorhiza the mycelium is more
-abundant within the tissues of the root, though some of the threads
-extend to the outside. In the case of the mycorhiza on the humus
-saprophytes which have no chlorophyll, or but little, it is thought
-by some that the fungus mycelium in the humus assists in converting
-organic substances and carbohydrates into a form available for food
-by the higher plant and then conducts it into the root, thus aiding
-also in the process of absorption, since there are few or no root
-hairs on the short and fleshy mycorhiza. The roots, however, of some
-of these humus saprophytes have the power of absorbing a portion of
-their organic compounds from the humus. It is thought by some, though
-not definitely demonstrated, that in the case of the oaks, beeches,
-hornbeans, and other chlorophyll-bearing symbionts, the fungus threads
-do not absorb any carbohydrates for the higher symbiont, but that they
-actually derive their carbohydrates from it.[14] But it is reasonably
-certain that the fungus threads do assimilate from the humus certain
-unoxidized, or feebly oxidized, nitrogenous substances (ammonia, for
-example), and transfer them over to the host, for the higher plants
-with difficulty absorb these substances, while they readily absorb
-nitrates which are not abundant in humus. This is especially important
-in the forest. It is likely therefore.
-
-
-5. Nitrogen gatherers.
-
-[Illustration: Fig. 81. Root of the common vetch, showing root
-tubercles.]
-
-=195. How clovers, peas, and other legumes gather nitrogen.=—It
-has long been known that clover plants, peas, beans, and many other
-leguminous plants are often able to thrive in soil where the cereals
-do but poorly. Soil poor in nitrogenous plant food becomes richer in
-this substance where clovers, peas, etc., are grown, and they are often
-planted for the purpose of enriching the soil. Leguminous plants,
-especially in poor soil, are almost certain to have enlargements, in
-the form of nodules, or “root-tubercles.” A root of the common vetch
-with some of these root-tubercles is shown in fig. 81.
-
-=196. A fungal or bacterial organism in these root-tubercles.=—If
-we cut one of these root-tubercles open, and mount a small portion
-of the interior in water for examination with the microscope, we
-shall find small rod-shaped bodies, some of which resemble bacteria,
-while others are more or less forked into forms like the letter Y, as
-shown in fig. 82. These bodies are rich in nitrogenous substances,
-or proteids. They are portions of a minute organism, of a fungus or
-bacterial nature, which attacks the roots of leguminous plants and
-causes these nodular outgrowths. The organism (Phytomyxa leguminosarum)
-exists in the soil and is widely distributed where legumes grow.
-
-=197. How the organism gets into the roots of the legumes.=—This
-minute organism in the soil makes its way through the wall of a root
-hair near the end. It then grows down the interior of the root hair in
-the form of a thread. When it reaches the cell walls it makes a minute
-perforation, through which it grows to enter the adjacent cell, when it
-enlarges again. In this way it passes from the root hair to the cells
-of the root and down to near the center of the root. As soon as it
-begins to enter the cells of the root it stimulates the cells of that
-portion to greater activity. So the root here develops a large lateral
-nodule, or “root-tubercle.” As this “root-tubercle” increases in size,
-the fungus threads branch in all directions, entering many cells. The
-threads are very irregular in form, and from certain enlargements it
-appears that the rod-like bodies are formed, or the thread later breaks
-into myriads of these small “bacteroids.”
-
-[Illustration: Fig. 82. Root-tubercle organism from vetch, old
-condition.]
-
-[Illustration: Fig. 83. Root-tubercle organism from Medicago
-denticulata.]
-
-=198. The root organism assimilates free nitrogen for its
-host.=—This organism assimilates the free nitrogen from the air
-in the soil, to make the proteid substance which is found stored in
-the bacteroids in large quantities. Some of the bacteroids, rich in
-proteids, are dissolved, and the proteid substance is made use of by
-the clover or pea, as the case may be. This is why such plants can
-thrive in soil with a poor nitrogen content. Later in the season some
-of the root-tubercles die and decay. In this way some of the proteid
-substance is set free in the soil. The soil thus becomes richer in
-nitrogenous plant food.
-
-The forms of the bacteroids vary. In some of the clovers they are oval,
-in vetch they are rod-like or forked, and other forms occur in some of
-the other genera.
-
-=199.= NOTE.—So far as we know the legume tubercle
-organism does not assimilate free nitrogen of the air unless it is
-within the root of the legume. But there are microörganisms in the
-soil which are capable of assimilating free nitrogen independently.
-Example, a bacterium, _Clostridium pasteurianum_. Certain bacteria
-and algæ live in _contact symbiosis_ in the soil, the bacteria fixing
-free nitrogen, while in return for the combined nitrogen, the algæ
-furnish the bacteria with carbohydrates. It seems that these bacteria
-cannot fix the free nitrogen of the air unless they are supplied with
-carbohydrates, and it is known that _Clostridium pasteurianum_ cannot
-assimilate free nitrogen unless sugar is present.
-
-
-6. Lichens.
-
-=200. Nutrition of lichens.=—Lichens are very curious plants
-which grow on rocks, on the trunks and branches of trees, and on the
-soil. They form leaf-like expansions more or less green in color, or
-brownish, or gray, or they occur in the form of threads, or small
-tree-like formations. Sometimes the plant fits so closely to the rock
-on which it grows that it seems merely to paint the rock a slightly
-different color, and in the case of many which occur on trees there
-appears to be to the eye only a very slight discoloration of the bark
-of the trunk, with here and there the darker colored points where fruit
-bodies are formed. The most curious thing about them is, however,
-that while they form plant bodies of various form, these bodies are
-of a “dual nature” as regards the organisms composing them. The plant
-bodies, in other words, are formed of two different organisms which,
-woven together, exist apparently as one. A fungus on the one hand grows
-around and encloses in the meshes of its mycelium the cells or threads
-of an alga, as the case may be.
-
-[Illustration: Fig. 84. Frond of lichen (peltigera), showing rhizoids.]
-
-If we take one of the leaf-like forms known as peltigera, which grows
-on damp soil or on the surfaces of badly decayed logs, we see that the
-plant body is flattened, thin, crumpled, and irregularly lobed. The
-color is dull greenish on the upper side, while the under side is white
-or light gray, and mottled with brown, especially the older portions.
-Here and there on the under surface are quite long slender blackish
-strands. These are composed entirely of fungus threads and serve as
-organs of attachment or holdfasts, and for the purpose of supplying
-the plant body with mineral substances which are in solution in the
-water of the soil. If we make a thin section of the leaf-like portion
-of a lichen as shown in fig. 85, we shall see that it is composed of a
-mesh of colorless threads which in certain definite portions contain
-entangled green cells. The colorless threads are those of the fungus,
-while the green cells are those of the alga. These green cells of the
-alga perform the function of chlorophyll bodies for the dual organism,
-while the threads of the fungus provide the mineral constituents of
-plant food. The alga, while it is not killed in the embrace of the
-fungus, does not reach the perfect state of development which it
-attains when not in connection with the fungus. On the other hand the
-fungus profits more than the alga by this association. It forms fruit
-bodies, and perfects spores in the special fruit bodies, which are so
-very distinct in the case of so many of the species of the lichens.
-These plants have lived for so long a time in this close association
-that the fungi are rarely found separate from the algæ in nature, but
-in a number of cases they have been induced to grow in artificial
-cultures separate from the alga. This fact, and also the fact that the
-algæ are often found to occur separate from the fungus in nature, is
-regarded by many as an indication that the plant body of the lichens is
-composed of two distinct organisms, and that the fungus is parasitic on
-the alga.
-
-[Illustration: Fig. 85.
-
-Lichen (peltigera), section of thallus; dark zone of rounded bodies
-made up largely of the algal cells. Fungus cells above, and threads
-beneath and among the algal cells.]
-
-=201.= Others regard the lichens as autonomous plants, that is,
-the two organisms have by this long-continued community of existence
-become unified into an individualized organism, which possesses a habit
-and mode of life distinct from that of either of the organisms forming
-the component parts. This community of existence between two different
-organisms is called by some _mutualism_, or _symbiosis_. While the alga
-enclosed within the meshes of the fungus is not so free to develop,
-and probably does not attain the full development which it would alone
-under favorable conditions, still it is very likely that it is often
-preserved from destruction during very dry periods, within the tough
-thallus, on the surface of bare rocks.
-
-[Illustration: Fig. 86. Section of fruit body or apothecium of lichen
-(parmelia), showing asci and spores of the fungus.]
-
-FOOTNOTES:
-
-[12] Calcium is not essential for the growth of the fungi.
-
-[13] For example, silicon is used by some plants in strengthening
-supporting tissues. Buckwheat thrives better when supplied with a
-chloride.
-
-[14] Evidence points to the belief that certain cells of the host form
-substances which attract, chemitropically, the fungus threads, and that
-in these cells the fungus threads are more abundant than in others.
-Furthermore in the vicinity of the nucleus of the host seems to be the
-place where these activities are more marked.
-
-
-
-
-CHAPTER X.
-
-HOW PLANTS OBTAIN THEIR FOOD, II.
-
-
-Seedlings.
-
-=202.= It is evident from some of the studies which we have made
-in connection with germination of seeds and nutrition of the plant
-that there is a period in the life of the seed plants in which they
-are able to grow if supplied with moisture, but may entirely lack any
-supply of food substance from the outside, though we understand that
-growth finally comes to a standstill unless they are supplied with food
-from the outside. In connection with the study of the nutrition of the
-plant, therefore, it will be well to study some of the representative
-seeds and seedlings to learn more accurately the method of germination
-and nutrition in seedlings during the germinating period.
-
-=203. To prepare seeds for germination.=—Soak a handful of
-seeds (or more if the class is large) in water for 12 to 24 hours.
-Take shallow crockery plates, or ordinary plates, or a germinator
-with a fluted bottom. Place in the bottom some sheets of paper, and
-if sphagnum moss is at hand scatter some over the paper. If the moss
-is not at hand, throw the upper layer of paper into numerous folds.
-Thoroughly wet the paper and moss, but do not have an excess of water.
-Scatter the seeds among the moss or the folds of the paper. Cover
-with some more wet paper and keep in a room where the temperature is
-about 20°C. to 25°C. The germinator should be looked after to see that
-the paper does not become dry. It may be necessary to cover it with
-another vessel to prevent the too rapid evaporation of the water. The
-germinator should be started about a week before the seedlings are
-wanted for study. Some of the soaked seeds should be planted in soil in
-pots and kept at the same temperature, for comparison with those grown
-in the germinator.
-
-[Illustration: Fig. 87. Section of corn seed; at upper right of each is
-the plantlet, next the cotyledon, at left the endosperm.]
-
-=204. Structure of the grain of corn.=—Take grains of corn that
-have been soaked in water for 24 hours and note the form and difference
-in the two sides (in all of these studies the form and structure of
-the seed, as well as the stages in germination, should be illustrated
-by the student). Make a longisection of a grain of corn through the
-middle line, if necessary making several in order to obtain one which
-shows the structures well near the smaller end of the grain. Note
-the following structures: 1st, the hard outer “wall” (formed of the
-consolidated wall of the ovary with the integuments of the ovules—see
-Chapters 35 and 36); 2d, the greater mass of starch and other plant
-food (the endosperm) in the centre; 3d, a somewhat crescent-shaped body
-(the _scutellum_) lying next the endosperm and near the smaller end of
-the grain; 4th, the remaining portion of the young embryo lying between
-the scutellum and the seed coat in the depression. When good sections
-are made one can make out the radicle at the smaller end of the seed,
-and a few successive leaves (the plumule) which lie at the opposite
-end of the embryo shown by sharply curved parallel lines. Observe the
-attachment of the scutellum to the caulicle at the point of junction
-of the plumule and the radicle. The scutellum is a part of the embryo
-and represents a cotyledon. The endosperm is also called _albumen_, and
-such a seed is _albuminous_.
-
-Dissect out an embryo from another seed, and compare with that seen in
-the section.
-
-=205.= In the germination of the grain of corn the endosperm
-supplies the food for the growth of the embryo until the roots are
-well established in the soil and the leaves have become expanded and
-green, in which stage the plant has become able to obtain its food from
-the soil and air and live independently. The starch in the endosperm
-cannot of course be used for food by the embryo in the form of starch.
-It is first converted into a soluble form and then absorbed through
-the surface of the scutellum or cotyledon and carried to all parts of
-the embryo. An enzyme developed by the embryo acts upon the starch,
-converting it into a form of sugar which is in solution and can thus
-be absorbed. This enzyme is one of the so-called diastatic “ferments”
-which are formed during the germination of all seeds which contain food
-stored in the form of starch. In some seedlings, this diastase formed
-is developed in much greater abundance than in others, for example,
-in barley. Examine grains of corn still attached to seedlings several
-weeks old and note that a large part of their content has been used up.
-The action of diastase on starch is described in Chapter 8.
-
-=206. Structure of the pumpkin seed.=—The pumpkin seed has a
-tough papery outer covering for the protection of the embryo plant
-within. This covering is made up of the seed coats. When the seed is
-opened by slitting off these coats there is seen within the “meat”
-of the pumpkin seed. This is nothing more than the embryo plant. The
-larger part of this embryo consists of two flattened bodies which
-are more prominent than any other part of the plantlet at this time.
-These two flattened bodies are the two first leaves, usually called
-_cotyledons_. If we spread these cotyledons apart we see that they are
-connected at one end. Lying between them at this point of attachment
-is a small bud. This is the _plumule_. The plumule consists of the
-very young leaves at the end of the stem which will grow as the seed
-germinates. At the other end where the cotyledons are joined is a small
-projection, the young root, often termed the _radicle_.
-
-=207. How the embryo gets out of a pumpkin seed.=—To see how the
-embryo gets out of the pumpkin seed we should examine seeds germinated
-in the folds of damp paper or on damp sphagnum, as well as some which
-have been germinated in earth. Seeds should be selected which represent
-several different stages of germination.
-
-[Illustration: Fig. 88. Germinating seed of pumpkin, showing how the
-heel or “peg” catches on the seed coat to cast it off.]
-
-[Illustration: Fig. 89. Escape of the pumpkin seedling from the seed
-coats.]
-
-=208. The peg helps to pull the seed coats apart.=—The root
-pushes its way out from between the stout seed coats at the smaller
-end, and then turns downward unless prevented from so doing by a hard
-surface. After the root is 2-4_cm_ long, and the two halves of the seed
-coats have begun to be pried apart, if we look in this rift at the
-junction of the root and stem, we shall see that one end of the seed
-coat is caught against a heel, or “peg,” which has grown out from the
-stem for this purpose. Now if we examine one which is a little more
-advanced, we shall see this heel more distinctly, and also that the
-stem is arching out away from the seed coats. As the stem arches up
-its back in this way it pries with the cotyledons against the upper
-seed coat, but the lower seed coat is caught against this heel, and
-the two are pulled gradually apart. In this way the embryo plant pulls
-itself out from between the seed coats. In the case of seeds which are
-planted deeply in the soil we do not see this contrivance unless we dig
-down into the earth. The stem of the seedling arches through the soil,
-pulling the cotyledons up at one end. Then it straightens up, the green
-cotyledons part, and open out their inner faces to the sunlight, as
-shown in fig. 90. If we dig into the soil we shall see that this same
-heel is formed on the stem, and that the seed coats are cast off into
-the soil.
-
-[Illustration: Fig. 90. Pumpkin seedling rising from the ground.]
-
-=209. Parts of the pumpkin seedling.=—During the germination of
-the seed all parts of the embryo have enlarged. This increase in size
-of a plant is one of the peculiarities of growth. The cotyledons have
-elongated and expanded somewhat, though not to such a great extent
-as the root and the stem. The cotyledons also have become green on
-exposure to the light. Very soon after the main root has emerged from
-the seed coats, other lateral roots begin to form, so that the root
-soon becomes very much branched. The main root with its branches makes
-up the root system of the seedling. Between the expanded cotyledons is
-seen the plumule. This has enlarged somewhat, but not nearly so much as
-the root, or the part of the stem which extends below the cotyledons.
-This part of the stem, i.e., that part below the cotyledons and
-extending to the beginning of the root, is called in all seedlings the
-_hypocotyl_, which means “below the cotyledon.”
-
-=210. The common garden bean.=—The common garden bean, or the
-lima bean, may be used for study. The garden bean is not so flattened
-or broadened as the lima bean. It is rounded compressed, elongate
-slightly curved, slightly concave on one side and convex on the other,
-and the ends are rounded. At the middle of the concave side note the
-distinct scar (the hilum) formed where the bean seed separates from
-its attachment to the wall of the pod. Upon one side of this scar is a
-slight prominence which is continued for a short distance toward the
-end of the bean in the form of a slight ridge. This is the _raphe_, and
-represents that part of the stalk of the ovule which is joined to the
-side of the ovule when the latter is curved around against it (see
-Chapter 36), and at the outer end of the raphe is the _chalaza_,
-the point where the stalk is joined to the end of the ovule, best
-understood in a straight ovule. Upon the opposite side of the scar
-and close to it can be seen a minute depression, the _micropyle_.
-Underneath the seed coat and lying between this point and the end of
-the seed is the _embryo_, which gives greater prominence to the bean at
-this point, but it is especially more prominent after the bean has been
-soaked in water. Soak the beans in water and as they are swelling note
-how the seed coats swell faster than the inner portion of the seed,
-which causes them to wrinkle in a curious way, but finally the inner
-portion swells and fills the seed coat out smooth again. Sketch a bean
-showing all the external features both in side view and in front. Split
-one lengthwise and sketch the half to which the embryo clings, noting
-the young root, stem, and the small leaves which were lying between
-the cotyledons. There is no endosperm here now, since it was all used
-up in the growth of the embryo, and a large part of its substance was
-stored up in the cotyledons. As the seed germinates the young plant
-gets its first food from that stored in the cotyledons. The hypocotyl
-elongates, becomes strongly arched, and at last straightens up, lifting
-the cotyledons from the soil. As the cotyledons become exposed to the
-light they assume a green color. Some of the stored food in them goes
-to nourish the embryo during germination, and they therefore become
-smaller, shrivel somewhat, and at last fall off.
-
-[Illustration: Fig. 91. Garden bean.
-
-_m_, micropyle; _h_, hilum or scar; _r_, raphe; _c_, point where
-chalaza lies.]
-
-[Illustration: Fig. 92. Bean seed split open to show plantlet.]
-
-=211. The castor-oil bean.=—This is not a true bean, since it
-belongs to a very different family of plants (Euphorbiaceæ). In the
-germination of this seed a very interesting comparison can be made with
-that of the garden bean. As the “bean” swells the very hard outer coat
-generally breaks open at the free end and slips off at the stem end.
-The next coat within, which is also hard and shining black, splits
-open at the opposite end, that is at the stem end. It usually splits
-open in the form of three ribs. Next within the inner coat is a very
-thin, whitish film (the remains of the nucellus, and corresponding to
-the perisperm) which shrivels up and loosens from the white mass, the
-endosperm, within. In the castor-oil bean, then, the endosperm is not
-all absorbed by the embryo during the formation of the seed. As the
-plant becomes older we should note that the fleshy endosperm becomes
-thinner and thinner, and at last there is nothing but a thin, whitish
-film covering the green faces of the cotyledons. The endosperm has been
-gradually absorbed by the germinating plant through its cotyledons and
-used for food.
-
-[Illustration: Fig. 93.
-
-How the garden bean comes out of the ground. First the looped
-hypocotyl, then the cotyledons pulled out, next casting off the seed
-coat, last the plant erect, bearing thick cotyledons, the expanding
-leaves, and the plumule between them.]
-
-
-Arisæma triphyllum.[15]
-
-=212. Germination of seeds of jack-in-the-pulpit.=—The ovaries
-of jack-in-the-pulpit form large, bright red berries with a soft pulp
-enclosing one to several large seeds. The seeds are oval in form. Their
-germination is interesting, and illustrates one type of germination of
-seeds common among monocotyledonous plants. If the seeds are covered
-with sand, and kept in a moist place, they will germinate readily.
-
-[Illustration: Fig. 94. Germination of castor-oil bean.]
-
-=213. How the embryo backs out of the seed.=—The embryo lies
-within the mass of the endosperm; the root end, near the smaller end of
-the seed. The club-shaped cotyledon lies near the middle of the seed,
-surrounded firmly on all sides by the endosperm. The stalk, or petiole,
-of the cotyledon, like the lower part of the petiole of the leaves, is
-a hollow cylinder, and contains the younger leaves, and the growing end
-of the stem or bud. When germination begins, the stalk, or petiole, of
-the cotyledon elongates. This pushes the root end of the embryo out
-at the small end of the seed. The free end of the embryo now enlarges
-somewhat, as seen in the figures, and becomes the bulb, or corm, of the
-young plant. At first no roots are visible, but in a short time one,
-two, or more roots appear on the enlarged end.
-
-=214. Section of an embryo.=—If we make a longisection of the
-embryo and seed at this time we can see how the club-shaped cotyledon
-is closely surrounded by the endosperm. Through the cotyledon, then,
-the nourishment from the endosperm is readily passed over to the
-growing embryo. In the hollow part of the petiole near the bulb can be
-seen the first leaf.
-
-[Illustration: Fig. 95. Seedlings of castor-oil bean casting the seed
-coats, and showing papery remnant of the endosperm.]
-
-[Illustration: Fig. 96. Seedlings of jack-in-the-pulpit; embryo backing
-out of the seed.]
-
-[Illustration: Fig. 97.
-
-Section of germinating embryos of jack-in-the-pulpit, showing young
-leaves inside the petiole of the cotyledon. At the left cotyledon shown
-surrounded by the endosperm in the seed; at right endosperm removed to
-show the club-shaped cotyledon.]
-
-=215. How the first leaf appears.=—As the embryo backs out of
-the seed, it turns downward into the soil, unless the seed is so lying
-that it pushes straight downward. On the upper side of the arch thus
-formed, in the petiole of the cotyledon, a slit appears, and through
-this opening the first leaf arches its way out. The loop of the petiole
-comes out first, and the leaf later, as shown in fig. 98. The petiole
-now gradually straightens up, and as it elongates the leaf expands.
-
-[Illustration: Fig. 98. Seedlings of jack-in-the-pulpit, first leaf
-arching out of the petiole of the cotyledon.]
-
-[Illustration: Fig. 99. Embryos of jack-in-the-pulpit still attached to
-the endosperm in seed coats, and showing the simple first leaf.]
-
-[Illustration: Fig. 100. Seedling of jack-in-the-pulpit; section of the
-endosperm and cotyledon.]
-
-=216. The first leaf of the jack-in-the-pulpit is a simple
-one.=—The first leaf of the embryo jack-in-the-pulpit is very
-different in form from the leaves which we are accustomed to see on
-mature plants. If we did not know that it came from the seed of this
-plant we would not recognize it. It is simple, that is it consists
-of one lamina or blade, and not of three leaflets as in the compound
-leaf of the mature plant. The simple leaf is ovate and with a broad
-heart-shaped base. The jack-in-the-pulpit, then, as trillium, and some
-other monocotyledonous plants which have compound leaves on the mature
-plants, have simple leaves during embryonic development. The ancestral
-monocotyledons are supposed to have had simple leaves. Thus there is in
-the embryonic development of the jack-in-the-pulpit, and others with
-compound leaves, a sort of recapitulation of the evolutionary history
-of the leaf in these forms.
-
-=216=_a_. =Germination of the pea.=—Compare with the bean.
-Note especially that the cotyledons are not lifted above the soil as in
-the beans. Compare germination of acorns.
-
-
-Digestion.
-
-=216=_b_. =To test for stored food substance in the seedlings
-studied.=—The pumpkin, squash, and castor-oil bean are examples
-of what are called oily seeds, since considerable oil is stored up
-in the protoplasm in the cotyledons. To test for this, remove a
-small portion of the substance from the cotyledon of the squash and
-crush it on a glass slip in a drop or two of osmic acid.[16] Put on a
-cover glass and examine with a microscope. The black amorphous matter
-shows the presence of oil in the protoplasm. The small bodies which are
-stained yellow are _aleurone_ grains, a form of protein or albuminous
-substance. Both the oil and the protein substance are used by the
-seedling during germination. The oil is converted into an available
-food form by the action of an enzyme called _lipase_, which splits up
-the fatty oil into glucose and other substances. Lipase has been found
-in the endosperm of the castor-oil, cocoanut, and in the cotyledons
-of the pumpkin, as well as in other seeds containing oil as a stored
-product. The aleurone is made available by an enzyme of the nature of
-trypsin. Test the endosperm of the castor-oil bean in the same way.
-Make another test of both the squash and castor-oil seeds with iodine
-to show that starch is not present.
-
-Test the cotyledon of the bean with iodine for the presence of
-starch. If the endosperm of corn seed has not been tested do so now
-with iodine. The endosperm consists largely of starch. The starch is
-converted to glucose by a diastatic “ferment” formed by the seedling as
-it germinates. Make a thin cross-section of a grain of wheat, including
-the seed coat and a portion of the interior, treat with iodine and
-mount for microscopic examination. Note the abundance of starch in the
-internal portion of endosperm. Note a layer of cells on the outside of
-the starch portions filled with small bodies which stain yellow. These
-are aleurone grains. The cellulose in the cell walls of the endosperm
-is dissolved by another enzyme called _cytase_, and some plants store
-up cellulose for food. For example, in the endosperm of the _date_ the
-cell walls are very much thickened and pitted. The cell walls consist
-of reserve cellulose and the seedling makes use of it for food during
-growth.
-
-=216=_c_. =Albuminous and exalbuminous seeds.=—In seeds
-where the food is stored outside of the embryo they are called
-_albuminous_; examples, corn, wheat and other cereals, Indian turnip,
-etc. In those seeds where the food is stored up in the embryo they are
-called _exalbuminous_; examples, bean, pea, pumpkin, squash, etc.
-
-=217. Digestion= has a well-defined meaning in animal physiology
-and relates to the conversion of solid food, usually within the
-stomach, into a soluble form by the action of certain gastric juices,
-so that the liquid food may be absorbed into the circulatory system.
-The term is not often applied in plant physiology, since the method
-of obtaining food is in general fundamentally different in plants and
-animals. It is usually applied to the process of the conversion of
-starch into some form of sugar in solution, as glucose, etc. This we
-have found takes place in the leaf, especially at night, through the
-action of a diastatic ferment developed more abundantly in darkness. As
-a result, the starch formed during the day in the leaves is digested
-at night and converted into sugar, in which form it is transferred to
-the growing parts to be employed in the making of new tissues, or it is
-stored for future use; in other cases it unites with certain inorganic
-substances, absorbed by the roots and raised to the leaf, to form
-proteids and other organic substances. In tubers, seeds, parts of stems
-or leaves where starch is stored, it must first be “digested” by the
-action of some enzyme before it can be used as food by the sprouting
-tubers or germinating seeds.
-
-For example, starch is converted to a glucose by the action of a
-diastase. Cellulose is converted to a glucose by cytase. Albuminoids
-are converted into available food by a tryptic ferment. Fatty oils are
-converted into glucose and other products by lipase.
-
-Inulin, a carbohydrate closely related to starch, is stored up for
-food in solution in many composite plants, as in the artichoke, the
-root tuber of dahlia, etc. When used for food by the growing plant
-it is converted into glucose by an enzyme, inulase. Make a section
-of a portion of a dahlia tuber or artichoke and treat with alcohol.
-The inulin is precipitated into sphæro crystals. (See also paragraphs
-156-161 and 216_b_.)
-
-=218.= Then there are certain fungi which feed on starch or other
-organic substances whether in the host or not, which excrete certain
-enzymes to dissolve the starch, etc., to bring it into a soluble
-form before they can absorb it as food. Such a process is a sort of
-_extracellular digestion_, i.e., the organism excretes the enzyme and
-digests the solid outside, since it cannot take the food within its
-cells in the solid form. To a certain degree the higher plants perform
-also extracellular digestion in the action of root hair excretion on
-insoluble substances, and in the case of the humus saprophytes. But for
-them soluble food is largely prepared by the action of acids, etc., in
-the soil or water, or by the work of fungi and bacteria as described in
-Chapter 9.
-
-=219. Assimilation.=—In plant physiology the term assimilation
-has been chiefly used for the process of carbon dioxide assimilation
-(= photosynthesis). Some objections have been raised against the use
-of assimilation here as one of the life processes of the plant, since
-its inception stages are due to the combined action of light, an
-external factor, and chlorophyll in the plant along with the living
-chloroplastid. So long, however, as it is not known that this process
-can take place without the aid of the living plant, it does not seem
-proper to deny that it is altogether not a process of assimilation. It
-is not necessary to restrict the term assimilation to the formation
-of new living matter in the plant cell; it can be applied also to
-the synthetic processes in the formation of carbohydrates, proteids,
-etc., and called synthetic assimilation. The sun supplies the energy,
-which is absorbed by the chlorophyll, for splitting up the carbonic
-acid, and the living chloroplast then assimilates by a synthetic
-process the carbon, hydrogen, and oxygen. This process then can be
-called _photosynthetic assimilation_. The nitrite and nitrate bacteria
-derive energy in the process of nitrification, which enables them
-to assimilate CO₂ from the air, and this is called _chemosynthetic
-assimilation_. The inorganic material in the form of mineral salts,
-nitrates, etc., absorbed by the root, and carried up to the leaves,
-here meets with the carbohydrates manufactured in the leaf. Under
-the influence of the protoplasm synthesis takes place, and proteids
-and other organic compounds are built up by the union of the salts,
-nitrates, etc., with the carbohydrates. This is also a process of
-synthetic assimilation. These are afterward stored as food, or
-assimilated by the protoplasm in the making of new living matter, or
-perhaps without the first process of synthetic assimilation some of the
-inorganic salts, nitrates, and carbohydrates meeting in the protoplasm
-are assimilated into new living matter directly.
-
-FOOTNOTES:
-
-[15] In lieu of Arisæma make a practical study of the pea. See
-paragraph 216_a_.
-
-[16] Dissolve a half gram of osmic acid in 50 _cc._ of water and keep
-tightly corked when not using.
-
-
-
-
-CHAPTER XI.
-
-RESPIRATION.
-
-
-=220.= One of the life processes in plants which is extremely
-interesting, and which is exactly the same as one of the life processes
-of animals, is easily demonstrated in several ways.
-
-=221. Simple experiment to demonstrate the evolution of CO₂ during
-germination.=—Where there are a number of students and a number of
-large cylinders are not at hand, take bottles of a pint capacity and
-place in the bottom some peas soaked for 12 to 24 hours. Cover with
-a glass plate which has been smeared with vaseline to make a tight
-joint with the mouth of the bottle. Set aside in a warm place for 24
-hours. Then slide the glass plate a little to one side and quickly
-pour in a little baryta water so that it will run down on the inside
-of the bottle. Cover the bottle again. Note the precipitate of barium
-carbonate which demonstrates the presence of CO₂ in the bottle. Lower a
-lighted taper. It is extinguished because of the great quantity of CO₂.
-If flower buds are accessible, place a small handful in each of several
-jars and treat the same as in the case of the peas. Young growing
-mushrooms are excellent also for this experiment, and serve to show
-that respiration takes place in the fungi.
-
-[Illustration: Fig. 101. Test for presence of carbon dioxide in vessel
-with germinating peas. (Sachs.)]
-
-[Illustration: Fig. 102. Apparatus to show respiration of germinating
-wheat.]
-
-=222.= If we now take some of the baryta water and blow our
-“breath” upon it the same film will be formed. The carbon dioxide which
-we exhale is absorbed by the baryta water, and forms barium carbonate,
-just as in the case of the peas. In the case of animals the process by
-which oxygen is taken into the body and carbon dioxide is given off is
-_respiration_. The process in plants which we are now studying is the
-same, and also is respiration. The oxygen in the vessel was partly used
-up in the process, and carbon dioxide was given off. (It will be seen
-that this process is exactly the opposite of that which takes place in
-carbon dioxide assimilation.)
-
-=223. To show that oxygen from the air is used up while plants
-respire.=—Soak some wheat for 24 hours in water. Remove it from
-the water and place it in the folds of damp cloth or paper in a moist
-vessel. Let it remain until it begins to germinate. Fill the bulb of
-a thistle tube with the germinating wheat. By the aid of a stand and
-clamp, support the tube upright, as shown in fig. 102. Let the small
-end of the tube rest in a strong solution of caustic potash (one stick
-caustic potash in two-thirds tumbler of water) to which red ink has
-been added to give a deep red color. Place a small glass plate over the
-rim of the bulb and seal it air-tight with an abundance of vaseline.
-Two tubes can be set up in one vessel, or a second one can be set up in
-strong baryta water colored in the same way.
-
-=224. The result.=—It will be seen that the solution of caustic
-potash rises slowly in the tube; the baryta water will also, if that is
-used. The solution is colored so that it can be plainly seen at some
-distance from the table as it rises in the tube. In the experiment
-from which the figure was made for the accompanying illustration, the
-solution had risen in 6 hours to the height shown in fig. 102. In 24
-hours it had risen to the height shown in fig. 103.
-
-=225. Why the solution of caustic potash rises in the
-tube.=—Since no air can get into the thistle tube from above or
-below, it must be that some part of the air which is inside of the
-tube is used up while the wheat is germinating. From our study of
-germinating peas, we know that a suffocating gas, carbon dioxide, is
-given off while respiration takes place. The caustic potash solution,
-or the baryta water, whichever is used, absorbs the carbon dioxide. The
-carbon dioxide is heavier than air, and so it settles down in the tube
-where it can be absorbed.
-
-[Illustration: Fig. 103. Apparatus to show respiration of germinating
-wheat.]
-
-[Illustration: Fig. 104. Pea seedlings; the one at the left had no
-oxygen and little growth took place, the one at the right in oxygen and
-growth was evident.]
-
-=226. Where does the carbon dioxide come from?=—We know it
-comes from the growing seedlings. The symbol for carbon dioxide is
-CO₂. The carbon comes from the plant, because there is not enough in
-the air. Nitrogen could not join with the carbon to make CO₂. Some
-oxygen from the air or from the protoplasm of the growing seedlings
-(more probably the latter) joins with some of the carbon of the plant.
-These break away from their association with the living substance and
-unite, making CO₂. The oxygen absorbed by the plant from the air unites
-with the living substance, or perhaps first with food substances, and
-from these the plant is replenished with carbon and oxygen. After the
-demonstration has been made, remove the glass plate which seals the
-thistle tube above, and pour in a small quantity of baryta water. The
-white precipitate formed affords another illustration that carbon
-dioxide is released.
-
-[Illustration: Fig. 105.
-
-Experiment to show that growth takes place more rapidly in presence of
-oxygen than in absence of oxygen. The two tubes in the vessel represent
-the condition at the beginning of the experiment. At the close of the
-experiment the roots in the tube at the left were longer than those
-in the tube filled at the start with mercury. The tube outside of
-the vessel represents the condition of things where the peas grew in
-absence of oxygen; the carbon dioxide given off has displaced a portion
-of the mercury. This also shows _anaerobic_ respiration.]
-
-=227. Respiration is necessary for growth.=—After performing
-experiment in paragraph 221, if the vessel has not been open too
-long so that oxygen has entered, we may use the vessel for another
-experiment, or set up a new one to be used in the course of 12 to 24
-hours, after some oxygen has been consumed. Place some folded damp
-filter paper on the germinating peas in the jar. Upon this place
-one-half dozen peas which have just been germinated, and in which the
-roots are about 20-25 _mm_ long. The vessel should be covered tightly
-again and set aside in a warm room. A second jar with water in the
-bottom instead of the germinating peas should be set up as a check.
-Damp folded filter paper should be supported above the water, and on
-this should be placed one-half dozen peas with roots of the same length
-as those in the jar containing carbon dioxide.
-
-=228.= In 24 hours examine and note how much growth has taken
-place. It will be seen that the roots have elongated but very little
-or none in the first jar, while in the second one we see that the
-roots have elongated considerably, if the experiment has been carried
-on carefully. Therefore in an atmosphere devoid of oxygen very little
-growth will take place, which shows that normal respiration with access
-of oxygen (aerobic respiration) is necessary for growth.
-
-=229. Another way of performing the experiment.=—If we wish we
-may use the following experiment instead of the simple one indicated
-above. Soak a handful of peas in water for 12-24 hours, and germinate
-so that twelve with the radicles 20-25 _mm_ long may be selected. Fill
-a test tube with mercury and carefully invert it in a vessel of mercury
-so that there will be no air in the upper end. Now nearly fill another
-tube and invert in the same way. In the latter there will be some air.
-Remove the outer coats from the peas so that no air will be introduced
-in the tube filled with the mercury, and insert them one at a time
-under the edge of the tube beneath the mercury, six in each tube,
-having first measured the length of the radicles. Place in a warm
-room. In 24 hours measure the roots. Those in the air will have grown
-considerably, while those in the other tube will have grown but little
-or none.
-
-=230. Anaerobic respiration.=—The last experiment is also an
-excellent one to show _anaerobic_ respiration. In the tube filled
-with mercury so that when inverted there will be no air, it will be
-seen after 24 hours that a gas has accumulated in the tube which has
-crowded out some of the mercury. With a wash bottle which has an exit
-tube properly curved, some water may be introduced in the tube. Then
-insert underneath a small stick of caustic potash. This will form a
-solution of potash, and the gas will be partly or completely absorbed.
-This shows that the gas was carbon dioxide. This evolution of carbon
-dioxide by living plants when there is no access of oxygen is anaerobic
-respiration (sometimes called intramolecular respiration). It occurs
-markedly in oily seeds and especially in the yeast plant.
-
-[Illustration: Fig. 106. Test for liberation of carbon dioxide from
-leafy plant during respiration. Baryta water in smaller vessel.
-(Sachs.)]
-
-=231. Energy set free during respiration.=—From what we have
-learned of the exchange of gases during respiration we infer that the
-plant loses carbon during this process. If the process of respiration
-is of any benefit to the plant, there must be some gain in some
-direction to compensate the plant for the loss of carbon which takes
-place.
-
-It can be shown by an experiment that during respiration there is a
-slight elevation of the temperature in the plant tissues. The plant
-then gains some heat during respiration. Energy is also manifested by
-growth.
-
-=232. Respiration in a leafy plant.=—We may take a potted plant
-which has a well-developed leaf surface and place it under a tightly
-fitting bell jar. Under the bell jar there also should be placed a
-small vessel containing baryta water. A similar apparatus should be set
-up, but with no plant, to serve as a check. The experiment must be set
-up in a room which is not frequented by persons, or the carbon dioxide
-in the room from respiration will vitiate the experiment. The bell jar
-containing the plant should be covered with a black cloth to prevent
-carbon assimilation. In the course of 10 or 12 hours, if everything has
-worked properly, the baryta water under the jar with the plant will
-show the film of barium carbonate, while the other one will show none.
-Respiration, therefore, takes place in a leafy plant as well as in
-germinating seeds.
-
-=233. Respiration in fungi.=—If several large actively growing
-mushrooms are accessible, place them in a tall glass jar as described
-for determining respiration in germinating peas. In the course of 12
-hours test with the lighted taper and the baryta water. Respiration
-takes place in fungi as well as in green plants.
-
-=234. Respiration in plants in general.=—Respiration is general
-in all plants, though not universal. There are some exceptions in the
-lower plants, notably in certain of the bacteria, which can only grow
-and thrive in the absence of oxygen.
-
-[Illustration: Fig. 107. Fermentation tube with culture of yeast.]
-
-[Illustration: Fig. 108. Fermentation tube filled with CO₂ from action
-of yeast in a sugar solution.]
-
-=235. Respiration a breaking-down process.=—We have seen that
-in respiration the plant absorbs oxygen and gives off carbon dioxide.
-We should endeavor to note some of the effects of respiration on the
-plant. Let us take, say, two dozen dry peas, weigh them, soak for 12-24
-hours in water, and, in the folds of a cloth kept moist by covering
-with wet paper or sphagnum, germinate them. When well germinated and
-before the green color appears dry well in the sun, or with artificial
-heat, being careful not to burn or scorch them. The aim should be to
-get them about as dry as the seeds were before germination. Now weigh.
-The germinated seeds weigh less than the dry peas. There has then been
-a loss of plant substance during respiration.
-
-[Illustration: Fig. 108_a_.
-
-Yeast. Saccharomyces ceriviseæ. _a_, small colony; _b_, single cell
-budding; _c_, single cell forming an ascus with four spores; _d_,
-spores free from the ascus. (After Rees.)]
-
-=236. Fermentation of yeast.=—Take two fermentation tubes. Fill
-the closed tubular parts of each with a weak solution of grape sugar,
-or with potato decoction, leaving the open bulb nearly empty. Into the
-liquid of one of the tubes place a piece of compressed yeast as large
-as a pea. If the tubes are kept in a warm place for 24 hours bubbles
-of gas may be noticed rising in the one in which the yeast was placed,
-while in the second tube no such bubbles appear, especially if the
-filled tubes are first sterilized. The tubes may be kept until the
-first is entirely filled with the gas. Now dissolve in the liquid a
-small piece of caustic potash. Soon the gas will begin to be absorbed,
-and the liquid will rise until it again fills the tube. The gas was
-carbon dioxide, which was chiefly produced during the anaerobic
-respiration of the rapidly growing yeast cells. In bread making this
-gas is produced in considerable quantities, and rising through the
-dough fills it with numerous cavities containing gas, so that the bread
-“rises.” When it is baked the heat causes the gas in the cavities to
-expand greatly. This causes the bread to “rise” more, and baked in this
-condition it is “light.” There are two special processes accompanying
-the fermentation by yeast: 1st, the evolution of carbon dioxide as
-shown above; and, 2d, the formation of alcohol. The best illustration
-of this second process is the brewing of beer, where a form of the same
-organism which is employed in “bread rising” is used to “brew beer.”
-
-=237. The yeast plant.=—Before the caustic potash is placed in
-the tube some of the fermented liquid should be taken for study of
-the yeast plant, unless separate cultures are made for this purpose.
-Place a drop of the fermented liquid on a glass slip, place on this
-a cover glass, and examine with the microscope. Note the minute oval
-cells with granular protoplasm. These are the yeast plant. Note in
-some a small “bud” at one side of the end. These buds increase in size
-and separate from the parent plant. The yeast plant is one-celled,
-and multiplies by “budding” or “sprouting.” It is a fungus, and some
-species of yeast like the present one do not form any mycelium. Under
-certain conditions, which are not very favorable for growth (example,
-when the yeast is grown in a weak nutrient substance on a thin layer of
-a plaster Paris slab), several spores are formed in many of the yeast
-cells. After a period of rest these spores will sprout and produce the
-yeast plant again. Because of this peculiar spore formation some place
-the yeast among the sac fungi. (See classification of the fungi.)
-
-=238. Organized ferments and unorganized ferments.=—An organism
-like the yeast plant which produces a fermentation of a liquid with
-evolution of gas and alcohol is sometimes called a _ferment_, or
-_ferment organism_, or an _organized_ ferment. On the other hand the
-diastatic ferments or enzymes like diastase, taka diastase, animal
-diastase (ptyalin in the saliva), cytase, etc., are _unorganized_
-ferments. In the case of these it is better to say _enzyme_ and leave
-the word ferment for the ferment organisms.
-
-=239. Importance of green plants in maintaining purity of air.=—By
-respiration, especially of animals, the air tends to become “foul”
-by the increase of CO₂. Green plants, i.e., plants with chlorophyll,
-purify the air during photosynthesis by absorbing CO₂ and giving off
-oxygen. Animals absorb in respiration large quantities of oxygen and
-exhale large quantities of CO₂. Plants absorb a comparatively small
-amount of oxygen in respiration and give off a comparatively small
-amount of CO₂. But they absorb during photosynthesis large quantities
-of CO₂ and give off large quantities of oxygen. In this way a balance is
-maintained between the two processes, so that the percentage of CO₂ in
-the air remains approximately the same, viz., about four-tenths of one
-per cent, while there are approximately 21 parts oxygen and 79 parts
-nitrogen.
-
-=239a. Comparison of respiration and photosynthesis.=
-
-                       { Carbon dioxide is taken in by the plant and
-                       {      oxygen is liberated.
-                       { Starch is formed as a result of the metabolism,
-                       {      or chemical change.
-                       { The process takes place only in green plants,
-    Starch formation   {      and in the green parts of plants, that is,
-    or Photosynthesis. {      in the presence of the chlorophyll.
-                       {     (Exception in purple bacterium.)
-                       { The process only takes place under the
-                       {      influence of sunlight.
-                       { It is a building-up process, because new plant
-                       {      substance is formed.
-
-                       { Oxygen is taken in by the plant and carbon
-                       {      dioxide is liberated.
-                       { Carbon dioxide is formed as a result of the
-                       {      metabolism, or chemical change.
-                       { The process takes place in all plants whether
-    Respiration.       {      they possess chlorophyll or not.
-                       {     (Exceptions in anaerobic bacteria).
-                       { The process takes place in the dark as well as
-                       {      in the sunlight.
-                       { It is a breaking-down process, because
-                       {      disintegration of plant substance occurs.
-
-
-
-
-CHAPTER XII.
-
-GROWTH.
-
-
-By growth is usually meant an increase in the bulk of the plant
-accompanied generally by an increase in plant substance. Among the
-lower plants growth is easily studied in some of the fungi.
-
-=240. Growth in mucor.=—Some of the gonidia (often called spores)
-may be sown in nutrient gelatine or agar, or even in prune juice. If
-the culture has been placed in a warm room, in the course of 24 hours,
-or even less, the preparation will be ready for study.
-
-=241. Form of the gonidia.=—It will be instructive if we first
-examine some of the gonidia which have not been sown in the culture
-medium. We should note their rounded or globose form, as well as
-their markings if they belong to one of the species with spiny walls.
-Particularly should we note the size, and if possible measure them with
-the micrometer, though this would not be absolutely necessary for a
-comparison, if the comparison can be made immediately. Now examine some
-of the gonidia which were sown in the nutrient medium. If they have not
-already germinated we note at once that they are much larger than those
-which have not been immersed in a moist medium.
-
-=242. The gonidia absorb water and increase in size before
-germinating.=—From our study of the absorption of water or watery
-solutions of nutriment by living cells, we can easily understand the
-cause of this enlargement of the gonidium of the mucor when surrounded
-by the moist nutrient medium. The cell-sap in the spore takes up more
-water than it loses by diffusion, thus drawing water forcibly through
-the protoplasmic membrane. Since it does not filter out readily, the
-increase in quantity of the water in the cell produces a pressure from
-within which stretches the membrane, and the elastic cell wall yields.
-Thus the gonidium becomes larger.
-
-[Illustration: Fig. 109. Spores of mucor, and different stages of
-germination.]
-
-=243. How the gonidia germinate.=—We should find at this time
-many of the gonidia extended on one side into a tube-like process the
-length of which varies according to time and temperature. The short
-process thus begun continues to elongate. This elongation of the plant
-is _growth_, or, more properly speaking, one of the phenomena of growth.
-
-=244. The germ tube branches and forms the mycelium.=—In the
-course of a day or so branches from the tube will appear. This branched
-form of the threads of the fungus is, as we remember, the mycelium. We
-can still see the point where growth started from the gonidium. Perhaps
-by this time several tubes have grown from a single one. The threads of
-the mycelium near the gonidium, that is, the older portions of them,
-have increased in diameter as they have elongated, though this increase
-in diameter is by no means so great as the increase in length. After
-increasing to a certain extent in diameter, growth in this direction
-ceases, while apical growth is practically unlimited, being limited
-only by the supply of nutriment.
-
-=245. Growth in length takes place only at the end of the thread.=—If
-there were any branches on the mycelium when the culture was first
-examined, we can now see that they remain practically the same distance
-from the gonidium as when they were first formed. That is, the older
-portions of the mycelium do not elongate. Growth in length of the
-mycelium is confined to the ends of the threads.
-
-=246. Protoplasm increases by assimilation of nutrient
-substances.=—As the plant increases in bulk we note that there
-is an increase in the protoplasm, for the protoplasm is very easily
-detected in these cultures of mucor. This increase in the quantity
-of the protoplasm has come about by the assimilation of the nutrient
-substance, which the plant has absorbed. The increase in the
-protoplasm, or the formation of additional plant substance, is another
-phenomenon of growth quite different from that of elongation, or
-increase in bulk.
-
-=247. Growth of roots.=—For the study of the growth of roots we
-may take any one of many different plants. The seedlings of such plants
-as peas, beans, corn, squash, pumpkin, etc., serve excellently for this
-purpose.
-
-=248. Roots of the pumpkin.=—The seeds, a handful or so, are
-soaked in water for about 12 hours, and then placed between layers of
-paper or between the folds of cloth, which must be kept quite moist but
-not very wet, and should be kept in a warm place. A shallow crockery
-plate, with the seeds lying on wet filter paper, and covered with
-additional filter paper, or with a bell jar, answers the purpose well.
-
-The primary or first root (radicle) of the embryo pushes its way out
-between the seed coats at the small end. When the seeds are well
-germinated, select several which have the root 4-5 _cm_ long. With a
-crow-quill pen we may now mark the terminal portion of the root off
-into very short sections as in fig. 110. The first mark should be
-not more than 1 _mm_ from the tip, and the others not more than 1mm
-apart. Now place the seedlings down on damp filter paper, and cover
-with a bell jar so that they will remain moist, and if the season is
-cold place them in a warm room. At intervals of 8 or 10 hours, if
-convenient, observe them and note the farther growth of the root.
-
-[Illustration: Fig. 110. Root of germinating pumpkin, showing region of
-elongation just back of the tip.]
-
-=249. The region of elongation.=—While the root has elongated,
-the region of elongation _is not at the tip of the root. It lies a
-little distance back from the tip_, beginning at about 2mm from the tip
-and extending over an area represented by from 4-5 of the millimeter
-marks. The root shown in fig. 110 was marked at 10 A.M. on
-July 5. At 6 P.M. of the same day, 8 hours later, growth had
-taken place as shown in the middle figure. At 9 A.M. on the
-following day, 15 hours later, the growth is represented in the lower
-one. Similar experiments upon a number of seedlings give the same
-result: the region of elongation in the growth of the root is situated
-a little distance back from the tip. Farther back very little or no
-elongation takes place, but growth in diameter continues for some time,
-as we should discover if we examined the roots of growing pumpkins, or
-other plants, at different periods.
-
-=250. Movement of region of greatest elongation.=—In the region
-of elongation the areas marked off do not all elongate equally at the
-same time. The middle spaces elongate most rapidly and the spaces
-marked off by the 6, 7, and 8 _mm_ marks elongate slowly, those
-farthest from the tip more slowly than the others, since elongation
-has nearly ceased here. The spaces marked off between the 2-4 _mm_
-marks also elongate slowly, but soon begin to elongate more rapidly,
-since that region is becoming the region of greatest elongation. Thus
-the region of greatest elongation moves forward as the root grows, and
-remains approximately at the same distance behind the tip.
-
-=251. Formative region.=—If we make a longitudinal section of the
-tip of a growing root of the pumpkin or other seedling, and examine it
-with the microscope, we see that there is a great difference in the
-character of the cells of the tip and those in the region of elongation
-of the root. First there is in the section a V-shaped cap of loose
-cells which are constantly being sloughed off. Just back of this tip
-the cells are quite regularly isodiametric, that is, of equal diameter
-in all directions. They are also very rich in protoplasm, and have
-thin walls. This is the region of the root where new cells are formed
-by division. It is the _formative region_. The cells on the outside
-of this area are the older, and pass over into the older parts of the
-root and root cap. If we examine successively the cells back from this
-_formative_ region we find that they become more and more elongated in
-the direction of the axis of the root. The elongation of the cells in
-this older portion of the root explains then why it is that this region
-of the root elongates more rapidly than the tip.
-
-=252. Growth of the stem.=—We may use a bean seedling growing
-in the soil. At the junction of the leaves with the stem there are
-enlargements. These are the _nodes_, and the spaces on the stem between
-successive nodes are the _internodes_. We should mark off several of
-these internodes, especially the younger ones, into sections about 5
-_mm_ long. Now observe these at several times for two or three days,
-or more. The region of elongation is greater than in the case of the
-roots, and extends back farther from the end of the stem. In some young
-garden bean plants the region of elongation extended over an area of 40
-_mm_ in one internode. See also Chapters 38, 39.
-
-=253. Force exerted by growth.=—One of the marvelous things
-connected with the growth of plants is the force which is exerted by
-various members of the plant under certain conditions. Observations on
-seedlings as they are pushing their way through the soil to the air
-often show us that considerable force is required to lift the hard soil
-and turn it to one side. A very striking illustration may be had in the
-case of mushrooms which sometimes make their way through the hard and
-packed soil of walks or roads. That succulent and tender plants should
-be capable of lifting such comparatively heavy weights seems incredible
-until we have witnessed it. Very striking illustrations of the force
-of roots are seen in the case of trees which grow in rocky situations,
-where rocks of considerable weight are lifted, or small rifts in large
-rocks are widened by the lateral pressure exerted by the growth of a
-root, which entered when it was small and wedged its way in.
-
-=254. Zone of maximum growth.=—Great variation exists in the
-rapidity of growth even when not influenced by outside conditions. In
-our study of the elongation of the root we found that the cells just
-back of the formative region elongated slowly at first. The rapidity of
-the elongation of these cells increases until it reaches the maximum.
-Then the rapidity of elongation lessens as the cells come to lie
-farther from the tip. The period of maximum elongation here is the
-_zone of maximum growth_ of these cells.
-
-[Illustration: Fig. 111. Lever auxanometer (Oels) for measuring
-elongation of the stem during growth.]
-
-=255.= Just as the cells exhibit a zone of maximum growth, so
-the members of the plant exhibit a similar zone of maximum growth.
-In the case of leaves, when they are young the rapidity of growth
-is comparatively slow, then it increases, and finally diminishes in
-rapidity again. So it is with the stem. When the plant is young the
-growth is not so rapid; as it approaches middle age the rapidity of
-growth increases; then it declines in rapidity at the close of the
-season.
-
-=256. Energy of growth.=—Closely related to the zone of maximum
-growth is what is termed the energy of growth. This is manifested in
-the comparative size of the members of a given plant. To take the
-sunflower for example, the lower and first leaves are comparatively
-small. As the plant grows larger the leaves are larger, and this
-increase in size of the leaves increases up to a maximum period, when
-the size decreases until we reach the small leaves at the top of the
-stem. The zone of maximum growth of the leaves corresponds with the
-maximum size of the leaves on the stem. The rapidity and energy of
-growth of the stem is also correlated with that of the leaves, and the
-zone of maximum growth is coincident with that of the leaves. It would
-be instructive to note it in the case of other plants and also in the
-case of fruits.
-
-=257. Nutation.=—During the growth of the stem all of the cells
-of a given section of the stem do not elongate simultaneously. For
-example the cells at a given moment on the south side are elongating
-more rapidly than the cells on the other side. This will cause the
-stem to bend slightly to the north. In a few moments later the cells
-on the west side are elongating more rapidly, and the stem is turned
-to the east; and so on, groups of cells in succession around the stem
-elongate more rapidly than the others. This causes the stem to describe
-a circle or ellipse about a central point. Since the region of greatest
-elongation of the cells of the stem is gradually moving toward the apex
-of the growing stem, this line of elongation of the cells which is
-traveling around the stem does so in a spiral manner. In the same way,
-while the end of the stem is moving upward by the elongation of the
-cells, and at the same time is slowly moved around, the line which the
-end of the stem describes must be a spiral one. This movement of the
-stem, which is common to all stems, leaves, and roots, is _nutation_.
-
-=258.= The importance of nutation to twining stems in their search
-for a place of support, as well as for the tendrils on leaves or stems,
-will be seen. In the case of the root it is of the utmost importance,
-as the root makes its way through the soil, since the particles of soil
-are more easily thrust aside. The same is also true in the case of many
-stems before they emerge from the soil.
-
-
-
-
-CHAPTER XIII.
-
-IRRITABILITY.
-
-
-=259.= We should now examine the movements of plant parts in
-response to the influence of certain stimuli. By this time we have
-probably observed that the direction which the root and stem take upon
-germination of the seed is not due to the position in which the seed
-happens to lie. Under normal conditions we have seen that the root
-grows downward and the stem upward.
-
-=260. Influence of the earth on the direction of growth.=—When
-the stem and root have been growing in these directions for a short
-time let us place the seedling in a horizontal position, so that the
-end of the root extends over an object of support in such a way that it
-will be free to go in any direction. It should be pinned to a cork and
-placed in a moist chamber. In the course of twelve to twenty-four hours
-the root which was formerly horizontal has turned the tip downward
-again. If we should mark off millimeter spaces beginning at the tip of
-the root, we should find that the motor zone, or region of curvature,
-lies in the same region as that of the elongation of the root.
-
-Knight found that the stimulus which influences the root to turn
-downward is the force of gravity. The reaction of the root in response
-to this stimulus is geotropism, a turning influenced by the earth. This
-term is applied to the growth movements of plants influenced by the
-earth with regard to direction. While the motor zone lies back of the
-root-tip, the latter receives the stimulus and is the perceptive zone.
-If the root-tip is cut off, the root is no longer geotropic, and will
-not turn downward when placed in a horizontal position. Growth toward
-the earth is _progeotropism_. The lateral growth of secondary roots is
-_diageotropism_.
-
-[Illustration: Fig. 112. Germinating pea placed in a horizontal
-position.]
-
-[Illustration: Fig. 113. In 24 hours gravity has caused the root to
-turn downward.
-
-Figs. 112, 113.—Progeotropism of the pea root.]
-
-The stem, on the other hand, which was placed in a horizontal position
-has become again erect. This turning of the stem in the upward
-direction takes place in the dark as well as in the light, as we can
-see if we start the experiment at nightfall, or place the plant in the
-dark. This upward growth of the stem is also influenced by the earth,
-and therefore is a case of geotropism. The special designation in the
-case of upright stems is _negative geotropism_, or _apogeotropism_, or
-the stems are said to be _apogeotropic_. If we place a rapidly growing
-potted plant in a horizontal position by laying the pot on its side,
-the ends of the shoots will soon turn upward again when placed in a
-horizontal position. Young bean plants growing in a pot began within
-two hours to turn the ends of the shoots upward.
-
-[Illustration: Fig. 114. Pumpkin seedling showing apogeotropism.
-Seedling at the left placed horizontally, in 24 hours the stem has
-become erect.]
-
-Horizontal leaves and shoots can be shown to be subject to the same
-influence, and are therefore _diageotropic_.
-
-=261. Influence of light.=—Not only is light a very important
-factor for plants during photosynthesis, it exerts great influence on
-plant growth and movement.
-
-[Illustration: Fig. 115. Radish seedlings grown in the dark, long,
-slender, not green.]
-
-[Illustration: Fig. 116. Radish seedlings grown in the light, shorter,
-stouter, and green in color. Growth retarded by light.]
-
-=262. Growth in the absence of light.=—Plants grown in the dark
-are subject to a number of changes. The stems are often longer,
-more slender and weaker since they contain a larger amount of water
-in proportion to building material which the plant obtains from
-carbohydrates manufactured in the light. On many plants the leaves are
-very small when grown in the dark.
-
-=263. Influence of light on direction of growth.=—While we are
-growing seedlings, the pots or boxes of some of them should be placed
-so that the plants will have a one-sided illumination. This can be
-done by placing them near an open window, in a room with a one-sided
-illumination, or they may be placed in a box closed on all sides but
-one which is facing the window or light. In 12-24 hours, or even in a
-much shorter time in some cases, the stems of the seedlings will be
-directed toward the source of light. This influence exerted by the rays
-of light is _heliotropism_, a turning influenced by the sun or sunlight.
-
-[Illustration: Fig. 117. Seedling of castor-oil bean, before and after
-a one-sided illumination.]
-
-[Illustration: Fig. 118. Dark chamber with opening at one side to show
-heliotropism. (After Schleichert.)]
-
-=264. Diaheliotropism.=—Horizontal leaves and shoots are
-_diaheliotropic_ as well as _diageotropic_. The general direction which
-leaves assume under this influence is that of placing them with the
-upper surface perpendicular to the rays of light which fall upon them.
-Leaves, then, exposed to the brightly lighted sky are, in general,
-horizontal. This position is taken in direct response to the stimulus
-of light. The leaves of plants with a one-sided illumination, as can be
-seen by trial, are turned with their upper surfaces toward the source
-of light, or perpendicular to the incidence of the light rays. In this
-way light overcomes for the time being the direction which growth
-gives to the leaves. The so-called “sleep” of plants is of course
-not sleep, though the leaves “nod,” or hang downward, in many cases.
-There are many plants in which we can note this drooping of the leaves
-at nightfall, and in order to prove that it is not determined by the
-time of day we can resort to a well-known experiment to induce this
-condition during the day. The plant which has been used to illustrate
-this is the sunflower. Some of these plants, which were grown in a box,
-when they were about 35 _cm_ high were covered for nearly two days,
-so that the light was excluded. At midday on the second day the box
-was removed, and the leaves on the covered plants are well represented
-by fig. 119, which was made from one of them. The leaves of the other
-plants in the box which were not covered were horizontal, as shown by
-fig. 120. Now on leaving these plants, which had exhibited induced
-“sleep” movements, exposed to the light they gradually assumed the
-horizontal position again.
-
-[Illustration: Fig. 119. Sunflower plant. Epinastic condition of leaves
-induced during the day in darkness.]
-
-[Illustration: Fig. 120. Sunflower plant removed from darkness, leaves
-extending under influence of light (diaheliotropism.)]
-
-=265. Epinasty and hyponasty.=—During the early stages of growth
-of many leaves, as in the sunflower plant, the direction of growth is
-different from what it is at a later period. The under surface of the
-young leaves grows more rapidly in a longitudinal direction than the
-upper side, so that the leaves are held upward close against the bud
-at the end of the stem. This is termed _hyponasty_, or the leaves are
-said to be _hyponastic_. Later the growth is more rapid on the upper
-side and the leaves turn downward or away from the bud. This is termed
-_epinasty_, or the leaves are said to be _epinastic_. This is shown by
-the night position of the leaves, or in the induced “sleep” of the
-sunflower plant in the experiment detailed above. The day position of
-the leaves on the other hand, which is more or less horizontal, is
-induced because of their irritability under the influence of light, the
-inherent downward or epinastic growth is overcome for the time. Then
-at nightfall or in darkness, the stimulus of light being removed, the
-leaves assume the position induced by the direction of growth.
-
-[Illustration: Fig. 121. Squash seedling. Position of cotyledons in
-light.]
-
-[Illustration: Fig. 122. Squash seedling. Position of cotyledons in the
-dark.]
-
-=266.= In the case of the cotyledons of some plants it would seem
-that the growth was hyponastic even after they have opened. The day
-position of the cotyledons of the pumpkin is more or less horizontal,
-as shown in fig. 121. At night, or if we darken the plant by covering
-with a tight box, the leaves assume the position shown in fig. 122.
-
-While the horizontal position is the general one which is assumed
-by plants under the influence of light, their position is dependent
-to a certain extent on the intensity of the light as well as on the
-incidence of the light rays. Some plants are so strongly heliotropic
-that they change their positions all during the day.
-
-[Illustration: Fig. 123. Coiling tendril of bryony.]
-
-=267. Leaves with a fixed diurnal position.=—Leaves of some
-plants when they are developed have a fixed diurnal position and are
-not subject to variation. Such leaves tend to arrange themselves in a
-vertical or paraheliotropic position, in which the surfaces are not
-exposed to the incidence of light of the greatest intensity, but to the
-incidence of the rays of diffused light. Interesting cases of the fixed
-position of leaves are found in the so-called compass plants (like
-Silphium laciniatum, Lactuca scariola, etc.). In these the horizontal
-leaves arrange themselves with the surfaces vertical, and also pointing
-north and south, so that the surfaces face east and west.
-
-=268. Importance of these movements.=—Not only are the leaves
-placed in a position favorable for the absorption of the rays of light
-which are concerned in making carbon available for food, but they
-derive other forms of energy from the light, as heat, which is absorbed
-during the day. Then with the nocturnal position, the leaves being
-drooped down toward the stem, or with the margin toward the sky, or
-with the cotyledons as in the pumpkin, castor-oil bean, etc., clasped
-upward together, the loss of heat by radiation is less than it would be
-if the upper surfaces of the leaves were exposed to the sky.
-
-=269. Influence of light on the structure of the leaf.=—In our
-study of the structure of a leaf we found that in the ivy leaf the
-palisade cells were on the upper surface. This is the case with a great
-many leaves, and is the normal arrangement of “dorsiventral” leaves
-which are diaheliotropic. Leaves which are paraheliotropic tend to have
-palisade cells on both surfaces. The palisade layer of cells as we
-have seen is made up of cells lying very close together, and they thus
-prevent rapid evaporation. They also check to some extent the entrance
-of the rays of light, at least more so than the loose spongy parenchyma
-cells do. Leaves developed in the shade have looser palisade and
-parenchyma cells. In the case of some plants, if we turn over a very
-young leaf, so that the under side will be uppermost, this side will
-develop the palisade layer. This shows that light has a great influence
-on the structure of the leaf.
-
-=270. Movement influenced by contact.=—In the case of tendrils,
-twining leaves, or stems, the irritability to contact is shown in a
-movement of the tendril, etc., toward the object in touch. This causes
-the tendril or stem to coil around the object for support. The stimulus
-is also extended down the part of the tendril below the point of
-contact (see fig. 123), and that part coils up like a wire coil spring,
-thus drawing the leaf or branch from which the tendril grows closer to
-the object of support. This coil between the object of support and the
-plant is also very important in easing up the plant when subject to
-violent gusts of wind which might tear the plant from its support were
-it not for the yielding and springing motion of this coil.
-
-[Illustration: Fig. 124. Sensitive plant leaf in normal position.]
-
-[Illustration: Fig. 125. Pinnæ folding up after stimulus.]
-
-[Illustration: Fig. 126. Later all the pinnæ folded and leaf drooped.]
-
-=271. Sensitive plants.=—These plants are remarkable for the
-rapid response to stimuli. Mimosa pudica is an excellent plant to study
-for this purpose.
-
-=272. Movement in response to stimuli.=—If we pinch with the
-forceps one of the terminal leaflets, or tap it with a pencil, the two
-end leaflets fold above the “vein” of the pinna. This is immediately
-followed by the movement of the next pair, and so on as shown in fig.
-125, until all the leaflets on this pinna are closed, then the stimulus
-travels down the other pinnæ in a similar manner, and soon the pinnæ
-approximate each other and the leaf then drops downward as shown in
-fig. 126. The normal position of the leaf is shown in fig. 124. If we
-jar the plant by striking it or by jarring the pot in which it is grown
-all the leaves quickly collapse into the position shown in fig. 126.
-If we examine the leaf now we see minute cushions at the base of each
-leaflet, at the junction of the pinnæ with the petiole, and a larger
-one at the junction of the petiole with the stem. We shall also note
-that the movement resides in these cushions.
-
-=273. Transmission of the stimulus.=—The transmission of the
-stimulus in this mimosa from one part of the plant has been found to be
-along the cells of the bast.
-
-=274. Cause of the movement.=—The movement is caused by a sudden
-loss of turgidity on the part of the cells in one portion of the
-pulvinus, as the cushion is called. In the case of the large pulvinus
-at the base of the petiole this loss of turgidity is in the cells of
-the lower surface. There is a sudden change in the condition of the
-protoplasm of the cells here so that they lose a large part of their
-water. This can be seen if with a sharp knife we cut off the petiole
-just above the pulvinus before movement takes place. A drop of liquid
-exudes from the cells of the lower side.
-
-=275. Paraheliotropism of the leaves of the sensitive plant.=—If
-the mimosa plant is placed in very intense light the leaflets will
-turn their edges toward the incidence of the rays of light. This is
-also true of other plants in intense light, and is _paraheliotropism_.
-Transpiration is thus lessened, and chlorophyll is protected from too
-intense light.
-
-[Illustration: Fig. 126_a_. Leaf of Venus fly-trap (Dionæa muscipula),
-showing winged petiole and toothed lobes.]
-
-[Illustration: Fig. 127. Leaf of Drosera rotundifolia, some of the
-glandular hairs folding inward as a result of a stimulus.]
-
-We thus see that variations in the intensity of light have an important
-influence in modifying movements. Variations in temperature also exert
-a considerable influence, rapid elevation of temperature causing
-certain flowers to open, and falling temperature causing them to close.
-
-=276. Sensitiveness of insectivorous plants.=—The Venus fly-trap
-(Dionæa muscipula) and the sundew (drosera) are interesting examples of
-sensitive plants, since the leaves close in response to the stimulus
-from insects.
-
-=277. Hydrotropism.=—Roots are sensitive to moisture. They will
-turn toward moisture. This is of the greatest importance for the
-well-being of the plant, since the roots will seek those places in the
-soil where suitable moisture is present. On the other hand, if the soil
-is too wet there is a tendency for the roots to grow away from the
-soil which is saturated with water. In such cases roots are often seen
-growing upon the surface of the soil so that they may obtain oxygen,
-which is important for the root in the processes of absorption and
-growth. Plants then may be injured by an excess of water as well as by
-a lack of water in the soil.
-
-=278. Temperature.=—In the experiments on germination thus
-far made it has probably been noted that the temperature has much
-to do with the length of time taken for seeds to germinate. It also
-influences the rate of growth. The effect of different temperatures
-on the germination of seed can be very well noted by attempting to
-germinate some in rooms at various temperatures. It will be found,
-other conditions being equal, that in a moderately warm room, or even
-in one quite warm, 25-30 degrees centigrade, germination and growth
-goes on more rapidly than in a cool room, and here more rapidly than in
-one which is decidedly cold. In the case of most plants in temperate
-climates, growth may go on at a temperature but little above freezing,
-but few will thrive at this temperature.
-
-=279.= If we place dry peas or beans in a temperature of about
-70° C. for 15 minutes they will not be killed, but if they have been
-thoroughly soaked in water and then placed at this temperature they
-will be killed, or even at a somewhat lower temperature. The same seeds
-in the dry condition will withstand a temperature of 10° C. below, but
-if they are first soaked in water this low temperature will kill them.
-
-=280.= In order to see the effect of freezing we may thoroughly
-freeze a section of a beet root, and after thawing it out place it in
-water. The water is colored by the cell-sap which escapes from the
-cells, just as we have seen it does as a result of a high temperature,
-while a section of an unfrozen beet placed in water will not color it
-if it was previously washed.
-
-If the slice of the beet is placed at about -6° C. in a shallow glass
-vessel, and covered, ice will be formed over the surface. If we examine
-it with the microscope ice crystals will be seen formed on the outside,
-and these will not be colored. The water for the formation of the
-crystals came from the cell-sap, but the concentrated solutions in the
-sap were not withdrawn by the freezing over the surface.
-
-=281.= If too much water is not withdrawn from the cells of many
-plants in freezing, and they are thawed out slowly, the water which was
-withdrawn from the cells will be absorbed again and the plant will not
-be killed. But if the plant is thawed out quickly the water will not
-be absorbed, but will remain on the surface and evaporate. Some will
-also remain in the intercellular spaces, and the plant will die. Some
-plants, however, no matter how slowly they are thawed out, are killed
-after freezing, as the leaves of the pumpkin, dahlia, or the tubers of
-the potato.
-
-=282.= It has been found that as a general rule when plants, or
-plant parts, contain little moisture they will withstand quite high
-degrees of temperature, as well as quite low degrees, but when the
-parts are filled with sap or water they are much more easily killed.
-For this reason dry seeds and the winter buds of trees, and other
-plants, because they contain but little water, are better able to
-resist the cold of winters. But when growth begins in the spring, and
-the tissues of these same parts become turgid and filled with water,
-they are quite easily killed by frosts. It should be borne in mind,
-however, that there is great individual variation in plants in this
-respect, some being more susceptible to cold than others. There is
-also great variation in plants as to their resistance to the cold of
-winters, and of arctic climates, the plants of the latter regions
-being able to resist very low temperatures. We have examples also in
-the arctic plants, and those which grow in arctic climates on high
-mountains, of plants which are able to carry on all the life functions
-at temperatures but little above freezing.
-
-For further discussion as to relation of plants to temperature, see
-Chapters 46, 48, 49, and 53.
-
-
-
-
-PART II.
-
-MORPHOLOGY AND LIFE HISTORY OF REPRESENTATIVE PLANTS.
-
-
-
-
-CHAPTER XIV.
-
-SPIROGYRA.
-
-
-=283.= In our study of protoplasm and some of the processes of
-plant life we became acquainted with the general appearance of the
-plant spirogyra. It is now a familiar object to us. And in taking up
-the study of representative plants of the different groups, we shall
-find that in knowing some of these lower plants the difficulties of
-understanding methods of reproduction and relationship are not so great
-as they would be if we were entirely ignorant of any members of the
-lower groups.
-
-[Illustration: Fig. 128. Thread of spirogyra, showing long cells,
-chlorophyll band, nucleus, strands of protoplasm, and the granular wall
-layer of protoplasm.]
-
-=284. Form of spirogyra.=—We have found that the plant spirogyra
-consists of simple threads, with cylindrical cells attached end to
-end. We have also noted that each cell of the thread is exactly alike,
-with the exception of certain “holdfasts” on some of the species. If
-we should examine threads in different stages of growth we should find
-that each cell is capable of growth and division, just as it is capable
-of performing all the functions of nutrition and assimilation. The
-cells of spirogyra then multiply by division. Not simply the cells at
-the ends of the threads but any and all of the cells divide as they
-grow, and in this way the threads increase in length.
-
-=285. Multiplication of the threads.=—In studying living material
-of this plant we have probably noted that the threads often become
-broken by two of the adjacent cells of a thread becoming separated.
-This may be and is accomplished in many cases without any injury to the
-cells. In this manner the threads or plants of spirogyra, if we choose
-to call a thread a plant, multiply, or increase. In this breaking of a
-thread the cell wall which separates any two cells splits. If we should
-examine several species of spirogyra we would probably find threads
-which present two types as regards the character of the walls at the
-ends of the cells. In fig. 128 we see that the ends are plain, that is,
-the cross walls are all straight. But in some other species the inner
-wall of the cells presents a peculiar appearance. This inner wall at
-the end of the cell is at first straight across. But it soon becomes
-folded back into the interior of its cell, just as the end of an empty
-glove finger may be pushed in. Then the infolded end is pushed partly
-out again, so that a peculiar figure is the result.
-
-=286. How some of the threads break.=—In the separation of the
-cells of a thread this peculiarity is often of advantage to the plant.
-The cell-sap within the protoplasmic membrane absorbs water and the
-pressure pushes on the ends of the infolded cell walls. The inner
-wall being so much longer than the outer wall, a pull is exerted on
-the latter at the junction of the cells. Being weaker at this point
-the outer wall is ruptured. The turgidity of the two cells causes
-these infolded inner walls to push out suddenly as the outer wall is
-ruptured, and the thread is snapped apart as quickly as a pipe-stem may
-be broken.
-
-[Illustration: Fig. 129. Zygospores of spirogyra.]
-
-=287. Conjugation of spirogyra.=—Under certain conditions, when
-vegetative growth and multiplication cease, a process of reproduction
-takes place which is of a kind termed sexual reproduction. If we select
-mats of spirogyra which have lost their deep green color, we are likely
-to find different stages of this sexual process, which in the case of
-spirogyra and related plants is called _conjugation_. A few threads
-of such a mat we should examine with the microscope. If the material
-is in the right condition we see in certain of the cells an oval or
-elliptical body. If we note carefully the cells in which these oval
-bodies are situated, there will be seen a tube at one side which
-connects with an empty cell of a thread which lies near as shown in
-fig. 129. If we search through the material we may see other threads
-connected in this ladder fashion, in which the contents of the cells
-are in various stages of collapse from what we have seen in the growing
-cell. In some the protoplasm and chlorophyll band have moved but little
-from the wall; in others it forms a mass near the center of the cell,
-and again in others we will see that the contents of the cell of one
-of the threads has moved partly through the tube into the cell of the
-thread with which it is connected.
-
-=289.= This suggests to us that the oval bodies found in the cells
-of one thread of the ladder, while the cells of the other thread were
-empty, are formed by the union of the contents of the two cells. In
-fact that is what does take place. This kind of union of the contents
-of two similar or nearly similar cells is _conjugation_. The oval
-bodies which are the result of this conjugation are _zygotes_, or
-_zygospores_. When we are examining living material of spirogyra in
-this stage it is possible to watch this process of conjugation. Fig.
-130 represents the different stages of conjugation of spirogyra.
-
-=290. How the threads conjugate, or join.=—The cells of two
-threads lying parallel put out short processes. The tubes from two
-opposite cells meet and join. The walls separating the contents of the
-two tubes dissolve so that there is an open communication between the
-two cells. The content of each one of these cells which take part in
-the conjugation is a _gamete_. The one which passes through the tube to
-the receiving cell is the _supplying gamete_, while that of the
-receiving cell is the _receiving gamete_.
-
-[Illustration: Fig. 130.
-
- Conjugation in spirogyra; from left to right beginning in the upper
-row is shown the gradual passage of the protoplasm from the supplying
-gamete to the receiving gamete.]
-
-=291. How the protoplasm moves from one cell to another.=—Before
-any movement of the protoplasm of the supplying cell takes place we can
-see that there is great activity in its protoplasm. Rounded vacuoles
-appear which increase in size, are filled with a watery fluid, and
-swell up like a vesicle, and then suddenly contract and disappear.
-As the vacuole disappears it causes a sudden movement or contraction
-of the protoplasm around it to take its place. Simultaneously with
-the disappearance of the vacuole the membrane of the protoplasm is
-separated from a part of the wall. This is probably brought about by a
-sudden loss of some of the water in the cell-sap. These activities go
-on, and the protoplasmic membrane continues to slip away from the wall.
-Every now and then there is a movement by which the protoplasm is moved
-a short distance. It is moved toward the tube and finally a portion of
-it with one end of the chlorophyll band begins to move into the tube.
-About this time the vacuoles can be seen in an active condition in the
-receptive cell. At short intervals movement continues until the content
-of the supplying cell has passed over into that of the receptive cell.
-The protoplasm of this one is now slipping away from the cell wall,
-until finally the two masses round up into the one zygospore.
-
-=292. The zygospore.=—This zygospore now acquires a thick wall
-which eventually becomes brown in color. The chlorophyll color fades
-out, and a large part of the protoplasm passes into an oily substance
-which makes it more resistant to conditions which would be fatal to the
-vegetative threads. The zygospores are capable therefore of enduring
-extremes of cold and dryness which would destroy the threads. They
-pass through a “resting” period, in which the water in the pond may be
-frozen, or dried, and with the oncoming of favorable conditions for
-growth in the spring or in the autumn they germinate and produce the
-green thread again.
-
-=293. Life cycle.=—The growth of the spirogyra thread, the
-conjugation of the gametes and formation of the zygospore, and the
-growth of the thread from the zygospore again, makes what is called a
-complete _life cycle_.
-
-=294. Fertilization.=—While conjugation results in the fusion of
-the two masses of protoplasm, fertilization is accomplished when the
-nuclei of the two cells come together in the zygospore and fuse into a
-single nucleus. The different stages in the fusion of the two nuclei of
-a recently formed zygospore are shown in figure 131.
-
-In the conjugation of the two cells, the chlorophyll band of the
-supplying cell is said to degenerate, so that in the new plant the
-number of chlorophyll bands in a cell is not increased by the union of
-the two cells.
-
-[Illustration: Fig. 131. Fertilization in spirogyra; shows different
-stages of fusion of the two nuclei, with mature zygospore at right.
-(After Overton.)]
-
-=295. Simplicity of the process.=—In spirogyra any cell of the
-thread may form a gamete (excepting the holdfasts of some species).
-Since all of the cells of a thread are practically alike, there is no
-structural difference between a vegetative cell and a cell about to
-conjugate. The difference is a physiological one. All the cells are
-capable of conjugation if the physiological conditions are present. All
-the cells therefore are potential gametes. (Strictly speaking the wall
-of the cell is the _garnetangium_, while the content forms the gamete.)
-
-While there is sometimes a slight difference in size between the
-conjugating cells, and the supplying cell may be the smaller, this is
-not general. We say, therefore, that there is no differentiation among
-the gametes, so that usually before the protoplasm begins to move one
-cannot say which is to be the supplying and which the receiving gamete.
-
-=296. Position of the plant spirogyra.=—From our study then we
-see that there is practically no differentiation among the vegetative
-cells, except where holdfasts grow out from some of the cells
-for support. They are all alike in form, in capacity for growth,
-division, or multiplication of the threads. Each cell is practically
-an independent plant. There is no differentiation between vegetative
-cell and conjugating cell. All the cells are potential gametes.
-Finally there is no structural differentiation between the gametes.
-This indicates then a simple condition of things, a low grade of
-organization.
-
-=297.= The alga spirogyra is one of the representatives of the
-lower algæ belonging to the group called _Conjugatæ_. Zygnema with
-star-shaped chloroplasts, mougeotia with straight or sometimes twisted
-chlorophyll bands, belong to the same group. In the latter genus only
-a portion of the protoplasm of each cell unites to form the zygospore,
-which is located in the tube between the cells.
-
-[Illustration: Fig. 132. Closterium.]
-
-[Illustration: Fig. 133. Micrasterias.]
-
-[Illustration: Fig. 134. Xanthidium.]
-
-[Illustration: Fig. 135. Staurastrum.]
-
-[Illustration: Fig. 136. Euastrum.]
-
-[Illustration: Fig. 137. Cosmarium.]
-
-=298.= The desmids also belong to the same group. The desmids
-usually live as separate cells. Many of them are beautiful in form.
-They grow entangled among other algæ, or on the surface of aquatic
-plants, or on wet soil. Several genera are illustrated in figures
-132-137.
-
-
-
-
-CHAPTER XV.
-
-VAUCHERIA.
-
-
-=299.= The plant vaucheria we remember from our study in an
-earlier chapter. It usually occurs in dense mats floating on the water
-or lying on damp soil. The texture and feeling of these mats remind one
-of “felt,” and the species are sometimes called the “green felts.” The
-branched threads are continuous, that is there are no cross walls in
-the vegetative threads. This plant multiplies itself in several ways
-which would be too tedious to detail here. But when fresh bright green
-mats can be obtained they should be placed in a large vessel of water
-and set in a cool place. Only a small amount of the alga should be
-placed in a vessel, since decay will set in more rapidly with a large
-quantity. For several days one should look for small green bodies which
-may be floating at the side of the vessel next the lighted window.
-
-[Illustration: Fig. 138. Portion of branched thread of vaucheria.]
-
-=300. Zoogonidia of vaucheria.=—If these minute floating green
-bodies are found, a small drop of water containing them should be
-mounted for examination. If they are rounded, with slender hair-like
-appendages over the surface, which vibrate and cause motion, they very
-likely are one of the kinds of reproductive bodies of vaucheria. The
-hair-like appendages are _cilia_, and they occur in pairs, several of
-them distributed over the surface. These rounded bodies are _gonidia_,
-and because they are motile they are called _zoogonidia_.
-
-By examining some of the threads in the vessel where they occurred we
-may have perhaps an opportunity to see how they are produced. Short
-branches are formed on the threads, and the contents are separated from
-those of the main thread by a septum. The protoplasm and other contents
-of this branch separate from the wall, round up into a mass, and escape
-through an opening which is formed in the end. Here they swim around in
-the water for a time, then come to rest, and germinate by growing out
-into a tube which forms another vaucheria plant. It will be observed
-that this kind of reproduction is not the result of the union of two
-different parts of the plant. It thus differs from that which is termed
-sexual reproduction. A small part of the plant simply becomes separated
-from it as a special body, and then grows into a new plant, a sort of
-multiplication. This kind of reproduction has been termed _asexual
-reproduction_.
-
-[Illustration: Fig. 139. Young antheridium and oogonium of Vaucheria
-sessilis, before separation from contents of thread by a septum.]
-
-=301. Sexual reproduction in vaucheria.=—The organs which
-are concerned in sexual reproduction in vaucheria are very readily
-obtained for study if one collects the material at the right season.
-They are found quite readily during the spring and autumn, and may be
-preserved in formalin for study at any season, if the material cannot
-be collected fresh at the time it is desired for study. Fine material
-for study often occurs on the soil of pots in greenhouses during the
-winter. While the zoogonidia are more apt to be found in material which
-is quite green and freshly growing, the sexual organs are usually more
-abundant when the threads appear somewhat yellowish, or yellow green.
-
-=302. Vaucheria sessilis; the sessile vaucheria.=—In this plant
-the sexual organs are sessile, that is they are not borne on a stalk
-as in some other species. The sexual organs usually occur several in a
-group. Fig. 139 represents a portion of a fruiting plant.
-
-=303. Sexual organs of vaucheria. Antheridium.=—The antheridia
-are short, slender, curved branches from a main thread. A septum is
-formed which separates an end portion from the stalk. This end cell
-is the _antheridium_. Frequently it is collapsed or empty as shown in
-fig. 140. The protoplasm in the antheridium forms numerous small oval
-bodies each with two slender lashes, the cilia. When these are formed
-the antheridium opens at the end and they escape. It is after the
-escape of these spermatozoids that the antheridium is collapsed. Each
-spermatozoid is a male gamete.
-
-[Illustration: Fig. 140. Vaucheria sessilis, one antheridium between
-two oogonia.]
-
-[Illustration: Fig. 141. Vaucheria sessilis; oogonium opening and
-emitting a bit of protoplasm; spermatozoids; spermatozoids entering
-oogonium. (After Pringsheim and Goebel.)]
-
-=304. Oogonium.=—The oogonia are short branches also, but
-they become large and somewhat oval. The septum which separates the
-protoplasm from that of the main thread is as we see near the junction
-of the branch with the main thread. The oogonium, as shown in the
-figure, is usually turned somewhat to one side. When mature the pointed
-end opens and a bit of the protoplasm escapes. The remaining protoplasm
-forms the large rounded egg-cell which fills the wall of the oogonium.
-In some of the oogonia which we examine this egg is surrounded by a
-thick brown wall, with starchy and oily contents. This is the
-fertilized egg (sometimes called here the oospore). It is freed from
-the oogonium by the disintegration of the latter, sinks into the mud,
-and remains here until the following autumn or spring, when it grows
-directly into a new plant.
-
-[Illustration: Fig. 142. Fertilization in vaucheria, _mn_, male
-nucleus; _fn_, female nucleus. Male nucleus entering the egg and
-approaching the female nucleus. (After Oltmans.)]
-
-=305. Fertilization.=—Fertilization is accomplished by the
-spermatozoids swimming in at the open end of the oogonium, when one of
-them makes its way down into the egg and fuses with the nucleus of the
-egg.
-
-[Illustration: Fig. 143. Fertilization of vaucheria. _fn_, female
-nucleus; _mn_, male nucleus. The different figures show various stages
-in the fusion of the nuclei.]
-
-=306. The twin vaucheria (V. geminata).=—Another species of
-vaucheria is the twin vaucheria. This is also a common one, and may be
-used for study instead of the sessile vaucheria if the latter cannot
-be obtained. The sexual organs are borne at the end of a club-shaped
-branch. There are usually two oogonia, and one antheridium between them
-which terminates the branch. In a closely related species, instead of
-the two oogonia there is a whorl of them with the antheridium in the
-center.
-
-=307. Vaucheria compared with spirogyra.=—In vaucheria we have a
-plant which is very interesting to compare with spirogyra in several
-respects. Growth takes place, not in all parts of the thread, but is
-localized at the ends of the thread and its branches. This represents a
-distinct advance on such a plant as spirogyra. Again, only specialized
-parts of the plant in vaucheria form the sexual organs. These are
-short branches. Farther there is a great difference in the size of the
-two organs, and especially in the size of the gametes, the supplying
-gametes (spermatozoids) being very minute, while the receptive gamete
-is large and contains all the nutriment for the fertilized egg. In
-spirogyra, on the other hand, there is usually no difference in size
-of the gametes, as we have seen, and each contributes equally in the
-matter of nutriment for the fertilized egg. Vaucheria, therefore,
-represents a distinct advance, not only in the vegetative condition of
-the plant, but in the specialization of the sexual organs. Vaucheria,
-with other related algæ, belongs to a group known as the _Siphoneæ_, so
-called because the plants are tube-like or _siphon_-like.
-
-[Illustration: Fig. 143_a_. Botrydium granulatum. _A_, the whole plant;
-_B_, swarm spore; _C_, planogametes; _a_, a single gamete; _b_-_e_, two
-gametes in process of fusion; _f_, zygote.]
-
-=308. Botrydium granulatum.=—An example of one of the simpler
-members of the Siphoneæ is Botrydium granulatum. It is found sometimes
-in abundance on wet ground which is colored green or red by its
-presence, according to the stage of development. The plant body is long
-pear-shaped, the smaller end attached to the ground by slender branched
-rhizoids (Fig. 143). The protoplasm contains many nuclei and lines the
-inside of the wall. When multiplication takes place large numbers of
-small zoospores with one cilium each are formed in the protoplasm, and
-escape at free end. Reproduction takes place by two-ciliated gametes,
-which fuse in pairs to form zygospores. In dry seasons the protoplasm
-in the pear-shaped plant passes down into the rhizoids and forms
-small rounded _planospores_. All the stages of development are too
-complicated to describe here.
-
-
-
-
-CHAPTER XVI.
-
-ŒDOGONIUM.
-
-
-=309.= Œdogonium is also an alga. The plant is sometimes
-associated with spirogyra, and occurs in similar situations. Our
-attention was called to it in the study of chlorophyll bodies. These we
-recollect are, in this plant, small oval disks, and thus differ from
-those in spirogyra.
-
-=310. Form of œdogonium.=—Like spirogyra, œdogonium forms simple
-threads which are made up of cylindrical cells placed end to end. But
-the plant is very different from any member of the group to which
-spirogyra belongs. In the first place each cell is not the equivalent
-of an individual plant as in spirogyra. Growth is localized or confined
-to certain cells of the thread which divide at one end in such a way
-as to leave a peculiar overlapping of the cell walls in the form of a
-series of shallow caps or vessels (fig. 144), and this is one of the
-characteristics of this genus. Other differences we find in the manner
-of reproduction.
-
-=311. Fruiting stage of œdogonium.=—Material in the fruiting
-stage is quite easily obtainable, and may be preserved for study in
-formalin if there is any doubt about obtaining it at the time we need
-it for study. This condition of the plant is easily detected because of
-the swollen condition of some of the cells, or by the presence of brown
-bodies with a thick wall in some of the cells.
-
-=312. Sexual organs of œdogonium. Oogonium and egg.=—The enlarged
-cell is the oogonium, the wall of the cell being the wall of the
-oogonium. (See fig. 145.) The protoplasm inside, before fertilization,
-is the egg-cell. In those cases where the brown body with a thick
-wall is present fertilization has taken place, and this body is the
-_fertilized egg_, or _oospore_. It contains large quantities of an oily
-substance, and, like the fertilized egg of spirogyra and vaucheria, is
-able to withstand greater changes in temperature than the vegetative
-stage, and can endure drying and freezing for some time without injury.
-
-[Illustration: Fig. 144. Portion of thread of œdogonium, showing
-chlorophyll grains, and peculiar cap cell walls.]
-
-[Illustration: Fig. 145. Œdogonium undulatum, with oogonia and dwarf
-males; the upper oogonium at the right has a mature oospore.]
-
-In the oogonium wall there can frequently be seen a rift near the
-middle of one side, or near the upper end. This is the opening through
-which the spermatozoid entered to fecundate the egg.
-
-=313. Dwarf male plants.=—In some species there will also be seen
-peculiar club-shaped dwarf plants attached to the side of the oogonium,
-or near it, and in many cases the end of this dwarf plant has an open
-lid on the end.
-
-=314. Antheridium.=—The end cell of the dwarf male in such
-species is the _antheridium_. In other species the spermatozoids are
-developed in different cells (antheridia) of the same thread which
-bears the oogonium, or on a different thread.
-
-[Illustration: Fig. 146. Zoogonidia of œdogonium escaping. At the right
-one is germinating and forming the holdfasts, by means of which these
-algæ attach themselves to objects for support. (After Pringsheim.)]
-
-=315. Zoospore stage of œdogonium.=—The egg after a period of
-rest starts into active life again. In doing so it does not develop
-the thread-like plant directly as in the case of vaucheria and
-spirogyra. It first divides into four zoospores which are exactly like
-the zoogonidia in form. (See fig. 152.) These germinate and develop
-the thread form again. This is a quite remarkable peculiarity of
-œdogonium when compared with either vaucheria or spirogyra. It is the
-introduction of an intermediate stage between the fertilized egg and
-that form of the plant which bears the sexual organs, and should be
-kept well in mind.
-
-=316. Asexual reproduction.=—Material for the study of this stage
-of œdogonium is not readily obtainable just when we wish it for study.
-But fresh plants brought in and placed in a quantity of fresh water may
-yield suitable material, and it should be examined at intervals for
-several days. This kind of reproduction takes place by the formation
-of _zoogonidia_. The entire contents of a cell round off into an oval
-body, the wall of the cell breaks, and the zoogonidium escapes. It has
-a clear space at the small end, and around this clear space is a row or
-crown of cilia as shown in fig. 146. By the vibration of these cilia
-the zoogonidium swims around for a time, then settles down on some
-object of support, and several slender holdfasts grow out in the form
-of short rhizoids which attach the young plant.
-
-[Illustration: Fig. 147. Portion of thread of œdogonium showing
-antheridia.]
-
-[Illustration: Fig. 148. Portion of thread of œdogonium showing upper
-half of egg open, and a spermatozoid ready to enter. (After Klebahn).]
-
-=317. Sexual reproduction. Antheridia.=—The antheridia are short
-cells which are formed by one of the ordinary cells dividing into a
-number of disk-shaped ones as shown in fig. 147. The protoplasm in each
-antheridium forms two spermatozoids (sometimes only one) which are of
-the same form as the zoogonidia but smaller, and yellowish instead of
-green. In some species a motile body intermediate in size and color
-between the spermatozoids and zoogonidia is first formed, which after
-swimming around comes to rest on the oogonium, or near it, and develops
-what is called a “dwarf male plant” from which the real spermatozoid is
-produced.
-
-[Illustration: Fig. 149. Male nucleus just entering egg at left side.]
-
-[Illustration: Fig. 150. Male nucleus fusing with female nucleus.]
-
-[Illustration: Fig. 151. The two nuclei fused, and fertilization
-complete.
-
-Figs. 149-151.—Fertilization in œdogonium. (After Klebahn).]
-
-=318. Oogonia.=—The oogonia are formed directly from one of the
-vegetative cells. In most species this cell first enlarges in diameter,
-so that it is easily detected. The protoplasm inside is the egg-cell.
-The oogonium wall opens, a bit of the protoplasm is emitted, and the
-spermatozoid then enters and fertilizes it (fig. 148). Now a hard brown
-wall is formed around it, and, just as in spirogyra and vaucheria, it
-passes through a resting period. At the time of germination it does
-not produce the thread-like plant again directly, but first forms four
-zoospores exactly like the zoogonidia (fig. 152). These zoospores then
-germinate and form the plant.
-
-=319. Œdogonium compared with spirogyra.=—Now if we compare
-œdogonium with spirogyra, as we did in the case of vaucheria, we find
-here also that there is an advance upon the simple condition which
-exists in spirogyra. Growth and division of the thread is limited to
-certain portions. The sexual organs are differentiated. They usually
-differ in form and size from the vegetative cells, though the oogonium
-is simply a changed vegetative cell. The sexual organs are
-differentiated among themselves, the antheridium is small, and the
-oogonium large. The gametes are also differentiated in size, and the
-male gamete is motile, and carries in its body the nucleus which fuses
-with the nucleus of the egg-cell.
-
-[Illustration: Fig. 152. Fertilized egg of œdogonium after a period of
-rest escaping from the wall of the oogonium, and dividing into the four
-zoospores. (After Juranyi.)]
-
-But a more striking advance is the fact that the fertilized egg does
-not produce the vegetative thread of œdogonium directly, but first
-forms four zoospores, each of which is then capable of developing into
-the thread. On the other hand we found that in spirogyra the zygospore
-develops directly into the thread form of the plant.
-
-[Illustration: Fig. 153. Tuft of chætophora, natural size.]
-
-[Illustration: Fig. 154. Portion of chætophora showing branching.]
-
-=320. Position of œdogonium.=—Œdogonium is one of the true
-thread-like algæ, green in color, and the threads are divided into
-distinct cells. It, along with many relatives, was once placed
-in the old genus conferva. These are all now placed in the group
-_Confervoideæ_, that is, the _conferva-like algæ_.
-
-=321. Relatives of œdogonium.=—Many other genera are related
-to œdogonium. Some consist of simple threads, and others of branched
-threads. An example of the branched forms is found in chætophora,
-represented in figures 153, 154. This plant grows in quiet pools or
-in slow-running water. It is attached to sticks, rocks, or to larger
-aquatic plants. Many threads spring from the same point of attachment
-and radiate in all directions. This, together with the branching of the
-threads, makes a small, compact, greenish, rounded mass, which is held
-firmly together by a gelatinous substance. The masses in this species
-are about the size of a small pea, or smaller. Growth takes place in
-chætophora at the ends of the threads and branches. That is, growth is
-apical. This, together with the branched threads and the tendency to
-form cell masses, is a great advance of the vegetative condition of the
-plant upon that which we find in the simple threads of œdogonium.
-
-
-
-
-CHAPTER XVII.
-
-COLEOCHÆTE.
-
-
-=322.= Among the green algæ coleochæte is one of the most
-interesting. Several species are known in this country. One of these at
-least should be examined if it is possible to obtain it. It occurs in
-the water of fresh lakes and ponds, attached to aquatic plants.
-
-[Illustration: Fig. 155. Stem of aquatic plant showing coleochæte,
-natural size.]
-
-[Illustration: Fig. 156. Thallus of Coleochæte scutata.]
-
-=323. The shield-shaped coleochæte.=—This plant (C. scutata) is
-in the form of a flattened, circular, green plate, as shown in fig.
-156. It is attached near the center on one side to rushes and other
-plants, and has been found quite abundantly for several years in the
-waters of Cayuga Lake at its southern extremity. As will be seen it
-consists of a single layer of green cells which radiate from the center
-in branched rows to the outside, the cells lying so close together as
-to form a continuous plate. The plant started its growth from a single
-cell at the central point, and grew at the margin in all directions.
-Sometimes they are quite irregular in outline, when they lie quite
-closely side by side and interfere with one another by pressure. If the
-surface is examined carefully there will be found long hairs, the base
-of which is enclosed in a narrow sheath. It is from this character that
-the genus takes its name of coleochæte (sheathed hair).
-
-[Illustration: Fig. 157. Portion of thallus of Coleochæte scutata,
-showing empty cells from which zoogonidia have escaped, one from each
-cell; zoogonidia at the left. (After Pringsheim.)]
-
-[Illustration: Fig. 158. Portion of thallus of Coleochæte scutata,
-showing four antheridia formed from one thallus cell; a single
-spermatozoid at the right. (After Pringsheim.)]
-
-=324. Fruiting stage of coleochæte.=—It is possible at some
-seasons of the year to find rounded masses of cells situated near the
-margin of this green disk. These have developed from a fertilized egg
-which remained attached to the plant, and probably by this time the
-parent plant has lost its color.
-
-=325. Zoospore stage.=—This mass of tissue does not develop
-directly into the circular green disk, but each of the cells forms a
-zoospore. Here then, as in œdogonium, we have another stage of the
-plant interpolated between the fertilized egg and that stage of the
-plant which bears the gametes. But in coleochæte we have a distinct
-advance in this stage upon what is present in œdogonium, for in
-coleochæte the fertilized egg develops first into a several-celled mass
-of tissue before the zoospores are formed, while in œdogonium only four
-zoospores are formed directly from the egg.
-
-=326. Asexual reproduction.=—In asexual reproduction any of the
-green cells on the plant may form zoogonida. The contents of a cell
-round off and form a single zoogonidium which has two cilia at the
-smaller end of the oval body, fig. 157. After swimming around for a
-time they come to rest, germinate, and produce another plant.
-
-=327. Sexual reproduction.—Oogonium.=—The oogonium is formed by
-the enlargement of a cell at the end of one of the threads, and then
-the end of the cell elongates into a slender tube which opens at the
-end to form a channel through which the spermatozoid may pass down to
-the egg. The egg is formed of the contents of the cell (fig. 159).
-Several oogonia are formed on one plant, and in such a plant as C.
-scutata they are formed in a ring near the margin of the disk.
-
-[Illustration: Fig. 159. Coleochæte soluta; at left branch bearing
-oogonium (_oog_); antheridia (_ant_); egg in oogonium and surrounded
-by enveloping threads; at center three antheridia open, and one
-spermatozoid; at right sporocarp, mature egg inside sporocarp wall.]
-
-[Illustration: Fig. 160. Two sporocarps still surrounded by thallus.
-Thallus finally decays and sets sporocarp free.]
-
-[Illustration: Fig. 161. Sporocarp ruptured by growth of egg to form
-cell mass. Cells of this sporophyte forming zoospores.
-
-Figs. 160, 161. C. scutata.]
-
-=328. Antheridia.=—In C. scutata certain of the cells of the
-plant divide into four smaller cells, and each one of these becomes
-an antheridium. In C. soluta the antheridia grow out from the end of
-terminal cells in the form of short flasks, sometimes four in number or
-less (fig. 159). A single spermatozoid is formed from the contents. It
-is oval and possesses two long cilia. After swimming around it passes
-down the tube of the oogonium and fertilizes the egg.
-
-=329. Sporocarp.=—After the egg is fertilized the cells of the
-threads near the egg grow up around it and form a firm covering one
-cell in thickness. This envelope becomes brown and hard, and serves
-to protect the egg. This is the “fruit” of the coleochæte, and is
-sometimes called a sporocarp (spore-fruit). The development of the cell
-mass and the zoospores from the egg has been described above.
-
-Some of the species of coleochæte consist of branched threads, while
-others form circular cushions several layers in thickness. These forms
-together with the form of our plant C. scutata make an interesting
-series of transitional forms from filamentous structures to an expanded
-plant body formed of a mass of cells.
-
-=330. COMPARATIVE TABLE FOR SPIROGYRA, VAUCHERIA, ŒDOGONIUM,
-COLEOCHÆTE.=
-
-  -----------+--------------------------------------------------------
-             |  GAMETOPHYTE. (Bears the sexual organs and gonidia.)
-  -----------+-----------+---------+------------+---------------------
-             |Vegetative | Growth. |Multipli-   | Sexual Reproduction.
-             |  Phase.   |         |     cation.+---------------------
-             |           |         |            |    Sexual Organs.
-  -----------+-----------+---------+------------+---------------------
-  Spirogyra. |Simple     |All      |By breaking |   Undifferentiated.
-             |threads of |cells    |up of       |  Any cell of thread.
-             |cylindrical|divide   |threads.    |   Conjugate by tube.
-             |cells.     |and      |            |
-             |           |grow.    |            |
-  -----------+-----------+---------+------------+---------------------
-             |Branched   |Limited  |By          |    Differentiated.
-             |threads,   |to ends  |multiciliate|Antheridia|Oogonium,
-  Vaucheria. |continuous.|of       |zoogonidia, |slender   |large
-             |           |threads  |and other   |cells on  |on special
-             |           |and      |cells, from |special   |rounded
-             |           |branches.|terminal    |branches. |cell,
-             |           |         |portions.   |          |branch,
-             |           |         |            |           opens
-             |           |         |            |          |and emits
-             |           |         |            |          |bit of
-             |           |         |            |          |protoplasm.
-  -----------+-----------+---------+------------+----------+----------
-             |Simple     |Limited  |By oval     |    Differentiated.
-             |threads of |to       |zoogonidia, |Antheridia|Oogonium,
-  Œdogonium. |cylindrical|certain  |with crown  |disk-     |changed
-             |cells.     |portions |of cilia.   |  shaped, |vegetative
-             |           | of      |Any cell    |several   |cell, opens
-             |           |thread.  |may form a  |from one  |and emits
-             |           |         |single      |vegetative|bit of
-             |           |         |zoogonidium.|cell.     |protoplasm.
-             |           |         |            |Sometimes |
-             |           |         |            |on dwarf  |
-             |           |         |            |males.    |
-  -----------+-----------+---------+------------+----------+----------
-  Coleochæte.|Branched   |Terminal |By          |    Differentiated.
-             |threads,   |   or    |zoogonidia  |Antheridia|Oogonium,
-             |or compact |marginal.|with two    |four or   |enlarged
-             |circular   |         |cilia.      |several   |veg. cell,
-             |plates.    |         |Any cell    |from      |with long
-             |           |         |may form    |single    |tube through
-             |           |         |a single    |veg. cell.|opening
-             |           |         |zoogonidium.|          |of which
-             |           |         |            |          |spermatozoid
-             |           |         |            |          |enters.
-             |           |         |            |          |After
-             |           |         |            |          |fertilization
-             |           |         |            |          |wall of
-             |           |         |            |          |enveloping
-             |           |         |            |          |threads
-             |           |         |            |          |surrounds
-             |           |         |            |          |oogonium.
-  -----------+-----------+---------+------------+----------+----------
-
-    -----------+------------------------+-------------+-----------
-               |        GAMETOPHYTE.    |             |
-               |    (Bears the sexual   |             |
-               |  organs and gonidia.)  | SPOROPHYTE  |How Veg.
-    -----------+------------------------+   Bears     |Phase of
-               |  Sexual Reproduction.  |   spores    |Gametophyte
-               +------------------------+-------------+  is
-               |        Gametes.        |   Fruit.    |Developed.
-    -----------+------------------------+-------------+-----------
-    Spirogyra. |   Undifferentiated.    |  Zygospore  |Develops
-               |  Entire contents of    |  Rests.     |veg. phase
-               |   conjugating cell.    |             |directly.
-    -----------+------------------------+-------------+-----------
-               |      Differentiated.   |  Egg (or    |Develops
-               |Small         |  Large  |  oospore).  |veg. phase
-    Vaucheria. |two-ciliated  |  egg    |  Rests.     |directly.
-               |spermatozoids.|  cell.  |             |
-    -----------+--------------+---------+-------------+-----------
-               |      Differentiated.   |  Egg (or    |Divides
-               |Oval          |  Large  |  oospore).  |into
-    Œdogonium. |spermatozoids |  egg    |  Rests.     |four cells;
-               |with          |  cell.  |             |each
-               |crown of      |         |             |forms
-               |cilia.        |         |             |zoospore
-               |Two from each |         |             |which
-               |antheridium.  |         |             |develops
-               |              |         |             |veg. phase
-               |              |         |             |again.
-    -----------+--------------+---------+-------------+-----------
-    Coleochæte.|      Differentiated.   |Egg          |Each forms
-               |Oval,         |  Large  |(surrounded  |a zoospore.
-               |biciliate     |  egg    |by           |Zoospore
-               |spermatozoid, |  cell.  |wall from    |develops
-               |one from each |         |gametophyte).|veg. phase
-               |antheridium.  |         |Rests.       |again.
-               |              |         |Divides      |
-               |              |         |and          |
-               |              |         |grows to     |
-               |              |         |form a mass  |
-               |              |         |of cells.    |
-    -----------+--------------+---------+-------------+-----------
-
-
-
-
-CHAPTER XVIII.
-
-CLASSIFICATION AND ADDITIONAL STUDIES OF THE ALGÆ.
-
-
-In order to show the general relationship of the algæ studied, the
-principal classes are here enumerated as well as some of the families.
-In some of the groups not represented by the examples studied above, a
-few species are described which may serve as the basis of additional
-studies if desired. The principal classes[17] of algæ are as follows:
-
-
-Class Chlorophyceæ.
-
-=331.= These are the green algæ, so called because the chlorophyll
-green is usually not masked by other pigments, though in some forms it
-is. There are three subclasses.
-
-=332. Subclass PROTOCOCCOIDEÆ.=—In the Protococcoideæ are found
-the simplest green plants. Many of them consist of single cells which
-live an independent life. Others form “colonies,” loose aggregations
-of individuals not yet having attained the permanency of even a simple
-plant body, for the cells often separate readily and are able to form
-new colonies. The colonies are often held together by a gelatinous
-membrane, or matrix. Some are motile, while others are non-motile. A
-few of the families are here enumerated.
-
-=333. Family Volvocaceæ.=—These are all motile, during the
-vegetative stage. The individuals are single or form more or less
-globose colonies.
-
-=334. The “red snow” plant (Sphærella nivalis).=—This is often
-found in arctic and alpine regions forming a red covering over more or
-less large areas of snow or ice. For this reason it is called the “red
-snow plant.”
-
-=335. Sphærella lacustris=, a closely related species, is very
-widely distributed in temperate regions along streams or on the borders
-of lakes and ponds. Here in dry weather it is often found closely
-adhering to the dry rock surface, and giving it a reddish color as
-if the rock were painted. This is especially the case in the shallow
-basins formed over the uneven surface of the rock near the water’s
-edge. These places during heavy rains or in high water are provided
-with sufficient water to fill the basins. During such times the red
-snow plant grows and multiplies, loses its red color and becomes green,
-and, being motile, is free swimming. It is a single-celled plant,
-oval in form, surrounded by a gelatinous sheath and with two cilia or
-flagella at the smaller end, by the vibration of which it moves (fig.
-162). The single cell multiplies by dividing into two cells. When the
-water dries out of the basin, the motile plant comes to rest, and many
-of the cells assume the red color. To obtain the plant for study,
-scrape some of the red covering from these rock basins and place it in
-fresh spring water, and in a day or so the swarmers are likely to be
-found. Under certain conditions small microzoids are formed.
-
-[Illustration: Fig. 162.
-
-Sphærella lacustris (Girod.) Wittrock. _A_, mature free swimming
-individual with central red spot. _B_, division of mother individual to
-form two. _C_, division of a red one to form four. _D_, division into
-eight. _E_, a typical resting cell, red. _F_, same beginning to divide.
-_G_, one of four daughter zoospores after swimming around for a time
-losing its red color and becoming green. (After Hazen.)]
-
-=336. Chlamydomonas= is a very interesting genus of motile
-one-celled green algæ, because the species are closely related to
-the Flagellates among the lower animals. The plant is oval, with a
-single chloroplast and surrounded by a gelatinous envelope through
-which the two cilia or flagella extend. One-celled organisms of this
-kind are sometimes called _monads_, i.e., a one-celled being. This
-one has a gelatinous cloak and is, therefore, a _cloaked monad_
-(_Chlamydomonas_). The species often are found as a very thin green
-film on fresh water. C. pulvisculus is shown in fig. 163. When it
-multiplies the single cell divides into two, as shown in _B_. Sometimes
-a non-motile palmella stage is formed, as shown in _C_ and _D_.
-Reproduction takes place by gametes which are of unequal size, the
-smaller one representing the sperm and the larger one the egg, as in
-_E_ and _F_. These conjugate as in _G_ and _H_, the protoplasm of the
-smaller one passing over into the larger one, and a zygospore is thus
-formed.
-
-[Illustration: Fig. 163.
-
-_Chlamydomonas pulvisculus_ (Müll.) Ehrb. _A_, an old motile
-individual; _n_, nucleus; _p_, pyrenoid; _s_, red eye spot; _v_,
-contractile vacuole; _B_, motile individual has drawn in its cilia
-and divided into two; _C_, mother plant has drawn in its cilia and
-divided into four non-motile cells; _D_, pamella stage; _E_, female
-gamete—egg; _F_, male gamete—sperm; _G_, early stage of conjugation;
-_H_, zygospore with conjugating tube and empty male cell attached.
-(After Wille.)]
-
-=337. Of those which form colonies=, Pandorina morum is widely
-distributed and not rare. It consists of a sphere formed of sixteen
-individuals enclosed in a thin gelatinous membrane. Each cell possesses
-two cilia (or flagella), which extend from the broader end out through
-the enveloping membrane. By the movement of these flagella the colony
-goes rolling around in the water. When the plant multiplies each
-individual cell divides into sixteen small cells, which then grow and
-form new colonies. Reproduction takes place when the individual cells
-of the young colonies separate, and usually a small individual unites
-with a larger one and a zygospore is formed (see fig. 164). Eudorina
-elegans is somewhat similar, but when the gametes are formed certain
-mother cells divide into sixteen small motile males or sperms, and
-certain other mother cells divide into sixteen large motile females or
-eggs. These separate from the colonies, and the sperms pair with the
-eggs and fuse to form zygospores. This plant as well as Chlamydomonas
-pulvisculus foreshadows the early differentiation of sex in plants.
-
-[Illustration: Fig. 164.
-
-Pandorina morum (Müll.) Bory. I, motile colony; II, colony divided into
-16 daughter colonies; III, sexual colony, gametes escaping; IV, V,
-conjugating gametes; VI, VII, young and old zygospore; VIII, zygospore
-forming a large swarm spore, which is free in IX; X, same large swarm
-spore divided to form young colony. (After Pringsheim.)]
-
-[Illustration: Fig. 165. Pleurococcus (protococcus) vulgaris.]
-
-=338. Family Tetrasporaceæ.=—This family is well represented by
-Tetraspora lubrica forming slimy green net-like sheets attached to
-objects in slow-running water. It is really a single-celled plant. The
-rounded cells divide by cross walls into four cells, and these again,
-and so on, large numbers being held in loose sheets by the slime in
-which they are imbedded.
-
-=339. Family Pleurococcaceæ.=—The members of this family are
-all non-motile in the vegetative stage. They consist of single
-individuals, or of colonies. Pleurococcus vulgaris (Protococcus
-vulgaris) is a single-celled alga, usually obtained with little
-difficulty. It is often found on the shaded, and cool, or moist side of
-trees, rocks, walls, etc., in damp places. This plant is not motile. It
-multiplies by fission (Fig. 165) into two, then four, etc. These cells
-remain united for a time, then separate. Sometimes the cells are found
-growing out into filaments, and it is thought by some that P. vulgaris
-may be only a simple stage of a higher alga. Eremosphæra viridis is
-another single-celled alga found in fresh water among filamentous
-forms. The cells are large and globose.
-
-[Illustration: Fig. 166.
-
-Pediastrum boryanum. _A_, mature colony, most of the young colonies
-have escaped from their mother cells; at _g_, a young colony is
-escaping; _sp_, empty mother cells; _B_, young colony; _C_, same colony
-with spores arranged in order. (After Braun.)]
-
-=340. Family Hydrodictyaceæ.=—These plants form colonies of
-cells. Hydrodictyon reticulatum, the water net, is made up of large
-numbers of cylindrical cells so joined at their ends as to form a large
-open mesh or net. Pediastrum forms circular flat colonies, as shown in
-fig. 166. Both of these plants are rather common in fresh-water pools,
-the latter one intermingled with filamentous algæ, while the former
-forms large sheets or nets. Multiplication in Hydrodictyon takes place
-by the protoplasm in one of the cells dividing into thousands of minute
-cells, which gradually arrange themselves in the form of a net, escape
-together from the mother cell, and grow into a large net. In Pediastrum
-multiplication takes place in a similar way, but the protoplasm in each
-cell usually divides into sixteen small cells, and escaping together
-from the mother cell arrange themselves and grow to full size (fig.
-166).
-
-=341. The Conjugateæ= include several families of green algæ,
-which probably should be included among the Chlorophyceæ. They have
-probably had their origin from some of the more simple members of the
-Protococcoideæ. They are represented by Spirogyra, Zygnema, and the
-desmids, studied in Chapter 14.
-
-=342. Subclass CONFERVOIDEÆ.=—These are mostly filamentous algæ,
-the filaments being composed of cells firmly united, and, with the
-exception of the simplest forms, there is a definite growing point. A
-few of the families are as follows:
-
-=343. Family Ulvaceæ.=—These contain the sea wracks, or sea
-lettuce, like Ulva, forming expanded green, ribbon-like growths in the
-sea.
-
-[Illustration: Fig. 167.
-
-Ulothrix zonata. _A_, base of thread. _B_, cells with zoospores, _C_,
-one cell with zoospores escaping another cell with small biciliate
-gametes escaping and some fusing to form zygospores, _E_, zoospores
-germinating and forming threads: _F_, _G_, zygospore growing and
-forming zoospores. (After Caldwell and Dodel-Port.)]
-
-=344. Family Ulotrichaceæ=, represented by Ulothrix zonata, not
-uncommon in slow-running water or in ponds of fresh water attached
-to rocks or wood. It consists of simple threads of short cells.
-Multiplication takes place by zoospores. Reproduction takes place by
-motile sexual cells (gametes) which fuse to form a zygospore (fig. 167).
-
-=345. Family Chætophoraceæ=, represented by Chætophora (in Chapter
-15) and Drapernaudia in fresh water.
-
-=346. Family Œdogoniaceæ=, represented by Œdogonium (Chapter 16).
-
-=347. Family Coleochætaceæ=, represented by Coleochæte (Chapter
-17).
-
-=348. Subclass SIPHONEÆ.=—There are several families.
-
-=349. Family Botrydiaceæ.=—This is represented by Botrydium
-granulatum (Chapter 15, p. 146).
-
-=350. Family Vaucheriaceæ=, represented by Vaucheria (Chapter 15),
-with quite a large number of species, is widely distributed.
-
-
-Class Schizophyceæ (= Cyanophyceæ).
-
-[Illustration: Fig. 168. Glœocapsa.]
-
-=351. The Blue-Green Algæ=, or =Cyanophyceæ= form slimy
-looking thin mats on damp wood or the ground, or floating mats or
-scum on the water. The color is usually bluish green, but in some
-species it is purple, red or brown. All have chlorophyll, but it is
-not in distinct chloroplasts and is more or less completely guised
-by the presence of other pigments. Two orders and eight families are
-recognized. The following include some of our common forms:
-
-=352. ORDER COCCOGONALES (COCCOGONEÆ).=—Single-celled plants,
-occurring singly or in colonies, in some forms forming short threads.
-One of the two families is mentioned.
-
-=353. Family Chroococcaceæ.=—The plants multiply only through cell
-division. Chroococcus, forms rounded, blue-green cells enclosed in a
-thick gelatinous coat, in fresh water and in damp places; certain
-species form “lichen-gonidia” in some genera of lichens. Glœocapsa is
-similar to Chroococcus, but the colonies are surrounded by an additional
-common gelatinous envelope (fig. 168); on damp rocks, etc.
-
-[Illustration: Fig. 169.
-
-_A_, Oscillatoria princeps, _a_, terminal cell; _b_, _c_, portions from
-the middle of a filament. In _c_, a dead cell is shown between the
-living cells; _B_, Oscillatoria froelichii, _b_, with granules along
-the partition walls.]
-
-=354. ORDER HORMOGONALES (HORMOGONEÆ).=—Plants filamentous,
-simple celled or with false or true branching, usually several celled
-(Spirulina is single celled). Multiplication takes place through
-_hormogones_, short sections of the threads becoming free; also through
-resting cells. Two of the six families are mentioned.
-
-=355. Family Oscillatoriaceæ.=—This family is represented by
-the genus Oscillatoria, and by several other genera common and widely
-distributed. Oscillatoria contains many species. They are found on the
-damp ground or wood, or floating in mats in the water. They often form
-on the soil at the bottom of the pool, and as gas becomes entangled
-in the mat of threads, it is lifted from the bottom and floated to
-the surface of the water. The plant is thread-like, and divided up
-into many short cells. The threads often show an oscillating movement,
-whence the name _Oscillatoria_.
-
-=356. Family Nostocaceæ.=—This family is represented by Nostoc,
-which forms rounded, slimy, blue-green masses on wet rocks. The
-individual plants in the slimy ball resemble strings of beads, each
-cell being rounded, and several of these arranged in chains as shown
-in fig. 170. Here and there are often found larger cells (heterocysts)
-in the chain. Nostoc punctiforme lives in the intercellular spaces
-of the roots of cycads (often found in greenhouses), and in the
-stems of Gunnera. N. sphæricum lives in the spaces between the cells
-in many species of liverworts (in the genera Anthoceros, Blasia,
-Pellia, Aneura, Riccia, etc.), and in the perforated cells of Sphagnum
-acutifolium. Anabæna is another common and widely distributed genus.
-The species occur in fresh or salt water, singly or in slimy masses.
-Anabæna azollæ lives endophytically in the leaves of the water fern,
-Azolla.
-
-[Illustration: Fig. 170.
-
-Nostoc linckii. _A_, filament with two heterocysts (_h_), and a large
-number of spores (_sp_); _B_, isolated spore beginning to germinate;
-_C_, young filament developed from spore. (After Bornet.)]
-
-[Illustration: Fig. 171.
-
-Bacteria. _A_, Bacillus subtilis. Spores in threads, unstained rods,
-and stained rods showing cilia; _B_, Bacillus tetani, the tetanus
-or lockjaw bacillus, found in garden soil and on old rusty nails.
-Spores in club-shaped ends. _C_, Micrococcus; _D_, Sarcina; _E_,
-Streptococcus; _F_, Spirillum. (After Migula.)]
-
-
-Class Schizomycetes.
-
-=357. Bacteriales.=—The bacteria are sometimes classified
-with the Cyanophyceæ, under the name Schizophyta, and represent the
-subdivision Schizomycetes, or fission fungi, because many of them
-multiply by a division of the cells just as the blue-green algæ do.
-For example, Bacillus forms rods which increase in length and divide
-into two rods, or it may grow into a long thread of many short rods.
-Micrococcus consists of single rounded cells. Streptococcus forms
-chains of rounded cells, Sarcina forms irregular cubes of rounded
-cells, while others like Spirillum are spiral in form. Bacillus
-subtilis may be obtained by making an infusion from hay and allowing
-it to stand for several days. Bacillus tetani occurs in the soil, on
-old rusty nails, etc. It is called the tetanus bacillus because it
-causes a permanent spasm of certain muscles, as in “lockjaw.” This
-bacillus grows and produces this result on the muscles when it occurs
-in deep and closed wounds such as are caused by stepping on an old nail
-or other object which pierces the flesh deeply. In such a deep wound
-oxygen is deficient, and in this condition the bacillus is virulent.
-Opening the wounds to admit oxygen and washing them out with a solution
-of bichloride of mercury prevents the tetanus. Many bacteria are of
-great importance in bringing about the decay of dead animal and plant
-matter, returning it to a condition for plant food. (See also nitrate
-and nitrite bacteria, Chapter IX.) While most bacteria are harmless
-there are many which cause very serious diseases of man and animals,
-as typhoid fever, diphtheria, tuberculosis, etc., while some others
-produce disease in plants. Others aid in certain fermentations of
-liquids and are employed for making certain kinds of wines or other
-beverages. Some work in symbiosis with yeasts, as in the kephir yeast,
-used in fermenting certain crude beverages by natives of some countries.
-
-=357=_a_. =Myxobacteriales (Myxobacteriaceæ
-Thaxter[18]).=—These plants consist of colonies of bacteria-like
-organisms, motile rods, which multiply by cross-division and secrete
-a gelatinous substance or matrix which surrounds the colonies. They
-form plasmodium-like masses which superficially resemble the slime
-moulds. In the fruiting stage some species become elevated from the
-substratum into cylindrical, clavate, or branched forms, which bear
-cysts of various shapes containing the rods in a resting stage, or the
-rods are converted into spore-like masses. Ex., Chondromyces crocatus
-on decaying plant parts, Myxobacter aureus on wet wood and bark,
-Myxococcus rubescens on dung, decaying lichens, paper, etc.
-
-
-Class Flagellata.
-
-=358. The flagellates= are organisms of very low organization
-resembling animals as much as they do plants. They are single celled
-and possess two cilia or flagella, by the vibration of which they
-move. Some are without a cell wall, while others have a well-defined
-membrane, but it rarely consists of cellulose. Some have chromatophores
-and are able to manufacture carbohydrates like ordinary green plants.
-These are green in Euglena, and brown in Hydrurus. Some possess a
-mouth-like opening and are able to ingest solid particles of food
-(more like animals), while others have no such opening and absorb food
-substances dissolved in water (more like plants). The Euglena viridis
-is not uncommon in stagnant water, often forming a greenish film on the
-water.
-
-
-Class Peridineæ.
-
-=358=_a_. These are peculiar one-celled organisms provided with
-two flagella and show some relationship to the Flagellates. They
-usually are provided with a cellulose membrane, which in some forms
-consists of curiously sculptured plates. In the higher forms this
-cellulose membrane consists of two valves fitting together in such a
-way as to resemble some of the diatoms. Like the Flagellates, some
-have green chromatophores, which in some are obscured by a yellow or
-brown pigment (resembling the diatoms), while still others have no
-chlorophyll. The Peridineæ are abundant in the sea, while some are
-found in fresh water.
-
-
-Class Diatomaphyceæ (Bacillariales, Diatomaceæ).
-
-[Illustration: Fig. 171_a_.
-
-A group of Diatoms: _c_ and _d_, top and side views of the same form;
-_e_, colony of stalked forms attached to an alga; _f_ and _g_, top and
-side views of the form shown at _e_; _h_, a colony; _i_, a colony, the
-top and side view shown at _k_ and _n_, forming auxospores. (After
-Kerner.)]
-
-=358=_b_. =The diatoms= are minute and peculiar organisms
-believed to be algæ. They live in fresh, brackish, and salt water. They
-are often found covering the surface of rocks, sticks, or the soil
-in thin sheets. They occur singly and free, or several individuals
-may be joined into long threads, or other species may be attached to
-objects by slender gelatinous stalks. Each protoplast is enclosed in a
-silicified skeleton in the form of a box with two halves, often shaped
-like an old-fashioned pill box, one half fitting over the other like
-the lid of a box. It is evident that in this condition the plant cannot
-increase much in size.
-
-They multiply by fission. This takes place longitudinally, i.e., in the
-direction of the two halves or _valves_ of the box. Each new plant then
-has a valve only on one side. A new valve is now formed over the naked
-half, and fits inside the old valve. At each division the individuals
-thus become smaller and smaller until they reach a certain point, when
-the valves are cast off and the cell forms an _auxospore_, i.e., it
-grows alone, or after conjugation with another, to the full size again,
-and eventually provides itself with new valves. The valves are often
-marked, with numerous and fine lines, often making beautiful figures,
-and some are used for test objects for microscopes.
-
-The free forms are capable of movement. The movement takes place in the
-longitudinal direction of the valves. They glide for some time in one
-direction, and then stop and move back again. It is not a difficult
-thing to mount them in fresh water and observe this movement.
-
-The diatoms have small chlorophyll plates, but the green color is
-disguised by a brownish pigment called diatomin. The relationships of
-the diatoms are uncertain, but some, because of the color, think they
-are related to the Phæophyceæ.
-
-
-Class Phæophyceæ.
-
-=359. The brown algæ. (Phæophyceæ).=—The members of this class
-possess chlorophyll, but it is obscured by a brown pigment. The plants
-are accessible at the seashore, and for inland laboratories may be
-preserved in formalin (2½ per cent). (See also Chapter LVI.)
-
-[Illustration: Fig. 172.
-
-_A_, Ectocarpus siliculosus; _B_, branch with a young and a ripe
-plurilocular sporangium; _E_, gametes fusing to form zygospore, (_B_,
-after Thuret; _E_, after Berthold.)]
-
-=360. Ectocarpus.=—The genus Ectocarpus represents well some
-of the simpler forms of the brown algæ (fig. 172). They are slender,
-filamentous branched algæ growing in tufts, either epiphytic on other
-marine algæ (often on Fucaceæ), or on stones. The slender threads are
-only divided crosswise, and thus consist of long series of short cells.
-The sporangia are usually plurilocular (sometimes unilocular), and
-usually occur in the place of lateral branches. The zoospores escape
-from the apex of the sporangium and are biciliate, and they fuse to
-form zygospores.
-
-=361. Sphacelaria.=—The species of this genus represent an
-advance in the development of the thallus. While they are filamentous
-and branched, division takes place longitudinally as well as crosswise
-(fig. 173).
-
-=362. Leathesia difformis= represents an interesting type because
-the plant body is small, globose, later irregular and hollow, and
-consists of short radiately arranged branches, the surface ones in the
-form of short, crowded, but free, trichome-like green branches. This
-trichothallic body recalls the similar form of Chætophora pisiformis
-(Chapter 16) among the Chlorophyceæ.
-
-[Illustration: Fig. 173. Sphacelaria, portion of plant showing
-longitudinal division of cells, and brood bud (plurilocular
-sporangium).]
-
-[Illustration: Fig. 174. Laminaria digitata, forma cloustoni, North
-Sea. (Reduced.)]
-
-=363. The Giant Kelps.=—Among the brown algæ are found the
-largest specimens, some of the laminarias or giant kelps, rivaling in
-size the largest land plants, and some of them have highly developed
-tissues. _Postelsia palmæformis_ has a long, stout stem, from the
-free end of which extend numerous large and long blades, while the
-stem is attached to the rocks by numerous “root” like outgrowths, the
-holdfasts. It occurs along the northern Pacific coast, and appears to
-flourish where it receives the shock of the surf beating on the shore.
-Several species of Laminaria occur on our north Atlantic coast. In L.
-digitata, the stem expands at the end into a broad blade, which becomes
-split into several smaller blades (fig. 174). _Macrocystis pyrifera_
-inhabits the ocean in the southern hemisphere, and sometimes is found
-along the north American coast. It is said to reach a length of 200-300
-meters.
-
-=364. Fucus, or Rockweed.=—This plant is a more or less branched
-and flattened thallus or “frond.” One of them, illustrated in fig. 119,
-measures 15-30 _cm_ (6-12 inches) in length. It is attached to rocks
-and stones which are more or less exposed at low tide. From the base
-of the plant are developed several short and more or less branched
-expansions called “holdfasts,” which, as their name implies, are organs
-of attachment. Some species (F. vesiculosus) have vesicular swellings
-in the thallus.
-
-The fruiting portions are somewhat thickened as shown in the figure.
-Within these portions are numerous oval cavities opening by a circular
-pore, which gives a punctate appearance to these fruiting cushions.
-Tufts of hairs frequently project through them.
-
-[Illustration: Fig. 175. Portion of plant of Fucus showing conceptacles
-in enlarged ends; and below the vesicles (Fucus vesiculosus).]
-
-[Illustration: Fig. 176. Section of conceptacle of Fucus, showing
-oogonia, and tufts of antheridia.]
-
-=365. Structure of the conceptacles.=—On making sections of the
-fruiting portions one finds the walls of the cavities covered with
-outgrowths. Some of these are short branches which bear a large rounded
-terminal sac, the oogonium, at maturity containing eight egg-cells.
-More slender and much-branched threads bear narrowly oval antheridia.
-In these are developed several two-ciliated spermatozoids.
-
-[Illustration: Fig. 177. Oogonium of Fucus with ripe eggs.]
-
-[Illustration: Fig. 178. Antheridia of Fucus, on branched threads.]
-
-=366. Fertilization.=—At maturity the spermatozoids and egg-cells
-float outside of the oval cavities, where fertilization takes place.
-The spermatozoid sinks into the protoplasm of the egg-cell, makes its
-way to the nucleus of the egg, and fuses with it as shown in fig. 181.
-The fertilized egg then grows into a new plant. Nearly all the brown
-algæ are marine.
-
-[Illustration: Fig. 179. Antheridia of Fucus with escaping
-spermatozoids.]
-
-[Illustration: Fig. 180. Eggs of Fucus surrounded by spermatozoids.]
-
-[Illustration: Fig. 181.
-
-Fertilization in Fucus; _fn_, female nucleus; _mn_, male nucleus;
-_n_, nucleolus. In the left figure the male nucleus is shown moving
-down through the cytoplasm of the egg; in the remaining figures the
-cytoplasm of the egg is omitted. (After Strasburger.)]
-
-=367. The Gulf weed= (=Sargassum bacciferum=) in the warmer
-Atlantic ocean unites in great masses which float on the water, whence
-comes the name “Sargassum Sea.” The Sargassum grows on the coast where
-it is attached to the rocks, but the beating of the waves breaks many
-specimens loose and these float out into the more quiet waters, where
-they continue to grow and multiply vegetatively.
-
-=368. Uses.=—Laminaria japonica and L. angustata are used as food
-by the Chinese and Japanese. Some species of the Laminariaceæ are used
-as food for cattle and are also used for fertilizers, while L. digitata
-is sometimes employed in surgery.
-
-_Classification._—Kjellman divides the Phæophyceæ into two orders.
-
-=369. Order Phæosporales (Phæosporeæ)= including 18 families.
-One of the most conspicuous families is the Laminariaceæ, including
-among others the Giant Kelps mentioned above (Laminaria, Postelsia,
-Macrocystis, etc.).
-
-=370. Order Cyclosporales (Cyclosporeæ).=—This includes one
-family, the _Fucaceæ_ with Ectocarpus, Sphacelaria, Læathesia, Fucus,
-Sargassum, etc.
-
-
-Class Rhodophyceæ.
-
-=371. The red algæ (Rhodophyceæ).=—The larger number of the
-so-called red algæ occur in salt water, though a few genera occur in
-fresh water. The plants possess chlorophyll, but it is usually obscured
-by a reddish or purple pigment.
-
-=372. Nemalion.=—This is one of the lower marine forms, though
-its thallus is not one of the simplest in structure. The plant body
-consists of a slender cylindrical branched shoot, sometimes very
-profusely branched. The central strand is rather firm, while the cortex
-is composed of rather loose filaments.
-
-[Illustration: Fig. 182.
-
-A red alga (Nemalion). _A_, sexual branches, showing antheridia (_a_);
-carpogonium or procarp (_o_) with its trichogyne (_t_), to which are
-attached two spermatia (_s_); _B_, beginning of a cystocarp (_o_),
-the trichogyne (_t_) still showing; _C_, an almost mature cystocarp
-(_o_), with the disorganizing trichogyne (_t_). (After Vines.)]
-
-=373. Batrachospermum.=—This genus occurs in fresh water, and the
-species are found in slow-running water of shallow streams or ditches.
-There is a central slender strand which is more or less branched,
-and on these branches are whorls of densely crowded slender branches
-occurring at regular intervals. The plants are usually very slippery.
-Gonidia are formed on the ends of some of these branches in globose
-sporangia, called monosporangia, since but a single spore or gonidium
-is developed in each. Other branches often terminate in long slender
-hyaline setæ.
-
-=374. Lemanea.=—This genus also occurs in fresh water. The
-species develop only during the cold winter months in rapids of streams
-or where the water from falls strikes the rocks and is thoroughly
-aerated. They form tufts of greenish threads, cylindrical or whiplike,
-which in the summer are usually much broken down. The threads are
-hollow and have a firm cortex. These are the sexual shoots, and they
-arise as branches from a sterile filamentous-branched, Chantransia-like
-form.
-
-=375. Fertilization in the lower red algæ.=—The sexual organs in
-the red algæ consist of antheridia and carpogonia. The antheridia are
-usually borne in crowded clusters, or surfaces, and bear terminally
-the small non-motile sperm cells. The carpogonium is a branch of one
-or several cells, the terminal cell (procarp) extending into a long
-slender process, the trichogyne. The sperm cell comes in contact with
-the trichogyne, and in the case of Nemalion and some others the nucleus
-has been found to pass down the inside and fuse with the nucleus of the
-procarp.
-
-[Illustration: Fig. 183.
-
-_A_, part of a shoot showing whorls of branches with clusters of
-carpospores. _B_, carpogonic branch or procarp. _c_, procarp cell;
-_tr_, trichogyne. _C_, same with sperm (_sp_) uniting with trichogyne.
-_D_, same with carpospores developing from procarp cell. _E_, male
-branch with one-celled antheridia. _F_, same with some of antheridia
-empty. (After Schmitz.)]
-
-From this point in the lower red algæ like Nemalion, Batrachospermum
-and Lemanea the formation of the spores is very simple. The procarp
-is stimulated to growth, and buds in different directions, producing
-branched chains of spores (carpospores). The carpospores form a rather
-compact cluster called the sporocarp, which means spore-fruit or
-spore-fruit body. In Batrachospermum it is seen as a compact tuft in
-the loose branching, in Nemalion it lies in the surface of the cortex,
-while in Lemanea the sporocarps lie at different positions in the
-hollow tube of the sexual shoot.
-
-[Illustration: Fig. 184.
-
-A red alga (Callithamnion), showing sporangium _A_, and the tetraspores
-discharged _B_. (After Thuret.)]
-
-[Illustration: Fig. 185. Gracilaria, portion of frond, showing position
-of cystocarps.]
-
-[Illustration: Fig. 186. Gracilaria, section of cystocarp showing
-spores.]
-
-=376. Gonidia in the red algæ.=—The common type of gonidium
-in the red algæ is found in the _tetraspores_. A single mother cell
-divides into four cells arranged usually in the form of tetrads within
-the _tetrasporangium_. In Callithamnion the tetrasporangium is exposed.
-In Polysiphonia, Rhabdonia, Gracilaria, etc., it is imbedded in the
-cortex. In Batrachospermum there are monosporangia, each monosporangium
-containing a single gonidium, while in Lemanea, and according to some
-also in Nemalion, gonidia are wanting.
-
-=377. Gracilaria.=—Gracilaria is one of the marine forms, and
-one species is illustrated in fig. 185. It measures 15-20_cm_ or more
-long, and is profusely branched in a palmate manner. The parts of the
-thallus are more or less flattened. The fruit is a cystocarp, which
-is characteristic of the Rhodophyceæ (Florideæ). In Gracilaria these
-fruit bodies occur scattered over the thallus. They are somewhat
-flask-shaped, are partly sunk in the thallus, and the conical end
-projects strongly above the surface. The carpospores are grouped in
-radiating threads within the oval cavity of the cystocarp. These
-cystocarps are developed as a result of fertilization. Other plants
-bear gonidia in groups of four, the so-called _tetraspores_.
-
-=378. Rhabdonia.=—This plant is about the same size as the
-gracilaria, though it possesses more filiform branches. The cystocarps
-form prominent elevations, while the carpospores lie in separated
-groups around the periphery of a sterile tissue within the cavity. (See
-figs. 187, 188.) Gonidia in the form of tetraspores are also developed
-in Rhabdonia.
-
-[Illustration: Fig. 187. Rhabdonia, branched portion of frond showing
-cystocarps.]
-
-[Illustration: Fig. 188. Section of cystocarp of rhabdonia, showing
-spores.]
-
-=379. Fertilization of the higher red algæ.=—The process of
-fertilization in most of the red algæ is very complicated, chiefly
-because the fertilized egg-cell (procarp) does not develop the spores
-directly, as in Nemalion, Lemanea, etc., but fuses directly, or by a
-short cell or long filament with one or more auxiliary cells before
-the sporocarp is finally formed. Examples are Rhabdonia, Polysiphonia,
-Callithamnion, Dudresnaya, etc. (fig. 189). The auxiliary cell then
-develops the sporocarp. See fig. 189 for conjugation of a filament from
-the fertilized procarp with an auxiliary cell.
-
-[Illustration: Fig. 189.
-
-Dudresnaya purpurifera. _tr_, trichogyne, with spermatozoids attached;
-_ct_, connecting-tube which grows out from below the base of the
-trichogyne, and comes in contact with the fertile branches _f_, _f_;
-_ct′_, young connecting-tube. (After Thuret and Bornet.)]
-
-=380. Uses of the red algæ.=—Many species produce a great amount
-of gelatinous substance in their tissues, and several of these are used
-for food, for the manufacture of gelatines and agar-agar. Some of these
-are Gracilaria lichenoides and wrightii, the former species occurring
-along the coast of India and China. The plant is easily converted into
-gelatinous substance (agar-agar). Chondrus crispus, widely distributed
-in the northern Atlantic is known as “Irish” moss and is used for food
-and for certain medicinal purposes. Gigartina mamillosa in the Atlantic
-and Arctic oceans is similarly employed. The following orders are
-recognized in the red algæ:
-
-=381. Order Bangiales.=—Example, Bangia atropurpurea (= Conferva
-atropurpurea) in springs and brooks in North America and Europe.
-Porphyra contains a number of species forming broad, thin, leaf-like
-purple sheets in the sea.
-
-=382. Order Nemalionales.=—Including Lemanea, Batrachospermum,
-Nemalion, described above, and many others.
-
-=383. Order Gigartinales.=—In this order occurs the common
-Iceland moss (Chondrus crispus) in the sea, and Rhabdonia and Gigartina
-mentioned above.
-
-=384. Order Rhodomeniales.=—In this order occurs Gracilaria and
-Polysiphonia mentioned above, also the beautiful marine forms like
-Ceramium.
-
-=385. Order Cryptonemiales.=—Examples are Dudresnaya, Melobesia,
-Corallina, etc., the last two genera include many species with a wide
-distribution.
-
-
-Class Charophyceæ, Order Charales.
-
-=386.= The Charales are by some thought to represent a distinct
-class of algæ standing near the mosses, perhaps, because of the
-biciliate character of the spermatozoids. There is one family, the
-Characeæ. The plants occur in fresh and brackish water. Aside from the
-peculiarity of the reproductive organs they are remarkable for the
-large size of the cells of the internodes and of the “leaves,” and the
-protoplasm exhibits to a remarkable degree the phenomenon of “cyclosis”
-(see paragraphs 17-20). Three of the genera are found in North America
-(Chara, Nitella (Fig. 8) and Tolypella).
-
-[Illustration: Fig. 172_a_.
-
-Reproductive organs of _Chara fragilis_. _A_, a central portion of a
-leaf, _b_, with an antheridium, _a_, and a carpogonium, _s_, surrounded
-by the spirally twisted enveloping cells; _c_, crown of five cells at
-apex; β, sterile lateral leaflets; β′, large lateral leaflet near the
-fruit; β″, bracteoles springing from the basal node of the reproductive
-organs. _B_, a young antheridium, _a_, and a young carpogonium, _sk_;
-_w_, nodal cell of leaf; _u_, intermediate cell between _w_ and the
-basal-node cell of the antheridium; _l_, cavity of the internode of
-the leaf; _br_, cortical cells of the leaf. _A_ × about 33; _B_ × 240.
-(After Sachs.)]
-
-=386a.= The complicated structure of the sexual organs shows a
-higher state of organization than any of the other living algæ known.
-While the internodes in Nitella are composed of a single, stout cell,
-some times a foot or more in length, the nodes in all are composed of
-a group of smaller cells. From the lateral cells of this group lateral
-axes (sometimes called leaves) arise in whorls.
-
-In Nitella the internodes are naked, but in most species of Chara
-they are _corticated_, i.e., they are covered by a layer of numerous
-elongated cells which grow downward from the nodes at the base of the
-whorl of lateral shoots.
-
-=386b.= The sexual organs are situated at the nodes of the whorled
-lateral shoots, and consist of antheridia and carpogonia. Most of the
-plants are monœcious, and both antheridia and carpogonia are often
-attached to the same node, the antheridium projecting downward while
-the carpogonium is more or less ascending. The sexual organs are
-visible to the unaided eye. The antheridium is a globose red body of
-an exceedingly complicated structure. The sperms are borne in several
-very long coiled slender threads which are divided transversely into
-numerous cells. The carpogonium is oval or elliptical in outline, the
-wall of which is composed of several closely coiled spiral threads
-enclosing the large egg.
-
-FOOTNOTES:
-
-[17] In Engler & Prantl’s Pflanzenfamilien, Wille uses the term class
-for these principal subdivisions of the algæ. Systematists are not yet
-agreed upon a uniform use of the terms.
-
-[18] See Bot. Gaz., 17, 389, 1892.
-
-
-
-
-CHAPTER XIX.
-
-FUNGI: MUCOR AND SAPROLEGNIA.
-
-
-Mucor.
-
-=387.= In the chapter on growth, and in our study of protoplasm,
-we have become familiar with the vegetative condition of mucor. We now
-wish to learn how the plant multiplies and reproduces itself. For this
-study we may take one of the mucors. Any one of several species will
-answer. This plant may be grown by placing partially decayed fruits,
-lemons, or oranges, from which the greater part of the juice has been
-removed, in a moist chamber; or often it occurs on animal excrement
-when placed under similar conditions. In growing the mucor in this way
-we are likely to obtain Mucor mucedo, or another plant sometimes known
-as Mucor stolonifer, or Rhizopus nigricans, which is illustrated in
-fig. 191. This latter one is sometimes very injurious to stored fruits
-or vegetables, especially sweet potatoes or rutabagas. Fig. 190 is from
-a photograph of this fungus on a banana.
-
-=388. Asexual reproduction.=—On the decaying surface of the
-vegetable matter where the mucor is growing there will be seen numerous
-small rounded bodies borne on very slender stalks. These heads contain
-the gonidia, and if we sow some of them in nutrient gelatine or agar
-in a Petrie dish the material can be taken out very readily for
-examination under the microscope. Or we may place glass slips close
-to the growing fungus in the moist chamber, so that the fungus will
-develop on them, though cultures in a nutrient medium are much better.
-Or we may take the material directly from the substance on which it is
-growing. After mounting a small quantity of the mycelium bearing these
-heads, if we have been careful to take it where the heads appear
-quite young, it may be possible to study the early stages of their
-development. We shall probably note at once that the stalks or upright
-threads which support the heads are stouter than the threads of the
-mycelium.
-
-[Illustration: Fig. 190. Portion of banana with a mould (Rhizopus
-nigricans) growing on one end.]
-
-These upright threads soon have formed near the end a cross wall which
-separates the protoplasm in the end from the remainder. This end cell
-now enlarges into a vesicle of considerable size, the head as it
-appears, but to which is applied the name of _sporangium_ (sometimes
-called gonidangium), because it encloses the _gonidia_.
-
-At the same time that this end cell is enlarging the cross wall is
-arching up into the interior. This forms the _columella_. All the
-protoplasm in the sporangium now divides into gonidia. These are
-small-rounded or oval bodies. The wall of the sporangium becomes
-dissolved, except a small collar around the stalk which remains
-attached below the columella (fig. 192). By this means the gonidia are
-freed. These gonidia germinate and produce the mycelium again.
-
-[Illustration: Fig. 191. Group of sporangia of a mucor (Rhizopus
-nigricans) showing rhizoids and the stolon extending from an older
-group.]
-
-=389. Sexual stage.=—This stage is not so frequently found, but
-may sometimes be obtained by growing the fungus on bread.
-
-Conjugation takes place in this way. Two threads of the mycelium which
-lie near each other put out each a short branch which is clavate in
-form. The ends of these branches meet, and in each a septum is formed
-which cuts off a portion of the protoplasm in the end from that of the
-rest of the mycelium. The meeting walls of the branches now dissolve
-and the protoplasm of each gamete fuses into one mass. A thick wall
-is now formed around this mass, and the outer layer becomes rough and
-brown. This is the _zygote_ or _zygospore_. The mycelium dies and it
-becomes free often with the suspensors, as the stalks of these sexual
-branches are called, still attached. This zygospore passes through
-a period of rest, when with the entrance of favorable conditions of
-growth it germinates, and usually produces directly a sporangium with
-gonidia. This completes the normal life cycle of the plant.
-
-=390. Gemmæ.=—Gemmæ, as they are sometimes called, are often
-formed on the mycelium. A short cell with a stout wall is formed on the
-side of a thread of the mycelium. In other cases large portions of the
-threads of the mycelium may separate into chains of cells. Both these
-kinds of cells are capable of growing and forming the mycelium again.
-They are sometimes called _chlamydospores_.
-
-[Illustration: Fig. 194.
-
-A mucor (Rhizopus nigricans); at left nearly mature sporangium with
-columella showing within; in the middle is ruptured sporangium with
-some of the gonidia clinging to the columella; at right two ruptured
-sporangia with everted columella.]
-
-=390=_a_. The Mucorineæ according to their manner of zygospore
-formation are of two kinds: 1st, the _homothallic_ (monœcious), in
-which all of the colonies of thalli developed from different spores
-are the same, and both gametes may be developed from the mycelium
-from a single spore, as in Sporodinia grandis, a mould common on old
-mushrooms; 2d, the _heterothallic_ (diœcious), in which certain plants
-are of a male nature and small in comparison with those of perhaps a
-female nature which are larger or more vigorous. When grown separately
-each of these two kinds of thalli, or colonies of mycelium, produce
-their own kind but only sporangia. If the two kinds are brought
-together, however, branches from one conjugate with branches from
-the other and zygospores are produced, as in Rhizopus nigricans, the
-common bread or fruit mould. This is one reason why we rarely find this
-fungus forming zygospores. (See Blakeslee, Sexual Reproduction in the
-Mucorineæ, Proc. Am. Acad. Arts and Sci., =40=, 205-319, pl. 1-4,
-1904.)
-
-
-Water Moulds (Saprolegnia).
-
-=391.= The water moulds are very interesting plants to study
-because they are so easy to obtain, and it is so easy to observe a type
-of gonidium here to which we have referred in our studies of the algæ,
-the motile gonidium, or zoogonidium. (See appendix for directions for
-cultivating this mould.)
-
-=392. Appearance of the saprolegnia.=—In the course of a few days
-we are quite certain to see in some of the cultures delicate whitish
-threads, radiating outward from the body of the fly in the water. A few
-threads should be examined from day to day to determine the stage of
-the fungus.
-
-[Illustration: Fig. 195. Sporangia of saprolegnia, one showing the
-escape of the zoogonidia.]
-
-=393. Sporangia of saprolegnia.=—The sporangia of saprolegnia
-can be easily detected because they are much stouter than the ordinary
-threads of the mycelium. Some of the threads should be mounted in fresh
-water. Search for some of those which show that the protoplasm is
-divided up into a great number of small areas, as shown in fig. 195.
-With the low power we should watch some of the older appearing ones,
-and if after a few minutes they do not open, other preparations should
-be made.
-
-[Illustration: Fig. 196. Branch of saprolegnia showing oogonia with
-oospores, eggs matured parthenogenetically.]
-
-[Illustration: Fig. 197.
-
-Downy mildew of grape (Plasmopora viticola), showing tuft of
-gonidiophores bearing gonidia, also intercellular mycelium. (After
-Millardet.)]
-
-[Illustration: Fig. 198. Phytophthora infestans showing peculiar
-branches; gonidia below.]
-
-=394. Zoogonidia of saprolegnia.=—The sporangium opens at the end, and
-the zoogonidia swirl out and swim around for a short time, when they
-come to rest. With a good magnifying power the two cilia on the end may
-be seen, or we may make them more distinct by treatment with Schultz’s
-solution, drawing some under the cover glass. The zoogonidium is oval
-and the cilia are at the pointed end. After they have been at rest for
-some time they often slip out of the thin wall, and swim again, this
-time with the two cilia on the side, and then the zoogonidium is this
-time more or less bean-shaped or reniform.
-
-[Illustration: Fig. 199.
-
-Fertilization in saprolegnia, tube of antheridium carrying in the
-nucleus of the sperm cell to the egg. In the right-hand figure a
-smaller sperm nucleus is about to fuse with the nucleus of the egg.
-(After Humphrey and Trow.)]
-
-[Illustration: Fig. 200. Branching hypha of Peronospora alsinearum.]
-
-[Illustration: Fig. 201. Branched hypha of downy mildew of grape
-showing peculiar branching (Plasmopara viticola).]
-
-=395. Sexual reproduction of saprolegnia.=—When such cultures are
-older we often see large rounded bodies either at the end of a thread,
-or of a branch, which contain several smaller rounded bodies as shown
-in fig. 196. These are the oogonia (unless the plant is attacked by a
-parasite), and the round bodies inside are the egg-cells, if before
-fertilization, or the eggs, if after this process has taken place.
-Sometimes the slender antheridium can be seen coiled partly around the
-oogonium, and one end entering to come in contact with the egg-cell.
-But in some species the antheridium is not present, and that is the
-case with the species figured at 196. In this case the eggs mature
-without fertilization. This maturity of the egg without fertilization
-is called _parthenogenesis_, which occurs in other plants also, but is
-a rather rare phenomenon.
-
-[Illustration: Fig. 202.
-
-Gonidiophores and gonidia of potato blight (Phytophthora infestans).
-_b_, an older stage showing how the branch enlarges where it grows
-beyond the older gonidium. (After de Bary.)]
-
-[Illustration: Fig. 203. Gonidia of potato blight forming zoogonidia.
-(After de Bary.)]
-
-=396.= In fig. 199 is shown the oogonium and an antheridium,
-and the antheridium is carrying in the male nucleus to the egg-cell.
-Spermatozoids are not developed here, but a nucleus in the antheridium
-reaches the egg-cell. It sinks in the protoplasm of the egg, comes
-in contact with the nucleus of the egg, and fuses with it. Thus
-fertilization is accomplished.
-
-
-Downy Mildews.
-
-=397.= The downy mildews make up a group of plants which are
-closely related to the water moulds, but they are parasitic on land
-plants, and some species produce very serious diseases. The mycelium
-grows between the cells of the leaves, stems, etc., of their hosts,
-and sends haustoria into the cells to take up nutriment. Gonidia are
-formed on threads which grow through the stomates to the outside and
-branch as shown in figs. 198-201. The gonidia are borne on the tips
-of the branches. The kind of branching bears some relation to the
-different genera. Fig. 200 is from Peronospora alsinearum on leaves of
-cerastium; figs. 197 and 199 are Plasmopara viticola, the grape mildew,
-while figs. 198 and 202 are from Phytophthora infestans which causes a
-disease known as potato blight. The gonidia of peronospora germinate
-by a germ tube, those of plasmopara first form zoogonidia, while in
-phytophthora the gonidium may either germinate forming a thread, or
-each gonidium may first form several zoogonidia, as shown in fig. 203.
-
-[Illustration: Fig. 204.
-
-Fertilization in Peronospora alsinearum; tube from antheridium carrying
-in the sperm nucleus in figure at the left, female nucleus near; fusion
-of the two nuclei shown in the two other figures. (After Berlese.)]
-
-[Illustration: Fig. 205. Ripe oospore of Peronospora alsinearum.]
-
-=398.= In sexual reproduction oogonia and antheridia are developed
-on the mycelium within the tissues. Fig. 204 represents the antheridium
-entering the oogonium, and the male nucleus fusing with the female
-nucleus in fertilization. The sexual organs of Phytophthora infestans
-are not sufficiently known.
-
-=399.= Mucor, saprolegnia, peronospora, and their relatives
-have few or no septa in the mycelium. In this respect they resemble
-certain of the algæ like vaucheria, but they lack chlorophyll. They are
-sometimes called the alga-like fungi and belong to a large group called
-_Phycomycetes_.
-
-
-
-
-CHAPTER XX.
-
-FUNGI CONTINUED.
-
-
-“Rusts” (Uredineæ).
-
-=400.= The fungi known as “rusts” are very important ones to
-study, since all the species are parasitic, and many produce serious
-injuries to crops.
-
-[Illustration: Fig. 206. Wheat leaf with red-rust, natural size.]
-
-[Illustration: Fig. 207. Portion of leaf enlarged to show sori.]
-
-[Illustration: Fig. 208. Natural size.]
-
-[Illustration: Fig. 209. Enlarged.]
-
-[Illustration: Fig. 210. Single sorus.
-
-Figs. 206, 207.—Puccinia graminis, red-rust stage (uredo stage).
-
-Figs. 208-210.—Black rust of wheat, showing sori of teleutospores.]
-
-=401. Wheat rust (Puccinia graminis).=—The wheat rust is one of
-the best known of these fungi, since a great deal of study has been
-given to it. One form of the plant occurs in long reddish-brown or
-reddish pustules, and is known as the “red-rust” (figs. 206, 207).
-Another form occurs in elongated black pustules, and this form is the
-one known as the “black rust” (figs. 208-211). These two forms occur on
-the stems, blades, etc., of the wheat, also on oats, rye, and some of
-the grasses.
-
-[Illustration: Fig. 211. Head of wheat showing black rust spots on the
-chaff and awns.]
-
-[Illustration: Fig. 212. Teleutospores of wheat rust, showing two cells
-and the pedicel.]
-
-[Illustration: Fig. 213. Uredospores of wheat rust, one showing
-remnants of the pedicel.]
-
-=402. Teleutospores of the black rust form.=—If we scrape off
-some portion of one of the black pustules (sori), tease it out in water
-on a slide, and examine with a microscope, we see numerous gonidia,
-composed of two cells, and having thick, brownish walls as shown
-in fig. 212. Usually there is a slender brownish stalk on one end.
-These gonidia are called _teleutospores_. They are somewhat oblong or
-elliptical, a little constricted where the septum separates the two
-cells, and the end cell varies from ovate to rounded. The mycelium of
-the fungus courses between the cells, just as is found in the case of
-the carnation rust, which belongs to the same family (see Parag. 186).
-
-[Illustration: Fig. 214. Barberry leaf with two diseased spots, natural
-size.]
-
-[Illustration: Fig. 215. Single spot showing cluster-cups enlarged.]
-
-[Illustration: Fig. 216. Two cluster-cups more enlarged, showing split
-margin.
-
-Figs. 214-216.—Cluster-cup stage of wheat rust.]
-
-=403. Uredospores of the red-rust form.=—If we make a similar
-preparation from the pustules of the red-rust form we see that instead
-of two-celled gonidia they are one-celled. The walls are thinner
-and not so dark in color, and they are covered with minute spines.
-They have also short stalks, but these fall away very easily. These
-one-celled gonidia of the red-rust form are called “uredospores.” The
-uredospores and teleutospores are sometimes found in the same pustule.
-
-It was once supposed that these two kinds of gonidia belonged to
-different plants, but now it is known that the one-celled form, the
-uredospores, is a form developed earlier in the season than the
-teleutospores.
-
-=404. Cluster-cup form on the barberry.=—On the barberry is found
-still another form of the wheat rust, the “_cluster-cup_” stage. The
-pustules on the under side of the barberry leaf are cup-shaped, the
-cups being partly sunk in the tissue of the leaf, while the rim is more
-or less curved backward against the leaf, and split at several places.
-These cups occur in clusters on the affected spots of the barberry leaf
-as shown in fig. 215. Within the cups numbers of one-celled gonidia
-(orange in color, called æcidiospores) are borne in chains from short
-branches of the mycelium, which fill the base of the cup. In fact the
-wall of the cup (peridium) is formed of similar rows of cells, which,
-instead of separating into gonidia, remain united to form a wall. These
-cups are usually borne on the under side of the leaf.
-
-=405. Spermagonia.=—Upon the upper side of the leaves in the
-same spot occur small, orange-colored pustules which are flask-shaped.
-They bear inside, minute, rod-like bodies on the ends of slender
-threads, which ooze out on the surface of the leaf. These flask-shaped
-pustules are called _spermagonia_, and the minute bodies within them
-_spermatia_, since they were once supposed to be the male element of
-the fungus. Their function is not known. They appear in the spots at an
-earlier time than the cluster-cups.
-
-[Illustration: Fig. 217. Section of an æcidium (cluster-cup) from
-barberry leaf. (After Marshall-Ward.)]
-
-=406. How the cluster-cup stage was found to be a part of the wheat
-rust.=—The cluster-cup stage of the wheat rust was once supposed
-also to be a different plant, and the genus was called _æcidium_.
-The occurrence of wheat rust in great abundance on the leeward side
-of affected barberry bushes in England suggested to the farmers that
-wheat rust was caused by barberry rust. It was later found that the
-æcidiospores of the barberry, when sown on wheat, germinate and the
-thread of mycelium enters the tissues of the wheat, forming mycelium
-between the cells. This mycelium then bears the uredospores, and later
-the teleutospores.
-
-=407. Uredospores can produce successive crops of
-uredospores.=—The uredospores are carried by the wind to other
-wheat or grass plants, germinate, form mycelium in the tissues,
-and later the pustules with a second crop of uredospores. Several
-successive crops of uredospores may be developed in one season, so
-this is the form in which the fungus is greatly multiplied and widely
-distributed.
-
-[Illustration: Fig. 218.
-
-Section through leaf of barberry at point affected with the cluster-cup
-stage of the wheat rust; spermagonia above, æcidia below. (After
-Marshall-Ward.)]
-
-[Illustration: Fig. 219.
-
-_A_, section through sorus of black rust of wheat, showing
-teleutospores. _B_, mycelium bearing both teleutospores and
-uredospores. (After de Bary.)]
-
-[Illustration: Fig. 220. Germinating uredospore of wheat rust. (After
-Marshall-Ward.)]
-
-[Illustration: Fig. 221. Germ tube entering the leaf through a stoma.]
-
-=407a. Teleutospores the last stage of the fungus in the season.=—The
-teleutospores are developed late in the season, or late in the
-development of the host plant (in this case the wheat is the host).
-They then rest during the winter. In the spring under favorable
-conditions each cell of the teleutospore germinates, producing a
-short mycelium called a _promycelium_, as shown in figs. 222, 223.
-This promycelium is usually divided into four cells. From each cell a
-short, pointed process is formed called a “_sterigma_.” Through this
-the protoplasm moves and forms a small gonidium on the end, sometimes
-called a _sporidium_.
-
-[Illustration: Fig. 222. Teleutospore germinating, forming promycelium.]
-
-[Illustration: Fig. 223. Promycelium of germinating teleutospore,
-forming sporidia.]
-
-[Illustration: Fig. 224. Germinating sporidia entering leaf of barberry
-by mycelium.
-
-Figs. 222-224.—Puccinia graminis (wheat rust). (After Marshall-Ward.)]
-
-=408. How the fungus gets from the wheat back to the barberry.=—If
-these sporidia from the teleutospores are carried by the wind so that
-they lodge on the leaves of the barberry, they germinate and produce
-the cluster-cup again. The plant has thus a very complex life history.
-Because of the presence of several different forms in the life cyle, it
-is called a _polymorphic_ fungus.
-
-The presence of the barberry does not seem necessary in all cases for the
-development of the fungus from one year to another.
-
-=409. Synopsis of life history of wheat rust.=
-
-_Cluster-cup stage on leaf of barberry._
-
-    Mycelium between cells of leaf in affected spots.
-    Spermagonia (sing. spermagonium), small flask-shaped
-        bodies sunk in upper side of leaf; contain “spermatia.”
-    Æcidia (sing. æcidium), cup-shaped bodies in under side
-        of leaf.
-    Wall or peridium, made up of outer layer of fungus
-        threads which are divided into short cells but
-        remain united.
-    At maturity bursts through epidermis of leaf; margin
-        of cup curves outward and downward toward surface
-        of leaf.
-    Central threads of the bundle are closely packed, but
-        free. Threads divide into short angular cells
-        which separate and become æcidiospores, with
-        orange-colored content.
-    Æcidiospores carried by the wind to wheat, oats, grasses,
-        etc. Here they germinate, mycelium enters at stomate,
-        and forms mycelium between cells of the host.
-
-_Uredo stage (red-rust) on wheat, oats, grasses, etc._
-
-    Mycelium between cells of host.
-    Bears uredospores (1-celled) in masses under epidermis,
-        which is later ruptured and uredospores set free.
-    Uredospores carried by wind to other individual hosts,
-        and new crops of uredospores formed.
-
-_Teleutospore stage (black rust), also on wheat, etc._
-
-    Mycelium between cells of host.
-    Bears teleutospores (2-celled) in masses (sori) under
-        epidermis, which is later ruptured.
-    Teleutospores rest during winter. In spring each cell
-        germinates and produces a promycelium, a short
-        thread, divided into four cells.
-    Promycelium bears four sterigmata and four gonidia
-        (or sporidia), which in favorable conditions pass
-        back to the barberry, germinate, the tube enters
-        between cells into the intercellular spaces of the
-        host to produce the cluster-cup again, and thus the
-        life cycle is completed.
-
-=410. Other examples of the rusts.=—Some of the rusts do great
-injury to fruit trees and also to forest trees. The “cedar apples” are
-abnormal growths on the leaves and twigs of the cedar stimulated by the
-presence of the mycelium of a rust known as Gymnosporangium macropus.
-The teleutospores are two-celled and are formed in the tissue of the
-“cedar apple” or gall. The teleutosori are situated at quite regular
-intervals over the surface of the gall at small circular depressions,
-and can be easily seen in late autumn and during the winter. A quantity
-of gelatine is developed along with the teleutospores. In early spring
-with the warm spring rains the gelatinous substance accompanying the
-teleutospores swells greatly, and causes the teleutospores to ooze
-out in long, dull, orange-colored strings, which taper gradually to
-a slender point and bristle all over the “cedar apple.” Here the
-teleutospores germinate and produce the sporidia. The sporidia are
-carried to apple trees where they infect leaves and even the fruit,
-producing here the cluster-cups. There are no uredospores.
-
-G. globosum is another species forming cedar apples, but the gelatinous
-strings of teleutospores are short and clavate, and the cluster-cups
-are formed on hawthorns. G. nidusavis forms “witches brooms” or “birds
-nests” in the branches of the cedar. The mycelium in the branches
-stimulates them to profuse branching so that numerous small branches
-are developed close together. The teleutosori form small pustules
-scattered over the branches. G. clavipes affects the branches of cedar
-only slightly deforming them or not at all, and the cluster-cups are
-formed on fruits, twigs, and leaves of the hawthorns or quinces, the
-cluster-cups being long, tubular, and orange in color.
-
-
-
-
-CHAPTER XXI.
-
-THE HIGHER FUNGI.
-
-
-=411. The series of the higher fungi.=—Of these there are two
-large series. One of these is represented by the sac fungi, and the
-other by the mushrooms, a good example of which is the common mushroom
-(Agaricus campestris).
-
-
-Sac Fungi (Ascomycetes).
-
-=412. The sac fungi= may be represented by the “powdery mildews”;
-examples, uncinula, microsphæra, podosphæra, etc. Fig. 225 is from a
-photograph of two willow leaves affected by one of these mildews. The
-leaves are first partly covered with a whitish growth of mycelium, and
-numerous chains of colorless gonidia are borne on short erect threads.
-The masses of gonidia give the leaf a powdery appearance. The mycelium
-lives on the outer surface of the leaf, but sends short haustoria into
-the epidermal cells.
-
-=413. Fruit bodies of the willow mildew.=—On this same mycelium
-there appear later numerous black specks scattered over the affected
-places of the leaf. These are the fruit bodies (_perithecia_). If
-we scrape some of these from the leaf, and mount them in water for
-microscopic examination, we shall be able to see their structure.
-Examining these first with a low power of the microscope, each one is
-seen to be a rounded body, from which radiate numerous filaments, the
-_appendages_. Each one of these appendages is coiled at the end into
-the form of a little hook. Because of these hooked appendages this
-genus is called _uncinula_. This rounded body is the _perithecium_.
-
-[Illustration: Fig. 225. Leaves of willow showing willow mildew. The
-black dots are the fruit bodies (perithecia) seated on the white
-mycelium.]
-
-=414. Asci and ascospores.=—While we are looking at a few of
-these through the microscope with the low power, we should press on the
-cover glass with a needle until we see a few of the perithecia rupture.
-If this is done carefully we see several small ovate sacs issue, each
-containing a number of spores, as shown in fig. 227. Such a sac is an
-_ascus_, and the spores are _ascospores_.
-
-[Illustration: Fig. 226. Willow mildew; bit of mycelium with erect
-conidiophores, bearing chain of gonidia; gonidium at left germinating.]
-
-[Illustration: Fig. 227. Fruit of willow mildew, showing hooked
-appendages. Genus uncinula.]
-
-[Illustration: Fig. 228. Fruit body of another mildew with dichotomous
-appendages. Genus microsphæra.
-
-Figs. 227-228.—Perithecia (perithecium) of two powdery mildews,
-showing escape of asci containing the spores from the crushed fruit
-bodies.]
-
-[Illustration: Fig. 229. Contact of antheridium and carpogonium
-(carpogonium the larger cell); beginning of fertilization.]
-
-[Illustration: Fig. 230. Disappearance of contact walls of antheridium
-and carpogonium, and fusion of the two nuclei.]
-
-[Illustration: Fig. 231. Fertilized egg surrounded by the enveloping
-threads which grow up around it.
-
-Figs. 229-231.—Fertilization in sphærotheca; one of the powdery
-mildews. (After Harper.)]
-
-=415. Number of spores in an ascus.=—The ascus is the most
-important character showing the general relationship of the members of
-the sac fungi. While many of the powdery mildews have a variable number
-of spores in an ascus, a large majority of the ascomycetes have just 8
-spores in an ascus, while some have 4, others 16, and some an
-indefinite number. The asci in a perithecium are more variable. In some
-ascomycetes there is no perithecium.
-
-[Illustration: Fig. 231_a_.
-
-Edible Morel. Morchella esculenta. The asci, forming hymenium, cover
-the pitted surface.]
-
-=416. The black fungi.=—These are very common on dead logs,
-branches, leaves, etc., and may be collected in the woods at almost any
-season. The perithecia are often numerous, scattered or densely crowded
-as in Rosellinia. Sometimes they are united to form a crust which is
-partly formed from sterile elements as in Hypoxylon, or they form black
-clavate or branched bodies as in Xylaria. The black knot of the plum
-and cherry is also an example.
-
-The lichens are mostly ascomycetes like the black fungi or cup fungi,
-while a few are basidiomycetes.
-
-=417. The morels (Morchella).=—There are several species of
-morels which are common in early spring on damp ground. Either one of
-the species is suitable for use if it is desired to include this in
-the study. Fig. 231a illustrates the Morchella esculenta. The stem is
-cylindrical and stout. The fruiting portion forms the “head,” and it
-is deeply pitted. The entire pitted surface is covered by the asci,
-which are cylindrical and eight spored. A thin section may be made of
-a portion for study, or a small piece may be crushed under the cover
-glass.
-
-=418. The cup fungi.=—These fungi are common on damp ground or
-on rotting logs in the summer. They may be preserved in 70 per cent
-alcohol for study. Many of them are shaped like broad open cups or
-saucers. The inner surface of the cup is the fruiting surface, and is
-covered with the cylindrical asci, which stand side by side. A bit of
-the cup may be sectioned or crushed under a cover glass for study.
-
-
-Mushrooms (Basidiomycetes).
-
-=419. The large group of fungi= to which the mushroom belongs is
-called the basidiomycetes because in all of them a structure resembling
-a club, or basidium, is present, and bears a limited number of spores,
-usually four, though in some genera the number is variable. Some place
-the rusts (Uredineæ) in the same series (basidium series), because of
-the short promycelium and four sporidia developed from each cell of the
-teleutospore.
-
-=420. The gill-bearing fungi (Agaricaceæ).=—A good example for
-this study is the common mushroom (Agaricus campestris).
-
-This occurs from July to November in lawns and grassy fields. The
-plant is somewhat umbrella-shaped, as shown in fig. 232, and possesses
-a cylindrical stem attached to the under side of the convex cap or
-pileus. On the under side of the pileus are thin radiating plates,
-shaped somewhat like a knife blade. These are the gills, or lamellæ,
-and toward the stem they are rounded on the lower angle and are not
-attached to the stem. The longer ones extend from near the stem to the
-margin of the pileus, and the V-shaped spaces between them are occupied
-by successively shorter ones. Around the stem a little below the gills
-is a collar, termed the ring or annulus.
-
-[Illustration: Fig. 232. Agaricus campestris. View of under side
-showing stem, annulus, gills, and margin of pileus.]
-
-[Illustration: Fig. 233.
-
-Agaricus campestris. Longitudinal section through stem and pileus.
-_a_, pileus; _b_, portion of veil on margin of pileus; _c_, gill; _d_,
-fragment of annulus; _e_, stipe.]
-
-[Illustration: Fig. 234.
-
-Portion of section of lamella of Agaricus campestris. _tr_, trama;
-_sh_, subhymenium; _b_, basidium; _st_, sterigma (_pl._ sterigmata);
-_g_, basidiospore.]
-
-[Illustration: Fig. 235. Portion of hymenium of Coprinus micaceus,
-showing large cystidium in the hymenium.]
-
-=421. Fruiting surface of the mushroom.=—The surface of these
-gills is the fruiting surface of the mushroom, and bears the gonidia
-of the mushroom, which are dark purplish brown when mature, and thus
-the gills when old are dark in color. If we make a thin section across
-a few of the gills, we see that each side of the gill is covered with
-closely crowded club-shaped bodies, each one of which is a _basidium_.
-In fig. 234 a few of these are enlarged, so that the structure of
-the gill can be seen. Each basidium of the common mushroom has two
-spinous processes at the free end. Each one is a _sterig′ma_ (plural
-_sterig′mata_), and bears a gonidium. In a majority of the members of
-the mushroom family each basidium bears four spores. When mature these
-spores easily fall away, and a mass of them gives a purplish-black
-color to objects on which they fall, so that a print of the under
-surface of the cap showing the arrangement of the gills can be obtained
-by cutting off the stem, and placing the pileus on white paper for a
-time.
-
-[Illustration: Fig. 236. Agaricus campestris. Soil washed from “spawn”
-and “buttons,” showing the minute young “buttons” attached to the
-strands of mycelium.]
-
-=422. How the mushroom is formed.=—The mycelium of the mushroom
-lives in the ground, and grows here for several months or even years,
-and at the proper seasons develops the mature mushroom plant. The
-mycelium lives on decaying organic matter, and a large number of the
-threads grow closely together forming strands, or cords, of mycelium,
-which are quite prominent if they are uncovered by removing the soil,
-as shown in fig. 236.
-
-[Illustration: Fig. 237. Agaricus campestris; sections of “buttons” of
-different sizes, showing formation of gills and veil covering them.]
-
-=423.= From these strands the buttons arise by numerous threads
-growing side by side in a vertical direction, each thread growing
-independently at the end, but all lying very closely side by side. When
-the buttons are quite small the gills begin to form on the under margin
-of the knob. They are formed by certain of the threads growing downward
-in radiating ridges, just as many of these ridges being started as
-there are to be gills formed. At the same time, threads of the stem
-grow upward to meet those at the margin of the button in such a manner
-that they cover up the forming gills, and thus enclose the gills in a
-minute cavity. Sections of buttons at different ages will show this, as
-is seen in fig. 237. This curtain of mycelium which is thus stretched
-across the gill cavity is the veil. As the cap expands more and more
-this is stretched into a thin and delicate texture as shown in fig.
-238. Finally, as shown in fig. 239, this veil is ruptured by the
-expansion of the pileus, and it either clings to the stem as a collar,
-or a portion of it remains clinging to the margin of the cap. When the
-buttons are very young the gills are white, but they soon become pink
-in color, and very soon after the veil breaks the spores mature, and
-then the gills are dark brown.
-
-[Illustration: Fig. 238. Agaricus campestris; nearly mature plants,
-showing veil still stretched across the gill cavity.]
-
-[Illustration: Fig. 239. Agaricus campestris; under view of two plants
-just after rupture of veil, fragments of the latter clinging both to
-margin of pileus and to stem.]
-
-[Illustration: Fig. 240. Agaricus campestris; plant in natural position
-just after rupture of veil, showing tendency to double annulus on the
-stem. Portions of the veil also dripping from margin of pileus.]
-
-[Illustration: Fig. 241. Agaricus campestris; spore print.]
-
-[Illustration: Fig. 242. “Fairy ring” formed by Agaricus arvensis
-(photograph by B. M. Duggar). The mycelium spreads centrifugally each
-year, consuming the available food, and thus the plants appear in a
-ring.]
-
-[Illustration: Fig. 243. Amanita phalloides; white form, showing
-pileus, stipe, annulus, and volva.]
-
-=424. Beware of the poisonous mushroom.=—The number of species
-of mushrooms, or toadstools as they are often called, is very great.
-Besides the common mushroom (Agaricus campestris) there are a large
-number of other edible species. But one should be very familiar with
-any species which is gathered for food, unless collected by one who
-certainly knows what the plant is, since carelessness in this respect
-sometimes results fatally from eating poisonous ones.
-
-[Illustration: Fig. 244. Amanita phalloides; plant turned to one side,
-after having been placed in a horizontal position, by the directive
-force of gravity.]
-
-=425.= A plant very similar in structure to the Agaricus
-campestris is the Lepiota naucina, but the spores are white, and thus
-the gills are white, except that in age they become a dirty pink. This
-plant occurs in grassy fields and lawns often along with the common
-mushroom. Great care should be exercised in collecting and noting the
-characters of these plants, for a very deadly poisonous species, the
-deadly amanita (Amanita phalloides) is perfectly white, has white
-spores, a ring, and grows usually in wooded places, but also sometimes
-occurs in the margins of lawns. In this plant the base of the stem is
-seated in a cup-shaped structure, the _volva_, shown in fig. 243. One
-should dig up the stem carefully so as not to tear off this volva if
-it is present, for with the absence of this structure the plant might
-easily be mistaken for the lepiota, and serious consequences would
-result.
-
-[Illustration: Fig. 245. Edible Boletus. Boletus edulis. Fruiting
-surface honey-combed on under side of cap.]
-
-=426. Tube-bearing fungi (Polyporaceæ).=—In the tube-bearing
-fungi, the fruiting surface, instead of lying over the surface of
-gills, lines the surface of tubes or pores on the under side of the
-cap. The fruit-bearing portion therefore is “honey-combed.” The sulphur
-polyporus (Polyporus sulphureus) illustrates one form. The tube-bearing
-fungi are sometimes called “bracket” fungi, or “shelf” fungi, because
-the pileus is attached to the tree or stump like a shelf or bracket.
-One very common form in the woods is the plant so much sought by
-“artists,” and often called Polyporus applanatus. It is hard and woody,
-reddish brown, brown or grayish on the upper side, according to age,
-and is marked by prominent and large concentric ridges. (This form is
-probably P. leucophæus.) The under side is white and honey-combed by
-numerous very minute pores. This plant is perennial, that is, it lives
-from year to year. Each year a new layer is added to the under side,
-and several new rings usually to the margin. If a plant two or three
-years old is cut in two, there will be seen several distinct tube
-layers or strata, each one representing a year’s growth.
-
-In some of these bracket fungi, each ring on the upper surface marks a
-year’s growth as in the pine polyporus (P. pinicola). In the birch
-polyporus (P. fomentarius) the tubes are quite large. It also occurs on
-other trees. The beech polyporus (P. igniarius, also on other trees)
-often becomes very old. I have seen one specimen over eighty years old.
-Not all the tube-bearing fungi are bracket form. Some have a stem and
-cap (see fig. 245). Some are spread on the surface of logs.
-
-[Illustration: Fig. 246. Coral fungus. Hydnum coralloides, spines
-hanging down from branches.]
-
-=427. Hedgehog fungi (Hydnaceæ).=—These plants are bracket in
-form or have a stem and cap, or are spread on the surface of wood; but
-the finest specimens resemble coral masses of fungus tissue (example,
-Hydnum, fig. 246). In most of them there are slender processes
-resembling teeth, spines or awls, which depend from the under surface
-(fig. 247). The fruiting surface covers these spines.
-
-=428. Coral fungi or fairy clubs (Clavariaceæ).=—These plants
-stand upright from the wood, leaves, or soil, on which they grow
-(example, Clavaria). The “coral” ones are branched, while the “fairy
-clubs” are simple. The fruiting surface covers the entire exposed
-surface of the plants (fig. 248).
-
-[Illustration: Fig. 247. Hydnum repandum, spines hanging down from
-under side of cap.]
-
-[Illustration: Fig. 248. Clavaria botrytes.]
-
-
-
-
-CHAPTER XXII.
-
-CLASSIFICATION OF THE FUNGI.
-
-
-=429. Classification of the fungi.=—Those who believe that the fungi
-represent a natural group of plants arrange them in three large series
-related to each other somewhat as follows:
-
-            The Gonidium Type or Series. The number of
-          gonidia in the sporangium is indefinite and
-          variable. It may be very large or very small,
-          or even only one in a sporangium. To this
-          series belong the lower fungi; examples: mucor,
-          saprolegnia, peronospora, etc.
-
-            The Basidium Type or Series. The number of
-          gonidia on a basidium is limited and definite,
-          and the basidium is a characteristic structure;
-          examples: uredineæ (rusts), mushrooms, etc.
-
-            The Ascus Type or Series. The number of spores
-          in an ascus is limited and definite, and the
-          ascus is a characteristic structure; examples:
-          leaf curl of peach (exoascus), powdery mildews,
-          black knot of plum, black rot of grapes, etc.
-
-=430.= Others believe that the fungi do not represent a natural
-group, but that they have developed off from different groups of
-the algæ by becoming parasitic. As parasites they no longer needed
-chlorophyll, and consequently lost it.
-
-According to this view the lower fungi have developed off from the
-lower algæ (saprolegnias, mucors, peronosporas, etc., being developed
-off from siphonaceous algæ like vaucheria), and the higher fungi being
-developed off from the higher algæ (the ascomycetes perhaps from the
-Rhodophyceæ).
-
-=431. A very general outline of classification=,[19] according to
-the former of these views, might be presented here to show the general
-relationships of the fungi studied, with the addition of a few more
-in orders not represented above. It should be borne in mind that the
-author in presenting this view of classification does not necessarily
-commit himself to it. It is based on that presented in Engler &
-Prantl’s Pflanzenfamilien. There are three classes.
-
-[19] =Class Myxomycetes=, or =Mycetozoa=.—To this class belong the
-“slime molds,” low organisms consisting of masses of naked protoplasm
-which flows among decaying leaves and in decaying wood, coming to
-the surface to fruit. The fruit in many cases resembles miniature
-puff-balls, and these plants were formerly classed with the puff-balls.
-The spores germinate by forming swarm spores which unite to form a
-small plasmodium, which in turn grows to form a large plasmodium or
-protoplasmic mass. It is doubtful if they are any more plant than
-animal organisms. Examples: Trichia, Arcyria, Stemonitis, Physarum,
-Ceratiomyxa, etc., on rotten wood; Plasmodiophora brassicæ is a
-parasite causing club foot of cabbage, radishes, etc. It lives within
-the roots, causing large knots and swellings on the same.
-
-[Illustration: Fig. 249.
-
-Chytrids. _A_, Harpochytrium hedenii, parasitic on spirogyra threads;
-_a_, sickle-form plant; _b_, the sporangium part with escaping
-zoospores; _c_, old plant proliferating by forming new sporangium
-in the old empty one; _d_, zoospore; _e_, two young plants just
-beginning to grow. _B_, Rhizophidium globosum parasitic on spirogyra.
-Globose sporangium with delicate threads inside of the host, zoospores
-escaping from one. _C_, Olpidium pendulum, parasitic in spirogyra cell.
-Elliptical sporangium with slender exit tube through which zoospores
-are escaping. _D_, Lagenidium rabenhorstii parasitic in spirogyra cell.
-Two slender sporangia with exit tubes through which protoplasm escapes
-forming a rounded mass at the end of tube, this protoplasm forming
-biciliate zoospores.]
-
-
-I. Class Phycomycetes (Alga-like Fungi).
-
-
-1. SUBCLASS OOMYCETES.
-
-=432.= These are the egg-spore fungi. They include the water mold
-(Saprolegnia), the downy mildew of the grape (Plasmopara), the potato
-blight (Phytophthora), the white rust of cruciferous plants (Cystopus
-= Albugo), the damping-off fungus (Pythium), and many parasites of
-the algæ known as chytrids, as Olpidium, Rhizophidium, Lagenidium,
-Chytridium, etc.
-
-The two following orders are sometimes placed in a separate subclass,
-_Archimycetes_.
-
-[Illustration: Fig. 250.
-
-Monoblepharis insignis Thaxter. End of hypha bearing oogonium (_oog_)
-and antheridium (_ant_). Sperms escaping from antheridium and creeping
-up on the oogonium. (After Thaxter.)]
-
-=433. Order Chytridiales (Chytridineæ).=—These include the lowest
-fungi. Many of them are parasitic on algæ and lack mycelium, the
-swarm spore either with or without minute rhizoids, developing into
-a globose sporangium (Rhizophidium, Chytridium, Olpidium, etc., fig.
-249), or the swarm spore attached to the wall of the host develops into
-a long sword-shaped body with a sterile base, which proliferates and
-forms a new sporangium in the old one (Harpochytrium), or with slight
-development of mycelium in aquatic plants (Cladochytrium). Some are
-parasitic in leaves and stems of land plants. Synchytrium decipiens is
-very common on the trailing legume, Amphicarpæa monoica.
-
-=434. Order Ancylistales (Ancylistineæ).=—The members of this
-order have a slight development of mycelium and many are parasitic in
-algæ (Lagenidium, fig. 249).
-
-=435. Order Saprolegniales (Saprolegniineæ).=—These include the
-water molds (Saprolegnia). See Chapter XIX.
-
-=436. Order Monoblepharidales (Monoblepharidineæ).=—These are
-peculiar water molds, related to the Saprolegniales, but motile sperm
-cells are formed (Monoblepharis, etc., fig. 250).
-
-=437. Order Peronosporales (Peronosporineæ).=—These include the
-downy mildews (Peronospora, Plasmopara, Phytopthora, etc.), and the
-white rust of crucifers and other plants (Cystopus = Albugo), Chapter
-XIX.
-
-
-2. SUBCLASS ZYGOMYCETES.
-
-=438.= These are the conjugating fungi.
-
-=439. Order Mucorales (Mucorineæ).=—This includes the black mold
-and its many relatives (Mucor, Rhizopus, etc.). Chapter XIX.
-
-=440. Order Entomophthorales (Entomophthorineæ).=—This order
-includes the “fly fungus” (Empusa) and its many relatives parasitic on
-insects. In the autumn and winter dead flies are often found stuck to
-window-panes, with a white ring of the conidia around each fly.
-
-
-II. Class Ascomycetes. (The ascus series.)
-
-
-1. SUBCLASS HEMIASCOMYCETES.
-
-[Illustration: Fig. 251.
-
-Dipodascus albidus. _A_, thread with sexual organs, ascogonium and
-antheridium; _B_, fertilized ascogonium developing ascus; _C_, ascus
-with spores; _D_, conidia. (After Lagerheim.)]
-
-=441. Order Hemiascales (Hemiascineæ).=—Fungi with a well
-developed, septate mycelium, but with a sporangium-like ascus, i.e.,
-a large and indefinite number of spores in the ascus. Examples:
-Protomyces macrosporus in stems of Umbelliferæ, or P. polysporus in
-Ambrosia trifida. These two are by some placed in the Ustilagineæ.
-Dipodascus albidus grows in the exuding sap of Bromeliaceæ in Brazil
-and the sap of the beech in Sweden. The ascus is developed as the
-result of the fertilization of an ascogonium with an antheridium (see
-fig. 251).
-
-
-2. SUBCLASS PROTOASCOMYCETES.
-
-=442. The asci are well-defined= and usually with a limited and
-definite number of spores (usually 8, sometimes 1, 2, 4, 16, or more).
-Mycelium often well developed and septate. Asci scattered on the
-mycelium, not associated in definite fields or groups.
-
-=443. Order Protoascales (Protoascineæ).=—The asci are separate
-cells, or are scattered irregularly in loose wefts of mycelium.
-No fruit body. (The yeast, Saccharomyces, see paragraph 237; and
-certain mold-like fungi, some of which are parasitic on mushrooms, as
-Endomyces, are examples.)
-
-
-3. SUBCLASS EUASCOMYCETES.
-
-Asci associated in surfaces forming a hymenium, or in groups or
-intermingled in the elements of a fruit body. Fruit body usually
-present.
-
-The following four or five orders comprise the Discomycetes, according
-to the usual classification.
-
-=444. Order Protodiscales (Protodiscineæ).=—The asci are exposed
-and form large and indefinite groups, but there is no definite fruit
-body. Examples: leaf curl of peach, plum pocket, etc. (Exoascus).
-
-=445. Order Helvellales (Helvellineæ).=—The asci form large
-fields over the upper portion of the fruit body. This order includes
-the morels (fig. 231_a_), helvellas, earth tongues (Geoglossum), etc.
-
-=446. Order Pezizales (Pezizineæ).=—The asci form a definite
-field or fruiting surface surrounded on the sides and below by a wall
-of fungus tissue, forming a fruit body in the shape of a cup. These are
-known as the cup fungi (Peziza, Lachnea, etc.).
-
-=447. Order Phacidiales (Phacidiineæ).=—Fungi mostly saprophytic,
-and fruit body similar to the cup fungi. Examples: Propolis in rotting
-wood, Rhytisma forming black crusts on leaves (maple for example),
-Urnula craterium, a large black beaker-shaped fungus on the ground.
-
-=448. Order Hysteriales (Hysteriineæ).=—Fungi with a more or less
-elongated fruit body with an enclosing wall opening by a long slit. In
-some forms the fruit body has the appearance of a two-lipped body; in
-others it is shaped like a clam shell, the asci being inside. Example,
-Hysterographium common on dry, dead, decorticated sticks.
-
-=449. Order Tuberales (Tuberineæ).=—The more or less rounded
-fruit bodies are usually subterranean. The most important fungi in this
-order are the truffles (Tuber). The mycelium of many species assists
-in the formation of mycorhiza on the roots of oaks, etc., and several
-species are partly cultivated, or protected, and collected for food.
-This is especially the case with Tuber brumale and its forms; more than
-a million francs worth of truffles are sold in France and Italy yearly.
-Dogs and pigs are employed in the collection of truffles from the
-ground.
-
-=450. Order Plectascales (Plectascineæ).=—The fruit body of these
-plants is more or less globose, and contains the asci distributed
-irregularly through the mycelium of the interior. Some are subterranean
-(Elaphomyces), while others grow in decaying plants, or certain food
-substances (Eurotium, Sterigmatocystis, Penicillium). Penicillium in
-its conidial stage forms blue mold on fruit, bread, etc.
-
-The following four orders comprise the Pyrenomycetes, according to the
-usual classification.
-
-=451. Order Perisporiales.=—The powdery mildews are good examples
-of this order (Uncinula, Microsphæra, etc., Chapter XXI).
-
-=452. Order Hypocreales.=[20]—The fruit bodies are colorless,
-or bright colored and entirely enclose the asci, sometimes opening
-by an apical pore. Nectria cinnabarina has clusters of minute orange
-oval fruit bodies, and is common on dead twigs. Cordyceps with a
-number of species is parasitic on insects, and on certain subterranean
-Ascomycetes, especially Elaphomyces (of the order _Plectascales_ =
-_Plectascineæ_).
-
-=453. Order Dothidiales.=[21]—Fungi with black stroma formed of
-mycelium in which are cavities containing the asci. The cavities are
-usually shaped like a perithecium, but there is no wall distinct from
-the tissue of the stroma (Dothidea, Phyllachora, on grasses).
-
-=454. Order Sphæriales.=[22]—These contain the so-called black
-fungi, with separate or clustered, oval, fruit bodies, black in color.
-The black wall encloses the asci, and usually opens by an apical pore.
-Examples are found in the black knot of plum and cherry, black rot of
-grapes, and in Rosellinia, Hypoxylon, Xylaria, etc., on dead wood.
-
-=455. Order Laboulbeniales (Laboulbineæ).=—These are peculiar
-fungi attached to the legs and bodies of insects by a short stalk, and
-provided with a sac-like fruit body which contains the asci. Example,
-Laboulbenia.
-
-
-III. Class Basidiomycetes. (The basidium series.)
-
-
-1. SUBCLASS HEMIBASIDIOMYCETES.
-
-=456. Order Ustilaginales (Ustilagineæ).=—This order includes the
-well-known smuts on corn, wheat, oats, etc. (Ustilago, Tilletia, etc.).
-
-
-2. SUBCLASS ÆCIDIOMYCETES.
-
-=457. Order Uredinales=[23] (Uredineæ).—This order includes the
-parasitic fungi known as rusts. Examples: wheat rust (Chapter XX), the
-cedar apple, etc.
-
-The true Basidiomycetes include the following orders:
-
-
-3. SUBCLASS PROTOBASIDIOMYCETES.
-
-=458. Order Auriculariales.=[24]—This order includes trembling
-fungi in which the basidium is long and divided transversely into
-usually four cells (example, Auricularia), and similar forms. Pilacre
-petersii on dead wood represents an angiocarpous form.
-
-=459. Order Tremellales (Tremellineæ)=, trembling or gelatinous
-fungi with the globose basidium divided longitudinally into four cells
-(Tremella).
-
-
-4. SUBCLASS EUBASIDIOMYCETES.
-
-=460. Order Dacryomycetales (Dacryomycetineæ).=—This order
-includes certain fungi of a gelatinous or waxy consistency, usually
-of bright colors. They resemble the Tremellales, but the basidia are
-slender and fork into two long sterigmata. (Example, Dacryomyces.)
-Gyrocephalus rufus is quite a large plant, 10-15 cm. high, growing on
-the ground in woods.
-
-=461. Order Exobasidiales (Exobasidiineæ).=—The fungus causing
-azalea apples is an example (Exobasidium).
-
-=462. Order Hymeniales (Hymenomycetineæ).=—In this order the
-basidia are usually club-shaped and undivided, and bear usually four
-spores on the end (sometimes two or six). There are several families.
-
-=463. Family Thelephoraceæ.=—The fruit bodies are more or less
-membranous and spread over wood or the ground, or somewhat leaf-like,
-growing on wood or the ground. The fruiting surface is nearly or quite
-even, and occupies the under side of the leaf-like bodies (Stereum,
-Thelephora) or the outside of the forms spread out on wood (Corticium,
-Coniophora).
-
-=464. Family Clavariaceæ.=—This order includes the fairy clubs,
-and some of the coral fungi. The larger number of species are in one
-genus (Clavaria, fig. 248).
-
-=465. Family Hydnaceæ.=—The fungi of this order are known as
-“hedgehog” fungi, because of the numerous awl-like teeth or spines over
-which the fruiting surface is spread, as in Hydnum (figs. 246, 247).
-
-=466. Family Polyporaceæ.=—The tube-bearing fungi (Polyporus,
-Boletus, etc., fig. 245).
-
-=467. Family Agaricaceæ.=—The gill-bearing fungi (Agaricus,
-Amanita, etc., see Chapter XXI).
-
-The above five orders, according to the earlier classification (still
-used at the present time by some), made up the order Hymenomycetes,
-while the following five orders made up the Gasteromycetes. The
-Hymenomycetes, according to this system, included those plants in which
-the fruiting portion (hymenium) is either exposed from the first, or
-if covered by a veil or volva (as in Agaricus, Amanita, etc.) this
-ruptures and exposes the fruiting surface before, or at the time of,
-the ripening of the spores, while the Gasteromycetes included those in
-which the fruit body is closed until after the maturity of the spores.
-
-=468. Order Phallales (Phallineæ).=—The “stink-horn” fungi, or
-“buzzard’s nose.” Usually foul-smelling fungi, the fruiting portion
-borne aloft on a stout stalk, and dissolving (Dictyophora, Ithyphallus,
-etc.).
-
-=469. Order Hymenogastrales (Hymenogastrineæ).=—The basidia form
-a distinct hymenium which does not break down at maturity. Some of
-the plants resemble Boletus or Agaricus in the way the fruit bodies
-open (Secotium, etc.), while others open irregularly on the surface
-(Rhizopogon) or like an earth star (Sclerogaster), or portions of the
-surface become gelatinized (Phallogaster). The last-named one grows on
-very rotten wood, while most of the others grow on the ground.
-
-=470. Order Lycoperdales (Lycoperdineæ).=—These include the
-“puff-balls,” or “devil’s snuff-box” (Lycoperdon), and the earth stars
-(Geaster). The basidia form a distinct hymenium, but at maturity the
-entire inner portion of the plant (except certain peculiar threads, the
-capillitium) disintegrates and with the spores forms a powdery mass.
-
-=471. Order Nidulariales (Nidulariineæ).=—These are known
-as bird-nest fungi. The fruit body when mature is cup-shaped,
-or goblet-shaped, and contains minute flattened circular bodies
-(peridiola) containing the spores. The intermediate portions of the
-fruit body disintegrate and set the peridiola free, which then lie in
-the cup-shaped base like eggs in a nest.
-
-=472. Order Plectobasidiales (Plectobasidiineæ).=—The basidia
-do not form a definite hymenium, but are interwoven with the threads
-inside, or are collected into knot-like groups. (Examples: Calostoma,
-Tulostoma, Astræus, Sphærobolus, etc.)
-
-=472a. Lichens.=—The plant body of the lichens (see paragraphs
-200, 201) consists of two component parts, the one a fungus, the other
-an alga. The fructification is that of the fungus. The fruit body
-shows the lichens to be related some to the Ascomycetes, others to
-the Hymenomycetes, and Gasteromycetes. They are usually classified as
-a distinct class or order from the fungi, but a natural arrangement
-would distribute them in several of the orders above. Their special
-relationship with these orders has not been satisfactorily worked out.
-For the present they are arranged as follows:
-
-=Ascolichenes.=
-
-_Pyrenocarpous lichens_ (those with a fruit body like the
-Pyrenomycetes).
-
-_Gymnocarpous lichens_ (those with a fruit body like the Discomycetes).
-
-=Hymenolichenes= (those with a fruit body like the Hymenomycetes).
-
-=Gasterolichenes= (those with a fruit body like the
-Gasteromycetes).
-
-From a vegetative standpoint there are two types according to the
-distribution of the elements.
-
-1st. Where the fungal and algal elements are evenly distributed in the
-plant body the lichen is said to be _homoiomerous_. There are two types
-of these:
-
-_a. Filamentous lichens_, example, Ephebe pubescens.
-
-_b. Gelatinous lichens_, example, Collema (with the alga nostoc),
-Physma (with the Chroococcaceæ).
-
-2d. Where the elements are stratified, as in Parmelia, etc., the lichen
-is said to be _heteromerous_. In these there are three types:
-
-_a. Crustaceous lichens_, the plant body is in the form of a thin
-incrustation on rocks, etc.
-
-_b. Foliaceous lichens_, the plant body is leaf-like and lobed and more
-or less loosely attached by rhizoids: Parmelia, Peltigera, etc.
-
-_c. Fruticose lichens_, the plant body is filamentous or band-like and
-branched, as in Usnea, Cladonia, etc.
-
-[Illustration: Fig. 251_a_. Rock lichen (Parmelia contigua).]
-
-FOOTNOTES:
-
-[20] As suborder in Engler and Prantl.
-
-[21] As suborder in Engler and Prantl.
-
-[22] As suborder in Engler and Prantl.
-
-[23] The Uredinales and Auriculariales in Engler and Prantl are placed
-in order, Auriculariineæ.
-
-[24] The Uredinales and Auriculariales in Engler and Prantl are placed
-in order, Auriculariineæ.
-
-
-
-
-CHAPTER XXIII.
-
-LIVERWORTS (HEPATICÆ).
-
-
-=473.= We come now to the study of representatives of another
-group of plants, a few of which we examined in studying the organs of
-assimilation and nutrition. I refer to what are called the liverworts.
-Two of these liverworts belonging to the genus riccia are illustrated
-in figs. 30, 252.
-
-
-Riccia.
-
-=474. Form of the floating riccia (R. fluitans).=—The general
-form of floating riccia is that of a narrow, irregular, flattened,
-ribbon-like object, which forks repeatedly, in a dichotomous manner,
-so that there are several lobes to a single plant. It receives its
-name from the fact that at certain seasons of the year it may be found
-floating on the water of pools or lakes. When the water lowers it comes
-to rest on the damp soil, and rhizoids are developed from the under
-side. Now the sexual organs, and later the fruit capsule, are developed.
-
-=475. Form of the circular riccia (R. crystallina).=—The circular
-riccia is shown in fig. 252. The form of this one is quite different
-from the floating one, but the manner of growth is much the same.
-The branching is more compact and even, so that a circular plant is
-the result. This riccia inhabits muddy banks, lying flat on the wet
-surface, and deriving its soluble food by means of the little rootlets
-(rhizoids) which grow out from the under surface.
-
-[Illustration: Fig. 252. Thallus of Riccia crystallina.]
-
-Here and there on the margin are narrow slits, which extend nearly to
-the central point. They are not real slits, however, for they were
-formed there as the plant grew. Each one of these V-shaped portions of
-the thallus is a lobe, and they were formed in the young condition of
-the plant by a branching in a forked manner. Since growth took place
-in all directions radially the plant became circular in form. These
-large lobes we can see are forked once or twice again, as shown by the
-seeming shorter slits in the margin.
-
-=476. Sexual organs.=—In order to study the sexual organs we
-must make thin sections through one of these lobes lengthwise and
-perpendicular to the thallus surface. These sections are mounted for
-examination with the microscope.
-
-=477. Archegonia.=—We are apt to find the organs in various
-stages of development, but we will select one of the flask-shaped
-structures shown in fig. 253 for study. This flask-shaped body we see
-is entirely sunk in the tissue of the thallus. This structure is the
-female organ, and is what we term in these plants the _archegonium_. It
-is more complicated in structure than the oogonium. The lower portion
-is enlarged and bellied out, and is the venter of the archegonium,
-while the narrow portion is the neck. We here see it in section. The
-wall is one cell layer in thickness. In the neck is a canal, and in
-the base of the venter we see a large rounded cell with a distinct and
-large nucleus. This cell is the _egg_ cell.
-
-=478. Antheridia.=—The antheridia are also borne in cavities sunk
-in the tissue of the thallus. There is here no illustration of the
-antheridium of this riccia, but fig. 259 represents an antheridium of
-another liverwort, and there is not a great difference between the two
-kinds. Each one of those little rectangular sperm mother cells in the
-antheridium changes into a swiftly moving body like a little club with
-two long lashes attached to the smaller end. By the violent lashing of
-these organs the spermatozoid is moved through the water, or moisture
-which is on the surface of the thallus. It moves through the canal of
-the archegonium neck and into the egg, where it fuses with the nucleus
-of the egg, and thus fertilization is effected.
-
-=479. Embryo.=—In the plants which we have selected thus far for
-study, the egg, immediately after fecundation, we recollect, passed
-into a resting state, and was enclosed by a thick protecting wall.
-But in riccia, and in the other plants of the group which we are now
-studying, this is not the case. The egg, on the other hand, after
-acquiring a thin wall, swells up and fills the cavity of the venter.
-Then it divides by a cross wall into two cells. These two grow, and
-divide again, and so on until there is formed a quite large mass
-of cells rounded in form and still contained in the venter of the
-archegonium, which itself increases in size by the growth of the cells
-of the wall.
-
-[Illustration: Fig. 253.
-
-Archegonium of riccia, showing neck, venter, and the egg; archegonium
-is partly surrounded by the tissue of the thallus. (Riccia
-crystallina.)]
-
-[Illustration: Fig. 254.
-
-Young embryo (sporogonium) of riccia, within the venter of the
-archegonium; the latter has now two layers of cells. (Riccia
-crystallina.)]
-
-=480. Sporogonium of riccia.=—The fruit of riccia, which is
-developed from the fertilized egg in the archegonium, forms a rounded
-capsule still enclosed in the venter of the archegonium, which grows
-also to provide space for it. Therefore a section through the plant at
-this time, as described for the study of the archegonium, should show
-this capsule. The capsule then is a rounded mass of cells developed
-from the egg. A single outer layer of cells forms the wall, and
-therefore is sterile. All the inner cells, which are richer in
-protoplasm, divide into four cells each. Each of these cells becomes
-a spore with a thick wall, and is shaped like a triangular pyramid
-whose sides are of the same extent as the base (tetrahedral). These
-cells formed in fours are the _spores_. At this time the wall of the
-spore-case dissolves, the spores separate from each other and fill the
-now enlarged venter of the archegonium. When the thallus dies they are
-liberated, or escape between the loosely arranged cells of the upper
-surface.
-
-[Illustration: Fig. 255. Nearly mature sporogonium of Riccia
-crystallina; mature spore at the right.]
-
-[Illustration: Fig. 256.
-
-Riccia glauca; archegonium containing nearly mature sporogonium. _sg_,
-spore-producing cells surrounded by single layer of sterile cells, the
-wall of the sporogonium.]
-
-=481. A new phase in plant life.=—Thus we have here in the
-sporogonium of _riccia_ a very interesting phase of plant life, in
-which the egg, after fertilization, instead of developing directly into
-the same phase of the plant on which it was formed, grows into a quite
-new phase, the sole function of which is the development of spores.
-Since the form of the plant on which the sexual organs are developed
-is called the _gametophyte_, this new phase in which the spores are
-developed is termed the _sporophyte_.
-
-Now the spores, when they germinate, develop the _gametophyte_, or
-thallus, again. So we have this very interesting condition of things,
-the thallus (gametophyte) bears the sexual organs and the unfertilized
-egg. The fertilized egg, starting as it does from a single-celled
-stage, develops the sporogonium (sporophyte). Here the single-cell
-stage is again reached in the spore, which now develops the thallus.
-
-=482. Riccia compared with coleochæte, œdogonium, etc.=—We have
-said that in the sporogonium of riccia we have formed a new phase in
-plant life. If we recur to our study of coleochæte we may see that
-there is here possibly a state of things which presages, as we say,
-this new phase which is so well formed in riccia. We recollect that
-after the fertilized egg passed the period of rest it formed a small
-rounded mass of cells, each of which now forms a zoospore. The zoospore
-in turn develops the normal thallus (gametophyte) of the coleochæte
-again. In coleochæte then we have two phases of the plant, each having
-its origin in a one-celled stage. Then if we go back to œdogonium,
-we remember that the fertilized egg, before it developed into the
-œdogonium plant again (which is the gametophyte), at first divides into
-_four_ cells which become zoospores. These then develop the œdogonium
-plant.
-
-      Note. Too much importance should not be attached to
-    this seeming homology of the sporophyte of œdogonium,
-    coleochæte, and riccia, for the nuclear phenomena
-    in the formation of the zoospores of œdogonium and
-    coleochæte are not known. They form, however, a very
-    suggestive series.
-
-
-Marchantia.
-
-=483.= The marchantia (M. polymorpha) has been chosen for study
-because it is such a common and easily obtained plant, and also for
-the reason that with comparative ease all stages of development can
-be obtained. It illustrates also very well certain features of the
-structure of the liverworts.
-
-[Illustration: Fig. 257. Male plant of marchantia bearing
-antheridiophores.]
-
-The plants are of two kinds, male and female. The two different organs,
-then, are developed on different plants. In appearance, however, before
-the beginning of the structures which bear the sexual organs they
-are practically the same. The thallus is flattened like nearly all
-of the thalloid forms, and branches in a forked manner. The color is
-dark green, and through the middle line of the thallus the texture is
-different from that of the margins, so that it possesses what we term a
-midrib, as shown in figs. 257, 261. The growing point of the thallus is
-situated in the little depression at the free end. If we examine the
-upper surface with a hand lens we see diamond-shaped areas, and at the
-center of each of these areas are the openings known as the stomates.
-
-[Illustration: Fig. 258. Section of antheridial receptacle from male
-plant of Marchantia polymorpha, showing cavities where the antheridia
-are borne.]
-
-=484. Antheridial plants.=—One of the male plants is figured at
-257. It bears curious structures, each held aloft by a short stalk.
-These are the antheridial receptacles (or male gametophores). Each
-one is circular, thick, and shaped somewhat like a biconvex lens. The
-upper surface is marked by radiating furrows, and the margin is
-crenate. Then we note, on careful examination of the upper surface,
-that there are numerous minute openings. If we make a thin section of
-this structure perpendicular to its surface we shall be able to unravel
-the mystery of its interior. Here we see, as shown in fig. 258, that
-each one of these little openings on the surface is an entrance to quite
-a large cavity. Within each cavity there is an oval or elliptical
-body, supported from the base of the cavity on a short stalk. This is
-an antheridium, and one of them is shown still more enlarged in fig.
-259. This shows the structure of the antheridium, and that there are
-within several angular areas, which are divided by numerous straight
-cross-lines into countless tiny cuboidal cells, the _sperm mother
-cells_. Each of these, as stated in the former chapter, changes into a
-swiftly moving body resembling a serpent with two long lashes attached
-to its tail.
-
-[Illustration: Fig. 259. Section of antheridium of marchantia, showing
-the groups of sperm mother cells.]
-
-[Illustration: Fig. 260. Spermatozoids of marchantia, uncoiling and one
-extended, showing the two cilia.]
-
-=485.= The way in which one of these sperm mother cells changes
-into this spermatozoid is very curious. We first note that a coiled
-spiral body is appearing within the thin wall of the cell, one end of
-the coil larger than the other. The other end terminates in a slender
-hair-like outgrowth with a delicate vesicle attached to its free end.
-This vesicle becomes more and more extended until it finally breaks and
-forms two long lashes which are clubbed at their free ends as shown in
-fig. 260.
-
-[Illustration: Fig. 261. Marchantia polymorpha, female plants bearing
-archegoniophores.]
-
-[Illustration: Fig. 262. Marchantia polymorpha, showing origin of
-gametophore.]
-
-=486. Archegonial plants.=—In fig. 261 we see one of the female
-plants of marchantia. Upon this there are also very curious structures,
-which remind one of miniature umbrellas. The general plan of the
-archegonial receptacle (or female gametophore), for this is what these
-structures are, is similar to that of the antheridial receptacle,
-but the rays are more pronounced, and the details of structure are
-quite different, as we shall see. Underneath the arms there hang down
-delicate fringed curtains. If we make sections of this in the same
-direction as we did of the antheridial receptacle, we shall be able to
-find what is secreted behind these curtains. Such a section is figured
-at 266. Here we find the archegonia, but instead of being sunk in
-cavities their bases are attached to the under surface, while the
-delicate, pendulous fringes afford them protection from drying. An
-archegonium we see is not essentially different in marchantia from
-what it is in riccia, and it will be interesting to learn whether the
-sporogonium is essentially different from what we find in riccia.
-
-=487. Homology of the gametophore of marchantia.=—To see the
-relation of the gametophore to the thallus of marchantia take portions
-of the thallus bearing the female receptacle. On the under side note
-that the prominent midrib continues beyond the thin lateral expansions
-and arches upward in the sinus or notch at the end, or at the side
-where the branch of the thallus has continued to grow beyond. The stalk
-of the gametophore is then a continuation of the midrib of the thallus.
-On the apex of this are organized several radial growing points which
-develop the digitate or ray-like receptacle. The gametophore is thus a
-specialized branch of the thallus. When young, or in many cases when
-nearly or quite mature, the gametophore, as one looks at the upper
-surface of the thallus, appears to arise from the upper surface, as in
-fig. 261. This is because the thin lateral expansions of the thallus
-project forward and overlap in advance of the stalk. It is sometimes
-necessary to tear these overlapping edges apart to see the real origin
-of the gametophore. But in quite old plants these expanded portions are
-farther apart and show clearly that the stalk arises from the midrib
-below and arches upward in the sinus, as in fig. 262.
-
-
-
-
-CHAPTER XXIV.
-
-LIVERWORTS CONTINUED.
-
-
-[Illustration: Fig. 263.
-
-Archegonial receptacles of marchantia bearing ripe sporogonia. The
-capsule of the sporogonium projects outside, while the stalk is
-attached to the receptacle underneath the curtain. In the left figure
-two of the capsules have burst and the elaters and spores are escaping.]
-
-=488. Sporogonium of marchantia.=—If we examine the plant shown
-in fig. 181 we shall see oval bodies which stand out between the
-rays of the female receptacle, supported on short stalks. These are
-the sporogonia, or spore-cases. We judge at once that they are quite
-different from those which we have studied in riccia, since those were
-not stalked. We can see that some of the spore-cases have opened, the
-wall splitting down from the apex in several lines. This is caused by
-the drying of the wall. These tooth-like divisions of the wall now
-curl backward, and we can see the yellowish mass of the spores in slow
-motion, falling here and there. It appears also as if there were
-twisting threads which aided the spores in becoming freed from the
-capsule.
-
-[Illustration: Fig. 264.
-
-Section of archegonial receptacle of Marchantia polymorpha; ripe
-sporogonia. One is open, scattering spores and elaters; two are still
-enclosed in the wall of the archegonium. The junction of the stalk of
-the sporogonium with the receptacle is the point of attachment of the
-sporophyte of marchantia with the gametophyte.]
-
-[Illustration: Fig. 265. Elater and spore of marchantia. _sp_, spore;
-_mc_, mother cell of spores, showing partly formed spores.]
-
-=489. Spores and elaters.=—If we take a bit of this mass of
-spores and mount it in water for examination with the microscope, we
-shall see that, besides the spores, there are very peculiar thread-like
-bodies, the markings of which remind one of a twisted rope. These are
-very long cells from the inner part of the spore-case, and their walls
-are marked by spiral thickenings. This causes them in drying, and also
-when they absorb moisture, to twist and curl in all sorts of ways. They
-thus aid in pushing the spores out of the capsule as it is drying.
-
-=490. Sporophyte of marchantia compared with riccia.=—We must
-recollect that the sporogonium in marchantia is larger than in riccia,
-and that it is also not lying in the tissue of the thallus, but is only
-attached to it at one side by a slender stalk. This shows us an
-increase in the size and complex structure of this new phase of the
-plant, the _sporophyte_. This is one of the very interesting things
-which we have to note as we go on in the study of the higher plants.
-
-[Illustration: Fig. 266.
-
-Marchantia polymorpha, archegonium at the left with egg; archegonium at
-the right with young sporogonium; _p_, curtain which hangs down around
-the archegonia; _e_, egg; _v_, venter of archegonium; _n_, neck of
-archegonium; _sp_, young sporogonium.]
-
-=491. Sporophyte dependent on the gametophyte for its
-nutriment.=—We thus see that at no time during the development of
-the sporogonium is it independent from the gametophyte. This new phase
-of plants then, the sporophyte, has not yet become an independent
-plant, but must rely on the earlier phase for sustenance.
-
-=492. Development of the sporogonium.=—It will be interesting
-to note briefly how the development of the marchantia sporogonium
-differs from that of riccia. The first division of the fertilized egg
-is the same as in riccia, that is a wall which runs crosswise of the
-axis of the archegonium divides it into two cells. In marchantia the
-cell at the base develops the stalk, so that here there is a radical
-difference. The outer cell forms the capsule. But here after the wall
-is formed the inner tissue does not all go to make spores, as is the
-case with riccia. But some of it forms the elaters. While in riccia
-only the outside layer of cells of the sporogonium remained sterile, in
-marchantia the basal half of the egg remains completely sterile and
-develops the stalk, and in the outer half the part which is formed from
-some of the inner tissue is also sterile.
-
-[Illustration: Fig. 267.
-
-Section of developing sporogonia of marchantia; _nt_, nutritive tissue
-of gametophyte; _st_, sterile tissue of sporophyte; _sp_, fertile part
-of sporophyte; _va_, enlarged venter of archegonium.]
-
-=493. Embryo.=—In the development of the embryo we can see all
-the way through this division line between the basal half, which is
-completely sterile, and the outer half, which is the fertile part. In
-fig. 267 we see a young embryo, and it is nearly circular in section
-although it is composed of numerous cells. The basal half is attached
-to the base of the inner surface of the archegonium, and at this time
-the archegonium still surrounds it. The archegonium continues to grow
-then as the embryo grows, and we can see the remains of the shrivelled
-neck. The portion of the embryo attached to the base of the archegonium
-is the sterile part and is called the “foot,” and later develops the
-stalk. The sporogonium during all the stages of its development derives
-its nourishment from the gametophyte at this point of attachment at
-the base of the archegonium. Soon, as shown in fig. 267 at the right,
-the outer portion of the sporogonium begins to differentiate into
-the cells which form the elaters and those which form spores. These
-lie in radiating lines side by side, and form what is termed the
-_archesporium_. Each fertile cell forms four spores just as in riccia.
-They are thus called the mother cells of the spores, or spore mother
-cells.
-
-=494. How marchantia multiplies.=—New plants of marchantia are
-formed by the germination of the spores, and growth of the same to the
-thallus. The plants may also be multiplied by parts of the old ones
-breaking away by the action of strong currents of water, and when they
-lodge in suitable places grow into well-formed plants. As the thallus
-lives from year to year and continues to grow and branch the older
-portions die off, and thus separate plants may be formed from a former
-single one.
-
-[Illustration: Fig. 268. Marchantia plant with cupules and gemmæ;
-rhizoids below.]
-
-=495. Buds, or gemmæ, of marchantia.=—But there is another
-way in which marchantia multiplies itself. If we examine the upper
-surface of such a plant as that shown in fig. 268, we shall see that
-there are minute cup-shaped or saucer-shaped vessels, and within them
-minute green bodies. If we examine a few of these minute bodies with
-the microscope we see that they are flattened, biconvex, and at two
-opposite points on the margin there is an indentation similar to that
-which appears at the growing end of the old marchantia thallus. These
-are the growing points of these little buds. When they free themselves
-from the cups they come to lie on one side. It does not matter on what
-side they lie, for whichever side it is, that will develop into the
-lower side of the thallus, and forms rhizoids, while the upper surface
-will develop the stomates.
-
-
-Leafy-stemmed liverworts.
-
-=496.= We should now examine more carefully than we have done
-formerly a few of the leafy-stemmed liverworts (called foliose
-liverworts).
-
-[Illustration: Fig. 269.
-
-Section of thallus of marchantia. _A_, through the middle portion; _B_,
-through the marginal portion; _p_, colorless layer; _chl_, chlorophyll
-layer; _sp_, stomate; _h_, rhizoids; _b_, leaf-like outgrowths on
-underside (Goebel).]
-
-=497. Frullania= (Fig. 32).—This plant grows on the bark of
-logs, as well as on the bark of standing trees. It lives in quite dry
-situations. If we examine the leaves we will see how it is able to do
-this. We note that there are two rows of lateral leaves, which are very
-close together, so close in fact that they overlap like the shingles
-on a roof. Then, as the creeping stems lie very close to the bark of
-the tree, these overlapping leaves, which also hug close to the stem
-and bark, serve to retain moisture which trickles down the bark during
-rains. If we examine these leaves from the under side as shown in fig.
-34, we see that the lower or basal part of each one is produced into a
-peculiar lobe which is more or less cup-shaped. This catches water and
-holds it during dry weather, and it also holds moisture which the plant
-absorbs during the night and in damp days. There is so much moisture in
-these little pockets of the under side of the leaf that minute animals
-have found them good places to live in, and one frequently discovers
-them in this retreat. There is here also a third row of poorly
-developed leaves on the under side of the stem.
-
-=498. Porella.=—Growing in similar situations is the plant known
-as porella. Sometimes there are a few plants in a group, and at other
-times large mats occur on the bark of a trunk. This plant, porella,
-also has closely overlapping leaves in rows on opposite sides of the
-stem, and the lower margin of each leaf is curved under somewhat as in
-frullania, though the pocket is not so well formed.
-
-The larger plants are female, that is they bear archegonia, while
-the male plants, those which bear antheridia, are smaller and the
-antheridia are borne on small lateral branches. The antheridia
-are borne in the axils of the leaves. Others of the leafy-stemmed
-liverworts live in damp situations. Some of these, as Cephalozia, grow
-on damp rotten logs. Cephalozia is much more delicate, and the leaves
-are farther apart. It could not live in such dry situations where the
-frullania is sometimes found. If possible the two plants should be
-compared in order to see the adaptation in the structure and form to
-their environment.
-
-[Illustration: Fig. 270. Thallus of a thalloid liverwort (blasia)
-showing lobed margin of the frond, intermediate between thalloid and
-foliose plant.]
-
-=499. Sporogonium of a foliose liverwort.=—The sporogonium of the
-leafy-stemmed liverworts is well represented by that of several genera.
-We may take for this study the one illustrated in fig. 274, but
-another will serve the purpose just as well. We note here that it
-consists of a rounded capsule borne aloft on a long stalk, the stalk
-being much longer proportionately than in marchantia. At maturity the
-capsule splits down into four quadrants, the wall forming four valves,
-which spread apart from the unequal drying of the cells, so that the
-spores are set free, as shown in fig. 276. Some of the cells inside
-of the capsule develop elaters here also as well as spores. These are
-illustrated in fig. 278.
-
-[Illustration: Fig. 271. Foliose liverwort, male plant showing
-antheridia in axils of the leaves (a jungermannia).]
-
-[Illustration: Fig. 272. Antheridium of a foliose liverwort
-(jungermannia).]
-
-[Illustration: Fig. 273. Foliose liverwort, female plant with rhizoids.]
-
-=500.= In this plant we see that the sporophyte remains attached to
-the gametophyte, and thus is dependent on it for sustenance. This is
-true of all the plants of this group. The sporophyte never becomes
-capable of an independent existence, and yet we see that it is becoming
-larger and more highly differentiated than in the simple riccia.
-
-[Illustration: Fig. 274. Fruiting plant of a foliose liverwort
-(jungermannia). Leafy part is the gametophyte; stalk and capsule is the
-sporophyte (sporogonium in the bryophytes).
-
-[Illustration: Fig. 275. Opening capsule showing escape of spores and
-elaters.
-
-[Illustration: Fig. 276. Capsule parted down to the stalk.
-
-[Illustration: Fig. 277. Four spores from mother cell held in a group.
-
-[Illustration: Fig. 278. Elaters, at left showing the two spiral marks,
-at right a branched elater.
-
-Figs. 275-278.—Sporogonium of liverwort (jungermannia) opening by
-splitting into four parts, showing details of elaters and spores.]
-
-
-The Horned Liverworts.[25]
-
-=501. The horned liverworts= take their name from the shape of
-the sporogonium. This is long, slender, cylindrical, pointed, and very
-slightly curved, suggesting the shape of a minute horn. Anthoceros is
-one of the most common and widely distributed species. The plant grows
-on damp soil or on mud.
-
-
-Anthoceros.
-
-=502. The gametophyte.=—The gametophyte is thalloid. It is thin,
-flattened, green, irregularly ribbon-shaped and branched. It lies on
-the soil and is more or less crisped or wavy, or curled, the edges
-nearly plane, or somewhat irregular, and with minute lobes, or notches,
-especially near the growing end. The general form and branching can
-be seen in fig. 279. Where the plants are much crowded the thallus is
-more irregular, and often possesses numerous small lateral branches
-in addition to the main lobes. Upon the under side are the slender
-rhizoids, which attach to the soil. With a hand lens there can be seen
-also upon the under side small dark, rounded and thickened spots, where
-an alga (nostoc) is located.
-
-
-Sexual Organs of Anthoceros.
-
-=502. The sexual organs of anthoceros= differ considerably from
-those of the other liverworts studied. In the first place they are
-immersed in the true tissue of the thallus, i.e., they do not project
-above the surface.
-
-[Illustration: Fig. 279.
-
-Anthoceros gracilis. _A_, several gametophytes, on which sporangia
-have developed; _B_, an enlarged sporogonium, showing its elongated
-character and dehiscence by two valves, leaving exposed the slender
-columella on the surface of which are the spores, _C_, _D_, _E_, _F_,
-elaters of various forms, _G_, spores. (After Schiffner.)]
-
-=503. Antheridia.=—The antheridium arises from an internal cell
-of the thallus, a cell just below the upper surface. This cell develops
-usually a group of antheridia which lie in a cavity formed around this
-cell as the thallus continues to grow. They are situated along the
-middle line of the thallus, and can be seen by making a section in this
-direction. The antheridia are oval or rounded, have a wall of one layer
-of cells which contains the sperm cells, and each antheridium has a
-slender stalk. The sperms are like those of the true liverworts.
-
-=504. Archegonia.=—The archegonia are also borne along the
-middle line of the thallus. Each one arises at an early stage in the
-development of the tissue of the thallus from a superficial cell,
-but the archegonium does not project above the surface. The venter
-therefore which contains the egg is deep down in the thallus, the wall
-of the neck is formed from cells indistinguishable from the adjoining
-cells of the thallus and opens at the surface.
-
-
-Sporophyte of Anthoceros.
-
-=505. The Sporogonium.=—The sporogonium is developed from the
-fertilized egg, fertilization resulting of course from the fusion of
-one of the sperms with the nucleus of the egg. From the lower part
-of the embryo certain cells elongate and push out like rhizoids into
-the thallus (gametophyte), but never reach the outside so that the
-sporogonium derives its nutriment from the gametophyte in a parasitic
-manner like the true liverworts. It is surrounded at the base by a
-sheath, an outgrowth of the gametophyte.
-
-=506. Growing point of the sporogonium.=—A remarkable thing
-about the sporogonium of anthoceros, and its relatives, is that the
-growing point instead of being situated at the free end is located near
-the base, just above the nourishing foot. Thus the upper part of the
-sporogonium is older. In the old sporogonia there may be ripe spores
-near the free end, young ones near the middle, and undifferentiated
-growing tissue near the base. A longitudinal section of a sporogonium
-just as the spores are ripening will show this.
-
-=507. Structure of the sporogonium.=—A longitudinal section
-of the sporogonium shows that the spore-bearing tissue occupies a
-comparatively small portion of the sporogonium. In the section there
-is a narrow layer (two cells thick) on either side and joined at the
-top. In the entire sporogonium this fertile tissue is in the shape of
-an inverted test tube situated inside of the sporogonium. The wall of
-the sporogonium is about four cells thick. The sterile tissue inside
-of the spore-bearing tube is the columella. The cells of the wall
-contain chlorophyll, and there are true stomata with guard cells in the
-epidermal layer.
-
-=508. Spores and elaters.=—In the spore-bearing tissue there
-are two layers of cells (the archesporium). Each cell is a potential
-mother cell. The cells, however, of alternate tiers do not form spores.
-They elongate some what and are somewhat irregular and sometimes divide
-or branch. They are supposed to represent rudimentary _elaters_. The
-cells in the other tiers are actual mother cells, and each one forms
-four spores.
-
-=509. The sporophyte of anthoceros= represents the highest type
-found in the liverworts. The spongy green parenchyma forming the
-wall, with the stomata in the epidermal layer, fits this tissue for
-the process of photosynthesis, so that this part of the sporophyte
-functions as the green leaf of the seed plants. It has been suggested
-by some that if the rhizoids on the nourishing foot could only extend
-outside and anchor in the soil, the sporophyte of anthoceros could live
-an independent existence. But we see that it stops short of that.
-
-
-Classification of the Liverworts.
-
-
-CLASS HEPATICÆ.
-
-=510. Order Marchantiales.=[26]—There are two families represented
-in the United States.
-
-Family Ricciaceæ, including Riccia and Ricciocarpus.
-
-Family Marchantiaceæ, including Marchantia, Fegatella (= Conocephalus),
-Fimbriaria, Targionia, etc.
-
-=511. Order Jungermanniales.=[27]—There are two subdivisions
-of this order. _The Anacrogynæ_ include chiefly thalloid forms with
-continued apical growth, the archegonia back of the apical cell.
-Examples: Blasia, Aneura, Pellia, etc.
-
-_The Acrogynæ_ include chiefly foliose forms, the archegonia arising
-from the apical cell and in such cases interrupting apical growth.
-Examples: Cephalozia, Frullania, Bazzania, Jungermannia, Ptilidium,
-Porella, etc.
-
-
-CLASS ANTHOCEROTES.
-
-=512. The Anthocerotes= have formerly been placed with the
-Hepaticæ as an order. But because of their wide divergence from
-the other liverworts in the development of the sexual organs, and
-especially in the structure of the sporophyte, they are now by some
-separated as a distinct class. There is one order.
-
-=Order Anthocerotales.=[28]—This includes one family
-(Anthocerotaceæ) with Anthoceros and Notothylas in Europe and North
-America, and Dendroceros in the tropics. The latter is epiphytic.
-
-FOOTNOTES:
-
-[25] May be used as an alternate study for marchantia.
-
-[26] As subclass in Engler and Prantl.
-
-[27] As subclass in Engler and Prantl.
-
-[28] As subclass in Engler and Prantl.
-
-
-
-
-CHAPTER XXV.
-
-MOSSES (MUSCI).
-
-
-=513.= We are now ready to take up the more careful study of the
-moss plant. There are a great many kinds of mosses, and they differ
-greatly from each other in the finer details of structure. Yet there
-are certain general resemblances which make it convenient to take for
-study almost any one of the common species in a neighborhood, which
-forms abundant fruit. Some, however, are more suited to a first study
-than others. (Polytrichum and funaria are good mosses to study.)
-
-=514. Mnium.=—We will select here the plant shown in fig. 280.
-This is known as a mnium (M. affine), and one or another of the species
-of mnium can be obtained without much difficulty. The mosses, as we
-have already learned, possess an axis (stem) and leaf-like expansions,
-so that they are leafy-stemmed plants also. Certain of the branches of
-the mnium stand upright, or nearly so, and the leaves are all of the
-same size at any given point on the stem, as seen in the figure. There
-are three rows of these leaves, and this is true of most of the mosses.
-
-=515.= The mnium plants usually form quite extensive and pretty
-mats of green in shady moist woods or ravines. Here and there among the
-erect stems are prostrate ones, with two rows of prominent leaves so
-arranged that it reminds one of some of the leafy-stemmed liverworts.
-If we examine some of the leaves of the mnium we see that the greater
-part of the leaf consists of a single layer of green cells, just as
-is the case in the leafy-stemmed liverworts. But along the middle
-line is a thicker layer, so that it forms a distinct midrib. This is
-characteristic of the leaves of mosses, and is one way in which they
-are separated from the leafy-stemmed liverworts, the latter never
-having a midrib.
-
-[Illustration: Fig. 280.
-
-Portion of moss plant of Mnium affine, showing two sporogonia from one
-branch. Capsule at left has just shed the cap or operculum; capsule at
-right is shedding spores, and the teeth are bristling at the mouth.
-Next to the right is a young capsule with calyptra still attached; next
-are two spores enlarged.]
-
-=516. The fruiting moss plant.=—In fig. 280 is a moss plant “in
-fruit,” as we say. Above the leafy stem a slender stalk bears the
-capsule, and in this capsule are borne the spores. The capsule then
-belongs to the _sporophyte phase_ of the moss plant, and we should
-inquire whether the entire plant as we see it here is the sporophyte,
-or whether part of it is gametophyte. If a part of it is gametophyte
-and a part sporophyte, then where does the one end and the other begin?
-If we strip off the leaves at the end of the leafy stem, and make a
-longisection in the middle line, we should find that the stalk which
-bears the capsule is simply stuck into the end of the leafy stem, and
-is not organically connected with it. This is the dividing line, then,
-between the gametophyte and the sporophyte. We shall find that here the
-archegonium containing the egg is borne, which is a surer way of
-determining the limits of the two phases of the plant.
-
-=517. The male and female moss plants.=—The two plants of mnium
-shown in figs. 281, 282 are quite different, as one can easily see,
-and yet they belong to the same species. One is a female plant, while
-the other is a male plant. The sexual organs then in mnium, as in many
-others of the mosses, are borne on separate plants. The archegonia are
-borne at the end of the stem, and are protected by somewhat narrower
-leaves which closely overlap and are wrapped together. They are similar
-to the archegonia of the liverworts.
-
-[Illustration: Fig. 281. Female plant (gametophyte) of a moss (mnium),
-showing rhizoids below, and the tuft of leaves above which protect the
-archegonia.]
-
-[Illustration: Fig. 282. Male plant (gametophyte) of a moss (mnium)
-showing rhizoids below and the antheridia at the center above
-surrounded by the rosette of leaves.]
-
-The male plants of mnium are easily selected, since the leaves at the
-end of the stem form a broad rosette with the antheridia, and some
-sterile threads packed closely together in the center. The ends of the
-mass of antheridia can be seen with the naked eye, as shown in fig.
-282. When the antheridia are ripe, if we make a section through a
-cluster, or if we merely tease out some from the end with a needle in
-a drop of water on the slide, then prepare for examination with the
-microscope, we can see the form of the antheridia. They are somewhat
-clavate or elliptical in outline, as seen in fig. 284. Between them
-there stand short threads composed of several cells containing
-chlorophyll grains. These are sterile threads (paraphyses).
-
-=518. Sporogonium.=—In fig. 280 we see illustrated a sporogonium
-of mnium, which is of course developed from the fertilized egg-cell of
-the archegonium. There is a nearly cylindrical capsule, bent downward,
-and supported on a long slender stalk. Upon the capsule is a peculiar
-cap,[29] shaped like a ladle or spatula. This is the remnant of the
-old archegonium, which, for a time surrounded and protected the young
-embryo of the sporogonium, just as takes place in the liverworts. In
-most of the mosses this old remnant of the archegonium is borne aloft
-on the capsule as a cap, while in the liverworts it is thrown to one
-side as the sporogonium elongates.
-
-[Illustration: Fig. 283. Section through end of stem of female plant of
-mnium, showing archegonia at the center. One archegonium shows the egg.
-On the sides are sections of the protecting leaves.]
-
-[Illustration: Fig. 284. Antheridium of mnium with jointed paraphysis
-at the left; spermatozoids at the right.]
-
-=519. Structure of the moss capsule.=—At the free end on the moss
-capsule as shown in the case of mnium in fig. 280, after the remnant
-of the archegonium falls away, there is seen a conical lid which fits
-closely over the end. When the capsule is ripe this lid easily falls
-away, and can be brushed off so that it is necessary to handle the
-plants with care if it is desired to preserve this for study.
-
-=520.= When the lid is brushed away as the capsule dries more we
-see that the end of the capsule covered by the lid appears “frazzled.”
-If we examine this end with the microscope we see that the tissue of
-the capsule here is torn with great regularity, so that there are two
-rows of narrow, sharp teeth which project outward in a ring around the
-opening. If we blow our “breath” upon these teeth they will be seen to
-move, and as the moisture disappears and reappears in the teeth, they
-close and open the mouth of the capsule, so sensitive are they to the
-changes in the humidity of the air. In this way all of the spores are
-prevented to some extent from escaping from the capsule at one time.
-
-=521.= Note. If we make a section longitudinal of the capsule of
-mnium, or some other moss, we find that the tissue which develops the
-spores is much more restricted than in the capsule of the liverworts
-which we have studied. The spore-bearing tissue is confined to a single
-layer which extends around the capsule some distance from the outside
-of the wall, so that a central cylinder is left of sterile tissue. This
-is the columella, and is present in nearly all the mosses. Each of the
-cells of the fertile layer divides into four spores.
-
-[Illustration: Fig. 285. Two different stages of young sporogonium of
-a moss, still within the archegonium and wedging their way into the
-tissue of the end of the stem. _h_, neck of archegonium; _f_, young
-sporogonium. This shows well the connection of the sporophyte with the
-gametophyte.]
-
-=522. Development of the sporogonium.=—The egg-cell after
-fertilization divides by a wall crosswise to the axis of the
-archegonium. Each of these cells continues to divide for a time, so
-that a cylinder pointed at both ends is formed. The lower end of
-this cylinder of tissue wedges its way down through the base of the
-archegonium into the tissue of the end of the moss stem as shown in
-fig. 285. This forms the foot through which the nutrient materials
-are passed from the gametophyte to the sporogonium. The upper part
-continues to grow, and finally the upper end differentiates into the
-mature capsule.
-
-=523. Protonema of the moss.=—When the spores of a moss germinate
-they form a thread-like body, with chlorophyll. This thread becomes
-branched, and sometimes quite extended tangles of these threads are
-formed. This is called the protonema, that is _first thread_. The older
-threads become finally brown, while the later ones are green. From this
-protonema at certain points buds appear which divide by close oblique
-walls. From these buds the leafy stem of the moss plant grows. Threads
-similar to these protonemal threads now grow out from the leafy stem,
-to form the rhizoids. These supply the moss plant with nutriment, and
-now the protonema usually dies, though in some few species it persists
-for long periods.
-
-
-Classification of the Mosses.
-
-CLASS MUSCINEÆ (MUSCI).
-
-=524. Order Sphagnales.=[30]—This order includes the peat mosses. There
-is but one family (Sphagnaceæ) and but a single genus (Sphagnum). The
-peat mosses are widely distributed over the globe, chiefly occurring
-in moors, or “bogs,” usually low ground around the shores of lakes,
-ponds, or along streams, but they often occur on wet dripping rocks in
-cool shady places. Small ponds are sometimes filled in by their growth.
-As the sphagnum growing in such an abundance of water only partially
-decays, “ground” is built up rather rapidly, and the sphagnum remains
-are known as “peat.” This “ground”-building peculiarity of sphagnum
-sometimes enables the plant (often in conjunction with others) to fill
-in ponds completely. (See Atoll Moor, Chapter LV.)
-
-The gametophyte of sphagnum, like that of all the mosses, is dimorphic,
-but the first part (or protonema) which develops from the spores is
-thalloid, and therefore more like the thallose liverworts. The leafy
-axis (or gametophore) which develops from the thalloid form is very
-characteristic (see Chapter LV).
-
-The archegonia are borne on the free end of the main axis, while the
-antheridia are borne on short branches which are brightly colored, red,
-yellow, etc. The sporophyte (sporogonium) is globose and possesses a
-broad foot anchored in the end of a naked prolongation of the end of
-the leafy gametophore. This naked prolongation of the gametophore looks
-like the stalk of the sporogonium, but a study of its connection with
-the sporogonium shows that it is part of the gametophyte, which is only
-developed after the fertilization of the egg in the archegonium. In the
-sporogonium there is a short columella, and the archesporium is in the
-form of an inverted cup.
-
-=525. Order Andreæales.=[31]—This order includes the single genus
-Andreæa. The plants are small but form extensive mats, growing on rocks
-in arctic or alpine regions usually. They are sometimes found in great
-abundance on bare, rather dry rocks on mountains. The protonema is
-somewhat thalloid. The sporogonium opens by splitting longitudinally
-into four valves. An elongated columella is present so that the
-archesporium is shaped like an inverted test tube.
-
-=526. Order Archidiales.=[32]—This order contains the single genus
-Archidium, and by some is placed as an aberrant genus in the Bryales.
-There is no columella in the simple sporogonium. The archesporium
-occupies all the internal part of the sporogonium, some cells being
-fertile and others sterile.
-
-=527. Order Bryales.=[33]—These include the higher mosses, and a very
-large number of genera and species. The protonema is filamentous and
-branched except in a few forms where it is partly thalloid as in
-Tetraphis (= Georgia). (Tetraphis pellucida is a common moss on very
-rotten logs. The capsule has four prominent teeth.) In a few of the
-lower genera (Phascum, Pleuridium, etc.) the capsule opens irregularly,
-but in the larger number the capsule opens by a lid (operculum). A
-cylindrical columella is present, and the archesporium is in the form
-of a tube open at both ends. (Examples: Polytrichum, Bryum, Mnium,
-Hypnum, etc.)
-
-=528.= TABLE SHOWING RELATION OF GAMETOPHYTE AND SPOROPHYTE IN THE
-LIVERWORTS AND MOSSES.
-
-  ----------------------------------------------------------------------
-                                GAMETOPHYTE.
-         (Prominent part of the plant. Leads an independent existence.)
-  -------------+--------------+---------------+-------------------------
-               | Vegetative   | Vegetative    |     Sexual Organs.
-               |   Stage.     |Multiplication.|
-  -------------+--------------+---------------+-------------------------
-  Riccia.      |Thallus       |Sometimes by   |Immersed by surrounding,
-               |flattened,    |branching and  |upward growth of thallus.
-               |ribbon-like,  |dying away of  +--------------+----------
-               |forked,       |older parts.   |Antheridia,   |Archegonia,
-               |or nearly     |               |with          |with egg
-               |circular.     |               |spermatozoids.|in each.
-  -------------+--------------+---------------+-------------------------
-  Marchantia.  |Thallus       |By dying away  |    Borne on special
-               |flattened,    |of older parts,|     receptacles on
-               |ribbon-like,  |and by gemmæ.  |    different plants.
-               |forked,       |               +--------------+----------
-               |male and      |               |Antheridia,   |Archegonia,
-               |female        |               |with          |borne on
-               |plants bear   |               |spermatozoids |female
-               |gametophores. |               |borne on      |gametophore
-               |              |               |antheridio-   | (or
-               |              |               |      phores, |archegonio-
-               |              |               |or male       |    phore),
-               |              |               |gametophores. |each with
-               |              |               |              |an egg.
-  -------------+--------------+---------------+-------------------------
-  Jungermannia |A plant with  |By dying away  |    On different plants.
-   (or         |apparent      |of older parts.+--------------+----------
-    Cephalozia,|leaves and    |               |Antheridia,   |Archegonia,
-    Porella    |stem; margins |               |with          |each with
-    etc.)      |of thallus    |               |spermatozoids,|egg, on
-               |have become   |               |in axils of   |female
-               |cut into      |               |leaves of     |plant.
-               |lobes. Male   |               |male plant.   |
-               |and female    |               |              |
-               |plants.       |               |              |
-               |              |               |              |
-               |              |               |              |
-  -------------+--------------+---------------+--------------+----------
-  Mosses.      |Plant with    |By branching,  |    On different plants.
-   {Mnium,     |apparent      |by growth of   +--------------+----------
-   {Funaria,   |leafy axis,   |protonema from |Antheridia,   |Archegonia,
-   {Polytrichum|3 rows  of    |axis, leaves,  |with          |each with
-   {etc.       |leaves        |or even        |spermatozoids,|egg, on
-               |(similar to   |sporogonium.   |at end of     |female
-               |jungermannia),|(In somegenera |stem of male  |plant.
-               |borne on an   |by gemmæ.)     |plant.        |(Calyptra
-               |earlier       |               |              |found on
-               |protonemal    |               |              |sporogonium
-               |stage Male    |               |              |is remnant
-               |and female    |               |              |of archeg-
-               |plants.       |               |              |    onium.)
-               |              |               |              |
-               |              |               |              |
-  -------------+--------------+---------------+--------------+----------
-
-    ----------------------------------------------------------+---------
-                              SPOROPHYTE.                     |
-               (Attached to gametophyte and dependent         |
-                        on it for nourishment.)               |
-    ---------------+--------------+------------+--------------+Beginning
-                   |  Beginning   | Sterile    |  Fertile     |  of
-                   |     of       |  Part.     |   Part.      |Gameto-
-                   | Sporophyte.  |            |              |   phyte.
-    ---------------+--------------+------------+--------------+
-    Riccia.        |Fertilized    |Wall of     |Central mass  |
-                   |egg. (Develops|sporogonium,|(archesporium)|
-                   |sporogonium.) |of one-layer|develops .....| Spores.
-                   |              |cells.      |              |
-    ---------------+--------------+------------+--------------+---------
-    Marchantia.    |Fertilized    |Sterile part|Central part  |
-                   |egg. (Develops|of stalked  |of capsule    |
-                   |sporogonium.) |capsule is  |(archesporium)| Spores.
-                   |              |stalk, wall |develops .....|
-                   |              |of capsule  |and elaters.  |
-                   |              |of several  |              |
-                   |              |layers,     |              |
-                   |              |elaters.    |              |
-    ---------------+--------------+------------+--------------+---------
-    Jungermannia   |Fertilized    |Sterile part|Central part  |
-     (or           |egg. (Develops|of stalked  |of capsule    |
-      Cephalozia,  |sporogonium.) |capsule is  |(archesporium)| Spores.
-      Porella,     |              |stalk, wall |develops .....|
-      etc.)        |              |of capsule  |and elaters.  |
-                   |              |of several  |              |
-                   |              |layers,     |              |
-                   |              |elaters.    |              |
-   ----------------+--------------+------------+--------------+---------
-    Mosses         |Fertilized    |Sterile part|Cylindrical   |
-     { Mnium,      |egg. (Develops|of stalked  |layer of      |
-     { Funaria,    |sporogonium.) |capsule is  |cells around  |
-     { Polytrichum,|              |stalk, wall |columella is  |
-     { etc.        |              |of capsule  |the           | Spores.
-                   |              |of several  |archesporium; |
-                   |              |layers,     |it            |
-                   |              |columella,  |develops .....|
-                   |              |lid, teeth  |              |
-                   |              |etc., of    |              |
-                   |              |the highly  |              |
-                   |              |specialized |              |
-                   |              |capsule.    |              |
-    ---------------+--------------+------------+--------------+---------
-
-FOOTNOTES:
-
-[29] Called the calyptra.
-
-[30] As subclass in Engler and Prantl.
-
-[31] As subclass in Engler and Prantl.
-
-[32] As subclass in Engler and Prantl.
-
-[33] As subclass in Engler and Prantl.
-
-
-
-
-CHAPTER XXVI.
-
-FERNS.
-
-
-=529.= In taking up the study of the ferns we find plants which
-are very beautiful objects of nature and thus have always attracted
-the interest of those who love the beauties of nature. But they are
-also very interesting to the student, because of certain remarkable
-peculiarities of the structure of the fruit bodies, and especially
-because of the intermediate position which they occupy within the
-plant kingdom, representing in the two phases of their development the
-primitive type of plant life on the one hand, and on the other the
-modern type. We will begin our study of the ferns by taking that form
-which is the more prominent, the fern plant itself.
-
-=530. The Christmas fern.=—One of the ferns which is very common
-in the Northern States, and occurs in rocky banks and woods, is the
-well-known Christmas fern (Aspidium acrostichoides) shown in fig. 286.
-The leaves are the most prominent part of the plant, as is the case
-with most if not all our native ferns. The stem is very short and
-for the most part under the surface of the ground, while the leaves
-arise very close together, and thus form a rosette as they rise and
-gracefully bend outward. The leaf is elongate and reminds one somewhat
-of a plume with the pinnæ extending in two rows on opposite sides of
-the midrib. These pinnæ alternate with one another, and at the base of
-each pinna is a little spur which projects upward from the upper edge.
-Such a leaf is said to be pinnate. While all the leaves have the same
-general outline, we notice that certain ones, especially those toward
-the center of the rosette, are much narrower from the middle portion
-toward the end. This is because of the shorter pinnæ here.
-
-[Illustration: Fig. 286. Christmas fern (Aspidium acrostichoides).]
-
-=531. Fruit “dots” (sorus, indusium).=—If we examine the under
-side of such short pinnæ of the Christmas fern we see that there
-are two rows of small circular dots, one row on either side of the
-pinna. These are called the “fruit dots,” or sori (a single one is a
-sorus). If we examine it with a low power of the microscope, or with
-a pocket lens, we see that there is a circular disk which covers more
-or less completely very minute objects, usually the ends of the latter
-projecting just beyond the edge if they are mature. This circular disk
-is what is called the _indusium_, and it is a special outgrowth of the
-epidermis of the leaf here for the protection of the spore-cases. These
-minute objects underneath are the fruit bodies, which in the case of
-the ferns and their allies are called _sporangia_. This indusium in the
-case of the Christmas fern, and also in some others, is attached to the
-leaf by means of a short slender stalk which is fastened to the middle
-of the under side of this shield, as seen in cross-section in fig. 292.
-
-=532. Sporangia.=—If we section through the leaf at one of the
-fruit dots, or if we tease off some of the sporangia so that the stalks
-are still attached, and examine them with the microscope, we can see
-the form and structure of these peculiar bodies. Different views of a
-sporangium are shown in fig. 293. The slender portion is the stalk,
-and the larger part is the spore-case proper. We should examine the
-structure of this spore-case quite carefully, since it will help us to
-understand better than we otherwise could the remarkable operations
-which it performs in scattering the spores.
-
-[Illustration: Fig. 287. Rhizome with bases of leaves, and roots of the
-Christmas fern.]
-
-=533. Structure of a sporangium.=—If we examine one of the
-sporangia in side view as shown in fig. 293, we note a prominent row
-of cells which extend around the margin of the dorsal edge from near
-the attachment of the stalk to the upper front angle. The cells are
-prominent because of the thick inner walls, and the thick radial walls
-which are perpendicular to the inner walls. The walls on the back of
-this row and on its sides are very thin and membranous. We should make
-this out carefully, for the structure of these cells is especially
-adapted to a special function which they perform. This row of cells is
-termed the _annulus_, which means a little ring. While this is not a
-complete ring, in some other ferns the ring is nearly complete.
-
-[Illustration: Fig. 288. Rhizome of sensitive fern (Onoclea
-sensibilis).]
-
-[Illustration: Fig. 289. Under side of pinna of Aspidium spinulosum
-showing fruit dots (sori).]
-
-=534.= In the front of the sporangium is another peculiar group
-of cells. Two of the longer ones resemble the lips of some creature,
-and since the sporangium opens between them they are sometimes termed
-the lip cells. These lip cells are connected with the upper end of the
-annulus on one side and with the upper end of the stalk on the other
-side by thin-walled cells, which may be termed connective cells, since
-they hold each lip cell to its part of the opening sporangium. The
-cells on the side of the sporangium are also thin-walled. If we now
-examine a sporangium from the back, or dorsal edge as we say, it will
-appear as in the left-hand figure. Here we can see how very prominent
-the annulus is. It projects beyond the surface of the other cells of
-the sporangium. The spores are contained inside this case.
-
-=535. Opening of the sporangium and dispersion of the spores.=—If
-we take some fresh fruiting leaves of the Christmas fern, or of any one
-of many of the species of the true ferns just at the ripening of the
-spores, and place a portion of it on a piece of white paper in a dry
-room, in a very short time we shall see that the paper is being dusted
-with minute brown objects which fly out from the leaf. Now if we take
-a portion of the same leaf and place it under the low power of the
-microscope, so that the full rounded sporangia can be seen, in a short
-time we note that the sporangium opens, the upper half curls backward
-as shown in fig. 294, and soon it snaps quickly, to near its former
-position, and the spores are at the same time thrown for a considerable
-distance. This movement can sometimes be seen with the aid of a good
-hand lens.
-
-[Illustration: Fig. 290. Four pinnæ of adiantum, showing recurved
-margins which cover the sporangia.]
-
-[Illustration: Fig. 291. Section through sorus of Polypodium vulgare
-showing different stages of sporangium, and one multicellular capitate
-hair.]
-
-=536. How does this opening and snapping of the sporangium take
-place?=—We are now more curious than ever to see just how this
-opening and snapping of the sporangium takes place. We should now mount
-some of the fresh sporangia in water and cover with a cover glass for
-microscopic examination. A drop of glycerine should be placed at one
-side of the cover glass on the slip so that the edge of the glycerine
-will come in touch with the water. Now as one looks through the
-microscope to watch the sporangia, the water should be drawn from under
-the cover glass with the aid of some bibulous paper, like filter paper,
-placed at the edge of the cover glass on the opposite side from the
-glycerine. As the glycerine takes the place of the water around the
-sporangia it draws the water out of the cells of the annulus, just as
-it took the water out of the cells of the spirogyra as we learned some
-time ago. As the water is drawn out of these cells there is produced
-a pressure from without, the atmospheric pressure upon the glycerine.
-This causes the walls of these cells of the annulus to bend inward,
-because, as we have already learned, the glycerine does not pass
-through the walls nearly so fast as the water comes out.
-
-[Illustration: Fig. 292. Section through sorus and shield-shaped
-indusium of aspidium.]
-
-=537.= Now the structure of the cells of this annulus, as we have
-seen, is such that the inner walls and the perpendicular walls are
-stout, and consequently they do not bend or collapse when this pressure
-is brought to bear on the outside of the cells. The thin membranous
-walls on the back (dorsal walls) and on the sides of the annulus,
-however, yield readily to the pressure and bend inward. This, as we
-can readily see, pulls on the ends of each of the perpendicular walls
-drawing them closer together. This shortens the outer surface of the
-annulus and causes it to first assume a nearly straight position, then
-curve backward until it quite or nearly becomes doubled on itself. The
-sporangium opens between the lip cells on the front and the lateral
-walls of the sporangium are torn directly across. The greater mass of
-spores are thus held in the upper end of the open sporangium, and when
-the annulus has nearly doubled on itself it suddenly snaps back again
-in position. While treating with the glycerine we can see all this
-movement take place. Each cell of the annulus acts independently, but
-often they all act in concert. When they do not all act in concert,
-some of them snap sooner than others, and this causes the annulus to
-snap in segments.
-
-[Illustration: Fig. 293. Rear, side, and front views of fern
-sporangium. _d_, _e_, annulus; _a_, lip cells.]
-
-[Illustration: Fig. 294. Dispersion of spores from sporangium of
-Aspidium acrostichoides, showing different stages in the opening and
-snapping of the annulus.]
-
-=538. The movements of the sporangium can take place in old and dried
-material.=—If we have no fresh material to study the sporangium
-with, we can use dried material, for the movements of the sporangia can
-be well seen in dried material, provided it was collected at about the
-time the sporangia are mature, that is at maturity, or soon afterward.
-We take some of the dry sporangia (or we may wash the glycerine off
-those which we have just studied) and mount them in water, and quickly
-examine them with a microscope. We notice that in each cell of the
-annulus there is a small sphere of some gas. The water which bathes the
-walls of the annulus is absorbed by some substance inside these cells.
-This we can see because of the fact that this sphere of gas becomes
-smaller and smaller until it is only a mere dot, when it disappears in
-a twinkling. The water has been taken in under such pressure that it
-has absorbed all the gas, and the farther pressure in most cases closes
-the partly opened sporangium more completely.
-
-=539.= Now we should add glycerine again and draw out the water,
-watching the sporangia at the same time. We see that the sporangia
-which have opened and snapped once will do it again. And so they may
-be made to go through this operation several times in succession. We
-should now note carefully the annulus, that is after the sporangia have
-opened by the use of glycerine. So soon as they have snapped in the
-glycerine we can see those minute spheres of gas again, and since there
-was no air on the outside of the sporangia, but only glycerine, this
-gas must, it is reasoned, have been given up by the water before it was
-all drawn out of the cells.
-
-=540. The common polypody.=—We may now take up a few other ferns
-for study. Another common fern is the polypody, one or more species of
-which have a very wide distribution. The stem of this fern is also not
-usually seen, but is covered with the leaves, except in the case of
-those species which grow on the surface of rocks. The stem is slender
-and prostrate, and is covered with numerous brown scales. The leaves
-are pinnate in this fern also, but we find no difference between the
-fertile and sterile leaves (except in some rare cases). The fruit dots
-occupy much the same positions on the under side of the leaf that they
-do in the Christmas fern, but we cannot find any indusium. In the place
-of an indusium are club-shaped hairs as shown in fig. 291. The enlarged
-ends of these clubs reaching beyond the sporangia give some protection
-to them when they are young.
-
-=541. Other ferns.=—We might examine a series of ferns to see
-how different they are in respect to the position which the fruit
-dots occupy on the leaf. The common brake, which sometimes covers
-extensive areas and becomes a troublesome weed, has a stout and smooth
-underground stem (rhizome) which is often 12 to 20 _cm_ beneath the
-surface of the soil. There is a long leaf stalk, which bears the
-lamina, the latter being several times pinnate. The margins of the
-fertile pinnæ are inrolled, and the sporangia are found protected
-underneath in this long sorus along the margin of the pinna. The
-beautiful maidenhair fern and its relatives have obovate pinnæ, and
-the sori are situated in the same positions as in the brake. In other
-ferns, as the walking fern, the sori are borne along by the side of the
-veins of the leaf.
-
-=542. Opening of the leaves of ferns.=—The leaves of ferns
-open in a peculiar manner. The tip of the leaf is the last portion
-developed, and the growing leaf appears as if it was rolled up as in
-fig. 287 of the Christmas fern. As the leaf elongates this portion
-unrolls.
-
-=543. Longevity of ferns.=—Most ferns live from year to year, by
-growth adding to the advance of the stem, while by decay of the older
-parts the stem shortens up behind. The leaves are short-lived, usually
-dying down each year, and a new set arising from the growing end of the
-stem. Often one can see just back or below the new leaves the old dead
-ones of the past season, and farther back the remains of the petioles
-of still older leaves.
-
-[Illustration: Fig. 295. Cystopteris bulbifera, young plant growing
-from bulb. At right is young bulb in axil of pinna of leaf.]
-
-=544. Budding of ferns.=—A few ferns produce what are called
-bulbils or bulblets on the leaves. One of these, which is found
-throughout the greater part of the eastern United States, is the
-bladder fern (Cystopteris bulbifera), which grows in shady rocky
-places. The long graceful delicate leaves form in the axils of the
-pinnæ, especially near the end of the leaf, small oval bulbs as shown
-in fig. 295. If we examine one of these bladder-like bulbs we see
-that the bulk of it is made up of short thick fleshy leaves, smaller
-ones appearing between the outer ones at the smaller end of the bulb.
-This bulb contains a stem, young root, and several pairs of these
-fleshy leaves. They easily fall to the ground or rocks, where, with
-the abundant moisture usually present in localities where the fern is
-found, the bulb grows until the roots attach the plant to the soil or
-in the crevices of the rocks. A young plant growing from one of these
-bulbils is shown in fig. 295.
-
-=545. Greenhouse ferns.=—Some of the ferns grown in
-conservatories have similar bulblets. Fig. 296 represents one of these
-which is found abundantly on the leaves of Asplenium bulbiferum. These
-bulbils have leaves which are very similar to the ordinary leaf except
-that they are smaller. The bulbs are also much more firmly attached to
-the leaf, so that they do not readily fall away.
-
-=546.= Plant conservatories usually furnish a number of very
-interesting ferns, and one should attempt to make the acquaintance of
-some of them, for here one has an opportunity during the winter season
-not only to observe these interesting plants, but also to obtain
-material for study. In the tree ferns which often are seen growing in
-such places we see examples of the massive trunks and leaves of some of
-the tropical species.
-
-[Illustration: Fig. 296. Bulbil growing from leaf of asplenium (_A_,
-bulbiferum).]
-
-=547. The fern plant is a sporophyte.=—We have now studied
-the fern plant, as we call it, and we have found it to represent
-the spore-bearing phase of the plant, that is the _sporophyte_
-(corresponding to the sporogonium of the liverworts and mosses).
-
-=548. Is there a gametophyte phase in ferns?=—But in the
-sporophyte of the fern, which we should not forget is the fern plant,
-we have a striking advance upon the sporophyte of the liverworts and
-mosses. In the latter plants the sporophyte remained attached to the
-gametophyte, and derived its nourishment from it. In the ferns, as we
-see, the sporophyte has a root of its own, and is attached to the soil.
-Through the aid of root hairs of its own it takes up mineral solutions.
-It possesses also a true stem, and true leaves in which carbon
-conversion takes place. It is able to live independently, then. Does
-a gametophyte phase exist among the ferns? Or has it been lost? If it
-does exist, what is it like, and where does it grow? From what we have
-already learned we should expect to find the gametophyte begin with the
-germination of the spores which are developed on the sporophyte, that
-is on the fern plant itself. We should investigate this and see.
-
-
-
-
-CHAPTER XXVII.
-
-FERNS CONTINUED.
-
-
-Gametophyte of ferns.
-
-=549. Sexual stage of ferns.=—We now wish to see what the sexual
-stage of the ferns is like. Judging from what we have found to take
-place in the liverworts and mosses we should infer that the form of the
-plant which bears the sexual organs is developed from the spores. This
-is true, and if we should examine old decaying logs, or decaying wood
-in damp places in the near vicinity of ferns, we should probably find
-tiny, green, thin, heart-shaped growths, lying close to the substratum.
-These are also found quite frequently on the soil of pots in plant
-conservatories where ferns are grown. Gardeners also in conservatories
-usually sow fern spores to raise new fern plants, and usually one can
-find these heart-shaped growths on the surface of the soil where they
-have sown the spores. We may call the gardener to our aid in finding
-them in conservatories, or even in growing them for us if we cannot
-find them outside. In some cases they may be grown in an ordinary room
-by keeping the surfaces where they are growing moist, and the air also
-moist, by placing a glass bell jar over them.
-
-[Illustration: Fig. 297. Prothallium of fern, under side, showing
-rhizoids, antheridia scattered among and near them, and the archegonia
-near the sinus.]
-
-=550.= In fig. 297 is shown one of these growths enlarged. Upon
-the under side we see numerous thread-like outgrowths, the rhizoids,
-which attach the plant to the substratum, and which act as organs for
-the absorption of nourishment. The sexual organs are borne on the under
-side also, and we will study them later. This heart-shaped, flattened,
-thin, green plant is the _prothallium_ of ferns, and we should now give
-it more careful study, beginning with the germination of the spores.
-
-[Illustration: Fig. 298. Spore of Pteris serrulata showing the
-three-rayed elevation along the side of which the spore wall cracks
-during germination.]
-
-[Illustration: Fig. 299. Spore of Aspidium acrostichoides with winged
-exospore.]
-
-[Illustration: Fig. 300. Spore crushed to remove exospore and show
-endospore.]
-
-=551. Spores.=—We can easily obtain material for the study of the
-spores of ferns. The spores vary in shape to some extent. Many of them
-are shaped like a three-sided pyramid. One of these is shown in fig.
-298. The outer wall is roughened, and on one end are three elevated
-ridges which radiate from a given point. A spore of the Christmas fern
-is shown in fig. 299. The outer wall here is more or less winged. At
-fig. 300 is a spore of the same species from which the outer wall has
-been crushed, showing that there is an inner wall also. If possible we
-should study the germination of the spores of some fern.
-
-=552. Germination of the spores.=—After the spores have been
-sown for about one week to ten days we should mount a few in water for
-examination with the microscope in order to study the early stages. If
-germination has begun, we find that here and there are short slender
-green threads, in many cases attached to brownish bits, the old walls
-of the spores. Often one will sow the sporangia along with the spores,
-and in such cases there may be found a number of spores still within
-the old sporangium wall that are germinating, when they will appear as
-in fig. 302.
-
-[Illustration: Fig. 301. Spores of asplenium; exospore removed from the
-one at the right.]
-
-[Illustration: Fig. 302. Germinating spores of Pteris aquilina still in
-the sporangium.]
-
-[Illustration: Fig. 303. Young prothallium of a fern (niphobolus).]
-
-=553. Protonema.=—These short green threads are called
-_protonemal_ threads, or _protonema_, which means a _first thread_, and
-it here signifies that this short thread only precedes a larger growth
-of the same object. In figs. 302, 303 are shown several stages of
-germination of different spores. Soon after the short germ tube emerges
-from the crack in the spore wall, it divides by the formation of a
-cross wall, and as it increases in length other cross walls are formed.
-But very early in its growth we see that a slender outgrowth takes
-place from the cell nearest the old spore wall. This slender thread is
-colorless, and is not divided into cells. It is the first rhizoid, and
-serves both as an organ of attachment for the thread, and for taking up
-nutriment.
-
-=554. Prothallium.=—Very soon, if the sowing has not been so
-crowded as to prevent the young plants from obtaining nutriment
-sufficient, we will see that the end of this protonema is broadening,
-as shown in fig. 303. This is done by the formation of the cell walls
-in different directions. It now continues to grow in this way, the end
-becoming broader and broader, and new rhizoids are formed from the
-under surface of the cells. The growing point remains at the middle of
-the advancing margin, and the cells which are cut off from either side,
-as they become old, widen out. In this way the “wings,” or margins of
-the little, green, flattened body, are in advance of the growing point,
-and the object is more or less heart-shaped, as shown in fig. 297. Thus
-we see how the prothallium of ferns is formed.
-
-=555. Sexual organs of ferns.=—If we take one of the prothallia
-of ferns which have grown from the sowings of fern spores, or one of
-those which may be often found growing on the soil of pots in
-conservatories, mount it in water on a slip, with the under side
-uppermost, we can then examine it for the sexual organs, for these are
-borne in most cases on the under side.
-
-[Illustration: Fig. 304. Male prothallium of a fern (niphobolus), in
-form of an alga or protonema. Spermatozoids escaping from antheridia.]
-
-[Illustration: Fig. 305. Male prothallium of fern (niphobolus), showing
-opened and unopened antheridia; section of unopened antheridium;
-spermatozoids escaping; spermatozoids which did not escape from the
-antheridium.]
-
-=556. Antheridia.=—If we search among the rhizoids we see small
-rounded elevations as shown in fig. 297 or 305 scattered over this
-portion of the prothallium. These are the antheridia. If the prothallia
-have not been watered for a day or so, we may have an opportunity of
-seeing the spermatozoids coming out of the antheridium, for when the
-prothallia are freshly placed in water the cells of the antheridium
-absorb water. This presses on the contents of the antheridium
-and bursts the cap cell if the antheridium is ripe, and all the
-spermatozoids are shot out. We can see here that each one is shaped
-like a screw, with the coils at first close. But as the spermatozoid
-begins to move this coil opens somewhat and by the vibration of the
-long cilia which are on the smaller end it whirls away. In such
-preparations one may often see them spinning around for a long while,
-and it is only when they gradually come to rest that one can make out
-their form.
-
-[Illustration: Fig. 306. Section of antheridia showing sperm cells, and
-spermatozoids in the one at the right.]
-
-[Illustration: Fig. 307. Different views of spermatozoids; in a quiet
-condition; in motion (Adiantum concinnum).]
-
-[Illustration: Fig. 308. Archegonium of fern. Large cell in the center
-is the egg, next is the ventral canal cell, and in the canal of the
-neck are two nuclei of the canal cell.]
-
-[Illustration: Fig. 309. Mature and open archegonium of fern (Adiantum
-cuneatum) with spermatozoids making their way down through the slime to
-the egg.]
-
-[Illustration: Fig. 310. Fertilization in a fern (Marattia). _sp_,
-spermatozoid fusing with the nucleus of the egg. (After Campbell.)]
-
-=557. Archegonia.=—If we now examine closely on the thicker part
-of the under surface of the prothallium, just back of the “sinus,” we
-may see longer stout projections from the surface of the prothallium.
-These are shown in fig. 297. They are the archegonia. One of them in
-longisection is shown in fig. 308. It is flask-shaped, and the broader
-portion is sunk in the tissue of the prothallium. The egg is in the
-larger part. The spermatozoids when they are swimming around over the
-under surface of the prothallium come near the neck, and here they are
-caught in the viscid substance which has oozed out of the canal of the
-archegonium. From here they slowly swim down the canal, and finally one
-sinks into the egg, fuses with the nucleus of the latter, and the egg
-is then fertilized. It is now ready to grow and develop into the fern
-plant. This brings us back to the sporophyte, which begins with the
-fertilized egg.
-
-
-Sporophyte.
-
-=558. Embryo.=—The egg first divides into two cells as shown in
-fig. 228, then into four. Now from each one of these quadrants of the
-embryo a definite part of the plant develops, from one the first leaf,
-from one the stem, from one the root, and from the other the organ
-which is called the foot, and which attaches the embryo to the
-prothallium, and transports nourishment for the embryo until it can
-become attached to the soil and lead an independent existence. During
-this time the wall of the archegonium grows somewhat to accommodate the
-increase in size of the embryo, as shown in figs. 312, 313. But soon
-the wall of the archegonium is ruptured and the embryo emerges, the
-root attaches itself to the soil, and soon the prothallium dies.
-
-[Illustration: Fig. 311. Two-celled embryo of Pteris serrulata. Remnant
-of archegonium neck below.]
-
-The embryo is first on the under side of the prothallium, and the first
-leaf and the stem curves upward between the lobes of the heart-shaped
-body, and then grows upright as shown in fig. 314. Usually only one
-embryo is formed on a single prothallium, but in one case I found a
-prothallium with two well-formed embryos, which are figured in 315.
-
-=559. Comparison of ferns with liverworts and mosses.=—In the
-ferns then we have reached a remarkable condition of things as compared
-with that which we found in the mosses and liverworts. In the mosses
-and liverworts the sexual phase of the plant (gametophyte) was the
-prominent one, and consisted of either a thallus or a leafy axis,
-but in either case it bore the sexual organs and led an independent
-existence; that is it was capable of obtaining its nourishment from the
-soil or water by means of organs of absorption belonging to itself, and
-it also performed the office of photosynthesis.
-
-[Illustration: Fig. 312. Young embryo of fern (Adiantum concinnum)
-in enlarged venter of the archegonium. _S_, stem; _L_, first leaf or
-cotyledon; _R_, root; _F_, foot.]
-
-=560.= The spore-bearing phase (sporophyte) of the liverworts
-and mosses, on the other hand, is quite small as compared with the
-sexual stage, and it is completely dependent on the sexual stage for
-its nourishment, remaining attached permanently throughout all its
-development, by means of the organ called a foot, and it dies after the
-spores are mature.
-
-=561.= Now in the ferns we see several striking differences. In
-the first place, as we have already observed, the spore-bearing phase
-(sporophyte) of the plant is the prominent one, and that which
-characterizes the plant. It also leads an independent existence, and,
-with the exception of a few cases, does not die after the development
-of the spores, but lives from year to year and develops successive
-crops of spores. There is a _distinct advance_ here in the _size_,
-_complexity_, and _permanency_ of this phase of the plant.
-
-=562.= On the other hand the sexual phase of the ferns
-(gametophyte), while it still is capable of leading an independent
-existence, is short-lived (with very few exceptions). It is also much
-smaller than most of the liverworts and mosses, especially as compared
-with the size of the spore-bearing phase. The gametophyte phase or
-stage of the plants, then, is decreasing in size and durance as the
-sporophyte stage is increasing. We shall be interested to see if this
-holds good of the fern allies, that is of the plants which belong to
-the same group as the ferns. And as we come later to take up the study
-of the higher plants we must bear in mind to carry on this comparison,
-and see if this progression on the one hand of the sporophyte
-continues, and if the retrogression of the gametophyte continues also.
-
-[Illustration: Fig. 313. Embryo of fern (Adiantum concinnum) still
-surrounded by the archegonium, which has grown in size, forming the
-“calyptra.” _L_, leaf; _S_, stem; _R_, root; _F_, foot.]
-
-[Illustration: Fig. 314. Young plant of Pteris serrulata still attached
-to prothallium.]
-
-[Illustration: Fig. 315. Two embryos from one prothallium of Adiantum
-cuneatum.]
-
-
-
-
-CHAPTER XXVIII.
-
-DIMORPHISM OF FERNS.
-
-
-=563.= In comparing the different members of the leaf series there
-are often striking illustrations of the transition from one form to
-another, as we have noted in the case of the trillium flower. This
-occurs in many other flowers, and in some, as in the water-lily, these
-transformations are always present, here showing a transition from the
-petals to the stamens. In the bud-scales of many plants, as in the
-butternut, walnut, currant, etc., there are striking gradations between
-the form of the simple bud-scales and the form of the leaf. Some of the
-most interesting of these transformations are found in the dimorphic
-ferns.
-
-=564. Dimorphism in the leaves of ferns.=—In the common polypody
-fern, the maidenhair, and in many other ferns, all the leaves are of
-the same form. That is, there is no difference between the fertile leaf
-and the sterile leaf. On the other hand, in the case of the Christmas
-fern we have seen that the fertile leaves are slightly different from
-the sterile leaves, the former having shorter pinnæ on the upper half
-of the leaf. The fertile pinnæ are here the shorter ones, and perform
-but little of the function of carbon conversion. This function is
-chiefly performed by the sterile leaves and by the sterile portions of
-the fertile leaves. This is a short step toward the division of labor
-between the two kinds of leaves, one performing chiefly the labor of
-carbon conversion, the other chiefly the labor of bearing the fruit.
-
-[Illustration: Fig. 316. Sensitive fern; normal condition of vegetative
-leaves and sporophylls.]
-
-=565. The sensitive fern.=—This division of labor is carried to
-an extreme extent in the case of some ferns. Some of our native ferns
-are examples of this interesting relation between the leaves like
-the common sensitive fern (Onoclea sensibilis) and the ostrich fern
-(O. struthiopteris) and the cinnamon-fern (Osmunda cinnamomea). The
-sensitive fern is here shown in fig. 316. The sterile leaves are large,
-broadly expanded, and pinnate, the pinnæ being quite large. The fertile
-leaves are shown also in the figure, and at first one would not take
-them for leaves at all. But if we examine them carefully we see that
-the general plan of the leaf is the same: the two rows of pinnæ which
-are here much shorter than in the sterile leaf, and the pinnules, or
-smaller divisions of the pinnæ, are inrolled into little spherical
-masses which lie close on the side of the pinnæ. If we unroll one
-of these pinnules we find that there are several fruit dots within
-protected by this roll. In fact when the spores are mature these
-pinnules open somewhat, so that the spores may be disseminated.
-
-[Illustration: Fig. 317. Sensitive fern; one fertile leaf nearly
-changed to vegetative leaf.]
-
-There is very little green color in these fertile leaves, and what
-green surface there is is very small compared with that of the broad
-expanse of the sterile leaves. So here there is practically a complete
-division of labor between these two kinds of leaves, the general plan
-of which is the same, and we recognize each as being a leaf.
-
-[Illustration: Fig. 318. Sensitive fern, showing one vegetative leaf
-and two sporophylls completely transformed.]
-
-=566. Transformation of the fertile leaves of onoclea to sterile
-ones.=—It is not a very rare thing to find plants of the sensitive
-fern which show intermediate conditions of the sterile and the
-fertile leaf. A number of years ago it was thought by some that this
-represented a different species, but now it is known that these
-intermediate forms are partly transformed fertile leaves. It is a
-very easy matter in the case of the sensitive fern to produce these
-transformations by experiment. If one in the spring, when the sterile
-leaves attain a height of 12 to 16 _cm_ (8-10 inches), cuts them away,
-and again when they have a second time reached the same height, some
-of the fruiting leaves which develop later will be transformed. A few
-years ago I cut off the sterile leaves from quite a large patch of
-the sensitive fern, once in May, and again in June. In July, when
-the fertile leaves were appearing above the ground, many of them
-were changed partly or completely into sterile leaves. In all some
-thirty plants showed these transformations, so that every conceivable
-gradation was obtained between the two kinds of leaves.
-
-[Illustration: Fig. 319. Normal and transformed sporophyll of sensitive
-fern.]
-
-=567.= It is quite interesting to note the form of these changed
-leaves carefully, to see how this change has affected the pinnæ and the
-sporangia. We note that the tip of the leaf as well as the tips of all
-the pinnæ are more expanded than the basal portions of the same.
-This is due to the fact that the tip of the leaf develops later
-than the basal portions. At the time the stimulus to the change in
-the development of the fertile leaves reached them they were partly
-formed, that is the basal parts of the fertile leaves were more or less
-developed and fixed and could not change. Those portions of the leaf,
-however, which were not yet completely formed, under this stimulus, or
-through correlation of growth, are incited to vegetative growth, and
-expand more or less completely into vegetative leaves.
-
-=568. The sporangia decrease as the fertile leaf expands.=—If
-we now examine the sporangia on the successive pinnæ of a partly
-transformed leaf we find that in case the lower pinnæ are not changed
-at all, the sporangia are normal. But as we pass to the pinnæ which
-show increasing changes, that is those which are more and more
-expanded, we see that the number of sporangia decrease, and many of
-them are sterile, that is they bear no spores. Farther up there are
-only rudiments of sporangia, until on the more expanded pinnæ sporangia
-are no longer formed, but one may still see traces of the indusium.
-On some of the changed leaves the only evidences that the leaf began
-once to form a fertile leaf are the traces of these indusia. In some of
-these cases the transformed leaf was even larger than the sterile leaf.
-
-=569. The ostrich fern.=—Similar changes were also produced in
-the case of the ostrich fern, and in fig. 319 is shown at the left a
-normal fertile leaf, then one partly changed, and at the right one
-completely transformed.
-
-=570. Dimorphism in tropical ferns.=—Very interesting forms
-of dimorphism are seen in some of the tropical ferns. One of these
-is often seen growing in plant conservatories, and is known as the
-staghorn fern (Platycerium alcicorne). This in nature grows attached to
-the trunks of quite large trees at considerable elevations on the tree,
-sometimes surrounding the tree with a massive growth. One kind of leaf,
-which may be either fertile or sterile, is narrow, and branched in a
-peculiar manner, so that it resembles somewhat the branching of the
-horn of a stag. Below these are other leaves which are different in
-form and sterile. These leaves are broad and hug closely around the
-roots and bases of the other leaves. Here they serve to catch and
-retain moisture, and they also catch leaves and other vegetable matter
-which falls from the trees. In this position the leaves decay and then
-serve as food for the fern.
-
-[Illustration: Fig. 320. Ostrich fern, showing one normal sporophyll,
-one partly transformed, and one completely transformed.]
-
-
-
-
-CHAPTER XXIX.
-
-HORSETAILS.
-
-
-=571.= Among the relatives of the ferns are the horsetails, so
-called because of the supposed resemblance of the branched stems of
-some of the species to a horse’s tail, as one might infer from the
-plant shown in fig. 325. They do not bear the least resemblance to the
-ferns which we have been studying. But then relationship in plants does
-not depend on mere resemblance of outward form, or of the prominent
-part of the plant.
-
-[Illustration: Fig. 321. Portion of fertile plant of Equisetum arvense
-showing whorls of leaves and the fruiting spike.]
-
-=572. The field equisetum. Fertile shoots.=—Fig. 321 represents
-the common horsetail (Equisetum arvense). It grows in moist sandy
-or gravelly places, and the fruiting portion of the plant (for this
-species is dimorphic), that is the portion which bears the spores,
-appears above the ground early in the spring. It is one of the first
-things to peep out of the recently frozen ground. This fertile shoot
-of the plant does not form its growth this early in the spring. Its
-development takes place under the ground in the autumn, so that with
-the advent of spring it pushes up without delay. This shoot is from
-10 to 20 _cm_. high, and at quite regular intervals there are slight
-enlargements, the nodes of the stem. The cylindrical portions between
-the nodes are the internodes. If we examine the region of the
-internodes carefully we note that there are thin membranous scales,
-more or less triangular in outline, and connected at their bases into a
-ring around the stem. Curious as it may seem, these are the leaves of
-the horsetail. The stem, if we examine it farther, will be seen to
-possess numerous ridges which extend lengthwise and which alternate
-with furrows. Farther, the ridges of one node alternate with those of
-the internode both above and below. Likewise the leaves of one node
-alternate with those of the nodes both above and below.
-
-[Illustration: Fig. 322. Peltate sporophyll of equisetum (side view)
-showing sporangia on under side.]
-
-=573. Sporangia.=—The end of this fertile shoot we see possesses
-a cylindrical to conic enlargement. This is the _fertile spike_, and we
-note that its surface is marked off into regular areas if the spores
-have not yet been disseminated. If we dissect off a few of these
-portions of the fertile spike, and examine one of them with a low
-magnifying power, it will appear like the fig. 322. We see here that
-the angular area is a disk-shaped body, with a stalk attached to its
-inner surface, and with several long sacs projecting from its inner
-face parallel with the stalk and surrounding the same. These elongated
-sacs are the _sporangia_, and the disk which bears them, together with
-the stalk which attaches it to the stem axis, is the _sporophyll_, and
-thus belongs to the leaf series. These sporophylls are borne in close
-whorls on the axis.
-
-=574. Spores.=—When the spores are ripe the tissue of the
-sporangium becomes dry, and it cracks open and the spores fall out.
-If we look at fig. 323 we see that the spore is covered with a very
-singular coil which lies close to the wall. When the spore dries this
-uncoils and thus rolls the spore about. Merely breathing upon these
-spores is sufficient to make them perform very curious evolutions by
-the twisting of these four coils which are attached to one place of the
-wall. They are formed by the splitting up of an outer wall of the spore.
-
-=575. Sterile shoot of the common horsetail.=—When the spores are
-ripe they are soon scattered, and then the fertile shoot dies down.
-Soon afterward, or even while some of the fertile shoots are still in
-good condition, sterile shoots of the plant begin to appear above the
-ground. One of these is shown in fig. 325. This has a much more slender
-stem and is provided with numerous branches. If we examine the stem of
-this shoot, and of the branches, we see that the same kind of leaves
-are present and that the markings on the stem are similar. Since the
-leaves of the horsetail are membranous and not green, the stem is green
-in color, and this performs the function of photosynthesis. These green
-shoots live for a great part of the season, building up material which
-is carried down into the underground stems, where it goes to supply the
-forming fertile shoots in the fall. On digging up some of these plants
-we see that the underground stems are often of great extent, and that
-both fertile and sterile shoots are attached to one and the same.
-
-[Illustration: Fig. 323. Spore of equisetum with elaters coiled up.]
-
-[Illustration: Fig. 324. Spore of equisetum with elaters uncoiled.]
-
-[Illustration: Fig. 325. Sterile plant of horsetail (Equisetum
-arvensis).]
-
-=576. The scouring rush, or shave grass.=—Another common species
-of horsetail in the Northern States grows on wet banks, or in sandy
-soil which contains moisture along railroad embankments. It is the
-scouring rush (E. hyemale), so called because it was once used for
-polishing purposes. This plant like all the species of the horsetails
-has underground stems. But unlike the common horsetail, there is but
-one kind of aerial shoot, which is green in color and fertile. The
-shoots range as high as one meter or more, and are quite stout. The new
-shoots which come up for the year are unbranched, and bear the fertile
-spike at the apex. When the spores are ripe the apex of the shoot dies,
-and the next season small branches may form from a number of the nodes.
-
-=577. Gametophyte of equisetum.=—The spores of equisetum have
-chlorophyll when they are mature, and they are capable of germinating
-as soon as mature. The spores are all of the same kind as regards size,
-just as we found in the case of the ferns. But they develop prothallia
-of different sizes, according to the amount of nutriment which they
-obtain. Those which obtain but little nutriment are smaller and develop
-only antheridia, while those which obtain more nutriment become larger,
-more or less branched, and develop archegonia. This character of an
-independent prothallium (gametophyte) with the characteristic sexual
-organs, and the also independent sporophyte, with spores, shows the
-relationship of the horsetails with the ferns. We thus see that these
-characters of the reproductive organs, and the phases and fruiting of
-the plant, are more essential in determining relationships of plants
-than the mere outward appearances.
-
-
-
-
-CHAPTER XXX.
-
-CLUB MOSSES.
-
-
-[Illustration: Fig. 326. Lycopodium clavatum, branch bearing two
-fruiting spikes; at right sporophyll with open sporangium; single spore
-near it.]
-
-=578.= What are called the “club mosses” make up another group
-of interesting plants which rank as allies of the ferns. They are not
-of course true mosses, but the general habit of some of the smaller
-species, and especially the form and size of the leaves, suggest a
-resemblance to the larger of the moss plants.
-
-=579. The clavate lycopodium.=—Here is one of the club mosses
-(fig. 326) which has a wide distribution and which is well entitled to
-hold the name of club because of the form of the upright club-shaped
-branches. As will be seen from the illustration, it has a prostrate
-stem. This stem runs for considerable distances on the surface of the
-ground, often partly buried in the leaves, and sometimes even buried
-beneath the soil. The leaves are quite small, are flattened-awl-shaped,
-and stand thickly over the stem, arranged in a spiral manner, which
-is the usual arrangement of the leaves of the club mosses. Here and
-there are upright branches which are forked several times. The end of
-one or more of these branches becomes produced into a slender upright
-stem which is nearly leafless, the leaves being reduced to mere scales.
-The end of this leafless branch then terminates in one or several
-cylindrical heads which form the club.
-
-=580. Fruiting spike of Lycopodium clavatum.=—This club is the
-fruiting spike or head (sometimes termed a _strobilus_). Here the
-leaves are larger again and broader, but still not so large as the
-leaves on the creeping shoots, and they are paler. If we bend down some
-of the leaves, or tear off a few, we see that in the axil of the leaf,
-where it joins the stem, there is a somewhat rounded, kidney-shaped
-body. This is the spore-case or sporangium, as we can see by an
-examination of its contents. There is but a single spore-case for each
-of the fertile leaves (sporophyll). When it is mature, it opens by a
-crosswise slit as seen in fig. 326. When we consider the number of
-spore-cases in one of these club-shaped fruit bodies we see that the
-number of spores developed in a large plant is immense. In mass the
-spores make a very fine, soft powder, which is used for some kinds of
-pyrotechnic material, and for various toilet purposes.
-
-[Illustration: Fig. 327. Lycopodium lucidulum, bulbils in axils of
-leaves near the top, sporangia in axils of leaves below them. At right
-is a bulbil enlarged.]
-
-=581. Lycopodium lucidulum.=—Another common species is figured
-at 327. This is Lycopodium lucidulum. The habit of the plant is quite
-different. It grows in damp ravines, woods, and moors. The older
-parts of the stem are prostrate, while the branches are more or less
-ascending. It branches in a forked manner. The leaves are larger than
-in the former species, and they are all of the same size, there being
-no appreciable difference between the sterile and fertile ones. The
-characteristic club is not present here, but the spore-cases occupy
-certain regions of the stem, as shown at 327. In a single season one
-region of the stem may bear spore-cases, and then a sterile portion
-of the same stem is developed, which later bears another series of
-spore-cases higher up.
-
-=582. Bulbils on Lycopodium lucidulum.=—There is one curious way
-in which this club moss multiplies. One may see frequently among the
-upper leaves small wedge-shaped or heart-shaped green bodies but little
-larger than the ordinary leaves. These are little buds which contain
-rudimentary shoot and root and several thick green leaves. When they
-fall to the ground they grow into new lycopodium plants, just as the
-bulbils of cystopteris do which were described in the chapter on ferns.
-
-=583.= Note.—The prothallia of the species of lycopodium which
-have been studied are singular objects. In L. cernuum a cylindrical
-body sunk in the earth is formed, and from the upper surface there
-are green lobes. In L. phlegmaria and some others slender branched,
-colorless bodies are formed which according to Treub grow as a
-saphrophyte in decayed bark of trees. Many of the prothallia examined
-have a fungus growing in their tissue which is supposed to play some
-part in the nutrition of the prothallium.
-
-
-The little club mosses (selaginella).
-
-=584.= Closely related to the club mosses are the selaginellas.
-These plants resemble closely the general habit of the club mosses, but
-are generally smaller and the leaves more delicate. Some species are
-grown in conservatories for ornament, the leaves of such usually having
-a beautiful metallic lustre. The leaves of some are arranged as in
-lycopodium, but many species have the leaves in four to six rows. Fig.
-328 represents a part of a selaginella plant (S. apus). The fruiting
-spike possesses similar leaves, but they are shorter, and their
-arrangement gives to the spike a four-sided appearance.
-
-[Illustration: Fig. 328. Selaginella with three fruiting spikes.
-(Selaginella apus.)]
-
-[Illustration: Fig. 329. Fruiting spike showing large and small
-sporangia.]
-
-[Illustration: Fig. 330. Large sporangium.]
-
-[Illustration: Fig. 331. Small sporangium.]
-
-=585. Sporangia.=—On examining the fruiting spike, we find as
-in lycopodium that there is but a single sporangium in the axil of a
-fertile leaf. But we see that they are of two different kinds, small
-ones in the axils of the upper leaves, and large ones in the axils of
-a few of the lower leaves of the spike. The _microspores_ are borne
-in the smaller spore-cases and the _macrospores_ in the larger ones.
-Figures 329-331 give the details. There are many microspores in a
-single small spore-case, but 3-4 macrospores in a large spore-case.
-
-=586. Male prothallia.=—The prothallia of selaginella are much
-reduced structures. The microspores when mature are already divided
-into two cells. When they grow into the mature prothallium a few more
-cells are formed, and some of the inner ones form the spermatozoids,
-as seen in fig. 332. Here we see that the antheridium itself is larger
-than the prothallia. Only antheridia are developed on the prothallia
-formed from the microspores, and for this reason the prothallia are
-called _male prothallia_. In fact a male prothallium of selaginella is
-nearly all antheridium, so reduced has the gametophyte become here.
-
-[Illustration: Fig. 332. Details of microspore and male prothallium
-of selaginella; 1st, microspore; 2d, wall removed to show small
-prothallial cell below; 3d, mature male prothallium still within the
-wall; 4th, small cell below is the prothallial cell, the remainder is
-antheridium with wall and four sperm cells within; 5th spermatozoid.
-After Beliaieff and Pfeffer.]
-
-=587. Female prothallia.=—The female prothallia are developed
-from the macrospores. The macrospores when mature have a rough, thick,
-hard wall. The female prothallium begins to develop inside of the
-macrospore before it leaves the sporangium. The protoplasm is richer
-near the wall of the spore and at the upper end. Here the nucleus
-divides a great many times, and finally cell walls are formed, so
-that a tissue of considerable extent is formed inside the wall of the
-spore, which is very different from what takes place in the ferns we
-have studied. As the prothallium matures the spore is cracked at the
-point where the three angles meet, as shown in fig. 334. The archegonia
-are developed in this exposed surface, and several can be seen in the
-illustration.
-
-[Illustration: Fig. 333. Section of mature macrospore of selaginella,
-showing female prothallium and archegonia. After Pfeffer.]
-
-[Illustration: Fig. 334. Mature female prothallium of selaginella,
-just bursting open the wall of macrospore, exposing archegonia. After
-Pfeffer.]
-
-[Illustration: Fig. 335. Seedling of selaginella still attached to the
-macrospore. After Campbell.]
-
-=588. Embryo.=—After fertilization the egg divides in such a way
-that a long cell called a suspensor is cut off from the upper side,
-which elongates and pushes the developing embryo down into the center
-of the spore, or what is now the female prothallium. Here it derives
-nourishment from the tissues of the prothallium, and eventually the
-root and stem emerge, while a process called the “foot” is still
-attached to the prothallium. When the root takes hold on the soil the
-embryo becomes free.
-
-
-
-
-CHAPTER XXXI.
-
-QUILLWORTS (ISOETES).
-
-
-[Illustration: Fig. 336. Isoetes, mature plant, sporophyte stage.]
-
-=589.= The quillworts, as they are popularly called, are very
-curious plants. They grow in wet marshy places. They receive their
-name from the supposed resemblance of the leaf to a quill. Fig. 336
-represents one of these quillworts (Isoetes engelmannii). The leaves
-are the prominent part of the plant, and they are about all that can
-be seen except the roots, without removing the leaves. Each leaf, it
-will be seen, is long and needle-like, except the basal part, which
-is expanded, not very unlike, in outline, a scale of an onion. These
-expanded basal portions of the leaves closely overlap each other, and
-the very short stem is completely covered at all times. Fig. 338 is
-from a longitudinal section of a quillwort. It shows the form of the
-leaves from this view (side view), and also the general outline of the
-short stem, which is triangular. The stem is therefore a very short
-object.
-
-=590. Sporangia of isoetes.=—If we pull off some of the leaves of
-the plant we see that they are somewhat spoon-shaped as in fig. 337. In
-the inner surface of the expanded base we note a circular depression
-which seems to be of a different texture from the other portions of the
-leaf. This is a _sporangium_. Beside the spores on the inside of the
-sporangium, there are strands of sterile tissue which extend across the
-cavity. This is peculiar to isoetes of all the members of the class
-of plants to which the ferns belong, but it will be remembered that
-sterile strands of tissue are found in some of the liverworts in the
-form of elaters.
-
-[Illustration: Fig. 337. Base of leaf of isoetes, showing sporangium
-with macrospores. (Isoetes engelmannii.)]
-
-[Illustration: Fig. 338. Section of plant of Isoetes engelmannii,
-showing cup-shaped stem, and longitudinal sections of the sporangia in
-the thickened bases of the leaves.]
-
-=591.= The spores of isoetes are of two kinds, small ones
-(microspores) and large ones (macrospores), so that in this respect
-it agrees with selaginella, though it is so very different in other
-respects. When one kind of spore is borne in a sporangium usually all
-in that sporangium are of the same kind, so that certain sporangia
-bear microspores, and others bear macrospores. But it is not uncommon
-to find both kinds in the same sporangium. When a sporangium bears
-only microspores the number is much greater than when one bears only
-macrospores.
-
-=592.= If we examine some of the microspores of isoetes we see
-that they are shaped like the quarters of an apple, that is they are of
-the bilateral type as seen in some of the ferns (asplenium).
-
-=593. Male prothallia.=—In isoetes, as in selaginella, the
-microspores develop only male prothallia, and these are very
-rudimentary, one division of the spore having taken place before the
-spore is mature, just as in selaginella.
-
-=594. Female prothallia.=—These are developed from the
-macrospores. The latter are of the tetrahedral type. The development
-of the female prothallium takes place in much the same way as in
-selaginella, the entire prothallium being enclosed in the macrospore,
-though the cell divisions take place after it has left the sporangium.
-When the archegonia begin to develop the macrospore cracks at the three
-angles and the surface bearing the archegonia projects slightly as in
-selaginella. Absorbing organs in the form of rhizoids are very rarely
-formed.
-
-=595. Embryo.=—The embryo lies well immersed in the tissue of the
-prothallium, though there is no suspensor developed as in selaginella.
-
-
-
-
-CHAPTER XXXII.
-
-COMPARISON OF FERNS AND THEIR RELATIVES.
-
-
-=596. Comparison of selaginella and isoetes with the ferns.=—On
-comparing selaginella and isoetes with the ferns, we see that the
-sporophyte is, as in the ferns, the prominent part of the plant. It
-possesses root, stem, and leaves. While these plants are not so large
-in size as some of the ferns, still we see that there has been a great
-advance in the sporophyte of selaginella and isoetes upon what exists
-in the ferns. There is a division of labor between the sporophylls,
-in which some of them bear microsporangia with microspores, and some
-bear macrosporangia with only macrospores. In the ferns and horsetails
-there is only one kind of sporophyll, sporangium, and spore in a
-species. By this division of labor, or differentiation, between the
-sporophylls, one kind of spore, the microspore, is compelled to form
-a male prothallium, while the other kind of spore, the macrospore, is
-compelled to form a female prothallium. This represents a progression
-of the sporophyte of a very important nature.
-
-=597.= On comparing the gametophyte of selaginella and isoetes
-with that of the ferns, we see that there has been a still farther
-retrogression in size from that which we found in the independent and
-large gametophyte of the liverworts and mosses. In the ferns, while it
-is reduced, it still forms rhizoids, and leads an independent life,
-absorbing its own nutrient materials, and assimilating carbon. In
-selaginella and isoetes the gametophyte does not escape from the spore,
-nor does it form absorbing organs, nor develop assimilative tissue.
-The reduced prothallium develops at the expense of food stored by the
-sporophyte while the spore is developing. Thus, while the gametophyte
-is separate from the sporophyte in selaginella and isoetes, it is
-really dependent on it for support or nourishment.
-
-=598.= The important general characters possessed by the ferns
-and their so-called allies, as we have found, are as follows: The
-spore-bearing part, which is the fern plant, leads an independent
-existence from the prothallium, and forms root, stem, and leaves. The
-spores are borne in sporangia on the leaves. The prothallium also leads
-an independent existence, though in isoetes and selaginella it has
-become almost entirely dependent on the sporophyte. The prothallium
-bears also well-developed antheridia and archegonia. The root, stem,
-and leaves of the sporophyte possess vascular tissue. All the ferns and
-their allies agree in the possession of these characters. The mosses
-and liverworts have well-developed antheridia and archegonia, and the
-higher plants have vascular tissue. But no plant of either of these
-groups possesses the combined characters which we find in the ferns and
-their relatives. The latter are, therefore, the fern-like plants, or
-_pteridophyta_. The living forms of the pteridophyta are classified as
-follows into families or orders. (See page 295.)
-
-=599.= TABLE SHOWING RELATION OF GAMETOPHYTE AND SPOROPHYTE IN THE
-PTERIDOPHYTES.
-
-    --------------------------------------------------------------------
-                 GAMETOPHYTE. (Becoming smaller, mostly independent.
-      In selaginella and isoetes becoming dependent on the sporophyte.)
-    ---------------+-----------------------+----------------------------
-                   |  Vegetative Part.     |    Sexual Organs.
-    ---------------+-----------------------+
-    Ferns.         |A green, thin,         |    Usually both kinds on
-    (Polypodiaceæ.)|expanded,              |     the same prothallium.
-                   |heart-shaped growth,   +---------------+------------
-                   |with rhizoids.         |Antheridia with|Archegonia,
-                   |                       |spermatozoids. |each with
-                   |                       |               |egg.
-   ----------------+-----------------------+---------------+------------
-    Equisetum.     |A green, thin,         |    Usually the two kinds
-                   |expanded,              |   on different prothallia.
-                   |lobed growth,          +---------------+------------
-                   ||with rhizoids.        |Antheridia, on |Archegonia
-                   |                       |small male     |on larger
-                   |                       |prothallia,    |female
-                   |                       |with           |prothallia,
-                   |                       |spermatozoids. |each with
-                   |                       |               |an egg.
-    ---------------+-----------------------+---------------+------------
-    Isoetes.       |Colorless, rounded     |
-                   |mass of cells,         |
-                   |inside of spore wall,  |
-                   |usually no rhizoids,   |  On different prothallia.
-                   |or but few. Two kinds. |
-                   +-----------+-----------+---------------+------------
-                   |Small ones,|Large ones,|One            |Few
-                   |male.      |female.    |antheridium,   |archegonia,
-                   |Developed  |Developed  |much larger    |in apex
-                   |into small |from       |than the       |of oval,
-                   |prothallial|nutriment  |single         |colorless,
-                   |cell, and  |stored in  |prothallial    |female
-                   |antherid   |macrospore |cell.          |prothallium,
-                   |cell while |from       |Antheridium    |each with
-                   |still in   |sporophyte.|with           |egg.
-                   |sporangium.|           |spermatozoids. |
-    ---------------+-----------+-----------+---------------+------------
-    Selaginella.   |Colorless, rounded     |
-                   |mass of cells inside   |
-                   |of spore wall, no      |
-                   |rhizoids, or but few.  |  On different prothallia.
-                   |Two kinds.             |
-                   +-----------+-----------+---------------+------------
-                   |Small ones,|Large ones,|One            |Few
-                   |male.      |female.    |antheridium,   |archegonia,
-                   |Developed  |Developed  |much larger    |in apex
-                   |into small |while      |than the       |of oval,
-                   |prothallial|still in   |single         |colorless,
-                   |cell, and  |sporangium |prothallial    |female
-                   |antherid   |and        |cell.          |prothallium,
-                   |cell while |dependent  |Antheridium    |each with
-                   |in         |on         |with           |egg.
-                   |sporangium.|sporophyte.|spermatozoids. |
-    ---------------+-----------+-----------+---------------+------------
-
-    ------------------------------------------------------------+-------
-                         SPOROPHYTE.                            |Begin-
-     (Largest part of the plant. The fern plant. Independent    | ning
-            of, and more hardy than, the gametophyte.           |  of
-                    Usually perennial.)                         |Gameto-
-                                                                | phyte.
-    ------------+-----------+-----------------+-----------------+-------
-                | Beginning |                 |                 |
-                |     of    |Vegetative Part. | Fruiting Part.  |
-                |Sporophyte.|                 |                 |
-    ------------+-----------+-----------------+-----------------+-------
-    Ferns.      |Fertilized |Root, stem, leaf.|Sporangia on     |
-    (Polypod-   |egg.       |                 |leaf. All of one |
-         iaceæ.)|(Develops  |                 |kind. Sporangium |
-                |into       |                 |    contains ....|Spores.
-                |fern       |                 |                 |
-                |plant.)    |                 |                 |
-    ------------+-----------+-----------------+-----------------+-------
-    Equisetum.  |Fertilized |Root, stem, leaf.|Sporangia on     |
-                |egg.       |                 |sporophylls. All |
-                |(Develops  |                 |of one kind.     |
-                |into       |                 |Sporangium       |
-                |equisetum  |                 |    contains ....|Spores.
-                |plant.)    |                 |                 |
-    ------------+-----------+-----------------+-----------------+-------
-    Isoetes.    |Fertilized |Root, stem, leaf.|Sporangia of     |
-                |egg.       |Stem very short. |two kinds. Small |
-                |(Develops  |Leaves bear      |ones contain ....|Micro-
-                |into       |sporangia in     |                 |spores.
-                |isoetes    |cavities at base;|Large ones       |
-                |plant.)    |outer leaves     |     contain ....|Macro-
-                |           |usually bear     |                 |spores.
-                |           |macrosporangia,  |                 |
-                |           |inner ones       |                 |
-                |           |microsporangia.  |                 |
-    ------------+-----------+-----------------+-----------------+-------
-    Selagniella.|Fertilized |Root, stem, leaf.|Sporangia of     |
-                |egg.       |Spore-bearing    |two kinds.  Small|
-                |(Develops  |leaves grouped   |ones contain ....|Micro-
-                |into       |on the end of    |                 |spores.
-                |selaginella|stem in a spike. |Large ones       |
-                |plant.)    |Lower ones bear  |     contain ....|Macro-
-                |           |macrosporangia,  |                 |spores.
-                |           |upper ones bear  |                 |
-                |           |microsporangia.  |                 |
-    ------------+-----------+-----------------+-----------------+-------
-
-
-Classification of the Pteridophytes.
-
-Of the living pteridophytes four classes may be recognized.
-
-
-CLASS FILICINEÆ.[34]
-
-This class includes the ferns. Four orders may be recognized.
-
-=600. Order Ophioglossales.= (One Family, Ophioglossaceæ).—This
-order includes the grapeferns (Botrychium), so called because of the
-large botryoid cluster of sporangia, resembling roughly a cluster
-of grapes; and the adder-tongue (Ophioglossum), the sporangia being
-embedded in a long tongue-like outgrowth from the green leaf.
-Botrychium and Ophioglossum are widely distributed. The roots are
-fleshy, nearly destitute of root hairs, and contain an endophytic
-fungus, so that the roots are mycorhiza. The gametophyte is
-subterranean, and devoid of chlorophyll. In Botrychium virginianum,
-an endophytic fungus has been found in the prothallium. Another genus
-(Helminthostachys) with one species is limited to the East Indies.
-
-=601. Order Marattiales= (One Family, Marattiaceæ).—These are
-tropical ferns, with only four or five living genera (Marattia, Danæa,
-etc.). They resemble the typical ferns, but the sporangia are usually
-united, several forming a compound sporangium, or _synangium_.
-
-The Ophioglossales and Marattiales are known as eusporangiate ferns,
-while the following order includes the leptosporangiate ferns.
-
-=602. Order Filicales.=—This order includes the typical ferns.
-Eight families are recognized.
-
-_Family Osmundaceæ._—Three genera are known in this family. Osmunda
-has a number of species, three of which are found in the Eastern United
-States; the cinnamon-fern (O. cinnamomea), the royal fern (O. regalis),
-and Clayton’s fern (O. claytoniana). No species of this family are
-found on the Pacific coast.
-
-_Family Gleicheniaceæ._—These ferns are found chiefly in the tropics,
-and in the mountain regions of the temperate zones of South America.
-There are two genera, Gleichenia containing all but one of the known
-species.
-
-_Family Matoniaceæ._—One genus, Matonia, in the Malayan region.
-
-_Family Schizæceæ._—These are chiefly tropical, but two species are
-found in eastern North America, Schizæa pusilla and Lygodium palmatum,
-the latter a climbing fern.
-
-_Family Hymenophyllaceæ._—These are known as the filmy ferns because
-of their thin, delicate leaves. They grow only in damp or wet regions,
-mostly in the tropics, but a few species occur in the southern United
-States.
-
-_Family Cyatheaceæ._—These are known as the tree ferns, because of the
-large size which many of them attain. They occur chiefly in tropical
-mountainous regions, many of them palm-like and imposing because of the
-large trunks and leaves. Dicksonia, Cyathea, Cibotium, Alsophila, are
-some of the most conspicuous genera.
-
-_Family Parkeriaceæ._—There is a single species in this family
-(Ceratopteris thalictroides), abundant in the tropics and extending
-into Florida. It is aquatic.
-
-_Family Polypodiaceæ._—This family includes the larger number of
-living ferns and many genera and species are found in North America.
-Examples, Polypodium, Pteridium (= Pteris), Adiantum, etc.
-
-=603. Order Hydropterales (or Salviniales).=—The members of this
-order are peculiar, aquatic ferns, some floating on the water (Azolla,
-Salvinia), while others are anchored to the soil by roots (Marsilia,
-Pilularia). They are known as water ferns. The sporangia are of two
-kinds, one containing large spores (macrospores) and the other small
-spores (microspores). They are therefore heterosporous ferns.
-
-_Family Salviniaceæ._—There are two genera, Salvinia and Azolla.
-
-_Family Marsiliaceæ._—Two genera, Marsilia and Pilularia. In this
-family the sporangia are enclosed in a sporocarp, which forms a
-pod-like structure.
-
-
-CLASS EQUISETINEÆ.[35]
-
-=604. Order Equisetales.=—The single order contains a single
-family, Equisetaceæ, among the living forms, and but a single genus,
-Equisetum. There are about twenty-four species, with fourteen in the
-United States (see Chapter XXIX).
-
-
-CLASS LYCOPODIINEÆ.[36]
-
-=605. Order Lycopodiales.=—The first two families of this order
-include the homosporous Lycopodiineæ, while the Selaginellaceæ are
-heterosporous.
-
-_Family Lycopodiaceæ._—There are two genera. Lycopodium (club moss)
-includes many species, most of them tropical, but a number in temperate
-and subarctic regions. The gametophyte of many species is tuberous,
-lacks chlorophyll, and in some there lives an endophytic fungus.
-Phylloglossum with one species is found in Australia.
-
-_Family Psilotaceæ._—There are two genera. Psilotum chiefly in the
-tropics has one species (P. triquetrum) in the region of Florida.
-
-_Family Selaginellaceæ._—These include the little club mosses, with
-one genus, Selaginella (see Chapter XXX).
-
-
-CLASS ISOETINEÆ.
-
-=606. Order Isoetales=, with one family Isoetaceæ and one genus
-Isoetes (see Chapter XXXI). There are about fifty species, with about
-sixteen in the United States.
-
-FOOTNOTES:
-
-[34] As class Filicales in Engler and Prantl.
-
-[35] As class Equisetales in Engler and Prantl.
-
-[36] As class Lycopodiales in Engler and Prantl.
-
-
-
-
-CHAPTER XXXIII.
-
-GYMNOSPERMS.
-
-
-The white pine.
-
-=607. General aspect of the white pine.=—The white pine (Pinus
-strobus) is found in the Eastern United States. In favorable situations
-in the forest it reaches a height of about 50 meters (about 160 feet),
-and the trunk a diameter of over 1 meter. In well-formed trees the
-trunk is straight and towering; the branches where the sunlight has
-access and the trees are not crowded, or are young, reaching out in
-graceful arms, form a pyramidal outline to the tree. In old and dense
-forests the lower branches, because of lack of sunlight, have died
-away, leaving tall, bare trunks for a considerable height.
-
-=608. The long shoots of the pine.=—The branches are of two
-kinds. Those which we readily recognize are the long branches, so
-called because the growth in length each year is considerable. The
-terminal bud of the long branches, as well as of the main stem,
-continues each year the growth of the main branch or shoot; while the
-lateral long branches arise each year from buds which are crowded close
-together around the base of the terminal bud. The lateral long branches
-of each year thus appear to be in a whorl. The distance between each
-false whorl of branches, then, represents one year’s growth in length
-of the main stem or long branch.
-
-=609. The dwarf shoots of the pine.=—The dwarf branches are all
-lateral on the long branches, or shoots. They are scattered over the
-year’s growth, and each bears a cluster of five long, needle-shaped,
-green leaves, which remain on the tree for several years. At the base
-of the green leaves are a number of chaff-like scales, the previous bud
-scales. While the dwarf branches thus bear green leaves, and scales,
-the long branches bear only thin scale-like leaves which are not green.
-
-=610. Spore-bearing leaves of the pine.=—The two kinds of
-spore-bearing leaves of the pine, and their close relatives, are so
-different from anything which we have yet studied, and are so unlike
-the green leaves of the pine, that we would scarcely recognize them as
-belonging to this category. Indeed there is great uncertainty regarding
-their origin.
-
-[Illustration: Fig. 339. Spray of white pine showing cluster of male
-cones just before the scattering of the pollen.]
-
-=611. Male cones, or male flowers.=—The male cones are borne in
-clusters as shown in fig. 339. Each compact, nearly cylindrical, or
-conical mass is termed a cone, or flower, and each arises in place of a
-long lateral branch. One of these cones is shown considerably enlarged
-in fig. 340. The central axis of each cone is a lateral branch, and
-belongs to the stem series. The stem axis of the cone can be seen
-in fig. 341. It is completely covered by stout, thick, scale-like
-outgrowths. These scales are obovate in outline, and at the inner
-angle of the upper end there are several rough, short spines. They
-are attached by their inner lower angle, which forms a short stalk
-or petiole, and continues through the inner face of the scale as
-a “midrib.” What corresponds to the lamina of the scale-like leaf
-bulges out on each side below and makes the bulk of the scale. These
-prominences on the under side are the sporangia (microsporangia). There
-are thus two sporangia on a sporophyll (microsporophyll). When the
-spores (microspores), which here are usually called pollen grains, are
-mature, each sporangium, or anther locule, splits down the middle as
-shown in fig. 342, and the spores are set free.
-
-[Illustration: Fig. 340. Staminate cone of white pine, with bud scales
-removed on one side.]
-
-[Illustration: Fig. 341. Section of staminate cone, showing sporangia.]
-
-[Illustration: Fig. 342. Two sporophylls removed, showing opening of
-sporangia.]
-
-[Illustration: Fig. 343. Pollen grain of white pine.]
-
-=612. Microspores of the pine, or pollen grains.=—A mature pollen
-grain of the pine is shown in fig. 343. It is a queer-looking object,
-possessing on two sides an air sac, formed by the upheaval of the outer
-coat of the spore at these two points. When the pollen is mature, the
-moisture dries out of the scale (or stamen, as it is often called here)
-while it ripens. When a limb, bearing a cluster of male cones, is
-jarred by the hand, or by currents of air, the split suddenly opens,
-and a cloud of pollen bursts out from the numerous anther locules. The
-pollen is thus borne on the wind and some of it falls on the female
-flowers.
-
-[Illustration: Fig. 344. White pine, branch with cluster of mature
-cones shedding the seed. A few young cones four months old are shown on
-branch at the left. Drawn from photograph.]
-
-[Illustration: Fig. 345. Mature cone of white pine at time of
-scattering of the seed, nearly natural size.]
-
-=613. Form of the mature female cone.=—A cluster of the
-white pine cones is shown in fig. 344. These are mature, and the scales
-have spread as they do when mature and becoming dry, in order that the
-seeds may be set at liberty. The general outline of the cone is
-lanceolate, or long oval, and somewhat curved. It measures about
-10-15_cm_ long. If we remove one of the scales, just as they are
-beginning to spread, or before the seeds have scattered, we shall find
-the seeds attached to the upper surface at the lower end. There are
-two seeds on each scale, one at each lower angle. They are ovate in
-outline, and shaped somewhat like a biconvex lens. At this time the
-seeds easily fall away, and may be freed by jarring the cone. As the
-seed is detached from the scale a strip of tissue from the latter is
-peeled off. This forms a “wing” for the seed. It is attached to one end
-and is shaped something like a knife blade. On the back of the scale is
-a small appendage known as the cover scale.
-
-[Illustration: Fig. 346. Sterile scale. Seeds undeveloped.]
-
-[Illustration: Fig. 347. Scale with well-developed seeds.]
-
-[Illustration: Fig. 348. Seeds have split off from scale.]
-
-[Illustration: Fig. 349. Back of scale with small cover scale.]
-
-[Illustration: Fig. 350. Winged seed free from scale.
-
-Figs. 346-350.—White pine showing details of mature scales and seed.]
-
-[Illustration: Fig. 351. Female cones of the pine at time of
-pollination, about natural size.]
-
-=614. Formation of the female pine cone.=—The female flowers
-begin their development rather late in the spring of the year. They
-are formed from terminal buds of the higher branches of the tree. In
-this way the cone may terminate the main shoot of a branch, or of the
-lateral shoots in a whorl. After growth has proceeded for some time in
-the spring, the terminal portion begins to assume the appearance of a
-young female cone or flower. These young female cones, at about the
-time that the pollen is escaping from the anthers, are long ovate,
-measuring about 6-10 _mm_ long. They stand upright as shown in fig. 351.
-
-=615. Form of a “scale” of the female flower.=—If we remove one
-of the scales from the cone at this stage we can better study it in
-detail. It is flattened, and oval in outline, with a stout “rib,” if
-it may be so called, running through the middle line and terminating
-in a point. The scale is in two parts as shown in fig. 354, which is
-a view of the under side. The small “outgrowth” which appears as an
-appendage is the cover scale, for while it is smaller in the pine than
-the other portion, in some of the relatives of the pine it is larger
-than its mate, and being on the outside, covers it. (The inner scale is
-sometimes called the ovuliferous scale, because it bears the ovules.)
-
-[Illustration: Fig. 352. Section of female cone of white pine, showing
-young ovules (macrosporangia) at base of the ovuliferous scales.]
-
-[Illustration: Fig. 353. Scale of white pine with the two ovules at
-base of ovuliferous scale.]
-
-[Illustration: Fig. 354. Scale of white pine seen from the outside,
-showing the cover scale.]
-
-=616. Ovules, or macrosporangia, of the pine.=—At each of the
-lower angles of the scale is a curious oval body with two curved,
-forceps-like processes at the lower and smaller end. These are the
-macrosporangia, or, as they are called in the higher plants, the
-ovules. These ovules, as we see, are in the positions of the seeds on
-the mature cones. In fact the wall of the ovule forms the outer coat of
-the seed, as we will later see.
-
-[Illustration: Fig. 355. Branch of white pine showing young female
-cones at time of pollination on the ends of the branches, and
-one-year-old cones below, near the time of fertilization.]
-
-=617. Pollination.=—At the time when the pollen is mature the
-female cones are still erect on the branches, and the scales, which
-during the earlier stages of growth were closely pressed against one
-another around the axis, are now spread apart. As the clouds of pollen
-burst from the clusters of the male cones, some of it is wafted by
-the wind to the female cones. It is here caught in the open scales,
-and rolls down to their bases, where some of it falls between these
-forceps-like processes at the lower end of the ovule. At this time the
-ovule has exuded a drop of a sticky fluid in this depression between
-the curved processes at its lower end. The pollen sticks to this, and
-later, as this viscid substance dries up, it pulls the pollen close up
-in the depression against the lower end of the ovule. This depression
-is thus known as the _pollen chamber_.
-
-=618.= Now the open scales on the young female cone close up
-again so tightly that water from rains is excluded. What is also very
-curious, the cones, which up to this time have been standing erect, so
-that the open scale could catch the pollen, now turn so that they hang
-downward. This more certainly excludes the rains, since the overlapping
-of the scales forms a shingled surface. Quantities of resin are also
-formed in the scales, which exudes and makes the cone practically
-impervious to water.
-
-=619.= The female cone now slowly grows during the summer and
-autumn, increasing but little in size during this time. During the
-winter it rests, that is, ceases to grow. With the coming of spring,
-growth commences again and at an accelerated rate. The increase in size
-is more rapid. The cone reaches maturity in September. We thus see that
-nearly eighteen months elapse from the beginning of the female flower
-to the maturity of the cone, and about fifteen months from the time
-that pollination takes place.
-
-[Illustration: Fig. 356.
-
-Macrosporangium of pine (ovule). _int_, integument; _n_, nucellus; _m_,
-macrospore; _pc_, pollen chamber; _pg_, pollen grain; _an_, axile row;
-_spt_, spongy tissue. (After Ferguson.)]
-
-=620. Female prothallium of the pine.=—To study this we must
-make careful longitudinal sections through the ovule (better made with
-the aid of a microtome). Such a section is shown in fig. 358. The
-outer layer of tissue, which at the upper end (point where the scale
-is attached to the axis of the cone) stands free, is the ovular coat,
-or _integument_. Within this integument, near the upper end, there is
-a cone-shaped mass of tissue. This mass of tissue is the _nucellus_,
-or the _macrosporangium_ proper. In the lower part of the nucellus in
-fig. 356 can be seen a rounded mass of “spongy tissue” (_spt_), which
-is a special nourishing tissue of the nucellus, or sporangium, around
-the macrospore. Within this can be seen an axile row of three cells
-(_an: m_). The lowest one, which is larger than the other two, is the
-_macrospore_. Sometimes there are four of these cells in the axile row.
-This axile row of three or four cells is formed by the two successive
-divisions of a mother cell in the nucellus. So it would appear that
-these three or four cells are all spores.
-
-Only one of them, however, the lower one, develops; the others are
-disorganized and disappear. The nucleus of the macrospore now divides
-several times to form several free nuclei in the now enlarging cavity,
-much as the nucleus of the macrospore in Selaginella and Isoetes
-divides within the spore. The development thus far takes place during
-the first summer, and now with the approach of winter the very young
-female prothallium goes into rest about the stage shown in fig. 358.
-The conical portion of the nucellus which lies above is the nucellar
-cap.
-
-[Illustration: Fig. 357.
-
-Pollen grains of pine. One of them germinating. _p_¹ and _p_², the two
-disintegrated prothallial cells, = sterile part of male gametophyte;
-_a.c._, central cell of antheridium; _v.n._, vegetative nucleus or tube
-nucleus of the single-wall cell of antheridium; _s.g._, starch grains.
-(After Ferguson.)]
-
-[Illustration: Fig. 358.
-
-Section of ovule of white pine. _int_, integument; _pc_, pollen
-chamber; _pt_, pollen tube; _n_, nucleus; _m_, macrospore cavity.]
-
-=621. Male prothallia.=—By the time the pollen is mature the
-male prothallium is already partly formed. In fig. 343 we can see two
-well-formed cells. Two other cells are formed earlier, but they become
-so flattened that it is difficult to make them out when the pollen
-grain is mature. These are shown in fig. 357, _p_¹ and _p_², and they
-are the only sterile cells of the male prothallium in the pines. The
-large cell is the antheridium wall, its nucleus _v.n._ in fig. 357. The
-smaller cell, _a.c._, is the central cell of the antheridium. During
-the summer and autumn the male prothallium makes some farther growth,
-but this is slow. The larger cell, called the vegetative cell or tube
-cell, which is in reality the wall of the antheridium, elongates by
-the formation of a tube, forming a sac, known as the pollen tube. It
-is either simple or branched. It grows down into the tissue of the
-nucellus, and at a stage represented in fig. 358, winter overtakes it
-and it rests. At this time the central cell has divided into two cells,
-and the vegetative nucleus is in the pollen tube.
-
-[Illustration: Fig. 359.
-
-Section of nucellus and endosperm of white pine. The inner layer
-of cells of the integument shown just outside of nucellus; _arch_,
-archegonium; _en_, egg nucleus. In the nucellar cap are shown three
-pollen tubes. _vn_, vegetative nucleus or tube nucleus; _stc_, stalk
-cell; _spn_, sperm nuclei, the larger one in advance is the one which
-unites with the egg nucleus. The archegonia are in the endosperm or
-female gametophyte. (After Ferguson.)]
-
-=622. The endosperm.=—In the following spring growth of all these
-parts continues. The nuclei in the macrospore divide to form more, and
-eventually cell walls are formed between them making a distinct tissue,
-known as the _endosperm_. This endosperm continues to grow until a
-large part of the nucellus is consumed for food.
-
-[Illustration: Fig. 360.
-
-Last division of the egg in the white pine cutting off the ventral
-canal cell at the apex of the archegonium. _End_, endosperm; _Arch_,
-archegonium.]
-
-=623. Female prothallium and archegonia.=—The endosperm is the
-female prothallium. This is very evident from the fact that several
-archegonia are developed in it usually on the side toward the pollen
-chamber. The archegonia are sexual organs, and since the sexual organs
-are developed on the gametophyte, therefore, the endosperm is the
-female gametophyte, or prothallium. In fig. 359 are represented two
-archegonia in the endosperm and the pollen tubes are growing down
-through the nucellus. The archegonia are quite large, the wall is a
-sheath or jacket of cells which encloses the very large egg which has a
-large nucleus in the center.
-
-=624. Pollen tube and sperm cells.=—While the endosperm (female
-prothallium) and archegonia are developing the pollen tube continues
-its growth down through the nucellar cap, as shown in fig. 359. At
-the same time the two cells which were formed in the pollen grain
-(antheridium) from the central cell move down into the tube. One of
-these is the “generative” cell, or “body” cell, and the other is called
-the stalk cell, though it is more properly a sterile half of the
-central cell. The nucleus of the generative cell, about the time the
-archegonium is mature, divides to form two nuclei, which are the sperm
-nuclei, and the one in advance is the larger, though it is much smaller
-than the egg nucleus.
-
-=625. Fertilization.=—Very soon after the archegonia are mature
-(early in June in the northern United States) the pollen tube grows
-through into the archegonium and empties the two sperm nuclei, the
-vegetative nucleus and the stalk cell, into the protoplasm of the large
-egg. The larger of the two sperm nuclei at once comes in contact with
-the very large egg nucleus and sinks down into a depression of the
-same, as shown in fig. 361. These two nuclei, in the pines, do not fuse
-into a resting nucleus, but at once organize the nuclear figure for the
-first division of the embryo. Two nuclei are thus formed, and these
-divide to form four nuclei which sink to the bottom of the archegonium
-and there organize the embryo which pushes its way into the endosperm
-from which it derives its food (fig. 362).
-
-[Illustration: Fig. 361.
-
-Archegonium of white pine at stage of fertilization, _en_, egg nucleus;
-_spn_, sperm nucleus in conjugation with it; _nb_, nutritive bodies in
-cytoplasm of large egg; _cpt_, cavity of pollen tube; _vn_, vegetative
-nucleus or tube nucleus; _stc_, stalk cell; _spn_, second sperm
-nucleus: _pr_, portion of prothallium or endosperm; _sg_, starch grains
-in pollen tube. The sheath of jacket cells of the archegonium is not
-shown. (After Ferguson.)]
-
-=626. Homology of the parts of the female cone.=—Opinions are
-divided as to the homology of the parts of the female cone of the pine.
-Some consider the entire cone to be homologous with a flower of the
-angiosperms. The entire scale according to this view is a carpel, or
-sporophyll, which is divided into the cover scale and the ovuliferous
-scale. This division of the sporophyll is considered similar to that
-which we have in isoetes, where the sporophyll has a ligule above the
-sporangium, or as in ophioglossum, where the leaf is divided into a
-fertile and a sterile portion.
-
-Others believe that the ovuliferous scale is composed of two leaves
-situated laterally and consolidated representing a shoot in the axis of
-the bract. There is some support for this in the fact that in certain
-abnormal cones which show proliferation a short axis appears in the
-axil of the bract and bears lateral leaves, and in some cases all
-gradations are present between these lateral leaves on the axis and
-their consolidation into an ovuliferous scale. In the normal condition
-of the ovuliferous scale the axis has disappeared and the shoot is
-represented only by the consolidated leaves, which would represent then
-the macrosporophylls (or carpels) each bearing one macrosporangium
-(ovule).
-
-[Illustration: Fig. 362.
-
-Pine seed, section of, _sc_, seed coat; _n_, remains of nucellus;
-_end_, endosperm (= female gametophyte); _emb_, embryo = young
-sporophyte. Seed coat and nucellus = remains of old sporophyte.]
-
-[Illustration: Fig. 363. Embryo of white pine removed from seed, showing
-several cotyledons.]
-
-[Illustration: Fig. 364. Pine seedling just emerging from the ground.]
-
-One of the most interesting and plausible views is that of Celakovsky.
-He believes that the axial shoot is reduced to two ovules, that the
-ovules have two integuments, but the outer integument of each has
-become proliferated into scales which are consolidated. In this
-proliferation of the outer integument it is thrown off from the ovule
-so that it only remains attached to one side and the larger part of the
-ovule is thus left with only one integument. This view is supported
-by the fact that in gingko, for example (another gymnosperm), the
-outer integument (the “collar”) sometimes proliferates into a leaf.
-Celakovsky’s view is, therefore, not very different from the second one
-mentioned above.
-
-[Illustration: Fig. 365. White pine seedling casting seed coats.]
-
-
-
-
-CHAPTER XXXIV.
-
-FURTHER STUDIES ON GYMNOSPERMS.
-
-
-Cycas.
-
-[Illustration: Fig. 366. Macrosporophyll of Cycas revoluta.]
-
-=627.= In such gymnosperms as cycas, illustrated in the
-frontispiece, there is a close resemblance to the members of the fern
-group, especially the ferns themselves. This is at once suggested by
-the form of the leaves. The stem is short and thick. The leaves have a
-stout midrib and numerous narrow pinnæ. In the center of this rosette
-of leaves are numerous smaller leaves, closely overlapping like bud
-scales. If we remove one of these at the time the fruit is forming we
-see that in general it conforms to the plan of the large leaves. There
-are a midrib and a number of narrow pinnæ near the free end, the entire
-leaf being covered with woolly hairs. But at the lower end, in place of
-the pinnæ, we see oval bodies. These are the macrosporangia (ovules)
-of cycas, and correspond to the macrosporangia of selaginella, and the
-leaf is the macrosporophyll.
-
-=628. Female prothallium of cycas.=—In figs. 367, 368, are
-shown mature ovules, or macrosporangia, of cycas. In 368, which is a
-roentgen-ray photograph of 367, the oval prothallium can be seen. So in
-cycas, as in selaginella, the female prothallium is developed entirely
-inside of the macrosporangium, and derives the nutriment for its growth
-from the cycas plant, which is the sporophyte. Archegonia are developed
-in this internal mass of cells. This aids us in determining that it is
-the prothallium. In cycas it is also called endosperm, just as in the
-pines.
-
-[Illustration: Fig. 367. Macrosporangium of Cycas revoluta.]
-
-[Illustration: Fig. 368. Roentgen photograph of same, showing female
-prothallium.]
-
-[Illustration: Fig. 369. A sporophyll (stamen) of cycas; sporangia in
-groups on the under side. _b_, group of sporangia; _c_, open sporangia.
-(From Warming.)]
-
-=629.= If we cut open one of the mature ovules, we can see the
-endosperm (prothallium) as a whitish mass of tissue. Immediately
-surrounding it at maturity is a thin, papery tissue, the remains of the
-nucellus (macrosporangium), and outside of this are the coats of the
-ovule, an outer fleshy one and an inner stony one.
-
-=630. Microspores, or pollen, of cycas.=—The cycas plant
-illustrated in the frontispiece is a female plant. Male plants also
-exist which have small leaves in the center that bear only
-microsporangia. These leaves, while they resemble the ordinary leaves,
-are smaller and correspond to the stamens. Upon the under side, as
-shown in fig. 369, the microsporangia are borne in groups of three
-or four, and these contain the microspores, or pollen grains. The
-arrangement of these microsporangia on the under side of the cycas
-leaves bears a strong resemblance to the arrangement of the sporangia
-on the under side of the leaves of some ferns.
-
-=631. The gingko tree= is another very interesting plant belonging
-to this same group. It is a relic of a genus which flourished in the
-remote past, and it is interesting also because of the resemblance of
-the leaves to some of the ferns like adiantum, which suggests that
-this form of the leaf in gingko has been inherited from some fern-like
-ancestor.
-
-[Illustration: Fig. 370. Zamia integrifolia, showing thick stem,
-fern-like leaves, and cone of male flowers.]
-
-[Illustration: Fig. 371. Two spermatozoids in end of pollen tube of
-cycas. (After drawing by Hirase and Ikeno.)]
-
-=632.= While the resemblance of the leaves of some of the
-gymnosperms to those of the ferns suggests fern-like ancestors for the
-members of this group, there is stronger evidence of such ancestry
-in the fact that a prothallium can well be determined in the ovules.
-The endosperm with its well-formed archegonia is to be considered a
-prothallium.
-
-=633. Spermatozoids in some gymnosperms.=—But within the past two
-years it has been discovered in gingko, cycas, and zamia, all belonging
-to this group, that the sperm cells are well-formed spermatozoids. In
-zamia each one is shaped somewhat like the half of a biconvex lens, and
-around the convex surface are several coils of cilia. After the pollen
-tube has grown down through the nucellus, and has reached a depression
-at the end of the prothallium (endosperm) where the archegonia are
-formed, the spermatozoids are set free from the pollen tube, swim
-around in a liquid in this depression, and later fuse with the egg. In
-gingko and cycas these spermatozoids were first discovered by Ikeno and
-Hirase in Japan, and later in zamia by Webber in this country. In figs.
-371-374 the details of the male prothallia and of fertilization are
-shown.
-
-[Illustration: Fig. 372. Fertilization in cycas, small spermatozoid
-fusing with the larger female nucleus of the egg. The egg protoplasm
-fills the archegonium. (From drawings by Hirase and Ikeno.)]
-
-[Illustration: Fig. 373. Spermatozoid of gingko. Some abnormal forms
-have a tail. (After Ikeno and Hirase.)]
-
-=634. The sporophyte in the gymnosperms.=—In the pollen grains
-of the gymnosperms we easily recognize the characters belonging to the
-spores in the ferns and their allies, as well as in the liverworts and
-mosses. They belong to the same series of organs, are borne on the
-same phase or generation of the plant, and are practically formed in
-the same general way, the variations between the different groups not
-being greater than those within a single group. These spores we have
-recognized as being the product of the sporophyte. We are able then to
-identify the sporophyte as that phase or generation of the plant formed
-from the fertilized egg and bearing ultimately the spores. We see from
-this that the sporophyte in the gymnosperms is the prominent part of
-the plant, just as we found it to be in the ferns. The pine tree, then,
-as well as the gingko, cycas, yew, hemlock-spruce, black spruce, the
-giant redwood of California, etc., are sporophytes.
-
-While the sporangia (anther sacs) of the male flowers open and permit
-the spores (pollen) to be scattered, the sporangia of the female
-flowers of the gymnosperms rarely open. The macrospore is developed
-within sporangium (nucellus) to form the female prothallium (endosperm).
-
-=635. The gametophyte has become dependent on the sporophyte.=—In
-this respect the gymnosperms differ widely from the pteridophytes,
-though we see suggestions of this condition of things in Isoetes and
-Selaginella, where the female prothallium is developed within the
-macrospore, and even in Selaginella begins, and nearly completes, its
-development while still in the sporangium.
-
-In comparing the female prothallium of the gymnosperms with that
-of the fern group we see a remarkable change has taken place. The
-female prothallium of the gymnosperms is very much reduced in size.
-Especially, it no longer leads an independent existence from the
-sporophyte, as is the case with nearly all the fern group. It remains
-enclosed within the macrosporangium (in cycas if not fertilized it
-sometimes grows outside of the macrosporangium and becomes green), and
-derives its nourishment through it from the sporophyte, to which the
-latter remains organically connected. This condition of the female
-prothallium of the gymnosperms necessitated a special adaptation of the
-male prothallium in order that the sperm cells may reach and fertilize
-the egg-cell.
-
-[Illustration: Fig. 374.
-
-Gingko biloba. _A_, mature pollen grain; _B_, germinating pollen grain,
-the branched tube entering among the cells of the nucellus; _Ex_,
-exine (outer wall of spore); _P_₁, prothallial cell; _P_₂, antheridial
-cell (divides later to form stalk cell and generative cell); _P_₃,
-vegetative cell; _Va_, vacuoles; _Nc_, nucellus. (After drawings by
-Hirase and Ikeno.)]
-
-[Illustration: Fig. 375.
-
-Gingko biloba, diagrammatic representation of the relation of pollen
-tube to the archegonium in the end of the nucellus. _pt_, pollen tube;
-_o_, archegonium. (After drawing by Hirase and Ikeno.)]
-
-=636. Gymnosperms are naked seed plants.=—The pine, as we have
-seen, has naked seeds. That is, the seeds are not enclosed within the
-carpel, but are exposed on the outer surface. All the plants of the
-great group to which the pine belongs have naked seeds. For this reason
-the name “_gymnosperms_” has been given to this great group.
-
-[Illustration: Fig. 376. Spermatozoids of zamia in pollen tube; _pg_,
-pollen grain; _a_, _a_, spermatozoids. (After Webber.)]
-
-[Illustration: Fig. 377. Spermatozoid of zamia showing spiral row of
-cilia. (After Webber.)]
-
-=637. Classification of gymnosperms.=—The gingko tree has until
-recently been placed with the pines, yew, etc., in the order _Pinales_,
-but the discovery of the spermatozoids in the pollen tube suggests
-that it is not closely allied with the Pinales, and that it represents
-an order coordinate with them. Engler arranges the living gymnosperms
-somewhat as follows:
-
-
-Class Gymnospermæ.
-
-    Order 1. Cycadales; family Cycadaceæ. Cycas, Zamia, etc.
-    Order 2. Gingkoales; family Gingkoaceæ. Gingko.
-    Order 3. Pinales (or Coniferæ);
-             family 1. Taxaceæ.
-                       Taxus, the common yew in the eastern
-                       United States, and Torreya, in the
-                       western United States, are examples.
-             family 2. Pinaceæ. Sequoia (redwood of California),
-                       firs, spruces, pines, cedars, cypress, etc.
-    Order 4. Gnetales. Welwitschia mirabilis, deserts of southwest
-                       Africa; Ephedra, deserts of the Mediterranean
-                       and of West Asia. Gnetum, climbers (Lianas),
-                       from tropical Asia and America.
-
-=638.= TABLE SHOWING HOMOLOGIES OF SPOROPHYTE AND GAMETOPHYTE IN
-THE PINE.
-
- TERMS CORRESPONDING TO THOSE USED IN PTERIDOPHYTES. COMMON TERMS.
-
-    -------------+--------------------------------------------------
-                 |  Sporophyte              = Pine tree.
-                 |  Spore-bearing part      = Male and female cones.
-    -------------+--------------------------------------------------
-    Sporophyte   | Microsporophyll          = Stamen.
-                 | Microsporangium          = Pollen sac.
-    -------------+--------------------------------------------------
-                 | Microspore               = Pollen grain.
-                 | Mature microspore is     = Mature pollen grain.
-                 |   rudimentary male
-                 |   prothallium with
-                 |   rudimentary
-                 |   antheridium
-                 | Large cell (part of      = Vegetative cell
-                 |    antheridium wall?)        of pollen grain.
-                 | Antheridium cell         = Small cell of pollen
-    Male         |                               grain.
-     gametophyte | Antheridium cell divides = Generative cell.
-                 |   to form stalk cell and
-                 |   central cell of
-                 |   antheridium
-                 |  (male sexual organ)
-                 | Central cell of          = Paternal cells,
-                 |   antheridium                or generative cells.
-                 |   divides to form
-                 |   two sperm cells
-    -------------+--------------------------------------------------
-                 | Macrosporophyll          = Ovuliferous scale (cover
-                 |                              scale and carpellary
-                 |                              outgrowth); or three
-                 |                              carpels united into
-    Sporophyte   |                              ovuliferous scale,
-                 |                              the central one sterile
-                 |                             (in axil of cover scale).
-                 | Macrosporangium covered  = Nucellus covered by
-                 |    by integument             integument = ovule.
-    -------------+--------------------------------------------------
-                 | Macrospore (remains in   = Large cell in center of
-                 |     sporangium)              nucellus which develops
-                 |                              embryo sac and endosperm
-                 |                              (remains in nucellus).
-    Female       | Female prothallium       = Endosperm, in nucellus.
-     gametophyte |     (in sporangium)
-                 | Archegonia (female       = Corpuscula, in endosperm.
-                 |      sexual organs)
-                 | Egg                      = Maternal cell, or germ
-                 |                               cell.
-    -------------+--------------------------------------------------
-                 | Egg (fertilized)         = Germ cell.
-                 | Young sporophyte         = Pine embryo in nucellus
-                 |                               and integument.
-    Young        | Young sporophyte         = Embryo     |
-      sporophyte |   In remains of          = Endosperm  |
-                 |   gametophyte            = Nucellus   | Seed.
-                 |   And sporangium         = Integument |
-                 |   Surrounded by new                   |
-                 |     growth of old                     |
-                 |     sporophyte                        |
-    -------------+---------------------------------------+----------
-
-
-
-
-CHAPTER XXXV.
-
-MORPHOLOGY OF THE ANGIOSPERMS: TRILLIUM; DENTARIA.
-
-
-Trillium.
-
-=639. General appearance.=—As one of the plants to illustrate
-this group we may take the wake-robin, as it is sometimes called,
-or trillium. There are several species of this genus in the United
-States; the commonest one in the eastern part is the “white wake-robin”
-(Trillium grandiflorum). This occurs in or near the woods. A picture of
-the plant is shown in fig. 378. There is a thick, fleshy, underground
-stem, or rhizome as it is usually called. This rhizome is perennial,
-and is marked by ridges and scars. The roots are quite stout and
-possess coarse wrinkles. From the growing end of the rhizome each year
-the leafy, flowering stem arises. This is 20-30_cm_ (8-12 inches) in
-height. Near the upper end is a whorl of three ovate leaves, and from
-the center of this rosette rises the flower stalk, bearing the flower
-at its summit.
-
-=640. Parts of the flower. Calyx.=—Now if we examine the flower
-we see that there are several leaf-like structures. These are arranged
-also in threes just as are the leaves. First there is a whorl of three,
-pointed, lanceolate, green, leaf-like members, which make up the
-_calyx_ in the higher plants, and the parts of the calyx are _sepals_,
-that is, each leaf-like member is a _sepal_. But while the sepals are
-part of the flower, so called, we easily recognize them as belonging to
-the _leaf series_.
-
-=641. Corolla.=—Next above the calyx is a whorl of white or
-pinkish members, in Trillium grandiflorum, which are also leaf-like in
-form, and broader than the sepals, being usually somewhat broader at
-the free end. These make up what is the _corolla_ in the higher plants,
-and each member of the corolla is a _petal_. But while they are parts
-of the flower, and are not green, their form and position would suggest
-that they also belong to the leaf series.
-
-[Illustration: Fig. 378. Trillium grandiflorum.]
-
-=642. Andrœcium.=—Within and above the insertion of the corolla
-is found another tier, or whorl, of members which do not at first
-sight resemble leaves in form. They are known in the higher plants
-as _stamens_. As seen in fig. 379 each stamen possesses a stalk (=
-filament), and extending along on either side for the greater part of
-the length are four ridges, two on each side. This part of the stamen
-is the _anther_, and the ridges form the anther sacs, or lobes. Soon
-after the flower is opened, these anther sacs open also by a split in
-the wall along the edge of the ridge. At this time we see quantities of
-yellowish powder or dust escaping from the ruptured anther locules. If
-we place some of this under the microscope we see that it is made up of
-minute bodies which resemble spores; they are rounded in form, and the
-outer wall is spiny. They are in fact spores, the microspores of the
-trillium, and here, as in the gymnosperms, are better known as _pollen_.
-
-[Illustration: Fig. 379. Sepal, petal, stamen, and pistil of Trillium
-grandiflorum.]
-
-[Illustration: Fig. 380.
-
-Trillium grandiflorum, with the compound pistil expanded into three
-leaf-like members. At the right these three are shown in detail.]
-
-=643. The stamen a sporophyll.=—Since these pollen grains are
-the spores, we would infer, from what we have learned of the ferns
-and gymnosperms, that this member of the flower which bears them is
-a sporophyll; and this is the case. It is in fact what is called the
-_microsporophyll_. Then we see also that the anther sacs, since they
-enclose the spores, would be the sporangia (microsporangia). From this
-it is now quite clear that the stamens belong also to the leaf series.
-They are just six in number, twice the number found in a whorl of
-leaves, or sepals, or corolla. It is believed, therefore, that there
-are two whorls of stamens in the flower of trillium.
-
-=644. Gynœcium.=—Next above the stamens and at the center of the
-flower is a stout, angular, ovate body which terminates in three long,
-slender, curved points. This is the pistil, and at present the only
-suggestion which it gives of belonging to the leaf series is the fact
-that the end is divided into three parts, the number of parts in each
-successive whorl of members of the flower. If we cut across the body of
-this pistil and examine it with a low power we see that there are three
-chambers or cavities, and at the junction of each the walls suggest to
-us that this body may have been formed by the infolding of the margins
-of three leaf-like members, the places of contact having then become
-grown together. We see also that from the incurved margins of each
-division of the pistil there stand out in the cavity oval bodies. These
-are the _ovules_. Now the ovules we have learned from our study of the
-gymnosperms are the _sporangia_ (here the macrosporangia). It is now
-more evident that this curious body, the pistil, is made up of three
-leaf-like members which have fused together, each member being the
-equivalent of a sporophyll (here the macrosporophyll). This must be a
-fascinating observation, that plants of such widely different groups
-and of such different grades of complexity should have members formed
-on the same plan and belonging to the same series of members, devoted
-to similar functions, and yet carried out with such great modifications
-that at first we do not see this common meeting ground which a
-comparative study brings out so clearly.
-
-[Illustration: Fig. 381. Abnormal trillium. The nine parts of the
-perianth are green, and the outer whorls of stamens are expanded into
-petal-like members.]
-
-[Illustration: Fig. 382. Transformed stamen of trillium showing anther
-locules on the margin.]
-
-=645. Transformations of the flower of trillium.=—If anything
-more were needed to make it clear that the parts of the flower of
-trillium belong to the leaf series we could obtain evidence from the
-transformations which the flower of trillium sometimes presents. In
-fig. 381 is a sketch of a flower of trillium, made from a photograph.
-One set of the stamens has expanded into petal-like organs, with the
-anther sacs on the margin. In fig. 380 is shown a plant of Trillium
-grandiflorum in which the pistil has separated into three distinct and
-expanded leaf-like structures, all green except portions of the margin.
-
-
-Dentaria.
-
-=646. General appearance.=—For another study we may take a plant which
-belongs to another division of the higher plants, the common “pepper
-root,” or “toothwort” (Dentaria diphylla) as it is sometimes called.
-This plant occurs in moist woods during the month of May, and is well
-distributed in the northeastern United States. A plant is shown in fig.
-383. It has a creeping underground rhizome, whitish in color, fleshy,
-and with a few scales. Each spring the annual flower-bearing stem rises
-from one of the buds of the rhizome, and after the ripening of the
-seeds, dies down.
-
-The leaves are situated a little above the middle point of the stem.
-They are opposite and the number is two, each one being divided into
-three dentate lobes, making what is called a compound leaf.
-
-[Illustration: Fig. 383. Toothwort (Dentaria diphylla).]
-
-[Illustration: Fig. 384. Flower of the toothwort (Dentaria diphylla).]
-
-=647. Parts of the flower.=—The flowers are several, and they
-are borne on quite long stalks (pedicels) scattered over the terminal
-portion of the stem. We should now examine the parts of the flower
-beginning with the calyx. This we can see, looking at the under side
-of some of the flowers, possesses four scale-like sepals, which easily
-fall away after the opening of the flower. They do not resemble leaves
-so much as the sepals of trillium, but they belong to the leaf series,
-and there are two pairs in the set of four. The corolla also possesses
-four petals, which are more expanded than the sepals and are whitish in
-color. The stamens are six in number, one pair lower than the others,
-and also shorter. The filament is long in proportion to the anther, the
-latter consisting of two lobes or sacs, instead of four as in trillium.
-The pistil is composed of two carpels, or leaves fused together. So we
-find in the case of the pepper root that the parts of the flower are
-in twos, or multiples of two. Thus they agree in this respect with the
-leaves; and while we do not see such a strong resemblance between the
-parts of the flower here and the leaves, yet from the presence of the
-pollen (microspores) in the anther sacs (microsporangia) and of ovules
-(macrosporangia) on the margins of each half of the pistil, we are,
-from our previous studies, able to recognize here that all the members
-of the flower belong to the leaf series.
-
-=648.= In trillium and in the pepper root we have seen that the
-parts of the flower in each apparent whorl are either of the same
-number as the leaves in a whorl, or some multiple of that number. This
-is true of a large number of other plants, but it is not true of all. A
-glance at the spring-beauty (Claytonia virginiana), and at the anemone
-(or Isopyrum biternatum, fig. 563) will serve to show that the number
-of the different members of the flower may vary. The trillium and the
-dentaria were selected as being good examples to study first, to make
-it very clear that the members of the flower are fundamentally leaf
-structures, or rather that they belong to the same series of members as
-do the leaves of the plant.
-
-=649. Synopsis of members of the sporophyte in angiosperms.=
-
-    Higher plant.
-    Sporophyte phase {Root.            {Foliage leaves.
-      (or modern     {Shoot. {Stem.    {Perianth leaves.     }
-       phase).               {   Leaf. {Spore-bearing leaves }
-                                       {  with sporangia.    } Flower.
-                                       {(Sporangia sometimes }
-                                       {  on shoot.)         }
-
-
-
-
-CHAPTER XXXVI.
-
-GAMETOPHYTE AND SPOROPHYTE OF ANGIOSPERMS.
-
-
-=650. Male prothallium of angiosperms.=—The first division which
-takes place in the nucleus of the pollen grain occurs, in the case of
-trillium and many others of the angiosperms, before the pollen grain
-is mature. In the case of some specimens of T. grandiflorum in which
-the pollen was formed during the month of October of the year before
-flowering, the division of the nucleus into two nuclei took place soon
-after the formation of the four cells from the mother cell. The nucleus
-divided in the young pollen grain is shown in fig. 385. After this
-takes place the wall of the pollen grain becomes stouter, and minute
-spiny projections are formed.
-
-[Illustration: Fig. 385. Nearly mature pollen grain of trillium. The
-smaller cell is the generative cell.]
-
-[Illustration: Fig. 386. Germinating spores (pollen grains) of
-peltandra; generative nucleus in one undivided, in other divided to
-form the two sperm nuclei; vegetative nucleus in each near the pollen
-grain.]
-
-=651.= The larger cell is the vegetative cell of the prothallium,
-while the smaller one, since it later forms the sperm cells, is
-the generative cell. This generative cell then corresponds to the
-central cell of the antheridium, and the vegetative cell perhaps
-corresponds to a wall cell of the antheridium. If this is so, then the
-male prothallium of angiosperms has become reduced to a very simple
-antheridium. The farther growth takes place after fertilization. In
-some plants the generative cell divides into the two sperm cells at
-the maturity of the pollen grain. In other cases the generative cell
-divides in the pollen tube after the germination of the pollen grain.
-For study of the pollen tube the pollen may be germinated in a weak
-solution of sugar, or on the cut surface of pear fruit, the latter
-being kept in a moist chamber to prevent drying the surface.
-
-=652.= In the spring after flowering the pollen escapes from the
-anther sacs, and as a result of pollination is brought to rest on
-the stigma of the pistil. Here it germinates, as we say, that is, it
-develops a long tube which makes its way down through the style, and in
-through the micropyle to the embryo sac, where, in accordance with what
-takes place in other plants examined, one of the sperm cells unites
-with the egg, and fertilization of the egg is the result.
-
-[Illustration: Fig. 387. Section of pistil of trillium, showing
-position of ovules (macrosporangia).]
-
-[Illustration: Fig. 388. Mandrake (Podophyllum peltatum).]
-
-=653. Macrospore and embryo sac.=—In trillium the three carpels
-are united into one, and in dentaria the two carpels are also united
-into one compound pistil. Simple pistils are found in many plants, for
-example in the ranunculaceæ, the buttercups, columbine, etc. These
-simple pistils bear a greater resemblance to a leaf, the margins of
-which are folded around so that they meet and enclose the ovules or
-sporangia.
-
-[Illustration: Fig. 389. Young ovule (macrosporangium) of podophyllum.
-_n_, nucellus containing the one-celled stage of the macrospore;
-_i.int_, inner integument; _o.int_, outer integument.]
-
-=654.= If we cut across the compound pistil of trillium we find
-that the infoldings of the three pistils meet to form three partial
-partitions which extend nearly to the center, dividing off three
-spaces. In these spaces are the ovules which are attached to the
-infolded margins. If we make cross-sections of a pistil of the
-May-apple (podophyllum) and through the ovules when they are quite
-young, we shall find that the ovule has a structure like that shown
-in fig. 389. At _m_ is a cell much larger than the surrounding ones.
-This is called the macrospore. The tissue surrounding it is called
-here the nucellus, but because it contains the macrospore it must be
-the macrosporangium. The two coats or integuments of the ovule are
-yet short and have not grown out over the end of the nucellus. This
-macrospore increases in size, forming first a cavity or sac in the
-nucellus, the _embryo sac_. The nucleus divides several times until
-eight are formed, four in the micropylar end of the embryo sac and
-four in the opposite end. In some plants it has been found that one
-nucleus from each group of four moves toward the middle of the embryo
-sac. Here they fuse together to form one nucleus, the _endosperm
-nucleus_ or _definitive nucleus_ shown in fig. 390. One of the nuclei
-at the micropylar end is the egg, while the two smaller ones nearer
-the end are the _synergids_. The egg-cell is all that remains of the
-archegonium in this reduced prothallium. The three nuclei at the lower
-end are the _antipodal_ cells.
-
-[Illustration: Fig. 390. Podophyllum peltatum, ovule containing mature
-embryo sac; two synergids, and eggs at left, endosperm nucleus in
-center, three antipodal cells at right.]
-
-[Illustration: Fig. 391. Macrospore (one-celled stage) of lilium.]
-
-=655. Embryo sac is the young female prothallium.=—In figs.
-391-393 are shown the different stages in the development of the
-embryo sac in lilium. The embryo sac at this stage is the young female
-prothallium, and the egg is the only remnant of the female sexual
-organ, the archegonium, in this reduced gametophyte.
-
-=656. Fertilization.=—When the pollen tube has reached the embryo
-sac (paragraph 652) it opens and the two sperm cells are emptied near
-the egg. The first sperm nucleus enters the protoplasm surrounding the
-egg nucleus and uniting with the latter brings about fertilization. The
-second sperm nucleus often unites with the endosperm nucleus (or with
-one or both of the “polar nuclei”), bringing about what some call a
-second fertilization. Where this takes place in addition to the union
-of the first sperm nucleus with the egg nucleus it is called _double
-fertilization_. The sperm nucleus is usually smaller than the egg
-nucleus, but often grows to near or quite the size of the egg nucleus
-before union. See figs. 394 and 395.
-
-[Illustration: Fig. 392. Two-and four-celled stage of embryo sac of
-lilium. The middle one shows division of nuclei to form the four-celled
-stage. (Easter lily.)]
-
-=657. Fertilization in plants is fundamentally the same as in
-animals.=—In all the great groups of plants as represented by
-spirogyra, œdogonium, vaucheria, peronospora, ferns, gymnosperms, and
-in the angiosperms, fertilization, as we have seen, consists in the
-fusion of a male nucleus with a female nucleus. Fertilization, then, in
-plants is identical with that which takes place in animals.
-
-=658. Embryo.=—After fertilization the egg develops into a short
-row of cells, the _suspensor_ of the embryo. At the free end the embryo
-develops. In figs. 397 and 398 is a young embryo of trillium.
-
-=659. Endosperm, the mature female prothallium.=—During the
-development of the embryo the endosperm nucleus divides into a great
-many nuclei in a mass of protoplasm, and cell walls are formed
-separating them into cells. This mass of cells is the _endosperm_,
-and it surrounds the embryo. It is the _mature female prothallium_,
-belated in its growth in the angiosperms, usually developing only when
-fertilization takes place, and its use has been assured.
-
-[Illustration: Fig. 393. Mature embryo sac (young prothallium) of
-lilium. _m_, micropylar end; _S_, synergids; _E_, egg; _Pn_, polar
-nuclei; _Ant_, antipodals. (Easter lily.)]
-
-[Illustration: Fig. 394. Section through nucellus and upper part of
-embryo sac of cotton at time of entrance of pollen tube. _E_, egg; _S_,
-synergids; _P_, pollen tube with sperm cell in the end. (Duggar.)]
-
-=660. Seed.=—As the embryo is developing it derives its
-nourishment from the endosperm (or in some cases perhaps from the
-nucellus). At the same time the integuments increase in extent and
-harden as the seed is formed.
-
-[Illustration: Fig. 395. Fertilization of cotton. _pt_, pollen tube;
-_Sn_, synergids; _E_, egg, with male and female nucleus fusing.
-(Duggar.)]
-
-[Illustration: Fig. 396.
-
-Diagrammatic section of ovary and ovule at time of fertilization in
-angiosperm. _f_, funicle of ovule; _n_, nucellus; _m_, micropyle; _b_,
-antipodal cells of embryo sac; _e_, endosperm nucleus; _k_, egg-cell
-and synergids; _ai_, outer integument of ovule; _ii_, inner integument.
-The track of the pollen tube is shown down through the style, walls of
-the ovary to the micropylar end of the embryo sac.]
-
-=661. Perisperm.=—In most plants the nucellus is all consumed
-in the development of the endosperm, so that only minute fragments
-of disorganized cell walls remain next the inner integument. In some
-plants, however, (the water-lily family, the pepper family, etc.,)
-a portion of the nucellus remains intact in the mature seed. In such
-seeds the remaining portion of the nucellus is the _perisperm_.
-
-=662. Presence or absence of endosperm in the seed.=—In many of
-the angiosperms all of the endosperm is consumed by the embryo during
-its growth in the formation of the seed. This is the case in the rose
-family, crucifers, composites, willows, oaks, legumes, etc., as in the
-acorn, the bean, pea and others. In some, as in the bean, a large part
-of the nutrient substance passing from the endosperm into the embryo is
-stored in the cotyledons for use during germination. In other plants
-the endosperm is not all consumed by the time the seed is mature.
-Examples of this kind are found in the buttercup family, the violet,
-lily, palm, jack-in-the-pulpit, etc. Here the remaining endosperm in
-the seed is used as food by the embryo during germination.
-
-[Illustration: Fig. 397. Section of one end of ovule of trillium,
-showing young embryo in endosperm.]
-
-[Illustration: Fig. 398. Embryo enlarged.]
-
-[Illustration: Fig. 399. Seed of violet, external view, and section.
-The section shows the embryo lying in the endosperm.]
-
-[Illustration: Fig. 400. Section of fruit of pepper (Piper nigrum),
-showing small embryo lying in a small quantity of whitish endosperm
-at one end, the perisperm occupying the larger part of the interior,
-surrounded by pericarp.]
-
-=663. Outer parts of the seed.=—While the embryo is forming within the
-ovule and the growth of the endosperm is taking place, where this is
-formed, other correlated changes occur in the outer parts of the ovule,
-and often in adjacent parts of the flower. These unite in making the
-“seed,” or the “fruit.” Especially in connection with the formation of
-the seed a new growth of the outer coat, or integument, of the ovule
-occurs, forming the outer coat of the seed, known as the _testa_, while
-the inner integument is absorbed. In some cases the inner integument
-of the ovule also forms a new growth, making an inner coat of the seed
-(rosaceæ). In still other cases neither of the integuments develops
-into a testa, and the embryo sac lies in contact with the wall of
-the ovary. Again an additional envelope grows up around the seed; an
-example of this is found in the case of the red berries of the “yew”
-(taxus), the red outer coat being an extra growth, called an _aril_.
-
-In the willow and the milkweed an aril is developed in the form of
-a tuft of hairs. (In the willow it is an outgrowth of the funicle,
-= stalk of the ovule, and is called a funicular aril; while in the
-milkweed it is an outgrowth of the micropyle, = the open end of the
-ovule, and is called a micropylar aril.)
-
-=664. Increase in size during seed formation.=—Accompanying this
-extra growth of the different parts of the ovule in the formation of
-the seed is an increase in the size, so that the seed is often much
-greater in size than the ovule at the time of fertilization. At the
-same time parts of the ovary, and in many plants, the adherent parts of
-the floral envelopes, as in the apple; or of the receptacle, as in the
-strawberry; or in the involucre, as in the acorn; are also stimulated
-to additional growth, and assist in making the fruit.
-
-=665. Synopsis of the seed.=
-
-                 {                 {Aril, rarely present.
-                 {                 {
-                 {                 {Ovular coats (one or two usually
-                 {                 {   present), the _testa_.
-                 {                 {
-                 {                 {_Funicle_ (stalk of ovule), _raphe_
-                 {                 {  (portion of funicle when bent on
-                 {                 {   to the side of ovule),
-                 {                 {_micropyle_, _hilum_ (scar where
-                 {_Ripened ovule._ {  seed was attached to ovary).
-                 {                 {
-                 {                 {_Remnant of the nucellus_ (central
-    _The seed._  {                 {   part of ovule); sometimes
-                 {                 {   nucellus remains as
-                 {                 {_Perisperm_ in some albuminous
-                 {                     seeds.
-                 {_Endosperm_, present in albuminous seeds.
-                 {
-                 {_Embryo_ within surrounded by endosperm when this is
-                 {   present, or by the remnant of nucellus, and by the
-                 {   ovular coats which make the _testa_. In many seeds
-                 {  (example, bean) the endospermis transferred to the
-                 {   cotyledons which become fleshy(exalbuminous seeds).
-
-=666. Parts of the ovule.=—In fig. 401 are represented three
-different kinds of ovules, which depend on the position of the ovule
-with reference to its stalk. The funicle is the stalk of the ovule,
-the hilum is the point of attachment of the ovule with the ovary, the
-raphe is the part of the funicle in contact with the ovule in inverted
-ovules, the chalaza is the portion of the ovule where the nucellus and
-the integuments merge at the base of the ovule, and the micropyle is
-the opening at the apex of the ovule where the coats do not meet.
-
-[Illustration: Fig. 401.
-
-_A_, represents a straight (orthotropous) ovule of polygonum; _B_, the
-inverted (anatropous) ovule of the lily; and _C_, the right-angled
-(campylotropous) ovule of the bean. _f_, funicle; _c_, chalaza;
-_k_, nucellus; _ai_, outer integument; _ii_, inner integument; _m_,
-micropyle; _em_, embryo sac.]
-
-
-Comparison of Organ and Member.
-
-=667. The stamens and pistils are not the sexual organs.=—Before
-the sexual organs and sexual processes in plants were properly
-understood it was customary for botanists to speak of the stamens and
-pistils of flowering plants as the sexual organs. Some of the early
-botanists, a century ago, found that in many plants the seed would not
-form unless first the pollen from the stamens came to be deposited on
-the stigma of the pistil. A little further study showed that the pollen
-germinated on the stigma and formed a tube which made its way down
-through the pistil and into the ovule.
-
-This process, including the deposition of the pollen on the stigma,
-was supposed to be fertilization, the stamen was looked on as the male
-sexual organ, and the pistil as the female sexual organ. We have found
-out, however, by further study, and especially by a comparison of the
-flowering plants and the lower plants, that the stamens and pistils are
-not the sexual organs of the flower.
-
-=668. The stamens and pistils are spore-bearing leaves.=—The
-stamen is the spore-bearing leaf, and the pollen grains are not
-unlike spores; in fact they are the small spores of the angiosperms.
-The pistil is also a spore-bearing leaf, the ovule the sporangium,
-which contains the large spore called an _embryo sac_. In the ferns
-we know that the spore germinates and produces the green heart-shaped
-prothallium. The prothallium bears the sexual organs. Now the fern leaf
-bears the spores and the spore forms the prothallium. So it is in the
-flowering plants. The stamen bears the small spores—pollen grains—and
-the pollen grain forms the prothallium. The prothallium in turn forms
-the sexual organs. The process is in general the same as it is in the
-ferns, but with this special difference: the prothallium and the sexual
-organ of the flowering plants are very much reduced.
-
-=669. Difference between organ and member.=—While it is not
-strictly correct then to say that the stamen is a sexual organ, or male
-organ, we might regard it as a _male member_ of the flower, and we
-should distinguish between _organ_ and _member_. It is an _organ_ when
-we consider _pollen production_, but it is not a sexual organ. When we
-consider _fertilization_ it is _not a sexual organ, but a male member_
-of the flower which bears the small spore.
-
-The following table will serve to indicate these relations.
-
-    Stamen        = spore-bearing leaf = male member of flower.
-    Anther locule = sporangium.
-    Pollen grain  = small spore = reduced male prothallium and
-                      sexual organ.
-
-So the pistil is not a sexual organ, but might be regarded as the
-female member of the flower.
-
-    Pistil     = spore-bearing leaf = female member of flower.
-    Ovule      = sporangium.
-    Embryo sac = large spore = female prothallium containing the egg.
-    The egg    = a reduced archegonium = the female sexual organ.
-
-
-Progression and Retrogression in Sporophyte and Gametophyte.
-
-=670. Sporophyte is prominent and highly developed.=—In the
-angiosperms then, as we have seen from the plants already studied, the
-trillium, dentaria, etc., are sporophytes, that is they represent the
-spore-bearing, or sporophytic, stage. Just as we found in the case of
-the gymnosperms and ferns, this stage is the prominent one, and the
-one by which we characterize and recognize the plant. We see also that
-the plants of this group are still more highly specialized and complex
-than the gymnosperms, just as they were more specialized and complex
-than the members of the fern group. From the very simple condition
-in which we possibly find the sporophyte in some of the algæ like
-spirogyra, vaucheria, and coleochæte, there has been a gradual increase
-in size, specialization of parts, and complexity of structure through
-the bryophytes, pteridophytes, and gymnosperms, up to the highest types
-of plant structure found in the angiosperms. Not only do we find that
-these changes have taken place, but we see that, from a condition of
-complete dependence of the spore-bearing stage on the sexual stage
-(gametophyte), as we find it in the liverworts and mosses, it first
-becomes free from the gametophyte in the members of the fern group, and
-is here able to lead an independent existence. The sporophyte, then,
-might be regarded as the modern phase of plant life, since it is that
-which has become and remains the prominent one in later times.
-
-=671. The gametophyte once prominent has become degenerate.=—On
-the other hand we can see that just as remarkable changes have come
-upon the other phase of plant life, the sexual stage, or gametophyte.
-There is reason to believe that the gametophyte was the stage of plant
-life which in early times existed almost to the exclusion of the
-sporophyte, since the characteristic thallus of the algæ is better
-adapted to an aquatic life than is the spore-bearing state of plants.
-At least, we now find in the plants of this group as well as in the
-liverworts, that the gametophyte is the prominent stage. When we reach
-the members of the fern group, and the sporophyte becomes independent,
-we find that the gametophyte is decreasing in size, in the higher
-members of the pteridophytes, the male prothallium consisting of only a
-few cells, while the female prothallium completes its development still
-within the spore wall. And in selaginella it is entirely dependent on
-the sporophyte for nourishment.
-
-=672.= As we pass through the gymnosperms we find that the
-condition of things which existed in the bryophytes has been reversed,
-and the gametophyte is now entirely dependent on the sporophyte for
-its nourishment, the female prothallium not even becoming free from
-the sporangium, which remains attached to the sporophyte, while the
-remnant of a male prothallium, during the stage of its growth, receives
-nourishment from the tissues of the nucellus through which it bores its
-way to the egg-cell.
-
-=673.= In the angiosperms this gradual degradation of the male
-and female prothallia has reached a climax in a one-celled male
-prothallium with two sperm cells, and in the embryo sac with no clearly
-recognizable traces of an archegonium to identify it as a female
-prothallium. The development of the endosperm subsequent, in most
-cases, to fertilization, providing nourishment for the sporophytic
-embryo at one stage or another, is believed to be the last remnant of
-the female prothallium in plants.
-
-=674. The seed.=—The seed is the only important character
-possessed by the higher plants (the gymnosperms and angiosperms) which
-is not possessed by one or another of the lower great groups. With the
-gradual evolution of the higher plants from the lower there has been
-developed at certain periods organs or structural characters which
-were not present in some of the lower groups. Thus the thallus is the
-plant body of the algæ and fungi, so that these two groups of plants
-are sometimes called _Thallophytes_. In the Bryophytes (liverworts and
-mosses) the thallus is still present, but there is added the highly
-organized archegonium in place of the simple female gamete or oogonium,
-or carpogonium of the algæ and fungi, and the sporophyte has become
-a distinct though still dependent structure. In the Pteridophytes
-the thallus is still present as the prothallium, archegoina are also
-present, and while both of these structures are retrograding the
-sporophyte has become independent and has organized for the first time
-a true vascular system for conduction of water and food. In the
-gymnosperms and angiosperms the thallus is present in the endosperm;
-distinct, though reduced, archegonia are present in most gymnosperms
-and represented only by the egg in the angiosperms; the vascular system
-is still more highly developed while the seed for the first time is
-organized, and characterizes these plants so that they are called seed
-plants, or _Spermatophytes_.
-
-
-Variation, Hybridization, Mutation.
-
-=674a. Variation.=—It is a well-known fact that plants as well
-as animals are subject to variation. Under certain conditions, some
-of which are partly understood and others are unknown, the progeny of
-plants differ in one or more characters from their parents. Some of
-these variations are believed to be due to the influence of environment
-(see Parts III and IV). Others are the result of the crossing of
-individuals which show greater or lesser differences in one or more
-characters, or the crossing of different species (_hybridization_). The
-most profound variations are those which spring suddenly into existence
-(_mutation_).
-
-=674b. Hybridization.=—Two different species are “crossed” where
-the egg-cell of one species is fertilized by the sperm of another
-species. The progeny resulting from such a cross is a _hybrid_. Hybrids
-sometimes resemble one parent, sometimes another, sometimes both. Where
-the parents differ only in respect to one character of an organ or
-structure, there is a regular law in respect to the progeny if they are
-self-fertilized. In the first generation all the individuals are alike
-and resemble one of the parents, and the special differential character
-of that parent is called the _dominant_ character. In the second
-generation 75% possess the dominant character, while 25% resemble
-the other original parent, and its differential character is called
-_recessive_. These are _pure_ recessives, since successive generations,
-if self-fertilized, are always recessive. Of the 75% which show the
-dominant character in the second generation, one-third (or 25% of the
-whole number) are pure dominants if self-fertilization is continued,
-while 50% are really “cross breds” like the first generation, and
-if self-fertilized split up again into approximately 25 dominants,
-50 cross breds, and 25 recessives. This is what is called Mendel’s
-law. Where the original parents differ in respect to more than one
-character, the result is more complicated (see Mendel’s Principles of
-Heredity; also de Vries, Das Spaltungsgesetz der Bastarde, Ber. d.
-deutsch. bot. Gesell., 18, 83, 1900).
-
-=674c. Mutation.=—This term is applied to those variations which
-appear so suddenly that some of the progeny of two like individuals
-differ from all the others to a marked degree. Some of these mutations
-are so different as to be regarded as new species. Some of the
-primroses show mutations, and Œnothera gigas is a mutation from Œnothera
-lamarkiana (see de Vries, Die Mutationstheorie, Leipzig).
-
-=675.= TABLE SHOWING HOMOLOGIES OF SPOROPHYTE AND GAMETOPHYTE IN
-ANGIOSPERMS.
-
-    TERMS CORRESPONDING TO THOSE USED IN PTERIDOPHYTES.  COMMON TERMS.
-
-    Sporophyte          {                            = Higher plant.
-    Spore-bearing part  {                            = Stamens and
-                        {                                carpels.
-    --------------------------------------------------------------------
-                        {                                     {Anther.
-    Sporophyte          {Microsporophyll             = Stamen {Filament.
-                        {
-                        {Microsporangium             = Pollen sac,
-                        {                                usually
-                        {                                two or four.
-    --------------------------------------------------------------------
-                        {Microspore at maturity      = Pollen grain.
-                        {   usually of 2 or 3 cells
-                        {  {young male prothallium}
-
-                        {
-                        {1. Large cell (part of      = Vegetative cell.
-                        {   antheridium wall?), with
-                        {   its nucleus surrounded
-                        {   by wall of spore
-    Male gametophyte    {2. Small cell with nucleus, = Generative cell.
-                        {   no wall, floating in
-                        {   protoplasm of large cell
-                        {   is the central cell of
-                        {   antheridium
-                        {  (male sexual organ)
-                        {Mature male prothallium     = Pollen grain
-                        {                                with tube.
-                        {Antheridium cell divided,   = Paternal cells,
-                        {  2 sperm cells                 or generative
-                        {                                cells.
-    --------------------------------------------------------------------
-                        {                                      {Stigma.
-                        {Macrosporophyll     = {Carpel or      {Style.
-    Sporophyte          {                      {simple pistil  {Ovary.
-                        {
-                        {
-                        {Macrosporangium, covered   = {Nucellus, covered
-                        {   by 1 or 2 coats           {   by 1 or 2
-                        {                             {   coats = ovule.
-    --------------------------------------------------------------------
-                        {Macrospore, cell in end of  = Uninuclear state
-                        {   macrosporangium, does         of embryo sac.
-                        {   not become free, cavity
-                        {   enlarges
-                        {Macrospore divides into
-                        {   8 cells to form young
-                        {   female prothallium       = Embryo sac.
-                        {
-    Female gametophyte. {Remnant of archegonium,     = Maternal cell,
-                        {  egg (female sexual organ)     or germ cell.
-                        {Growing part of prothallium = {Two polar nuclei
-                        {                              {   fused, making
-                        {                              {   endosperm
-                        {                              {   nucleus.
-                        {Mature female prothallium   = {Endosperm,
-                        {                              {  developed by
-                        {                              {  many divisions
-                        {                              {  of endosperm
-                        {                              {  nucleus.
-    --------------------------------------------------------------------
-    Young sporophyte    {After fecundation of egg, egg divides
-       surrounded by    {  to form embryo. Embryo in endosperm
-       parts of the     { (sometimes latter nearly or quite
-       gametophyte and  {   absent) surrounded by coats          = Seed.
-       new growth of old{
-       sporophyte       {
-       Young sporophyte surrounded by remnants of gametophyte and new
-         parts of old sporophyte (remains of endosperm and of nucellus,
-         and ovular coat) = the seed.
-
-
-
-
-CHAPTER XXXVII.
-
-MORPHOLOGY OF THE NUCLEUS AND SIGNIFICANCE OF GAMETOPHYTE AND
-SPOROPHYTE.
-
-
-=676.= In the development of the spores of the liverworts,
-mosses, ferns, and their allies, as well as in the development of the
-microspores of the gymnosperms and angiosperms, we have observed that
-four spores are formed from a single mother cell. These mother cells
-are formed as a last division of the fertile tissue (archesporium) of
-the sporangium. In ordinary cell division the nucleus always divides
-prior to the division of the cell. In many cases it is directly
-connected with the laying down of the dividing cell wall.
-
-[Illustration: Fig. 402. Forming spores in mother cells (Polypodium
-vulgare).]
-
-[Illustration: Fig. 403. Spores just mature and wall of mother cell
-broken (Asplenium bulbiferum).]
-
-=677. Direct division of the nucleus.=—The nucleus divides in two
-different ways. On the one hand the process is very simple. The nucleus
-simply fragments, or cuts itself in two. This is direct division.
-
-=678. Indirect division of the nucleus.=—On the other hand very
-complicated phenomena precede and attend the division of the nucleus,
-giving rise to a succession of nuclear figures presented by a definite
-but variable series of evolutions on the part of the nuclear substance.
-This is _indirect division_ of the nucleus, or _karyokinesis_. Indirect
-division of the nucleus is the usual method, and it occurs in the
-normal growth and division of the cell. The nuclear figures which are
-formed in the division of the mother cell into the four spores are
-somewhat different from those occurring in vegetative division, but
-their study will serve to show the general character of the process.
-
-=679. Chromatin and linin of the nucleus.=—In figure 404 is
-represented a pollen mother cell of the May-apple (podophyllum). The
-nucleus is in the resting stage. There is a network consisting of very
-delicate threads, the _linin_ network. Upon this network are numerous
-small granules, and at the junction of the threads are distinct knots.
-The nucleolus is quite large and prominent. The numerous small granules
-upon the linin stain very deeply when treated with certain dyes used in
-differentiating the nuclear structure. This deeply staining substance
-is the _chromatin_ of the nucleus.
-
-[Illustration: Fig. 404. Pollen mother cell of podophyllum, resting
-nucleus. Chromatin forming a network.]
-
-[Illustration: Fig. 405. Spirem stage of nucleus. _nu_, nuclear cavity;
-_n_, nucleolus; _Sp_, spirem.]
-
-[Illustration: Fig. 406. Forming spindle, threads from protoplasm with
-several poles, roping the chromosomes up to nuclear plate.
-
-(Figures 404-406 after Mottier.)]
-
-=680. The chromatin skein.=—One of the first nuclear figures in the
-preparatory stages of division is the chromatin _skein_ or _spirem_.
-The chromatin substance unites to form this. The spirem is in the form
-of a narrow continuous ribbon, or band, woven into an irregular skein,
-or gnarl, as shown in figure 405. This band splits longitudinally
-into two narrow ones, and then each divides into a definite number
-of segments, about eight in the case of podophyllum. Sometimes the
-longitudinal splitting of the band appears to take place after the
-separation into the chromatin segments. The segments remain in pairs
-until they separate at the nuclear plate.
-
-[Illustration: Fig. 407.
-
-Karyokinesis in pollen mother cells of podophyllum. At the left the
-spindle with the chromosomes separating at the nuclear plate; in the
-middle figure the chromosomes have reached the poles of the spindle,
-and at the right the chromosomes are forming the daughter nuclei.
-(After Mottier.)]
-
-=681. Chromosomes, nuclear plate, and nuclear spindle.=—Each
-one of these rod-like chromatin segments is a _chromosome_.
-The pairs of chromosomes arrange themselves in a median plane
-of the nucleus, radiating somewhat in a stellate fashion, forming
-the _nuclear plate_, or _monaster_. At the same time threads of the
-protoplasm (kinoplasm) become arranged in the form of a spindle,
-the axis of which is perpendicular to the nuclear plate of chromosomes,
-as shown in figure 407, at left. Each pair of chromosomes
-now separate in the line of the division of the original spirem,
-one chromosome of each pair going to one pole of the spindle,
-while the other chromosome of each pair goes to the opposite pole.
-The chromosomes here unite to form the daughter nuclei. Each of these
-nuclei now divide as shown in figure 409 (whether the chromosomes in
-this second division in the mother cell split longitudinally or divide
-transversely has not been definitely settled), and four nuclei are
-formed in the pollen mother cell. The protoplasm about each one of
-these four nuclei now surrounds itself with a wall and the spores are
-formed.
-
-[Illustration: Fig. 408. Different stages in the separation of divided
-U-shaped chromosomes at the nuclear plate. (After Mottier.) In
-podophyllum.]
-
-[Illustration: Fig. 409. Second division of nuclei in pollen mother
-cell of podophyllum, chromosomes at poles.]
-
-[Illustration: Fig. 410. Chromosomes uniting at poles to form the
-nuclei of the four spores. (After Mottier.)]
-
-=The number of chromosomes usually the same in a given species
-throughout one phase of the plant.=—In those plants which have been
-carefully studied, the number of chromosomes in the dividing nucleus
-has been found to be fairly constant in a given species, through all
-the divisions in that stage or phase of the plant, especially in the
-embryonic, or young growing parts. For example, in the prothallium, or
-gametophyte, of certain ferns, as osmunda, the number of chromosomes
-in the dividing nucleus is always twelve. So in the development of the
-pollen of lilium from the mother cells, and in the divisions of the
-antherid cell to form the generative cells or sperm cells, there are
-always twelve chromosomes so far as has been found. In the development
-of the egg of lilium from the macrospore there are also twelve
-chromosomes.
-
-=When fertilization takes place the number of chromosomes is doubled
-in the embryo.=—In the spermatozoid of osmunda then, as well as in
-the egg, since these are developed on the gametophyte, there are twelve
-chromosomes each. The same is true in the sperm cell (generative cell)
-of lilium, and also in the egg-cell. When these nuclei unite, as they
-do in fertilization, the paternal nucleus with the maternal nucleus,
-the number of chromosomes in the fertilized egg, if we take lilium as
-an example, is twenty-four instead of twelve; the number is doubled.
-The fertilized egg is the beginning of the sporophyte, as we have seen.
-Curiously throughout all the divisions of the nucleus in the embryonic
-tissues of the sporophyte, so far as has been determined, up to the
-formation of the mother cells of the spores, the number of chromosomes
-is usually the same.
-
-[Illustration: Fig. 411. Karyokinesis in sporophyte cells of
-podophyllum (twice the number of chromosomes here that are found in the
-dividing spore mother cells).]
-
-=682. Reduction of the number of chromosomes in the nucleus.=—If
-there were no reduction in the number of chromosomes at any point in
-the life cycle of plants, the number would thus become infinitely
-large. A reduction, however, does take place. This usually occurs,
-either in the mother cell of the spores or in the divisions of its
-nucleus, at the time the spores are formed. In the mother cells a sort
-of pseudo-reduction is effected by the chromatin band separating into
-one half the usual number of nuclear segments. So that in lilium during
-the first division of the nucleus of the mother cell the chromatin band
-divides into twelve segments, instead of twenty-four as it has done
-throughout the sporophyte stage. So in podophyllum during the first
-division in the mother cell it separates into eight instead of into
-sixteen. Whether a qualitative reduction by transverse division of the
-spirem band, unaccompanied by a longitudinal splitting, takes place
-during the first or second karyokinesis is still in doubt. Qualitative
-reduction does take place in some plants according to Beliaieff and
-others. Recently the author has found that it takes place in Trillium
-grandiflorum during the second karyokinesis, and in Arisæma triphyllum
-the chromosomes divide both transversely and longitudinally during
-the first karyokinesis forming four chromosomes, and a qualitative
-reduction takes place here.
-
-=683. Significance of karyokinesis and reduction.=—The precision
-with which the chromatin substance of the nucleus is divided, when
-in the spirem stage, and later the halves of the chromosomes are
-distributed to the daughter nuclei, has led to the belief that this
-substance bears the hereditary qualities of the organism, and that
-these qualities are thus transmitted with certainty to the offspring.
-In reduction not only is the original number of chromosomes restored,
-it is believed by some that there is also a qualitative reduction of
-the chromatin, i.e. that each of the four spores possesses different
-qualitative elements of the chromatin as a result of the reducing
-division of the nucleus during their formation.
-
-The increase in number of chromosomes in the nucleus occurs with the
-beginning of the sporophyte, and the numerical reduction occurs at the
-beginning of the gametophyte stage. The full import of karyokinesis and
-reduction is perhaps not yet known, but there is little doubt that a
-profound significance is to be attached to these interesting phenomena
-in plant life.
-
-=684. The gametophyte may develop directly from the tissue of the
-sporophyte.=—If portions of the sporophyte of certain of the
-mosses, as sections of a growing seta, or of the growing capsule, be
-placed on a moist substratum, under favorable conditions some of the
-external cells will grow directly into protonemal threads. In some
-of the ferns, as in the sensitive fern (onoclea), when the fertile
-leaves are expanding into the sterile ones, protonemal outgrowths occur
-among the aborted sporangia on the leaves of the sporophyte. Similar
-rudimentary protonemal growths sometimes occur on the leaves of the
-common brake (pteris) among the sporangia, and some of the rudimentary
-sporangia become changed into the protonema. In some other ferns, as
-in asplenium (A. filix-fœmina, var. clarissima), prothallia are borne
-among the aborted sporangia, which bear antheridia and archegonia. In
-these cases the gametophyte develops from the tissue of the sporophyte
-without the intervention or necessity of the spores. This is _apospory_.
-
-[Illustration: Fig. 412. Apogamy in Pteris cretica.]
-
-=685. The sporophyte may develop directly from the tissue of the
-gametophyte.=—In some of the ferns, Pteris cretica for example,
-the embryo fern sporophyte arises directly from the tissue of the
-prothallium, without the intervention of sexual organs, and in some
-cases no sexual organs are developed on such prothallia. Sexual organs,
-then, and the fusion of the spermatozoid and egg nucleus are not here
-necessary for the development of the sporophyte. This is _apogamy_.
-Apogamy occurs in some other species of ferns, and in other groups of
-plants as well, though it is in general a rare occurrence except in
-certain species, where it may be the general rule.
-
-=686. Types of nuclear division.=—The nuclear figures in the
-vegetative cells are usually different from those in the spore
-mother cells. In the spore mother cells there are two types of
-nuclear division. (1) The first division in the mother cell is called
-_heterotypic_. The early stages of this division usually extend over a
-longer period than the second, and the figures are more complex. Before
-the chromosomes arrive at the nuclear plate they are often in the form
-of rings, or tetrads, or in the form of X, V, or Y, and the number is
-usually one half the number in the preceding cells of the sporophyte.
-(2) The _homotypic_ division immediately follows the heterotypic and
-the figures are simpler, often the chromosomes being of a hook form,
-or sometimes much stouter than in the heterotypic division. In the
-vegetative cells (sometimes called somatic cells, or body cells in
-contrast with reproductive cells) there is another type, called by some
-the _vegetative type_. The chromosomes here are often in the form of
-the letter U, and the figures are much simpler than in the heterotypic
-division. In the somatic cells of the sporophyte, as stated above,
-the number of chromosomes is double that found in the heterotypic
-and homotypic divisions of the mother cells and in the somatic cells
-of the gametophyte, Fig. 411 represents a late stage in the division
-of somatic cells in the sporophyte of podophyllum. The root-tips of
-various plants as the onion, lily, etc., are excellent places in which
-to study nuclear division in the somatic cells of the sporophyte.
-
-=687. Comparison with animals.=—In animals there does not seem
-to be anything which corresponds with the gametophyte of plants unless
-the sperm cells and eggs themselves represent it. Heterotypic and
-homotypic division with the accompanying reduction of the number of the
-chromosomes takes place in animals usually in the mother cells of the
-sperms and eggs. At the time of fertilization the number of chromosomes
-is doubled, so that all the somatic cells (except in rare instances)
-from the fertilized egg to the mother cells of sperms and eggs have the
-doubled number of chromosomes. Reduction, therefore, takes place in
-animals just prior to the formation of the gametes, while in plants it
-takes place just prior to the formation of the gametophytes.
-
-=688. Perhaps there is not a fundamental difference between
-gametophyte and sporophyte.=—This development of sporophyte, or
-leafy-stemmed plant of the fern (parag. 685), from the tissue of the
-gametophyte is taken by some to indicate that there is not such a great
-difference between the gametophyte and sporophyte of plants as others
-contend. In accordance with this view it has been suggested that the
-leafy-stemmed moss plant, as well as the leafy stem of the liverworts,
-is homologous with the sporophyte or leafy stem of the fern plant; that
-it arises by budding from the protonema; and that the sexual organs are
-borne then on the sporophyte.
-
-
-
-
-PART III.
-
-PLANT MEMBERS IN RELATION TO ENVIRONMENT.
-
-
-
-
-CHAPTER XXXVIII.
-
-THE ORGANIZATION OF THE PLANT.
-
-
-I. Organization of Plant Members.[37]
-
-=689.= It is now generally conceded that the earliest plants to
-appear in the world were very simple in form and structure. Perhaps the
-earliest were mere bits of naked protoplasm, not essentially different
-from early animal life. The simplest ones which are clearly recognized
-as plants are found among the lower algæ and fungi. These are single
-cells of very minute size, roundish, oval, or oblong, existing
-during their growing period in water or in a very moist substratum
-or atmosphere. Examples are found in the red snow plant (_Sphærella
-nivalis_), the Pleurococcus, the bacteria; and among small colonies of
-these simple organisms (Pandorina) or the thread-like forms (Spirogyra,
-Œdogonium, etc.). It is evident that some of the life relations of such
-very simple organisms are very easily obtained—that is, the adjustment
-to environment is not difficult. All of the living substance is very
-closely surrounded by food material in solution. These food solutions
-are easily absorbed. Because of the minute size of the protoplasts and
-of the plant body, they do not have to solve problems of transport of
-food to distant parts of the body. When we pass to more bulky organisms
-consisting of large numbers of protoplasts closely compacted together,
-the problem of relation to environment and of food transport become
-felt; the larger the organism usually the greater are these problems.
-A point is soon reached at which there is a gain by a differentiation
-in the work of different protoplasts, some for absorption, some for
-conduction, some for the light relation, some for reproduction, and
-so on. There is also a gain in splitting the form of the plant body
-up into parts so that a larger surface is exposed to environment
-with an economy in the amount of building material required. In this
-differentiation of the plant body into parts, there are two general
-problems to be solved, and the plant to be successful in its struggle
-for existence must control its development in such a way as to preserve
-the balance between them. (1) A ready display of a large surface to
-environment for the purpose of acquiring food and the disposition of
-waste. (2) The protection of the plant from injuries incident to an
-austere environment.
-
-It is evident with the great variety of conditions met with in
-different parts of the same locality or region, and in different parts
-of the globe, that the plant has had very complex problems to meet and
-in the solution of them it has developed into a great variety of forms.
-It is also likely that different plants would in many cases meet these
-difficulties in different ways, sometimes with equal success, at other
-times with varied success. Just as different persons, given some one
-piece of work to do, are likely to employ different methods and reach
-results that are varied as to their value. While we cannot attribute
-consciousness or choice to plants in the sense in which we understand
-these qualities in higher animals, still there is something in their
-“constitution” or “character” whereby they respond in a different
-manner to the same influences of environment. This is, perhaps,
-imperceptible to us in the different individuals of the same species,
-but it is more marked in different species. Because of our ignorance of
-this occult power in the plant, we often speak of it as an “inherent”
-quality.
-
-      Perhaps the most striking examples one might use to
-    illustrate the different line of organization among
-    plants in two regions where the environment is very
-    different are to be found in the adaptation of the
-    cactus or the yucca to desert regions, and the oak or
-    the cucurbits to the land conditions of our climate.
-    The cactus with stem and leaf function combined in a
-    massive trunk, or the yucca with bulky leaves expose
-    little surface in comparison to the mass of substance,
-    to the dry air. They have tissue for water storage and
-    through their thick epidermis dole it out slowly since
-    there is but little water to obtain from dry soil.
-
-      The cucurbits and the oak in their foliage leaves
-    expose a very large surface in proportion to the mass
-    of their substance, to an atmosphere not so severely
-    dry as that of the desert, while the roots are able
-    to obtain an abundant supply of water from the moist
-    soil. The cactus and the yucca have differentiated
-    their parts in a very different way from the oak or the
-    cucurbits, in order to adapt themselves to the peculiar
-    conditions of the environment.
-
-      When we say that certain plants have the power to
-    adapt themselves to certain conditions of environment,
-    we do not mean to say that if the cucurbits were
-    transferred to the desert they would take on the form
-    of the cactus or the yucca. They could do neither.
-    They would perish, since the change would be too great
-    for their organization. Nor do we mean, that, if the
-    cactus or yucca were transferred from the desert to our
-    climate, they would change into forms with thin foliage
-    leaves. They could not. The fact is that they are
-    enabled to live in our climate when we give them some
-    care, but they show no signs of assuming characters
-    like those of our vegetation. What we do mean is, that
-    where the change is not too great nor too sudden, some
-    of the plants become slightly modified. This would
-    indicate that the process of organization and change of
-    form is a very slow one, and is therefore a question of
-    time—ages it may be—in which change in environment
-    and adaptation in form and structure have gone on
-    slowly hand in hand.
-
-=690. Members of the plant body.=—The different parts into which
-the plant body has become differentiated are from one point of view,
-spoken of as members. It is evident that the simplest forms of life
-spoken of above do not have members. It is only when differentiation
-has reached the stage in which certain more or less prominent parts
-perform certain functions for the plant that members are recognized.
-In the algæ and fungi there is no differentiation into stem and leaf,
-though there is an approach to it in some of the higher forms. Where
-this simple plant body is flattened, as in the sea-wrack, or ulva, it
-is a _frond_. The Latin word for frond is _thallus_, and this name is
-applied to the plant body of all the lower plants, the algæ and fungi.
-The algæ and fungi together are sometimes called _thallophytes_, or
-_thallus plants_. The word thallus is also sometimes applied to the
-flattened body of the liverworts. In the foliose liverworts and mosses
-there is an axis with leaf-like expansions. These are believed by some
-to represent true stems and leaves; by others to represent a flattened
-thallus in which the margins are deeply and regularly divided, or in
-which the expansion has only taken place at regular intervals.
-
-In the higher plants there is usually great differentiation of the
-plant body, though in many forms, as in the duckweeds, it is in the
-form of a frond. While there is a great variety in the form and
-function of the members of the plant body, they are all reducible to a
-few fundamental members. Some reduce these forms to three, the _root_,
-_stem_, _leaf_; while others to two, the _root_, and _shoot_, which is
-perhaps the best primary subdivision, and the shoot is then divided
-into stem and leaf, the leaf being a lateral outgrowth of the stem, and
-can be indicated by the following diagram:
-
-
-                            {Stem.
-                  {Shoot····{
-    Plant body····{         {Leaf.
-                  {Root.
-
-
-KINDS OF SHOOTS.
-
-=691.= Since it is desirable to consider the shoot in its relation
-to environment, for convenience in discussion we may group shoots into
-four prominent kinds: (1) _Foliage shoots_; (2) _Shoots without foliage
-leaves_; (3) _Floral shoots_; (4) _Winter conditions of shoots and
-buds._ Topic (4) will be treated in Chapter XXXIX, section IV.
-
-[Illustration: Fig. 413. Lupinus perennis. Foliage shoot and floral
-shoot.]
-
-=692. (1st) Foliage shoots.=—Foliage shoots are either aerial,
-when their relation is to both light and air; or they are aquatic,
-when their relation is to both light and water. They bear green
-leaves, and whether in the air or water we see that light is one of
-the necessary relations for all. Naturally there are several ways in
-which a shoot may display its leaves to the light and air or water.
-Because of the great variety of conditions on the face of the earth
-and the multitudinous kinds of plants, there is the greatest diversity
-presented in the method of meeting these conditions. There is to be
-considered the problem of support to the shoot in the air, or in the
-water. The methods for solving this problem are fundamentally different
-in each case, because of the difference in the density of air and
-water, the latter being able to buoy up the plant to a great degree,
-particularly when the shoot is provided with air in its intercellular
-spaces or air cavities. In the solution of the problem in the relation
-of the shoot to aerial environment, stem and leaf have in most cases
-coöperated;[38] but in view of the great variety of stems and their
-modifications, as well as of leaves, it will be convenient to discuss
-them in separate chapters.
-
-[Illustration: Fig. 413_a_. Burrowing type, the mandrake, a “rhizome.”]
-
-=693. (2d) Shoots without foliage leaves.=—These are subterranean
-or aerial. Nearly all subterranean shoots have also aerial shoots,
-the latter being for the display of foliage leaves (foliage-shoots),
-and also for the display of flowers (flower-shoots). The subterranean
-kinds bear scale leaves, i.e., the leaves not having a light relation
-are reduced in size, being small, and they lack chlorophyll. Examples
-are found in Solomon’s seal, mandrake (fig. 413_a_), etc. Here the
-scale leaves are on the bud at the end of the underground stem from
-which the foliage shoot arises. Aerial shoots which lack foliage
-leaves are the dodder, Indian-pipe-plant, beech drops, etc. These
-plants are saprophytes or parasites (see Chapter IX). Deriving their
-carbohydrate food from other living plants, or from humus, they do not
-need green leaves. The leaves have, therefore, probably been reduced
-in size to mere scales, and accompanying this there has been a loss of
-the chlorophyll. Other interesting examples of aerial shoots without
-foliage leaves are the cacti where the stem has assumed the leaf
-function and the leaves have become reduced to mere spines. The various
-modifications which shoots have undergone accompanying a change in
-their leaf relation will be discussed under stems in Chapter XXXIX.
-
-=694. (3d) Floral shoots.=—The floral shoot is the part of the
-plant bearing the flower. As interpreted here it may consist of but a
-single flower with its stalk, as in Trillium, mandrake, etc., or of
-the clusters of flowers on special parts of the stem, termed flower
-clusters, as the _catkin_, _raceme_, _spike_, _umbel_, _head_, etc. In
-the floral shoot as thus interpreted there are several peculiarities to
-observe which distinguish it from the foliage shoot and adapt it to its
-life relations.
-
-The floral shoot in many respects is comparable to the foliage shoot,
-as seen from the following peculiarities:
-
-      (1) It usually possesses, beside the flowers, small
-    green leaves which are in fact foliage though they are
-    very much reduced in size, because the function of
-    the shoot as a foliage shoot is subordinated to the
-    function of the floral shoot. These small leaves on the
-    floral shoot are termed _bracts_.
-
-      (2) It may be (_a_) unbranched, when it would consist
-    of a single flower, or (_b_) branched, when there would
-    be several to many flowers in the flower cluster.
-
-      (3) The flower bud has the same origin on the shoot
-    as the leaf bud; it is either terminal or axillary, or
-    both.
-
-      (4) The members of the flower belong to the leaf
-    series, i.e., they are leaves, but usually different
-    in color from foliage leaves, because of the different
-    life relation which they have to perform. Evidence
-    of this is seen in the transition of sepals, petals,
-    stamens, or pistils, to foliage leaves in many flowers,
-    as in the pond lily, the abnormal forms of trillium,
-    and many monstrosities in other flowers (see Chapter
-    XXXIV).
-
-      (5) The position of the members of the flower on
-    its axis, though usually more crowded, in many cases
-    follows the same plan as the leaves on the stem.
-
-The various kinds of floral shoots or flower clusters will be discussed
-in Chapter XLII, on the Floral Shoot.
-
-
-II. Organization of Plant Tissues.
-
-=695.= A tissue is a group of cells of the same kind having a
-similar position and function. In large and bulky plants different
-kinds of tissue are necessary, not only because the work of the plant
-can be more economically performed by a division of labor, but also
-cells in the interior of the mass or at a distance from the source
-of the food could not be supplied with food and air unless there
-were specialized channels for conducting food and specialized tissue
-for support of the large plant body. In these two ways most of the
-higher plants differ from the simple ones. The tissues for conduction
-are sometimes called collectively the _mestome_, while tissues for
-mechanical support are called _stereome_. Division of labor has
-gone further also so that there are special tissues for absorption,
-assimilation, perception, reproduction, and the like. The tissues of
-plants are usually grouped into three systems: (1) The Fundamental
-System, (2) The Fibrovascular System, (3) The Epidermal System. Some of
-the principal tissues are as follows:
-
-
-1. THE FUNDAMENTAL SYSTEM.
-
-=696. Parenchyma.=—Tissue composed of thin-walled cells which
-in the normal state are living. Parenchyma forms the loose and spongy
-tissue in leaves, as well as the palisade tissue (see Chapter IV); the
-soft tissue in the cortex of root and stem (Fig. 414); as well as that
-of the pith, of the pith-rays or medullary rays of the stem; and is
-mixed in with the other elements of the vascular bundle where it is
-spoken of as wood parenchyma and bast parenchyma; and it also includes
-the undifferentiated tissue (meristem) in the growing tips of roots and
-shoots; also the “intrafascicular” cambium (i.e., between the bundles,
-some also include the cambium within the bundle).
-
-=697. Collenchyma.=—This is a strengthening tissue often found
-in the cortex of certain shoots. It also is composed of living cells.
-The cells are thickened at the angles, as in the tomato and many other
-herbs (fig. 414).
-
-=698. Sclerenchyma, or stone-tissue.=—This is also a
-strengthening tissue and consists of cells which do not taper at the
-ends and the walls are evenly thickened, sometimes so thick that the
-inside (lumen) of the cell has nearly disappeared. Usually such cells
-contain no living contents at maturity. Sclerenchyma is very common in
-the hard parts of nuts, and underneath the epidermis of stems and
-leaves of many plants, as in the underground stems of the bracken fern,
-the leaves of pines (fig. 415), etc.
-
-[Illustration: Fig. 414. Transverse section of portion of tomato stem.
-_ep_, epidermis; _ch_ chlorophyll-bearing cells; _co_, collenchyma;
-_cp_, parenchyma.]
-
-[Illustration: Fig. 415. Margin of leaf of Pinus pinaster, transverse
-section, _c_, cuticularized layer of outer wall of epidermis;
-_i_, inner non-cuticularized layer; _c´_, thickened outer wall of
-marginal cell; _g_, _i´_, hypoderma of elongated sclerenchyma; _p_,
-chlorophyll-bearing parenchyma; _pr_, contracted protoplasmic contents.
-×800. (After Sachs.)]
-
-[Illustration: Fig. 416. Section through a lenticel of Betula alba
-showing stoma at top, phellogen below producing rows of flattened
-cells, the cork. (After De Bary.)]
-
-=699. Cork.=—In many cases there is a development of “cork”
-tissue underneath the epidermis. Cork tissue is developed by repeated
-division of parenchyma cells in such a way that rows of parallel cells
-are formed toward the outside. These are in distinct layers, soon lose
-their protoplasm and die; there are no intercellular spaces and the
-cells are usually of regular shape and fit close to each other. In
-some plants the cell walls are thin (cork oak), while in others they
-are thickened (beech). The tissue giving rise to cork is called “cork
-cambium,” or phellogen, and may occur in other parts of the plant. For
-example, where plants are wounded the living exposed parenchyma cells
-often change to cork cambium and develop a protective layer of cork.
-The walls of cork cells contain a substance termed _suberin_, which
-renders them nearly waterproof.
-
-=700. Lenticels.=—These are developed quite abundantly underneath
-stomates on the twigs of birch, cherry, beech, elder, etc. The
-phellogen underneath the stoma develops a cushion of cork which presses
-outward in the form of an elevation at the summit of which is the stoma
-(fig. 416). The lenticels can easily be seen.
-
-
-2. THE FIBROVASCULAR SYSTEM.
-
-=701. Fibrous tissue.=[39]—This consists of thick-walled cells,
-usually without living contents which are elongated and taper at the
-ends so that the cells, or fibers, overlap. It is common as one of the
-elements of the vascular bundles, as wood fibers and bast fibers.
-
-=702. Vascular tissue, or tracheary tissue.=—This consists of the
-vessels or ducts, and tracheides, which are so characteristic of the
-vascular bundle (see Chapter V) and forms a conducting tissue for the
-flow of water. The vascular tissue contains spiral, annular, pitted,
-and scalariform vessels and tracheides according to the marking on the
-walls (figs. 58, 59). These are all without protoplasmic contents when
-mature. There are also thin-walled living cells intermingled called
-wood parenchyma. In the conifers (pines, etc.) the tracheary tissue is
-devoid of true vessels except a few spiral vessels in the young stage,
-while it is characterized by tracheides with peculiar markings. These
-marks on the tracheides are due to the “bordered” pits appearing as two
-concentric rings one within the other. These can be easily seen in a
-longitudinal section of wood of conifers.
-
-=703. Sieve tissue.=—This consists of elongated tubular cells
-connected at the ends, the cross walls being perforated at the ends.
-These are in the phloem part of the bundle, and serve to conduct
-downwards the dissolved substances elaborated in the leaves.
-
-=704. Fascicular cambium.=—This is the living, cell-producing
-tissue in the vascular bundle, which in the open bundle adds to the
-phloem on one side and the xylem on the other.
-
-
-3. THE EPIDERMAL SYSTEM.
-
-=705.= To the epidermal system belong the epidermis and the
-various outgrowths of its cells in the form of hairs, or _trichomes_,
-as well as the guard cells of the stomates, and probably some of the
-reproductive organs.
-
-=706. The epidermis.=—The epidermis proper consists of a
-single layer of external cells originating from the outer layer of
-parenchyma cells at the growing apex of the stem or root. These cells
-undergo various modifications of form. In many cases they lose their
-protoplasmic contents. In many cases the outer wall becomes thickened,
-especially in plants growing in dry situations or where they are
-exposed to drying conditions. The epidermal cells generally become
-considerably flattened, and are usually covered with a more or less
-well developed waterproof cuticle, a continuous layer over the
-epidermis. In many plants the cuticle is covered with a waxy exudation
-in the form of a thin layer, or of rounded grains, or slender rods,
-or grains and needles in several layers. These waxy coverings are
-sometimes spoken of as “bloom” on leaves and fruit.
-
-=707. Trichomes.=—Trichome is a general term including various
-hair-like outgrowths from the epidermis, as well as scales, prickles,
-etc. These include root hairs, rhizoids, simple or branched hairs,
-glandular hairs, glandular scales, etc. Glandular hairs are found on
-many plants, as tomato, verbena, primula, etc.; glandular scales on
-the hop; simple-celled hairs on the evening primrose, cabbage, etc.;
-many-celled hairs on the primrose, pumpkin; branched hairs on the
-shepherd’s-purse, mullein, etc., stellate hairs on some oak leaves.
-
-For stomates see Chapter IV.
-
-
-4. ORIGIN OF THE TISSUES.
-
-=708. Meristem tissue.=—The various tissues consisting of cells
-of dissimilar form are derived from young growing tissue known as
-_meristem_. Meristem tissue consists of cells nearly alike in form,
-with thin cell walls and rich in protoplasm. It is situated at the
-growing regions of the plants. In the higher plants these regions in
-general are three in number, the stem and root apex, and the cambium
-cylinder beneath the cortex. Tissues produced from the stem and root
-apex are called _primary_, those from the cambium _secondary_. In most
-cases the main bulk of the plant is secondary tissue, while in the corn
-plant it is all primary.
-
-[Illustration: Fig. 417. Section through growing point of stem, _d_,
-dermatogen; _p_, plerome; periblem between. (After De Bary.)]
-
-=709. Origin of stem tissues.=—Just back of the apical meristem
-in a longitudinal section of a growing point it can be seen that the
-cells are undergoing a change in form, and here are organized three
-formative regions. The outer layer of cells is called _dermatogen_
-(skin producer), because later it becomes the epidermis. The central
-group of elongating cells is the _plerome_ (to fill). This later
-develops the _central cylinder_, or _stele_, as it is called
-(fig. 417). Surrounding the plerome and filling the space between it
-and the dermatogen is the third formative tissue called the _periblem_,
-which later forms the cortex (bark or rind), and consists of
-parenchyma, collenchyma, sclerenchyma, or cork, etc., as the case may
-be. It should be understood that all these different forms and kinds
-of cells have been derived from meristem by gradual change. In the
-mature stems, therefore, there are three distinct regions, the central
-cylinder or stele, the cortex, and the epidermis.
-
-[Illustration: Fig. 418. Concentric bundle from stem of Polypodium
-vulgare. Xylem in the center, surrounded by phloem, and this by the
-endodermis. (From the author’s Biology of Ferns.)]
-
-=710. Central cylinder or stele.=—As the central cylinder is
-organized from the plerome it becomes differentiated into the vascular
-bundles, the pith, the pith-rays (medullary rays) which radiate from
-the pith in the center between the bundles out to the cortex, and
-the pericycle, a layer of cells lying between the central cylinder
-and the cortex. The bundles then are farther organized into the
-xylem and phloem portions with their different elements, and the
-fascicular cambium (meristem) separating the xylem and phloem, as
-described in Chapter V. Such a bundle, where the xylem and phloem
-portions are separated by the cambium is called an open bundle (as
-in fig. 58). Where the phloem and xylem lie side by side in the same
-radius the bundle is a _collateral_ one. Dicotyledons and conifers are
-characterized by open collateral bundles. This is why trees and many
-other perennial plants continue to grow in diameter each year.
-The cambium in the open bundle forms new tissue each spring and
-summer, thus adding to the phloem on the outside and the xylem on
-the inside. In the spring and early summer the large vessels in the
-xylem predominate, while in late summer wood fibers and small vessels
-predominate and this part of the wood is firmer. Since the vascular
-bundles in the stem form a circle in the cylinder, this difference
-in the size of the spring and late summer wood produces the “annual”
-rings, so evident in the cross-section of a tree trunk. Branches
-originate at the surface involving epidermis, cortex, and the bundles.
-
-In monocotyledonous plants (corn, palm, etc.) the bundles are not
-regularly arranged to form a hollow cylinder, but are irregularly
-situated through the stele. There is no meristem, or cambium, left
-between the xylem and phloem portions of the bundle and the bundle is
-thus _closed_ (as in fig. 60), since it all passes over into permanent
-tissue. In most monocotyledons there is, therefore, practically no
-annual increase in diameter of the stem.
-
-[Illustration: Fig. 419. Section of stem (rhizome) of Pteris aquilina.
-_sc_, thick-walled sclerenchyma; _a_, thin-walled sclerenchyma; _par_,
-parenchyma.]
-
-=711. Ferns.=—In the ferns and most of the Pteridophytes an
-apical meristem tissue is wanting, its place being taken by a single
-apical cell from the several sides of which cells are successively
-cut off, though Isoetes and many species of Lycopodium have an apical
-meristem group. In most of the Pteridophytes also the bundles are
-_concentric_ instead of collateral. Fig. 418 represents one of the
-bundles from the stem of the polypody fern. The xylem is in the center,
-this surrounded by the phloem, the phloem by the phloem sheath, and
-this in turn by the endodermis, giving a concentric arrangement of the
-component tissues. A cross-section of the stem (fig. 419) shows two
-large areas of sclerenchyma, which gives the chief mechanical support,
-the bundles being comparatively weak.
-
-=712. Origin of root tissues.=—A similar apical meristem exists
-in roots, but there is in addition a fourth region of formative
-tissue in front of the meristem called _calyptrogen_ (fig. 420). This
-gives rise to the “root cap” which serves to protect the meristem.
-The vascular cylinder in roots is very different from that of the
-stem. There is a solid central cylinder in which the groups of xylem
-radiate from the center and groups of phloem alternate with them but
-do not extend so near the center (fig. 421). As the root ages, changes
-take place which obscure this arrangement more or less. Branches of
-the roots arise from the central cylinder. In fern roots the apical
-meristem is replaced by a single four-sided (tetrahedral) apical cell,
-the root cap being cut off by successive divisions of the outer face,
-while the primary root tissues are derived from the three lateral faces.
-
-[Illustration: Fig. 420. Median longitudinal section of the apex of a
-root of the barley, Hordeum vulgare. _k_, calyptrogen; _d_, dermatogen;
-_c_, its thickened wall; _pr_, periblem; _pl_, plerome; _en_,
-endodermis; _i_, intercellular air-space in process of formation; _a_,
-cell row destined to form a vessel; _r_, exfoliated cells of the root
-cap. (After Strasburger.)]
-
-[Illustration: Fig. 421. Cross-section of fibrovascular bundle in
-adventitious root of Ranunculus repens. _w_, pericycle; _g_, four
-radial plates of xylem; alternating with them are groups of phloem.
-This is a radial bundle. (After De Bary.)]
-
-=Function of the root cap.=—The root cap serves an important
-function in protecting the delicate meristem or cambium at the tip of
-the root. These cells are, of course, very thin-walled, and while there
-is not so much danger that they would be injured from dryness, since
-the soil is usually moist enough to prevent evaporation, they would be
-liable to injury from friction with the rough particles of soil. No
-similar cap is developed on the end of the stem, but the meristem here
-is protected by the overlapping bud-scales. One of the most striking
-illustrations of a root cap may be seen in the case of the Pandanus, or
-screw-pine, often grown in conservatories (see fig. 447). On the prop
-roots which have not yet reached the ground the root caps can readily
-be seen, since they are so large that they fit over the end of the root
-like a thimble on the finger.
-
-=713. Descriptive Classification of Tissues.=
-
-                  { Epidermis.
-                  {
-                  {                 { Simple hairs.
-                  {                 { Many-celled hairs.
-                  {                 { Branched hairs, often stellate.
-    Epidermal     { Trichomes.      { Clustered, tufted hairs.
-      System. ····{                 { Glandular hairs.
-                  {                 { Root hairs.
-                  {                 { Prickles.
-                  {
-                  { Guard cells of stomates.
-                                    { Spiral vessels.
-                                    { Pitted vessels.
-                                    { Scalariform vessels.
-                  { Xylem (wood).   { Annular vessels.
-                  {                 { Tracheides.
-                  {                 { Wood fibers.
-                  {                 { Wood parenchyma.
-    Fibrovascular {
-      System. ····{ Cambium (fascicular).
-                  {
-                  {                 { Sieve tubes.
-                  { Phloem (bast).  { Bast fibers.
-                                    { Companion cells.
-                                    { Bast parenchyma.
-                                                 { Cork.
-                                                 { Collenchyma.
-                                    { Cortex.····{ Parenchyma.
-                                    {            { Fibers.
-                                    {            { Milk tissue.
-                                    {
-                                    { Pith-ray.··{ Parenchyma.
-                                    {            { Intrafascicular
-                  { Stem and root.  {                      cambium.
-                  {                 { Pith.······{ Parenchyma.
-                  {                 {            { Sclerenchyma.
-                  {                 {
-    Fundamental   {                 { Bundle-sheath.
-      System. ····{                 {
-                  {                 { Endodermis.
-                  {
-                  { Leaves.         { Palisade tissue.
-                  {                 { Spongy parenchyma.
-                  {
-                  { Reproductive Organs (mainly fundamental).
-
-=714. Physiological Classification of Tissues.=
-
-_Formative Tissue._
-
-Thin-walled cells composing the meristem, capable of division and from
-which other tissues are formed.
-
-_Protective Tissue._
-
-_Tegumentary System._—Epidermis, periderm, bark protecting the plant
-from external contact.
-
-_Mechanical System._—Bast tissue, bast-like tissue, collenchyma,
-sclerenchyma, afford protection against harmful bending, pulling, etc.
-
-_Nutritive Tissues._
-
-_Absorptive System._—Root hairs and cells, rhizoids, aerial root
-tissue, absorptive leaf glands, absorptive organs in seeds, haustoria
-of parasites, etc.
-
-_Assimilatory System._—Assimilating cells in leaf and stem.
-
-_Conductive System._—Sieve tissue, tracheary tissue, milk tissue,
-conducting parenchyma, etc.
-
-_Food-storing System._—Water reservoir, water tissue, slime tissue,
-fleshy roots and stems, endosperm and cotyledons, etc.
-
-_Aerating System._—Air spaces and tubes, special air tissue,
-air-seeking roots, stomates, lenticels, etc.
-
-_Secretory and Excretory System._—Water glands, digestive glands,
-resin glands, nectaries, tannin, pitch and oil receptacles, etc.
-
-_Apparatus and Tissues for Special Duties._
-
-Holdfasts.
-
-Tissues of movement, parachute hairs, floating tissue, hygroscopic
-tissue, living tissue.
-
-For perceiving stimuli.
-
-For conducting stimuli, etc.
-
-FOOTNOTES:
-
-[37] =Suggestions to the teacher.=—In the study of the flowering plants
-in the secondary school and in elementary courses three general topics
-are suggested. 1st, the study of the form and members of the plant and
-their arrangement, as in Chapters XXXVIII-XLV. 2d, the study of a few
-plants representative of the more important families, in order that the
-members of the plant, as studied under the first topic, may be seen in
-correlation with the plant as a whole in a number of different types.
-3d, the study of plants in their relation to environment, as in Chapter
-XLVI. The first and second topics can be conducted consecutively in the
-classroom and laboratory. The third topic can be studied at opportune
-times during the progress of topics 1 and 2. For example, while
-studying topic 1 excursions can be made to study winter conditions of
-buds, shoots, etc., if in winter period, or the relations of leaves,
-etc., to environment, if in the growing period. While studying topic 2
-excursions can be made to study flower relations, and also vegetation
-relations to environment (see Chapters XLVI-LVII of the author’s
-“College Text-book of Botany”). It is believed that a study of these
-three general topics is of much more value to the beginning student
-than the ordinary plant analysis and determination of species.
-
-[38] It is interesting to note that in some foliage shoots the stem is
-entirely subterranean. See discussion of the bracken fern and sensitive
-fern in Chapter XXXIX.
-
-[39] Some fibers occur also very frequently in the Fundamental System,
-forming bundle-sheaths, or strands of mechanical tissue in the cortex.
-
-
-
-
-CHAPTER XXXIX.
-
-THE DIFFERENT TYPES OF STEMS. WINTER SHOOTS AND BUDS.
-
-
-I. Erect Stems.
-
-=715. Columnar type.=—The columnar type of stem may be simple or
-branched. When branching occurs the branches are usually small and in
-general subordinate to the main axis. The sunflower (Helianthus annuus)
-is an example. The foliage part is mainly simple. The main axis remains
-unbranched during the larger part of the growth-period. The principal
-flowerhead terminates the stem. Short branches bearing small heads
-then arise in the axils of a few of the upper leaves. In dry, poor
-soil, or where other conditions are unfavorable, there may be only the
-single terminal flowerhead, when the stem is unbranched. The mullein
-is another columnar stem. The foliage part is rarely branched, though
-branches sometimes occur where the main axis has become injured or
-broken. The flower stem is terminal. The corn plant and the Easter lily
-are good illustrations also of the columnar stem.
-
-Among trees the Lombardy poplar (Populus fastigiata) is an excellent
-example of the columnar type. Though this is profusely branched, the
-branches are quite slender and small in contrast with the main axis,
-unless by some injury or other cause two large axes may be developed.
-As the technical name indicates, the branching is fastigiate, i.e., the
-branches are crowded close together and closely surround the central
-axis. The royal palm and some of the tree ferns have columnar, simple
-stems, but the large, wide-spreading leaves at the top of the stem give
-the plant anything but a cylindrical habit. Some cedars and arbor-vitæ
-are also columnar.
-
-The advantages of the columnar habit of stem are three: (1) That the
-plant stands above other neighboring ones of equal foliage area and
-thus is enabled to obtain a more favorable light relation; (2) where
-large numbers of plants of the same species are growing close together,
-they can maintain practically the same habit as where growing alone;
-(3) the advantage gained by other types in their neighborhood in less
-shading than if the type were spreading. The cylindrical type can,
-therefore, grow between other types with less competition for existence.
-
-[Illustration: Fig. 422. Cylindrical stem of mullein.]
-
-[Illustration: Fig. 423. Conical type of larch.]
-
-=716. The cone type.=—This is well exampled in the larches,
-spruces, the gingko tree, some of the pines, cedars, and other
-gymnosperms. In the cone type, the main axis extends through the system
-of branches like a tall shaft, i.e., the trunk is _excurrent_. The
-lower branches are wide-spreading, and the branches become successively
-shorter, usually uniformly, as one ascends the stem. The branching is
-of two types: (1) the branches are in false whorls; (2) the branches are
-distributed along the stem. To the first type belong the pines, Norway
-spruce, Douglas spruce, etc. _The white pine_ is an exquisite example,
-and in young and middle-aged trees shows the style of branching to
-very good advantage. The branches are nearly horizontal, with a
-slight sigmoid graceful curve, while towards the top the branches are
-ascending. This direction of the branches is due to the light relation.
-The few whorls at the top are ascending because of the strong light
-from above. They soon become extended in a horizontal direction as the
-main source of light is shifting to the side by the shading of the top.
-The ascending direction first taken by the upper branches and their
-subsequent turning downward, while the ends often still have a slight
-ascending direction gives to the older branches their sigmoid curve.
-
-The young vernal shoots of the pines show some very interesting
-growth movements. There are two growth periods: (1) the elongation of
-the shoot, and (2) the elongation of the leaves. The elongation of the
-shoot takes place first and is completed in about six weeks or two
-months’ time. The direction of the shoot in the first period seems to
-be entirely influenced by geotropism. It grows directly upward and
-stands up as a very conspicuous object in strong contrast with the dark
-green foliage of the more or less horizontal shoots. When the second
-period of growth takes place, and the leaves elongate, the shoot bends
-downward and outward in a lateral direction.
-
-The rate of growth of the pines can be very easily observed since each
-whorl of branches (between the whorls of long shoots there are short
-shoots bearing the needle leaves), whether on the main axis or on the
-lateral branches, marks a year, the new branches arising each year
-at the end of the shoot of the previous year. The rate of growth is
-sometimes as high as twelve to twenty-four inches or more per year.
-
-The _spruces_ form a more perfect cone than the pines. The long
-branches are mostly in whorls, but often there are intermediate ones,
-though the rate of growth per year can usually be easily determined. In
-the _hemlock-spruce_, the branching is distributed. The _larch_ has a
-similar mode of branching, but it is deciduous, shedding its leaves in
-the autumn, and it has a tall, conical form.
-
-It would seem that trees of the cone type possessed certain advantages
-in some latitudes or elevations over other trees. (1) A conical tree,
-like the spruces and larches and the pines, and hemlocks also, before
-they get very old, meets with less injury during high winds than trees
-of an oval or spreading type. The slender top of the tree where the
-force of the wind is greatest presents a small area to the wind, while
-the trunk and short slender branches yield without breaking. Perhaps
-this is one reason why trees of this type exist in more northern
-latitudes and at higher elevations in mountainous regions, and why
-the spruce type reaches a higher latitude and altitude even than the
-pines. (2) The form of the tree is such as to admit light to a large
-foliage area, even where the trees are growing near each other. The
-evergreen foliage, persistent for several years, on the wide-spreading
-lower branches, probably affords some protection to the trees since
-this cover would aid in maintaining a more equable temperature in the
-forest cover than if the trees were bare during the winter. (3) There
-is less danger of injury from the weight of snow since the greater
-load of snow would lie on the lower branches. The form of the branches
-also, especially in the spruces, permits them to bend downward without
-injury, and if necessary unload the snow if the load becomes too heavy.
-
-=717. The oval type.=—This type is illustrated by the oak,
-chestnut, apple, etc. The trees are usually deciduous, i.e., cast
-their leaves with the approach of winter. The main axis is sometimes
-maintained, but more often disappears (trunk is _deliquescent_),
-because of the large branches which maintain an ascending direction,
-and thus lessen the importance of the central axis which is so marked
-in the cone type. Trees of this type, and in fact all deciduous trees,
-exhibit their character or habit to better advantage during the winter
-season when they are bare. Trees of this type are not so well adapted
-to conditions in the higher altitudes and latitudes as the cone type,
-for the reason given in the discussion of that type. The deciduous
-habit of the oaks, etc., enables them to withstand heavy winds far
-better than if they retained their foliage through the winter, even
-were the foliage of the needle kind and adapted to endure cold.
-
-=718. The deliquescent type.=—The elm is a good illustration of
-this type. The main axes and the branches fork by a false dichotomy, so
-that a trunk is not developed except in the forest. The branches rise
-at a narrow angle, and high above diverge in the form of an arch. The
-chief foliage development is lofty and spreading.
-
-Trees possess several advantages over vegetation less lofty. They may
-start their growth later, but in the end they outgrow the other kinds,
-shade the ground and drive out the sun-loving kinds.
-
-
-II. Creeping, Climbing, and Floating Stems.
-
-=719. Prostrate type.=—This type is illustrated by creeping or
-procumbent stems, as the strawberry, certain roses, of which a good
-type is one of the Japanese roses (Rosa wichuriana), which creeps very
-close to the ground, some of the raspberries, the cucurbits like the
-squash, pumpkin, melons, etc. These often cover extensive areas by
-branching and reaching out radially on the ground or climbing over low
-objects. The cucurbits should perhaps be classed with the climbers,
-since they are capable of climbing where there are objects for support,
-but they are prostrate when grown in the field or where there are no
-objects high enough to climb upon. In the prostrate type, there is
-economy in stem building. The plants depend on the ground for support,
-and it is not necessary to build strong, woody trunks for the display
-of the foliage which would be necessary in the case of an erect plant
-with a foliage area as great as some of the prostrate stems. This
-gain is offset, at least to a great extent, by the loss in ability to
-display a great amount of foliage, which can be done only on the upper
-side of the stem.
-
-[Illustration: Fig. 424. Prostrate type of the water fern (_marsilia_).]
-
-Other advantages gained by the prostrate stems are protection from
-wind, from cold in the more rigorous climates, and some propagate
-themselves by taking root here and there, as in certain roses, the
-strawberry plant, etc. Some plants have erect stems, and then send
-out runners below which take root and aid the plant in spreading and
-multiplying its numbers.
-
-=720. The decumbent type.=—In this type the stem is first erect,
-but later bends down in the form of an arch, and strikes root where the
-tip touches the ground. Some of the raspberries and blackberries are of
-this type.
-
-=721. The climbing type.=—The grapes, clematis, some roses, the
-ivies, trumpet-creeper, the climbing bittersweet, etc., are climbing
-stems. Like the prostrate type, the climbers economize in the material
-for stem building. They climb over shrubs, up the trunks of trees and
-often reach to a great height and acquire the power of displaying a
-great amount of foliage by sending branches out on the limbs of the
-trees, sometimes developing an amount of foliage sufficient to cover
-and nearly smother the foliage of large trees; while the main stem of
-the vine may be not over two inches in diameter and the trunk of the
-supporting tree may be three feet in diameter.
-
-=722. Floating stems.=—These are necessarily found in aquatic
-plants. The stems may be ascending or horizontal. The stems are
-usually not very large, nor very strong, since the water bears them
-up. The plants may grow in shallow water, or in water 10-12 feet or
-more deep, but the leaves are usually formed at or near the surface of
-the water in order to bring them near the light. Various species of
-Potamogeton, Myriophyllum, and other plants common along the shores of
-lakes, in ponds, sluggish streams, etc., are examples. Among the algæ
-are examples like Chara, Nitella, etc., in fresh water; Sargassum,
-Macrocystis, etc., in the ocean. In these plants, however, the plant
-body is a thallus, which is divided into stem-like (_caulidium_) and
-leaf-like (_phyllidium_) structures.
-
-=723. The burrowing type, or rhizomes.=—These are horizontal,
-subterranean stems. The bracken fern, sensitive fern, the mandrake
-(see fig. 413_a_), Solomon’s seal, Trillium, Dentaria, and the like,
-are examples. The subterranean habit affords them protection from the
-cold, the wind, and from injury by certain animals. Many of these stems
-act as reservoirs for the storage of food material to be used in the
-rapid growth of the short-lived aerial shoot. In the ferns mentioned,
-the subterranean is the only shoot, and this bears scale leaves which
-are devoid of chlorophyll, and foliage leaves which are larger, and the
-only member of the plant body which is aerial. The foliage leaf has
-assumed the function of the aerial shoot. The latter is not necessary
-since flowers are not formed. The mandrake, Solomon’s seal, Trillium,
-etc., have scale leaves on the fleshy underground stems, while foliage
-leaves are formed on the aerial stems, the latter also bearing the
-flowers. Some of the advantages of the rhizomes are protection from
-injury, food storage for the rapid development of the aerial shoot, and
-propagation.
-
-Many of the grasses have subterranean stems which ramify for great
-distances and form a dense turf. For the display of foliage and for
-flower and seed production, aerial shoots are developed from these
-lateral upright branches.
-
-
-III. Specialized Shoots and Shoots for Storage of Food.[40]
-
-=724. The bulb.=—The bulb is in the form of a bud, but the scale
-leaves are large, thick, and fleshy, and contain stored in them food
-products manufactured in the green aerial leaves and transported to
-the underground bases of the leaves. Or when the bulb is aerial in its
-formation, it is developed as a short branch of the aerial stem from
-which the reserve food material is transported. Examples are found
-in many lilies, as Easter lily, Chinese lilies, onion, tulip, etc.
-The thick scale leaves are closely overlapped and surround the short
-stem within (also called a _tunicated_ stem). In many lilies there
-is a sufficient amount of food to supply the aerial stem for the
-development of flower and seed. There are roots, however, from the bulb
-and these acquire water for the aerial shoot, and when planted in soil
-additional food is obtained by them.
-
-[Illustration: Fig. 425. Bulb of hyacinth.]
-
-[Illustration: Fig. 426. Corm of Jack-in-the-pulpit.]
-
-=725. Corm.=—A corm is a thick, short, fleshy, underground stem.
-A good example is found in the jack-in-the-pulpit (Arisæma).
-
-=726. Tubers.=—These are thickened portions of the subterranean
-stems. The most generally known example is the potato tuber (“Irish”
-potato, not the sweet potato, which is a root). The “eyes” of the
-potato are buds on the stem from which the aerial shoots arise when the
-potato sprouts. The potato tuber is largely composed of starch which is
-used for food by the young sprouts.
-
-=726=_a_. =Phylloclades.=—These are trees, shrubs, or
-herbs in which the leaves are reduced to mere bracts and stems,
-are not only green and function as leaves, but some or all of the
-branches are flattened and resemble leaves in form as in Phyllanthus,
-Ruscus, Semele, Asparagus, etc. The flowers are borne directly on
-these flattened axes. The prickly-pear cactus (Opuntia) is also
-a phylloclade. Examples of phylloclades are often to be found in
-greenhouses.
-
-=727. Undifferentiated stems= are found in such plants as the
-duckweed, or duckmeat (Lemna, Wolffia, etc. See Chapter III).
-
-
-IV. Annual Growth and Winter Protection of Shoots and Buds.[41]
-
-=728. Winter conditions.=[42]—While herbs are subjected only to
-the damp warm atmosphere of summer, woody plants are also exposed
-during the cold dry winter, and must protect themselves against such
-conditions. The air is dryer in winter than in summer; while at the
-same time root absorption is much retarded by the cold soil. Then, too,
-the osmotic activity of the dormant twig-cells being much reduced, the
-water-raising forces are at a minimum. It is easy to see, therefore,
-that a tree in winter is practically under desert conditions. Moreover,
-it has been found by various investigators, contrary to the general
-belief, that cold in freezing is only indirectly the cause of death.
-The real cause is the abstraction of water from the cell by the ice
-crystals forming in the intercellular spaces. Death ensues because the
-water content is reduced below the danger-point for that particular
-cell. It was formerly thought that on freezing, the cells in the tissue
-were ruptured. This is not so. Ice almost never forms within the cell,
-but in the spaces between. Freezing then is really a drying process,
-and dryness, not cold, causes death in winter. To protect themselves
-in winter, trees provide various waterproof coverings for the exposed
-surfaces and reduce the activity of the protoplasm so that it will be
-less easily harmed by the loss of water abstracted by the freezing
-process.
-
-[Illustration: Fig. 427. Two-year-old twig of horse-chestnut, showing
-buds and leaf-scars. (A twig with a terminal bud should have been
-selected for this figure.)]
-
-=729. Protection of the twig.=—Woody plants protect the living
-cells within the twigs by the production of a dull or rough corky bark,
-or by a thick glossy epidermis over the entire surface. At intervals
-occur small whitish specks called lenticels, which here perform nearly
-the same function as do stomates in the leaf.
-
-=730. Bark of trunk.=—A similar service is performed by the
-bark for the main trunk and branches of the tree. To admit of growth
-in diameter the old bark is constantly being thrown off in strips,
-flakes, etc., and replaced by a new but larger cylinder of young bark.
-The external appearance thus produced enables experienced persons to
-recognize many kinds of trees by the trunk alone.
-
-=731. Leaf-scars and bundle-scars.=—The presence of foliage
-leaves during the winter would greatly increase the transpiring surface
-without being of use to the plant; hence they are usually thrown off on
-the approach of winter. The scars left by the fallen leaves are termed
-leaf-scars. The small dots on the leaf-scars left by the vascular
-bundles which extended through the petiole into the twig are termed
-bundle-scars. Sometimes stipule-scars are left on each side of the
-leaf-scar by the fallen stipules.
-
-=732. Nodes and internodes.=—The region upon a stem where a leaf
-is borne is termed a node. The space between two nodes is an internode.
-
-[Illustration: Fig. 428.—Shoot of butternut showing leaf-scars,
-axillary buds, and adventitious buds (buds coming from above the
-axils).]
-
-[Illustration: Fig. 429.—Shoot and bud of white oak.]
-
-=733. Phyllotaxy.=—Investigation of a horse-chestnut or willow
-twig will show that the leaf-scars occupy definite positions which
-are constant for each plant but different for the two species.
-The arrangement of the leaves on the stem in any plant is termed
-phyllotaxy. In the horse-chestnut we find two scars placed at the same
-node, but on opposite sides of the stem. Somewhat higher up we find two
-more similarly placed, but in a position perpendicular to that of the
-first pair. Such phyllotaxy is termed opposite. If in any plant several
-leaves occur at a node, the phyllotaxy is whorled. If but one at each
-node, as in the willow, the phyllotaxy is alternate. The opposite and
-alternate types are very commonly met with. Closer observation will
-show that in the willow, if a line be drawn connecting the successive
-leaf-scars, it will pass spirally up the twig until at length a scar is
-reached directly over the one taken as a starting-point. Such spiral
-arrangement always accompanies alternate phyllotaxy. The section of the
-spiral thus delineated is termed a cycle. We express the nature of the
-cycle by the fractions ½, ⅓, ⅖, ⅜, ⁵/₁₃, etc., in which the numerator
-denotes the number of turns around the stem in each cycle, and the
-denominator the number of leaf-scars in the same distance. In a general
-way we find in plants only such arrangements as are represented by
-the fractions given above. These fractions show the curious condition
-that the numerator and denominator of each is equal to the sum of
-the numerator or denominator of the two preceding fractions. Much
-speculation has been indulged in regarding the significance of these
-definite laws of leaf arrangement. In part they may be due to the
-desire that each leaf receive the maximum amount of light. Only certain
-definite geometrical conditions will insure this. More likely it is due
-to the economy of space allotted to the leaf-fundaments in the bud.
-Here, again, geometrical laws govern this economy. The phyllotaxy is
-nearly constant for a given species.
-
-=734. Buds.=—The growing point of the stem or branch together
-with its leaf or flower fundaments and protective structures is termed
-a bud. Winter buds on woody plants are terminal when inclosing the
-growing point of the main axis of the twig; lateral when the growing
-point is that of a branch of the main axis. Lateral buds are always
-axillary, i.e., situated on the upper angle between a leaf and the main
-axis.
-
-=735. Buds occupying special positions.=—Several species of trees
-and shrubs produce more than one bud in each leaf-axil. The additional
-ones are termed accessory or supernumerary buds. These may be lateral
-to one another or they may be superposed as in the walnut or butternut.
-In such cases some of the buds usually contain simply floral shoots and
-are termed flower buds. In some species buds are frequently produced
-on the side of the branches and trunk at some distance from the
-leaf-axils, and entirely without regard for the latter; or more rarely
-may occur upon the root. Such buds are termed adventitious, and are the
-source of the feathery branchlets upon the trunks of the American elm.
-
-=736. Branching follows the phyllotaxy.=—Since the lateral or
-branch-producing buds are always located in the axil of a leaf, the
-branches necessarily follow the same arrangement upon the main axis
-as do the leaves. Since, however, many of the axillary buds fail to
-develop, this arrangement may be more or less obscured.
-
-[Illustration: Fig. 430. Bud of European elm in section, showing
-overlapping of scales.]
-
-=737. Coverings of winter buds.=—These are of two sorts, hair
-and cork, or scales. Buds protected simply by dense hair or sunk in
-the cork of the twig are termed naked buds, and are comparatively
-rare. Most species protect their buds by the addition of an imbricated
-covering of closely appressed scales, the whole frequently being
-rendered still more waterproof by the excretion of resin between the
-scales or over the whole surface. The scales when studied carefully
-are found to be much reduced leaves or parts of leaves. In some cases
-they represent a modified whole leaf, when they are said to be laminar,
-or a leaf-petiole, when they are petiolar, or stipular, when they are
-much-specialized stipules of a leaf which itself is usually absent. The
-latter type is much the less common. The form of the bud, the nature
-and form of the scales, when combined with characters furnished by the
-leaf- and bundle-scars, enable one to recognize and classify the winter
-twigs of the various woody species.
-
-=738. Phyllotaxy of the bud-scales.=—Since the bud-scales are
-leaves, they follow a definite phyllotaxy. This may or may not be
-the same as that of the foliage leaves. Twigs with opposite leaves
-have opposite bud-scales, or if with alternate leaves, then alternate
-bud-scales, but the fractions vary. If the scales are stipular, then
-there are of course two at each node.
-
-=739. Function of the bud coverings.=—It is popularly believed
-that the scales and hairy coverings serve to keep the bud warm.
-Research, however, shows this to be almost entirely erroneous, and that
-the thin bud coverings are entirely inadequate to keep out the cold of
-winter. They cannot keep the bud even a degree or two warmer than the
-outside air, except when the changes are very rapid. Experiment also
-shows that the modifying effect of the covering when the bud thaws
-out is so slight as to be almost negligible. Indeed, a thermometer
-bulb covered with scales taken from a horse-chestnut bud warmed up
-more rapidly than a naked one when exposed to sunshine. The wool in
-the horse-chestnut bud is not for the purpose of keeping it warm, but
-to protect the young shoot from too great transpiration after the bud
-opens the following spring. Research has also shown that such tempering
-of the heat conditions is not especially beneficial to the plant,
-as was once thought. Neither can we find the main function in the
-prevention of water from entering the bud. This might be accomplished
-in much simpler ways, even if we could demonstrate the desirability of
-keeping the water out at all.
-
-The true functions of the bud-scales are two in number: Firstly, the
-prevention of too great loss of water from the young and delicate
-parts within; and secondly, the protection of these same parts from
-mechanical injury. Without some such protection the delicate young
-structures would be beaten off by the wind, or become the food for
-hungry birds during the long winter months.
-
-[Illustration: Fig. 431. Opening buds of hickory.]
-
-=740. Opening of the buds.=—When the young shoot begins to
-grow in the spring, the bud-scales are forced apart or open of their
-own accord. During the young condition the shoot is very soft and
-brittle, and also possesses a very thin, little cutinized epidermis.
-In this condition it is especially liable to mechanical injury and to
-injury from drying out. We find, therefore, a tendency for the inner
-bud-scales to elongate during vernation, thus forming a tube around the
-delicate tissue much like the opening out of a telescope. The young
-leaves and internodes themselves are often provided with a woody or
-hairy covering to retard transpiration. When the epidermis becomes more
-efficient the hairy covering often falls away.
-
-In the case of naked buds protection is afforded in other ways: by
-the protection of hairy covering, by physiological adaptation of the
-tissue, or in many cases by the late appearance of the shoot in spring
-after the very dry April and May winds have ceased.
-
-=741. Bud-scars, and how to tell the age of the plant.=—In
-general the bud-scales when they fall away in the spring leave scars
-termed scale-scars, and the whole aggregate of scale-scars makes up the
-bud-scar. The position of the buds of previous winters is, therefore,
-marked. It becomes an easy matter to determine the age of a branch,
-since all that is necessary is to follow back from one bud-scar to
-another, the portion of the stem between representing, except in rare
-cases, one year’s growth.
-
-A woody plant grows in height only by the formation of new sections
-of stem added to the apex or side of similar sections produced the
-previous season, never, as is commonly supposed, by the further
-elongation of the previous year’s growth. Hence a branch once formed
-upon a tree is fixed as regards its distance from the ground. The
-apparent rise of the branches away from the ground in forest trees is
-an illusion caused by the dying away of the lower branches.
-
-=742. Definite and indefinite growth.=—With the opening of the
-buds in spring, growth begins. In some cases, when all the members
-for the season were formed, but still minute, within the bud, such
-growth consists solely in the expansion of parts already formed; in
-others only a few members are thus present to expand, while new ones
-are produced by the growing point as the season progresses. In most
-cases growth is completed by the middle of July, soon after which buds
-are formed for next year’s growth. Such a method of growth is termed
-definite.
-
-In a few woody plants, as, for example, sumach, locust, and raspberry,
-growth continues until late in the autumn. In such cases the most
-recently formed nodes and internodes are unable to become sufficiently
-“hardened” before winter sets in, and are killed back more or less.
-Next season’s shoot is a branch from some axillary bud. Such growth is
-termed indefinite.
-
-[Illustration: Fig. 432. Three-year-old twig of the American ash, with
-sections of each year’s growth showing annual rings.]
-
-=743. Structure of woody stems.=—If we make a cross-section of a
-woody twig three general regions are presented to view. On the outside
-is the rather soft, often greenish “bark,” so called, made up of
-sieve tubes, ordinary parenchyma cells, and in many cases long fibrous
-cells composing the “fibrous bark.” From a growing layer in this
-region, termed the phellogen, the true corky bark of the older trunk is
-formed.
-
-Next within the bark we find the so-called “woody” portion of the
-twig. This is strong and resistant to both breaking and cutting. The
-microscope shows it to be composed of the ordinary already known woody
-elements,[43] wood fibers, for strengthening purposes, pitted and spiral
-vessels as conducting tissue; and intermixed with these some living
-parenchyma cells. A cross-section of the stem also shows narrow radial
-lines through the wood. These are pith-rays, composed of vertical
-plates of living parenchyma cells. These cells, unlike the others in
-the wood, are elongated radially, not vertically. The height of the
-pith-rays as well as their thickness varies with the species studied.
-In the older trunk only the outer portion, a few inches in thickness,
-remains light-colored and fresh, and is called sap-wood. The inner
-wood is usually darker and harder, and is termed heart-wood. Living
-parenchyma cells, in general, are present only in the sap-wood, and
-in this almost solely the ascent of sap occurs. Dyestuffs and other
-substances are frequently deposited in the walls of the heart-wood.
-
-The third region occupying the center of the twig is the pith. This is
-composed ordinarily of angular, little elongated, parenchyma cells,
-when mature mostly without cell-contents and filled with air. The pith
-region in different trees is quite diversified. It may be hollow,
-chambered, contain scattered thick-walled cells, have woody partitions,
-or rarely be entirely thick-walled.
-
-The nature of the woody ring is rather perplexing at first; but
-its origin is simple. We may conceive that it has developed from a
-stem-type like the sunflower, in which the bundles, though separate,
-are connected by a continuous cambium ring. In the woody twigs the
-numerous bundles are closely packed together, and only separated by
-the primary pith-rays extending from the pith to the cortex. Other
-secondary pith-rays are produced within each bundle, but they usually
-extend only part way from the cortex to the pith. The wood represents
-the xylem of the bundle, and the sieve tubes of the bark, the phloem.
-
-=744. Growth in thickness.=—Although the year’s growth does not
-increase in length after the first season has passed, it does increase
-in diameter very much. From the size of an ordinary little twig it may
-at length become a large tree trunk several feet in thickness. Only a
-portion of the first year’s growth is produced by the growing point.
-All the rest is a product of the cambium, a cylinder of wood being
-added to the exterior of the old wood each season. The cambium, here,
-as in the sunflower, lies between the phloem and the xylem, forming a
-cylinder entirely around the stem. In spring, when active, it becomes
-soft and delicate, thus enabling one to easily strip off the bark from
-some trees, such as willow, etc., at that season.
-
-=745. Annual rings in woody stems.=—The wood produced by the
-cambium each season is not homogeneous throughout, but is usually much
-denser toward the outer part of the yearly cylinder, wood fibers here
-predominating. In the inner portion vessels predominate, giving a much
-more porous effect. The transition from one year’s growth to another is
-very abrupt, giving rise to the appearance of rings in cross-section.
-Since ordinarily in temperate climates but one cylinder of wood is
-added each year, the number of rings will indicate the age of the trunk
-or branch. This is not absolutely accurate, since in some trees under
-certain conditions more than one ring may be produced in a summer. The
-porous part of the ring is often termed “spring wood,” and the denser
-portion “fall wood,” but since growth from the cambium ceases in most
-trees by the middle of July, “summer wood” would be more appropriate
-for the latter. It is mainly the alternation of the cylinders of the
-spring and summer wood that gives the characteristic grain to lumber.
-Pith-rays play an important part in wood graining only in a few woods,
-as, for instance, in quartered oak. The reason for the production of
-porous spring wood and dense summer wood is still one of the unsolved
-problems of botany.
-
-FOOTNOTES:
-
-[40] Besides these specialized shoots for the storage of food,
-food substances are stored in ordinary shoots. For example, in the
-trunks of many trees starch is stored. With the approach of cold
-weather the starch is converted into oil, in the spring it is converted
-into starch again, and later as the buds begin to grow the starch is
-converted into glucose to be used for food. In many other trees, on the
-other hand, the starch changes to sugar on the approach of winter.
-
-[41] This topic was prepared by Dr. K. M. Wiegand.
-
-[42] See discussion of Tropophytes in Chapter XLVI.
-
-[43] Chapter V, and Organization of Tissues in Chapter XXXVIII.
-
-
-
-
-CHAPTER XL.
-
-FOLIAGE LEAVES.
-
-
-I. General Form and Arrangement of Leaves.
-
-=746. Influence of foliage leaves on the form of the stem.=—The
-marked effect which foliage has upon the aspect of the plant or upon
-the landscape is evident to all observers. Perhaps it is usual to
-look upon the stem as having been developed for the display of the
-foliage without taking into account the possibility that the foliage
-may have a great influence upon the form or habit of the stem. It is
-very evident, however, that the foliage exercises a great influence
-on the form of the stem. For example, as trees increase in age and
-size, the development of branches on the interior ceases and some of
-those already formed die, since the dense foliage on the periphery
-of the trees cuts off the necessary light stimulus. The tree,
-therefore, possesses fewer branches and a more open interior. In the
-forest also, the dense foliage above makes possible the shapely,
-clean timber trunks. Note certain trees where by accident, or by
-design, the terminal foliage-bearing branches have been removed that
-foliage-bearing branches may arise in the interior of the tree system.
-
-Without foliage leaves the stems of green plants would develop a very
-different habit from what they do. This development could take place in
-three different directions under the influence of light: (1) The light
-stimulus would induce profuse branching, so that there would be many
-small branches. (2) The stem would develop fewer branches, but they
-would be flattened. (3) Massive trunks with but few or no branches. In
-fact, all these forms are found in certain green stems which do not
-bear leaves. An example of the first is found in asparagus with its
-numerous crowded slender branches. But such forms in our climate are
-rare, since foliage leaves are more efficient. The second and third
-forms are found among cacti, which usually grow in dry regions under
-conditions which would be fatal to ordinary thin foliage leaves.
-
-=747. Relation of foliage leaves to the stem.=—In the study
-of the position of the leaves on the stem we observe two important
-modes of distribution: (1) the distribution along the individual
-stem or branch which bears them, usually classed under the head of
-_Phyllotaxy_; (2) the distribution of the leaves with reference to the
-plant as a whole.
-
-=748. Phyllotaxy, or arrangement of leaves.=—In examining buds on
-the winter shoots of woody plants, we cannot fail to be impressed with
-some peculiarities in the arrangement of these members on the stem of
-the plant.
-
-In the horse-chestnut, as we have already observed, the leaves are in
-pairs, each one of the pair standing opposite its partner, while the
-pair just below or above stand across the stem at right angles to the
-position of the former pair. In other cases (the common bed-straw) the
-leaves are in whorls, that is, several stand at the same level on the
-axis, distributed around the stem. By far the larger number of plants
-have their leaves arranged alternately. A simple example of alternate
-leaves is presented by the elm, where the leaves stand successively on
-alternate sides of the stem, so that the distance from one leaf to the
-next, as one would measure around the stem, is exactly one half the
-distance around the stem. This arrangement is one half, or the angle of
-divergence of one leaf from the next is one half. In the case of the
-sedges the angle of divergence is less, that is one-third.
-
-By far the larger number of those plants which have the alternate
-arrangement have the leaves set at an angle of divergence represented
-by the fraction two fifths. Other angles of divergence have been
-discovered, and much stress has been laid on what is termed a law in
-the growth of the stem with reference to the position which the leaves
-occupy. Singularly by adding together the numerators and denominators
-of the last two fractions gives the next higher angle of divergence.
-Example:
-
-     1  +  2    3       2  +  3    5
-     —-   —- = —-;      —-   —- = —-;
-     3  +  5    8       5  +  8   13
-
-and so on. There are, however, numerous exceptions to this regular
-arrangement, which have caused some to question the importance of any
-theory like that of the “spiral theory” of growth propounded by Goethe
-and others of his time.
-
-=749. Adaptation in leaf arrangement.=—As a result, however, of
-one arrangement or another we see a beautiful adaptation of the plant
-parts to environment, or the influence which environment, especially
-light, has had on the arrangement of the leaves and branches of the
-plant. Access to light and air are of the greatest importance to
-green plants, and one cannot fail to be profoundly impressed with the
-workings of the natural laws in obedience to which the great variety of
-plants have worked out this adaptation in manifold ways.
-
-=750. Distribution of leaves with reference to the entire
-plant.=—In this case, as in the former, we recognize that it is
-primarily a light relation. As the plant becomes larger and more
-branched the lower and inner leaves disappear. The trees and shrubs
-have by far the larger number of leaves on the periphery of the branch
-system. A comparison of different kinds of trees in this respect shows,
-however, that there is great variation. Trees with dense foliage (elm,
-Norway maple, etc.) present numerous leaves on the periphery which
-admit but little light to the interior where leaves are very few or
-wanting. The sugar maple and red maple do not cast such a dense shade
-and there are more leaves in the interior. This is more marked in the
-silver maple, and still more so in the locust (Gleditschia tricanthos).
-
-=751. Color of foliage leaves.=—The great majority of foliage
-leaves are green in color. This we have learned (Chapter VII) is due
-to the presence of a green pigment, chlorophyll, in the chloroplastids
-thickly scattered in the cells of the leaf. We have also learned that
-in the great majority of cases, the light stimulus is necessary for
-the production of chlorophyll green. There are many foliage leaves
-which possess other colors, as red (Rosa rubrifolia), purple (the
-purple barberry, hazel, beech, birch, etc.), yellow (the golden oak,
-elder, etc.); while many others have more or less deep tints of pink,
-red, purple, yellow, when young. All of these leaves, however, possess
-chlorophyll in addition to red, yellow, purple or other pigment.
-These other pigments are sometimes developed in great quantity in the
-cell-sap. They obscure the chlorophyll from view, but do not interfere
-seriously with the action of light and the function of chlorophyll, and
-perhaps in some cases serve as a screen to protect the protoplast.
-
-=752. Autumn colors.=—Foliage leaves of many trees display in
-the autumn gorgeous colors. These colors are principally shades of
-red or yellow, and sometimes purple. The autumn color is more marked
-in some trees than in others. In the red maple, the red and scarlet
-oak, the sourwood, etc., red predominates, though sometimes yellow
-may be present with the red in a single leaf. Sugar maples, poplars,
-hickories, etc., are principally yellow in autumn. The sweet gum has a
-rich variety of color-red, purple, maroon, yellow; sometimes all these
-colors are present on the same tree.
-
-The red and purple colors are found suffused in the cell-sap of
-certain cells in the leaf much as we have found it in the cells of
-the red beet. The yellow color is chiefly due to the disappearance
-and degeneration of the chlorophyll while the leaf is in a moribund
-state. A similar phenomenon is seen in the yellowing of crops when
-the soil becomes too wet, or in the blanching of grass when covered
-with a board, or of celery as the earth is ridged up over the leaves
-in late summer and autumn. A number of different theories have been
-advanced to explain autumn coloring, i.e., the appearance of the
-red coloring matter. It has been attributed to the approach of cold
-weather, and this has likely led to the erroneous belief on the part
-of some that it is caused by frost. It very often precedes frost. Some
-have attributed it to the action of the more oblique light rays during
-autumn, and still others to the diminishing water-supply with the
-approach of cool weather. The question is one which has not met as yet
-with a satisfactory solution, and is certainly a very obscure one. It
-is likely that the low temperature or the declining activities of the
-leaf affect certain organic substances in the leaf and give rise to
-the red color, and it is quite certain that in some years the display
-is more brilliant than in others. The color is more striking in some
-regions than in others and the different soil, as well as climate, has
-been supposed to have some influence. The North American forests are
-noted for the brilliant display of autumnal color. This is perhaps due
-to some extent to the great variety or number of species which display
-color. It would seem that there is some specific as well as individual
-peculiarities in certain trees. Some individuals, for example, exhibit
-brilliant colors every autumn, while others near of the same species
-are more subdued.
-
-It has been shown by experiment that when sunlight passes through
-red colors the temperature is slightly increased, and it has been
-suggested that this may be of protection to the living substance which
-has ceased working and is in danger of injury from cold. There does
-not seem to be much ground for this suggestion, however. It certainly
-could not protect the protoplasm of the leaf at night when the cold
-is more intense, and during the day would only aggravate matters
-by supplying an increased amount of heat, since extremes of heat
-and cold in alternation are more harmful to plant life than uniform
-cold. Especially would this be the case in alpine climates where the
-alternation of heat and cold between day and night is extreme, and
-brilliancy of the colors of alpine plants is well known. It seems
-more reasonable to suppose that the red color acts as a screen, as
-the chlorophyll is disappearing, to protect from the injurious action
-of light, certain organic substances which are to be transferred back
-from the leaf to the stem for winter storage. So in the case of many
-stems in the spring or early summer when the young leaves often have
-a reddish color, it is likely that it acts as a screen to protect the
-living substance from the strong light at that season of the year until
-the chlorophyll screen, which is weak in young leaves, becomes darker
-in color and more effective, when the red color often disappears.
-
-=753. Function of foliage leaves.=—In general the function of
-the foliage leaf as an organ of the plant is fivefold (see Chapters
-IV, VII, VIII, XI), (1) that of carbon dioxide assimilation or
-_photosynthesis_, (2) that of transpiration, (3) that of the synthesis
-of other organic compounds, (4) that of respiration, and (5) that of
-assimilation proper, or the making of new living substance. While none
-of these functions are solely carried on in the leaf, it is the chief
-seat of the first three of these processes, its form, position, and
-structure being especially adapted to the purpose. Assimilation proper,
-as well as respiration, probably take place equally in all growing or
-active parts.
-
-=754. Parts of the leaf.=—All foliage leaves possess a _blade_
-or _lamina_, so called because of its _expanded_ and _thin_ character.
-The blade is the essential part. Many leaves, however, are provided
-with a stalk or _petiole_ by which the blade is held out at a greater
-or lesser distance from the stem. Leaves with no petiole are _sessile_,
-the blade is attached by one end directly on the stem. In some cases
-the base of the blade is wrapped partly around the stem, or in others
-it extends entirely around the stem and is _perfoliate_. Besides, many
-leaves have short appendages, termed _stipules_, attached usually on
-opposite sides of the petiole at its junction with the stem. In some
-species of magnolia the stipules are so large that each one envelops
-the entire portion of the bud which has not yet opened. Many leaves
-possess outgrowths in the form of hairs, scales, etc. (See leaf
-protection.)
-
-=755. Simple leaves.=—Simple leaves are those in which the
-blade is plane along the edge, not divided. The edge may be entire or
-indented (serrate) to a slight extent as in the elm. The form of the
-simple leaf varies greatly but is usually constant for a given species,
-or it may vary in shape in the same species on different parts of the
-plant. Some of the terms applied to the outline of the leaf are ovate,
-oval, elliptical, lanceolate, linear, needle-like, etc., but it is idle
-for one to waste time on matters of minute detail in form until it
-becomes necessary for those in the future who pursue taxonomic work. It
-is evident that a simple leaf, except those of minute size, possesses
-advantages over a divided leaf in the amount of surface it exposes to
-the light. But in other respects it is at a disadvantage, especially
-as it increases in size, since it casts a deeper shade and does not
-admit of such a free circulation of air. It will be found, however, in
-our study of the relation of leaves to light and air that the balance
-between the leaf and its environment is obtained in the relation of the
-leaves to each other.
-
-=756. Venation of leaves.=—A very prominent character of the
-leaf is its “venation.” This is indicated by the presence of numerous
-“veins,” indicated usually by narrow depressed lines on the upper
-surface, and by more or less distinct elevated lines on the under
-surface. There are two general types: (1) In the corn, Smilacina,
-Solomon’s seal, etc., the veins extend lengthwise of the leaf and
-are nearly parallel. Such leaves are said to be _parallel-veined_.
-It is generally, though not always, a character of monocotyledenous
-plants. (2) In the elm, rose, hawthorn, maple, oak, etc., the veins
-are not all parallel. The larger ones either diverge from the base
-of the blade (palmate leaf, maple), or the midvein extends through
-the middle line of the leaf, while other prominent ones branch off
-from this and extend, nearly parallel, toward the edge of the leaf
-(pinnate venation). The smaller intermediate veins which are also
-very distinct extend irregularly and branch and anastomose in such a
-fashion as to give the figure of a net with very fine meshes. These
-are _netted-veined_ leaves. These are characteristic of most of the
-dicotyledenous plants. It is evident from what has been said of the
-examples cited that there are two types of netted-veined leaves, the
-_palmate_ and _pinnate_.
-
-      NOTE. As we have already learned in Chapter
-    V the veins contain the vascular bundles of the
-    leaf. Through them the water and food solutions are
-    distributed to all parts of the leaf, and the return
-    current of food material elaborated in the leaf moves
-    back through the bast portion into the shoot. The veins
-    also possess a small amount of mechanical tissue. This
-    forms the framework of the leaf and aids in giving
-    rigidity to the leaf and in holding it in the expanded
-    position. The mechanical tissue in the framework
-    alone could not support the leaf. Turgescence of the
-    mesophyll is needed in addition.
-
-=757. Cut or lobed leaves.=—In many leaves, the indentations
-on the margin are few and deep. Such leaves present several lobes
-the proportionate size of which is dependent upon the depth of the
-indentation or “incision.” Several of the maples, oaks, birches, the
-poison ivy, thistles, the dandelion, etc., have lobed leaves. Where
-the indentation reaches to or very near the midrib the leaf is said
-to be cut. A study of various leaves will show all gradations from
-simple leaves with plane edges to those which are cut or divided, as in
-compound leaves, and the lobes are often variously indented.
-
-[Illustration: Fig. 433. Lobed leaves of oak forming a mosaic.]
-
-[Illustration: Fig. 434. Twice compound leaf. Leaflets arranged in one
-plane, but open spaces permit free circulation of air through the large
-leaf.]
-
-=758. Divided, or compound leaves.=—The rose, sumac, elder,
-hickory, walnut, locust, pea, clover, American creeper, etc., are
-examples of divided or compound leaves. The former are pinnately
-compound, and the latter are palmately compound. The leaf of the
-honey-locust is twice pinnately compound or bipinnate, and some are
-three times pinnately compound.[44] It is evident that compound leaves
-are only extreme forms of lobed or cut leaves and that the form of all
-bears a definite relation to the primary venation. There has been a
-reduction of mesophyll and of the area of smaller venation.
-
-_Unifoliate_ (for a single leaflet, as in orange and lemon where
-the compound leaf is greatly reduced and consists of one pinna
-attached to the petiole by a joint). _Bifoliate_ for one with two
-leaflets; _trifoliate_ for one with three leaflets, as in the clover;
-_plurifoliate_ for many leaflets. _Odd pinnate_ for a pinnate leaf with
-one or more pairs of leaflets and one odd leaflet at the end.
-
-So leaves are _palmately bifoliate_, etc., _pinnately bifoliate_, etc.
-_Decompound_ leaves are those where they are more than twice compound,
-as _ternately decompound_ in the common meadow rue (Thalictrum).
-
-_Perfoliate_ leaves are seen in the bellwort (Uvularia), _connate
-perfoliate_, as in some of the honeysuckles where the bases of opposite
-leaves are joined together around the stem. _Equitant_ leaves are found
-in the iris, where the leaves fit over one another at the base like a
-saddle.
-
-=759.= These forms of leaves probably have some definite
-significance. It is not quite clear why they should have developed as
-they have; though it is possible to explain several important relations
-of these forms to their environment. (1) The reduction of the surface
-of the leaf, with the retention of the firmer portions, allows freer
-movement of the air and affords the leaf greater protection from injury
-during violent winds, just as the finely dissected leaves of some
-water plants are less liable to injury from movement of the more dense
-medium in which they live. It is possible that here we may have an
-explanation of one of the factors involved in this reduction of leaf
-surface. (2) In trees with compound leaves, like the hickory, walnut,
-locust, ailanthus, etc., the midvein, and in the case of the Kentucky
-coffee-tree (Gymnocladus) the primary lateral veins also, serve in
-place of terminal branches of the stem. By the increase in the outline
-of the leaf and the reduction of its surface between the larger veins,
-the tree has attained the same leaf development that it would were the
-larger veins replaced by stems bearing simple leaves. The tree as
-it is, however, has the advantage of being able to cast off for the
-winter period a layer of what otherwise would have been a portion of
-the stem system, to retain which through the winter would use more
-energy than with the present reduced stem system, and the stouter
-stem is less liable to dry out. In the case of herbaceous plants, in
-the case of plants like most of the ferns where the stem is on the
-underground rootstock (Pteris), or a very short erect stem, as in the
-Christmas fern, the leaf replaces the aerial stem, and the division (or
-branching, as it is sometimes styled) of the leaf corresponds to the
-branching of the stem. This is more marked in the gigantic exotics like
-Cibotium regale, and in the tree ferns which have quite tall trunks,
-the massive compound leaves replace branches. In the palms and cycads
-are similar examples. Those who choose to observe can doubtless find
-many examples close at hand. (3) While divided leaves have probably not
-been evolved in response to the light relation, still their relation in
-this respect is an important one, since if the leaf with its present
-size were entire, it would cast too dense a shade on other leaves below.
-
-=760. General structure of the leaf.=—The general structure of
-the leaf has been already studied (see Chapters IV, V, VII). It is
-only necessary to recall the main points. The upper and lower surfaces
-of the leaf are provided with a layer of cells usually devoid of
-chlorophyll. The mesophyll of the leaf consists usually of a layer of
-palisade cells beneath the epidermis, and the remainder consists of
-loose parenchyma with large intercellular spaces. Through the mesophyll
-course the “veins,” or fibrovascular strands, consisting of the xylem
-and phloem portions and serving as conduits for water, salts, and
-foodstuffs. In the epidermis are the stomata, each one protected by
-the two guard cells. The guard cells as well as the mesophyll contain
-chlorophyll. The stomata and the communicating intercellular spaces
-furnish the avenues for the ingress and egress of gases, and for the
-escape of water vapor.
-
-=761. Protection of leaves.=—There are many modifications of
-the general plan of structure in different leaves, many of them being
-adaptations for the protection of the leaf under adverse or trying
-conditions. Many leaves are also capable of assuming certain positions
-which afford them protection. The discussion of this subject may be
-presented under two general heads: Protective modifications; protective
-positions.
-
-
-II. Protective Modification of Leaves.
-
-=762. General directions in which these modifications have taken
-place.=—The usual type of foliage leaf selected is that of
-deciduous trees or shrubs or of our common herbs. Such a leaf is
-usually greatly expanded and thin in order to present as great a
-surface as possible in comparison with its mass, since the kind of
-work which the leaf has to do can be more effectually carried on when
-it possesses this form. This form of leaf is best adapted for work in
-regions where there is a medium amount of moisture such as exists in
-the temperate zones. But since there are very great variations in the
-climatic and soil conditions of these regions, and even greater changes
-in desert and arctic regions, the type of leaf described is unsuited
-for all. Its own life would be endangered, and it would also endanger
-the life of the plant. Modifications have therefore taken place to
-meet these conditions, or at least those plants whose leaves have
-become modified in those directions which are suited to the surrounding
-conditions have been able to persist. Excessive cold or heat, drought,
-winds, intense light, rain, etc., are some of the conditions which
-endanger leaves. The protective modifications of leaves may be grouped
-under four general heads: (1) Structural adaptations; (2) Protective
-covering; (3) Reduction of surface; (4) Elimination of the leaf through
-the complete assumption of the leaf function by the stem.
-
-[Illustration: Fig. 435. Structure of leaf of Lactuca scariola. Upper
-one grown in sunlight, palisade cells on both sides. Lower one grown in
-shade, no palisade tissue.]
-
-=763.= (1) =Structural adaptations.=—The general structure
-of the leaf presents certain features which are protective. The
-palisade layer of cells found usually beneath the upper epidermis forms
-a compact layer of long cells which not only acts as a light screen
-cutting off a certain amount of the light, since too intense light
-would be harmful; it also aids in lessening the loss of water from the
-upper surface, where radiation is greater. The stomata are usually on
-the under side of aerial leaves, and the mechanism which closes them
-when the leaf is losing too much water is protective. As a protection
-against intense light the number of palisade layers is sometimes
-increased or the cells of this layer are narrow and long. This is often
-beautifully shown when comparing leaves of the same plant grown in
-strong light with those grown in the shade. The compass plant (Lactuca
-scariola) affords an interesting example. The leaves grown in the light
-are usually vertical, so that the light reaches both sides. Such leaves
-often have all of the mesophyll organized into palisade cells (fig.
-435), while leaves grown in the deep shade may have no palisade cells.
-
-=764.= (2) =Protective covering.=—_Epidermis and
-cuticle._—The walls of the epidermal cells are much thickened in some
-plants. Sometimes this thickening occurs in the outer wall, or both
-walls may be thickened. Variation in this respect as well as the extent
-of the thickening occur in different plants and are often correlated
-with the extremes of conditions which they serve to meet. The cuticle,
-a waxy exudation from the thick wall of the epidermis of many leaves,
-also serves as a protection against too great loss of water, or against
-the leaf becoming saturated with water during rains. The cabbage,
-carnation, etc., have a well-developed cuticle. The effect of the
-cuticle in shedding water can be nicely shown by spraying water on a
-cabbage leaf or by immersing it in water. Sunken stomata also retard
-the loss of water vapor.
-
-_Covers of hair or scales._—In many leaves certain of the cells of the
-epidermis grow out into the form of hairs or scales of various forms,
-and they serve a variety of purposes. When the hairs form a felt-like
-covering as in the common mullein, some antennarias, etc., they lessen
-the loss of water vapor because the air-currents close to the surface
-of the leaf are retarded. Spines (see the thistles, etc.) also afford a
-protection against certain animals.
-
-=765.= (3) =Reduction of surface.=—Reduction of leaf surface
-is brought about in a variety of ways. There are two general modes:
-(1st) Reduction of surface along with reduction of mass; (2d) Reduction
-of surface inversely as the mass. Examples of the first mode are
-seen in the dissected leaves of many aquatic plants. In this finely
-dissected condition the mass of the leaf substance is much reduced as
-well as the leaf surface, but the leaf is less liable to be injured
-by movement of the water. In addition it has already been pointed out
-that lobed and divided aerial leaves are much less liable to injury
-from violent movements of the air, than if a leaf with the same general
-outline were entire. The needle leaves of the conifers are also
-examples, and they show as well structural provisions for protection
-in the thick, hard cell-walls of the epidermis. To offset the reduced
-surface there are numerous crowded leaves. Reduction of surface
-inversely as the mass, i.e., the mass of the leaf may not be reduced
-at all, or it may be more or less increased. In other words, there is
-less leaf surface in proportion to the mass of leaf substance. It is
-probable in many cases, example: the crowded, overlapping small scale
-leaves of the juniper, arbor-vitæ, cypress, cassiope, pyxidanthera,
-etc., that there has been a reduction in the size of the leaf, and at
-the same time an increase in thickness. This with the crowding together
-of the leaves and their thick cell-walls greatly lessens the radiation
-of moisture and heat, thus protecting the leaves both in dry and cold
-weather. The succulents, like “live-forever,” have a small amount of
-surface in proportion to the mass of the leaf. In the yucca, though the
-leaves are often large, they are very thick and expose a comparatively
-small amount of surface to the dry air and intense sunlight of the
-desert regions. The epidermal covering is also hard and thick. In
-addition, such leaves, as well as those of many succulents, are so
-thick they provide water storage sufficient for the plants, which
-radiate so slowly from their surface.
-
-[Illustration: Fig. 436. A “Phylloclade,” leaves absent, stems
-broadened to function as leaves, on the edges numerous flowers are
-borne.]
-
-=766.= (4) =Elimination of the leaf.=—Perhaps the most
-striking illustration of the reduction of leaf surface is in those
-cases where the leaf is either completely eliminated as in certain
-euphorbias, or in certain of the cacti where the leaves are thought
-to be reduced to spines. Whether the cactus spine belongs to the
-leaf series or not, the leaf as an organ for assimilation and
-transpiration has been completely eliminated and the same is true in
-the phylloclades. The leaf function has been assumed by the stem. The
-stem in this case contains all the chlorophyll; is bulky, and provides
-water storage.
-
-
-III. Protective Positions.
-
-=767.= In many cases the leaves are arranged either in relation
-to the stem, or to each other, or to the ground, in such a way as to
-give protection from too great radiation of heat or moisture. In the
-examples already cited the imbricated leaves of cassiope, pyxidanthera,
-juniper, etc., come also under this head. In the junipers the leaves
-spread out in the summer, while in the winter they are closely
-overlapped. An interesting example of protective position is to be seen
-in the case of the leaves of the white pine. During quite cold winter
-weather the needles are appressed to the stem, and sometimes the trees
-present a striking appearance in contrast with the spreading position
-of the needles in summer. On windy days in winter, the needles turn
-with the wind and become rigid in that position so that they remain in
-a horizontal position for some time, often until the wind dies down,
-or until milder weather. The following day, should there be a cold
-strong wind from the opposite direction, the needles again assume a
-leeward direction. In quiet weather appressed to the stem and in the
-form of a brush there is less radiation of heat than if they diverged.
-In strong winds by turning in the leeward direction the wind is not
-driven between the needle bases and scales. Some plants, especially
-many of those in arctic and alpine regions, have very short stems and
-the leaves are developed near the ground, or the rock. Lying close on
-the ground they do not feel the full force of the drying winds, there
-is less radiation from them, and the radiation of heat from the ground
-protects them. Many plants exhibit movement in response to certain
-stimuli which place them in a position for protection. Some of these
-examples have been discussed under the head of irritability (see
-Chapter XIII). The night position of leaves and cotyledons presented
-by many plants, but especially by many of the Leguminosæ, is brought
-about by the removal of the light stimulus at evening. In many leaves,
-when the light influence is removed, the influence of growth turns
-the leaves downward, or the cotyledons of some plants upward. In this
-vertical position of the leaf-blade there is less radiation of heat
-during the cool night. The most striking cases of protection movements
-are seen in the sensitive plant. As we have seen, the leaves of mimosa
-close in a vertical position at midday if the light and heat are too
-strong. Excessive transpiration is thus prevented. At night the vertical
-position prevents excessive radiation of heat. The vertical or profile
-position of the leaves of the compass plant already referred to not
-only lessens transpiration, but the intense heat and light of the
-midday sun is avoided. This profile position is characteristic of
-certain plants in the dry regions of Australia, and the topmost leaves
-of tropical forests.
-
-
-IV. Relation of Leaves to Light.
-
-=768.= It is very obvious from our study of the function of the
-foliage leaf that its most important relation to environment is that
-which brings it in touch with light and air. It is necessary that light
-penetrate the leaf tissue that the gases of the air and plant may
-readily diffuse and that water vapor may pass out of the leaf. The thin
-expanded leaf-blade is the most economical and efficient organ for leaf
-work. We have seen that leaves respond to fight stimulus in such a way
-as to bring their upper sides usually to face the source of fight, at
-right angles to it or nearly so (_heliotropism_, see Chapter XIII). How
-fully this is brought about depends on the kind of plant, as well as on
-other elements of the environment, for as we have seen in our study of
-leaf protection there is danger to some plants in any region, and to
-other plants in certain regions that the intense light and heat may
-harm the protoplast, or the chlorophyll, or both.
-
-[Illustration: Fig. 437. Mosaic form by trailing shoots of Panicum
-variegatum, “ribbon-grass.”]
-
-The statement that leaves usually face the light at right angles is to
-be taken as a generalized one. The source of the strongest illumination
-varies on different days and again at different times of the day.
-On cloudy days the zenith is the source of strongest illumination.
-The horizontal position of a leaf, where there are no intercepting
-lateral or superior objects would receive its strongest light rays
-perpendicular to its surface. The fact is, however, that leaves on the
-same stem, because of taller or shorter adjacent stems, are so situated
-that the rays of greatest illuminating power are directed at some angle
-between the zenith and horizon. Many leaves, then, which may have
-their upper sides facing the general source of strongest illumination,
-do not necessarily face the sun, and they are thus protected from
-possible injury from intense light and heat because the direct rays of
-sunlight are for the most part oblique. This does not apply, of course,
-to those leaves which “follow the sun” during the day. Their specific
-constitution is such that intense illumination is beneficial.
-
-The leaf is adjusted as well as may be in different species of varying
-constitution, and under different conditions, to a certain balance in
-its relation to the factors concerned. The problem then is to interpret
-from this point of view the positions and grouping of leaves. Because
-of the specific constitution of different plants, and because of a
-great variety of conditions in the environment, we see that it is a
-more or less complex question.
-
-[Illustration: Fig. 438. Sunflower with young head turned toward morning
-sun.]
-
-=769. Day and night positions contrasted.=—In many plants the
-day and night positions of the leaves are different. At night the
-leaves assume a position more or less vertical, known as the _profile_
-position. This is generally regarded as a protective position, since
-during the cool of the night the radiation of heat is less than if the
-leaf were in a vertical position. In many of these plants, however, the
-leaves in assuming the night position become closely appressed which
-would also lessen the radiation. This peculiarity of leaves is largely
-possessed by the members of the family Leguminoseæ (clovers, peas,
-beans, etc.), and by the sensitive plants.[45] But it is also shared by
-some other plants as well (oxalis, for example). The leaves of these
-plants are usually provided with a mechanism which enables them to
-execute these movements with ease. There is a cushion (_pulvinus_) of
-tissue at the base of the petiole, and in the case of compound leaves,
-at the base of the pinnæ and pinnules which undergoes changes in turgor
-in its cells. The collapsing of the cells by loss of water into the
-intercellular spaces causes the leaf to droop. When the cells regain
-their turgor by the absorption of the water from the intercellular
-spaces the leaf is raised to the horizontal, or day position. The light
-stimulus induces turgor of the pulvinus, the disappearance of the
-stimulus is accompanied by a loss of turgor. It is a remarkable fact
-that in some sensitive plants, intense light stimuli are alarm signals
-which result in the same movement as if the light stimulus were
-entirely removed. As we know also contact or pressure stimulus, or
-jarring produces the same result in “sensitive” plants like mimosa,
-some species of rubus, etc. In many plants there is no well-developed
-pulvinus, and yet the leaves show similar movements in assuming the
-day and night positions. Examples are seen in the sunflower, and in
-the cotyledons of many plants. A little observation will enable any
-one interested to discover some of these plants.[46] In these cases the
-night position is due to epinastic growth, and while this influence is
-not removed during the day the light stimulus overcomes it and the leaf
-is raised to the day position.
-
-[Illustration: Fig. 439. Same sunflower plant photographed just at
-sundown.]
-
-=770. Leaves which rotate with the sun.=—During the growth period
-the leaves of the sunflower as well as the growing end of the stem
-respond readily to the direct sunlight. The response is so complete
-that during sunny days the leaves toward the growing end of the stem
-are drawn close together in the form of a rosette and the entire
-rosette as well as the end of the stem are turned so that they face the
-sun directly. In the morning under the stimulus of the rising sun the
-rosette is formed and faces the east. All through the day, if the sun
-continues to shine, the leaves follow it, and at sundown the rosette
-faces squarely the western horizon. For a week or more the young
-sunflower head will also face the sun directly and follow it all day as
-surely as the rosette of leaves. At length, a little while before the
-flowers in the head blossom, the head ceases to turn, but the rosette
-of leaves and the stem also, to some extent, continue to turn with the
-sun. When the leaves become mature they also cease to turn. This is
-well shown in all three photographs (figs. 438-439). The lower leaves
-on the stem being older have assumed the fixed horizontal position
-usually characteristic of the plant with cylindrical habit.
-
-[Illustration: Fig. 440. Same plant a little older when the head does
-not turn, but the stem and leaves do.]
-
-It is not true, as is commonly supposed, that the fully opened
-sunflower head turns with the sun. But I have observed young heads
-four or five inches in diameter rotate with the sun all day. This is
-because the growing end of the stem as well as the young head responds
-to the light stimulus. So there is some truth as well as a great deal
-of fiction in the popular belief that the sunflower head follows the
-sun. The young head will follow the sun all day even if all the leaves
-are cut off, and the growing stem will also if all the leaves as well
-as the flower head are cut away. Young seedlings will also turn even if
-the cotyledons and plumule are cut off.
-
-This phenomenon of the rotation of leaves with the sun is much more
-general than one would infer, as may be seen from a little careful
-observation of rapidly growing plants on bright sunny days. In Alabama
-I have observed beautiful rosettes of _Cassia marilandica_ rotate with
-the sun all day. The peculiarity is very striking in the cotton plant,
-especially when the rows extend north and south. In the forenoon or
-afternoon it is most striking as the entire row shows the leaves tilted
-up facing the sun. There are many of our weeds and common flowers of
-field and garden which show this rotation of the leaves. Some of these
-form rotating rosettes; while in others the leaves rotate independently
-as in the sweet clover.
-
-=771. Fixed position of old leaves.=—In many of the cases cited
-in the preceding paragraph, the rotation of the leaf only occurs
-on sunny days. During cloudy days the leaves of the sunflower, for
-example, are in a nearly horizontal position, or the lower ones may
-be somewhat oblique, since the stronger illumination on such a plant
-would be the oblique rays rather than the zenith rays. As the leaves
-reach maturity also the epinastic growth is equalized by hyponastic
-growth so that the growth movements bring the leaf to stand in a nearly
-horizontal position, or that position in which it receives the best
-illumination. In age, then, many leaves have a fixed position and this
-corresponds with the position assumed on cloudy days.
-
-=772. Position on horizontal stems.=—On horizontal stems the
-leaves have a horizontal position, and if such a stem is stood in an
-erect position the appearance is very odd. If the leaf arises directly
-from the horizontal stem, its petiole will be twisted part way around
-in order to bring the face of the leaf uppermost. It is interesting
-to observe the different relation of stem, petiole and blade and the
-amount of twisting as the horizontal stem or vine trails over
-irregularities in the surface, or climbs over and through other
-vegetation.
-
-=773. Position of leaflets on divided leaves.=—An interesting
-comparison can be made with entire, lobed, divided and dissected
-leaves. The entire leaf usually lies in one plane, since usually the
-problem of adjustment is the same for the entire surface. So the lobes
-of a leaf usually lie all in the same plane as they would if the leaf
-were entire. We find the same is true usually of the compound leaf.
-It forms an incomplete mosaic. Some of the pieces having been removed
-allow much of the light to pass through to leaves beneath. Leaves,
-especially those of some size rarely lie in a flat plane. Some are more
-or less depressed. Some curve downward. Compound leaves often curve
-more or less and the leaflets often droop more or less in a graceful
-fashion. It is interesting, however, that these far separated leaflets
-all lie in the same general plane. This is because the area of the
-leaf, if not too large, makes the problem of position with reference
-to light much the same as if the leaf were entire. The leaflets or
-divisions, though separated, are laminate, and they can work more
-efficiently facing the light. But suppose we extend our observation to
-the finely dissected capillary leaves of some of the parsley family
-(Umbelliferæ), or to the upper leaves of the fennel-leaved thoroughwort
-(Eupatorium fœniculaceum) among the aerial plants, and to Myriophyllum
-among the aquatic plants. The divisions are thread-like or cylindrical.
-One side of the leaflet is just as efficient when presented to the
-light as another. As a result the leaflets are not arranged in the same
-plane, but stand out in many directions.
-
-Occasionally one finds a divided or compound leaf in such a position
-that one portion, because of being shaded above, receives the stronger
-light stimulus from the side, while the other portion is lighted from
-above. If this relation continues throughout the growth-period of the
-leaf the leaflets of one portion may lie in a different plane from
-those of the other portion. In such cases, some of the leaflets are
-permanently twisted to bring them into their proper light relation.
-
-
-V. Leaf Patterns.
-
-MOSAICS, OR CLOSE PATTERNS.
-
-[Illustration: Fig. 441. Fittonia showing leaves arranged to form
-compact mosaic. The netted venation of the leaf is very distinctly
-shown in this plant. (Photo by the Author.)]
-
-=774.= Where the leaves of a plant, or a portion of a plant, are
-approximate and arranged in the form of a pattern, the leaves fitting
-together to form a more or less even and continuous surface, such
-patterns are sometimes termed “mosaics,” since the relation of leaves
-to one another is roughly like the relation of the pieces of a mosaic.
-A good illustration of a mosaic is presented by a greenhouse plant
-Fittonia (fig. 441). The stems are prostrate and the erect branches
-quite short, but it may have quite a wide system by the spreading of
-the runners; the branches of such a length that the leaves borne near
-the tips all fit together forming a broad surface of leaves so closely
-fitted together often that the stems cannot be seen. The advantage of
-a mosaic over a separate disposition of leaves at somewhat different
-levels is that the leaves do not shade one another. Were all the light
-rays coming down at right angles to the leaves, there would not be
-any shading of the lower ones, but the oblique rays of light would be
-cut off from many of the leaves. In the case of a mosaic all the rays
-of light play upon all the leaves. Some of the mosaics which can be
-observed are as follows:
-
-[Illustration: Fig. 442. Rosette pattern of leaves.]
-
-=775. Rosette pattern.=—The rosette pattern is presented by
-many plants with “radial” leaves, or leaves which arise in a cluster
-near the surface of the ground, and are thus more or less crowded in
-their arrangement on the stem. The pretty gloxinia often presents fine
-examples of a loose rosette. In the rosette pattern the petioles of
-the lower leaves are longer than the upper ones, and the blade is thus
-carried out beyond the inner leaves. The leaves being so crowded in
-their attachment to the stem lie very nearly in the same plane.
-
-=776. Vines and climbers.=—Some of the most extensive mosaic
-patterns are shown in creeping and climbing vines. A very common
-example is that of the ivies trained on the walls of buildings,
-covering in some instances many square yards of surface. Where the
-vines trail over the ground or clamber over other vegetation, it is
-interesting to observe the various patterns, and the distortion of
-petioles brought about by turning of the leaves. Of examples found in
-greenhouses, the Pellonia is excellent, and the trailing ribbon-grass
-often forms loose mosaics.
-
-=777. Branch patterns.=—These patterns are very common. They
-are often formed in the woods on the ends of branches by the leaves
-adjusting themselves so as to largely avoid shading each other. Figure
-443 illustrates one of them from a maple branch. It is interesting to
-note the way in which the leaves fit themselves in the pattern, how in
-some the petioles have elongated, while others have remained short. Of
-course, it should be understood that the pattern is made during the
-growth of the leaves.
-
-[Illustration: Fig. 443. Spray of leaves of striped maple, showing
-different lengths of leafstalks.]
-
-[Illustration: Fig. 444. Cedar of Lebanon, strong light only from one
-side of tree (Syria).]
-
-=778. The tree pattern.=—Mosaics are often formed by the exterior
-foliage on a tree, though they are rarely so regular as some of those
-mentioned above. Still it is common to see in some trees with drooping
-limbs like the elm, beautiful and large mosaics. The weeping elm
-sometimes forms a very close and quite even pattern over the entire
-outer surface. In most trees the leaf arrangement is not such as to
-form large patterns, but is more or less open. While the conifers do
-not form mosaics there are many interesting examples of grouping of
-foliage on branch systems into broadly expanded areas, as seen in the
-branches of white pine trees, especially in the edge of a wood, or as
-seen in the arbor-vitæ.
-
-
-OTHER PATTERNS.
-
-=779. Imbricate pattern of short stems.=—This pattern is quite
-common, and differs from the rosette in that the leaves are distributed
-further apart on the stem so that the central ones are considerably
-higher up than in the mosaic. The lower petioles are longer, as in
-the rosette, so that the outer lower leaves extend further out. Some
-begonias show fine imbricate patterns.
-
-[Illustration: Fig. 445. Imbricate pattern of leaves; Begonia.]
-
-=780. Spiral patterns.=—They are very common on stems of the
-cylindrical type, which are unbranched, or but little branched. The
-sunflower, mullein, chrysanthemum, as it is grown in greenhouses, the
-Easter lily, etc., are examples. The spiral arrangement of the leaves
-provides that each successive leaf on the stem, as one ascends the
-stem, is a little to one side so that it does not cast shade on the leaf
-just below. In some stems, according to the leaf arrangement (or
-phyllotaxy), one would pass several times around in ascending the stem
-before a leaf would be found directly above another, which would be
-such a distance below that it would not be shaded to an appreciable
-extent. Interesting observations can be made on different plants to
-work out the relation of distance of leaves on the stem to length of
-the upper and lower leaves; the number of vertical rows on the stem
-compared to the width of the leaves; and the relation of these facts to
-the problem of light supply. Related to the spiral pattern is that of
-erect stems with opposite leaves. Here each pair is set at right angles
-to the direction of the pair above or below.
-
-[Illustration: Fig. 446. Palm showing radiate arrangement of leaves and
-the petiole of the leaf functions as stem in lifting leaf to the light.]
-
-=781. Radiate pattern.=—This pattern is present in many grasses
-and related plants with narrow leaves and short stems. The leaves are
-often very crowded at the base, but by radiating in all directions from
-the horizontal to the vertical, abundant exposure to light is gained
-with little shading. The dragon tree screw-pine, and plants grown in
-greenhouses also illustrate this type. It is also shown in cycads,
-palms, and many ferns, although these have divided leaves.
-
-[Illustration: Fig. 447. Screw-pine (Pandanus) showing prop roots and
-radiate pattern of leaves.]
-
-=782. Compass plants.=—These plants with vertical leaf
-arrangement, and exposure of both surfaces to the lateral rays of light
-have been mentioned in other sections (Lactuca scariola).
-
-=783. Open patterns.=—Open patterns are presented by divided or
-“branched” leaves. Where the leaves are very finely dissected, they may
-be clustered in great profusion and yet admit sufficient light for some
-depth below. Where the leaflets are broader, the leaves are likely to
-be fewer in number and so arranged as to admit light to a great depth
-so that successive leaves below on the same or adjacent stems may not
-be too much shaded. On such plants, often the leaves lying next the
-ground are entire or less divided.
-
-FOOTNOTES:
-
-[44] Some of the different terms used to express the kinds of compound
-leaves are as follows:
-
-[45] The most remarkable case is that of the “telegraph” plant
-(Desmodium gyrans). Aside from the day and night positions which the
-leaves assume, there is a pair of small lateral leaflets to each leaf
-which constantly execute a jerky motion, and swing around in a circle
-like the second hand of a watch.
-
-[46] Seedlings are usually very sensitive to light and are good objects
-to study.
-
-
-
-
-CHAPTER XLI.
-
-THE ROOT.
-
-
-I. Function of Roots.
-
-=784.= The most obvious function of the roots of ordinary
-plants are two: 1st, To furnish anchorage and partial support, and
-2d, absorption of liquid nutriment from the soil. The environmental
-relation of such roots, then, in broad terms, is with the soil. It is
-very clear that in some plants the root serves both functions, while in
-other plants the root may fulfil only one of these requirements.
-
-The problems which the plant has to solve in working out these
-relations are:
-
-    (1) Permeation of the soil or substratum.
-    (2) Grappling the substratum.
-    (3) A congenial moisture or water relation.
-    (4) Distribution of roots for the purpose of reaching
-          food-laden soil.
-    (5) Exposure of surface for absorption.
-    (6) The renewal of the delicate structures for absorption.
-    (7) Aid in preparation of food from raw material.
-    (8) The maintenance of the required balance between the
-          environment as a whole and the increasing or changing
-          requirements of the plant.
-
-=785.= (1) =Permeation of the soil or substratum.=—The
-fundamental divergence of character in the environmental relations of
-root and stem are manifest as soon as they emerge from the germinating
-seed. Under the influence of the same stimulus (_gravity_) the root
-shows its geotropic character by growing downward, while the geotropic
-character of the stem is shown in its upward growth.
-
-The medium which the root has to penetrate offers considerable
-resistance, and the form of the root as well as its manner of growth is
-adapted to overcome this difficulty. The slender, conical, penetrating
-root-tip wedges its way between the minute particles of soil or into
-the minute crevices of the rock, while the nutation of the root enables
-it to search for the points of least resistance. The root-tips having
-penetrated the soil, the older portions of the root continue this wedge
-action by growth in diameter, though, of course, elongation of the old
-parts of the root does not take place. It is the widening growth of the
-tapering root that produces the wedge-like action. The crevices of the
-rock are sometimes broadened, but the resistance here is so great, the
-root is often greatly flattened out.
-
-=786.= (2) =Grappling the substratum.=—The mere penetration
-of a single root into the soil gives it some hold on the soil and it
-offers some resistance to a “pull” since it has wedged its way in
-and the contact of soil particles offers resistance. The root hairs
-formed on the first entering root growing laterally in great numbers
-and applying themselves very closely to the soil particles, increase
-greatly the hold of the plant on the soil, as one can readily see by
-pulling up a young seedling. Lateral roots are soon formed, and as
-these continue to extend and ramify in all directions, the hold is
-increased until in the case of some of the larger plants the resistance
-their hold would offer would equal many tons. Even in some of the
-smaller shrubs and herbs the resistance is considerable, as one can
-easily test by pulling with the hand. To obtain some idea of the amount
-of resistance the roots of these smaller plants offer, they can be
-tested by pulling with the ordinary spring scales.
-
-=787.= (3) =A congenial moisture, or water relation.=—In
-general, the roots seek those portions of the soil provided with a
-modicum of moisture. Usually a suitable moisture condition is present
-in those portions of the soil containing the plant food. But if
-portions of the soil are too dry and very nearby other portions
-containing moisture, the roots grow mainly into the moist substratum
-(_hydrotropism_). If the soil is too wet, the roots grow away from it
-to soil with less water, or in some cases will grow to and upon the
-surface of the soil.
-
-The roots need _aeration_, and where the supply of water is too great,
-the air is shut out, and we know that corn, wheat, and many other
-plants become “sickly” in low and undrained soil in wet seasons. This
-can only be said in the case of our ordinary dry land plants, i.e.,
-those that occupy an intermediate position between _water-loving_
-plants and _dry-conditioned_ plants. This phase of the subject must be
-reserved for special treatment. (See Chapter XLVI.)
-
-=788.= (4) =Distribution of roots for the purpose of reaching
-food-laden soil.=—This is one of the essential relations of the
-root in the case of the land plant, and probably accounts for the very
-extensive ramification of the roots. To some extent it also explains
-the different root systems in some plants. The pines, spruces, etc.,
-usually grow in regions where the soil is very shallow. The root
-system does not extend deeply into the soil. It spreads laterally and
-extends widely through the shallow surface soil and presents a very
-different aspect from the stem system in the air. The root system of
-the broad-leaved trees usually extends more deeply into the soil, while
-of course, extending laterally to great distances. The hickory, walnut,
-etc., especially have strong tap-roots which extend deeply into the
-soil, and the root system of such a tree is more comparable in aspect,
-if it were entirely uncovered, to the stem system in the air. The
-tap-root is more pronounced in some trees than in others. It may be
-that in the hickory and walnut the deep tap-root is important in
-supplying the tree with water in dry seasons, especially when growing
-on dry, gravelly soil which does not retain moisture on the surface
-nor hold it within two or three feet of the surface. Experiment has
-demonstrated, by pot culture of plants, that where soil rich in plant
-food lies adjacent to poor soil, no matter in what part of the pot the
-rich soil is, the greatest growth and branching of roots is in the rich
-soil.
-
-=789.= (5) =Exposure of root surface for absorption.=—The
-principal part of root absorption takes place in the young root and
-the root hairs growing near the root-tip. The root-tips and root hairs
-in their relation to the root systems on which they are borne are
-not to be compared morphologically with the leaves and stem system.
-But the root-tips and hairs are absorbing organs of the roots while
-the main root system supports them, brings them into relation with
-the soil and moisture, and conducts food and other substances to and
-from them. One of the important relations of the leaf is that of
-light, and since the source of light is restricted, i.e., it is not
-equally strong from all sides, an expanded and thin leaf-blade is more
-effective than an equal expenditure of plant material in the form of
-thread-like outgrowths. It is different, however, with the plant food
-dissolved in the soil water. It is equally accessible on all sides. A
-greater surface for absorption is exposed with the same expenditure of
-material by multiplication of the organs and a reduction in their size.
-Numerous delicate root hairs present a greater absorbing surface than
-if the same amount of material were massed into leaf-like expansions.
-There is another important advantage also. Its slender roots and
-thread-like root hairs allow greater freedom of circulation of water,
-food solutions, and air than if the absorbing organs of the roots were
-broadly expanded.
-
-=790.= (6) =The renewal of the delicate structures for
-absorption.=—The delicate root hairs are easily injured. The thin
-cell-walls through which food solutions flow become more or less choked
-by the gradual deposit of substances in solution in the water, and
-continued growth of the root in diameter forms a firmer epidermis and
-cortex through which the solutions taken up by the root hairs would
-pass with difficulty. For this reason new root hairs are constantly
-being formed on the growing root-tip throughout the growing season,
-and in the case of perennial plants, through each season of their
-growth.
-
-=791.= (7) =Aid in preparation of food from raw
-materials.=—For most plants the food obtained from the soil is
-already in solution in the soil water. But there are certain substances
-(examples, some of the chemical compounds of potash, phosphoric acid,
-etc.) which are insoluble in water. Certain acids excreted by the
-roots aid in making these substances soluble (see Chapter III). In
-a number of plants the roots have become associated with fungus or
-bacterial organisms which assist in the manufacture of nitrogenous food
-substances, or even in the absorption of ordinary food solution from
-the soil, or in making use of the decaying humus of the forest (see
-Chapter IX).
-
-=792.= (8) =The maintenance of the required balance between
-the environment and the increasing or changing requirements of the
-plant.=—In this matter the entire plant participates. Mention is
-made here only of the general relation which the root sustains to its
-own environment and the increased burden placed upon it by the shoot.
-The increase in the root system keeps pace with the increasing size of
-the stem system. The roots become stronger, their ramifications wider,
-and the number of absorbing rootlets more numerous. The observation
-is sometimes offered that the correlation between the root system of
-a plant, and the form of the stem system and position of the leaves,
-is of such a nature that plants with a tap-root system have their
-leaves so arranged as to shed the water to the center of the system,
-while plants with a fibrous-root system have their leaves so arranged
-as to shed the water outward. In support of this attention is called
-to the radiate type of the leaf system of the dandelion, beet, etc.
-In the second place the imbricate type as manifested in broad-leaved
-trees, and in the overlapping branch systems of many pines, etc. One
-should note, however, that in the former class the leaves are often
-arranged to shed as much water outward as inward. As to the latter
-class, there is need of experiment to determine whether these empirical
-observations are correct, for the following reasons: 1st, Root and leaf
-distribution are governed by other and more important laws, the root
-being influenced by the location of food in the soil which usually
-forms a very thin stratum while the shoot and leaf is mainly influenced
-by light, and root distribution is much wider in a lateral direction
-than that of the branches. 2d, In light rains the leaf surface holds
-back practically all the rain which is then evaporated into the air
-and lost to the root systems. 3d, In heavy and long-continued rains
-the water breaks through the leaf system to such an extent that roots
-under the tree would be as well supplied as those outside, and the
-ground outside being saturated anyway, the roots do not need the
-small additional water which may have been shed outward. 4th, It is
-the habit of plants where left undisturbed (except in rare cases), to
-grow in more or less dense formations or societies. Here there is no
-opportunity for any appreciable centrifugal distribution of rainfall
-and yet the root distribution is practically the same, except that the
-root systems of adjacent plants are interlaced.
-
-
-II. Kinds of Roots.
-
-=793. The root system.=—From the foregoing, it will be understood
-that the roots of a plant taken together form the _root system_ of that
-plant. In soil-roots in general we usually recognize two kinds of root
-systems.
-
-=794. The fibrous-root system.=—Roots which are composed of
-numerous slender branching roots resembling “fibers,” are termed
-_fibrous_, or the plant is said to have a _fibrous-root system_. The
-bean, corn, most grasses, and many other plants have fibrous-root
-systems.
-
-=795. The tap-root system.=—Plants with a recognizable central
-shaft-like root, more or less thickened and considerably stouter
-than the lateral roots, are said to have _tap_ roots, or they have a
-_tap-root system_. The dandelion, beet, carrot (see crown tuber) are
-examples. The hickory, walnut, and some other trees have very prominent
-tap-roots when young. The tap-root is maintained in old age, but the
-lateral roots often become finally as large as the tap-root. Besides
-tap-roots and fibrous-roots, which include the larger number, several
-other kinds of roots are to be enumerated.
-
-=796. Aerial roots.=—Aerial roots are most abundantly developed
-in certain tropical plants, especially in the orchids and aroids. Many
-examples of these plants are grown in conservatories. The amount of
-moisture is so great in these tropical regions that the roots are
-abundantly supplied without the soil relation. Certain of the roots
-hang free in the air and are provided with a special sheath of spongy
-tissue called the _velamen_, through which moisture is absorbed from
-the air. Other roots attach themselves to the trunk or branches of
-the tree on which the orchid is growing, and furnish the support to
-the _epiphyte_, as such plants are often called. Among the tangle
-of these clinging roots falling leaves are caught. Here they decay
-and nourishing roots grow from the clinging roots into this mass
-of decaying leaves and supply some of the plant food. Aerial roots
-sometimes possess chlorophyll.
-
-There are a number of plants, however, in temperate regions which
-have aerial roots. These are chiefly used to give the stem support as
-it climbs on trees or on walls. They are sometimes called clinging
-roots. A common example is the climbing poison-ivy (Rhus radicans), the
-trumpet creeper, etc. Such aerial roots are called _adventitious_ roots.
-
-=797. Bracing roots, or prop roots.=—These are developed in a
-great variety of plants and serve to brace or prop the plant where
-the fibrous-root system is insufficient to support the heavy shoot
-system, or the shoot system branches so widely props are needed to hold
-up the branches. In the common Indian corn several whorls of bracing
-roots arise from the nodes near the ground and extend outward and
-downward to the ground, though the upper whorls do not always succeed
-in reaching the ground. The screw-pine so common in greenhouses affords
-an excellent example of prop roots. The roots are quite large, and long
-before the root reaches the soil the large root cap is evident. The
-banyan tree of India is a classic example of prop roots for supporting
-the wide-reaching branches. The mangrove in our own subtropical forests
-of Florida is a nearer example.
-
-[Illustration: Fig. 448. Bracing roots of Indian corn.]
-
-[Illustration: Fig. 449. Buttresses of silk-cotton tree, Nassau.]
-
-=798. Buttresses= are formed at the junction of the root and
-trunk, and therefore are part root and part stem. Splendid examples
-of buttresses are formed on the silk-cotton tree. They are sometimes
-formed on the elm and other trees in low swampy ground.
-
-=799. Fleshy roots, or root tubers.=—These are enlargements of
-the root in the form of tubers, as in the sweet potato, the dahlia,
-etc. They are storage reservoirs for food. Portions of the roots become
-thick and fleshy and contain large quantities of sugar, as in the sweet
-potato, or of _inulin_ (a carbohydrate) in the root tubers of the
-dahlia and other composites.
-
-=800. Water-roots and roots of water plants.=—These are roots
-which are developed in the water, or in the soil. Water-roots are
-sometimes formed on land plants where the root comes in contact with a
-body of water, or a stream. Water-roots usually possess no root hairs,
-or but a few, as can be seen by comparing water-roots with soil-roots,
-or by comparing roots of plants grown in water cultures. The greater
-body of water in contact with the root and the more delicate epidermis
-of the root render less necessary the root hairs. The duck-meats
-(Lemna) are good examples of plants having only water-roots. Other
-aquatic plants like the potamogetons, etc., have true roots which grow
-into the soil and serve to anchor the plant, but they are not developed
-as special organs of absorption, since the stem and leaves largely
-perform this function.
-
-=801. Holdfasts.=—These are organs for anchorage which are not
-true roots. These are especially well developed in some of the algæ
-(Fucus, Laminaria, etc.). They are usually called _holdfasts_. The
-holdfasts of the larger algæ are mainly for anchoring the plant. They
-do not function as absorbing organs, and the structure is different
-from that of true roots.
-
-=802. Haustoria or suckers= is a name applied to another kind of
-holdfast employed by parasitic plants. In the dodder the haustorium
-penetrates the tissue of the _host_ (the plant on which the parasite
-grows), and besides furnishing a means of attachment, it serves as an
-absorbing organ by means of which the parasite absorbs food from its
-host. The parasitic fungi like the powdery mildews which grow on the
-surface of their hosts have simple haustoria which serve both as organs
-of attachment and absorption, while in the rusts which grow in the
-interior of their hosts the haustoria are merely absorbing organs.
-
-=803. Rootlets, or rhizoids.=—Many of the algæ, liverworts and
-mosses have slender, hair-like organs of attachment and absorption.
-These plants do not have true roots. Because of the slender form and
-small size of these organs, they are called _rhizoids_, or _rootlets_.
-In form many of them resemble the root hairs of higher plants.
-
-
-
-
-CHAPTER XLII.
-
-THE FLORAL SHOOT.
-
-
-I. The Parts of the Flower.
-
-The portion of the stem on which the flowers are borne is the _flower_
-shoot or axis, or taken together with the flowers, it is known as the
-_Flower Cluster_.
-
-=804. The flower.=—The flower is best understood by an
-examination, first of one of the types known as a “complete” flower,
-as in the buttercup, the spring-beauty, the blood-root, the apple, the
-rose, etc.
-
-There are two sets of organs or members in the complete flower—(1) the
-floral envelope; (2) the essential or necessary members or organs.
-
-The floral envelope when complete consists of—1st, an outer envelope,
-the _calyx_, made up of several leaf-like structures (_sepals_), very
-often possessing chlorophyll, which envelop all the other parts of the
-flower when in bud; 2d, an inner envelope, the _corolla_, also made up
-of several leaf-like parts (_petals_), usually bright colored and larger
-than the sepals. The outer and inner floral envelopes are usually in
-whorls (though in close spirals in many of the buttercup family, etc.),
-and for reasons discussed elsewhere (Chapter XXXIV) represent leaves.
-The essential or necessary members of the flower are also usually in
-whorls and likewise represent leaves, but only in rare cases is there
-any suggestion, either in their form or color, of a leaf relationship.
-These members are in two sets: (1) The outer, or _andrœcium_,
-consisting of a few or many parts (_stamens_); (2) the inner set, the
-_gynœcium_, consisting of a few or many parts (_carpels_).
-
-=805. Purpose of the flower.=—While the ultimate purpose of
-all plants is the production of seed or its equivalent through
-which the plant gains distribution and perpetuation, the flower is
-the specialized part of the seed plant which utilizes the food and
-energies contributed by other members of the plant organization for the
-production of seed. In addition to this there are definite functions
-performed by the members of the flower, which come under the general
-head of plant work, or flower work.
-
-=806. The calyx, or the sepals.=—These are chiefly protective,
-affording protection to the young stamens and carpels in the flower
-bud. Where the corolla is absent, sepals are usually present and then
-assume the function of the petals. In a few instances the calyx may
-possibly ultimately join in the formation of the fruit (examples: the
-butternut, walnut, hickory).
-
-=807. The corolla, or petals.=—The petals are partly protective
-in the bud, but their chief function where well developed seems to be
-that of attracting insects, which through their visits to the flower
-aid in “_pollination_,” especially “_cross pollination_.”
-
-=808. The stamens.=—The stamens (= microsporophylls) are
-flower organs for the production of _pollen_, or _pollen-spores_ (=
-microspores). The _stalk_ (not always present) is the _filament_, the
-_anther_ is borne on the filament when the latter is present. The
-anther consists of the _anther sacs_ or _pollen sacs_ (microsporangium)
-containing the pollen-spores, and the _connective_, the sterile tissue
-lying between and supporting the anther sac. The stamens are usually
-separate, but sometimes they are united by their filaments, or by their
-anthers. When the pollen is ripe they open by slits or pores and the
-pollen is scattered; or in rarer cases the pollen mass (_pollinium_) is
-removed through the agency of insects (see Insect pollination, Chap.
-XLIII).
-
-=809. The pistil.=—The pistil consists of the “_ovary_,” the
-_style_ (not always present), and the _stigma_. These are well shown in
-a _simple pistil_, common examples of which are found in the buttercup,
-marsh marigold, the pea, bean, etc. The simple pistil is equivalent to
-a _carpel_ (= macrosporophyll), while the _compound pistil_ consists of
-two or several carpels joined, as in the toothwort, trillium, lily,
-etc. The _ovary_ is the enlarged part which below is attached to
-the receptacle of the flower, and contains within the _ovules_. The
-_style_, when present, is a slender elongation of the upper end of
-the ovary. The _stigma_ is supported on the end of the style when the
-latter is present. It is often on a capitate enlargement of the style
-or extends down one side, or when the style is absent it is usually
-seated directly on the upper end of the ovary. The stigmatic surface is
-glutinous or “sticky,” and serves to hold the pollen-spores when they
-come in contact with it.
-
-The _ovules_ are within the ovary and are arranged in different ways
-in different plants. The pollen grain (or better pollen-spore =
-microspore), after it has been transferred to the stigma, “germinates,”
-and the pollen tube grows down through the tissue of the stigma and
-style, or courses down the stylar canal until it reaches the ovule.
-Here it usually enters the ovule (macrosporangium) at the _micropyle_
-(in some of the ament-bearing plants it enters at the _chalaza_), and
-the sperm cells are emptied into the embryo sac in the interior of the
-ovule.
-
-=810. Fertilization.=—One of the sperms unites with the egg
-in the embryo sac. This is _fertilization_, and from the fertilized
-egg the young embryo is formed still within the ovule. _Double
-fertilization_,—the other sperm cell sometimes unites with one or both
-of the “polar” nuclei which have united to form the “definitive” or
-“endosperm” nucleus. As a result of fertilization, the embryo plant is
-formed within the ovule, the coats of which enlarge by growth forming
-the seed coats, and altogether forming the seed. (See Chapters XXXIV,
-XXXV, XXXVI.)
-
-
-II. Kinds of Flowers.
-
-=811. Absence of certain flower parts.=—The _complete_ flower
-contains all the four series of parts. When any one of the series of
-parts is lacking, the flower is said to be _incomplete_. Where only one
-series of the floral envelopes is present the flowers are said to be
-_apetalous_ (the petals are absent), examples: elm, buckwheat, etc.
-Flowers which lack both floral envelopes are _naked_. When pistils are
-absent but stamens are present the flowers are _staminate_, whether
-floral envelopes are present or not; and so when stamens are absent and
-pistils present the flower is _pistillate_. If both stamens and pistils
-are absent the flower is said to be _sterile_ or _neutral_ (snowball,
-marginal or showy flowers in hydrangea). Flowers with both stamens and
-pistils, whether or not they have floral envelopes, are _perfect_ (or
-hermaphrodite), so if only one of these sets of _essential organs_
-of the flower is present the flower is _imperfect_, or _diclinous_.
-Sometimes the imperfect, or diclinous, flowers are on the same plant,
-and the plant is said to be _monœcious_ (of one household). When
-staminate flowers are on certain individual plants, and the pistillate
-flowers of the same species are on other individuals, the plant is
-_diœcious_ (or of two households). When some of the flowers of a plant
-are diclinous and others are perfect, they are said to be _polygamous_.
-
-Many of these variations relating to the presence or absence of flower
-parts in one way or another contribute to the well-being of the plant.
-Some indicate a division of labor; thus in the neutral flowers of
-certain species of hydrangea or viburnum, the showy petals serve to
-attract insects which aid in the pollination of the fertile flowers. It
-must not be understood, however, that all variations in plants which
-results in new or different forms of flowers is for the good of the
-species. For example, under cultivation the flowers of viburnum and
-hydrangea sometimes are all neutral and showy. While such variations
-sometimes contribute to the happiness of man, the plant has lost the
-power of developing seed. In diclinous flowers cross pollination is
-necessitated.
-
-=812. Form of the flower.=—The flower as a whole has _form_.
-This is so characteristic that in general all flowers of the different
-individuals of a species are of the same shape, though they may vary
-in size. In general, flowers of closely related plants of different
-species are of the same type as to form, so that often in the shape of
-the flower alone we can see the relationship of kind, though the form
-of the flower is not the most important nor always the sure index of
-kinship. Since many flowers resemble certain familiar objects, names
-are often used which relate to these objects.
-
-Flowers are said to be _regular_, or _irregular_. In a regular flower
-all of the parts of a set or series are of the same shape and size,
-while in irregular flowers the parts are of a different shape or size
-in some of the sets. The flowers of the pea family (_Papilionaceæ_),
-of the mint family (_Labiatæ_), of the morning glory, larkspur,
-monkshood, etc., are irregular (fig. 450). The corolla usually gives
-the characteristic form to the flower, and the name is usually applied
-to the form of the corolla.
-
-[Illustration: Fig. 450. Several forms of flowers. Regular flowers.
-_wh_, wheel-shaped corolla; _sa_, salver-shaped; _tub_, tubular-shaped.
-Irregular flowers. _pa_, butterfly or papilionaceous; _per_, personate
-or masked flower; _lab_, gaping or ringent corolla. The two latter are
-called bilabiate flowers.]
-
-Some of the different forms are wheel-shaped or _rotate_ corolla when
-the petals spread out at once like the spokes of a wheel, as in the
-potato, tomato, or bittersweet; _salver-shaped_ when the petals spread
-out at right angles from the end of a corolla tube, as in the phlox;
-_bell-shaped_, or _campanulate_, as in the harebell or campanula;
-_funnel-shaped_, as in the morning glory; _tubular_, when the ends of
-the petals spread but little or none from the end of the corolla tube,
-as in the turnip flower or in the disk florets of the composites. The
-_butterfly_, or _papilionaceous_ corolla is peculiar as in the pea
-or bean. The upper petal is the “banner,” the two lateral ones the
-“wings,” and the two lower the “keel.”
-
-The _labiate_ corolla is characteristic of the mint family where the
-gamosepalous corolla is unequally divided, so that the two upper lobes
-are sharply separated from the three lower forming two “lips.” The
-labiate corolla of the toad-flax, or snapdragon is _personate_, or
-_masked_, because the lower lip arches upward like a palate and closes
-the entrance to the corolla tube; that of the dead nettle (_Lamium_) is
-_ringent_ or _gaping_, because the lips are spread wide apart. In some
-plants the labiate corolla is not very marked and differs but slightly
-from a regular form.
-
-The _ligulate_ or _strap-shaped_ corolla is characteristic of the
-flowers of the dandelion or chicory, or of the ray flowers of other
-composites (fig. 451). The lower part of the gamosepalous corolla is
-tubular, and the upper part is strap-shaped, as if that part of the
-tube were split on one side and spread out flat.
-
-These forms of the flower should be studied in appropriate examples.
-
-=813. Union of flower parts.=—In the buttercup flower all the
-parts of each series are separate from one another and from other
-series of parts. Each one is attached to the _receptacle_ of the
-flower, which is a very much shortened portion of the flower axis.
-The calyx being composed of separate and distinct parts is said to be
-_polysepalous_, and the corolla is likewise _polypetalous_. The stamens
-are _distinct_, and the pistils are _simple_. In many flowers, however,
-there is a greater or lesser _union_ of parts.
-
-=814. Union of parts of the same series or cycle.=—The parts
-_coalesce_, either slightly or to a great extent. Usually they are not
-so completely coalesced but what the number of parts of the series can
-be determined. Where the sepals are united the calyx is _gamosepalous_,
-when the petals are united the corolla is _gamopetalous_.
-
-Union of the sepals or of the corolla is quite common, but union
-of the stamens is rare except in a few families where it is quite
-characteristic. When the stamens are united by their anthers, they
-are _syngenœsious_. This is the case in most flowers of the composite
-family. When all the stamens are united into one group by their
-filaments, they are _monadelphous_ (one brotherhood), as in
-hollyhock, hibiscus, cotton, marsh-mallow, etc. When they are united
-by their filaments in two groups, they are _diadelphous_ (two
-brotherhoods), as in the pea and most members of the pea family. In
-most species of St. John’s wort (Hypericum), the stamens are united in
-threes (_triadelphous_).
-
-=815. The carpels are often united.=—The pistil is then said to
-be _compound_. Where the pistils are consolidated, usually the adjacent
-walls coalesce and thus separate the cavity of each ovary. Each cavity
-in the compound pistil is a _locule_. In some cases the adjacent walls
-disappear so that there is one common cavity for the compound pistil
-(examples: purslane, chickweeds, pinks, etc.). In a few cases there is a
-false partition (example, in the toothwort and other crucifers). The
-compound pistil is very often lobed slightly, so that the different
-pistils can be discerned. More often the styles or stigmas are
-distinct, and thus indicate the number of pistils united.
-
-=816. Union of the parts of different series.=—While in the
-buttercup and many other flowers, all the different parts are inserted
-on the torus or receptacle, in other flowers one series of parts may
-be joined to another. This is _adnation_ of parts, or the two or more
-series are _adnate_. In the morning glory the stamens are inserted
-on the inner face of the corolla tube; the same is true in the mint
-family, and there are many other examples. The insertion of parts,
-whether free or adnate, is usually spoken of in reference to their
-relation to the pistil. Thus, in the buttercup the floral envelopes and
-stamens are all free and _hypogynous_, they are _below_ the pistil.
-The pistil in this case is _superior_. In the cherry, pear, etc., the
-petals and stamens are borne on the edge of the more or less elevated
-tube of the calyx, and are said to be _perigynous_, i.e., around the
-pistil. In the cranberry, huckleberry, etc., the calyx is for the
-most part united with the wall of the ovary with the short calyx
-limbs projecting from the upper surface. The petals and stamens are
-inserted on the edge of the calyx above the ovary; they are, therefore,
-_epigynous_, and the ovary being under the calyx, as it were, is
-_inferior_.
-
-
-III. Arrangement of Flowers, or Mode of Inflorescence.
-
-=817. Flowers are solitary or clustered.=—_Solitary flowers_
-are more simple in their arrangement, i.e., it is easier for us to
-determine and name their relation to each other and to other parts of
-the plant. They are either _axillary_, i.e., on short lateral shoots
-in the axils of ordinary foliage leaves, or they are _terminal_, i.e.,
-they are borne on the end of the main axis of an ordinary foliage
-shoot. In either case they are so far separated, and the foliage
-leaves are so prominent, they do not form recognizable groups or
-clusters. The manner of arrangement of flowers on the shoot is called
-_inflorescence_, while the group of flowers so arranged is the _flower
-cluster_.
-
-Two different modes of inflorescence are usually recognized in
-the arrangement of flowers on the stem. (1) The _corymbose_, or
-_indeterminate inflorescence_ (also indefinite inflorescence), in
-which the flowers arise from axillary buds, and the terminal bud may
-continue to grow. (2) The _cymose_ or _determinate inflorescence_ (also
-_definite inflorescence_) in which the flowers arise from terminal
-buds. This arrests the growth of the shoot in length.
-
-There are several advantages to the plant in the different modes of
-inflorescence, chief among which is the massing of the flowers, thus
-increasing the chances for effective pollination.
-
-
-A. FLOWER CLUSTERS WITH INDETERMINATE INFLORESCENCE.
-
-=818. The simplest mode of indeterminate inflorescence= is where
-the flowers arise in the axils of normal foliage leaves, while the
-terminal bud, as in the florist’s smilax, the bellwort, moneywort,
-apricot, etc., continues to grow. The flowers are _solitary_ and
-_axillary_. In other cases which are far more numerous, the flowers are
-associated into more or less definite clusters in which are a number
-of recognizable types. The word type used in this sense, it should be
-understood, does not refer to an original structure which is the
-source of others. It merely refers to a mode of inflorescence which we
-attempt to recognize, and about which we group those forms which have
-a resemblance to one another. There are many forms of flower clusters
-which do not conform to any one of our recognized types, and are very
-puzzling. The evolution of the flower clusters has been _natural_, and
-we cannot make them all conform to an _artificial_ classification.
-These _types_ are named merely as a matter of convenience in the
-expression of our ideas. The types usually recognized are as follows:
-
-=819. The raceme.=—The flower-shoot is more or less elongated,
-and the leaves are reduced to a minute size termed _bracts_, while the
-flowers on lateral axes are solitary in the axils of the bracts. The
-reduction in the size of the leaves and the somewhat limited growth
-of the shoot in length, makes the flowers more prominent, and brings
-them into closer relation than if they were formed in the axils of
-the leaves on the ordinary foliage shoot. The choke cherry, currant,
-pokeweed, sourwood, etc., are examples of a raceme (fig. 569). In most
-plants with the raceme type, while the inflorescence is indeterminate,
-and the uppermost flowers (those toward the end of the main shoot)
-are younger, still the period of flowering is somewhat restricted
-and the raceme stops growing. In a few plants, however, as in the
-common “shepherd’s-purse,” the raceme continues to grow throughout the
-summer, so that the lower flowers may have ripened their seed while
-the terminal portion of the raceme is still growing and producing
-new flowers. Compound racemes are formed when by branching of the
-flower-shoot there are several racemes in a cluster, as in the false
-Solomon’s seal (Smilacina racemosa).
-
-=820. The panicle.=—The panicle is developed from the raceme type
-by the branching of the lateral flower-axes forming a loose open flower
-cluster, as in the _oat_.
-
-=821. The thyrsus= is a compact panicle of pyramidal form, as in
-the lilac, horse-chestnut, etc.
-
-=822. The corymb.=—The corymb shows likewise an easy transition
-from the raceme type, by the shortening of the main axis of
-inflorescence, and the lengthening of the lower, lateral flower
-peduncles so that the flower cluster is more or less flattened on
-top. This represents the _simple corymb_. A _compound corymb_ is one
-in which some of the flower peduncles branch again forming secondary
-corymbs, as in the mountain-ash. It is like a panicle with the lower
-flower stalks elongated.
-
-=823. The umbel.=—The umbel is developed from the raceme, or
-corymb. The main flower-shoot remains very short or undeveloped with
-several flowers on long peduncles arising close together around this
-shortened axis, in the form of a whorl or cluster. Examples are found
-in the milkweed, water pennywort (Hydrocotyle), the oxheart cherry,
-etc. A _compound_ umbel is one in which the peduncles are branched,
-forming secondary umbels, as in the caraway, parsnip, carrot, etc.
-
-=824. The spike.=—In the spike the main axis is long, and the
-solitary flowers in the axils of the bracts are usually sessile, and
-often very much crowded. The plaintain, mullein (fig. 422), etc.,
-are examples. The spike is a raceme, only the flowers are sessile
-and crowded. In the grasses the flower cluster is branched, and the
-branchlets bearing a few flowers are spikelets.
-
-=825. The head.=—When the flower axis is very much shortened
-and the flowers crowded and sessile or nearly so, forming a globose
-or compressed cluster, it is a _head_ or _capitulum_. The transition
-is from a spike by the shortening of the main axis, as in the clover,
-button bush (_Cephalanthus_), etc., or in the shortening of the
-peduncles in an umbel, as in the daisy, dandelion, and other composite
-flowers. In these the head is surrounded by an involucre, which in
-the young head often envelopes the mass of flowers, thus affording
-them protection. In some other composites (Lactuca, for example) the
-involucre affords protection for a longer period, even while the seeds
-are ripening.
-
-=826. The spadix.=—When the main axis of the flower cluster is
-fleshy, the spike or head forms a _spadix_, as in the Indian turnip,
-the skunk-cabbage, the calla, etc. The spadix is usually more or less
-enclosed in a _spathe_, a somewhat strap-shaped leaf.
-
-=827. The catkin.=—A spike which is usually caducous, i.e., falls
-away after the maturity of the flower or fruit, is called a catkin,
-or an _ament_. The flower clusters of the alder, willow, (fig. 555),
-poplar, and the staminate flower clusters of the oak, hickory,
-hazel, birch, etc., are _aments_. So characteristic is this mode
-of inflorescence that the plants are called _amentiferous_, or
-_amentaceous_.
-
-[Illustration: Fig. 451. Head of sunflower showing centripetal
-inflorescence of tubular flowers. (Photo by the Author.)]
-
-=828. Anthesis of flowers with indeterminate inflorescence.=—In
-the anthesis of the raceme as well as in other corymbose forms the
-lower (or outer) flowers being older, open first. The opening of the
-flowers then takes place from below, upward; or from the outside,
-inward toward the center of inflorescence. The _anthesis_, i.e., the
-opening of the flowers of corymbose forms is said to be _centripetal_,
-i.e., it progresses from outside, inward. The anthesis of the fuller’s
-teazel is peculiar, since it shows both types. There are several
-distinct advantages to the plant where anthesis extends over a period
-of time, as it favors cross pollination, favors the formation of seed
-in case conditions should be unfavorable at one period of anthesis,
-distributes the drain on the plant for food, etc.
-
-[Illustration: Fig. 452. Heads of fuller’s teazel in different stages
-of flowering.]
-
-
-B. FLOWER CLUSTERS WITH DETERMINATE INFLORESCENCE.
-
-=829. The simplest mode of determinate inflorescence= is a plant
-with a solitary terminal flower, as in the hepatica, the tulip,
-etc. The leaves in these two plants are clustered in the form of a
-rosette, and the aerial shoot is naked and bears the single flower at
-its summit. Such a flower-shoot is a _scape_. As in the case of the
-indeterminate inflorescence, so here the larger number of flower-shoots
-are more complex and specialized, resulting in the evolution of flower
-clusters or masses. Accompanying the association of flowers into
-clusters there has been a reduction in leaf surface on the flower-shoot
-so that the flowers predominate in mass and are more conspicuous. Among
-the recognized modes of determinate inflorescence, the following are
-the chief ones:
-
-=830. The cyme.=—In the cyme the terminal flower on the main axis
-opens first and the remaining flowers are borne on lateral shoots,
-which arise from the axils of leaves or bracts, below. These lateral
-shoots usually branch and elongate so that the terminal flowers on all
-the branches reach nearly the same height as the terminal flower on the
-main shoot, forming a somewhat flattened or convex top of the flower
-cluster. This is illustrated in the basswood flower. The anthesis of
-the cyme is _centrifugal_, i.e., from the inside outward to the margin.
-But it is often more or less mixed, since the lateral shoots if they
-bear more than one flower are diminutive cymes and the terminal flower
-opens before the lateral ones. Where the flower cluster is quite large
-and the branching quite extensive, _compound cymes_ are formed, as in
-the dogwood, hydrangea, etc.
-
-[Illustration: Fig. 453. Diagrams of cymose inflorescence. _A_,
-dichasium; _B_, scorpioid cyme; _C_, helicoid cyme. (After
-Strasburger.)]
-
-=831. The helicoid cyme.=—Where successive lateral branching
-takes place, and always continues on the same side a curved flower
-cluster is formed, as in the forget-me-not and most members of the
-borage family. This is known as a _helicoid cyme_ (fig. 453, _C_). Each
-new branch becomes in turn the “false” axis bearing a new branch on the
-same side.
-
-=832. The scorpioid cyme.=—_A scorpioid cyme_ (fig. 453, _B_) is
-formed where each new branch arises on alternate sides of the “false”
-axis.
-
-=833. The forking cyme= is where each “false” axis produces two
-branches opposite, so that it represents a false dichotomy (example,
-the flower cluster of chickweed).
-
-=834.= Some of these flower clusters are peculiar and it is
-difficult to see how the helicoid, or scorpioid, cymes are of any
-advantage to the plant over a true cyme. The inflorescence of the
-plant being determinate, if the flowering is to be extended over a
-considerable period a peculiar form would necessarily result. In the
-_helicoid cyme_ continued branching takes place on one side, and
-the result in the forget-me-not is a continued inflorescence in its
-effect like that of a continued raceme (compare shepherd’s-purse).
-But we should not expect that all of the complex and specialized
-structures from simple and generalized ones are beneficial to the
-plant. In many plants we recognize evolution in the direction of
-advantageous structures. But since the plant cannot consciously
-evolve these structures, we must also recognize that there may be
-phases of retrogression in which the structures evolved are not so
-beneficial to the plant as the more simple and generalized ones of its
-ancestors. Variation and change do not result in advancing the plant
-or plant structures merely along the lines which will be beneficial.
-The tendency is in all directions. The result in general may be
-diagramed by a tree with divergent and wide-reaching branches. Some die
-out; others remain subordinate or dormant; while still others droop
-downward, showing a retrogression. But in this backward evolution
-they do not return to the condition of their ancestors, nor is the
-same course retraced. A new downward course is followed just as the
-downward-growing branch follows a course of its own, and does not
-return in the trunk.
-
-
-
-
-CHAPTER XLIII.
-
-POLLINATION.
-
-
-Origin of heterospory, and the necessity for pollination.
-
-=835. Both kinds of sexual organs on the same prothallium.=—In
-the ferns, as we have seen, the sexual organs are borne on the
-prothallium, a small, leaf-like, heart-shaped body growing in moist
-situations. In a great many cases both kinds of sexual organs are
-borne on the same prothallium. While it is perhaps not uncommon, in
-some species, that the egg-cell in an archegonium may be fertilized
-by a spermatozoid from an antheridium on the same prothallium, it
-happens many times that it is fertilized by a spermatozoid from another
-prothallium. This may be accomplished in several ways. In the first
-place antheridia are usually found much earlier on the prothallium than
-are the archegonia. When these antheridia are ripe, the spermatozoids
-escape before the archegonia on the same prothallium are mature.
-
-=836. Cross fertilization in monœcious prothallia.=—By swimming
-about in the water or drops of moisture which are at times present in
-these moist situations, these spermatozoids may reach and fertilize
-an egg which is ripe in an archegonium borne on another and older
-prothallium. In this way what is termed cross fertilization is brought
-about nearly as effectually as if the prothallia were diœcious, i.e. if
-the antheridia and archegonia were all borne on separate prothallia.
-
-=837. Tendency toward diœcious prothallia.=—In other cases
-some fern prothallia bear chiefly archegonia, while others bear only
-antheridia. In these cases cross fertilization is enforced because
-of this separation of the sexual organs on different prothallia.
-These different prothallia, the male and female, are largely due to a
-difference in food supply, as has been clearly proven by experiment.
-
-=838. The two kinds of sexual organs on different prothallia.=—In
-the horsetails (equisetum) the separation of the sexual organs on
-different prothallia has become quite constant. Although all the spores
-are alike, so far as we can determine, some produce small male plants
-exclusively, while others produce large female plants, though in some
-cases the latter bear also antheridia. It has been found that when the
-spores are given but little nutriment they form male prothallia, and
-the spores supplied with abundant nutriment form female prothallia.
-
-=839. Permanent separation of sexes by different amounts of nutriment
-supplied the spores.=—This separation of the sexual organs of
-different prothallia, which in most of the ferns, and in equisetum, is
-dependent on the chance supply of nutriment to the germinating spores,
-is made certain when we come to such plants as isoetes and selaginella.
-Here certain of the spores receive more nutriment while they are
-forming than others. In the large sporangia (macrosporangia) only a few
-of the cells of the spore-producing tissue form spores, the remaining
-cells being dissolved to nourish the growing macrospores, which are few
-in number. In the small sporangia (microsporangia) all the cells of the
-spore-producing tissue form spores. Consequently each one has a less
-amount of nutriment, and it is very much smaller, a microspore. The
-sexual nature of the prothallium in selaginella and isoetes, then, is
-predetermined in the spores while they are forming on the sporophyte.
-The microspores are to produce male prothallia, while the macrospores
-are to produce female prothallia.
-
-=840. Heterospory.=—This production of two kinds of spores
-by isoetes, selaginella, and some of the other fern plants is
-_heterospory_, or such plants are said to be _heterosporous_.
-Heterospory, then, so far as we know from living forms, has originated
-in the fern group. In all the higher plants, in the gymnosperms and
-angiosperms, it has been perpetuated, the microspores being represented
-by the pollen, while the macrospores are represented by the embryo sac;
-the male organ of the gymnosperms and angiosperms being the antherid
-cell in the pollen or pollen tube, or in some cases perhaps the pollen
-grain itself, and the female organ in the angiosperms perhaps reduced
-to the egg-cell of the embryo sac.
-
-=841. In the pteridophytes water serves as the medium for conveying
-the sperm cell to the female organ.=—In the ferns and their allies,
-as well as in the liverworts and mosses, surface water is a necessary
-medium through which the generative or sperm cell of the male organ,
-the spermatozoid, may reach the germ cell of the female organ. The
-sperm cell is here motile. This is true in a large number of cases
-in the algæ, which are mostly aquatic plants, while in other cases
-currents of water float the sperm cell to the female organ.
-
-=842. In the higher plants a modification of the prothallium is
-necessary.=—As we pass to the gymnosperms and angiosperms,
-however, where the primitive phase (the gametophyte) of the plants
-has become dependent solely on the modern phase (the sporophyte) of
-the plant, surface water no longer serves as the medium through which
-a motile sperm cell reaches the egg-cell to fertilize it. The female
-prothallium, or macrospore, is, in nearly all cases, permanently
-enclosed within the sporangium, so that if there were motile sperm
-cells on the outside of the ovary, they could never reach the egg to
-fertilize it.
-
-=843.= But a modification of the microspore, the pollen tube,
-enables the sperm cell to reach the egg-cell. The tube grows through
-the nucellus, or first through the tissues of the ovary, deriving
-nutriment therefrom.
-
-=844.= But here an important consideration should not escape us.
-The pollen grains (microspores) must in nearly all cases first reach
-the pistil, in order that in the growth of this tube a channel may be
-formed through which the generative cell can make its way to the egg
-cell. The pollen passes from the anther locule, then, to the stigma of
-the ovary. This process is termed _pollination_.
-
-
-Pollination.
-
-=845. Self pollination, or close pollination.=—Perhaps very few
-of the admirers of the pretty blue violet have ever noticed that there
-are other flowers than those which appeal to us through the beautiful
-colors of the petals. How many have observed that the brightly colored
-flowers of the blue violet rarely “set fruit”? Underneath the soil
-or débris at the foot of the plant are smaller flowers on shorter,
-curved stalks, which do not open. When the anthers dehisce, they are
-lying close upon the stigma of the ovary, and the pollen is deposited
-directly upon the stigma of the same flower. This method of pollination
-is _self pollination_, or _close pollination_. These small, closed
-flowers of the violet have been termed “_cleistogamous_,” because they
-are pollinated while the flower is closed, and fertilization takes
-place as a result.
-
-But self pollination takes place in the case of some open flowers.
-In some cases it takes place by chance, and in other cases by such
-movements of the stamens, or of the flower at the time of the
-dehiscence of the pollen, that it is quite certainly deposited upon the
-stigma of the same flower.
-
-=846. Wind pollination.=—The pine is an example of
-wind-pollinated flowers. Since the pollen floats in the air or
-is carried by the “wind,” such flowers are _anemophilous_. Other
-anemophilous flowers are found in other conifers, in grasses, sedges,
-many of the ament-bearing trees, and other dicotyledons. Such plants
-produce an abundance of pollen and always in the form of “dust,” so
-that the particles readily separate and are borne on the wind.
-
-=847. Pollination by insects.=—A large number of the plants which
-we have noted as being anemophilous are monœcious or diœcious, i.e. the
-stamens and pistils are borne in separate flowers. The two kinds of
-flowers thus formed, the male and the female, are borne either on the
-same individual (monœcious) or on different individuals (diœcious). In
-such cases cross pollination, i.e. the pollination of the pistil of
-one flower by pollen from another, is sure to take place, if it is
-pollinated at all. Even in monœcious plants cross pollination often
-takes place between flowers of different individuals, so that more
-widely different stocks are united in the fertilized egg, and the
-strain is kept more vigorous than if very close or identical strains
-were united.
-
-[Illustration: Fig. 454. Viola cucullata; blue flowers above,
-cleistogamous flowers smaller and curved below. Section of pistil at
-right.]
-
-=848.= But there are many flowers in which both stamens and
-pistils are present, and yet in which cross pollination is accomplished
-through the agency of insects.
-
-=859. Pollination of the bluet.=—In the pretty bluet the stamens
-and styles of the flowers are of different length as shown in figures
-455, 456. The stamens of the long-styled flower are at about the same
-level as the stigma of the short-styled flower, while the stamens of
-the latter are on about the same level as the stigma of the former.
-What does this interesting relation of the stamens and pistils in the
-two different flowers mean? As the butterfly thrusts its “tongue” down
-into the tube of the long-styled flower for the nectar, some of the
-pollen will be rubbed off and adhere to it. When now the butterfly
-visits a short-styled flower this pollen will be in the right position
-to be rubbed off onto the stigma of the short style. The positions
-of the long stamens and long style are such that a similar cross
-pollination will be effected.
-
-[Illustration: Fig. 455. Dichogamous flower of the bluet (Houstonia
-cœrulea), the long-styled form.]
-
-[Illustration: Fig. 456. Dichogamous flower of bluet (Houstonia
-cœrulea), the short-styled form.]
-
-=850. Pollination of the primrose.=—In the primroses, of which
-we have examples growing in conservatories, that blossom during the
-winter, we have almost identical examples of the beautiful adaptations
-for cross pollination by insects found in the bluet. The general shape
-of the corolla is the same, but the parts of the flower are in
-fives, instead of in fours as in the bluet. While the pollen of the
-short-styled primulas sometimes must fall on the stigma of the same
-flower, Darwin has found that such pollen is not so potent on the
-stigma of its own flower as on that of another, an additional provision
-which tends to necessitate cross pollination.
-
-[Illustration: Fig. 457. Dichogamous flowers of primula.]
-
-In the case of some varieties of pear trees, as the Bartlett, it
-has been found that the flowers remain largely sterile not only to
-their own pollen, or pollen of the flowers on the same tree, but to
-all flowers of that variety. However, they become fertile if cross
-pollinated from a different variety of pear.
-
-=851. Pollination of the skunk’s cabbage.=—In many other flowers
-cross pollination is brought about through the agency of insects,
-where there is a difference in time of the maturing of the stamens and
-pistils of the same flower. The skunk’s cabbage (Spathyema fœtida),
-though repulsive on account of its fetid odor, is nevertheless a very
-interesting plant to study for several reasons. Early in the spring,
-before the leaves appear, and in many cases as soon as the frost is out
-of the hard ground, the hooked beak of the large fleshy spathe of this
-plant pushes its way through the soil.
-
-If we cut away one side of the spathe as shown in fig. 459 we shall
-have the flowering spadix brought closely to view. In this spadix the
-pistil of each crowded flower has pushed its style through between the
-plates of armor formed by the converging ends of the sepals, and stands
-out alone with the brush-like stigma ready for pollination, while the
-stamens of all the flowers of this spadix are yet hidden beneath. The
-insects which pass from the spadix of one plant to another will, in
-crawling over the projecting stigmas, rub off some of the pollen which
-has been caught while visiting a plant where the stamens are scattering
-their pollen. In this way cross pollination is brought about. Such
-flowers, in which the stigma is prepared for pollination before the
-anthers of the same flower are ripe, are _proterogynous_.
-
-[Illustration: Fig. 458. Skunk’s cabbage.]
-
-[Illustration: Fig. 459. Proterogyny in skunk’s cabbage. (Photograph by
-the author.)]
-
-[Illustration: Fig. 460. Skunk’s cabbage; upper flowers proterandrous,
-lower ones proterogynous.]
-
-
-=852.= Now if we observe the spadix of another plant we may see a
-condition of things similar to that shown in fig. 460. In the flowers
-in the upper part of the spadix here the anthers are wedging their way
-through between the armor-like plates formed by the sepals, while the
-styles of the same flowers are still beneath, and the stigmas are not
-ready for pollination. Such flowers are _proterandrous_, that is, the
-anthers are ripe before the stigmas of the same flowers are ready for
-pollination. In this spadix the upper flowers are proterandrous, while
-the lower ones are proterogynous, so that it might happen here that
-the lower flowers would be pollinated by the pollen falling on them
-from the stamens of the upper flowers. This would be cross pollination
-so far as the flowers are concerned, but not so far as the plants
-are concerned. In some individuals, however, we find all the flowers
-proterandrous.
-
-=853. Spiders have discovered this curious relation of the flowers
-and insects.=—On several different occasions, while studying
-the adaptations of the flowers of the skunk’s cabbage for cross
-pollination, I was interested to find that the spiders long ago had
-discovered something of the kind, for they spread their nets here to
-catch the unwary but useful insects. I have not seen the net spread
-over the opening in the spathe, but it is spread over the spadix
-within, reaching from tip to tip of either the stigmas, or stamens, or
-both. Behind the spadix crouches the spider-trapper. The insect crawls
-over the edge of the spadix, and plunges unsuspectingly into the dimly
-lighted chamber below, where it becomes entangled in the meshes of the
-net.
-
-Flowers in which the ripening of the anthers and maturing of the
-stigmas occur at different times are also said to be _dichogamous_.
-
-=854. Pollination of jack-in-the-pulpit.=—The jack-in-the-pulpit
-(Arisæma triphyllum) has made greater advance in the art of enforcing
-cross pollination. The larger number of plants here are, as we have
-found, diœcious, the staminate flowers being on the spadix of one
-plant, while the pistillate flowers are on the spadix of another. In a
-few plants, however, we find both female and male flowers on the same
-spadix.
-
-=855.= The pretty bell-flower (Campanula rotundifolia) is
-dichogamous and proterandrous (fig. 462). Many of the composites are
-also dichogamous.
-
-=856. Pollination of orchids.=—But some of the most marvellous
-adaptations for cross pollination by insects are found in the orchids,
-or members of the orchis family. The larger number of the members of
-this family grow in the tropics. Many of these in the forests are
-supported in lofty trees where they are brought near the sunlight,
-and such are called “epiphytes.” A number of species of orchids are
-distributed in temperate regions.
-
-[Illustration: Fig. 461. A group of jacks.]
-
-=857. Cypripedium, or lady-slipper.=—One species of the
-lady-slipper is shown in fig. 468. The labellum in this genus is shaped
-like a shoe, as one can see by the section of the flower in fig. 468.
-The stigma is situated at _st_, while the anther is situated at _a_,
-upon the style. The insect enters about the middle of the boat-shaped
-labellum. In going out it passes up and out at the end near the flower
-stalk. In doing this it passes the stigma first and the anther last,
-rubbing against both. The pollen caught on the head of the insect, will
-not touch the stigma of the same flower, but will be in position to
-come in contact with the stigma of the next flower visited.
-
-[Illustration: Fig. 462. Proterandry in the bell-flower (campanula).
-Left figure shows the syngenœcious stamens surrounding the immature
-style and stigma. Middle figure shows the immature stigma being pushed
-through the tube and brushing out the pollen; while in the right-hand
-figure, after the pollen has disappeared, the lobes of the stigma open
-out to receive pollen from another flower.]
-
-=858. Epipactis.=—In epipactis, shown in fig. 469, the action is
-similar to that of the blue iris.
-
-[Illustration: Fig. 463. Kalmia latifolia, showing position of anthers
-before insect visits, and at the right the scattering of the pollen
-when disturbed by insects. Middle figure section of flower.]
-
-=849.= In some of the tropical orchids the pollinia are set free
-when the insect touches a certain part of the flower, and are thrown
-in such a way that the disk of the pollinium strikes the insect’s head
-and stands upright. By the time the insect reaches another flower the
-pollinium has bent downward sufficiently to strike against the stigma
-when the insect alights on the labellum. In the mountains of North
-Carolina I have seen a beautiful little orchid, in which, if one
-touches a certain part of the flower with a lead-pencil or other
-suitable object, the pollinium is set free suddenly, turns a complete
-somersault in the air, and lands with the disk sticking to the pencil.
-Many of the orchids grown in conservatories can be used to demonstrate
-some of these peculiar mechanisms.
-
-[Illustration: Fig. 464. Spray of leaves and flowers of cytisus.]
-
-[Illustration: Fig. 465. Flower of cytisus grown in conservatory. Same
-flower scattering pollen.]
-
-=860. Pollination of the canna.=—In the study of some of the
-marvellous adaptations of flowers for cross pollination one is led to
-inquire if, after all, plants are not intelligent beings, instead of
-mere automatons which respond to various sorts of stimuli. No plant
-has puzzled me so much in this respect as the canna, and any one will
-be well repaid for a study of recently opened flowers, even though it
-may be necessary to rise early in the morning to unravel the mystery,
-before bees or the wind have irritated the labellum. The canna flower
-is a bewildering maze of petals and petal-like members. The calyx
-is green, adherent to the ovary, and the limb divides into three,
-lanceolate lobes. The petals are obovate and spreading, while the
-stamens have all changed to petal-like members, called _staminodia_.
-Only one still shows its stamen origin, since the anther is seen at one
-side, while the filament is expanded laterally and upwards to form the
-_staminodium_.
-
-[Illustration: Fig. 466. Spartium, showing the dusting of the pollen
-through the opening keels on the under side of an insect. (From Kerner
-and Oliver.)]
-
-=861.= The ovary has three locules, and the three styles are
-usually united into a long, thin, strap-shaped style, as seen in the
-figure, though in some cases three, nearly distinct, filamentous styles
-are present. The end of this strap-shaped style has a peculiar curve on
-one side, the outline being sometimes like a long narrow letter S. It
-is on the end of this style, and along the crest of this curve, that
-the stigmatic surface lies, so that the pollen must be deposited on the
-stigmatic end or margin in order that fertilization may take place.
-
-[Illustration: Fig. 467. Cypripedium.]
-
-[Illustration: Fig. 468. Section of flower of cypripedium. _st_,
-stigma; _a_, at the left stamen. The insect enters the labellum at
-the center, passes under and against the stigma, and out through the
-opening _b_, where it rubs against the pollen. In passing through
-another flower this pollen is rubbed off on the stigma.]
-
-=862.= If we open carefully canna flower buds which are nearly
-ready to open naturally, by unwrapping the folded petals and
-staminodia, we shall see the anther-bearing staminodium is so wrapped
-around the flattened style that the anther lies closely pressed against
-the face of the style, near the margin _opposite that on which the
-stigma lies_.
-
-[Illustration: Fig. 469. Epipactis with portion of perianth removed
-to show details. _l_, labellum; _st_, stigma; _r_, rostellum; _p_,
-pollinium. When the insect approaches the flower its head strikes the
-disk of the pollinium and pulls the pollinium out. At this time the
-pollinium stands up out of the way of the stigma. By the time the
-insect moves to another flower the pollinia have moved downward so that
-they are in position to strike the stigma and leave the pollen. At the
-right is the head of a bee, with two pollinia (_a_) attached.]
-
-[Illustration: Fig. 470. Canna flowers with the perianth removed to
-show the depositing of the pollen on the style by the stamen.]
-
-=863.= The walls of the anther locules which lie against the style
-become changed to a sticky substance for their entire length, so that
-they cling firmly to the surface of the style and also to the mass of
-pollen within the locules. The result is that when the flower opens,
-and this staminodium unwraps itself from the embrace of the style,
-the mass of pollen is left there deposited, while the empty anther is
-turned around to one side.
-
-=668.= Why does the flower deposit its own pollen on the style?
-Some have regarded this as the act of pollination, and have concluded,
-therefore, that cannas are necessarily self pollinated, and that cross
-pollination does not take place. But why is there such evident care to
-deposit the pollen on the side of the style away from the stigmatic
-margin? If we visit the cannas some morning, when a number of the
-flowers have just opened, and the bumblebees are humming around seeking
-for nectar, we may be able to unlock the secret.
-
-=864.= We see that in a recently opened canna flower, the petal
-which directly faces the style in front stands upward quite close to
-it, so that the flower now is somewhat funnel-shaped. This front petal
-is the _labellum_, and is the landing place for the bumblebee as he
-alights on the flower. Here he comes humming along and alights on the
-labellum with his head so close to the style that it touches it. But
-just the instant that the bee attempts to crowd down in the flower the
-labellum suddenly bends downward, as shown in fig. 468. In so doing the
-head of the bumblebee scrapes against the pollen, bearing some of it
-off. Now while the bee is sipping the nectar it is too far below the
-stigma to deposit any pollen on the latter. When the bumblebee flies to
-another newly opened flower, as it alights, some of the pollen of the
-former flower is brushed on the stigma.
-
-=865.= One can easily demonstrate the sensitiveness of the
-labellum of recently opened canna flowers, if the labellum has not
-already moved down in response to some stimulus. Take a lead-pencil, or
-a knife blade, or even the finger, and touch the upper surface of the
-labellum by thrusting it between the latter and the style. The labellum
-curves quickly downward.
-
-=866.= Sometimes the bumblebees, after sipping the nectar, will
-crawl up over the style in a blundering manner. In this way the flower
-may be pollinated with its own pollen, which is equivalent to self
-pollination. Undoubtedly self pollination does take place often in
-flowers which are adapted, to a greater or less degree, for cross
-pollination by insects.
-
-[Illustration: Fig. 471. Pollination of the canna flower by bumblebee.]
-
-[Illustration: Canna flower. Pollen on style, stamen at left.]
-
-
-
-
-CHAPTER XLIV.
-
-THE FRUIT.
-
-
-I. Parts of the Fruit.
-
-=867. After the flower comes the fruit.=—With the perfection of
-the fruit the seed is usually formed. This is the end towards which the
-energies of the plant have been directed. While the seed consists only
-of the ripened ovule and the contained embryo, the fruit consists of
-the ripened ovary in addition, and in many cases with other accessory
-parts, as calyx, receptacle, etc., combined with it. The wall of the
-ripened ovary is called a _pericarp_, and the walls of the ovary form
-the walls of the fruit.
-
-=868. Pericarp, endocarp, exocarp, etc.=—This is the part of the
-fruit which envelops the seed and may consist of the carpels alone, or
-of the carpels and the adherent part of the receptacle, or calyx. In
-many fruits the pericarp shows a differentiation into layers, or zones
-of tissue, as in the cherry, peach, plum, etc. The outer, which is
-here soft and fleshy, is _exocarp_, while the inner, which is hard, is
-the _endocarp_. An intermediate layer is sometimes recognized and is
-called _mesocarp_. In such cases the skin of the fruit is recognized as
-the _epicarp_. Epicarp and mesocarp are more often taken together as
-exocarp.
-
-In general fruits are _dry_ or _fleshy_. Dry fruits may be grouped
-under two heads. Those which open at maturity and scatter the seed are
-_dehiscent_. Those which do not open are _indehiscent_.
-
-
-II. Indehiscent Fruits.
-
-=869. The akene.=—The thin dry wall of the ovary encloses the
-single seed. It usually does not open and free the seed within. Such a
-fruit is an _akene_. An _akene_ is a dry, _indehiscent_ fruit. All of
-the crowded but separate pistils in the buttercup flower when ripe make
-a head of akenes, which form the fruit of the buttercup. Other examples
-of akenes are found in other members of the buttercup family, also in
-the composites, etc. The sunflower seed is a good example of an akene.
-
-[Illustration: Fig. 472. Seed, or akene, of buttercup.]
-
-[Illustration: Fig. 473. Fruit of red oak. An acorn.]
-
-=870. The samara.=—The winged fruits of the maple, elm, etc., are
-indehiscent fruits. They are sometimes called key fruits.
-
-=871. The caryopsis= is a dry fruit in which the seed is
-consolidated with the wall of the ovary, as in the wheat, corn, and
-other grasses.
-
-=872. The schizocarp= is a dry fruit consisting of several locules
-(from a _syncarpous gynœcium_). At maturity the carpels separate from
-each other, but do not themselves dehisce and free the seed, as in the
-carrot family, mallow family.
-
-=873. The acorn.=—The acorn fruit consists of the acorn and
-the “cup” at the base in which the acorn sits. The cup is a curious
-structure, and is supposed to be composed of an involucre of numerous
-small leaves at the base of the pistillate flower, which become
-consolidated into a hard cup-shaped body. When the acorn is ripe it
-easily separates from the cup, but the hard pericarp forming the
-“shell” of the acorn remains closed. Frost may cause it to crack, but
-very often the pericarp is split open at the smaller end by wedge-like
-pressure exerted by the emerging radicle during germination.
-
-[Illustration: Fig. 474. Germinating acorn of white oak.]
-
-=874. The hazelnut, chestnut, and beechnut.=—In these fruits a
-crown of leaves (involucre) at the base of the flower grows around
-the nut and completely envelops it, forming the husk or burr. When
-the fruit is ripe the nut is easily shelled out from the husk. In the
-beechnut and chestnut the burr dehisces as it dries and allows the nut
-to drop out. But the fruit is not dehiscent, since the pericarp is
-still intact and encloses the seed.
-
-=875. The hickory-nut, walnut, and butternut.=—In these fruits the
-“shuck” of the hickory-nut and the “hull” of the walnut and butternut
-are different from the involucre of the acorn or hazelnut, etc. In the
-hickory-nut the “shuck” probably consists partly of calyx and partly of
-involucral bracts consolidated, probably the calyx part predominating.
-This part of the fruit splits open as it dries and frees the “nut,” the
-pericarp being very hard and indehiscent. In the walnut and butternut
-the “hull” is probably of like origin as the “shuck” of the hickory
-nut, but it does not split open as it ripens. It remains fleshy. The
-walnut and butternut are often called _drupes_ or _stone-fruits_, but
-the fleshy part of the fruit is not of the same origin as the fleshy
-part of the true drupes, like the cherry, peach, plum, etc.
-
-
-III. Dehiscent Fruits.
-
-=876. Of the dehiscent fruits= several prominent types are
-recognized, and in general they are sometimes called _pods_. There is a
-single carpel (simple pistil), and the pericarp is dry (gynœcium
-_apocarpous_); or where there are several carpels united the pistil is
-compound (gynœcium _syncarpous_).
-
-[Illustration: Fig. 475. Diagrams illustrating three types (in
-cross-section) of the dehiscence of dry fruits. _Loc_, loculicidal;
-_Sep_, Septicidal, Septifragal.]
-
-[Illustration: Fig. 476. Fruit of sweet pea; a pod.]
-
-=877. The capsule.=—When the capsule is _syncarpous_ it may
-dehisce in three different ways: 1st. When the carpels split along
-the line of their union with each other longitudinally (_septicidal
-dehiscence_), as in the azalea or rhododendron. 2d. When the carpels
-_split down the middle line_ (_loculicidal dehiscence_), as in the
-fruit of the iris, lily, etc. 3d. When the carpels open by pores
-(_poricidal dehiscence_), as in the poppy. Some syncarpous capsules
-have but one locule, the partitions between the different locules when
-young having disappeared. The “bouncing-bet” is an example, and the
-seeds are attached to a central column in four rows corresponding to
-the four locules present in the young stage.
-
-=878. A follicle= is a capsule with a single carpel which splits
-open along the ventral or upper suture, as in the larkspur, peony.
-
-=879. The legume, or true pod=, is a capsule with a single carpel
-which splits along both sutures, as the pea, bean, etc. As the pod
-ripens and dries, a strong twisting tension is often produced, which
-splits the pod suddenly, scattering the seeds.
-
-=880. The silique.=—In the toothwort, shepherd’s-purse, and
-nearly all of the plants in the mustard family the fruit consists of
-two united carpels, which separate at maturity, leaving the partition
-wall persistent. Such a fruit is a _silique_; when short it is a
-_silicle_, or _pouch_.
-
-=881. A pyxidium, or pyxis=, is a capsule which opens with a lid,
-as in the plantain.
-
-
-IV. Fleshy and Juicy Fruits.
-
-=882. The drupe, or stone-fruit.=—In the plum, cherry, peach,
-apricot, etc., the outer portion (exocarp) of the pericarp (ovary)
-becomes fleshy, while the inner portion (endocarp) becomes hard and
-stony, and encloses the seed, or “pit.” Such a fruit is known as a
-drupe, or as a stone-fruit. In the almond the fleshy part of the fruit
-is removed.
-
-[Illustration: Fig. 477. Drupe, or stone-fruit, of plum.]
-
-=883. The raspberry and blackberry.=—While these fruits are
-known popularly as “berries,” they are not berries in the technical
-sense. Each ovary, or pericarp, in the flower forms a single small
-fruit, the outer portion being fleshy and the inner stony, just as
-in the cherry or plum. It is a _drupelet_ (little drupe). All of the
-drupelets together make the “berry,” and as they ripen the separate
-drupelets cohere more or less. It is a collection, or aggregation, of
-fruits, and consequently they are sometimes called _collective fruits_,
-or _aggregate fruits_. In the raspberry the fruit separates from the
-receptacle, leaving the latter on the stem, while the drupelets of
-the blackberry and dewberry adhere to the receptacle and the latter
-separates from the stem.
-
-=884. The berry.=—In the true berry both exocarp (including
-mesocarp) and endocarp are fleshy or juicy. Good examples are found
-in cranberries, huckleberries, gooseberries, currants, snowberries,
-tomatoes, etc. The calyx and wall of the pistil are adnate, and in
-fruit become fleshy so that the seeds are imbedded in the pulpy juice.
-The seeds themselves are more or less stony. In the case of berries,
-as well as in strawberries, raspberries, and blackberries, the fruits
-are eagerly sought by birds and other animals for food. The seeds being
-hard are not digested, but are passed with the other animal excrement
-and thus gain dispersal.
-
-
-V. Reinforced, or Accessory, Fruits.
-
-When the torus (receptacle) is grown to the pericarp in fruit, the
-fruit is said to be _reinforced_. The torus may enclose the pericarps,
-or the latter may be seated upon the torus.
-
-[Illustration: Fig. 478. Fruit of raspberry.]
-
-=885. In the strawberry= the receptacle of the flower becomes
-larger and fleshy, while the “seeds,” which are akenes, are sunk in the
-surface and are hard and stony. The strawberry thus differs from the
-raspberry and blackberry, but like them it is not a true berry.
-
-=886. The apple, pear, quince, etc.=—In the flower the calyx,
-corolla, and stamens are perigynous, i.e., they are seated on the
-margin of the receptacle, or torus, which is elevated around the
-pistils. In fruit the receptacle becomes consolidated with the wall
-of the ovary (with the pericarp). The torus thus _reinforces_ the
-pericarp. The torus and outer portion of the pericarp become fleshy,
-while the inner portion of the pericarp becomes papery and forms the
-“core.” The calyx persists on the free end of the fruit. Such a fruit
-is called a _pome_. The receptacle, or torus, of the rose-flower,
-closely related to the apple, is instructive when used in comparison.
-The rose-fruit is called a “hip.”
-
-=887. The pepo.=—The fruit of the squash, pumpkin, cucumber,
-etc., is called a _pepo_. The outer part of the fruit is the receptacle
-(or torus), which is consolidated with the outer part of the
-three-loculed ovary. The calyx, which, with the corolla and stamens,
-was epigynous, falls off from the young fruit.
-
-
-VI. Fruits of Gymnosperms.
-
-The fruits of the gymnosperms differ from nearly all of the angiosperms
-in that the seed formed from the ripened ovule is naked from the first,
-i.e., the ovary, or carpel, does not enclose the seed.
-
-=888. The cone-fruit= is the most prominent fruit of the
-gymnosperms, as can be seen in the cones of various species of pine,
-spruce, balsam, etc.
-
-=889. Fleshy fruits of the gymnosperms.=—Some of the fleshy
-fruits resemble the stone-fruits and berries of the angiosperms. The
-_cedar_ “_berries_,” for example, are fleshy and contain several seeds.
-But the fleshy part of the fruit is formed, not from pericarp, since
-there is no pericarp, but from the outer portion of the ovules, while
-the inner walls of the ovules form the hard stone surrounding the
-endosperm and embryo. An examination of the pistillate flower of the
-cedar (juniper) shows usually three flask-shaped ovules on the end
-of a fertile shoot subtended by as many bracts (carpels?). The young
-ovules are free, but as they grow they coalesce, and the outer walls
-become fleshy, forming a berry-like fruit with a three-rayed crevice
-at the apex marking the number of ovules. The red fleshy fruit of the
-yew (taxus) resembles a drupe which is open at the apex. The stony
-seed is formed from the single ovule on the fertile shoot, while the
-red cup-shaped fleshy part is formed from the outer integument of the
-ovule. The so-called “aril” of the young ovule is a rudimentary outer
-integument.
-
-The fruit of the maidenhair tree (ginkgo) is about the size of a plum
-and resembles very closely a stone-fruit. But it is merely a ripened
-ovule, the outer layer becoming fleshy while the inner layer becomes
-stony and forms the pit which encloses the embryo and endosperm.
-The so-called “aril,” or “collar,” at the base of the fruit is the
-rudimentary carpel, which sometimes is more or less completely expanded
-into a true leaf. The fruit of cycas is similar to that of ginkgo, but
-there is no collar at the base. In zamia the fruit is more like a cone,
-the seeds being formed, however, on the under sides of the scales.
-
-
-VII. The “Fruit” of Ferns, Mosses, etc.
-
-=890. The term “fruit”= is often applied in a general or popular
-sense to the groups of spore-producing bodies of ferns (_fruit dots_,
-or _sori_), the spore-capsules of mosses and liverworts, and also to
-the fruit-bodies, or spore-bearing parts, of the fungi and algæ.
-
-
-
-
-CHAPTER XLV.
-
-SEED DISPERSAL.
-
-
-=891. Means for dissemination of seeds.=—During late summer
-or autumn a walk in the woods or afield often convinces us of the
-perfection and variety of means with which plants are provided for the
-dissemination of their seeds, especially when we discover that several
-hundred seeds or fruits of different plants are stealing a ride at
-our expense and annoyance. The hooks and barbs on various seed-pods
-catch into the hairs of passing animals and the seeds may thus be
-transported considerable distances. Among the plants familiar to us,
-which have such contrivances for unlawfully gaining transportation,
-are the beggar-ticks or stick tights, or sometimes called bur-marigold
-(bidens), the tick-treefoil (desmodium), or cockle-bur (xanthium), and
-burdock (arctium).
-
-[Illustration: Fig. 479. Bur of bidens or bur-marigold, showing barbed
-seeds.]
-
-[Illustration: Fig. 480. Seed pod of tick-treefoil (desmodium); at the
-right some of the hooks greatly magnified.]
-
-=892.= Other plants like some of the sedges, etc., living on the
-margins of streams and of lakes, have seeds which are provided with
-floats. The wind or the flowing of the water transports them often to
-distant points.
-
-=893.= Many plants possess attractive devices, and offer a
-substantial reward, as a price for the distribution of their seeds.
-Fruits and berries are devoured by birds and other animals; the seeds
-within, often passing unharmed, may be carried long distances. Starchy
-and albuminous seeds and grains are also devoured, and while many
-such seeds are destroyed, others are not injured, and finally are
-lodged in suitable places for growth, often remote from the original
-locality. Thus animals willingly or unwillingly become agents in the
-dissemination of plants over the earth. Man in the development of
-commerce is often responsible for the wide distribution of harmful as
-well as beneficial species.
-
-[Illustration: Fig. 481. Seeds of geum showing the hooklets where the
-end of the style is kneed.]
-
-=894.= Other plants are more independent, and mechanisms are
-employed for violently ejecting seeds from the pod or fruit. The
-unequal tension of the pods of the common vetch (Vicia sativa) when
-drying causes the valves to contract unequally, and on a dry summer day
-the valves twist and pull in opposite directions until they suddenly
-snap apart, and the seeds are thrown forcibly for some distance. In the
-impatiens, or touch-me-not as it is better known, when the pods are
-ripe, often the least touch, or a pinch, or jar, sets the five valves
-free, they coil up suddenly, and the small seeds are thrown for several
-yards in all directions. During autumn, on dry days, the pods of the
-witch hazel contract unequally, and the valves are suddenly spread
-apart, and the seeds are hurled away.
-
-Other plants have seeds provided with tufts of pappus, or hair-like
-masses, or wing-like outgrowths which serve to buoy them up as they are
-whirled along, often miles away. In late spring or early summer the
-pods of the willow burst open, exposing the seeds, each with a tuft of
-white hairs making a mass of soft down. As the delicate hairs dry, they
-straighten out in a loose spreading tuft, which frees the individual
-seeds from the compact mass. Here they are caught by currents of air
-and float off singly or in small clouds.
-
-[Illustration: Fig. 482. Touch-me-not (Impatiens fulva); side and front
-view of flower below; above unopened pod, and opening to scatter the
-seed.]
-
-=895. The prickly lettuce.=—In late summer or early autumn the
-seeds of the prickly lettuce (Lactuca scariola) are caught up from the
-roadsides by the winds, and carried to fields where they are unbidden
-as well as unwelcome guests. This plant is shown in fig. 483.
-
-=896. The wild lettuce.=—A related species, the wild lettuce
-(Lactuca canadensis) occurs on roadsides and in the borders of fields,
-and is about one meter in height. The heads of small yellow or purple
-flowers are arranged in a loose or branching panicle. The flowers are
-rather inconspicuous, the rays projecting but little above the apex of
-the enveloping involucral bracts, which closely press together, forming
-a flowerhead more or less flask-shaped.
-
-[Illustration: Fig. 483. Lactuca scariola.]
-
-At the time of flowering the involucral bracts spread somewhat at the
-apex, and the tips of the flowers are a little more prominent. As the
-flowers then wither, the bracts press closely together again and the
-head is closed. As the seeds ripen the bracts die, and in drying bend
-outward and downward, around the flower stem below, or they fall away.
-The seeds are thus exposed. The dark brown achenes stand over the
-surface of the receptacle, each one tipped with the long slender
-beak of the ovary. The “pappus,” which is so abundant in many of the
-plants belonging to the composite family, forms here a pencil-like
-tuft at the tip of this long beak. As the involucral bracts dry and
-curve downward, the pappus also dries, and in doing so bends downward
-and stands outward, bristling like the spokes of a small wheel. It is
-an interesting coincidence that this takes place simultaneously with
-the pappus of all the seeds of a head, so that the ends of the pappus
-bristles of adjoining seeds meet, forming a many-sided dome of a
-delicate and beautiful texture. This causes the beaks of the achenes to
-be crowded apart, and with the leverage thus brought to bear upon the
-achenes they are pried off the receptacle. They are thus in a position
-to be wafted away by the gentlest zephyr, and they go sailing away on
-the wind like a miniature parachute. As they come slowly to the ground
-the seed is thus carefully lowered first, so that it touches the ground
-in a position for the end which contains the root of the embryo to come
-in contact with the soil.
-
-=897. The milkweed, or silkweed.=—The common milkweed, or
-silkweed (Asclepias cornuti), so abundant in rich grounds, is
-attractive not only because of the peculiar pendent flower clusters,
-but also for the beautiful floats with which it sends its seeds
-skyward, during a puff of wind, to finally lodge on the earth.
-
-[Illustration: Fig. 484. Milkweed (Asclepias cornuti); dissemination of
-seed.]
-
-=898.= The large boat-shaped, tapering pods, in late autumn, are
-packed with oval, flattened, brownish seeds, which overlap each other
-in rows like shingles on a roof. These make a pretty picture as the pod
-in drying splits along the suture on the convex side, and exposes them
-to view. The silky tufts of numerous long, delicate white hairs on the
-inner end of each seed, in drying, bristle out, and thus lift the seeds
-out of their enclosure, where they are caught by the breeze and borne
-away often to a great distance, where they will germinate if conditions
-become favorable, and take their places as contestants in the battle
-for existence.
-
-=899. The virgin’s bower.=—The virgin’s bower (Clematis
-virginiana), too, clambering over fence and shrub, makes a show of
-having transformed its exquisite white flower clusters into
-grayish-white tufts, which scatter in the autumn gusts into hundreds
-of arrow-headed, spiral plumes. The achenes have plumose styles, and
-the spiral form of the plume gives a curious twist to the falling seed
-(fig. 485).
-
-[Illustration: Fig. 485. Seed distribution of virgin’s bower
-(clematis).]
-
-
-
-
-CHAPTER XLVI.
-
-VEGETATION IN RELATION TO ENVIRONMENT.[47]
-
-
-I. Factors Influencing Vegetation Types.
-
-=900.= All plants are subject to the influence of environment
-from the time the seed begins to germinate until the seed is formed
-again, or until the plant ceases to live. A suitable amount of warmth
-and moisture is necessary that the seed may germinate. Moisture may
-be present, but if it is too cold, germination will not take place.
-So in all the processes of life there are several conditions of the
-environment, or the “outside” of plants, which must be favorable for
-successful growth and reproduction. Not only is this true, but the
-surroundings of plants to a large extent determine the kind of plants
-which can grow in particular localities. It is also evident that the
-reaction of environment on plants has in a large measure caused them
-to take on certain forms and structures which fit them better to exist
-under local conditions. In other cases where plants have varied by
-mutation (p. 338) some of the new forms may be more suited to the
-conditions of environment than others and they are more apt to survive.
-These conditions of environment acting on the plant are _factors_ which
-have an important determining influence on the existence, habitat,
-habit, and form of the plant. These factors are sometimes spoken of
-as _ecological factors_, and the study of plants in this relation is
-sometimes spoken of as ecology,[48] which means a study of plants in
-their home or a study of the household relations of plants. These
-factors are of three sorts: 1st, physical factors; 2d, climatic
-factors; 3d, biotic factors.
-
-=901. Physical factors.=—Some of these factors are water, light,
-heat, wind, chemical or physical condition of the soil, etc. _Water_
-is a very important factor for all plants. Even those growing on land
-contain a large percentage of water, which we have seen is rapidly lost
-by transpiration, and unless water is available for root absorption
-the plant soon suffers, and aquatic plants are injured very quickly by
-drying when taken from the water. Excess of soil water is injurious to
-some plants. _Light_ is important in photosynthesis, in determining
-direction of growth as well as in determining the formation of suitable
-leaves in most plants, and has an influence in the structure of the
-leaf according as the light may be strong, weak, etc. _Heat_ has great
-influence on plant growth and on the distribution of plants. The
-growth period for most vegetation begins at 6° C. (= 43° F.), or in
-the tropics at 10°-12° C., but a much higher temperature is usually
-necessary for reproduction. Some arctic algæ, however, fruit at 1.8° C.
-The upper limit favorable for plants in general is 45°-50° C., while
-the optimum temperature is below this. Very high temperatures are
-injurious, and fatal to most plants, but some algæ grow in hot springs
-where the temperature reaches 80°-90° C. Some desert plants are able to
-endure a temperature of 70° C., while some flowering plants of other
-regions are killed at 45° C. Some plants are specifically susceptible
-to cold, but most plants which are injured by freezing suffer because
-the freezing is a drying process of the protoplasm (see p. 374). _Wind_
-may serve useful purposes in pollination and in aeration, but severe
-winds injure plants by causing too rapid transpiration, by felling
-trees, by breaking plant parts, by deforming trees and shrubs, and by
-mechanical injuries from “sand-blast.” _Ground covers_ protect plants
-in several ways. Snow during the winter checks radiation of heat from
-the ground so that it does not freeze to so great a depth, and this is
-very important for many trees and shrubs. It also prevents alternate
-freezing and thawing of the ground, which “heaves” some plants from
-the soil. Leaves and other plant remains mulch the soil and check
-evaporation of water. The influence of the _chemical condition_ of the
-soil is very marked in alkaline areas where the concentration of salt
-in the soil permits a very limited range of species. So the physical
-and mechanical conditions of the soil influence plants because the
-moisture content of the ground is so closely dependent on its physical
-condition. Rocky and gravelly soil, other things being equal, is dry.
-Clay is more retentive of moisture than sand, and moisture also varies
-according to the per cent of humus mixed with it, the humus increasing
-the percentage of moisture retained.
-
-=902. Climatic factors.=—These factors are operative over very
-wide areas. There are two climatic factors: rainfall or atmospheric
-moisture, and temperature. A very low annual rainfall in warm or
-tropical countries causes a desert; an abundance of rain permits the
-growth of forests; extreme cold prevents the growth of forests and
-gives us the low vegetation of arctic and alpine regions.
-
-=903. Biotic factors.=—These are animals which act favorably
-in pollination, seed distribution, or unfavorably in destroying or
-injuring plants, and man himself is one of the great agencies in
-checking the growth of some plants while favoring the growth of others.
-Plants also react on themselves in a multitude of ways for good or
-evil. Some are parasites on others; some in symbiosis (see p. 85) aid
-in providing food; shade plants are protected by those which overtop
-them; mushrooms and other fungi disintegrate dead plants to make humus
-and finally plant food; certain bacteria by nitrification prepare
-nitrates for the higher plants (see p. 83).
-
-
-II. Vegetation Types and Structures.
-
-=904. Responsive type of vegetation.=—In studying vegetation in
-relation to environment we are more concerned with the form of the
-plants which fits them to exist under the local conditions than we are
-with the classification of plants according to natural relationships.
-Plants may have the same vegetation type, grow side by side, and still
-belong to very different floristic types. For example, the cactus,
-yucca, three-leaved sumac, the sage-brush, etc., have all the same
-general vegetation type and thrive in desert regions. The red oaks, the
-elms, many goldenrods, trillium, etc., have the same general vegetation
-type, but represent very different floristic types. The latter plants
-grow in regions with abundant rainfall throughout the year, where
-the growing season is not very short and temperature conditions are
-moderate. Some goldenrods grow in very sandy soil which dries out
-quickly. These have fleshy or succulent leaves for storing water,
-and while they are of the same floristic type as goldenrods growing
-in other places, the vegetation type is very different. The types of
-vegetation which fit plants for growing in special regions or under
-special conditions, they have taken on in response to the influence
-of the conditions of their environment. While we find all gradations
-between the different types of vegetation, looking at the vegetation
-in a broad way, several types are recognized which were proposed by
-Warming as follows:
-
-=905. Mesophytes.=—These are represented by land plants under
-temperate or moderate climatic and soil conditions. The normal
-land vegetation of our temperate region is composed of mesophytes,
-that is, the plants have mesophytic structures during the growing
-season. The deciduous forests or thickets of trees and shrubs with
-their undergrowth, the meadows, pastures, prairies, weeds, etc., are
-examples. In those portions of the tropics where rainfall is great the
-vegetation is mesophytic the year around.
-
-=906. Xerophytes.=—These are plants which are provided with
-structures which enable them to live under severe conditions of
-dryness, where the air and soil are very dry, as in deserts or
-semideserts, or where the soil is very dry or not retentive of
-moisture, as in very sandy soil which is above ground water, or in
-rocky areas. Since the plants cannot obtain much water from the soil
-they must be provided with structures which will enable them to
-retain the small amount they can absorb from the soil and give it off
-slowly. Otherwise they would dry out by evaporation and die. Some
-of the structures which enable xerophytic plants to withstand the
-conditions of dry climate and soil are lessened leaf surface, increase
-in thickness of leaf, increase in thickness of cuticle, deeply sunken
-stomates, compact growth, also succulent leaves and stems, and in some
-cases loss of the leaf. Evergreens of the north temperate and the
-arctic regions are xerophytes.
-
-=907. Hydrophytes.=—These are plants which grow in fresh water
-or in very damp situations. The leaves of aerial hydrophytes are very
-thin, have a thin cuticle, and lose water easily, so that if the air
-becomes quite dry they are in danger of drying up even though the roots
-may be supplied with an abundance of water. The aquatic plants which
-are entirely submerged have often thin leaves, or very finely divided
-or slender leaves, since these are less liable to be torn by currents
-of water. The stems are slender and especially lack strengthening
-tissue, since the water buoys them up. Removed from the water they
-droop of their own weight, and soon dry up. The stems and leaves have
-large intercellular spaces filled with air which aids in aeration and
-in the diffusion of gases. Some use the term _hygrophytes_.
-
-=908. Halophytes.=—These are salt-loving plants. They grow in
-salt water, or in salt marshes where the water is brackish, or in
-soil which contains a high per cent of certain salts, for example the
-alkaline soils of the West, especially in the so-called “Bad Lands”
-of Dakota and Nebraska, and in alkaline soils of the Southwest and
-California. These plants are able to withstand a stronger concentration
-of salts in the water than other plants. They are also found in soil
-about salt springs.
-
-=909. Tropophytes.=[49]—Tropophytes are plants which can live as
-mesophytes during the growing season, and then turn to a xerophytic
-habit in the resting season. Deciduous trees and shrubs, and perennial
-herbs of our temperate regions, are in this sense tropophytes, while
-many are at the same time mesophytes if they exist in the portions of
-the temperate region where rainfall is abundant. In the spring and
-summer they have broad and comparatively thin leaves, transpiration
-goes on rapidly, but there is an abundance of moisture in the soil,
-so that root absorption quickly replaces the loss and the plant does
-not suffer. In the autumn the trees shed their leaves, and in this
-condition with the bare twigs they are able to stand the drying effect
-of the cold and winds of the winter because transpiration is now at a
-minimum, while root absorption is also at a minimum because of the cold
-condition of the soil. Perennial herbs like trillium, dentaria, the
-goldenrods, etc., turn to xerophytic habit by the death of their aerial
-shoots, while the thick underground shoot which is also protected by
-its subterranean habit carries the plant through the winter.
-
-=910.= While these different vegetation types are generally
-dominant in certain climatic regions or under certain soil conditions,
-they are not the exclusive vegetation types of the regions. For
-example, in desert or semidesert regions the dominant vegetation
-type is made up of xerophytes. But there is a mesophytic flora even
-in deserts, which appears during the rainy season where temperature
-conditions are favorable for growth. This is sometimes spoken of as the
-rainy-season flora. The plants are annuals and by formation of seed can
-tide over the dry season. So in the region where mesophytes grow there
-are xerophytes, examples being the evergreens like the pines, spruces,
-rhododendrons; or succulent plants like the stonecrop, the purslane,
-etc. Then among hydrophytes the semiaquatics are really xerophytes. The
-roots are in water, and absorption is slow because there are no root
-hairs, or but few, and the aerial parts of the plant are xerophytic.
-
-
-III. Plant Formations.
-
-=911.= The term plant formation is applied to associations of
-plants of the same kind, though there is a great difference in the use
-of the word by different writers which leads to some confusion.[50] It
-is sometimes applied to an association of individuals of a species, or
-of several species occupying a rather definite area of ground where the
-soil conditions are not greatly different (individual formation); by
-others it is applied to the plants of a definite physiographic area, as
-a swamp, moor, strand, or beach, bank, rock hill, clay hill, ravine,
-bluff, etc. (principal formation); and in a broad sense it is applied
-to the plants of climatic regions, of those in bodies of water, etc.
-(general formations). Space here is too limited to discuss all these
-kinds of formations, but the nature of the general formations will be
-pointed out. The general formations may be grouped into four divisions:
-
-    1st. Climatic formations.
-     2d. Edaphic formations.
-     3d. Aquatic formations.
-    4th. Culture formations.
-
-=912. Climatic formations.=—Climatic influences extend over
-wide regions, so that climate controls the general type of vegetation
-of a region. In the sense of control there are two climatic factors,
-temperature and moisture, especially soil moisture. Temperature exerts
-a controlling influence over the vegetation type only where the total
-heat during the period of growth and reproduction is very low. This
-occurs in polar lands and at high elevations where the climate is
-alpine. In the temperate and tropical regions of the globe moisture,
-not heat, controls the general vegetation type. These vegetation types
-in general are coincident with rainfall distribution, and Schimper
-recognizes here three types, which with the arctic-alpine type would
-make four climatic formations as follows:
-
-1st. _The woodland formation._—This formation is characterized by
-trees and shrubs, and it is what is called a _close_ formation. By this
-it is meant that so far as the climate is concerned the conditions are
-favorable for the development of trees and shrubs in such abundance
-that they become the dominant vegetation type of the region and grow
-close together. Other plants, as herbs, grasses, etc., occur, but
-they grow as subordinate elements of the general vegetation type, and
-as undergrowth. The land portion of the globe, therefore, outside of
-arctic and alpine regions, where the annual precipitation is 40 to 60
-or more inches, is the area for woodland formation. In some places,
-the eastern part of England, for example, the annual precipitation is
-25 to 30 inches, but the cool temperature permits a forest growth. It
-is true there are places where forests do not grow,—where man cuts
-them down, for example. But if cultivated lands in this region were
-allowed to go to waste, they would in time grow up to forest again.
-So there are swamps where the soil is too wet for trees, or sandy or
-rocky areas where there is not a sufficient amount of soil or water to
-support forest trees. But here it is the soil conditions, not climatic
-conditions, which prevent the development of the forest. But we know
-that swamps are being filled in and the ground gradually becoming
-higher and drier, and that soil is slowly accumulating in rocky areas,
-so that in time if left to natural forces these places would become
-forested. So this area of heavy annual rainfall is a _potential_ forest
-area. These areas are determined by warm currents of moisture-laden
-air from the ocean moving over cooler land areas where the moisture
-is precipitated. In general these areas are along the coasts of great
-continents and on mountains. Therefore the interior of a continent is
-apt to be dry because most of the moisture has been precipitated before
-it reaches the interior. Deserts or steppes are therefore usually near
-the interior of continents. Some exceptions to this general rule are
-found: central South America, which is a region of exceptional rainfall
-because the moisture-laden winds here come from the warmest part of the
-ocean; the desert region west of the Andes mountains, where the winds
-are not favorable; southern California, where the winds come chiefly
-from a cooler portion of the Pacific ocean and move over an area of
-high temperature, etc.
-
-[Illustration: Fig. 486. Typical prairie scene, a few miles west of
-Lincoln, Nebraska. (Bot. Dept., Univ. Nebraska.)]
-
-2d. _Grassland formation._—Grasses form the dominant vegetation
-type where the annual rainfall is approximately 15 to 25 inches. In
-true grasslands the formation is a close one since there is still a
-sufficient amount of moisture to provide for all the plants which can
-stand on the ground. Yet there is not enough moisture to permit the
-growth of forest as the dominant type without aid and protection by
-man. The so-called prairie regions are examples. Trees and shrubs do
-occur, but they cannot compete successfully with the grasses because
-the climatic conditions are favorable for the latter and unfavorable
-for the former. On the border line between forest and prairie the line
-of division is not a clear-cut one because conditions grade from one to
-the other. The two formations are somewhat mixed, like the outposts of
-contending armies, arms of the forest or prairie extending out here and
-there. In the United States the prairies extend from Illinois to about
-the 100th meridian, and beyond this to the foothills of the Rockies and
-southwest to the Sonora Nevada desert the region is drier, the rainfall
-varying from 10 to 20 inches. This is the area of the Great Plains,
-and while grasses of the bunch type are dominant, they make a more or
-less open formation because the moisture is not sufficient to supply
-all the plants which could be crowded on the ground, each individual
-tuft needing an area of ground surrounding it on which it can draw
-for moisture. Such a formation is an open one, and in this respect is
-similar to desert formations.
-
-[Illustration: Fig. 487. Winter range in northwestern Nevada, showing
-open formation; white sage (Eurotia lanata) in foreground, salt-bush
-(Atriplex confertifolia) and bud-sage (Artemisia spinescens) at base
-of hill, red sage (Kochia americana) on the higher slope. (After
-Griffiths, Bull. 38, Bureau Plant Ind., U. S. Dept. Agr.)]
-
-3d. _Desert formations._—These occur where the annual rainfall is
-still lower, 10 to 4 inches or even less, 2 to 3 inches, while in
-one place in Chili it is as low as ½ inch. In the great Sahara desert
-it is about 8 inches, while in the Sonora Nevada desert in the
-southwestern United States it is 4 to 8 inches. Here the formation is
-an open one. In the forest and prairie formations the plants compete
-with each other for occupancy of the ground, since climatic conditions
-are favorable, so that the struggle against climate is not severe.
-But in the desert plants do not compete with each other; since the
-climate is so austere, the struggle is against the climate. Hence
-plants stand at some distance from each other because the roots need
-the moisture from the ground for some distance around them. There is
-not enough moisture for all the plants that begin, and those which get
-the start take the moisture away from the intervening ones, which then
-die. Since the struggle is against the adverse conditions of climate
-and not a competition between plants to occupy the ground, no one
-floristic type dominates as in the case of the grasses and forests of
-the grassland and woodland formations, but grassland and woodland types
-grow together. So we find grasses, trees, and shrubs growing without
-competition in the desert. The dominant vegetation type is xerophytic.
-
-[Illustration: Fig. 488. Northern limit of tree growth, Alaska.
-(Copyright, 1899, by E. H. Harriman.)]
-
-4th. _Arctic-alpine formation._ This formation extends from the limit
-of tree growth to the region of perpetual ice and snow. The forest
-here comes in competition with climate, with the severe cold of the
-long winter night, so that tree growth is limited, and on the border
-line with the woodland formation the trees are stunted, bent to one
-side by the heavy snows, or the tops are killed by the cold wind. The
-arctic zone of plant growth is sometimes spoken of as the “cold waste,”
-since conditions here are somewhat similar to those in the desert, the
-extreme cold exercising a drying effect on vegetation, and the
-vegetation type then is largely xerophytic.
-
-=913. Edaphic[51] formations.=—Edaphic formations may occur
-in any of the climatic-formation areas. They are controlled by the
-condition of soil or ground. The condition of the soil is unfavorable
-for the growth of the general vegetation type of that region, or is
-more favorable for another vegetation type, so that soil conditions
-overcome the climatic conditions. These areas include swamps, moors,
-the strand or beach, rocky areas, etc., as well as oases in the desert,
-warm oases in the arctic zone, river bottoms in the prairie and plains
-region, alkaline areas, etc. The edaphic formations may be close or
-open according to the nature of the soil. The edaphic formations then
-are infiltrated in the climatic formations, the different vegetation
-types fitting together like pieces of mosaic, which can be seen in some
-places from a mountain top, or if one could take a bird’s-eye view of
-the landscape or from a balloon.
-
-=914. Aquatic formations.=—These are made up of water plants and
-are of two general kinds: fresh-water plant formations in ponds, lakes,
-streams; and salt-water plant formations in the ocean and inland salt
-seas.
-
-=915. Culture formations.=—Culture formations are largely
-controlled by man, who destroys the climatic or edaphic formation and
-by cultivation protects cultivated types, or by allowing land to go to
-“waste” permits the growth of weeds, though weeds are often abundant
-in the culture areas. In general the culture formations may be grouped
-into two subdivisions: 1st, the vegetation of cultivated places; and
-2d, the vegetation of waste places, as abandoned fields, roadsides, etc.
-
-
-IV. Plant Societies.
-
-=916. Plant societies= are somewhat definite associations of the
-vegetation of an area marked by physiographic conditions. A single
-plant society is nearly if not altogether identical with a “_principal
-formation_,” but is a more popular expression, and besides includes all
-the plants growing on the area, while in the use of the term “principal
-formation” we have reference mainly to the dominant plants and the most
-conspicuous subordinate species.
-
-=917. Complex character of plant societies.=—In their broadest
-analysis all plant societies are complex. Every plant society has one
-or several dominant species, the individuals of which, because of
-their number and size, give it its peculiar character. The society may
-be so nearly pure that it appears to consist of the individuals of a
-single species. But even in those cases there are small and conspicuous
-plants of other species which occupy spaces between the dominant ones.
-Usually there are several or more kinds in the same society. The larger
-individuals come into competition for first place in regard to ground
-and light, the smaller ones come into competition for the intervening
-spaces for shade, and so on down in the scale of size and shade
-tolerance. Then climbing plants (lianas) and epiphytes (lichens, algæ,
-mosses, ferns, tree orchids, etc.) gain access to light and support by
-growing on other larger and stouter members of the society.
-
-Parasites (dodder, mistletoes, rusts, smuts, mildews, bacteria, etc.)
-are present, either actually or potentially, in all societies, and in
-their methods of obtaining food sap the life and health of their hosts.
-Then come the scavenger members, whose work it is to clean house, as it
-were, the great army of saprophytic fungi (molds, mushrooms, etc.), and
-bacteria ready to lay hold on dead and dying leaves, branches, trunks,
-roots, etc., disintegrate them, and reduce them to humus, where other
-fungi change them into a form in which the larger members of the plant
-society can utilize them as plant food and thus continue the cycle of
-matter through life, death, decay, and into life again. Mycorhiza (see
-Chapter IX) or other forms of mutualistic symbiosis occur which make
-atmospheric nitrogen available for food, or shorten the path from humus
-to available food, or the humus plants feed on the humus directly.
-Nor should we leave out of account the myriads of nitrate and nitrite
-bacteria (see Chapter IX) which make certain substances in the soil
-available to the higher members of the society. Most plant societies
-are also benefited or profoundly influenced in other ways by animals,
-as the flower-visiting insects, birds which feed on injurious insects,
-the worms which mellow up the soil and cover dead organic matter so
-that it may more thoroughly decay. In short, every plant society is
-a great cosmos like the universe itself of which it is a part, where
-multitudinous forms, processes, influences, evolutions, degenerations,
-and regenerations are at work.
-
-=918. Forest Societies.=[52]—Each different climatic belt or
-region has its characteristic forest. For example, the forests of
-the Hudsonian zone in North America are different from those of
-the Canadian zone, and these in turn different from those in the
-transition zone (mainly in northern United States). The forests of
-the Rocky mountains and of the Pacific coast differ from those of the
-Alleghanian, Carolinian (mainly middle United States) or Austroriparian
-(southern United States) areas. Finally, tropical forests are
-strikingly different from those of other regions. Similar variations
-occur in the forests of other regions of the globe. The character of
-these forests depends largely on climatic factors. The character of
-the forest varies, however, even in the same climatic area, dependent
-on soil conditions, or success in seeding and ground-gaining of the
-different species in competition, etc.
-
-=919. General structure of the forest.=—Structurally the forest
-possesses three subdivisions: the floor, the canopy, and the interior.
-The floor is the surface soil, which holds the rootage of the trees,
-with its covering of leaf-mold and carpet of leaves, mosses, or other
-low, more or less compact vegetation. The canopy is formed by the
-spreading foliage of the tree crowns, which, in a forest of an even
-and regular stand, meet and form a continuous mass of foliage through
-which some light filters down into the interior. Where the stand is
-irregular, i.e., the trees of different heights, the canopy is said to
-be “compound” or “storied.” Where it is uneven, there are open places
-in the canopy which admit more light, in which case the undergrowth
-may be different. The interior of the forest lies between the canopy
-and the floor. It provides for aeration of the floor and interior
-occupants, and also room for the boles or tree trunks (called by
-foresters the wood mass of the forest) which support the canopy and
-provide the channels for communication and food exchange between the
-floor and canopy. The canopy manufactures the carbohydrate food and
-assimilates the mineral and proteid substances absorbed by the roots in
-the soil; and also gets rid of the surplus water needed for conveying
-food materials from the floor to the place where they are elaborated.
-It is the seat where energy is created for work, and also the place for
-seed production.
-
-[Illustration: Fig. 489. Mature forest of redwood (Sequoia
-sempervirens). (Bureau of Forestry, U. S. Dept. Agr., Bull. 38.)]
-
-=920. Longevity of the forest.=—The forest is capable of
-self-perpetuation, and, except in case of unusual disaster or the
-action of man, it should live indefinitely. As the old trees die they
-are gradually replaced by younger ones. So while trees may come and
-trees may go, the forest goes on forever.
-
-=921. Autumn colors.=—One of the striking effects produced by
-the deciduous forests is that of the autumn coloring of the leaves.
-It is more pronounced in the forests of the United States than in
-corresponding life zones in the eastern hemisphere because of the
-greater number of species. With the disintegration of the chlorophyll
-bodies, other colors, which in some cases were masked by the green,
-appear. In other cases decomposition products result in the formation
-of other colors, as red, scarlet, yellow, brown, purple, maroon, etc.,
-in different species. These coloring substances to some extent are
-believed to protect the nitrogenous substances in the leaf from injury.
-The colors absorb the sun’s rays, which otherwise might destroy these
-nitrogenous substances before they have passed back through the petiole
-of the leaf into the stem, where they may be stored for food. The
-gorgeous display of color, then, which the leaves of many trees and
-shrubs put on is one of the many useful adaptations of the plants.
-
-=922. Importance of the forest in the disposal of rainfall.=—The
-importance of the forest in disposing of the rainfall is very great.
-The great accumulation of humus on the forest floor holds back the
-water both by absorption and by checking its flow, so that it does not
-immediately flow quickly off the slopes into the drainage system of the
-valley. It percolates into the soil. Much of it is held in the humus
-and soil. What is not retained thus filters slowly through the soil
-and is doled out more gradually into the valley streams and mountain
-tributaries, so that the flood period is extended, and its injury
-lessened or entirely prevented, because the body of water moving at any
-one time is not dangerously high. The winter snow is shaded and in the
-spring melts slowly, and the spring freshets are thus lessened. The
-action of the leaves and humus in retarding the flow of the water
-prevents the washing away of the soil; the roots of trees bind the soil
-also and assist in holding it.
-
-=923. Absence of forest encourages serious floods.=—The great
-floods of the Mississippi and its tributaries are due to the rapidity
-with which heavy rainfall flows from the rolling prairies of the west,
-and from the deforested areas west of the Alleghany system. The serious
-floods in recent years in some of the South Atlantic States are in
-part due to the increasing area of deforestation in the Blue Ridge and
-southern Alleghany system.
-
-=924. The prairie and plains societies.=—These are to be found
-in the grassland formation. In the prairies “meadows” are formed in
-the lower ground near river courses where there is greater moisture
-in soil. The grasses here are principally “sod-formers” which have
-creeping underground stems which mat together, forming a dense sod. On
-the higher and drier ground the “bunch” grasses, like buffalo-grass,
-beard-grass, or broom-sedge, etc., are dominant, and in the drier
-regions as one approaches desert conditions the vegetation gradually
-takes on more the character of the desert, so that in the plains
-sage-brush, the prickly-pear cactus, etc., occur. Besides the dominant
-vegetation of the society there are subordinate species, and the
-societies are especially marked by a spring and autumn flora of
-conspicuous flowering plants which are mixed with the grasses.
-
-=925. Desert societies.=—These are composed of plants which
-possess a form or structure which enables them to exist in a very
-dry climate where the air is very dry and the soil contains but
-little moisture. The true desert plants are perennial. The growth and
-flowering period occurs during the rainy season, or those portions
-of the rainy season when the temperature is favorable, and they rest
-during the very dry season and cold. Characteristic desert plants are
-the cacti with thick succulent green stems or massive trunks, the
-leaves being absent or reduced to mere spines which no longer function
-in photosynthesis; yuccas with thick, narrow and long leaves with a
-firm and thick cuticle; small shrubs or herbs with compact rounded
-habit and small thick gray leaves. All of these structures conserve
-moisture. The mesquite tree is one of the common trees in portions
-of the Sonora Nevada desert. Besides the true desert plants, desert
-societies have a rainy-season flora consisting of annuals, which can
-germinate, vegetate, flower, and seed during the period of rain and
-before the ground moisture has largely disappeared, and these pass the
-resting period in seed.
-
-[Illustration: Fig. 490. Desert vegetation, Arizona, showing large
-succulent trunks of cactus with shrubs and stunted trees. Open
-formation. (Photograph by Tuomey.)]
-
-[Illustration: Fig. 491. Polar tundra with scattered flowers, Alaska.
-(Copyright by E. H. Harriman.)]
-
-[Illustration: Fig. 492. Perennial rosette plant from alpine flora of
-the Andes, showing short stem, rosette of leaves, and large flower.
-(After Schimper.)]
-
-=926. Arctic-alpine societies.=—The most striking of the arctic
-plant societies are the “polar tundra,” extensive mats of vegetation
-largely made up of mosses, lichens, etc., only partially decayed
-because of the great cold of the subsoil, and perhaps also because
-of humus acid in the partially decayed vegetation. These tundras
-are brightened by numerous flowering plants which are characterized
-by short stems, a rosette of leaves near the ground, and by large
-bright-colored flowers. Heaths, saxifrages, and dwarf willow abound.
-Alpine plant societies are similar to the arctic, although some of the
-conditions are more severe than in the arctic region. This is
-principally due to the fact that during the summer while the plants are
-growing they are subject to a high temperature during the day and a
-very low temperature at night, whereas during the summer in arctic
-regions while the plants are growing there is continuous warmth for
-growth and continuous light for photosynthesis. Five types of alpine
-plants are recognized by some. 1st. _Elfin tree._ This type has short,
-gnarled, often horizontal stems, as seen in pines, birches, and other
-trees growing in alpine heights. 2d. _The alpine shrubs._ In the
-highest alpine belts they are dwarfed and creeping, richly branched and
-spreading close to the ground, while at lower belts they are more like
-lowland shrubs. 3d. _The cushion type._ The branching is very profuse
-and the branches are short and touch each other on all sides, forming
-compact masses (examples saxifrages, androsace, mosses, etc.). 4th.
-_Rosette plants._ These are perennial, short stems and very strong
-roots, and play an important part in the alpine meadows. 5th. _Alpine
-grasses._ These usually have much shorter leaves than grasses of the
-lowlands and consequently form a low sward.
-
-=927. Edaphic plant societies.=—These are equivalent to edaphic
-plant formations, and the vegetation is of course controlled by the
-peculiar conditions of the soil. There are a number of different
-kinds of edaphic plant societies determined by the character of the
-physiographic areas. 1st. _Sphagnum moors._ These are formed in shallow
-basins originally with more or less water. The growth of the sphagnum
-moss along with other vegetation and its partial decay in the water
-builds up ground rapidly so that in course of time the pond may be
-completely filled in. This filling in proceeds from the shore toward
-the center, and in the early stages of course there would be a pond
-in the center. The partial decay of vegetation creates an excess of
-humus acid which retards absorption by the roots. The conditions are
-such, then, as require aerial structures for retarding the loss of
-water, and plants growing in such moors are usually xerophytes. Some of
-the plants are identical with those growing in the arctic tundra. 2d.
-_Sand_[53] _strand of beach._ The quantity of sand with very little or
-no admixture of humus or plant food makes it difficult for plants to
-obtain a sufficient amount of water even where rainfall is abundant.
-The same may be said of the sand dunes farther back from the shore. The
-plants of these areas are then usually xerophytes. Some of the plants
-accustomed to growing in such localities are American sea-rocket,
-seaside spurge, bugseed, sea-blite, sea-purslane, the sandcherry, dwarf
-willow, marram-grass, certain species of beard-grass, etc. 3d. _Rocky
-shores or areas._ Here lichens and mosses first grow, later to be
-followed by herbs, grasses, shrubs, and trees, as decayed plant remains
-accumulate in the rock crevices. 4th. _Shores of ponds, or swamp
-moors._ Here the vegetation often takes on a zonal arrangement if the
-ground gradually slopes to the shore and out into the pond. In Fig. 493
-is shown zonal distribution of plants. The different kinds of plants
-are drawn into these zones by the varying amount of ground water in
-the soil, or the varying depth of the water on the margin of the pond
-as one proceeds from the land towards the deeper water. On the border
-lines or tension lines between the different zones the plants are
-struggling to occupy here ground which is suitable for each adjacent
-individual formation. Other edaphic societies are those of marl ponds,
-alkaline areas, oases in deserts, warm oases in arctic lands, the
-forested areas along river bottoms in prairie or plains regions, etc.
-
-[Illustration: Fig. 493. Macrophytes in the upper zone of the photic
-region. Ascophyllum and Fucus at low tide, Hunter’s Island, New York
-City. (Photograph by M. A. Howe.)]
-
-[Illustration: Fig. 494.
-
-Zonal distribution of plants, South Shore, Cayuga Lake.]
-
-=928. Aquatic plant societies.=—In general we might distinguish
-three kinds, 1st. _Fresh-water plant societies_, with floating algæ
-like spirogyra, œdogonium, etc., the floating duck-meats, riccias; the
-plants of the lily type with roots and stems attached to the bottom
-and leaves floating on the surface, like the water-lily and certain
-pondweeds, and finally the completely submerged ones like certain
-pondweeds, the bassweed (Chara), etc. 2d. _Marine plant societies_,
-which are made up mostly of the red and brown algæ or “seaweeds,”
-though some green algæ and flowering plants also occur. 3d. _The salt
-marshes_ where the water is brackish and there is usually a luxuriant
-growth of marsh-grasses.
-
-FOOTNOTES:
-
-[47] For a fuller discussion of this subject by the author see Chapters
-XLVI-LVII of his “College Text-book of Botany” (Henry Holt & Co.).
-
-[48] =οῖκος= = house, and =λόγος= = discourse.
-
-[49] Term used by Schimper.
-
-[50] See the author’s “College Text-book of Botany.” Chapter XLIX.
-
-[51] =ἔδαφος= = ground.
-
-[52] For a full discussion of forest societies see Chapter L in the
-author’s “College Text-book of Botany.”
-
-[53] See Chapter LIV of the author’s “College Text-book of Botany.”
-
-
-
-
-CHAPTER XLVII.
-
-CLASSIFICATION OF THE ANGIOSPERMS.
-
-
-Relation of Species, Genus, Family, Order, etc.
-
-=929. Species.=—It is not necessary for one to be a botanist in
-order to recognize, during a stroll in the woods where the trillium
-is flowering, that there are many individual plants very like each
-other. They may vary in size, and the parts may differ a little in
-form. When the flowers first open they are usually white, and in age
-they generally become pinkish. In some individuals they are pinkish
-when they first open. Even with these variations, which are trifling
-in comparison with the points of close agreement, we recognize the
-individuals to be of the _same kind_, just as we recognize the corn
-plants, grown from the seed of an ear of corn, as of the same kind.
-Individuals of the same kind, in this sense, form a _species_. The
-white wake-robin, then, is a species.
-
-But there are other trilliums which differ greatly from this one. The
-purple trillium (T. erectum) shown in fig. 495 is very different from
-it. So are a number of others. But the purple trillium is a species. It
-is made up of individuals variable, yet very like one another, more so
-than any one of them is like the white wake-robin.
-
-=930. Genus.=—Yet if we study all parts of the plant, the
-perennial rootstock, the annual shoot, and the parts of the flower, we
-find a great resemblance. In this respect we find that there are
-several species which possess the same general characters. In other
-words, there is a relationship between these different species, a
-relationship which includes more than the individuals of one kind. It
-includes several kinds. Obviously, then, this is a relationship with
-broader limits, and of a higher grade, than that of the individuals
-of a species. The grade next higher than species we call _genus_.
-Trillium, then, is a genus. Briefly the characters of the genus
-trillium are as follows:
-
-[Illustration: Fig. 495. Trillium erectum (purple form), two plants
-from one rootstock.]
-
-=931. Genus trillium.=—Perianth of six parts: sepals 3,
-herbaceous, persistent; petals colored. Stamens 6 (in two whorls),
-anthers opening inward. Ovary 3-loculed, 3-6-angled; stigmas 3,
-slender, spreading. Herbs with a stout perennial rootstock, with
-fleshy, scale-like leaves, from which the low annual shoot arises,
-bearing a terminal flower and 3 large netted-veined leaves in a whorl.
-
-      _Note._—In speaking of the genus the present usage
-    is to say trillium, but two words are usually employed
-    in speaking of the species, as Trillium grandiflorum,
-    T. erectum, etc.
-
-=932. Genus erythronium.=—The yellow adder-tongue, or dogtooth
-violet (Erythronium americanum), shown in fig. 496, is quite different
-from any species of trillium. It differs more from any of the species
-of trillium than they do from each other. The perianth is of six parts,
-light yellow, often spotted near the base. Stamens are 6. The ovary is
-obovate, tapering at the base, 3-valved, seeds rather numerous, and the
-style is elongated. The flower stem, or scape, arises from a scaly bulb
-deep in the soil, and is sheathed by two elliptical-lanceolate, mottled
-leaves. The smaller plants have no flower and but one leaf, while the
-bulb is nearer the surface. Each year new bulbs are formed at the end
-of runners from a parent bulb. These runners penetrate each year deeper
-into the soil. The deeper bulbs bear the flower stems.
-
-=933. Genus lilium.=—While the lily differs from either the
-trillium or erythronium, yet we recognize a relationship when we
-compare the perianth of six colored parts, the 6 stamens, and the
-3-sided and long 3-loculed ovary.
-
-[Illustration: Fig. 496. Adder-tongue (erythronium). At left below
-pistil, and three stamens opposite three parts of the perianth. Bulb at
-the right.]
-
-=934. Family Liliaceæ.=—The relationship between genera, as
-between trillium, erythronium, and lilium, brings us to a still higher
-order of relationship, where the limits are broader than in the genus.
-Genera which are thus related make up the _family_. In the case of
-these genera the family has been named after the lily, and is the lily
-family, or _Liliaceæ_.
-
-=935. Order, class, group.=—In like manner the lily family, the
-iris family, the amaryllis family, and others which show characters of
-close relationship are united into an _order_ which has broader limits
-than the family. This order is the lily order, or order _Liliales_. The
-various orders unite to make up the _class_, and the classes unite to
-form a _group_.
-
-=936. Variations in usage of the terms class, order, etc.=—Thus,
-according to the system of classification adopted by some, the
-angiosperms form a _group_. The group angiosperms is then divided into
-two _classes_, the _monocotyledones_ and _dicotyledones_. (It should
-be remembered that all systematists do not agree in assigning the
-same grade and limits to the classes, subclasses, etc. For example,
-some treat of the angiosperms as a class, and the monocotyledons
-and dicotyledons as subclasses; while others would divide the
-monocotyledons and dicotyledons into classes, instead of treating each
-one as a class or as a subclass. Systematists differ also in usage as
-to the termination of the ordinal name; for example, some use the word
-_Liliales_ for _Liliifloræ_, in writing of the order.)
-
-[Illustration: Fig. 497.
-
-_A._ Cross-section of the stem of an oak tree thirty-seven years old,
-showing the annual rings. _rm_, the medullary rays; _m_, the pith
-(medulla). _B._ Cross-section of the stem of a palm tree, showing the
-scattered bundles.]
-
-=937. Monocotyledones.=—In the monocotyledons there is a single
-cotyledon on the embryo; the leaves are parallel-veined; the parts
-of the flower are usually in threes; endosperm is usually present in
-the seed; the vascular bundles are usually closed, and are scattered
-irregularly through the stem as shown by a cross-section of the stem
-of a palm (fig. 497), or by the arrangement of the bundles in the corn
-stem (fig. 57). Thus a single character is not sufficient to show
-relationship in the class (nor is it in orders, nor in many of the
-lower grades), but one must use the sum of several important characters.
-
-=938. Dicotyledones.=—In the dicotyledons there are two
-cotyledons on the embryo; the venation of the leaves is reticulate;
-the endosperm is usually absent in the seed; the parts of the flower
-are frequently in fives; the vascular bundles of the stem are
-generally open and arranged in rings around the stem, as shown in the
-cross-section of the oak (fig. 497). There are exceptions to all the
-above characters, and the sum of the characters must be considered,
-just as in the case of the monocotyledons.
-
-=939. Taxonomy.=—This grouping of plants into species, genera,
-families, etc., according to characters and relationships is
-_classification_, or _taxonomy_.
-
-To take Trillium grandiflorum for example, its position in the system,
-if all the principal subdivisions should be included in the outline,
-would be indicated as follows:
-
-    Group, Angiosperms.
-      Class, Monocotyledones.
-        Order, Liliales.
-          Family, Liliaceæ.
-            Genus, Trillium.
-              Species, grandiflorum.
-
-In the same way the position of the toothwort would be indicated as
-follows:
-
-    Group, Angiosperms.
-      Class, Dicotyledones.
-        Order, Papaverales.
-          Family, Cruciferæ.
-            Genus, Dentaria.
-              Species, diphylla.
-
-But in giving the technical name of the plant only two of these names
-are used, the genus and species, so that for the toothwort we say
-_Dentaria diphylla_, and for the white wake-robin we say _Trillium
-grandiflorum_.
-
-=940. Kingdom and Subkingdom.=—Organic beings form altogether two
-kingdoms, the Animal Kingdom and the Plant Kingdom. The Plant Kingdom
-is then divided into a number of subkingdoms as follows: 1st,
-Subkingdom Thallophyta, the thallus plants, including the Algæ and
-Fungi; 2d, Subkingdom Bryophyta, the moss-like plants, including the
-Liverworts and Mosses; 3d, Subkingdom Pteridophyta, the fern-like
-plants, including Ferns, Lycopods, Equisetum, Isoetes, etc.; 4th,
-Subkingdom Spermatophyta, the seed plants, including Gymnosperms and
-Angiosperms. Subkingdoms are divided into groups of lower order down to
-the classes. So there are subclasses, subfamilies or tribes, subgenera,
-and even subspecies. But taking the principal taxonomic divisions from
-the greater to the lesser rank, the order would be as follows:
-
-    Plant Kingdom.
-      Subkingdom, Spermatophyta.
-        Group (not used in a definite sense).
-          Class, Gymnospermæ.
-            Order, Pinales.
-              Family, Pinaceæ.
-                Genus, Pinus.
-                  Species, strobus, or, in full,
-        Pinus strobus, the white pine.
-
-
-Group Angiospermæ.
-
-
-I. CLASS MONOCOTYLEDONES.
-
-=941. Order Pandanales.=—Aquatic or marsh plants. The cattail
-flags (Typha) and the bur-reeds (Sparganium), each representing a
-family. The name of the order is taken from the tropical genus Pandanus
-(the screw-pine often grown in greenhouses).
-
-=942. Order Naiadales.=—Aquatic or marsh herbs. Three families
-are mentioned here.
-
-The pondweed family (Naiadaceæ), named after one genus, Naias. The
-largest genus is Potamogeton, the species of which are known as
-pondweeds. Ruppia occidentalis occurs in saline ponds in Nebraska, and
-R. maritima along the seacoast and in saline districts in the interior.
-
-The water-plantain family (Alismaceæ) includes the water-plantain
-(Alisma) and the arrow-leaves (Sagittaria).
-
-The tape-grass family (Vallisneriaceæ) includes the tape-grass, or
-eel-grass (the curious Vallisneria spiralis).
-
-=943. Order Graminales.=—Two families.
-
-The grass family (Gramineæ), the grasses and grains.
-
-The sedge family (Cyperaceæ), the sedges.
-
-=944. Order Palmales=, with one family, Palmaceæ, includes the
-palms, abundant in the tropics and extending into Florida. Cultivated
-in greenhouses.
-
-=945. Order Arales.=
-
-The arum family (Araceæ). Flowers in a fleshy spadix. Examples: Indian
-turnip (Arisæma), sweet-flag (Acorus), skunk-cabbage (Spathyema).
-
-The duckweed family (Lemnaceæ). (Examples: Lemna, Spirodela, Wolffia.
-See paragraphs 51-53.)
-
-=946. Order Xyridales=, from the genus Xyris, the yellow-eyed
-grass family (Xyridaceæ). Species mostly tropical, but a few in North
-America. Other examples are the pipewort family (Eriocaulaceæ, example,
-Eriocaulon septangulare), the pineapple family (Bromeliaceæ, example,
-the pineapple cultivated in Florida); the Florida moss or hanging moss
-(Tillandsia usneoides); the spiderwort family (Commelinaceæ), including
-the spiderwort (Tradescantia, several species in North America); the
-pickerel-weed family (Pontederiaceæ), including the genus Pontederia in
-borders of ponds and streams.
-
-=947. Order Liliales.=—Some of the families are as follows:
-
-The rush family (Juncaceæ, example, Juncus), with many species, plants
-of usually swamp habit.
-
-The lily family (Liliaceæ, examples: Lilium, Allium = Onion,
-Erythronium, Yucca).
-
-The iris family (Iridaceæ, examples: Iris, the blue-flag, fleur-de-lis,
-etc.).
-
-The lily-of-the-valley family (Convallariaceæ, examples:
-lily-of-the-valley, Trillium, etc.)
-
-The amaryllis family (Amaryllidaceæ, examples: Narcissus, the daffodil;
-Cooperia, in southwestern United States).
-
-=948. Order Scitaminales.=—This order includes the large showy
-cultivated Canna of the canna family.
-
-=949. Order Orchidales.= Example, the orchid family (Orchidaceæ)
-with Cypripedium, Orchis, etc.
-
-
-II. CLASS DICOTYLEDONES.
-
-SERIES 1. CHORIPETALÆ. Petals wanting (Apetalæ, or
-Archichlamydæ of some authors), or present and distinct from one
-another (Polypetalæ, or Metachlamydæ).
-
-=950. Order Casuarinales=, confined to tropical seacoasts
-(example, Casuarina).
-
-=951. Order Piperales= includes the lizard’s-tail family
-(Saururaceæ), Saururus cernuus, lizard’s-tail, in the eastern United
-States.
-
-=952. Order Salicales.=—Shrubs or trees, flowers in aments.
-Includes the willows and poplars (Salix and Populus of the willow
-family, Salicaceæ).
-
-=953. Order Myricales.=—Shrubs or small trees. Includes the
-sweet-gale (Myrica gale) in wet places in northern United States and
-British North America, Myrica cerifera forming thickets on sand dunes
-along the Atlantic coast, and the sweet-fern (Comptonia peregrina = C.
-asplenifolia) in the eastern United States in dry soil of hillsides.
-
-=954. Order Leitneriales.=—Shrubs or trees. Includes the
-cork-wood, Leitneria floridana (Leitneriaceæ).
-
-=955. Order Juglandales.=—Trees, staminate flowers in aments. The
-walnut family (Juglandaceæ, examples: walnut, butternut, etc. Juglans;
-hickory, Hicoria = Carya).
-
-=956. Order Fagales.=—Trees and shrubs. Flowers in aments, or the
-pistillate ones with an involucre which forms a cup in fruit, as in the
-acorn of the oak.
-
-The birch family (Betulaceæ, examples: Betula, birch; Corylus,
-hazelnut; Alnus, alder, etc.).
-
-The beech family (Fagaceæ = Cupuliferæ, examples: Fagus, beech;
-Castanea, chestnut; Quercus, oak).
-
-=957. Order Urticales.=—Trees, shrubs, or herbs. Examples: the
-elm family (Ulmaceæ), the mulberry family (Moraceæ), and the nettle
-family (Urticaceæ).
-
-=958. Order Santalales=, herbs or shrubs, mostly parasitic.
-
-The mistletoe family (Loranthaceæ), with the American mistletoe
-(Phoradendron flavescens), parasitic on deciduous trees in the South
-Atlantic, Central, and Gulf States (N. J. to Ind. Ter.).
-
-The sandalwood family (Santalaceæ, example, the bastard toad-flax,
-Comandra umbellata), widely distributed in North America.
-
-=959. Order Aristolochiales.=—Herbs or vines with heart-shaped or
-kidney-shaped leaves. The birthwort family (Aristolochiaceæ, example,
-Aristolochia serpentaria, the Virginia snake-root, eastern United
-States; wild ginger, or heart-leaf, Asarum canadense, eastern North
-America.)
-
-=960. Order Polygonales.=—Examples: the buckwheat family
-(Polygonaceæ), including buckwheat (Fagopyrum), and numerous species
-of Polygonum, known as smartweed, water-pepper, tear-thumb, bindweed,
-knotweed, prince’s-feather, etc.
-
-=961. Order Chenopodiales.=—Herbs. There are several families;
-one of the largest is the goosefoot family (Chenopodiaceæ). The genus
-Chenopodium includes many species, known as goosefoot, lamb’s-quarters,
-etc. Here belong also the Russian thistle (Salsola tragus) and the
-saltwort (S. kali). The former is sometimes a troublesome weed in the
-central and western United States, naturalized from Europe. The latter
-occurs along the Atlantic coast on seabeaches. Atriplex occurs in salty
-or alkaline soil, also the glasswort (Salicornia herbacea), the bugseed
-(Corispermum). The pokeweed family (Phytolaccaceæ), the Amaranth family
-(Amaranthaceæ), the purslane family (Portulacaceæ, including the
-purslane or “pursley,” Portulaca oleracea, and the spring-beauty,
-Claytonia virginica), and the pink family (Caryophyllaceæ), belong here.
-
-=962. Order Ranales.=—Herbs, shrubs, or trees. Examples are:
-
-The water-lily family (Nymphæaceæ), with the yellow water-lily (Nymphæa
-advena = Nuphar advena) and the white water-lily (Castalia odorata =
-Nymphæa odorata).
-
-The magnolia family (Magnoliaceæ), including the magnolias
-(Magnolia) and the tulip-tree (Liriodendron). The crowfoot family
-(Ranunculaceæ), with the buttercups, hepatica, clematis, etc.
-
-=963. Order Papaverales.=—Mostly herbs. Examples are:
-
-The poppy family (Papaveraceæ), including the opium or garden poppy
-(Papaver somniferum), the blood-root (Sanguinaria canadensis), the
-Dutchman’s-breeches (Bicuculla cucullaria = Dicentra cucullaria),
-squirrel’s-corn (Bicuculla canadensis = D. canadensis).
-
-The mustard family (Cruciferæ), including the toothwort (Dentaria),
-shepherd’s-purse (Bursa bursa-pastoris = Capsella bursa-pastoris), the
-cabbage, turnip, etc.
-
-=964. Order Sarraceniales.=—Insectivorous plants.
-
-The pitcher-plant family (Sarraceniaceæ). Examples: Sarracenia
-purpurea, the pitcher-plant, in peat-bogs, northern and eastern North
-America.
-
-The sundew family (Droseraceæ). Examples: Drosera rotundifolia, and
-other sundews.
-
-=965. Order Rosales.=—Herbs, shrubs or trees. Seventeen families
-are given in the eastern United States. Examples:
-
-The riverweed family (Podostemaceæ), containing the riverweed
-(Podostemon).
-
-The saxifrage family (Saxifragaceæ), containing a number of species.
-Example, Saxifraga virginiensis.
-
-The gooseberry family (Grossulariaceæ), including the wild and the
-cultivated gooseberry.
-
-The witch-hazel family (Hamamelidaceæ), including the witch-hazel
-(Hamamelis), in eastern North America, and the sweet gum (Liquidambar
-styraciflua).
-
-The plane-tree family (Platanaceæ), with the plane-tree, or buttonwood
-(Platanus occidentalis), eastern North America. (Other species occur in
-western United States.)
-
-The rose family (Rosaceæ), including roses, spiræas, raspberries,
-strawberries, the shrubby cinquefoil (Dasiphora fruticosa), etc.
-
-The apple family (Pomaceæ), including the apple, mountain-ash, pear,
-June-berry (or shadbush, also service-berry), the hawthorns (Cratægus).
-
-The plum family (Drupaceæ), including the cherries, plums, peaches, etc.
-
-The pea family (Papilionaceæ), including the pea, bean, clover, vetch,
-lupine, etc., a very large family.
-
-=966. Order Geraniales.=—Herbs, shrubs, or trees. Nine families
-in the eastern United States. Examples:
-
-The geranium family (Geraniaceæ), with the cranesbill (Geranium
-maculatum) and others.
-
-The wood-sorrel family (Oxalidaceæ), with the wood-sorrel (Oxalis
-acetosella) and others.
-
-The flax family (Linaceæ). Example, flax (Linum vulgaris).
-
-The spurge family (Euphorbiaceæ). Plants with a milky juice, and
-curious, degenerate flowers. Examples: the castor-oil plant (Ricinus),
-the spurges (many species of Euphorbia).
-
-=967. Order Sapindales.=—Mostly trees or shrubs. Twelve families
-in the eastern United States. Example:
-
-The sumac family (Anacardiaceæ), containing the sumacs in the genus
-Rhus. Examples: the poison-ivy (R. radicans), a climbing vine, in
-thickets and along fences, in eastern United States. Sometimes
-trained over porches. The poison-oak (R. toxicodendron), a low shrub.
-Poison-sumac or poison-alder (R. vernix = R. venenata), sometimes
-called “thunderwood,” or dogwood, is a large shrub or small tree, very
-poisonous. The smoke-tree (Cotinus cotinoides) belongs to the same
-family, and is often planted as an ornamental tree. The maple family
-(Aceraceæ), including the maples (Acer).
-
-The buckeye family (Hippocastanaceæ), including the horse-chestnut
-(Æsculus hippocastanum), much planted as a shade tree along streets.
-Also there are several species of buckeye in the same genus.
-
-The jewelweed family (Balsaminaceæ), including the touch-me-not
-(Impatiens biflora and aurea) in moist places. The garden balsam (Imp.
-balsamea) also belongs here.
-
-=968. Order Rhamnales.=—Shrubs, vines, or small trees. There are
-two families, the buckthorn (Rhamnaceæ), the grape family (Vitaceæ),
-including the grapes (Vitis), the American ivy (Parthenocissus
-quinquefolia = Ampelopsis quinquefolia), in woods and thickets, eastern
-North America, and much planted as a trailer over porches. The Japanese
-ivy (P. tricuspidata = A. veitchii) used as a trailer on the sides of
-buildings belongs here.
-
-=969. Order Malvales.=—Herbs, shrubs, or trees.
-
-The linden family (Tiliaceæ). Example, the basswood or American linden
-(Tilia americana.)
-
-The mallow family (Malvaceæ), including the hollyhock, the mallows,
-rose of Sharon (Hibiscus), etc.
-
-=970. Order Parietales=, with seven families in the eastern United
-States. The St. John’s wort (Hypericum) and the violets each represent
-a family. The violets (Violaceæ) are well-known flowers.
-
-=971. Order Opuntiales.=—These include the cacti (Cactaceæ),
-chiefly growing in the dry or desert regions of America.
-
-=972. Order Thymeleales=, with two families and few species.
-
-=973. Order Myrtales.=—Land, marsh, or aquatic plants. The most
-conspicuous are in the evening primrose family (Onagraceæ), including
-the fireweeds, or willow herbs (Epilobium), and the evening primrose
-(Onagra biennis = Œnothera biennis).
-
-=974. Order Umbellales.=—Herbs, shrubs, or trees, flowers in
-umbels.
-
-The ginseng family (Araliaceæ). This includes the spikenards and
-sarsaparillas in the genus Aralia, and the ginseng (or “sang”), Panax
-quinquefolium.
-
-The carrot family (Umbelliferæ). This family includes the wild carrot
-(Daucus carota), the poison-hemlock (Cicuta), the cultivated carrot and
-parsnip, and a large number of other genera and species.
-
-The dogwood family (Cornaceæ). The flowering dogwood (Cornus florida),
-abundant in eastern North America, is an example.
-
-SERIES 2. GAMOPETALÆ (= Sympetalæ or Metachlamydæ). Petals
-partly or wholly united, rarely separate or wanting.
-
-=975. Order Ericales.=—There are six families in eastern United
-States. Examples:
-
-The wintergreen family (Pyrolaceæ), including the shin-leaf (Pyrola
-elliptica).
-
-The Indian-pipe family (Monotropaceæ), with the Indian-pipe (Monotropa
-uniflora) and other humus saprophytes. (See paragraphs 182-191.)
-
-The heath family (Ericaceæ). Examples: Labrador tea (Ledum), in bogs
-and swamps in northern North America. The azaleas, with several
-species widely distributed, are beautiful flowering shrubs, and many
-varieties are cultivated. The rhododendrons are larger with larger
-flower clusters, also beautiful flowering shrubs. R. maximum in the
-Alleghany Mountains and vicinity, from Nova Scotia to Ohio and Georgia.
-R. catawbiense, usually at somewhat higher elevations, Virginia to
-Georgia. The mountain laurel (Kalmia latifolia) and other species rival
-the rhododendrons and azaleas in beauty. The trailing arbutus (Epigæa
-repens) in sandy or rocky woods is a well-known small trailing shrub
-in eastern North America. The sourwood (Oxydendrum arboreum) is a tree
-with white racemes of flowers in August, and scarlet leaves in autumn.
-The spring or creeping wintergreen (Gaultheria procumbens) is a small
-shrub with aromatic leaves, and bright red spicy berries.
-
-The huckleberry family (Vaccinaceæ) includes the huckleberries
-(example, Gaylussacia resinosa, the black or high-bush huckleberry,
-eastern United States), the mountain cranberry (Vitis-Idæa vitisidæa
-= Vaccinium vitisidæa) in the northern hemisphere; the bilberries and
-blueberries (of genus Vaccinium); the cranberries (examples: the large
-American cranberry, Oxycoccus macrocarpus and the European cranberry,
-Oxycoccus oxycoccus, in cold bogs of northern North America, the latter
-also in Europe and Asia).
-
-=976. Order Primulales.=—Two families here. The primrose family
-(Primulaceæ) contains the loosestrifes (Steironema), star-flower
-(Trientalis), etc.
-
-=977. Order Ebenales.=—Of the four families, the ebony family
-(Ebenaceæ) contains the well-known persimmon (Diospyros virginiana) and
-the storax family (Styracaceæ) with the silverbell, or snowdrop tree
-(Mohrodendron carolinum).
-
-=978. Order Gentianales.=—Herbs, shrubs, vines, or trees. Six
-families in the United States.
-
-The olive family (Oleaceæ) includes the common lilac (Syringa), the ash
-trees (Fraxinus), the privet (Ligustrum).
-
-The gentian family (Gentianaceæ) among other genera includes the
-gentians (Gentiana).
-
-The milkweed family (Asclepiadaceæ) contains plants mostly with a milky
-juice. Asclepias with many species is one of the most prominent genera.
-
-=979. Order Polemoniales.=—Mostly herbs, rarely shrubs and trees.
-Fifteen families in the eastern United States.
-
-The morning glory family (Convolvulaceæ) includes the bindweeds
-(Convolvulus), the morning glory (Ipomæa), etc.
-
-The dodder family (Cuscutaceæ) includes the dodders, or “love-vines.”
-There are nearly thirty species in the United States. The stems are
-slender and twine around other plants upon which they are parasitic
-(see paragraph 179).
-
-The phlox family (Polemoniaceæ). The most prominent genus is Phlox.
-Over forty species occur in North America.
-
-The borage family (Boraginaceæ) includes the heliotrope (Heliotropium),
-the hound’s-tongue (Cynoglossum), the forget-me-not (Myosotis), and
-others.
-
-The vervain family (verbenaceæ) contains the verbenas.
-
-The mint family (Labiatæ) contains the mints (Mentha), skull-cap
-(Scutellaria), dead-nettles (Lamium).
-
-The potato family (Solanaceæ) includes the ground-cherry (Physalis),
-the nightshades (Solanum), the tomato (Lycopersicon), tobacco
-(Nicotiana).
-
-The figwort family (Scrophulariaceæ) includes the common mullein
-(Verbascum), the monkey-flower (Mimulus), the toad-flax (Linaria),
-turtle’s-head (Chelone), and many other genera and species.
-
-The bladderwort family (Lentibulariaceæ) includes the curious bog or
-aquatic plants with finely dissected leaves, and with bladders in which
-insects are caught (Utricularia).
-
-The trumpet-creeper family (Bignoniaceæ) includes the trumpet-creeper
-(Bignonia), the catalpa tree, and others.
-
-=980. Order Plantaginales= with one family (Plantaginaceæ)
-includes the plantains (Plantago).
-
-=981. Order Rubiales= with three families is represented by the
-madder family (Rubiaceæ) with the bluets (Houstonia), the button-bush
-(Cephalanthus), the partridge-berry (Mitchella), the bedstraws
-(Galium), etc.
-
-The honeysuckle family (Caprifoliaceæ) with the elder (Sambucus), the
-arrowwoods and cranberry trees (Viburnum), the honeysuckles (Lonicera),
-etc.
-
-=982. Order Valerianales= with two families includes the teasel
-family (Dipsacaceæ). Example, Fuller’s teasel (Dipsacus).
-
-=983. Order Campanulales= with five families, the corolla usually
-gamopetalous.
-
-The gourd family (Cucurbitaceæ) includes the pumpkin, squash, melon,
-and a few feral species. Example, the star-cucumber (Sicyos angulatus),
-in moist places in eastern and middle United States.
-
-The bell-flower family (Campanulaceæ) includes the hare-bells or
-bell-flowers (Campanula), the lobelias (example, Lobelia cardinalis,
-the cardinal-flower), etc.
-
-The chicory family (Cichoriaceæ) includes the chicory or succory
-(Cichorium intybus, known also as blue-sailors), the oyster-plant or
-salsify (Tragopogon porrifolius), the dandelion (Taraxacum taraxacum =
-T. densleonis), the lettuce (Lactuca), the hawkweed (Hieraceum), and
-others.
-
-The ragweed family (Ambrosiaceæ) includes the ragweeds (Ambrosia), the
-cockle-bur (Xanthium), and others.
-
-The thistle family (Compositæ) includes the thistle (Carduus), asters
-(Aster), goldenrods (Solidago), sunflowers (Helianthus), eupatoriums or
-joepye-weeds, thoroughworts (Eupatorium), cone-flowers or black-eyed
-Susans (Rudbeckia), tickseed (Coreopsis), bur-marigold or beggar-ticks
-or devil’s-bootjack (Bidens), chrysanthemums, etc.
-
-
-
-
-INDEX.
-
-
-    Absorption, 13, 22-28
-    Aceraceæ, 497
-    Acorn, 451
-    Acorus, 493
-    Æcidiomycetes, 218
-    Æcidiospore, 189
-    Æsculus hippocastanum, 498
-    Agaricaceæ, 199, 219
-    Agaricus arvensis, 206
-    Agaricus campestris, 200-207
-    Akene, 451
-    Albumen, 98
-    Albuminous, 98, 108
-    Alder, 495
-    Algæ, 136-176
-    Algæ, absorption by, 22
-    Alismaceæ, 493
-    Alpine formation, 474
-    Alpine plant societies, 483
-    Amanita phalloides, 207, 208
-    Amaranth, 495
-    Amaryllidaceæ, 494
-    Aments, 429
-    American mistletoe, 495
-    Ampelopsis, 498
-    Ancylistales, 215
-    Andreales, 249
-    Andrœcium, 319, 419
-    Anemophilous, 435
-    Angiosperms, morphology of, 318-348;
-       classification, 487
-    Antheridiophore, 227
-    Antheridium, 144, 149, 155, 176, 223, 228,
-                 240, 245, 246, 266, 287, 433
-    Anthesis, 429
-    Anthoceros, 240, 241
-    Anthocerotales, 242
-    Anthocerotes, 242
-    Apogamy, 346
-    Apogeotropic (ap″o-ge″o-trop´ic), 126
-    Apogeotropism (ap″o-ge-ot′ro-pism), 126
-    Apple, 456, 497
-    Apple family, 497
-    Aquatic formations, 475
-    Aquatic plant societies, 486
-    Araceæ, 493
-    Archegonia (ar-che-go′ni-a), 223, 229, 233, 241, 244-246,
-                                 267, 288, 291, 307, 308
-    Archegoniophore, 229
-    Archegonium, 433
-    Archesporium (ar″che-spo´ri-um), 235
-    Archidiales, 249
-    Arctic formation, 481
-    Aril, 457
-    Arisæma, 493
-    Arisæma triphyllum, 442, 443
-    Aristolochiales, 495
-    Arrow leaf, 492
-    Arum family, 493
-    Asclepias, 500
-    Asclepias cornuti, 462
-    Ascomycetes (as-co-my-ce′tes), 195-198, 216-218
-    Ascus, 190, 213
-    Ash of plants, 79, 80
-    Ash tree, 500
-    Aspidium acrostichoides, 253, 257
-    Assimilation, 67, 109
-    Aster, 502
-    Atriplex, 495
-    Auriculariales, 218
-    Autotrophic plants, 85
-    Azalea, 499
-    Azolla, 296
-
-    Bacteria, 164, 165
-    Bacteria, nitrite and nitrate, 83
-    Bacteriales, 164, 165
-    Bacteroid, 93
-    Bangiales, 175
-    Basidiomycetes (ba-sid″i-o-my-ce′tes), 199-208, 218
-    Basidium, 201, 213
-    Bast, 50-52
-    Batrachospermum, 171-173, 175
-    Bazzania, 25
-    Beard-grasses, 480
-    Bedstraws, 501
-    Beechnut, 452
-    Beet, osmose in, 15, 16, 17, 18
-    Begonia, 407
-    Bellflower, 501
-    Berry, 454, 455, 456
-    Betulaceæ, 495
-    Bicuculla, 496
-    Bidens, 458
-    Bignonia, 501
-    Bilberries, 500
-    Biotic factors, 466
-    Birch, 495
-    Bird’s-nest fungi, 220
-    Blackberry, 454
-    Black fungi, 198
-    Bladderwort, 501
-    Blasia, 164, 236
-    Bloodroot, 496
-    Bluets, 436, 437, 501
-    Boletus, 209
-    Boletus edulis, 209
-    Boraginaceæ, 500
-    Botrychium, 295
-    Botrydiaceæ, 162
-    Botrydium granulatum, 146, 162
-    Broom-sedge, 480
-    Brown algæ, 167-170
-    Bryales, 349
-    Buckeye family, 498
-    Buckthorn, 498
-    Buckwheat, 495
-    Buds, winter condition of, 374-377
-    Buffalo-grass, 480
-    Bug seed, 495
-    Bulb, 372
-    Bunch-grasses, 480
-    Butternut, 452, 494
-    Buttonbush, 501
-    Buttonwood, 497
-
-    Cacti, 395, 498
-    Callithamnion, 173
-    Calyptrogen, 361
-    Cambium, 50, 52, 358, 363
-    Campanula rotundifolia, 442, 444, 510
-    Campanulales, 501
-    Canna, 445-449, 494
-    Capsella bursa-pastoris, 496
-    Capsule, 453
-    Carbohydrate, 71, 75, 80, 90
-    Carbon dioxide, 62-67, 110-113
-    Cardinal-flower, 501
-    Carpogonium, 172, 176
-    Carrot family, 499
-    Caryophyllaceæ, 496
-    Caryopsis, 451
-    Cassia marilandica, 402
-    Cassiope, 395
-    Castalia odorata, 496
-    Castor-oil plant, 497
-    Catalpa, 501
-    Catkin, 428
-    Cattail-flag, 492
-    Caulidium, 371
-    Cedar apples, 194
-    Cell, 3;
-       artificial 20
-    Cell-sap, 3, 40
-    Ceratopteris thalictroides, 296
-    Chætophora, 151, 162
-    Chætophoraceæ, 162
-    Chara, 176
-    Charales, 176
-    Chemical condition of soil, 466
-    Chemosynthetic assimilation, 109
-    Chenopodiales, 495
-    Chenopods, 495
-    Chestnut, 452, 494
-    Chicory family, 502
-    Chlamydomonas, 159, 160
-    Chlamydospores, 180
-    Chloral hydrate, 65, 87
-    Chlorophyceæ, 158
-    Chlorophyll, 2, 67, 72
-    Chloroplast, 68, 69, 71
-    Christmas fern, 251-253
-    Chromoplast, 71
-    Chromosomes, 342-345
-    Chroococcaceæe, 163
-    Chrysanthemum, 502
-    Chytridiales, 215
-    Cichoriaceæ, 502
-    Cichorium intybus, 502
-    Clavaria botrytes, 212
-    Clavariaceæ, 210, 219
-    Claytonia virginica, 496
-    Cleistogamous, 435
-    Clematis virginiana, 462, 463, 496
-    Climatic factors, 466
-    Climatic formations, 470
-    Clostridium pasteurianum, 93
-    Clover, 497
-    Club mosses, 284, 289
-    Coccogonales, 163
-    Cocklebur, 502
-    Cold wastes, 474
-    Coleochætaceæ, 162
-    Coleochæte, 153-156, 226
-    Collenchyma, 356, 363
-    Comandra, 495
-    Compass plants, 409
-    Compositæ, 502
-    Comptonia asplenifolia, 494
-    Cone-fruit, 456
-    Confervoideæ, 162
-    Coniferæ, 316
-    Conjugation, 137, 141, 160, 162, 179
-    Convallariaceæ, 494
-    Cooperia, 494
-    Cordyceps, 218
-    Coreopsis, 502
-    Cork, 357, 363
-    Corm, 373
-    Cortex, 50
-    Corymb, 427
-    Cotyledon, 99-101
-    Cranberry, 500
-    Cratægus, 497
-    Crowfoot family, 496
-    Cruciferæ, 496
-    Cryptonemiales, 175
-    Cucurbitaceæ, 501
-    Culture formations, 470, 475
-    Cultures, water, 28, 29
-    Cup fungi, 199
-    Cupuliferæ, 495
-    Cuscuta, 83, 500
-    Cushion type of vegetation, 483
-    Cuticle, 43
-    Cyanophyceæ, 163
-    Cyatheaceæ, 295
-    Cycadales, 316
-    Cycas, 311, 312, 457
-    Cyclosis, 9, 10
-    Cyclosporales, 171
-    Cyme, 430, 432
-    Cyperaceæ, 493
-    Cypripedium, 443, 447, 494
-    Cystocarp, 174
-    Cystopteris bulbifera, 260
-    Cystopus, 215
-    Cytase, 92, 108
-    Cytisus, 445
-    Cytoplasm (cy′to-plasm), 5
-
-    Dacryomycetales, 219
-    Dahlia, 108
-    Dandelion, 502
-    Dasiphora fruticosa, 497
-    Daucus carota, 499
-    Dehiscence, 453
-    Dentaria, 322-324
-    Dentaria diphylla, 496
-    Dermatogen, 359
-    Desert formation, 473
-    Desert societies, 480
-    Desmodium, 458
-    Desmodium gyrans, 399
-    Diadelphous (di″a-del′phous), 425
-    Diageotropism (di″a-ge-ot′ro-pism), 126
-    Diaheliotropic (di″a-he″li-o-trop′ic), 127
-    Diaheliotropism (di″a-he″li-ot′ro-pism), 127
-    Diastase, 77, 78, 108, 116
-    Diatoms, 166
-    Dichogamous (di-chog′a-mous), 437, 442
-    Dicentra, 496
-    Dicotyledons, 494
-    Dictyophora, 219
-    Diffusion, 13-20
-    Digestion, 107, 108, 109
-    Dimorphism of ferns, 273-280
-    Diœcious, 435
-    Dionæa muscipula, 133
-    Dipodascus, 216
-    Dipsacus, 501
-    Discomycetes, 217
-    Dodder, 83, 84, 500
-    Dogwood, 499
-    Dothidiales, 218
-    Downy mildews, 185
-    Drosera rotundifolia, 133, 496
-    Drupaceæ, 497
-    Drupe, 454
-    Duckweeds, 26, 28
-    Dudresnaya, 175
-    Dunes, 484
-
-    Ebenales, 500
-    Ecological factors, 464
-    Ecology (sometimes written œcology), 464
-    Ectocarpus, 167
-    Edaphic formations, 475
-    Elaphomyces, 217, 218
-    Elder, 501
-    Elm family, 495
-    Elodea, 61-63
-    Embryo of ferns, 269-272
-    Embryo sac, 326-328
-    Empusa, 215
-    Endocarp, 450
-    Endomyces, 216
-    Endosperm, 103, 105, 107, 306, 309;
-       nucleus, 327, 329-334
-    Entomophthorales, 215
-    Enzyme, 92, 98, 116, 117
-    Epidermal system, 358
-    Epidermis, 358, 359, 363
-    Epigæa repens, 499
-    Epigynous, 425
-    Epilobium, 498
-    Epinastic (ep-i-nas′tic), 129
-    Epinasty (ep′i-nas-ty), 129
-    Epipactis, 444, 447
-    Epiphegus, 84
-    Epiphytes, 416
-    Equisetales, 296
-    Equisetineæ, 296
-    Equisetum, 280-283
-    Ericaceæ, 499
-    Ericales, 499
-    Erythronium, 493
-    Etiolated plants (e′ti-o-la″ted), 68
-    Euascomycetes, 217
-    Eubasidiomycetes, 219
-    Eupatorium, 403, 502
-    Euphorbiaceæ, 497
-    Eurotium oryzæ, 78
-    Evening primrose family, 498
-    Exalbuminous, 108
-    Exoascus, 217
-    Exobasidiales, 219
-    Exocarp, 450
-
-    Fagales, 494
-    Fehling’s solution, 75, 76
-    Ferment, 98, 108, 116
-    Ferns, 251-279, 292, 457;
-       classification of, 295
-    Fertilization, 307, 308, 328, 329, 140, 145,
-                   169, 172, 174, 197, 421
-    Fibrovascular bundles, 49-54
-    Figwort family, 501
-    Filicales, 295
-    Filicineæ, 295
-    Fittonia, 404
-    Flagellates, 83, 165
-    Flax, 497
-    Flower cluster, 419
-    Flower, form of, 422;
-       parts of, 419;
-       union of parts, 424
-    Flowers, arrangements of, 426;
-       kinds of, 421
-    Follicle, 453
-    Forest, formations 471;
-       societies, 477
-    Forests, relation to rainfall, 479
-    Fresh-water societies, 486
-    Frond, 352
-    Fruit, 450-457;
-       parts of, 450
-    Frullania, 25, 236
-    Fucus, 168-170
-    Fungi, absorption by, 22;
-       classification of, 213-222;
-       nutrition of, 86-90;
-       respiration in, 115
-
-    Gametangium (gam″et-an′gi-um), 140
-    Gamete (gam′ete), 138, 139
-    Gametophore (gam′et-o-phore), 230, 248
-    Gametophyte (gam′et-o-phyte), 225, 226, 244, 245, 250, 262, 270,
-                                  283, 292, 294, 305, 314, 317,
-                                  336-339, 340-348, 434
-    Gamopetalous (gam″o-pet′a-lous), 424
-    Gamosepalous (gam-o-sep′a-lous), 424
-    Gas in plants, 60-64
-    Gasteromycetes, 219
-    Gemmæ, 179, 235
-    General formations, 470
-    Gentian, 500
-    Geotropism (ge-ot′ro-pism), 125-127, 410
-    Geraniaceæ, 497
-    Geraniales, 497
-    Geranium family, 497
-    Germ, 459
-    Gigartinales, 175
-    Gingko, 313-315, 457
-    Gingkoales, 316
-    Ginseng, 499
-    Glasswort, 495
-    Gleicheniaceæ, 295
-    Glucose, 108. See sugar.
-    Gnetales, 316
-    Gonidia, 118, 143, 172, 174, 178-184
-    Gonidiangium (go″nid-an′gi-um), 178
-    Gonidium, 213
-    Gooseberry, 496
-    Goosefoot family, 495
-    Gracilaria, 173, 174, 175
-    Graminales, 492
-    Gramineæ, 492
-    Grape, 498
-    Grass family, 492
-    Grassland formation, 471
-    Green algæ, 158
-    Growth, 118-124, 380
-    Gulfweed, 170
-    Gymnosperms, 311, 456
-    Gymnosporangium, 194
-    Gynœcium, 320, 419, 451, 452
-    Gyrocephalus, 219
-
-    Halophytes, 468
-    Harpochytrium, 214, 215
-    Haustorium, 87, 88
-    Hawkweed, 502
-    Hawthorn, 497
-    Hazelnut, 452, 495
-    Head, 428
-    Heart-leaf, 495
-    Heath family, 499
-    Heliotrope, 500
-    Heliotropism (he-li-ot′ro-pism), 127-131, 133, 397
-    Helvellales, 217
-    Hemiascomycetes, 216
-    Hemibasidiomycetes, 218
-    Hepaticæ, 242
-    Heterospory (het″er-os′po-ry), 434
-    Heterothallic, 180
-    Heterotrophic plants, 85
-    Hickory, 494
-    Hickory-nut, 452
-    Hilum, 101, 102
-    Hippocastanaceæ, 498
-    Holdfasts, 418
-    Hollyhock, 498
-    Homothallic, 180
-    Honeysuckle, 501
-    Hormogonales, 163
-    Horse-chestnut, 498
-    Horsetails, 280-283
-    Houstonia cœrulea, 437
-    Huckleberry, 499
-    Humus saprophytes, 85, 91
-    Hybridization, 338
-    Hydnaceæ, 210, 219
-    Hydnum coralloides, 210
-    Hydnum repandum, 211
-    Hydrocarbon, 75
-    Hydrodictyaceæ, 161
-    Hydrophytes, 468
-    Hydropterales, 295
-    Hydrotropism (hy-drot′ro′pism), 133, 134, 412
-    Hygrophytes, 468
-    Hymeniales, 219
-    Hymenogastrales, 219
-    Hymenomycetes, 219
-    Hymenomycetineæ, 219
-    Hymenophyllaceæ, 295
-    Hypericum, 498
-    Hypocotyl (hy′po-co″tyl), 101
-    Hypocreales, 217
-    Hypogenous, 425
-    Hyponastic (hy-po-nas′tic), 129
-    Hyponasty (hy′po-nas-ty), 129
-    Hysteriales, 217
-
-    Impatiens, 498
-    Impatiens fulva, 460
-    Indian-pipe, 499
-    Indian turnip, 493
-    Indusium, 252
-    Inflorescence, 426
-    Insectivorous plants, 133, 496
-    Integument, 304
-    Intramolecular respiration, 113, 114
-    Inulase, 108
-    Inulin, 108, 417
-    Iodine, 65
-    Ipomœa, 500
-    Iridaceæ, 493
-    Iris, 493
-    Irritability, 125-135
-    Isoetales, 296
-    Isoetes, 289-291, 292
-    Isoetineæ, 296
-    Ivy, 498
-
-    Jack-in-the-pulpit, 373
-    Jewelweed, 498
-    Juglandales, 494
-    June-berry, 497
-    Jungermanniales, 242
-
-    Kalmia latifolia, 444
-    Karyokinesis, 341-344
-    Kelps, 168
-    Kingdom, 492
-
-    Labiatæ, 423, 501
-    Laboulbeniales, 218
-    Labrador tea, 499
-    Lactuca canadensis, 460
-    Lactuca scariola, 409, 460, 461
-    Lagenidium, 214, 215
-    Laminaria, 168, 169
-    Lamium, 424, 501
-    Larch, 367
-    Laurel, 499
-    Leaf patterns, 404
-    Leathesia difformis, 168
-    Leaves, form and arrangement, 383-391;
-       function of, 387;
-       protective modifications of, 392;
-       protective positions, 395;
-       reduction of surface, 394;
-       relation to light, 397;
-       structure of, 40-43, 131, 391, 393
-    Legumes, 92, 93, 453
-    Leguminosæ (= Papilionaceæ), 396, 399
-    Leitneria floridana, 494
-    Leitneriales, 494
-    Lemanea, 171, 173, 175, 492
-    Lemna, 418
-    Lemna trisulca, 26, 27
-    Lenticel, 357, 358
-    Lepiota naucina, 208
-    Lettuce, 502
-    Leucoplast, 71
-    Lichens, 86, 93-95, 220, 221
-    Light, 465
-    Liliaceæ, 490, 493
-    Liliales, 490, 493
-    Lilium, 489-493
-    Linaria vulgaris, 501
-    Linden, 498
-    Linum vulgaris, 497
-    Lipase, 108
-    Liquidambar, 496
-    Liriodendron, 496
-    Live-forever, 394
-    Liverworts, 222-239;
-       absorption by, 23-25;
-       classification of, 242
-    Lobelia, 501
-    Lupinus perennis, 353
-    Lycoperdales, 220
-    Lycopodiaceæ, 296
-    Lycopodiales, 296
-    Lycopodiineæ, 296
-    Lycopodium, 284-286
-
-    Macrosporangium, 94, 302, 304, 311, 312, 321
-    Macrospore, 287, 290, 326-328, 434
-    Magnolia, 496
-    Mallow family, 498
-    Malvales, 498
-    Maple family, 497
-    Marchantia, 24, 226-236
-    Marchantiales, 242
-    Marine plant societies, 486
-    Marratiales, 295
-    Marsilia, 370
-    Marsiliaceæ, 296
-    Matoniaceæ, 295
-    Medicago denticulata, 92
-    Medulla, 50
-    Members of the flower, 335
-    Members of the plant, 349-353
-    Meristem, 359
-    Mesocarp, 450
-    Mesophytes, 467
-    Microsporangia, 294, 299
-    Microspore, 287, 290, 299, 312, 435
-    Microsporophylls, 299, 320, 420
-    Milkweed family, 500
-    Mimosa, 132, 396
-    Mimulus, 501
-    Mint family, 501
-    Mistletoe, 84, 495
-    Mitchella, 501
-    Mixotrophic plants, 85
-    Mnium, 243-246
-    Molds, nutrition of, 86-90
-    Molds, water, 181
-    Monadelphous, 424
-    Monoblepharidales, 215
-    Monoblepharis, 215
-    Monocotyledons, 490, 492
-    Monœcious, 435
-    Monotropa uniflora, 499
-    Morchella, 198, 199
-    Morel, 198, 199
-    Morning-glories, 500
-    Mosaics, 405
-    Mosses, 243-248, 457;
-       absorption by, 25;
-       classification of, 248
-    Mucor, 6, 7, 15, 118, 119, 177-180, 215
-    Mucorales, 215
-    Mulberry, 495
-    Mullein, 366, 394, 501
-    Mushrooms, 199-208
-    Mustard family, 496
-    Mutation, 338
-    Mutualism, 95
-    Mycelium, 6, 86-90
-    Mycetozoa, 213, 214
-    Mycorhiza, 86, 91, 92, 217
-    Myosotis, 500
-    Myrica cerifera, 494
-    Myrica gale, 494
-    Myricales, 494
-    Myriophyllum, 403
-    Myrtales, 498
-    Myxobacteriales, 165
-    Myxomycetes, 83, 213, 214
-
-    Naiadaceæ, 492
-    Naiadales, 492
-    Naias, 492
-    Nemalion, 171, 172, 175
-    Nemalionales, 175
-    Nettle, 495
-    Nicotiana, 501
-    Nidulariales, 220
-    Nitella, 8, 9, 176
-    Nitrobacter, 83
-    Nitrogen, 92, 93
-    Nitromonas, 83
-    Nostocaceæ, 164
-    Nucellus, 304
-    Nucleus, 3, 4;
-       morphology of, 340-345
-    Nuphar advena, 496
-    Nutation, 123, 124
-    Nymphæa odorata, 496
-
-    Oak, 495
-    Oak family, 495
-    Œdogoniaceæ, 162
-    Œdogonium, 147-151, 350
-    Œnothera biennis, 498
-    Œnothera gigas, 338
-    Œnothera lamarkiana, 338
-    Olpidium, 214, 215
-    Onagar biennis, 498
-    Onagraceæ, 498
-    Onoclea sensibilis, 254, 273-278
-    Oogonium, 144, 150, 155
-    Oomycetes, 214, 215
-    Ophioglossales, 295
-    Ophioglossum, 295
-    Opuntiales, 498
-    Orchidaceæ, 494
-    Orchidales, 494
-    Orchids, 442
-    Oscillatoriaceæ, 163
-    Osmosis, 13-20
-    Osmundaceæ, 295
-    Ostrich fern, 279
-    Ovule, 302, 321, 334, 421
-    Oxalis, 497
-    Oxycoccus, 500
-    Oxydendrum arboreum, 501
-    Oxygen, 63, 110-113
-
-    Palisade cells, 41, 43
-    Palmaceæ, 493
-    Palmales, 493
-    Palms, 408
-    Pandanales, 492
-    Pandanus, 492
-    Pandorina, 160, 350
-    Panicle, 427
-    Papaverales, 496
-    Papilionaceæ, 423, 497
-    Parasites, 83, 84, 86
-    Parasitic fungi, nutrition of, 86-90
-    Parenchyma, 50, 356, 363
-    Parietales, 498
-    Parkeriaceæ, 296
-    Parmelia, 96
-    Parthenogenesis, 184
-    Partridge-berry, 501
-    Pea, 497
-    Pea family, 497
-    Pear, 456
-    Pediastrum, 161
-    Pellia, 164
-    Pellonia, 405
-    Peltigera, 94, 95
-    Pepo, 456
-    Pericycle, 360
-    Peridineæ, 166
-    Perigynous, 425
-    Perisperm, 331, 332
-    Perisporiales, 217
-    Peronospora, 183, 215
-    Peronosporales, 215
-    Persimmon, 500
-    Pezizales, 217
-    Phacidiales, 217
-    Phæophyceæ, 167
-    Phæosporales, 171
-    Phallales, 219
-    Phloem, 50-52, 360, 361, 363
-    Phlox family, 500
-    Phoradendron flavescens, 495
-    Photosynthesis, 67, 68, 70, 117
-    Phycomycetes (Phy″co-my-ce′tes), 214, 215
-    Phyllidium, 371
-    Phylloclades, 373, 395
-    Phyllotaxy, 375, 384
-    Physical condition of soil, 465
-    Physical factors, 465
-    Phytolaccaceæ, 495
-    Phytomyxa leguminosarum, 92
-    Phytophthora, 182, 184, 215
-    Pickerel-weed, 493
-    Pilularia, 296
-    Pinales, 216
-    Pine, white, 297-310
-    Piperales, 494
-    Pitcher-plant, 496
-    Pith, 50
-    Plant food, sources of, 81
-    Plant formations, 496
-    Plant substance, analysis of, 79, 80
-    Plantaginales, 501
-    Plantago, 501
-    Plasmolysis (plas-mol′y-sis), 19
-    Plasmopara, 183, 215
-    Plectascales, 217
-    Plectobasidiales, 220
-    Pleurococcaceæ, 161
-    Pleurococcus, 161
-    Plum family, 497
-    Plumule, 99
-    Podostemon, 496
-    Poison-hemlock, 499
-    Poison-ivy, 497
-    Poison-oak, 497
-    Poisonous mushrooms, 207, 208
-    Poison-sumac, 497
-    Pokeweed, 495
-    Polemoneales, 500
-    Pollen grain, 299, 305
-    Pollination, 303, 304, 420, 430, 433-449
-    Pollinium, 420
-    Polygonales, 495
-    Polygonum, 495
-    Polypodiaceæ, 296
-    Polyporaceæ, 209, 219
-    Polyporus, 209, 210
-    Polyporus mollis, 92
-    Polyporus sulphureus, 209
-    Pomaceæ, 497
-    Pondweeds, 492
-    Poppy, 496
-    Porella, 237
-    Portulaca, 495
-    Potamogeton, 492
-    Potato, 501
-    Powdery mildews, 195-198, 217
-    Primrose, 498, 500
-    Primula, 438
-    Primulales, 500
-    Procarp, 172, 174, 175
-    Progeotropism (pro″ge-ot′ro-pism), 126
-    Promycelium (pro″my-ce′li-um), 192
-    Proterandrous, 441, 442
-    Proterandry, 444
-    Proterogenous, 441, 442
-    Proterogeny, 440
-    Prothallium, 265, 287, 288, 291, 292, 304, 305,
-                 311, 325, 328, 335, 433, 434
-    Protoascales, 216
-    Protoascomycetes, 216
-    Protobasidiomycetes, 218
-    Protococcoideæ, 158, 162
-    Protodiscales, 217
-    Protomyces, 216
-    Protonema (pro″to-ne′ma), 248, 264
-    Protoplasm, 1-12, 42-43, 342;
-       movement of, 7-11
-    Psilotaceæ, 296
-    Pteridophytes, 295, 434
-    Pteris cretica, 346
-    Puccinia, 187
-    Puff-balls, 220
-    Pumpkin, 501
-    Purslane, 495
-    Pyrenoid, 2, 3
-    Pyrenomycetes, 217
-    Pyrola, 499
-    Pyxidium, 453
-
-    Quercus, 495
-    Quillworts, 289-291
-    Quince, 456
-
-    Raceme, 427
-    Radicle, 99
-    Ragweed, 502
-    Rainy-season flora, 481
-    Ranales, 496
-    Ranunculaceæ, 496
-    Raspberry, 454, 455
-    Red algæ, 171, 174;
-       uses of, 175
-    Reproduction, 137, 143, 149, 154, 155, 179, 185, 186
-    Respiration, 110-116, 117
-    Rhamnales, 498
-    Rhizoids, 24-26
-    Rhizome, 354
-    Rhizomorph (rhi′zo-morph), 89
-    Rhizophidium, 214, 215
-    Rhizopus, 177-180, 215
-    Rhododendron, 499
-    Rhodomeniales, 175
-    Rhodophyceæ, 171
-    Rhus radicans, 416, 497
-    Riccia, 23, 164, 222-226
-    Ricinus, 497
-    Riverweed, 496
-    Root, function of, 410-418
-    Root hairs, absorption by, 19, 30, 32
-    Root hairs, action on soil, 82
-    Root pressure, 33, 34, 45
-    Root, structure of, 30, 361, 362
-    Root-tubercles, 92
-    Roots, kinds of, 415
-    Rosaceæ, 497
-    Rosales, 496
-    Rose family, 497
-    Rosette, 405
-    Rosette plants, 483
-    Rubiales, 501
-    Rudbeckia, 502
-    Rusts, 187-194
-
-    Salicaceæ, 494
-    Salix, 494
-    Salsify, 502
-    Salviniaceæ, 296
-    Samara, 451
-    Sandalwood, 495
-    Sanguinaria, 496
-    Santalales, 495
-    Sap, rise of, 53, 54
-    Sapindales, 497
-    Saprolegnia, 181-184
-    Saprolegniales, 215
-    Saprophytes, 83-85
-    Sargassum, 170
-    Sarraceniales, 496
-    Sarsaparilla, 499
-    Saxifrage, 496
-    Schizæaceæ, 295
-    Schizocarp, 451
-    Schizomycetes, 164
-    Schizophyceæ, 163
-    Sclerenchyma, 356-357, 361, 363
-    Scouring rush, 282
-    Screw-pine, 409, 492
-    Scrophulariaceæ, 501
-    Sedge family, 492
-    Seed, dispersal of, 458-463
-    Seed plants, 338
-    Seed, structure of, 98, 102
-    Seedlings, 97-107
-    Seeds, 330-334
-    Selaginella, 286-288, 292
-    Selaginellaceæ, 296
-    Sensitive fern, 273
-    Sensitive plants, 132, 396, 399
-    Sexual organs, 144, 147
-    Shadbush, 497
-    Shepherd’s-purse, 496
-    Shoot, floral, 419, 432
-    Shoots, 353-355;
-       types of, 361-373;
-       winter condition of, 374-377
-    Sieve tissue, 358, 363
-    Sieve tubes, 52, 53
-    Silique, 453
-    Silk-cotton tree, 417
-    Silver bell, 500
-    Siphoneæ, 146, 162
-    Skunk’s cabbage, 439-442
-    Slime molds, 83
-    Smoke-tree, 497
-    Societies, 475
-    Solanum, 501
-    Solidago, 502
-    Sourwood, 499
-    Spadix, 428
-    Spartium, 446
-    Spathyema fœtida, 438, 493
-    Spermagonia, 190
-    Spermatophytes, 338
-    Sphacelaria, 168
-    Sphærella lacustris, 158, 159
-    Sphærella nivalis, 158, 350
-    Sphæriales, 218
-    Sphagnales, 248
-    Sphagnum, 164
-    Spiderwort, 11, 493
-    Spike, 428
-    Spirodela polyrhiza, 27
-    Spirogyra, 1-5, 13, 14, 60, 72, 136-140, 350
-    Sporangia, 178-182
-    Sporangium, 253-258, 281, 290
-    Spores, 225, 256-258, 263, 264, 281
-    Sporocarp, 173
-    Sporogonium (spo″ro-go′ni-um), 224, 231, 233, 234, 237, 238,
-                                    239, 241, 246, 247, 248
-    Sporophyll, 274, 281, 292
-    Sporophyte (spo′ro-phyte), 225, 226, 232, 234, 237-239, 241, 242,
-                               250, 261, 268, 270, 283, 292, 294, 314,
-                               315, 317, 336-339, 340-348 434
-    Spurge family, 497
-    Squash, 501
-    Staminodium, 446
-    Starch, formation of, 68, 70-74;
-       changed to sugar, 77, 78;
-       translocation of, 73;
-       digestion of, 75
-    Stems, types of, 365-373
-    Stems, woody, structure of, 381-382
-    Stoma (pl. stomata) (sto′ma-ta), 42-44, 46
-    Strawberry, 455, 497
-    Sugar, test for, 75, 76
-    Sumac, 497
-    Sundew, 133, 496
-    Sunflower, 399-401, 502
-    Sweet gum, 496
-    Symbiosis, 85, 86, 92-95
-    Synergids (syn´er-gids), 327, 330
-    Syngenœsious, 424
-    Synthetic assimilation, 67
-
-    Tape-grass, 493
-    Taraxacum densleonis, 502
-    Teasel, 501
-    Telegraph-plant, 399
-    Teleutospore, 188
-    Temperature, 134, 135, 465
-    Tetrasporaceæ, 161
-    Tetraspores, 173, 174
-    Thallophytes, 352
-    Thallus, 352
-    Thelephoraceæ, 219
-    Thistle family, 502
-    Thunderwood, 497
-    Thyrsus, 427
-    Tilia, 498
-    Tillandsia, 493
-    Tissue, tensions of, 57-59
-    Tissues, classification of, 363, 364;
-       kinds of, 356-359;
-       organization of, 356-362
-    Toad-flax, 501
-    Tomato, 501
-    Tradescantia, 493
-    Tragopogon, 502
-    Trailing arbutus, 499
-    Trametes pini, 90
-    Transpiration, 35-46
-    Tremellales, 218, 219
-    Triadelphous, 425
-    Trillium, 318-322, 494
-    Trumpet-creeper, 501
-    Tuberales, 217
-    Tubers, 373
-    Tundra, 481
-    Turgescence, 14, 15
-    Turgor, 20;
-       restoration of, 56, 57
-    Typha, 493
-
-    Ulmaceæ, 495
-    Ulmus americana, 495
-    Ulothrix, 162
-    Ulotrichaceæ, 162
-    Ulvaceæ, 162
-    Umbel, 428
-    Umbellales, 498
-    Uredinales, 218
-    Uredineæ, 187-194, 218
-    Uredospore, 189
-    Uromyces caryophyllinus, 87
-    Urticales, 495
-    Ustilaginales, 218
-    Ustilagineæ, 218
-    Utricularia, 501
-
-    Vaccinium, 499
-    Vacuoles, 7, 8
-    Valerianales, 501
-    Vallisneria spiralis, 493
-    Variation, 338
-    Vascular tissue, 358, 363
-    Vaucheria, 142-146
-    Vaucheriaceæ, 162
-    Vegetation types, 464
-    Venus fly-trap, 133
-    Verbascum, 501
-    Verbena, 501
-    Vessels, 52, 53
-    Vetch, 92, 497
-    Viburnum, 501
-    Vicia sativa, 459
-    Viola cucullata, 436
-    Violaceæ, 498
-    Virgin’s bower, 462, 463
-    Viscum album, 84
-    Vitaceæ, 498
-    Volvocaceæ, 158
-
-    Walnut, 452, 494
-    Water, 465;
-       flow of, in plants, 53, 54
-    Water-lilies, 496
-    Water-plantain, 493
-    White pine, 396
-    Wild carrot, 499
-    Willow family, 494
-    Wind, 471
-    Wintergreen, 499;
-       leaf of, 43
-    Witch-hazel, 496
-    Wolffia, 28
-    Woodland formation, 470
-
-    Xerophytes, 467
-    Xylem, 50, 52, 360, 361, 363
-    Xylogen, 92
-    Xyridales, 493
-
-    Yeast, 216;
-       fermentation of, 115, 116
-    Yucca, 480, 493
-
-    Zamia, 313, 316, 457
-    Zoogonidia, 143, 149, 178-184
-    Zoospore, 149, 154
-    Zygomycetes, 215
-    Zygospore, 2, 138-140, 157, 160, 179, 180
-    Zygote (zy′gote), 138, 179
-
-
-
-
-TWO NOTABLE NATURE BOOKS.
-
-
-                         FERNS
-
-    A Manual for the Northeastern States. By C. E. WATERS,
-      Ph.D. (Johns Hopkins). With Analytical Keys Based
-      on the Stalks. _With over 200 illustrations_ from
-      original drawings and photographs. 362 pp. Square
-      8vo. Boxed. $3.00 _net_. (By mail, $3.34.)
-
-      A popular, but thoroughly scientific book, including
-    all the ferns in the region covered by Britton’s
-    Manual. Much information is also given concerning
-    reproduction and classification, fern photography, etc.
-
-                PROF. L. M. UNDERWOOD, OF COLUMBIA:
-          “It is really more scientific than one would
-        expect from a work of a somewhat popular nature.
-        The photographs are very fine, very carefully
-        selected and will add much to the text. I do not
-        see how they could be much finer.”
-
-                      THE PLANT WORLD:
-          “This book is likely to prove the leading popular
-        work on ferns. The majority of the illustrations
-        are from original photographs; in respect to this
-        feature, it can be confidently asserted that _no
-        finer examples of fern photography have ever been
-        produced_.... May be expected to prove of permanent
-        scientific value, as well as to satisfy a want
-        which existing treatises have but imperfectly
-        filled.”
-
-
-                          MUSHROOMS
-
-    Edible, Poisonous Mushrooms, etc. By Prof. GEO. F. ATKINSON,
-        of Cornell.
-
-          With recipes for cooking by Mrs. S. T. RORER, and
-        the chemistry and toxicology of mushrooms, by J.
-        F. CLARK. With 230 illustrations from photographs,
-        including fifteen colored plates. 320pp. 8vo. $3.00
-        _net_ (by mail, $3.23).
-
-      Among the additions in this second edition are ten
-    new plates, chapters on the “Uses of Mushrooms,” and on
-    the “Cultivation of Mushrooms,” illustrated by several
-    flash-light photographs.
-
-                     EDUCATIONAL REVIEW:
-          “It would be difficult to conceive of a more
-        attractive and useful book, nor one that is
-        destined to exert a greater influence in the study
-        of an important class of plants that have been
-        overlooked and avoided simply because of ignorance
-        of their qualities, and the want of a suitable
-        book of low price. In addition to its general
-        attractiveness and the beauty of its illustrations,
-        it is written in a style well calculated to win the
-        merest tyro or the most accomplished student of the
-        fungi.... These clear photographs and the plain
-        descriptions make the book especially valuable for
-        the amateur fungus hunter in picking out the edible
-        from the poisonous species of the most common
-        kinds.”
-
-                         THE PLANT WORLD:
-          “This is, without doubt, the most important and
-        valuable work of its kind that has appeared in this
-        country in recent years.... No student, either
-        amateur or professional, can afford to be without
-        it.”
-
-                        HENRY HOLT AND COMPANY,
-                NEW YORK.     (xii, ’03).     CHICAGO.
-
-
-
-
-                =BRITTON’S MANUAL OF THE FLORA OF THE
-                    NORTHERN STATES AND CANADA.=
-
-              By Director N. L. BRITTON
-                        of the New York Botanical Garden.
-                        1080 pp. 8vo. $2.25, net.
-
-      A comprehensive manual of over a thousand pages, containing
-    about 4,500 descriptions, probably one-third more than any other.
-    It is designed to meet modern requirements and outline modern
-    conceptions of the science. It is based on _An Illustrated
-    Flora_, prepared by Prof. Britton in co-operation with Judge
-    Addison Brown. The text has been revised and brought up to
-    date, and much of novelty has been added. All illustrations are
-    omitted, but specific reference has been made to all of the 4,162
-    figures in the _Illustrated Flora_.
-
-      “It is the most complete and reliable work that ever appeared
-    in the form of a flora of this region, and for the first time we
-    have a manual in which the plant descriptions are drawn from the
-    plants themselves, and do not represent compiled descriptions
-    made by the early writers.”—Prof. D. M. Underwood of Columbia.
-
-      “This work will at once take its place as the standard manual
-    of the region that it covers. It is far superior to any other
-    work of its class ever published in America.”—Prof. Conway
-    MacMillan of University of Minnesota.
-
-      “This book must at once find its way into the schools and
-    colleges, to which it may be commended for the students in
-    systematic botany.”—Prof. Chas. E. Bessey in “Science.”
-
-      “It is nothing if it is not compact; it is nothing if it is
-    not up to date; it is nothing if it is not the work of a master.
-    What more can be said, save that the more it is used the greater
-    the appreciation by the plant-lovers in the region which it
-    covers.”—Prof. Byron D. Halsted of Rutgers College.
-
-      “The work is well done; and as it is the only volume which
-    gives in a way suitable for students the present state of
-    the science, it cannot fail to take its place as a standard
-    work.”—Prof. George Macloskie of Princeton.
-
-      “I regard the book as one that we cannot do without and one
-    that will henceforth take its place as a necessary means of
-    determination of the plant species within its range.”—Prof. V.
-    M. Spalding of University of Michigan.
-
-      “An exceedingly valuable contribution to our botanical
-    literature.... It is convenient to handle, and the low price will
-    help to give it a large circulation.”—Prof. T. J. Burrill of the
-    University of Illinois.
-
-                           HENRY HOLT & CO.
-                   =29 West 23d Street, New York=
-                    =378 Wabash Avenue, Chicago=
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-                 CHAMPLIN’S YOUNG FOLKS’
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-
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-
-        A whole “nature library” about animals prepared by
-      experts. Scientific facts are presented in simple
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-                   Cyclopædia of Literature and Art
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-        illustrative. Old pictures and sculpture are
-        presented in the usual line of drawings, but modern
-        scenes and buildings are pictured through excellent
-        half-tone reproductions of photographs.”—_N. Y.
-        Times Saturday Review._
-
-       Earlier Volumes of Champlin’s Young Folks’ Cyclopædia.
-            With numerous illustrations. 8vo. $2.50 each.
-
-            COMMON THINGS.             PERSONS and PLACES.
-                        GAMES and SPORTS.
-
-     ⁂ _12-page circular, with sample pages of Champlin’s Young
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-
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-
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-            and Dr. W. W. RANDALL. (_For Briefer
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-             and ROLLIN D. SALISBURY,
-             Univ. of Chicago. Vol. I., 684 pp.,          $4.00.
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-            University of Idaho. 413 pp. 12mo.            60c., _net_.
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-                        Physical Science
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-            Principles of Chemistry.
-            By Prof. A. A. NOYES,
-            Mass. Institute of Technology. 160 pp. 8vo.  $1.50, _net_.
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-            By Prof. WM. A. NOYES,
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-
-        Qualitative Analysis (Elementary) x + 91 pp. 8vo.  80c., _net_.
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-          is one of the indispensable books for the library
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-          in Harvard University_:—The book appears to
-          be an excellent statement of modern American
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-          based upon the most recent work of government and
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-
-
-
-THE METRIC SYSTEM.
-
-
-[Illustration: 10-centimeter rule. The upper edge is in millimeters,
-the lower in centimeters and half centimeters.]
-
-   UNITS.           THE MOST COMMONLY USED DIVISIONS AND MULTIPLES.
-
-               { _Centimeter_ (cm), 1/100 meter; _Millimeter_ (mm),
-               { 1/1000 meter; _Micron_ (μ), 1/1000 millimeter.
-THE METER, for {    The micron is the unit in micrometry.
-  LENGTH       { _Kilometer_, 1000 meters; used in measuring roads and
-               {    other long distances.
-
-               { _Milligram_ (mg), 1/1000 gram.
-THE GRAM, for  { _Kilogram_, 1000 grams, used for ordinary masses, like
-  WEIGHT       {    groceries, etc.
-
-THE LITER, for { _Cubic Centimeter_ (cc), 1/1000 liter. This is more
-  CAPACITY     {    common than the correct form, Milliliter.
-
-_Divisions_ of the _units_ are indicated by Latin prefixes: _deci_,
-1/10; _centi_, 1/100; _milli_, 1/1000.
-
-_Multiples_ are designated by Greek prefixes: _deka_, 10 times;
-_hecto_, 100 times; _kilo_, 1000 times; _myria_, 10,000 times.
-
-
-TABLE OF METRIC AND ENGLISH MEASURES.
-
-METER = 100 centimeters, 1000 millimeters, 1,000,000 microns,
-39.3704 inches.
-
-Millimeter (mm) = 1000 microns, 1/10 millimeter, 1/1000 meter, 1/25
-inch, approximately.
-
-MICRON (μ) (unit of measure in micrometry) = 1/1000 mm,
-1/1000000 meter (0.000039 inch), 1/25000 inch, approximately.
-
-Inch (in.) = 25.399772 mm (25.4 mm, approx.).
-
-LITER = 1000 milliliters or 1000 cubic centimeters, 1 quart
-(approx.).
-
-Cubic centimeter (cc or cctm) = 1/1000 liter.
-
-Fluid ounce (8 fluidrachms) = 29.578 cc (30 cc, approx.).
-
-GRAM = 15.432 grains.
-
-Kilogram (kilo) = 2.204 avoirdupois pounds (2⅕ pounds, approx.).
-
-  Ounce Avoirdupois (437½ grains) = 28.349 grams          } (30 grams,
-  Ounce Troy or Apothecaries’ (480 grains) = 31.103 grams }   approx.).
-
-
-TEMPERATURE.
-
-  To change Centigrade to Fahrenheit: (C. × ⁹/₅) + 32 = F.
-  For example, to find the equivalent of 10° Centigrade,
-             C. = 10°, (10° × ⁹/₅) + 32 = 50° F.
-
-  To change Fahrenheit to Centigrade: (F. - 32°) × ⁵/₉ = C.
-  For example, to reduce 50° Fahrenheit to Centigrade,
-             F. = 50°, and (50° - 32°) × ⁵/₉ = 10° C.;
-  or - 40° Fahrenheit to Centigrade,
-             F. = - 40°, (- 40° - 32°) = - 72°,
-  whence - 72° × ⁵/₉; = - 40° C.
-
-              —_From “The Microscope” (by S. H. Gage) by permission._
-
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-<div style='text-align:center; font-size:1.2em; font-weight:bold'>The Project Gutenberg eBook of Elementary Botany, by George Francis Atkinson</div>
-
-<div style='display:block; margin:1em 0'>
-This eBook is for the use of anyone anywhere in the United States and
-most other parts of the world at no cost and with almost no restrictions
-whatsoever. You may copy it, give it away or re-use it under the terms
-of the Project Gutenberg License included with this eBook or online
-at <a href="https://www.gutenberg.org">www.gutenberg.org</a>. If you
-are not located in the United States, you will have to check the laws of the
-country where you are located before using this eBook.
-</div>
-
-<div style='display:block; margin-top:1em; margin-bottom:1em; margin-left:2em; text-indent:-2em'>Title: Elementary Botany</div>
-
-<div style='display:block; margin-top:1em; margin-bottom:1em; margin-left:2em; text-indent:-2em'>Author: George Francis Atkinson</div>
-
-<div style='display:block; margin:1em 0'>Release Date: February 20, 2021 [eBook #64601]</div>
-
-<div style='display:block; margin:1em 0'>Language: English</div>
-
-<div style='display:block; margin:1em 0'>Character set encoding: UTF-8</div>
-
-<div style='display:block; margin-left:2em; text-indent:-2em'>Produced by: Sonya Schermann and the Online Distributed Proofreading Team at https://www.pgdp.net (This file was produced from images generously made available by The Internet Archive)</div>
-
-<div style='margin-top:2em; margin-bottom:4em'>*** START OF THE PROJECT GUTENBERG EBOOK ELEMENTARY BOTANY ***</div>
-<hr class="chap" />
-
-<div class="figcenter">
-    <img src="images/frontis.jpg" alt="" width="600" height="369" />
-   <div class="blockquot">
-    <p class="center"><span class="smcap">Cycas revoluta</span> (<a href="#Page_311">see page 311</a>).</p>
-    <p class="author">(<i>Frontispiece.</i>)</p>
-   </div>
-</div>
-<hr class="chap" />
-<h1>ELEMENTARY BOTANY</h1>
-
-<p class="f90 space-above3">BY</p>
-<p class="center">GEORGE FRANCIS ATKINSON, <span class="smcap">Ph.B.</span></p>
-<p class="f90"><i>Professor of Botany in Cornell University</i></p>
-
-<p class="center space-above2 space-below2"><i>THIRD EDITION, REVISED</i></p>
-
-<div class="figcenter">
-    <img src="images/logo.jpg" alt="" width="150" height="129" />
-</div>
-
-<p class="center space-above2">NEW YORK<br />HENRY HOLT AND COMPANY<br />1905</p>
-
-<p class="center space-above2 space-below2 ">Copyright, 1898, 1905<br />BY<br />
-HENRY HOLT AND COMPANY</p>
-
-<p class="center space-below2">ROBERT DRUMMOND, PRINTER, NEW YORK</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_iii" id="Page_iii">[Pg iii]</a></span></p>
-
-<div class="chapter"><h2 class="nobreak">PREFACE.</h2></div>
-
-<p>The present book is the result of a revision and elaboration of the
-author’s “Elementary Botany,” New York, 1898. The general plan of the
-parts on physiology and general morphology remains unchanged. A number
-of the chapters in the physiological part are practically untouched,
-while others are thoroughly revised and considerable new matter is
-added, especially on the subjects of nutrition and digestion. The
-principal chapters on general morphology are unchanged or only slightly
-modified, the greatest change being in a revision of the subject of
-the morphology of fertilization in the gymnosperms and angiosperms in
-order to bring this subject abreast of the discoveries of the past few
-years. One of the greatest modifications has been in the addition of
-chapters on the classification of the algæ and fungi with studies of
-additional examples for the benefit of those schools where the time
-allowed for the first year’s course makes desirable the examination of
-a broader range of representative plants. The classification is also
-carried out with greater definiteness, so that the regular sequence
-of classes, orders, and families is given at the close of each of the
-subkingdoms. Thus all the classes, all the orders (except a few in the
-algæ), and many of the families, are given for the algæ, fungi, mosses,
-liverworts, pteridophytes, gymnosperms, and angiosperms.</p>
-
-<p>But by far the greatest improvement has been in the complete
-reorganization, rewriting, and elaboration of the part dealing with
-ecology, which has been made possible by studies of the past few years,
-so that the subject can be presented in a more logical and coherent
-<span class="pagenum"><a name="Page_iv" id="Page_iv">[Pg iv]</a></span>
-form. As a result the subject-matter of the book falls naturally into
-three parts, which may be passed in review as follows:</p>
-
-<p>Part I. <i>Physiology.</i> This deals with the life processes of plants,
-as absorption, transpiration, conduction, photosynthesis, nutrition,
-assimilation, digestion, respiration, growth, and irritability. Since
-protoplasm is fundamental to all the life work of the plant, this
-subject is dealt with first, and the student is led through the study
-of, and experimentation with, the simpler as well as some of the higher
-plants, to a general understanding of protoplasm and the special way in
-which it enables the plant to carry on its work and to adjust itself to
-the conditions of its existence. This study also serves the purpose of
-familiarizing the pupil with some of the lower and unfamiliar plants.</p>
-
-<p>Some teachers will prefer to begin the study with general morphology
-and classification, thus studying first the representatives of the
-great groups of plants, and others will prefer to dwell first on the
-ecological aspects of vegetation. This can be done in the use of this
-book by beginning with Part II or with Part III.</p>
-
-<p>But the author believes that morphology can best be comprehended after
-a general study of life processes and functions of the different parts
-of plants, including in this study some of the lower forms of plant
-life where some of these processes can more readily be observed. The
-pupil is then prepared for a more intelligent consideration of general
-and comparative morphology and relationships. Even more important is
-a first study of physiology before taking up the subject of ecology.
-The great value to be derived from a study of plants in their relation
-to environment lies in the ability to interpret the different states,
-conditions, behavior, and associations of the plant, and for this
-physiology is indispensable. It is true that a considerable measure
-of success can be obtained by a good teacher in beginning with either
-subject, but the writer believes that measure of success would be
-greater if the subjects were taken up in the order presented here.
-<span class="pagenum"><a name="Page_v" id="Page_v">[Pg v]</a></span></p>
-
-<p>Part II. <i>Morphology and life history of representative plants.</i> This
-includes a rather careful study of representative examples among the
-algæ, fungi, liverworts, mosses, ferns and their allies, gymnosperms
-and angiosperms, with especial emphasis on the form of plant parts,
-and a comparison of them in the different groups, with a comparative
-study of development, reproduction, and fertilization, rounding out
-the work with a study of life histories and noting progression and
-retrogression of certain organs and phases in proceeding from the
-lower to the higher plants. Thus, in the algæ a first critical study
-is made of four examples which illustrate in a marked way progressive
-stages of the plant body, sexual organs, and reproduction. Additional
-examples are then studied for the purpose of acquiring a knowledge of
-variations from these types and to give a broader basis for the brief
-consideration of general relationships and classification.</p>
-
-<p>A similar plan is followed in the other great groups. The processes of
-fertilization and reproduction can be most easily observed in the lower
-plants like the algæ and fungi, and this is an additional argument in
-favor of giving emphasis to these forms of plant life as well as the
-advantage of proceeding logically from simpler to more complex forms.
-Having also learned some of these plants in our study of physiology,
-we are following another recognized rule of pedagogy, i.e., proceeding
-from known objects to unknown structures and processes. Through
-the study of the organs of reproduction of the lower plants and by
-general comparative morphology we have come to an understanding of the
-morphology of the parts of the flower, and of the true sexual organs
-of the seed plants, and no student can hope to properly interpret the
-significance of the flower, or the sexual organs of the seed plants who
-neglects a careful study of the general morphology of the lower plants.</p>
-
-<p>Part III. <i>Plant members in relation to environment.</i> This part deals
-with the organization of the plant body as a whole in its relation to
-environment, the organization of plant tissues with a discussion of
-the principal tissues and a descriptive synopsis of the same. This is
-<span class="pagenum"><a name="Page_vi" id="Page_vi">[Pg vi]</a></span>
-followed by a complete study from a biological standpoint of the
-different members of the plant, their special function and their
-special relations to environment. The stem, root, leaf, flower, etc.,
-are carefully examined and their ecological relations pointed out. This
-together with the study of physiology and representatives in the groups
-of plants forms a thorough basis for pure plant ecology, or the special
-study of vegetation in its relation to environment.</p>
-
-<p>There is a study of the factors of environment or ecological factors,
-which in general are grouped under the physical, climatic, and biotic
-factors. This is followed by an analysis of vegetation forms and
-structures, plant formations and societies. Then in order are treated
-briefly forest societies, prairie societies, desert societies, arctic
-and alpine societies, aquatic societies, and the special societies of
-sandy, rocky, and marshy places.</p>
-
-<p><i>Acknowledgments.</i> The author wishes to express his gratefulness to
-all those who have given aid in the preparation of this work, or of
-the earlier editions of Elementary Botany; to his associates, Dr.
-E. J. Durand, Dr. K. M. Wiegand, and Professor W. W. Rowlee, of the
-botanical department, and to Professor B. M. Duggar of the University
-of Missouri, Professor J. C. Arthur of Purdue University, and Professor
-W. F. Ganong of Smith College, for reading one or more portions of the
-text; as well as to all those who have contributed illustrations.</p>
-
-<p><i>Illustrations.</i> The large majority of the illustrations are new
-(or are the same as those used in earlier editions of the author’s
-Elementary Botany) and were made with special reference to the method
-of treatment followed in the text. Many of the photographs were made
-by the author. Others were contributed by Professor Rowlee of Cornell
-University; Mr. John Gifford of New Jersey; Professor B. M. Duggar,
-University of Missouri; Professor C. E. Bessey, University of Nebraska;
-Dr. M. B. Howe, New York Botanical Garden; Mr. Gifford Pinchot, Chief
-of the Bureau of Forestry; Mr. B. T. Galloway, Chief of the Bureau of
-Plant Industry; Professor Tuomey of Yale University; and Mr. E. H.
-Harriman, who through Dr. C. H. Merriam of the National Museum allowed
-<span class="pagenum"><a name="Page_vii" id="Page_vii">[Pg vii]</a></span>
-the use of several of his copyrighted photographs from Alaska. To those
-who have contributed drawings the author is indebted as follows: to
-Professor Margaret C. Ferguson, Wellesley College; Professor Bertha
-Stoneman of Huguenot College, South Africa; Mr. H. Hasselbring of
-Chicago; Dr. K. Miyake, formerly of Cornell University and now of
-Doshisha College, Japan; and Professors Ikeno and Hirase of the Tokio
-Imperial University. The author is also indebted to Ginn &amp; Co., Boston,
-for the privilege to use from his “First Studies of Plant Life” the
-following figures: 28, 29, 46, 48, 49, 56, 62, 66, 67, 87, 102, 103,
-422-426, 429, 430, 438-440, 443, 444, 448, 449, 452, 472-475. A few
-others are acknowledged in the text.</p>
-
-<p><span class="smcap">Cornell University</span>, April, 1905.</p>
-<p><span class="pagenum"><a name="Page_viii" id="Page_viii">[Pg viii]</a></span></p>
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_ix" id="Page_ix">[Pg ix]</a></span></p>
-
-<div class="chapter"><h2 class="nobreak">TABLE OF CONTENTS.</h2></div>
-
-<table border="0" cellspacing="0" summary="TOC" cellpadding="0" >
-  <tbody><tr>
-      <td class="tdc lgfnt150" colspan="2">PART I.&emsp;PHYSIOLOGY.</td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER I.</td>
-   </tr><tr>
-      <td class="tdr " colspan="2"><small>PAGE</small></td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Protoplasm.</span></td>
-      <td class="tdr"><a href="#CHAPTER_I">&nbsp;1</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER II.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Absorption, Diffusion, Osmose.</span></td>
-      <td class="tdr"><a href="#CHAPTER_II">13</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER III.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">How Plants Obtain Water.</span></td>
-      <td class="tdr"><a href="#CHAPTER_III">22</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER IV.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Transpiration, or the Loss of Water by Plants.</span></td>
-      <td class="tdr"><a href="#CHAPTER_IV">35</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER V.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Path of Movement of Water in Plants.</span></td>
-      <td class="tdr"><a href="#CHAPTER_V">48</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER VI.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Mechanical Uses of Water.</span></td>
-      <td class="tdr"><a href="#CHAPTER_VI">56</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER VII.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Starch and Sugar Formation.</span></td>
-      <td class="tdr"><a href="#CHAPTER_VII">60</a></td>
-   </tr><tr>
-      <td class="tdl_ws1">1. The Gases Concerned.</td>
-      <td class="tdr"><a href="#VII_1">60</a></td>
-   </tr><tr>
-      <td class="tdl_ws1">2. Where Starch is Formed.</td>
-      <td class="tdr"><a href="#VII_2">64</a></td>
-   </tr><tr>
-      <td class="tdl_ws1">3. Chlorophyll and the Formation of Starch.</td>
-      <td class="tdr"><a href="#VII_3">67</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER VIII.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Starch and Sugar Concluded; Analysis of Plant Substance.</span></td>
-      <td class="tdr"><a href="#CHAPTER_VIII">73</a></td>
-   </tr><tr>
-      <td class="tdl_ws1">1. Translocation of Starch.</td>
-      <td class="tdr"><a href="#VIII_1">73</a></td>
-   </tr><tr>
-      <td class="tdl_ws1">2. Sugar, and Digestion of Starch.</td>
-      <td class="tdr"><a href="#VIII_2">75</a>
-              <span class="pagenum"><a name="Page_x" id="Page_x">[Pg x]</a></span></td>
-   </tr><tr>
-      <td class="tdl_ws1">3. Rough Analysis of Plant Substance.</td>
-      <td class="tdr"><a href="#VIII_3">79</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER IX.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">How Plants Obtain their Food, I.</span></td>
-      <td class="tdr"><a href="#CHAPTER_IX">81</a></td>
-   </tr><tr>
-      <td class="tdl_ws1">1. Sources of Plant Food.</td>
-      <td class="tdr"><a href="#IX_1">81</a></td>
-   </tr><tr>
-      <td class="tdl_ws1">2. Parasites and Saprophytes.</td>
-      <td class="tdr"><a href="#IX_2">83</a></td>
-   </tr><tr>
-      <td class="tdl_ws1">3. How Fungi Obtain their Food.</td>
-      <td class="tdr"><a href="#IX_3">86</a></td>
-   </tr><tr>
-      <td class="tdl_ws1">4. Mycorhiza.</td>
-      <td class="tdr"><a href="#IX_4">91</a></td>
-   </tr><tr>
-      <td class="tdl_ws1">5. Nitrogen gatherers.</td>
-      <td class="tdr"><a href="#IX_5">92</a></td>
-   </tr><tr>
-      <td class="tdl_ws1">6. Lichens.</td>
-      <td class="tdr"><a href="#IX_6">93</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER X.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">How Plants Obtain their Food, II.</span></td>
-      <td class="tdr"><a href="#CHAPTER_X">97</a></td>
-   </tr><tr>
-      <td class="tdl_ws1">&emsp;Seedlings,</td>
-      <td class="tdr"><a href="#X_1">97</a></td>
-   </tr><tr>
-      <td class="tdl_ws1">&emsp;Digestion,</td>
-      <td class="tdr"><a href="#X_2">107</a></td>
-   </tr><tr>
-      <td class="tdl_ws1">&emsp;Assimilation</td>
-      <td class="tdr"><a href="#X_3">109</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XI.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Respiration.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XI">110</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XII.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Growth.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XII">118</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XIII.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Irritability.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XIII">125</a></td>
-   </tr><tr>
-      <td class="tdc_space-above2 lgfnt150" colspan="2">PART II.&emsp;MORPHOLOGY AND LIFE HISTORY<br />
-                                    OF REPRESENTATIVE PLANTS.</td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XIV.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Spirogyra.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XIV">136</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XV.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Vaucheria.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XV">142</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XVI.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Œdogonium.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XVI">147</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XVII.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Coleochæte.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XVII">153</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XVIII.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Classification and Additional Studies of the Algæ.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XVIII">158</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XIX.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Fungi: Mucor and Saprolegnia.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XIX">177</a>
-                 <span class="pagenum"><a name="Page_xi" id="Page_xi">[Pg xi]</a></span></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XX.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Fungi Continued</span> (“Rusts” Uredineæ).</td>
-      <td class="tdr"><a href="#CHAPTER_XX">187</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXI.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">The Higher Fungi.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XXI">195</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXII.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Classification of the Fungi.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XXII">213</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXIII.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Liverworts</span> (Hepaticæ).</td>
-      <td class="tdr"><a href="#CHAPTER_XXIII">222</a></td>
-   </tr><tr>
-      <td class="tdl_ws1">Riccia,</td>
-      <td class="tdr"><a href="#XXIII_1">222</a></td>
-   </tr><tr>
-      <td class="tdl_ws1">Marchantia.</td>
-      <td class="tdr"><a href="#XXIII_2">226</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXIV.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Liverworts Continued.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XXIV">231</a></td>
-   </tr><tr>
-      <td class="tdl_ws1">Sporogonium of Marchantia.</td>
-      <td class="tdr"><a href="#XXIV_1">231</a></td>
-   </tr><tr>
-      <td class="tdl_ws1">Leafy-stemmed Liverworts.</td>
-      <td class="tdr"><a href="#XXIV_2">236</a></td>
-   </tr><tr>
-      <td class="tdl_ws1">The Horned Liverworts.</td>
-      <td class="tdr"><a href="#XXIV_3">240</a></td>
-   </tr><tr>
-      <td class="tdl_ws1">Classification of the Liverworts.</td>
-      <td class="tdr"><a href="#XXIV_4">242</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXV.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Mosses</span> (Musci).</td>
-      <td class="tdr"><a href="#CHAPTER_XXV">243</a></td>
-   </tr><tr>
-      <td class="tdl_ws1">Classification of Mosses.</td>
-      <td class="tdr"><a href="#XXV_1">248</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXVI.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Ferns.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XXVI">251</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXVII.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Ferns Continued.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XXVII">262</a></td>
-   </tr><tr>
-      <td class="tdl_ws1">Gametophyte of Ferns.</td>
-      <td class="tdr"><a href="#XXVII_1">262</a></td>
-   </tr><tr>
-      <td class="tdl_ws1">Sporophyte.</td>
-      <td class="tdr"><a href="#XXVII_2">268</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXVIII.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Dimorphism of Ferns.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XXVIII">273</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXIX.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Horsetails.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XXIX">280</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXX.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Club mosses.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XXX">284</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXXI.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Quillworts</span> (Isoetes).</td>
-      <td class="tdr"><a href="#CHAPTER_XXXI">289</a>
-                   <span class="pagenum"><a name="Page_xii" id="Page_xii">[Pg xii]</a></span></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXXII.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Comparison of Ferns and their Relatives.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XXXII">292</a></td>
-   </tr><tr>
-      <td class="tdl_ws1">Classification of the Pteridophytes.</td>
-      <td class="tdr"><a href="#XXXII_1">295</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXXIII.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Gymnosperms.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XXXIII">297</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXXIV.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Further Studies on Gymnosperms.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XXXIV">311</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXXV.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Morphology of the Angiosperms: Trillium; Dentaria.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XXXV">318</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXXVI.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Gametophyte and Sporophyte of Angiosperms.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XXXVI">325</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="2">CHAPTER XXXVII.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Morphology of the Nucleus and Significance of</span></td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl_ws1"><span class="smcap">Gametophyteand Sporophyte.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XXXVII">340</a></td>
-   </tr>
- </tbody>
-</table>
-
-<table border="0" cellspacing="0" summary="TOC" cellpadding="0" >
-  <tbody><tr>
-      <td class="tdc_space-above2 lgfnt150" colspan="3">PART III.&emsp;PLANT MEMBERS IN RELATION<br /> TO ENVIRONMENT.</td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="3">CHAPTER XXXVIII.</td>
-   </tr><tr>
-      <td class="tdl" colspan="2"><span class="smcap">The Organization of the Plant.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XXXVIII">349</a></td>
-   </tr><tr>
-      <td class="tdr">I.</td>
-      <td class="tdl_toc">Organization of Plant Members.</td>
-      <td class="tdr"><a href="#XXXVIII_1">349</a></td>
-   </tr><tr>
-      <td class="tdr">II.</td>
-      <td class="tdl_toc">Organization of Plant Tissues.</td>
-      <td class="tdr"><a href="#XXXVIII_2">356</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="3">CHAPTER XXXIX.</td>
-   </tr><tr>
-      <td class="tdl" colspan="2"><span class="smcap">The Different Types of Stems.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XXXIX">365</a></td>
-   </tr><tr>
-      <td class="tdr">I.</td>
-      <td class="tdl_toc">Erect Stems.</td>
-      <td class="tdr"><a href="#XXXIX_1">365</a></td>
-   </tr><tr>
-      <td class="tdr">II.</td>
-      <td class="tdl_toc">Creeping, Climbing, and Floating Stems.</td>
-      <td class="tdr"><a href="#XXXIX_2">369</a></td>
-   </tr><tr>
-      <td class="tdr">III.</td>
-      <td class="tdl_toc">Specialized Shoots and Shoots for Storage of Food.</td>
-      <td class="tdr"><a href="#XXXIX_3">372</a></td>
-   </tr><tr>
-      <td class="tdr">IV.</td>
-      <td class="tdl_toc">Annual Growth and Winter Protection of Shoots and Buds.</td>
-      <td class="tdr"><a href="#XXXIX_4">374</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="3">CHAPTER XL.</td>
-   </tr><tr>
-      <td class="tdl" colspan="2"><span class="smcap">Foliage Leaves.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XL">383</a></td>
-   </tr><tr>
-      <td class="tdr">I.</td>
-      <td class="tdl_toc">General Form and Arrangement of Leaves.</td>
-      <td class="tdr"><a href="#XL_1">383</a></td>
-   </tr><tr>
-      <td class="tdr">II.</td>
-      <td class="tdl_toc">Protective Modifications of Leaves.</td>
-      <td class="tdr"><a href="#XL_2">392</a></td>
-   </tr><tr>
-      <td class="tdr">III.</td>
-      <td class="tdl_toc">Protective Positions.</td>
-      <td class="tdr"><a href="#XL_3">395</a></td>
-   </tr><tr>
-      <td class="tdr">IV.</td>
-      <td class="tdl_toc">Relation of Leaves to Light.</td>
-      <td class="tdr"><a href="#XL_4">397</a></td>
-   </tr><tr>
-      <td class="tdr">V.</td>
-      <td class="tdl_toc">Leaf Patterns.</td>
-      <td class="tdr"><a href="#XL_5">404</a>
-           <span class="pagenum"><a name="Page_xiii" id="Page_xiii">[Pg xiii]</a></span></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="3">CHAPTER XLI.</td>
-   </tr><tr>
-      <td class="tdl" colspan="2"><span class="smcap">The Root.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XLI">410</a></td>
-   </tr><tr>
-      <td class="tdr">I.</td>
-      <td class="tdl_toc">Function of Roots.</td>
-      <td class="tdr"><a href="#XLI_1">410</a></td>
-   </tr><tr>
-      <td class="tdr">II.</td>
-      <td class="tdl_toc">Kinds of Roots.</td>
-      <td class="tdr"><a href="#XLI_2">415</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="3">CHAPTER XLII.</td>
-   </tr><tr>
-      <td class="tdl" colspan="2"><span class="smcap">The Floral Shoot.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XLII">419</a></td>
-   </tr><tr>
-      <td class="tdr">I.</td>
-      <td class="tdl_toc">The Parts of the Flower.</td>
-      <td class="tdr"><a href="#XLII_1">419</a></td>
-   </tr><tr>
-      <td class="tdr">II.</td>
-      <td class="tdl_toc">Kinds of Flowers.</td>
-      <td class="tdr"><a href="#XLII_2">421</a></td>
-   </tr><tr>
-      <td class="tdr">III.</td>
-      <td class="tdl_toc">Arrangement of Flowers, or Mode of Inflorescence.</td>
-      <td class="tdr"><a href="#XLII_3">426</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="3">CHAPTER XLIII.</td>
-   </tr><tr>
-      <td class="tdl" colspan="2"><span class="smcap">Pollination.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XLIII">433</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="3">CHAPTER XLIV.</td>
-   </tr><tr>
-      <td class="tdl" colspan="2"><span class="smcap">The Fruit.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XLIV">450</a></td>
-   </tr><tr>
-      <td class="tdr">I.</td>
-      <td class="tdl_toc">Parts of the Fruit.</td>
-      <td class="tdr"><a href="#XLIV_1">450</a></td>
-   </tr><tr>
-      <td class="tdr">II.</td>
-      <td class="tdl_toc">Indehiscent Fruits.</td>
-      <td class="tdr"><a href="#XLIV_2">451</a></td>
-   </tr><tr>
-      <td class="tdr">III.</td>
-      <td class="tdl_toc">Dehiscent Fruits.</td>
-      <td class="tdr"><a href="#XLIV_3">452</a></td>
-   </tr><tr>
-      <td class="tdr">IV.</td>
-      <td class="tdl_toc">Fleshy and Juicy Fruits.</td>
-      <td class="tdr"><a href="#XLIV_4">454</a></td>
-   </tr><tr>
-      <td class="tdr">V.</td>
-      <td class="tdl_toc">Reinforced, or Accessory, Fruits.</td>
-      <td class="tdr"><a href="#XLIV_5">455</a></td>
-   </tr><tr>
-      <td class="tdr">VI.</td>
-      <td class="tdl_toc">Fruits of Gymnosperms.</td>
-      <td class="tdr"><a href="#XLIV_6">456</a></td>
-   </tr><tr>
-      <td class="tdr">VII.</td>
-      <td class="tdl_toc">“Fruit” of Ferns, Mosses, etc.</td>
-      <td class="tdr"><a href="#XLIV_7">457</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="3">CHAPTER XLV.</td>
-   </tr><tr>
-      <td class="tdl" colspan="2"><span class="smcap">Seed Dispersal.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XLV">458</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="3">CHAPTER XLVI.</td>
-   </tr><tr>
-      <td class="tdl" colspan="2"><span class="smcap">Vegetation in Relation to Environment.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XLVI">464</a></td>
-   </tr><tr>
-      <td class="tdc_space-above1 lgfnt125" colspan="3">CHAPTER XLVII.</td>
-   </tr><tr>
-      <td class="tdl" colspan="2"><span class="smcap">Classification of Angiosperms.</span></td>
-      <td class="tdr"><a href="#CHAPTER_XLVII">487</a></td>
-   </tr><tr>
-      <td class="tdl" colspan="2"><br /><span class="smcap">Index.</span></td>
-      <td class="tdr"><a href="#INDEX">503</a></td>
-   </tr>
- </tbody>
-</table>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_1" id="Page_1">[Pg 1]</a></span></p>
-<div class="chapter">
-<h2 class="nobreak">PART I.<br /> PHYSIOLOGY.</h2>
-<hr class="r5" />
-<h3 class="nobreak"><a name="CHAPTER_I" id="CHAPTER_I">CHAPTER I.</a><br />
-<span class="h_subtitle">PROTOPLASM.</span>
-<a name="FNanchor_1_1" id="FNanchor_1_1"></a><a href="#Footnote_1_1" class="fnanchor">[1]</a></h3>
-</div>
-
-<p><b>1.</b> In the study of plant life and growth, it will be found
-convenient first to inquire into the nature of the substance which we
-call the living material of plants. For plant growth, as well as some
-of the other processes of plant life, are at bottom dependent on this
-living matter. This living matter is called in general <i>protoplasm</i>.</p>
-
-<p><b>2.</b> In most cases protoplasm cannot be seen without the help of
-a microscope, and it will be necessary for us here to employ one if we
-wish to see protoplasm, and to satisfy ourselves by examination that
-the substance we are dealing with <i>is</i> protoplasm.</p>
-
-<p><b>3.</b> We shall find it convenient first to examine protoplasm
-in some of the simpler plants; plants which from their minute size
-and simple structure are so transparent that when examined with the
-microscope the interior can be seen.</p>
-
-<p>For our first study let us take a plant known as <i>spirogyra</i>, though
-there are a number of others which would serve the purpose quite as
-well, and may quite as easily be obtained for study.
-<span class="pagenum"><a name="Page_2" id="Page_2">[Pg 2]</a></span></p>
-
-<h4>Protoplasm in spirogyra.</h4>
-
-<p><b>4. The plant spirogyra.</b>—This plant is found in the water of
-pools, ditches, ponds, or in streams of slow-running water. It is green
-in color, and occurs in loose mats, usually floating near the surface.
-The name “pond-scum” is sometimes given to this plant, along with
-others which are more or less closely related. It is an <i>alga</i>, and
-belongs to a group of plants known as <i>algæ</i>. If we lift a portion of
-it from the water, we see that the mat is made up of a great tangle of
-green silky threads. Each one of these threads is a plant, so that the
-number contained in one of these floating mats is very great.</p>
-
-<p>Let us place a bit of this thread tangle on a glass slip, and examine
-with the microscope and we will see certain things about the plant
-which are peculiar to it, and which enable us to distinguish it from
-other minute green water plants. We shall also wish to learn what these
-peculiar parts of the plant are, in order to demonstrate the protoplasm
-in the plant.<a name="FNanchor_2_2" id="FNanchor_2_2"></a><a href="#Footnote_2_2" class="fnanchor">[2]</a></p>
-
-<p><b>5. Chlorophyll bands in spirogyra.</b>—We first observe the
-presence of bands; green in color, the edges of which are usually
-very irregularly notched. These bands course along in a spiral manner
-near the surface of the thread. There may be one or several of these
-spirals, according to the species which we happen to select for
-study. This green coloring matter of the band is <i>chlorophyll</i>, and
-this substance, which also occurs in the higher green plants, will
-be considered in a later chapter. At quite regular intervals in the
-chlorophyll band are small starch grains, grouped in a rounded mass
-enclosing a minute body, the <i>pyrenoid</i>, which is peculiar to many algæ.
-<span class="pagenum"><a name="Page_3" id="Page_3">[Pg 3]</a></span></p>
-
-<div class="figright_20">
-    <img src="images/fig01.jpg" alt="" width="75" height="435" />
-   <div class="blockquot">
-    <p class="center">Fig. 1.</p>
-    <p class="center">Thread of spirogyra, showing long cells, chlorophyll band, nucleus,
-              strands of protoplasm, and the granular wall layer of protoplasm.</p>
-   </div>
-</div>
-
-<p><b>6. The spirogyra thread consists of cylindrical cells end to
-end.</b>—Another thing which attracts our attention, as we examine a
-thread of spirogyra under the microscope, is that the thread is made up
-of cylindrical segments or compartments placed end to end. We can see a
-distinct separating line between the ends. Each one of these segments
-or compartments of the thread is a <i>cell</i>, and the boundary wall is
-in the form of a cylinder with closed ends.</p>
-
-<p><b>7. Protoplasm.</b>—Having distinguished these parts of the plant
-we can look for the protoplasm. It occurs within the cells. It is
-colorless (i.e., hyaline) and consequently requires close observation.
-Near the center of the cell can be seen a rather dense granular body
-of an elliptical or irregular form, with its long diameter transverse
-to the axis of the cell in some species; or triangular, or quadrate in
-others. This is the <i>nucleus</i>. Around the nucleus is a granular layer
-from which delicate threads of a shiny granular substance radiate in a
-starlike manner, and terminate in the chlorophyll band at one of the
-pyrenoids. A granular layer of the same substance lines the inside of
-the cell wall, and can be seen through the microscope if it is properly
-focussed. This granular substance in the cell is <i>protoplasm</i>.</p>
-
-<p><b>8. Cell-sap in spirogyra.</b>—The greater part of the interior
-space of the cell, that between the radiating strands of protoplasm, is
-occupied by a watery fluid, the “cell-sap.”</p>
-
-<p><b>9. Reaction of protoplasm to certain reagents.</b>—We can employ
-certain tests to demonstrate that this granular substance which we have
-seen is protoplasm, for it has been found, by repeated experiments with
-a great many kinds of plants, that protoplasm gives a definite reaction
-in response to treatment with certain substances called reagents. Let
-us mount a few threads of the spirogyra in a drop of a solution of
-<span class="pagenum"><a name="Page_4" id="Page_4">[Pg 4]</a></span>
-iodine, and observe the results with the aid of the microscope. The
-iodine gives a yellowish-brown color to the protoplasm, and it can be
-more distinctly seen. The nucleus is also much more prominent since it
-colors deeply, and we can perceive within the nucleus one small rounded
-body, sometimes more, the <i>nucleolus</i>. The iodine here kills and stains
-the protoplasm. The protoplasm, however, in a living condition will
-resist for a time some other reagents, as we shall see if we attempt
-to stain it with a one per cent aqueous solution of a dye known as
-<i>eosin</i>. Let us mount a few living threads in such a solution of eosin,
-and after a time wash off the stain. The protoplasm remains uncolored.
-Now let us place these threads for a short time, two or three minutes,
-in strong alcohol, which kills the protoplasm. Then mount them in
-the eosin solution. The protoplasm now takes the eosin stain. After
-the protoplasm has been killed we note that the nucleus is no longer
-elliptical or angular in outline, but is rounded. The strands of
-protoplasm are no longer in tension as they were when alive.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <img src="images/fig02.jpg" alt="" width="200" height="303" />
-   <p class="center">Fig. 2.<br /> Cell of spirogyra before<br />
-             treatment with iodine.</p>
-  </div>
-  <div class="figsub">
-   <a><img  src="images/fig03.jpg" alt="" width="200" height="296" /></a>
-   <p class="center">Fig. 3.<br /> Cell of spirogyra after<br />
-                  treatment with alcohol and iodine.</p>
-   </div>
-</div>
-
-<p><b>10.</b> Let us now take some fresh living threads and mount them in
-water. Place a small drop of dilute glycerine on the slip at one side
-of the cover glass, and with a bit of filter paper at the other side
-draw out the water. The glycerine will flow under the cover glass and
-come in contact with the spirogyra threads. Glycerine absorbs water
-promptly. Being in contact with the threads it draws water out of the
-<span class="pagenum"><a name="Page_5" id="Page_5">[Pg 5]</a></span>
-cell cavity, thus causing the layer of protoplasm which lines the
-inside of the cell wall to collapse, and separate from the wall,
-drawing the chlorophyll band inward toward the center also. The wall
-layer of protoplasm can now be more distinctly seen and its granular
-character observed.</p>
-
-<p>We have thus employed three tests to demonstrate that this substance
-with which we are dealing shows the reactions which we know by
-experience to be given by protoplasm. We therefore conclude that this
-colorless and partly granular, slimy substance in the spirogyra cell
-is protoplasm, and that when we have performed these experiments, and
-noted carefully the results, we have <i>seen</i> protoplasm.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <img src="images/fig04.jpg" alt="" width="110" height="340" />
-   <p class="center">Fig. 4.</p>
-   <p class="center">Cell of spirogyra before<br /> treatment with glycerine.</p>
-  </div>
-
-  <div class="figsub">
-   <a><img  src="images/fig05.jpg" alt="" width="250" height="343" /></a>
-   <p class="center">Fig. 5.</p>
-   <p class="center">Cells of spirogyra after<br /> treatment with glycerine.</p>
-   </div>
-</div>
-
-<div class="blockquot">
-<p><b>11. Earlier use of the term protoplasm.</b>—Early students of the
-living matter in the cell considered it to be alike in substance, but
-differing in density; so the term protoplasm was applied to all of this
-living matter. The nucleus was looked upon as simply a denser portion
-of the protoplasm, and the nucleolus as a still denser portion. Now it
-is believed that the nucleus is a distinct substance, and a permanent
-organ of the cell. The remaining portion of the protoplasm is now
-usually spoken of as the <i>cytoplasm</i>.</p>
-
-<p>In spirogyra then the cytoplasm in each cell consists of a layer
-which lines the inside of the cell wall, a nuclear layer, which
-surrounds the nucleus, and radiating strands which connect the nucleus
-and wall layers, thus suspending the nucleus near the center of the
-cell. But it seems best in this elementary study to use the term
-protoplasm in its general sense.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_6" id="Page_6">[Pg 6]</a></span></p>
-<h4>Protoplasm in mucor.</h4>
-
-<p><b>12.</b> Let us now examine in a similar way another of the simple
-plants with the special object in view of demonstrating the protoplasm.
-For this purpose we may take one of the plants belonging to the group
-of <i>fungi</i>. These plants possess no chlorophyll. One of several species
-of <i>mucor</i>, a common mould, is readily obtainable, and very suitable
-for this study.<a name="FNanchor_3_3" id="FNanchor_3_3"></a><a href="#Footnote_3_3" class="fnanchor">[3]</a></p>
-
-<p><b>13. Mycelium of mucor.</b>—A few days after sowing in some
-gelatinous culture medium we find slender, hyaline threads, which are
-very much branched, and, radiating from a central point, form circular
-colonies, if the plant has not been too thickly sown, as shown in
-<a href="#FIG_06">fig. 6</a>. These threads of the fungus form the <i>mycelium</i>.
-From these characters of the plant, which we can readily see without the aid
-of a microscope, we note how different it is from spirogyra.</p>
-
-<p>To examine for protoplasm let us lift carefully a thin block of
-gelatine containing the mucor threads, and mount it in water on a
-glass slip. Under the microscope we see only a small portion of the
-branched threads. In addition to the absence of chlorophyll, which we
-have already noted, we see that the mycelium is not divided at short
-intervals into cells, but appears like a delicate tube with branches,
-which become successively smaller toward the ends.</p>
-
-<p><b>14. Appearance of the protoplasm.</b>—Within the tube-like thread
-now note the protoplasm. It has the same general appearance as that
-which we noted in spirogyra. It is slimy, or semi-fluid, partly
-hyaline, and partly granular, the granules consisting of minute
-particles (the <i>microsomes</i>). While in mucor the protoplasm has the
-same general appearance as in spirogyra, its arrangement is very
-<span class="pagenum"><a name="Page_7" id="Page_7">[Pg 7]</a></span>
-different. In the first place it is plainly continuous throughout the
-tube. We do not see the prominent radiations of strands around a large
-nucleus, but still the protoplasm does not fill the interior of the
-threads. Here and there are rounded clear spaces termed <i>vacuoles</i>,
-which are filled with the watery fluid, cell-sap. The nuclei in mucor
-are very minute, and cannot be seen except after careful treatment with
-special reagents.</p>
-
-<div class="figcenter">
-   <img id="FIG_06" src="images/fig06.jpg" alt="" width="600" height="471" />
-   <div class="blockquot">
-    <p class="center">Fig. 6.<br /> Colonies of mucor.</p>
-   </div>
-</div>
-
-<p><b>15. Movement of the protoplasm in mucor.</b>—While examining the
-protoplasm in mucor we are likely to note streaming movements. Often a
-current is seen flowing slowly down one side of the thread, and another
-flowing back on the other side, or it may all stream along in the same
-direction.</p>
-
-<p><b>16. Test for protoplasm.</b>—Now let us treat the threads with
-a solution of iodine. The yellowish-brown color appears which is
-<span class="pagenum"><a name="Page_8" id="Page_8">[Pg 8]</a></span>
-characteristic of protoplasm when subject to this reagent. If we
-attempt to stain the living protoplasm with a one per cent aqueous
-solution of eosin it resists it for a time, but if we first kill the
-protoplasm with strong alcohol, it reacts quickly to the application of
-the eosin. If we treat the living threads with glycerine the protoplasm
-is contracted away from the wall, as we found to be the case with
-spirogyra. While the color, form and structure of the plant mucor is
-different from spirogyra, and the arrangement of the protoplasm within
-the plant is also quite different, the reactions when treated by
-certain reagents are the same. We are justified then in concluding that
-the two plants possess in common a substance which we call protoplasm.</p>
-
-<div class="figcenter">
-    <img src="images/fig07.jpg" alt="" width="600" height="190" />
-   <div class="blockquot">
-    <p class="center">Fig. 7.<br /> Thread of mucor, showing protoplasm and vacuoles.</p>
-   </div>
-</div>
-
-<h4>Protoplasm in nitella.</h4>
-
-<p><a id="PARA_17" name="PARA_17"><b>17.</b></a> One of the most interesting plants for the study of one
-remarkable peculiarity of protoplasm is <i>Nitella</i>. This plant belongs
-to a small group known as stoneworts. They possess chlorophyll, and,
-while they are still quite simple as compared with the higher plants,
-they are much higher in the scale than spirogyra or mucor.</p>
-
-<p><b>18. Form of nitella.</b>—A common species of nitella is <i>Nitella
-flexilis</i>. It grows in quiet pools of water. The plant consists of a
-main axis, in the form of a cylinder. At quite regular intervals are
-whorls of several smaller thread-like outgrowths, which, because of
-their position, are termed “leaves,” though they are not true leaves.
-These are branched in a characteristic fashion at the tip. The main
-axis also branches, these branches arising in the axil of a whorl,
-usually singly. The portions of the axis where the whorls arise are the
-<i>nodes</i>. Each node is made up of a number of small cells definitely
-arranged. The portion of the axis between two adjacent whorls is an
-<span class="pagenum"><a name="Page_9" id="Page_9">[Pg 9]</a></span>
-internode. These internodes are peculiar. They consist of but a single
-“cell,” and are cylindrical, with closed ends. They are sometimes 5-10
-cm. long.</p>
-
-<div class="figright">
-    <img id="FIG_08" src="images/fig08.jpg" alt="" width="200" height="307" />
-    <p class="center">Fig. 8.</p>
-    <p class="center">Portion of plant<br /> nitella.</p>
-</div>
-
-<p><b>19. Internode of nitella.</b>—For the study of an internode of
-nitella, a small one, near the end, or the ends of one of the “leaves”
-is best suited, since it is more transparent. A small portion of the
-plant should be placed on the glass slip in water with the cover glass
-over a tuft of the branches near the growing end. Examined with the
-microscope the green chlorophyll bodies, which form oval or oblong
-discs, are seen to be very numerous. They lie quite closely side by
-side and form in perfect rows along the inner surface of the wall.
-One peculiar feature of the arrangement of the chlorophyll bodies is
-that there are two lines, extending from one end of the internode to
-the other on opposite sides, where the chlorophyll bodies are wanting.
-These are known as neutral lines. They run parallel with the axis of
-the internode, or in a more or less spiral manner as shown in <a href="#FIG_09">fig. 9</a>.</p>
-
-<p><b>20. Cyclosis in nitella.</b>—The chlorophyll bodies are stationary
-on the inner surface of the wall, but if the microscope be properly
-focussed just beneath this layer we notice a rotary motion of particles
-in the protoplasm. There are small granules and quite large masses of
-granular matter which glide slowly along in one direction on a given
-side of the neutral line. If now we examine the protoplasm on the other
-side of the neutral line, we see that the movement is in the opposite
-direction. If we examine this movement at the end of an internode
-the particles are seen to glide around the end from one side of the
-neutral line to the other. So that when conditions are favorable, such
-as temperature, healthy state of the plant, etc., this gliding of the
-particles or apparent streaming of the protoplasm down one side of
-the “cell,” and back upon the other, continues in an uninterrupted
-rotation, or <i>cyclosis</i>. There are many nuclei in an internode of
-nitella, and they move also.</p>
-
-<p><b>21. Test for protoplasm.</b>—If we treat the plant with a solution
-of iodine we get the same reaction as in the case of spirogyra and
-mucor. The protoplasm becomes yellowish-brown.
-<span class="pagenum"><a name="Page_10" id="Page_10">[Pg 10]</a></span></p>
-
-<div class="figleft">
-    <img id="FIG_09" src="images/fig09.jpg" alt="" width="200" height="64" />
-    <p class="center">Fig. 9.<br /> Cyclosis in nitella.</p>
-</div>
-
-<p><b>22. Protoplasm in one of the higher plants.</b>—We now wish to
-examine, and test for, protoplasm in one of the higher plants. Young
-or growing parts of any one of various plants—the petioles of young
-leaves, or young stems of growing plants—are suitable for study.
-Tissue from the pith of corn (Zea mays) in young shoots just back of
-the growing point or quite near the joints of older but growing corn
-stalks furnishes excellent material.</p>
-
-<p>If we should place part of the stem of this plant under the microscope
-we should find it too opaque for observation of the interior of the
-cells. This is one striking difference which we note as we pass from
-the low and simple plants to the higher and more complex ones; not
-only in general is there an increase of size, but also in general an
-increase in thickness of the parts. The cells, instead of lying end to
-end or side by side, are massed together so that the parts are quite
-opaque. In order to study the interior of the plant we have selected
-it must be cut into such thin layers that the light will pass readily
-through them.</p>
-
-<p>For this purpose we section the tissue selected by making with a razor,
-or other very sharp knife, very thin slices of it. These are mounted in
-water in the usual way for microscopic study. In this section we notice
-that the cells are polygonal in form. This is brought about by mutual
-pressure of all the cells. The granular protoplasm is seen to form a
-layer just inside the wall, which is connected with the nuclear layer
-by radiating strands of the same substance. The nucleus does not always
-lie at the middle of the cell, but often is near one side. If we now
-apply an alcohol solution of iodine the characteristic yellowish-brown
-color appears. So we conclude here also that this substance is
-identical with the living matter in the other very different plants
-which we have studied.</p>
-
-<p><b>23. Movement of protoplasm in the higher plants.</b>—Certain
-parts of the higher plants are suitable objects for the study of the
-so-called streaming movement of protoplasm, especially the delicate
-<span class="pagenum"><a name="Page_11" id="Page_11">[Pg 11]</a></span>
-hairs, or thread-like outgrowths, such as the silk of corn, or the
-delicate staminal hairs of some plants, like those of the common
-spiderwort, tradescantia, or of the tradescantias grown for ornament in
-greenhouses and plant conservatories.</p>
-
-<p>Sometimes even in the living cells of the corn plant which we have just
-studied, slow streaming or gliding movements of the granules are seen
-along the strands of protoplasm where they radiate from the nucleus.
-<a href="#NOTE_1">See note</a> at close of this chapter.</p>
-
-<p><b>24. Movement of protoplasm in cells of the staminal hair of
-“spiderwort.”</b>—A cell of one of these hairs from a stamen of a
-tradescantia grown in glass houses is shown in <a href="#FIG_10">fig. 10</a>. The
-nucleus is quite prominent, and its location in the cell varies considerably in
-different cells and at different times. There is a layer of protoplasm
-all around the nucleus, and from this the strands of protoplasm extend
-outward to the wall layer. The large spaces between the strands are, as
-we have found in other cases, filled with the cell-sap.</p>
-
-<div class="figcenter">
-    <img id="FIG_10" src="images/fig10.jpg" alt="" width="600" height="125" />
-    <p class="center">Fig. 10.<br /> Cell from stamen hair of tradescantia
-                    showing movement of the protoplasm.</p>
-</div>
-
-<p class="blockquot">An entire stamen, or a portion of the stamen,
-having several hairs attached, should be carefully mounted in water.
-Care should be taken that the room be not cold, and if the weather is
-cold the water in which the preparation is mounted should be warm. With
-these precautions there should be little difficulty in observing the
-streaming movement.</p>
-
-<p>The movement is detected by observing the gliding of the granules.
-These move down one of the strands from the nucleus along the wall
-layer, and in towards the nucleus in another strand. After a little the
-direction of the movement in any one portion may be reversed.</p>
-
-<p><b>25. Cold retards the movement.</b>—While the protoplasm is moving,
-if we rest the glass slip on a block of ice, the movement will become
-<span class="pagenum"><a name="Page_12" id="Page_12">[Pg 12]</a></span>
-slower, or will cease altogether. Then if we warm the slip gently, the
-movement becomes normal again. We may now apply here the usual tests
-for protoplasm. The result is the same as in the former cases.</p>
-
-<p><b>26. Protoplasm occurs in the living parts of all plants.</b>—In
-these plants representing such widely different groups, we find a
-substance which is essentially alike in all. Though its arrangement
-in the cell or plant body may differ in the different plants or in
-different parts of the same plant, its general appearance is the same.
-Though in the different plants it presents, while alive, varying
-phenomena, as regards mobility, yet when killed and subjected to
-well known reagents the reaction is in general identical. Knowing
-by the experience of various investigators that protoplasm exhibits
-these reactions under given conditions, we have demonstrated to
-our satisfaction that we have seen protoplasm in the simple alga,
-spirogyra, in the common mould, mucor, in the more complex stonewort,
-nitella, and in the cells of tissues of the highest plants.</p>
-
-<p><b>27.</b> By this simple process of induction of these facts
-concerning this substance in these different plants, we have learned an
-important method in science study. Though these facts and deductions
-are well known, the repetition of the methods by which they are
-obtained on the part of each student helps to form habits of scientific
-carefulness and patience, and trains the mind to logical processes in
-the search for knowledge.</p>
-
-<p><b>28.</b> While we have by no means exhausted the study of protoplasm,
-we can, from this study, draw certain conclusions as to its occurrence
-and appearance in plants. Protoplasm is found in the living and growing
-parts of all plants. It is a semi-fluid, or slimy, granular, substance;
-in some plants, or parts of plants, the protoplasm exhibits a streaming
-or gliding movement of the granules. It is irritable. In the living
-condition it resists more or less for some time the absorption of
-certain coloring substances. The water may be withdrawn by glycerine.
-The protoplasm may be killed by alcohol. When treated with iodine it
-becomes a yellowish-brown color.</p>
-
-<p class="blockquot"><a name="NOTE_1" id="NOTE_1"><i>Note.</i></a>
-In some plants, like elodea for example, it has been found that
-the streaming of the protoplasm is often induced by some injury or
-stimulus, while in the normal condition the protoplasm does not move.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_13" id="Page_13">[Pg 13]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_II" id="CHAPTER_II">CHAPTER II.</a><br />
-<span class="h_subtitle">ABSORPTION, DIFFUSION, OSMOSE.</span></h3>
-</div>
-
-<p><b>29.</b> We may next endeavor to learn how plants absorb water or
-nutrient substances in solution. There are several very instructive
-experiments, which can be easily performed, and here again some of the
-lower plants will be found useful.</p>
-
-<p><b>30. Osmose in spirogyra.</b>—Let us mount a few threads of this
-plant in water for microscopic examination, and then draw under the
-cover glass a five per cent solution of ordinary table salt (NaCl)
-with the aid of filter paper. We shall soon see that the result is
-similar to that which was obtained when glycerine was used to extract
-the water from the cell-sap, and to contract the protoplasmic membrane
-from the cell wall. But the process goes on evenly and the plant is not
-injured. The protoplasmic layer contracts slowly from the cell wall,
-and the movement of the membrane can be watched by looking through the
-microscope. The membrane contracts in such a way that all the contents
-of the cell are finally collected into a rounded or oval mass which
-occupies the center of the cell.</p>
-
-<p>If we now add fresh water and draw off the salt solution, we can see
-the protoplasmic membrane expand again, or move out in all directions,
-and occupy its former position against the inner surface of the cell
-wall. This would indicate that there is some pressure from within while
-this process of absorption is going on, which causes the membrane to
-move out against the cell wall.</p>
-
-<p>The salt solution draws water from the cell-sap. There is thus a
-tendency to form a vacuum in the cell, and the pressure on the outside
-<span class="pagenum"><a name="Page_14" id="Page_14">[Pg 14]</a></span>
-of the protoplasmic membrane causes it to move toward the center of the
-cell. When the salt solution is removed and the thread of spirogyra is
-again bathed with water, the movement of the water is <i>inward</i> in the
-cell. This would suggest that there is some substance dissolved in the
-cell-sap which does not readily filter out through the membrane, but
-draws on the water outside. It is this which produces the pressure from
-within and crowds the membrane out against the cell wall again.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <img src="images/fig11.jpg" alt="" width="50" height="299" />
-   <p class="center">Fig. 11.</p>
-   <p class="center">Spirogyra before placing<br /> in salt solution.</p>
-  </div>
-  <div class="figsub">
-   <img  src="images/fig12.jpg" alt="" width="150" height="260" />
-   <p class="center space-above2">Fig. 12.</p>
-   <p class="center">Spirogyra in<br /> 5% salt solution.</p>
-   </div>
-  <div class="figsub">
-   <img  src="images/fig13.jpg" alt="" width="90" height="278" />
-   <p class="center">Fig. 13.</p>
-   <p class="center">Spirogyra from salt<br /> solution into water.</p>
-   </div>
-</div>
-
-<p><b>31. Turgescence.</b>—Were it not for the resistance which the cell
-<span class="pagenum"><a name="Page_15" id="Page_15">[Pg 15]</a></span>
-wall offers to the pressure from within, the delicate protoplasmic
-membrane would stretch to such an extent that it would be ruptured, and
-the protoplasm therefore would be killed. If we examine the cells at
-the ends of the threads of spirogyra we shall see in most cases that
-the cell wall at the free end is arched outward. This is brought about
-by the pressure from within upon the protoplasmic membrane which itself
-presses against the cell wall, and causes it to arch outward. This is
-beautifully shown in the case of threads which are recently broken.
-The cell wall is therefore <i>elastic</i>; it yields to a certain extent to
-the pressure from within, but a point is soon reached beyond which it
-will not stretch, and an equilibrium then exists between the pressure
-from within on the protoplasmic membrane, and the pressure from without
-by the elastic cell wall. This state of equilibrium in a cell is
-<i>turgescence</i>, or such a cell is said to be <i>turgescent</i>, or <i>turgid</i>.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <img src="images/fig14.jpg" alt="" width="150" height="173" />
-   <p class="center">Fig. 14.</p>
-   <p class="center">Before treatment with<br /> salt solution.</p>
-  </div>
-  <div class="figsub">
-   <img  src="images/fig15.jpg" alt="" width="160" height="174" />
-   <p class="center">Fig. 15.</p>
-   <p class="center">After treatment with<br /> salt solution.</p>
-   </div>
-  <div class="figsub">
-   <img  src="images/fig16.jpg" alt="" width="200" height="170" />
-   <p class="center">Fig. 16.</p>
-   <p class="center">From salt solution placed<br /> in water.</p>
-   </div>
-   <p class="center space-below1">Figs. 14-16.—Osmosis in threads of mucor.</p>
-</div>
-
-<p><b>32. Experiment with beet in salt and sugar solutions.</b>—We may
-now test the effect of a five per cent salt solution on a portion of
-the tissues of a beet or carrot. Let us cut several slices of equal
-size and about 5mm in thickness. Immerse a few slices in water, a few
-in a five per cent salt solution and a few in a strong sugar solution.
-It should be first noted that all the slices are quite rigid when an
-attempt is made to bend them between the fingers. In the course of one
-<span class="pagenum"><a name="Page_16" id="Page_16">[Pg 16]</a></span>
-or two hours or less, if we examine the slices we shall find that those in water
-remain, as at first, quite rigid, while those in the salt and sugar solutions
-are more or less flaccid or limp, and readily bend by pressure
-between the fingers, the specimens in the salt solution,
-perhaps, being more flaccid than those in the sugar solution.
-The salt solution, we judge after our experiment with spirogyra,
-withdraws some of the water from the cell-sap, the cells thus
-losing their turgidity and the tissues becoming limp or flaccid
-from the loss of water.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <img src="images/fig17.jpg" alt="" width="150" height="130" />
-   <p class="center">Fig. 17.</p>
-   <p class="center">Before treatment with<br /> salt solution.</p>
-  </div>
-  <div class="figsub">
-   <img  src="images/fig18.jpg" alt="" width="140" height="136" />
-   <p class="center">Fig. 18.</p>
-   <p class="center">After treatment with<br /> salt solution.</p>
-   </div>
-  <div class="figsub">
-   <img  src="images/fig19.jpg" alt="" width="140" height="135" />
-   <p class="center">Fig. 19.</p>
-   <p class="center">From salt solution into<br /> water again.</p>
-   </div>
-   <p class="center space-below1">Figs. 17-19.—Osmosis in cells of Indian corn.</p>
-</div>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <img src="images/fig20.jpg" alt="" width="150" height="325" />
-   <p class="center">Fig. 20.</p>
-   <p class="center">Rigid condition of<br /> fresh beet section.</p>
-  </div>
-  <div class="figsub">
-   <p class="space-above2">&nbsp;</p>
-   <img  src="images/fig21.jpg" alt="" width="150" height="245" />
-   <p class="center">Fig. 21.</p>
-   <p class="center">Limp condition after<br /> lying in salt<br /> solution.</p>
-   </div>
-  <div class="figsub">
-   <img  src="images/fig22.jpg" alt="" width="150" height="367" />
-   <p class="center">Fig. 22.</p>
-   <p class="center">Rigid again after<br /> lying again in water.</p>
-   </div>
-   <p class="center space-below1">Figs. 20-22.—Turgor and osmosis in slices of beet.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_17" id="Page_17">[Pg 17]</a></span>
-<b>33.</b> Let us now remove some of the slices of the beet from the
-sugar and salt solutions, wash them with water and then immerse them in
-fresh water. In the course of thirty minutes to one hour, if we examine
-them again, we find that they have regained, partly or completely,
-their rigidity. Here again we infer from the former experiment with
-spirogyra that the substances in the cell-sap now draw water inward;
-that is, the diffusion current is inward through the cell walls and the
-protoplasmic membrane, and the tissue becomes turgid again.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <img id="FIG_23" src="images/fig23.jpg" alt="" width="150" height="179" />
-   <p class="center">Fig. 23.</p>
-   <p class="center">Before treatment with<br /> salt solution.</p>
-  </div>
-  <div class="figsub">
-   <img id="FIG_24"  src="images/fig24.jpg" alt="" width="150" height="184" />
-   <p class="center">Fig. 24.</p>
-   <p class="center">After treatment with<br /> salt solution.</p>
-   </div>
-  <div class="figsub">
-   <img id="FIG_25"  src="images/fig25.jpg" alt="" width="150" height="185" />
-   <p class="center">Fig. 25.</p>
-   <p class="center">Later stage of<br /> the same.</p>
-   </div>
-   <p class="center space-below1">Figs. 23-25.—Cells from beet treated with salt solution to<br />
-                                  show osmosis and movement of the protoplasmic membrane.</p>
-</div>
-
-<p><b>34. Osmose in the cells of the beet.</b>—We should now make a
-section of the fresh tissue of a red colored beet for examination with
-the microscope, and treat this section with the salt solution. Here we
-can see that the effect of the salt solution is to draw water out of
-the cell, so that the protoplasmic membrane can be seen to move inward
-from the cell wall just as was observed in the case of spirogyra.<a name="FNanchor_4_4" id="FNanchor_4_4"></a><a href="#Footnote_4_4" class="fnanchor">[4]</a>
-Now treating the section with water and removing the salt solution, the
-<span class="pagenum"><a name="Page_18" id="Page_18">[Pg 18]</a></span>
-diffusion current is in the opposite direction, that is inward through
-the protoplasmic membrane, so that the latter is pressed outward until
-it comes in contact with the cell wall again, which by its elasticity
-soon resists the pressure and the cells again become turgid.</p>
-
-<p><b>35. The coloring matter in the cell-sap does not readily escape
-from the living protoplasm of the beet.</b>—The red coloring matter,
-as seen in the section under the microscope, does not escape from the
-cell-sap through the protoplasmic membrane. When the slices are placed
-in water, the water is not colored thereby. The same is true when the
-slices are placed in the salt or sugar solutions. Although water is
-withdrawn from the cell-sap, this coloring substance does not escape,
-or if it does it escapes slowly and after a considerable time.</p>
-
-<p><b>36. The coloring matter escapes from dead protoplasm.</b>—If,
-however, we heat the water containing a slice of beet up to a point
-which is sufficient to kill the protoplasm, the red coloring matter
-in the cell-sap filters out through the protoplasmic membrane and
-colors the water. If we heat a preparation made for study under the
-microscope up to the thermal death point we can see here that the red
-coloring matter escapes through the membrane into the water outside.
-This teaches that certain substances cannot readily filter through
-the living membrane of protoplasm, but that they can filter through
-when the protoplasm is dead. A very important condition, then, for
-the successful operation of some of the physical processes connected
-with absorption in plants is that the protoplasm should be in a living
-condition.</p>
-
-<p><b>37. Osmose experiments with leaves.</b>—We may next take the leaves
-of certain plants like the geranium, coleus or other plant, and place
-them in shallow vessels containing water, salt, and sugar solutions
-respectively. The leaves should be immersed, but the petioles should
-project out of the water or solutions. Seedlings of corn or beans,
-especially the latter, may also be placed in these solutions, so that
-the leafy ends are immersed. After one or two hours an examination
-shows that the specimens in the water are still turgid. But if we lift
-a leaf or a bean plant from the salt or sugar solution, we find that
-it is flaccid and limp. The blade, or lamina, of the leaf droops as if
-wilted, though it is still wet. The bean seedling also is flaccid, the
-succulent stem bending nearly double as the lower part of the stem is
-held upright. This loss of turgidity is brought about by the loss of
-water from the tissues, and judging from the experiments on spirogyra
-and the beet, we conclude that the loss of turgidity is caused by the
-withdrawal of some of the water from the cell-sap by the strong salt solution.</p>
-
-<p><b>38.</b> Now if we wash carefully these leaves and seedlings, which
-have been in the salt and sugar solutions, with water, and then immerse
-them in fresh water for a few hours, they will regain their turgidity.
-Here again we are led to infer that the diffusion current is now inward
-through the protoplasmic membranes of all the living cells of the leaf,
-and that the resulting turgidity of the individual cells causes the
-turgidity of the leaf or stem.
-<span class="pagenum"><a name="Page_19" id="Page_19">[Pg 19]</a></span></p>
-
-<div class="figleft">
-    <img src="images/fig26.jpg" alt="" width="150" height="81" />
-    <p class="center">Fig. 26.<br />
-           Seedling of radish,<br /> showing root hairs.</p>
-</div>
-
-<p><b>39. Absorption by root hairs.</b>—If we examine seedlings, which
-have been grown in a germinator or in the folds of paper or cloths so
-that the roots will be free from particles of soil, we see near the
-growing point of the roots that the surface is covered with numerous
-slender, delicate, thread-like bodies, the root hairs. Let us place a
-portion of a small root containing some of these root hairs in water on
-a glass slip, and prepare it for examination with the microscope. We
-see that each thread, or root hair, is a continuous tube, or in other
-words it is a single cell which has become very much elongated. The
-protoplasmic membrane lines the wall, and strands of protoplasm extend
-across at irregular intervals, the interspaces being occupied by the
-cell-sap.</p>
-
-<div class="figcenter">
-    <img src="images/fig27.jpg" alt="" width="600" height="145" />
-    <p class="center">Fig. 27.<br />
-           Root hair of corn before and after treatment with 5% salt solution.</p>
-</div>
-
-<p>We should now draw under the cover glass some of the five per cent salt
-solution. The protoplasmic membrane moves away from the cell wall at
-certain points, showing that <i>plasmolysis</i> is taking place, that is,
-the diffusion current is outward so that the cell-sap loses some of its
-water, and the pressure from the outside moves the membrane inward.
-We should not allow the salt solution to work on the root hairs long.
-It should be very soon removed by drawing in fresh water before the
-protoplasmic membrane has been broken at intervals, as is apt to be the
-case by the strong diffusion current and the consequent strong pressure
-from without. The membrane of protoplasm now moves outward as the
-diffusion current is inward, and soon regains its former position next
-the inner side of the cell wall. The root hairs then, like other parts
-<span class="pagenum"><a name="Page_20" id="Page_20">[Pg 20]</a></span>
-of the plant which we have investigated, have the power of taking up
-water under pressure.</p>
-
-<p><b>40. Cell-sap a solution of certain substances.</b>—From these
-experiments we are led to believe that certain substances reside in the
-cell-sap of plants, which behave very much like the salt solution when
-separated from water by the protoplasmic membrane. Let us attempt to
-interpret these phenomena by recourse to diffusion experiments, where
-an animal membrane separates two liquids of different concentration.</p>
-
-<p><b>41. An artificial cell to illustrate turgor.</b>—Fill a small
-wide-mouthed vial with a <i>very strong</i> sugar solution. Over the mouth
-tie firmly a piece of <i>bladder</i> membrane. Be certain that as the
-membrane is tied over the open end of the vial, the sugar solution
-fills it in order to keep out air bubbles. Sink the vial in a vessel of
-fresh water and leave it there for twenty-four hours. Remove the vial
-and note that the membrane is arched outward. Thrust a sharp needle
-through the membrane when it is arched outward, and quickly pull it
-out. The liquid spurts out because of the inside pressure.</p>
-
-<div class="figcenter">
-    <img src="images/fig28.jpg" alt="" width="600" height="240" />
-    <p class="center">Fig. 28.<br />
-           Puncturing a make-believe cell after it has been lying in water.</p>
-    <img src="images/fig29.jpg" alt="" width="600" height="184" />
-    <p class="center">Fig. 29.<br />
-           Same as Fig. 28 after needle is removed.</p>
-</div>
-
-<p><b>42. Diffusion through an animal membrane.</b>—For this experiment
-we may use a thistle tube, across the larger end of which should be
-stretched and tied tightly a piece of a bladder membrane. A strong
-sugar solution (three parts sugar to one part water) is now placed in
-<span class="pagenum"><a name="Page_21" id="Page_21">[Pg 21]</a></span>
-the tube so that the bulb is filled and the liquid extends part way in
-the neck of the tube. This is immersed in water within a wide-mouth
-bottle, the neck of the tube being supported in a perforated cork in
-such a way that the sugar solution in the tube is on a level with the
-water in the bottle or jar. In a short while the liquid begins to
-rise in the thistle tube, in the course of several hours having risen
-several centimeters. The diffusion current is thus stronger through the
-membrane in the direction of the sugar solution, so that this gains
-more water than it loses.</p>
-
-<p>We have here two liquids separated by an animal membrane, water on
-the one hand which diffuses readily through the membrane, while on
-the other is a solution of sugar which diffuses through the animal
-membrane with difficulty. The water, therefore, not containing any
-solvent, according to a general law which has been found to obtain in
-such cases, diffuses more readily through the membrane into the sugar
-solution, which thus increases in volume, and also becomes more dilute.
-The bladder membrane is what is sometimes called a diffusion membrane,
-since the diffusion currents travel through it.</p>
-
-<p><b>43.</b> In this experiment then the bulk of the sugar solution is
-increased, and the liquid rises in the tube by this pressure above
-the level of the water in the jar outside of the thistle tube. The
-diffusion of liquids through a membrane is <i>osmosis</i>.</p>
-
-<p><b>44. Importance of these physical processes in plants.</b>—Now if
-we recur to our experiment with spirogyra we find that exactly the
-same processes take place. The protoplasmic membrane is the diffusion
-membrane, through which the diffusion takes place. The salt solution
-which is first used to bathe the threads of the plant is a stronger
-solution than that of the cell-sap within the cell. Water therefore
-is drawn out of the cell-sap, but the substances in solution in
-the cell-sap do not readily move out. As the bulk of the cell-sap
-diminishes the pressure from the outside pushes the protoplasmic
-membrane away from the wall. Now when we remove the salt solution and
-bathe the thread with water again, the cell-sap, being a solution of
-certain substances, diffuses with more difficulty than the water, and
-the diffusion current is inward, while the protoplasmic membrane moves
-out against the cell wall, and turgidity again results. Also in the
-experiments with salt and sugar solutions on the leaves of geranium,
-on the leaves and stems of the seedlings, on the tissues and cells of
-the beet and carrot, and on the root hairs of the seedlings, the same
-processes take place.</p>
-
-<p>These experiments not only teach us that in the protoplasmic membrane,
-the cell wall, and the cell-sap of plants do we have structures which
-are capable of performing these physical processes, but they also show
-that these processes are of the utmost importance to the plant; not
-only in giving the plant the power to take up solutions of nutriment
-from the soil, but they serve also other purposes, as we shall see later.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_22" id="Page_22">[Pg 22]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_III" id="CHAPTER_III">CHAPTER III.</a><br />
-<span class="h_subtitle">HOW PLANTS OBTAIN WATER.</span></h3>
-</div>
-
-<p>In connection with the study of the means of absorption from the soil
-or water by plants, it will be found convenient to observe carefully
-the various forms of the plant. Without going into detail here, the
-suggestion is made that simple thread forms like spirogyra, œdogonium,
-and vaucheria; expanded masses of cells as are found in the thalloid
-liverworts, the duckweed, etc., be compared with those liverworts, and
-with the mosses, where leaf-like expansions of a central axis have been
-differentiated. We should then note how this differentiation, from the
-physiological standpoint, has been carried farther in the higher land plants.</p>
-
-<p><b>45. Absorption by Algæ and Fungi.</b>—In the simpler forms of
-plant life, as in spirogyra and many of the algæ and fungi, the plant
-body is not differentiated into parts.<a name="FNanchor_5_5" id="FNanchor_5_5"></a><a href="#Footnote_5_5" class="fnanchor">[5]</a>
-In many other cases the only differentiation is between the growing
-part and the fruiting part. In the algæ and fungi there is no
-differentiation into stem and leaf, though there is an approach to it
-in some of the higher forms. Where this simple plant body is flattened,
-as in the sea-wrack, or ulva, it is a <i>frond</i>. The Latin word for
-frond is <i>thallus</i>, and this name is applied to the plant body of all
-the lower plants, the algæ and fungi. The algæ and fungi together
-are sometimes called the <i>thallophytes</i>, or <i>thallus plants</i>. The
-word thallus is also sometimes applied to the flattened body of the
-liverworts. In the foliose liverworts and mosses there is an axis with
-leaf-like expansions. These are believed by some to represent true
-stems and leaves, by others to represent a flattened thallus in which
-the margins are deeply and regularly divided, or in which the expansion
-has only taken place at regular intervals.</p>
-
-<p>In nearly all of the algæ the plant body is submerged in water. In these
-<span class="pagenum"><a name="Page_23" id="Page_23">[Pg 23]</a></span>
-cases absorption takes place through all portions of the surface in
-contact with the water, as in spirogyra, vaucheria, and all of the
-larger seaweeds. Comparatively few of the algæ grow on the surfaces
-of rocks or trees. In these examples it is likely that at times only
-portions of the plant body serve in the process of absorption of water
-from the substratum. A few of the algæ are parasitic, living in the
-tissues of higher plants, where they are surrounded by the water or
-liquids within the host. Absorption takes place in the same way in many
-of the fungi. The aquatic fungi are immersed in water. In other forms,
-like mucor, a portion of the mycelium is within the substratum, and
-being bathed by the water or watery solutions absorbs the same, while
-the fruiting portion and the aerial mycelium obtain their water and
-food solutions from the mycelium in the substratum. In higher fungi,
-like the mushrooms, the mycelium within the ground or decaying wood
-absorbs the water necessary for the fruiting portion; while in the case
-of the parasitic fungi the mycelium lies in the water or liquid within
-the host.</p>
-
-<div class="figright">
-   <a id="FIG_30" name="FIG_30">&nbsp;</a>
-    <img src="images/fig30.jpg" alt="" width="200" height="177" />
-    <p class="center">Fig. 30.<br />Thallus of Riccia lutescens.</p>
-</div>
-
-<p><b>46. Absorption by liverworts.</b>—In many of the plants termed
-liverworts the vegetative part of the plant is a thin, flattened, more
-or less elongated green body known as a thallus.</p>
-
-<p><i>Riccia.</i>—One of these, belonging to the genus riccia, is shown in
-<a href="#FIG_30">fig. 30</a>. Its shape is somewhat like that of a minute ribbon
-which is forked at intervals in a dichotomous manner, the characteristic kind of
-branching found in these thalloid liverworts. This riccia (known as R.
-lutescens) occurs on damp soil; long, slender, hair-like processes grow
-out from the under surface of the thallus which resemble root hairs and
-serve the same purpose in the processes of absorption. Another species
-of riccia (R. crystallina) is shown in <a href="#FIG_252">fig. 252</a>. This
-plant is quite circular in outline and occurs on muddy flats. Some species float
-on the water.</p>
-
-<p><b>47. Marchantia.</b>—One of the larger and coarser liverworts is
-<a href="#FIG_31">figured at 31</a>. This is a very common liverwort, growing in
-very damp and muddy places and also along the margins of streams, on the mud or
-<span class="pagenum"><a name="Page_24" id="Page_24">[Pg 24]</a></span>
-upon the surfaces of rocks which are bathed with the water. This is
-known as <i>Marchantia polymorpha</i>. If we examine the under surface of
-the marchantia we see numerous hair-like processes which attach the
-plant to the soil. Under the microscope we see that some of these are
-similar to the root hairs of the seedlings which we have been studying,
-and they serve the purpose of absorption. Since, however, there are no
-roots on the marchantia plant, these hair-like outgrowths are usually
-termed here <i>rhizoids</i>. In marchantia they are of two kinds, one kind
-the simple ones with smooth walls, and the other kind in which the
-inner surfaces of the walls are roughened by processes which extend
-inward in the form of irregular tooth-like points. Besides the hairs on
-the under side of the thallus we note especially near the growing end
-that there are two rows of leaf-like scales, those at the end of the
-thallus curving up over the growing end, thus serving to protect the
-delicate tissues at the growing point.</p>
-
-<div class="figcenter">
-   <a id="FIG_31" name="FIG_31">&nbsp;</a>
-    <img src="images/fig31.jpg" alt="" width="600" height="364" />
-    <p class="center">Fig. 31.<br />
-           Marchantia plant with cupules and gemmæ; rhizoids below.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_25" id="Page_25">[Pg 25]</a></span></p>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <img id="FIG_32" src="images/fig32.jpg" alt="" width="100" height="248" />
-   <p class="center">Fig. 32.</p>
-   <p class="center">Portion of plant<br /> of Frullania,<br /> a foliose<br /> liverwort.</p>
-  </div>
-  <div class="figsub">
-   <img id="FIG_33"  src="images/fig33.jpg" alt="" width="150" height="245" />
-   <p class="center">Fig. 33.</p>
-   <p class="center">Portion of same<br /> more highly<br /> magnified, showing<br /> overlapping leaves.</p>
-   </div>
-  <div class="figsub">
-   <img id="FIG_34"  src="images/fig34.jpg" alt="" width="150" height="257" />
-   <p class="center">Fig. 34.</p>
-   <p class="center">Under side,<br /> showing forked<br /> under row of<br />
-                      leaves and lobes<br /> of lateral leaves.</p>
-   </div>
-</div>
-
-<p><b>48. Frullania.</b>—In <a href="#FIG_32">fig. 32</a> is shown another liverwort,
-which differs greatly in form from the ones we have just been studying in
-that there is a well-defined axis with lateral leaf-like outgrowths.
-Such liverworts are called foliose liverworts. Besides these two quite
-prominent rows of leaves there is a third row of poorly developed
-leaves on the under surface. Also from the under surface of the axis we
-see here and there slender outgrowths, the rhizoids, through which much
-of the water is absorbed.</p>
-
-<div class="figcenter">
-    <img src="images/fig35.jpg" alt="" width="600" height="337" />
-    <p class="center">Fig. 35.<br />Foliose liverwort (bazzania) showing<br />
-               dichotomous branching and overlapping leaves.</p>
-</div>
-
-<p><b>49. Absorption by the mosses.</b>—Among the mosses, which are
-usually common in moist and shaded situations, examples are abundant
-which are suitable for the study of the organs of absorption. If we
-take for example a plant of mnium (M. affine), which is illustrated in
-<a href="#FIG_36">fig. 36</a>, we note that it consists of a slender axis with thin flat,
-<span class="pagenum"><a name="Page_26" id="Page_26">[Pg 26]</a></span>
-green, leaf-like expansions, Examining with the microscope the lower
-end of the axis, which is attached to the substratum, there are seen
-numerous brown-colored threads more or less branched.</p>
-
-<div class="figleft">
-    <img id="FIG_36" src="images/fig36.jpg" alt="" width="100" height="297" />
-    <p class="center">Fig. 36.<br /><br />Female plant (gametophyte)<br />
-         of a moss (mnium), showing<br />rhizoids below, and the<br />
-         tuft of leaves above,<br /> which protect the<br />archegonia.</p>
-</div>
-
-<p><b>50. Absorption by the higher aquatic plants.</b>—Examples of
-the water plants which are entirely submerged in water are the
-water-crowfoots, some of the pondweeds, elodea or water-weeds, the
-tape-grass, vallisneria, etc. In these plants all parts of the body
-being submerged, they absorb water with which they are in contact. In
-other aquatic plants, like the water-lilies, some of the pondweeds, the
-duck-meats, etc., are only partially submerged in the water; the upper
-surface of the leaf or of the leaf-like expansion being exposed to the
-air, while the under surface lies in close contact with the water, and
-the stems and the petioles of the leaves are also immersed in water. In
-these plants absorption takes place through those parts in contact with
-the water.</p>
-
-<p><a id="PARA_51" name="PARA_51"><b>51. Absorption by the duck-meats.</b></a>—These
-plants are very curious examples of the higher plants.</p>
-
-<p class="blockquot"><i>Lemna.</i>—One of these is illustrated in <a href="#FIG_37">fig. 37</a>.
-This is the common duckweed, <i>Lemna trisulca</i>. It is very peculiar
-in form and in its mode of growth. Each one of the lateral leaf-like
-expansions extends outwards by the elongation of the basal part,
-which becomes long and slender. Next, two new lateral expansions are
-formed on these by prolification from near the base, and thus the
-plant continues to extend. The plant occurs in ponds and ditches and
-is sometimes very common and abundant. It floats on the surface of the
-water. While the flattened part of the plant resembles a leaf, it is
-really the stem, no leaves being present. This expanded green body is
-usually termed a “frond.” A single rootlet grows out from the under
-side and is destitute of root hairs. Absorption of water therefore
-takes place through this rootlet and through the under side of the “frond.”
-<span class="pagenum"><a name="Page_27" id="Page_27">[Pg 27]</a></span></p>
-
-<div class="figcenter">
-    <img id="FIG_37" src="images/fig37.jpg" alt="" width="600" height="302" />
-    <p class="center">Fig. 37.<br />Fronds of the duckweed (Lemna trisculca).</p>
-</div>
-<div class="figcenter">
-    <img id="FIG_38" src="images/fig38.jpg" alt="" width="400" height="301" />
-    <p class="center">Fig. 38.<br />Spirodela polyrhiza.</p>
-</div>
-
-<p><b>52. Spirodela polyrhiza.</b>—This is a very curious plant, closely
-related to the lemna and sometimes placed in the same genus. It occurs
-in similar situations, and is very readily grown in aquaria. It reminds
-one of a little insect as seen in <a href="#FIG_38">fig. 38</a>. There are several
-rootlets on the under side of the frond. Absorption of water takes place here in
-the same way as in lemna.</p>
-
-<p><b>53. Absorption in wolffia.</b>—Perhaps the most curious of these
-modified water plants is the little wolffia, which contains the
-smallest specimens of the flowering plants. Two species of this genus
-are shown in <a href="#FIG_39">figs. 39-41</a>. The plant body is reduced to
-nothing but a rounded or oval green body, which represents the stem. No leaves or
-roots are present. The plants multiply by “prolification,” the new
-fronds growing out from a depression on the under side of one end.
-Absorption takes place through the under surface.</p>
-
-<p><a id="PARA_54" name="PARA_54"><b>54. Absorption by land plants.</b></a>—<i>Water cultures.</i>—In connection
-<span class="pagenum"><a name="Page_28" id="Page_28">[Pg 28]</a></span>
-with our inquiry as to how land plants obtain their water, it will be
-convenient to prepare some water cultures to illustrate this and which
-can also be used later in our study of nutrition (<a href="#CHAPTER_IX">Chapter IX</a>).</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <img id="FIG_39" src="images/fig39.jpg" alt="" width="150" height="237" />
-   <p class="center space-above3">Fig. 39.<br /> Young frond of wolffia<br /> growing out of older one.</p>
-  </div>
-  <div class="figsub">
-   <img id="FIG_40" src="images/fig40.jpg" alt="" width="150" height="269" />
-   <p class="center space-above1">Fig. 40.<br /> Young frond of wolffia<br /> separating from older one.</p>
-   </div>
-  <div class="figsub">
-   <img id="FIG_41" src="images/fig41.jpg" alt="" width="150" height="293" />
-   <p class="center">Fig. 41.<br /> Another species of<br /> wolffia, the two fronds<br /> still connected.</p>
-   </div>
-</div>
-
-<p>Chemical analysis shows that certain mineral substances are common
-constituents of plants. By growing plants in different solutions of
-these various substances it has been possible to determine what ones
-are necessary constituents of plant food. While the proportion of the
-mineral elements which enter into the composition of plant food may
-vary considerably within certain limits, the concentration of the
-solutions should not exceed certain limits. A very useful solution is
-one recommended by Sachs, and is as follows:</p>
-
-<p><b>55. Formula for water cultures</b>:</p>
-
-<table border="0" cellspacing="0" summary=" " cellpadding="0" >
-  <tbody><tr>
-      <td class="tdl">Water</td>
-      <td class="tdr_ws1">1000</td>
-      <td class="tdc">cc.</td>
-   </tr><tr>
-      <td class="tdl">Potassium nitrate</td>
-      <td class="tdr_ws1">0.5</td>
-      <td class="tdc">gr.</td>
-   </tr><tr>
-      <td class="tdl">Sodium chloride</td>
-      <td class="tdr_ws1">0.5</td>
-      <td class="tdc">“</td>
-   </tr><tr>
-      <td class="tdl">Calcium sulphate</td>
-      <td class="tdr_ws1">0.5</td>
-      <td class="tdc">“</td>
-   </tr><tr>
-      <td class="tdl">Magnesium sulphate&nbsp;&emsp;&nbsp;</td>
-      <td class="tdr_ws1">0.5</td>
-      <td class="tdc">“</td>
-   </tr><tr>
-      <td class="tdl">Calcium phosphate</td>
-      <td class="tdr_ws1">0.5</td>
-      <td class="tdc">“</td>
-   </tr>
- </tbody>
-</table>
-
-<p>The calcium phosphate is only partly soluble. The solution which is not
-in use should be kept in a dark cool place to prevent the growth of
-minute algæ.</p>
-
-<p><b>56.</b> Several different plants are useful for experiments in water
-cultures, as peas, corn, beans, buckwheat, etc. The seeds of these
-plants may be germinated, after soaking them for several hours in warm
-<span class="pagenum"><a name="Page_29" id="Page_29">[Pg 29]</a></span>
-water, by placing them between the folds of wet paper on shallow trays,
-or in the folds of wet cloth. The seeds should not be kept immersed in
-water after they have imbibed enough to thoroughly soak and swell them.
-At the same time that the seeds are placed in damp paper or cloth for
-germination, one lot of the soaked seeds should be planted in good soil
-and kept under the same temperature conditions, for control. When the
-plants have germinated one series should be grown in distilled water,
-which possesses no plant food; another in the nutrient solution, and
-still another in the nutrient solution to which has been added a few
-drops of a solution of iron chloride or ferrous sulphate. There would
-then be four series of cultures which should be carried out with the
-same kind of seed in each series so that the comparisons can be made on
-the same species under the different conditions. The series should be
-numbered and recorded as follows:</p>
-
-<ul class="index">
-<li class="isub1">No. 1, soil.</li>
-<li class="isub1">No. 2, distilled water.</li>
-<li class="isub1">No. 3, nutrient solution.</li>
-<li class="isub1">No. 4, nutrient solution with a few drops of iron solution added.</li>
-</ul>
-
-<div class="figright">
-    <img src="images/fig42.jpg" alt="" width="200" height="304" />
-    <p class="center">Fig. 42.<br />Culture cylinder to<br />
-             show position of corn<br /> seedling (Hansen).</p>
-</div>
-
-<p><b>57.</b> Small jars or wide-mouth bottles, or crockery jars, can be
-used for the water cultures, and the cultures are set up as follows: A
-cork which will just fit in the mouth of the bottle, or which can be
-supported by pins, is perforated so that there is room to insert the
-seedling, with the root projecting below into the liquid. The seed can
-be fastened in position by inserting a pin through one side, if it is a
-large one, or in the case of small seeds a cloth of a coarse mesh can
-be tied over the mouth of the bottle instead of using the cork. After
-properly setting up the experiments the cultures should be arranged
-in a suitable place, and observed from time to time during several
-weeks. In order to obtain more satisfactory results several duplicate
-series should be set up to guard against the error which might arise
-from variation in individual plants and from accident. Where there are
-several students in a class, a single series set up by several will
-act as checks upon one another. If glass jars are used for the liquid
-cultures they should be wrapped with black paper or cloth to exclude
-the light from the liquid, otherwise numerous minute algæ are apt to
-grow and interfere with the experiment. Or the jars may be sunk in pots
-of earth to serve the same purpose. If crockery jars are used they will
-not need covering.</p>
-
-<p><b>58.</b> For some time all the plants grow equally well, until the
-nutriment stored in the seed is exhausted. The numbers 1, 3 and 4, in
-<span class="pagenum"><a name="Page_30" id="Page_30">[Pg 30]</a></span>
-soil and nutrient solutions, should outstrip number 2, the plants in
-the distilled water. No. 4 in the nutrient solution with iron, having a
-perfect food, compares favorably with the plants in the soil.</p>
-
-<p><b>59. Plants take liquid food from the soil.</b>—From these
-experiments then we judge that such plants take up the food they
-receive from the soil in the form of a liquid, the elements being in
-solution in water.</p>
-
-<p>If we recur now to the experiments which were performed with the salt
-solution in producing plasmolysis in the cells of spirogyra, in the
-cells of the beet or corn, and in the root hairs of the corn and bean
-seedlings, and the way in which these cells become turgid again when
-the salt solution is removed and they are again bathed with water, we
-shall have an explanation of the way in which plants take up nutrient
-solutions of food material through their roots.</p>
-
-<div class="figcenter">
-    <img id="FIG_43" src="images/fig43.jpg" alt="" width="600" height="467" />
-    <p class="center">Fig. 43.<br /> Section of corn root, showing rhizoids<br />
-                  formed from elongated epidermal cells.</p>
-</div>
-
-<p><b>60. How food solutions are carried into the plant.</b>—We can see
-<span class="pagenum"><a name="Page_31" id="Page_31">[Pg 31]</a></span>
-how water and food solutions are carried into the plant, and we must
-next turn our attention to the way in which these solutions are carried
-farther into the plant. We should make a section across the root of a
-seedling in the region of the root hairs and examine it with the aid
-of a microscope. We here see that the root hairs are formed by the
-elongation of certain of the surface cells of the root. These cells
-elongate perpendicularly to the root, and become <i>3mm</i> to <i>6mm</i> long.
-They are flexuous or irregular in outline and cylindrical, as shown in
-<a href="#FIG_43">fig. 43</a>. The end of the hair next the root fits in between
-the adjacent superficial cells of the root and joins closely to the next deeper
-layer of cells. In studying the section of the young root we see that
-the root is made up of cells which lie closely side by side, each with
-its wall, its protoplasm and cell-sap, the protoplasmic membrane lying
-on the inside of each cell wall.</p>
-
-<p><b>61.</b> In the absorption of the watery solutions of plant food
-by the root hairs, the cell-sap, being a more concentrated solution,
-gains some of the former, since the liquid of less concentration flows
-through the protoplasmic membrane into the more concentrated cell-sap,
-increasing the bulk of the latter. This makes the root hairs turgid,
-and at the same time dilutes the cell-sap so that the concentration is
-not so great. The cells of the root lying inside and close to the base
-of the root hairs have a cell-sap which is now more concentrated than
-the diluted cell-sap of the hairs, and consequently gain some of the
-food solutions from the latter, which tends to lessen the content of
-the root hairs and also to increase the concentration of the cell-sap
-of the same. This makes it possible for the root hairs to draw on
-the soil for more of the food solutions, and thus, by a variation in
-the concentration of the substances in solution in the cell-sap of
-the different cells, the food solutions are carried along until they
-reach the <i>vascular bundles</i>, through which the solutions are carried
-to distant parts of the plant. Some believe that there is a rhythmic
-action of the elastic cell walls in these cells between the root hairs
-and the vascular bundles. This occurs in such a way that, after the
-cell becomes turgid, it contracts, thus reducing the size of the cell
-and forcing some of the food solutions into the adjacent cells, when
-by absorption of more food solutions, or water, the cell increases in
-turgidity again. This rhythmic action of the cells, if it does take
-place, would act as a pump to force the solutions along, and would form
-one of the causes of root pressure.</p>
-
-<p><b>62. How the root hairs get the watery solutions from the
-soil.</b>—If we examine the root hairs of a number of seedlings which
-are growing in the soil under normal conditions, we shall see that a
-large quantity of soil readily clings to the roots. We should note also
-that unless the soil has been recently watered there is no free water
-<span class="pagenum"><a name="Page_32" id="Page_32">[Pg 32]</a></span>
-in it; the soil is only moist. We are curious to know how plants can
-obtain water from soil which is not wet. If we attempt to wash off the
-soil from the roots, being careful not to break away the root hairs,
-we find, that small particles cling so tenaciously to the root hairs
-that they are not removed. Placing a few such root hairs under the
-microscope it appears as if here and there the root hairs were glued to
-the minute soil particles.</p>
-
-<div class="figcenter">
-    <img src="images/fig44.jpg" alt="" width="600" height="415" />
-    <p class="center">Fig. 44.<br /> Root hairs of corn seedling with
-                     soil particles adhering closely.</p>
-</div>
-
-<p><b>63.</b> If now we take some of the soil which is only moist, weigh
-it, and then permit it to become quite dry on exposure to dry air, and
-weigh again, we find that it loses weight in drying. Moisture has been
-given off. This moisture, it has been found, forms an exceedingly thin
-film on the surface of the minute soil particles. Where these soil
-particles lie closely together, as they usually do when massed together
-in the pot or elsewhere, this thin film of moisture is continuous from
-the surface of one particle to that of another. Thus the soil particles
-which are so closely attached to the root hairs connect the surface
-of the root hairs with this film of moisture. As the cell-sap of the
-root hairs draws on the moisture film with which they are in contact,
-the tension of this film is sufficient to draw moisture from distant
-particles. In this way the roots are supplied with water in soil which
-is only moist.</p>
-
-<p><b>64. Plants cannot remove all the moisture from the soil.</b>—If we
-now take a potted plant, or a pot containing a number of seedlings,
-place it in a moderately dry room, and do not add water to the soil we
-find in a few days that the plant is wilting. The soil if examined will
-appear quite dry to the sense of touch. Let us weigh some of this soil,
-<span class="pagenum"><a name="Page_33" id="Page_33">[Pg 33]</a></span>
-then dry it by artificial heat, and weigh again. It has lost in weight.
-This has been brought about by driving off the moisture which still
-remained in the soil after the plant began to wilt. This teaches that
-while plants can obtain water from soil which is only moist or which is
-even rather dry, they are not able to withdraw all the moisture from
-the soil.</p>
-
-<div class="figleft">
-    <img id="FIG_45" src="images/fig45.jpg" alt="" width="150" height="366" />
-    <p class="center">Fig. 45.<br /> Experiment to show<br /> root pressure<br />
-                       (Detmer).</p>
-</div>
-
-<p><b>65. “Root pressure” or exudation pressure.</b>—It is a very common
-thing to note, when certain shrubs or vines are pruned in the spring,
-the exudation of a watery fluid from the cut surfaces. In the case of
-the grape vine this has been known to continue for a number of days,
-and in some cases the amount of liquid, called “sap,” which escapes is
-considerable. In many cases it is directly traceable to the activity
-of the roots, or root hairs, in the absorption of water from the soil.
-For this reason the term <i>root pressure</i> has been used to denote the
-force exerted in supplying the water from the soil. But there are some
-who object to the use of this term “root pressure.” The principal
-objection is that the pressure which brings about the phenomenon
-known as “bleeding” by plants is not present in the roots alone. This
-pressure exists under certain conditions in all parts of the plant. The
-term exudation pressure has been proposed in lieu of root pressure. It
-should be remembered that the movement of water in the plant is started
-by the pressure which exists in the root. If the term “root pressure”
-is used, it should be borne clearly in mind that it does not express
-the phenomenon exactly in all cases.</p>
-
-<p><b>Root pressure may be measured.</b>—It is possible to measure
-not only the amount of water which the roots will raise in a given
-time, but also to measure the force exerted by the roots during root
-pressure. It has been found that root pressure in the case of the
-nettle is sufficient to hold a column of water about 4.5 meters (15
-ft.) high (Vines), while the root pressure of the vine (Hales, 1721)
-will hold a column of water about 10 meters (36.5 ft.) high, and the
-birch (Betula lutea) (Clark, 1873) has a root pressure sufficient to
-hold a column of water about 25 meters (84.7 ft.) high.</p>
-
-<p><b>66. Experiment to demonstrate root pressure.</b>—By a very simple
-method this lifting of water by root pressure is shown. During the
-<span class="pagenum"><a name="Page_34" id="Page_34">[Pg 34]</a></span>
-summer season plants in the open may be used if it is preferred, but
-plants grown in pots are also very serviceable, and one may use a
-potted begonia or balsam, the latter being especially useful. The
-plants are usually convenient to obtain from the greenhouses, to
-illustrate this phenomenon. The stem is cut off rather close to the
-soil and a long glass tube is attached to the cut end of the stem,
-still connected with the roots, by the use of rubber tubing, as shown
-in <a href="#FIG_45">figure 45</a>, and a very small quantity of water may be poured
-in to moisten the cut end of the stem. In a few minutes the water begins to
-rise in the glass tube. In some cases it rises quite rapidly, so that
-the column of water can readily be seen to extend higher and higher up
-in the tube when observed at quite short intervals. (To measure the
-force of root pressure is rather difficult for elementary work. To
-measure it see Ganong, Plant Physiology, pp. 67, 68, or some other book
-for advanced work.)</p>
-
-<p><b>67.</b> In either case where the experiment is continued for
-several days it is noticed that the column of water or of mercury
-rises and falls at different times during the same day, that is, the
-column stands at varying heights; or in other words the root pressure
-varies during the day. With some plants it has been found that the
-pressure is greatest at certain times of the day, or at certain
-seasons of the year. Such variation of root pressure exhibits what
-is termed a periodicity, and in the case of some plants there is a
-daily periodicity; while in others there is in addition an annual
-periodicity. With the grape vine the root pressure is greatest in
-the forenoon, and decreases from 12-6 <span class="smcap">p.m.</span>,
-while with the sunflower it is greatest before 10 <span class="smcap">a.m.</span>,
-when it begins to decrease. Temperature of the soil is one of the most
-important external conditions affecting the activity of root pressure.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_35" id="Page_35">[Pg 35]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_IV" id="CHAPTER_IV">CHAPTER IV.</a><br />
-<span class="h_subtitle">TRANSPIRATION, OR THE LOSS OF WATER<br /> BY PLANTS.</span></h3>
-</div>
-
-<p><b>68.</b> We should now inquire if all the water which is taken up in
-excess of that which actually suffices for turgidity is used in the
-elaboration of new materials of construction. We notice when a leaf
-or shoot is cut away from a plant, unless it is kept in quite a moist
-condition, or in a damp, cool place, that it becomes flaccid, and
-droops. It wilts, as we say. The leaves and shoot lose their turgidity.
-This fact suggests that there has been a loss of water from the shoot
-or leaf. It can be readily seen that this loss is not in the form of
-drops of water which issue from the cut end of the shoot or petiole.
-What then becomes of the water in the cut leaf or shoot?</p>
-
-<p><b>69. Loss of water from excised leaves.</b>—Let us take a handful of
-<span class="pagenum"><a name="Page_36" id="Page_36">[Pg 36]</a></span>
-fresh, green, rather succulent leaves, which are free from water on
-the surface, and place them under a glass bell jar, which is tightly
-closed below but which contains no water. Now place this in a brightly
-lighted window, or in sunlight. In the course of fifteen to thirty
-minutes we notice that a thin film of moisture is accumulating on the
-inner surface of the glass jar. After an hour or more the moisture has
-accumulated so that it appears in the form of small drops of condensed
-water. We should set up at the same time a bell jar in exactly the same
-way but which contains no leaves. In this jar there is no condensed
-moisture on the inner surface. We thus are justified in concluding that
-the moisture in the former jar comes from the leaves. Since there is no
-visible water on the surfaces of the leaves, or at the cut ends, before
-it may have condensed there, we infer that the water escapes from the
-leaves in the form of <i>water vapor</i>, and that this water vapor, when
-it comes in contact with the surface of the cold glass, condenses and
-forms the moisture film, and later the drops of water. The leaves of
-these cut shoots therefore lose water in the form of water vapor, and
-thus a loss of turgidity results.</p>
-
-<div class="figcenter">
-    <img src="images/fig46.jpg" alt="" width="600" height="188" />
-    <p class="center">Fig. 46.<br />To show loss of water from leaves,
-                    the leaves just covered.</p>
-    <img src="images/fig47.jpg" alt="" width="600" height="181" />
-    <p class="center">Fig. 47.<br />After a few hours drops of water have accumulated<br />
-                     on the inside of the jar covering the leaves.</p>
-</div>
-
-<p><b>70. Loss of water from growing plants.</b>—Suppose we now take a
-small and actively growing plant in a pot, and cover the pot and the
-<span class="pagenum"><a name="Page_37" id="Page_37">[Pg 37]</a></span>
-soil with a sheet of rubber cloth or flexible oilcloth which fits
-tightly around the stem of the plant so that the moisture from the soil
-or from the surface of the pot cannot escape. Then place a bell jar
-over the plant, and set in a brightly lighted place, at a temperature
-suitable for growth. In the course of a few minutes on a dry day a
-moisture film forms on the inner surface of the glass, just as it did
-in the case of the glass jar containing the cut shoots and leaves.
-Later the moisture has condensed so that it is in the form of drops. If
-we have the same leaf surface here as we had with the cut shoots, we
-shall probably find that a larger amount of water accumulates on the
-surface of the jar from the plant that is still attached to its roots.</p>
-
-<p><b>71. Water escapes from the surfaces of living leaves in the form of
-water vapor.</b>—This living plant then has lost water, which also
-escapes in the form of water vapor. Since here there are no cut places
-on the shoots or leaves, we infer that the loss of water vapor takes
-place from the surfaces of the leaves and from the shoots. It is also
-to be noted that, while this plant is losing water from the surfaces of
-the leaves, it does not wilt or lose its turgidity. The roots by their
-activity and pressure supply water to take the place of that which is
-given off in the form of water vapor. This loss of water in the form of
-water vapor by plants is <i>transpiration</i>.</p>
-
-<p><b>72. A test for the escape of water vapor from plants.</b>—Make
-a solution of cobalt chloride in water. Saturate several pieces of
-filter paper with it. Allow them to dry. The water solution of cobalt
-chloride is red. The paper is also red when it is moist, but when it
-is thoroughly dry it is blue. It is very sensitive to moisture and the
-moisture of the air is often sufficient to redden it. Before using dry
-the paper in an oven or over a flame.</p>
-
-<p><b>73.</b> Take two bell jars, as shown in <a href="#FIG_49">fig. 49</a>. Under
-one place a potted plant, the pot and earth being covered by oiled paper. Or cover
-the plant with a fruit jar. To a stake in the pot pin a piece of the
-<span class="pagenum"><a name="Page_38" id="Page_38">[Pg 38]</a></span>
-dried cobalt paper, and at the same time pin to a stake, in another
-jar covering no plant, another piece of cobalt paper. They should both
-be put under the jars at the same time. In a few moments the paper in
-the jar with the plant will begin to redden. In a short while, ten or
-fifteen minutes, probably, it will be entirely red, while the paper
-under the other jar will remain blue, or be only slightly reddened. The
-water vapor passing off from the living plant comes in contact with
-the sensitive cobalt chloride in the paper and reddens it before there
-is sufficient vapor present to condense as a film of moisture on the
-surface of the jar.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <img id="FIG_48" src="images/fig48.jpg" alt="" width="200" height="387" />
-   <p class="center">Fig. 48.</p>
-  </div>
-  <div class="figsub">
-   <img id="FIG_49"  src="images/fig49.jpg" alt="" width="400" height="378" />
-   <p class="center">Fig. 49.</p>
-   </div>
-   <div class="blockquot">
-   <p>Fig. 48.—Water vapor is given off by the leaves when attached to the
-                  living plant. It condenses into drops of water on the cool surface of
-                  the glass covering the plant.</p>
-   <p>Fig. 49.—A good way to show that the water passes off
-                   from the leaves in the form of water vapor.</p>
-   </div>
-</div>
-
-<p><b>74. Experiment to compare loss of water in a dry and a humid
-atmosphere.</b>—We should now compare the escape of water from the
-leaves of a plant covered by a bell jar, as in the last experiment,
-<span class="pagenum"><a name="Page_39" id="Page_39">[Pg 39]</a></span>
-with that which takes place when the plant is exposed in a normal way
-in the air of the room or in the open. To do this we should select
-two plants of the same kind growing in pots, and of approximately the
-same leaf surface. The potted plants are placed one each on the arms
-of a scale. One of the plants is covered in this position with a bell
-jar. With weights placed on the pan of the other arm the two sides are
-balanced. In the course of an hour, if the air of the room is dry,
-moisture has probably accumulated on the inner surface of the glass jar
-which is used to cover one of the plants. This indicates that there has
-here been a loss of water. But there is no escape of water vapor into
-the surrounding air so that the weight on this arm is practically the
-same as at the beginning of the experiment. We see, however, that the
-other arm of the balance has risen. We infer that this is the result of
-the loss of water vapor from the plant on that arm. Now let us remove
-the bell jar from the other plant, and with a cloth wipe off all the
-moisture from the inner surface, and replace the jar over the plant. We
-note that the end of the scale which holds this plant is still lower
-than the other end.</p>
-
-<p><b>75. The loss of water is greater in a dry than in a humid
-atmosphere.</b>—This teaches us that while water vapor escaped from
-the plant under the bell jar, the air in this receiver soon became
-saturated with the moisture, and thus the farther escape of moisture
-from the leaves was checked. It also teaches us another very important
-fact, viz., that plants lose water more rapidly through their leaves in
-a dry air than in a humid or moist atmosphere. We can now understand
-why it is that during the very hot and dry part of certain days plants
-often wilt, while at nightfall, when the atmosphere is more humid, they
-revive. They lose more water through their leaves during the dry part
-of the day, other things being equal, than at other times.</p>
-
-<p><b>76. How transpiration takes place.</b>—Since the water of
-transpiration passes off in the form of water vapor we are led to
-inquire if this process is simply <i>evaporation</i> of water through the
-surface of the leaves, or whether it is controlled to any appreciable
-<span class="pagenum"><a name="Page_40" id="Page_40">[Pg 40]</a></span>
-extent by any condition of the living plant. An experiment which is
-instructive in this respect we shall find in a comparison between the
-transpiration of water from the leaves of a cut shoot, allowed to lie
-unprotected in a dry room, and a similar cut shoot the leaves of which
-have been killed.</p>
-
-<p><b>77.</b> Almost any plant will answer for the experiment. For this
-purpose I have used the following method. Small branches of the locust
-(Robinia pseudacacia), of sweet clover (Melilotus alba), and of a
-heliopsis were selected. One set of the shoots was immersed for a
-moment in hot water near the boiling point to kill them. The other set
-was immersed for the same length of time in cold water, so that the
-surfaces of the leaves might be well wetted, and thus the two sets of
-leaves at the beginning of the experiment would be similar, so far as
-the amount of water on their surfaces is concerned. All the shoots were
-then spread out on a table in a dry room, the leaves of the killed
-shoots being separated where they are inclined to cling together. In
-a short while all the water has evaporated from the surface of the
-living leaves, while the leaves of the dead shoots are still wet on
-the surface. In six hours the leaves of the dead shoots from which the
-surface water had now evaporated were beginning to dry up, while the
-leaves of the living plants were only becoming flaccid. In twenty-four
-hours the leaves of the dead shoots were crisp and brittle, while those
-of the living shoots were only wilted. In twenty-four hours more the
-leaves of the sweet clover and of the heliopsis were still soft and
-flexible, showing that they still contained more water than the killed
-shoots which had been crisp for more than a day.</p>
-
-<p><b>78.</b> It must be then that during what is termed transpiration
-the living plant is capable of holding back the water to some extent,
-which in a dead plant would escape more rapidly by evaporation. It is
-also known that a body of water with a surface equal to that of a given
-leaf surface of a plant loses more water by evaporation during the same
-length of time than the plant loses by transpiration.</p>
-
-<p><b>79. Structure of a leaf.</b>—We are now led to inquire why it is
-that a living leaf loses water less rapidly than dead ones, and why
-less water escapes from a given leaf surface than from an equal surface
-of water. To understand this it will be necessary to examine the minute
-structure of a leaf. For this purpose we may select the leaf of an ivy,
-though many other leaves will answer equally well. From a portion of
-the leaf we should make very thin cross-sections with a razor or other
-sharp instrument. These sections should be perpendicular to the surface
-<span class="pagenum"><a name="Page_41" id="Page_41">[Pg 41]</a></span>
-of the leaf and should be then mounted in water for microscopic
-examination.<a name="FNanchor_6_6" id="FNanchor_6_6"></a><a href="#Footnote_6_6" class="fnanchor">[6]</a></p>
-
-<p><b>80. Epidermis of the leaf.</b>—In this section we see that the
-green part of the leaf is bordered on what are its upper and lower
-surfaces by a row of cells which possess no green color. The walls of
-the cells of each row have nearly parallel sides, and the cross walls
-are perpendicular. These cells form a single layer over both surfaces
-of the leaf and are termed the <i>epidermis</i>. Their walls are quite stout
-and the outer walls are <i>cuticularized</i>.</p>
-
-<div class="figcenter">
-    <img src="images/fig50.jpg" alt="" width="200" height="252" />
-    <p class="center">Fig. 50.<br /> Section through ivy leaf showing<br /> communication between stomate<br />
-                       and the large intercellular spaces<br /> of the leaf, stoma closed.</p>
-</div>
-<div class="figcontainer">
-  <div class="figsub">
-   <img id="FIG_51" src="images/fig51.jpg" alt="" width="250" height="228" />
-   <p class="center">Fig. 51.<br /> Stoma open.</p>
-  </div>
-  <div class="figsub">
-   <img id="FIG_52" src="images/fig52.jpg" alt="" width="250" height="223" />
-   <p class="center">Fig. 52.<br /> Stoma closed.</p>
-  </div>
-      <p class="center">Figs. 51, 52.—Section through stomata of ivy leaf.</p>
-</div>
-
-<p><b>81. Soft tissue of the leaf.</b>—The cells which contain the green
-chlorophyll bodies are arranged in two different ways. Those on the
-upper side of the leaf are usually long and prismatic in form and
-lie closely parallel to each other. Because of this arrangement of
-these cells they are termed the <i>palisade</i> cells, and form what is
-called the <i>palisade layer</i>. The other green cells, lying below, vary
-greatly in size in different plants and to some extent also in the same
-plant. Here we notice that they are elongated, or oval, or somewhat
-irregular in form. The most striking peculiarity, however, in their
-arrangement is that they are not usually packed closely together, but
-each cell touches the other adjacent cells only at certain points. This
-arrangement of these cells forms quite large spaces between them, the
-intercellular spaces. If we should examine such a section of a leaf
-<span class="pagenum"><a name="Page_42" id="Page_42">[Pg 42]</a></span>
-before it is mounted in water we would see that the intercellular
-spaces are not filled with water or cell-sap, but are filled with air
-or some gas. Within the cells, on the other hand, we find the cell-sap
-and the protoplasm.</p>
-
-<p><b>82. Stomata.</b>—If we examine carefully the row of epidermal cells
-on the under surface of the leaf, we find here and there a peculiar
-arrangement of cells shown at figs. <a href="#FIG_51">51</a>, <a href="#FIG_52">52</a>. This
-opening through the epidermal layer is a <i>stoma</i>. The cells which immediately surround
-the openings are the <i>guard cells</i>. The form of the guard cells can be
-better seen if we tear a leaf in such a way as to strip off a short
-piece of the lower epidermis, and mount this in water. The guard cells
-are nearly crescent-shaped, and the stoma is elliptical in outline. The
-epidermal cells are very irregular in outline in this view. We should
-also note that while the epidermal cells contain no chlorophyll, the
-guard cells do.</p>
-
-<div class="figcenter">
-    <img src="images/fig53.jpg" alt="" width="600" height="305" />
-    <p class="center">Fig. 53.<br /> Portion of epidermis of ivy, showing irregular<br />
-                     epidermal cells, stoma and guard cells.</p>
-</div>
-
-<p><b>82</b><i>a</i>. In the ivy leaf the guard cells are quite plain, but in
-most plants the form as seen in cross-section is irregular in outline,
-as shown in <a href="#FIG_53A">fig. 53<i>a</i></a>, which is from a section of a
-wintergreen leaf. This leaf is interesting because it shows the characteristic structure
-of leaves of many plants growing in soil where absorption of water by
-the roots is difficult owing to the cold water, acids, or salts in the
-water or soil, or in dry soil (see Chapters <a href="#CHAPTER_XLVII">47</a>,
-54, 55). The cuticle over the upper epidermis is quite thick. This
-lessens the loss of water by the leaf. The compact palisades of cells
-are in two to three cell layers, also reducing the loss of water.</p>
-
-<p><b>83. The living protoplasm retards the evaporation of water from the
-leaf.</b>—If we now take into consideration a few facts which we have
-<span class="pagenum"><a name="Page_43" id="Page_43">[Pg 43]</a></span>
-learned in a previous chapter, with reference to the physical
-properties of the living cell, we shall be able to give a partial
-explanation of the comparative slowness with which the water escapes
-from the leaves. The inner surfaces of the cell walls are lined with
-the membrane of protoplasm, and within this is the cell-sap. These
-cells have become turgid by the absorption of the water which has
-passed up to them from the roots. While the protoplasmic membrane of
-the cells does not readily permit the water to filter through, yet it
-is saturated with water, and the elastic cell wall with which it is in
-contact is also saturated. From the cell wall the water evaporates into
-the intercellular spaces. But the water is given up slowly through the
-protoplasmic membrane, so that the water vapor cannot be given off as
-rapidly from the cell walls as it could if the protoplasm were dead.
-The living protoplasmic membrane then which is only slowly permeable to
-the water of the cell-sap is here a very important factor in checking
-the too rapid loss of water from the leaves.</p>
-
-<div class="figcenter">
-    <img id="FIG_53A" src="images/fig53a.jpg" alt="" width="600" height="437" />
-    <p class="center">Fig. 53<i>a</i>.<br /> Cross-section of leaf of wintergreen. <i>Cu.</i>, cuticle; <i>Epid.</i>,<br />
-                   epidermis; <i>v.d.</i>, vascular duct; <i>Int. c. sp.</i>, intercellular space;<br />
-                   <i>L. ep.</i>, lower epidermis; <i>St.</i>, stoma.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_44" id="Page_44">[Pg 44]</a></span>
-By an examination of our leaf section we see that the intercellular
-spaces are all connected, and that the stomata, where they occur, open
-also into intercellular spaces. There is here an opportunity for the
-water vapor in the intercellular spaces to escape when the stomata are
-open.</p>
-
-<p><b>84. Action of the stomata.</b>—The guard cells serve an important
-function in regulating transpiration. During normal transpiration the
-guard cells are turgid and their peculiar form then causes them to arch
-away from each other, allowing the escape of water vapor. When the air
-becomes too dry transpiration is in excess of absorption by the roots.
-The guard cells lose some of their water, and collapse so that their
-inner faces meet in a straight line and close the stoma. Thus the rapid
-transpiration is checked. Some evaporation of water vapor, however,
-takes place through the epidermal cells, and if the air remains too
-dry, the leaves eventually become flaccid and droop. During the day
-the effect of sunlight is to increase certain sugars or salts in the
-guard cells so that they readily become turgid and open the stomates,
-but at night the cell-sap is less concentrated and the stomates are
-usually closed. Light therefore favors transpiration, while in darkness
-transpiration is checked.</p>
-
-<p><b>85. Compare transpiration from the two surfaces of the
-leaf.</b>—This can be done by using the cobalt chloride paper. This
-paper can be kept from year to year and used repeatedly. It is thus a
-very simple matter to make these experiments. Provide two pieces of
-glass (discarded glass negatives, cleaned, are excellent), two pieces
-of cobalt chloride paper, and some geranium leaves entirely free from
-surface water. Dry the paper until it is blue. Place one piece of the
-paper on a glass plate; place the geranium leaf with the under side on
-the paper. On the upper side of the leaf now place the other cobalt
-paper, and next the second piece of glass. On the pile place a light
-weight to keep the parts well in contact. In fifteen or twenty minutes
-open and examine. The paper next the under side of the geranium leaf
-is red where it lies under the leaf. The paper on the upper side is
-only slightly reddened. The greater loss of water, then, is through the
-under side of the geranium leaf. This is true of a great many leaves,
-but it is not true of all.</p>
-
-<p><b>86. Negative pressure.</b>—This is not only indicated by the
-drooping of the leaves, but may be determined in another way. If the
-shoot of such a plant be cut underneath mercury, or underneath a strong
-solution of eosin, it will be found that some of the mercury or eosin,
-as the case may be, will be forcibly drawn up into the stem toward the
-roots. This is seen on quickly splitting the cut end of the stem. When
-plants in the open cannot be obtained in this condition, one may take
-a plant like a balsam plant from the greenhouse, or some other potted
-plant, knock it out of the pot, free the roots from the soil and allow
-to partly wilt. The stem may then be held under the eosin solution and cut.
-<span class="pagenum"><a name="Page_45" id="Page_45">[Pg 45]</a></span></p>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <img id="FIG_54" src="images/fig54.jpg" alt="" width="150" height="236" />
-   <p class="center">Fig. 54.<br /> Experiment to show lifting<br /> power of transpiration.</p>
-  </div>
-  <div class="figsub">
-   <a><img id="FIG_55"  src="images/fig55.jpg" alt="" width="350" height="226" /></a>
-   <p class="center">Fig. 55.<br /> Estimation of the amount of transpiration. The tubes are filled with<br />
-                 water, and as the water transpires from the leaf surface its movement<br />
-                 in the tube from <i>a</i> to <i>b</i> can be measured. (After Mangin.)</p>
-   </div>
-</div>
-
-<p><b>87. Lifting power of transpiration.</b>—Not only does transpiration
-go on quite independently of root pressure, as we have discovered
-from other experiments, but transpiration is capable of exerting a
-lifting power on the water in the plant. This may be demonstrated in
-the following way: Place the cut end of a leafy shoot in one end of a
-U tube and fit it water-tight. Partly fill this arm of the U tube with
-water, and add mercury to the other arm until it stands at a level in
-the two arms as in <a href="#FIG_54">fig. 54</a>. In a short time
-we note that the mercury is rising in the tube.</p>
-
-<p><b>88. Root pressure may exceed transpiration.</b>—If we cover small
-actively growing plants, such as the pea, corn, wheat, bean, etc.,
-with a bell jar, and place them in the sunlight where the temperature
-is suitable for growth, in a few hours, if conditions are favorable,
-we shall see that there are drops of water standing out on the margins
-of the leaves. These drops of water have exuded through the ordinary
-stomata, or in other cases what are called water stomata, through the
-influence of root pressure. The plant being covered by the glass jar,
-the air soon becomes saturated with moisture and transpiration is
-checked. Root pressure still goes on, however, and the result is shown
-in the exuding drops. Root pressure is here in excess of transpiration.
-This phenomenon is often to be observed during the summer season in the
-case of low-growing plants. During the bright warm day transpiration
-equals, or may be in excess of, root pressure, and the leaves are
-consequently flaccid. As nightfall comes on the air becomes more
-moist, and the conditions of light are such also that transpiration
-is lessened. Root pressure, however, is still active because the soil
-is still warm. In these cases drops of water may be seen exuding from
-the margins of the leaves due to the excess of root pressure over
-transpiration. Were it not for this provision for the escape of the
-excess of water raised by root pressure, serious injury by lesions, as
-a result of the great pressure, might result. The plant is thus to some
-extent a self-regulatory piece of apparatus so far as root pressure and
-transpiration are concerned.</p>
-
-<p><b>89. Injuries caused by excessive root pressure.</b>—Some varieties
-of tomatoes when grown in poorly lighted and poorly ventilated
-<span class="pagenum"><a name="Page_46" id="Page_46">[Pg 46]</a></span>
-greenhouses suffer serious injury through lesions of the tissues.
-This is brought about by the cells at certain parts becoming charged
-so full with water through the activity of root pressure and lessened
-transpiration, assisted also probably by an accumulation of certain
-acids in the cell-sap which cannot be got rid of by transpiration.
-Under these conditions some of the cells here swell out, forming
-extensive cushions, and the cell walls become so weakened that they
-burst. It is possible to imitate the excess of root pressure in the
-case of some plants by connecting the stems with a system of water
-pressure, when very quickly the drops of water will begin to exude from
-the margins of the leaves.</p>
-
-<div class="figleft">
-    <img src="images/fig56.jpg" alt="" width="250" height="402" />
-    <p class="center">Fig. 56.<br /> The roots are lifting more water into the plant than<br />
-                         can be given off in the form of water vapor, so it is<br />
-                          pressed out in drops. From “First Studies Plant Life.”</p>
-</div>
-
-<p><b>90.</b> It should be stated that in reality there is no difference
-between transpiration and evaporation, if we bear in mind that
-evaporation takes place more slowly from living plants than from dead
-ones, or from an equal surface of water.</p>
-
-<p><b>91.</b> The escape of water vapor is not the only function of the
-stomata. The exchange of gases takes place through them as we shall
-later see. A large number of experiments show that normally the stomata
-are open when the leaves are turgid. But when plants lose excessive
-quantities of water on dry and hot days, so that the leaves become
-flaccid, the guard cells automatically close the stomata to check the
-escape of water vapor. Some water escapes through the epidermis of many
-plants, though the cuticularized membrane of the epidermis largely
-prevents evaporation. In arid regions plants are usually provided
-with an epidermis of several layers of cells to more securely prevent
-evaporation there. In such cases the guard cells are often protected by
-being sunk deeply in the epidermal layer.</p>
-
-<p><b>92. Demonstration of stomates and intercellular air spaces.</b>—A
-good demonstration of the presence of stomates in leaves, as well as
-the presence and intercommunication of the intercellular spaces, can be
-made by blowing into the cut end of the petiole of the leaf of a calla
-<span class="pagenum"><a name="Page_47" id="Page_47">[Pg 47]</a></span>
-lily, the lamina being immersed in water. The air is forced out
-through the stomata and rises as bubbles to the surface of the water.
-At the close of the experiment some of the air bubbles will still be
-in contact with the leaf surface at the opening of the stomata. The
-pressure of the water gradually forces this back into the leaf. Other
-plants will answer for the experiment, but some are more suitable than
-others.</p>
-
-<p><b>92a. Number of stomata.</b>—The larger number of stomata are on the
-under side of the leaf. (In leaves which float on the surface of the
-water all of the stomata are on the upper side of the leaf, as in the
-water-lily.) It has been estimated by investigation that in general
-there are 40-300 stomata to the square millimeter of surface. In some
-plants this number is exceeded, as in the olive, where there are 625.
-In an entire leaf of Brassica rapa there are about 11,000,000 stomata,
-and in an entire leaf of the sunflower there are about 13,000,000 stomata.</p>
-
-<p><b>92b. Amount of water transpired by plants.</b>—The amount of water
-transpired by plants is very great. According to careful estimates a
-sunflower 6 feet high transpires on the average about one quart per
-day; an acre of cabbages 2,000,000 quarts in four months; an oak tree
-with 700,000 leaves transpires about 180 gallons of water per day.
-According to von Höhnel, a beech tree 110 years old transpired about
-2250 gallons of water in one summer. A hectare of such trees (about 400
-on 2½ acres) would at the same rate transpire about 900,000 gallons, or
-about 30,000 barrels in one summer.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_48" id="Page_48">[Pg 48]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_V" id="CHAPTER_V">CHAPTER V.</a><br />
-<span class="h_subtitle">PATH OF MOVEMENT OF WATER IN PLANTS.</span></h3>
-</div>
-
-<p><b>93.</b> In our study of root pressure and transpiration we have
-seen that large quantities of water or solutions move upward through
-the stems of plants. We are now led to inquire through what part of the
-stems the liquid passes in this upward movement, or in other words,
-what is the path of the “sap” as it rises in the stem. This we can
-readily see by the following trial.</p>
-
-<p><b>94. Place the cut ends of leafy shoots in a solution of some of
-the red dyes.</b>—We may cut off leafy shoots of various plants and
-insert the cut ends in a vessel of water to which have been added a few
-crystals of the dye known as fuchsin to make a deep red color (other
-red dyes may be used, but this one is especially good). If the study is
-made during the summer, the “touch-me-not” (impatiens) will be found a
-very useful plant, or the garden balsam, which may also be had in the
-winter from conservatories. Almost any plant will do, however, but we
-should also select one like the corn plant (zea mays) if in the summer,
-or the petioles of a plant like caladium, which can be obtained from
-the conservatory. If seedlings of the castor-oil bean are at hand we
-may cut off some shoots which are 8-10 inches high, and place them in
-the solution also.</p>
-
-<p><b>95. These solutions color the tracts in the stem and leaves through
-which they flow.</b>—After a few hours in the case of the impatiens,
-or the more tender plants, we can see through the stem that certain
-tracts are colored red by the solution, and after 12 to 24 hours there
-<span class="pagenum"><a name="Page_49" id="Page_49">[Pg 49]</a></span>
-may be seen a red coloration of the leaves of some of the plants
-used. After the shoots have been standing in the solution for a few
-hours, if we cut them at various places we will note that there are
-several points in the section where the tissues are colored red. In
-the impatiens perhaps from four to five, in the sunflower a larger
-number. In these plants the colored areas on a cross-section of the
-stem are situated in a concentric ring which separates more or less
-completely an outer ring of the stem from the central portion. If we
-now split portions of the stem lengthwise we see that these colored
-areas continue throughout the length of the stem, in some cases even
-up to the leaves and into them.</p>
-
-<div class="figcenter">
-    <img id="FIG_57" src="images/fig57.jpg" alt="" width="600" height="373" />
-    <p class="center">Fig. 57.<br /> Broken corn stalk, showing fibrovascular bundles.</p>
-</div>
-
-<p><b>96.</b> If we cut across the stem of a corn plant which has been
-in the solution, we see that instead of the colored areas being in
-a concentric ring they are irregularly scattered, and on splitting
-the stem we see here also that these colored areas extend for long
-distances through the stem. If we take a corn stem which is mature, or
-an old and dead one, cut around through the outer hard tissues, and
-then break the stem at this point, from the softer tissue long strings
-of tissue will pull out as shown in <a href="#FIG_57">fig. 57</a>. These strings of
-denser tissue correspond to the areas which are colored by the dye. They are
-in the form of minute bundles, and are called <i>vascular bundles</i>.
-<span class="pagenum"><a name="Page_50" id="Page_50">[Pg 50]</a></span></p>
-
-<p><b>97.</b> We thus see that instead of the liquids passing through the
-entire stem they are confined to definite courses. Now that we have
-discovered the path of the upward movement of water in the stem, we are
-curious to see what the structure of these definite portions of the
-stem is.</p>
-
-<div class="figcenter">
-    <img id="FIG_58" src="images/fig58.jpg" alt="" width="600" height="349" />
-<table border="0" cellspacing="0" summary=" " cellpadding="0" >
-  <tbody><tr>
-      <td class="tdc" colspan="3">Fig. 58.</td>
-     </tr><tr>
-      <td class="tdl">Xylem portion of bundle.&emsp;&nbsp;</td>
-      <td class="tdc">Cambium portion of bundle.&emsp;&nbsp;</td>
-      <td class="tdr">&emsp;Bast portion of bundle.</td>
-     </tr><tr>
-      <td class="tdc" colspan="3">Section of vascular bundle of sunflower stem.</td>
-   </tr>
- </tbody>
-</table>
-</div>
-
-<p><b>98. Structure of the fibrovascular bundles.</b>—We should now
-make quite thin cross-sections, either free hand and mount in water
-for microscopic examination, or they may be made with a microtome and
-mounted in Canada balsam, and in this condition will answer for future
-study. To illustrate the structure of the bundle in one type we may
-take the stem of the castor-oil bean. On examining these cross-sections
-we see that there are groups of cells which are denser than the ground
-tissue. These groups correspond to the colored areas in the former
-experiments, and are the vascular bundles cut across. These groups are
-somewhat oval in outline, with the pointed end directed toward the
-center of the stem. If we look at the section as a whole we see that
-there is a narrow continuous ring<a name="FNanchor_7_7" id="FNanchor_7_7"></a><a href="#Footnote_7_7" class="fnanchor">[7]</a>
-of small cells situated at the same distance from the center of the
-stem as the middle part of the bundles, and that it divides the bundles
-into two groups of cells.</p>
-
-<p><span class="pagenum"><a name="Page_51" id="Page_51">[Pg 51]</a></span>
-<b>99. Woody portion of the bundle.</b>—In that portion of the bundle
-on the inside of the ring, i.e., toward the “pith,” we note large,
-circular, or angular cavities. The walls of these cells are quite thick
-and woody. They are therefore called wood cells, and because they
-are continuous with cells above and below them in the stem in such a
-way that long tubes are formed, they are called woody vessels. Mixed
-in with these are smaller cells, some of which also have thick walls
-and are wood cells. Some of these cells may have thin walls. This
-is the case with all when they are young, and they are then classed
-with the fundamental tissue or soft tissue (parenchyma). This part of
-the bundle, since it contains woody vessels and fibres, is the <i>wood
-portion</i> of the bundle, or technically the <i>xylem</i>.</p>
-
-<p><b>100. Bast portion of the bundle.</b>—If our section is through a
-part of the stem which is not too young, the tissues of the outer part
-of the bundle will show either one or several groups of cells which
-have white and shiny walls, that are thickened as much or more than
-those of the wood vessels. These cells are <i>bast</i> cells, and for this
-reason this part of the bundle is the <i>bast</i> portion, or the <i>phloem</i>.
-Intermingled with these, cells may often be found which have thin
-walls, unless the bundle is very old. Nearer the center of the bundle
-and still within the bast portion are cells with thin walls, angular
-and irregularly arranged. This is the softer portion of the bast, and
-some of these cells are what are called <i>sieve</i> tubes, which can be
-better seen and studied in a longitudinal section of the stem.</p>
-
-<p><b>101. Cambium region of the bundle.</b>—Extending across the center
-of the bundle are several rows of small cells, the smallest of the
-bundle, and we can see that they are more regularly arranged, usually
-in quite regular rows, like bricks piled upon one another. These cells
-have thinner walls than any others of the bundle, and they usually take
-a deeper stain when treated with a solution of some of the dyes. This
-is because they are younger, and are therefore richer in protoplasmic
-contents. This zone of young cells across the bundle is the <i>cambium</i>.
-Its cells grow and divide, and thus increase the size of the bundle.
-By this increase in the number of the cells of the cambium layer, the
-outermost cells on either side are continually passing over into the
-phloem, on the one hand, and into the wood portion of the bundle, on
-the other hand.</p>
-
-<p><b>102. Longitudinal section of the bundle.</b>—If we make thin
-longisections of the vascular bundle of the castor-oil seedling (or
-other dicotyledon) so that we have thin ones running through a bundle
-radially, as shown in <a href="#FIG_59">fig. 59</a>, we can see the
-structure of these parts of the bundle in side view. We see here that
-the form of the cells is very different from what is presented in a
-cross-section of the same. The walls of the various ducts have peculiar
-markings on them. These markings are caused by the walls being
-<span class="pagenum"><a name="Page_52" id="Page_52">[Pg 52]</a></span>
-thicker in some places than in others, and this thickening takes place
-so regularly in some instances as to form regular spiral thickenings.
-Others have the thickenings in the form of the rounds of a ladder,
-while still others have pitted walls or the thickenings are in the form
-of rings.</p>
-
-<div class="figcenter">
-    <img id="FIG_59" src="images/fig59.jpg" alt="" width="600" height="308" />
-   <div class="blockquot">
-    <p class="center">Fig. 59.</p>
-    <p class="center">Longitudinal section of vascular bundle of sunflower
-      stem; spiral, scalariform and pitted vessels at left; next are wood
-      fibers with oblique cross walls; in middle are cambium cells with
-      straight cross walls, next two sieve tubes, then phloem or bast cells.</p>
-   </div>
-</div>
-
-<p><b>103. Vessels or ducts.</b>—One way in which the cells in side view
-differ greatly from an end view, in a cross-section in the bundle, is
-that they are much longer in the direction of the axis of the stem. The
-cells have become elongated greatly. If we search for the place where
-two of these large cells with spiral, or ladder-like, markings meet end
-to end, we see that the wall which formerly separated the cells has
-nearly or quite disappeared. In other words the two cells have now an
-open communication at the ends. This is so for long distances in the
-stem, so that long columns of these large cells form tubes or vessels
-through which the water rises in the stems of plants.</p>
-
-<p><b>104.</b> In the bast portion of the bundle we detect the cells of
-the bast fibers by their thick walls. They are very much elongated and
-the ends taper out to thin points so that they overlap. In this way
-they serve to strengthen the stem.</p>
-
-<p><b>105. Sieve tubes.</b>—Lying near the bast cells, usually toward
-the cambium, are elongated cells standing end to end, with delicate
-markings on their cross walls which appear like finely punctured plates
-or sieves. The protoplasm in such cells is usually quite distinct, and
-sometimes contracted away from the side walls, but attached to the
-cross walls, and this aids in the detection of the sieve tubes (<a href="#FIG_59">fig. 59</a>.)
-The granular appearance which these plates present is caused by minute
-perforations through the wall so that there is a communication
-between the cells. The tubes thus formed are therefore called sieve
-tubes and they extend for long distances through the tube so that there
-<span class="pagenum"><a name="Page_53" id="Page_53">[Pg 53]</a></span>
-is communication throughout the entire length of the stem. (The
-function of the sieve tubes is supposed to be that for the downward
-transportation of substances elaborated in the leaves.)</p>
-
-<p><b>106.</b> If we section in like manner the stem of the sunflower we
-shall see similar bundles, but the number is greater than eight. In
-the garden balsam the number is from four to six in an ordinary stem
-3-4<i>mm</i> diameter. Here we can see quite well the origin of the vascular
-bundle. Between the larger bundles we can see especially in free-hand
-sections of stems through which a colored solution has been lifted by
-transpiration, as in our former experiments, small groups of the minute
-cells in the cambial ring which are colored. These groups of cells
-which form strands running through the stem are <i>pro-cambium strands</i>.
-The cells divide and increase just like the cambium cells, and the
-older ones thrown off on either side change, those toward the center
-of the stem to wood vessels and fibers, and those on the outer side to
-bast cells and sieve tubes.</p>
-
-<p><b>107. Fibrovascular bundles in the Indian corn.</b>—We should now
-make a thin transection of a portion of the center of the stem of
-Indian corn, in order to compare the structure of the bundle with that
-of the plants which we have just examined. In <a href="#FIG_60">fig. 60</a> is
-represented a fibrovascular bundle of the stem of the Indian corn. The large
-cells are those of the spiral and reticulated and annular vessels. This is
-the woody portion of the bundle or xylem. Opposite this is the bast
-portion or phloem, marked by the lighter colored tissue at <i>i</i>. The
-larger of these cells are the sieve tubes, and intermingled with them
-are smaller cells with thin walls. Surrounding the entire bundle are
-small cells with thick walls. These are elongated and the tapering ends
-overlap. They are thus slender and long and form fibers. In such a
-bundle all of the cambium has passed over into permanent tissue and is
-said to be closed.</p>
-
-<div class="figcenter">
-    <img id="FIG_60" src="images/fig60.jpg" alt="" width="600" height="357" />
-   <div class="blockquot">
-    <p class="center">Fig. 60.</p>
-    <p class="center">Transection of fibrovascular bundle of Indian corn. <i>a</i>, toward
-       periphery of stem; <i>g</i>, large pitted vessels; <i>s</i>, spiral vessel; <i>r</i>,
-       annular vessel; <i>l</i>, air cavity formed by breaking apart of the cells;<i>i</i>,
-       soft bast, a form of sieve tissue; <i>p</i>, thin-walled parenchyma. (Sachs.)</p>
-   </div>
-</div>
-
-<p><b>108. Rise of water in the vessels.</b>—During the movement of the
-water or nutrient solutions upward in the stem the vessels of the wood
-portion of the bundle in certain plants are nearly or quite filled,
-if root pressure is active and transpiration is not very rapid. If,
-however, on dry days transpiration is in excess of root pressure, as
-often happens, the vessels are not filled with the water, but are
-<span class="pagenum"><a name="Page_54" id="Page_54">[Pg 54]</a></span>
-partly filled with certain gases because the air or other gases in
-the plant become rarefied as a result of the excessive loss of water.
-There are then successive rows of air or gas bubbles in the vessels
-separated by films of water which also line the walls of the vessels.
-The condition of the vessel is much like that of a glass tube through
-which one might pass the “froth” which is formed on the surface of
-soapy water. This forms a chain of bubbles in the vessels. This chain
-has been called Jamin’s chain because of the discoverer.</p>
-
-<p><b>109.</b> Why water or food solutions can be raised by the plant
-to the height attained by some trees has never been satisfactorily
-explained. There are several theories propounded which cannot be
-discussed here. It is probably a very complex process. Root pressure
-and transpiration both play a part, or at least can be shown, as we
-have seen, to be capable of lifting water to a considerable height. In
-addition to this, the walls of the vessels absorb water by diffusion,
-and in the other elements of the bundle capillarity comes also into
-play, as well as osmosis.</p>
-
-<p>See Organization of Tissues, <a href="#CHAPTER_XXXVIII">Chapter 38</a>.</p>
-
-<p><b>110. Flow of sap in the spring.</b>—The cause of the bleeding of
-trees and the flow of sap in the spring is little understood. One of
-the remarkable cases is the flow of sap in maple trees. It begins
-in early spring and ceases as the buds are opening, and seems to be
-initiated by alternation of high and low temperatures of day and night.
-It has been found that the pressures inside of the tree at this time
-are enormously increased during the day, when the temperature rises
-after a cold night. This has led to the belief that the pressure is
-caused by the expansion of the gases in the vascular ducts. The warming
-up of the twigs and branches of the tree would take place rapidly
-during the day, while the interior of the trunk would be only slightly
-affected. The pressures then would cause the sap to flow downward
-during the day, and at night the branches becoming cool, sap would flow
-back again from the roots and trunk.</p>
-
-<p>Recent experiments by Jones <i>et al.</i> show that while some of the
-pressure is due to the expansion of gas in the tree by the rise of
-temperature, this cannot account for the enormous pressures which are
-often present, for example, when after a rise in the temperature of 2°
-C. there was an increase of 20 lbs. pressure.</p>
-
-<p>Then again, after the cessation of the flow in late spring there are
-often as great differences between night and day temperatures. It
-therefore seems reasonable to conclude that the expansion of gases by a
-rise in temperature is not the direct cause.</p>
-
-<p><b>Activities of the cells.</b>—It has been suggested by some that
-the rise in temperature exercises an influence on the protoplasts,
-or living cells, so that they are stimulated to a special activity
-resulting in an exudation pressure from the individual cells, which is
-<span class="pagenum"><a name="Page_55" id="Page_55">[Pg 55]</a></span>
-known to take place. With the fall of temperature at night this
-activity would cease and there might result a lessened pressure in
-the cells. Since the specific activities of cells are known to vary
-in different plants, and in the same plant at different seasons, some
-support is gained for this theory, though it is generally believed that
-the activities of the living cells in the stems are not necessary for
-the upward flow of water. It must be admitted, however, that at present
-we know very little about this interesting problem.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_56" id="Page_56">[Pg 56]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_VI" id="CHAPTER_VI">CHAPTER VI.</a><br />
-<span class="h_subtitle">MECHANICAL USES OF WATER.</span></h3>
-</div>
-
-<p><b>111. Turgidity of plant parts.</b>—As we have seen by the
-experiments on the leaves, turgescence of the cells is one of the
-conditions which enables the leaves to stand out from the stem, and the
-lamina of the leaves to remain in an expanded position, so that they
-are better exposed to the light, and to the currents of air. Were it
-not for this turgidity the leaves would hang down close against the stem.</p>
-
-<div class="figleft">
-    <img id="FIG_61" src="images/fig61.jpg" alt="" width="200" height="312" />
-    <p class="center">Fig. 61.<br /> Restoration<br /> of turgidity<br /> (Sachs).</p>
-</div>
-
-<p><b>112. Restoration of turgidity in shoots.</b>—If we cut off a living
-stem of geranium, coleus, tomato, or “balsam,” and allow the leaves
-to partly wilt so that the shoot loses its turgidity, it is possible
-for this shoot to regain turgidity. The end may be freshly cut again,
-placed in a vessel of water, covered with a bell jar and kept in a room
-where the temperature is suitable for the growth of the plant. The
-shoot will usually become turgid again from the water which is absorbed
-through the cut end of the stem and is carried into the leaves where
-the individual cells become turgid, and the leaves are again expanded.
-Such shoots, and the excised leaves also, may often be made turgid
-again by simply immersing them in water, as one of the experiments with
-the salt solution would teach.</p>
-
-<p><b>113.</b> Turgidity may be restored more certainly and quickly in a
-partially wilted shoot in another way. The cut end of the shoot may be
-inserted in a U tube as shown in <a href="#FIG_61">fig. 61</a>, the end of the tube around
-<span class="pagenum"><a name="Page_57" id="Page_57">[Pg 57]</a></span>
-the stem of the plant being made air-tight. The arm of the tube in
-which the stem is inserted is filled with water and the water is
-allowed to partly fill the other arm. Into this other arm is then
-poured mercury. The greater weight of the mercury causes such pressure
-upon the water that it is pushed into the stem, where it passes up
-through the vessels in the stems and leaves, and is brought more
-quickly and surely to the cells which contain the protoplasm and
-cell-sap, so that turgidity is more quickly and certainly attained.</p>
-
-<p><b>114. Tissue tensions.</b>—Besides the turgescence of the cells
-of the leaves and shoots there are certain tissue tensions without
-which certain tender and succulent shoots, etc., would be limp, and
-would droop. There are a number of plants usually accessible, some at
-one season and some at others, which may be used to illustrate tissue
-tension.</p>
-
-<p><b>115. Longitudinal tissue tension.</b>—For this in early summer one
-may use the young and succulent shoots of the elder (sambucus); or the
-petioles of rhubarb during the summer and early autumn; or the petioles
-of richardia. Petioles of caladium are excellent for this purpose, and
-these may be had at almost any season of the year from the greenhouses,
-and are thus especially advantageous for work during late autumn or
-winter. The tension is so strong that a portion of such a petiole
-10-15<i>cm</i> long is ample to demonstrate it. As we grasp the lower end of
-the petiole of a caladium, or rhubarb leaf, we observe how rigid it is,
-and how well it supports the heavy expanded lamina of the leaf.</p>
-
-<p><b>116.</b> The ends of a portion of such a petiole or other object
-which may be used are cut off squarely. With a knife a strip from
-2-3<i>mm</i> in thickness is removed from one side the full length of the
-object. This strip we now find is shorter than the larger part from
-which it was removed. The outer tissue then exerts a tension upon the
-petiole which tends to shorten it. Let us remove another strip lying
-next this one, and another, and so on until the outer tissues remain
-only upon one side. The object will now bend toward that side. Now
-remove this strip and compare the length of the strips removed with the
-<span class="pagenum"><a name="Page_58" id="Page_58">[Pg 58]</a></span>
-central portion. We find that they are much shorter now. In other words
-there is also a tension in the tissue of the central portion of the
-petiole, the direction of which is opposite to that of the superficial
-tissue. The parts of the petiole now are not rigid, and they easily
-bend. These two longitudinal tissue tensions acting in opposition to
-each other therefore give rigidity to the succulent shoot. It is only
-when the individual cells of such shoots or petioles are turgid that
-these tissue tensions in succulent shoots manifest themselves or are
-prominent.</p>
-
-<div class="figleft">
-    <img id="FIG_62" src="images/fig62.jpg" alt="" width="200" height="287" />
-    <p class="center">Fig. 62.<br /> Strip from dandelion<br /> stem made
-           to<br /> imitate a plant tendril.</p>
-</div>
-
-<p><b>117.</b> To demonstrate the efficiency of this tension in giving
-support, let us take a long petiole of caladium or of rhubarb. Hold it
-by one end in a horizontal position. It is firm and rigid, and does not
-droop, or but little. Remove all of the outer portion of the tissues,
-as described above, leaving only the central portion. Now attempt to
-hold it in a horizontal position by one end. It is flabby and droops
-downward because the longitudinal tension is removed.</p>
-
-<p><b>118. Longitudinal tension in dandelion stems.</b>—Take long
-and fresh dandelion stems. Split them. Note that they coil. The
-longitudinal tension is very great. Place some of these strips in fresh
-water. They coil up into close curls because by the absorption of water
-by the cells the turgescence of the individual cells is increased, and
-this increases the tension in the stem. Now place them in salt water (a
-5 per cent solution). Why do they uncoil?</p>
-
-<p><b>119. To imitate the coiling of a tendril.</b>—Cut out a narrow
-strip from a long dandelion stem. Fasten to a piece of soft wood, with
-the ends close together, as shown in <a href="#FIG_62">fig. 62</a>. Now place it
-in fresh water and watch it coil. Part of it coils one way and part another way,
-<span class="pagenum"><a name="Page_59" id="Page_59">[Pg 59]</a></span>
-just as a tendril does after the free end has caught hold of some place
-for support.</p>
-
-<p><b>120. Transverse tissue tension.</b>—To illustrate this one may take
-a willow shoot 3-5 <i>cm</i> diameter and saw off sections about 2 cm long.
-Cut through the bark on one side and peel it off in a single strip. Now
-attempt to replace it. The bark will not quite cover the wood again,
-since the ends will not meet. It must then have been held in transverse
-tension by the woody part of the shoot.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_60" id="Page_60">[Pg 60]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_VII" id="CHAPTER_VII">CHAPTER VII.</a><br />
-<span class="h_subtitle">STARCH AND SUGAR FORMATION.</span></h3>
-</div>
-
-<h4><a name="VII_1" id="VII_1">1. The Gases Concerned.</a></h4>
-
-<p><b>121. Gas given off by green plants in the sunlight.</b>—Let us take
-some green alga, like spirogyra, which is in a fresh condition, and
-place one lot in a beaker or tall glass vessel of water and set this in
-the direct sunlight or in a well lighted place. At the same time cover
-a similar vessel of spirogyra with black cloth so that it will be in
-the dark, or at least in very weak light.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-      <img src="images/fig63.jpg" alt="" width="200" height="328" />
-      <p class="center">Fig. 63.<br /> Oxygen gas given<br /> off by spirogyra.</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig64.jpg" alt="" width="275" height="321" />
-      <p class="center">Fig. 64.<br /> Bubbles of oxygen gas given off from<br />
-               elodea in presence of sunlight. (Oels.)</p>
-   </div>
-</div>
-
-<p><b>122.</b> In a short time we note that in the first vessel small
-bubbles of gas are accumulating on the surface of the threads of the
-spirogyra, and now and then some free themselves and rise to the
-surface of the water. Where there is quite a tangle of the threads the
-gas is apt to become caught and held back in larger bubbles, which on
-agitation of the vessel are freed.</p>
-
-<p>If we now examine the second vessel we see that there are no bubbles,
-or only a very few of them. We are led to believe then that sunlight
-has had something to do with the setting free of this gas from the
-plant.</p>
-
-<p><b>123.</b> We may now take another alga-like vaucheria and perform the
-experiment in the same way, or to save time the two may be set up at
-<span class="pagenum"><a name="Page_61" id="Page_61">[Pg 61]</a></span>
-once. In fact if we take any of the green algæ and treat them as
-described above gas will be given off in a similar manner.</p>
-
-<p><b>124.</b> We may now take one of the higher green plants, an aquatic
-plant like elodea, callitriche, etc. Place the plant in the water with
-the cut end of the stem uppermost, but still immersed, the plant being
-weighted down by a glass rod or other suitable object. If we place the
-vessel of water containing these leafy stems in the bright sunlight,
-in a short time bubbles of gas will pass off quite rapidly from the
-cut end of the stem. If in the same vessel we place another stem, from
-which the leaves have been cut, the number of bubbles of gas given
-off will be very few. This indicates that a large part of the gas is
-furnished by the leaves.</p>
-
-<p><b>125.</b> Another vessel fitted up in the same way should be placed
-in the dark or shaded by covering with a box or black cloth. It will
-be seen here, as in the case of spirogyra, that very few or no bubbles
-of gas will be set free. Sunlight here also is necessary for the rapid
-escape of the gas.</p>
-
-<p><b>126.</b> We may easily compare the rapidity with which light of
-varying intensity effects the setting free of this gas. After cutting
-the end of the stem let us plunge the cut surface several times in
-melted paraffine, or spread over the cut surface a coat of varnish.
-Then prick with a needle a small hole through the paraffine or varnish.
-Immerse the plant in water and place in sunlight as before. The gas now
-comes from the puncture through the coating of the cut end, and the
-number of bubbles given off during a given period can be ascertained by
-counting. If we duplicate this experiment by placing one plant in weak
-light or diffused sunlight, and another in the shade, we can easily
-compare the rapidity of the escape of the gas under the different
-conditions, which represent varying intensities of light. We see then
-that not only is sunlight necessary for the setting free of this gas,
-but that in diffused light or in the shade the activity of the plant in
-this respect is less than in direct sunlight.</p>
-
-<p><b>127. What this gas is.</b>—If we take quite a quantity of the
-plants of elodea and place them under an inverted funnel which is
-immersed in water, the gas will be given off in quite large quantities
-<span class="pagenum"><a name="Page_62" id="Page_62">[Pg 62]</a></span>
-and will rise into the narrow exit of the funnel. The funnel should be
-one with a short tube, or the vessel one which is quite deep so that
-a small test tube which is filled with water may in this condition be
-inverted over the opening of the funnel tube. With this arrangement
-of the experiment the gas will rise in the inverted test tube, slowly
-displace a portion of the water, and become collected in a sufficient
-quantity to afford us a test. When a considerable quantity has
-accumulated in the test tube, we may close the end of the tube in
-the water with the thumb, lift it from the water and invert. The gas
-will rise against the thumb. A dry soft-pine splinter should be then
-lighted, and after it has burned a short time, extinguish the flame by
-blowing upon it, when the still burning end of the splinter should be
-brought to the mouth of the tube as the thumb is quickly moved to one
-side. The glowing of the splinter shows that the gas is <i>oxygen</i>.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-      <img src="images/fig65.jpg" alt="" width="250" height="381" />
-      <p class="center">Fig. 65.<br /> Apparatus for collecting quantity<br />
-                  of oxygen from elodea.<br /> (Detmer.)</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig66.jpg" alt="" width="250" height="359" />
-      <p class="center">Fig. 66.<br /> Ready to see what the gas is.</p>
-   </div>
-</div>
-
-<p><b>128.</b> It is better to allow the apparatus to stand several days
-in the sunlight in order to catch a full tube of the gas. Or on a sunny
-day carbon dioxide gas can be led into the water in the jar from a
-generator, such an one as is used for the evolution of CO₂. The CO₂
-can be produced by the action of hydrochloric acid on bits of marble.
-The CO₂ should not be run below the funnel. The test tube should be
-fastened so that the light oxygen gas will not raise it off the funnel.
-With the tube full of gas the test for oxygen can be made by lifting
-<span class="pagenum"><a name="Page_63" id="Page_63">[Pg 63]</a></span>
-the tube with one hand and quickly thrusting the glowing end of the
-splinter in with the other hand. If properly handled, the splinter will
-flame again. If it is necessary to keep the apparatus standing for more
-than one day it is well to add fresh water in the place of most of the
-water in the jar. Do not use leaves of land plants in this experiment,
-since the bubbles which rise when these leaves are placed in water are
-not evidence that this process is taking place.</p>
-
-<div class="figcenter">
-    <img src="images/fig67.jpg" alt="" width="600" height="194" />
-    <p class="center">Fig. 67.<br /> The splinter lights again
-                     in the presence of oxygen gas.</p>
-</div>
-
-<p class="blockquot"><b>129. Oxygen given off by green land plants
-also.</b>—If we should extend our experiments to land plants we should
-find that oxygen is given off by them under these conditions of light.
-Land plants, however, will not do this when they are immersed in
-water, but it is necessary to set up rather complicated apparatus and
-to make analyses of the gases at the beginning and at the close of
-the experiments. This has been done, however, in a sufficiently large
-number of cases so that we know that all green plants in the sunlight,
-if temperature and other conditions are favorable, give off oxygen.</p>
-
-<p><b>130. Absorption of carbon dioxide.</b>—We have next to inquire
-where the oxygen comes from which is given off by green plants when
-exposed to the sunlight, and also to learn something more of the
-conditions necessary for the process. We know that water which has been
-for some time exposed to the air and soil, and has been agitated, like
-running water of streams, or the water of springs, has mixed with it a
-considerable quantity of oxygen and carbon dioxide.</p>
-
-<p>If we boil spring water or hydrant water which comes from a stream
-containing oxygen and carbon dioxide, for about 20 minutes, these
-gases are driven off. We should set this aside where it will not be
-agitated, until it has cooled sufficiently to receive plants without
-injury. Let us now place some spirogyra or vaucheria, and elodea, or
-other green water plant, in this boiled water and set the vessel in the
-bright sunlight under the same conditions which were employed in the
-experiments for the evolution of oxygen. No oxygen is given off.
-<span class="pagenum"><a name="Page_64" id="Page_64">[Pg 64]</a></span></p>
-
-<p>Can it be that this is because the oxygen was driven from the water in
-boiling? We shall see. Let us take the vessel containing the water,
-or some other boiled water, and agitate it so that the air will be
-thoroughly mixed with it. In this way oxygen is again mixed with the
-water. Now place the plant again in the water, set in the sunlight, and
-in several minutes observe the result. No oxygen or but little is given off.
-There must be then some other requisite for the evolution of the oxygen.</p>
-
-<p><b>132. The gases are interchanged in the plants.</b>—We will now
-introduce carbon dioxide again in the water. This can be done by
-leading CO₂ from a gas generator into the water. Broken bits of marble
-are placed in the generator, acted upon by hydrochloric acid, and the
-gas is led over by glass tubing. Now if we place the plant in the water
-and set the vessel in the sunlight, in a few minutes the oxygen is
-given off rapidly.</p>
-
-<p><b>133. A chemical change of the gas takes place within the plant
-cell.</b>—This leads us to believe then that CO₂ is in some way
-necessary for the plant in this process. Since oxygen is given off
-while carbon dioxide, a different gas, is necessary, it would seem that
-a chemical change takes place in the gases within the plant. Since the
-process takes place in such simple plants as spirogyra as well as in
-the more bulky and higher plants, it appears that the changes go on
-within the cell, in fact within the protoplasm.</p>
-
-<p><b>134. Gases as well as water can diffuse through the protoplasmic
-membrane.</b>—Carbon dioxide then is absorbed by the plant while
-oxygen is given off. We see therefore that gases as well as water can
-diffuse through the protoplasmic membrane of plants under certain
-conditions.</p>
-
-<h4><a name="VII_2" id="VII_2">2. Where Starch is Formed.</a></h4>
-
-<p>We have found by these simple experiments that some chemical change
-takes place within the protoplasm of the green cells of plants during
-the absorption of carbon dioxide and the giving off of oxygen. We
-should examine some of the green parts of those plants used in the
-<span class="pagenum"><a name="Page_65" id="Page_65">[Pg 65]</a></span>
-experiments, or if they are not at hand we should set up others in
-order to make this examination.</p>
-
-<p><b>135. Starch formed as a result of this process.</b>—We may take
-spirogyra which has been standing in water in the bright sunlight for
-several hours. A few of the threads should be placed in alcohol for a
-short time to kill the protoplasm. From the alcohol we transfer the
-threads to a solution of iodine in potassium iodide. We find that
-at certain points in the chlorophyll band a bluish tinge, or color,
-is imparted to the ring or sphere which surrounds the pyrenoid. In
-our first study of the spirogyra cell we noted this sphere as being
-composed of numerous small grains of starch which surround the pyrenoid.</p>
-
-<p><b>136. Iodine used as a test for starch.</b>—This color reaction
-which we have obtained in treating the threads with iodine is the
-well-known reaction, or test, for starch. We have demonstrated then
-that starch is present in spirogyra threads which have stood in the
-sunlight with free access to carbon dioxide.</p>
-
-<p>If we examine in the same way some threads which have stood in the
-dark for a few days we obtain no reaction for starch, or at best only
-a slight reaction. This gives us some evidence that a chemical change
-does take place during this process (absorption of CO₂ and giving off
-of oxygen), and that starch is a product of that chemical change.</p>
-
-<p><b>137. Schimper’s method of testing for the presence of
-starch.</b>—Another convenient and quick method of testing for the
-presence of starch is what is known as Schimper’s method. A strong
-solution of chloral hydrate is made by taking 8 grams of chloral
-hydrate for every 5<i>cc</i> of water. To this solution is added a little
-of an alcoholic tincture of iodine. The threads of spirogyra may be placed
-directly in this solution, and in a few moments mounted in water on the
-glass slip and examined with the microscope. The reaction is strong and
-easily seen.</p>
-
-<p>We should also examine the leaves of elodea, or one of the higher green
-plants which has been for some time in the sunlight. We may use here
-Schimper’s method by placing the leaves directly in the solution of
-<span class="pagenum"><a name="Page_66" id="Page_66">[Pg 66]</a></span>
-chloral hydrate and iodine. The leaves are made transparent by the
-chloral hydrate so that the starch reaction from the iodine is easily
-detected.</p>
-
-<p>The following is a convenient and safe method of extracting chlorophyll
-from leaves. Fill a large pan, preferably a dishpan, half full of
-hot water. This may be kept hot by a small flame. On the water float
-an evaporating dish partly filled with alcohol. The leaves should be
-first immersed in the hot water for several minutes, then placed in the
-alcohol, which will quickly remove the chlorophyll. Now immerse the
-leaves in the iodine solution.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-      <img id="FIG_68" src="images/fig68.jpg" alt="" width="250" height="328" />
-      <p class="center">Fig. 68.<br /> Leaf of coleus showing green and white<br />
-                               areas, before treatment with iodine.</p>
-   </div>
-  <div class="figsub">
-      <img id="FIG_69" src="images/fig69.jpg" alt="" width="250" height="334" />
-      <p class="center">Fig. 69.<br /> Similar leaf treated with iodine,<br />
-            the starch reaction only showing<br /> where the leaf was green.</p>
-   </div>
-</div>
-
-<p><b>138. Green parts of plants form starch when exposed to
-light.</b>—Thus we find that in the case of all the green plants we
-have examined, starch is present in the green cells of those which have
-been standing for some time in the sunlight where the process of the
-absorption of CO₂ and the giving off of oxygen can go on, and that in
-<span class="pagenum"><a name="Page_67" id="Page_67">[Pg 67]</a></span>
-the case of plants grown in the dark, or in leaves of plants which have
-stood for some time in the dark, starch is absent. We reason from this
-that starch is the product of the chemical change which takes place in
-the green cells under these conditions. The CO₂ which is absorbed by
-the plant mixes with the water (H₂O) in the cell and immediately forms
-carbonic acid. The chlorophyll in the leaf absorbs radiant energy from
-the sun which splits up the carbonic acid, and its elements then are
-put together into a more complex compound, starch. This process of
-putting together the elements of an organic compound is a <i>synthesis</i>,
-or a <i>synthetic assimilation</i>, since it is done by the living plant.
-It is therefore a synthetic assimilation of carbon dioxide. Since
-the sunlight supplies the energy it is also called <i>photosynthesis</i>,
-or <i>photosynthetic assimilation</i>. We can also say carbon dioxide
-assimilation, or CO₂ assimilation (<a href="#X_3">see paragraph on assimilation at
-close of Chapter 10</a>).</p>
-
-<p><b>139. Starch is formed only in the green parts of variegated
-leaves.</b>—If we test for starch in variegated leaves like the leaf
-of a coleus plant, we shall have an interesting demonstration of the
-fact that the green parts of plants only form starch. We may take
-a leaf which is partly green and partly white, from a plant which
-has been standing for some time in bright light. <a href="#FIG_68">Fig. 68</a> is
-from a photograph of such a leaf. We should first boil it in alcohol to remove
-the green color. Now immerse it in the potassium iodide of iodine
-solution for a short time. The parts which were formerly green are
-now dark blue or nearly black, showing the presence of starch in
-those portions of the leaf, while the white part of the leaf is still
-uncolored. This is well shown in <a href="#FIG_69">fig. 69</a>, which is
-from a photograph of another coleus leaf treated with the iodine solution.</p>
-
-<h4><a name="VII_3" id="VII_3">3. Chlorophyll and the Formation of Starch.</a></h4>
-
-<p><b>140.</b> In our experiments thus far in treating of the absorption
-of carbon dioxide and the evolution of oxygen, with the accompanying
-formation of starch, we have used green plants.
-<span class="pagenum"><a name="Page_68" id="Page_68">[Pg 68]</a></span></p>
-
-<p><b>141. Fungi cannot form starch.</b>—If we should extend our
-experiments to the fungi, which lack the green color so characteristic
-of the majority of plants, we should find that photosynthesis does not
-take place even though the plants are exposed to direct sunlight. These
-plants cannot then form starch, but obtain carbohydrates for food from
-other sources.</p>
-
-<p><b>142. Photosynthesis cannot take place in etiolated
-plants.</b>—Moreover photosynthesis is usually confined to the green
-plants, and if by any means one of the ordinary green plants loses its
-green color this process cannot take place in that plant, even when
-brought into the sunlight, until the green color has appeared under the
-influence of light.</p>
-
-<p>This may be very easily demonstrated by growing seedlings of the
-bean, squash, corn, pea, etc. (pine seedlings are green even when
-grown in the dark), in a dark room, or in a dark receiver of some
-kind which will shut out the rays of light. The room or receiver must
-be quite dark. As the seedlings are “coming up,” and as long as they
-remain in the dark chamber, they will present some other color than
-green; usually they are somewhat yellowed. Such plants are said to be
-<i>etiolated</i>. If they are brought into the sunlight now for a few hours
-and then tested for the presence of starch the result will be negative.
-But if the plant is left in the light, in a few days the leaves
-begin to take on a green color, and then we find that carbon dioxide
-assimilation begins.</p>
-
-<p><b>143. Chlorophyll and chloroplasts.</b>—The green substance in
-plants is then one of the important factors in this complicated
-process of forming starch. This green substance is <i>chlorophyll</i>,
-and it usually occurs in definite bodies, the chlorophyll bodies, or
-<i>chloroplasts</i>.</p>
-
-<p class="blockquot">The material for new growth of plants grown in the
-dark is derived from the seed. Plants grown in the dark consist largely
-of water and protoplasm, the walls being very thin.</p>
-
-<p><b>144. Form of the chlorophyll bodies.</b>—Chlorophyll bodies vary in
-<span class="pagenum"><a name="Page_69" id="Page_69">[Pg 69]</a></span>
-form in some different plants, especially in some of the lower
-plants. This we have already seen in the case of spirogyra, where the
-chlorophyll body is in the form of a very irregular band, which courses
-around the inner side of the cell wall in a spiral manner. In zygnema,
-which is related to spirogyra, the chlorophyll bodies are star-shaped.
-In the desmids the form varies greatly. In œdogonium, another of the
-thread-like algæ, illustrated in <a href="#FIG_144">fig. 144</a>, the chlorophyll
-bodies are more or less flattened oval disks. In vaucheria, too, a branched
-thread-like alga shown in <a href="#FIG_138">fig. 138</a>, the chlorophyll bodies
-are oval in outline. These two plants, œdogonium and vaucheria, should be examined
-here if possible, in order to become familiar with their form, since
-they will be studied later under morphology (see chapters on <a href="#CHAPTER_XVI">œdogonium</a>
-and <a href="#CHAPTER_XV">vaucheria</a>, for the occurrence and form of these plants). The form
-of the chlorophyll body found in œdogonium and vaucheria is that which
-is common to many of the green algæ, and also occurs in the mosses,
-liverworts, ferns, and the higher plants. It is a more or less rounded,
-oval, flattened body.</p>
-
-<div class="figcenter">
-    <img src="images/fig69a.jpg" alt="" width="600" height="257" />
-    <p class="center">Fig. 69<i>a</i>.<br /> Section of ivy leaf, palisade cells above, loose parenchyma,<br />
-              with large intercellular spaces in center. Epidermal cells<br />
-              on either edge, with no chlorophyll bodies.</p>
-</div>
-
-<p><b>145. Chlorophyll is a pigment which resides in the
-chloroplast.</b>—That the chlorophyll is a coloring substance which
-resides in the chloroplastid, and does not form the body itself, can
-be demonstrated by dissolving out the chlorophyll when the framework
-of the chloroplastid is apparent. The green parts of plants which have
-<span class="pagenum"><a name="Page_70" id="Page_70">[Pg 70]</a></span>
-been placed for some time in alcohol lose their green color. The
-alcohol at the same time becomes tinged with green. In sectioning such
-plant tissue we find that the chlorophyll bodies, or chloroplastids as
-they are more properly called, are still intact, though the green color
-is absent. From this we know that chlorophyll is a substance distinct
-from that of the chloroplastid.</p>
-
-<p><b>146. Chlorophyll absorbs energy from sunlight for
-photosynthesis.</b>—It has been found by analysis with the
-spectroscope that chlorophyll absorbs certain of the rays of the
-sunlight. The energy which is thus obtained from the sun, called
-<i>kinetic</i> energy, acts on the molecules of CH₂O₃, separating them into
-molecules of C, H, and O. (When the CO₂ from the air enters the plant
-cell it immediately unites with some of the water, forming carbonic
-acid = CH₂O₃.) After a series of complicated chemical changes starch is
-formed by the union of carbon, oxygen, and hydrogen. In this process
-of the reduction of the CH₂O₃ and the formation of starch there is a
-surplus of oxygen, which accounts for the giving off of oxygen during
-the process.</p>
-
-<p><b>147. Rays of light concerned in photosynthesis.</b>—If a solution
-of chlorophyll be made, and light be passed through it, and this
-light be examined with the spectroscope, there appear what are called
-absorption bands. These are dark bands which lie across certain
-portions of the spectrum. These bands lie in the red, orange, yellow,
-green, blue, and violet, but the bands are stronger in the red, which
-shows that chlorophyll absorbs more of the red rays of light than of
-the other rays. These are the rays of low refrangibility. The kinetic
-energy derived by the absorption of these rays of light is transformed
-into potential energy. That is, the molecule of CH₂O₃ is broken up, and
-then by a different combination of certain elements starch is formed.<a name="FNanchor_8_8" id="FNanchor_8_8"></a><a href="#Footnote_8_8" class="fnanchor">[8]</a></p>
-
-<p><b>148. Starch grains formed in the chloroplasts.</b>—During
-photosynthesis the starch formed is deposited generally in small grains
-within the green chloroplast in the leaf. We can see this easily by
-examining the leaves of some moss-like funaria which has been in the
-light, or in the chloroplasts of the prothallia of ferns, etc. Starch
-grains may also be formed in the chloroplasts from starch which was
-<span class="pagenum"><a name="Page_71" id="Page_71">[Pg 71]</a></span>
-formed in some other part of the plant, but which has passed in
-solution. Thus the functions of the chloroplast are twofold, that of
-photosynthesis and the formation of starch grains.</p>
-
-<p><b>149.</b> In the translocation of starch when it becomes stored up in
-various parts of the plant, it passes from the state of solution into
-starch grains in connection with plastids similar to the chloroplasts,
-but which are not green. The green ones are sometimes called
-<i>chloroplasts</i>, while the colorless ones are termed <i>leucoplasts</i>,
-and those possessing other colors, as red and yellow, in floral leaves, the
-root of the carrot, etc., are called <i>chromoplasts</i>.</p>
-
-<p><b>150. Photosynthesis in other than green plants.</b>—While
-carbohydrates are usually only formed by green plants, there are some
-exceptions. Apparent exceptions are found in the blue-green algæ, like
-oscillatoria, nostoc, or in the brown and red sea weeds like fucus,
-rhabdonia, etc. These plants, however, possess chlorophyll, but it is
-disguised by another pigment or color. There are plants, however, which
-do not have chlorophyll and yet form carbohydrates with evolution of
-oxygen in the presence of light, as for example a purple bacterium,
-in which the purple coloring substance absorbs light, though the rays
-absorbed most energetically are not the red.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-      <img id="FIG_70" src="images/fig70.jpg" alt="" width="250" height="169" />
-      <p class="center">Fig. 70.<br /> Cell exposed to weak diffused light showing<br />
-                       chlorophyll bodies along the horizontal walls.</p>
-   </div>
-  <div class="figsub">
-      <img id="FIG_71" src="images/fig71.jpg" alt="" width="250" height="148" />
-      <p class="center">Fig. 71.<br /> Same cell exposed to strong light,<br />
-                                       showing chlorophyll bodies have<br />
-                                       moved to perpendicular walls.</p>
-   </div>
-      <p class="center space-below2">Figs. 70, 71.—Cell of prothallium of fern.</p>
-</div>
-
-<p><b>151. Influence of light on the movement of chlorophyll
-bodies.</b>—<i>In fern prothallia</i>.—If we place fern prothallia in
-weak light for a few hours, and then examine them under the microscope,
-we find that the most of the chlorophyll bodies in the cells are
-arranged along the inner surface of the horizontal wall. If now the
-same prothallia are placed in a brightly lighted place for a short
-time most of the chlorophyll bodies move so that they are arranged
-along the surfaces of the perpendicular walls, and instead of having
-the flattened surfaces exposed to the light as in the former case, the
-edges of the chlorophyll bodies are now turned toward the light.
-<span class="pagenum"><a name="Page_72" id="Page_72">[Pg 72]</a></span>
-(See figs. <a href="#FIG_70">70</a>, <a href="#FIG_71">71</a>.) The same phenomenon has been
-observed in many plants. Light then has an influence on chlorophyll bodies, to some extent
-determining their position. In weak light they are arranged so that the
-flattened surfaces are exposed to the incidence of the rays of light,
-so that the chlorophyll will absorb as great an amount as possible
-of kinetic energy; but intense light is stronger than necessary, and
-the chlorophyll bodies move so that their edges are exposed to the
-incidence of the rays. This movement of the chlorophyll bodies is
-different from that which takes place in some water plants like elodea.
-The chlorophyll bodies in elodea are free in the protoplasm. The
-protoplasm in the cells of elodea streams around the inside of the cell
-wall much as it does in nitella and the chlorophyll bodies are carried
-along in the currents, while in nitella they are stationary.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_73" id="Page_73">[Pg 73]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_VIII" id="CHAPTER_VIII">CHAPTER VIII.</a><br />
-<span class="h_subtitle">STARCH AND SUGAR CONCLUDED.<br />
-ANALYSIS OF PLANT SUBSTANCE.</span></h3>
-</div>
-
-<h4><a name="VIII_1" id="VIII_1">1. Translocation of Starch.</a></h4>
-
-<p><b>152. Translocation of starch.</b>—It has been found that leaves of
-many plants grown in the sunlight contain starch when examined after
-being in the sunlight for several hours. But when the plants are left
-in the dark for a day or two the leaves contain no starch, or a much
-smaller amount. This suggests that starch after it has been formed may
-be transferred from the leaves, or from those areas of the leaves where
-it has been formed.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-      <img id="FIG_72" src="images/fig72.jpg" alt="" width="150" height="238" />
-      <p class="center">Fig. 72.<br /> Leaf of tropæolum<br />
-                                       with portion covered<br />
-                                       with corks to prevent<br />
-                                       the formation of starch.<br />
-                                       (After Detmer.)</p>
-   </div>
-  <div class="figsub">
-      <img id="FIG_73" src="images/fig73.jpg" alt="" width="250" height="247" />
-      <p class="center">Fig. 73.<br /> Leaf of tropæolum treated with<br />
-                                 iodine after removal of cork, to<br />
-                                 show that starch is removed from<br />
-                                 the leaf during the night.</p>
-   </div>
-</div>
-
-<p>To test this let us perform an experiment which is often made. We may
-take a plant such as a garden tropæolum or a clover plant, or other
-land plant in which it is easy to test for the presence of starch. Pin
-a piece of circular cork, which is smaller than the area of the leaf,
-on either side of the leaf, as in <a href="#FIG_72">fig. 72</a>, but allow free
-circulation of air between the cork and the under side of the leaf. Place the plant
-where it will be in the sunlight. On the afternoon of the following
-day, if the sun has been shining, test the entire leaf for starch. The
-part covered by the cork will not give the reaction for starch, as
-shown by the absence of the bluish color, while the other parts of the
-leaf will show it. The starch which was in that part of the leaf the
-day before was dissolved and removed during the night, and then during
-the following day, the parts being covered from the light, no starch
-was formed in them.
-<span class="pagenum"><a name="Page_74" id="Page_74">[Pg 74]</a></span></p>
-
-<p><b>153. Starch in other parts of plants than the leaves.</b>—We may
-use the iodine test to search for starch in other parts of plants than
-the leaves. If we cut a potato tuber, scrape some of the cut surface
-into a pulp, and apply the iodine test, we obtain a beautiful and
-distinct reaction showing the presence of starch. Now we have learned
-that starch is only formed in the parts containing chlorophyll. We
-have also learned that the starch which has been formed in the leaves
-disappears from the leaf or is transferred from the leaf. We judge
-therefore that the starch which we have found in the tuber of the
-potato was formed first in the green leaves of the plant, as a result
-of photosynthesis. From the leaves it is transferred in solution to
-the underground stems, and stored in the tubers. The starch is stored
-here by the plant to provide food for the growth of new plants from the
-tubers, which are thus much more vigorous than the plants would be if
-grown from the seed.</p>
-
-<p><b>154. Form of starch grains.</b>—Where starch is stored as a reserve
-material it occurs in grains which usually have certain characters
-peculiar to the species of plant in which they are found. They vary
-in size in many different plants, and to some extent in form also.
-If we scrape some of the cut surface of the potato tuber into a pulp
-and mount a small quantity in water, or make a thin section for
-microscopic examination, we find large starch grains of a beautiful
-structure. The grains are oval in form and more or less irregular in
-outline. But the striking peculiarity is the presence of what seem to
-be alternating dark and light lines in the starch grain. We note that
-the lines form irregular rings, which are smaller and smaller until
-we come to the small central spot termed the “hilum” of the starch
-grain. It is supposed that these apparent lines in the starch grain are
-caused by the starch substance being deposited in alternating dense
-and dilute layers, the dilute layers containing more water than the
-dense ones; others think that the successive layers from the hilum
-outward are regularly of diminishing density, and that this gives the
-appearance of alternating lines. The starch formed by plants is one of
-the organic substances which are manufactured by plants, and it (or
-glucose) is the basis for the formation of other organic substances in
-the plant. Without such organic substances green plants cannot make any
-appreciable increase of plant substance, though a considerable increase
-in size of the plant may take place.</p>
-
-<p class="blockquot"><span class="smcap">Note.</span>—The organic
-compounds resulting from photosynthesis, since they are formed by the
-union of carbon, hydrogen, and oxygen in such a way that the hydrogen
-<span class="pagenum"><a name="Page_75" id="Page_75">[Pg 75]</a></span>
-and oxygen are usually present in the same proportion as in water, are
-called <i>carbohydrates</i>. The most common carbohydrates are sugars (cane
-sugar, C₁₂H₂₂O₁₁ for example, in beet roots, sugar cane, sugar maple,
-etc.), starch, and cellulose.</p>
-
-<p><b>155. Vaucheria.</b>—The result of carbon dioxide assimilation in
-the threads of Vaucheria is not clearly understood. Starch is absent or
-difficult to find in all except a few species, while oil globules are
-present in most species. These oil globules are spherical, colorless,
-globose and highly refringent. Often small ones are seen lying against
-chlorophyll bodies. Oil is a <i>hydrocarbon</i> (containing C, H, and O,
-but the H and O are in different proportions from what they are in H₂O)
-and until recently it was supposed that this oil in Vaucheria was the
-direct result of photosynthesis. But the oil does not disappear when
-the plant is kept for a long time in the dark, which seems to show
-that it is not the direct product of carbon dioxide assimilation, and
-indicates that it comes either from a temporary starch body or from
-glucose. Schimper found glucose in several species of Vaucheria, and
-Waltz says that some starch is present in Vaucheria sericea, while
-in V. tuberosa starch is abundant and replaces the oil. To test for
-oil bodies in Vaucheria treat the threads with weak osmic acid, or
-allow them to stand for twenty-four hours in Fleming’s solution (which
-contains osmic acid). Mount some threads and examine with microscope.
-The oil globules are stained black.</p>
-
-<h4><a name="VIII_2" id="VIII_2">2. Sugar, and Digestion of
-Starch.</a><a name="FNanchor_9_9" id="FNanchor_9_9"></a><a href="#Footnote_9_9" class="fnanchor">[9]</a></h4>
-
-<p><a name="PARA_156" id="PARA_156"><b>156.</b></a> It is probable that
-some form of sugar is always produced as the result of photosynthesis.
-The sugar thus formed may be stored as such or changed to starch. In
-general it may be said that sugar is most common in the green parts of
-monocotyledonous plants, while starch is most frequent in dicotyledons.
-Plant sugars are of three general kinds: cane sugar abundant in the
-sugar cane, sugar beet, sugar maple, etc.; glucose and fruit sugar,
-found in the fruits of a majority of plants, and abundant in some, as
-in apples, pears, grapes, etc.; and maltose, a variety produced in
-germinating seeds, as in malted barley.</p>
-
-<p><b>157. Test for sugar.</b>—A very pretty experiment maybe made by
-taking two test tubes, placing in one a solution of commercial grape
-sugar (glucose), in the other one of granulated cane sugar, and adding
-to each a few drops of Fehling’s solution.<a name="FNanchor_10_10" id="FNanchor_10_10"></a><a href="#Footnote_10_10" class="fnanchor">[10]</a>
-After these tubes have stood in a warm place for half an hour, it will
-<span class="pagenum"><a name="Page_76" id="Page_76">[Pg 76]</a></span>
-be found that a bright orange brown or cinnabar-colored precipitate
-of copper and cuprous oxide has formed in the tube containing grape
-sugar, while the other solution is unchanged. Grape sugar or glucose,
-therefore, reduces Fehling’s solution, while cane sugar as such has no
-effect upon it.</p>
-
-<p>Cane sugar may be changed or converted to glucose by being boiled for a
-short time with a dilute acid, or by adding Fehling’s solution to the
-sugar solution and boiling. In the latter case the change is brought
-about by the alkali and the precipitate of copper and cuprous oxide
-forms.</p>
-
-<p><b>158. Tests for sugar in plant tissue.</b>—(<i>a</i>) Scrape out a little
-of the tissue from the inside of a ripe apple or pear, place it with a
-little water in a test tube, and add a few drops of Fehling’s solution.
-After standing half an hour the characteristic precipitate of copper
-and cuprous oxide appears, showing that grape sugar is present in
-quantity.</p>
-
-<p>Make thin sections of the apple and mount in a drop of Fehling’s
-solution on a slide. After half an hour examine with the microscope.
-The granules of cuprous oxide are present in the cells of the tissue in
-great abundance.</p>
-
-<p>(<i>b</i>) Cut up several leaves of a young vigorous corn seedling,
-cover with water in a test tube and boil for a minute. After the
-decoction has cooled add the Fehling’s solution and allow to stand.
-The precipitate will appear. For comparison take similar corn leaves,
-remove the chlorophyll with alcohol and test with iodine. No starch
-reaction appears. The carbohydrate in corn leaves is therefore glucose
-and not starch. If now the corn seed be examined the cells will be
-found to be full of starch grains which give the beautiful blue
-reaction with iodine. This experiment shows that grape sugar is formed
-in the leaves of the corn plant, but is changed to starch when stored
-in the seed.</p>
-
-<p>(<i>c</i>) Take two leaves of bean seedling or coleus, test one for sugar
-and the other for starch. Both are present.</p>
-
-<p>(<i>d</i>) Procure some maple sap in the spring, or in the winter months
-make a decoction of the broken tips of young branches of the sugar
-maple by boiling them in water in a test tube. To the sap or cool
-decoction add Fehling’s solution. No precipitate appears after
-<span class="pagenum"><a name="Page_77" id="Page_77">[Pg 77]</a></span>
-standing. Now heat the same solution to the boiling point, and the
-precipitate forms, showing the presence of cane sugar in the maple
-sap which was converted to glucose and fruit sugar by boiling in the
-presence of an alkali.</p>
-
-<p>(<i>e</i>) Scrape out some of the tissue from a sugar beet root, cover with
-water in a test tube and add Fehling’s solution. No change takes place
-after standing. Boil the same solution and the precipitate forms,
-showing the presence of cane sugar, inverted to grape sugar and fruit
-sugar by the hot alkali.</p>
-
-<p><b>159. How starch is changed to sugar.</b>—We have seen that in
-many plants the carbohydrate formed as the result of carbon dioxide
-assimilation is stored as starch. This substance being insoluble
-in water must be changed to sugar, which is soluble before it can
-be used as food or transported to other parts of the plant. This
-is accomplished through the action of certain enzymes, principally
-diastase. This substance has the power of acting upon starch under
-proper conditions of temperature and moisture, causing it to take up
-the elements of water, and so to become sugar.</p>
-
-<p>This process takes place commonly in the leaves where starch is formed,
-but especially in seeds, tubers (during the sprouting, etc.), and
-other parts which the plant uses as storehouses for starch food. It is
-probable that the same conditions of temperature and moisture which
-favor germination or active growth are also favorable to the production
-of diastase.</p>
-
-<p><b>160. Experiments to show the action of diastase.</b>—(<i>a</i>) Place
-a bit of starch half as large as a pea in a test tube, and cover with
-a weak solution<a name="FNanchor_11_11" id="FNanchor_11_11"></a><a href="#Footnote_11_11" class="fnanchor">[11]</a>
-(about ⅕ per cent) of commercial taka diastase. After it has stood in
-a warm place for five or ten minutes test with Fehling’s solution. The
-precipitate of cuprous oxide appears showing that some of the starch
-has been changed to sugar. By using measured quantities, and by testing
-with iodine at frequent intervals, it can be determined just how long
-it takes a given quantity of diastase to change a known quantity of
-starch. In this connection one should first test a portion of the same
-starch with Fehling’s solution to show that no sugar is present.</p>
-
-<p>(<i>b</i>) Repeat the above experiment using a little tissue from a potato,
-and some from a corn seed.</p>
-
-<p>(<i>c</i>) Take 25 germinating barley seeds in which the radicle is just
-appearing. Grind up thoroughly in a mortar with about three parts of
-water. After this has stood for ten or fifteen minutes, filter. Fill a
-test tube one-third full of water, add a piece of starch half the size
-of a pea or less, and boil the mixture to make starch-paste. Add the
-barley extract. Put in a warm place and test from time to time with
-iodine. The first samples so treated will be blue, later ones violet,
-<span class="pagenum"><a name="Page_78" id="Page_78">[Pg 78]</a></span>
-brown, and finally colorless, showing that the starch has all
-disappeared. This is due to the action of the diastase which was
-present in the germinating seeds, and which was dissolved out and added
-to the starch mixture. The office of this diastase is to change the
-starch in the seeds to sugar. Germinating wheat is sweet, and it is a
-matter of common observation that bread made from sprouted wheat is sweet.</p>
-
-<p>(<i>d</i>) Put a little starch-paste in a test tube and cover it with saliva
-from the mouth. After ten or fifteen minutes test with Fehling’s
-solution. A strong reaction appears showing how quickly and effectively
-saliva acts in converting starch to sugar. Successive tests with iodine
-will show the gradual disappearance of the starch.</p>
-
-<p><b>161. These experiments have shown us that diastase</b> from three
-different sources can act upon starch converting it into sugar. The
-active principle in the saliva is an <i>animal</i> diastase (<i>ptyalin</i>),
-which is necessary as one step in the digestion of starch food in
-animals. The <i>taka</i> diastase is derived from a fungus (Eurotium oryzæ)
-which feeds on the starch in rice grains converting it into sugar
-which the fungus absorbs for food. The <i>malt</i> diastase and <i>leaf</i>
-diastase are formed by the seed plants. That in seeds converts the
-starch to sugar which is absorbed by the embryo for food. That in the
-leaf converts the starch into sugar so that it can be transported to
-other parts of the plant to be used in building new tissue, or to be
-stored again in the form of starch (example, the potato, in seeds,
-etc.). The starch is formed in the leaf during the daylight. The light
-renders the leaf diastase inactive. But at night the leaf diastase
-becomes active and converts the starch made during the day. Starch is
-not soluble in water, while the sugar is, and the sugar in solution is
-thus easily transported throughout the plant. In those green plants
-which do not form starch in their leaves (sugar beet, corn, and many
-monocotyledons), grape sugar and fruit sugar are formed in the green
-parts as the result of photosynthesis. In some, like the corn, the
-grape sugar formed in the leaves is transported to other parts of the
-plant, and some of it is stored up in the seed as starch. In others
-like the sugar beet the glucose and fruit sugar formed in the leaves
-flow to other parts of the plant, and much of it is stored up as cane
-sugar in the beet root. The process of photosynthesis probably proceeds
-in the same way in all cases up to the formation of the grape sugar and
-fruit sugar in the leaves. In the beet, corn, etc., the process stops
-here, while in the bean, clover, and most dicotyledons the process is
-carried one step farther in the leaf and starch is formed.
-<span class="pagenum"><a name="Page_79" id="Page_79">[Pg 79]</a></span></p>
-
-<h4><a name="VIII_3" id="VIII_3">3. Rough Analysis of Plant Substance.</a></h4>
-
-<p><b>162. Some simple experiments to indicate the nature of plant
-substance.</b>—After these building-up processes of the plant, it is
-instructive to perform some simple experiments which indicate roughly
-the nature of the plant substance, and serve to show how it can be
-separated into other substances, some of them being reduced to the
-form in which they existed when the plant took them as food. For exact
-experiments and results it would be necessary to make chemical analyses.</p>
-
-<p><b>163. The water in the plant.</b>—Take fresh leaves or leafy shoots
-or other fresh plant parts. Weigh. Permit them to remain in a dry room
-until they are what we call “dry.” Now weigh. The plants have lost
-weight, and from what we have learned in studies of transpiration this
-loss in weight we know to result from the loss of water from the plant.</p>
-
-<p><b>164. The dry plant material contains water.</b>—Take air-dry
-leaves, shavings, or other dry parts of plants. Place them in a test
-tube. With a holder rest the tube in a nearly horizontal position,
-with the bottom of the tube in the flame of a Bunsen burner. Very
-soon, before the plant parts begin to “burn,” note that moisture is
-accumulating on the inner surface of the test tube. This is water
-driven off which could not escape by drying in air, without the
-addition of artificial heat, and is called “hygroscopic water.”</p>
-
-<p><b>165. Water formed on burning the dry plant material.</b>—Light a
-soft-pine or basswood splinter. Hold a thistle tube in one hand with the
-bulb downward and above the flame of the splinter. Carbon will be
-deposited over the inner surface of the bulb. After a time hold the
-tube toward the window and look through it above the carbon. Drops of
-water have accumulated on the inside of the tube. This water is formed
-by the rearrangement of some of the hydrogen and oxygen, which is set
-free by the burning of the plant material, where they were combined
-with carbon, as in the cellulose, and with other elements.</p>
-
-<p><b>166. Formation of charcoal by burning.</b>—Take dried leaves, and
-shavings from some soft wood. Place in a porcelain crucible, and cover
-about 3 cm. deep with dry fine earth. Place the crucible in the flame
-of a Bunsen burner and let it remain for about fifteen minutes. Remove
-and empty the contents. If the flame was hot the plant material will be
-reduced to a good quality of charcoal. The charcoal consists largely of
-carbon.</p>
-
-<p><b>167. The ash of the plant.</b>—Place in the porcelain crucible
-dried leaves and shavings as before. Do not cover with earth. Place the
-crucible in the flame of the Bunsen burner, and for a moment place on
-the porcelain cover; then remove the cover, and note the moisture on
-the under surface from the escaping water. Permit the plant material to
-burn; it may even flame for a time. In the course of fifteen minutes it
-<span class="pagenum"><a name="Page_80" id="Page_80">[Pg 80]</a></span>
-is reduced to a whitish powder, much smaller in bulk than the charcoal
-in the former experiment. This is the ash of the plant.</p>
-
-<p><b>168. What has become of the carbon?</b>—In this experiment the air
-was not excluded from the plant material, so that oxygen combined with
-carbon as the water was freed, and formed carbon dioxide, passing off
-into the air in this form. This it will be remembered is the form in
-which the plant took the carbon-food in through the leaves. Here the
-carbon dioxide met the water coming from the soil, and the two united
-to form, ultimately, starch, cellulose, and other compounds of carbon;
-while with the addition of nitrogen, sulphur, etc., coming also from
-the soil, still other plant substances were formed.</p>
-
-<p><b>169.</b> The carbohydrates are classed among the non-nitrogenous
-substances. Other non-nitrogenous plant substances are the organic
-acids like oxalic acid (H₂C₂O₄), malic acid (H₂C₄H₄O₅), etc.; the fats
-and fixed oils, which occur in the seeds and fruits of many plants. Of
-the nitrogenous substances the proteids have a very complex chemical
-formula and contain carbon, hydrogen, oxygen, nitrogen, sulphur, etc.
-(example, <i>aleuron</i>, or proteid grains, found in seeds). The proteids
-are the source of nitrogenous food for the seedling during germination.
-Of the amides, <i>asparagin</i> (C₄H₈N₂O₃) is an example of a nitrogenous
-substance; and of the alkaloids, nicotin (C₁₀H₁₄N₂) from tobacco.</p>
-
-<p>All living plants contain a large per cent of water. According to
-Vines “ripe seeds dried in the air contain 12 to 15 per cent of water,
-herbaceous plants 60 to 80 per cent, and many water plants and fungi as
-much as 95 per cent of their weight.” When heated to 100° C. the water
-is driven off. The dry matter remaining is made up partly of organic
-compounds, examples of which are given above, and inorganic compounds.
-By burning this dry residue the organic substances are mostly changed
-into volatile products, principally carbonic acid, water, and nitrogen.
-The inorganic substances as a result of combustion remain as a white or
-gray powder, the <i>ash</i>.</p>
-
-<p>The amount of the ash increases with the age of the plant, though the
-percentage of ash may vary at different times in the different members
-of the plant. The following table taken from Vines will give an idea of
-the amount and composition of the ash in the dry solid of a few plants:</p>
-
-<p class="f120 space-above2">CONTENT OF 1000 PARTS OF DRY SOLID MATTER.</p>
-
-<table border="0" cellspacing="0" summary=" " cellpadding="0" rules="cols" >
-  <thead><tr>
-      <th class="tdc bb" colspan="7">&nbsp;</th>
-   </tr><tr>
-      <th class="tdc bb">&nbsp;</th>
-      <th class="tdc bb">&nbsp;Clover, in&nbsp;<br  /> blossom</th>
-      <th class="tdc bb">&nbsp;Wheat,&nbsp;<br /> grain</th>
-      <th class="tdc bb">&nbsp;Wheat,&nbsp;<br /> straw</th>
-      <th class="tdc bb">&nbsp;&nbsp;Potato&nbsp;&nbsp;<br />tubers</th>
-      <th class="tdc bb">&nbsp;Apples&nbsp;</th>
-      <th class="tdc bb"> Peas<br />&nbsp; (the seed)</th>
-   </tr>
-  </thead>
-  <tbody><tr>
-      <td class="tdl">Ash</td>
-      <td class="tdr_ws1">68.3&#8199;</td>
-      <td class="tdr_ws1">19.7&#8199;</td>
-      <td class="tdr_ws1">53.7&#8199;</td>
-      <td class="tdr_ws1">37.7&#8199;</td>
-      <td class="tdr_ws1">14.4</td>
-      <td class="tdr">27.3&#8199;</td>
-   </tr><tr>
-      <td class="tdl">Potash.</td>
-      <td class="tdr_ws1">21.96</td>
-      <td class="tdr_ws1">6.14</td>
-      <td class="tdr_ws1">7.33</td>
-      <td class="tdr_ws1">22.76</td>
-      <td class="tdr_ws1">5.14</td>
-      <td class="tdr">11.41</td>
-   </tr><tr>
-      <td class="tdl">Soda.</td>
-      <td class="tdr_ws1">1.39</td>
-      <td class="tdr_ws1">0.44</td>
-      <td class="tdr_ws1">0.74</td>
-      <td class="tdr_ws1">0.99</td>
-      <td class="tdr_ws1">3.76</td>
-      <td class="tdr">0.26</td>
-   </tr><tr>
-      <td class="tdl">Lime.</td>
-      <td class="tdr_ws1">24.06</td>
-      <td class="tdr_ws1">0.66</td>
-      <td class="tdr_ws1">3.09</td>
-      <td class="tdr_ws1">0.97</td>
-      <td class="tdr_ws1">0.59</td>
-      <td class="tdr">1.36</td>
-   </tr><tr>
-      <td class="tdl">Magnesium.</td>
-      <td class="tdr_ws1">7.44</td>
-      <td class="tdr_ws1">2.36</td>
-      <td class="tdr_ws1">1.33</td>
-      <td class="tdr_ws1">1.77</td>
-      <td class="tdr_ws1">1.26</td>
-      <td class="tdr">2.17</td>
-   </tr><tr>
-      <td class="tdl">Ferric Oxide.</td>
-      <td class="tdr_ws1">0.72</td>
-      <td class="tdr_ws1">0.26</td>
-      <td class="tdr_ws1">0.33</td>
-      <td class="tdr_ws1">0.45</td>
-      <td class="tdr_ws1">0.2&#8199;</td>
-      <td class="tdr">0.16</td>
-   </tr><tr>
-      <td class="tdl">Phosphoric Acid.&nbsp;</td>
-      <td class="tdr_ws1">6.74</td>
-      <td class="tdr_ws1">9.26</td>
-      <td class="tdr_ws1">2.58</td>
-      <td class="tdr_ws1">6.53</td>
-      <td class="tdr_ws1">1.96</td>
-      <td class="tdr">9.95</td>
-   </tr><tr>
-      <td class="tdl">Sulphuric Acid.</td>
-      <td class="tdr_ws1">2.06</td>
-      <td class="tdr_ws1">0.07</td>
-      <td class="tdr_ws1">1.32</td>
-      <td class="tdr_ws1">2.45</td>
-      <td class="tdr_ws1">0.88</td>
-      <td class="tdr">0.95</td>
-   </tr><tr>
-      <td class="tdl">Silica.</td>
-      <td class="tdr_ws1">1.62</td>
-      <td class="tdr_ws1">0.42</td>
-      <td class="tdr_ws1">36.25</td>
-      <td class="tdr_ws1">0.8&#8199;</td>
-      <td class="tdr_ws1">0.62</td>
-      <td class="tdr">0.24</td>
-   </tr><tr>
-      <td class="tdl">Chlorine.</td>
-      <td class="tdr_ws1">2.66</td>
-      <td class="tdr_ws1">0.04</td>
-      <td class="tdr_ws1">0.9&#8199;</td>
-      <td class="tdr_ws1">1.17</td>
-      <td class="tdr_ws1">....</td>
-      <td class="tdr">0.42</td>
-   </tr>
- </tbody>
-</table>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_81" id="Page_81">[Pg 81]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_IX" id="CHAPTER_IX">CHAPTER IX.</a><br />
-<span class="h_subtitle">HOW PLANTS OBTAIN THEIR FOOD. I.</span></h3>
-</div>
-
-<h4><a name="IX_1" id="IX_1">1. Sources of Plant Food.</a></h4>
-
-<p><b>170. The necessary constituents of plant food.</b>—As indicated in
-<a href="#CHAPTER_III">Chapter 3</a>, investigation has taught us the principal constituents of
-plant food. Some suggestion as to the food substances is derived by a
-chemical analysis of various plants. In <a href="#CHAPTER_VIII">Chapter 8</a> it was noted that
-there are two principal kinds of compounds in plant substances, the
-organic compounds and the inorganic compounds or mineral substances.
-The principal elements in the organic compounds are <i>hydrogen</i>,
-<i>carbon</i>, <i>oxygen</i> and <i>nitrogen</i>. The elements in the inorganic
-compounds which have been found indispensable to plant growth are
-<i>calcium</i>,<a name="FNanchor_12_12" id="FNanchor_12_12"></a><a href="#Footnote_12_12" class="fnanchor">[12]</a>
-<i>potassium</i>, <i>magnesium</i>, <i>phosphorus</i>, <i>sulphur</i> and
-<i>iron</i>. (<a href="#PARA_54">See paragraphs 54-58</a>, and complete observations
-on water cultures.) Other elements are found in the ash of plants; and while
-they are not absolutely necessary for growth, some<a name="FNanchor_13_13" id="FNanchor_13_13"></a><a href="#Footnote_13_13" class="fnanchor">[13]</a>
-of them are beneficial in one way or another.</p>
-
-<p><b>171.</b> The carbohydrates are derived, as we have learned, from
-the CO₂ of the air, and water in the plant tissue drawn from the soil;
-though in the case of aquatic plants entirely submerged, all the
-constituents are absorbed from the surrounding water.</p>
-
-<p><b>172. Food substances in the soil.</b>—Land plants derive their
-mineral food from the soil, the soil received the mineral substances
-from dissolving and disintegrating rocks. Nitrogenous food is chiefly
-derived from the same source, but under a variety of conditions which
-will be discussed in later paragraphs, but the nitrogen comes primarily
-from the air. Some of the mineral substances, those which are soluble
-as well as some of the nitrogenous substances, are found in solution in
-the soil. These are absorbed by the plant, as needed, along with water,
-through the root hairs.
-<span class="pagenum"><a name="Page_82" id="Page_82">[Pg 82]</a></span></p>
-
-<p><b>173. Absorption of soluble substances.</b>—Since these substances
-are dissolved in the water of the soil, it is not necessary for us
-to dwell on the process of absorption. This in general is dwelt upon
-in <a href="#CHAPTER_III">Chapter 3</a>. It should be noted, however, that food substances in
-solution, during absorption, diffuse through the protoplasmic membrane
-independently of each other and also independently of the rate of
-movement of the water from the soil into the root hairs and cells of
-the root.</p>
-
-<p>When the cells have absorbed a certain amount of a given substance,
-no more is absorbed until the concentration of the cell-sap in that
-particular substance is reduced. This, however, does not interfere
-with the absorption of water, or of other substances in solution by
-the same cells. Plants have therefore a certain selective power in the
-absorption of food substances.</p>
-
-<p><b>174. Action of root hairs on insoluble substances. Acidity of root
-hairs.</b>—If we take a seedling which has been grown in a germinator,
-or in the folds of cloths or paper, so that the roots are free from the
-soil, and touch the moist root hairs to blue litmus paper, the paper
-becomes red in color where the root hairs have come in contact. This
-is the reaction for the presence of an acid salt, and indicates that
-the root hairs excrete certain acid substances. This acid property of
-the root hairs serves a very important function in the preparation
-of certain of the elements of plant food in the soil. Certain of the
-chemical compounds of potash, phosphoric acid, etc., become deposited
-on the soil particles, and are not soluble in water. The acid of the
-root hairs dissolves some of these compounds where the particles of
-soil are in close contact with them, and the solutions can then be
-taken up by the roots. Carbonic acid and other acids are also formed in
-the soil, and aid in bringing these substances into solution.</p>
-
-<p><b>175.</b> This corrosive action of the roots can be shown by the
-well-known experiment of growing a plant on a marble plate which is
-covered by soil. In lieu of the marble plate, the peas may be planted
-in clam or oyster shells, which are then buried in the soil of the
-pot, so that the roots of the seedlings will come in contact with the
-smooth surface of the shell. After a few weeks, if the soil be washed
-from the marble where the roots have been in close contact, there will
-be an outline of this part of the root system. Several different acid
-substances are excreted from the roots of plants which have been found
-to redden blue litmus paper by contact. Experiments by Czapek show,
-however, that the carbonic acid excreted by the roots has the power of
-<span class="pagenum"><a name="Page_83" id="Page_83">[Pg 83]</a></span>
-directly bringing about these corrosion phenomena. The acid salts are
-the substances which are most actively concerned in reddening the blue
-litmus paper. They do not directly aid in the corrosion phenomena. In
-the soil, however, where these compounds of potash, phosphoric acid,
-etc., are which are not soluble in water, the acid salt (primary acid
-potassium phosphate) which is most actively concerned in reddening
-the blue litmus paper may act indirectly on these mineral substances,
-making them available for plant food. This salt soon unites with
-certain chlorides in the soil, making among other things small
-quantities of hydrochloric acid.</p>
-
-<p><b>176.</b> <span class="smcap">Note.</span>—It is a general rule that plants
-cannot take solid food into their bodies, but obtain all food in either a
-liquid or gaseous state. The only exception to this is in the case of
-the plasmodia of certain <i>Myxomycetes</i> (Slime Moulds), and also perhaps
-some of the Flagellates and other very low forms, which engulf solid
-particles of food. It is uncertain, however, whether these organisms
-belong to the plant or animal kingdom, and they probably occupy a more
-or less intermediate position.</p>
-
-<p><b>177. Action of nitrite and nitrate bacteria.</b>—Many of the
-higher green plants prefer their nitrogenous food in the form of
-nitrates. (Example, nitrate of soda, potassium nitrate, saltpetre.)
-Nitrates are constantly being formed in soil by the action of certain
-bacteria. The nitrite bacteria (Nitromonas) convert ammonia in the
-soil to <i>nitrous acid</i> (a <i>nitrite</i>), while at this point the nitrate
-bacteria (Nitrobacter) convert the nitrites into nitrates. The fact
-that this nitrification is going on constantly in soil is of the utmost
-importance, for while commercial nitrates are often applied to the
-soil, the nitrates are easily washed from the soil by heavy rains.
-These nitrite and nitrate bacteria require oxygen for their activity,
-and they are able to obtain their carbohydrates by decomposing organic
-matter in the soil, or directly by assimilating the CO₂ in the soil,
-deriving the energy for the assimilation of the carbon dioxide from
-the chemical process of nitrification. This kind of carbon dioxide
-assimilation is called <i>chemosynthetic</i> assimilation.</p>
-
-<h4><a name="IX_2" id="IX_2">2. Parasites and Saprophytes.</a></h4>
-
-<p><b>178. Parasites among the fungi.</b>—A parasite is an organism
-which derives all or a part of its food directly from another living
-organism (its host) and at the latter’s expense. The larger number
-of plant parasites are found among the fungi (rusts, smuts, mildews,
-etc.). (<a href="#PARA_185">See Nutrition of the Fungi, paragraph 185</a>.) Some
-of these are not capable of development unless upon their host, and are called
-<i>obligate</i> parasites. Others can grow not only as parasites but at
-other times can also grow on dead organic matter, and are called
-<i>facultative</i> parasites, i.e. they can choose either a parasitic life
-or a saprophytic one.</p>
-
-<p><a id="PARA_179" name="PARA_179"><b>179. Parasites among the seed plants.</b></a>—<i>Cuscuta.</i>—There are,
-however, parasites among the seed plants; for example, the dodder
-<span class="pagenum"><a name="Page_84" id="Page_84">[Pg 84]</a></span>
-(Cuscuta), parasitic on clover, and a great variety of other plants.
-There is food enough in the seed for the young plant to take root and
-develop a slender stem until it takes hold of its host. It then twines
-around the stem of its host sending wedge-shaped haustoria into the
-stem to obtain food. The part then in connection with the ground dies.</p>
-
-<p>The haustoria of the dodder form a complete junction with the vascular
-bundles of its host so that through the vessels water and salts are
-obtained, while through the junction of sieve tubes the elaborated
-organic food is obtained. The union of the dodder with its host is like
-that between a graft and the graft stock. The beech drops (Epiphegus)
-is another example of a parasitic seed plant. It is parasitic on the
-roots of the beech.</p>
-
-<div class="figcenter">
-    <img src="images/fig74.jpg" alt="" width="500" height="556" />
-    <p class="center">Fig. 74.<br /> Dodder.</p>
-</div>
-
-<p><b>180. The mistletoe</b> (Viscum album), which grows on the branches
-of trees, sends its roots into the branches, and only the vessels
-of the vascular system are fused according to some. If this is true
-then it probably obtains only water and salts from its host. But the
-mistletoe has green leaves and is thus able to assimilate carbon
-<span class="pagenum"><a name="Page_85" id="Page_85">[Pg 85]</a></span>
-dioxide and manufacture its own organic substances. It is claimed by
-some, however, that the host derives some food from the parasite during
-the winter when the host has shed its leaves, and if this is true it
-would seem that organic food could also be derived during the summer
-from the host by the mistletoe.</p>
-
-<p><b>181. Saprophytes.</b>—A saprophyte is a plant which is enabled
-to obtain its food, especially its organic food, directly from dead
-animals or plants or from dead organic substances. Many fungi are
-saprophytes, as the moulds, mushrooms, etc. (<a href="#PARA_185">See Nutrition of the Fungi</a>.)</p>
-
-<p><a id="PARA_182" name="PARA_182"><b>182. Humus saprophytes.</b></a>—The
-action of fungi as described in the preceding chapter, as well as of
-certain bacteria, gradually converts the dead plants or plant parts
-into the finely powdered brown substance known as <i>humus</i>. In general
-the green plants cannot absorb organic food from humus directly. But
-plants which are devoid of chlorophyll can live saprophytically on this
-humus. They are known as <i>humus saprophytes</i>. Many of the mushrooms
-and other fungi, as well as some seed plants which lack chlorophyll or
-possess only a small quantity, are able to absorb all their organic
-food from humus. It is uncertain whether any seed plants can obtain
-all of their organic food directly from humus, though it is believed
-that many can so obtain a portion of it. But a number of seed plants,
-like the Indian-pipe (Monotropa) and certain orchids, obtain organic
-food from humus. These plants lack chlorophyll and cannot therefore
-manufacture their own carbohydrate food. Not being parasitic on plants
-which can, as in the case of the dodder and beech drops mentioned
-above, they undoubtedly derive their organic food from the humus. But
-fungus mycelium growing in the humus is attached to their roots, and
-in some orchids enters the roots and forms a nutritive connection. The
-fungus mycelium can absorb organic food from the humus and in some
-cases at least can transfer it over to the roots of the higher plant
-(<a href="#IX_4">see Mycorhiza</a>).</p>
-
-<p><b>183. Autotrophic, heterotrophic, and mixotrophic plants.</b>—An
-<i>autotrophic</i> plant is one which is self-nourishing, i.e. it is
-provided with an abundant chlorophyll apparatus for carbon dioxide
-assimilation and with absorbing organs for obtaining water and salts.
-Heterotrophic plants are not provided with a chlorophyll apparatus
-sufficient to assimilate all the carbon dioxide necessary, so they
-nourish themselves by other means. <i>Mixotrophic</i> plants are those
-which are intermediate between the other two, i.e. they have some
-chlorophyll but not enough to provide all the organic food necessary,
-so they obtain a portion of it by other means. Evidently there are all
-gradations of mixotrophic plants between the two other kinds (example,
-the mistletoe).</p>
-
-<p><b>184. Symbiosis.</b>—Symbiosis means a living with or living
-together, and is said of those organisms which live so closely in
-connection with each other as to be influenced for better or worse,
-especially from a nutrition standpoint. <i>Conjunctive</i> symbiosis has
-<span class="pagenum"><a name="Page_86" id="Page_86">[Pg 86]</a></span>
-reference to those cases where there is a direct interchange of
-food material between the two organisms (lichens, mycorhiza, etc.).
-<i>Disjunctive</i> symbiosis has reference to an inter-life relation without
-any fixed union between them (example, the relations between flowers
-and insects, ants and plants, and even in a broad sense the relation
-between saprophytic plants in reducing organic matter to a condition
-in which it may be used for food by the green plants, and these in
-turn provide organic matter for the saprophytes to feed upon, etc.).
-<i>Antagonistic</i> symbiosis is shown in the relation of parasite to its
-host, <i>reciprocal</i> symbiosis, or <i>mutualistic</i> symbiosis is shown
-in those cases where both symbionts derive food as a result of the union
-(lichens, mycorhiza, etc.).</p>
-
-<h4><a name="IX_3" id="IX_3">3. How Fungi Obtain their Food.</a></h4>
-
-<div class="figleft">
-    <img id="FIG_75" src="images/fig75.jpg" alt="" width="200" height="349" />
-    <p class="center">Fig. 75.<br /> Carnation rust on leaf<br />
-                     and flower stem.<br /> From photograph.</p>
-</div>
-
-<p><a id="PARA_185" name="PARA_185"><b>185. Nutrition of moulds.</b></a>—In
-our study of mucor, as we have seen, the growing or vegetative part of
-the plant, the mycelium, lies within the substratum, which contains the
-food materials in solution, and the slender threads are thus bathed on
-all sides by them. The mycelium absorbs the watery solutions throughout
-the entire system of ramifications. When the upright fruiting threads
-are developed they derive the materials for their growth directly from
-the mycelium with which they are in connection. The moulds which grow
-on decaying fruit or on other organic matter derive their nutrient
-materials in the same way. The portion of the mould which we usually
-see on the surface of these substances is in general the fruiting part.
-The larger part of the mycelium lies hidden within the substratum.</p>
-
-<p><a id="PARA_186" name="PARA_186">&nbsp;</a><b>186. Nutrition of parasitic fungi.</b>—Certain
-of the fungi grow on or within the higher plants and derive their food materials from them
-and at their expense. Such a fungus is called a <i>parasite</i>, and there
-<span class="pagenum"><a name="Page_87" id="Page_87">[Pg 87]</a></span>
-are a large number of these plants which are known as <i>parasitic
-fungi</i>. The plant at whose expense they grow is called the “<i>host</i>.”</p>
-
-<p>One of these parasitic fungi, which it is quite easy to obtain in
-greenhouses or conservatories during the autumn and winter, is the
-carnation rust (<i>Uromyces caryophyllinus</i>), since it breaks out in
-rusty dark brown patches on the leaves and stems of the carnation (see
-<a href="#FIG_75">fig. 75</a>). If we make thin cross-sections through one of these
-spots on a leaf, and place them for a few minutes in a solution of chloral
-hydrate, portions of the tissues of the leaf will be dissolved. After
-a few minutes we wash the sections in water on a glass slip, and stain
-them with a solution of eosin. If the sections were carefully made, and
-thin, the threads of the mycelium will be seen coursing between the
-cells of the leaf as slender threads. Here and there will be seen short
-branches of these threads which penetrate the cell wall of the host and
-project into the interior of the cell in the form of an irregular knob.
-Such a branch is a <i>haustorium</i>. By means of this haustorium, which is
-<span class="pagenum"><a name="Page_88" id="Page_88">[Pg 88]</a></span>
-here only a short branch of the mycelium, nutritive substances are
-taken by the fungus from the protoplasm or cell-sap of the carnation.
-From here it passes to the threads of the mycelium. These in turn
-supply food material for the development of the dark brown gonidia,
-which we see form the dark-looking powder on the spots. Many other
-fungi form haustoria, which take up nutrient matters in the way
-described for the carnation rust. In the case of other parasitic fungi
-the threads of the mycelium themselves penetrate the cells of the host,
-while in still others the mycelium courses only between the cells of
-the host (fungus of peach leaf curl for example) and derives food
-materials from the protoplasm or cell-sap of the host by the process of
-osmosis.</p>
-
-<div class="figcenter">
-    <img src="images/fig76.jpg" alt="" width="600" height="139" />
-    <p class="center">Fig. 76.<br /> Several teleutospores, showing the variations in form.</p>
-</div>
-<div class="figcenter">
-    <img src="images/fig77.jpg" alt="" width="600" height="348" />
-    <p class="center">Fig. 77.<br /> Cells from the stem of a rusted carnation,<br />
-                     showing the intercellular mycelium and haustoria.<br />
-                     Object magnified 30 times more than the scale.</p>
-</div>
-<div class="figcontainer">
-  <div class="figsub">
-      <img src="images/fig78.jpg" alt="" width="150" height="252" />
-      <p class="center">Fig. 78.<br /> Cell from carnation leaf,<br />
-              showing haustorium of rust<br /> mycelium grasping the<br />
-              nucleus of the host. <i>h</i>,<br /> haustorium; <i>n</i>,<br />
-              nucleus of host.</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig79.jpg" alt="" width="300" height="281" />
-      <p class="center">Fig. 79.<br /> Intercellular mycelium with haustoria entering the cells.<br />
-                 <i>A</i>, of Cystopus candidus (white rust); &nbsp;<br />
-                 <i>B</i>, of Peronospora calotheca. (De Bary.)<br /></p>
-   </div>
-</div>
-
-<p><b>187. Nutrition of the larger fungi.</b>—If we select some one of
-the larger fungi, the majority of which belong to the mushroom family
-and its relatives, which is growing on a decaying log or in the soil,
-we shall see on tearing open the log, or on removing the bark or part
-of the soil, as the case may be, that the stem of the plant, if it have
-one, is connected with whitish strands. During the spring, summer, or
-autumn months, examples of the mushrooms connected with these strands
-may usually be found readily in the fields or woods, but during the
-<span class="pagenum"><a name="Page_89" id="Page_89">[Pg 89]</a></span>
-winter and colder parts of the year often they may be seen in forcing
-houses, especially those cellars devoted to the propagation of the
-mushroom of commerce.</p>
-
-<p><b>188.</b> These strands are made up of numerous threads of the
-mycelium which are closely twisted and interwoven into a cord or
-strand, which is called a mycelium strand, or <i>rhizomorph</i>. These are
-well shown in <a href="#FIG_236">fig. 236</a>, which is from a photograph of the
-mycelium strands, or “spawn” as the grower of mushrooms calls it, of Agaricus
-campestris. The little knobs or enlargements on the strands are the
-young fruit bodies, or “buttons.”</p>
-
-<div class="figcenter">
-    <img id="FIG_80" src="images/fig80.jpg" alt="" width="500" height="460" />
-    <p class="center">Fig. 80.<br /> Sterile mycelium on wood props in coal mine,<br />
-                   400 feet below surface.</p>
-     <p class="author">(Photographed by the author.)</p>
-</div>
-
-<p><b>189.</b> While these threads or strands of the mycelium in the
-<span class="pagenum"><a name="Page_90" id="Page_90">[Pg 90]</a></span>
-decaying wood or in the decaying organic matter of the soil are not
-true roots, they function as roots, or root hairs, in the absorption
-of food materials. In old cellars and on damp soil in moist places we
-sometimes see fine examples of this vegetative part of the fungi, the
-mycelium. But most magnificent examples are to be seen in abandoned
-mines where timber has been taken down into the tunnels far below
-the surface of the ground to support the rock roof above the mining
-operations. I have visited some of the coal mines at Wilkesbarre, Pa.,
-and here on the wood props and doors, several hundred feet below the
-surface, and in blackest darkness, in an atmosphere almost completely
-saturated at all times, the mycelium of some of the wood destroying
-fungi grows in a profusion and magnificence which is almost beyond
-belief. <a href="#FIG_80">Fig. 80</a> is from a flash-light photograph of a beautiful
-example 400 feet below the surface of the ground. This was growing over the
-surface of a wood prop or post, and the picture is much reduced. On
-the doors in the mine one can see the strands of the mycelium which
-radiate in fan-like figures at certain places near the margin of
-growth, and farther back the delicate tassels of mycelium which hang
-down in fantastic figures, all in spotless white and rivalling the most
-beautiful fabric in the exquisiteness of its construction.</p>
-
-<p><b>190. How fungi derive carbohydrate food.</b>—The fungi being
-devoid of chlorophyll cannot assimilate the CO₂ from the air. They
-are therefore dependent on the green plants for their carbohydrate
-food. Among the saprophytes, the leaf and wood destroying fungi
-excrete certain substances (known as <i>enzymes</i>) which dissolve the
-carbohydrates and certain other organic compounds in the woody or
-leafy substratum in which they grow. They thus produce a sort of
-extracellular digestion of carbohydrates, converting them into a
-soluble form which can be absorbed by the mycelium. The parasitic
-fungi also obtain their carbohydrates and other organic food from the
-host. The mycelium of certain parasitic, and of wood destroying fungi,
-excretes enzymes (<i>cytase</i>) which dissolve minute perforations in the
-cell walls of the host and thus aid the hypha during its boring action
-in penetrating cell walls.</p>
-
-<p><span class="smcap">Note.</span>—Certain wood destroying fungi growing in oaks absorb
-tannin directly, i.e. in an unchanged form. One of the pine destroying
-fungi (<i>Trametes pini</i>) absorbs the xylogen from the wood cells,
-leaving the pure cellulose in which the xylogen was filtrated; while
-<i>Polyporus mollis</i> absorbs the cellulose, leaving behind only the wood element.
-<span class="pagenum"><a name="Page_91" id="Page_91">[Pg 91]</a></span></p>
-
-<h4><a name="IX_4" id="IX_4">4. Mycorhiza.</a></h4>
-
-<p><b>191.</b> While such plants as the Indian-pipe (Monotropa), some
-of the orchids, etc., are <i>humus saprophytes</i> and some of them are
-possibly able to absorb organic food from the humus, many of them have
-fungus mycelium in close connection with their roots, and these fungus
-threads aid in the absorption of organic food. The roots of plants
-which have fungus mycelium intimately associated in connection with
-the process of nutrition, are termed <i>mycorhiza</i>. There is a mutual
-interchange of food between the fungus and the host, a <i>reciprocal
-symbiosis</i>.</p>
-
-<p><b>192. Mycorhiza are of two kinds</b> as regards the relation of
-the fungus to the root; <i>ectotrophic</i> (or <i>epiphytic</i>), where the
-mycelium is chiefly on the outside of the root, and <i>endotrophic</i> (or
-<i>endophytic</i>) where the mycelium is chiefly within the tissue of the root.</p>
-
-<p><b>193. Ectotrophic mycorhiza.</b>—Ectotrophic mycorhiza occur on the
-roots of the oak, beech, hornbean, etc., in forests where there is a
-great deal of humus from decaying leaves and other vegetation. The
-young growing roots of these trees become closely covered with a thick
-felt of the mycelium, so that no root hairs can develop. The terminal
-roots also branch profusely and are considerably thickened. The fungus
-serves here as the absorbent organ for the tree. It also acts on the
-humus, converting some of it into available plant food and transferring
-it over to the tree.</p>
-
-<p><b>194. Endotrophic mycorhiza.</b>—These are found on many of the
-humus saprophytes, which are devoid of chlorophyll, as well as on those
-possessing little or even on some plants possessing an abundance, of
-chlorophyll. Examples are found in many orchids (see the coral root
-orchid, for example), some of the ferns (Botrychium), the pines,
-leguminous plants, etc. In endotrophic mycorhiza the mycelium is more
-abundant within the tissues of the root, though some of the threads
-extend to the outside. In the case of the mycorhiza on the humus
-saprophytes which have no chlorophyll, or but little, it is thought
-by some that the fungus mycelium in the humus assists in converting
-organic substances and carbohydrates into a form available for food
-by the higher plant and then conducts it into the root, thus aiding
-also in the process of absorption, since there are few or no root
-hairs on the short and fleshy mycorhiza. The roots, however, of some
-of these humus saprophytes have the power of absorbing a portion of
-their organic compounds from the humus. It is thought by some, though
-not definitely demonstrated, that in the case of the oaks, beeches,
-hornbeans, and other chlorophyll-bearing symbionts, the fungus threads
-do not absorb any carbohydrates for the higher symbiont, but that they
-actually derive their carbohydrates from it.<a name="FNanchor_14_14" id="FNanchor_14_14"></a><a href="#Footnote_14_14" class="fnanchor">[14]</a>
-But it is reasonably certain that the fungus threads do assimilate from
-<span class="pagenum"><a name="Page_92" id="Page_92">[Pg 92]</a></span>
-the humus certain unoxidized, or feebly oxidized, nitrogenous
-substances (ammonia, for example), and transfer them over to the host,
-for the higher plants with difficulty absorb these substances, while
-they readily absorb nitrates which are not abundant in humus. This is
-especially important in the forest. It is likely therefore.</p>
-
-<h4><a name="IX_5" id="IX_5">5. Nitrogen gatherers.</a></h4>
-
-<div class="figleft">
-    <img id="FIG_81" src="images/fig81.jpg" alt="" width="150" height="225" />
-    <p class="center">Fig. 81.<br /> Root of the<br /> common vetch,<br />
-                showing root<br /> tubercles.</p>
-</div>
-
-<p><b>195. How clovers, peas, and other legumes gather nitrogen.</b>—It
-has long been known that clover plants, peas, beans, and many other
-leguminous plants are often able to thrive in soil where the cereals
-do but poorly. Soil poor in nitrogenous plant food becomes richer in
-this substance where clovers, peas, etc., are grown, and they are often
-planted for the purpose of enriching the soil. Leguminous plants,
-especially in poor soil, are almost certain to have enlargements, in
-the form of nodules, or “root-tubercles.” A root of the common vetch
-with some of these root-tubercles is shown in <a href="#FIG_81">fig. 81</a>.</p>
-
-<p><b>196. A fungal or bacterial organism in these root-tubercles.</b>—If
-we cut one of these root-tubercles open, and mount a small portion
-of the interior in water for examination with the microscope, we
-shall find small rod-shaped bodies, some of which resemble bacteria,
-while others are more or less forked into forms like the letter Y, as
-shown in <a href="#FIG_82">fig. 82</a>. These bodies are rich in nitrogenous
-substances, or proteids. They are portions of a minute organism, of a fungus or
-bacterial nature, which attacks the roots of leguminous plants and
-causes these nodular outgrowths. The organism (Phytomyxa leguminosarum)
-exists in the soil and is widely distributed where legumes grow.
-<span class="pagenum"><a name="Page_93" id="Page_93">[Pg 93]</a></span></p>
-
-<p><b>197. How the organism gets into the roots of the legumes.</b>—This
-minute organism in the soil makes its way through the wall of a root
-hair near the end. It then grows down the interior of the root hair in
-the form of a thread. When it reaches the cell walls it makes a minute
-perforation, through which it grows to enter the adjacent cell, when it
-enlarges again. In this way it passes from the root hair to the cells
-of the root and down to near the center of the root. As soon as it
-begins to enter the cells of the root it stimulates the cells of that
-portion to greater activity. So the root here develops a large lateral
-nodule, or “root-tubercle.” As this “root-tubercle” increases in size,
-the fungus threads branch in all directions, entering many cells. The
-threads are very irregular in form, and from certain enlargements it
-appears that the rod-like bodies are formed, or the thread later breaks
-into myriads of these small “bacteroids.”</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-      <img id="FIG_82" src="images/fig82.jpg" alt="" width="250" height="165" />
-      <p class="center">Fig. 82.<br /> Root-tubercle organism from<br /> vetch, old condition.</p>
-   </div>
-  <div class="figsub">
-      <img id="FIG_83" src="images/fig83.jpg" alt="" width="250" height="151" />
-      <p class="center">Fig. 83.<br /> Root-tubercle organism from<br /> Medicago denticulata.</p>
-   </div>
-</div>
-
-<p><b>198. The root organism assimilates free nitrogen for its
-host.</b>—This organism assimilates the free nitrogen from the air
-in the soil, to make the proteid substance which is found stored in
-the bacteroids in large quantities. Some of the bacteroids, rich in
-proteids, are dissolved, and the proteid substance is made use of by
-the clover or pea, as the case may be. This is why such plants can
-thrive in soil with a poor nitrogen content. Later in the season some
-of the root-tubercles die and decay. In this way some of the proteid
-substance is set free in the soil. The soil thus becomes richer in
-nitrogenous plant food.</p>
-
-<p>The forms of the bacteroids vary. In some of the clovers they are oval,
-in vetch they are rod-like or forked, and other forms occur in some of
-the other genera.</p>
-
-<p class="blockquot"><b>199.</b> <span class="smcap">Note.</span>—So
-far as we know the legume tubercle organism does not assimilate free
-nitrogen of the air unless it is within the root of the legume. But
-there are microörganisms in the soil which are capable of assimilating
-free nitrogen independently. Example, a bacterium, <i>Clostridium
-pasteurianum</i>. Certain bacteria and algæ live in <i>contact symbiosis</i>
-in the soil, the bacteria fixing free nitrogen, while in return for the
-combined nitrogen, the algæ furnish the bacteria with carbohydrates.
-It seems that these bacteria cannot fix the free nitrogen of the air
-unless they are supplied with carbohydrates, and it is known that
-<i>Clostridium pasteurianum</i> cannot assimilate free nitrogen unless
-sugar is present.</p>
-
-<h4><a name="IX_6" id="IX_6">6. Lichens.</a></h4>
-
-<p><a id="PARA_200" name="PARA_200"><b>200. Nutrition of lichens.</b></a>—Lichens are very
-curious plants which grow on rocks, on the trunks and branches of trees, and on the
-soil. They form leaf-like expansions more or less green in color, or
-brownish, or gray, or they occur in the form of threads, or small
-<span class="pagenum"><a name="Page_94" id="Page_94">[Pg 94]</a></span>
-tree-like formations. Sometimes the plant fits so closely to the rock
-on which it grows that it seems merely to paint the rock a slightly
-different color, and in the case of many which occur on trees there
-appears to be to the eye only a very slight discoloration of the bark
-of the trunk, with here and there the darker colored points where fruit
-bodies are formed. The most curious thing about them is, however,
-that while they form plant bodies of various form, these bodies are
-of a “dual nature” as regards the organisms composing them. The plant
-bodies, in other words, are formed of two different organisms which,
-woven together, exist apparently as one. A fungus on the one hand grows
-around and encloses in the meshes of its mycelium the cells or threads
-of an alga, as the case may be.</p>
-
-<div class="figcenter">
-    <img src="images/fig84.jpg" alt="" width="600" height="345" />
-    <p class="center">Fig. 84.<br /> Frond of lichen (peltigera), showing rhizoids.</p>
-</div>
-
-<p>If we take one of the leaf-like forms known as peltigera, which grows
-on damp soil or on the surfaces of badly decayed logs, we see that the
-plant body is flattened, thin, crumpled, and irregularly lobed. The
-color is dull greenish on the upper side, while the under side is white
-or light gray, and mottled with brown, especially the older portions.
-Here and there on the under surface are quite long slender blackish
-strands. These are composed entirely of fungus threads and serve as
-organs of attachment or holdfasts, and for the purpose of supplying
-the plant body with mineral substances which are in solution in the
-water of the soil. If we make a thin section of the leaf-like portion
-of a lichen as shown in <a href="#FIG_85">fig. 85</a>, we shall see that it is
-composed of a mesh of colorless threads which in certain definite portions contain
-entangled green cells. The colorless threads are those of the fungus,
-while the green cells are those of the alga. These green cells of the
-alga perform the function of chlorophyll bodies for the dual organism,
-while the threads of the fungus provide the mineral constituents of
-<span class="pagenum"><a name="Page_95" id="Page_95">[Pg 95]</a></span>
-plant food. The alga, while it is not killed in the embrace of the
-fungus, does not reach the perfect state of development which it
-attains when not in connection with the fungus. On the other hand the
-fungus profits more than the alga by this association. It forms fruit
-bodies, and perfects spores in the special fruit bodies, which are so
-very distinct in the case of so many of the species of the lichens.
-These plants have lived for so long a time in this close association
-that the fungi are rarely found separate from the algæ in nature, but
-in a number of cases they have been induced to grow in artificial
-cultures separate from the alga. This fact, and also the fact that the
-algæ are often found to occur separate from the fungus in nature, is
-regarded by many as an indication that the plant body of the lichens is
-composed of two distinct organisms, and that the fungus is parasitic on
-the alga.</p>
-
-<div class="figcenter">
-    <img id="FIG_85" src="images/fig85.jpg" alt="" width="600" height="412" />
-    <p class="center">Fig. 85.<br /> Lichen (peltigera), section of thallus; dark zone of rounded<br />
-               bodies made up largely of the algal cells. Fungus cells<br />
-               above, and threads beneath and among the algal cells.</p>
-</div>
-
-<p><b>201.</b> Others regard the lichens as autonomous plants, that is,
-the two organisms have by this long-continued community of existence
-become unified into an individualized organism, which possesses a habit
-<span class="pagenum"><a name="Page_96" id="Page_96">[Pg 96]</a></span>
-and mode of life distinct from that of either of the organisms forming
-the component parts. This community of existence between two different
-organisms is called by some <i>mutualism</i>, or <i>symbiosis</i>. While
-the alga enclosed within the meshes of the fungus is not so free to develop,
-and probably does not attain the full development which it would alone
-under favorable conditions, still it is very likely that it is often
-preserved from destruction during very dry periods, within the tough
-thallus, on the surface of bare rocks.</p>
-
-<div class="figcenter">
-    <img id="FIG_86" src="images/fig86.jpg" alt="" width="600" height="331" />
-    <p class="center">Fig. 86.<br /> Section of fruit body or apothecium
-            of lichen (parmelia),<br /> showing asci and spores of the fungus.</p>
-</div>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_97" id="Page_97">[Pg 97]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_X" id="CHAPTER_X">CHAPTER X.</a><br />
-<span class="h_subtitle">HOW PLANTS OBTAIN THEIR FOOD, II.</span></h3>
-</div>
-
-<h4><a name="X_1" id="X_1">Seedlings.</a></h4>
-
-<p><b>202.</b> It is evident from some of the studies which we have made
-in connection with germination of seeds and nutrition of the plant
-that there is a period in the life of the seed plants in which they
-are able to grow if supplied with moisture, but may entirely lack any
-supply of food substance from the outside, though we understand that
-growth finally comes to a standstill unless they are supplied with food
-from the outside. In connection with the study of the nutrition of the
-plant, therefore, it will be well to study some of the representative
-seeds and seedlings to learn more accurately the method of germination
-and nutrition in seedlings during the germinating period.</p>
-
-<p><b>203. To prepare seeds for germination.</b>—Soak a handful of
-seeds (or more if the class is large) in water for 12 to 24 hours.
-Take shallow crockery plates, or ordinary plates, or a germinator
-with a fluted bottom. Place in the bottom some sheets of paper, and
-if sphagnum moss is at hand scatter some over the paper. If the moss
-is not at hand, throw the upper layer of paper into numerous folds.
-Thoroughly wet the paper and moss, but do not have an excess of water.
-Scatter the seeds among the moss or the folds of the paper. Cover
-with some more wet paper and keep in a room where the temperature is
-about 20°C. to 25°C. The germinator should be looked after to see that
-the paper does not become dry. It may be necessary to cover it with
-another vessel to prevent the too rapid evaporation of the water. The
-germinator should be started about a week before the seedlings are
-wanted for study. Some of the soaked seeds should be planted in soil in
-pots and kept at the same temperature, for comparison with those grown
-in the germinator.</p>
-
-<div class="figleft">
-    <img src="images/fig87.jpg" alt="" width="250" height="55" />
-    <p class="center">Fig. 87.<br /> Section of corn seed; at upper<br />
-              right of each is the plantlet,<br />
-              next the cotyledon, at left<br /> the endosperm.</p>
-</div>
-
-<p><b>204. Structure of the grain of corn.</b>—Take grains of corn that
-<span class="pagenum"><a name="Page_98" id="Page_98">[Pg 98]</a></span>
-have been soaked in water for 24 hours and note the form and difference
-in the two sides (in all of these studies the form and structure of
-the seed, as well as the stages in germination, should be illustrated
-by the student). Make a longisection of a grain of corn through the
-middle line, if necessary making several in order to obtain one which
-shows the structures well near the smaller end of the grain. Note
-the following structures: 1st, the hard outer “wall” (formed of the
-consolidated wall of the ovary with the integuments of the ovules—see
-Chapters <a href="#CHAPTER_XXXV">35</a> and <a href="#CHAPTER_XXXVI">36</a>);
-2d, the greater mass of starch and other plant food (the endosperm)
-in the centre; 3d, a somewhat crescent-shaped body (the <i>scutellum</i>)
-lying next the endosperm and near the smaller end of the grain; 4th,
-the remaining portion of the young embryo lying between the scutellum
-and the seed coat in the depression. When good sections are made one
-can make out the radicle at the smaller end of the seed, and a few
-successive leaves (the plumule) which lie at the opposite end of the
-embryo shown by sharply curved parallel lines. Observe the attachment
-of the scutellum to the caulicle at the point of junction of the
-plumule and the radicle. The scutellum is a part of the embryo and
-represents a cotyledon. The endosperm is also called <i>albumen</i>, and
-such a seed is <i>albuminous</i>.</p>
-
-<p>Dissect out an embryo from another seed, and compare with that seen
-in the section.</p>
-
-<p><b>205.</b> In the germination of the grain of corn the endosperm
-supplies the food for the growth of the embryo until the roots are
-well established in the soil and the leaves have become expanded and
-green, in which stage the plant has become able to obtain its food from
-the soil and air and live independently. The starch in the endosperm
-cannot of course be used for food by the embryo in the form of starch.
-It is first converted into a soluble form and then absorbed through
-the surface of the scutellum or cotyledon and carried to all parts of
-the embryo. An enzyme developed by the embryo acts upon the starch,
-converting it into a form of sugar which is in solution and can thus
-be absorbed. This enzyme is one of the so-called diastatic “ferments”
-which are formed during the germination of all seeds which contain food
-stored in the form of starch. In some seedlings, this diastase formed
-is developed in much greater abundance than in others, for example,
-in barley. Examine grains of corn still attached to seedlings several
-weeks old and note that a large part of their content has been used up.
-The action of diastase on starch is described in <a href="#CHAPTER_VIII">Chapter 8</a>.
-<span class="pagenum"><a name="Page_99" id="Page_99">[Pg 99]</a></span></p>
-
-<p><b>206. Structure of the pumpkin seed.</b>—The pumpkin seed has a
-tough papery outer covering for the protection of the embryo plant
-within. This covering is made up of the seed coats. When the seed is
-opened by slitting off these coats there is seen within the “meat”
-of the pumpkin seed. This is nothing more than the embryo plant. The
-larger part of this embryo consists of two flattened bodies which
-are more prominent than any other part of the plantlet at this time.
-These two flattened bodies are the two first leaves, usually called
-<i>cotyledons</i>. If we spread these cotyledons apart we see that they are
-connected at one end. Lying between them at this point of attachment
-is a small bud. This is the <i>plumule</i>. The plumule consists of the
-very young leaves at the end of the stem which will grow as the seed
-germinates. At the other end where the cotyledons are joined is a small
-projection, the young root, often termed the <i>radicle</i>.</p>
-
-<p><b>207. How the embryo gets out of a pumpkin seed.</b>—To see how the
-embryo gets out of the pumpkin seed we should examine seeds germinated
-in the folds of damp paper or on damp sphagnum, as well as some which
-have been germinated in earth. Seeds should be selected which represent
-several different stages of germination.</p>
-
-<div class="figcenter">
-    <img src="images/fig88.jpg" alt="" width="600" height="192" />
-    <p class="center">Fig. 88.<br /> Germinating seed of pumpkin, showing how the heel<br />
-                   or “peg” catches on the seed coat to cast it off.</p>
-</div>
-<div class="figcenter">
-    <img src="images/fig89.jpg" alt="" width="500" height="460" />
-    <p class="center">Fig. 89.<br /> Escape of the pumpkin seedling from the seed coats.</p>
-</div>
-
-<p><b>208. The peg helps to pull the seed coats apart.</b>—The root
-pushes its way out from between the stout seed coats at the smaller
-<span class="pagenum"><a name="Page_100" id="Page_100">[Pg 100]</a></span>
-end, and then turns downward unless prevented from so doing by a hard
-surface. After the root is 2-4 <i>cm</i> long, and the two halves of the
-seed coats have begun to be pried apart, if we look in this rift at the
-junction of the root and stem, we shall see that one end of the seed
-coat is caught against a heel, or “peg,” which has grown out from the
-stem for this purpose. Now if we examine one which is a little more
-advanced, we shall see this heel more distinctly, and also that the
-stem is arching out away from the seed coats. As the stem arches up
-its back in this way it pries with the cotyledons against the upper
-seed coat, but the lower seed coat is caught against this heel, and
-the two are pulled gradually apart. In this way the embryo plant pulls
-itself out from between the seed coats. In the case of seeds which are
-planted deeply in the soil we do not see this contrivance unless we dig
-down into the earth. The stem of the seedling arches through the soil,
-pulling the cotyledons up at one end. Then it straightens up, the green
-cotyledons part, and open out their inner faces to the sunlight, as
-shown in <a href="#FIG_90">fig. 90</a>. If we dig into the soil we shall see that this
-same heel is formed on the stem, and that the seed coats are cast off into the soil.
-<span class="pagenum"><a name="Page_101" id="Page_101">[Pg 101]</a></span></p>
-
-<div class="figcenter">
-    <img id="FIG_90" src="images/fig90.jpg" alt="" width="600" height="382" />
-    <p class="center">Fig. 90.<br /> Pumpkin seedling rising from the ground.</p>
-</div>
-
-<p><b>209. Parts of the pumpkin seedling.</b>—During the germination of
-the seed all parts of the embryo have enlarged. This increase in size
-of a plant is one of the peculiarities of growth. The cotyledons have
-elongated and expanded somewhat, though not to such a great extent
-as the root and the stem. The cotyledons also have become green on
-exposure to the light. Very soon after the main root has emerged from
-the seed coats, other lateral roots begin to form, so that the root
-soon becomes very much branched. The main root with its branches makes
-up the root system of the seedling. Between the expanded cotyledons is
-seen the plumule. This has enlarged somewhat, but not nearly so much as
-the root, or the part of the stem which extends below the cotyledons.
-This part of the stem, i.e., that part below the cotyledons and
-extending to the beginning of the root, is called in all seedlings the
-<i>hypocotyl</i>, which means “below the cotyledon.”</p>
-
-<p><b>210. The common garden bean.</b>—The common garden bean, or the
-lima bean, may be used for study. The garden bean is not so flattened
-or broadened as the lima bean. It is rounded compressed, elongate
-slightly curved, slightly concave on one side and convex on the other,
-and the ends are rounded. At the middle of the concave side note the
-distinct scar (the hilum) formed where the bean seed separates from
-its attachment to the wall of the pod. Upon one side of this scar is a
-slight prominence which is continued for a short distance toward the
-end of the bean in the form of a slight ridge. This is the <i>raphe</i>, and
-represents that part of the stalk of the ovule which is joined to the
-<span class="pagenum"><a name="Page_102" id="Page_102">[Pg 102]</a></span>
-side of the ovule when the latter is curved around against it (see
-<a href="#CHAPTER_XXXVI">Chapter 36</a>), and at the outer end of the raphe is
-the <i>chalaza</i>, the point where the stalk is joined to the end of the ovule,
-best understood in a straight ovule. Upon the opposite side of the scar
-and close to it can be seen a minute depression, the <i>micropyle</i>.
-Underneath the seed coat and lying between this point and the end of
-the seed is the <i>embryo</i>, which gives greater prominence to the bean
-at this point, but it is especially more prominent after the bean has been
-soaked in water. Soak the beans in water and as they are swelling note
-how the seed coats swell faster than the inner portion of the seed,
-which causes them to wrinkle in a curious way, but finally the inner
-portion swells and fills the seed coat out smooth again. Sketch a bean
-showing all the external features both in side view and in front. Split
-one lengthwise and sketch the half to which the embryo clings, noting
-the young root, stem, and the small leaves which were lying between
-the cotyledons. There is no endosperm here now, since it was all used
-up in the growth of the embryo, and a large part of its substance was
-stored up in the cotyledons. As the seed germinates the young plant
-gets its first food from that stored in the cotyledons. The hypocotyl
-elongates, becomes strongly arched, and at last straightens up, lifting
-the cotyledons from the soil. As the cotyledons become exposed to the
-light they assume a green color. Some of the stored food in them goes
-to nourish the embryo during germination, and they therefore become
-smaller, shrivel somewhat, and at last fall off.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-      <img src="images/fig91.jpg" alt="" width="150" height="196" />
-      <p class="center">Fig. 91.<br /> Garden bean.<br />
-             <i>m</i>, micropyle;<br /> <i>h</i>, hilum or scar;<br />
-             <i>r</i>, raphe;<br /> <i>c</i>, point where<br /> chalaza lies.</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig92.jpg" alt="" width="300" height="206" />
-      <p class="center space-above2">Fig. 92.<br /> Bean seed split open<br />
-                     to show plantlet.</p>
-   </div>
-</div>
-
-<p><b>211. The castor-oil bean.</b>—This is not a true bean, since it
-belongs to a very different family of plants (Euphorbiaceæ). In the
-germination of this seed a very interesting comparison can be made with
-that of the garden bean. As the “bean” swells the very hard outer coat
-generally breaks open at the free end and slips off at the stem end.
-<span class="pagenum"><a name="Page_103" id="Page_103">[Pg 103]</a></span>
-The next coat within, which is also hard and shining black, splits
-open at the opposite end, that is at the stem end. It usually splits
-open in the form of three ribs. Next within the inner coat is a very
-thin, whitish film (the remains of the nucellus, and corresponding to
-the perisperm) which shrivels up and loosens from the white mass, the
-endosperm, within. In the castor-oil bean, then, the endosperm is not
-all absorbed by the embryo during the formation of the seed. As the
-plant becomes older we should note that the fleshy endosperm becomes
-thinner and thinner, and at last there is nothing but a thin, whitish
-film covering the green faces of the cotyledons. The endosperm has been
-gradually absorbed by the germinating plant through its cotyledons and
-used for food.</p>
-
-<div class="figcenter">
-    <img src="images/fig93.jpg" alt="" width="500" height="389" />
-    <p class="center space-below2">Fig. 93.<br /> How the garden bean comes out of the ground. First the looped<br />
-                hypocotyl, then the cotyledons pulled out, next casting off the<br />
-                seed coat, last the plant erect, bearing thick cotyledons,<br />
-                the expanding leaves, and the plumule between them.</p>
-</div>
-
-<p class="center"><b>Arisæma triphyllum.</b><a name="FNanchor_15_15" id="FNanchor_15_15"></a><a href="#Footnote_15_15" class="fnanchor">[15]</a></p>
-
-<p><b>212. Germination of seeds of jack-in-the-pulpit.</b>—The ovaries
-of jack-in-the-pulpit form large, bright red berries with a soft pulp
-enclosing one to several large seeds. The seeds are oval in form. Their
-<span class="pagenum"><a name="Page_104" id="Page_104">[Pg 104]</a></span>
-germination is interesting, and illustrates one type of germination of
-seeds common among monocotyledonous plants. If the seeds are covered
-with sand, and kept in a moist place, they will germinate readily.</p>
-
-<div class="figcenter">
-    <img src="images/fig94.jpg" alt="" width="600" height="343" />
-    <p class="center space-below2">Fig. 94.<br /> Germination of castor-oil bean.</p>
-</div>
-
-<p><b>213. How the embryo backs out of the seed.</b>—The embryo lies
-within the mass of the endosperm; the root end, near the smaller end of
-the seed. The club-shaped cotyledon lies near the middle of the seed,
-surrounded firmly on all sides by the endosperm. The stalk, or petiole,
-of the cotyledon, like the lower part of the petiole of the leaves, is
-a hollow cylinder, and contains the younger leaves, and the growing end
-of the stem or bud. When germination begins, the stalk, or petiole, of
-the cotyledon elongates. This pushes the root end of the embryo out
-at the small end of the seed. The free end of the embryo now enlarges
-somewhat, as seen in the figures, and becomes the bulb, or corm, of the
-young plant. At first no roots are visible, but in a short time one,
-two, or more roots appear on the enlarged end.</p>
-
-<p><b>214. Section of an embryo.</b>—If we make a longisection of the
-embryo and seed at this time we can see how the club-shaped cotyledon
-is closely surrounded by the endosperm. Through the cotyledon, then,
-the nourishment from the endosperm is readily passed over to the
-growing embryo. In the hollow part of the petiole near the bulb can be
-seen the first leaf.
-<span class="pagenum"><a name="Page_105" id="Page_105">[Pg 105]</a></span></p>
-
-<div class="figcenter">
-    <img src="images/fig95.jpg" alt="" width="600" height="443" />
-    <p class="center space-below2">Fig. 95.<br /> Seedlings of castor-oil bean
-                  casting the seed coats,<br /> and showing papery remnant of
-                  the endosperm.</p>
-</div>
-<div class="figcontainer">
-  <div class="figsub">
-      <img src="images/fig96.jpg" alt="" width="200" height="277" />
-      <p class="center">Fig. 96.<br /> Seedlings of jack-in-the-pulpit;<br />
-                     embryo backing out of the seed.</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig97.jpg" alt="" width="250" height="202" />
-      <p class="center">Fig. 97.<br /> Section of germinating embryos of<br />
-        jack-in-the-pulpit, showing young<br /> leaves inside the petiole of the<br />
-        cotyledon. At the left cotyledon<br /> shown surrounded by the endosperm<br />
-        in the seed; at right endosperm<br /> removed to show the club-shaped<br />
-        cotyledon.</p>
-   </div>
-</div>
-
-<p><span class="pagenum"><a name="Page_106" id="Page_106">[Pg 106]</a></span>
-<b>215. How the first leaf appears.</b>—As the embryo backs out of
-the seed, it turns downward into the soil, unless the seed is so lying
-that it pushes straight downward. On the upper side of the arch thus
-formed, in the petiole of the cotyledon, a slit appears, and through
-this opening the first leaf arches its way out. The loop of the petiole
-comes out first, and the leaf later, as shown in <a href="#FIG_98">fig. 98</a>.
-The petiole now gradually straightens up, and as it elongates the leaf expands.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-      <img id="FIG_98" src="images/fig98.jpg" alt="" width="100" height="320" />
-      <p class="center">Fig. 98.<br /> Seedlings of<br /> jack-in-the-pulpit,<br />
-              first leaf arching<br /> out of the<br /> petiole of<br /> the cotyledon.</p>
-   </div>
-  <div class="figsub">
-      <img id="FIG_99" src="images/fig99.jpg" alt="" width="150" height="329" />
-      <p class="center">Fig. 99.<br /> Embryos of<br /> jack-in-the-pulpit<br />
-               still attached to <br /> the endosperm<br /> in seed coats,<br /> and showing<br /> the
-                simple<br /> first leaf.</p>
-  </div>
-  <div class="figsub">
-      <img id="FIG_100" src="images/fig100.jpg" alt="" width="100" height="339" />
-      <p class="center">Fig. 100.<br /> Seedling of<br /> jack-in-the-pulpit;<br />
-            section of the<br /> endosperm<br /> and cotyledon.</p>
-   </div>
-</div>
-
-<p><b>216. The first leaf of the jack-in-the-pulpit is a simple
-one.</b>—The first leaf of the embryo jack-in-the-pulpit is very
-different in form from the leaves which we are accustomed to see on
-<span class="pagenum"><a name="Page_107" id="Page_107">[Pg 107]</a></span>
-mature plants. If we did not know that it came from the seed of this
-plant we would not recognize it. It is simple, that is it consists
-of one lamina or blade, and not of three leaflets as in the compound
-leaf of the mature plant. The simple leaf is ovate and with a broad
-heart-shaped base. The jack-in-the-pulpit, then, as trillium, and some
-other monocotyledonous plants which have compound leaves on the mature
-plants, have simple leaves during embryonic development. The ancestral
-monocotyledons are supposed to have had simple leaves. Thus there is in
-the embryonic development of the jack-in-the-pulpit, and others with
-compound leaves, a sort of recapitulation of the evolutionary history
-of the leaf in these forms.</p>
-
-<p><b>216</b><i>a</i>. <b>Germination of the pea.</b>—Compare with the bean.
-Note especially that the cotyledons are not lifted above the soil as in
-the beans. Compare germination of acorns.</p>
-
-<h4><a name="X_2" id="X_2">Digestion.</a></h4>
-
-<p><a name="PARA_216" id="PARA_216"><b>216</b></a><i>b</i>. <b>To test for stored food substance in the seedlings
-studied.</b>—The pumpkin, squash, and castor-oil bean are examples
-of what are called oily seeds, since considerable oil is stored up
-in the protoplasm in the cotyledons. To test for this, remove a
-small portion of the substance from the cotyledon of the squash and
-crush it on a glass slip in a drop or two of osmic acid.<a name="FNanchor_16_16" id="FNanchor_16_16"></a><a href="#Footnote_16_16" class="fnanchor">[16]</a>
-Put on a cover glass and examine with a microscope. The black amorphous matter
-shows the presence of oil in the protoplasm. The small bodies which are
-stained yellow are <i>aleurone</i> grains, a form of protein or albuminous
-substance. Both the oil and the protein substance are used by the
-seedling during germination. The oil is converted into an available
-food form by the action of an enzyme called <i>lipase</i>, which splits up
-the fatty oil into glucose and other substances. Lipase has been found
-in the endosperm of the castor-oil, cocoanut, and in the cotyledons
-of the pumpkin, as well as in other seeds containing oil as a stored
-product. The aleurone is made available by an enzyme of the nature of
-trypsin. Test the endosperm of the castor-oil bean in the same way.
-Make another test of both the squash and castor-oil seeds with iodine
-to show that starch is not present.</p>
-
-<p>Test the cotyledon of the bean with iodine for the presence of
-starch. If the endosperm of corn seed has not been tested do so now
-with iodine. The endosperm consists largely of starch. The starch is
-<span class="pagenum"><a name="Page_108" id="Page_108">[Pg 108]</a></span>
-converted to glucose by a diastatic “ferment” formed by the seedling as
-it germinates. Make a thin cross-section of a grain of wheat, including
-the seed coat and a portion of the interior, treat with iodine and
-mount for microscopic examination. Note the abundance of starch in the
-internal portion of endosperm. Note a layer of cells on the outside of
-the starch portions filled with small bodies which stain yellow. These
-are aleurone grains. The cellulose in the cell walls of the endosperm
-is dissolved by another enzyme called <i>cytase</i>, and some plants store
-up cellulose for food. For example, in the endosperm of the <i>date</i> the
-cell walls are very much thickened and pitted. The cell walls consist of
-reserve cellulose and the seedling makes use of it for food during growth.</p>
-
-<p><b>216</b><i>c</i>. <b>Albuminous and exalbuminous seeds.</b>—In seeds
-where the food is stored outside of the embryo they are called
-<i>albuminous</i>; examples, corn, wheat and other cereals, Indian turnip,
-etc. In those seeds where the food is stored up in the embryo they are
-called <i>exalbuminous</i>; examples, bean, pea, pumpkin, squash, etc.</p>
-
-<p><b>217. Digestion</b> has a well-defined meaning in animal physiology
-and relates to the conversion of solid food, usually within the
-stomach, into a soluble form by the action of certain gastric juices,
-so that the liquid food may be absorbed into the circulatory system.
-The term is not often applied in plant physiology, since the method
-of obtaining food is in general fundamentally different in plants and
-animals. It is usually applied to the process of the conversion of
-starch into some form of sugar in solution, as glucose, etc. This we
-have found takes place in the leaf, especially at night, through the
-action of a diastatic ferment developed more abundantly in darkness. As
-a result, the starch formed during the day in the leaves is digested
-at night and converted into sugar, in which form it is transferred to
-the growing parts to be employed in the making of new tissues, or it is
-stored for future use; in other cases it unites with certain inorganic
-substances, absorbed by the roots and raised to the leaf, to form
-proteids and other organic substances. In tubers, seeds, parts of stems
-or leaves where starch is stored, it must first be “digested” by the
-action of some enzyme before it can be used as food by the sprouting
-tubers or germinating seeds.</p>
-
-<p>For example, starch is converted to a glucose by the action of a
-diastase. Cellulose is converted to a glucose by cytase. Albuminoids
-are converted into available food by a tryptic ferment. Fatty oils are
-converted into glucose and other products by lipase.</p>
-
-<p>Inulin, a carbohydrate closely related to starch, is stored up for
-food in solution in many composite plants, as in the artichoke, the
-root tuber of dahlia, etc. When used for food by the growing plant
-it is converted into glucose by an enzyme, inulase. Make a section
-of a portion of a dahlia tuber or artichoke and treat with alcohol.
-The inulin is precipitated into sphæro crystals. (See also paragraphs
-<a href="#PARA_156">156-161</a> and <a href="#PARA_216">216<i>b</i></a>.)
-<span class="pagenum"><a name="Page_109" id="Page_109">[Pg 109]</a></span></p>
-
-<p><b>218.</b> Then there are certain fungi which feed on starch or other
-organic substances whether in the host or not, which excrete certain
-enzymes to dissolve the starch, etc., to bring it into a soluble
-form before they can absorb it as food. Such a process is a sort of
-<i>extracellular digestion</i>, i.e., the organism excretes the enzyme and
-digests the solid outside, since it cannot take the food within its
-cells in the solid form. To a certain degree the higher plants perform
-also extracellular digestion in the action of root hair excretion on
-insoluble substances, and in the case of the humus saprophytes. But for
-them soluble food is largely prepared by the action of acids, etc., in
-the soil or water, or by the work of fungi and bacteria as described in
-<a href="#CHAPTER_IX">Chapter 9</a>.</p>
-
-<p><a name="X_3" id="X_3"><b>219. Assimilation.</b></a>—In plant
-physiology the term assimilation has been chiefly used for the process
-of carbon dioxide assimilation (= photosynthesis). Some objections
-have been raised against the use of assimilation here as one of the
-life processes of the plant, since its inception stages are due to the
-combined action of light, an external factor, and chlorophyll in the
-plant along with the living chloroplastid. So long, however, as it
-is not known that this process can take place without the aid of the
-living plant, it does not seem proper to deny that it is altogether
-not a process of assimilation. It is not necessary to restrict the
-term assimilation to the formation of new living matter in the plant
-cell; it can be applied also to the synthetic processes in the
-formation of carbohydrates, proteids, etc., and called synthetic
-assimilation. The sun supplies the energy, which is absorbed by the
-chlorophyll, for splitting up the carbonic acid, and the living
-chloroplast then assimilates by a synthetic process the carbon,
-hydrogen, and oxygen. This process then can be called <i>photosynthetic
-assimilation</i>. The nitrite and nitrate bacteria derive energy in
-the process of nitrification, which enables them to assimilate CO₂
-from the air, and this is called <i>chemosynthetic assimilation</i>. The
-inorganic material in the form of mineral salts, nitrates, etc.,
-absorbed by the root, and carried up to the leaves, here meets with
-the carbohydrates manufactured in the leaf. Under the influence of
-the protoplasm synthesis takes place, and proteids and other organic
-compounds are built up by the union of the salts, nitrates, etc., with
-the carbohydrates. This is also a process of synthetic assimilation.
-These are afterward stored as food, or assimilated by the protoplasm in
-the making of new living matter, or perhaps without the first process
-of synthetic assimilation some of the inorganic salts, nitrates, and
-carbohydrates meeting in the protoplasm are assimilated into new living
-matter directly.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_110" id="Page_110">[Pg 110]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XI" id="CHAPTER_XI">CHAPTER XI.</a><br />
-<span class="h_subtitle">RESPIRATION.</span></h3>
-</div>
-
-<p><b>220.</b> One of the life processes in plants which is extremely
-interesting, and which is exactly the same as one of the life processes
-of animals, is easily demonstrated in several ways.</p>
-
-<p><b>221. Simple experiment to demonstrate the evolution of CO₂ during
-germination.</b>—Where there are a number of students and a number of
-large cylinders are not at hand, take bottles of a pint capacity and
-place in the bottom some peas soaked for 12 to 24 hours. Cover with
-a glass plate which has been smeared with vaseline to make a tight
-joint with the mouth of the bottle. Set aside in a warm place for 24
-hours. Then slide the glass plate a little to one side and quickly
-pour in a little baryta water so that it will run down on the inside
-of the bottle. Cover the bottle again. Note the precipitate of barium
-carbonate which demonstrates the presence of CO₂ in the bottle. Lower a
-lighted taper. It is extinguished because of the great quantity of CO₂.
-If flower buds are accessible, place a small handful in each of several
-jars and treat the same as in the case of the peas. Young growing
-mushrooms are excellent also for this experiment, and serve to show
-that respiration takes place in the fungi.
-<span class="pagenum"><a name="Page_111" id="Page_111">[Pg 111]</a></span></p>
-
-<div class="figcontainer">
-  <div class="figsub">
-      <img id="FIG_101" src="images/fig101.jpg" alt="" width="200" height="349" />
-      <p class="center space-above2">Fig. 101.<br /> Test for presence of carbon dioxide in<br />
-                    vessel with germinating peas. (Sachs.)</p>
-   </div>
-  <div class="figsub">
-      <img id="FIG_102" src="images/fig102.jpg" alt="" width="250" height="408" />
-      <p class="center">Fig. 102.<br /> Apparatus to show respiration<br /> of germinating wheat.</p>
-  </div>
-</div>
-
-<p><b>222.</b> If we now take some of the baryta water and blow our
-“breath” upon it the same film will be formed. The carbon dioxide which
-we exhale is absorbed by the baryta water, and forms barium carbonate,
-just as in the case of the peas. In the case of animals the process by
-which oxygen is taken into the body and carbon dioxide is given off is
-<i>respiration</i>. The process in plants which we are now studying is the
-same, and also is respiration. The oxygen in the vessel was partly used
-up in the process, and carbon dioxide was given off. (It will be seen
-that this process is exactly the opposite of that which takes place in
-carbon dioxide assimilation.)</p>
-
-<p><b>223. To show that oxygen from the air is used up while plants
-respire.</b>—Soak some wheat for 24 hours in water. Remove it from
-the water and place it in the folds of damp cloth or paper in a moist
-vessel. Let it remain until it begins to germinate. Fill the bulb of
-a thistle tube with the germinating wheat. By the aid of a stand and
-clamp, support the tube upright, as shown in <a href="#FIG_102">fig. 102</a>.
-Let the small end of the tube rest in a strong solution of caustic potash (one stick
-caustic potash in two-thirds tumbler of water) to which red ink has
-been added to give a deep red color. Place a small glass plate over the
-rim of the bulb and seal it air-tight with an abundance of vaseline.
-Two tubes can be set up in one vessel, or a second one can be set up in
-strong baryta water colored in the same way.</p>
-
-<p><b>224. The result.</b>—It will be seen that the solution of caustic
-potash rises slowly in the tube; the baryta water will also, if that is
-<span class="pagenum"><a name="Page_112" id="Page_112">[Pg 112]</a></span>
-used. The solution is colored so that it can be plainly seen at some
-distance from the table as it rises in the tube. In the experiment
-from which the figure was made for the accompanying illustration, the
-solution had risen in 6 hours to the height shown in <a href="#FIG_102">fig. 102</a>.
-In 24 hours it had risen to the height shown in <a href="#FIG_103">fig. 103</a>.</p>
-
-<p><b>225. Why the solution of caustic potash rises in the
-tube.</b>—Since no air can get into the thistle tube from above or
-below, it must be that some part of the air which is inside of the
-tube is used up while the wheat is germinating. From our study of
-germinating peas, we know that a suffocating gas, carbon dioxide, is
-given off while respiration takes place. The caustic potash solution,
-or the baryta water, whichever is used, absorbs the carbon dioxide. The
-carbon dioxide is heavier than air, and so it settles down in the tube
-where it can be absorbed.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img id="FIG_103" src="images/fig103.jpg" alt="" width="100" height="239" />
-    <p class="center">Fig. 103.<br /> Apparatus to show<br />
-             respiration of<br /> germinating wheat.</p>
-   </div>
-  <div class="figsub">
-      <img id="FIG_104" src="images/fig104.jpg" alt="" width="200" height="263" />
-      <p class="center">Fig. 104.<br /> Pea seedlings; the one at the left<br />
-             had no oxygen and little growth took<br />
-             place, the one at the right in oxygen<br /> and growth was evident.</p>
-  </div>
-</div>
-
-<p><b>226. Where does the carbon dioxide come from?</b>—We know it
-comes from the growing seedlings. The symbol for carbon dioxide is
-CO₂. The carbon comes from the plant, because there is not enough in
-the air. Nitrogen could not join with the carbon to make CO₂. Some
-oxygen from the air or from the protoplasm of the growing seedlings
-(more probably the latter) joins with some of the carbon of the plant.
-These break away from their association with the living substance and
-unite, making CO₂. The oxygen absorbed by the plant from the air unites
-with the living substance, or perhaps first with food substances, and
-from these the plant is replenished with carbon and oxygen. After the
-demonstration has been made, remove the glass plate which seals the
-thistle tube above, and pour in a small quantity of baryta water. The
-white precipitate formed affords another illustration that carbon
-dioxide is released.
-<span class="pagenum"><a name="Page_113" id="Page_113">[Pg 113]</a></span></p>
-
-<div class="figcenter">
-    <img src="images/fig105.jpg" alt="" width="400" height="426" />
-    <p class="center">Fig. 105.</p>
-    <p class="blockquot">Experiment to show that growth takes place more rapidly in presence of
-            oxygen than in absence of oxygen. The two tubes in the vessel represent
-            the condition at the beginning of the experiment. At the close of the
-            experiment the roots in the tube at the left were longer than those
-            in the tube filled at the start with mercury. The tube outside of
-            the vessel represents the condition of things where the peas grew in
-            absence of oxygen; the carbon dioxide given off has displaced a portion
-            of the mercury. This also shows <i>anaerobic</i> respiration.</p>
-</div>
-
-<p><b>227. Respiration is necessary for growth.</b>—After performing
-experiment in paragraph 221, if the vessel has not been open too
-long so that oxygen has entered, we may use the vessel for another
-experiment, or set up a new one to be used in the course of 12 to 24
-hours, after some oxygen has been consumed. Place some folded damp
-filter paper on the germinating peas in the jar. Upon this place
-one-half dozen peas which have just been germinated, and in which the
-roots are about 20-25 <i>mm</i> long. The vessel should be covered tightly
-again and set aside in a warm room. A second jar with water in the
-bottom instead of the germinating peas should be set up as a check.
-Damp folded filter paper should be supported above the water, and on
-this should be placed one-half dozen peas with roots of the same length
-as those in the jar containing carbon dioxide.</p>
-
-<p><b>228.</b> In 24 hours examine and note how much growth has taken
-place. It will be seen that the roots have elongated but very little
-or none in the first jar, while in the second one we see that the
-roots have elongated considerably, if the experiment has been carried
-on carefully. Therefore in an atmosphere devoid of oxygen very little
-growth will take place, which shows that normal respiration with access
-of oxygen (aerobic respiration) is necessary for growth.</p>
-
-<p><b>229. Another way of performing the experiment.</b>—If we wish we
-may use the following experiment instead of the simple one indicated
-above. Soak a handful of peas in water for 12-24 hours, and germinate
-so that twelve with the radicles 20-25 <i>mm</i> long may be selected. Fill
-a test tube with mercury and carefully invert it in a vessel of mercury
-<span class="pagenum"><a name="Page_114" id="Page_114">[Pg 114]</a></span>
-so that there will be no air in the upper end. Now nearly fill another
-tube and invert in the same way. In the latter there will be some air.
-Remove the outer coats from the peas so that no air will be introduced
-in the tube filled with the mercury, and insert them one at a time
-under the edge of the tube beneath the mercury, six in each tube,
-having first measured the length of the radicles. Place in a warm
-room. In 24 hours measure the roots. Those in the air will have grown
-considerably, while those in the other tube will have grown but little
-or none.</p>
-
-<p><b>230. Anaerobic respiration.</b>—The last experiment is also an
-excellent one to show <i>anaerobic</i> respiration. In the tube filled
-with mercury so that when inverted there will be no air, it will be
-seen after 24 hours that a gas has accumulated in the tube which has
-crowded out some of the mercury. With a wash bottle which has an exit
-tube properly curved, some water may be introduced in the tube. Then
-insert underneath a small stick of caustic potash. This will form a
-solution of potash, and the gas will be partly or completely absorbed.
-This shows that the gas was carbon dioxide. This evolution of carbon
-dioxide by living plants when there is no access of oxygen is anaerobic
-respiration (sometimes called intramolecular respiration). It occurs
-markedly in oily seeds and especially in the yeast plant.</p>
-
-<div class="figleft">
-    <img src="images/fig106.jpg" alt="" width="400" height="302" />
-    <p class="center">Fig. 106.</p>
-    <p class="blockquot">Test for liberation of carbon dioxide from
-          leafy plant during respiration. Baryta water in smaller
-          vessel. (Sachs.)</p>
-</div>
-
-<p><b>231. Energy set free during respiration.</b>—From what we have
-learned of the exchange of gases during respiration we infer that the
-plant loses carbon during this process. If the process of respiration
-is of any benefit to the plant, there must be some gain in some
-direction to compensate the plant for the loss of carbon which takes
-place.</p>
-
-<p>It can be shown by an experiment that during respiration there is a
-slight elevation of the temperature in the plant tissues. The plant
-then gains some heat during respiration. Energy is also manifested by
-growth.</p>
-
-<p><b>232. Respiration in a leafy plant.</b>—We may take a potted plant
-which has a well-developed leaf surface and place it under a tightly
-fitting bell jar. Under the bell jar there also should be placed a
-small vessel containing baryta water. A similar apparatus should be set
-up, but with no plant, to serve as a check. The experiment must be set
-up in a room which is not frequented by persons, or the carbon dioxide
-in the room from respiration will vitiate the experiment. The bell jar
-containing the plant should be covered with a black cloth to prevent
-carbon assimilation. In the course of 10 or 12 hours, if everything has
-worked properly, the baryta water under the jar with the plant will
-show the film of barium carbonate, while the other one will show none.
-Respiration, therefore, takes place in a leafy plant as well as in
-germinating seeds.
-<span class="pagenum"><a name="Page_115" id="Page_115">[Pg 115]</a></span></p>
-
-<p><b>233. Respiration in fungi.</b>—If several large actively growing
-mushrooms are accessible, place them in a tall glass jar as described
-for determining respiration in germinating peas. In the course of 12
-hours test with the lighted taper and the baryta water. Respiration
-takes place in fungi as well as in green plants.</p>
-
-<p><b>234. Respiration in plants in general.</b>—Respiration is general
-in all plants, though not universal. There are some exceptions in the
-lower plants, notably in certain of the bacteria, which can only grow
-and thrive in the absence of oxygen.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img src="images/fig107.jpg" alt="" width="200" height="487" />
-    <p class="center">Fig. 107.<br /> Fermentation tube<br /> with culture of yeast.</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig108.jpg" alt="" width="220" height="454" />
-      <p class="center space-above1">Fig. 108.<br /> Fermentation tube<br />
-             filled with CO₂ from<br /> action of yeast in a<br /> sugar solution.</p>
-  </div>
-</div>
-
-<p><b>235. Respiration a breaking-down process.</b>—We have seen that
-in respiration the plant absorbs oxygen and gives off carbon dioxide.
-We should endeavor to note some of the effects of respiration on the
-plant. Let us take, say, two dozen dry peas, weigh them, soak for 12-24
-hours in water, and, in the folds of a cloth kept moist by covering
-with wet paper or sphagnum, germinate them. When well germinated and
-before the green color appears dry well in the sun, or with artificial
-heat, being careful not to burn or scorch them. The aim should be to
-get them about as dry as the seeds were before germination. Now weigh.
-The germinated seeds weigh less than the dry peas. There has then been
-a loss of plant substance during respiration.</p>
-
-<div class="figcenter">
-    <img src="images/fig108a.jpg" alt="" width="400" height="250" />
-    <p class="center">Fig. 108<i>a</i>.</p>
-    <p class="blockquot">Yeast. Saccharomyces ceriviseæ. <i>a</i>,
-         small colony; <i>b</i>, single cell budding; <i>c</i>,
-         single cell forming an ascus with four spores; <i>d</i>,
-         spores free from the ascus. (After Rees.)</p>
-</div>
-
-<p><b>236. Fermentation of yeast.</b>—Take two fermentation tubes. Fill
-the closed tubular parts of each with a weak solution of grape sugar,
-or with potato decoction, leaving the open bulb nearly empty. Into the
-liquid of one of the tubes place a piece of compressed yeast as large
-as a pea. If the tubes are kept in a warm place for 24 hours bubbles
-of gas may be noticed rising in the one in which the yeast was placed,
-while in the second tube no such bubbles appear, especially if the
-filled tubes are first sterilized. The tubes may be kept until the
-first is entirely filled with the gas. Now dissolve in the liquid a
-small piece of caustic potash. Soon the gas will begin to be absorbed,
-and the liquid will rise until it again fills the tube. The gas was
-carbon dioxide, which was chiefly produced during the anaerobic
-respiration of the rapidly growing yeast cells. In bread making this
-gas is produced in considerable quantities, and rising through the
-dough fills it with numerous cavities containing gas, so that the bread
-“rises.” When it is baked the heat causes the gas in the cavities to
-<span class="pagenum"><a name="Page_116" id="Page_116">[Pg 116]</a></span>
-expand greatly. This causes the bread to “rise” more, and baked in this
-condition it is “light.” There are two special processes accompanying
-the fermentation by yeast: 1st, the evolution of carbon dioxide as
-shown above; and, 2d, the formation of alcohol. The best illustration
-of this second process is the brewing of beer, where a form of the same
-organism which is employed in “bread rising” is used to “brew beer.”</p>
-
-<p><a id="PARA_237" name="PARA_237"><b>237. The yeast plant.</b></a>—Before the
-caustic potash is placed in the tube some of the fermented liquid should be taken
-for study of the yeast plant, unless separate cultures are made for this purpose.
-Place a drop of the fermented liquid on a glass slip, place on this
-a cover glass, and examine with the microscope. Note the minute oval
-cells with granular protoplasm. These are the yeast plant. Note in
-some a small “bud” at one side of the end. These buds increase in size
-and separate from the parent plant. The yeast plant is one-celled,
-and multiplies by “budding” or “sprouting.” It is a fungus, and some
-species of yeast like the present one do not form any mycelium. Under
-certain conditions, which are not very favorable for growth (example,
-when the yeast is grown in a weak nutrient substance on a thin layer of
-a plaster Paris slab), several spores are formed in many of the yeast
-cells. After a period of rest these spores will sprout and produce the
-yeast plant again. Because of this peculiar spore formation some place
-the yeast among the sac fungi. (<a href="#CHAPTER_XXII">See classification of the fungi</a>.)</p>
-
-<p><b>238. Organized ferments and unorganized ferments.</b>—An organism
-like the yeast plant which produces a fermentation of a liquid with
-evolution of gas and alcohol is sometimes called a <i>ferment</i>, or
-<i>ferment organism</i>, or an <i>organized</i> ferment. On the other hand
-the diastatic ferments or enzymes like diastase, taka diastase, animal
-diastase (ptyalin in the saliva), cytase, etc., are <i>unorganized</i>
-ferments. In the case of these it is better to say <i>enzyme</i> and leave
-the word ferment for the ferment organisms.
-<span class="pagenum"><a name="Page_117" id="Page_117">[Pg 117]</a></span></p>
-
-<p><b>239. Importance of green plants in maintaining purity of
-air.</b>—By respiration, especially of animals, the air tends to
-become “foul” by the increase of CO₂. Green plants, i.e., plants
-with chlorophyll, purify the air during photosynthesis by absorbing
-CO₂ and giving off oxygen. Animals absorb in respiration large
-quantities of oxygen and exhale large quantities of CO₂. Plants
-absorb a comparatively small amount of oxygen in respiration and
-give off a comparatively small amount of CO₂. But they absorb during
-photosynthesis large quantities of CO₂ and give off large quantities of
-oxygen. In this way a balance is maintained between the two processes,
-so that the percentage of CO₂ in the air remains approximately the
-same, viz., about four-tenths of one per cent, while there are
-approximately 21 parts oxygen and 79 parts nitrogen.</p>
-
-<p><b>239a. Comparison of respiration and photosynthesis.</b></p>
-
-<table border="0" cellspacing="0" summary=" " cellpadding="0" >
-  <tbody><tr>
-      <td class="tdc bb" colspan="2">&nbsp;</td>
-   </tr><tr>
-      <td class="tdc br bb" rowspan="5">Starch formation or Photosynthesis.</td>
-       <td class="tdl_ws1"><p class="neg-indent">Carbon dioxide is taken in by the plant and oxygen is liberated.</p></td>
-   </tr><tr>
-      <td class="tdl_ws1"><p class="neg-indent">Starch is formed as a result of the metabolism, or chemical change.</p></td>
-   </tr><tr>
-      <td class="tdl_ws1"><p class="neg-indent">The process takes place only in green plants, and in the green
-                      parts of plants, that is, in the presence of the chlorophyll.
-                      (Exception in purple bacterium.)</p></td>
-   </tr><tr>
-      <td class="tdl_ws1"><p class="neg-indent">The process only takes place under the influence of sunlight.</p></td>
-   </tr><tr>
-       <td class="tdl_ws1 bb"><p class="neg-indent">It is a building-up process, because new plant substance is formed.</p></td>
-   </tr><tr>
-      <td class="tdc br" rowspan="5">Respiration.</td>
-       <td class="tdl_ws1"><p class="neg-indent">Oxygen is taken in by the plant and carbon dioxide is liberated.</p></td>
-   </tr><tr>
-      <td class="tdl_ws1"><p class="neg-indent">Carbon dioxide is formed as a result of the
-                     metabolism, or chemical change.</p></td>
-   </tr><tr>
-      <td class="tdl_ws1"><p class="neg-indent">The process takes place in all plants whether they possess
-                              chlorophyll or not. (Exceptions in anaerobic bacteria).</p></td>
-   </tr><tr>
-      <td class="tdl_ws1"><p class="neg-indent">The process takes place in the dark as well as in the sunlight.</p></td>
-   </tr><tr>
-      <td class="tdl_ws1"><p class="neg-indent">It is a breaking-down process, because disintegration of plant substance occurs.</p></td>
-   </tr><tr>
-      <td class="tdc bt" colspan="2">&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_118" id="Page_118">[Pg 118]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XII" id="CHAPTER_XII">CHAPTER XII.</a><br />
-<span class="h_subtitle">GROWTH.</span></h3>
-</div>
-
-<p>By growth is usually meant an increase in the bulk of the plant
-accompanied generally by an increase in plant substance. Among the
-lower plants growth is easily studied in some of the fungi.</p>
-
-<p><b>240. Growth in mucor.</b>—Some of the gonidia (often called spores)
-may be sown in nutrient gelatine or agar, or even in prune juice. If
-the culture has been placed in a warm room, in the course of 24 hours,
-or even less, the preparation will be ready for study.</p>
-
-<p><b>241. Form of the gonidia.</b>—It will be instructive if we first
-examine some of the gonidia which have not been sown in the culture
-medium. We should note their rounded or globose form, as well as
-their markings if they belong to one of the species with spiny walls.
-Particularly should we note the size, and if possible measure them with
-the micrometer, though this would not be absolutely necessary for a
-comparison, if the comparison can be made immediately. Now examine some
-of the gonidia which were sown in the nutrient medium. If they have not
-already germinated we note at once that they are much larger than those
-which have not been immersed in a moist medium.</p>
-
-<p><b>242. The gonidia absorb water and increase in size before
-germinating.</b>—From our study of the absorption of water or watery
-solutions of nutriment by living cells, we can easily understand the
-cause of this enlargement of the gonidium of the mucor when surrounded
-by the moist nutrient medium. The cell-sap in the spore takes up more
-<span class="pagenum"><a name="Page_119" id="Page_119">[Pg 119]</a></span>
-water than it loses by diffusion, thus drawing water forcibly through
-the protoplasmic membrane. Since it does not filter out readily, the
-increase in quantity of the water in the cell produces a pressure from
-within which stretches the membrane, and the elastic cell wall yields.
-Thus the gonidium becomes larger.</p>
-
-<div class="figcenter">
-    <img src="images/fig109.jpg" alt="" width="600" height="209" />
-    <p class="center">Fig. 109.<br /> Spores of mucor, and different stages of germination.</p>
-</div>
-
-<p><b>243. How the gonidia germinate.</b>—We should find at this time
-many of the gonidia extended on one side into a tube-like process the
-length of which varies according to time and temperature. The short
-process thus begun continues to elongate. This elongation of the plant
-is <i>growth</i>, or, more properly speaking, one of the phenomena of growth.</p>
-
-<p><b>244. The germ tube branches and forms the mycelium.</b>—In the
-course of a day or so branches from the tube will appear. This branched
-form of the threads of the fungus is, as we remember, the mycelium. We
-can still see the point where growth started from the gonidium. Perhaps
-by this time several tubes have grown from a single one. The threads of
-the mycelium near the gonidium, that is, the older portions of them,
-have increased in diameter as they have elongated, though this increase
-in diameter is by no means so great as the increase in length. After
-increasing to a certain extent in diameter, growth in this direction
-ceases, while apical growth is practically unlimited, being limited
-only by the supply of nutriment.</p>
-
-<p><b>245. Growth in length takes place only at the end of the thread.</b>—If
-<span class="pagenum"><a name="Page_120" id="Page_120">[Pg 120]</a></span>
-there were any branches on the mycelium when the culture was first
-examined, we can now see that they remain practically the same distance
-from the gonidium as when they were first formed. That is, the older
-portions of the mycelium do not elongate. Growth in length of the
-mycelium is confined to the ends of the threads.</p>
-
-<p><b>246. Protoplasm increases by assimilation of nutrient
-substances.</b>—As the plant increases in bulk we note that there
-is an increase in the protoplasm, for the protoplasm is very easily
-detected in these cultures of mucor. This increase in the quantity
-of the protoplasm has come about by the assimilation of the nutrient
-substance, which the plant has absorbed. The increase in the
-protoplasm, or the formation of additional plant substance, is another
-phenomenon of growth quite different from that of elongation, or
-increase in bulk.</p>
-
-<p><b>247. Growth of roots.</b>—For the study of the growth of roots we
-may take any one of many different plants. The seedlings of such plants
-as peas, beans, corn, squash, pumpkin, etc., serve excellently for this
-purpose.</p>
-
-<p><b>248. Roots of the pumpkin.</b>—The seeds, a handful or so, are
-soaked in water for about 12 hours, and then placed between layers of
-paper or between the folds of cloth, which must be kept quite moist but
-not very wet, and should be kept in a warm place. A shallow crockery
-plate, with the seeds lying on wet filter paper, and covered with
-additional filter paper, or with a bell jar, answers the purpose well.</p>
-
-<p>The primary or first root (radicle) of the embryo pushes its way out
-between the seed coats at the small end. When the seeds are well
-germinated, select several which have the root 4-5 <i>cm</i> long. With a
-crow-quill pen we may now mark the terminal portion of the root off
-into very short sections as in <a href="#FIG_110">fig. 110</a>. The first mark should
-be not more than 1 <i>mm</i> from the tip, and the others not more than 1mm
-apart. Now place the seedlings down on damp filter paper, and cover
-with a bell jar so that they will remain moist, and if the season is
-cold place them in a warm room. At intervals of 8 or 10 hours, if
-convenient, observe them and note the farther growth of the root.
-<span class="pagenum"><a name="Page_121" id="Page_121">[Pg 121]</a></span></p>
-
-<div class="figcenter">
-    <img id="FIG_110" src="images/fig110.jpg" alt="" width="600" height="266" />
-    <p class="center">Fig. 110.<br /> Root of germinating pumpkin, showing region
-                of elongation just back of the tip.</p>
-</div>
-
-<p><b>249. The region of elongation.</b>—While the root has elongated,
-the region of elongation <i>is not at the tip of the root. It lies a
-little distance back from the tip</i>, beginning at about 2mm from the tip
-and extending over an area represented by from 4-5 of the millimeter
-marks. The root shown in <a href="#FIG_110">fig. 110</a> was marked at 10 <span class="smcap">a.m.</span> on
-July 5. At 6 <span class="smcap">p.m.</span> of the same day, 8 hours later, growth had
-taken place as shown in the middle figure. At 9 <span class="smcap">a.m.</span> on the
-following day, 15 hours later, the growth is represented in the lower
-one. Similar experiments upon a number of seedlings give the same
-result: the region of elongation in the growth of the root is situated
-a little distance back from the tip. Farther back very little or no
-elongation takes place, but growth in diameter continues for some time,
-as we should discover if we examined the roots of growing pumpkins, or
-other plants, at different periods.</p>
-
-<p><b>250. Movement of region of greatest elongation.</b>—In the region
-of elongation the areas marked off do not all elongate equally at the
-same time. The middle spaces elongate most rapidly and the spaces
-marked off by the 6, 7, and 8 <i>mm</i> marks elongate slowly, those
-farthest from the tip more slowly than the others, since elongation
-has nearly ceased here. The spaces marked off between the 2-4 <i>mm</i>
-marks also elongate slowly, but soon begin to elongate more rapidly,
-since that region is becoming the region of greatest elongation. Thus
-the region of greatest elongation moves forward as the root grows, and
-remains approximately at the same distance behind the tip.</p>
-
-<p><b>251. Formative region.</b>—If we make a longitudinal section of the
-tip of a growing root of the pumpkin or other seedling, and examine it
-<span class="pagenum"><a name="Page_122" id="Page_122">[Pg 122]</a></span>
-with the microscope, we see that there is a great difference in the
-character of the cells of the tip and those in the region of elongation
-of the root. First there is in the section a V-shaped cap of loose
-cells which are constantly being sloughed off. Just back of this tip
-the cells are quite regularly isodiametric, that is, of equal diameter
-in all directions. They are also very rich in protoplasm, and have
-thin walls. This is the region of the root where new cells are formed
-by division. It is the <i>formative region</i>. The cells on the outside
-of this area are the older, and pass over into the older parts of the
-root and root cap. If we examine successively the cells back from this
-<i>formative</i> region we find that they become more and more elongated in
-the direction of the axis of the root. The elongation of the cells in
-this older portion of the root explains then why it is that this region
-of the root elongates more rapidly than the tip.</p>
-
-<p><b>252. Growth of the stem.</b>—We may use a bean seedling growing
-in the soil. At the junction of the leaves with the stem there are
-enlargements. These are the <i>nodes</i>, and the spaces on the stem between
-successive nodes are the <i>internodes</i>. We should mark off several of
-these internodes, especially the younger ones, into sections about 5
-<i>mm</i> long. Now observe these at several times for two or three days,
-or more. The region of elongation is greater than in the case of the
-roots, and extends back farther from the end of the stem. In some young
-garden bean plants the region of elongation extended over an area of 40
-<i>mm</i> in one internode. See also Chapters <a href="#CHAPTER_XXXVIII">38</a>,
-<a href="#CHAPTER_XXXIX">39</a>.</p>
-
-<p><b>253. Force exerted by growth.</b>—One of the marvelous things
-connected with the growth of plants is the force which is exerted by
-various members of the plant under certain conditions. Observations on
-seedlings as they are pushing their way through the soil to the air
-often show us that considerable force is required to lift the hard soil
-and turn it to one side. A very striking illustration may be had in the
-case of mushrooms which sometimes make their way through the hard and
-packed soil of walks or roads. That succulent and tender plants should
-be capable of lifting such comparatively heavy weights seems incredible
-until we have witnessed it. Very striking illustrations of the force
-of roots are seen in the case of trees which grow in rocky situations,
-where rocks of considerable weight are lifted, or small rifts in large
-rocks are widened by the lateral pressure exerted by the growth of a
-root, which entered when it was small and wedged its way in.</p>
-
-<p><b>254. Zone of maximum growth.</b>—Great variation exists in the
-rapidity of growth even when not influenced by outside conditions. In
-our study of the elongation of the root we found that the cells just
-<span class="pagenum"><a name="Page_123" id="Page_123">[Pg 123]</a></span>
-back of the formative region elongated slowly at first. The rapidity of
-the elongation of these cells increases until it reaches the maximum.
-Then the rapidity of elongation lessens as the cells come to lie
-farther from the tip. The period of maximum elongation here is the
-<i>zone of maximum growth</i> of these cells.</p>
-
-<div class="figcenter">
-    <img src="images/fig111.jpg" alt="" width="400" height="387" />
-    <p class="center">Fig. 111.<br /> Lever auxanometer (Oels) for measuring<br />
-              elongation of the stem during growth.</p>
-</div>
-
-<p><b>255.</b> Just as the cells exhibit a zone of maximum growth, so
-the members of the plant exhibit a similar zone of maximum growth.
-In the case of leaves, when they are young the rapidity of growth
-is comparatively slow, then it increases, and finally diminishes in
-rapidity again. So it is with the stem. When the plant is young the
-growth is not so rapid; as it approaches middle age the rapidity of
-growth increases; then it declines in rapidity at the close of the
-season.</p>
-
-<p><b>256. Energy of growth.</b>—Closely related to the zone of maximum
-growth is what is termed the energy of growth. This is manifested in
-the comparative size of the members of a given plant. To take the
-sunflower for example, the lower and first leaves are comparatively
-small. As the plant grows larger the leaves are larger, and this
-increase in size of the leaves increases up to a maximum period, when
-the size decreases until we reach the small leaves at the top of the
-stem. The zone of maximum growth of the leaves corresponds with the
-maximum size of the leaves on the stem. The rapidity and energy of
-growth of the stem is also correlated with that of the leaves, and the
-zone of maximum growth is coincident with that of the leaves. It would
-be instructive to note it in the case of other plants and also in the
-case of fruits.</p>
-
-<p><b>257. Nutation.</b>—During the growth of the stem all of the cells
-of a given section of the stem do not elongate simultaneously. For
-example the cells at a given moment on the south side are elongating
-more rapidly than the cells on the other side. This will cause the
-stem to bend slightly to the north. In a few moments later the cells
-on the west side are elongating more rapidly, and the stem is turned
-to the east; and so on, groups of cells in succession around the stem
-elongate more rapidly than the others. This causes the stem to describe
-a circle or ellipse about a central point. Since the region of greatest
-elongation of the cells of the stem is gradually moving toward the apex
-of the growing stem, this line of elongation of the cells which is
-<span class="pagenum"><a name="Page_124" id="Page_124">[Pg 124]</a></span>
-traveling around the stem does so in a spiral manner. In the same way,
-while the end of the stem is moving upward by the elongation of the
-cells, and at the same time is slowly moved around, the line which the
-end of the stem describes must be a spiral one. This movement of the
-stem, which is common to all stems, leaves, and roots, is <i>nutation</i>.</p>
-
-<p><b>258.</b> The importance of nutation to twining stems in their search
-for a place of support, as well as for the tendrils on leaves or stems,
-will be seen. In the case of the root it is of the utmost importance,
-as the root makes its way through the soil, since the particles of soil
-are more easily thrust aside. The same is also true in the case of many
-stems before they emerge from the soil.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_125" id="Page_125">[Pg 125]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XIII" id="CHAPTER_XIII">CHAPTER XIII.</a><br />
-<span class="h_subtitle">IRRITABILITY.</span></h3>
-</div>
-
-<p><b>259.</b> We should now examine the movements of plant parts in
-response to the influence of certain stimuli. By this time we have
-probably observed that the direction which the root and stem take upon
-germination of the seed is not due to the position in which the seed
-happens to lie. Under normal conditions we have seen that the root
-grows downward and the stem upward.</p>
-
-<p><b>260. Influence of the earth on the direction of growth.</b>—When
-the stem and root have been growing in these directions for a short
-time let us place the seedling in a horizontal position, so that the
-end of the root extends over an object of support in such a way that it
-will be free to go in any direction. It should be pinned to a cork and
-placed in a moist chamber. In the course of twelve to twenty-four hours
-the root which was formerly horizontal has turned the tip downward
-again. If we should mark off millimeter spaces beginning at the tip of
-the root, we should find that the motor zone, or region of curvature,
-lies in the same region as that of the elongation of the root.</p>
-
-<p>Knight found that the stimulus which influences the root to turn
-downward is the force of gravity. The reaction of the root in response
-to this stimulus is geotropism, a turning influenced by the earth. This
-term is applied to the growth movements of plants influenced by the
-earth with regard to direction. While the motor zone lies back of the
-root-tip, the latter receives the stimulus and is the perceptive zone.
-If the root-tip is cut off, the root is no longer geotropic, and will
-not turn downward when placed in a horizontal position. Growth toward
-<span class="pagenum"><a name="Page_126" id="Page_126">[Pg 126]</a></span>
-the earth is <i>progeotropism</i>. The lateral growth of secondary roots is
-<i>diageotropism</i>.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img src="images/fig112.jpg" alt="" width="250" height="141" />
-    <p class="center">Fig. 112.<br /> Germinating pea placed in<br /> a horizontal position.</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig113.jpg" alt="" width="300" height="140" />
-      <p class="center">Fig. 113.<br /> In 24 hours gravity has caused<br /> the root to turn downward.</p>
-  </div>
-      <p class="center space-below2">Figs. 112, 113.—Progeotropism of the pea root.</p>
-</div>
-
-<p>The stem, on the other hand, which was placed in a horizontal position
-has become again erect. This turning of the stem in the upward
-direction takes place in the dark as well as in the light, as we can
-see if we start the experiment at nightfall, or place the plant in the
-dark. This upward growth of the stem is also influenced by the earth,
-and therefore is a case of geotropism. The special designation in the
-case of upright stems is <i>negative geotropism</i>, or <i>apogeotropism</i>, or
-the stems are said to be <i>apogeotropic</i>. If we place a rapidly growing
-potted plant in a horizontal position by laying the pot on its side,
-the ends of the shoots will soon turn upward again when placed in a
-horizontal position. Young bean plants growing in a pot began within
-two hours to turn the ends of the shoots upward.</p>
-
-<div class="figcenter">
-    <img src="images/fig114.jpg" alt="" width="600" height="358" />
-    <p class="center">Fig. 114.<br /> Pumpkin seedling showing apogeotropism.<br />
-          Seedling at the left placed horizontally,<br /> in 24 hours the stem has become erect.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_127" id="Page_127">[Pg 127]</a></span>
-Horizontal leaves and shoots can be shown to be subject to the same
-influence, and are therefore <i>diageotropic</i>.</p>
-
-<p><b>261. Influence of light.</b>—Not only is light a very important
-factor for plants during photosynthesis, it exerts great influence on
-plant growth and movement.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-      <p>&nbsp;</p>
-    <img src="images/fig115.jpg" alt="" width="300" height="250" />
-    <p class="center">Fig. 115.<br /> Radish seedlings grown in the<br /> dark, long, slender, not green.</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig116.jpg" alt="" width="150" height="286" />
-      <p class="center">Fig. 116.<br /> Radish seedlings grown in the<br />
-            light, shorter, stouter, and green<br /> in color. Growth retarded by light.</p>
-  </div>
-</div>
-
-<p><b>262. Growth in the absence of light.</b>—Plants grown in the
-dark are subject to a number of changes. The stems are often longer,
-more slender and weaker since they contain a larger amount of water
-in proportion to building material which the plant obtains from
-carbohydrates manufactured in the light. On many plants the leaves are
-very small when grown in the dark.</p>
-
-<p><b>263. Influence of light on direction of growth.</b>—While we are
-growing seedlings, the pots or boxes of some of them should be placed
-so that the plants will have a one-sided illumination. This can be
-done by placing them near an open window, in a room with a one-sided
-illumination, or they may be placed in a box closed on all sides but
-one which is facing the window or light. In 12-24 hours, or even in a
-much shorter time in some cases, the stems of the seedlings will be
-directed toward the source of light. This influence exerted by the rays
-of light is <i>heliotropism</i>, a turning influenced by the sun or sunlight.
-<span class="pagenum"><a name="Page_128" id="Page_128">[Pg 128]</a></span></p>
-
-<div class="figcenter">
-    <img src="images/fig117.jpg" alt="" width="500" height="448" />
-    <p class="center">Fig. 117.<br /> Seedling of castor-oil bean,<br />
-                    before and after a one-sided illumination.</p>
-</div>
-<div class="figcenter">
-    <img src="images/fig118.jpg" alt="" width="500" height="206" />
-    <p class="center">Fig. 118.<br /> Dark chamber with opening at one side to<br />
-                 show heliotropism. (After Schleichert.)</p>
-</div>
-
-<p><b>264. Diaheliotropism.</b>—Horizontal leaves and shoots are
-<i>diaheliotropic</i> as well as <i>diageotropic</i>. The general direction
-which leaves assume under this influence is that of placing them with the
-upper surface perpendicular to the rays of light which fall upon them.
-Leaves, then, exposed to the brightly lighted sky are, in general,
-horizontal. This position is taken in direct response to the stimulus
-of light. The leaves of plants with a one-sided illumination, as can be
-seen by trial, are turned with their upper surfaces toward the source
-of light, or perpendicular to the incidence of the light rays. In this
-way light overcomes for the time being the direction which growth
-gives to the leaves. The so-called “sleep” of plants is of course
-not sleep, though the leaves “nod,” or hang downward, in many cases.
-There are many plants in which we can note this drooping of the leaves
-at nightfall, and in order to prove that it is not determined by the
-time of day we can resort to a well-known experiment to induce this
-condition during the day. The plant which has been used to illustrate
-<span class="pagenum"><a name="Page_129" id="Page_129">[Pg 129]</a></span>
-this is the sunflower. Some of these plants, which were grown in a box,
-when they were about 35 <i>cm</i> high were covered for nearly two days,
-so that the light was excluded. At midday on the second day the box
-was removed, and the leaves on the covered plants are well represented
-by <a href="#FIG_119">fig. 119</a>, which was made from one of them. The leaves
-of the other plants in the box which were not covered were horizontal, as shown by
-<a href="#FIG_120">fig. 120</a>. Now on leaving these plants, which had exhibited
-induced “sleep” movements, exposed to the light they gradually assumed the
-horizontal position again.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img id="FIG_119" src="images/fig119.jpg" alt="" width="150" height="250" />
-    <p class="center">Fig. 119.<br /> Sunflower plant. Epinastic condition of<br />
-                   leaves induced during the day in darkness.</p>
-   </div>
-  <div class="figsub">
-      <img id="FIG_120" src="images/fig120.jpg" alt="" width="300" height="233" />
-      <p class="center">Fig. 120.<br /> Sunflower plant removed from darkness,<br />
-             leaves extending under influence of light<br /> (diaheliotropism.)</p>
-  </div>
-</div>
-
-<p><b>265. Epinasty and hyponasty.</b>—During the early stages of growth
-of many leaves, as in the sunflower plant, the direction of growth is
-different from what it is at a later period. The under surface of the
-young leaves grows more rapidly in a longitudinal direction than the
-upper side, so that the leaves are held upward close against the bud
-at the end of the stem. This is termed <i>hyponasty</i>, or the leaves are
-said to be <i>hyponastic</i>. Later the growth is more rapid on the upper
-side and the leaves turn downward or away from the bud. This is termed
-<i>epinasty</i>, or the leaves are said to be <i>epinastic</i>. This is shown by
-<span class="pagenum"><a name="Page_130" id="Page_130">[Pg 130]</a></span>
-the night position of the leaves, or in the induced “sleep” of the
-sunflower plant in the experiment detailed above. The day position of
-the leaves on the other hand, which is more or less horizontal, is
-induced because of their irritability under the influence of light, the
-inherent downward or epinastic growth is overcome for the time. Then
-at nightfall or in darkness, the stimulus of light being removed, the
-leaves assume the position induced by the direction of growth.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img id="FIG_121" src="images/fig121.jpg" alt="" width="200" height="263" />
-    <p class="center">Fig. 121.<br /> Squash seedling. Position<br /> of cotyledons in light.</p>
-   </div>
-  <div class="figsub">
-      <img id="FIG_122" src="images/fig122.jpg" alt="" width="150" height="266" />
-      <p class="center">Fig. 122.<br /> Squash seedling. Position<br /> of cotyledons in the dark.</p>
-  </div>
-</div>
-
-<p><b>266.</b> In the case of the cotyledons of some plants it would seem
-that the growth was hyponastic even after they have opened. The day
-position of the cotyledons of the pumpkin is more or less horizontal,
-as shown in <a href="#FIG_121">fig. 121</a>. At night, or if we darken the plant
-by covering with a tight box, the leaves assume the position shown in
-<a href="#FIG_122">fig. 122</a>.</p>
-
-<p>While the horizontal position is the general one which is assumed
-by plants under the influence of light, their position is dependent
-to a certain extent on the intensity of the light as well as on the
-incidence of the light rays. Some plants are so strongly heliotropic
-that they change their positions all during the day.
-<span class="pagenum"><a name="Page_131" id="Page_131">[Pg 131]</a></span></p>
-
-<div class="figleft">
-    <img id="FIG_123" src="images/fig123.jpg" alt="" width="200" height="407" />
-    <p class="center">Fig. 123.<br /> Coiling tendril<br /> of bryony.</p>
-</div>
-
-<p><b>267. Leaves with a fixed diurnal position.</b>—Leaves of some
-plants when they are developed have a fixed diurnal position and are
-not subject to variation. Such leaves tend to arrange themselves in a
-vertical or paraheliotropic position, in which the surfaces are not
-exposed to the incidence of light of the greatest intensity, but to the
-incidence of the rays of diffused light. Interesting cases of the fixed
-position of leaves are found in the so-called compass plants (like
-Silphium laciniatum, Lactuca scariola, etc.). In these the horizontal
-leaves arrange themselves with the surfaces vertical, and also pointing
-north and south, so that the surfaces face east and west.</p>
-
-<p><b>268. Importance of these movements.</b>—Not only are the leaves
-placed in a position favorable for the absorption of the rays of light
-which are concerned in making carbon available for food, but they
-derive other forms of energy from the light, as heat, which is absorbed
-during the day. Then with the nocturnal position, the leaves being
-drooped down toward the stem, or with the margin toward the sky, or
-with the cotyledons as in the pumpkin, castor-oil bean, etc., clasped
-upward together, the loss of heat by radiation is less than it would be
-if the upper surfaces of the leaves were exposed to the sky.</p>
-
-<p><b>269. Influence of light on the structure of the leaf.</b>—In our
-study of the structure of a leaf we found that in the ivy leaf the
-palisade cells were on the upper surface. This is the case with a great
-many leaves, and is the normal arrangement of “dorsiventral” leaves
-which are diaheliotropic. Leaves which are paraheliotropic tend to have
-palisade cells on both surfaces. The palisade layer of cells as we
-have seen is made up of cells lying very close together, and they thus
-prevent rapid evaporation. They also check to some extent the entrance
-of the rays of light, at least more so than the loose spongy parenchyma
-cells do. Leaves developed in the shade have looser palisade and
-parenchyma cells. In the case of some plants, if we turn over a very
-young leaf, so that the under side will be uppermost, this side will
-develop the palisade layer. This shows that light has a great influence
-on the structure of the leaf.</p>
-
-<p><b>270. Movement influenced by contact.</b>—In the case of tendrils,
-twining leaves, or stems, the irritability to contact is shown in a
-movement of the tendril, etc., toward the object in touch. This causes
-the tendril or stem to coil around the object for support. The stimulus
-is also extended down the part of the tendril below the point of
-<span class="pagenum"><a name="Page_132" id="Page_132">[Pg 132]</a></span>
-contact (see <a href="#FIG_123">fig. 123</a>), and that part coils up like a wire
-coil spring, thus drawing the leaf or branch from which the tendril grows closer to
-the object of support. This coil between the object of support and the
-plant is also very important in easing up the plant when subject to
-violent gusts of wind which might tear the plant from its support were
-it not for the yielding and springing motion of this coil.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img id="FIG_124" src="images/fig124.jpg" alt="" width="300" height="193" />
-    <p class="center">Fig. 124.<br /> Sensitive plant leaf<br /> in normal position.</p>
-   </div>
-  <div class="figsub">
-      <img id="FIG_125" src="images/fig125.jpg" alt="" width="115" height="199" />
-      <p class="center">Fig. 125.<br /> Pinnæ folding up<br /> after stimulus.</p>
-  </div>
-</div>
-<div class="figcenter">
-    <img id="FIG_126" src="images/fig126.jpg" alt="" width="500" height="399" />
-    <p class="center">Fig. 126.<br /> Later all the pinnæ folded and leaf drooped.</p>
-</div>
-
-<p><b>271. Sensitive plants.</b>—These plants are remarkable for the
-rapid response to stimuli. Mimosa pudica is an excellent plant to study
-for this purpose.</p>
-
-<p><b>272. Movement in response to stimuli.</b>—If we pinch with the
-forceps one of the terminal leaflets, or tap it with a pencil, the two
-end leaflets fold above the “vein” of the pinna. This is immediately
-followed by the movement of the next pair, and so on as shown in <a href="#FIG_125">fig. 125</a>,
-until all the leaflets on this pinna are closed, then the stimulus
-travels down the other pinnæ in a similar manner, and soon the pinnæ
-approximate each other and the leaf then drops downward as shown in
-<a href="#FIG_126">fig. 126</a>. The normal position of the leaf is shown in <a href="#FIG_124">fig. 124.</a>
-If we jar the plant by striking it or by jarring the pot in which it is grown
-all the leaves quickly collapse into the position shown in <a href="#FIG_126">fig. 126</a>.
-If we examine the leaf now we see minute cushions at the base of each
-leaflet, at the junction of the pinnæ with the petiole, and a larger
-one at the junction of the petiole with the stem. We shall also note
-that the movement resides in these cushions.
-<span class="pagenum"><a name="Page_133" id="Page_133">[Pg 133]</a></span></p>
-
-<p><b>273. Transmission of the stimulus.</b>—The transmission of the
-stimulus in this mimosa from one part of the plant has been found to be
-along the cells of the bast.</p>
-
-<p><b>274. Cause of the movement.</b>—The movement is caused by a sudden
-loss of turgidity on the part of the cells in one portion of the
-pulvinus, as the cushion is called. In the case of the large pulvinus
-at the base of the petiole this loss of turgidity is in the cells of
-the lower surface. There is a sudden change in the condition of the
-protoplasm of the cells here so that they lose a large part of their
-water. This can be seen if with a sharp knife we cut off the petiole
-just above the pulvinus before movement takes place. A drop of liquid
-exudes from the cells of the lower side.</p>
-
-<p><b>275. Paraheliotropism of the leaves of the sensitive plant.</b>—If
-the mimosa plant is placed in very intense light the leaflets will
-turn their edges toward the incidence of the rays of light. This is
-also true of other plants in intense light, and is <i>paraheliotropism</i>.
-Transpiration is thus lessened, and chlorophyll is protected from too
-intense light.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-      <p>&nbsp;</p>
-    <img src="images/fig126a.jpg" alt="" width="250" height="333" />
-    <p class="center">Fig. 126<i>a</i>.<br /> Leaf of Venus fly-trap (Dionæa muscipula),<br />
-                   showing winged petiole and toothed lobes.</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig127.jpg" alt="" width="250" height="358" />
-      <p class="center">Fig. 127.<br /> Leaf of Drosera rotundifolia, some of the<br />
-               glandular hairs folding inward as a result<br /> of a stimulus.</p>
-  </div>
-</div>
-
-<p>We thus see that variations in the intensity of light have an important
-influence in modifying movements. Variations in temperature also exert
-a considerable influence, rapid elevation of temperature causing
-certain flowers to open, and falling temperature causing them to close.</p>
-
-<p><b>276. Sensitiveness of insectivorous plants.</b>—The Venus fly-trap
-(Dionæa muscipula) and the sundew (drosera) are interesting examples of
-sensitive plants, since the leaves close in response to the stimulus
-from insects.</p>
-
-<p><b>277. Hydrotropism.</b>—Roots are sensitive to moisture. They will
-turn toward moisture. This is of the greatest importance for the
-well-being of the plant, since the roots will seek those places in the
-<span class="pagenum"><a name="Page_134" id="Page_134">[Pg 134]</a></span>
-soil where suitable moisture is present. On the other hand, if the soil
-is too wet there is a tendency for the roots to grow away from the
-soil which is saturated with water. In such cases roots are often seen
-growing upon the surface of the soil so that they may obtain oxygen,
-which is important for the root in the processes of absorption and
-growth. Plants then may be injured by an excess of water as well as by
-a lack of water in the soil.</p>
-
-<p><b>278. Temperature.</b>—In the experiments on germination thus
-far made it has probably been noted that the temperature has much
-to do with the length of time taken for seeds to germinate. It also
-influences the rate of growth. The effect of different temperatures
-on the germination of seed can be very well noted by attempting to
-germinate some in rooms at various temperatures. It will be found,
-other conditions being equal, that in a moderately warm room, or even
-in one quite warm, 25-30 degrees centigrade, germination and growth
-goes on more rapidly than in a cool room, and here more rapidly than in
-one which is decidedly cold. In the case of most plants in temperate
-climates, growth may go on at a temperature but little above freezing,
-but few will thrive at this temperature.</p>
-
-<p><b>279.</b> If we place dry peas or beans in a temperature of about
-70° C. for 15 minutes they will not be killed, but if they have been
-thoroughly soaked in water and then placed at this temperature they
-will be killed, or even at a somewhat lower temperature. The same seeds
-in the dry condition will withstand a temperature of 10° C. below, but
-if they are first soaked in water this low temperature will kill them.</p>
-
-<p><b>280.</b> In order to see the effect of freezing we may thoroughly
-freeze a section of a beet root, and after thawing it out place it in
-water. The water is colored by the cell-sap which escapes from the
-cells, just as we have seen it does as a result of a high temperature,
-while a section of an unfrozen beet placed in water will not color it
-if it was previously washed.</p>
-
-<p>If the slice of the beet is placed at about -6° C. in a shallow glass
-vessel, and covered, ice will be formed over the surface. If we examine
-it with the microscope ice crystals will be seen formed on the outside,
-and these will not be colored. The water for the formation of the
-crystals came from the cell-sap, but the concentrated solutions in the
-sap were not withdrawn by the freezing over the surface.</p>
-
-<p><b>281.</b> If too much water is not withdrawn from the cells of many
-plants in freezing, and they are thawed out slowly, the water which was
-withdrawn from the cells will be absorbed again and the plant will not
-be killed. But if the plant is thawed out quickly the water will not
-be absorbed, but will remain on the surface and evaporate. Some will
-also remain in the intercellular spaces, and the plant will die. Some
-<span class="pagenum"><a name="Page_135" id="Page_135">[Pg 135]</a></span>
-plants, however, no matter how slowly they are thawed out, are killed
-after freezing, as the leaves of the pumpkin, dahlia, or the tubers of
-the potato.</p>
-
-<p><b>282.</b> It has been found that as a general rule when plants, or
-plant parts, contain little moisture they will withstand quite high
-degrees of temperature, as well as quite low degrees, but when the
-parts are filled with sap or water they are much more easily killed.
-For this reason dry seeds and the winter buds of trees, and other
-plants, because they contain but little water, are better able to
-resist the cold of winters. But when growth begins in the spring, and
-the tissues of these same parts become turgid and filled with water,
-they are quite easily killed by frosts. It should be borne in mind,
-however, that there is great individual variation in plants in this
-respect, some being more susceptible to cold than others. There is
-also great variation in plants as to their resistance to the cold of
-winters, and of arctic climates, the plants of the latter regions
-being able to resist very low temperatures. We have examples also in
-the arctic plants, and those which grow in arctic climates on high
-mountains, of plants which are able to carry on all the life functions
-at temperatures but little above freezing.</p>
-
-<p>For further discussion as to relation of plants to temperature, see
-Chapters <a href="#CHAPTER_XLVI">46</a>, 48, 49, and 53.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_136" id="Page_136">[Pg 136]</a></span></p>
-<div class="chapter">
-<h2 class="nobreak">PART II.<br />
-MORPHOLOGY AND LIFE HISTORY<br /> OF REPRESENTATIVE PLANTS.</h2>
-<hr class="r5" />
-<h3 class="nobreak"><a name="CHAPTER_XIV" id="CHAPTER_XIV">CHAPTER XIV.</a><br />
-<span class="h_subtitle">SPIROGYRA.</span></h3>
-</div>
-
-<p><b>283.</b> In our study of protoplasm and some of the processes of
-plant life we became acquainted with the general appearance of the
-plant spirogyra. It is now a familiar object to us. And in taking up
-the study of representative plants of the different groups, we shall
-find that in knowing some of these lower plants the difficulties of
-understanding methods of reproduction and relationship are not so great
-as they would be if we were entirely ignorant of any members of the
-lower groups.</p>
-
-<div class="figcenter">
-    <img id="FIG_128" src="images/fig128.jpg" alt="" width="600" height="102" />
-    <p class="center">Fig. 128.<br /> Thread of spirogyra, showing long cells, chlorophyll band,<br />
-           nucleus, strands of protoplasm, and the granular wall layer<br /> of protoplasm.</p>
-</div>
-
-<p><b>284. Form of spirogyra.</b>—We have found that the plant spirogyra
-consists of simple threads, with cylindrical cells attached end to
-end. We have also noted that each cell of the thread is exactly alike,
-with the exception of certain “holdfasts” on some of the species. If
-we should examine threads in different stages of growth we should find
-that each cell is capable of growth and division, just as it is capable
-of performing all the functions of nutrition and assimilation. The
-cells of spirogyra then multiply by division. Not simply the cells at
-the ends of the threads but any and all of the cells divide as they
-grow, and in this way the threads increase in length.</p>
-
-<p><b>285. Multiplication of the threads.</b>—In studying living material
-of this plant we have probably noted that the threads often become
-broken by two of the adjacent cells of a thread becoming separated.
-<span class="pagenum"><a name="Page_137" id="Page_137">[Pg 137]</a></span>
-This may be and is accomplished in many cases without any injury to the
-cells. In this manner the threads or plants of spirogyra, if we choose
-to call a thread a plant, multiply, or increase. In this breaking of a
-thread the cell wall which separates any two cells splits. If we should
-examine several species of spirogyra we would probably find threads
-which present two types as regards the character of the walls at the
-ends of the cells. In <a href="#FIG_128">fig. 128</a> we see that the
-ends are plain, that is, the cross walls are all straight. But in some other species
-the inner wall of the cells presents a peculiar appearance. This inner wall at
-the end of the cell is at first straight across. But it soon becomes
-folded back into the interior of its cell, just as the end of an empty
-glove finger may be pushed in. Then the infolded end is pushed partly
-out again, so that a peculiar figure is the result.</p>
-
-<p><b>286. How some of the threads break.</b>—In the separation of the
-cells of a thread this peculiarity is often of advantage to the plant.
-The cell-sap within the protoplasmic membrane absorbs water and the
-pressure pushes on the ends of the infolded cell walls. The inner
-wall being so much longer than the outer wall, a pull is exerted on
-the latter at the junction of the cells. Being weaker at this point
-the outer wall is ruptured. The turgidity of the two cells causes
-these infolded inner walls to push out suddenly as the outer wall is
-ruptured, and the thread is snapped apart as quickly as a pipe-stem may
-be broken.</p>
-
-<div class="figcenter">
-    <img id="FIG_129" src="images/fig129.jpg" alt="" width="600" height="241" />
-    <p class="center">Fig. 129.<br /> Zygospores of spirogyra.</p>
-</div>
-
-<p><b>287. Conjugation of spirogyra.</b>—Under certain conditions, when
-vegetative growth and multiplication cease, a process of reproduction
-takes place which is of a kind termed sexual reproduction. If we select
-mats of spirogyra which have lost their deep green color, we are likely
-to find different stages of this sexual process, which in the case of
-spirogyra and related plants is called <i>conjugation</i>. A few threads
-of such a mat we should examine with the microscope. If the material
-is in the right condition we see in certain of the cells an oval or
-elliptical body. If we note carefully the cells in which these oval
-bodies are situated, there will be seen a tube at one side which
-<span class="pagenum"><a name="Page_138" id="Page_138">[Pg 138]</a></span>
-connects with an empty cell of a thread which lies near as shown in
-<a href="#FIG_129">fig. 129</a>. If we search through the material we may see other
-threads connected in this ladder fashion, in which the contents of the cells
-are in various stages of collapse from what we have seen in the growing
-cell. In some the protoplasm and chlorophyll band have moved but little
-from the wall; in others it forms a mass near the center of the cell,
-and again in others we will see that the contents of the cell of one
-of the threads has moved partly through the tube into the cell of the
-thread with which it is connected.</p>
-
-<p><b>289.</b> This suggests to us that the oval bodies found in the cells
-of one thread of the ladder, while the cells of the other thread were
-empty, are formed by the union of the contents of the two cells. In
-fact that is what does take place. This kind of union of the contents
-of two similar or nearly similar cells is <i>conjugation</i>. The oval
-bodies which are the result of this conjugation are <i>zygotes</i>, or
-<i>zygospores</i>. When we are examining living material of spirogyra in
-this stage it is possible to watch this process of conjugation. <a href="#FIG_130">Fig. 130</a>
-represents the different stages of conjugation of spirogyra.</p>
-
-<p><b>290. How the threads conjugate, or join.</b>—The cells of two
-threads lying parallel put out short processes. The tubes from two
-opposite cells meet and join. The walls separating the contents of the
-two tubes dissolve so that there is an open communication between the
-two cells. The content of each one of these cells which take part in
-the conjugation is a <i>gamete</i>. The one which passes through the tube to
-<span class="pagenum"><a name="Page_139" id="Page_139">[Pg 139]</a></span>
-the receiving cell is the <i>supplying gamete</i>, while that of the
-receiving cell is the <i>receiving gamete</i>.</p>
-
-<div class="figcenter">
-    <img id="FIG_130" src="images/fig130a.jpg" alt="" width="600" height="193" />
-    <img src="images/fig130b.jpg" alt="" width="600" height="201" />
-    <p class="center">Fig. 130.</p>
-    <p class="blockquot space-below2">Conjugation in spirogyra; from left
-             to right beginning in the upper row is shown the gradual passage
-             of the protoplasm from the supplying gamete to the receiving gamete.</p>
-</div>
-
-<p><b>291. How the protoplasm moves from one cell to another.</b>—Before
-any movement of the protoplasm of the supplying cell takes place we can
-see that there is great activity in its protoplasm. Rounded vacuoles
-appear which increase in size, are filled with a watery fluid, and
-swell up like a vesicle, and then suddenly contract and disappear.
-As the vacuole disappears it causes a sudden movement or contraction
-of the protoplasm around it to take its place. Simultaneously with
-the disappearance of the vacuole the membrane of the protoplasm is
-separated from a part of the wall. This is probably brought about by a
-sudden loss of some of the water in the cell-sap. These activities go
-on, and the protoplasmic membrane continues to slip away from the wall.
-Every now and then there is a movement by which the protoplasm is moved
-a short distance. It is moved toward the tube and finally a portion of
-it with one end of the chlorophyll band begins to move into the tube.
-About this time the vacuoles can be seen in an active condition in the
-<span class="pagenum"><a name="Page_140" id="Page_140">[Pg 140]</a></span>
-receptive cell. At short intervals movement continues until the content
-of the supplying cell has passed over into that of the receptive cell.
-The protoplasm of this one is now slipping away from the cell wall,
-until finally the two masses round up into the one zygospore.</p>
-
-<p><b>292. The zygospore.</b>—This zygospore now acquires a thick wall
-which eventually becomes brown in color. The chlorophyll color fades
-out, and a large part of the protoplasm passes into an oily substance
-which makes it more resistant to conditions which would be fatal to the
-vegetative threads. The zygospores are capable therefore of enduring
-extremes of cold and dryness which would destroy the threads. They
-pass through a “resting” period, in which the water in the pond may be
-frozen, or dried, and with the oncoming of favorable conditions for
-growth in the spring or in the autumn they germinate and produce the
-green thread again.</p>
-
-<p><b>293. Life cycle.</b>—The growth of the spirogyra thread, the
-conjugation of the gametes and formation of the zygospore, and the
-growth of the thread from the zygospore again, makes what is called a
-complete <i>life cycle</i>.</p>
-
-<p><b>294. Fertilization.</b>—While conjugation results in the fusion of
-the two masses of protoplasm, fertilization is accomplished when the
-nuclei of the two cells come together in the zygospore and fuse into a
-single nucleus. The different stages in the fusion of the two nuclei of
-a recently formed zygospore are shown in <a href="#FIG_131">figure 131</a>.</p>
-
-<p>In the conjugation of the two cells, the chlorophyll band of the
-supplying cell is said to degenerate, so that in the new plant the
-number of chlorophyll bands in a cell is not increased by the union of
-the two cells.</p>
-
-<div class="figcenter">
-    <img id="FIG_131" src="images/fig131.jpg" alt="" width="600" height="153" />
-    <p class="center">Fig. 131.</p>
-    <p class="blockquot space-below2">Fertilization in spirogyra; shows different stages of fusion of
-                     the two nuclei, with mature zygospore at right. (After Overton.)</p>
-</div>
-
-<p><b>295. Simplicity of the process.</b>—In spirogyra any cell of the
-thread may form a gamete (excepting the holdfasts of some species).
-Since all of the cells of a thread are practically alike, there is no
-structural difference between a vegetative cell and a cell about to
-conjugate. The difference is a physiological one. All the cells are
-capable of conjugation if the physiological conditions are present. All
-the cells therefore are potential gametes. (Strictly speaking the wall
-of the cell is the <i>garnetangium</i>, while the content forms the gamete.)</p>
-
-<p>While there is sometimes a slight difference in size between the
-<span class="pagenum"><a name="Page_141" id="Page_141">[Pg 141]</a></span>
-conjugating cells, and the supplying cell may be the smaller, this is
-not general. We say, therefore, that there is no differentiation among
-the gametes, so that usually before the protoplasm begins to move one
-cannot say which is to be the supplying and which the receiving gamete.</p>
-
-<p><b>296. Position of the plant spirogyra.</b>—From our study then we
-see that there is practically no differentiation among the vegetative
-cells, except where holdfasts grow out from some of the cells
-for support. They are all alike in form, in capacity for growth,
-division, or multiplication of the threads. Each cell is practically
-an independent plant. There is no differentiation between vegetative
-cell and conjugating cell. All the cells are potential gametes.
-Finally there is no structural differentiation between the gametes.
-This indicates then a simple condition of things, a low grade of
-organization.</p>
-
-<p><b>297.</b> The alga spirogyra is one of the representatives of the
-lower algæ belonging to the group called <i>Conjugatæ</i>. Zygnema with
-star-shaped chloroplasts, mougeotia with straight or sometimes twisted
-chlorophyll bands, belong to the same group. In the latter genus only
-a portion of the protoplasm of each cell unites to form the zygospore,
-which is located in the tube between the cells.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-      <a id="FIG_132-137" name="FIG_132-137">&nbsp;</a>
-    <img src="images/fig132.jpg" alt="" width="100" height="388" />
-    <p class="center">Fig. 132.<br /> Closterium.</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig133.jpg" alt="" width="200" height="333" />
-      <p class="center">Fig. 133.<br /> Micrasterias.</p>
-  </div>
-  <div class="figsub">
-      <img src="images/fig134.jpg" alt="" width="200" height="332" />
-      <p class="center">Fig. 134.<br /> Xanthidium.</p>
-  </div>
-</div>
-<div class="figcontainer">
-  <div class="figsub">
-    <img src="images/fig135.jpg" alt="" width="200" height="270" />
-    <p class="center">Fig. 135.<br /> Staurastrum.</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig136.jpg" alt="" width="200" height="261" />
-      <p class="center">Fig. 136.<br /> Euastrum.</p>
-  </div>
-  <div class="figsub">
-      <img src="images/fig137.jpg" alt="" width="200" height="272" />
-      <p class="center">Fig. 137.<br /> Cosmarium.</p>
-  </div>
-</div>
-
-<p><b>298.</b> The desmids also belong to the same group. The desmids
-usually live as separate cells. Many of them are beautiful in form.
-They grow entangled among other algæ, or on the surface of aquatic
-plants, or on wet soil. Several genera are illustrated in <a href="#FIG_132-137">figures 132-137</a>.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_142" id="Page_142">[Pg 142]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XV" id="CHAPTER_XV">CHAPTER XV.</a><br />
-<span class="h_subtitle">VAUCHERIA.</span></h3>
-</div>
-
-<p><b>299.</b> The plant vaucheria we remember from our study in an
-earlier chapter. It usually occurs in dense mats floating on the water
-or lying on damp soil. The texture and feeling of these mats remind one
-of “felt,” and the species are sometimes called the “green felts.” The
-branched threads are continuous, that is there are no cross walls in
-the vegetative threads. This plant multiplies itself in several ways
-which would be too tedious to detail here. But when fresh bright green
-mats can be obtained they should be placed in a large vessel of water
-and set in a cool place. Only a small amount of the alga should be
-placed in a vessel, since decay will set in more rapidly with a large
-quantity. For several days one should look for small green bodies which
-may be floating at the side of the vessel next the lighted window.</p>
-
-<div class="figcenter">
-    <img id="FIG_138" src="images/fig138.jpg" alt="" width="400" height="410" />
-    <p class="center">Fig. 138.<br /> Portion of branched thread of vaucheria.</p>
-</div>
-
-<p><b>300. Zoogonidia of vaucheria.</b>—If these minute floating green
-bodies are found, a small drop of water containing them should be
-<span class="pagenum"><a name="Page_143" id="Page_143">[Pg 143]</a></span>
-mounted for examination. If they are rounded, with slender hair-like
-appendages over the surface, which vibrate and cause motion, they very
-likely are one of the kinds of reproductive bodies of vaucheria. The
-hair-like appendages are <i>cilia</i>, and they occur in pairs, several of
-them distributed over the surface. These rounded bodies are <i>gonidia</i>,
-and because they are motile they are called <i>zoogonidia</i>.</p>
-
-<p>By examining some of the threads in the vessel where they occurred we
-may have perhaps an opportunity to see how they are produced. Short
-branches are formed on the threads, and the contents are separated from
-those of the main thread by a septum. The protoplasm and other contents
-of this branch separate from the wall, round up into a mass, and escape
-through an opening which is formed in the end. Here they swim around in
-the water for a time, then come to rest, and germinate by growing out
-into a tube which forms another vaucheria plant. It will be observed
-that this kind of reproduction is not the result of the union of two
-different parts of the plant. It thus differs from that which is termed
-sexual reproduction. A small part of the plant simply becomes separated
-from it as a special body, and then grows into a new plant, a sort of
-multiplication. This kind of reproduction has been termed <i>asexual
-reproduction</i>.</p>
-
-<div class="figcenter">
-    <img id="FIG_139" src="images/fig139.jpg" alt="" width="400" height="265" />
-    <p class="center">Fig. 139.<br /> Young antheridium and oogonium of Vaucheria sessilis,<br />
-                   before separation from contents of thread by a septum.</p>
-</div>
-
-<p><b>301. Sexual reproduction in vaucheria.</b>—The organs which
-are concerned in sexual reproduction in vaucheria are very readily
-obtained for study if one collects the material at the right season.
-They are found quite readily during the spring and autumn, and may be
-preserved in formalin for study at any season, if the material cannot
-be collected fresh at the time it is desired for study. Fine material
-for study often occurs on the soil of pots in greenhouses during the
-winter. While the zoogonidia are more apt to be found in material which
-is quite green and freshly growing, the sexual organs are usually more
-abundant when the threads appear somewhat yellowish, or yellow green.</p>
-
-<p><b>302. Vaucheria sessilis; the sessile vaucheria.</b>—In this plant
-the sexual organs are sessile, that is they are not borne on a stalk
-as in some other species. The sexual organs usually occur several in a
-group. <a href="#FIG_139">Fig. 139</a> represents a portion of a fruiting plant.
-<span class="pagenum"><a name="Page_144" id="Page_144">[Pg 144]</a></span></p>
-
-<p><b>303. Sexual organs of vaucheria. Antheridium.</b>—The antheridia
-are short, slender, curved branches from a main thread. A septum is
-formed which separates an end portion from the stalk. This end cell
-is the <i>antheridium</i>. Frequently it is collapsed or empty as shown in
-<a href="#FIG_140">fig. 140</a>. The protoplasm in the antheridium forms numerous
-small oval bodies each with two slender lashes, the cilia. When these are formed
-the antheridium opens at the end and they escape. It is after the
-escape of these spermatozoids that the antheridium is collapsed. Each
-spermatozoid is a male gamete.</p>
-
-<div class="figcenter">
-    <img id="FIG_140" src="images/fig140.jpg" alt="" width="600" height="222" />
-    <p class="center space-below2">Fig. 140.<br /> Vaucheria sessilis,
-               one antheridium between two oogonia.</p>
-</div>
-<div class="figcenter">
-    <img src="images/fig141.jpg" alt="" width="400" height="205" />
-    <p class="center">Fig. 141.</p>
-    <p class="blockquot">Vaucheria sessilis; oogonium opening and emitting a bit
-              of protoplasm; spermatozoids; spermatozoids entering
-              oogonium. (After Pringsheim and Goebel.)</p>
-</div>
-
-<p><b>304. Oogonium.</b>—The oogonia are short branches also, but
-they become large and somewhat oval. The septum which separates the
-protoplasm from that of the main thread is as we see near the junction
-of the branch with the main thread. The oogonium, as shown in the
-figure, is usually turned somewhat to one side. When mature the pointed
-end opens and a bit of the protoplasm escapes. The remaining protoplasm
-forms the large rounded egg-cell which fills the wall of the oogonium.
-In some of the oogonia which we examine this egg is surrounded by a
-<span class="pagenum"><a name="Page_145" id="Page_145">[Pg 145]</a></span>
-thick brown wall, with starchy and oily contents. This is the
-fertilized egg (sometimes called here the oospore). It is freed from
-the oogonium by the disintegration of the latter, sinks into the mud,
-and remains here until the following autumn or spring, when it grows
-directly into a new plant.</p>
-
-<div class="figcenter">
-    <img src="images/fig142.jpg" alt="" width="600" height="206" />
-    <p class="center">Fig. 142.</p>
-    <p class="blockquot">Fertilization in vaucheria, <i>mn</i>, male nucleus;
-               <i>fn</i>, female nucleus. Male nucleus entering the
-               egg and approaching the female nucleus. (After Oltmans.)</p>
-</div>
-
-<p><b>305. Fertilization.</b>—Fertilization is accomplished by the
-spermatozoids swimming in at the open end of the oogonium, when one of
-them makes its way down into the egg and fuses with the nucleus of the egg.</p>
-
-<div class="figcenter">
-    <img id="FIG_143" src="images/fig143.jpg" alt="" width="600" height="154" />
-    <p class="center">Fig. 143.</p>
-    <p class="blockquot">Fertilization of vaucheria. <i>fn</i>, female nucleus; <i>mn</i>,
-           male nucleus. The different figures show various stages in the fusion of the nuclei.</p>
-</div>
-
-<p><b>306. The twin vaucheria (V. geminata).</b>—Another species of
-vaucheria is the twin vaucheria. This is also a common one, and may be
-used for study instead of the sessile vaucheria if the latter cannot
-be obtained. The sexual organs are borne at the end of a club-shaped
-branch. There are usually two oogonia, and one antheridium between them
-which terminates the branch. In a closely related species, instead of
-the two oogonia there is a whorl of them with the antheridium in the
-center.</p>
-
-<p><b>307. Vaucheria compared with spirogyra.</b>—In vaucheria we have a
-plant which is very interesting to compare with spirogyra in several
-<span class="pagenum"><a name="Page_146" id="Page_146">[Pg 146]</a></span>
-respects. Growth takes place, not in all parts of the thread, but is
-localized at the ends of the thread and its branches. This represents a
-distinct advance on such a plant as spirogyra. Again, only specialized
-parts of the plant in vaucheria form the sexual organs. These are
-short branches. Farther there is a great difference in the size of the
-two organs, and especially in the size of the gametes, the supplying
-gametes (spermatozoids) being very minute, while the receptive gamete
-is large and contains all the nutriment for the fertilized egg. In
-spirogyra, on the other hand, there is usually no difference in size
-of the gametes, as we have seen, and each contributes equally in the
-matter of nutriment for the fertilized egg. Vaucheria, therefore,
-represents a distinct advance, not only in the vegetative condition of
-the plant, but in the specialization of the sexual organs. Vaucheria,
-with other related algæ, belongs to a group known as the <i>Siphoneæ</i>, so
-called because the plants are tube-like or <i>siphon</i>-like.</p>
-
-<div class="figcenter">
-    <img src="images/fig143a.jpg" alt="" width="500" height="534" />
-    <p class="center">Fig. 143<i>a</i>.</p>
-    <p class="blockquot">Botrydium granulatum. <i>A</i>, the whole plant; <i>B</i>, swarm spore;
-              <i>C</i>, planogametes; <i>a</i>, a single gamete; <i>b</i>-<i>e</i>,
-              two gametes in process of fusion; <i>f</i>, zygote.</p>
-</div>
-
-<p><b>308. Botrydium granulatum.</b>—An example of one of the simpler
-members of the Siphoneæ is Botrydium granulatum. It is found sometimes
-in abundance on wet ground which is colored green or red by its
-presence, according to the stage of development. The plant body is long
-pear-shaped, the smaller end attached to the ground by slender branched
-rhizoids (<a href="#FIG_143">Fig. 143</a>). The protoplasm contains many nuclei and
-lines the inside of the wall. When multiplication takes place large numbers of
-small zoospores with one cilium each are formed in the protoplasm, and
-escape at free end. Reproduction takes place by two-ciliated gametes,
-which fuse in pairs to form zygospores. In dry seasons the protoplasm
-in the pear-shaped plant passes down into the rhizoids and forms
-small rounded <i>planospores</i>. All the stages of development are too
-complicated to describe here.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_147" id="Page_147">[Pg 147]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XVI" id="CHAPTER_XVI">CHAPTER XVI.</a><br />
-<span class="h_subtitle">ŒDOGONIUM.</span></h3>
-</div>
-
-<p><b>309.</b> Œdogonium is also an alga. The plant is sometimes
-associated with spirogyra, and occurs in similar situations. Our
-attention was called to it in the study of chlorophyll bodies. These we
-recollect are, in this plant, small oval disks, and thus differ from
-those in spirogyra.</p>
-
-<p><b>310. Form of œdogonium.</b>—Like spirogyra, œdogonium forms simple
-threads which are made up of cylindrical cells placed end to end. But
-the plant is very different from any member of the group to which
-spirogyra belongs. In the first place each cell is not the equivalent
-of an individual plant as in spirogyra. Growth is localized or confined
-to certain cells of the thread which divide at one end in such a way
-as to leave a peculiar overlapping of the cell walls in the form of a
-series of shallow caps or vessels (<a href="#FIG_144">fig. 144</a>), and this is one
-of the characteristics of this genus. Other differences we find in the manner
-of reproduction.</p>
-
-<p><b>311. Fruiting stage of œdogonium.</b>—Material in the fruiting
-stage is quite easily obtainable, and may be preserved for study in
-formalin if there is any doubt about obtaining it at the time we need
-it for study. This condition of the plant is easily detected because of
-the swollen condition of some of the cells, or by the presence of brown
-bodies with a thick wall in some of the cells.</p>
-
-<p><b>312. Sexual organs of œdogonium. Oogonium and egg.</b>—The enlarged
-cell is the oogonium, the wall of the cell being the wall of the
-<span class="pagenum"><a name="Page_148" id="Page_148">[Pg 148]</a></span>
-oogonium. (See <a href="#FIG_145">fig. 145</a>.) The protoplasm inside, before
-fertilization, is the egg-cell. In those cases where the brown body with a thick
-wall is present fertilization has taken place, and this body is the
-<i>fertilized egg</i>, or <i>oospore</i>. It contains large quantities of an oily
-substance, and, like the fertilized egg of spirogyra and vaucheria, is
-able to withstand greater changes in temperature than the vegetative
-stage, and can endure drying and freezing for some time without injury.</p>
-
-<div class="figcenter">
-    <img id="FIG_144" src="images/fig144.jpg" alt="" width="600" height="111" />
-    <p class="center space-below2">Fig. 144.<br /> Portion of thread of œdogonium, showing chlorophyll<br />
-                    grains, and peculiar cap cell walls.</p>
-</div>
-<div class="figcenter">
-    <img id="FIG_145" src="images/fig145.jpg" alt="" width="600" height="376" />
-    <p class="center">Fig. 145.<br /> Œdogonium undulatum, with oogonia and dwarf males;<br />
-           the upper oogonium at the right has a mature oospore.</p>
-</div>
-
-<p>In the oogonium wall there can frequently be seen a rift near the
-<span class="pagenum"><a name="Page_149" id="Page_149">[Pg 149]</a></span>
-middle of one side, or near the upper end. This is the opening through
-which the spermatozoid entered to fecundate the egg.</p>
-
-<p><b>313. Dwarf male plants.</b>—In some species there will also be seen
-peculiar club-shaped dwarf plants attached to the side of the oogonium,
-or near it, and in many cases the end of this dwarf plant has an open
-lid on the end.</p>
-
-<p><b>314. Antheridium.</b>—The end cell of the dwarf male in such
-species is the <i>antheridium</i>. In other species the spermatozoids are
-developed in different cells (antheridia) of the same thread which
-bears the oogonium, or on a different thread.</p>
-
-<div class="figcenter">
-    <img id="FIG_146" src="images/fig146.jpg" alt="" width="500" height="382" />
-    <p class="center">Fig. 146.</p>
-    <p class="blockquot">Zoogonidia of œdogonium escaping. At the right one is germinating
-              and forming the holdfasts, by means of which these algæ attach
-              themselves to objects for support. (After Pringsheim.)</p>
-</div>
-
-<p><b>315. Zoospore stage of œdogonium.</b>—The egg after a period of
-rest starts into active life again. In doing so it does not develop
-the thread-like plant directly as in the case of vaucheria and
-spirogyra. It first divides into four zoospores which are exactly like
-the zoogonidia in form. (See <a href="#FIG_152">fig. 152</a>.) These germinate and
-develop the thread form again. This is a quite remarkable peculiarity of
-œdogonium when compared with either vaucheria or spirogyra. It is the
-introduction of an intermediate stage between the fertilized egg and
-that form of the plant which bears the sexual organs, and should be
-kept well in mind.</p>
-
-<p><b>316. Asexual reproduction.</b>—Material for the study of this stage
-of œdogonium is not readily obtainable just when we wish it for study.
-But fresh plants brought in and placed in a quantity of fresh water may
-yield suitable material, and it should be examined at intervals for
-several days. This kind of reproduction takes place by the formation
-of <i>zoogonidia</i>. The entire contents of a cell round off into an oval
-body, the wall of the cell breaks, and the zoogonidium escapes. It has
-a clear space at the small end, and around this clear space is a row or
-crown of cilia as shown in <a href="#FIG_146">fig. 146</a>. By the vibration of
-these cilia the zoogonidium swims around for a time, then settles down on some
-object of support, and several slender holdfasts grow out in the form
-of short rhizoids which attach the young plant.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img id="FIG_147" src="images/fig147.jpg" alt="" width="150" height="315" />
-    <p class="center">Fig. 147.<br /> Portion of thread of œdogonium<br />
-             showing antheridia.</p>
-   </div>
-  <div class="figsub">
-      <img id="FIG_148" src="images/fig148.jpg" alt="" width="250" height="308" />
-      <p class="center">Fig. 148.<br /> Portion of thread of œdogonium<br />
-                    showing upper half of egg open,<br /> and a spermatozoid ready<br />
-                    to enter. (After Klebahn).</p>
-  </div>
-</div>
-
-<p><b>317. Sexual reproduction. Antheridia.</b>—The antheridia are short
-cells which are formed by one of the ordinary cells dividing into a
-number of disk-shaped ones as shown in <a href="#FIG_147">fig. 147</a>. The protoplasm in each
-<span class="pagenum"><a name="Page_150" id="Page_150">[Pg 150]</a></span>
-antheridium forms two spermatozoids (sometimes only one) which are of
-the same form as the zoogonidia but smaller, and yellowish instead of
-green. In some species a motile body intermediate in size and color
-between the spermatozoids and zoogonidia is first formed, which after
-swimming around comes to rest on the oogonium, or near it, and develops
-what is called a “dwarf male plant” from which the real spermatozoid is
-produced.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img src="images/fig149.jpg" alt="" width="150" height="121" />
-    <p class="center">Fig. 149.<br /> Male nucleus<br /> just entering<br /> egg at left side.</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig150.jpg" alt="" width="150" height="136" />
-      <p class="center">Fig. 150.<br /> Male nucleus<br /> fusing with<br /> female nucleus.</p>
-  </div>
-  <div class="figsub">
-      <img src="images/fig151.jpg" alt="" width="150" height="118" />
-      <p class="center">Fig. 151.<br /> The two nuclei<br /> fused, and<br /> fertilization<br /> complete.</p>
-  </div>
-    <p class="center">Figs. 149-151.—Fertilization in œdogonium. (After Klebahn).</p>
-</div>
-
-<p><b>318. Oogonia.</b>—The oogonia are formed directly from one of the
-vegetative cells. In most species this cell first enlarges in diameter,
-so that it is easily detected. The protoplasm inside is the egg-cell.
-The oogonium wall opens, a bit of the protoplasm is emitted, and the
-spermatozoid then enters and fertilizes it (<a href="#FIG_148">fig. 148</a>).
-Now a hard brown wall is formed around it, and, just as in spirogyra and vaucheria,
-it passes through a resting period. At the time of germination it does
-not produce the thread-like plant again directly, but first forms four
-zoospores exactly like the zoogonidia (<a href="#FIG_152">fig. 152</a>).
-These zoospores then germinate and form the plant.</p>
-
-<p><b>319. Œdogonium compared with spirogyra.</b>—Now if we compare
-œdogonium with spirogyra, as we did in the case of vaucheria, we find
-here also that there is an advance upon the simple condition which
-exists in spirogyra. Growth and division of the thread is limited to
-certain portions. The sexual organs are differentiated. They usually
-differ in form and size from the vegetative cells, though the oogonium
-<span class="pagenum"><a name="Page_151" id="Page_151">[Pg 151]</a></span>
-is simply a changed vegetative cell. The sexual organs are
-differentiated among themselves, the antheridium is small, and the
-oogonium large. The gametes are also differentiated in size, and the
-male gamete is motile, and carries in its body the nucleus which fuses
-with the nucleus of the egg-cell.</p>
-
-<div class="figcenter">
-    <img id="FIG_152" src="images/fig152.jpg" alt="" width="600" height="170" />
-    <p class="center">Fig. 152.</p>
-    <p class="blockquot">Fertilized egg of œdogonium after a period of rest escaping
-         from the wall of the oogonium, and dividing into the four zoospores. (After Juranyi.)</p>
-</div>
-
-<p>But a more striking advance is the fact that the fertilized egg does
-not produce the vegetative thread of œdogonium directly, but first
-forms four zoospores, each of which is then capable of developing into
-the thread. On the other hand we found that in spirogyra the zygospore
-develops directly into the thread form of the plant.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img id="FIG_153" src="images/fig153.jpg" alt="" width="140" height="346" />
-    <p class="center">Fig. 153.<br /> Tuft of chætophora,<br /> natural size.</p>
-   </div>
-  <div class="figsub">
-      <img id="FIG_154" src="images/fig154.jpg" alt="" width="250" height="341" />
-      <p class="center">Fig. 154.<br /> Portion of chætophora<br /> showing branching.</p>
-  </div>
-</div>
-
-<p><b>320. Position of œdogonium.</b>—Œdogonium is one of the true
-thread-like algæ, green in color, and the threads are divided into
-distinct cells. It, along with many relatives, was once placed
-in the old genus conferva. These are all now placed in the group
-<i>Confervoideæ</i>, that is, the <i>conferva-like algæ</i>.</p>
-
-<p><b>321. Relatives of œdogonium.</b>—Many other genera are related
-to œdogonium. Some consist of simple threads, and others of branched
-threads. An example of the branched forms is found in chætophora,
-represented in figures <a href="#FIG_153">153</a>, <a href="#FIG_154">154</a>. This plant grows in
-quiet pools or in slow-running water. It is attached to sticks, rocks, or to larger
-aquatic plants. Many threads spring from the same point of attachment
-and radiate in all directions. This, together with the branching of the
-<span class="pagenum"><a name="Page_152" id="Page_152">[Pg 152]</a></span>
-threads, makes a small, compact, greenish, rounded mass, which is held
-firmly together by a gelatinous substance. The masses in this species
-are about the size of a small pea, or smaller. Growth takes place in
-chætophora at the ends of the threads and branches. That is, growth is
-apical. This, together with the branched threads and the tendency to
-form cell masses, is a great advance of the vegetative condition of the
-plant upon that which we find in the simple threads of œdogonium.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_153" id="Page_153">[Pg 153]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XVII" id="CHAPTER_XVII">CHAPTER XVII.</a><br />
-<span class="h_subtitle">COLEOCHÆTE.</span></h3>
-</div>
-
-<p><b>322.</b> Among the green algæ coleochæte is one of the most
-interesting. Several species are known in this country. One of these at
-least should be examined if it is possible to obtain it. It occurs in
-the water of fresh lakes and ponds, attached to aquatic plants.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img id="FIG_155" src="images/fig155.jpg" alt="" width="125" height="347" />
-    <p class="center">Fig. 155.<br /> Stem of aquatic plant<br /> showing coleochæte,<br /> natural size.</p>
-   </div>
-  <div class="figsub">
-      <p class="space-below2">&nbsp;</p>
-      <img id="FIG_156" src="images/fig156.jpg" alt="" width="300" height="276" />
-      <p class="center">Fig. 156.<br /> Thallus of Coleochæte scutata.</p>
-  </div>
-</div>
-
-<p><b>323. The shield-shaped coleochæte.</b>—This plant (C. scutata) is
-in the form of a flattened, circular, green plate, as shown in <a href="#FIG_156">fig. 156</a>.
-<span class="pagenum"><a name="Page_154" id="Page_154">[Pg 154]</a></span>
-It is attached near the center on one side to rushes and other
-plants, and has been found quite abundantly for several years in the
-waters of Cayuga Lake at its southern extremity. As will be seen it
-consists of a single layer of green cells which radiate from the center
-in branched rows to the outside, the cells lying so close together as
-to form a continuous plate. The plant started its growth from a single
-cell at the central point, and grew at the margin in all directions.
-Sometimes they are quite irregular in outline, when they lie quite
-closely side by side and interfere with one another by pressure. If the
-surface is examined carefully there will be found long hairs, the base
-of which is enclosed in a narrow sheath. It is from this character that
-the genus takes its name of coleochæte (sheathed hair).</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img id="FIG_157" src="images/fig157.jpg" alt="" width="250" height="271" />
-    <p class="center">Fig. 157.<br /> Portion of thallus of Coleochæte scutata,<br />
-          showing empty cells from which zoogonidia<br />
-          have escaped, one from each cell;<br />
-          zoogonidia at the left. (After Pringsheim.)</p>
-   </div>
-  <div class="figsub">
-      <p class="space-below2">&nbsp;</p>
-      <img id="FIG_158" src="images/fig158.jpg" alt="" width="250" height="289" />
-      <p class="center">Fig. 158.<br /> Portion of thallus of Coleochæte<br />
-           scutata, showing four antheridia<br /> formed from one thallus cell; a<br />
-           single spermatozoid at the right.<br /> (After Pringsheim.)</p>
-  </div>
-</div>
-
-<p><b>324. Fruiting stage of coleochæte.</b>—It is possible at some
-seasons of the year to find rounded masses of cells situated near the
-margin of this green disk. These have developed from a fertilized egg
-which remained attached to the plant, and probably by this time the
-parent plant has lost its color.</p>
-
-<p><b>325. Zoospore stage.</b>—This mass of tissue does not develop
-directly into the circular green disk, but each of the cells forms a
-zoospore. Here then, as in œdogonium, we have another stage of the
-plant interpolated between the fertilized egg and that stage of the
-plant which bears the gametes. But in coleochæte we have a distinct
-advance in this stage upon what is present in œdogonium, for in
-coleochæte the fertilized egg develops first into a several-celled mass
-of tissue before the zoospores are formed, while in œdogonium only four
-zoospores are formed directly from the egg.</p>
-
-<p><b>326. Asexual reproduction.</b>—In asexual reproduction any of the
-green cells on the plant may form zoogonida. The contents of a cell
-<span class="pagenum"><a name="Page_155" id="Page_155">[Pg 155]</a></span>
-round off and form a single zoogonidium which has two cilia at the
-smaller end of the oval body, <a href="#FIG_157">fig. 157</a>. After swimming
-around for a time they come to rest, germinate, and produce another plant.</p>
-
-<p><b>327. Sexual reproduction.—Oogonium.</b>—The oogonium is formed by
-the enlargement of a cell at the end of one of the threads, and then
-the end of the cell elongates into a slender tube which opens at the
-end to form a channel through which the spermatozoid may pass down to
-the egg. The egg is formed of the contents of the cell (<a href="#FIG_159">fig. 159</a>).
-Several oogonia are formed on one plant, and in such a plant as C.
-scutata they are formed in a ring near the margin of the disk.</p>
-
-<div class="figcenter">
-    <img id="FIG_159" src="images/fig159.jpg" alt="" width="600" height="341" />
-    <p class="center">Fig. 159.</p>
-    <p class="blockquot">Coleochæte soluta; at left branch bearing oogonium (<i>oog</i>);
-           antheridia (<i>ant</i>); egg in oogonium and surrounded by
-           enveloping threads; at center three antheridia open, and one
-           spermatozoid; at right sporocarp, mature egg inside sporocarp wall.</p>
-</div>
-<div class="figcontainer">
-  <div class="figsub">
-    <img src="images/fig160.jpg" alt="" width="250" height="273" />
-    <p class="center">Fig. 160.<br /> Two sporocarps<br /> still surrounded<br /> by thallus.<br />
-                Thallus finally<br /> decays and sets<br /> sporocarp free.</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig161.jpg" alt="" width="250" height="252" />
-      <p class="center">Fig. 161.<br /> Sporocarp ruptured by growth<br /> of egg to form cell
-                       mass.<br /> Cells of this sporophyte<br /> forming zoospores.</p>
-  </div>
-    <p class="center space-below2">Figs. 160, 161. C. scutata.</p>
-</div>
-
-<p><b>328. Antheridia.</b>—In C. scutata certain of the cells of the
-plant divide into four smaller cells, and each one of these becomes
-an antheridium. In C. soluta the antheridia grow out from the end of
-terminal cells in the form of short flasks, sometimes four in number or
-less (<a href="#FIG_159">fig. 159</a>). A single spermatozoid is formed from the contents.
-<span class="pagenum"><a name="Page_156" id="Page_156">[Pg 156]</a></span>
-It is oval and possesses two long cilia. After swimming around it passes
-down the tube of the oogonium and fertilizes the egg.</p>
-
-<p><b>329. Sporocarp.</b>—After the egg is fertilized the cells of the
-threads near the egg grow up around it and form a firm covering one
-cell in thickness. This envelope becomes brown and hard, and serves
-to protect the egg. This is the “fruit” of the coleochæte, and is
-sometimes called a sporocarp (spore-fruit). The development of the cell
-mass and the zoospores from the egg has been described above.</p>
-
-<p>Some of the species of coleochæte consist of branched threads, while
-others form circular cushions several layers in thickness. These forms
-together with the form of our plant C. scutata make an interesting
-series of transitional forms from filamentous structures to an expanded
-plant body formed of a mass of cells.
-<span class="pagenum"><a name="Page_157" id="Page_157">[Pg 157]</a></span></p>
-
-<p class="space-above2"><b>330. COMPARATIVE TABLE FOR SPIROGYRA, VAUCHERIA,
-ŒDOGONIUM, COLEOCHÆTE.</b></p>
-
-<table class="smallfont" border="0" cellspacing="0" summary=" " cellpadding="0" rules="cols" >
-  <thead><tr>
-      <th class="tdc bb2" colspan="10">&nbsp;</th>
-   </tr><tr>
-      <th class="tdc bb2" rowspan="3">&nbsp;</th>
-      <th class="tdc bb2" colspan="7">GAMETOPHYTE. (Bears the sexual organs and gonidia.)</th>
-      <th class="tdc bb2" rowspan="2">SPOROPHYTE<br />Bears spores</th>
-      <th class="tdc bb2" rowspan="3"><span class="smcap">How Veg. Phase<br />of Gametophyte<br /> is Developed.</span></th>
-   </tr><tr>
-      <th class="tdc bb2" rowspan="2"><span class="smcap">Vegetative<br />Phase</span></th>
-      <th class="tdc bb2" rowspan="2"><span class="smcap">Growth.</span></th>
-      <th class="tdc bb2" rowspan="2"><span class="smcap">Mulitipl-<br />ication.</span></th>
-      <th class="tdc bb2" colspan="4"><span class="smcap">Sexual Reproduction.</span></th>
-   </tr><tr>
-      <th class="tdc bb2" colspan="2"><span class="smcap">Sexual Organs.</span></th>
-      <th class="tdc bb2" colspan="2"><span class="smcap">Gametes.</span></th>
-      <th class="tdc bb2"><span class="smcap">Fruit.</span></th>
-   </tr>
-  </thead>
-  <tbody><tr>
-      <td class="tdl bb" rowspan="2">Spirogyra.</td>
-      <td class="tdl_table bb" rowspan="2"><p>Simple threads of cylindrical cells.</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>All cells divide and grow.</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>By breaking up of threads.</p></td>
-      <td class="tdc greyish" colspan="2">Undifferentiated.</td>
-      <td class="tdc greyish" colspan="2">Undifferentiated.</td>
-      <td class="tdl_table bb" rowspan="2"><p>Zygospore<br />Rests.</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>Develops vegetative phase directly.</p></td>
-    </tr><tr>
-      <td class="tdl_table bb" colspan="2"><p>Any cell of thread. Conjugate by tube.</p></td>
-      <td class="tdl_table bb" colspan="2"><p>Entire contents of cojugating cells.</p></td>
-   </tr><tr>
-      <td class="tdl bb" rowspan="2">Vaucheria.</td>
-      <td class="tdl_table bb" rowspan="2"><p>Branched threads, continuous.</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>Limited to ends of threads and branches.</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>By multiciliate zoogonidia, and other cells, from terminal portions.</p></td>
-      <td class="tdc greyish" colspan="2">Differentiated.</td>
-      <td class="tdc greyish" colspan="2">Differentiated.</td>
-      <td class="tdl_table bb" rowspan="2"><p>Egg (or oospore). Rests.</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>Develops vegetative phase directly.</p></td>
-    </tr><tr>
-      <td class="tdl_table bb"><p>Antheridia slender cells on special branches.</p></td>
-      <td class="tdl_table bb"><p>Oogonium, large rounded cell on special branch, opens and emits bit of protoplasm.</p></td>
-      <td class="tdl_table bb"><p>Small two-ciliated spermatozoids.</p></td>
-      <td class="tdc bb">&nbsp;&nbsp;Large&nbsp;&nbsp;<br /> egg<br /> cell.</td>
-    </tr><tr>
-      <td class="tdl bb" rowspan="2">Œdogonium.</td>
-      <td class="tdl_table bb" rowspan="2"><p>Simple threads of cylindrical cells.</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>Limited to certain portions of thread.</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>By oval zoogonidia, with crown of cilia.
-                              Any cell may form a single zoogonidium.</p></td>
-      <td class="tdc greyish" colspan="2">Differentiated.</td>
-      <td class="tdc greyish" colspan="2">Differentiated.</td>
-      <td class="tdl_table bb" rowspan="2"><p>Egg (or oospore). Rests.</p></td>
-      <td class="tdl_table bb" rowspan="2"><p></p>Divides into four cells;
-                            each forms zoospore which develops veg.phase again.</td>
-    </tr><tr>
-      <td class="tdl_table bb"><p>Antheridia disk-shaped, several from one vegetative cell.
-                           Sometimes on dwarf males.</p></td>
-      <td class="tdl_table bb"><p>Oogonium, changed vegetative cell, opens and emits bit of protoplasm.</p></td>
-      <td class="tdl_table bb"><p>Oval spermatozoids with crown of cilia. Two from each antheridium.</p></td>
-      <td class="tdc bb">Large<br /> egg<br /> cell.</td>
-    </tr><tr>
-      <td class="tdl bb" rowspan="2">Coleochæte.</td>
-      <td class="tdl_table bb" rowspan="2"><p>Branched threads, or compact circular plates.</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>Terminal or marginal.</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>By zoogonidia with two cilia.
-                    Any cell may form a single zoogonidium.</p></td>
-      <td class="tdc greyish" colspan="2">Differentiated.</td>
-      <td class="tdc greyish" colspan="2">Differentiated.</td>
-      <td class="tdl_table bb" rowspan="2"><p>Egg (surrounded by wall from gametophyte).
-                     Rests. Divides and grows to form a mass of cells.</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>Each forms a zoospore.
-                      Zoospore develops veg. phase again.</p></td>
-    </tr><tr>
-      <td class="tdl_table bb"><p>Antheridia, four or several from single veg. cell.</p></td>
-      <td class="tdl_table bb"><p>Oogonium, enlarged veg. cell, with long tube through
-             opening of which spermatozoid enters. After fertilization wall of enveloping threads
-             surrounds oogonium.</p></td>
-      <td class="tdl_table bb"><p>Oval, biciliate spermatozoid, one from each ntheridium.</p></td>
-      <td class="tdc bb">Large<br /> egg<br /> cell.</td>
-    </tr><tr>
-      <td class="tdc bt2" colspan="10">&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_158" id="Page_158">[Pg 158]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XVIII" id="CHAPTER_XVIII">CHAPTER XVIII.</a><br />
-<span class="h_subtitle">CLASSIFICATION AND ADDITIONAL<br /> STUDIES OF THE ALGÆ.</span></h3>
-</div>
-
-<p>In order to show the general relationship of the algæ studied, the
-principal classes are here enumerated as well as some of the families.
-In some of the groups not represented by the examples studied above, a
-few species are described which may serve as the basis of additional
-studies if desired. The principal classes<a name="FNanchor_17_17" id="FNanchor_17_17"></a><a href="#Footnote_17_17" class="fnanchor">[17]</a>
-of algæ are as follows:</p>
-
-<p class="center"><b>Class Chlorophyceæ.</b></p>
-
-<p><b>331.</b> These are the green algæ, so called because the chlorophyll
-green is usually not masked by other pigments, though in some forms it
-is. There are three subclasses.</p>
-
-<p><b>332. Subclass PROTOCOCCOIDEÆ.</b>—In the Protococcoideæ are found
-the simplest green plants. Many of them consist of single cells which
-live an independent life. Others form “colonies,” loose aggregations
-of individuals not yet having attained the permanency of even a simple
-plant body, for the cells often separate readily and are able to form
-new colonies. The colonies are often held together by a gelatinous
-membrane, or matrix. Some are motile, while others are non-motile. A
-few of the families are here enumerated.</p>
-
-<p><b>333. Family Volvocaceæ.</b>—These are all motile, during the
-vegetative stage. The individuals are single or form more or less
-globose colonies.</p>
-
-<p><b>334. The “red snow” plant (Sphærella nivalis).</b>—This is often
-found in arctic and alpine regions forming a red covering over more or
-less large areas of snow or ice. For this reason it is called the “red
-snow plant.”</p>
-
-<p><b>335. Sphærella lacustris</b>, a closely related species, is very
-widely distributed in temperate regions along streams or on the borders
-<span class="pagenum"><a name="Page_159" id="Page_159">[Pg 159]</a></span>
-of lakes and ponds. Here in dry weather it is often found closely
-adhering to the dry rock surface, and giving it a reddish color as
-if the rock were painted. This is especially the case in the shallow
-basins formed over the uneven surface of the rock near the water’s
-edge. These places during heavy rains or in high water are provided
-with sufficient water to fill the basins. During such times the red
-snow plant grows and multiplies, loses its red color and becomes green,
-and, being motile, is free swimming. It is a single-celled plant,
-oval in form, surrounded by a gelatinous sheath and with two cilia or
-flagella at the smaller end, by the vibration of which it moves (<a href="#FIG_162">fig. 162).</a>
-The single cell multiplies by dividing into two cells. When the
-water dries out of the basin, the motile plant comes to rest, and many
-of the cells assume the red color. To obtain the plant for study,
-scrape some of the red covering from these rock basins and place it in
-fresh spring water, and in a day or so the swarmers are likely to be
-found. Under certain conditions small microzoids are formed.</p>
-
-<div class="figcenter">
-    <img id="FIG_162" src="images/fig162.jpg" alt="" width="600" height="230" />
-    <p class="center">Fig. 162.</p>
-    <p class="blockquot">Sphærella lacustris (Girod.) Wittrock. <i>A</i>, mature free swimming
-         individual with central red spot. <i>B</i>, division of mother individual to
-         form two. <i>C</i>, division of a red one to form four. <i>D</i>, division into
-         eight. <i>E</i>, a typical resting cell, red. <i>F</i>, same beginning to divide.
-         <i>G</i>, one of four daughter zoospores after swimming around for a time
-         losing its red color and becoming green. (After Hazen.)</p>
-</div>
-
-<p><b>336. Chlamydomonas</b> is a very interesting genus of motile
-one-celled green algæ, because the species are closely related to
-the Flagellates among the lower animals. The plant is oval, with a
-single chloroplast and surrounded by a gelatinous envelope through
-which the two cilia or flagella extend. One-celled organisms of this
-kind are sometimes called <i>monads</i>, i.e., a one-celled being. This
-one has a gelatinous cloak and is, therefore, a <i>cloaked monad</i>
-(<i>Chlamydomonas</i>). The species often are found as a very thin green
-film on fresh water. C. pulvisculus is shown in <a href="#FIG_163">fig. 163</a>. When
-it multiplies the single cell divides into two, as shown in <i>B</i>. Sometimes
-a non-motile palmella stage is formed, as shown in <i>C</i> and <i>D</i>.
-<span class="pagenum"><a name="Page_160" id="Page_160">[Pg 160]</a></span>
-Reproduction takes place by gametes which are of unequal size, the
-smaller one representing the sperm and the larger one the egg, as in
-<i>E</i> and <i>F</i>. These conjugate as in <i>G</i> and <i>H</i>, the
-protoplasm of the smaller one passing over into the larger one, and a
-zygospore is thus formed.</p>
-
-<div class="figcenter">
-    <img id="FIG_163" src="images/fig163.jpg" alt="" width="600" height="137" />
-    <p class="center">Fig. 163.</p>
-    <p class="blockquot"><i>Chlamydomonas pulvisculus</i> (Müll.) Ehrb. <i>A</i>, an old motile
-           individual; <i>n</i>, nucleus; <i>p</i>, pyrenoid; <i>s</i>, red eye spot; <i>v</i>,
-           contractile vacuole; <i>B</i>, motile individual has drawn in its cilia
-           and divided into two; <i>C</i>, mother plant has drawn in its cilia and
-           divided into four non-motile cells; <i>D</i>, pamella stage; <i>E</i>, female
-           gamete—egg; <i>F</i>, male gamete—sperm; <i>G</i>, early stage of conjugation;
-           <i>H</i>, zygospore with conjugating tube and empty male cell attached. (After Wille.)</p>
-</div>
-
-<p><b>337. Of those which form colonies</b>, Pandorina morum is widely
-distributed and not rare. It consists of a sphere formed of sixteen
-individuals enclosed in a thin gelatinous membrane. Each cell possesses
-two cilia (or flagella), which extend from the broader end out through
-the enveloping membrane. By the movement of these flagella the colony
-goes rolling around in the water. When the plant multiplies each
-individual cell divides into sixteen small cells, which then grow and
-form new colonies. Reproduction takes place when the individual cells
-of the young colonies separate, and usually a small individual unites
-with a larger one and a zygospore is formed (see <a href="#FIG_164">fig. 164</a>).
-Eudorina elegans is somewhat similar, but when the gametes are formed certain
-mother cells divide into sixteen small motile males or sperms, and
-certain other mother cells divide into sixteen large motile females or
-eggs. These separate from the colonies, and the sperms pair with the
-eggs and fuse to form zygospores. This plant as well as Chlamydomonas
-pulvisculus foreshadows the early differentiation of sex in plants.
-<span class="pagenum"><a name="Page_161" id="Page_161">[Pg 161]</a></span></p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_164" src="images/fig164.jpg" alt="" width="400" height="480" />
-    <p class="center">Fig. 164.<br />Pandorina morum (Müll.) Bory.</p>
-<table border="0" cellspacing="0" summary=" " cellpadding="0" >
-  <tbody><tr>
-      <td class="tdr">I,&nbsp;</td>
-      <td class="tdl">motile colony;</td>
-   </tr><tr>
-      <td class="tdr">II,&nbsp;</td>
-      <td class="tdl">colony divided into</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl">&nbsp;&emsp;16 daughter colonies;</td>
-   </tr><tr>
-      <td class="tdr">III,&nbsp;</td>
-      <td class="tdl">sexual colony, gametes escaping;</td>
-   </tr><tr>
-      <td class="tdr">IV, V,&nbsp;</td>
-      <td class="tdl">conjugating gametes;</td>
-   </tr><tr>
-      <td class="tdr">VI, VII,&nbsp;</td>
-      <td class="tdl">young and old zygospore;</td>
-   </tr><tr>
-      <td class="tdr">VIII,&nbsp;</td>
-      <td class="tdl">zygospore forming a large swarm</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl">&nbsp;&emsp;spore, which is free in IX;</td>
-   </tr><tr>
-      <td class="tdr">X,&nbsp;</td>
-      <td class="tdl">same large swarm spore divided</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl">&nbsp;&emsp;to form young colony.</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl">(After Pringsheim.)</td>
-   </tr>
- </tbody>
-</table>
-</div>
-  <div class="figsub">
-      <p class="space-below3">&nbsp;</p>
-      <img  id="FIG_165" src="images/fig165.jpg" alt="" width="200" height="401" />
-      <p class="center">Fig. 165.<br /> Pleurococcus<br /> (protococcus)<br /> vulgaris.</p>
-  </div>
-</div>
-
-<p><b>338. Family Tetrasporaceæ.</b>—This family is well represented by
-Tetraspora lubrica forming slimy green net-like sheets attached to
-objects in slow-running water. It is really a single-celled plant. The
-rounded cells divide by cross walls into four cells, and these again,
-and so on, large numbers being held in loose sheets by the slime in
-which they are imbedded.</p>
-
-<p><b>339. Family Pleurococcaceæ.</b>—The members of this family are
-all non-motile in the vegetative stage. They consist of single
-individuals, or of colonies. Pleurococcus vulgaris (Protococcus
-vulgaris) is a single-celled alga, usually obtained with little
-difficulty. It is often found on the shaded, and cool, or moist side of
-trees, rocks, walls, etc., in damp places. This plant is not motile. It
-multiplies by fission (<a href="#FIG_165">Fig. 165</a>) into two, then four, etc.
-These cells remain united for a time, then separate. Sometimes the cells are found
-growing out into filaments, and it is thought by some that P. vulgaris
-may be only a simple stage of a higher alga. Eremosphæra viridis is
-another single-celled alga found in fresh water among filamentous
-forms. The cells are large and globose.</p>
-
-<div class="figcenter">
-    <img  id="FIG_166" src="images/fig166.jpg" alt="" width="600" height="264" />
-   <div class="blockquot">
-    <p class="center">Fig. 166.</p>
-    <p>Pediastrum boryanum. <i>A</i>, mature colony, most of the young colonies
-       have escaped from their mother cells; at <i>g</i>, a young colony is
-       escaping; <i>sp</i>, empty mother cells; <i>B</i>, young colony; <i>C</i>,
-       same colony with spores arranged in order. (After Braun.)</p>
-   </div>
-</div>
-
-<p><b>340. Family Hydrodictyaceæ.</b>—These plants form colonies of
-cells. Hydrodictyon reticulatum, the water net, is made up of large
-numbers of cylindrical cells so joined at their ends as to form a large
-open mesh or net. Pediastrum forms circular flat colonies, as shown in
-<a href="#FIG_166">fig. 166</a>. Both of these plants are rather common in fresh-water
-pools, the latter one intermingled with filamentous algæ, while the former
-forms large sheets or nets. Multiplication in Hydrodictyon takes place
-<span class="pagenum"><a name="Page_162" id="Page_162">[Pg 162]</a></span>
-by the protoplasm in one of the cells dividing into thousands of minute
-cells, which gradually arrange themselves in the form of a net, escape
-together from the mother cell, and grow into a large net. In Pediastrum
-multiplication takes place in a similar way, but the protoplasm in each
-cell usually divides into sixteen small cells, and escaping together
-from the mother cell arrange themselves and grow to full size (<a href="#FIG_166">fig. 166</a>).</p>
-
-<p><b>341. The Conjugateæ</b> include several families of green algæ,
-which probably should be included among the Chlorophyceæ. They have
-probably had their origin from some of the more simple members of the
-Protococcoideæ. They are represented by Spirogyra, Zygnema, and the
-desmids, studied in <a href="#CHAPTER_XIV">Chapter 14</a>.</p>
-
-<p><b>342. Subclass CONFERVOIDEÆ.</b>—These are mostly filamentous algæ,
-the filaments being composed of cells firmly united, and, with the
-exception of the simplest forms, there is a definite growing point. A
-few of the families are as follows:</p>
-
-<p><b>343. Family Ulvaceæ.</b>—These contain the sea wracks, or sea
-lettuce, like Ulva, forming expanded green, ribbon-like growths in the sea.</p>
-
-<div class="figcenter">
-    <img  id="FIG_167" src="images/fig167.jpg" alt="" width="500" height="388" />
-   <div class="blockquot">
-    <p class="center">Fig. 167.</p>
-    <p>Ulothrix zonata. <i>A</i>, base of thread. <i>B</i>, cells with zoospores, <i>C</i>,
-       one cell with zoospores escaping another cell with small biciliate
-       gametes escaping and some fusing to form zygospores, <i>E</i>, zoospores
-       germinating and forming threads: <i>F</i>, <i>G</i>, zygospore growing and
-       forming zoospores. (After Caldwell and Dodel-Port.)</p>
-   </div>
-</div>
-
-<p><b>344. Family Ulotrichaceæ</b>, represented by Ulothrix zonata, not
-uncommon in slow-running water or in ponds of fresh water attached
-to rocks or wood. It consists of simple threads of short cells.
-Multiplication takes place by zoospores. Reproduction takes place by
-motile sexual cells (gametes) which fuse to form a zygospore (<a href="#FIG_167">fig. 167</a>).</p>
-
-<p><b>345. Family Chætophoraceæ</b>, represented by Chætophora (in <a href="#CHAPTER_XV">Chapter
-15</a>) and Drapernaudia in fresh water.</p>
-
-<p><b>346. Family Œdogoniaceæ</b>, represented by Œdogonium (<a href="#CHAPTER_XVI">Chapter 16</a>).</p>
-
-<p><b>347. Family Coleochætaceæ</b>, represented by Coleochæte (<a href="#CHAPTER_XVII">Chapter 17</a>).</p>
-
-<p><b>348. Subclass SIPHONEÆ.</b>—There are several families.</p>
-
-<p><b>349. Family Botrydiaceæ.</b>—This is represented by Botrydium
-granulatum (Chapter 15, <a href="#Page_146">p. 146</a>).</p>
-
-<p><b>350. Family Vaucheriaceæ</b>, represented by Vaucheria (<a href="#CHAPTER_XV">Chapter 15</a>),
-with quite a large number of species, is widely distributed.
-<span class="pagenum"><a name="Page_163" id="Page_163">[Pg 163]</a></span></p>
-
-<p class="center"><b>Class Schizophyceæ</b> (= Cyanophyceæ).</p>
-
-<div class="figright">
-    <img  id="FIG_168" src="images/fig168.jpg" alt="" width="200" height="211" />
-    <p class="center">Fig. 168.<br /> Glœocapsa.</p>
-</div>
-
-<p><b>351. The Blue-Green Algæ</b>, or <b>Cyanophyceæ</b> form slimy
-looking thin mats on damp wood or the ground, or floating mats or
-scum on the water. The color is usually bluish green, but in some
-species it is purple, red or brown. All have chlorophyll, but it is
-not in distinct chloroplasts and is more or less completely guised
-by the presence of other pigments. Two orders and eight families are
-recognized. The following include some of our common forms:</p>
-
-<p><b>352. ORDER COCCOGONALES (COCCOGONEÆ).</b>—Single-celled plants,
-occurring singly or in colonies, in some forms forming short threads.
-One of the two families is mentioned.</p>
-
-<p><b>353. Family Chroococcaceæ.</b>—The plants multiply only through cell
-division. Chroococcus, forms rounded, blue-green cells enclosed in a
-thick gelatinous coat, in fresh water and in damp places; certain
-species form “lichen-gonidia” in some genera of lichens. Glœocapsa is
-similar to Chroococcus, but the colonies are surrounded by an additional
-common gelatinous envelope (<a href="#FIG_168">fig. 168</a>); on damp rocks, etc.</p>
-
-<div class="figcenter">
-    <img src="images/fig169.jpg" alt="" width="500" height="382" />
-   <div class="blockquot">
-    <p class="center">Fig. 169.</p>
-    <p><i>A</i>, Oscillatoria princeps, <i>a</i>, terminal cell; <i>b</i>, <i>c</i>,
-       portions from the middle of a filament. In <i>c</i>, a dead cell is shown between
-       the living cells; <i>B</i>, Oscillatoria froelichii, <i>b</i>, with granules along
-       the partition walls.</p>
-   </div>
-</div>
-
-<p class="space-above2"><b>354. ORDER HORMOGONALES (HORMOGONEÆ).</b>—Plants filamentous,
-simple celled or with false or true branching, usually several celled
-(Spirulina is single celled). Multiplication takes place through
-<i>hormogones</i>, short sections of the threads becoming free; also through
-resting cells. Two of the six families are mentioned.</p>
-
-<p><b>355. Family Oscillatoriaceæ.</b>—This family is represented by
-the genus Oscillatoria, and by several other genera common and widely
-distributed. Oscillatoria contains many species. They are found on the
-damp ground or wood, or floating in mats in the water. They often form
-<span class="pagenum"><a name="Page_164" id="Page_164">[Pg 164]</a></span>
-on the soil at the bottom of the pool, and as gas becomes entangled
-in the mat of threads, it is lifted from the bottom and floated to
-the surface of the water. The plant is thread-like, and divided up
-into many short cells. The threads often show an oscillating movement,
-whence the name <i>Oscillatoria</i>.</p>
-
-<p><b>356. Family Nostocaceæ.</b>—This family is represented by Nostoc,
-which forms rounded, slimy, blue-green masses on wet rocks. The
-individual plants in the slimy ball resemble strings of beads, each
-cell being rounded, and several of these arranged in chains as shown
-in <a href="#FIG_170">fig. 170</a>. Here and there are often found larger cells
-(heterocysts) in the chain. Nostoc punctiforme lives in the intercellular spaces
-of the roots of cycads (often found in greenhouses), and in the
-stems of Gunnera. N. sphæricum lives in the spaces between the cells
-in many species of liverworts (in the genera Anthoceros, Blasia,
-Pellia, Aneura, Riccia, etc.), and in the perforated cells of Sphagnum
-acutifolium. Anabæna is another common and widely distributed genus.
-The species occur in fresh or salt water, singly or in slimy masses.
-Anabæna azollæ lives endophytically in the leaves of the water fern, Azolla.</p>
-
-<div class="figcenter">
-    <img  id="FIG_170" src="images/fig170.jpg" alt="" width="400" height="380" />
-   <div class="blockquot">
-    <p class="center">Fig. 170.</p>
-    <p>Nostoc linckii. <i>A</i>, filament with two heterocysts (<i>h</i>), and a large
-       number of spores (<i>sp</i>); <i>B</i>, isolated spore beginning to germinate;
-       <i>C</i>, young filament developed from spore. (After Bornet.)</p>
-   </div>
-</div>
-<div class="figcenter">
-    <img src="images/fig171.jpg" alt="" width="600" height="208" />
-   <div class="blockquot">
-    <p class="center">Fig. 171.</p>
-    <p>Bacteria. <i>A</i>, Bacillus subtilis. Spores in threads, unstained rods,
-       and stained rods showing cilia; <i>B</i>, Bacillus tetani, the tetanus
-       or lockjaw bacillus, found in garden soil and on old rusty nails.
-       Spores in club-shaped ends. <i>C</i>, Micrococcus; <i>D</i>, Sarcina; <i>E</i>,
-       Streptococcus; <i>F</i>, Spirillum. (After Migula.)</p>
-   </div>
-</div>
-
-<p class="center"><b>Class Schizomycetes.</b></p>
-
-<p><b>357. Bacteriales.</b>—The bacteria are sometimes classified
-with the Cyanophyceæ, under the name Schizophyta, and represent the
-subdivision Schizomycetes, or fission fungi, because many of them
-multiply by a division of the cells just as the blue-green algæ do.
-For example, Bacillus forms rods which increase in length and divide
-into two rods, or it may grow into a long thread of many short rods.
-Micrococcus consists of single rounded cells. Streptococcus forms
-chains of rounded cells, Sarcina forms irregular cubes of rounded
-cells, while others like Spirillum are spiral in form. Bacillus
-<span class="pagenum"><a name="Page_165" id="Page_165">[Pg 165]</a></span>
-subtilis may be obtained by making an infusion from hay and allowing
-it to stand for several days. Bacillus tetani occurs in the soil, on
-old rusty nails, etc. It is called the tetanus bacillus because it
-causes a permanent spasm of certain muscles, as in “lockjaw.” This
-bacillus grows and produces this result on the muscles when it occurs
-in deep and closed wounds such as are caused by stepping on an old nail
-or other object which pierces the flesh deeply. In such a deep wound
-oxygen is deficient, and in this condition the bacillus is virulent.
-Opening the wounds to admit oxygen and washing them out with a solution
-of bichloride of mercury prevents the tetanus. Many bacteria are of
-great importance in bringing about the decay of dead animal and plant
-matter, returning it to a condition for plant food. (See also nitrate
-and nitrite bacteria, <a href="#CHAPTER_IX">Chapter IX</a>.) While most bacteria
-are harmless there are many which cause very serious diseases of man and animals,
-as typhoid fever, diphtheria, tuberculosis, etc., while some others
-produce disease in plants. Others aid in certain fermentations of
-liquids and are employed for making certain kinds of wines or other
-beverages. Some work in symbiosis with yeasts, as in the kephir yeast,
-used in fermenting certain crude beverages by natives of some countries.</p>
-
-<p><b>357</b><i>a</i>. <b>Myxobacteriales (Myxobacteriaceæ
-Thaxter<a name="FNanchor_18_18" id="FNanchor_18_18"></a><a href="#Footnote_18_18" class="fnanchor">[18]</a>).</b>—These
-plants consist of colonies of bacteria-like organisms, motile rods,
-which multiply by cross-division and secrete a gelatinous substance or
-matrix which surrounds the colonies. They form plasmodium-like masses
-which superficially resemble the slime moulds. In the fruiting stage
-some species become elevated from the substratum into cylindrical,
-clavate, or branched forms, which bear cysts of various shapes
-containing the rods in a resting stage, or the rods are converted into
-spore-like masses. Ex., Chondromyces crocatus on decaying plant parts,
-Myxobacter aureus on wet wood and bark, Myxococcus rubescens on dung,
-decaying lichens, paper, etc.</p>
-
-<p class="center"><b>Class Flagellata.</b></p>
-
-<p><b>358. The flagellates</b> are organisms of very low organization
-resembling animals as much as they do plants. They are single celled
-and possess two cilia or flagella, by the vibration of which they
-move. Some are without a cell wall, while others have a well-defined
-membrane, but it rarely consists of cellulose. Some have chromatophores
-and are able to manufacture carbohydrates like ordinary green plants.
-These are green in Euglena, and brown in Hydrurus. Some possess a
-mouth-like opening and are able to ingest solid particles of food
-(more like animals), while others have no such opening and absorb food
-substances dissolved in water (more like plants). The Euglena viridis is not
-uncommon in stagnant water, often forming a greenish film on the water.
-<span class="pagenum"><a name="Page_166" id="Page_166">[Pg 166]</a></span></p>
-
-<p class="center"><b>Class Peridineæ.</b></p>
-
-<p><b>358</b><i>a</i>. These are peculiar one-celled organisms provided
-with two flagella and show some relationship to the Flagellates. They
-usually are provided with a cellulose membrane, which in some forms
-consists of curiously sculptured plates. In the higher forms this
-cellulose membrane consists of two valves fitting together in such a
-way as to resemble some of the diatoms. Like the Flagellates, some
-have green chromatophores, which in some are obscured by a yellow or
-brown pigment (resembling the diatoms), while still others have no
-chlorophyll. The Peridineæ are abundant in the sea, while some are
-found in fresh water.</p>
-
-<p class="center"><b>Class Diatomaphyceæ<br /> (Bacillariales, Diatomaceæ).</b></p>
-
-<div class="figcenter">
-    <img src="images/fig171a.jpg" alt="" width="600" height="300" />
-   <div class="blockquot">
-    <p class="center">Fig. 171<i>a</i>.</p>
-    <p>A group of Diatoms: <i>c</i> and <i>d</i>, top and side views of the same form;
-       <i>e</i>, colony of stalked forms attached to an alga; <i>f</i> and <i>g</i>, top and
-       side views of the form shown at <i>e</i>; <i>h</i>, a colony; <i>i</i>, a colony, the
-       top and side view shown at <i>k</i> and <i>n</i>, forming auxospores. (After Kerner.)</p>
-   </div>
-</div>
-
-<p><b>358</b><i>b</i>. <b>The diatoms</b> are minute and peculiar organisms
-believed to be algæ. They live in fresh, brackish, and salt water. They
-are often found covering the surface of rocks, sticks, or the soil
-in thin sheets. They occur singly and free, or several individuals
-may be joined into long threads, or other species may be attached to
-objects by slender gelatinous stalks. Each protoplast is enclosed in a
-silicified skeleton in the form of a box with two halves, often shaped
-like an old-fashioned pill box, one half fitting over the other like
-the lid of a box. It is evident that in this condition the plant cannot
-increase much in size.</p>
-
-<p>They multiply by fission. This takes place longitudinally, i.e., in the
-direction of the two halves or <i>valves</i> of the box. Each new plant then
-has a valve only on one side. A new valve is now formed over the naked
-half, and fits inside the old valve. At each division the individuals
-thus become smaller and smaller until they reach a certain point, when
-the valves are cast off and the cell forms an <i>auxospore</i>, i.e., it
-grows alone, or after conjugation with another, to the full size again,
-<span class="pagenum"><a name="Page_167" id="Page_167">[Pg 167]</a></span>
-and eventually provides itself with new valves. The valves are often
-marked, with numerous and fine lines, often making beautiful figures,
-and some are used for test objects for microscopes.</p>
-
-<p>The free forms are capable of movement. The movement takes place in the
-longitudinal direction of the valves. They glide for some time in one
-direction, and then stop and move back again. It is not a difficult
-thing to mount them in fresh water and observe this movement.</p>
-
-<p>The diatoms have small chlorophyll plates, but the green color is
-disguised by a brownish pigment called diatomin. The relationships of
-the diatoms are uncertain, but some, because of the color, think they
-are related to the Phæophyceæ.</p>
-
-<p class="center"><b>Class Phæophyceæ.</b></p>
-
-<p><b>359. The brown algæ. (Phæophyceæ).</b>—The members of this class
-possess chlorophyll, but it is obscured by a brown pigment. The plants
-are accessible at the seashore, and for inland laboratories may be
-preserved in formalin (2½ per cent). (See also Chapter LVI.)</p>
-
-<div class="figcenter">
-    <img  id="FIG_172" src="images/fig172.jpg" alt="" width="500" height="474" />
-   <div class="blockquot">
-    <p class="center">Fig. 172.</p>
-    <p><i>A</i>, Ectocarpus siliculosus; <i>B</i>, branch with a young and a ripe
-       plurilocular sporangium; <i>E</i>, gametes fusing to form zygospore, (<i>B</i>,
-       after Thuret; <i>E</i>, after Berthold.)</p>
-   </div>
-</div>
-
-<p><b>360. Ectocarpus.</b>—The genus Ectocarpus represents well some
-of the simpler forms of the brown algæ (<a href="#FIG_172">fig. 172</a>). They are
-slender, filamentous branched algæ growing in tufts, either epiphytic on other
-marine algæ (often on Fucaceæ), or on stones. The slender threads are
-only divided crosswise, and thus consist of long series of short cells.
-<span class="pagenum"><a name="Page_168" id="Page_168">[Pg 168]</a></span>
-The sporangia are usually plurilocular (sometimes unilocular), and
-usually occur in the place of lateral branches. The zoospores escape
-from the apex of the sporangium and are biciliate, and they fuse to
-form zygospores.</p>
-
-<p><b>361. Sphacelaria.</b>—The species of this genus represent an
-advance in the development of the thallus. While they are filamentous
-and branched, division takes place longitudinally as well as crosswise
-(<a href="#FIG_173">fig. 173</a>).</p>
-
-<p><b>362. Leathesia difformis</b> represents an interesting type because
-the plant body is small, globose, later irregular and hollow, and
-consists of short radiately arranged branches, the surface ones in the
-form of short, crowded, but free, trichome-like green branches. This
-trichothallic body recalls the similar form of Chætophora pisiformis
-(<a href="#CHAPTER_XVI">Chapter 16</a>) among the Chlorophyceæ.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_173" src="images/fig173.jpg" alt="" width="300" height="469" />
-    <p class="center">Fig. 173.<br /> Sphacelaria, portion of plant<br />
-                                      showing longitudinal division<br />
-                                      of cells, and brood bud<br /> (plurilocular sporangium).</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_174" src="images/fig174.jpg" alt="" width="270" height="469" />
-      <p class="center">Fig. 174.<br /> Laminaria digitata, forma cloustoni,<br /> North Sea. (Reduced.)</p>
-  </div>
-</div>
-
-<p><b>363. The Giant Kelps.</b>—Among the brown algæ are found the
-largest specimens, some of the laminarias or giant kelps, rivaling in
-size the largest land plants, and some of them have highly developed
-tissues. <i>Postelsia palmæformis</i> has a long, stout stem, from the
-free end of which extend numerous large and long blades, while the
-stem is attached to the rocks by numerous “root” like outgrowths, the
-holdfasts. It occurs along the northern Pacific coast, and appears to
-flourish where it receives the shock of the surf beating on the shore.
-Several species of Laminaria occur on our north Atlantic coast. In L.
-digitata, the stem expands at the end into a broad blade, which becomes
-split into several smaller blades (<a href="#FIG_174">fig. 174</a>). <i>Macrocystis pyrifera</i>
-inhabits the ocean in the southern hemisphere, and sometimes is found
-along the north American coast. It is said to reach a length of 200-300
-meters.</p>
-
-<p><b>364. Fucus, or Rockweed.</b>—This plant is a more or less branched
-and flattened thallus or “frond.” One of them, illustrated in <a href="#FIG_119">fig. 119</a>,
-measures 15-30 <i>cm</i> (6-12 inches) in length. It is attached to rocks
-and stones which are more or less exposed at low tide. From the base
-of the plant are developed several short and more or less branched
-expansions called “holdfasts,” which, as their name implies, are organs
-of attachment. Some species (F. vesiculosus) have vesicular swellings
-in the thallus.
-<span class="pagenum"><a name="Page_169" id="Page_169">[Pg 169]</a></span></p>
-
-<p>The fruiting portions are somewhat thickened as shown in the figure.
-Within these portions are numerous oval cavities opening by a circular
-pore, which gives a punctate appearance to these fruiting cushions.
-Tufts of hairs frequently project through them.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img src="images/fig175.jpg" alt="" width="210" height="266" />
-    <p class="center">Fig. 175.<br /> Portion of plant of Fucus<br />
-           showing conceptacles in<br /> enlarged ends; and below<br />
-           the vesicles<br /> (Fucus vesiculosus).</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig176.jpg" alt="" width="300" height="261" />
-      <p class="center">Fig. 176.<br /> Section of conceptacle<br /> of Fucus, showing oogonia,<br />
-             and tufts of antheridia.</p>
-  </div>
-</div>
-
-<p><b>365. Structure of the conceptacles.</b>—On making sections of the
-fruiting portions one finds the walls of the cavities covered with
-outgrowths. Some of these are short branches which bear a large rounded
-terminal sac, the oogonium, at maturity containing eight egg-cells.
-More slender and much-branched threads bear narrowly oval antheridia.
-In these are developed several two-ciliated spermatozoids.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img src="images/fig177.jpg" alt="" width="250" height="384" />
-    <p class="center">Fig. 177.<br /> Oogonium of Fucus<br /> with ripe eggs.</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig178.jpg" alt="" width="300" height="373" />
-      <p class="center">Fig. 178.<br /> Antheridia of Fucus,<br /> on branched threads.</p>
-  </div>
-</div>
-
-<p><b>366. Fertilization.</b>—At maturity the spermatozoids and egg-cells
-float outside of the oval cavities, where fertilization takes place.
-<span class="pagenum"><a name="Page_170" id="Page_170">[Pg 170]</a></span>
-The spermatozoid sinks into the protoplasm of the egg-cell, makes its
-way to the nucleus of the egg, and fuses with it as shown in <a href="#FIG_181">fig. 181</a>.
-The fertilized egg then grows into a new plant. Nearly all the brown
-algæ are marine.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img src="images/fig179.jpg" alt="" width="250" height="392" />
-    <p class="center">Fig. 179.<br /> Antheridia of Fucus with<br /> escaping spermatozoids.</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig180.jpg" alt="" width="250" height="378" />
-      <p class="center">Fig. 180.<br /> Eggs of Fucus surrounded<br /> by spermatozoids.</p>
-  </div>
-</div>
-<div class="figcenter">
-    <img  id="FIG_181" src="images/fig181.jpg" alt="" width="600" height="185" />
-   <div class="blockquot">
-    <p class="center">Fig. 181.</p>
-    <p>Fertilization in Fucus; <i>fn</i>, female nucleus; <i>mn</i>, male nucleus;
-        <i>n</i>, nucleolus. In the left figure the male nucleus is shown moving
-        down through the cytoplasm of the egg; in the remaining figures the
-        cytoplasm of the egg is omitted. (After Strasburger.)</p>
-   </div>
-</div>
-
-<p><b>367. The Gulf weed</b> (<b>Sargassum bacciferum</b>) in the warmer
-Atlantic ocean unites in great masses which float on the water, whence
-comes the name “Sargassum Sea.” The Sargassum grows on the coast where
-it is attached to the rocks, but the beating of the waves breaks many
-specimens loose and these float out into the more quiet waters, where
-they continue to grow and multiply vegetatively.</p>
-
-<p><b>368. Uses.</b>—Laminaria japonica and L. angustata are used as food
-by the Chinese and Japanese. Some species of the Laminariaceæ are used
-as food for cattle and are also used for fertilizers, while L. digitata
-is sometimes employed in surgery.
-<span class="pagenum"><a name="Page_171" id="Page_171">[Pg 171]</a></span></p>
-
-<p><i>Classification.</i>—Kjellman divides the Phæophyceæ into two orders.</p>
-
-<p><b>369. Order Phæosporales (Phæosporeæ)</b> including 18 families.
-One of the most conspicuous families is the Laminariaceæ, including
-among others the Giant Kelps mentioned above (Laminaria, Postelsia,
-Macrocystis, etc.).</p>
-
-<p><b>370. Order Cyclosporales (Cyclosporeæ).</b>—This includes one
-family, the <i>Fucaceæ</i> with Ectocarpus, Sphacelaria, Læathesia, Fucus,
-Sargassum, etc.</p>
-
-<p class="center"><b>Class Rhodophyceæ.</b></p>
-
-<p><b>371. The red algæ (Rhodophyceæ).</b>—The larger number of the
-so-called red algæ occur in salt water, though a few genera occur in
-fresh water. The plants possess chlorophyll, but it is usually obscured
-by a reddish or purple pigment.</p>
-
-<p><b>372. Nemalion.</b>—This is one of the lower marine forms, though
-its thallus is not one of the simplest in structure. The plant body
-consists of a slender cylindrical branched shoot, sometimes very
-profusely branched. The central strand is rather firm, while the cortex
-is composed of rather loose filaments.</p>
-
-<div class="figcenter">
-    <img src="images/fig182.jpg" alt="" width="400" height="371" />
-   <div class="blockquot">
-    <p class="center">Fig. 182.</p>
-    <p>A red alga (Nemalion). <i>A</i>, sexual branches, showing antheridia (<i>a</i>);
-       carpogonium or procarp (<i>o</i>) with its trichogyne (<i>t</i>), to which are
-       attached two spermatia (<i>s</i>); <i>B</i>, beginning of a cystocarp (<i>o</i>),
-       the trichogyne (<i>t</i>) still showing; <i>C</i>, an almost mature cystocarp
-       (<i>o</i>), with the disorganizing trichogyne (<i>t</i>). (After Vines.)</p>
-   </div>
-</div>
-
-<p><b>373. Batrachospermum.</b>—This genus occurs in fresh water, and the
-species are found in slow-running water of shallow streams or ditches.
-There is a central slender strand which is more or less branched,
-and on these branches are whorls of densely crowded slender branches
-occurring at regular intervals. The plants are usually very slippery.
-Gonidia are formed on the ends of some of these branches in globose
-sporangia, called monosporangia, since but a single spore or gonidium
-is developed in each. Other branches often terminate in long slender
-hyaline setæ.</p>
-
-<p><b>374. Lemanea.</b>—This genus also occurs in fresh water. The
-species develop only during the cold winter months in rapids of streams
-or where the water from falls strikes the rocks and is thoroughly
-aerated. They form tufts of greenish threads, cylindrical or whiplike,
-which in the summer are usually much broken down. The threads are
-<span class="pagenum"><a name="Page_172" id="Page_172">[Pg 172]</a></span>
-hollow and have a firm cortex. These are the sexual shoots, and they arise
-as branches from a sterile filamentous-branched, Chantransia-like form.</p>
-
-<p><b>375. Fertilization in the lower red algæ.</b>—The sexual organs in
-the red algæ consist of antheridia and carpogonia. The antheridia are
-usually borne in crowded clusters, or surfaces, and bear terminally
-the small non-motile sperm cells. The carpogonium is a branch of one
-or several cells, the terminal cell (procarp) extending into a long
-slender process, the trichogyne. The sperm cell comes in contact with
-the trichogyne, and in the case of Nemalion and some others the nucleus
-has been found to pass down the inside and fuse with the nucleus of the
-procarp.</p>
-
-<div class="figcenter">
-    <img src="images/fig183.jpg" alt="" width="600" height="513" />
-   <div class="blockquot">
-    <p class="center">Fig. 183.</p>
-    <p><i>A</i>, part of a shoot showing whorls of branches with clusters of
-        carpospores. <i>B</i>, carpogonic branch or procarp. <i>c</i>, procarp cell;
-        <i>tr</i>, trichogyne. <i>C</i>, same with sperm (<i>sp</i>) uniting with trichogyne.
-        <i>D</i>, same with carpospores developing from procarp cell. <i>E</i>, male
-        branch with one-celled antheridia. <i>F</i>, same with some of antheridia
-        empty. (After Schmitz.)</p>
-   </div>
-</div>
-
-<p>From this point in the lower red algæ like Nemalion, Batrachospermum
-and Lemanea the formation of the spores is very simple. The procarp
-is stimulated to growth, and buds in different directions, producing
-branched chains of spores (carpospores). The carpospores form a rather
-<span class="pagenum"><a name="Page_173" id="Page_173">[Pg 173]</a></span>
-compact cluster called the sporocarp, which means spore-fruit or
-spore-fruit body. In Batrachospermum it is seen as a compact tuft in
-the loose branching, in Nemalion it lies in the surface of the cortex,
-while in Lemanea the sporocarps lie at different positions in the
-hollow tube of the sexual shoot.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_184" src="images/fig184.jpg" alt="" width="300" height="293" />
-    <p class="center">Fig. 184.<br /> A red alga (Callithamnion),<br /> showing sporangium <i>A</i>, and<br />
-                  the tetraspores discharged <i>B</i>.<br /> (After Thuret.)</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_185" src="images/fig185.jpg" alt="" width="150" height="301" />
-      <p class="center">Fig. 185.<br /> Gracilaria, portion of frond,<br /> showing position of cystocarps.</p>
-  </div>
-</div>
-
-<div class="figleft">
-    <img src="images/fig186.jpg" alt="" width="200" height="206" />
-    <p class="center">Fig. 186.<br /> Gracilaria, section of<br /> cystocarp showing spores.</p>
-</div>
-
-<p><b>376. Gonidia in the red algæ.</b>—The common type of gonidium
-in the red algæ is found in the <i>tetraspores</i>. A single mother cell
-divides into four cells arranged usually in the form of tetrads within
-the <i>tetrasporangium</i>. In Callithamnion the tetrasporangium is exposed.
-In Polysiphonia, Rhabdonia, Gracilaria, etc., it is imbedded in the
-cortex. In Batrachospermum there are monosporangia, each monosporangium
-containing a single gonidium, while in Lemanea, and according to some
-also in Nemalion, gonidia are wanting.
-<span class="pagenum"><a name="Page_174" id="Page_174">[Pg 174]</a></span></p>
-
-<p><b>377. Gracilaria.</b>—Gracilaria is one of the marine forms, and
-one species is illustrated in <a href="#FIG_185">fig. 185</a>. It measures 15-20<i>cm</i>
-or more long, and is profusely branched in a palmate manner. The parts of the
-thallus are more or less flattened. The fruit is a cystocarp, which
-is characteristic of the Rhodophyceæ (Florideæ). In Gracilaria these
-fruit bodies occur scattered over the thallus. They are somewhat
-flask-shaped, are partly sunk in the thallus, and the conical end
-projects strongly above the surface. The carpospores are grouped in
-radiating threads within the oval cavity of the cystocarp. These
-cystocarps are developed as a result of fertilization. Other plants
-bear gonidia in groups of four, the so-called <i>tetraspores</i>.</p>
-
-<p><b>378. Rhabdonia.</b>—This plant is about the same size as the
-gracilaria, though it possesses more filiform branches. The cystocarps
-form prominent elevations, while the carpospores lie in separated
-groups around the periphery of a sterile tissue within the cavity. (See
-figs. <a href="#FIG_187">187</a>, <a href="#FIG_187">188</a>.) Gonidia
-in the form of tetraspores are also developed in Rhabdonia.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_187" src="images/fig187.jpg" alt="" width="200" height="343" />
-    <p class="center">Fig. 187.<br /> Rhabdonia, branched portion<br /> of frond showing cystocarps.</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_188" src="images/fig188.jpg" alt="" width="250" height="320" />
-      <p class="center">Fig. 188.<br /> Section of cystocarp of<br /> rhabdonia, showing spores.</p>
-  </div>
-</div>
-
-<p><b>379. Fertilization of the higher red algæ.</b>—The process of
-fertilization in most of the red algæ is very complicated, chiefly
-because the fertilized egg-cell (procarp) does not develop the spores
-<span class="pagenum"><a name="Page_175" id="Page_175">[Pg 175]</a></span>
-directly, as in Nemalion, Lemanea, etc., but fuses directly, or by a
-short cell or long filament with one or more auxiliary cells before
-the sporocarp is finally formed. Examples are Rhabdonia, Polysiphonia,
-Callithamnion, Dudresnaya, etc. (<a href="#FIG_189">fig. 189</a>). The auxiliary cell
-then develops the sporocarp. See fig. 189 for conjugation of a filament from
-the fertilized procarp with an auxiliary cell.</p>
-
-<div class="figcenter">
-    <img  id="FIG_189" src="images/fig189.jpg" alt="" width="500" height="413" />
-   <div class="blockquot">
-    <p class="center">Fig. 189.</p>
-    <p>Dudresnaya purpurifera. <i>tr</i>, trichogyne, with spermatozoids attached;
-        <i>ct</i>, connecting-tube which grows out from below the base of the
-        trichogyne, and comes in contact with the fertile branches <i>f</i>, <i>f</i>;
-        <i>ct′</i>, young connecting-tube. (After Thuret and Bornet.)</p>
-   </div>
-</div>
-
-<p><b>380. Uses of the red algæ.</b>—Many species produce a great amount
-of gelatinous substance in their tissues, and several of these are used
-for food, for the manufacture of gelatines and agar-agar. Some of these
-are Gracilaria lichenoides and wrightii, the former species occurring
-along the coast of India and China. The plant is easily converted into
-gelatinous substance (agar-agar). Chondrus crispus, widely distributed
-in the northern Atlantic is known as “Irish” moss and is used for food
-and for certain medicinal purposes. Gigartina mamillosa in the Atlantic
-and Arctic oceans is similarly employed. The following orders are
-recognized in the red algæ:</p>
-
-<p><b>381. Order Bangiales.</b>—Example, Bangia atropurpurea (= Conferva
-atropurpurea) in springs and brooks in North America and Europe.
-Porphyra contains a number of species forming broad, thin, leaf-like
-purple sheets in the sea.</p>
-
-<p><b>382. Order Nemalionales.</b>—Including Lemanea, Batrachospermum,
-Nemalion, described above, and many others.</p>
-
-<p><b>383. Order Gigartinales.</b>—In this order occurs the common
-Iceland moss (Chondrus crispus) in the sea, and Rhabdonia and Gigartina
-mentioned above.</p>
-
-<p><b>384. Order Rhodomeniales.</b>—In this order occurs Gracilaria and
-Polysiphonia mentioned above, also the beautiful marine forms like
-Ceramium.</p>
-
-<p><b>385. Order Cryptonemiales.</b>—Examples are Dudresnaya, Melobesia,
-Corallina, etc., the last two genera include many species with a wide distribution.
-<span class="pagenum"><a name="Page_176" id="Page_176">[Pg 176]</a></span></p>
-
-<p class="center"><b>Class Charophyceæ,<br /> Order Charales.</b></p>
-
-<p><b>386.</b> The Charales are by some thought to represent a distinct
-class of algæ standing near the mosses, perhaps, because of the
-biciliate character of the spermatozoids. There is one family, the
-Characeæ. The plants occur in fresh and brackish water. Aside from the
-peculiarity of the reproductive organs they are remarkable for the
-large size of the cells of the internodes and of the “leaves,” and the
-protoplasm exhibits to a remarkable degree the phenomenon of “cyclosis”
-(<a href="#PARA_17">see paragraphs 17-20</a>). Three of the genera are found
-in North America (Chara, Nitella (<a href="#FIG_08">Fig. 8</a>) and Tolypella).</p>
-
-<div class="figcenter">
-    <img src="images/fig172a.jpg" alt="" width="500" height="443" />
-   <div class="blockquot">
-    <p class="center">Fig. 172<i>a</i>.</p>
-    <p>Reproductive organs of <i>Chara fragilis</i>. <i>A</i>, a central portion of a
-       leaf, <i>b</i>, with an antheridium, <i>a</i>, and a carpogonium, <i>s</i>, surrounded
-       by the spirally twisted enveloping cells; <i>c</i>, crown of five cells at
-       apex; β, sterile lateral leaflets; β′, large lateral leaflet near the
-       fruit; β″, bracteoles springing from the basal node of the reproductive
-       organs. <i>B</i>, a young antheridium, <i>a</i>, and a young carpogonium, <i>sk</i>;
-       <i>w</i>, nodal cell of leaf; <i>u</i>, intermediate cell between <i>w</i> and the
-       basal-node cell of the antheridium; <i>l</i>, cavity of the internode of
-       the leaf; <i>br</i>, cortical cells of the leaf. <i>A</i> × about 33; <i>B</i> × 240.
-       (After Sachs.)</p>
-   </div>
-</div>
-
-<p><b>386a.</b> The complicated structure of the sexual organs shows a
-higher state of organization than any of the other living algæ known.
-While the internodes in Nitella are composed of a single, stout cell,
-some times a foot or more in length, the nodes in all are composed of
-a group of smaller cells. From the lateral cells of this group lateral
-axes (sometimes called leaves) arise in whorls.</p>
-
-<p>In Nitella the internodes are naked, but in most species of Chara
-they are <i>corticated</i>, i.e., they are covered by a layer of numerous
-elongated cells which grow downward from the nodes at the base of the
-whorl of lateral shoots.</p>
-
-<p><b>386b.</b> The sexual organs are situated at the nodes of the whorled
-lateral shoots, and consist of antheridia and carpogonia. Most of the
-plants are monœcious, and both antheridia and carpogonia are often
-attached to the same node, the antheridium projecting downward while
-the carpogonium is more or less ascending. The sexual organs are
-visible to the unaided eye. The antheridium is a globose red body of
-an exceedingly complicated structure. The sperms are borne in several
-very long coiled slender threads which are divided transversely into
-numerous cells. The carpogonium is oval or elliptical in outline, the
-wall of which is composed of several closely coiled spiral threads
-enclosing the large egg.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_177" id="Page_177">[Pg 177]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XIX" id="CHAPTER_XIX">CHAPTER XIX.</a><br />
-<span class="h_subtitle">FUNGI: MUCOR AND SAPROLEGNIA.</span></h3>
-</div>
-
-<p class="center"><b>Mucor.</b></p>
-
-<p><b>387.</b> In the chapter on growth, and in our study of protoplasm,
-we have become familiar with the vegetative condition of mucor. We now
-wish to learn how the plant multiplies and reproduces itself. For this
-study we may take one of the mucors. Any one of several species will
-answer. This plant may be grown by placing partially decayed fruits,
-lemons, or oranges, from which the greater part of the juice has been
-removed, in a moist chamber; or often it occurs on animal excrement
-when placed under similar conditions. In growing the mucor in this way
-we are likely to obtain Mucor mucedo, or another plant sometimes known
-as Mucor stolonifer, or Rhizopus nigricans, which is illustrated in
-<a href="#FIG_191">fig. 191</a>. This latter one is sometimes very injurious to
-stored fruits or vegetables, especially sweet potatoes or rutabagas.
-<a href="#FIG_190">Fig. 190</a> is from a photograph of this fungus on a banana.</p>
-
-<p><b>388. Asexual reproduction.</b>—On the decaying surface of the
-vegetable matter where the mucor is growing there will be seen numerous
-small rounded bodies borne on very slender stalks. These heads contain
-the gonidia, and if we sow some of them in nutrient gelatine or agar
-in a Petrie dish the material can be taken out very readily for
-examination under the microscope. Or we may place glass slips close
-to the growing fungus in the moist chamber, so that the fungus will
-develop on them, though cultures in a nutrient medium are much better.
-Or we may take the material directly from the substance on which it is
-<span class="pagenum"><a name="Page_178" id="Page_178">[Pg 178]</a></span>
-growing. After mounting a small quantity of the mycelium bearing these
-heads, if we have been careful to take it where the heads appear
-quite young, it may be possible to study the early stages of their
-development. We shall probably note at once that the stalks or upright
-threads which support the heads are stouter than the threads of the
-mycelium.</p>
-
-<div class="figcenter">
-    <img  id="FIG_190" src="images/fig190.jpg" alt="" width="600" height="405" />
-    <p class="center">Fig. 190.<br /> Portion of banana with a mould
-               (Rhizopus nigricans) growing on one end.</p>
-</div>
-
-<p>These upright threads soon have formed near the end a cross wall which
-separates the protoplasm in the end from the remainder. This end cell
-now enlarges into a vesicle of considerable size, the head as it
-appears, but to which is applied the name of <i>sporangium</i> (sometimes
-called gonidangium), because it encloses the <i>gonidia</i>.</p>
-
-<p>At the same time that this end cell is enlarging the cross wall is
-arching up into the interior. This forms the <i>columella</i>. All the
-protoplasm in the sporangium now divides into gonidia. These are
-<span class="pagenum"><a name="Page_179" id="Page_179">[Pg 179]</a></span>
-small-rounded or oval bodies. The wall of the sporangium becomes
-dissolved, except a small collar around the stalk which remains
-attached below the columella (fig. 192). By this means the
-gonidia are freed. These gonidia germinate and produce the mycelium again.</p>
-
-<div class="figcenter">
-    <img  id="FIG_191" src="images/fig191.jpg" alt="" width="600" height="356" />
-    <p class="center">Fig. 191.<br /> Group of sporangia of a mucor (Rhizopus nigricans) showing<br />
-               rhizoids and the stolon extending from an older group.</p>
-</div>
-
-<p><b>389. Sexual stage.</b>—This stage is not so frequently found, but
-may sometimes be obtained by growing the fungus on bread.</p>
-
-<p>Conjugation takes place in this way. Two threads of the mycelium which
-lie near each other put out each a short branch which is clavate in
-form. The ends of these branches meet, and in each a septum is formed
-which cuts off a portion of the protoplasm in the end from that of the
-rest of the mycelium. The meeting walls of the branches now dissolve
-and the protoplasm of each gamete fuses into one mass. A thick wall
-is now formed around this mass, and the outer layer becomes rough and
-brown. This is the <i>zygote</i> or <i>zygospore</i>. The mycelium dies and
-it becomes free often with the suspensors, as the stalks of these sexual
-branches are called, still attached. This zygospore passes through
-a period of rest, when with the entrance of favorable conditions of
-growth it germinates, and usually produces directly a sporangium with
-gonidia. This completes the normal life cycle of the plant.</p>
-
-<p><b>390. Gemmæ.</b>—Gemmæ, as they are sometimes called, are often
-formed on the mycelium. A short cell with a stout wall is formed on the
-<span class="pagenum"><a name="Page_180" id="Page_180">[Pg 180]</a></span>
-side of a thread of the mycelium. In other cases large portions of the
-threads of the mycelium may separate into chains of cells. Both these
-kinds of cells are capable of growing and forming the mycelium again.
-They are sometimes called <i>chlamydospores</i>.</p>
-
-<div class="figcenter">
-    <img src="images/fig194.jpg" alt="" width="600" height="345" />
-   <div class="blockquot">
-    <p class="center">Fig. 194.</p>
-    <p>A mucor (Rhizopus nigricans); at left nearly mature sporangium with
-       columella showing within; in the middle is ruptured sporangium with
-       some of the gonidia clinging to the columella; at right two ruptured
-       sporangia with everted columella.</p>
-  </div>
-</div>
-
-<p><b>390</b><i>a</i>. The Mucorineæ according to their manner of zygospore
-formation are of two kinds: 1st, the <i>homothallic</i> (monœcious), in
-which all of the colonies of thalli developed from different spores
-are the same, and both gametes may be developed from the mycelium
-from a single spore, as in Sporodinia grandis, a mould common on old
-mushrooms; 2d, the <i>heterothallic</i> (diœcious), in which certain plants
-are of a male nature and small in comparison with those of perhaps a
-female nature which are larger or more vigorous. When grown separately
-each of these two kinds of thalli, or colonies of mycelium, produce
-their own kind but only sporangia. If the two kinds are brought
-together, however, branches from one conjugate with branches from
-the other and zygospores are produced, as in Rhizopus nigricans, the
-common bread or fruit mould. This is one reason why we rarely find this
-fungus forming zygospores. (See Blakeslee, Sexual Reproduction in the
-Mucorineæ, Proc. Am. Acad. Arts and Sci., <b>40</b>, 205-319, pl. 1-4, 1904.)
-<span class="pagenum"><a name="Page_181" id="Page_181">[Pg 181]</a></span></p>
-
-<p class="center"><b>Water Moulds</b><br /> (Saprolegnia).</p>
-
-<p><b>391.</b> The water moulds are very interesting plants to study
-because they are so easy to obtain, and it is so easy to observe a type
-of gonidium here to which we have referred in our studies of the algæ,
-the motile gonidium, or zoogonidium. (See appendix for directions for
-cultivating this mould.)</p>
-
-<p><b>392. Appearance of the saprolegnia.</b>—In the course of a few days
-we are quite certain to see in some of the cultures delicate whitish
-threads, radiating outward from the body of the fly in the water. A few
-threads should be examined from day to day to determine the stage of
-the fungus.</p>
-
-<div class="figcenter">
-    <img  id="FIG_195" src="images/fig195.jpg" alt="" width="600" height="386" />
-    <p class="center">Fig. 195.<br /> Sporangia of saprolegnia, one showing the escape of the zoogonidia.</p>
-</div>
-
-<p><b>393. Sporangia of saprolegnia.</b>—The sporangia of saprolegnia
-can be easily detected because they are much stouter than the ordinary
-threads of the mycelium. Some of the threads should be mounted in fresh
-water. Search for some of those which show that the protoplasm is
-divided up into a great number of small areas, as shown in <a href="#FIG_195">fig. 195</a>.
-With the low power we should watch some of the older appearing ones, and if
-after a few minutes they do not open, other preparations should be made.
-<span class="pagenum"><a name="Page_182" id="Page_182">[Pg 182]</a></span></p>
-
-<div class="figcenter">
-    <img  id="FIG_196" src="images/fig196.jpg" alt="" width="600" height="181" />
-    <p class="center">Fig. 196.<br /> Branch of saprolegnia showing oogonia with<br />
-                    oospores, eggs matured parthenogenetically.</p>
-</div>
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_197" src="images/fig197.jpg" alt="" width="250" height="412" />
-    <p class="center">Fig. 197.<br /> Downy mildew of grape (Plasmopora viticola),<br />
-         showing tuft of gonidiophores bearing gonidia,<br /> also intercellular mycelium.
-         (After Millardet.)</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_198" src="images/fig198.jpg" alt="" width="300" height="407" />
-      <p class="center">Fig. 198.<br /> Phytophthora infestans showing<br />
-                  peculiar branches; gonidia below.</p>
-  </div>
-</div>
-
-<p><b>394. Zoogonidia of saprolegnia.</b>—The sporangium opens at the
-end, and the zoogonidia swirl out and swim around for a short time,
-when they come to rest. With a good magnifying power the two cilia on
-<span class="pagenum"><a name="Page_183" id="Page_183">[Pg 183]</a></span>
-the end may be seen, or we may make them more distinct by treatment
-with Schultz’s solution, drawing some under the cover glass. The
-zoogonidium is oval and the cilia are at the pointed end. After they
-have been at rest for some time they often slip out of the thin wall,
-and swim again, this time with the two cilia on the side, and then the
-zoogonidium is this time more or less bean-shaped or reniform.</p>
-
-<div class="figcenter">
-    <img  id="FIG_199" src="images/fig199.jpg" alt="" width="600" height="174" />
-   <div class="blockquot">
-    <p class="center">Fig. 199.<br /> </p>
-      <p>Fertilization in saprolegnia, tube of antheridium carrying in the
-         nucleus of the sperm cell to the egg. In the right-hand figure a
-         smaller sperm nucleus is about to fuse with the nucleus of the egg.
-         (After Humphrey and Trow.)</p>
-  </div>
-</div>
-<div class="figcontainer">
-  <div class="figsub">
-    <p>&nbsp;</p>
-    <img  id="FIG_200" src="images/fig200.jpg" alt="" width="250" height="449" />
-    <p class="center">Fig. 200.<br /> Branching hypha of<br  /> Peronospora alsinearum.</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_201" src="images/fig201.jpg" alt="" width="250" height="466" />
-      <p class="center">Fig. 201.<br /> Branched hypha of downy mildew<br />
-            of grape showing peculiar branching<br /> (Plasmopara viticola).</p>
-  </div>
-</div>
-
-<p><span class="pagenum"><a name="Page_184" id="Page_184">[Pg 184]</a></span>
-<b>395. Sexual reproduction of saprolegnia.</b>—When such cultures are
-older we often see large rounded bodies either at the end of a thread,
-or of a branch, which contain several smaller rounded bodies as shown
-in <a href="#FIG_196">fig. 196</a>. These are the oogonia (unless the plant is attacked
-by a parasite), and the round bodies inside are the egg-cells, if before
-fertilization, or the eggs, if after this process has taken place.
-Sometimes the slender antheridium can be seen coiled partly around the
-oogonium, and one end entering to come in contact with the egg-cell.
-But in some species the antheridium is not present, and that is the
-case with the species <a href="#FIG_196">figured at 196</a>. In this case the
-eggs mature without fertilization. This maturity of the egg without fertilization
-is called <i>parthenogenesis</i>, which occurs in other plants also, but is
-a rather rare phenomenon.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_202" src="images/fig202.jpg" alt="" width="300" height="195" />
-    <p class="center">Fig. 202.<br /> Gonidiophores and gonidia of potato blight<br />
-          (Phytophthora infestans). <i>b</i>, an older stage<br />
-          showing how the branch enlarges where it<br />
-          grows beyond the older gonidium.<br /> (After de Bary.)</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_203" src="images/fig203.jpg" alt="" width="125" height="197" />
-      <p class="center">Fig. 203.<br /> Gonidia of potato blight forming<br /> zoogonidia.
-           (After de Bary.)</p>
-  </div>
-</div>
-
-<p><b>396.</b> In <a href="#FIG_199">fig. 199</a> is shown the oogonium and an
-antheridium, and the antheridium is carrying in the male nucleus to the egg-cell.
-Spermatozoids are not developed here, but a nucleus in the antheridium
-reaches the egg-cell. It sinks in the protoplasm of the egg, comes
-in contact with the nucleus of the egg, and fuses with it. Thus
-fertilization is accomplished.
-<span class="pagenum"><a name="Page_185" id="Page_185">[Pg 185]</a></span></p>
-
-<p class="center"><b>Downy Mildews.</b></p>
-
-<p><b>397.</b> The downy mildews make up a group of plants which are
-closely related to the water moulds, but they are parasitic on land
-plants, and some species produce very serious diseases. The mycelium
-grows between the cells of the leaves, stems, etc., of their hosts,
-and sends haustoria into the cells to take up nutriment. Gonidia are
-formed on threads which grow through the stomates to the outside and
-branch as shown in <a href="#FIG_198">figs. 198</a>-<a href="#FIG_201">201</a>.
-The gonidia are borne on the tips of the branches. The kind of branching bears some
-relation to the different genera. <a href="#FIG_200">Fig. 200</a> is from Peronospora
-alsinearum on leaves of cerastium; <a href="#FIG_197">figs. 197</a> and <a href="#FIG_199">199</a> are Plasmopara
-viticola, the grape mildew, while <a href="#FIG_198">figs. 198</a> and <a href="#FIG_202">202</a>
-are from Phytophthora infestans which causes a disease known as potato
-blight. The gonidia of peronospora germinate by a germ tube, those of
-plasmopara first form zoogonidia, while in phytophthora the gonidium
-may either germinate forming a thread, or each gonidium may first form
-several zoogonidia, as shown in <a href="#FIG_203">fig. 203</a>.</p>
-
-<div class="figcenter">
-    <img  id="FIG_204" src="images/fig204.jpg" alt="" width="600" height="206" />
-   <div class="blockquot">
-    <p class="center">Fig. 204.<br /> </p>
-      <p>Fertilization in Peronospora alsinearum; tube from antheridium carrying
-         in the sperm nucleus in figure at the left, female nucleus near; fusion
-         of the two nuclei shown in the two other figures. (After Berlese.)</p>
-  </div>
-</div>
-<div class="figcenter">
-    <img src="images/fig205.jpg" alt="" width="400" height="339" />
-    <p class="center">Fig. 205.<br /> Ripe oospore of Peronospora alsinearum.</p>
-</div>
-
-<p><b>398.</b> In sexual reproduction oogonia and antheridia are developed
-on the mycelium within the tissues. <a href="#FIG_204">Fig. 204</a> represents the antheridium
-<span class="pagenum"><a name="Page_186" id="Page_186">[Pg 186]</a></span>
-entering the oogonium, and the male nucleus fusing with the female
-nucleus in fertilization. The sexual organs of Phytophthora infestans
-are not sufficiently known.</p>
-
-<p><b>399.</b> Mucor, saprolegnia, peronospora, and their relatives
-have few or no septa in the mycelium. In this respect they resemble
-certain of the algæ like vaucheria, but they lack chlorophyll. They are
-sometimes called the alga-like fungi and belong to a large group called
-<i>Phycomycetes</i>.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_187" id="Page_187">[Pg 187]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XX" id="CHAPTER_XX">CHAPTER XX.</a><br />
-<span class="h_subtitle">FUNGI CONTINUED.</span></h3>
-</div>
-
-<p class="center"><b>“Rusts”</b> (Uredineæ).</p>
-
-<p><b>400.</b> The fungi known as “rusts” are very important ones to
-study, since all the species are parasitic, and many produce serious
-injuries to crops.</p>
-
-<div class="figcontainer">
-  <a id="FIG_206-210" name="FIG_206-210">&nbsp;</a>
-  <div class="figsub">
-    <img src="images/fig206.jpg" alt="" width="100" height="215" />
-    <p class="center">Fig. 206.<br /> Wheat leaf<br /> with red-rust,<br /> natural size.</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig207.jpg" alt="" width="100" height="224" />
-      <p class="center">Fig. 207.<br /> Portion of<br /> leaf enlarged<br /> to show sori.</p>
-  </div>
-  <div class="figsub">
-      <img src="images/fig208.jpg" alt="" width="100" height="230" />
-      <p class="center">Fig. 208.<br /> Natural size.</p>
-  </div>
-  <div class="figsub">
-      <img src="images/fig209.jpg" alt="" width="100" height="263" />
-      <p class="center">Fig. 209.<br /> Enlarged.</p>
-  </div>
-  <div class="figsub">
-      <img src="images/fig210.jpg" alt="" width="100" height="219" />
-      <p class="center">Fig. 210.<br /> Single sorus.</p>
-  </div>
-    <p class="center">Figs. 206, 207.—Puccinia graminis, red-rust stage (uredo stage).&emsp;&nbsp;</p>
-    <p class="center space-below2">Figs. 208-210.—Black rust of wheat, showing sori of teleutospores.</p>
-</div>
-
-<p><b>401. Wheat rust (Puccinia graminis).</b>—The wheat rust is one of
-the best known of these fungi, since a great deal of study has been
-given to it. One form of the plant occurs in long reddish-brown or
-reddish pustules, and is known as the “red-rust” (<a href="#FIG_206-210">figs. 206, 207</a>).
-Another form occurs in elongated black pustules, and this form is the
-<span class="pagenum"><a name="Page_188" id="Page_188">[Pg 188]</a></span>
-one known as the “black rust” (<a href="#FIG_206-210">figs. 208</a>-<a href="#FIG_211">211</a>).
-These two forms occur on the stems, blades, etc., of the wheat, also on
-oats, rye, and some of the grasses.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_211" src="images/fig211.jpg" alt="" width="210" height="401" />
-    <p class="center">Fig. 211.<br /> Head of wheat showing<br /> black rust spots on<br /> the chaff and awns.</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_212" src="images/fig212.jpg" alt="" width="150" height="253" />
-      <p class="center">Fig. 212.<br /> Teleutospores of wheat<br /> rust, showing two cells<br /> and the pedicel.</p>
-      <img  id="FIG_213" src="images/fig213.jpg" alt="" width="150" height="93" />
-      <p class="center">Fig. 213.<br /> Uredospores of wheat<br /> rust, one showing<br /> remnants of the<br /> pedicel.</p>
-  </div>
-</div>
-
-<p><b>402. Teleutospores of the black rust form.</b>—If we scrape off
-some portion of one of the black pustules (sori), tease it out in water
-on a slide, and examine with a microscope, we see numerous gonidia,
-composed of two cells, and having thick, brownish walls as shown
-in <a href="#FIG_212">fig. 212</a>. Usually there is a slender brownish stalk
-on one end. These gonidia are called <i>teleutospores</i>. They are somewhat oblong
-or elliptical, a little constricted where the septum separates the two
-cells, and the end cell varies from ovate to rounded. The mycelium of
-<span class="pagenum"><a name="Page_189" id="Page_189">[Pg 189]</a></span>
-the fungus courses between the cells, just as is found in the case of
-the carnation rust, which belongs to the same family (<a href="#PARA_186">see Parag. 186</a>).</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_214" src="images/fig214.jpg" alt="" width="200" height="485" />
-    <p class="center">Fig. 214.<br /> Barberry leaf with<br /> two diseased spots,<br /> natural size.</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_215" src="images/fig215.jpg" alt="" width="100" height="409" />
-      <p class="center">Fig. 215.<br /> Single spot<br /> showing<br /> cluster-cups<br /> enlarged.</p>
-  </div>
-  <div class="figsub">
-      <img  id="FIG_216" src="images/fig216.jpg" alt="" width="110" height="403" />
-      <p class="center">Fig. 216.<br /> Two cluster-cups<br /> more
-                       enlarged,<br /> showing<br /> split margin.</p>
-  </div>
-      <p class="center">Figs. 214-216.—Cluster-cup stage of wheat rust.</p>
-</div>
-
-<p><b>403. Uredospores of the red-rust form.</b>—If we make a similar
-preparation from the pustules of the red-rust form we see that instead
-of two-celled gonidia they are one-celled. The walls are thinner
-and not so dark in color, and they are covered with minute spines.
-They have also short stalks, but these fall away very easily. These
-one-celled gonidia of the red-rust form are called “uredospores.” The
-uredospores and teleutospores are sometimes found in the same pustule.</p>
-
-<p>It was once supposed that these two kinds of gonidia belonged to
-different plants, but now it is known that the one-celled form, the
-uredospores, is a form developed earlier in the season than the teleutospores.</p>
-
-<p><b>404. Cluster-cup form on the barberry.</b>—On the barberry is found
-still another form of the wheat rust, the “<i>cluster-cup</i>” stage. The
-pustules on the under side of the barberry leaf are cup-shaped, the
-cups being partly sunk in the tissue of the leaf, while the rim is more
-or less curved backward against the leaf, and split at several places.
-These cups occur in clusters on the affected spots of the barberry leaf
-as shown in <a href="#FIG_215">fig. 215</a>. Within the cups numbers of one-celled
-gonidia (orange in color, called æcidiospores) are borne in chains from short
-branches of the mycelium, which fill the base of the cup. In fact the
-<span class="pagenum"><a name="Page_190" id="Page_190">[Pg 190]</a></span>
-wall of the cup (peridium) is formed of similar rows of cells, which,
-instead of separating into gonidia, remain united to form a wall. These
-cups are usually borne on the under side of the leaf.</p>
-
-<p><b>405. Spermagonia.</b>—Upon the upper side of the leaves in the
-same spot occur small, orange-colored pustules which are flask-shaped.
-They bear inside, minute, rod-like bodies on the ends of slender
-threads, which ooze out on the surface of the leaf. These flask-shaped
-pustules are called <i>spermagonia</i>, and the minute bodies within them
-<i>spermatia</i>, since they were once supposed to be the male element of
-the fungus. Their function is not known. They appear in the spots at an
-earlier time than the cluster-cups.</p>
-
-<div class="figcenter">
-    <img src="images/fig217.jpg" alt="" width="600" height="397" />
-    <p class="center">Fig. 217.<br /> Section of an æcidium (cluster-cup)
-                  from barberry leaf.<br /> (After Marshall-Ward.)</p>
-</div>
-
-<p><b>406. How the cluster-cup stage was found to be a part of the wheat
-rust.</b>—The cluster-cup stage of the wheat rust was once supposed
-also to be a different plant, and the genus was called <i>æcidium</i>.
-The occurrence of wheat rust in great abundance on the leeward side
-of affected barberry bushes in England suggested to the farmers that
-wheat rust was caused by barberry rust. It was later found that the
-æcidiospores of the barberry, when sown on wheat, germinate and the
-thread of mycelium enters the tissues of the wheat, forming mycelium
-between the cells. This mycelium then bears the uredospores, and later
-the teleutospores.
-<span class="pagenum"><a name="Page_191" id="Page_191">[Pg 191]</a></span></p>
-
-<p><b>407. Uredospores can produce successive crops of
-uredospores.</b>—The uredospores are carried by the wind to other
-wheat or grass plants, germinate, form mycelium in the tissues,
-and later the pustules with a second crop of uredospores. Several
-successive crops of uredospores may be developed in one season, so
-this is the form in which the fungus is greatly multiplied and widely
-distributed.</p>
-
-<div class="figcenter">
-    <img src="images/fig218.jpg" alt="" width="600" height="269" />
-    <p class="center">Fig. 218.<br /> Section through leaf of barberry at point affected with the cluster-cup<br />
-                stage of the wheat rust; spermagonia above, æcidia below.<br />
-                (After Marshall-Ward.)</p>
-</div>
-<div class="figcenter">
-    <img src="images/fig219.jpg" alt="" width="600" height="391" />
-    <p class="center">Fig. 219.<br /> <i>A</i>, section through sorus of black rust of wheat, showing teleutospores.<br />
-               <i>B</i>, mycelium bearing both teleutospores and uredospores.<br /> (After de Bary.)</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_192" id="Page_192">[Pg 192]</a></span></p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img src="images/fig220.jpg" alt="" width="300" height="449" />
-    <p class="center">Fig. 220.<br /> Germinating uredospore of wheat rust.<br /> (After Marshall-Ward.)</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig221.jpg" alt="" width="230" height="443" />
-      <p class="center">Fig. 221.<br /> Germ tube entering the<br /> leaf through a stoma.</p>
-  </div>
-</div>
-
-<p><b>407a. Teleutospores the last stage of the fungus in the
-season.</b>—The teleutospores are developed late in the season, or
-late in the development of the host plant (in this case the wheat
-is the host). They then rest during the winter. In the spring under
-favorable conditions each cell of the teleutospore germinates,
-producing a short mycelium called a <i>promycelium</i>, as shown
-in figs. <a href="#FIG_222">222</a>, <a href="#FIG_223">223</a>.
-This promycelium is usually divided into four cells. From
-each cell a short, pointed process is formed called a “<i>sterigma</i>.”
-Through this the protoplasm moves and forms a small gonidium on the
-end, sometimes called a <i>sporidium</i>.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_222" src="images/fig222.jpg" alt="" width="150" height="347" />
-    <p class="center">Fig. 222.<br /> Teleutospore<br /> germinating,<br /> forming<br /> promycelium.</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_223" src="images/fig223.jpg" alt="" width="200" height="290" />
-      <p class="center">Fig. 223.<br /> Promycelium<br /> of germinating<br /> teleutospore,<br /> forming sporidia.</p>
-  </div>
-  <div class="figsub">
-      <img  id="FIG_224" src="images/fig224.jpg" alt="" width="200" height="287" />
-      <p class="center">Fig. 224.<br /> Germinating<br /> sporidia<br />
-             entering<br /> leaf of<br /> barberry by<br /> mycelium.</p>
-  </div>
-      <p class="center">Figs. 222-224.—Puccinia graminis (wheat rust).<br /> (After Marshall-Ward.)</p>
-</div>
-
-<p><b>408. How the fungus gets from the wheat back to the
-barberry.</b>—If these sporidia from the teleutospores are carried by
-<span class="pagenum"><a name="Page_193" id="Page_193">[Pg 193]</a></span>
-the wind so that they lodge on
-the leaves of the barberry, they germinate and produce the cluster-cup again.
-The plant has thus a very complex life history. Because of the presence of
-several different forms in the life cyle, it is called a <i>polymorphic</i> fungus.</p>
-
-<p>The presence of the barberry does not seem necessary in all cases for the
-development of the fungus from one year to another.</p>
-
-<p><b>409. Synopsis of life history of wheat rust.</b></p>
-
-<p><i>Cluster-cup stage on leaf of barberry.</i></p>
-
-<div class="blockquot">
-<p class="neg-indent">Mycelium between cells of leaf in affected spots.</p>
-
-<p class="neg-indent">Spermagonia (sing. spermagonium), small
-flask-shaped bodies sunk in upper side of leaf; contain “spermatia.”</p>
-
-<p class="neg-indent">Æcidia (sing. æcidium), cup-shaped bodies in
-under side of leaf.</p>
-
-<p class="neg-indent">Wall or peridium, made up of outer layer of
-fungus threads which are divided into short cells but remain united.</p>
-
-<p class="neg-indent">At maturity bursts through epidermis of leaf;
-margin of cup curves outward and downward toward surface of leaf.</p>
-
-<p class="neg-indent">Central threads of the bundle are closely packed,
-but free. Threads divide into short angular cells which separate and
-become æcidiospores, with orange-colored content.</p>
-
-<p class="neg-indent">Æcidiospores carried by the wind to wheat, oats,
-grasses, etc. Here they germinate, mycelium enters at stomate, and
-forms mycelium between cells of the host.</p>
-</div>
-
-<p><i>Uredo stage (red-rust) on wheat, oats, grasses, etc.</i></p>
-
-<div class="blockquot">
-<p class="neg-indent">Mycelium between cells of host.</p>
-
-<p class="neg-indent">Bears uredospores (1-celled) in masses under
-epidermis, which is later ruptured and uredospores set free.</p>
-
-<p class="neg-indent">Uredospores carried by wind to other individual
-hosts, and new crops of uredospores formed.</p>
-</div>
-
-<p><i>Teleutospore stage (black rust), also on wheat, etc.</i></p>
-
-<div class="blockquot">
-<p class="neg-indent">Mycelium between cells of host.</p>
-
-<p class="neg-indent">Bears teleutospores (2-celled) in masses (sori)
-under epidermis, which is later ruptured.</p>
-
-<p class="neg-indent">Teleutospores rest during winter. In spring each
-<span class="pagenum"><a name="Page_194" id="Page_194">[Pg 194]</a></span>
-cell germinates and produces a promycelium, a short thread, divided
-into four cells.</p>
-
-<p class="neg-indent">Promycelium bears four sterigmata and four
-gonidia (or sporidia), which in favorable conditions pass back to
-the barberry, germinate, the tube enters between cells into the
-intercellular spaces of the host to produce the cluster-cup again, and
-thus the life cycle is completed.</p>
-</div>
-
-<p><b>410. Other examples of the rusts.</b>—Some of the rusts do great
-injury to fruit trees and also to forest trees. The “cedar apples” are
-abnormal growths on the leaves and twigs of the cedar stimulated by the
-presence of the mycelium of a rust known as Gymnosporangium macropus.
-The teleutospores are two-celled and are formed in the tissue of the
-“cedar apple” or gall. The teleutosori are situated at quite regular
-intervals over the surface of the gall at small circular depressions,
-and can be easily seen in late autumn and during the winter. A quantity
-of gelatine is developed along with the teleutospores. In early spring
-with the warm spring rains the gelatinous substance accompanying the
-teleutospores swells greatly, and causes the teleutospores to ooze
-out in long, dull, orange-colored strings, which taper gradually to
-a slender point and bristle all over the “cedar apple.” Here the
-teleutospores germinate and produce the sporidia. The sporidia are
-carried to apple trees where they infect leaves and even the fruit,
-producing here the cluster-cups. There are no uredospores.</p>
-
-<p>G. globosum is another species forming cedar apples, but the gelatinous
-strings of teleutospores are short and clavate, and the cluster-cups
-are formed on hawthorns. G. nidusavis forms “witches brooms” or “birds
-nests” in the branches of the cedar. The mycelium in the branches
-stimulates them to profuse branching so that numerous small branches
-are developed close together. The teleutosori form small pustules
-scattered over the branches. G. clavipes affects the branches of cedar
-only slightly deforming them or not at all, and the cluster-cups are
-formed on fruits, twigs, and leaves of the hawthorns or quinces, the
-cluster-cups being long, tubular, and orange in color.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_195" id="Page_195">[Pg 195]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XXI" id="CHAPTER_XXI">CHAPTER XXI.</a><br />
-<span class="h_subtitle">THE HIGHER FUNGI.</span></h3>
-</div>
-
-<p><b>411. The series of the higher fungi.</b>—Of these there are two
-large series. One of these is represented by the sac fungi, and the
-other by the mushrooms, a good example of which is the common mushroom
-(Agaricus campestris).</p>
-
-<p class="center"><b>Sac Fungi</b> (Ascomycetes).</p>
-
-<p><b>412. The sac fungi</b> may be represented by the “powdery mildews”;
-examples, uncinula, microsphæra, podosphæra, etc. <a href="#FIG_225">Fig. 225</a>
-is from a photograph of two willow leaves affected by one of these mildews. The
-leaves are first partly covered with a whitish growth of mycelium, and
-numerous chains of colorless gonidia are borne on short erect threads.
-The masses of gonidia give the leaf a powdery appearance. The mycelium
-lives on the outer surface of the leaf, but sends short haustoria into
-the epidermal cells.</p>
-
-<p><b>413. Fruit bodies of the willow mildew.</b>—On this same mycelium
-there appear later numerous black specks scattered over the affected
-places of the leaf. These are the fruit bodies (<i>perithecia</i>). If
-we scrape some of these from the leaf, and mount them in water for
-microscopic examination, we shall be able to see their structure.
-Examining these first with a low power of the microscope, each one is
-seen to be a rounded body, from which radiate numerous filaments, the
-<i>appendages</i>. Each one of these appendages is coiled at the end into
-the form of a little hook. Because of these hooked appendages this
-genus is called <i>uncinula</i>. This rounded body is the <i>perithecium</i>.
-<span class="pagenum"><a name="Page_196" id="Page_196">[Pg 196]</a></span></p>
-
-<div class="figcenter">
-    <img  id="FIG_225" src="images/fig225.jpg" alt="" width="500" height="528" />
-    <p class="center">Fig. 225.<br /> Leaves of willow showing willow mildew. The black dots are the<br />
-           fruit bodies (perithecia) seated on the white mycelium.</p>
-</div>
-
-<p><b>414. Asci and ascospores.</b>—While we are looking at a few of
-these through the microscope with the low power, we should press on the
-cover glass with a needle until we see a few of the perithecia rupture.
-If this is done carefully we see several small ovate sacs issue, each
-containing a number of spores, as shown in <a href="#FIG_227">fig. 227</a>.
-Such a sac is an <i>ascus</i>, and the spores are <i>ascospores</i>.
-<span class="pagenum"><a name="Page_197" id="Page_197">[Pg 197]</a></span></p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_226" src="images/fig226.jpg" alt="" width="100" height="232" />
-    <p class="center">Fig. 226.<br /> Willow mildew;<br /> bit of mycelium<br /> with erect<br />
-             conidiophores,<br /> bearing chain<br /> of gonidia;<br />
-             gonidium<br /> at left<br /> germinating.</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_227" src="images/fig227.jpg" alt="" width="250" height="281" />
-      <p class="center">Fig. 227.<br /> Fruit of willow mildew,<br /> showing hooked
-                    appendages.<br /> Genus uncinula.</p>
-  </div>
-  <div class="figsub">
-      <img  id="FIG_228" src="images/fig228.jpg" alt="" width="100" height="219" />
-      <p class="center">Fig. 228.<br /> Fruit body<br /> of another<br /> mildew with<br /> dichotomous<br />
-                   appendages.<br /> Genus microsphæra.</p>
-  </div>
-      <p class="center">Figs. 227-228.—Perithecia (perithecium) of two powdery mildews, showing<br  />
-               escape of asci containing the spores from the crushed fruit bodies.</p>
-</div>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img src="images/fig229.jpg" alt="" width="125" height="285" />
-    <p class="center">Fig. 229.<br /> Contact of<br /> antheridium<br /> and carpogonium<br />
-           (carpogonium<br /> the larger cell);<br /> beginning of<br /> fertilization.</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig230.jpg" alt="" width="125" height="285" />
-      <p class="center">Fig. 230.<br /> Disappearance of<br /> contact walls of<br />
-            antheridium and<br /> carpogonium,<br /> and fusion of<br /> the two nuclei.</p>
-  </div>
-  <div class="figsub">
-      <img src="images/fig231.jpg" alt="" width="250" height="291" />
-      <p class="center">Fig. 231.<br /> Fertilized egg surrounded<br /> by the enveloping threads<br />
-             which grow up around it.</p>
-  </div>
-      <p class="center">Figs. 229-231.—Fertilization in sphærotheca; one of the powdery
-                  mildews.<br /> (After Harper.)</p>
-</div>
-
-<p><b>415. Number of spores in an ascus.</b>—The ascus is the most
-important character showing the general relationship of the members of
-the sac fungi. While many of the powdery mildews have a variable number
-of spores in an ascus, a large majority of the ascomycetes have just
-<span class="pagenum"><a name="Page_198" id="Page_198">[Pg 198]</a></span>
-8 spores in an ascus, while some have 4, others 16, and some an
-indefinite number. The asci in a perithecium are more variable. In some
-ascomycetes there is no perithecium.</p>
-
-<div class="figcenter">
-    <img  id="FIG_231A" src="images/fig231a.jpg" alt="" width="400" height="502" />
-    <p class="center">Fig. 231<i>a</i>.<br /> Edible Morel. Morchella esculenta.<br />
-                 The asci, forming hymenium, cover the pitted surface.</p>
-</div>
-
-<p><b>416. The black fungi.</b>—These are very common on dead logs,
-branches, leaves, etc., and may be collected in the woods at almost any
-season. The perithecia are often numerous, scattered or densely crowded
-<span class="pagenum"><a name="Page_199" id="Page_199">[Pg 199]</a></span>
-as in Rosellinia. Sometimes they are united to form a crust which is
-partly formed from sterile elements as in Hypoxylon, or they form black
-clavate or branched bodies as in Xylaria. The black knot of the plum
-and cherry is also an example.</p>
-
-<p>The lichens are mostly ascomycetes like the black fungi or cup fungi,
-while a few are basidiomycetes.</p>
-
-<p><b>417. The morels (Morchella).</b>—There are several species of
-morels which are common in early spring on damp ground. Either one of
-the species is suitable for use if it is desired to include this in
-the study. <a href="#FIG_231A">Fig. 231a</a> illustrates the Morchella esculenta.
-The stem is cylindrical and stout. The fruiting portion forms the “head,” and it
-is deeply pitted. The entire pitted surface is covered by the asci,
-which are cylindrical and eight spored. A thin section may be made of
-a portion for study, or a small piece may be crushed under the cover
-glass.</p>
-
-<p><b>418. The cup fungi.</b>—These fungi are common on damp ground or
-on rotting logs in the summer. They may be preserved in 70 per cent
-alcohol for study. Many of them are shaped like broad open cups or
-saucers. The inner surface of the cup is the fruiting surface, and is
-covered with the cylindrical asci, which stand side by side. A bit of
-the cup may be sectioned or crushed under a cover glass for study.</p>
-
-<p class="center"><b>Mushrooms</b><br /> (Basidiomycetes).</p>
-
-<p><b>419. The large group of fungi</b> to which the mushroom belongs is
-called the basidiomycetes because in all of them a structure resembling
-a club, or basidium, is present, and bears a limited number of spores,
-usually four, though in some genera the number is variable. Some place
-the rusts (Uredineæ) in the same series (basidium series), because of
-the short promycelium and four sporidia developed from each cell of the
-teleutospore.</p>
-
-<p><b>420. The gill-bearing fungi (Agaricaceæ).</b>—A good example for
-this study is the common mushroom (Agaricus campestris).</p>
-
-<p>This occurs from July to November in lawns and grassy fields. The
-plant is somewhat umbrella-shaped, as shown in <a href="#FIG_232">fig. 232</a>,
-and possesses a cylindrical stem attached to the under side of the convex cap
-or pileus. On the under side of the pileus are thin radiating plates,
-shaped somewhat like a knife blade. These are the gills, or lamellæ,
-and toward the stem they are rounded on the lower angle and are not
-attached to the stem. The longer ones extend from near the stem to the
-margin of the pileus, and the V-shaped spaces between them are occupied
-by successively shorter ones. Around the stem a little below the gills
-is a collar, termed the ring or annulus.
-<span class="pagenum"><a name="Page_200" id="Page_200">[Pg 200]</a></span></p>
-
-<div class="figcenter">
-    <img  id="FIG_232" src="images/fig232.jpg" alt="" width="600" height="360" />
-    <p class="center">Fig. 232.<br /> Agaricus campestris. View of under side showing stem,<br />
-             annulus, gills, and margin of pileus.</p>
-</div>
-<div class="figcenter">
-    <img src="images/fig233.jpg" alt="" width="450" height="452" />
-    <p class="center">Fig. 233.<br /> Agaricus campestris.<br /> Longitudinal section through stem and pileus.<br />
-            <i>a</i>, pileus; <i>b</i>, portion of veil on margin of pileus;<br />
-            <i>c</i>, gill; <i>d</i>, fragment of annulus; <i>e</i>, stipe.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_201" id="Page_201">[Pg 201]</a></span></p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_234" src="images/fig234.jpg" alt="" width="300" height="307" />
-    <p class="center">Fig. 234.<br /> Portion of section of lamella of Agaricus campestris.<br />
-           <i>tr</i>, trama; <i>sh</i>, subhymenium; <i>b</i>, basidium;<br />
-           <i>st</i>, sterigma (<i>pl.</i> sterigmata); <i>g</i>, basidiospore.</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_235" src="images/fig235.jpg" alt="" width="150" height="301" />
-      <p class="center">Fig. 235.<br /> Portion of hymenium<br /> of Coprinus micaceus,<br />
-                 showing large cystidium<br /> in the hymenium.</p>
-  </div>
-</div>
-
-<p><b>421. Fruiting surface of the mushroom.</b>—The surface of these
-gills is the fruiting surface of the mushroom, and bears the gonidia
-of the mushroom, which are dark purplish brown when mature, and thus
-the gills when old are dark in color. If we make a thin section across
-a few of the gills, we see that each side of the gill is covered with
-closely crowded club-shaped bodies, each one of which is a <i>basidium</i>.
-In <a href="#FIG_234">fig. 234</a> a few of these are enlarged, so that the
-structure of the gill can be seen. Each basidium of the common mushroom has two
-spinous processes at the free end. Each one is a <i>sterig′ma</i> (plural
-<i>sterig′mata</i>), and bears a gonidium. In a majority of the members of
-the mushroom family each basidium bears four spores. When mature these
-spores easily fall away, and a mass of them gives a purplish-black
-color to objects on which they fall, so that a print of the under
-surface of the cap showing the arrangement of the gills can be obtained
-by cutting off the stem, and placing the pileus on white paper for a time.
-<span class="pagenum"><a name="Page_202" id="Page_202">[Pg 202]</a></span></p>
-
-<div class="figcenter">
-    <img  id="FIG_236" src="images/fig236.jpg" alt="" width="600" height="327" />
-    <p class="center">Fig. 236.<br /> Agaricus campestris.<br />
-       Soil washed from “spawn” and “buttons,” showing the minute<br />
-       young “buttons” attached to the strands of mycelium.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_203" id="Page_203">[Pg 203]</a></span>
-<b>422. How the mushroom is formed.</b>—The mycelium of the mushroom
-lives in the ground, and grows here for several months or even years,
-and at the proper seasons develops the mature mushroom plant. The
-mycelium lives on decaying organic matter, and a large number of the
-threads grow closely together forming strands, or cords, of mycelium,
-which are quite prominent if they are uncovered by removing the soil,
-as shown in <a href="#FIG_236">fig. 236</a>.</p>
-
-<div class="figcenter">
-    <img  id="FIG_237" src="images/fig237.jpg" alt="" width="600" height="313" />
-    <p class="center">Fig. 237.<br /> Agaricus campestris; sections of “buttons” of different<br />
-             sizes, showing formation of gills and veil covering them.</p>
-</div>
-
-<p><b>423.</b> From these strands the buttons arise by numerous threads
-growing side by side in a vertical direction, each thread growing
-independently at the end, but all lying very closely side by side. When
-the buttons are quite small the gills begin to form on the under margin
-of the knob. They are formed by certain of the threads growing downward
-in radiating ridges, just as many of these ridges being started as
-there are to be gills formed. At the same time, threads of the stem
-grow upward to meet those at the margin of the button in such a manner
-that they cover up the forming gills, and thus enclose the gills in a
-minute cavity. Sections of buttons at different ages will show this, as
-is seen in <a href="#FIG_237">fig. 237</a>. This curtain of mycelium which is thus
-stretched across the gill cavity is the veil. As the cap expands more and more
-this is stretched into a thin and delicate texture as shown in <a href="#FIG_238">fig. 238</a>.
-Finally, as shown in <a href="#FIG_239">fig. 239</a>, this veil is ruptured by the expansion
-of the pileus, and it either clings to the stem as a collar, or a
-portion of it remains clinging to the margin of the cap. When the
-buttons are very young the gills are white, but they soon become pink
-in color, and very soon after the veil breaks the spores mature, and
-then the gills are dark brown.
-<span class="pagenum"><a name="Page_204" id="Page_204">[Pg 204]</a></span></p>
-
-<div class="figcenter">
-    <img  id="FIG_238" src="images/fig238.jpg" alt="" width="600" height="406" />
-    <p class="center">Fig. 238.<br /> Agaricus campestris; nearly mature plants, showing<br />
-             veil still stretched across the gill cavity.</p>
-</div>
-<div class="figcenter">
-    <img  id="FIG_239" src="images/fig239.jpg" alt="" width="600" height="363" />
-    <p class="center">Fig. 239.<br /> Agaricus campestris; under view of two plants just<br />
-          after rupture of veil, fragments of the latter<br />
-          clinging both to margin of pileus and to stem.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_205" id="Page_205">[Pg 205]</a></span></p>
-
-<div class="figcenter">
-    <img src="images/fig240.jpg" alt="" width="400" height="440" />
-    <p class="center">Fig. 240.<br /> Agaricus campestris; plant in natural position just after<br />
-              rupture of veil, showing tendency to double annulus on the<br />
-               stem. Portions of the veil also dripping from margin of pileus.</p>
-</div>
-<div class="figcenter">
-    <img src="images/fig241.jpg" alt="" width="400" height="385" />
-    <p class="center">Fig. 241.<br /> Agaricus campestris; spore print.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_206" id="Page_206">[Pg 206]</a></span></p>
-
-<div class="figcenter">
-    <img src="images/fig242.jpg" alt="" width="600" height="364" />
-    <p class="center">Fig. 242.<br /> “Fairy ring” formed by Agaricus arvensis (photograph by B. M. Duggar).<br />
-              The mycelium spreads centrifugally each year, consuming the available<br />
-               food, and thus the plants appear in a ring.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_207" id="Page_207">[Pg 207]</a></span></p>
-
-<div class="figcenter">
-    <img  id="FIG_243" src="images/fig243.jpg" alt="" width="250" height="461" />
-    <p class="center">Fig. 243.<br /> Amanita phalloides; white form,<br />
-              showing pileus, stipe, annulus,<br /> and volva.</p>
-</div>
-
-<p><b>424. Beware of the poisonous mushroom.</b>—The number of species
-of mushrooms, or toadstools as they are often called, is very great.
-<span class="pagenum"><a name="Page_208" id="Page_208">[Pg 208]</a></span>
-Besides the common mushroom (Agaricus campestris) there are a large
-number of other edible species. But one should be very familiar with
-any species which is gathered for food, unless collected by one who
-certainly knows what the plant is, since carelessness in this respect
-sometimes results fatally from eating poisonous ones.</p>
-
-<div class="figcenter">
-    <img src="images/fig244.jpg" alt="" width="600" height="312" />
-    <p class="center">Fig. 244.<br /> Amanita phalloides;<br />
-             plant turned to one side, after having been placed in a<br />
-             horizontal position, by the directive force of gravity.</p>
-</div>
-
-<p><b>425.</b> A plant very similar in structure to the Agaricus
-campestris is the Lepiota naucina, but the spores are white, and thus
-the gills are white, except that in age they become a dirty pink. This
-plant occurs in grassy fields and lawns often along with the common
-mushroom. Great care should be exercised in collecting and noting the
-characters of these plants, for a very deadly poisonous species, the
-deadly amanita (Amanita phalloides) is perfectly white, has white
-spores, a ring, and grows usually in wooded places, but also sometimes
-occurs in the margins of lawns. In this plant the base of the stem is
-seated in a cup-shaped structure, the <i>volva</i>, shown in <a href="#FIG_243">fig. 243</a>.
-One should dig up the stem carefully so as not to tear off this volva if
-it is present, for with the absence of this structure the plant might
-easily be mistaken for the lepiota, and serious consequences would result.
-<span class="pagenum"><a name="Page_209" id="Page_209">[Pg 209]</a></span></p>
-
-<div class="figcenter">
-    <img  id="FIG_245" src="images/fig245.jpg" alt="" width="400" height="334" />
-    <p class="center">Fig. 245.<br /> Edible Boletus. Boletus edulis.<br /> Fruiting
-              surface honey-combed on under side of cap.</p>
-</div>
-
-<p><b>426. Tube-bearing fungi (Polyporaceæ).</b>—In the tube-bearing
-fungi, the fruiting surface, instead of lying over the surface of
-gills, lines the surface of tubes or pores on the under side of the
-cap. The fruit-bearing portion therefore is “honey-combed.” The sulphur
-polyporus (Polyporus sulphureus) illustrates one form. The tube-bearing
-fungi are sometimes called “bracket” fungi, or “shelf” fungi, because
-the pileus is attached to the tree or stump like a shelf or bracket.
-One very common form in the woods is the plant so much sought by
-“artists,” and often called Polyporus applanatus. It is hard and woody,
-reddish brown, brown or grayish on the upper side, according to age,
-and is marked by prominent and large concentric ridges. (This form is
-probably P. leucophæus.) The under side is white and honey-combed by
-numerous very minute pores. This plant is perennial, that is, it lives
-from year to year. Each year a new layer is added to the under side,
-and several new rings usually to the margin. If a plant two or three
-years old is cut in two, there will be seen several distinct tube
-layers or strata, each one representing a year’s growth.</p>
-
-<p>In some of these bracket fungi, each ring on the upper surface marks a
-<span class="pagenum"><a name="Page_210" id="Page_210">[Pg 210]</a></span>
-year’s growth as in the pine polyporus (P. pinicola). In the birch
-polyporus (P. fomentarius) the tubes are quite large. It also occurs on
-other trees. The beech polyporus (P. igniarius, also on other trees)
-often becomes very old. I have seen one specimen over eighty years old.
-Not all the tube-bearing fungi are bracket form. Some have a stem and
-cap (see<a href="#FIG_245"> fig. 245</a>). Some are spread on the
-surface of logs.</p>
-
-<div class="figcenter">
-    <img  id="FIG_246" src="images/fig246.jpg" alt="" width="600" height="503" />
-    <p class="center">Fig. 246.<br /> Coral fungus. Hydnum coralloides,<br />
-            spines hanging down from branches.</p>
-</div>
-
-<p><b>427. Hedgehog fungi (Hydnaceæ).</b>—These plants are bracket in
-form or have a stem and cap, or are spread on the surface of wood; but
-the finest specimens resemble coral masses of fungus tissue (example,
-Hydnum, <a href="#FIG_246">fig. 246</a>). In most of them there are slender processes
-resembling teeth, spines or awls, which depend from the under surface
-(<a href="#FIG_247">fig. 247</a>). The fruiting surface covers these spines.</p>
-
-<p><b>428. Coral fungi or fairy clubs (Clavariaceæ).</b>—These plants
-stand upright from the wood, leaves, or soil, on which they grow
-(example, Clavaria). The “coral” ones are branched, while the “fairy
-clubs” are simple. The fruiting surface covers the entire exposed
-surface of the plants (<a href="#FIG_248">fig. 248</a>).
-<span class="pagenum"><a name="Page_211" id="Page_211">[Pg 211]</a></span></p>
-
-<div class="figcenter">
-    <img  id="FIG_247" src="images/fig247.jpg" alt="" width="450" height="508" />
-    <p class="center">Fig. 247.<br /> Hydnum repandum, spines hanging down from under side of cap.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_212" id="Page_212">[Pg 212]</a></span></p>
-
-<div class="figcenter">
-    <img  id="FIG_248" src="images/fig248.jpg" alt="" width="500" height="480" />
-    <p class="center">Fig. 248.<br /> Clavaria botrytes.</p>
-</div>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_213" id="Page_213">[Pg 213]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XXII" id="CHAPTER_XXII">CHAPTER XXII.</a><br />
-<span class="h_subtitle">CLASSIFICATION OF THE FUNGI.</span></h3>
-</div>
-
-<p><b>429. Classification of the fungi.</b>—Those who believe that the fungi represent
-a natural group of plants arrange them in three large series related to
-each other somewhat as follows:</p>
-
-<div class="blockquot">
-<p>The Gonidium Type or Series. The number of gonidia in the sporangium
-is indefinite and variable. It may be very large or very small, or
-even only one in a sporangium. To this series belong the lower fungi;
-examples: mucor, saprolegnia, peronospora, etc.</p>
-
-<p>The Basidium Type or Series. The number of gonidia on a basidium is
-limited and definite, and the basidium is a characteristic structure;
-examples: uredineæ (rusts), mushrooms, etc.</p>
-
-<p>The Ascus Type or Series. The number of spores in an ascus is
-limited and definite, and the ascus is a characteristic structure;
-examples: leaf curl of peach (exoascus), powdery mildews, black knot of
-plum, black rot of grapes, etc.</p>
-</div>
-
-<p><b>430.</b> Others believe that the fungi do not represent a natural
-group, but that they have developed off from different groups of
-the algæ by becoming parasitic. As parasites they no longer needed
-chlorophyll, and consequently lost it.</p>
-
-<p>According to this view the lower fungi have developed off from the
-lower algæ (saprolegnias, mucors, peronosporas, etc., being developed
-off from siphonaceous algæ like vaucheria), and the higher fungi being
-developed off from the higher algæ (the ascomycetes perhaps from the
-Rhodophyceæ).</p>
-
-<p><b>431. A very general outline of classification</b>,<a name="FNanchor_19_19" id="FNanchor_19_19"></a><a href="#Footnote_19_19" class="fnanchor">[19]</a>
-according to the former of these views, might be presented here to show the general
-<span class="pagenum"><a name="Page_214" id="Page_214">[Pg 214]</a></span>
-relationships of the fungi studied, with the addition of a few more
-in orders not represented above. It should be borne in mind that the
-author in presenting this view of classification does not necessarily
-commit himself to it. It is based on that presented in Engler &amp;
-Prantl’s Pflanzenfamilien. There are three classes.</p>
-
-<div class="figcenter">
-    <img  id="FIG_249" src="images/fig249.jpg" alt="" width="600" height="377" />
-    <p class="center">Fig. 249.</p>
-    <p class="blockquot">Chytrids. <i>A</i>, Harpochytrium hedenii, parasitic on spirogyra threads;
-         <i>a</i>, sickle-form plant; <i>b</i>, the sporangium part with escaping
-         zoospores; <i>c</i>, old plant proliferating by forming new sporangium
-         in the old empty one; <i>d</i>, zoospore; <i>e</i>, two young plants just
-         beginning to grow. <i>B</i>, Rhizophidium globosum parasitic on spirogyra.
-         Globose sporangium with delicate threads inside of the host, zoospores
-         escaping from one. <i>C</i>, Olpidium pendulum, parasitic in spirogyra cell.
-         Elliptical sporangium with slender exit tube through which zoospores
-         are escaping. <i>D</i>, Lagenidium rabenhorstii parasitic in spirogyra cell.
-         Two slender sporangia with exit tubes through which protoplasm escapes
-         forming a rounded mass at the end of tube, this protoplasm forming
-         biciliate zoospores.</p>
-</div>
-
-<p class="center"><b>I. Class Phycomycetes</b> (Alga-like Fungi).</p>
-
-<p class="center"><b>1. SUBCLASS OOMYCETES.</b></p>
-
-<p><b>432.</b> These are the egg-spore fungi. They include the water mold
-(Saprolegnia), the downy mildew of the grape (Plasmopara), the potato
-<span class="pagenum"><a name="Page_215" id="Page_215">[Pg 215]</a></span>
-blight (Phytophthora), the white rust of cruciferous plants (Cystopus
-= Albugo), the damping-off fungus (Pythium), and many parasites of
-the algæ known as chytrids, as Olpidium, Rhizophidium, Lagenidium,
-Chytridium, etc.</p>
-
-<p>The two following orders are sometimes placed in a separate subclass,
-<i>Archimycetes</i>.</p>
-
-<div class="figcenter">
-    <img  id="FIG_250" src="images/fig250.jpg" alt="" width="400" height="391" />
-    <p class="center">Fig. 250.</p>
-    <p class="blockquot">Monoblepharis insignis Thaxter. End of hypha bearing oogonium (<i>oog</i>)
-            and antheridium (<i>ant</i>). Sperms escaping from antheridium and creeping
-            up on the oogonium. (After Thaxter.)</p>
-</div>
-
-<p><b>433. Order Chytridiales (Chytridineæ).</b>—These include the lowest
-fungi. Many of them are parasitic on algæ and lack mycelium, the
-swarm spore either with or without minute rhizoids, developing into
-a globose sporangium (Rhizophidium, Chytridium, Olpidium, etc., <a href="#FIG_249">fig. 249</a>),
-or the swarm spore attached to the wall of the host develops into
-a long sword-shaped body with a sterile base, which proliferates and
-forms a new sporangium in the old one (Harpochytrium), or with slight
-development of mycelium in aquatic plants (Cladochytrium). Some are
-parasitic in leaves and stems of land plants. Synchytrium decipiens is
-very common on the trailing legume, Amphicarpæa monoica.</p>
-
-<p><b>434. Order Ancylistales (Ancylistineæ).</b>—The members of this
-order have a slight development of mycelium and many are parasitic in
-algæ (Lagenidium, <a href="#FIG_249">fig. 249</a>).</p>
-
-<p><b>435. Order Saprolegniales (Saprolegniineæ).</b>—These include the
-water molds (Saprolegnia). See <a href="#CHAPTER_XIX">Chapter XIX</a>.</p>
-
-<p><b>436. Order Monoblepharidales (Monoblepharidineæ).</b>—These are
-peculiar water molds, related to the Saprolegniales, but motile sperm
-cells are formed (Monoblepharis, etc., <a href="#FIG_250">fig. 250</a>).</p>
-
-<p><b>437. Order Peronosporales (Peronosporineæ).</b>—These include the
-downy mildews (Peronospora, Plasmopara, Phytopthora, etc.), and the
-white rust of crucifers and other plants (Cystopus = Albugo), <a href="#CHAPTER_XIX">Chapter XIX</a>.</p>
-
-<p class="center"><b>2. SUBCLASS ZYGOMYCETES.</b></p>
-
-<p><b>438.</b> These are the conjugating fungi.</p>
-
-<p><b>439. Order Mucorales (Mucorineæ).</b>—This includes the black mold
-and its many relatives (Mucor, Rhizopus, etc.). <a href="#CHAPTER_XIX">Chapter XIX</a>.</p>
-
-<p><b>440. Order Entomophthorales (Entomophthorineæ).</b>—This order
-includes the “fly fungus” (Empusa) and its many relatives parasitic on
-<span class="pagenum"><a name="Page_216" id="Page_216">[Pg 216]</a></span>
-insects. In the autumn and winter dead flies are often found stuck to
-window-panes, with a white ring of the conidia around each fly.</p>
-
-<p class="center"><b>II. Class Ascomycetes.</b> (The ascus series.)</p>
-
-<p class="center">1. SUBCLASS HEMIASCOMYCETES.</p>
-
-<div class="figcenter">
-    <img  id="FIG_251" src="images/fig251.jpg" alt="" width="400" height="449" />
-    <p class="center">Fig. 251.</p>
-    <p class="blockquot">Dipodascus albidus. <i>A</i>, thread with sexual organs, ascogonium and
-            antheridium; <i>B</i>, fertilized ascogonium developing ascus; <i>C</i>,
-            ascus with spores; <i>D</i>, conidia. (After Lagerheim.)</p>
-</div>
-
-<p><b>441. Order Hemiascales (Hemiascineæ).</b>—Fungi with a well
-developed, septate mycelium, but with a sporangium-like ascus, i.e.,
-a large and indefinite number of spores in the ascus. Examples:
-Protomyces macrosporus in stems of Umbelliferæ, or P. polysporus in
-Ambrosia trifida. These two are by some placed in the Ustilagineæ.
-Dipodascus albidus grows in the exuding sap of Bromeliaceæ in Brazil
-and the sap of the beech in Sweden. The ascus is developed as the
-result of the fertilization of an ascogonium with an antheridium (see
-<a href="#FIG_251">fig. 251</a>).</p>
-
-<p class="center">2. SUBCLASS PROTOASCOMYCETES.</p>
-
-<p><b>442. The asci are well-defined</b> and usually with a limited and
-definite number of spores (usually 8, sometimes 1, 2, 4, 16, or more).
-Mycelium often well developed and septate. Asci scattered on the
-mycelium, not associated in definite fields or groups.</p>
-
-<p><b>443. Order Protoascales (Protoascineæ).</b>—The asci are separate
-cells, or are scattered irregularly in loose wefts of mycelium.
-No fruit body. (The yeast, Saccharomyces, <a href="#PARA_237">see paragraph 237</a>;
-and certain mold-like fungi, some of which are parasitic on mushrooms, as
-Endomyces, are examples.)
-<span class="pagenum"><a name="Page_217" id="Page_217">[Pg 217]</a></span></p>
-
-<p class="center">3. SUBCLASS EUASCOMYCETES.</p>
-
-<p>Asci associated in surfaces forming a hymenium, or in groups or
-intermingled in the elements of a fruit body. Fruit body usually present.</p>
-
-<p>The following four or five orders comprise the Discomycetes, according
-to the usual classification.</p>
-
-<p><b>444. Order Protodiscales (Protodiscineæ).</b>—The asci are exposed
-and form large and indefinite groups, but there is no definite fruit
-body. Examples: leaf curl of peach, plum pocket, etc. (Exoascus).</p>
-
-<p><b>445. Order Helvellales (Helvellineæ).</b>—The asci form large
-fields over the upper portion of the fruit body. This order includes
-the morels (<a href="#FIG_231A">fig. 231<i>a</i></a>), helvellas,
-earth tongues (Geoglossum), etc.</p>
-
-<p><b>446. Order Pezizales (Pezizineæ).</b>—The asci form a definite
-field or fruiting surface surrounded on the sides and below by a wall
-of fungus tissue, forming a fruit body in the shape of a cup. These are
-known as the cup fungi (Peziza, Lachnea, etc.).</p>
-
-<p><b>447. Order Phacidiales (Phacidiineæ).</b>—Fungi mostly saprophytic,
-and fruit body similar to the cup fungi. Examples: Propolis in rotting
-wood, Rhytisma forming black crusts on leaves (maple for example),
-Urnula craterium, a large black beaker-shaped fungus on the ground.</p>
-
-<p><b>448. Order Hysteriales (Hysteriineæ).</b>—Fungi with a more or less
-elongated fruit body with an enclosing wall opening by a long slit. In
-some forms the fruit body has the appearance of a two-lipped body; in
-others it is shaped like a clam shell, the asci being inside. Example,
-Hysterographium common on dry, dead, decorticated sticks.</p>
-
-<p><b>449. Order Tuberales (Tuberineæ).</b>—The more or less rounded
-fruit bodies are usually subterranean. The most important fungi in this
-order are the truffles (Tuber). The mycelium of many species assists
-in the formation of mycorhiza on the roots of oaks, etc., and several
-species are partly cultivated, or protected, and collected for food.
-This is especially the case with Tuber brumale and its forms; more than
-a million francs worth of truffles are sold in France and Italy yearly.
-Dogs and pigs are employed in the collection of truffles from the ground.</p>
-
-<p><b>450. Order Plectascales (Plectascineæ).</b>—The fruit body of these
-plants is more or less globose, and contains the asci distributed
-irregularly through the mycelium of the interior. Some are subterranean
-(Elaphomyces), while others grow in decaying plants, or certain food
-substances (Eurotium, Sterigmatocystis, Penicillium). Penicillium in
-its conidial stage forms blue mold on fruit, bread, etc.</p>
-
-<p>The following four orders comprise the Pyrenomycetes, according to the
-usual classification.</p>
-
-<p><b>451. Order Perisporiales.</b>—The powdery mildews are good examples
-of this order (Uncinula, Microsphæra, etc., <a href="#CHAPTER_XXI">Chapter XXI</a>).
-<span class="pagenum"><a name="Page_218" id="Page_218">[Pg 218]</a></span></p>
-
-<p><b>452. Order Hypocreales.</b><a name="FNanchor_20_20" id="FNanchor_20_20"></a><a href="#Footnote_20_20" class="fnanchor">[20]</a>—The
-fruit bodies are colorless, or bright colored and entirely enclose the
-asci, sometimes opening by an apical pore. Nectria cinnabarina has
-clusters of minute orange oval fruit bodies, and is common on dead
-twigs. Cordyceps with a number of species is parasitic on insects, and
-on certain subterranean Ascomycetes, especially Elaphomyces (of the
-order <i>Plectascales</i> = <i>Plectascineæ</i>).</p>
-
-<p><b>453. Order Dothidiales.</b><a name="FNanchor_21_21" id="FNanchor_21_21"></a><a href="#Footnote_21_21" class="fnanchor">[21]</a>—Fungi
-with black stroma formed of mycelium in which are cavities containing
-the asci. The cavities are usually shaped like a perithecium, but
-there is no wall distinct from the tissue of the stroma (Dothidea,
-Phyllachora, on grasses).</p>
-
-<p><b>454. Order Sphæriales.</b><a name="FNanchor_22_22" id="FNanchor_22_22"></a><a href="#Footnote_22_22" class="fnanchor">[22]</a>—These
-contain the so-called black fungi, with separate or clustered, oval,
-fruit bodies, black in color. The black wall encloses the asci, and
-usually opens by an apical pore. Examples are found in the black knot
-of plum and cherry, black rot of grapes, and in Rosellinia, Hypoxylon,
-Xylaria, etc., on dead wood.</p>
-
-<p><b>455. Order Laboulbeniales (Laboulbineæ).</b>—These are peculiar
-fungi attached to the legs and bodies of insects by a short stalk, and
-provided with a sac-like fruit body which contains the asci. Example,
-Laboulbenia.</p>
-
-<p class="center">III. Class Basidiomycetes. (The basidium series.)</p>
-
-<p class="center">1. SUBCLASS HEMIBASIDIOMYCETES.</p>
-
-<p><b>456. Order Ustilaginales (Ustilagineæ).</b>—This order includes the
-well-known smuts on corn, wheat, oats, etc. (Ustilago, Tilletia, etc.).</p>
-
-<p class="center">2. SUBCLASS ÆCIDIOMYCETES.</p>
-
-<p><b>457. Order Uredinales</b><a name="FNanchor_23_23" id="FNanchor_23_23"></a><a href="#Footnote_23_23" class="fnanchor">[23]</a> (Uredineæ).—This
-order includes the parasitic fungi known as rusts. Examples: wheat rust
-(<a href="#CHAPTER_XX">Chapter XX</a>), the cedar apple, etc.</p>
-
-<p>The true Basidiomycetes include the following orders:</p>
-
-<p class="center">3. SUBCLASS PROTOBASIDIOMYCETES.</p>
-
-<p><b>458. Order Auriculariales.</b><a name="FNanchor_24_24" id="FNanchor_24_24"></a><a href="#Footnote_24_24" class="fnanchor">[24]</a>—This
-order includes trembling fungi in which the basidium is long and
-divided transversely into usually four cells (example, Auricularia),
-and similar forms. Pilacre petersii on dead wood represents an
-angiocarpous form.</p>
-
-<p><b>459. Order Tremellales (Tremellineæ)</b>, trembling or gelatinous
-fungi with the globose basidium divided longitudinally into four cells (Tremella).
-<span class="pagenum"><a name="Page_219" id="Page_219">[Pg 219]</a></span></p>
-
-<p class="center">4. SUBCLASS EUBASIDIOMYCETES.</p>
-
-<p><b>460. Order Dacryomycetales (Dacryomycetineæ).</b>—This order
-includes certain fungi of a gelatinous or waxy consistency, usually
-of bright colors. They resemble the Tremellales, but the basidia are
-slender and fork into two long sterigmata. (Example, Dacryomyces.)
-Gyrocephalus rufus is quite a large plant, 10-15 cm. high, growing on
-the ground in woods.</p>
-
-<p><b>461. Order Exobasidiales (Exobasidiineæ).</b>—The fungus causing
-azalea apples is an example (Exobasidium).</p>
-
-<p><b>462. Order Hymeniales (Hymenomycetineæ).</b>—In this order the
-basidia are usually club-shaped and undivided, and bear usually four
-spores on the end (sometimes two or six). There are several families.</p>
-
-<p><b>463. Family Thelephoraceæ.</b>—The fruit bodies are more or less
-membranous and spread over wood or the ground, or somewhat leaf-like,
-growing on wood or the ground. The fruiting surface is nearly or quite
-even, and occupies the under side of the leaf-like bodies (Stereum,
-Thelephora) or the outside of the forms spread out on wood (Corticium,
-Coniophora).</p>
-
-<p><b>464. Family Clavariaceæ.</b>—This order includes the fairy clubs,
-and some of the coral fungi. The larger number of species are in one
-genus (Clavaria, <a href="#FIG_248">fig. 248</a>).</p>
-
-<p><b>465. Family Hydnaceæ.</b>—The fungi of this order are known as
-“hedgehog” fungi, because of the numerous awl-like teeth or spines over
-which the fruiting surface is spread, as in Hydnum (figs. <a href="#FIG_246">246</a>,
-<a href="#FIG_247">247</a>).</p>
-
-<p><b>466. Family Polyporaceæ.</b>—The tube-bearing fungi (Polyporus,
-Boletus, etc., <a href="#FIG_245">fig. 245</a>).</p>
-
-<p><b>467. Family Agaricaceæ.</b>—The gill-bearing fungi (Agaricus,
-Amanita, etc., see <a href="#CHAPTER_XXI">Chapter XXI</a>).</p>
-
-<p>The above five orders, according to the earlier classification (still
-used at the present time by some), made up the order Hymenomycetes,
-while the following five orders made up the Gasteromycetes. The
-Hymenomycetes, according to this system, included those plants in which
-the fruiting portion (hymenium) is either exposed from the first, or
-if covered by a veil or volva (as in Agaricus, Amanita, etc.) this
-ruptures and exposes the fruiting surface before, or at the time of,
-the ripening of the spores, while the Gasteromycetes included those in
-which the fruit body is closed until after the maturity of the spores.</p>
-
-<p><b>468. Order Phallales (Phallineæ).</b>—The “stink-horn” fungi, or
-“buzzard’s nose.” Usually foul-smelling fungi, the fruiting portion
-borne aloft on a stout stalk, and dissolving (Dictyophora, Ithyphallus,
-etc.).</p>
-
-<p><b>469. Order Hymenogastrales (Hymenogastrineæ).</b>—The basidia form
-a distinct hymenium which does not break down at maturity. Some of
-the plants resemble Boletus or Agaricus in the way the fruit bodies
-open (Secotium, etc.), while others open irregularly on the surface
-<span class="pagenum"><a name="Page_220" id="Page_220">[Pg 220]</a></span>
-(Rhizopogon) or like an earth star (Sclerogaster), or portions of the
-surface become gelatinized (Phallogaster). The last-named one grows on
-very rotten wood, while most of the others grow on the ground.</p>
-
-<p><b>470. Order Lycoperdales (Lycoperdineæ).</b>—These include the
-“puff-balls,” or “devil’s snuff-box” (Lycoperdon), and the earth stars
-(Geaster). The basidia form a distinct hymenium, but at maturity the
-entire inner portion of the plant (except certain peculiar threads, the
-capillitium) disintegrates and with the spores forms a powdery mass.</p>
-
-<p><b>471. Order Nidulariales (Nidulariineæ).</b>—These are known
-as bird-nest fungi. The fruit body when mature is cup-shaped,
-or goblet-shaped, and contains minute flattened circular bodies
-(peridiola) containing the spores. The intermediate portions of the
-fruit body disintegrate and set the peridiola free, which then lie in
-the cup-shaped base like eggs in a nest.</p>
-
-<p><b>472. Order Plectobasidiales (Plectobasidiineæ).</b>—The basidia
-do not form a definite hymenium, but are interwoven with the threads
-inside, or are collected into knot-like groups. (Examples: Calostoma,
-Tulostoma, Astræus, Sphærobolus, etc.)</p>
-
-<p><b>472a. Lichens.</b>—The plant body of the lichens (<a href="#PARA_200">see paragraphs
-200, 201</a>) consists of two component parts, the one a fungus, the other
-an alga. The fructification is that of the fungus. The fruit body
-shows the lichens to be related some to the Ascomycetes, others to
-the Hymenomycetes, and Gasteromycetes. They are usually classified as
-a distinct class or order from the fungi, but a natural arrangement
-would distribute them in several of the orders above. Their special
-relationship with these orders has not been satisfactorily worked out.
-For the present they are arranged as follows:</p>
-
-<ul class="index">
-<li class="isub1"><b>Ascolichenes.</b></li>
-
-<li class="isub3"><i>Pyrenocarpous lichens</i> (those with a fruit body like the Pyrenomycetes).</li>
-
-<li class="isub3"><i>Gymnocarpous lichens</i> (those with a fruit body like the Discomycetes).</li>
-
-<li class="isub1"><b>Hymenolichenes</b> (those with a fruit body like the Hymenomycetes).</li>
-
-<li class="isub1"><b>Gasterolichenes</b> (those with a fruit body like the Gasteromycetes).</li>
-</ul>
-
-<p>From a vegetative standpoint there are two types according to the
-distribution of the elements.</p>
-
-<p>1st. Where the fungal and algal elements are evenly distributed in the
-plant body the lichen is said to be <i>homoiomerous</i>. There are two types
-of these:</p>
-
-<div class="blockquot">
-<p><i>a. Filamentous lichens</i>, example, Ephebe pubescens.</p>
-
-<p><i>b. Gelatinous lichens</i>, example, Collema (with the alga nostoc),
-Physma (with the Chroococcaceæ).</p>
-</div>
-
-<p>2d. Where the elements are stratified, as in Parmelia, etc., the lichen
-is said to be <i>heteromerous</i>. In these there are three types:</p>
-
-<div class="blockquot">
-<p><i>a. Crustaceous lichens</i>, the plant body is in the form of a thin
-incrustation on rocks, etc.
-<span class="pagenum"><a name="Page_221" id="Page_221">[Pg 221]</a></span></p>
-
-<p><i>b. Foliaceous lichens</i>, the plant body is leaf-like and lobed and more
-or less loosely attached by rhizoids: Parmelia, Peltigera, etc.</p>
-
-<p><i>c. Fruticose lichens</i>, the plant body is filamentous or band-like and
-branched, as in Usnea, Cladonia, etc.</p>
-</div>
-
-<div class="figcenter">
-    <img src="images/fig251a.jpg" alt="" width="450" height="459" />
-    <p class="center">Fig. 251<i>a</i>.<br /> Rock lichen (Parmelia contigua).</p>
-
-</div>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_222" id="Page_222">[Pg 222]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XXIII" id="CHAPTER_XXIII">CHAPTER XXIII.</a><br />
-<span class="h_subtitle">LIVERWORTS (HEPATICÆ).</span></h3>
-</div>
-
-<p><b>473.</b> We come now to the study of representatives of another
-group of plants, a few of which we examined in studying the organs of
-assimilation and nutrition. I refer to what are called the liverworts.
-Two of these liverworts belonging to the genus riccia are illustrated
-in figs. <a href="#FIG_30">30</a>, <a href="#FIG_252">252</a>.</p>
-
-<h4><a name="XXIII_1" id="XXIII_1">Riccia.</a></h4>
-
-<p><b>474. Form of the floating riccia (R. fluitans).</b>—The general
-form of floating riccia is that of a narrow, irregular, flattened,
-ribbon-like object, which forks repeatedly, in a dichotomous manner,
-so that there are several lobes to a single plant. It receives its
-name from the fact that at certain seasons of the year it may be found
-floating on the water of pools or lakes. When the water lowers it comes
-to rest on the damp soil, and rhizoids are developed from the under
-side. Now the sexual organs, and later the fruit capsule, are developed.</p>
-
-<p><b>475. Form of the circular riccia (R. crystallina).</b>—The circular
-riccia is shown in <a href="#FIG_252">fig. 252</a>. The form of this one is quite
-different from the floating one, but the manner of growth is much the same.
-The branching is more compact and even, so that a circular plant is
-the result. This riccia inhabits muddy banks, lying flat on the wet
-surface, and deriving its soluble food by means of the little rootlets
-(rhizoids) which grow out from the under surface.
-<span class="pagenum"><a name="Page_223" id="Page_223">[Pg 223]</a></span></p>
-
-<div class="figright">
-    <img  id="FIG_252" src="images/fig252.jpg" alt="" width="200" height="184" />
-    <p class="center">Fig. 252.<br /> Thallus of<br /> Riccia crystallina.</p>
-</div>
-
-<p>Here and there on the margin are narrow slits, which extend nearly to
-the central point. They are not real slits, however, for they were
-formed there as the plant grew. Each one of these V-shaped portions of
-the thallus is a lobe, and they were formed in the young condition of
-the plant by a branching in a forked manner. Since growth took place
-in all directions radially the plant became circular in form. These
-large lobes we can see are forked once or twice again, as shown by the
-seeming shorter slits in the margin.</p>
-
-<p><b>476. Sexual organs.</b>—In order to study the sexual organs we
-must make thin sections through one of these lobes lengthwise and
-perpendicular to the thallus surface. These sections are mounted for
-examination with the microscope.</p>
-
-<p><b>477. Archegonia.</b>—We are apt to find the organs in various
-stages of development, but we will select one of the flask-shaped
-structures shown in <a href="#FIG_253">fig. 253</a> for study. This flask-shaped
-body we see is entirely sunk in the tissue of the thallus. This structure is the
-female organ, and is what we term in these plants the <i>archegonium</i>.
-It is more complicated in structure than the oogonium. The lower portion
-is enlarged and bellied out, and is the venter of the archegonium,
-while the narrow portion is the neck. We here see it in section. The
-wall is one cell layer in thickness. In the neck is a canal, and in
-the base of the venter we see a large rounded cell with a distinct and
-large nucleus. This cell is the <i>egg</i> cell.</p>
-
-<p><b>478. Antheridia.</b>—The antheridia are also borne in cavities sunk
-in the tissue of the thallus. There is here no illustration of the
-antheridium of this riccia, but <a href="#FIG_259">fig. 259</a> represents an
-antheridium of another liverwort, and there is not a great difference between
-the two kinds. Each one of those little rectangular sperm mother cells in the
-antheridium changes into a swiftly moving body like a little club with
-two long lashes attached to the smaller end. By the violent lashing of
-these organs the spermatozoid is moved through the water, or moisture
-which is on the surface of the thallus. It moves through the canal of
-the archegonium neck and into the egg, where it fuses with the nucleus
-of the egg, and thus fertilization is effected.
-<span class="pagenum"><a name="Page_224" id="Page_224">[Pg 224]</a></span></p>
-
-<p><b>479. Embryo.</b>—In the plants which we have selected thus far for
-study, the egg, immediately after fecundation, we recollect, passed
-into a resting state, and was enclosed by a thick protecting wall.
-But in riccia, and in the other plants of the group which we are now
-studying, this is not the case. The egg, on the other hand, after
-acquiring a thin wall, swells up and fills the cavity of the venter.
-Then it divides by a cross wall into two cells. These two grow, and
-divide again, and so on until there is formed a quite large mass
-of cells rounded in form and still contained in the venter of the
-archegonium, which itself increases in size by the growth of the cells
-of the wall.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_253" src="images/fig253.jpg" alt="" width="250" height="341" />
-    <p class="center">Fig. 253.<br /> Archegonium of riccia, showing<br />
-        neck, venter, and the egg;<br /> archegonium is partly<br />
-        surrounded by the tissue of<br /> the thallus.<br />
-        (Riccia crystallina.)</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_254" src="images/fig254.jpg" alt="" width="200" height="338" />
-      <p class="center">Fig. 254.<br /> Young embryo (sporogonium)<br />
-            of riccia, within the<br /> venter of the archegonium;<br />
-            the latter has now two<br /> layers of cells.<br />
-            (Riccia crystallina.)</p>
-  </div>
-</div>
-
-<p><b>480. Sporogonium of riccia.</b>—The fruit of riccia, which is
-developed from the fertilized egg in the archegonium, forms a rounded
-capsule still enclosed in the venter of the archegonium, which grows
-also to provide space for it. Therefore a section through the plant at
-this time, as described for the study of the archegonium, should show
-this capsule. The capsule then is a rounded mass of cells developed
-from the egg. A single outer layer of cells forms the wall, and
-<span class="pagenum"><a name="Page_225" id="Page_225">[Pg 225]</a></span>
-therefore is sterile. All the inner cells, which are richer in
-protoplasm, divide into four cells each. Each of these cells becomes
-a spore with a thick wall, and is shaped like a triangular pyramid
-whose sides are of the same extent as the base (tetrahedral). These
-cells formed in fours are the <i>spores</i>. At this time the wall of the
-spore-case dissolves, the spores separate from each other and fill the
-now enlarged venter of the archegonium. When the thallus dies they are
-liberated, or escape between the loosely arranged cells of the upper surface.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img src="images/fig255.jpg" alt="" width="300" height="308" />
-    <p class="center">Fig. 255.<br /> Nearly mature sporogonium of Riccia<br />
-                  crystallina; mature spore at the right.</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig256.jpg" alt="" width="200" height="318" />
-      <p class="center">Fig. 256.<br /> Riccia glauca; archegonium containing<br />
-             nearly mature sporogonium. <i>sg</i>,<br /> spore-producing cells surrounded by<br />
-             single layer of sterile cells, the<br /> wall of the sporogonium.</p>
-  </div>
-</div>
-
-<p><b>481. A new phase in plant life.</b>—Thus we have here in the
-sporogonium of <i>riccia</i> a very interesting phase of plant life, in
-which the egg, after fertilization, instead of developing directly into
-the same phase of the plant on which it was formed, grows into a quite
-new phase, the sole function of which is the development of spores.
-Since the form of the plant on which the sexual organs are developed
-is called the <i>gametophyte</i>, this new phase in which the spores are
-developed is termed the <i>sporophyte</i>.</p>
-
-<p>Now the spores, when they germinate, develop the <i>gametophyte</i>, or
-<span class="pagenum"><a name="Page_226" id="Page_226">[Pg 226]</a></span>
-thallus, again. So we have this very interesting condition of things,
-the thallus (gametophyte) bears the sexual organs and the unfertilized
-egg. The fertilized egg, starting as it does from a single-celled
-stage, develops the sporogonium (sporophyte). Here the single-cell
-stage is again reached in the spore, which now develops the thallus.</p>
-
-<p><b>482. Riccia compared with coleochæte, œdogonium, etc.</b>—We have
-said that in the sporogonium of riccia we have formed a new phase in
-plant life. If we recur to our study of coleochæte we may see that
-there is here possibly a state of things which presages, as we say,
-this new phase which is so well formed in riccia. We recollect that
-after the fertilized egg passed the period of rest it formed a small
-rounded mass of cells, each of which now forms a zoospore. The zoospore
-in turn develops the normal thallus (gametophyte) of the coleochæte
-again. In coleochæte then we have two phases of the plant, each having
-its origin in a one-celled stage. Then if we go back to œdogonium,
-we remember that the fertilized egg, before it developed into the
-œdogonium plant again (which is the gametophyte), at first divides
-into <i>four</i> cells which become zoospores. These then develop
-the œdogonium plant.</p>
-
-<p class="blockquot">Note. Too much importance should not be attached
-to this seeming homology of the sporophyte of œdogonium, coleochæte,
-and riccia, for the nuclear phenomena in the formation of the zoospores
-of œdogonium and coleochæte are not known. They form, however, a very
-suggestive series.</p>
-
-<h4><a name="XXIII_2" id="XXIII_2">Marchantia.</a></h4>
-
-<p><b>483.</b> The marchantia (M. polymorpha) has been chosen for study
-because it is such a common and easily obtained plant, and also for
-the reason that with comparative ease all stages of development can
-be obtained. It illustrates also very well certain features of the
-structure of the liverworts.</p>
-
-<div class="figcenter">
-    <img  id="FIG_257" src="images/fig257.jpg" alt="" width="600" height="399" />
-    <p class="center">Fig. 257.<br /> Male plant of marchantia bearing antheridiophores.</p>
-</div>
-
-<p>The plants are of two kinds, male and female. The two different organs,
-then, are developed on different plants. In appearance, however, before
-the beginning of the structures which bear the sexual organs they
-are practically the same. The thallus is flattened like nearly all
-of the thalloid forms, and branches in a forked manner. The color is
-dark green, and through the middle line of the thallus the texture is
-different from that of the margins, so that it possesses what we term a
-<span class="pagenum"><a name="Page_227" id="Page_227">[Pg 227]</a></span>
-midrib, as shown in figs. <a href="#FIG_257">257</a>, <a href="#FIG_261">261</a>.
-The growing point of the thallus is situated in the little depression
-at the free end. If we examine the upper surface with a hand lens we
-see diamond-shaped areas, and at the center of each of these areas are
-the openings known as the stomates.</p>
-
-<div class="figcenter">
-    <img  id="FIG_258" src="images/fig258.jpg" alt="" width="600" height="183" />
-  <div class="blockquot">
-    <p class="center">Fig. 258.<br /> </p>
-    <p>Section of antheridial receptacle from male plant of Marchantia polymorpha,
-          showing cavities where the antheridia are borne.</p>
-  </div>
-</div>
-
-<p><b>484. Antheridial plants.</b>—One of the male plants is figured at
-257. It bears curious structures, each held aloft by a short stalk.
-These are the antheridial receptacles (or male gametophores). Each
-one is circular, thick, and shaped somewhat like a biconvex lens. The
-upper surface is marked by radiating furrows, and the margin is
-crenate. Then we note, on careful examination of the upper surface,
-that there are numerous minute openings. If we make a thin section of
-this structure perpendicular to its surface we shall be able to unravel
-the mystery of its interior. Here we see, as shown in <a href="#FIG_258">fig. 258</a>,
-that each one of these little openings on the surface is an entrance to quite
-<span class="pagenum"><a name="Page_228" id="Page_228">[Pg 228]</a></span>
-a large cavity. Within each cavity there is an oval or elliptical
-body, supported from the base of the cavity on a short stalk. This is
-an antheridium, and one of them is shown still more enlarged in <a href="#FIG_259">fig. 259</a>.
-This shows the structure of the antheridium, and that there are
-within several angular areas, which are divided by numerous straight
-cross-lines into countless tiny cuboidal cells, the <i>sperm mother
-cells</i>. Each of these, as stated in the former chapter, changes into a
-swiftly moving body resembling a serpent with two long lashes attached
-to its tail.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_259" src="images/fig259.jpg" alt="" width="300" height="386" />
-    <p class="center">Fig. 259.<br /> Section of antheridium of marchantia,<br />
-                 showing the groups of sperm mother cells.</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_260" src="images/fig260.jpg" alt="" width="250" height="345" />
-      <p class="center">Fig. 260.<br /> Spermatozoids of marchantia,<br />
-             uncoiling and one extended,<br /> showing the two cilia.</p>
-  </div>
-</div>
-
-<p><b>485.</b> The way in which one of these sperm mother cells changes
-into this spermatozoid is very curious. We first note that a coiled
-spiral body is appearing within the thin wall of the cell, one end of
-the coil larger than the other. The other end terminates in a slender
-hair-like outgrowth with a delicate vesicle attached to its free end.
-This vesicle becomes more and more extended until it finally breaks and
-forms two long lashes which are clubbed at their free ends as shown in
-<a href="#FIG_260">fig. 260</a>.</p>
-
-<div class="figcenter">
-    <img  id="FIG_261" src="images/fig261.jpg" alt="" width="500" height="458" />
-    <p class="center">Fig. 261.<br /> Marchantia polymorpha, female plants bearing archegoniophores.</p>
-
-</div>
-<div class="figleft">
-    <img  id="FIG_262" src="images/fig262.jpg" alt="" width="150" height="245" />
-    <p class="center">Fig. 262.<br /> Marchantia polymorpha,<br /> showing origin of<br /> gametophore.</p>
-</div>
-
-<p><b>486. Archegonial plants.</b>—In <a href="#FIG_261">fig. 261</a> we see one of
-the female plants of marchantia. Upon this there are also very curious structures,
-which remind one of miniature umbrellas. The general plan of the
-<span class="pagenum"><a name="Page_229" id="Page_229">[Pg 229]</a></span>
-archegonial receptacle (or female gametophore), for this is what these
-structures are, is similar to that of the antheridial receptacle,
-but the rays are more pronounced, and the details of structure are
-quite different, as we shall see. Underneath the arms there hang down
-delicate fringed curtains. If we make sections of this in the same
-direction as we did of the antheridial receptacle, we shall be able to
-find what is secreted behind these curtains. Such a section is figured
-at 266. Here we find the archegonia, but instead of being sunk in
-<span class="pagenum"><a name="Page_230" id="Page_230">[Pg 230]</a></span>
-cavities their bases are attached to the under surface, while the
-delicate, pendulous fringes afford them protection from drying. An
-archegonium we see is not essentially different in marchantia from
-what it is in riccia, and it will be interesting to learn whether the
-sporogonium is essentially different from what we find in riccia.</p>
-
-<p><b>487. Homology of the gametophore of marchantia.</b>—To see the
-relation of the gametophore to the thallus of marchantia take portions
-of the thallus bearing the female receptacle. On the under side note
-that the prominent midrib continues beyond the thin lateral expansions
-and arches upward in the sinus or notch at the end, or at the side
-where the branch of the thallus has continued to grow beyond. The stalk
-of the gametophore is then a continuation of the midrib of the thallus.
-On the apex of this are organized several radial growing points which
-develop the digitate or ray-like receptacle. The gametophore is thus a
-specialized branch of the thallus. When young, or in many cases when
-nearly or quite mature, the gametophore, as one looks at the upper
-surface of the thallus, appears to arise from the upper surface, as in
-<a href="#FIG_261">fig. 261</a>. This is because the thin lateral expansions of
-the thallus project forward and overlap in advance of the stalk. It is sometimes
-necessary to tear these overlapping edges apart to see the real origin
-of the gametophore. But in quite old plants these expanded portions are
-farther apart and show clearly that the stalk arises from the midrib
-below and arches upward in the sinus, as in <a href="#FIG_262">fig. 262</a>.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_231" id="Page_231">[Pg 231]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XXIV" id="CHAPTER_XXIV">CHAPTER XXIV.</a><br />
-<span class="h_subtitle">LIVERWORTS CONTINUED.</span></h3>
-</div>
-
-<div class="figcenter">
-    <img src="images/fig263.jpg" alt="" width="600" height="370" />
-   <div class="blockquot">
-    <p class="center">Fig. 263.</p>
-    <p>Archegonial receptacles of marchantia bearing ripe sporogonia. The
-        capsule of the sporogonium projects outside, while the stalk is
-        attached to the receptacle underneath the curtain. In the left figure
-        two of the capsules have burst and the elaters and spores are escaping.</p>
-  </div>
-</div>
-
-<p><a name="XXIV_1" id="XXIV_1"><b>488. Sporogonium of marchantia.</b></a>—If we examine the plant shown
-in <a href="#FIG_181">fig. 181</a> we shall see oval bodies which stand out between the
-rays of the female receptacle, supported on short stalks. These are
-the sporogonia, or spore-cases. We judge at once that they are quite
-different from those which we have studied in riccia, since those were
-not stalked. We can see that some of the spore-cases have opened, the
-wall splitting down from the apex in several lines. This is caused by
-the drying of the wall. These tooth-like divisions of the wall now
-curl backward, and we can see the yellowish mass of the spores in slow
-<span class="pagenum"><a name="Page_232" id="Page_232">[Pg 232]</a></span>
-motion, falling here and there. It appears also as if there were twisting
-threads which aided the spores in becoming freed from the capsule.</p>
-
-<div class="figcenter">
-    <img src="images/fig264.jpg" alt="" width="600" height="216" />
-   <div class="blockquot">
-    <p class="center">Fig. 264.</p>
-    <p>Section of archegonial receptacle of Marchantia polymorpha; ripe
-        sporogonia. One is open, scattering spores and elaters; two are still
-        enclosed in the wall of the archegonium. The junction of the stalk of
-        the sporogonium with the receptacle is the point of attachment of the
-        sporophyte of marchantia with the gametophyte.</p>
-  </div>
-</div>
-<div class="figcenter">
-    <img src="images/fig265.jpg" alt="" width="600" height="415" />
-   <div class="blockquot">
-    <p class="center">Fig. 265.</p>
-    <p>Elater and spore of marchantia. <i>sp</i>, spore;
-         <i>mc</i>, mother cell of spores, showing partly formed spores.</p>
-  </div>
-</div>
-
-<p><b>489. Spores and elaters.</b>—If we take a bit of this mass of
-spores and mount it in water for examination with the microscope, we
-shall see that, besides the spores, there are very peculiar thread-like
-bodies, the markings of which remind one of a twisted rope. These are
-very long cells from the inner part of the spore-case, and their walls
-are marked by spiral thickenings. This causes them in drying, and also
-when they absorb moisture, to twist and curl in all sorts of ways. They
-thus aid in pushing the spores out of the capsule as it is drying.</p>
-
-<p><b>490. Sporophyte of marchantia compared with riccia.</b>—We must
-recollect that the sporogonium in marchantia is larger than in riccia,
-and that it is also not lying in the tissue of the thallus, but is only
-<span class="pagenum"><a name="Page_233" id="Page_233">[Pg 233]</a></span>
-attached to it at one side by a slender stalk. This shows us an
-increase in the size and complex structure of this new phase of the
-plant, the <i>sporophyte</i>. This is one of the very interesting things
-which we have to note as we go on in the study of the higher plants.</p>
-
-<div class="figcenter">
-    <img src="images/fig266.jpg" alt="" width="600" height="416" />
-   <div class="blockquot">
-    <p class="center">Fig. 266.</p>
-    <p>Marchantia polymorpha, archegonium at the left with egg; archegonium at
-        the right with young sporogonium; <i>p</i>, curtain which hangs down around
-        the archegonia; <i>e</i>, egg; <i>v</i>, venter of archegonium; <i>n</i>,
-        neck of archegonium; <i>sp</i>, young sporogonium.</p>
-  </div>
-</div>
-
-<p><b>491. Sporophyte dependent on the gametophyte for its
-nutriment.</b>—We thus see that at no time during the development of
-the sporogonium is it independent from the gametophyte. This new phase
-of plants then, the sporophyte, has not yet become an independent
-plant, but must rely on the earlier phase for sustenance.</p>
-
-<p><b>492. Development of the sporogonium.</b>—It will be interesting
-to note briefly how the development of the marchantia sporogonium
-differs from that of riccia. The first division of the fertilized egg
-is the same as in riccia, that is a wall which runs crosswise of the
-axis of the archegonium divides it into two cells. In marchantia the
-cell at the base develops the stalk, so that here there is a radical
-difference. The outer cell forms the capsule. But here after the wall
-is formed the inner tissue does not all go to make spores, as is the
-case with riccia. But some of it forms the elaters. While in riccia
-only the outside layer of cells of the sporogonium remained sterile, in
-marchantia the basal half of the egg remains completely sterile and
-<span class="pagenum"><a name="Page_234" id="Page_234">[Pg 234]</a></span>
-develops the stalk, and in the outer half the part which is formed from
-some of the inner tissue is also sterile.</p>
-
-<div class="figcenter">
-    <img  id="FIG_267" src="images/fig267.jpg" alt="" width="600" height="487" />
-   <div class="blockquot">
-    <p class="center">Fig. 267.</p>
-    <p>Section of developing sporogonia of marchantia; <i>nt</i>, nutritive tissue
-        of gametophyte; <i>st</i>, sterile tissue of sporophyte; <i>sp</i>, fertile part
-        of sporophyte; <i>va</i>, enlarged venter of archegonium.</p>
-  </div>
-</div>
-
-<p><b>493. Embryo.</b>—In the development of the embryo we can see all
-the way through this division line between the basal half, which is
-completely sterile, and the outer half, which is the fertile part. In
-<a href="#FIG_267">fig. 267</a> we see a young embryo, and it is nearly circular
-in section although it is composed of numerous cells. The basal half is attached
-to the base of the inner surface of the archegonium, and at this time
-the archegonium still surrounds it. The archegonium continues to grow
-then as the embryo grows, and we can see the remains of the shrivelled
-neck. The portion of the embryo attached to the base of the archegonium
-is the sterile part and is called the “foot,” and later develops the
-stalk. The sporogonium during all the stages of its development derives
-<span class="pagenum"><a name="Page_235" id="Page_235">[Pg 235]</a></span>
-its nourishment from the gametophyte at this point of attachment at
-the base of the archegonium. Soon, as shown in <a href="#FIG_267">fig. 267</a> at
-the right, the outer portion of the sporogonium begins to differentiate into
-the cells which form the elaters and those which form spores. These
-lie in radiating lines side by side, and form what is termed the
-<i>archesporium</i>. Each fertile cell forms four spores just as in riccia.
-They are thus called the mother cells of the spores, or spore mother cells.</p>
-
-<p><b>494. How marchantia multiplies.</b>—New plants of marchantia are
-formed by the germination of the spores, and growth of the same to the
-thallus. The plants may also be multiplied by parts of the old ones
-breaking away by the action of strong currents of water, and when they
-lodge in suitable places grow into well-formed plants. As the thallus
-lives from year to year and continues to grow and branch the older
-portions die off, and thus separate plants may be formed from a former
-single one.</p>
-
-<div class="figcenter">
-    <img  id="FIG_268" src="images/fig268.jpg" alt="" width="600" height="423" />
-     <p class="center">Fig. 268.</p>
-     <p class="center">Marchantia plant with cupules and gemmæ; rhizoids below.</p>
-</div>
-
-<p><b>495. Buds, or gemmæ, of marchantia.</b>—But there is another
-way in which marchantia multiplies itself. If we examine the upper
-surface of such a plant as that shown in <a href="#FIG_268">fig. 268</a>, we shall
-see that there are minute cup-shaped or saucer-shaped vessels, and within them
-minute green bodies. If we examine a few of these minute bodies with
-the microscope we see that they are flattened, biconvex, and at two
-opposite points on the margin there is an indentation similar to that
-which appears at the growing end of the old marchantia thallus. These
-are the growing points of these little buds. When they free themselves
-<span class="pagenum"><a name="Page_236" id="Page_236">[Pg 236]</a></span>
-from the cups they come to lie on one side. It does not matter on what
-side they lie, for whichever side it is, that will develop into the
-lower side of the thallus, and forms rhizoids, while the upper surface
-will develop the stomates.</p>
-
-<h4><a name="XXIV_2" id="XXIV_2">Leafy-stemmed liverworts.</a></h4>
-
-<p><b>496.</b> We should now examine more carefully than we have done
-formerly a few of the leafy-stemmed liverworts (called foliose liverworts).</p>
-
-<div class="figcenter">
-    <img src="images/fig269.jpg" alt="" width="600" height="394" />
-   <div class="blockquot">
-    <p class="center">Fig. 269.</p>
-    <p>Section of thallus of marchantia. <i>A</i>, through the middle portion; <i>B</i>,
-         through the marginal portion; <i>p</i>, colorless layer; <i>chl</i>, chlorophyll
-         layer; <i>sp</i>, stomate; <i>h</i>, rhizoids; <i>b</i>, leaf-like outgrowths on
-         underside (Goebel).</p>
-  </div>
-</div>
-
-<p><b>497. Frullania</b> (<a href="#FIG_32">Fig. 32</a>).—This plant grows on
-the bark of logs, as well as on the bark of standing trees. It lives in quite dry
-situations. If we examine the leaves we will see how it is able to do
-this. We note that there are two rows of lateral leaves, which are very
-close together, so close in fact that they overlap like the shingles
-on a roof. Then, as the creeping stems lie very close to the bark of
-the tree, these overlapping leaves, which also hug close to the stem
-and bark, serve to retain moisture which trickles down the bark during
-rains. If we examine these leaves from the under side as shown in <a href="#FIG_34">fig. 34</a>,
-we see that the lower or basal part of each one is produced into a
-peculiar lobe which is more or less cup-shaped. This catches water and
-holds it during dry weather, and it also holds moisture which the plant
-<span class="pagenum"><a name="Page_237" id="Page_237">[Pg 237]</a></span>
-absorbs during the night and in damp days. There is so much moisture in
-these little pockets of the under side of the leaf that minute animals
-have found them good places to live in, and one frequently discovers
-them in this retreat. There is here also a third row of poorly
-developed leaves on the under side of the stem.</p>
-
-<p><b>498. Porella.</b>—Growing in similar situations is the plant known
-as porella. Sometimes there are a few plants in a group, and at other
-times large mats occur on the bark of a trunk. This plant, porella,
-also has closely overlapping leaves in rows on opposite sides of the
-stem, and the lower margin of each leaf is curved under somewhat as in
-frullania, though the pocket is not so well formed.</p>
-
-<p>The larger plants are female, that is they bear archegonia, while
-the male plants, those which bear antheridia, are smaller and the
-antheridia are borne on small lateral branches. The antheridia
-are borne in the axils of the leaves. Others of the leafy-stemmed
-liverworts live in damp situations. Some of these, as Cephalozia, grow
-on damp rotten logs. Cephalozia is much more delicate, and the leaves
-are farther apart. It could not live in such dry situations where the
-frullania is sometimes found. If possible the two plants should be
-compared in order to see the adaptation in the structure and form to
-their environment.</p>
-
-<div class="figcenter">
-    <img src="images/fig270.jpg" alt="" width="500" height="409" />
-   <div class="blockquot">
-    <p class="center">Fig. 270.</p>
-    <p>Thallus of a thalloid liverwort (blasia) showing lobed margin
-       of the frond, intermediate between thalloid and foliose plant.</p>
-  </div>
-</div>
-
-<p><b>499. Sporogonium of a foliose liverwort.</b>—The sporogonium of the
-leafy-stemmed liverworts is well represented by that of several genera.
-<span class="pagenum"><a name="Page_238" id="Page_238">[Pg 238]</a></span>
-We may take for this study the one illustrated in <a href="#FIG_274">fig. 274</a>,
-but another will serve the purpose just as well. We note here that it
-consists of a rounded capsule borne aloft on a long stalk, the stalk
-being much longer proportionately than in marchantia. At maturity the
-capsule splits down into four quadrants, the wall forming four valves,
-which spread apart from the unequal drying of the cells, so that the
-spores are set free, as shown in <a href="#FIG_278">fig. 276</a>. Some of the
-cells inside of the capsule develop elaters here also as well as spores. These are
-illustrated in <a href="#FIG_278">fig. 278</a>.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <p class="space-below1">&nbsp;</p>
-    <img src="images/fig271.jpg" alt="" width="250" height="458" />
-    <p class="center">Fig. 271.<br /> Foliose liverwort, male plant<br />
-            showing antheridia in axils of<br /> the leaves (a jungermannia).</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig272.jpg" alt="" width="175" height="230" />
-      <p class="center">Fig. 272.<br /> Antheridium of a foliose<br /> liverwort (jungermannia).</p>
-
-      <img src="images/fig273.jpg" alt="" width="140" height="228" />
-      <p class="center">Fig. 273.<br /> Foliose liverwort,<br /> female plant with<br /> rhizoids.</p>
-  </div>
-</div>
-
-<p><b>500.</b> In this plant we see that the sporophyte remains attached to
-<span class="pagenum"><a name="Page_239" id="Page_239">[Pg 239]</a></span>
-the gametophyte, and thus is dependent on it for sustenance. This is
-true of all the plants of this group. The sporophyte never becomes
-capable of an independent existence, and yet we see that it is becoming
-larger and more highly differentiated than in the simple riccia.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_274" src="images/fig274.jpg" alt="" width="150" height="473" />
-    <p class="center">Fig. 274.<br /> Fruiting plant of<br /> a foliose liverwort<br /> (jungermannia).<br />
-            Leafy part is the<br /> gametophyte; stalk<br /> and capsule is<br />
-            the sporophyte<br /> (sporogonium in<br /> the bryophytes).</p>
-   </div>
-  <div class="figsub">
-       <p>&nbsp;</p>
-      <img  id="FIG_275-277" src="images/fig275.jpg" alt="" width="100" height="111" />
-      <p class="center">Fig. 275.<br /> Opening capsule<br /> showing escape<br /> of spores and<br /> elaters.</p>
-
-      <img src="images/fig276.jpg" alt="" width="100" height="135" />
-      <p class="center">Fig. 276.<br /> Capsule parted<br /> down to the<br /> stalk.</p>
-
-      <img src="images/fig277.jpg" alt="" width="100" height="69" />
-      <p class="center">Fig. 277.<br /> Four spores<br /> from mother<br /> cell held<br /> in a group.</p>
-  </div>
-  <div class="figsub">
-    <img  id="FIG_278" src="images/fig278.jpg" alt="" width="180" height="513" />
-    <p class="center">Fig. 278.<br /> Elaters, at left<br /> showing the two<br />
-             spiral marks, at<br /> right a branched<br /> elater.</p>
-   </div>
-        <p class="center">Figs. 275-278.—Sporogonium of liverwort (jungermannia) opening by
-                          splitting into four parts,<br /> showing details of elaters and spores.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_240" id="Page_240">[Pg 240]</a></span></p>
-
-<h4><a name="XXIV_3" id="XXIV_3">The Horned Liverworts.</a><a name="FNanchor_25_25" id="FNanchor_25_25"></a><a href="#Footnote_25_25" class="fnanchor">[25]</a></h4>
-
-<p><b>501. The horned liverworts</b> take their name from the shape of
-the sporogonium. This is long, slender, cylindrical, pointed, and very
-slightly curved, suggesting the shape of a minute horn. Anthoceros is
-one of the most common and widely distributed species. The plant grows
-on damp soil or on mud.</p>
-
-<p class="center">Anthoceros.</p>
-
-<p><b>502. The gametophyte.</b>—The gametophyte is thalloid. It is thin,
-flattened, green, irregularly ribbon-shaped and branched. It lies on
-the soil and is more or less crisped or wavy, or curled, the edges
-nearly plane, or somewhat irregular, and with minute lobes, or notches,
-especially near the growing end. The general form and branching can
-be seen in <a href="#FIG_279">fig. 279</a>. Where the plants are much crowded the
-thallus is more irregular, and often possesses numerous small lateral branches
-in addition to the main lobes. Upon the under side are the slender
-rhizoids, which attach to the soil. With a hand lens there can be seen
-also upon the under side small dark, rounded and thickened spots, where
-an alga (nostoc) is located.</p>
-
-<p class="center">Sexual Organs of Anthoceros.</p>
-
-<p><b>502. The sexual organs of anthoceros</b> differ considerably from
-those of the other liverworts studied. In the first place they are
-immersed in the true tissue of the thallus, i.e., they do not project
-above the surface.</p>
-
-<div class="figcenter">
-    <img  id="FIG_279" src="images/fig279.jpg" alt="" width="450" height="463" />
-   <div class="blockquot">
-    <p class="center">Fig. 279.</p>
-    <p>Anthoceros gracilis. <i>A</i>, several gametophytes, on which sporangia
-       have developed; <i>B</i>, an enlarged sporogonium, showing its elongated
-       character and dehiscence by two valves, leaving exposed the slender
-       columella on the surface of which are the spores, <i>C</i>, <i>D</i>, <i>E</i>, <i>F</i>,
-       elaters of various forms, <i>G</i>, spores. (After Schiffner.)</p>
-  </div>
-</div>
-
-<p><b>503. Antheridia.</b>—The antheridium arises from an internal cell
-of the thallus, a cell just below the upper surface. This cell develops
-<span class="pagenum"><a name="Page_241" id="Page_241">[Pg 241]</a></span>
-usually a group of antheridia which lie in a cavity formed around this
-cell as the thallus continues to grow. They are situated along the
-middle line of the thallus, and can be seen by making a section in this
-direction. The antheridia are oval or rounded, have a wall of one layer
-of cells which contains the sperm cells, and each antheridium has a
-slender stalk. The sperms are like those of the true liverworts.</p>
-
-<p><b>504. Archegonia.</b>—The archegonia are also borne along the
-middle line of the thallus. Each one arises at an early stage in the
-development of the tissue of the thallus from a superficial cell,
-but the archegonium does not project above the surface. The venter
-therefore which contains the egg is deep down in the thallus, the wall
-of the neck is formed from cells indistinguishable from the adjoining
-cells of the thallus and opens at the surface.</p>
-
-<p class="center">Sporophyte of Anthoceros.</p>
-
-<p><b>505. The Sporogonium.</b>—The sporogonium is developed from the
-fertilized egg, fertilization resulting of course from the fusion of
-one of the sperms with the nucleus of the egg. From the lower part
-of the embryo certain cells elongate and push out like rhizoids into
-the thallus (gametophyte), but never reach the outside so that the
-sporogonium derives its nutriment from the gametophyte in a parasitic
-manner like the true liverworts. It is surrounded at the base by a
-sheath, an outgrowth of the gametophyte.</p>
-
-<p><b>506. Growing point of the sporogonium.</b>—A remarkable thing
-about the sporogonium of anthoceros, and its relatives, is that the
-growing point instead of being situated at the free end is located near
-the base, just above the nourishing foot. Thus the upper part of the
-sporogonium is older. In the old sporogonia there may be ripe spores
-near the free end, young ones near the middle, and undifferentiated
-growing tissue near the base. A longitudinal section of a sporogonium
-just as the spores are ripening will show this.</p>
-
-<p><b>507. Structure of the sporogonium.</b>—A longitudinal section
-of the sporogonium shows that the spore-bearing tissue occupies a
-comparatively small portion of the sporogonium. In the section there
-is a narrow layer (two cells thick) on either side and joined at the
-top. In the entire sporogonium this fertile tissue is in the shape of
-an inverted test tube situated inside of the sporogonium. The wall of
-the sporogonium is about four cells thick. The sterile tissue inside
-of the spore-bearing tube is the columella. The cells of the wall
-contain chlorophyll, and there are true stomata with guard cells in the
-epidermal layer.</p>
-
-<p><b>508. Spores and elaters.</b>—In the spore-bearing tissue there
-are two layers of cells (the archesporium). Each cell is a potential
-mother cell. The cells, however, of alternate tiers do not form spores.
-<span class="pagenum"><a name="Page_242" id="Page_242">[Pg 242]</a></span>
-They elongate some what and are somewhat irregular and sometimes divide
-or branch. They are supposed to represent rudimentary <i>elaters</i>. The
-cells in the other tiers are actual mother cells, and each one forms
-four spores.</p>
-
-<p><b>509. The sporophyte of anthoceros</b> represents the highest type
-found in the liverworts. The spongy green parenchyma forming the
-wall, with the stomata in the epidermal layer, fits this tissue for
-the process of photosynthesis, so that this part of the sporophyte
-functions as the green leaf of the seed plants. It has been suggested
-by some that if the rhizoids on the nourishing foot could only extend
-outside and anchor in the soil, the sporophyte of anthoceros could live
-an independent existence. But we see that it stops short of that.</p>
-
-<h4><a name="XXIV_4" id="XXIV_4">Classification of the Liverworts.</a></h4>
-
-<p class="center">CLASS HEPATICÆ.</p>
-
-<p><b>510. Order Marchantiales.</b><a name="FNanchor_26_26" id="FNanchor_26_26"></a><a href="#Footnote_26_26" class="fnanchor">[26]</a>
-—There are two families represented in the United States.</p>
-
-<p>Family Ricciaceæ, including Riccia and Ricciocarpus.</p>
-
-<p>Family Marchantiaceæ, including Marchantia, Fegatella (= Conocephalus),
-Fimbriaria, Targionia, etc.</p>
-
-<p><b>511. Order Jungermanniales.</b><a name="FNanchor_27_27" id="FNanchor_27_27"></a><a href="#Footnote_27_27" class="fnanchor">[27]</a>—There
-are two subdivisions of this order. <i>The Anacrogynæ</i> include chiefly
-thalloid forms with continued apical growth, the archegonia back of the
-apical cell. Examples: Blasia, Aneura, Pellia, etc.</p>
-
-<p><i>The Acrogynæ</i> include chiefly foliose forms, the archegonia arising
-from the apical cell and in such cases interrupting apical growth.
-Examples: Cephalozia, Frullania, Bazzania, Jungermannia, Ptilidium, Porella, etc.</p>
-
-<p class="center">CLASS ANTHOCEROTES.</p>
-
-<p><b>512. The Anthocerotes</b> have formerly been placed with the
-Hepaticæ as an order. But because of their wide divergence from
-the other liverworts in the development of the sexual organs, and
-especially in the structure of the sporophyte, they are now by some
-separated as a distinct class. There is one order.</p>
-
-<p><b>Order Anthocerotales.</b><a name="FNanchor_28_28" id="FNanchor_28_28"></a><a href="#Footnote_28_28" class="fnanchor">[28]</a>—This
-includes one family (Anthocerotaceæ) with Anthoceros and Notothylas in
-Europe and North America, and Dendroceros in the tropics. The latter is epiphytic.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_243" id="Page_243">[Pg 243]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XXV" id="CHAPTER_XXV">CHAPTER XXV.</a><br />
-<span class="h_subtitle">MOSSES (MUSCI).</span></h3>
-</div>
-
-<p><b>513.</b> We are now ready to take up the more careful study of the
-moss plant. There are a great many kinds of mosses, and they differ
-greatly from each other in the finer details of structure. Yet there
-are certain general resemblances which make it convenient to take for
-study almost any one of the common species in a neighborhood, which
-forms abundant fruit. Some, however, are more suited to a first study
-than others. (Polytrichum and funaria are good mosses to study.)</p>
-
-<p><b>514. Mnium.</b>—We will select here the plant shown in <a href="#FIG_280">fig. 280</a>.
-This is known as a mnium (M. affine), and one or another of the species
-of mnium can be obtained without much difficulty. The mosses, as we
-have already learned, possess an axis (stem) and leaf-like expansions,
-so that they are leafy-stemmed plants also. Certain of the branches of
-the mnium stand upright, or nearly so, and the leaves are all of the
-same size at any given point on the stem, as seen in the figure. There
-are three rows of these leaves, and this is true of most of the mosses.</p>
-
-<p><b>515.</b> The mnium plants usually form quite extensive and pretty
-mats of green in shady moist woods or ravines. Here and there among the
-erect stems are prostrate ones, with two rows of prominent leaves so
-arranged that it reminds one of some of the leafy-stemmed liverworts.
-If we examine some of the leaves of the mnium we see that the greater
-part of the leaf consists of a single layer of green cells, just as
-is the case in the leafy-stemmed liverworts. But along the middle
-line is a thicker layer, so that it forms a distinct midrib. This is
-<span class="pagenum"><a name="Page_244" id="Page_244">[Pg 244]</a></span>
-characteristic of the leaves of mosses, and is one way in which they
-are separated from the leafy-stemmed liverworts, the latter never
-having a midrib.</p>
-
-<div class="figcenter">
-    <img  id="FIG_280" src="images/fig280.jpg" alt="" width="450" height="456" />
-   <div class="blockquot">
-    <p class="center">Fig. 280.</p>
-    <p>Portion of moss plant of Mnium affine, showing two sporogonia from one
-       branch. Capsule at left has just shed the cap or operculum; capsule at
-       right is shedding spores, and the teeth are bristling at the mouth.
-       Next to the right is a young capsule with calyptra still attached; next
-       are two spores enlarged.</p>
-  </div>
-</div>
-
-<p><b>516. The fruiting moss plant.</b>—In <a href="#FIG_280">fig. 280</a> is
-a moss plant “in fruit,” as we say. Above the leafy stem a slender stalk bears
-the capsule, and in this capsule are borne the spores. The capsule then
-belongs to the <i>sporophyte phase</i> of the moss plant, and we should
-inquire whether the entire plant as we see it here is the sporophyte,
-or whether part of it is gametophyte. If a part of it is gametophyte
-and a part sporophyte, then where does the one end and the other begin?
-If we strip off the leaves at the end of the leafy stem, and make a
-longisection in the middle line, we should find that the stalk which
-bears the capsule is simply stuck into the end of the leafy stem, and
-is not organically connected with it. This is the dividing line, then,
-between the gametophyte and the sporophyte. We shall find that here the
-<span class="pagenum"><a name="Page_245" id="Page_245">[Pg 245]</a></span>
-archegonium containing the egg is borne, which is a surer way of
-determining the limits of the two phases of the plant.</p>
-
-<p><b>517. The male and female moss plants.</b>—The two plants of mnium
-shown in figs. <a href="#FIG_281">281</a>, <a href="#FIG_281">282</a> are quite different,
-as one can easily see, and yet they belong to the same species. One is a female plant,
-while the other is a male plant. The sexual organs then in mnium, as in many
-others of the mosses, are borne on separate plants. The archegonia are
-borne at the end of the stem, and are protected by somewhat narrower
-leaves which closely overlap and are wrapped together. They are similar
-to the archegonia of the liverworts.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <img  id="FIG_281" src="images/fig281.jpg" alt="" width="200" height="459" />
-   <p class="center">Fig. 281.<br /> Female plant (gametophyte) of<br />
-      a moss (mnium), showing<br /> rhizoids below, and the<br />
-      tuft of leaves above which<br /> protect the archegonia.</p>
-  </div>
-  <div class="figsub">
-   <img  id="FIG_282" src="images/fig282.jpg" alt="" width="235" height="456" />
-   <p class="center">Fig. 282.<br /> Male plant (gametophyte) of<br />
-      a moss (mnium) showing<br /> rhizoids below and the<br />
-      antheridia at the center<br /> above surrounded by<br />
-      the rosette of leaves.</p>
-  </div>
-</div>
-
-<p>The male plants of mnium are easily selected, since the leaves at the
-end of the stem form a broad rosette with the antheridia, and some
-sterile threads packed closely together in the center. The ends of the
-mass of antheridia can be seen with the naked eye, as shown in <a href="#FIG_282">fig. 282</a>.
-<span class="pagenum"><a name="Page_246" id="Page_246">[Pg 246]</a></span>
-When the antheridia are ripe, if we make a section through a
-cluster, or if we merely tease out some from the end with a needle in
-a drop of water on the slide, then prepare for examination with the
-microscope, we can see the form of the antheridia. They are somewhat
-clavate or elliptical in outline, as seen in <a href="#FIG_284">fig. 284</a>.
-Between them there stand short threads composed of several cells containing
-chlorophyll grains. These are sterile threads (paraphyses).</p>
-
-<p><b>518. Sporogonium.</b>—In <a href="#FIG_280">fig. 280</a> we see illustrated
-a sporogonium of mnium, which is of course developed from the fertilized egg-cell
-of the archegonium. There is a nearly cylindrical capsule, bent downward,
-and supported on a long slender stalk. Upon the capsule is a peculiar
-cap,<a name="FNanchor_29_29" id="FNanchor_29_29"></a><a href="#Footnote_29_29" class="fnanchor">[29]</a>
-shaped like a ladle or spatula. This is the remnant of the old
-archegonium, which, for a time surrounded and protected the young
-embryo of the sporogonium, just as takes place in the liverworts. In
-most of the mosses this old remnant of the archegonium is borne aloft
-on the capsule as a cap, while in the liverworts it is thrown to one
-side as the sporogonium elongates.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <img  id="FIG_283" src="images/fig283.jpg" alt="" width="300" height="319" />
-   <p class="center">Fig. 283.<br /> Section through end of stem of<br />
-     female plant of mnium, showing<br /> archegonia at the center. One<br />
-     archegonium shows the egg. On<br /> the sides are sections of the<br />
-     protecting leaves.</p>
-  </div>
-  <div class="figsub">
-   <a><img  id="FIG_284" src="images/fig284.jpg" alt="" width="140" height="321" /></a>
-   <p class="center">Fig. 284.<br /> Antheridium of mnium with<br />
-     jointed paraphysis at the<br /> left; spermatozoids at<br />
-     the right.</p>
-  </div>
-</div>
-
-<p><b>519. Structure of the moss capsule.</b>—At the free end on the moss
-<span class="pagenum"><a name="Page_247" id="Page_247">[Pg 247]</a></span>
-capsule as shown in the case of mnium in <a href="#FIG_280">fig. 280</a>, after the
-remnant of the archegonium falls away, there is seen a conical lid which fits
-closely over the end. When the capsule is ripe this lid easily falls
-away, and can be brushed off so that it is necessary to handle the
-plants with care if it is desired to preserve this for study.</p>
-
-<p><b>520.</b> When the lid is brushed away as the capsule dries more we
-see that the end of the capsule covered by the lid appears “frazzled.”
-If we examine this end with the microscope we see that the tissue of
-the capsule here is torn with great regularity, so that there are two
-rows of narrow, sharp teeth which project outward in a ring around the
-opening. If we blow our “breath” upon these teeth they will be seen to
-move, and as the moisture disappears and reappears in the teeth, they
-close and open the mouth of the capsule, so sensitive are they to the
-changes in the humidity of the air. In this way all of the spores are
-prevented to some extent from escaping from the capsule at one time.</p>
-
-<p><b>521.</b> Note. If we make a section longitudinal of the capsule of
-mnium, or some other moss, we find that the tissue which develops the
-spores is much more restricted than in the capsule of the liverworts
-which we have studied. The spore-bearing tissue is confined to a single
-layer which extends around the capsule some distance from the outside
-of the wall, so that a central cylinder is left of sterile tissue. This
-is the columella, and is present in nearly all the mosses. Each of the
-cells of the fertile layer divides into four spores.</p>
-
-<div class="figcenter">
-    <img  id="FIG_285" src="images/fig285.jpg" alt="" width="350" height="500" />
-   <div class="blockquot">
-    <p class="center">Fig. 285.</p>
-    <p>Two different stages of young sporogonium of a moss, still within the
-         archegonium and wedging their way into the tissue of the end of the
-         stem. <i>h</i>, neck of archegonium; <i>f</i>, young sporogonium. This
-         shows well the connection of the sporophyte with the gametophyte.</p>
-  </div>
-</div>
-
-<p><b>522. Development of the sporogonium.</b>—The egg-cell after
-fertilization divides by a wall crosswise to the axis of the
-archegonium. Each of these cells continues to divide for a time, so
-that a cylinder pointed at both ends is formed. The lower end of
-this cylinder of tissue wedges its way down through the base of the
-archegonium into the tissue of the end of the moss stem as shown in
-<span class="pagenum"><a name="Page_248" id="Page_248">[Pg 248]</a></span>
-<a href="#FIG_285">fig. 285</a>. This forms the foot through which the nutrient
-materials are passed from the gametophyte to the sporogonium. The upper part
-continues to grow, and finally the upper end differentiates into the
-mature capsule.</p>
-
-<p><b>523. Protonema of the moss.</b>—When the spores of a moss germinate
-they form a thread-like body, with chlorophyll. This thread becomes
-branched, and sometimes quite extended tangles of these threads are
-formed. This is called the protonema, that is <i>first thread</i>. The older
-threads become finally brown, while the later ones are green. From this
-protonema at certain points buds appear which divide by close oblique
-walls. From these buds the leafy stem of the moss plant grows. Threads
-similar to these protonemal threads now grow out from the leafy stem,
-to form the rhizoids. These supply the moss plant with nutriment, and
-now the protonema usually dies, though in some few species it persists
-for long periods.</p>
-
-<h4><a name="XXV_1" id="XXV_1">Classification of the Mosses.</a></h4>
-
-<p class="center">CLASS MUSCINEÆ (MUSCI).</p>
-
-<p><b>524. Order Sphagnales.</b><a name="FNanchor_30_30" id="FNanchor_30_30"></a><a href="#Footnote_30_30" class="fnanchor">[30]</a>—This
-order includes the peat mosses. There is but one family (Sphagnaceæ)
-and but a single genus (Sphagnum). The peat mosses are widely
-distributed over the globe, chiefly occurring in moors, or “bogs,”
-usually low ground around the shores of lakes, ponds, or along streams,
-but they often occur on wet dripping rocks in cool shady places. Small
-ponds are sometimes filled in by their growth. As the sphagnum growing
-in such an abundance of water only partially decays, “ground” is built
-up rather rapidly, and the sphagnum remains are known as “peat.” This
-“ground”-building peculiarity of sphagnum sometimes enables the plant
-(often in conjunction with others) to fill in ponds completely. (See
-Atoll Moor, Chapter LV.)</p>
-
-<p>The gametophyte of sphagnum, like that of all the mosses, is dimorphic,
-but the first part (or protonema) which develops from the spores is
-thalloid, and therefore more like the thallose liverworts. The leafy
-axis (or gametophore) which develops from the thalloid form is very
-characteristic (see Chapter LV).</p>
-
-<p>The archegonia are borne on the free end of the main axis, while the
-antheridia are borne on short branches which are brightly colored, red,
-yellow, etc. The sporophyte (sporogonium) is globose and possesses a
-broad foot anchored in the end of a naked prolongation of the end of
-the leafy gametophore. This naked prolongation of the gametophore looks
-like the stalk of the sporogonium, but a study of its connection with
-the sporogonium shows that it is part of the gametophyte, which is only
-developed after the fertilization of the egg in the archegonium. In the
-sporogonium there is a short columella, and the archesporium is in the
-form of an inverted cup.
-<span class="pagenum"><a name="Page_249" id="Page_249">[Pg 249]</a></span></p>
-
-<p><b>525. Order Andreæales.</b><a name="FNanchor_31_31" id="FNanchor_31_31"></a><a href="#Footnote_31_31" class="fnanchor">[31]</a>—This
-order includes the single genus Andreæa. The plants are small but form
-extensive mats, growing on rocks in arctic or alpine regions usually.
-They are sometimes found in great abundance on bare, rather dry rocks
-on mountains. The protonema is somewhat thalloid. The sporogonium opens
-by splitting longitudinally into four valves. An elongated columella
-is present so that the archesporium is shaped like an inverted
-test tube.</p>
-
-<p><b>526. Order Archidiales.</b><a name="FNanchor_32_32" id="FNanchor_32_32"></a><a href="#Footnote_32_32" class="fnanchor">[32]</a>—This
-order contains the single genus Archidium, and by some is placed as
-an aberrant genus in the Bryales. There is no columella in the simple
-sporogonium. The archesporium occupies all the internal part of the
-sporogonium, some cells being fertile and others sterile.</p>
-
-<p><b>527. Order Bryales.</b><a name="FNanchor_33_33" id="FNanchor_33_33"></a><a href="#Footnote_33_33" class="fnanchor">[33]</a>—These
-include the higher mosses, and a very large number of genera and
-species. The protonema is filamentous and branched except in a few
-forms where it is partly thalloid as in Tetraphis (= Georgia).
-(Tetraphis pellucida is a common moss on very rotten logs. The capsule
-has four prominent teeth.) In a few of the lower genera (Phascum,
-Pleuridium, etc.) the capsule opens irregularly, but in the larger
-number the capsule opens by a lid (operculum). A cylindrical columella
-is present, and the archesporium is in the form of a tube open at both
-ends. (Examples: Polytrichum, Bryum, Mnium, Hypnum, etc.)
-<span class="pagenum"><a name="Page_250" id="Page_250">[Pg 250]</a></span></p>
-
-<p><b>528.</b></p>
-<p class="center">TABLE SHOWING RELATION OF GAMETOPHYTE AND<br />
-                  SPOROPHYTE IN THE LIVERWORTS AND MOSSES.</p>
-
-<table class="smallfont" border="0" cellspacing="0" summary=" " cellpadding="0" rules="cols" >
-  <thead><tr>
-      <th class="tdc bb2" colspan="9">&nbsp;</th>
-   </tr><tr>
-      <th class="tdc bb2" rowspan="2">&nbsp;</th>
-      <th class="tdc bb2" colspan="4">GAMETOPHYTE.<br /> (Prominent part of the plant.<br /> Leads an independent existence.)</th>
-      <th class="tdc bb2" colspan="3">SPOROPHYTE<br />(Attached to gametophyte and dependent on it for nourishment.)</th>
-      <th class="tdc bb2" rowspan="2"><span class="smcap">Beginning<br /> of<br /> Gametophyte.</span></th>
-   </tr><tr>
-      <th class="tdc bb2"><span class="smcap">Vegetative<br />Phase</span></th>
-      <th class="tdc bb2"><span class="smcap">Vegetative<br />Mulitipl-<br />ication.</span></th>
-      <th class="tdc bb2" colspan="2">&nbsp;<span class="smcap">Sexual&nbsp;Organs.</span>&nbsp;</th>
-      <th class="tdc bb2"><span class="smcap">Beginning<br /> of<br /> Sporophyte.</span></th>
-      <th class="tdc bb2"><span class="smcap">Sterile&nbsp;Part.</span></th>
-      <th class="tdc bb2"><span class="smcap">Fertile&nbsp;Part.</span></th>
-   </tr>
-  </thead>
-  <tbody><tr>
-      <td class="tdl bb" rowspan="2"><span class="smcap">Riccia.</span></td>
-      <td class="tdl_table bb" rowspan="2"><p>Thallus flattened, ribbon-like, forked, or nearly circular.</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>Sometimes by branching and dying away of older parts.</p></td>
-      <td class="tdc" colspan="2"><p>Immersed by surrounding, upward growth of thallus.</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>Fertilized egg. (Develops sporogonium.)</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>Wall of sporogonium, of one-layer cells.</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>Central mass (archesporium) develops&nbsp;.....</p></td>
-      <td class="tdl bb" rowspan="2">&nbsp;Spores.</td>
-   </tr><tr>
-      <td class="tdl_table bb"><p>Antheridia, with spermatozoids.</p></td>
-      <td class="tdl_table bb"><p>Archegonia, with egg in each.</p></td>
-   </tr><tr>
-      <td class="tdl bb" rowspan="2"><span class="smcap">Marchantia.</span></td>
-      <td class="tdl_table bb" rowspan="2"><p>Thallus flattened, ribbon-like, forked,
-                      male and female plants bear gametophores.</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>By dying away of older parts, and by gemmæ.</p></td>
-      <td class="tdc" colspan="2">Borne on special receptacles on different plants.</td>
-      <td class="tdl_table bb" rowspan="2"><p>Fertilized egg. (Develops sporogonium.)</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>Sterile part of stalked is stalk, wall of capsule
-                      of several layers, elaters.</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>Central part of capsule (archesporium)
-                      develops .....<br /> and elaters.</p></td>
-      <td class="tdl bb" rowspan="2">&nbsp;Spores.</td>
-   </tr><tr>
-      <td class="tdl_table bb"><p>Antheridia, with spermatozoids, borne on antheridiphores,
-                      or male gametophores.</p></td>
-      <td class="tdl_table bb"><p>Archegonia, borne on female gametophore (or archegoniophore),
-                      each with an egg.</p></td>
-   </tr><tr>
-      <td class="tdl bb" rowspan="2"><span class="smcap">Jungermannia&nbsp;<br /> (or Cephalozia,<br /> Porella,</span> etc.)</td>
-      <td class="tdl_table bb" rowspan="2"><p>A plant with apparent leaves and stem; margins of thallus
-                        have become cut into lobes. Male and female plants.</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>By dying away of older parts.</p></td>
-      <td class="tdc" colspan="2">On different plants.</td>
-      <td class="tdl_table bb" rowspan="2"><p>Fertilized egg. (Develops sporogonium.)</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>Sterile part of stalked capsule is stalk, wall
-                         of capsule of several layers, elaters.</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>Central part of capsule (archesporium) develops&nbsp;.....<br />
-                          and elaters.</p></td>
-      <td class="tdl bb" rowspan="2">&nbsp;Spores.</td>
-   </tr><tr>
-      <td class="tdl_table bb"><p>Antheridia, with spermatozoids, in axils of leaves of male plant.</p></td>
-      <td class="tdl_table bb"><p>Archegonia, each with egg, on female plant.</p></td>
-   </tr><tr>
-      <td class="tdl bb" rowspan="2"><span class="smcap">Mosses.<br />
-            &nbsp; Mnium,<br />&nbsp; Polytrichum</span><br />&nbsp; etc.</td>
-      <td class="tdl_table bb" rowspan="2"><p>Plant with apparent leafy axis, 3 rows  of leaves
-                         (similar to jungermannia), borne on an earlier protonemal stage.
-                          Male and female plants.</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>By branching, by growth of protonema from axis, leaves,
-                         or even  sporogonium. (In some genera by gemmæ.)</p></td>
-      <td class="tdc" colspan="2">On different plants.</td>
-      <td class="tdl_table bb" rowspan="2"><p>Fertilized egg. (Develops sporogonium.)</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>Sterile part of stalked capsule is stalk, wall
-                         of capsule of several layers, columella, lid, teeth etc., of
-                         the highly specialized capsule.</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>Cylindrical layer of cells around columella is the
-                          archesporium; it develops&nbsp;.....</p></td>
-      <td class="tdl bb" rowspan="2">&nbsp;Spores.</td>
-   </tr><tr>
-      <td class="tdl_table bb"><p>Antheridia, with spermatozoids, at end of stem of male plant.</p></td>
-      <td class="tdl_table bb"><p>Archegonia each with egg, on female plant. (Calyptra found on
-                         sporogonium is remnant of archegonium.)</p></td>
-   </tr><tr>
-      <td class="tdc bt" colspan="9">&nbsp;</td>
-    </tr>
- </tbody>
-</table>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_251" id="Page_251">[Pg 251]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XXVI" id="CHAPTER_XXVI">CHAPTER XXVI.</a><br />
-<span class="h_subtitle">FERNS.</span></h3>
-</div>
-
-<p><b>529.</b> In taking up the study of the ferns we find plants which
-are very beautiful objects of nature and thus have always attracted
-the interest of those who love the beauties of nature. But they are
-also very interesting to the student, because of certain remarkable
-peculiarities of the structure of the fruit bodies, and especially
-because of the intermediate position which they occupy within the
-plant kingdom, representing in the two phases of their development the
-primitive type of plant life on the one hand, and on the other the
-modern type. We will begin our study of the ferns by taking that form
-which is the more prominent, the fern plant itself.</p>
-
-<p><b>530. The Christmas fern.</b>—One of the ferns which is very common
-in the Northern States, and occurs in rocky banks and woods, is the
-well-known Christmas fern (Aspidium acrostichoides) shown in <a href="#FIG_286">fig. 286</a>.
-The leaves are the most prominent part of the plant, as is the case
-with most if not all our native ferns. The stem is very short and
-for the most part under the surface of the ground, while the leaves
-arise very close together, and thus form a rosette as they rise and
-gracefully bend outward. The leaf is elongate and reminds one somewhat
-of a plume with the pinnæ extending in two rows on opposite sides of
-the midrib. These pinnæ alternate with one another, and at the base of
-each pinna is a little spur which projects upward from the upper edge.
-Such a leaf is said to be pinnate. While all the leaves have the same
-general outline, we notice that certain ones, especially those toward
-<span class="pagenum"><a name="Page_252" id="Page_252">[Pg 252]</a></span>
-the center of the rosette, are much narrower from the middle portion
-toward the end. This is because of the shorter pinnæ here.</p>
-
-<div class="figcenter">
-    <img  id="FIG_286" src="images/fig286.jpg" alt="" width="450" height="471" />
-    <p class="center">Fig. 286.<br /> Christmas fern<br /> (Aspidium acrostichoides).</p>
-</div>
-
-<p><b>531. Fruit “dots” (sorus, indusium).</b>—If we examine the under
-side of such short pinnæ of the Christmas fern we see that there
-are two rows of small circular dots, one row on either side of the
-pinna. These are called the “fruit dots,” or sori (a single one is a
-sorus). If we examine it with a low power of the microscope, or with
-a pocket lens, we see that there is a circular disk which covers more
-or less completely very minute objects, usually the ends of the latter
-projecting just beyond the edge if they are mature. This circular disk
-is what is called the <i>indusium</i>, and it is a special outgrowth of the
-epidermis of the leaf here for the protection of the spore-cases. These
-minute objects underneath are the fruit bodies, which in the case of
-the ferns and their allies are called <i>sporangia</i>. This indusium in the
-case of the Christmas fern, and also in some others, is attached to the
-<span class="pagenum"><a name="Page_253" id="Page_253">[Pg 253]</a></span>
-leaf by means of a short slender stalk which is fastened to the middle
-of the under side of this shield, as seen in cross-section in <a href="#FIG_292">fig. 292</a>.</p>
-
-<p><b>532. Sporangia.</b>—If we section through the leaf at one of the
-fruit dots, or if we tease off some of the sporangia so that the stalks
-are still attached, and examine them with the microscope, we can see
-the form and structure of these peculiar bodies. Different views of a
-sporangium are shown in <a href="#FIG_293">fig. 293</a>. The slender portion is
-the stalk, and the larger part is the spore-case proper. We should examine the
-structure of this spore-case quite carefully, since it will help us to
-understand better than we otherwise could the remarkable operations
-which it performs in scattering the spores.</p>
-
-<div class="figcenter">
-    <img  id="FIG_287" src="images/fig287.jpg" alt="" width="350" height="482" />
-    <p class="center">Fig. 287.<br /> Rhizome with bases of leaves, and<br />
-              roots of the Christmas fern.</p>
-</div>
-
-<p><b>533. Structure of a sporangium.</b>—If we examine one of the
-sporangia in side view as shown in <a href="#FIG_293">fig. 293</a>, we note a prominent
-row of cells which extend around the margin of the dorsal edge from near
-the attachment of the stalk to the upper front angle. The cells are
-prominent because of the thick inner walls, and the thick radial walls
-which are perpendicular to the inner walls. The walls on the back of
-this row and on its sides are very thin and membranous. We should make
-this out carefully, for the structure of these cells is especially
-<span class="pagenum"><a name="Page_254" id="Page_254">[Pg 254]</a></span>
-adapted to a special function which they perform. This row of cells is
-termed the <i>annulus</i>, which means a little ring. While this is not a
-complete ring, in some other ferns the ring is nearly complete.</p>
-
-<div class="figcenter">
-    <img src="images/fig288.jpg" alt="" width="600" height="280" />
-    <p class="center">Fig. 288.<br /> Rhizome of sensitive fern<br />
-                  (Onoclea sensibilis).</p>
-</div>
-<div class="figleft">
-    <img src="images/fig289.jpg" alt="" width="200" height="199" />
-    <p class="center">Fig. 289.<br /> Under side of pinna of<br />
-         Aspidium spinulosum<br /> showing fruit dots<br /> (sori).</p>
-</div>
-
-<p><b>534.</b> In the front of the sporangium is another peculiar group
-of cells. Two of the longer ones resemble the lips of some creature,
-and since the sporangium opens between them they are sometimes termed
-the lip cells. These lip cells are connected with the upper end of the
-annulus on one side and with the upper end of the stalk on the other
-side by thin-walled cells, which may be termed connective cells, since
-they hold each lip cell to its part of the opening sporangium. The
-cells on the side of the sporangium are also thin-walled. If we now
-examine a sporangium from the back, or dorsal edge as we say, it will
-appear as in the left-hand figure. Here we can see how very prominent
-the annulus is. It projects beyond the surface of the other cells of
-<span class="pagenum"><a name="Page_255" id="Page_255">[Pg 255]</a></span>
-the sporangium. The spores are contained inside this case.</p>
-
-<p><b>535. Opening of the sporangium and dispersion of the spores.</b>—If
-we take some fresh fruiting leaves of the Christmas fern, or of any one
-of many of the species of the true ferns just at the ripening of the
-spores, and place a portion of it on a piece of white paper in a dry
-room, in a very short time we shall see that the paper is being dusted
-with minute brown objects which fly out from the leaf. Now if we take
-a portion of the same leaf and place it under the low power of the
-microscope, so that the full rounded sporangia can be seen, in a short
-time we note that the sporangium opens, the upper half curls backward
-as shown in <a href="#FIG_294">fig. 294</a>, and soon it snaps quickly, to near
-its former position, and the spores are at the same time thrown for a considerable
-distance. This movement can sometimes be seen with the aid of a good
-hand lens.</p>
-
-<div class="figcenter">
-    <img src="images/fig290.jpg" alt="" width="600" height="263" />
-    <p class="center">Fig. 290.<br /> Four pinnæ of adiantum, showing recurved<br />
-            margins which cover the sporangia.</p>
-</div>
-<div class="figcenter">
-    <img  id="FIG_291" src="images/fig291.jpg" alt="" width="600" height="348" />
-    <p class="center">Fig. 291.<br /> Section through sorus of Polypodium vulgare
-          showing different<br /> stages of sporangium, and one multicellular capitate hair.</p>
-</div>
-
-<p><b>536. How does this opening and snapping of the sporangium take
-place?</b>—We are now more curious than ever to see just how this
-opening and snapping of the sporangium takes place. We should now mount
-some of the fresh sporangia in water and cover with a cover glass for
-microscopic examination. A drop of glycerine should be placed at one
-side of the cover glass on the slip so that the edge of the glycerine
-will come in touch with the water. Now as one looks through the
-<span class="pagenum"><a name="Page_256" id="Page_256">[Pg 256]</a></span>
-microscope to watch the sporangia, the water should be drawn from under
-the cover glass with the aid of some bibulous paper, like filter paper,
-placed at the edge of the cover glass on the opposite side from the
-glycerine. As the glycerine takes the place of the water around the
-sporangia it draws the water out of the cells of the annulus, just as
-it took the water out of the cells of the spirogyra as we learned some
-time ago. As the water is drawn out of these cells there is produced
-a pressure from without, the atmospheric pressure upon the glycerine.
-This causes the walls of these cells of the annulus to bend inward,
-because, as we have already learned, the glycerine does not pass
-through the walls nearly so fast as the water comes out.</p>
-
-<div class="figcenter">
-    <img  id="FIG_292" src="images/fig292.jpg" alt="" width="600" height="158" />
-    <p class="center">Fig. 292.<br /> Section through sorus and shield-shaped indusium of aspidium.</p>
-</div>
-
-<p><b>537.</b> Now the structure of the cells of this annulus, as we have
-seen, is such that the inner walls and the perpendicular walls are
-stout, and consequently they do not bend or collapse when this pressure
-<span class="pagenum"><a name="Page_257" id="Page_257">[Pg 257]</a></span>
-is brought to bear on the outside of the cells. The thin membranous
-walls on the back (dorsal walls) and on the sides of the annulus,
-however, yield readily to the pressure and bend inward. This, as we
-can readily see, pulls on the ends of each of the perpendicular walls
-drawing them closer together. This shortens the outer surface of the
-annulus and causes it to first assume a nearly straight position, then
-curve backward until it quite or nearly becomes doubled on itself. The
-sporangium opens between the lip cells on the front and the lateral
-walls of the sporangium are torn directly across. The greater mass of
-spores are thus held in the upper end of the open sporangium, and when
-the annulus has nearly doubled on itself it suddenly snaps back again
-in position. While treating with the glycerine we can see all this
-movement take place. Each cell of the annulus acts independently, but
-often they all act in concert. When they do not all act in concert,
-some of them snap sooner than others, and this causes the annulus to
-snap in segments.</p>
-
-<div class="figcenter">
-    <img  id="FIG_293" src="images/fig293.jpg" alt="" width="600" height="358" />
-    <p class="center">Fig. 293.<br /> Rear, side, and front views of fern sporangium.<br />
-               <i>d</i>, <i>e</i>, annulus; <i>a</i>, lip cells.</p>
-</div>
-<hr class="r25" />
-<div class="figcenter">
-    <img  id="FIG_294" src="images/fig294.jpg" alt="" width="600" height="529" />
-    <p class="center">Fig. 294.<br /> Dispersion of spores from sporangium of Aspidium acrostichoides,<br />
-                showing different stages in the opening and snapping of the annulus.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_258" id="Page_258">[Pg 258]</a></span>
-<b>538. The movements of the sporangium can take place in old and dried
-material.</b>—If we have no fresh material to study the sporangium
-with, we can use dried material, for the movements of the sporangia can
-be well seen in dried material, provided it was collected at about the
-time the sporangia are mature, that is at maturity, or soon afterward.
-We take some of the dry sporangia (or we may wash the glycerine off
-those which we have just studied) and mount them in water, and quickly
-examine them with a microscope. We notice that in each cell of the
-annulus there is a small sphere of some gas. The water which bathes the
-walls of the annulus is absorbed by some substance inside these cells.
-This we can see because of the fact that this sphere of gas becomes
-<span class="pagenum"><a name="Page_259" id="Page_259">[Pg 259]</a></span>
-smaller and smaller until it is only a mere dot, when it disappears in
-a twinkling. The water has been taken in under such pressure that it
-has absorbed all the gas, and the farther pressure in most cases closes
-the partly opened sporangium more completely.</p>
-
-<p><b>539.</b> Now we should add glycerine again and draw out the water,
-watching the sporangia at the same time. We see that the sporangia
-which have opened and snapped once will do it again. And so they may
-be made to go through this operation several times in succession. We
-should now note carefully the annulus, that is after the sporangia have
-opened by the use of glycerine. So soon as they have snapped in the
-glycerine we can see those minute spheres of gas again, and since there
-was no air on the outside of the sporangia, but only glycerine, this
-gas must, it is reasoned, have been given up by the water before it was
-all drawn out of the cells.</p>
-
-<p><b>540. The common polypody.</b>—We may now take up a few other ferns
-for study. Another common fern is the polypody, one or more species of
-which have a very wide distribution. The stem of this fern is also not
-usually seen, but is covered with the leaves, except in the case of
-those species which grow on the surface of rocks. The stem is slender
-and prostrate, and is covered with numerous brown scales. The leaves
-are pinnate in this fern also, but we find no difference between the
-fertile and sterile leaves (except in some rare cases). The fruit dots
-occupy much the same positions on the under side of the leaf that they
-do in the Christmas fern, but we cannot find any indusium. In the place
-of an indusium are club-shaped hairs as shown in <a href="#FIG_291">fig. 291</a>.
-The enlarged ends of these clubs reaching beyond the sporangia give some protection
-to them when they are young.</p>
-
-<p><b>541. Other ferns.</b>—We might examine a series of ferns to see
-how different they are in respect to the position which the fruit
-dots occupy on the leaf. The common brake, which sometimes covers
-extensive areas and becomes a troublesome weed, has a stout and smooth
-underground stem (rhizome) which is often 12 to 20 <i>cm</i> beneath the
-surface of the soil. There is a long leaf stalk, which bears the
-lamina, the latter being several times pinnate. The margins of the
-fertile pinnæ are inrolled, and the sporangia are found protected
-underneath in this long sorus along the margin of the pinna. The
-beautiful maidenhair fern and its relatives have obovate pinnæ, and
-the sori are situated in the same positions as in the brake. In other
-ferns, as the walking fern, the sori are borne along by the side of the
-veins of the leaf.</p>
-
-<p><b>542. Opening of the leaves of ferns.</b>—The leaves of ferns
-open in a peculiar manner. The tip of the leaf is the last portion
-<span class="pagenum"><a name="Page_260" id="Page_260">[Pg 260]</a></span>
-developed, and the growing leaf appears as if it was rolled up as in
-<a href="#FIG_287">fig. 287</a> of the Christmas fern. As the leaf
-elongates this portion unrolls.</p>
-
-<p><b>543. Longevity of ferns.</b>—Most ferns live from year to year, by
-growth adding to the advance of the stem, while by decay of the older
-parts the stem shortens up behind. The leaves are short-lived, usually
-dying down each year, and a new set arising from the growing end of the
-stem. Often one can see just back or below the new leaves the old dead
-ones of the past season, and farther back the remains of the petioles
-of still older leaves.</p>
-
-<div class="figcenter">
-    <img  id="FIG_295" src="images/fig295.jpg" alt="" width="400" height="438" />
-    <p class="center">Fig. 295.<br /> Cystopteris bulbifera, young plant growing from bulb.<br />
-                  At right is young bulb in axil of pinna of leaf.</p>
-</div>
-
-<p><b>544. Budding of ferns.</b>—A few ferns produce what are called
-bulbils or bulblets on the leaves. One of these, which is found
-throughout the greater part of the eastern United States, is the
-bladder fern (Cystopteris bulbifera), which grows in shady rocky
-places. The long graceful delicate leaves form in the axils of the
-pinnæ, especially near the end of the leaf, small oval bulbs as shown
-in <a href="#FIG_295">fig. 295</a>. If we examine one of these bladder-like bulbs
-we see that the bulk of it is made up of short thick fleshy leaves, smaller
-ones appearing between the outer ones at the smaller end of the bulb.
-This bulb contains a stem, young root, and several pairs of these
-fleshy leaves. They easily fall to the ground or rocks, where, with
-the abundant moisture usually present in localities where the fern is
-found, the bulb grows until the roots attach the plant to the soil or
-in the crevices of the rocks. A young plant growing from one of these
-bulbils is shown in <a href="#FIG_295">fig. 295</a>.</p>
-
-<p><b>545. Greenhouse ferns.</b>—Some of the ferns grown in
-conservatories have similar bulblets. <a href="#FIG_296">Fig. 296</a> represents
-one of these which is found abundantly on the leaves of Asplenium bulbiferum. These
-bulbils have leaves which are very similar to the ordinary leaf except
-that they are smaller. The bulbs are also much more firmly attached to
-the leaf, so that they do not readily fall away.</p>
-
-<p><b>546.</b> Plant conservatories usually furnish a number of very
-interesting ferns, and one should attempt to make the acquaintance of
-<span class="pagenum"><a name="Page_261" id="Page_261">[Pg 261]</a></span>
-some of them, for here one has an opportunity during the winter season
-not only to observe these interesting plants, but also to obtain
-material for study. In the tree ferns which often are seen growing in
-such places we see examples of the massive trunks and leaves of some of
-the tropical species.</p>
-
-<div class="figcenter">
-    <img  id="FIG_296" src="images/fig296.jpg" alt="" width="400" height="295" />
-    <p class="center">Fig. 296.<br /> Bulbil growing from leaf of asplenium<br /> (<i>A</i>, bulbiferum).</p>
-</div>
-
-<p><b>547. The fern plant is a sporophyte.</b>—We have now studied
-the fern plant, as we call it, and we have found it to represent
-the spore-bearing phase of the plant, that is the <i>sporophyte</i>
-(corresponding to the sporogonium of the liverworts and mosses).</p>
-
-<p><b>548. Is there a gametophyte phase in ferns?</b>—But in the
-sporophyte of the fern, which we should not forget is the fern plant,
-we have a striking advance upon the sporophyte of the liverworts and
-mosses. In the latter plants the sporophyte remained attached to the
-gametophyte, and derived its nourishment from it. In the ferns, as we
-see, the sporophyte has a root of its own, and is attached to the soil.
-Through the aid of root hairs of its own it takes up mineral solutions.
-It possesses also a true stem, and true leaves in which carbon
-conversion takes place. It is able to live independently, then. Does
-a gametophyte phase exist among the ferns? Or has it been lost? If it
-does exist, what is it like, and where does it grow? From what we have
-already learned we should expect to find the gametophyte begin with the
-germination of the spores which are developed on the sporophyte, that
-is on the fern plant itself. We should investigate this and see.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_262" id="Page_262">[Pg 262]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XXVII" id="CHAPTER_XXVII">CHAPTER XXVII.</a><br />
-<span class="h_subtitle">FERNS CONTINUED.</span></h3>
-</div>
-
-<h4><a name="XXVII_1" id="XXVII_1">Gametophyte of ferns.</a></h4>
-
-<p><b>549. Sexual stage of ferns.</b>—We now wish to see what the sexual
-stage of the ferns is like. Judging from what we have found to take
-place in the liverworts and mosses we should infer that the form of the
-plant which bears the sexual organs is developed from the spores. This
-is true, and if we should examine old decaying logs, or decaying wood
-<span class="pagenum"><a name="Page_263" id="Page_263">[Pg 263]</a></span>
-in damp places in the near vicinity of ferns, we should probably find
-tiny, green, thin, heart-shaped growths, lying close to the substratum.
-These are also found quite frequently on the soil of pots in plant
-conservatories where ferns are grown. Gardeners also in conservatories
-usually sow fern spores to raise new fern plants, and usually one can
-find these heart-shaped growths on the surface of the soil where they
-have sown the spores. We may call the gardener to our aid in finding
-them in conservatories, or even in growing them for us if we cannot
-find them outside. In some cases they may be grown in an ordinary room
-by keeping the surfaces where they are growing moist, and the air also
-moist, by placing a glass bell jar over them.</p>
-
-<div class="figcenter">
-    <img  id="FIG_297" src="images/fig297.jpg" alt="" width="600" height="419" />
-  <div class="blockquot">
-    <p class="center">Fig. 297.</p>
-    <p>Prothallium of fern, under side, showing rhizoids, antheridia
-       scattered among and near them, and the archegonia near the sinus.</p>
-  </div>
-</div>
-
-<p><b>550.</b> In <a href="#FIG_297">fig. 297</a> is shown one of these growths
-enlarged. Upon the under side we see numerous thread-like outgrowths, the rhizoids,
-which attach the plant to the substratum, and which act as organs for
-the absorption of nourishment. The sexual organs are borne on the under
-side also, and we will study them later. This heart-shaped, flattened,
-thin, green plant is the <i>prothallium</i> of ferns, and we should now give
-it more careful study, beginning with the germination of the spores.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <p>&nbsp;</p>
-    <img  id="FIG_298" src="images/fig298.jpg" alt="" width="150" height="155" />
-    <p class="center">Fig. 298.<br /> Spore of Pteris serrulata<br /> showing the three-rayed<br />
-          elevation along the side<br /> of which the spore wall<br /> cracks during germination.</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_299" src="images/fig299.jpg" alt="" width="150" height="214" />
-      <p class="center">Fig. 299.<br /> Spore of Aspidium<br /> acrostichoides with<br /> winged exospore.</p>
-  </div>
-  <div class="figsub">
-      <img  id="FIG_300" src="images/fig300.jpg" alt="" width="300" height="206" />
-      <p class="center">Fig. 300.<br /> Spore crushed to remove exospore<br /> and show endospore.</p>
-  </div>
-</div>
-
-<p><b>551. Spores.</b>—We can easily obtain material for the study of the
-spores of ferns. The spores vary in shape to some extent. Many of them
-are shaped like a three-sided pyramid. One of these is shown in <a href="#FIG_298">fig. 298</a>.
-The outer wall is roughened, and on one end are three elevated
-<span class="pagenum"><a name="Page_264" id="Page_264">[Pg 264]</a></span>
-ridges which radiate from a given point. A spore of the Christmas fern
-is shown in <a href="#FIG_299">fig. 299</a>. The outer wall here is more or less
-winged. At <a href="#FIG_300">fig. 300</a> is a spore of the same species from
-which the outer wall has been crushed, showing that there is an inner wall also.
-If possible we should study the germination of the spores of some fern.</p>
-
-<p><b>552. Germination of the spores.</b>—After the spores have been
-sown for about one week to ten days we should mount a few in water for
-examination with the microscope in order to study the early stages. If
-germination has begun, we find that here and there are short slender
-green threads, in many cases attached to brownish bits, the old walls
-of the spores. Often one will sow the sporangia along with the spores,
-and in such cases there may be found a number of spores still within
-the old sporangium wall that are germinating, when they will appear as
-in <a href="#FIG_302">fig. 302</a>.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <p class="space-below2">&nbsp;</p>
-    <img  id="FIG_301" src="images/fig301.jpg" alt="" width="150" height="233" />
-    <p class="center">Fig. 301.<br /> Spores of asplenium;<br /> exospore
-                removed from<br /> the one at the right.</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_302" src="images/fig302.jpg" alt="" width="200" height="297" />
-      <p class="center">Fig. 302.<br /> Germinating spores<br /> of Pteris aquilina<br />
-              still in the sporangium.</p>
-  </div>
-</div>
-<div class="figcenter">
-    <img  id="FIG_303" src="images/fig303.jpg" alt="" width="600" height="297" />
-    <p class="center">Fig. 303.<br />
-          Young prothallium of a fern (niphobolus).</p>
-</div>
-
-<p><b>553. Protonema.</b>—These short green threads are called
-<i>protonemal</i> threads, or <i>protonema</i>, which means a <i>first thread</i>,
-and it here signifies that this short thread only precedes a larger growth
-of the same object. In figs. <a href="#FIG_302">302</a>, <a href="#FIG_303">303</a> are
-shown several stages of germination of different spores. Soon after the short germ tube emerges
-<span class="pagenum"><a name="Page_265" id="Page_265">[Pg 265]</a></span>
-from the crack in the spore wall, it divides by the formation of a
-cross wall, and as it increases in length other cross walls are formed.
-But very early in its growth we see that a slender outgrowth takes
-place from the cell nearest the old spore wall. This slender thread is
-colorless, and is not divided into cells. It is the first rhizoid, and
-serves both as an organ of attachment for the thread, and for taking up
-nutriment.</p>
-
-<p><b>554. Prothallium.</b>—Very soon, if the sowing has not been so
-crowded as to prevent the young plants from obtaining nutriment
-sufficient, we will see that the end of this protonema is broadening,
-as shown in <a href="#FIG_303">fig. 303</a>. This is done by the formation of the
-cell walls in different directions. It now continues to grow in this way, the end
-becoming broader and broader, and new rhizoids are formed from the
-under surface of the cells. The growing point remains at the middle of
-the advancing margin, and the cells which are cut off from either side,
-as they become old, widen out. In this way the “wings,” or margins of
-the little, green, flattened body, are in advance of the growing point,
-and the object is more or less heart-shaped, as shown in <a href="#FIG_297">fig. 297</a>.
-Thus we see how the prothallium of ferns is formed.</p>
-
-<p><b>555. Sexual organs of ferns.</b>—If we take one of the prothallia
-of ferns which have grown from the sowings of fern spores, or one of
-<span class="pagenum"><a name="Page_266" id="Page_266">[Pg 266]</a></span>
-those which may be often found growing on the soil of pots in
-conservatories, mount it in water on a slip, with the under side
-uppermost, we can then examine it for the sexual organs, for these are
-borne in most cases on the under side.</p>
-
-<div class="figcenter">
-    <img src="images/fig304.jpg" alt="" width="600" height="151" />
-  <div class="blockquot">
-    <p class="center">Fig. 304.</p>
-    <p>Male prothallium of a fern (niphobolus), in form of an alga
-          or protonema. Spermatozoids escaping from antheridia.</p>
-  </div>
-</div>
-<hr class="r25" />
-<div class="figcenter">
-    <img  id="FIG_305" src="images/fig305.jpg" alt="" width="500" height="425" />
-  <div class="blockquot">
-    <p class="center">Fig. 305.</p>
-    <p>Male prothallium of fern (niphobolus), showing opened and unopened
-       antheridia; section of unopened antheridium; spermatozoids escaping;
-       spermatozoids which did not escape from the antheridium.</p>
-  </div>
-</div>
-
-<p><b>556. Antheridia.</b>—If we search among the rhizoids we see small
-<span class="pagenum"><a name="Page_267" id="Page_267">[Pg 267]</a></span>
-rounded elevations as shown in <a href="#FIG_297">fig. 297</a> or <a href="#FIG_305">305</a>
-scattered over this portion of the prothallium. These are the antheridia. If the prothallia
-have not been watered for a day or so, we may have an opportunity of
-seeing the spermatozoids coming out of the antheridium, for when the
-prothallia are freshly placed in water the cells of the antheridium
-absorb water. This presses on the contents of the antheridium
-and bursts the cap cell if the antheridium is ripe, and all the
-spermatozoids are shot out. We can see here that each one is shaped
-like a screw, with the coils at first close. But as the spermatozoid
-begins to move this coil opens somewhat and by the vibration of the
-long cilia which are on the smaller end it whirls away. In such
-preparations one may often see them spinning around for a long while,
-and it is only when they gradually come to rest that one can make out
-their form.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <p class="space-below2">&nbsp;</p>
-    <img  id="FIG_306" src="images/fig306.jpg" alt="" width="200" height="165" />
-    <p class="center">Fig. 306.<br /> Section of antheridia<br /> showing sperm cells,<br />
-                   and spermatozoids in<br /> the one at the right.</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_307" src="images/fig307.jpg" alt="" width="200" height="259" />
-      <p class="center">Fig. 307.<br /> Different views of<br /> spermatozoids; in<br />
-                    a quiet condition;<br /> in motion<br /> (Adiantum concinnum).</p>
-  </div>
-  <div class="figsub">
-      <img  id="FIG_308" src="images/fig308.jpg" alt="" width="200" height="282" />
-      <p class="center">Fig. 308.<br /> Archegonium of fern.<br /> Large cell in the center<br />
-              is the egg, next is the<br /> ventral canal cell, and<br />
-              in the canal of the neck<br /> are two nuclei of the<br />
-              canal cell.</p>
-  </div>
-</div>
-<div class="figcenter">
-    <img src="images/fig309.jpg" alt="" width="600" height="285" />
-  <div class="blockquot">
-    <p class="center">Fig. 309.</p>
-    <p>Mature and open archegonium of fern (Adiantum cuneatum) with
-        spermatozoids making their way down through the slime to the egg.</p>
-  </div>
-</div>
-<div class="figleft">
-    <img src="images/fig310.jpg" alt="" width="250" height="165" />
-    <p class="center">Fig. 310.<br /> Fertilization in a fern<br /> (Marattia).<br />
-          <i>sp</i>, spermatozoid fusing with<br /> the nucleus of the egg.<br />
-          (After Campbell.)</p>
-</div>
-
-<p><b>557. Archegonia.</b>—If we now examine closely on the thicker part
-of the under surface of the prothallium, just back of the “sinus,” we
-may see longer stout projections from the surface of the prothallium.
-<span class="pagenum"><a name="Page_268" id="Page_268">[Pg 268]</a></span>
-These are shown in <a href="#FIG_297">fig. 297</a>. They are the archegonia. One
-of them in longisection is shown in <a href="#FIG_308">fig. 308</a>. It is flask-shaped,
-and the broader portion is sunk in the tissue of the prothallium. The egg is in the
-larger part. The spermatozoids when they are swimming around over the
-under surface of the prothallium come near the neck, and here they are
-caught in the viscid substance which has oozed out of the canal of the
-archegonium. From here they slowly swim down the canal, and finally one
-sinks into the egg, fuses with the nucleus of the latter, and the egg
-is then fertilized. It is now ready to grow and develop into the fern
-plant. This brings us back to the sporophyte, which begins with the
-fertilized egg.</p>
-
-<h4><a name="XXVII_2" id="XXVII_2">Sporophyte.</a></h4>
-
-<p><b>558. Embryo.</b>—The egg first divides into two cells as shown in
-<a href="#FIG_228">fig. 228</a>, then into four. Now from each one of these quadrants
-of the embryo a definite part of the plant develops, from one the first leaf,
-<span class="pagenum"><a name="Page_269" id="Page_269">[Pg 269]</a></span>
-from one the stem, from one the root, and from the other the organ
-which is called the foot, and which attaches the embryo to the
-prothallium, and transports nourishment for the embryo until it can
-become attached to the soil and lead an independent existence. During
-this time the wall of the archegonium grows somewhat to accommodate the
-increase in size of the embryo, as shown in figs. <a href="#FIG_312">312</a>,
-<a href="#FIG_313">313</a>. But soon the wall of the archegonium is
-ruptured and the embryo emerges, the root attaches itself to the soil,
-and soon the prothallium dies.</p>
-
-<div class="figcenter">
-    <img src="images/fig311.jpg" alt="" width="500" height="433" />
-    <p class="center">Fig. 311.<br /> Two-celled embryo of Pteris serrulata.<br />
-                Remnant of archegonium neck below.</p>
-</div>
-
-<p>The embryo is first on the under side of the prothallium, and the first
-leaf and the stem curves upward between the lobes of the heart-shaped
-body, and then grows upright as shown in <a href="#FIG_314">fig. 314</a>. Usually
-only one embryo is formed on a single prothallium, but in one case I found a
-prothallium with two well-formed embryos, which are <a href="#FIG_315">figured in 315</a>.</p>
-
-<p><b>559. Comparison of ferns with liverworts and mosses.</b>—In the
-ferns then we have reached a remarkable condition of things as compared
-with that which we found in the mosses and liverworts. In the mosses
-<span class="pagenum"><a name="Page_270" id="Page_270">[Pg 270]</a></span>
-and liverworts the sexual phase of the plant (gametophyte) was the
-prominent one, and consisted of either a thallus or a leafy axis,
-but in either case it bore the sexual organs and led an independent
-existence; that is it was capable of obtaining its nourishment from the
-soil or water by means of organs of absorption belonging to itself, and
-it also performed the office of photosynthesis.</p>
-
-<div class="figcenter">
-    <img  id="FIG_312" src="images/fig312.jpg" alt="" width="500" height="422" />
-  <div class="blockquot">
-    <p class="center">Fig. 312.</p>
-    <p>Young embryo of fern (Adiantum concinnum) in enlarged venter of the archegonium.
-        <i>S</i>, stem; <i>L</i>, first leaf or cotyledon; <i>R</i>, root; <i>F</i>, foot.</p>
-  </div>
-</div>
-
-<p><b>560.</b> The spore-bearing phase (sporophyte) of the liverworts
-and mosses, on the other hand, is quite small as compared with the
-sexual stage, and it is completely dependent on the sexual stage for
-its nourishment, remaining attached permanently throughout all its
-development, by means of the organ called a foot, and it dies after the
-spores are mature.</p>
-
-<p><b>561.</b> Now in the ferns we see several striking differences. In
-the first place, as we have already observed, the spore-bearing phase
-<span class="pagenum"><a name="Page_271" id="Page_271">[Pg 271]</a></span>
-(sporophyte) of the plant is the prominent one, and that which
-characterizes the plant. It also leads an independent existence, and,
-with the exception of a few cases, does not die after the development
-of the spores, but lives from year to year and develops successive
-crops of spores. There is a <i>distinct advance</i> here in the <i>size</i>,
-<i>complexity</i>, and <i>permanency</i> of this phase of the plant.</p>
-
-<p><b>562.</b> On the other hand the sexual phase of the ferns
-(gametophyte), while it still is capable of leading an independent
-existence, is short-lived (with very few exceptions). It is also much
-smaller than most of the liverworts and mosses, especially as compared
-with the size of the spore-bearing phase. The gametophyte phase or
-stage of the plants, then, is decreasing in size and durance as the
-sporophyte stage is increasing. We shall be interested to see if this
-holds good of the fern allies, that is of the plants which belong to
-the same group as the ferns. And as we come later to take up the study
-of the higher plants we must bear in mind to carry on this comparison,
-and see if this progression on the one hand of the sporophyte
-continues, and if the retrogression of the gametophyte continues also.</p>
-
-<div class="figcenter">
-    <img  id="FIG_313" src="images/fig313.jpg" alt="" width="600" height="366" />
-  <div class="blockquot">
-    <p class="center">Fig. 313.</p>
-    <p>Embryo of fern (Adiantum concinnum) still surrounded by the
-       archegonium, which has grown in size, forming the“calyptra.”
-        <i>L</i>, leaf; <i>S</i>, stem; <i>R</i>, root; <i>F</i>, foot.</p>
-  </div>
-</div>
-
-<p><span class="pagenum"><a name="Page_272" id="Page_272">[Pg 272]</a></span></p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_314" src="images/fig314.jpg" alt="" width="200" height="435" />
-    <p class="center">Fig. 314.<br /> Young plant of Pteris serrulata<br /> still attached to prothallium.</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_315" src="images/fig315.jpg" alt="" width="200" height="437" />
-      <p class="center">Fig. 315.<br /> Two embryos from one prothallium<br /> of Adiantum cuneatum.</p>
-  </div>
-</div>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_273" id="Page_273">[Pg 273]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XXVIII" id="CHAPTER_XXVIII">CHAPTER XXVIII.</a><br />
-<span class="h_subtitle">DIMORPHISM OF FERNS.</span></h3>
-</div>
-
-<p><b>563.</b> In comparing the different members of the leaf series there
-are often striking illustrations of the transition from one form to
-another, as we have noted in the case of the trillium flower. This
-occurs in many other flowers, and in some, as in the water-lily, these
-transformations are always present, here showing a transition from the
-petals to the stamens. In the bud-scales of many plants, as in the
-butternut, walnut, currant, etc., there are striking gradations between
-the form of the simple bud-scales and the form of the leaf. Some of the
-most interesting of these transformations are found in the dimorphic ferns.</p>
-
-<p><b>564. Dimorphism in the leaves of ferns.</b>—In the common polypody
-fern, the maidenhair, and in many other ferns, all the leaves are of
-the same form. That is, there is no difference between the fertile leaf
-and the sterile leaf. On the other hand, in the case of the Christmas
-fern we have seen that the fertile leaves are slightly different from
-the sterile leaves, the former having shorter pinnæ on the upper half
-of the leaf. The fertile pinnæ are here the shorter ones, and perform
-but little of the function of carbon conversion. This function is
-chiefly performed by the sterile leaves and by the sterile portions of
-the fertile leaves. This is a short step toward the division of labor
-between the two kinds of leaves, one performing chiefly the labor of
-carbon conversion, the other chiefly the labor of bearing the fruit.</p>
-
-<div class="figcenter">
-    <img  id="FIG_316" src="images/fig316.jpg" alt="" width="300" height="480" />
-    <p class="center">Fig. 316.<br /> Sensitive fern; normal condition of<br />
-                 vegetative leaves and sporophylls.</p>
-</div>
-
-<p><b>565. The sensitive fern.</b>—This division of labor is carried to
-<span class="pagenum"><a name="Page_274" id="Page_274">[Pg 274]</a></span>
-an extreme extent in the case of some ferns. Some of our native ferns
-are examples of this interesting relation between the leaves like
-the common sensitive fern (Onoclea sensibilis) and the ostrich fern
-(O. struthiopteris) and the cinnamon-fern (Osmunda cinnamomea). The
-sensitive fern is here shown in <a href="#FIG_316">fig. 316</a>. The sterile leaves
-are large, broadly expanded, and pinnate, the pinnæ being quite large. The fertile
-leaves are shown also in the figure, and at first one would not take
-them for leaves at all. But if we examine them carefully we see that
-the general plan of the leaf is the same: the two rows of pinnæ which
-are here much shorter than in the sterile leaf, and the pinnules, or
-<span class="pagenum"><a name="Page_275" id="Page_275">[Pg 275]</a></span>
-smaller divisions of the pinnæ, are inrolled into little spherical
-masses which lie close on the side of the pinnæ. If we unroll one
-of these pinnules we find that there are several fruit dots within
-protected by this roll. In fact when the spores are mature these
-pinnules open somewhat, so that the spores may be disseminated.</p>
-
-<div class="figcenter">
-    <img src="images/fig317.jpg" alt="" width="300" height="488" />
-    <p class="center">Fig. 317.<br /> Sensitive fern; one fertile leaf<br />
-                   nearly changed to vegetative leaf.</p>
-</div>
-
-<p>There is very little green color in these fertile leaves, and what
-green surface there is is very small compared with that of the broad
-expanse of the sterile leaves. So here there is practically a complete
-<span class="pagenum"><a name="Page_276" id="Page_276">[Pg 276]</a></span>
-division of labor between these two kinds of leaves, the general plan
-of which is the same, and we recognize each as being a leaf.</p>
-
-<div class="figcenter">
-    <img src="images/fig318.jpg" alt="" width="300" height="434" />
-    <p class="center">Fig. 318.<br /> Sensitive fern, showing one vegetative leaf<br />
-                 and two sporophylls completely transformed.</p>
-</div>
-
-<p><b>566. Transformation of the fertile leaves of onoclea to sterile
-ones.</b>—It is not a very rare thing to find plants of the sensitive
-fern which show intermediate conditions of the sterile and the
-fertile leaf. A number of years ago it was thought by some that this
-represented a different species, but now it is known that these
-intermediate forms are partly transformed fertile leaves. It is a
-very easy matter in the case of the sensitive fern to produce these
-transformations by experiment. If one in the spring, when the sterile
-leaves attain a height of 12 to 16 <i>cm</i> (8-10 inches), cuts them away,
-and again when they have a second time reached the same height, some
-of the fruiting leaves which develop later will be transformed. A few
-<span class="pagenum"><a name="Page_277" id="Page_277">[Pg 277]</a></span>
-years ago I cut off the sterile leaves from quite a large patch of
-the sensitive fern, once in May, and again in June. In July, when
-the fertile leaves were appearing above the ground, many of them
-were changed partly or completely into sterile leaves. In all some
-thirty plants showed these transformations, so that every conceivable
-gradation was obtained between the two kinds of leaves.</p>
-
-<div class="figcenter">
-    <img  id="FIG_319" src="images/fig319.jpg" alt="" width="300" height="445" />
-    <p class="center">Fig. 319.<br /> Normal and transformed sporophyll<br /> of sensitive fern.</p>
-</div>
-
-<p><b>567.</b> It is quite interesting to note the form of these changed
-leaves carefully, to see how this change has affected the pinnæ and the
-sporangia. We note that the tip of the leaf as well as the tips of all
-<span class="pagenum"><a name="Page_278" id="Page_278">[Pg 278]</a></span>
-the pinnæ are more expanded than the basal portions of the same.
-This is due to the fact that the tip of the leaf develops later
-than the basal portions. At the time the stimulus to the change in
-the development of the fertile leaves reached them they were partly
-formed, that is the basal parts of the fertile leaves were more or less
-developed and fixed and could not change. Those portions of the leaf,
-however, which were not yet completely formed, under this stimulus, or
-through correlation of growth, are incited to vegetative growth, and
-expand more or less completely into vegetative leaves.</p>
-
-<p><b>568. The sporangia decrease as the fertile leaf expands.</b>—If
-we now examine the sporangia on the successive pinnæ of a partly
-transformed leaf we find that in case the lower pinnæ are not changed
-at all, the sporangia are normal. But as we pass to the pinnæ which
-show increasing changes, that is those which are more and more
-expanded, we see that the number of sporangia decrease, and many of
-them are sterile, that is they bear no spores. Farther up there are
-only rudiments of sporangia, until on the more expanded pinnæ sporangia
-are no longer formed, but one may still see traces of the indusium.
-On some of the changed leaves the only evidences that the leaf began
-once to form a fertile leaf are the traces of these indusia. In some of
-these cases the transformed leaf was even larger than the sterile leaf.</p>
-
-<p><b>569. The ostrich fern.</b>—Similar changes were also produced in
-the case of the ostrich fern, and in <a href="#FIG_319">fig. 319</a> is shown at
-the left a normal fertile leaf, then one partly changed, and at the right one
-completely transformed.</p>
-
-<p><b>570. Dimorphism in tropical ferns.</b>—Very interesting forms
-of dimorphism are seen in some of the tropical ferns. One of these
-is often seen growing in plant conservatories, and is known as the
-staghorn fern (Platycerium alcicorne). This in nature grows attached to
-the trunks of quite large trees at considerable elevations on the tree,
-sometimes surrounding the tree with a massive growth. One kind of leaf,
-which may be either fertile or sterile, is narrow, and branched in a
-peculiar manner, so that it resembles somewhat the branching of the
-<span class="pagenum"><a name="Page_279" id="Page_279">[Pg 279]</a></span>
-horn of a stag. Below these are other leaves which are different in
-form and sterile. These leaves are broad and hug closely around the
-roots and bases of the other leaves. Here they serve to catch and
-retain moisture, and they also catch leaves and other vegetable matter
-which falls from the trees. In this position the leaves decay and then
-serve as food for the fern.</p>
-
-<div class="figcenter">
-    <img src="images/fig320.jpg" alt="" width="300" height="447" />
-    <p class="center">Fig. 320.<br /> Ostrich fern, showing one normal sporophyll, one<br />
-                 partly transformed, and one completely transformed.</p>
-</div>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_280" id="Page_280">[Pg 280]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XXIX" id="CHAPTER_XXIX">CHAPTER XXIX.</a><br />
-<span class="h_subtitle">HORSETAILS.</span></h3>
-</div>
-
-<p><b>571.</b> Among the relatives of the ferns are the horsetails, so
-called because of the supposed resemblance of the branched stems of
-some of the species to a horse’s tail, as one might infer from the
-plant shown in <a href="#FIG_325">fig. 325</a>. They do not bear the least
-resemblance to the ferns which we have been studying. But then
-relationship in plants does not depend on mere resemblance of outward
-form, or of the prominent part of the plant.</p>
-
-<div class="figcenter">
-    <img  id="FIG_321" src="images/fig321.jpg" alt="" width="600" height="136" />
-    <p class="center">Fig. 321.<br /> Portion of fertile plant of Equisetum arvense<br />
-             showing whorls of leaves and the fruiting spike.</p>
-</div>
-
-<p><b>572. The field equisetum. Fertile shoots.</b>—<a href="#FIG_321">Fig. 321</a>
-represents the common horsetail (Equisetum arvense). It grows in moist sandy
-or gravelly places, and the fruiting portion of the plant (for this
-species is dimorphic), that is the portion which bears the spores,
-appears above the ground early in the spring. It is one of the first
-things to peep out of the recently frozen ground. This fertile shoot
-of the plant does not form its growth this early in the spring. Its
-development takes place under the ground in the autumn, so that with
-the advent of spring it pushes up without delay. This shoot is from
-10 to 20 <i>cm</i>. high, and at quite regular intervals there are slight
-enlargements, the nodes of the stem. The cylindrical portions between
-the nodes are the internodes. If we examine the region of the
-internodes carefully we note that there are thin membranous scales,
-more or less triangular in outline, and connected at their bases into a
-<span class="pagenum"><a name="Page_281" id="Page_281">[Pg 281]</a></span>
-ring around the stem. Curious as it may seem, these are the leaves of
-the horsetail. The stem, if we examine it farther, will be seen to
-possess numerous ridges which extend lengthwise and which alternate
-with furrows. Farther, the ridges of one node alternate with those of
-the internode both above and below. Likewise the leaves of one node
-alternate with those of the nodes both above and below.</p>
-
-<div class="figleft">
-    <img  id="FIG_322" src="images/fig322.jpg" alt="" width="200" height="180" />
-    <p class="center">Fig. 322.<br /> Peltate sporophyll of<br /> equisetum (side view)<br />
-                showing sporangia<br /> on under side.</p>
-</div>
-
-<p><b>573. Sporangia.</b>—The end of this fertile shoot we see possesses
-a cylindrical to conic enlargement. This is the <i>fertile spike</i>, and we
-note that its surface is marked off into regular areas if the spores
-have not yet been disseminated. If we dissect off a few of these
-portions of the fertile spike, and examine one of them with a low
-magnifying power, it will appear like the <a href="#FIG_322">fig. 322</a>. We see
-here that the angular area is a disk-shaped body, with a stalk attached to its
-inner surface, and with several long sacs projecting from its inner
-face parallel with the stalk and surrounding the same. These elongated
-sacs are the <i>sporangia</i>, and the disk which bears them, together with
-the stalk which attaches it to the stem axis, is the <i>sporophyll</i>, and
-thus belongs to the leaf series. These sporophylls are borne in close
-whorls on the axis.</p>
-
-<p><b>574. Spores.</b>—When the spores are ripe the tissue of the
-sporangium becomes dry, and it cracks open and the spores fall out.
-If we look at <a href="#FIG_323">fig. 323</a> we see that the spore is covered
-with a very singular coil which lies close to the wall. When the spore dries this
-uncoils and thus rolls the spore about. Merely breathing upon these
-spores is sufficient to make them perform very curious evolutions by
-the twisting of these four coils which are attached to one place of the
-wall. They are formed by the splitting up of an outer wall of the spore.</p>
-
-<p><b>575. Sterile shoot of the common horsetail.</b>—When the spores are
-ripe they are soon scattered, and then the fertile shoot dies down.
-Soon afterward, or even while some of the fertile shoots are still in
-<span class="pagenum"><a name="Page_282" id="Page_282">[Pg 282]</a></span>
-good condition, sterile shoots of the plant begin to appear above the
-ground. One of these is shown in <a href="#FIG_325">fig. 325</a>. This has a much
-more slender stem and is provided with numerous branches. If we examine the stem of
-this shoot, and of the branches, we see that the same kind of leaves
-are present and that the markings on the stem are similar. Since the
-leaves of the horsetail are membranous and not green, the stem is green
-in color, and this performs the function of photosynthesis. These green
-shoots live for a great part of the season, building up material which
-is carried down into the underground stems, where it goes to supply the
-forming fertile shoots in the fall. On digging up some of these plants
-we see that the underground stems are often of great extent, and that
-both fertile and sterile shoots are attached to one and the same.</p>
-
-<div class="figcontainer">
- <div class="figsub">
-    <p class="space-below2">&nbsp;</p>
-    <img  id="FIG_323" src="images/fig323.jpg" alt="" width="100" height="193" />
-    <p class="center">Fig. 323.<br /> Spore of equisetum<br /> with elaters<br /> coiled up.</p>
-   </div>
-  <div class="figsub">
-    <p class="space-below2">&nbsp;</p>
-      <img  id="FIG_324" src="images/fig324.jpg" alt="" width="200" height="178" />
-      <p class="center">Fig. 324.<br /> Spore of equisetum with<br /> elaters uncoiled.</p>
-  </div>
-  <div class="figsub">
-      <img  id="FIG_325" src="images/fig325.jpg" alt="" width="150" height="337" />
-      <p class="center">Fig. 325.<br /> Sterile plant of horsetail<br /> (Equisetum arvensis).</p>
-  </div>
-</div>
-
-<p><b>576. The scouring rush, or shave grass.</b>—Another common species
-of horsetail in the Northern States grows on wet banks, or in sandy
-soil which contains moisture along railroad embankments. It is the
-scouring rush (E. hyemale), so called because it was once used for
-polishing purposes. This plant like all the species of the horsetails
-<span class="pagenum"><a name="Page_283" id="Page_283">[Pg 283]</a></span>
-has underground stems. But unlike the common horsetail, there is but
-one kind of aerial shoot, which is green in color and fertile. The
-shoots range as high as one meter or more, and are quite stout. The new
-shoots which come up for the year are unbranched, and bear the fertile
-spike at the apex. When the spores are ripe the apex of the shoot dies,
-and the next season small branches may form from a number of the nodes.</p>
-
-<p><b>577. Gametophyte of equisetum.</b>—The spores of equisetum have
-chlorophyll when they are mature, and they are capable of germinating
-as soon as mature. The spores are all of the same kind as regards size,
-just as we found in the case of the ferns. But they develop prothallia
-of different sizes, according to the amount of nutriment which they
-obtain. Those which obtain but little nutriment are smaller and develop
-only antheridia, while those which obtain more nutriment become larger,
-more or less branched, and develop archegonia. This character of an
-independent prothallium (gametophyte) with the characteristic sexual
-organs, and the also independent sporophyte, with spores, shows the
-relationship of the horsetails with the ferns. We thus see that these
-characters of the reproductive organs, and the phases and fruiting of
-the plant, are more essential in determining relationships of plants
-than the mere outward appearances.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_284" id="Page_284">[Pg 284]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XXX" id="CHAPTER_XXX">CHAPTER XXX.</a><br />
-<span class="h_subtitle">CLUB MOSSES.</span></h3>
-</div>
-
-<div class="figright">
-    <img  id="FIG_326" src="images/fig326.jpg" alt="" width="200" height="269" />
-    <p class="center">Fig. 326.<br /> Lycopodium clavatum,<br /> branch bearing two<br />
-       fruiting spikes; at<br /> right sporophyll with<br /> open sporangium;<br />
-       single spore near it.</p>
-</div>
-
-<p><b>578.</b> What are called the “club mosses” make up another group
-of interesting plants which rank as allies of the ferns. They are not
-of course true mosses, but the general habit of some of the smaller
-species, and especially the form and size of the leaves, suggest a
-resemblance to the larger of the moss plants.</p>
-
-<p><b>579. The clavate lycopodium.</b>—Here is one of the club mosses
-(<a href="#FIG_326">fig. 326</a>) which has a wide distribution and which is well
-entitled to hold the name of club because of the form of the upright club-shaped
-branches. As will be seen from the illustration, it has a prostrate
-stem. This stem runs for considerable distances on the surface of the
-ground, often partly buried in the leaves, and sometimes even buried
-beneath the soil. The leaves are quite small, are flattened-awl-shaped,
-and stand thickly over the stem, arranged in a spiral manner, which
-is the usual arrangement of the leaves of the club mosses. Here and
-there are upright branches which are forked several times. The end of
-one or more of these branches becomes produced into a slender upright
-stem which is nearly leafless, the leaves being reduced to mere scales.
-The end of this leafless branch then terminates in one or several
-cylindrical heads which form the club.
-<span class="pagenum"><a name="Page_285" id="Page_285">[Pg 285]</a></span></p>
-
-<p><b>580. Fruiting spike of Lycopodium clavatum.</b>—This club is the
-fruiting spike or head (sometimes termed a <i>strobilus</i>). Here the
-leaves are larger again and broader, but still not so large as the
-leaves on the creeping shoots, and they are paler. If we bend down some
-of the leaves, or tear off a few, we see that in the axil of the leaf,
-where it joins the stem, there is a somewhat rounded, kidney-shaped
-body. This is the spore-case or sporangium, as we can see by an
-examination of its contents. There is but a single spore-case for each
-of the fertile leaves (sporophyll). When it is mature, it opens by a
-crosswise slit as seen in <a href="#FIG_326">fig. 326</a>. When we consider the
-number of spore-cases in one of these club-shaped fruit bodies we see that the
-number of spores developed in a large plant is immense. In mass the
-spores make a very fine, soft powder, which is used for some kinds of
-pyrotechnic material, and for various toilet purposes.</p>
-
-<div class="figcenter">
-    <img  id="FIG_327" src="images/fig327.jpg" alt="" width="400" height="467" />
-  <div class="blockquot">
-    <p class="center">Fig. 327.</p>
-    <p>Lycopodium lucidulum, bulbils in axils of leaves near
-        the top, sporangia in axils of leaves below them. At right
-        is a bulbil enlarged.</p>
-  </div>
-</div>
-
-<p><b>581. Lycopodium lucidulum.</b>—Another common species is <a href="#FIG_327">figured
-at 327</a>. This is Lycopodium lucidulum. The habit of the plant is quite
-different. It grows in damp ravines, woods, and moors. The older
-parts of the stem are prostrate, while the branches are more or less
-ascending. It branches in a forked manner. The leaves are larger than
-in the former species, and they are all of the same size, there being
-no appreciable difference between the sterile and fertile ones. The
-characteristic club is not present here, but the spore-cases occupy
-certain regions of the stem, as shown at 327. In a single season one
-region of the stem may bear spore-cases, and then a sterile portion
-of the same stem is developed, which later bears another series of
-spore-cases higher up.</p>
-
-<p><b>582. Bulbils on Lycopodium lucidulum.</b>—There is one curious way
-in which this club moss multiplies. One may see frequently among the
-upper leaves small wedge-shaped or heart-shaped green bodies but little
-<span class="pagenum"><a name="Page_286" id="Page_286">[Pg 286]</a></span>
-larger than the ordinary leaves. These are little buds which contain
-rudimentary shoot and root and several thick green leaves. When they
-fall to the ground they grow into new lycopodium plants, just as the
-bulbils of cystopteris do which were described in the <a href="#CHAPTER_XXVI">chapter on ferns</a>.</p>
-
-<p><b>583.</b> Note.—The prothallia of the species of lycopodium which
-have been studied are singular objects. In L. cernuum a cylindrical
-body sunk in the earth is formed, and from the upper surface there
-are green lobes. In L. phlegmaria and some others slender branched,
-colorless bodies are formed which according to Treub grow as a
-saphrophyte in decayed bark of trees. Many of the prothallia examined
-have a fungus growing in their tissue which is supposed to play some
-part in the nutrition of the prothallium.</p>
-
-<p class="center"><b>The little club mosses (selaginella).</b></p>
-
-<p><b>584.</b> Closely related to the club mosses are the selaginellas.
-These plants resemble closely the general habit of the club mosses, but
-are generally smaller and the leaves more delicate. Some species are
-grown in conservatories for ornament, the leaves of such usually having
-a beautiful metallic lustre. The leaves of some are arranged as in
-lycopodium, but many species have the leaves in four to six rows. <a href="#FIG_328">Fig. 328</a>
-represents a part of a selaginella plant (S. apus). The fruiting
-spike possesses similar leaves, but they are shorter, and their
-arrangement gives to the spike a four-sided appearance.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <p class="space-below2">&nbsp;</p>
-    <img  id="FIG_328" src="images/fig328.jpg" alt="" width="200" height="318" />
-    <p class="center">Fig. 328.<br /> Selaginella with three<br /> fruiting spikes.<br />
-               (Selaginella apus.)</p>
-   </div>
-  <div class="figsub">
-    <p class="space-below2">&nbsp;</p>
-      <img  id="FIG_329" src="images/fig329.jpg" alt="" width="150" height="297" />
-      <p class="center">Fig. 329.<br /> Fruiting spike<br /> showing large<br /> and small sporangia.</p>
-  </div>
-  <div class="figsub">
-      <p class="space-below2">&nbsp;</p>
-      <img  id="FIG_330" src="images/fig330.jpg" alt="" width="100" height="274" />
-      <p class="center">Fig. 330.<br /> Large<br /> sporangium.</p>
-  </div>
-  <div class="figsub">
-      <p class="space-below2">&nbsp;</p>
-      <img  id="FIG_331" src="images/fig331.jpg" alt="" width="100" height="272" />
-      <p class="center">Fig. 331.<br /> Small<br /> sporangium.</p>
-  </div>
-</div>
-
-<p><span class="pagenum"><a name="Page_287" id="Page_287">[Pg 287]</a></span>
-<b>585. Sporangia.</b>—On examining the fruiting spike, we find as
-in lycopodium that there is but a single sporangium in the axil of a
-fertile leaf. But we see that they are of two different kinds, small
-ones in the axils of the upper leaves, and large ones in the axils of
-a few of the lower leaves of the spike. The <i>microspores</i> are borne
-in the smaller spore-cases and the <i>macrospores</i> in the larger ones.
-<a href="#FIG_329">Figures 329-331</a> give the details. There are many microspores
-in a single small spore-case, but 3-4 macrospores in a large spore-case.</p>
-
-<p><b>586. Male prothallia.</b>—The prothallia of selaginella are much
-reduced structures. The microspores when mature are already divided
-into two cells. When they grow into the mature prothallium a few more
-cells are formed, and some of the inner ones form the spermatozoids,
-as seen in <a href="#FIG_332">fig. 332</a>. Here we see that the antheridium itself
-is larger than the prothallia. Only antheridia are developed on the prothallia
-formed from the microspores, and for this reason the prothallia are
-called <i>male prothallia</i>. In fact a male prothallium of selaginella
-is nearly all antheridium, so reduced has the gametophyte become here.</p>
-
-<div class="figcenter">
-    <img  id="FIG_332" src="images/fig332.jpg" alt="" width="600" height="231" />
-  <div class="blockquot">
-    <p class="center">Fig. 332.</p>
-    <p>Details of microspore and male prothallium of selaginella; 1st,
-        microspore; 2d, wall removed to show small prothallial cell below; 3d,
-        mature male prothallium still within the wall; 4th, small cell below is
-        the prothallial cell, the remainder is antheridium with wall and four
-        sperm cells within; 5th spermatozoid. After Beliaieff and Pfeffer.</p>
-  </div>
-</div>
-
-<p><b>587. Female prothallia.</b>—The female prothallia are developed
-from the macrospores. The macrospores when mature have a rough, thick,
-hard wall. The female prothallium begins to develop inside of the
-macrospore before it leaves the sporangium. The protoplasm is richer
-<span class="pagenum"><a name="Page_288" id="Page_288">[Pg 288]</a></span>
-near the wall of the spore and at the upper end. Here the nucleus
-divides a great many times, and finally cell walls are formed, so
-that a tissue of considerable extent is formed inside the wall of the
-spore, which is very different from what takes place in the ferns we
-have studied. As the prothallium matures the spore is cracked at the
-point where the three angles meet, as shown in <a href="#FIG_334">fig. 334</a>.
-The archegonia are developed in this exposed surface, and several
-can be seen in the illustration.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <p class="space-below2">&nbsp;</p>
-    <img  id="FIG_333" src="images/fig333.jpg" alt="" width="150" height="211" />
-    <p class="center">Fig. 333.<br /> Section of mature macrospore<br />
-             of selaginella, showing female<br /> prothallium and archegonia.<br />
-             After Pfeffer.</p>
-   </div>
-  <div class="figsub">
-    <p class="space-below2">&nbsp;</p>
-      <img  id="FIG_334" src="images/fig334.jpg" alt="" width="150" height="276" />
-      <p class="center">Fig. 334.<br /> Mature female prothallium of<br /> selaginella, just bursting<br />
-            open the wall of macrospore,<br /> exposing archegonia.<br /> After Pfeffer.</p>
-  </div>
-  <div class="figsub">
-      <p class="space-below2">&nbsp;</p>
-      <img  id="FIG_335" src="images/fig335.jpg" alt="" width="150" height="369" />
-      <p class="center">Fig. 335.<br /> Seedling of selaginella still<br />
-                   attached to the macrospore.<br /> After Campbell.</p>
-  </div>
-</div>
-
-<p><b>588. Embryo.</b>—After fertilization the egg divides in such a way
-that a long cell called a suspensor is cut off from the upper side,
-which elongates and pushes the developing embryo down into the center
-of the spore, or what is now the female prothallium. Here it derives
-nourishment from the tissues of the prothallium, and eventually the
-root and stem emerge, while a process called the “foot” is still
-attached to the prothallium. When the root takes hold on the soil the
-embryo becomes free.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_289" id="Page_289">[Pg 289]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XXXI" id="CHAPTER_XXXI">CHAPTER XXXI.</a><br />
-<span class="h_subtitle">QUILLWORTS (ISOETES).</span></h3>
-</div>
-
-<div class="figleft">
-    <img  id="FIG_336" src="images/fig336.jpg" alt="" width="100" height="234" />
-    <p class="center">Fig. 336.<br /> Isoetes,<br /> mature plant,<br /> sporophyte stage.</p>
-</div>
-
-<p><b>589.</b> The quillworts, as they are popularly called, are very
-curious plants. They grow in wet marshy places. They receive their
-name from the supposed resemblance of the leaf to a quill. <a href="#FIG_336">Fig. 336</a>
-represents one of these quillworts (Isoetes engelmannii). The leaves
-are the prominent part of the plant, and they are about all that can
-be seen except the roots, without removing the leaves. Each leaf, it
-will be seen, is long and needle-like, except the basal part, which
-is expanded, not very unlike, in outline, a scale of an onion. These
-expanded basal portions of the leaves closely overlap each other, and
-the very short stem is completely covered at all times. <a href="#FIG_338">Fig. 338</a>
-is from a longitudinal section of a quillwort. It shows the form of the
-leaves from this view (side view), and also the general outline of the
-short stem, which is triangular. The stem is therefore a very short object.
-<span class="pagenum"><a name="Page_290" id="Page_290">[Pg 290]</a></span></p>
-
-<p><b>590. Sporangia of isoetes.</b>—If we pull off some of the leaves of
-the plant we see that they are somewhat spoon-shaped as in <a href="#FIG_337">fig. 337</a>.
-In the inner surface of the expanded base we note a circular depression
-which seems to be of a different texture from the other portions of the
-leaf. This is a <i>sporangium</i>. Beside the spores on the inside of the
-sporangium, there are strands of sterile tissue which extend across the
-cavity. This is peculiar to isoetes of all the members of the class
-of plants to which the ferns belong, but it will be remembered that
-sterile strands of tissue are found in some of the liverworts in the
-form of elaters.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_337" src="images/fig337.jpg" alt="" width="200" height="385" />
-    <p class="center">Fig. 337.<br /> Base of leaf of isoetes, showing<br />
-                sporangium with macrospores.<br /> (Isoetes engelmannii.)</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_338" src="images/fig338.jpg" alt="" width="300" height="360" />
-      <p class="center">Fig. 338.<br /> Section of plant of Isoetes engelmannii,<br />
-         showing cup-shaped stem, and longitudinal<br /> sections of the sporangia
-         in the thickened<br /> bases of the leaves.</p>
-  </div>
-</div>
-
-<p><b>591.</b> The spores of isoetes are of two kinds, small ones
-(microspores) and large ones (macrospores), so that in this respect
-it agrees with selaginella, though it is so very different in other
-<span class="pagenum"><a name="Page_291" id="Page_291">[Pg 291]</a></span>
-respects. When one kind of spore is borne in a sporangium usually all
-in that sporangium are of the same kind, so that certain sporangia
-bear microspores, and others bear macrospores. But it is not uncommon
-to find both kinds in the same sporangium. When a sporangium bears
-only microspores the number is much greater than when one bears only
-macrospores.</p>
-
-<p><b>592.</b> If we examine some of the microspores of isoetes we see
-that they are shaped like the quarters of an apple, that is they are of
-the bilateral type as seen in some of the ferns (asplenium).</p>
-
-<p><b>593. Male prothallia.</b>—In isoetes, as in selaginella, the
-microspores develop only male prothallia, and these are very
-rudimentary, one division of the spore having taken place before the
-spore is mature, just as in selaginella.</p>
-
-<p><b>594. Female prothallia.</b>—These are developed from the
-macrospores. The latter are of the tetrahedral type. The development
-of the female prothallium takes place in much the same way as in
-selaginella, the entire prothallium being enclosed in the macrospore,
-though the cell divisions take place after it has left the sporangium.
-When the archegonia begin to develop the macrospore cracks at the three
-angles and the surface bearing the archegonia projects slightly as in
-selaginella. Absorbing organs in the form of rhizoids are very rarely
-formed.</p>
-
-<p><b>595. Embryo.</b>—The embryo lies well immersed in the tissue of the
-prothallium, though there is no suspensor developed as in selaginella.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_292" id="Page_292">[Pg 292]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XXXII" id="CHAPTER_XXXII">CHAPTER XXXII.</a><br />
-<span class="h_subtitle">COMPARISON OF FERNS AND<br /> THEIR RELATIVES.</span></h3>
-</div>
-
-<p><b>596. Comparison of selaginella and isoetes with the ferns.</b>—On
-comparing selaginella and isoetes with the ferns, we see that the
-sporophyte is, as in the ferns, the prominent part of the plant. It
-possesses root, stem, and leaves. While these plants are not so large
-in size as some of the ferns, still we see that there has been a great
-advance in the sporophyte of selaginella and isoetes upon what exists
-in the ferns. There is a division of labor between the sporophylls,
-in which some of them bear microsporangia with microspores, and some
-bear macrosporangia with only macrospores. In the ferns and horsetails
-there is only one kind of sporophyll, sporangium, and spore in a
-species. By this division of labor, or differentiation, between the
-sporophylls, one kind of spore, the microspore, is compelled to form
-a male prothallium, while the other kind of spore, the macrospore, is
-compelled to form a female prothallium. This represents a progression
-of the sporophyte of a very important nature.</p>
-
-<p><b>597.</b> On comparing the gametophyte of selaginella and isoetes
-with that of the ferns, we see that there has been a still farther
-retrogression in size from that which we found in the independent and
-large gametophyte of the liverworts and mosses. In the ferns, while it
-is reduced, it still forms rhizoids, and leads an independent life,
-absorbing its own nutrient materials, and assimilating carbon. In
-selaginella and isoetes the gametophyte does not escape from the spore,
-nor does it form absorbing organs, nor develop assimilative tissue.
-The reduced prothallium develops at the expense of food stored by the
-sporophyte while the spore is developing. Thus, while the gametophyte
-is separate from the sporophyte in selaginella and isoetes, it is
-really dependent on it for support or nourishment.</p>
-
-<p><b>598.</b> The important general characters possessed by the ferns
-and their so-called allies, as we have found, are as follows: The
-spore-bearing part, which is the fern plant, leads an independent
-existence from the prothallium, and forms root, stem, and leaves. The
-spores are borne in sporangia on the leaves. The prothallium also leads
-an independent existence, though in isoetes and selaginella it has
-<span class="pagenum"><a name="Page_293" id="Page_293">[Pg 293]</a></span>
-become almost entirely dependent on the sporophyte. The prothallium
-bears also well-developed antheridia and archegonia. The root, stem,
-and leaves of the sporophyte possess vascular tissue. All the ferns and
-their allies agree in the possession of these characters. The mosses
-and liverworts have well-developed antheridia and archegonia, and the
-higher plants have vascular tissue. But no plant of either of these
-groups possesses the combined characters which we find in the ferns and
-their relatives. The latter are, therefore, the fern-like plants, or
-<i>pteridophyta</i>. The living forms of the pteridophyta are classified as
-follows into families or orders. (<a href="#Page_295">See page 295</a>.)
-<span class="pagenum"><a name="Page_294" id="Page_294">[Pg 294]</a></span></p>
-
-<p><b>599.</b></p>
-<p class="center"> TABLE SHOWING RELATION OF GAMETOPHYTE<br />
-AND SPOROPHYTE IN THE PTERIDOPHYTES.</p>
-
-<table class="smallfont" border="0" cellspacing="0" summary=" " cellpadding="0" rules="cols" >
-  <thead><tr>
-      <th class="tdc bb2" colspan="9">&nbsp;</th>
-   </tr><tr>
-      <th class="tdc bb2" colspan="5">GAMETOPHYTE.<br />(Becoming smaller, mostly independent.<br /> In selaginella
-                                       and isoetes becoming<br /> dependent on the sporophyte.)</th>
-      <th class="tdc bb2" colspan="3">SPOROPHYTE<br />(Largest part of the plant. The fern plant. Independent of,<br />
-                            and more hardy than, the gametophyte. Usually perennial.)</th>
-      <th class="tdc bb2" rowspan="2"><span class="smcap">Beginning<br /> of<br /> Gametophyte.</span></th>
-   </tr><tr>
-      <th class="tdc bb2">&nbsp;</th>
-      <th class="tdc bb2" colspan="2"><span class="smcap">Vegetative&nbsp;Part.</span></th>
-      <th class="tdc bb2" colspan="2">&nbsp;<span class="smcap">Sexual&nbsp;Organs.</span>&nbsp;</th>
-      <th class="tdc bb2"><span class="smcap">Beginning<br /> of<br /> Sporophyte.</span></th>
-      <th class="tdc bb2"><span class="smcap">Vegetative&nbsp;Part.</span></th>
-      <th class="tdc bb2"><span class="smcap">Fruiting&nbsp;Part.</span></th>
-   </tr>
-  </thead>
-  <tbody><tr>
-      <td class="tdl bb" rowspan="2"><span class="smcap">Ferns.</span> <br />(Polypodiaceæ.)</td>
-      <td class="tdl_table bb" colspan="2" rowspan="2"><p>A green, thin, expanded, heart-shaped growth, with rhizoids.</p></td>
-      <td class="tdc" colspan="2">Usually both kinds on<br /> the same prothallium.</td>
-      <td class="tdl_table bb" rowspan="2"><p>Fertilized egg. (Develops into fern plant.)</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>Root, stem, leaf.</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>Sporangia on leaf. All of one kind. Sporangium contains&nbsp;....</p></td>
-      <td class="tdl bb" rowspan="2">&nbsp;Spores.</td>
-   </tr><tr>
-      <td class="tdl_table bb"><p>Antheridia with spermatozoids.</p></td>
-      <td class="tdl_table bb"><p>Archegonia, each with egg.</p></td>
-   </tr><tr>
-      <td class="tdl bb" rowspan="2"><span class="smcap">Equisetum.</span></td>
-      <td class="tdl_table bb" colspan="2" rowspan="2"><p>A green, thin, expanded, lobed growth, with rhizoids.</p></td>
-      <td class="tdc" colspan="2">Usually the two kinds<br /> on different prothallia.</td>
-      <td class="tdl_table bb" rowspan="2"><p>Fertilized egg. (Develops into equisetum plant.)</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>Root, stem, leaf.</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>Sporangia on sporophylls. All of one kind. Sporangium contains&nbsp;....</p></td>
-      <td class="tdl bb" rowspan="2">&nbsp;Spores.</td>
-   </tr><tr>
-      <td class="tdl_table bb"><p>Antheridia, on small male prothallia, with spermatozoids.</p></td>
-      <td class="tdl_table bb"><p>Archegonia on larger female prothallia, each with an egg.</p></td>
-   </tr><tr>
-      <td class="tdl bb" rowspan="2"><span class="smcap">Isoetes.</span></td>
-      <td class="tdl_table" colspan="2"><p>Colorless, rounded mass of cells, inside of spore wall,
-                    usually no rhizoids, or but few. Two kinds.</p></td>
-      <td class="tdc" colspan="2">On different prothallia.</td>
-      <td class="tdl_table bb" rowspan="2"><p>Fertilized egg. (Develops into isoetes plant.)</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>Root, stem, leaf. Stem very short. Leaves bear sporangia in
-                    cavities at base; outer leaves usually bear macrosporangia, inner ones microsporangia.</p></td>
-      <td class="tdl_table"><p>Sporangia of two kinds. Small ones contain&nbsp;....</p></td>
-      <td class="tdl">&nbsp;Microspores.</td>
-   </tr><tr>
-      <td class="tdl_table bb"><p>Small ones, male. Developed into small prothallial cell,
-                           and antherid cell while still in sporangium.</p></td>
-      <td class="tdl_table bb"><p>Large ones, female. Developed from nutriment stored
-                           in macrospore from sporophyte.</p></td>
-      <td class="tdl_table bb"><p>One antheridium, much larger than the single prothallial
-                           cell. Antheridium with spermatozoids.</p></td>
-      <td class="tdl_table bb"><p>Few archegonia, in apex of oval colorless, female
-                           prothallium, each with egg.</p></td>
-      <td class="tdl_table bb"><p>Large ones contain&nbsp;....</p></td>
-      <td class="tdl bb">&nbsp;Macrospores.</td>
-   </tr><tr>
-      <td class="tdl bb" rowspan="2"><span class="smcap">Selaginella.</span></td>
-      <td class="tdl_table" colspan="2"><p>Colorless, rounded mass of cells inside of spore wall,
-                            no rhizoids, or but few. Two kinds.</p></td>
-      <td class="tdc" colspan="2">On different prothallia.</td>
-      <td class="tdl_table bb" rowspan="2"><p>Fertilized egg. (Develops into selaginella plant.)</p></td>
-      <td class="tdl_table bb" rowspan="2"><p>Root, stem, leaf. Spore-bearing leaves grouped on
-                            the end of stem in a spike. Lower ones bear macrosporangia, upper
-                            ones bear microsporangia.</p></td>
-      <td class="tdl_table"><p>Sporangia of two kinds.  Small ones contain&nbsp;....</p></td>
-      <td class="tdl">&nbsp;Microspores.</td>
-   </tr><tr>
-      <td class="tdl_table bb"><p>Small ones, male. Developed into small prothallial cell, and
-                           antherid cell while in sporangium.</p></td>
-      <td class="tdl_table bb"><p>Large ones, female. Developed while still in sporangium and
-                           dependent on sporophyte.</p></td>
-      <td class="tdl_table bb"><p>One antheridium, much larger than the single prothallial cell.
-                           Antheridium with spermatozoids.</p></td>
-      <td class="tdl_table bb"><p>Few archegonia, in apex of oval, colorless, female prothallium,
-                           each with egg.</p></td>
-      <td class="tdl_table bb"><p>Large ones contain&nbsp;....</p></td>
-      <td class="tdl bb">&nbsp;Macrospores.</td>
-   </tr><tr>
-      <td class="tdc bt" colspan="9">&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-
-<p><span class="pagenum"><a name="Page_295" id="Page_295">[Pg 295]</a></span></p>
-<h4><a name="XXXII_1" id="XXXII_1">Classification of the Pteridophytes.</a></h4>
-
-<p class="center">Of the living pteridophytes four classes may be recognized.</p>
-
-<p class="center">CLASS FILICINEÆ.<a name="FNanchor_34_34" id="FNanchor_34_34"></a><a href="#Footnote_34_34" class="fnanchor">[34]</a></p>
-
-<p>This class includes the ferns. Four orders may be recognized.</p>
-
-<p><b>600. Order Ophioglossales.</b> (One Family, Ophioglossaceæ).—This
-order includes the grapeferns (Botrychium), so called because of the
-large botryoid cluster of sporangia, resembling roughly a cluster
-of grapes; and the adder-tongue (Ophioglossum), the sporangia being
-embedded in a long tongue-like outgrowth from the green leaf.
-Botrychium and Ophioglossum are widely distributed. The roots are
-fleshy, nearly destitute of root hairs, and contain an endophytic
-fungus, so that the roots are mycorhiza. The gametophyte is
-subterranean, and devoid of chlorophyll. In Botrychium virginianum,
-an endophytic fungus has been found in the prothallium. Another genus
-(Helminthostachys) with one species is limited to the East Indies.</p>
-
-<p><b>601. Order Marattiales</b> (One Family, Marattiaceæ).—These are
-tropical ferns, with only four or five living genera (Marattia, Danæa,
-etc.). They resemble the typical ferns, but the sporangia are usually
-united, several forming a compound sporangium, or <i>synangium</i>.</p>
-
-<p>The Ophioglossales and Marattiales are known as eusporangiate ferns,
-while the following order includes the leptosporangiate ferns.</p>
-
-<p><b>602. Order Filicales.</b>—This order includes the typical ferns.
-Eight families are recognized.</p>
-
-<p><i>Family Osmundaceæ.</i>—Three genera are known in this family. Osmunda
-has a number of species, three of which are found in the Eastern United
-States; the cinnamon-fern (O. cinnamomea), the royal fern (O. regalis),
-and Clayton’s fern (O. claytoniana). No species of this family are
-found on the Pacific coast.</p>
-
-<p><i>Family Gleicheniaceæ.</i>—These ferns are found chiefly in the tropics,
-and in the mountain regions of the temperate zones of South America. There
-are two genera, Gleichenia containing all but one of the known species.</p>
-
-<p><i>Family Matoniaceæ.</i>—One genus, Matonia, in the Malayan region.</p>
-
-<p><i>Family Schizæceæ.</i>—These are chiefly tropical, but two species are
-found in eastern North America, Schizæa pusilla and Lygodium palmatum,
-the latter a climbing fern.</p>
-
-<p><i>Family Hymenophyllaceæ.</i>—These are known as the filmy ferns because
-of their thin, delicate leaves. They grow only in damp or wet regions,
-mostly in the tropics, but a few species occur in the southern United States.
-<span class="pagenum"><a name="Page_296" id="Page_296">[Pg 296]</a></span></p>
-
-<p><i>Family Cyatheaceæ.</i>—These are known as the tree ferns, because of the
-large size which many of them attain. They occur chiefly in tropical
-mountainous regions, many of them palm-like and imposing because of the
-large trunks and leaves. Dicksonia, Cyathea, Cibotium, Alsophila, are
-some of the most conspicuous genera.</p>
-
-<p><i>Family Parkeriaceæ.</i>—There is a single species in this family
-(Ceratopteris thalictroides), abundant in the tropics and extending
-into Florida. It is aquatic.</p>
-
-<p><i>Family Polypodiaceæ.</i>—This family includes the larger number of
-living ferns and many genera and species are found in North America.
-Examples, Polypodium, Pteridium (= Pteris), Adiantum, etc.</p>
-
-<p><b>603. Order Hydropterales (or Salviniales).</b>—The members of this
-order are peculiar, aquatic ferns, some floating on the water (Azolla,
-Salvinia), while others are anchored to the soil by roots (Marsilia,
-Pilularia). They are known as water ferns. The sporangia are of two
-kinds, one containing large spores (macrospores) and the other small
-spores (microspores). They are therefore heterosporous ferns.</p>
-
-<p><i>Family Salviniaceæ.</i>—There are two genera, Salvinia and Azolla.</p>
-
-<p><i>Family Marsiliaceæ.</i>—Two genera, Marsilia and Pilularia. In this
-family the sporangia are enclosed in a sporocarp, which forms a
-pod-like structure.</p>
-
-<p class="center">CLASS EQUISETINEÆ.<a name="FNanchor_35_35" id="FNanchor_35_35"></a><a href="#Footnote_35_35" class="fnanchor">[35]</a></p>
-
-<p><b>604. Order Equisetales.</b>—The single order contains a single
-family, Equisetaceæ, among the living forms, and but a single genus,
-Equisetum. There are about twenty-four species, with fourteen in the
-United States (see <a href="#CHAPTER_XXIX">Chapter XXIX</a>).</p>
-
-<p class="center">CLASS LYCOPODIINEÆ.<a name="FNanchor_36_36" id="FNanchor_36_36"></a><a href="#Footnote_36_36" class="fnanchor">[36]</a></p>
-
-<p><b>605. Order Lycopodiales.</b>—The first two families of this order
-include the homosporous Lycopodiineæ, while the Selaginellaceæ are
-heterosporous.</p>
-
-<p><i>Family Lycopodiaceæ.</i>—There are two genera. Lycopodium (club moss)
-includes many species, most of them tropical, but a number in temperate
-and subarctic regions. The gametophyte of many species is tuberous,
-lacks chlorophyll, and in some there lives an endophytic fungus.
-Phylloglossum with one species is found in Australia.</p>
-
-<p><i>Family Psilotaceæ.</i>—There are two genera. Psilotum chiefly in the
-tropics has one species (P. triquetrum) in the region of Florida.</p>
-
-<p><i>Family Selaginellaceæ.</i>—These include the little club mosses, with
-one genus, Selaginella (see <a href="#CHAPTER_XXX">Chapter XXX</a>).</p>
-
-<p class="center">CLASS ISOETINEÆ.</p>
-
-<p><b>606. Order Isoetales</b>, with one family Isoetaceæ and one genus
-Isoetes (see <a href="#CHAPTER_XXXI">Chapter XXXI</a>). There are about fifty species,
-with about sixteen in the United States.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_297" id="Page_297">[Pg 297]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XXXIII" id="CHAPTER_XXXIII">CHAPTER XXXIII.</a><br />
-<span class="h_subtitle">GYMNOSPERMS.</span></h3>
-</div>
-
-<p class="center">The white pine.</p>
-
-<p><b>607. General aspect of the white pine.</b>—The white pine (Pinus
-strobus) is found in the Eastern United States. In favorable situations
-in the forest it reaches a height of about 50 meters (about 160 feet),
-and the trunk a diameter of over 1 meter. In well-formed trees the
-trunk is straight and towering; the branches where the sunlight has
-access and the trees are not crowded, or are young, reaching out in
-graceful arms, form a pyramidal outline to the tree. In old and dense
-forests the lower branches, because of lack of sunlight, have died
-away, leaving tall, bare trunks for a considerable height.</p>
-
-<p><b>608. The long shoots of the pine.</b>—The branches are of two
-kinds. Those which we readily recognize are the long branches, so
-called because the growth in length each year is considerable. The
-terminal bud of the long branches, as well as of the main stem,
-continues each year the growth of the main branch or shoot; while the
-lateral long branches arise each year from buds which are crowded close
-together around the base of the terminal bud. The lateral long branches
-of each year thus appear to be in a whorl. The distance between each
-false whorl of branches, then, represents one year’s growth in length
-of the main stem or long branch.</p>
-
-<p><b>609. The dwarf shoots of the pine.</b>—The dwarf branches are all
-lateral on the long branches, or shoots. They are scattered over the
-year’s growth, and each bears a cluster of five long, needle-shaped,
-green leaves, which remain on the tree for several years. At the base
-of the green leaves are a number of chaff-like scales, the previous bud
-scales. While the dwarf branches thus bear green leaves, and scales,
-the long branches bear only thin scale-like leaves which are not green.
-<span class="pagenum"><a name="Page_298" id="Page_298">[Pg 298]</a></span></p>
-
-<p><b>610. Spore-bearing leaves of the pine.</b>—The two kinds of
-spore-bearing leaves of the pine, and their close relatives, are so
-different from anything which we have yet studied, and are so unlike
-the green leaves of the pine, that we would scarcely recognize them as
-belonging to this category. Indeed there is great uncertainty regarding
-their origin.</p>
-
-<div class="figcenter">
-    <img  id="FIG_339" src="images/fig339.jpg" alt="" width="450" height="474" />
-    <p class="center">Fig. 339.<br /> Spray of white pine showing cluster of male cones<br />
-                     just before the scattering of the pollen.</p>
-
-</div>
-
-<p><b>611. Male cones, or male flowers.</b>—The male cones are borne in
-clusters as shown in <a href="#FIG_339">fig. 339</a>. Each compact, nearly cylindrical,
-or conical mass is termed a cone, or flower, and each arises in place of a
-<span class="pagenum"><a name="Page_299" id="Page_299">[Pg 299]</a></span>
-long lateral branch. One of these cones is shown considerably enlarged
-in <a href="#FIG_340">fig. 340</a>. The central axis of each cone is a lateral
-branch, and belongs to the stem series. The stem axis of the cone can be seen
-in <a href="#FIG_341">fig. 341</a>. It is completely covered by stout, thick,
-scale-like outgrowths. These scales are obovate in outline, and at the inner
-angle of the upper end there are several rough, short spines. They
-are attached by their inner lower angle, which forms a short stalk
-or petiole, and continues through the inner face of the scale as
-a “midrib.” What corresponds to the lamina of the scale-like leaf
-bulges out on each side below and makes the bulk of the scale. These
-prominences on the under side are the sporangia (microsporangia). There
-are thus two sporangia on a sporophyll (microsporophyll). When the
-spores (microspores), which here are usually called pollen grains, are
-mature, each sporangium, or anther locule, splits down the middle as
-shown in <a href="#FIG_342">fig. 342</a>, and the spores are set free.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_340" src="images/fig340.jpg" alt="" width="150" height="282" />
-    <p class="center">Fig. 340.<br /> Staminate cone of white pine, with<br />
-                    bud scales removed on one side.</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_341" src="images/fig341.jpg" alt="" width="150" height="273" />
-      <p class="center">Fig. 341.<br /> Section of staminate cone,<br /> showing sporangia.</p>
-  </div>
-  <div class="figsub">
-      <img  id="FIG_342" src="images/fig342.jpg" alt="" width="100" height="259" />
-      <p class="center">Fig. 342.<br /> Two sporophylls<br />
-                removed, showing<br /> opening of sporangia.</p>
-  </div>
-</div>
-<div class="figleft">
-    <img  id="FIG_343" src="images/fig343.jpg" alt="" width="150" height="89" />
-    <p class="center">Fig. 343.<br /> Pollen grain of<br /> white pine.</p>
-</div>
-
-<p><b>612. Microspores of the pine, or pollen grains.</b>—A mature pollen
-grain of the pine is shown in <a href="#FIG_343">fig. 343</a>. It is a queer-looking
-object, possessing on two sides an air sac, formed by the upheaval of the outer
-<span class="pagenum"><a name="Page_300" id="Page_300">[Pg 300]</a></span>
-coat of the spore at these two points. When the pollen is mature, the
-moisture dries out of the scale (or stamen, as it is often called here)
-while it ripens. When a limb, bearing a cluster of male cones, is
-jarred by the hand, or by currents of air, the split suddenly opens,
-and a cloud of pollen bursts out from the numerous anther locules. The
-pollen is thus borne on the wind and some of it falls on the female flowers.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_344" src="images/fig344.jpg" alt="" width="250" height="421" />
-    <p class="center">Fig. 344.<br /> White pine, branch with cluster of<br />
-            mature cones shedding the seed. A few<br /> young cones four months old are shown<br />
-            on branch at the left.<br /> Drawn from photograph.</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_345" src="images/fig345.jpg" alt="" width="300" height="462" />
-      <p class="center">Fig. 345.<br /> Mature cone of white pine at<br />
-             time of scattering of the seed,<br /> nearly natural size.</p>
-  </div>
-</div>
-
-<p><b>613. Form of the mature female cone.</b>—A cluster of the
-white pine cones is shown in <a href="#FIG_344">fig. 344</a>. These are mature,
-and the scales have spread as they do when mature and becoming dry, in order that the
-<span class="pagenum"><a name="Page_301" id="Page_301">[Pg 301]</a></span>
-seeds may be set at liberty. The general outline of the cone is
-lanceolate, or long oval, and somewhat curved. It measures about
-10-15<i>cm</i> long. If we remove one of the scales, just as they are
-beginning to spread, or before the seeds have scattered, we shall find
-the seeds attached to the upper surface at the lower end. There are
-two seeds on each scale, one at each lower angle. They are ovate in
-outline, and shaped somewhat like a biconvex lens. At this time the
-seeds easily fall away, and may be freed by jarring the cone. As the
-seed is detached from the scale a strip of tissue from the latter is
-peeled off. This forms a “wing” for the seed. It is attached to one end
-and is shaped something like a knife blade. On the back of the scale is
-a small appendage known as the cover scale.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img src="images/fig346.jpg" alt="" width="100" height="202" />
-    <p class="center">Fig. 346.<br /> Sterile scale.<br /> Seeds undeveloped.</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig347.jpg" alt="" width="100" height="184" />
-      <p class="center">Fig. 347.<br /> Scale with<br /> well-developed<br /> seeds.</p>
-  </div>
-  <div class="figsub">
-      <img src="images/fig348.jpg" alt="" width="100" height="191" />
-      <p class="center">Fig. 348.<br /> Seeds have split<br /> off from scale.</p>
-  </div>
-  <div class="figsub">
-      <img src="images/fig349.jpg" alt="" width="100" height="201" />
-      <p class="center">Fig. 349.<br /> Back of scale<br /> with small<br /> cover scale.</p>
-  </div>
-  <div class="figsub">
-      <img src="images/fig350.jpg" alt="" width="100" height="213" />
-      <p class="center">Fig. 350.<br /> Winged seed<br /> free from<br /> scale.</p>
-  </div>
-           <p class="center">Figs. 346-350.—White pine showing details
-                 of mature scales and seed.</p>
-</div>
-<div class="figcenter">
-    <img  id="FIG_351" src="images/fig351.jpg" alt="" width="600" height="221" />
-    <p class="center">Fig. 351.<br /> Female cones of the pine at time<br />
-              of pollination, about natural size.</p>
-</div>
-
-<p><b>614. Formation of the female pine cone.</b>—The female flowers
-begin their development rather late in the spring of the year. They
-are formed from terminal buds of the higher branches of the tree. In
-this way the cone may terminate the main shoot of a branch, or of the
-lateral shoots in a whorl. After growth has proceeded for some time in
-the spring, the terminal portion begins to assume the appearance of a
-<span class="pagenum"><a name="Page_302" id="Page_302">[Pg 302]</a></span>
-young female cone or flower. These young female cones, at about the
-time that the pollen is escaping from the anthers, are long ovate,
-measuring about 6-10 <i>mm</i> long. They stand upright as shown in <a href="#FIG_351">fig. 351</a>.</p>
-
-<p><b>615. Form of a “scale” of the female flower.</b>—If we remove one
-of the scales from the cone at this stage we can better study it in
-detail. It is flattened, and oval in outline, with a stout “rib,” if
-it may be so called, running through the middle line and terminating
-in a point. The scale is in two parts as shown in <a href="#FIG_354">fig. 354</a>,
-which is a view of the under side. The small “outgrowth” which appears as an
-appendage is the cover scale, for while it is smaller in the pine than
-the other portion, in some of the relatives of the pine it is larger
-than its mate, and being on the outside, covers it. (The inner scale is
-sometimes called the ovuliferous scale, because it bears the ovules.)</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_352" src="images/fig352.jpg" alt="" width="125" height="443" />
-    <p class="center">Fig. 352.<br /> Section of female cone<br /> of white pine, showing<br />
-            young ovules<br /> (macrosporangia)<br /> at base of the<br /> ovuliferous scales.</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_353" src="images/fig353.jpg" alt="" width="150" height="449" />
-      <p class="center">Fig. 353.<br /> Scale of white pine<br /> with the two ovules<br />
-                 at base of<br /> ovuliferous scale.</p>
-  </div>
-  <div class="figsub">
-      <img  id="FIG_354" src="images/fig354.jpg" alt="" width="150" height="472" />
-      <p class="center">Fig. 354.<br /> Scale of white pine seen<br />
-                   from the outside, showing<br /> the cover scale.</p>
-  </div>
-</div>
-
-<p><b>616. Ovules, or macrosporangia, of the pine.</b>—At each of the
-lower angles of the scale is a curious oval body with two curved,
-forceps-like processes at the lower and smaller end. These are the
-macrosporangia, or, as they are called in the higher plants, the
-ovules. These ovules, as we see, are in the positions of the seeds on
-<span class="pagenum"><a name="Page_303" id="Page_303">[Pg 303]</a></span>
-the mature cones. In fact the wall of the ovule forms the outer coat of
-the seed, as we will later see.</p>
-
-<div class="figcenter">
-    <img src="images/fig355.jpg" alt="" width="500" height="491" />
-  <div class="blockquot">
-    <p class="center">Fig. 355.</p>
-    <p>Branch of white pine showing young female cones at time of
-       pollination on the ends of the branches, and one-year-old cones
-       below, near the time of fertilization.</p>
-  </div>
-</div>
-
-<p><b>617. Pollination.</b>—At the time when the pollen is mature the
-female cones are still erect on the branches, and the scales, which
-during the earlier stages of growth were closely pressed against one
-another around the axis, are now spread apart. As the clouds of pollen
-burst from the clusters of the male cones, some of it is wafted by
-the wind to the female cones. It is here caught in the open scales,
-and rolls down to their bases, where some of it falls between these
-forceps-like processes at the lower end of the ovule. At this time the
-ovule has exuded a drop of a sticky fluid in this depression between
-the curved processes at its lower end. The pollen sticks to this, and
-later, as this viscid substance dries up, it pulls the pollen close up
-<span class="pagenum"><a name="Page_304" id="Page_304">[Pg 304]</a></span>
-in the depression against the lower end of the ovule. This depression
-is thus known as the <i>pollen chamber</i>.</p>
-
-<p><b>618.</b> Now the open scales on the young female cone close up
-again so tightly that water from rains is excluded. What is also very
-curious, the cones, which up to this time have been standing erect, so
-that the open scale could catch the pollen, now turn so that they hang
-downward. This more certainly excludes the rains, since the overlapping
-of the scales forms a shingled surface. Quantities of resin are also
-formed in the scales, which exudes and makes the cone practically
-impervious to water.</p>
-
-<p><b>619.</b> The female cone now slowly grows during the summer and
-autumn, increasing but little in size during this time. During the
-winter it rests, that is, ceases to grow. With the coming of spring,
-growth commences again and at an accelerated rate. The increase in size
-is more rapid. The cone reaches maturity in September. We thus see that
-nearly eighteen months elapse from the beginning of the female flower
-to the maturity of the cone, and about fifteen months from the time
-that pollination takes place.</p>
-
-<div class="figleft">
-    <img  id="FIG_356" src="images/fig356.jpg" alt="" width="200" height="243" />
-    <p class="center">Fig. 356.<br /> Macrosporangium of pine (ovule).<br />
-          <i>int</i>, integument; <i>n</i>, nucellus;<br />
-          <i>m</i>, macrospore; <i>pc</i>, pollen chamber;<br />
-          <i>pg</i>, pollen grain; <i>an</i>, axile row;<br />
-          <i>spt</i>, spongy tissue.<br /> (After Ferguson.)</p>
-</div>
-
-<p><b>620. Female prothallium of the pine.</b>—To study this we must
-make careful longitudinal sections through the ovule (better made with
-the aid of a microtome). Such a section is shown in <a href="#FIG_358">fig. 358</a>.
-The outer layer of tissue, which at the upper end (point where the scale
-is attached to the axis of the cone) stands free, is the ovular coat,
-or <i>integument</i>. Within this integument, near the upper end, there is
-a cone-shaped mass of tissue. This mass of tissue is the <i>nucellus</i>,
-or the <i>macrosporangium</i> proper. In the lower part of the nucellus in
-<a href="#FIG_356">fig. 356</a> can be seen a rounded mass of “spongy tissue” (<i>spt</i>),
-which is a special nourishing tissue of the nucellus, or sporangium, around
-the macrospore. Within this can be seen an axile row of three cells
-(<i>an: m</i>). The lowest one, which is larger than the other two, is the
-<i>macrospore</i>. Sometimes there are four of these cells in the axile row.
-This axile row of three or four cells is formed by the two successive
-<span class="pagenum"><a name="Page_305" id="Page_305">[Pg 305]</a></span>
-divisions of a mother cell in the nucellus. So it would appear that
-these three or four cells are all spores.</p>
-
-<p>Only one of them, however, the lower one, develops; the others are
-disorganized and disappear. The nucleus of the macrospore now divides
-several times to form several free nuclei in the now enlarging cavity,
-much as the nucleus of the macrospore in Selaginella and Isoetes
-divides within the spore. The development thus far takes place during
-the first summer, and now with the approach of winter the very young
-female prothallium goes into rest about the stage shown in <a href="#FIG_358">fig. 358</a>.
-The conical portion of the nucellus which lies above is the nucellar cap.</p>
-
-<div class="figcenter">
-    <img  id="FIG_357" src="images/fig357.jpg" alt="" width="600" height="350" />
-  <div class="blockquot">
-    <p class="center">Fig. 357.</p>
-    <p>Pollen grains of pine. One of them germinating. <i>p</i>¹ and <i>p</i>², the two
-       disintegrated prothallial cells, = sterile part of male gametophyte;
-       <i>a.c.</i>, central cell of antheridium; <i>v.n.</i>, vegetative nucleus or tube
-       nucleus of the single-wall cell of antheridium; <i>s.g.</i>, starch grains.
-        (After Ferguson.)</p>
-  </div>
-</div>
-<div class="figcenter">
-    <img  id="FIG_358" src="images/fig358.jpg" alt="" width="300" height="486" />
-  <div class="blockquot">
-    <p class="center">Fig. 358.</p>
-    <p>Section of ovule of white pine. <i>int</i>, integument; <i>pc</i>, pollen
-       chamber; <i>pt</i>, pollen tube; <i>n</i>, nucleus; <i>m</i>, macrospore cavity.</p>
-  </div>
-</div>
-
-<p><b>621. Male prothallia.</b>—By the time the pollen is mature the
-male prothallium is already partly formed. In <a href="#FIG_343">fig. 343</a> we can
-see two well-formed cells. Two other cells are formed earlier, but they become
-so flattened that it is difficult to make them out when the pollen
-grain is mature. These are shown in <a href="#FIG_357">fig. 357</a>, <i>p</i>¹ and <i>p</i>²,
-and they are the only sterile cells of the male prothallium in the pines. The
-large cell is the antheridium wall, its nucleus <i>v.n.</i> in <a href="#FIG_357">fig. 357</a>.
-The smaller cell, <i>a.c.</i>, is the central cell of the antheridium. During
-the summer and autumn the male prothallium makes some farther growth,
-but this is slow. The larger cell, called the vegetative cell or tube
-<span class="pagenum"><a name="Page_306" id="Page_306">[Pg 306]</a></span>
-cell, which is in reality the wall of the antheridium, elongates by
-the formation of a tube, forming a sac, known as the pollen tube. It
-is either simple or branched. It grows down into the tissue of the
-nucellus, and at a stage represented in <a href="#FIG_358">fig. 358</a>, winter
-overtakes it and it rests. At this time the central cell has divided into two cells,
-and the vegetative nucleus is in the pollen tube.</p>
-
-<div class="figcenter">
-    <img  id="FIG_359" src="images/fig359.jpg" alt="" width="450" height="460" />
-  <div class="blockquot">
-    <p class="center">Fig. 359.</p>
-    <p>Section of nucellus and endosperm of white pine. The inner layer
-       of cells of the integument shown just outside of nucellus; <i>arch</i>,
-       archegonium; <i>en</i>, egg nucleus. In the nucellar cap are shown three
-       pollen tubes. <i>vn</i>, vegetative nucleus or tube nucleus; <i>stc</i>, stalk
-       cell; <i>spn</i>, sperm nuclei, the larger one in advance is the one which
-        unites with the egg nucleus. The archegonia are in the endosperm or
-        female gametophyte. (After Ferguson.)</p>
-  </div>
-</div>
-
-<p><b>622. The endosperm.</b>—In the following spring growth of all these
-parts continues. The nuclei in the macrospore divide to form more, and
-eventually cell walls are formed between them making a distinct tissue,
-<span class="pagenum"><a name="Page_307" id="Page_307">[Pg 307]</a></span>
-known as the <i>endosperm</i>. This endosperm continues to grow until a
-large part of the nucellus is consumed for food.</p>
-
-<div class="figcenter">
-    <img src="images/fig360.jpg" alt="" width="600" height="274" />
-  <div class="blockquot">
-    <p class="center">Fig. 360.</p>
-    <p>Last division of the egg in the white pine cutting off the ventral canal
-        cell at the apex of the archegonium. <i>End</i>, endosperm; <i>Arch</i>, archegonium.</p>
-  </div>
-</div>
-
-<p><b>623. Female prothallium and archegonia.</b>—The endosperm is the
-female prothallium. This is very evident from the fact that several
-archegonia are developed in it usually on the side toward the pollen
-chamber. The archegonia are sexual organs, and since the sexual organs
-are developed on the gametophyte, therefore, the endosperm is the
-female gametophyte, or prothallium. In <a href="#FIG_359">fig. 359</a> are
-represented two archegonia in the endosperm and the pollen tubes are growing
-down through the nucellus. The archegonia are quite large, the wall is a
-sheath or jacket of cells which encloses the very large egg which has a
-large nucleus in the center.</p>
-
-<p><b>624. Pollen tube and sperm cells.</b>—While the endosperm (female
-prothallium) and archegonia are developing the pollen tube continues
-its growth down through the nucellar cap, as shown in <a href="#FIG_359">fig. 359</a>.
-At the same time the two cells which were formed in the pollen grain
-(antheridium) from the central cell move down into the tube. One of
-these is the “generative” cell, or “body” cell, and the other is called
-the stalk cell, though it is more properly a sterile half of the
-central cell. The nucleus of the generative cell, about the time the
-archegonium is mature, divides to form two nuclei, which are the sperm
-nuclei, and the one in advance is the larger, though it is much smaller
-than the egg nucleus.</p>
-
-<p><b>625. Fertilization.</b>—Very soon after the archegonia are mature
-(early in June in the northern United States) the pollen tube grows
-through into the archegonium and empties the two sperm nuclei, the
-vegetative nucleus and the stalk cell, into the protoplasm of the large
-egg. The larger of the two sperm nuclei at once comes in contact with
-the very large egg nucleus and sinks down into a depression of the
-same, as shown in <a href="#FIG_361">fig. 361</a>. These two nuclei, in the pines,
-do not fuse into a resting nucleus, but at once organize the nuclear figure for the
-first division of the embryo. Two nuclei are thus formed, and these
-divide to form four nuclei which sink to the bottom of the archegonium
-<span class="pagenum"><a name="Page_308" id="Page_308">[Pg 308]</a></span>
-and there organize the embryo which pushes its way into the endosperm
-from which it derives its food (<a href="#FIG_362">fig. 362</a>).</p>
-
-<div class="figcenter">
-    <img  id="FIG_361" src="images/fig361.jpg" alt="" width="600" height="455" />
-  <div class="blockquot">
-    <p class="center">Fig. 361.</p>
-    <p>Archegonium of white pine at stage of fertilization, <i>en</i>, egg nucleus;
-       <i>spn</i>, sperm nucleus in conjugation with it; <i>nb</i>, nutritive bodies in
-       cytoplasm of large egg; <i>cpt</i>, cavity of pollen tube; <i>vn</i>, vegetative
-       nucleus or tube nucleus; <i>stc</i>, stalk cell; <i>spn</i>, second sperm
-       nucleus: <i>pr</i>, portion of prothallium or endosperm; <i>sg</i>, starch grains
-       in pollen tube. The sheath of jacket cells of the archegonium is not
-       shown. (After Ferguson.)</p>
-  </div>
-</div>
-
-<p><b>626. Homology of the parts of the female cone.</b>—Opinions are
-divided as to the homology of the parts of the female cone of the pine.
-Some consider the entire cone to be homologous with a flower of the
-angiosperms. The entire scale according to this view is a carpel, or
-sporophyll, which is divided into the cover scale and the ovuliferous
-scale. This division of the sporophyll is considered similar to that
-which we have in isoetes, where the sporophyll has a ligule above the
-sporangium, or as in ophioglossum, where the leaf is divided into a
-fertile and a sterile portion.</p>
-
-<p>Others believe that the ovuliferous scale is composed of two leaves
-situated laterally and consolidated representing a shoot in the axis of
-the bract. There is some support for this in the fact that in certain
-abnormal cones which show proliferation a short axis appears in the
-<span class="pagenum"><a name="Page_309" id="Page_309">[Pg 309]</a></span>
-axil of the bract and bears lateral leaves, and in some cases all
-gradations are present between these lateral leaves on the axis and
-their consolidation into an ovuliferous scale. In the normal condition
-of the ovuliferous scale the axis has disappeared and the shoot is
-represented only by the consolidated leaves, which would represent then
-the macrosporophylls (or carpels) each bearing one macrosporangium (ovule).</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_362" src="images/fig362.jpg" alt="" width="150" height="288" />
-    <p class="center">Fig. 362.<br /> Pine seed,<br /> section of,<br />
-           <i>sc</i>, seed coat;<br /> <i>n</i>, remains of nucellus;<br />
-           <i>end</i>, endosperm<br /> (= female gametophyte);<br />
-           <i>emb</i>, embryo =<br /> young sporophyte.<br />
-           Seed coat and nucellus =<br /> remains of old sporophyte.</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_363" src="images/fig363.jpg" alt="" width="150" height="430" />
-      <p class="center">Fig. 363.<br /> Embryo of white pine<br />
-                 removed from seed,<br /> showing several cotyledons.</p>
-  </div>
-  <div class="figsub">
-      <img  id="FIG_364" src="images/fig364.jpg" alt="" width="150" height="412" />
-      <p class="center">Fig. 364.<br /> Pine seedling<br /> just emerging<br /> from the ground.</p>
-  </div>
-</div>
-
-<p>One of the most interesting and plausible views is that of Celakovsky.
-He believes that the axial shoot is reduced to two ovules, that the
-ovules have two integuments, but the outer integument of each has
-become proliferated into scales which are consolidated. In this
-proliferation of the outer integument it is thrown off from the ovule
-so that it only remains attached to one side and the larger part of the
-ovule is thus left with only one integument. This view is supported
-by the fact that in gingko, for example (another gymnosperm), the
-outer integument (the “collar”) sometimes proliferates into a leaf.
-Celakovsky’s view is, therefore, not very different from the second one
-mentioned above.
-<span class="pagenum"><a name="Page_310" id="Page_310">[Pg 310]</a></span></p>
-
-<div class="figcenter">
-    <img src="images/fig365.jpg" alt="" width="450" height="463" />
-    <p class="center">Fig. 365.<br /> White pine seedling casting seed coats.</p>
-</div>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_311" id="Page_311">[Pg 311]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XXXIV" id="CHAPTER_XXXIV">CHAPTER XXXIV.</a><br />
-<span class="h_subtitle">FURTHER STUDIES ON<br /> GYMNOSPERMS.</span></h3>
-</div>
-
-<h4>Cycas.</h4>
-
-<div class="figleft">
-    <img src="images/fig366.jpg" alt="" width="100" height="147" />
-    <p class="center">Fig. 366.<br /> Macrosporophyll of<br />  Cycas revoluta.</p>
-</div>
-
-<p><b>627.</b> In such gymnosperms as cycas, illustrated in the
-frontispiece, there is a close resemblance to the members of the fern
-group, especially the ferns themselves. This is at once suggested by
-the form of the leaves. The stem is short and thick. The leaves have a
-stout midrib and numerous narrow pinnæ. In the center of this rosette
-of leaves are numerous smaller leaves, closely overlapping like bud
-scales. If we remove one of these at the time the fruit is forming we
-see that in general it conforms to the plan of the large leaves. There
-are a midrib and a number of narrow pinnæ near the free end, the entire
-leaf being covered with woolly hairs. But at the lower end, in place of
-the pinnæ, we see oval bodies. These are the macrosporangia (ovules)
-of cycas, and correspond to the macrosporangia of selaginella, and the
-leaf is the macrosporophyll.</p>
-
-<p><b>628. Female prothallium of cycas.</b>—In figs. <a href="#FIG_367">367</a>, <a href="#FIG_368">368</a>,
-are shown mature ovules, or macrosporangia, of cycas. In 368, which is a
-roentgen-ray photograph of 367, the oval prothallium can be seen. So in
-<span class="pagenum"><a name="Page_312" id="Page_312">[Pg 312]</a></span>
-cycas, as in selaginella, the female prothallium is developed entirely
-inside of the macrosporangium, and derives the nutriment for its growth
-from the cycas plant, which is the sporophyte. Archegonia are developed
-in this internal mass of cells. This aids us in determining that it is
-the prothallium. In cycas it is also called endosperm, just as in the pines.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_367" src="images/fig367.jpg" alt="" width="250" height="316" />
-    <p class="center">Fig. 367.<br /> Macrosporangium of<br /> Cycas revoluta.</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_368" src="images/fig368.jpg" alt="" width="252" height="316" />
-      <p class="center">Fig. 368.<br /> Roentgen photograph of same,<br /> showing female prothallium.</p>
-  </div>
-</div>
-<div class="figcenter">
-    <img  id="FIG_369" src="images/fig369.jpg" alt="" width="450" height="436" />
-  <div class="blockquot">
-    <p class="center">Fig. 369.</p>
-    <p>A sporophyll (stamen) of cycas; sporangia in groups on the under side.
-       <i>b</i>, group of sporangia; <i>c</i>, open sporangia. (From Warming.)</p>
-  </div>
-</div>
-
-<p><b>629.</b> If we cut open one of the mature ovules, we can see the
-endosperm (prothallium) as a whitish mass of tissue. Immediately
-surrounding it at maturity is a thin, papery tissue, the remains of the
-nucellus (macrosporangium), and outside of this are the coats of the
-ovule, an outer fleshy one and an inner stony one.</p>
-
-<p><b>630. Microspores, or pollen, of cycas.</b>—The cycas plant
-illustrated in the frontispiece is a female plant. Male plants also
-<span class="pagenum"><a name="Page_313" id="Page_313">[Pg 313]</a></span>
-exist which have small leaves in the center that bear only
-microsporangia. These leaves, while they resemble the ordinary leaves,
-are smaller and correspond to the stamens. Upon the under side, as
-shown in <a href="#FIG_369">fig. 369</a>, the microsporangia are borne in groups
-of three or four, and these contain the microspores, or pollen grains. The
-arrangement of these microsporangia on the under side of the cycas
-leaves bears a strong resemblance to the arrangement of the sporangia
-on the under side of the leaves of some ferns.</p>
-
-<p><b>631. The gingko tree</b> is another very interesting plant belonging
-to this same group. It is a relic of a genus which flourished in the
-remote past, and it is interesting also because of the resemblance of
-the leaves to some of the ferns like adiantum, which suggests that
-this form of the leaf in gingko has been inherited from some fern-like
-ancestor.</p>
-
-<div class="figcenter">
-    <img src="images/fig370.jpg" alt="" width="400" height="387" />
-    <p class="center">Fig. 370. <br />Zamia integrifolia, showing thick stem,<br />
-             fern-like leaves, and cone of male flowers.</p>
-</div>
-<div class="figcenter">
-    <img  id="FIG_371" src="images/fig371.jpg" alt="" width="400" height="486" />
-    <p class="center">Fig. 371. <br />Two spermatozoids in end of pollen tube of<br />
-                cycas. (After drawing by Hirase and Ikeno.)</p>
-
-</div>
-
-<p><b>632.</b> While the resemblance of the leaves of some of the
-gymnosperms to those of the ferns suggests fern-like ancestors for the
-members of this group, there is stronger evidence of such ancestry
-in the fact that a prothallium can well be determined in the ovules.
-The endosperm with its well-formed archegonia is to be considered a
-prothallium.</p>
-
-<p><b>633. Spermatozoids in some gymnosperms.</b>—But within the past two
-years it has been discovered in gingko, cycas, and zamia, all belonging
-<span class="pagenum"><a name="Page_314" id="Page_314">[Pg 314]</a></span>
-to this group, that the sperm cells are well-formed spermatozoids. In
-zamia each one is shaped somewhat like the half of a biconvex lens, and
-around the convex surface are several coils of cilia. After the pollen
-tube has grown down through the nucellus, and has reached a depression
-at the end of the prothallium (endosperm) where the archegonia are
-formed, the spermatozoids are set free from the pollen tube, swim
-around in a liquid in this depression, and later fuse with the egg. In
-gingko and cycas these spermatozoids were first discovered by Ikeno and
-Hirase in Japan, and later in zamia by Webber in this country. In figs.
-<a href="#FIG_371">371</a>-<a href="#FIG_374">374</a> the details
-of the male prothallia and of fertilization are shown.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img src="images/fig372.jpg" alt="" width="250" height="273" />
-    <p class="center">Fig. 372.<br /> Fertilization in cycas, small spermatozoid<br />
-             fusing with the larger female nucleus of the<br />
-             egg. The egg protoplasm fills the archegonium.<br />
-             (From drawings by Hirase and Ikeno.)</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig373.jpg" alt="" width="250" height="273" />
-      <p class="center">Fig. 373.<br /> Spermatozoid of gingko.<br />
-               Some abnormal forms have a tail.<br /> (After Ikeno and Hirase.)</p>
-  </div>
-</div>
-
-<p><b>634. The sporophyte in the gymnosperms.</b>—In the pollen grains
-of the gymnosperms we easily recognize the characters belonging to the
-spores in the ferns and their allies, as well as in the liverworts and
-mosses. They belong to the same series of organs, are borne on the
-same phase or generation of the plant, and are practically formed in
-the same general way, the variations between the different groups not
-being greater than those within a single group. These spores we have
-recognized as being the product of the sporophyte. We are able then to
-identify the sporophyte as that phase or generation of the plant formed
-from the fertilized egg and bearing ultimately the spores. We see from
-this that the sporophyte in the gymnosperms is the prominent part of
-the plant, just as we found it to be in the ferns. The pine tree, then,
-as well as the gingko, cycas, yew, hemlock-spruce, black spruce, the
-giant redwood of California, etc., are sporophytes.</p>
-
-<p>While the sporangia (anther sacs) of the male flowers open and permit
-the spores (pollen) to be scattered, the sporangia of the female
-flowers of the gymnosperms rarely open. The macrospore is developed
-within sporangium (nucellus) to form the female prothallium (endosperm).</p>
-
-<p><b>635. The gametophyte has become dependent on the sporophyte.</b>—In
-this respect the gymnosperms differ widely from the pteridophytes,
-though we see suggestions of this condition of things in Isoetes and
-Selaginella, where the female prothallium is developed within the
-macrospore, and even in Selaginella begins, and nearly completes, its
-development while still in the sporangium.
-<span class="pagenum"><a name="Page_315" id="Page_315">[Pg 315]</a></span></p>
-
-<p>In comparing the female prothallium of the gymnosperms with that
-of the fern group we see a remarkable change has taken place. The
-female prothallium of the gymnosperms is very much reduced in size.
-Especially, it no longer leads an independent existence from the
-sporophyte, as is the case with nearly all the fern group. It remains
-enclosed within the macrosporangium (in cycas if not fertilized it
-sometimes grows outside of the macrosporangium and becomes green), and
-derives its nourishment through it from the sporophyte, to which the
-latter remains organically connected. This condition of the female
-prothallium of the gymnosperms necessitated a special adaptation of the
-male prothallium in order that the sperm cells may reach and fertilize
-the egg-cell.</p>
-
-<div class="figcenter">
-    <img  id="FIG_374" src="images/fig374.jpg" alt="" width="500" height="466" />
-  <div class="blockquot">
-    <p class="center">Fig. 374.</p>
-    <p>Gingko biloba. <i>A</i>, mature pollen grain; <i>B</i>, germinating pollen grain,
-       the branched tube entering among the cells of the nucellus; <i>Ex</i>,
-       exine (outer wall of spore); <i>P</i>₁, prothallial cell; <i>P</i>₂, antheridial
-       cell (divides later to form stalk cell and generative cell); <i>P</i>₃,
-       vegetative cell; <i>Va</i>, vacuoles; <i>Nc</i>, nucellus. (After drawings by
-       Hirase and Ikeno.)</p>
-  </div>
-</div>
-<div class="figcenter">
-    <img src="images/fig375.jpg" alt="" width="600" height="158" />
-  <div class="blockquot">
-    <p class="center">Fig. 375.</p>
-    <p>Gingko biloba, diagrammatic representation of the relation of pollen
-       tube to the archegonium in the end of the nucellus. <i>pt</i>, pollen tube;
-       <i>o</i>, archegonium. (After drawing by Hirase and Ikeno.)</p>
-  </div>
-</div>
-
-<p><b>636. Gymnosperms are naked seed plants.</b>—The pine, as we have
-seen, has naked seeds. That is, the seeds are not enclosed within the
-<span class="pagenum"><a name="Page_316" id="Page_316">[Pg 316]</a></span>
-carpel, but are exposed on the outer surface. All the plants of the
-great group to which the pine belongs have naked seeds. For this reason
-the name “<i>gymnosperms</i>” has been given to this great group.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img src="images/fig376.jpg" alt="" width="250" height="251" />
-    <p class="center">Fig. 376.<br /> Spermatozoids of zamia<br /> in pollen tube;<br />
-          <i>pg</i>, pollen grain;<br /> <i>a</i>, <i>a</i>, spermatozoids.<br />
-          (After Webber.)</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig377.jpg" alt="" width="250" height="269" />
-      <p class="center">Fig. 377.<br /> Spermatozoid of zamia<br /> showing
-               spiral row of<br /> cilia. (After Webber.)</p>
-  </div>
-</div>
-
-<p><b>637. Classification of gymnosperms.</b>—The gingko tree has until
-recently been placed with the pines, yew, etc., in the order <i>Pinales</i>,
-but the discovery of the spermatozoids in the pollen tube suggests
-that it is not closely allied with the Pinales, and that it represents
-an order coordinate with them. Engler arranges the living gymnosperms
-somewhat as follows:</p>
-
-<h4>Class Gymnospermæ.</h4>
-
-<table border="0" cellspacing="0" summary=" " cellpadding="0" >
-  <tbody><tr>
-      <td class="tdl">Order&nbsp;1.</td>
-      <td class="tdl_ws1">Cycadales;</td>
-      <td class="tdl_ws1">family&nbsp;Cycadaceæ.</td>
-      <td class="tdl_ws1">Cycas, Zamia, etc.</td>
-   </tr><tr>
-      <td class="tdl">Order&nbsp;2.</td>
-      <td class="tdl_ws1">Gingkoales;</td>
-      <td class="tdl_ws1">family&nbsp;Gingkoaceæ.</td>
-      <td class="tdl_ws1">Gingko.</td>
-   </tr><tr>
-      <td class="tdc" colspan="4">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl_top">Order&nbsp;3.</td>
-      <td class="tdl_ws1">Pinales (or Coniferæ);</td>
-      <td class="tdl_ws1">family 1. Taxaceæ.</td>
-      <td class="tdl_table"><p class="no-indent">Taxus, the common yew in the eastern United States,
-                      and Torreya, in the western United States, are examples.</p></td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl_ws1">&nbsp;</td>
-      <td class="tdl_ws1">family 2. Pinaceæ.</td>
-      <td class="tdl_table"><p class="no-indent">Sequoia (redwood of California), firs, spruces,
-                      pines, cedars, cypress, etc.</p></td>
-   </tr><tr>
-      <td class="tdl_top">Order&nbsp;4.</td>
-      <td class="tdl_ws1">Gnetales.</td>
-      <td class="tdl_table" colspan="2"><p class="no-indent">Welwitschia mirabilis, deserts of southwest
-               Africa; Ephedra, deserts of the Mediterranean and of West Asia. Gnetum, climbers (Lianas),
-               from tropical Asia and America.</p></td>
-   </tr>
- </tbody>
-</table>
-
-<p><span class="pagenum"><a name="Page_317" id="Page_317">[Pg 317]</a></span></p>
-
-<p><b>638.</b></p>
-<p class="center"> TABLE SHOWING HOMOLOGIES OF SPOROPHYTE<br /> AND GAMETOPHYTE IN THE PINE.</p>
-
-<table border="0" cellspacing="0" summary=" " cellpadding="0" >
-  <thead><tr>
-      <th class="tdc">&nbsp;</th>
-      <th class="tdc bb"><span class="smcap">Terms Corresponding to those<br /> used in Pteridophytes.</span></th>
-      <th class="tdc bb">&nbsp;</th>
-      <th class="tdc bb"><span class="smcap">Common Terms.</span></th>
-  </tr>
-  </thead>
-  <tbody><tr>
-      <td class="tdl br">&nbsp;</td>
-      <td class="tdl_ws1">Sporophyte</td>
-      <td class="tdc_ws1">=</td>
-      <td class="tdl" colspan="2">Pine tree.</td>
-   </tr><tr>
-      <td class="tdl br">&nbsp;</td>
-      <td class="tdl_ws1">Spore-bearing part</td>
-      <td class="tdc_ws1">=</td>
-      <td class="tdl" colspan="2">Male and female cones.</td>
-   </tr><tr>
-      <td class="tdl br bb bt" rowspan="2">Sporophyte</td>
-      <td class="tdl_ws1 bt">Microsporophyll</td>
-      <td class="tdc_ws1 bt">=</td>
-      <td class="tdl bt" colspan="2">Stamen.</td>
-   </tr><tr>
-      <td class="tdl_ws1 bb">Microsporangium</td>
-      <td class="tdc_ws1 bb">=</td>
-      <td class="tdl bb" colspan="2">Pollen sac.</td>
-   </tr><tr>
-      <td class="tdl bb br" rowspan="9">Male<br />&nbsp; gametophyte</td>
-      <td class="tdl_ws1">Microspore</td>
-      <td class="tdc_ws1">=</td>
-      <td class="tdl" colspan="2">Pollen grain.</td>
-   </tr><tr>
-      <td class="tdl_ws1"> Mature microspore is rudimentary male prothallium</td>
-      <td class="tdc_ws1" rowspan="2">=</td>
-      <td class="tdl" rowspan="2" colspan="2">Mature pollen grain.</td>
-   </tr><tr>
-      <td class="tdl_ws1">&nbsp;&emsp;with rudimentary antheridium</td>
-   </tr><tr>
-      <td class="tdl_ws1">Large cell (part of antheridium wall?)</td>
-      <td class="tdc_ws1">=</td>
-      <td class="tdl" colspan="2">Vegetative cell of pollen grain.</td>
-   </tr><tr>
-      <td class="tdl_ws1">Antheridium cell</td>
-      <td class="tdc_ws1">=</td>
-      <td class="tdl" colspan="2">Small cell of pollen</td>
-   </tr><tr>
-      <td class="tdl_ws1">Antheridium cell divides to form stalk cell and</td>
-      <td class="tdc_ws1" rowspan="2">=</td>
-      <td class="tdl" rowspan="2" colspan="2">Generative cell.</td>
-   </tr><tr>
-      <td class="tdl_ws1">&nbsp;&emsp;central cell of antheridium (male sexual organ)</td>
-   </tr><tr>
-      <td class="tdl_ws1">Central cell of antheridium divides to form</td>
-      <td class="tdc_ws1 bb" rowspan="2">=</td>
-      <td class="tdl" colspan="2">Paternal cells, or</td>
-   </tr><tr>
-      <td class="tdl_ws1 bb">&nbsp;&emsp;two sperm cells</td>
-      <td class="tdl bb" colspan="2">&nbsp;&emsp;generative cells.</td>
-   </tr><tr>
-      <td class="tdl br bb" rowspan="7">Sporophyte</td>
-      <td class="tdl_ws1">Macrosporophyll</td>
-      <td class="tdc_ws1">=</td>
-      <td class="tdl" colspan="2">Ovuliferous scale (cover scale</td>
-   </tr><tr>
-      <td class="tdl_ws1">&nbsp;</td>
-      <td class="tdc_ws1" rowspan="4">&nbsp;</td>
-      <td class="tdl" colspan="2">and carpellary outgrowth); or</td>
-   </tr><tr>
-      <td class="tdl_ws1">&nbsp;</td>
-      <td class="tdl" colspan="2">three carpels united into</td>
-   </tr><tr>
-      <td class="tdl_ws1">&nbsp;</td>
-      <td class="tdl" colspan="2">ovuliferous scale, the central one</td>
-   </tr><tr>
-      <td class="tdl_ws1">&nbsp;</td>
-      <td class="tdl" colspan="2"> sterile (in axil of cover scale).</td>
-   </tr><tr>
-      <td class="tdl_ws1">Macrosporangium covered by integument</td>
-      <td class="tdc_ws1">=</td>
-      <td class="tdl" colspan="2">Nucellus covered by</td>
-   </tr><tr>
-      <td class="tdl_ws1 bb">&nbsp;&emsp;by integument</td>
-      <td class="tdc_ws1 bb">&nbsp;</td>
-      <td class="tdl bb" colspan="2">&nbsp; integument = ovule.</td>
-   </tr><tr>
-      <td class="tdl bb br" rowspan="6">Female<br />&nbsp; gametophyte&nbsp;</td>
-      <td class="tdl_ws1">Macrospore (remains in sporangium)</td>
-      <td class="tdc_ws1">=</td>
-      <td class="tdl" colspan="2">Large cell in center of nucellus</td>
-   </tr><tr>
-      <td class="tdl_ws1">&nbsp;</td>
-      <td class="tdc_ws1">&nbsp;</td>
-      <td class="tdl" colspan="2">which develops embryo sac and</td>
-   </tr><tr>
-      <td class="tdl_ws1">&nbsp;</td>
-      <td class="tdc_ws1">&nbsp;</td>
-      <td class="tdl" colspan="2">endosperm (remains in nucellus).</td>
-   </tr><tr>
-      <td class="tdl_ws1">Female prothallium (in sporangium)</td>
-      <td class="tdc_ws1">=</td>
-      <td class="tdl" colspan="2">Endosperm, in nucellus.</td>
-   </tr><tr>
-      <td class="tdl_ws1">Archegonia (female sexual organs)</td>
-      <td class="tdc_ws1">=</td>
-      <td class="tdl" colspan="2">Corpuscula, in endosperm.</td>
-   </tr><tr>
-      <td class="tdl_ws1 bb">Egg</td>
-      <td class="tdc_ws1 bb">=</td>
-      <td class="tdl bb" colspan="2">Maternal cell, or germ cell.</td>
-   </tr><tr>
-      <td class="tdl bb br" rowspan="7">Young<br />&nbsp; sporophyte</td>
-      <td class="tdl_ws1">Egg (fertilized)</td>
-      <td class="tdc_ws1">=</td>
-      <td class="tdl" colspan="2">Germ cell.</td>
-   </tr><tr>
-      <td class="tdl_ws1">Young sporophyte</td>
-      <td class="tdc_ws1">=</td>
-      <td class="tdl" colspan="2">Pine embryo in nucellus</td>
-   </tr><tr>
-      <td class="tdl_ws1">&nbsp;</td>
-      <td class="tdc_ws1">&nbsp;</td>
-      <td class="tdl" colspan="2">&nbsp;&emsp;and integument.</td>
-   </tr><tr>
-      <td class="tdl_ws1">Young sporophyte</td>
-      <td class="tdc_ws1">=</td>
-      <td class="tdl br bt">Embryo</td>
-      <td class="tdl bb" rowspan="4">&nbsp;Seed.</td>
-   </tr><tr>
-      <td class="tdl_ws1">In remains of gametophyte</td>
-      <td class="tdc_ws1">=</td>
-      <td class="tdl br">Endosperm</td>
-   </tr><tr>
-      <td class="tdl_ws1">And sporangium</td>
-      <td class="tdc_ws1">=</td>
-      <td class="tdl br">Nucellus</td>
-   </tr><tr>
-      <td class="tdl_ws1 bb">Surrounded by new growth of old sporophyte</td>
-      <td class="tdc_ws1 bb">=</td>
-      <td class="tdl bb br">Integument</td>
-   </tr><tr>
-      <td class="tdc" colspan="4">&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_318" id="Page_318">[Pg 318]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XXXV" id="CHAPTER_XXXV">CHAPTER XXXV.</a><br />
-<span class="h_subtitle">MORPHOLOGY OF THE ANGIOSPERMS:<br /> TRILLIUM; DENTARIA.</span></h3>
-</div>
-
-<h4>Trillium.</h4>
-
-<p><b>639. General appearance.</b>—As one of the plants to illustrate
-this group we may take the wake-robin, as it is sometimes called,
-or trillium. There are several species of this genus in the United
-States; the commonest one in the eastern part is the “white wake-robin”
-(Trillium grandiflorum). This occurs in or near the woods. A picture of
-the plant is shown in <a href="#FIG_378">fig. 378</a>. There is a thick, fleshy,
-underground stem, or rhizome as it is usually called. This rhizome is perennial,
-and is marked by ridges and scars. The roots are quite stout and
-possess coarse wrinkles. From the growing end of the rhizome each year
-the leafy, flowering stem arises. This is 20-30<i>cm</i> (8-12 inches) in
-height. Near the upper end is a whorl of three ovate leaves, and from
-the center of this rosette rises the flower stalk, bearing the flower
-at its summit.</p>
-
-<p><b>640. Parts of the flower. Calyx.</b>—Now if we examine the flower
-we see that there are several leaf-like structures. These are arranged
-also in threes just as are the leaves. First there is a whorl of three,
-pointed, lanceolate, green, leaf-like members, which make up the
-<i>calyx</i> in the higher plants, and the parts of the calyx are <i>sepals</i>,
-that is, each leaf-like member is a <i>sepal</i>. But while the sepals are
-part of the flower, so called, we easily recognize them as belonging to
-the <i>leaf series</i>.
-<span class="pagenum"><a name="Page_319" id="Page_319">[Pg 319]</a></span></p>
-
-<p><b>641. Corolla.</b>—Next above the calyx is a whorl of white or
-pinkish members, in Trillium grandiflorum, which are also leaf-like in
-form, and broader than the sepals, being usually somewhat broader at
-the free end. These make up what is the <i>corolla</i> in the higher plants,
-and each member of the corolla is a <i>petal</i>. But while they are parts
-of the flower, and are not green, their form and position would suggest
-that they also belong to the leaf series.</p>
-
-<div class="figcenter">
-    <img  id="FIG_378" src="images/fig378.jpg" alt="" width="250" height="462" />
-    <p class="center">Fig. 378. <br /> Trillium grandiflorum.</p>
-</div>
-
-<p><b>642. Andrœcium.</b>—Within and above the insertion of the corolla
-is found another tier, or whorl, of members which do not at first
-sight resemble leaves in form. They are known in the higher plants
-as <i>stamens</i>. As seen in <a href="#FIG_379">fig. 379</a> each stamen
-possesses a stalk (= filament), and extending along on either side for the greater
-part of the length are four ridges, two on each side. This part of the stamen
-is the <i>anther</i>, and the ridges form the anther sacs, or lobes. Soon
-after the flower is opened, these anther sacs open also by a split in
-the wall along the edge of the ridge. At this time we see quantities of
-yellowish powder or dust escaping from the ruptured anther locules. If
-<span class="pagenum"><a name="Page_320" id="Page_320">[Pg 320]</a></span>
-we place some of this under the microscope we see that it is made up of
-minute bodies which resemble spores; they are rounded in form, and the
-outer wall is spiny. They are in fact spores, the microspores of the
-trillium, and here, as in the gymnosperms, are better known as <i>pollen</i>.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_379" src="images/fig379.jpg" alt="" width="300" height="240" />
-    <p class="center">Fig. 379.<br /> Sepal, petal, stamen, and pistil<br />
-                 of Trillium grandiflorum.</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_380" src="images/fig380.jpg" alt="" width="150" height="273" />
-      <p class="center">Fig. 380.<br /> Trillium grandiflorum,<br /> with the compound pistil<br />
-             expanded into three leaf-like<br /> members. At the right these<br />
-             three are shown in detail.</p>
-  </div>
-</div>
-
-<p><b>643. The stamen a sporophyll.</b>—Since these pollen grains are
-the spores, we would infer, from what we have learned of the ferns
-and gymnosperms, that this member of the flower which bears them is
-a sporophyll; and this is the case. It is in fact what is called the
-<i>microsporophyll</i>. Then we see also that the anther sacs, since they
-enclose the spores, would be the sporangia (microsporangia). From this
-it is now quite clear that the stamens belong also to the leaf series.
-They are just six in number, twice the number found in a whorl of
-leaves, or sepals, or corolla. It is believed, therefore, that there
-are two whorls of stamens in the flower of trillium.</p>
-
-<p><b>644. Gynœcium.</b>—Next above the stamens and at the center of the
-flower is a stout, angular, ovate body which terminates in three long,
-<span class="pagenum"><a name="Page_321" id="Page_321">[Pg 321]</a></span>
-slender, curved points. This is the pistil, and at present the only
-suggestion which it gives of belonging to the leaf series is the fact
-that the end is divided into three parts, the number of parts in each
-successive whorl of members of the flower. If we cut across the body of
-this pistil and examine it with a low power we see that there are three
-chambers or cavities, and at the junction of each the walls suggest to
-us that this body may have been formed by the infolding of the margins
-of three leaf-like members, the places of contact having then become
-grown together. We see also that from the incurved margins of each
-division of the pistil there stand out in the cavity oval bodies. These
-are the <i>ovules</i>. Now the ovules we have learned from our study of the
-gymnosperms are the <i>sporangia</i> (here the macrosporangia). It is now
-more evident that this curious body, the pistil, is made up of three
-leaf-like members which have fused together, each member being the
-equivalent of a sporophyll (here the macrosporophyll). This must be a
-fascinating observation, that plants of such widely different groups
-and of such different grades of complexity should have members formed
-on the same plan and belonging to the same series of members, devoted
-to similar functions, and yet carried out with such great modifications
-that at first we do not see this common meeting ground which a
-comparative study brings out so clearly.</p>
-
-<div class="figcenter">
-    <img  id="FIG_381" src="images/fig381.jpg" alt="" width="500" height="343" />
-  <div class="blockquot">
-    <p class="center">Fig. 381.</p>
-    <p>Abnormal trillium. The nine parts of the perianth are green, and the
-       outer whorls of stamens are expanded into petal-like members.</p>
-  </div>
-</div>
-<div class="figleft">
-    <img src="images/fig382.jpg" alt="" width="200" height="196" />
-    <p class="center">Fig. 382.<br /> Transformed stamen of<br />
-              trillium showing anther<br /> locules on the margin.</p>
-</div>
-
-<p><b>645. Transformations of the flower of trillium.</b>—If anything
-more were needed to make it clear that the parts of the flower of
-trillium belong to the leaf series we could obtain evidence from the
-<span class="pagenum"><a name="Page_322" id="Page_322">[Pg 322]</a></span>
-transformations which the flower of trillium sometimes presents. In
-<a href="#FIG_381">fig. 381</a> is a sketch of a flower of trillium, made from
-a photograph. One set of the stamens has expanded into petal-like organs, with the
-anther sacs on the margin. In <a href="#FIG_380">fig. 380</a> is shown a plant of
-Trillium grandiflorum in which the pistil has separated into three distinct and
-expanded leaf-like structures, all green except portions of the margin.</p>
-
-<h4>Dentaria.</h4>
-
-<p><b>646. General appearance.</b>—For another study we may take a plant
-which belongs to another division of the higher plants, the common
-“pepper root,” or “toothwort” (Dentaria diphylla) as it is sometimes
-called. This plant occurs in moist woods during the month of May, and
-is well distributed in the northeastern United States. A plant is shown
-in <a href="#FIG_383">fig. 383</a>. It has a creeping underground rhizome,
-whitish in color, fleshy, and with a few scales. Each spring the annual flower-bearing
-stem rises from one of the buds of the rhizome, and after the ripening
-of the seeds, dies down.</p>
-
-<p>The leaves are situated a little above the middle point of the stem.
-They are opposite and the number is two, each one being divided into
-three dentate lobes, making what is called a compound leaf.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_383" src="images/fig383.jpg" alt="" width="300" height="471" />
-    <p class="center">Fig. 383.<br /> Toothwort (Dentaria diphylla).</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_384" src="images/fig384.jpg" alt="" width="150" height="186" />
-      <p class="center">Fig. 384.<br /> Flower of the toothwort<br /> (Dentaria diphylla).</p>
-  </div>
-</div>
-
-<p><b>647. Parts of the flower.</b>—The flowers are several, and they
-are borne on quite long stalks (pedicels) scattered over the terminal
-portion of the stem. We should now examine the parts of the flower
-beginning with the calyx. This we can see, looking at the under side
-of some of the flowers, possesses four scale-like sepals, which easily
-fall away after the opening of the flower. They do not resemble leaves
-so much as the sepals of trillium, but they belong to the leaf series,
-and there are two pairs in the set of four. The corolla also possesses
-four petals, which are more expanded than the sepals and are whitish in
-color. The stamens are six in number, one pair lower than the others,
-<span class="pagenum"><a name="Page_323" id="Page_323">[Pg 323]</a></span>
-and also shorter. The filament is long in proportion to the anther, the
-latter consisting of two lobes or sacs, instead of four as in trillium.
-The pistil is composed of two carpels, or leaves fused together. So we
-find in the case of the pepper root that the parts of the flower are
-in twos, or multiples of two. Thus they agree in this respect with the
-leaves; and while we do not see such a strong resemblance between the
-parts of the flower here and the leaves, yet from the presence of the
-<span class="pagenum"><a name="Page_324" id="Page_324">[Pg 324]</a></span>
-pollen (microspores) in the anther sacs (microsporangia) and of ovules
-(macrosporangia) on the margins of each half of the pistil, we are,
-from our previous studies, able to recognize here that all the members
-of the flower belong to the leaf series.</p>
-
-<p><b>648.</b> In trillium and in the pepper root we have seen that the
-parts of the flower in each apparent whorl are either of the same
-number as the leaves in a whorl, or some multiple of that number. This
-is true of a large number of other plants, but it is not true of all. A
-glance at the spring-beauty (Claytonia virginiana), and at the anemone
-(or Isopyrum biternatum, fig. 563) will serve to show that the number
-of the different members of the flower may vary. The trillium and the
-dentaria were selected as being good examples to study first, to make
-it very clear that the members of the flower are fundamentally leaf
-structures, or rather that they belong to the same series of members as
-do the leaves of the plant.</p>
-
-<p><b>649. Synopsis of members of the sporophyte in angiosperms.</b></p>
-
-<table border="0" class="no-wrap" cellspacing="0" summary=" " cellpadding="0"  >
-  <tbody><tr>
-      <td class="tdl">Higher plant.</td>
-      <td class="tdc" colspan="8">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl">Sporophyte phase</td>
-      <td class="tdc" rowspan="2"><img src="images/cbl-2.jpg" alt="" width="9" height="32" /></td>
-      <td class="tdl_ws1">Root.</td>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdl_ws1">&nbsp;</td>
-      <td class="tdc" rowspan="6"><img src="images/cbl-6.jpg" alt="" width="37" height="132" /></td>
-      <td class="tdl_ws1">Foliage leaves.</td>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdl_ws1">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl">(or modern phase)&nbsp;&nbsp;</td>
-      <td class="tdl_ws1">Shoot.</td>
-      <td class="tdc" rowspan="2"><img src="images/cbl-2.jpg" alt="" width="9" height="32" /></td>
-      <td class="tdl_ws1">Stem.</td>
-      <td class="tdl_ws1">Perianth leaves.</td>
-      <td class="tdc" rowspan="5"><img src="images/cbr-5.jpg" alt="" width="30" height="107" /></td>
-      <td class="tdl_ws1">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdl_ws1">&nbsp;</td>
-      <td class="tdl_ws1">&emsp;Leaf.</td>
-      <td class="tdl_ws1">Spore-bearing leaves</td>
-      <td class="tdl_ws1">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdl_ws1">&nbsp;</td>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdl_ws1">&nbsp;</td>
-      <td class="tdl_ws1">&nbsp;&emsp;with sporangia.</td>
-      <td class="tdl_ws1">Flower.</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdl_ws1"></td>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdl_ws1">&nbsp;</td>
-      <td class="tdl_ws1">(Sporangia sometimes</td>
-      <td class="tdl_ws1">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdl_ws1"></td>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdl_ws1">&nbsp;</td>
-      <td class="tdl_ws1">&nbsp;&emsp;on shoot.)</td>
-      <td class="tdl_ws1">&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_325" id="Page_325">[Pg 325]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XXXVI" id="CHAPTER_XXXVI">CHAPTER XXXVI.</a><br />
-<span class="h_subtitle">GAMETOPHYTE AND SPOROPHYTE<br /> OF ANGIOSPERMS.</span></h3>
-</div>
-
-<p><b>650. Male prothallium of angiosperms.</b>—The first division which
-takes place in the nucleus of the pollen grain occurs, in the case of
-trillium and many others of the angiosperms, before the pollen grain
-is mature. In the case of some specimens of T. grandiflorum in which
-the pollen was formed during the month of October of the year before
-flowering, the division of the nucleus into two nuclei took place soon
-after the formation of the four cells from the mother cell. The nucleus
-divided in the young pollen grain is shown in <a href="#FIG_385">fig. 385</a>.
-After this takes place the wall of the pollen grain becomes stouter, and minute
-spiny projections are formed.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_385" src="images/fig385.jpg" alt="" width="150" height="101" />
-    <p class="center">Fig. 385.<br /> Nearly mature pollen<br /> grain of trillium. The<br />
-                    smaller cell is the<br /> generative cell.</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_386" src="images/fig386.jpg" alt="" width="300" height="253" />
-      <p class="center">Fig. 386.<br /> Germinating spores (pollen grains) of peltandra;<br />
-          generative nucleus in one undivided, in other<br />
-          divided to form the two sperm nuclei; vegetative<br />
-          nucleus in each near the pollen grain.</p>
-  </div>
-</div>
-
-<p><b>651.</b> The larger cell is the vegetative cell of the prothallium,
-while the smaller one, since it later forms the sperm cells, is
-the generative cell. This generative cell then corresponds to the
-central cell of the antheridium, and the vegetative cell perhaps
-corresponds to a wall cell of the antheridium. If this is so, then the
-male prothallium of angiosperms has become reduced to a very simple
-antheridium. The farther growth takes place after fertilization. In
-some plants the generative cell divides into the two sperm cells at
-the maturity of the pollen grain. In other cases the generative cell
-divides in the pollen tube after the germination of the pollen grain.
-For study of the pollen tube the pollen may be germinated in a weak
-<span class="pagenum"><a name="Page_326" id="Page_326">[Pg 326]</a></span>
-solution of sugar, or on the cut surface of pear fruit, the latter
-being kept in a moist chamber to prevent drying the surface.</p>
-
-<p><b>652.</b> In the spring after flowering the pollen escapes from the
-anther sacs, and as a result of pollination is brought to rest on
-the stigma of the pistil. Here it germinates, as we say, that is, it
-develops a long tube which makes its way down through the style, and in
-through the micropyle to the embryo sac, where, in accordance with what
-takes place in other plants examined, one of the sperm cells unites
-with the egg, and fertilization of the egg is the result.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img src="images/fig387.jpg" alt="" width="250" height="405" />
-    <p class="center">Fig. 387.<br /> Section of pistil of trillium,<br />
-           showing position of ovules<br /> (macrosporangia).</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig388.jpg" alt="" width="250" height="482" />
-      <p class="center">Fig. 388.<br /> Mandrake<br /> (Podophyllum peltatum).</p>
-  </div>
-</div>
-
-<p><b>653. Macrospore and embryo sac.</b>—In trillium the three carpels
-are united into one, and in dentaria the two carpels are also united
-into one compound pistil. Simple pistils are found in many plants, for
-example in the ranunculaceæ, the buttercups, columbine, etc. These
-simple pistils bear a greater resemblance to a leaf, the margins of
-which are folded around so that they meet and enclose the ovules or
-sporangia.</p>
-
-<div class="figcenter">
-    <img  id="FIG_389" src="images/fig389.jpg" alt="" width="600" height="469" />
-  <div class="blockquot">
-    <p class="center">Fig. 389.</p>
-    <p>Young ovule (macrosporangium) of podophyllum. <i>n</i>, nucellus
-       containing the one-celled stage of the macrospore; <i>i.int</i>, inner
-       integument; <i>o.int</i>, outer integument.</p>
-  </div>
-</div>
-
-<p><b>654.</b> If we cut across the compound pistil of trillium we
-find that the infoldings of the three pistils meet to form three
-partial partitions which extend nearly to the center, dividing off
-three spaces. In these spaces are the ovules which are attached to
-the infolded margins. If we make cross-sections of a pistil of the
-<span class="pagenum"><a name="Page_327" id="Page_327">[Pg 327]</a></span>
-May-apple (podophyllum) and through the ovules when they are quite young, we
-shall find that the ovule has a structure like that shown in <a href="#FIG_389">fig. 389</a>.
-At <i>m</i> is a cell much larger than the surrounding ones. This is
-called the macrospore. The tissue surrounding it is called here the
-nucellus, but because it contains the macrospore it must be the
-macrosporangium. The two coats or integuments of the ovule are
-yet short and have not grown out over the end of the nucellus.
-This macrospore increases in size, forming first a cavity or sac
-in the nucellus, the <i>embryo sac</i>. The nucleus divides several
-times until eight are formed, four in the micropylar end of the
-embryo sac and four in the opposite end. In some plants it
-has been found that one nucleus from each group of four moves
-toward the middle of the embryo sac. Here they fuse together
-to form one nucleus, the <i>endosperm nucleus</i> or <i>definitive nucleus</i>
-shown in <a href="#FIG_390">fig. 390</a>. One of the nuclei at the micropylar end is
-<span class="pagenum"><a name="Page_328" id="Page_328">[Pg 328]</a></span>
-the egg, while the two smaller ones nearer the end are the <i>synergids</i>.
-The egg-cell is all that remains of the archegonium in this reduced prothallium.
-The three nuclei at the lower end are the <i>antipodal</i> cells.</p>
-
-<div class="figcenter">
-    <img  id="FIG_390" src="images/fig390.jpg" alt="" width="600" height="326" />
-  <div class="blockquot">
-    <p class="center">Fig. 390.</p>
-    <p>Podophyllum peltatum, ovule containing mature embryo sac; two
-       synergids, and eggs at left, endosperm nucleus in center, three
-       antipodal cells at right.</p>
-  </div>
-</div>
-<div class="figleft">
-    <img  id="FIG_391" src="images/fig391.jpg" alt="" width="150" height="140" />
-    <p class="center">Fig. 391.<br /> Macrospore<br /> (one-celled stage)<br /> of lilium.</p>
-</div>
-
-<p><b>655. Embryo sac is the young female prothallium.</b>—In figs.
-<a href="#FIG_391">391</a>-<a href="#FIG_393">393</a> are shown the different
-stages in the development of the embryo sac in lilium. The embryo sac
-at this stage is the young female prothallium, and the egg is the only
-remnant of the female sexual organ, the archegonium, in this reduced
-gametophyte.</p>
-
-<p><b>656. Fertilization.</b>—When the pollen tube has reached the embryo
-sac (paragraph 652) it opens and the two sperm cells are emptied near
-the egg. The first sperm nucleus enters the protoplasm surrounding the
-egg nucleus and uniting with the latter brings about fertilization. The
-second sperm nucleus often unites with the endosperm nucleus (or with
-one or both of the “polar nuclei”), bringing about what some call a
-second fertilization. Where this takes place in addition to the union
-<span class="pagenum"><a name="Page_329" id="Page_329">[Pg 329]</a></span>
-of the first sperm nucleus with the egg nucleus it is called <i>double
-fertilization</i>. The sperm nucleus is usually smaller than the egg
-nucleus, but often grows to near or quite the size of the egg nucleus
-before union. See figs. <a href="#FIG_394">394</a> and <a href="#FIG_395">395</a>.</p>
-
-<div class="figcenter">
-    <img src="images/fig392.jpg" alt="" width="500" height="429" />
-  <div class="blockquot">
-    <p class="center">Fig. 392.</p>
-    <p>Two-and four-celled stage of embryo sac of lilium. The middle one
-       shows division of nuclei to form the four-celled stage. (Easter lily.)</p>
-  </div>
-</div>
-
-<p><b>657. Fertilization in plants is fundamentally the same as in
-animals.</b>—In all the great groups of plants as represented by
-spirogyra, œdogonium, vaucheria, peronospora, ferns, gymnosperms, and
-in the angiosperms, fertilization, as we have seen, consists in the
-fusion of a male nucleus with a female nucleus. Fertilization, then, in
-plants is identical with that which takes place in animals.</p>
-
-<p><b>658. Embryo.</b>—After fertilization the egg develops into a short
-row of cells, the <i>suspensor</i> of the embryo. At the free end the embryo
-develops. In figs. <a href="#FIG_397">397</a> and <a href="#FIG_398">398</a>
-is a young embryo of trillium.</p>
-
-<p><b>659. Endosperm, the mature female prothallium.</b>—During the
-<span class="pagenum"><a name="Page_330" id="Page_330">[Pg 330]</a></span>
-development of the embryo the endosperm nucleus divides into a great
-many nuclei in a mass of protoplasm, and cell walls are formed
-separating them into cells. This mass of cells is the <i>endosperm</i>,
-and it surrounds the embryo. It is the <i>mature female prothallium</i>,
-belated in its growth in the angiosperms, usually developing only when
-fertilization takes place, and its use has been assured.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_393" src="images/fig393.jpg" alt="" width="150" height="455" />
-    <p class="center">Fig. 393.<br /> Mature embryo sac<br /> (young prothallium) of<br />
-        lilium. <i>m</i>, micropylar end;<br /> <i>S</i>, synergids; <i>E</i>, egg;<br />
-        <i>Pn</i>, polar nuclei; <i>Ant</i>,<br /> antipodals. (Easter lily.)</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_394" src="images/fig394.jpg" alt="" width="200" height="445" />
-      <p class="center">Fig. 394.<br /> Section through nucellus and<br />
-          upper part of embryo sac of<br /> cotton at time of entrance of<br />
-          pollen tube. <i>E</i>, egg; <i>S</i>,<br /> synergids; <i>P</i>, pollen tube with<br />
-          sperm cell in the end. (Duggar.)</p>
-  </div>
-</div>
-
-<p><span class="pagenum"><a name="Page_331" id="Page_331">[Pg 331]</a></span>
-<b>660. Seed.</b>—As the embryo is developing it derives its
-nourishment from the endosperm (or in some cases perhaps from the
-nucellus). At the same time the integuments increase in extent and
-harden as the seed is formed.</p>
-
-<div class="figcenter">
-    <img  id="FIG_395" src="images/fig395.jpg" alt="" width="500" height="314" />
-  <div class="blockquot">
-    <p class="center">Fig. 395.</p>
-    <p>Fertilization of cotton. <i>pt</i>, pollen tube; <i>Sn</i>,
-       synergids; <i>E</i>, egg, with male and female nucleus fusing.
-      (Duggar.)</p>
-  </div>
-</div>
-<div class="figcenter">
-    <img src="images/fig396.jpg" alt="" width="400" height="530" />
-  <div class="blockquot">
-    <p class="center">Fig. 396.</p>
-    <p>Diagrammatic section of ovary and ovule at time of fertilization in
-       angiosperm. <i>f</i>, funicle of ovule; <i>n</i>, nucellus; <i>m</i>, micropyle; <i>b</i>,
-       antipodal cells of embryo sac; <i>e</i>, endosperm nucleus; <i>k</i>, egg-cell
-       and synergids; <i>ai</i>, outer integument of ovule; <i>ii</i>, inner integument.
-       The track of the pollen tube is shown down through the style, walls of
-       the ovary to the micropylar end of the embryo sac.</p>
-  </div>
-</div>
-
-<p><b>661. Perisperm.</b>—In most plants the nucellus is all consumed
-in the development of the endosperm, so that only minute fragments
-of disorganized cell walls remain next the inner integument. In some
-plants, however, (the water-lily family, the pepper family, etc.,)
-a portion of the nucellus remains intact in the mature seed. In such
-seeds the remaining portion of the nucellus is the <i>perisperm</i>.</p>
-
-<p><b>662. Presence or absence of endosperm in the seed.</b>—In many of
-the angiosperms all of the endosperm is consumed by the embryo during
-its growth in the formation of the seed. This is the case in the rose
-family, crucifers, composites, willows, oaks, legumes, etc., as in the
-acorn, the bean, pea and others. In some, as in the bean, a large part
-<span class="pagenum"><a name="Page_332" id="Page_332">[Pg 332]</a></span>
-of the nutrient substance passing from the endosperm into the embryo is
-stored in the cotyledons for use during germination. In other plants
-the endosperm is not all consumed by the time the seed is mature.
-Examples of this kind are found in the buttercup family, the violet,
-lily, palm, jack-in-the-pulpit, etc. Here the remaining endosperm in
-the seed is used as food by the embryo during germination.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_397" src="images/fig397.jpg" alt="" width="350" height="260" />
-    <p class="center">Fig. 397.<br /> Section of one end of ovule of trillium,<br />
-                showing young embryo in endosperm.</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_398" src="images/fig398.jpg" alt="" width="100" height="238" />
-      <p class="center">Fig. 398.<br /> Embryo<br /> enlarged.</p>
-  </div>
-</div>
-<div class="figcontainer">
-  <div class="figsub">
-    <img src="images/fig399.jpg" alt="" width="250" height="207" />
-    <p class="center">Fig. 399.<br /> Seed of violet, external view,<br />
-          and section. The section shows<br /> the embryo lying in the endosperm.</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig400.jpg" alt="" width="250" height="183" />
-      <p class="center">Fig. 400.<br /> Section of fruit of pepper (Piper nigrum),<br />
-           showing small embryo lying in a small<br /> quantity of whitish endosperm at one end,<br />
-           the perisperm occupying the larger part of<br /> the interior, surrounded by pericarp.</p>
-  </div>
-</div>
-
-<p><b>663. Outer parts of the seed.</b>—While the embryo is forming within
-<span class="pagenum"><a name="Page_333" id="Page_333">[Pg 333]</a></span>
-the ovule and the growth of the endosperm is taking place, where this
-is formed, other correlated changes occur in the outer parts of the
-ovule, and often in adjacent parts of the flower. These unite in making
-the “seed,” or the “fruit.” Especially in connection with the formation
-of the seed a new growth of the outer coat, or integument, of the ovule
-occurs, forming the outer coat of the seed, known as the <i>testa</i>, while
-the inner integument is absorbed. In some cases the inner integument
-of the ovule also forms a new growth, making an inner coat of the seed
-(rosaceæ). In still other cases neither of the integuments develops
-into a testa, and the embryo sac lies in contact with the wall of
-the ovary. Again an additional envelope grows up around the seed; an
-example of this is found in the case of the red berries of the “yew”
-(taxus), the red outer coat being an extra growth, called an <i>aril</i>.</p>
-
-<p>In the willow and the milkweed an aril is developed in the form of
-a tuft of hairs. (In the willow it is an outgrowth of the funicle,
-= stalk of the ovule, and is called a funicular aril; while in the
-milkweed it is an outgrowth of the micropyle, = the open end of the
-ovule, and is called a micropylar aril.)</p>
-
-<p><b>664. Increase in size during seed formation.</b>—Accompanying this
-extra growth of the different parts of the ovule in the formation of
-the seed is an increase in the size, so that the seed is often much
-greater in size than the ovule at the time of fertilization. At the
-same time parts of the ovary, and in many plants, the adherent parts of
-the floral envelopes, as in the apple; or of the receptacle, as in the
-strawberry; or in the involucre, as in the acorn; are also stimulated
-to additional growth, and assist in making the fruit.
-<span class="pagenum"><a name="Page_334" id="Page_334">[Pg 334]</a></span></p>
-
-<p><b>665. Synopsis of the seed.</b></p>
-
-<table border="0" cellspacing="0" summary=" " cellpadding="0"  >
-  <tbody><tr>
-      <td class="tdl br" rowspan="7"><i>The&nbsp;seed.&nbsp;</i></td>
-      <td class="tdc br">&nbsp;</td>
-      <td class="tdl bt">Aril, rarely present.</td>
-   </tr><tr>
-      <td class="tdc br">&nbsp;</td>
-      <td class="tdl_ws1"><p class="neg-indent2">Ovular coats (one or two usually present), the <i>testa</i>.</p></td>
-   </tr><tr>
-      <td class="tdc br">&nbsp;</td>
-      <td class="tdl_ws1"><p class="neg-indent2"><i>Funicle</i> (stalk of ovule), <i>raphe</i> (portion of funicle when bent on to
-              the side of ovule), <i>micropyle</i>, <i>hilum</i> (scar where seed was attached
-              to ovary).</p></td>
-   </tr><tr>
-      <td class="tdr br"><i>Ripened&nbsp;ovule.</i><span class="ws4">&nbsp;</span></td>
-      <td class="tdl_ws1 bb"><p class="neg-indent2"><i>Remnant of the nucellus</i> (central part of ovule); sometimes
-               nucellus remains as <i>Perisperm</i> in some albuminous seeds.</p></td>
-   </tr><tr>
-      <td class="tdc" colspan="3">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl_ws1"><i>Endosperm</i>, present in albuminous seeds.</td>
-   </tr><tr>
-      <td class="tdl_ws1"><p class="neg-indent2"><i>Embryo</i> within surrounded by endosperm when this
-             is present, or by the remnant of nucellus, and by the ovular coats
-             which make the <i>testa</i>. In many seeds (example, bean) the endospermis
-             transferred to the cotyledons which become fleshy(exalbuminous seeds).</p></td>
-   </tr>
- </tbody>
-</table>
-
-<p><b>666. Parts of the ovule.</b>—In <a href="#FIG_401">fig. 401</a> are represented
-three different kinds of ovules, which depend on the position of the ovule
-with reference to its stalk. The funicle is the stalk of the ovule,
-the hilum is the point of attachment of the ovule with the ovary, the
-raphe is the part of the funicle in contact with the ovule in inverted
-ovules, the chalaza is the portion of the ovule where the nucellus and
-the integuments merge at the base of the ovule, and the micropyle is
-the opening at the apex of the ovule where the coats do not meet.</p>
-
-<div class="figcenter">
-    <img  id="FIG_401" src="images/fig401.jpg" alt="" width="600" height="221" />
-  <div class="blockquot">
-    <p class="center">Fig. 401.</p>
-    <p><i>A</i>, represents a straight (orthotropous) ovule of polygonum; <i>B</i>, the
-       inverted (anatropous) ovule of the lily; and <i>C</i>, the right-angled
-       (campylotropous) ovule of the bean. <i>f</i>, funicle; <i>c</i>, chalaza;
-       <i>k</i>, nucellus; <i>ai</i>, outer integument; <i>ii</i>, inner integument; <i>m</i>,
-       micropyle; <i>em</i>, embryo sac.</p>
-  </div>
-</div>
-<p><span class="pagenum"><a name="Page_335" id="Page_335">[Pg 335]</a></span></p>
-
-<p class="center"><b>Comparison of Organ and Member.</b></p>
-
-<p><b>667. The stamens and pistils are not the sexual organs.</b>—Before
-the sexual organs and sexual processes in plants were properly
-understood it was customary for botanists to speak of the stamens and
-pistils of flowering plants as the sexual organs. Some of the early
-botanists, a century ago, found that in many plants the seed would not
-form unless first the pollen from the stamens came to be deposited on
-the stigma of the pistil. A little further study showed that the pollen
-germinated on the stigma and formed a tube which made its way down
-through the pistil and into the ovule.</p>
-
-<p>This process, including the deposition of the pollen on the stigma,
-was supposed to be fertilization, the stamen was looked on as the male
-sexual organ, and the pistil as the female sexual organ. We have found
-out, however, by further study, and especially by a comparison of the
-flowering plants and the lower plants, that the stamens and pistils are
-not the sexual organs of the flower.</p>
-
-<p><b>668. The stamens and pistils are spore-bearing leaves.</b>—The
-stamen is the spore-bearing leaf, and the pollen grains are not
-unlike spores; in fact they are the small spores of the angiosperms.
-The pistil is also a spore-bearing leaf, the ovule the sporangium,
-which contains the large spore called an <i>embryo sac</i>. In the ferns
-we know that the spore germinates and produces the green heart-shaped
-prothallium. The prothallium bears the sexual organs. Now the fern leaf
-bears the spores and the spore forms the prothallium. So it is in the
-flowering plants. The stamen bears the small spores—pollen grains—and
-the pollen grain forms the prothallium. The prothallium in turn forms
-the sexual organs. The process is in general the same as it is in the
-ferns, but with this special difference: the prothallium and the sexual
-organ of the flowering plants are very much reduced.</p>
-
-<p><b>669. Difference between organ and member.</b>—While it is not
-<span class="pagenum"><a name="Page_336" id="Page_336">[Pg 336]</a></span>
-strictly correct then to say that the stamen is a sexual organ, or male
-organ, we might regard it as a <i>male member</i> of the flower, and we
-should distinguish between <i>organ</i> and <i>member</i>. It is an <i>organ</i> when
-we consider <i>pollen production</i>, but it is not a sexual organ. When we
-consider <i>fertilization</i> it is <i>not a sexual organ, but a male member</i>
-of the flower which bears the small spore.</p>
-
-<p>The following table will serve to indicate these relations.</p>
-
-<table border="0" cellspacing="0" summary=" " cellpadding="0" >
-  <tbody><tr>
-      <td class="tdl_top">Stamen</td>
-      <td class="tdc_top">&nbsp;=&nbsp;</td>
-      <td class="tdl">spore-bearing leaf = male member of flower.</td>
-   </tr><tr>
-      <td class="tdl_top">Anther&nbsp;locule</td>
-      <td class="tdc_top">&nbsp;=&nbsp;</td>
-      <td class="tdl">sporangium.</td>
-   </tr><tr>
-      <td class="tdl_top">Pollen grain</td>
-      <td class="tdc_top">&nbsp;=&nbsp;</td>
-      <td class="tdl">small spore = reduced male prothallium and sexual organ.</td>
-   </tr>
- </tbody>
-</table>
-
-<p>So the pistil is not a sexual organ, but might be regarded as the
-female member of the flower.</p>
-
-<table border="0" cellspacing="0" summary=" " cellpadding="0" >
-  <tbody><tr>
-      <td class="tdl_top">Pistil</td>
-      <td class="tdc_top">&nbsp;=&nbsp;</td>
-      <td class="tdl">spore-bearing leaf = female member of flower.</td>
-   </tr><tr>
-      <td class="tdl_top">Ovule</td>
-      <td class="tdc_top">&nbsp;=&nbsp;</td>
-      <td class="tdl">sporangium.</td>
-   </tr><tr>
-      <td class="tdl_top">Embryo&nbsp;sac</td>
-      <td class="tdc_top">&nbsp;=&nbsp;</td>
-      <td class="tdl">large spore = female prothallium containing the egg.</td>
-   </tr><tr>
-      <td class="tdl_top">The egg</td>
-      <td class="tdc_top">&nbsp;=&nbsp;</td>
-      <td class="tdl">a reduced archegonium = the female sexual organ.</td>
-   </tr>
- </tbody>
-</table>
-
-<p class="center"><b>Progression and Retrogression in<br /> Sporophyte and Gametophyte.</b></p>
-
-<p><b>670. Sporophyte is prominent and highly developed.</b>—In the
-angiosperms then, as we have seen from the plants already studied, the
-trillium, dentaria, etc., are sporophytes, that is they represent the
-spore-bearing, or sporophytic, stage. Just as we found in the case of
-the gymnosperms and ferns, this stage is the prominent one, and the
-one by which we characterize and recognize the plant. We see also that
-the plants of this group are still more highly specialized and complex
-than the gymnosperms, just as they were more specialized and complex
-than the members of the fern group. From the very simple condition
-in which we possibly find the sporophyte in some of the algæ like
-spirogyra, vaucheria, and coleochæte, there has been a gradual increase
-in size, specialization of parts, and complexity of structure through
-the bryophytes, pteridophytes, and gymnosperms, up to the highest types
-of plant structure found in the angiosperms. Not only do we find that
-these changes have taken place, but we see that, from a condition of
-complete dependence of the spore-bearing stage on the sexual stage
-(gametophyte), as we find it in the liverworts and mosses, it first
-becomes free from the gametophyte in the members of the fern group, and
-is here able to lead an independent existence. The sporophyte, then,
-<span class="pagenum"><a name="Page_337" id="Page_337">[Pg 337]</a></span>
-might be regarded as the modern phase of plant life, since it is that
-which has become and remains the prominent one in later times.</p>
-
-<p><b>671. The gametophyte once prominent has become degenerate.</b>—On
-the other hand we can see that just as remarkable changes have come
-upon the other phase of plant life, the sexual stage, or gametophyte.
-There is reason to believe that the gametophyte was the stage of plant
-life which in early times existed almost to the exclusion of the
-sporophyte, since the characteristic thallus of the algæ is better
-adapted to an aquatic life than is the spore-bearing state of plants.
-At least, we now find in the plants of this group as well as in the
-liverworts, that the gametophyte is the prominent stage. When we reach
-the members of the fern group, and the sporophyte becomes independent,
-we find that the gametophyte is decreasing in size, in the higher
-members of the pteridophytes, the male prothallium consisting of only a
-few cells, while the female prothallium completes its development still
-within the spore wall. And in selaginella it is entirely dependent on
-the sporophyte for nourishment.</p>
-
-<p><b>672.</b> As we pass through the gymnosperms we find that the
-condition of things which existed in the bryophytes has been reversed,
-and the gametophyte is now entirely dependent on the sporophyte for
-its nourishment, the female prothallium not even becoming free from
-the sporangium, which remains attached to the sporophyte, while the
-remnant of a male prothallium, during the stage of its growth, receives
-nourishment from the tissues of the nucellus through which it bores its
-way to the egg-cell.</p>
-
-<p><b>673.</b> In the angiosperms this gradual degradation of the male
-and female prothallia has reached a climax in a one-celled male
-prothallium with two sperm cells, and in the embryo sac with no clearly
-recognizable traces of an archegonium to identify it as a female
-prothallium. The development of the endosperm subsequent, in most
-cases, to fertilization, providing nourishment for the sporophytic
-embryo at one stage or another, is believed to be the last remnant of
-the female prothallium in plants.</p>
-
-<p><b>674. The seed.</b>—The seed is the only important character
-possessed by the higher plants (the gymnosperms and angiosperms) which
-is not possessed by one or another of the lower great groups. With the
-gradual evolution of the higher plants from the lower there has been
-developed at certain periods organs or structural characters which
-were not present in some of the lower groups. Thus the thallus is the
-plant body of the algæ and fungi, so that these two groups of plants
-are sometimes called <i>Thallophytes</i>. In the Bryophytes (liverworts and
-mosses) the thallus is still present, but there is added the highly
-organized archegonium in place of the simple female gamete or oogonium,
-or carpogonium of the algæ and fungi, and the sporophyte has become
-a distinct though still dependent structure. In the Pteridophytes
-the thallus is still present as the prothallium, archegoina are also
-present, and while both of these structures are retrograding the
-sporophyte has become independent and has organized for the first time
-<span class="pagenum"><a name="Page_338" id="Page_338">[Pg 338]</a></span>
-a true vascular system for conduction of water and food. In the
-gymnosperms and angiosperms the thallus is present in the endosperm;
-distinct, though reduced, archegonia are present in most gymnosperms
-and represented only by the egg in the angiosperms; the vascular system
-is still more highly developed while the seed for the first time is
-organized, and characterizes these plants so that they are called seed
-plants, or <i>Spermatophytes</i>.</p>
-
-<p class="center"><b>Variation, Hybridization, Mutation.</b></p>
-
-<p><b>674a. Variation.</b>—It is a well-known fact that plants as well
-as animals are subject to variation. Under certain conditions, some
-of which are partly understood and others are unknown, the progeny of
-plants differ in one or more characters from their parents. Some of
-these variations are believed to be due to the influence of environment
-(see Parts III and IV). Others are the result of the crossing of
-individuals which show greater or lesser differences in one or more
-characters, or the crossing of different species (<i>hybridization</i>). The
-most profound variations are those which spring suddenly into existence
-(<i>mutation</i>).</p>
-
-<p><b>674b. Hybridization.</b>—Two different species are “crossed” where
-the egg-cell of one species is fertilized by the sperm of another
-species. The progeny resulting from such a cross is a <i>hybrid</i>. Hybrids
-sometimes resemble one parent, sometimes another, sometimes both. Where
-the parents differ only in respect to one character of an organ or
-structure, there is a regular law in respect to the progeny if they are
-self-fertilized. In the first generation all the individuals are alike
-and resemble one of the parents, and the special differential character
-of that parent is called the <i>dominant</i> character. In the second
-generation 75% possess the dominant character, while 25% resemble
-the other original parent, and its differential character is called
-<i>recessive</i>. These are <i>pure</i> recessives, since successive generations,
-if self-fertilized, are always recessive. Of the 75% which show the
-dominant character in the second generation, one-third (or 25% of the
-whole number) are pure dominants if self-fertilization is continued,
-while 50% are really “cross breds” like the first generation, and
-if self-fertilized split up again into approximately 25 dominants,
-50 cross breds, and 25 recessives. This is what is called Mendel’s
-law. Where the original parents differ in respect to more than one
-character, the result is more complicated (see Mendel’s Principles of
-Heredity; also de Vries, Das Spaltungsgesetz der Bastarde, Ber. d.
-deutsch. bot. Gesell., 18, 83, 1900).</p>
-
-<p><b>674c. Mutation.</b>—This term is applied to those variations which
-appear so suddenly that some of the progeny of two like individuals
-differ from all the others to a marked degree. Some of these mutations
-are so different as to be regarded as new species. Some of the
-primroses show mutations, and Œnothera gigas is a mutation from Œnothera
-lamarkiana (see de Vries, Die Mutationstheorie, Leipzig).
-<span class="pagenum"><a name="Page_339" id="Page_339">[Pg 339]</a></span></p>
-
-<p><b>675.</b></p>
-
-<p class="center">TABLE SHOWING HOMOLOGIES OF SPOROPHYTE AND<br />
-GAMETOPHYTE IN ANGIOSPERMS.</p>
-
-<p class="center"><span class="smcap">Terms Corresponding to those used in Pteridophytes.</span>  <span class="smcap">Common Terms.</span></p>
-
-<table border="0" cellspacing="0" summary=" " cellpadding="0" >
-  <thead><tr>
-      <th class="tdc">&nbsp;</th>
-      <th class="tdc bb"><span class="smcap">Terms Corresponding to those<br /> used in Pteridophytes.</span></th>
-      <th class="tdc bb">&nbsp;</th>
-      <th class="tdc bb" colspan="2"><span class="smcap">Common Terms.</span></th>
-  </tr>
-  </thead>
-  <tbody><tr>
-      <td class="tdl br">&nbsp;</td>
-      <td class="tdl_ws1">Sporophyte</td>
-      <td class="tdc_ws1">=</td>
-      <td class="tdl" colspan="2">Higher plant.</td>
-   </tr><tr>
-      <td class="tdl br">&nbsp;</td>
-      <td class="tdl_ws1">Spore-bearing part</td>
-      <td class="tdc_ws1">=</td>
-      <td class="tdl" colspan="2">Stamens and carpels.</td>
-   </tr><tr>
-      <td class="tdl br bt" rowspan="3">Sporophyte</td>
-      <td class="tdl bt" rowspan="2">&emsp;Microsporophyll</td>
-      <td class="tdc_ws1 bt" rowspan="2">=</td>
-      <td class="tdl bt br" rowspan="2">Stamen</td>
-      <td class="tdl bt">Anther</td>
-   </tr><tr>
-      <td class="tdl">Filament.</td>
-   </tr><tr>
-      <td class="tdl_ws1 ">Microsporangium</td>
-      <td class="tdc_ws1 ">=</td>
-      <td class="tdl " colspan="2">Pollen sac, usually two or four.</td>
-   </tr><tr>
-      <td class="tdl br bb bt" rowspan="9">Male&nbsp;gametophyte</td>
-      <td class="tdl_ws1 bt">Microspore at maturity usually of 2 or 3</td>
-      <td class="tdc_ws1 bt">=</td>
-      <td class="tdl bt" colspan="2">Pollen grain.</td>
-   </tr><tr>
-      <td class="tdl_ws1">&nbsp;&emsp;cells {young male prothallium}</td>
-      <td class="tdc_ws1">&nbsp;</td>
-      <td class="tdl" colspan="2">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;1. Large cell (part of antheridium wall?), with</td>
-      <td class="tdc_ws1">&nbsp;</td>
-      <td class="tdl" colspan="2">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl_ws1">its nucleus surrounded by wall of spore</td>
-      <td class="tdc_ws1">=</td>
-      <td class="tdl" colspan="2">Vegetative cell.</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;2. Small cell with nucleus, no wall, floating</td>
-      <td class="tdc_ws1">&nbsp;</td>
-      <td class="tdl" colspan="2"></td>
-   </tr><tr>
-      <td class="tdl_ws1">in protoplasm of large cell is the central</td>
-      <td class="tdc_ws1">&nbsp;</td>
-      <td class="tdl" colspan="2">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl_ws1">cell of antheridium (male sexual organ)</td>
-      <td class="tdc_ws1">=</td>
-      <td class="tdl" colspan="2">Generative cell.</td>
-   </tr><tr>
-      <td class="tdl_ws1">Mature male prothallium</td>
-      <td class="tdc_ws1">=</td>
-      <td class="tdl" colspan="2">Pollen grain with tube.</td>
-   </tr><tr>
-      <td class="tdl_ws1 bb">Antheridium cell divided, 2 sperm cells</td>
-      <td class="tdc_ws1 bb">=</td>
-      <td class="tdl bb" colspan="2">Paternal cells, or generative cells.</td>
-   </tr><tr>
-      <td class="tdl br bb" rowspan="4">Sporophyte</td>
-      <td class="tdl " rowspan="2">&emsp;Macrosporophyll</td>
-      <td class="tdc_ws1" rowspan="2">=</td>
-      <td class="tdl br" rowspan="2">Carpel or simple pistil</td>
-      <td class="tdl" rowspan="2">Stigma.<br />Style.<br />Ovary.</td>
-   </tr><tr>
-      <td class="tdc" colspan="5">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl_ws1 bb" rowspan="2">Macrosporangium, covered by 1 or 2 coats</td>
-      <td class="tdc_top bb" rowspan="2">=</td>
-      <td class="tdl bb"  rowspan="2" colspan="2">Nucellus, covered by 1 or 2 coats&nbsp;=&nbsp;ovule.</td>
-   </tr><tr>
-      <td class="tdc" colspan="5">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl br bb" rowspan="5">Female&nbsp;gametophyte</td>
-      <td class="tdl_ws1"><p class="no-indent">Macrospore, cell in end of macrosporangium,
-                         does not become free, cavity enlarges</p></td>
-      <td class="tdc_ws1">=</td>
-      <td class="tdl" colspan="2">Uninuclear state of embryo sac.</td>
-   </tr><tr>
-      <td class="tdl_ws1"><p class="no-indent">Macrospore divides into
-                        8 cells to form young female prothallium</p></td>
-      <td class="tdc_ws1">=</td>
-      <td class="tdl" colspan="2">Embryo sac.</td>
-   </tr><tr>
-      <td class="tdl_ws1"><p class="no-indent">Remnant of archegonium,  egg (female sexual organ)</p></td>
-      <td class="tdc_ws1">=</td>
-      <td class="tdl" colspan="2">Maternal cell, or germ cell.</td>
-   </tr><tr>
-      <td class="tdl_ws1"><p class="no-indent">Growing part of prothallium</p></td>
-      <td class="tdc_ws1">=</td>
-      <td class="tdl" colspan="2">Two polar nuclei fused, making endosperm nucleus.</td>
-   </tr><tr>
-      <td class="tdl_ws1 bb"><p class="no-indent">Mature female prothallium</p></td>
-      <td class="tdc_ws1 bb">=</td>
-      <td class="tdl bb" colspan="2">Endosperm, developed by many divisions of endosperm nucleus.</td>
-   </tr><tr>
-      <td class="tdl_ws1 br bb"><p class="no-indent">Young sporophyte surrounded by parts of the gametophyte
-                           and new growth of old sporophyte</p></td>
-      <td class="tdl_ws1 bb"><p class="no-indent">After fecundation of egg, egg divides to form embryo.
-                           Embryo in endosperm (sometimes latter nearly or quite absent) surrounded
-                           by coats</p></td>
-      <td class="tdc_ws1 bb">=</td>
-      <td class="tdl bb" colspan="2">Seed.</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="3"><p class="no-indent">Young sporophyte surrounded by remnants
-                           of gametophyte and new parts of old sporophyte (remains of endosperm and
-                           of nucellus, and ovular coat) = the seed.</p></td>
-      <td class="tdl" colspan="2">&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_340" id="Page_340">[Pg 340]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XXXVII" id="CHAPTER_XXXVII">CHAPTER XXXVII.</a><br />
-<span class="h_subtitle">MORPHOLOGY OF THE NUCLEUS AND SIGNIFICANCE<br />
-              OF GAMETOPHYTE AND SPOROPHYTE.</span></h3>
-</div>
-
-<p><b>676.</b> In the development of the spores of the liverworts,
-mosses, ferns, and their allies, as well as in the development of the
-microspores of the gymnosperms and angiosperms, we have observed that
-four spores are formed from a single mother cell. These mother cells
-are formed as a last division of the fertile tissue (archesporium) of
-the sporangium. In ordinary cell division the nucleus always divides
-prior to the division of the cell. In many cases it is directly
-connected with the laying down of the dividing cell wall.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img src="images/fig402.jpg" alt="" width="250" height="220" />
-    <p class="center">Fig. 402.<br /> Forming spores in mother cells<br />
-               (Polypodium vulgare).</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig403.jpg" alt="" width="250" height="229" />
-      <p class="center">Fig. 403.<br /> Spores just mature and wall of mother<br />
-               cell broken (Asplenium bulbiferum).</p>
-  </div>
-</div>
-
-<p><b>677. Direct division of the nucleus.</b>—The nucleus divides in two
-different ways. On the one hand the process is very simple. The nucleus
-simply fragments, or cuts itself in two. This is direct division.</p>
-
-<p><b>678. Indirect division of the nucleus.</b>—On the other hand very
-<span class="pagenum"><a name="Page_341" id="Page_341">[Pg 341]</a></span>
-complicated phenomena precede and attend the division of the nucleus,
-giving rise to a succession of nuclear figures presented by a definite
-but variable series of evolutions on the part of the nuclear substance.
-This is <i>indirect division</i> of the nucleus, or <i>karyokinesis</i>.
-Indirect division of the nucleus is the usual method, and it occurs in the
-normal growth and division of the cell. The nuclear figures which are
-formed in the division of the mother cell into the four spores are
-somewhat different from those occurring in vegetative division, but
-their study will serve to show the general character of the process.</p>
-
-<p><b>679. Chromatin and linin of the nucleus.</b>—In <a href="#FIG_404">figure 404</a>
-is represented a pollen mother cell of the May-apple (podophyllum). The
-nucleus is in the resting stage. There is a network consisting of very
-delicate threads, the <i>linin</i> network. Upon this network are numerous
-small granules, and at the junction of the threads are distinct knots.
-The nucleolus is quite large and prominent. The numerous small granules
-upon the linin stain very deeply when treated with certain dyes used in
-differentiating the nuclear structure. This deeply staining substance
-is the <i>chromatin</i> of the nucleus.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_404" src="images/fig404.jpg" alt="" width="150" height="297" />
-    <p class="center">Fig. 404.<br /> Pollen mother cell of podophyllum,<br />
-            resting nucleus. Chromatin forming<br /> a network.</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_405" src="images/fig405.jpg" alt="" width="175" height="281" />
-      <p class="center">Fig. 405.<br /> Spirem stage of nucleus. <i>nu</i>,<br />
-         nuclear cavity; <i>n</i>, nucleolus;<br /> <i>Sp</i>, spirem.</p>
-  </div>
-  <div class="figsub">
-      <img  id="FIG_406" src="images/fig406.jpg" alt="" width="150" height="269" />
-      <p class="center">Fig. 406.<br /> Forming spindle, threads from<br />
-             protoplasm with several poles,<br /> roping the chromosomes up to<br />
-             nuclear plate.</p>
-  </div>
-<p class="center space-below1">(Figures 404-406 after Mottier.)</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_342" id="Page_342">[Pg 342]</a></span>
-<b>680. The chromatin skein.</b>—One of the first nuclear figures
-in the preparatory stages of division is the chromatin <i>skein</i> or
-<i>spirem</i>. The chromatin substance unites to form this. The
-spirem is in the form of a narrow continuous ribbon, or band,
-woven into an irregular skein, or gnarl, as shown in <a href="#FIG_405">figure 405</a>.
-This band splits longitudinally into two narrow ones, and then
-each divides into a definite number of segments, about eight in
-the case of podophyllum. Sometimes the longitudinal splitting of
-the band appears to take place after the separation into the chromatin
-segments. The segments remain in pairs until they separate
-at the nuclear plate.</p>
-
-<div class="figcenter">
-    <img  id="FIG_407" src="images/fig407.jpg" alt="" width="600" height="253" />
-  <div class="blockquot">
-    <p class="center">Fig. 407.</p>
-    <p>Karyokinesis in pollen mother cells of podophyllum. At the left the spindle with the
-       chromosomes separating at the nuclear plate; in the middle figure the chromosomes have
-       reached the poles of the spindle, and at the right the chromosomes are forming the daughter
-       nuclei. (After Mottier.)</p>
-  </div>
-</div>
-
-<p><b>681. Chromosomes, nuclear plate, and nuclear spindle.</b>—Each
-one of these rod-like chromatin segments is a <i>chromosome</i>.
-The pairs of chromosomes arrange themselves in a median plane
-of the nucleus, radiating somewhat in a stellate fashion, forming
-the <i>nuclear plate</i>, or <i>monaster</i>. At the same time threads of
-the protoplasm (kinoplasm) become arranged in the form of a spindle,
-the axis of which is perpendicular to the nuclear plate of chromosomes,
-as shown in <a href="#FIG_407">figure 407</a>, at left. Each pair of
-chromosomes now separate in the line of the division of the original
-spirem, one chromosome of each pair going to one pole of the spindle,
-<span class="pagenum"><a name="Page_343" id="Page_343">[Pg 343]</a></span>
-while the other chromosome of each pair goes to the opposite pole.
-The chromosomes here unite to form the daughter nuclei. Each of these
-nuclei now divide as shown in <a href="#FIG_409">figure 409</a> (whether the
-chromosomes in this second division in the mother cell split longitudinally or
-divide transversely has not been definitely settled), and four nuclei are
-formed in the pollen mother cell. The protoplasm about each one of these
-four nuclei now surrounds itself with a wall and the spores are formed.</p>
-
-<div class="figcenter">
-    <img src="images/fig408.jpg" alt="" width="500" height="265" />
-  <div class="blockquot">
-    <p class="center">Fig. 408.</p>
-    <p>Different stages in the separation of divided U-shaped chromosomes
-       at the nuclear plate. (After Mottier.) In podophyllum.</p>
-  </div>
-</div>
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_409" src="images/fig409.jpg" alt="" width="200" height="371" />
-    <p class="center">Fig. 409.<br /> Second division of nuclei<br />
-        in pollen mother cell of<br /> podophyllum, chromosomes<br />
-        at poles.</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_410" src="images/fig410.jpg" alt="" width="250" height="352" />
-      <p class="center">Fig. 410.<br /> Chromosomes uniting at<br />
-         poles to form the nuclei<br /> of the four spores.<br />
-         (After Mottier.)</p>
-  </div>
-</div>
-
-<p><b>The number of chromosomes usually the same in a given species
-throughout one phase of the plant.</b>—In those plants which have been
-carefully studied, the number of chromosomes in the dividing nucleus
-has been found to be fairly constant in a given species, through all
-the divisions in that stage or phase of the plant, especially in the
-embryonic, or young growing parts. For example, in the prothallium, or
-gametophyte, of certain ferns, as osmunda, the number of chromosomes
-in the dividing nucleus is always twelve. So in the development of the
-pollen of lilium from the mother cells, and in the divisions of the
-antherid cell to form the generative cells or sperm cells, there are
-always twelve chromosomes so far as has been found. In the development
-of the egg of lilium from the macrospore there are also twelve chromosomes.
-<span class="pagenum"><a name="Page_344" id="Page_344">[Pg 344]</a></span></p>
-
-<p><b>When fertilization takes place the number of chromosomes is doubled
-in the embryo.</b>—In the spermatozoid of osmunda then, as well as in
-the egg, since these are developed on the gametophyte, there are twelve
-chromosomes each. The same is true in the sperm cell (generative cell)
-of lilium, and also in the egg-cell. When these nuclei unite, as they
-do in fertilization, the paternal nucleus with the maternal nucleus,
-the number of chromosomes in the fertilized egg, if we take lilium as
-an example, is twenty-four instead of twelve; the number is doubled.
-The fertilized egg is the beginning of the sporophyte, as we have seen.
-Curiously throughout all the divisions of the nucleus in the embryonic
-tissues of the sporophyte, so far as has been determined, up to the
-formation of the mother cells of the spores, the number of chromosomes
-is usually the same.</p>
-
-<div class="figcenter">
-    <img  id="FIG_411" src="images/fig411.jpg" alt="" width="600" height="390" />
-  <div class="blockquot">
-    <p class="center">Fig. 411.</p>
-    <p>Karyokinesis in sporophyte cells of podophyllum (twice the number of
-       chromosomes here that are found in the dividing spore mother cells).</p>
-  </div>
-</div>
-
-<p><b>682. Reduction of the number of chromosomes in the nucleus.</b>—If
-there were no reduction in the number of chromosomes at any point in
-the life cycle of plants, the number would thus become infinitely
-<span class="pagenum"><a name="Page_345" id="Page_345">[Pg 345]</a></span>
-large. A reduction, however, does take place. This usually occurs,
-either in the mother cell of the spores or in the divisions of its
-nucleus, at the time the spores are formed. In the mother cells a sort
-of pseudo-reduction is effected by the chromatin band separating into
-one half the usual number of nuclear segments. So that in lilium during
-the first division of the nucleus of the mother cell the chromatin band
-divides into twelve segments, instead of twenty-four as it has done
-throughout the sporophyte stage. So in podophyllum during the first
-division in the mother cell it separates into eight instead of into
-sixteen. Whether a qualitative reduction by transverse division of the
-spirem band, unaccompanied by a longitudinal splitting, takes place
-during the first or second karyokinesis is still in doubt. Qualitative
-reduction does take place in some plants according to Beliaieff and
-others. Recently the author has found that it takes place in Trillium
-grandiflorum during the second karyokinesis, and in Arisæma triphyllum
-the chromosomes divide both transversely and longitudinally during
-the first karyokinesis forming four chromosomes, and a qualitative
-reduction takes place here.</p>
-
-<p><b>683. Significance of karyokinesis and reduction.</b>—The precision
-with which the chromatin substance of the nucleus is divided, when
-in the spirem stage, and later the halves of the chromosomes are
-distributed to the daughter nuclei, has led to the belief that this
-substance bears the hereditary qualities of the organism, and that
-these qualities are thus transmitted with certainty to the offspring.
-In reduction not only is the original number of chromosomes restored,
-it is believed by some that there is also a qualitative reduction of
-the chromatin, i.e. that each of the four spores possesses different
-qualitative elements of the chromatin as a result of the reducing
-division of the nucleus during their formation.</p>
-
-<p>The increase in number of chromosomes in the nucleus occurs with the
-beginning of the sporophyte, and the numerical reduction occurs at the
-beginning of the gametophyte stage. The full import of karyokinesis and
-reduction is perhaps not yet known, but there is little doubt that a
-profound significance is to be attached to these interesting phenomena
-in plant life.
-<span class="pagenum"><a name="Page_346" id="Page_346">[Pg 346]</a></span></p>
-
-<p><b>684. The gametophyte may develop directly from the tissue of the
-sporophyte.</b>—If portions of the sporophyte of certain of the
-mosses, as sections of a growing seta, or of the growing capsule, be
-placed on a moist substratum, under favorable conditions some of the
-external cells will grow directly into protonemal threads. In some
-of the ferns, as in the sensitive fern (onoclea), when the fertile
-leaves are expanding into the sterile ones, protonemal outgrowths occur
-among the aborted sporangia on the leaves of the sporophyte. Similar
-rudimentary protonemal growths sometimes occur on the leaves of the
-common brake (pteris) among the sporangia, and some of the rudimentary
-sporangia become changed into the protonema. In some other ferns, as
-in asplenium (A. filix-fœmina, var. clarissima), prothallia are borne
-among the aborted sporangia, which bear antheridia and archegonia. In
-these cases the gametophyte develops from the tissue of the sporophyte
-without the intervention or necessity of the spores. This is <i>apospory</i>.</p>
-
-<div class="figright">
-    <img src="images/fig412.jpg" alt="" width="200" height="180" />
-    <p class="center">Fig. 412.<br /> Apogamy in Pteris cretica.</p>
-</div>
-
-<p><b>685. The sporophyte may develop directly from the tissue of the
-gametophyte.</b>—In some of the ferns, Pteris cretica for example,
-the embryo fern sporophyte arises directly from the tissue of the
-prothallium, without the intervention of sexual organs, and in some
-cases no sexual organs are developed on such prothallia. Sexual organs,
-then, and the fusion of the spermatozoid and egg nucleus are not here
-necessary for the development of the sporophyte. This is <i>apogamy</i>.
-Apogamy occurs in some other species of ferns, and in other groups of
-plants as well, though it is in general a rare occurrence except in
-certain species, where it may be the general rule.
-<span class="pagenum"><a name="Page_347" id="Page_347">[Pg 347]</a></span></p>
-
-<p><b>686. Types of nuclear division.</b>—The nuclear figures in the
-vegetative cells are usually different from those in the spore
-mother cells. In the spore mother cells there are two types of
-nuclear division. (1) The first division in the mother cell is called
-<i>heterotypic</i>. The early stages of this division usually extend over a
-longer period than the second, and the figures are more complex. Before
-the chromosomes arrive at the nuclear plate they are often in the form
-of rings, or tetrads, or in the form of X, V, or Y, and the number is
-usually one half the number in the preceding cells of the sporophyte.
-(2) The <i>homotypic</i> division immediately follows the heterotypic and
-the figures are simpler, often the chromosomes being of a hook form,
-or sometimes much stouter than in the heterotypic division. In the
-vegetative cells (sometimes called somatic cells, or body cells in
-contrast with reproductive cells) there is another type, called by some
-the <i>vegetative type</i>. The chromosomes here are often in the form of
-the letter U, and the figures are much simpler than in the heterotypic
-division. In the somatic cells of the sporophyte, as stated above,
-the number of chromosomes is double that found in the heterotypic
-and homotypic divisions of the mother cells and in the somatic cells
-of the gametophyte, <a href="#FIG_411">Fig. 411</a> represents a late stage in
-the division of somatic cells in the sporophyte of podophyllum. The root-tips of
-various plants as the onion, lily, etc., are excellent places in which
-to study nuclear division in the somatic cells of the sporophyte.</p>
-
-<p><b>687. Comparison with animals.</b>—In animals there does not seem
-to be anything which corresponds with the gametophyte of plants unless
-the sperm cells and eggs themselves represent it. Heterotypic and
-homotypic division with the accompanying reduction of the number of the
-chromosomes takes place in animals usually in the mother cells of the
-sperms and eggs. At the time of fertilization the number of chromosomes
-is doubled, so that all the somatic cells (except in rare instances)
-from the fertilized egg to the mother cells of sperms and eggs have the
-doubled number of chromosomes. Reduction, therefore, takes place in
-<span class="pagenum"><a name="Page_348" id="Page_348">[Pg 348]</a></span>
-animals just prior to the formation of the gametes, while in plants it
-takes place just prior to the formation of the gametophytes.</p>
-
-<p><b>688. Perhaps there is not a fundamental difference between
-gametophyte and sporophyte.</b>—This development of sporophyte, or
-leafy-stemmed plant of the fern (parag. 685), from the tissue of the
-gametophyte is taken by some to indicate that there is not such a great
-difference between the gametophyte and sporophyte of plants as others
-contend. In accordance with this view it has been suggested that the
-leafy-stemmed moss plant, as well as the leafy stem of the liverworts,
-is homologous with the sporophyte or leafy stem of the fern plant; that
-it arises by budding from the protonema; and that the sexual organs are
-borne then on the sporophyte.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_349" id="Page_349">[Pg 349]</a></span></p>
-<div class="chapter">
-<h2 class="nobreak">PART III.<br />
-PLANT MEMBERS IN RELATION<br /> TO ENVIRONMENT.</h2>
-<h3 class="nobreak"><a name="CHAPTER_XXXVIII" id="CHAPTER_XXXVIII">CHAPTER XXXVIII.</a><br />
-<span class="h_subtitle">THE ORGANIZATION OF THE PLANT.</span></h3>
-</div>
-
-<h4><a name="XXXVIII_1" id="XXXVIII_1">I. Organization of Plant Members.</a><a name="FNanchor_37_37" id="FNanchor_37_37"></a><a href="#Footnote_37_37" class="fnanchor">[37]</a></h4>
-
-<p><b>689.</b> It is now generally conceded that the earliest plants to
-appear in the world were very simple in form and structure. Perhaps the
-<span class="pagenum"><a name="Page_350" id="Page_350">[Pg 350]</a></span>
-earliest were mere bits of naked protoplasm, not essentially different
-from early animal life. The simplest ones which are clearly recognized
-as plants are found among the lower algæ and fungi. These are single
-cells of very minute size, roundish, oval, or oblong, existing
-during their growing period in water or in a very moist substratum
-or atmosphere. Examples are found in the red snow plant (<i>Sphærella
-nivalis</i>), the Pleurococcus, the bacteria; and among small colonies of
-these simple organisms (Pandorina) or the thread-like forms (Spirogyra,
-Œdogonium, etc.). It is evident that some of the life relations of such
-very simple organisms are very easily obtained—that is, the adjustment
-to environment is not difficult. All of the living substance is very
-closely surrounded by food material in solution. These food solutions
-are easily absorbed. Because of the minute size of the protoplasts and
-of the plant body, they do not have to solve problems of transport of
-food to distant parts of the body. When we pass to more bulky organisms
-consisting of large numbers of protoplasts closely compacted together,
-the problem of relation to environment and of food transport become
-felt; the larger the organism usually the greater are these problems.
-A point is soon reached at which there is a gain by a differentiation
-in the work of different protoplasts, some for absorption, some for
-conduction, some for the light relation, some for reproduction, and
-so on. There is also a gain in splitting the form of the plant body
-up into parts so that a larger surface is exposed to environment
-with an economy in the amount of building material required. In this
-differentiation of the plant body into parts, there are two general
-problems to be solved, and the plant to be successful in its struggle
-for existence must control its development in such a way as to preserve
-the balance between them. (1) A ready display of a large surface to
-environment for the purpose of acquiring food and the disposition of
-waste. (2) The protection of the plant from injuries incident to an
-austere environment.</p>
-
-<p>It is evident with the great variety of conditions met with in
-different parts of the same locality or region, and in different parts
-of the globe, that the plant has had very complex problems to meet and
-<span class="pagenum"><a name="Page_351" id="Page_351">[Pg 351]</a></span>
-in the solution of them it has developed into a great variety of forms.
-It is also likely that different plants would in many cases meet these
-difficulties in different ways, sometimes with equal success, at other
-times with varied success. Just as different persons, given some one
-piece of work to do, are likely to employ different methods and reach
-results that are varied as to their value. While we cannot attribute
-consciousness or choice to plants in the sense in which we understand
-these qualities in higher animals, still there is something in their
-“constitution” or “character” whereby they respond in a different
-manner to the same influences of environment. This is, perhaps,
-imperceptible to us in the different individuals of the same species,
-but it is more marked in different species. Because of our ignorance of
-this occult power in the plant, we often speak of it as an “inherent” quality.</p>
-
-<div class="blockquot">
-<p>Perhaps the most striking examples one might use to illustrate the
-different line of organization among plants in two regions where the
-environment is very different are to be found in the adaptation of the
-cactus or the yucca to desert regions, and the oak or the cucurbits
-to the land conditions of our climate. The cactus with stem and leaf
-function combined in a massive trunk, or the yucca with bulky leaves
-expose little surface in comparison to the mass of substance, to the
-dry air. They have tissue for water storage and through their thick
-epidermis dole it out slowly since there is but little water to obtain
-from dry soil.</p>
-
-<p>The cucurbits and the oak in their foliage leaves expose a very
-large surface in proportion to the mass of their substance, to an
-atmosphere not so severely dry as that of the desert, while the
-roots are able to obtain an abundant supply of water from the moist
-soil. The cactus and the yucca have differentiated their parts in a
-very different way from the oak or the cucurbits, in order to adapt
-themselves to the peculiar conditions of the environment.</p>
-
-<p>When we say that certain plants have the power to adapt themselves
-to certain conditions of environment, we do not mean to say that if the
-cucurbits were transferred to the desert they would take on the form
-of the cactus or the yucca. They could do neither. They would perish,
-since the change would be too great for their organization. Nor do we
-mean, that, if the cactus or yucca were transferred from the desert to
-our climate, they would change into forms with thin foliage leaves.
-They could not. The fact is that they are enabled to live in our
-<span class="pagenum"><a name="Page_352" id="Page_352">[Pg 352]</a></span>
-climate when we give them some care, but they show no signs of assuming
-characters like those of our vegetation. What we do mean is, that where
-the change is not too great nor too sudden, some of the plants become
-slightly modified. This would indicate that the process of organization
-and change of form is a very slow one, and is therefore a question of
-time—ages it may be—in which change in environment and adaptation in
-form and structure have gone on slowly hand in hand.</p>
-</div>
-
-<p><b>690. Members of the plant body.</b>—The different parts into which
-the plant body has become differentiated are from one point of view,
-spoken of as members. It is evident that the simplest forms of life
-spoken of above do not have members. It is only when differentiation
-has reached the stage in which certain more or less prominent parts
-perform certain functions for the plant that members are recognized.
-In the algæ and fungi there is no differentiation into stem and leaf,
-though there is an approach to it in some of the higher forms. Where
-this simple plant body is flattened, as in the sea-wrack, or ulva, it
-is a <i>frond</i>. The Latin word for frond is <i>thallus</i>, and this name
-is applied to the plant body of all the lower plants, the algæ and fungi.
-The algæ and fungi together are sometimes called <i>thallophytes</i>, or
-<i>thallus plants</i>. The word thallus is also sometimes applied to the
-flattened body of the liverworts. In the foliose liverworts and mosses
-there is an axis with leaf-like expansions. These are believed by some
-to represent true stems and leaves; by others to represent a flattened
-thallus in which the margins are deeply and regularly divided, or in
-which the expansion has only taken place at regular intervals.</p>
-
-<p>In the higher plants there is usually great differentiation of the
-plant body, though in many forms, as in the duckweeds, it is in the
-form of a frond. While there is a great variety in the form and
-function of the members of the plant body, they are all reducible to a
-few fundamental members. Some reduce these forms to three, the <i>root</i>,
-<i>stem</i>, <i>leaf</i>; while others to two, the <i>root</i>, and <i>shoot</i>,
-which is perhaps the best primary subdivision, and the shoot is then divided
-into stem and leaf, the leaf being a lateral outgrowth of the stem, and
-can be indicated by the following diagram:
-<span class="pagenum"><a name="Page_353" id="Page_353">[Pg 353]</a></span></p>
-
-<table border="0" cellspacing="0" summary=" " cellpadding="0" >
-  <tbody><tr>
-      <td class="tdl" rowspan="4"><br />Plant body····&nbsp;</td>
-      <td class="tdc">&nbsp;</td>
-      <td class="tdr_ws1">&nbsp;</td>
-      <td class="tdc" rowspan="3"><img src="images/cbl-3.jpg" alt="" width="16" height="57" /></td>
-      <td class="tdr_ws1">Stem.</td>
-   </tr><tr>
-
-      <td class="tdc" rowspan="3"><img src="images/cbl-3.jpg" alt="" width="16" height="57" /></td>
-      <td class="tdl">Shoot····&nbsp;</td>
-      <td class="tdr_ws1">&nbsp;</td>
-   </tr><tr>
-
-      <td class="tdr_ws1">&nbsp;</td>
-      <td class="tdr_ws1">Leaf.</td>
-   </tr><tr>
-      <td class="tdl">Root.</td>
-   </tr>
- </tbody>
-</table>
-
-<p class="center">KINDS OF SHOOTS.</p>
-
-<p><b>691.</b> Since it is desirable to consider the shoot in its relation
-to environment, for convenience in discussion we may group shoots into
-four prominent kinds: (1) <i>Foliage shoots</i>; (2) <i>Shoots without foliage
-leaves</i>; (3) <i>Floral shoots</i>; (4) <i>Winter conditions of shoots and
-buds.</i> Topic (4) will be treated in <a href="#XXXIX_4">Chapter XXXIX, section IV</a>.</p>
-
-<div class="figcenter">
-    <img src="images/fig413.jpg" alt="" width="400" height="378" />
-    <p class="center">Fig. 413.<br />
-       Lupinus perennis.<br /> Foliage shoot and floral shoot.</p>
-</div>
-
-<p><b>692. (1st) Foliage shoots.</b>—Foliage shoots are either aerial,
-when their relation is to both light and air; or they are aquatic,
-when their relation is to both light and water. They bear green
-leaves, and whether in the air or water we see that light is one of
-the necessary relations for all. Naturally there are several ways in
-which a shoot may display its leaves to the light and air or water.
-Because of the great variety of conditions on the face of the earth
-and the multitudinous kinds of plants, there is the greatest diversity
-presented in the method of meeting these conditions. There is to be
-considered the problem of support to the shoot in the air, or in the
-water. The methods for solving this problem are fundamentally different
-in each case, because of the difference in the density of air and
-water, the latter being able to buoy up the plant to a great degree,
-particularly when the shoot is provided with air in its intercellular
-<span class="pagenum"><a name="Page_354" id="Page_354">[Pg 354]</a></span>
-spaces or air cavities. In the solution of the problem in the relation
-of the shoot to aerial environment, stem and leaf have in most cases
-coöperated;<a name="FNanchor_38_38" id="FNanchor_38_38"></a><a href="#Footnote_38_38" class="fnanchor">[38]</a>
-but in view of the great variety of stems and their
-modifications, as well as of leaves, it will be convenient to discuss
-them in separate chapters.</p>
-
-<div class="figcenter">
-    <img  id="FIG_413A" src="images/fig413a.jpg" alt="" width="600" height="255" />
-    <p class="center">Fig. 413<i>a</i>.<br />
-           Burrowing type, the mandrake,<br /> a “rhizome.”</p>
-</div>
-
-<p><b>693. (2d) Shoots without foliage leaves.</b>—These are subterranean
-or aerial. Nearly all subterranean shoots have also aerial shoots,
-the latter being for the display of foliage leaves (foliage-shoots),
-and also for the display of flowers (flower-shoots). The subterranean
-kinds bear scale leaves, i.e., the leaves not having a light relation
-are reduced in size, being small, and they lack chlorophyll. Examples
-are found in Solomon’s seal, mandrake (<a href="#FIG_413A">fig. 413<i>a</i></a>), etc.
-Here the scale leaves are on the bud at the end of the underground stem from
-which the foliage shoot arises. Aerial shoots which lack foliage
-leaves are the dodder, Indian-pipe-plant, beech drops, etc. These
-plants are saprophytes or parasites (see <a href="#CHAPTER_IX">Chapter IX</a>).
-Deriving their carbohydrate food from other living plants, or from humus, they
-do not need green leaves. The leaves have, therefore, probably been reduced
-in size to mere scales, and accompanying this there has been a loss of
-the chlorophyll. Other interesting examples of aerial shoots without
-<span class="pagenum"><a name="Page_355" id="Page_355">[Pg 355]</a></span>
-foliage leaves are the cacti where the stem has assumed the leaf
-function and the leaves have become reduced to mere spines. The various
-modifications which shoots have undergone accompanying a change in
-their leaf relation will be discussed under stems in <a href="#CHAPTER_XXXIX">Chapter XXXIX</a>.</p>
-
-<p><b>694. (3d) Floral shoots.</b>—The floral shoot is the part of the
-plant bearing the flower. As interpreted here it may consist of but a
-single flower with its stalk, as in Trillium, mandrake, etc., or of
-the clusters of flowers on special parts of the stem, termed flower
-clusters, as the <i>catkin</i>, <i>raceme</i>, <i>spike</i>, <i>umbel</i>,
-<i>head</i>, etc. In the floral shoot as thus interpreted there are several
-peculiarities to observe which distinguish it from the foliage shoot and
-adapt it to its life relations.</p>
-
-<p>The floral shoot in many respects is comparable to the foliage shoot,
-as seen from the following peculiarities:</p>
-
-<div class="blockquot">
-<p>(1) It usually possesses, beside the flowers, small green leaves
-which are in fact foliage though they are very much reduced in size,
-because the function of the shoot as a foliage shoot is subordinated
-to the function of the floral shoot. These small leaves on the floral
-shoot are termed <i>bracts</i>.</p>
-
-<p>(2) It may be (<i>a</i>) unbranched, when it would consist of a single
-flower, or (<i>b</i>) branched, when there would be several to many flowers
-in the flower cluster.</p>
-
-<p>(3) The flower bud has the same origin on the shoot as the leaf bud;
-it is either terminal or axillary, or both.</p>
-
-<p>(4) The members of the flower belong to the leaf series, i.e., they
-are leaves, but usually different in color from foliage leaves, because
-of the different life relation which they have to perform. Evidence of
-this is seen in the transition of sepals, petals, stamens, or pistils,
-to foliage leaves in many flowers, as in the pond lily, the abnormal
-forms of trillium, and many monstrosities in other flowers
-(see <a href="#CHAPTER_XXXIV">Chapter XXXIV</a>).</p>
-
-<p>(5) The position of the members of the flower on its axis, though
-usually more crowded, in many cases follows the same plan as the leaves
-on the stem.</p>
-</div>
-
-<p>The various kinds of floral shoots or flower clusters will be discussed
-in <a href="#CHAPTER_XLII">Chapter XLII</a>, on the Floral Shoot.
-<span class="pagenum"><a name="Page_356" id="Page_356">[Pg 356]</a></span></p>
-
-<h4><a name="XXXVIII_2" id="XXXVIII_2">II. Organization of Plant Tissues.</a></h4>
-
-<p><b>695.</b> A tissue is a group of cells of the same kind having a
-similar position and function. In large and bulky plants different
-kinds of tissue are necessary, not only because the work of the plant
-can be more economically performed by a division of labor, but also
-cells in the interior of the mass or at a distance from the source
-of the food could not be supplied with food and air unless there
-were specialized channels for conducting food and specialized tissue
-for support of the large plant body. In these two ways most of the
-higher plants differ from the simple ones. The tissues for conduction
-are sometimes called collectively the <i>mestome</i>, while tissues for
-mechanical support are called <i>stereome</i>. Division of labor has
-gone further also so that there are special tissues for absorption,
-assimilation, perception, reproduction, and the like. The tissues of
-plants are usually grouped into three systems: (1) The Fundamental
-System, (2) The Fibrovascular System, (3) The Epidermal System. Some of
-the principal tissues are as follows:</p>
-
-<p class="center">1. THE FUNDAMENTAL SYSTEM.</p>
-
-<p><b>696. Parenchyma.</b>—Tissue composed of thin-walled cells which
-in the normal state are living. Parenchyma forms the loose and spongy
-tissue in leaves, as well as the palisade tissue (see <a href="#CHAPTER_IV">Chapter IV</a>);
-the soft tissue in the cortex of root and stem (<a href="#FIG_414">Fig. 414</a>); as well
-as that of the pith, of the pith-rays or medullary rays of the stem; and is
-mixed in with the other elements of the vascular bundle where it is
-spoken of as wood parenchyma and bast parenchyma; and it also includes
-the undifferentiated tissue (meristem) in the growing tips of roots and
-shoots; also the “intrafascicular” cambium (i.e., between the bundles,
-some also include the cambium within the bundle).</p>
-
-<p><b>697. Collenchyma.</b>—This is a strengthening tissue often found
-in the cortex of certain shoots. It also is composed of living cells.
-The cells are thickened at the angles, as in the tomato and many other
-herbs (<a href="#FIG_414">fig. 414</a>).</p>
-
-<p><b>698. Sclerenchyma, or stone-tissue.</b>—This is also a
-strengthening tissue and consists of cells which do not taper at the
-ends and the walls are evenly thickened, sometimes so thick that the
-inside (lumen) of the cell has nearly disappeared. Usually such cells
-contain no living contents at maturity. Sclerenchyma is very common in
-<span class="pagenum"><a name="Page_357" id="Page_357">[Pg 357]</a></span>
-the hard parts of nuts, and underneath the epidermis of stems and
-leaves of many plants, as in the underground stems of the bracken fern,
-the leaves of pines (<a href="#FIG_415">fig. 415</a>), etc.</p>
-
-<div class="figcenter">
-    <img  id="FIG_414" src="images/fig414.jpg" alt="" width="500" height="448" />
-  <div class="blockquot">
-    <p class="center">Fig. 414.</p>
-    <p>Transverse section of portion of tomato stem. <i>ep</i>, epidermis; <i>ch</i>
-       chlorophyll-bearing cells; <i>co</i>, collenchyma; <i>cp</i>, parenchyma.</p>
-  </div>
-</div>
-<div class="figcenter">
-    <img  id="FIG_415" src="images/fig415.jpg" alt="" width="400" height="388" />
-  <div class="blockquot">
-    <p class="center">Fig. 415.</p>
-    <p>Margin of leaf of Pinus pinaster, transverse section, <i>c</i>,
-       cuticularized layer of outer wall of epidermis; <i>i</i>, inner
-       non-cuticularized layer; <i>c´</i>, thickened outer wall of marginal
-       cell; <i>g</i>, <i>i´</i>, hypoderma of elongated sclerenchyma; <i>p</i>,
-       chlorophyll-bearing parenchyma; <i>pr</i>, contracted protoplasmic contents.
-       ×800. (After Sachs.)</p>
-  </div>
-</div>
-<div class="figcenter">
-    <img  id="FIG_416" src="images/fig416.jpg" alt="" width="500" height="300" />
-  <div class="blockquot">
-    <p class="center">Fig. 416.</p>
-    <p>Section through a lenticel of Betula alba showing stoma at top,
-       phellogen below producing rows of flattened cells, the cork. (After De Bary.)</p>
-  </div>
-</div>
-
-<p><b>699. Cork.</b>—In many cases there is a development of “cork”
-tissue underneath the epidermis. Cork tissue is developed by repeated
-division of parenchyma cells in such a way that rows of parallel cells
-are formed toward the outside. These are in distinct layers, soon lose
-their protoplasm and die; there are no intercellular spaces and the
-cells are usually of regular shape and fit close to each other. In
-some plants the cell walls are thin (cork oak), while in others they
-are thickened (beech). The tissue giving rise to cork is called “cork
-cambium,” or phellogen, and may occur in other parts of the plant. For
-example, where plants are wounded the living exposed parenchyma cells
-often change to cork cambium and develop a protective layer of cork.
-The walls of cork cells contain a substance termed <i>suberin</i>, which
-renders them nearly waterproof.
-<span class="pagenum"><a name="Page_358" id="Page_358">[Pg 358]</a></span></p>
-
-<p><b>700. Lenticels.</b>—These are developed quite abundantly underneath
-stomates on the twigs of birch, cherry, beech, elder, etc. The
-phellogen underneath the stoma develops a cushion of cork which presses
-outward in the form of an elevation at the summit of which is the stoma
-(<a href="#FIG_416">fig. 416</a>). The lenticels can easily be seen.</p>
-
-<p class="center">2. THE FIBROVASCULAR SYSTEM.</p>
-
-<p><b>701. Fibrous tissue.</b><a name="FNanchor_39_39" id="FNanchor_39_39"></a><a href="#Footnote_39_39" class="fnanchor">[39]</a>—This
-consists of thick-walled cells, usually without living contents which
-are elongated and taper at the ends so that the cells, or fibers,
-overlap. It is common as one of the elements of the vascular bundles,
-as wood fibers and bast fibers.</p>
-
-<p><b>702. Vascular tissue, or tracheary tissue.</b>—This consists of the
-vessels or ducts, and tracheides, which are so characteristic of the
-vascular bundle (see <a href="#CHAPTER_V">Chapter V</a>) and forms a conducting tissue
-for the flow of water. The vascular tissue contains spiral, annular, pitted,
-and scalariform vessels and tracheides according to the marking on the
-walls (figs. <a href="#FIG_58">58</a>, <a href="#FIG_59">59</a>). These
-are all without protoplasmic contents when mature. There are also
-thin-walled living cells intermingled called wood parenchyma. In
-the conifers (pines, etc.) the tracheary tissue is devoid of true
-vessels except a few spiral vessels in the young stage, while it is
-characterized by tracheides with peculiar markings. These marks on the
-tracheides are due to the “bordered” pits appearing as two concentric
-rings one within the other. These can be easily seen in a longitudinal
-section of wood of conifers.</p>
-
-<p><b>703. Sieve tissue.</b>—This consists of elongated tubular cells
-connected at the ends, the cross walls being perforated at the ends.
-These are in the phloem part of the bundle, and serve to conduct
-downwards the dissolved substances elaborated in the leaves.</p>
-
-<p><b>704. Fascicular cambium.</b>—This is the living, cell-producing
-tissue in the vascular bundle, which in the open bundle adds to the
-phloem on one side and the xylem on the other.</p>
-
-<p class="center">3. THE EPIDERMAL SYSTEM.</p>
-
-<p><b>705.</b> To the epidermal system belong the epidermis and the
-various outgrowths of its cells in the form of hairs, or <i>trichomes</i>,
-as well as the guard cells of the stomates, and probably some of the
-reproductive organs.</p>
-
-<p><b>706. The epidermis.</b>—The epidermis proper consists of a
-single layer of external cells originating from the outer layer of
-parenchyma cells at the growing apex of the stem or root. These cells
-undergo various modifications of form. In many cases they lose their
-protoplasmic contents. In many cases the outer wall becomes thickened,
-<span class="pagenum"><a name="Page_359" id="Page_359">[Pg 359]</a></span>
-especially in plants growing in dry situations or where they are
-exposed to drying conditions. The epidermal cells generally become
-considerably flattened, and are usually covered with a more or less
-well developed waterproof cuticle, a continuous layer over the
-epidermis. In many plants the cuticle is covered with a waxy exudation
-in the form of a thin layer, or of rounded grains, or slender rods,
-or grains and needles in several layers. These waxy coverings are
-sometimes spoken of as “bloom” on leaves and fruit.</p>
-
-<p><b>707. Trichomes.</b>—Trichome is a general term including various
-hair-like outgrowths from the epidermis, as well as scales, prickles,
-etc. These include root hairs, rhizoids, simple or branched hairs,
-glandular hairs, glandular scales, etc. Glandular hairs are found on
-many plants, as tomato, verbena, primula, etc.; glandular scales on
-the hop; simple-celled hairs on the evening primrose, cabbage, etc.;
-many-celled hairs on the primrose, pumpkin; branched hairs on the
-shepherd’s-purse, mullein, etc., stellate hairs on some oak leaves.</p>
-
-<p>For stomates see <a href="#CHAPTER_IV">Chapter IV</a>.</p>
-
-<p class="center">4. ORIGIN OF THE TISSUES.</p>
-
-<p><b>708. Meristem tissue.</b>—The various tissues consisting of cells
-of dissimilar form are derived from young growing tissue known as
-<i>meristem</i>. Meristem tissue consists of cells nearly alike in form,
-with thin cell walls and rich in protoplasm. It is situated at the
-growing regions of the plants. In the higher plants these regions in
-general are three in number, the stem and root apex, and the cambium
-cylinder beneath the cortex. Tissues produced from the stem and root
-apex are called <i>primary</i>, those from the cambium <i>secondary</i>.
-In most cases the main bulk of the plant is secondary tissue, while in
-the corn plant it is all primary.</p>
-
-<div class="figcenter">
-    <img  id="FIG_417" src="images/fig417.jpg" alt="" width="500" height="271" />
-  <div class="blockquot">
-    <p class="center">Fig. 417.</p>
-    <p>Section through growing point of stem, <i>d</i>,
-        dermatogen; <i>p</i>, plerome; periblem between. (After De Bary.)</p>
-  </div>
-</div>
-
-<p><b>709. Origin of stem tissues.</b>—Just back of the apical meristem
-in a longitudinal section of a growing point it can be seen that the
-cells are undergoing a change in form, and here are organized three
-formative regions. The outer layer of cells is called <i>dermatogen</i>
-(skin producer), because later it becomes the epidermis. The central
-group of elongating cells is the <i>plerome</i> (to fill). This later
-develops the <i>central cylinder</i>, or <i>stele</i>, as it is called
-<span class="pagenum"><a name="Page_360" id="Page_360">[Pg 360]</a></span>
-(<a href="#FIG_417">fig. 417</a>). Surrounding the plerome and filling the space between
-it and the dermatogen is the third formative tissue called the <i>periblem</i>,
-which later forms the cortex (bark or rind), and consists of
-parenchyma, collenchyma, sclerenchyma, or cork, etc., as the case may
-be. It should be understood that all these different forms and kinds
-of cells have been derived from meristem by gradual change. In the
-mature stems, therefore, there are three distinct regions, the central
-cylinder or stele, the cortex, and the epidermis.</p>
-
-<div class="figcenter">
-    <img  id="FIG_418" src="images/fig418.jpg" alt="" width="600" height="365" />
-  <div class="blockquot">
-    <p class="center">Fig. 418.</p>
-    <p>Concentric bundle from stem of Polypodium vulgare. Xylem in the
-       center, surrounded by phloem, and this by the endodermis. (From the
-       author’s Biology of Ferns.)</p>
-  </div>
-</div>
-
-<p><b>710. Central cylinder or stele.</b>—As the central cylinder is
-organized from the plerome it becomes differentiated into the vascular
-bundles, the pith, the pith-rays (medullary rays) which radiate from
-the pith in the center between the bundles out to the cortex, and
-the pericycle, a layer of cells lying between the central cylinder
-and the cortex. The bundles then are farther organized into the
-xylem and phloem portions with their different elements, and the
-fascicular cambium (meristem) separating the xylem and phloem, as
-described in <a href="#CHAPTER_V">Chapter V</a>. Such a bundle, where the xylem
-and phloem portions are separated by the cambium is called an open bundle (as
-in <a href="#FIG_58">fig. 58</a>). Where the phloem and xylem lie side by side in
-the same radius the bundle is a <i>collateral</i> one. Dicotyledons and conifers
-are characterized by open collateral bundles. This is why trees and many
-<span class="pagenum"><a name="Page_361" id="Page_361">[Pg 361]</a></span>
-other perennial plants continue to grow in diameter each year.
-The cambium in the open bundle forms new tissue each spring and
-summer, thus adding to the phloem on the outside and the xylem on
-the inside. In the spring and early summer the large vessels in the
-xylem predominate, while in late summer wood fibers and small vessels
-predominate and this part of the wood is firmer. Since the vascular
-bundles in the stem form a circle in the cylinder, this difference
-in the size of the spring and late summer wood produces the “annual”
-rings, so evident in the cross-section of a tree trunk. Branches
-originate at the surface involving epidermis, cortex, and the bundles.</p>
-
-<p>In monocotyledonous plants (corn, palm, etc.) the bundles are not
-regularly arranged to form a hollow cylinder, but are irregularly
-situated through the stele. There is no meristem, or cambium, left
-between the xylem and phloem portions of the bundle and the bundle is
-thus <i>closed</i> (as in<a href="#FIG_60"> fig. 60</a>), since it all passes over
-into permanent tissue. In most monocotyledons there is, therefore, practically no
-annual increase in diameter of the stem.</p>
-
-<div class="figright">
-    <img  id="FIG_419" src="images/fig419.jpg" alt="" width="200" height="150" />
-    <p class="center">Fig. 419.<br /> Section of stem (rhizome)<br />
-        of Pteris aquilina.<br /> <i>sc</i>, thick-walled sclerenchyma;<br />
-        <i>a</i>, thin-walled sclerenchyma;<br />
-        <i>par</i>, parenchyma.<br /></p>
-</div>
-
-<p><b>711. Ferns.</b>—In the ferns and most of the Pteridophytes an
-apical meristem tissue is wanting, its place being taken by a single
-apical cell from the several sides of which cells are successively
-cut off, though Isoetes and many species of Lycopodium have an apical
-meristem group. In most of the Pteridophytes also the bundles are
-<i>concentric</i> instead of collateral. <a href="#FIG_418">Fig. 418</a> represents
-one of the bundles from the stem of the polypody fern. The xylem is in the center,
-this surrounded by the phloem, the phloem by the phloem sheath, and
-this in turn by the endodermis, giving a concentric arrangement of the
-component tissues. A cross-section of the stem (<a href="#FIG_419">fig. 419</a>)
-shows two large areas of sclerenchyma, which gives the chief mechanical support,
-the bundles being comparatively weak.</p>
-
-<p><b>712. Origin of root tissues.</b>—A similar apical meristem exists
-in roots, but there is in addition a fourth region of formative
-tissue in front of the meristem called <i>calyptrogen</i> (<a href="#FIG_420">fig. 420</a>).
-This gives rise to the “root cap” which serves to protect the meristem.
-The vascular cylinder in roots is very different from that of the
-stem. There is a solid central cylinder in which the groups of xylem
-radiate from the center and groups of phloem alternate with them but
-do not extend so near the center (<a href="#FIG_421">fig. 421</a>). As the root
-ages, changes take place which obscure this arrangement more or less. Branches of
-the roots arise from the central cylinder. In fern roots the apical
-<span class="pagenum"><a name="Page_362" id="Page_362">[Pg 362]</a></span>
-meristem is replaced by a single four-sided (tetrahedral) apical cell,
-the root cap being cut off by successive divisions of the outer face,
-while the primary root tissues are derived from the three lateral faces.</p>
-
-<div class="figcenter">
-    <img  id="FIG_420" src="images/fig420.jpg" alt="" width="400" height="482" />
-  <div class="blockquot">
-    <p class="center">Fig. 420.</p>
-    <p>Median longitudinal section of the apex of a root of the barley,
-       Hordeum vulgare. <i>k</i>, calyptrogen; <i>d</i>, dermatogen; <i>c</i>, its
-       thickened wall; <i>pr</i>, periblem; <i>pl</i>, plerome; <i>en</i>, endodermis; <i>i</i>,
-       intercellular air-space in process of formation; <i>a</i>, cell row destined
-       to form a vessel; <i>r</i>, exfoliated cells of the root cap.
-      (After Strasburger.)</p>
-  </div>
-</div>
-<div class="figcenter">
-    <img  id="FIG_421" src="images/fig421.jpg" alt="" width="500" height="411" />
-  <div class="blockquot">
-    <p class="center">Fig. 421.</p>
-    <p>Cross-section of fibrovascular bundle in
-       adventitious root of Ranunculus repens. <i>w</i>, pericycle; <i>g</i>, four
-       radial plates of xylem; alternating with them are groups of phloem.
-       This is a radial bundle. (After De Bary.)</p>
-  </div>
-</div>
-
-<p><b>Function of the root cap.</b>—The root cap serves an important
-function in protecting the delicate meristem or cambium at the tip of
-the root. These cells are, of course, very thin-walled, and while there
-is not so much danger that they would be injured from dryness, since
-the soil is usually moist enough to prevent evaporation, they would be
-liable to injury from friction with the rough particles of soil. No
-similar cap is developed on the end of the stem, but the meristem here
-is protected by the overlapping bud-scales. One of the most striking
-illustrations of a root cap may be seen in the case of the Pandanus, or
-screw-pine, often grown in conservatories (see <a href="#FIG_447">fig. 447</a>).
-On the prop roots which have not yet reached the ground the root caps can readily
-be seen, since they are so large that they fit over the end of the root
-like a thimble on the finger.
-<span class="pagenum"><a name="Page_363" id="Page_363">[Pg 363]</a></span></p>
-
-<p><b>713.</b></p>
-<p class="center"><b>Descriptive Classification of Tissues.</b></p>
-<table border="0" cellspacing="0" summary=" " cellpadding="0" >
-  <tbody><tr>
-      <td class="tdl br" rowspan="9">Epidermal<br />&emsp;System.····</td>
-      <td class="tdl_ws1" colspan="3">Epidermis.<br />&nbsp;</td>
-   </tr><tr>
-      <td class="tdc_ws1 br" rowspan="7">Trichomes.</td>
-      <td class="tdl_ws1 bt" colspan="2">Simple hairs.</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="2">Many-celled hairs.</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="2">Branched hairs, often stellate.</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="2">Clustered, tufted hairs.</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="2">Glandular hairs.</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="2">Root hairs.</td>
-   </tr><tr>
-      <td class="tdl_ws1 bb" colspan="2">Prickles.</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="3">&nbsp;<br />Guard cells of stomates.</td>
-   </tr><tr>
-      <td class="tdc" colspan="4">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl br" rowspan="12">Fibrovascular<br />&emsp;System.····</td>
-      <td class="tdc_ws1 br" rowspan="7">Xylem (wood).</td>
-      <td class="tdl_ws1 bt" colspan="2">Spiral vessels.</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="2">Pitted vessels.</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="2">Scalariform vessels.</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="2">Annular vessels.</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="2">Tracheides.</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="2">Wood fibers.</td>
-   </tr><tr>
-      <td class="tdl_ws1 bb" colspan="2">Wood parenchyma.</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="3">&nbsp;<br />Cambium (fascicular).<br />&nbsp;</td>
-   </tr><tr>
-      <td class="tdc_ws1 br" rowspan="4">Phloem (bast).</td>
-      <td class="tdl_ws1 bt" colspan="2">Sieve tubes.</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="2">Bast fibers.</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="2">Companion cells.</td>
-   </tr><tr>
-      <td class="tdl_ws1 bb" colspan="2">Bast parenchyma.</td>
-   </tr><tr>
-      <td class="tdc" colspan="4">&nbsp;</td>
-   </tr><tr>
-      <td class="tdc_ws1 br" rowspan="25">Fundamental<br />System.····</td>
-      <td class="tdc_ws1 br" rowspan="16">Stem and root.</td>
-      <td class="tdc_ws1 br" rowspan="5">Cortex.····</td>
-      <td class="tdl_ws1 bt">Cork.</td>
-   </tr><tr>
-      <td class="tdl_ws1">Collenchyma.</td>
-   </tr><tr>
-      <td class="tdl_ws1">Parenchyma.</td>
-   </tr><tr>
-      <td class="tdl_ws1">Fibers.</td>
-   </tr><tr>
-      <td class="tdl_ws1 bb">Milk tissue.</td>
-   </tr><tr>
-      <td class="tdl_ws1">&nbsp;</td>
-   </tr><tr>
-      <td class="tdc_ws1 br" rowspan="2">Pith-ray.··</td>
-      <td class="tdl_ws1 bt">Parenchyma.</td>
-   </tr><tr>
-      <td class="tdl_ws1 bb">Intrafascicular&nbsp;cambium.</td>
-   </tr><tr>
-      <td class="tdl_ws1">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl_ws1">&nbsp;</td>
-   </tr><tr>
-      <td class="tdc_ws1 br" rowspan="2">Pith.······</td>
-      <td class="tdl_ws1 bt">Parenchyma.</td>
-   </tr><tr>
-      <td class="tdl_ws1 bb">Sclerenchyma.</td>
-   </tr><tr>
-      <td class="tdl_ws1">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="2">Bundle-sheath.</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="2"><br />Endodermis.</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="3">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="3">&nbsp;</td>
-   </tr><tr>
-      <td class="tdc_ws1 br" rowspan="2">Leaves.</td>
-      <td class="tdl_ws1 bt" colspan="2">Palisade tissue.</td>
-   </tr><tr>
-      <td class="tdl_ws1 bb" colspan="2">Spongy parenchyma.</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="3">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="3">Reproductive Organs (mainly fundamental).</td>
-   </tr>
- </tbody>
-</table>
-
-<p class="space-above2"><span class="pagenum"><a name="Page_364" id="Page_364">[Pg 364]</a></span>
-<b>714. Physiological Classification of Tissues.</b></p>
-
-<p><i>Formative Tissue.</i></p>
-
-<p>Thin-walled cells composing the meristem, capable of division and from
-which other tissues are formed.</p>
-
-<p><i>Protective Tissue.</i></p>
-
-<p><i>Tegumentary System.</i>—Epidermis, periderm, bark protecting the plant
-from external contact.</p>
-
-<p><i>Mechanical System.</i>—Bast tissue, bast-like tissue, collenchyma,
-sclerenchyma, afford protection against harmful bending, pulling, etc.</p>
-
-<p><i>Nutritive Tissues.</i></p>
-
-<p><i>Absorptive System.</i>—Root hairs and cells, rhizoids, aerial root
-tissue, absorptive leaf glands, absorptive organs in seeds, haustoria
-of parasites, etc.</p>
-
-<p><i>Assimilatory System.</i>—Assimilating cells in leaf and stem.</p>
-
-<p><i>Conductive System.</i>—Sieve tissue, tracheary tissue, milk tissue,
-conducting parenchyma, etc.</p>
-
-<p><i>Food-storing System.</i>—Water reservoir, water tissue, slime tissue,
-fleshy roots and stems, endosperm and cotyledons, etc.</p>
-
-<p><i>Aerating System.</i>—Air spaces and tubes, special air tissue,
-air-seeking roots, stomates, lenticels, etc.</p>
-
-<p><i>Secretory and Excretory System.</i>—Water glands, digestive glands,
-resin glands, nectaries, tannin, pitch and oil receptacles, etc.</p>
-
-<p><i>Apparatus and Tissues for Special Duties.</i></p>
-
-<p>Holdfasts.</p>
-
-<p>Tissues of movement, parachute hairs, floating tissue, hygroscopic
-tissue, living tissue.</p>
-
-<p>For perceiving stimuli.</p>
-
-<p>For conducting stimuli, etc.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_365" id="Page_365">[Pg 365]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XXXIX" id="CHAPTER_XXXIX">CHAPTER XXXIX.</a><br />
-<span class="h_subtitle">THE DIFFERENT TYPES OF STEMS.<br /> WINTER SHOOTS AND BUDS.</span></h3>
-</div>
-
-<h4><a name="XXXIX_1" id="XXXIX_1">I. Erect Stems.</a></h4>
-
-<p><b>715. Columnar type.</b>—The columnar type of stem may be simple or
-branched. When branching occurs the branches are usually small and in
-general subordinate to the main axis. The sunflower (Helianthus annuus)
-is an example. The foliage part is mainly simple. The main axis remains
-unbranched during the larger part of the growth-period. The principal
-flowerhead terminates the stem. Short branches bearing small heads
-then arise in the axils of a few of the upper leaves. In dry, poor
-soil, or where other conditions are unfavorable, there may be only the
-single terminal flowerhead, when the stem is unbranched. The mullein
-is another columnar stem. The foliage part is rarely branched, though
-branches sometimes occur where the main axis has become injured or
-broken. The flower stem is terminal. The corn plant and the Easter lily
-are good illustrations also of the columnar stem.</p>
-
-<p>Among trees the Lombardy poplar (Populus fastigiata) is an excellent
-example of the columnar type. Though this is profusely branched, the
-branches are quite slender and small in contrast with the main axis,
-unless by some injury or other cause two large axes may be developed.
-As the technical name indicates, the branching is fastigiate, i.e., the
-branches are crowded close together and closely surround the central
-axis. The royal palm and some of the tree ferns have columnar, simple
-<span class="pagenum"><a name="Page_366" id="Page_366">[Pg 366]</a></span>
-stems, but the large, wide-spreading leaves at the top of the stem give
-the plant anything but a cylindrical habit. Some cedars and arbor-vitæ
-are also columnar.</p>
-
-<p>The advantages of the columnar habit of stem are three: (1) That the
-plant stands above other neighboring ones of equal foliage area and
-thus is enabled to obtain a more favorable light relation; (2) where
-large numbers of plants of the same species are growing close together,
-they can maintain practically the same habit as where growing alone;
-(3) the advantage gained by other types in their neighborhood in less
-shading than if the type were spreading. The cylindrical type can,
-therefore, grow between other types with less competition for existence.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img  id="FIG_422" src="images/fig422.jpg" alt="" width="150" height="429" />
-    <p class="center">Fig. 422.<br /> Cylindrical stem<br /> of mullein.</p>
-   </div>
-  <div class="figsub">
-      <img  id="FIG_423" src="images/fig423.jpg" alt="" width="300" height="445" />
-      <p class="center">Fig. 423.<br /> Conical type of larch.</p>
-  </div>
-</div>
-
-<p><b>716. The cone type.</b>—This is well exampled in the larches,
-spruces, the gingko tree, some of the pines, cedars, and other
-gymnosperms. In the cone type, the main axis extends through the system
-of branches like a tall shaft, i.e., the trunk is <i>excurrent</i>. The
-lower branches are wide-spreading, and the branches become successively
-shorter, usually uniformly, as one ascends the stem. The branching is
-of two types: (1) the branches are in false whorls; (2) the branches are
-<span class="pagenum"><a name="Page_367" id="Page_367">[Pg 367]</a></span>
-distributed along the stem. To the first type belong the pines, Norway
-spruce, Douglas spruce, etc. <i>The white pine</i> is an exquisite example,
-and in young and middle-aged trees shows the style of branching to
-very good advantage. The branches are nearly horizontal, with a
-slight sigmoid graceful curve, while towards the top the branches are
-ascending. This direction of the branches is due to the light relation.
-The few whorls at the top are ascending because of the strong light
-from above. They soon become extended in a horizontal direction as the
-main source of light is shifting to the side by the shading of the top.
-The ascending direction first taken by the upper branches and their
-subsequent turning downward, while the ends often still have a slight
-ascending direction gives to the older branches their sigmoid curve.</p>
-
-<p>The young vernal shoots of the pines show some very interesting
-growth movements. There are two growth periods: (1) the elongation of
-the shoot, and (2) the elongation of the leaves. The elongation of the
-shoot takes place first and is completed in about six weeks or two
-months’ time. The direction of the shoot in the first period seems to
-be entirely influenced by geotropism. It grows directly upward and
-stands up as a very conspicuous object in strong contrast with the dark
-green foliage of the more or less horizontal shoots. When the second
-period of growth takes place, and the leaves elongate, the shoot bends
-downward and outward in a lateral direction.</p>
-
-<p>The rate of growth of the pines can be very easily observed since each
-<span class="pagenum"><a name="Page_368" id="Page_368">[Pg 368]</a></span>
-whorl of branches (between the whorls of long shoots there are short
-shoots bearing the needle leaves), whether on the main axis or on the
-lateral branches, marks a year, the new branches arising each year
-at the end of the shoot of the previous year. The rate of growth is
-sometimes as high as twelve to twenty-four inches or more per year.</p>
-
-<p>The <i>spruces</i> form a more perfect cone than the pines. The long
-branches are mostly in whorls, but often there are intermediate ones,
-though the rate of growth per year can usually be easily determined. In
-the <i>hemlock-spruce</i>, the branching is distributed. The <i>larch</i> has a
-similar mode of branching, but it is deciduous, shedding its leaves in
-the autumn, and it has a tall, conical form.</p>
-
-<p>It would seem that trees of the cone type possessed certain advantages
-in some latitudes or elevations over other trees. (1) A conical tree,
-like the spruces and larches and the pines, and hemlocks also, before
-they get very old, meets with less injury during high winds than trees
-of an oval or spreading type. The slender top of the tree where the
-force of the wind is greatest presents a small area to the wind, while
-the trunk and short slender branches yield without breaking. Perhaps
-this is one reason why trees of this type exist in more northern
-latitudes and at higher elevations in mountainous regions, and why
-the spruce type reaches a higher latitude and altitude even than the
-pines. (2) The form of the tree is such as to admit light to a large
-foliage area, even where the trees are growing near each other. The
-evergreen foliage, persistent for several years, on the wide-spreading
-lower branches, probably affords some protection to the trees since
-this cover would aid in maintaining a more equable temperature in the
-forest cover than if the trees were bare during the winter. (3) There
-is less danger of injury from the weight of snow since the greater
-load of snow would lie on the lower branches. The form of the branches
-also, especially in the spruces, permits them to bend downward without
-injury, and if necessary unload the snow if the load becomes too heavy.</p>
-
-<p><b>717. The oval type.</b>—This type is illustrated by the oak,
-<span class="pagenum"><a name="Page_369" id="Page_369">[Pg 369]</a></span>
-chestnut, apple, etc. The trees are usually deciduous, i.e., cast
-their leaves with the approach of winter. The main axis is sometimes
-maintained, but more often disappears (trunk is <i>deliquescent</i>),
-because of the large branches which maintain an ascending direction,
-and thus lessen the importance of the central axis which is so marked
-in the cone type. Trees of this type, and in fact all deciduous trees,
-exhibit their character or habit to better advantage during the winter
-season when they are bare. Trees of this type are not so well adapted
-to conditions in the higher altitudes and latitudes as the cone type,
-for the reason given in the discussion of that type. The deciduous
-habit of the oaks, etc., enables them to withstand heavy winds far
-better than if they retained their foliage through the winter, even
-were the foliage of the needle kind and adapted to endure cold.</p>
-
-<p><b>718. The deliquescent type.</b>—The elm is a good illustration of
-this type. The main axes and the branches fork by a false dichotomy, so
-that a trunk is not developed except in the forest. The branches rise
-at a narrow angle, and high above diverge in the form of an arch. The
-chief foliage development is lofty and spreading.</p>
-
-<p>Trees possess several advantages over vegetation less lofty. They may
-start their growth later, but in the end they outgrow the other kinds,
-shade the ground and drive out the sun-loving kinds.</p>
-
-<h4><a name="XXXIX_2" id="XXXIX_2">II. Creeping, Climbing, and Floating Stems.</a></h4>
-
-<p><b>719. Prostrate type.</b>—This type is illustrated by creeping or
-procumbent stems, as the strawberry, certain roses, of which a good
-type is one of the Japanese roses (Rosa wichuriana), which creeps very
-close to the ground, some of the raspberries, the cucurbits like the
-squash, pumpkin, melons, etc. These often cover extensive areas by
-branching and reaching out radially on the ground or climbing over low
-objects. The cucurbits should perhaps be classed with the climbers,
-since they are capable of climbing where there are objects for support,
-<span class="pagenum"><a name="Page_370" id="Page_370">[Pg 370]</a></span>
-but they are prostrate when grown in the field or where there are no
-objects high enough to climb upon. In the prostrate type, there is
-economy in stem building. The plants depend on the ground for support,
-and it is not necessary to build strong, woody trunks for the display
-of the foliage which would be necessary in the case of an erect plant
-with a foliage area as great as some of the prostrate stems. This
-gain is offset, at least to a great extent, by the loss in ability to
-display a great amount of foliage, which can be done only on the upper
-side of the stem.</p>
-
-<div class="figcenter">
-    <img src="images/fig424.jpg" alt="" width="500" height="318" />
-    <p class="center">Fig. 424.<br /> Prostrate type of the water fern (<i>marsilia</i>).</p>
-</div>
-
-<p>Other advantages gained by the prostrate stems are protection from
-wind, from cold in the more rigorous climates, and some propagate
-themselves by taking root here and there, as in certain roses, the
-strawberry plant, etc. Some plants have erect stems, and then send
-out runners below which take root and aid the plant in spreading and
-multiplying its numbers.</p>
-
-<p><b>720. The decumbent type.</b>—In this type the stem is first erect,
-but later bends down in the form of an arch, and strikes root where the tip
-touches the ground. Some of the raspberries and blackberries are of this type.
-<span class="pagenum"><a name="Page_371" id="Page_371">[Pg 371]</a></span></p>
-
-<p><b>721. The climbing type.</b>—The grapes, clematis, some roses, the
-ivies, trumpet-creeper, the climbing bittersweet, etc., are climbing
-stems. Like the prostrate type, the climbers economize in the material
-for stem building. They climb over shrubs, up the trunks of trees and
-often reach to a great height and acquire the power of displaying a
-great amount of foliage by sending branches out on the limbs of the
-trees, sometimes developing an amount of foliage sufficient to cover
-and nearly smother the foliage of large trees; while the main stem of
-the vine may be not over two inches in diameter and the trunk of the
-supporting tree may be three feet in diameter.</p>
-
-<p><b>722. Floating stems.</b>—These are necessarily found in aquatic
-plants. The stems may be ascending or horizontal. The stems are
-usually not very large, nor very strong, since the water bears them
-up. The plants may grow in shallow water, or in water 10-12 feet or
-more deep, but the leaves are usually formed at or near the surface of
-the water in order to bring them near the light. Various species of
-Potamogeton, Myriophyllum, and other plants common along the shores of
-lakes, in ponds, sluggish streams, etc., are examples. Among the algæ
-are examples like Chara, Nitella, etc., in fresh water; Sargassum,
-Macrocystis, etc., in the ocean. In these plants, however, the plant
-body is a thallus, which is divided into stem-like (<i>caulidium</i>)
-and leaf-like (<i>phyllidium</i>) structures.</p>
-
-<p><b>723. The burrowing type, or rhizomes.</b>—These are horizontal,
-subterranean stems. The bracken fern, sensitive fern, the mandrake
-(see <a href="#FIG_413A">fig. 413<i>a</i></a>), Solomon’s seal, Trillium, Dentaria,
-and the like, are examples. The subterranean habit affords them protection from the
-cold, the wind, and from injury by certain animals. Many of these stems
-act as reservoirs for the storage of food material to be used in the
-rapid growth of the short-lived aerial shoot. In the ferns mentioned,
-the subterranean is the only shoot, and this bears scale leaves which
-are devoid of chlorophyll, and foliage leaves which are larger, and the
-only member of the plant body which is aerial. The foliage leaf has
-<span class="pagenum"><a name="Page_372" id="Page_372">[Pg 372]</a></span>
-assumed the function of the aerial shoot. The latter is not necessary
-since flowers are not formed. The mandrake, Solomon’s seal, Trillium,
-etc., have scale leaves on the fleshy underground stems, while foliage
-leaves are formed on the aerial stems, the latter also bearing the
-flowers. Some of the advantages of the rhizomes are protection from
-injury, food storage for the rapid development of the aerial shoot,
-and propagation.</p>
-
-<p>Many of the grasses have subterranean stems which ramify for great
-distances and form a dense turf. For the display of foliage and for
-flower and seed production, aerial shoots are developed from these
-lateral upright branches.</p>
-
-<h4><a name="XXXIX_3" id="XXXIX_3">III. Specialized Shoots and Shoots for Storage of Food.</a><a name="FNanchor_40_40" id="FNanchor_40_40"></a><a href="#Footnote_40_40" class="fnanchor">[40]</a></h4>
-
-<p><b>724. The bulb.</b>—The bulb is in the form of a bud, but the scale
-leaves are large, thick, and fleshy, and contain stored in them food
-products manufactured in the green aerial leaves and transported to
-the underground bases of the leaves. Or when the bulb is aerial in its
-formation, it is developed as a short branch of the aerial stem from
-which the reserve food material is transported. Examples are found
-in many lilies, as Easter lily, Chinese lilies, onion, tulip, etc.
-The thick scale leaves are closely overlapped and surround the short
-stem within (also called a <i>tunicated</i> stem). In many lilies there
-is a sufficient<span class="pagenum"><a name="Page_373" id="Page_373">[Pg 373]</a></span>
-amount of food to supply the aerial stem for the development of flower
-and seed. There are roots, however, from the bulb and these acquire
-water for the aerial shoot, and when planted in soil additional food is
-obtained by them.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <p>&nbsp;</p>
-    <img src="images/fig425.jpg" alt="" width="300" height="279" />
-    <p class="center">Fig. 425.<br /> Bulb of hyacinth.</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig426.jpg" alt="" width="225" height="300" />
-      <p class="center">Fig. 426.<br /> Corm of Jack-in-the-pulpit.</p>
-  </div>
-</div>
-
-<p><b>725. Corm.</b>—A corm is a thick, short, fleshy, underground stem.
-A good example is found in the jack-in-the-pulpit (Arisæma).</p>
-
-<p><b>726. Tubers.</b>—These are thickened portions of the subterranean
-stems. The most generally known example is the potato tuber (“Irish”
-potato, not the sweet potato, which is a root). The “eyes” of the
-potato are buds on the stem from which the aerial shoots arise when the
-potato sprouts. The potato tuber is largely composed of starch which is
-used for food by the young sprouts.</p>
-
-<p><b>726</b><i>a</i>. <b>Phylloclades.</b>—These are trees, shrubs, or
-herbs in which the leaves are reduced to mere bracts and stems,
-are not only green and function as leaves, but some or all of the
-branches are flattened and resemble leaves in form as in Phyllanthus,
-Ruscus, Semele, Asparagus, etc. The flowers are borne directly on
-these flattened axes. The prickly-pear cactus (Opuntia) is also
-a phylloclade. Examples of phylloclades are often to be found in
-greenhouses.</p>
-
-<p><b>727. Undifferentiated stems</b> are found in such plants as the
-duckweed, or duckmeat (Lemna, Wolffia, etc.<a href="#CHAPTER_III"> See Chapter III</a>).
-<span class="pagenum"><a name="Page_374" id="Page_374">[Pg 374]</a></span></p>
-
-<h4><a name="XXXIX_4" id="XXXIX_4">IV. Annual Growth and Winter Protection of Shoots and Buds.</a><a name="FNanchor_41_41" id="FNanchor_41_41"></a><a href="#Footnote_41_41" class="fnanchor">[41]</a></h4>
-
-<p><b>728. Winter conditions.</b><a name="FNanchor_42_42" id="FNanchor_42_42"></a><a href="#Footnote_42_42" class="fnanchor">[42]</a>—While
-herbs are subjected only to the damp warm atmosphere of summer, woody
-plants are also exposed during the cold dry winter, and must protect
-themselves against such conditions. The air is dryer in winter than in
-summer; while at the same time root absorption is much retarded by the
-cold soil. Then, too, the osmotic activity of the dormant twig-cells
-being much reduced, the water-raising forces are at a minimum. It
-is easy to see, therefore, that a tree in winter is practically
-under desert conditions. Moreover, it has been found by various
-investigators, contrary to the general belief, that cold in freezing is
-only indirectly the cause of death. The real cause is the abstraction
-of water from the cell by the ice crystals forming in the intercellular
-spaces. Death ensues because the water content is reduced below the
-danger-point for that particular cell. It was formerly thought that on
-freezing, the cells in the tissue were ruptured. This is not so. Ice
-almost never forms within the cell, but in the spaces between. Freezing
-then is really a drying process, and dryness, not cold, causes death
-in winter. To protect themselves in winter, trees provide various
-waterproof coverings for the exposed surfaces and reduce the activity
-of the protoplasm so that it will be less easily harmed by the loss of
-water abstracted by the freezing process.</p>
-
-<div class="figcenter">
-    <img src="images/fig427.jpg" alt="" width="600" height="100" />
-  <div class="blockquot">
-    <p class="center">Fig. 427.</p>
-    <p>Two-year-old twig of horse-chestnut, showing buds and leaf-scars. (A
-       twig with a terminal bud should have been selected for this figure.)</p>
-  </div>
-</div>
-
-<p><b>729. Protection of the twig.</b>—Woody plants protect the living
-cells within the twigs by the production of a dull or rough corky bark,
-<span class="pagenum"><a name="Page_375" id="Page_375">[Pg 375]</a></span>
-or by a thick glossy epidermis over the entire surface. At intervals
-occur small whitish specks called lenticels, which here perform nearly
-the same function as do stomates in the leaf.</p>
-
-<p><b>730. Bark of trunk.</b>—A similar service is performed by the
-bark for the main trunk and branches of the tree. To admit of growth
-in diameter the old bark is constantly being thrown off in strips,
-flakes, etc., and replaced by a new but larger cylinder of young bark.
-The external appearance thus produced enables experienced persons to
-recognize many kinds of trees by the trunk alone.</p>
-
-<p><b>731. Leaf-scars and bundle-scars.</b>—The presence of foliage
-leaves during the winter would greatly increase the transpiring surface
-without being of use to the plant; hence they are usually thrown off on
-the approach of winter. The scars left by the fallen leaves are termed
-leaf-scars. The small dots on the leaf-scars left by the vascular
-bundles which extended through the petiole into the twig are termed
-bundle-scars. Sometimes stipule-scars are left on each side of the
-leaf-scar by the fallen stipules.</p>
-
-<p><b>732. Nodes and internodes.</b>—The region upon a stem where a leaf
-is borne is termed a node. The space between two nodes is an internode.</p>
-
-<div class="figcenter">
-    <img src="images/fig428.jpg" alt="" width="600" height="99" />
-  <div class="blockquot">
-    <p>Fig. 428.—Shoot of butternut showing leaf-scars, axillary buds,
-       and adventitious buds (buds coming from above the axils).</p>
-  </div>
-</div>
-<div class="figcenter">
-    <img src="images/fig429.jpg" alt="" width="600" height="81" />
-      <p class="center space-below2">Fig. 429.—Shoot and bud of white oak.</p>
-</div>
-
-<p><b>733. Phyllotaxy.</b>—Investigation of a horse-chestnut or willow
-twig will show that the leaf-scars occupy definite positions which
-are constant for each plant but different for the two species.
-The arrangement of the leaves on the stem in any plant is termed
-phyllotaxy. In the horse-chestnut we find two scars placed at the same
-node, but on opposite sides of the stem. Somewhat higher up we find two
-more similarly placed, but in a position perpendicular to that of the
-first pair. Such phyllotaxy is termed opposite. If in any plant several
-leaves occur at a node, the phyllotaxy is whorled. If but one at each
-node, as in the willow, the phyllotaxy is alternate. The opposite and
-alternate types are very commonly met with. Closer observation will
-show that in the willow, if a line be drawn connecting the successive
-leaf-scars, it will pass spirally up the twig until at length a scar is
-reached directly over the one taken as a starting-point. Such spiral
-arrangement always accompanies alternate phyllotaxy. The section of the
-spiral thus delineated is termed a cycle. We express the nature of the
-<span class="pagenum"><a name="Page_376" id="Page_376">[Pg 376]</a></span>
-cycle by the fractions ½, ⅓, ⅖, ⅜, ⁵/₁₃, etc., in which the numerator
-denotes the number of turns around the stem in each cycle, and the
-denominator the number of leaf-scars in the same distance. In a general
-way we find in plants only such arrangements as are represented by
-the fractions given above. These fractions show the curious condition
-that the numerator and denominator of each is equal to the sum of
-the numerator or denominator of the two preceding fractions. Much
-speculation has been indulged in regarding the significance of these
-definite laws of leaf arrangement. In part they may be due to the
-desire that each leaf receive the maximum amount of light. Only certain
-definite geometrical conditions will insure this. More likely it is due
-to the economy of space allotted to the leaf-fundaments in the bud.
-Here, again, geometrical laws govern this economy. The phyllotaxy is
-nearly constant for a given species.</p>
-
-<p><b>734. Buds.</b>—The growing point of the stem or branch together
-with its leaf or flower fundaments and protective structures is termed
-a bud. Winter buds on woody plants are terminal when inclosing the
-growing point of the main axis of the twig; lateral when the growing
-point is that of a branch of the main axis. Lateral buds are always
-axillary, i.e., situated on the upper angle between a leaf and the main axis.</p>
-
-<p><b>735. Buds occupying special positions.</b>—Several species of trees
-and shrubs produce more than one bud in each leaf-axil. The additional
-<span class="pagenum"><a name="Page_377" id="Page_377">[Pg 377]</a></span>
-ones are termed accessory or supernumerary buds. These may be lateral
-to one another or they may be superposed as in the walnut or butternut.
-In such cases some of the buds usually contain simply floral shoots and
-are termed flower buds. In some species buds are frequently produced
-on the side of the branches and trunk at some distance from the
-leaf-axils, and entirely without regard for the latter; or more rarely
-may occur upon the root. Such buds are termed adventitious, and are the
-source of the feathery branchlets upon the trunks of the American elm.</p>
-
-<p><b>736. Branching follows the phyllotaxy.</b>—Since the lateral or
-branch-producing buds are always located in the axil of a leaf, the
-branches necessarily follow the same arrangement upon the main axis
-as do the leaves. Since, however, many of the axillary buds fail to
-develop, this arrangement may be more or less obscured.</p>
-
-<div class="figleft">
-    <img src="images/fig430.jpg" alt="" width="200" height="400" />
-    <p class="center">Fig. 430.<br /> Bud of European elm<br />
-            in section, showing<br /> overlapping of scales.<br /></p>
-</div>
-
-<p><b>737. Coverings of winter buds.</b>—These are of two sorts, hair
-and cork, or scales. Buds protected simply by dense hair or sunk in
-the cork of the twig are termed naked buds, and are comparatively
-rare. Most species protect their buds by the addition of an imbricated
-covering of closely appressed scales, the whole frequently being
-rendered still more waterproof by the excretion of resin between the
-scales or over the whole surface. The scales when studied carefully
-are found to be much reduced leaves or parts of leaves. In some cases
-they represent a modified whole leaf, when they are said to be laminar,
-or a leaf-petiole, when they are petiolar, or stipular, when they are
-much-specialized stipules of a leaf which itself is usually absent. The
-latter type is much the less common. The form of the bud, the nature
-and form of the scales, when combined with characters furnished by the
-leaf- and bundle-scars, enable one to recognize and classify the winter
-twigs of the various woody species.</p>
-
-<p><b>738. Phyllotaxy of the bud-scales.</b>—Since the bud-scales are
-leaves, they follow a definite phyllotaxy. This may or may not be
-the same as that of the foliage leaves. Twigs with opposite leaves
-have opposite bud-scales, or if with alternate leaves, then alternate
-bud-scales, but the fractions vary. If the scales are stipular, then
-there are of course two at each node.
-<span class="pagenum"><a name="Page_378" id="Page_378">[Pg 378]</a></span></p>
-
-<p><b>739. Function of the bud coverings.</b>—It is popularly believed
-that the scales and hairy coverings serve to keep the bud warm.
-Research, however, shows this to be almost entirely erroneous, and that
-the thin bud coverings are entirely inadequate to keep out the cold of
-winter. They cannot keep the bud even a degree or two warmer than the
-outside air, except when the changes are very rapid. Experiment also
-shows that the modifying effect of the covering when the bud thaws
-out is so slight as to be almost negligible. Indeed, a thermometer
-bulb covered with scales taken from a horse-chestnut bud warmed up
-more rapidly than a naked one when exposed to sunshine. The wool in
-the horse-chestnut bud is not for the purpose of keeping it warm, but
-to protect the young shoot from too great transpiration after the bud
-opens the following spring. Research has also shown that such tempering
-of the heat conditions is not especially beneficial to the plant,
-as was once thought. Neither can we find the main function in the
-prevention of water from entering the bud. This might be accomplished
-in much simpler ways, even if we could demonstrate the desirability of
-keeping the water out at all.</p>
-
-<p>The true functions of the bud-scales are two in number: Firstly, the
-prevention of too great loss of water from the young and delicate
-parts within; and secondly, the protection of these same parts from
-mechanical injury. Without some such protection the delicate young
-structures would be beaten off by the wind, or become the food for
-hungry birds during the long winter months.
-<span class="pagenum"><a name="Page_379" id="Page_379">[Pg 379]</a></span></p>
-
-<div class="figcenter">
-    <img src="images/fig431.jpg" alt="" width="400" height="508" />
-      <p class="center space-below2">Fig. 431.<br /> Opening buds of hickory.</p>
-</div>
-
-<p><b>740. Opening of the buds.</b>—When the young shoot begins to
-grow in the spring, the bud-scales are forced apart or open of their
-own accord. During the young condition the shoot is very soft and
-brittle, and also possesses a very thin, little cutinized epidermis.
-In this condition it is especially liable to mechanical injury and to
-injury from drying out. We find, therefore, a tendency for the inner
-bud-scales to elongate during vernation, thus forming a tube around the
-delicate tissue much like the opening out of a telescope. The young
-<span class="pagenum"><a name="Page_380" id="Page_380">[Pg 380]</a></span>
-leaves and internodes themselves are often provided with a woody or
-hairy covering to retard transpiration. When the epidermis becomes more
-efficient the hairy covering often falls away.</p>
-
-<p>In the case of naked buds protection is afforded in other ways: by
-the protection of hairy covering, by physiological adaptation of the
-tissue, or in many cases by the late appearance of the shoot in spring
-after the very dry April and May winds have ceased.</p>
-
-<p><b>741. Bud-scars, and how to tell the age of the plant.</b>—In
-general the bud-scales when they fall away in the spring leave scars
-termed scale-scars, and the whole aggregate of scale-scars makes up the
-bud-scar. The position of the buds of previous winters is, therefore,
-marked. It becomes an easy matter to determine the age of a branch,
-since all that is necessary is to follow back from one bud-scar to
-another, the portion of the stem between representing, except in rare
-cases, one year’s growth.</p>
-
-<p>A woody plant grows in height only by the formation of new sections
-of stem added to the apex or side of similar sections produced the
-previous season, never, as is commonly supposed, by the further
-elongation of the previous year’s growth. Hence a branch once formed
-upon a tree is fixed as regards its distance from the ground. The
-apparent rise of the branches away from the ground in forest trees is
-an illusion caused by the dying away of the lower branches.</p>
-
-<p><b>742. Definite and indefinite growth.</b>—With the opening of the
-buds in spring, growth begins. In some cases, when all the members
-for the season were formed, but still minute, within the bud, such
-growth consists solely in the expansion of parts already formed; in
-others only a few members are thus present to expand, while new ones
-are produced by the growing point as the season progresses. In most
-cases growth is completed by the middle of July, soon after which buds
-are formed for next year’s growth. Such a method of growth is termed
-definite.</p>
-
-<p>In a few woody plants, as, for example, sumach, locust, and raspberry,
-growth continues until late in the autumn. In such cases the most
-recently formed nodes and internodes are unable to become sufficiently
-<span class="pagenum"><a name="Page_381" id="Page_381">[Pg 381]</a></span>
-“hardened” before winter sets in, and are killed back more or less.
-Next season’s shoot is a branch from some axillary bud. Such growth is
-termed indefinite.</p>
-
-<div class="figcenter">
-    <img src="images/fig432.jpg" alt="" width="400" height="482" />
-      <p class="center space-below2">Fig. 432.<br /> Three-year-old twig of the American ash,<br />
-          with sections of each year’s growth<br /> showing annual rings.</p>
-</div>
-
-<p><b>743. Structure of woody stems.</b>—If we make a cross-section of a
-woody twig three general regions are presented to view. On the outside
-is the rather soft, often greenish “bark,” so called, made up of
-sieve tubes, ordinary parenchyma cells, and in many cases long fibrous
-cells composing the “fibrous bark.” From a growing layer in this region,
-termed the phellogen, the true corky bark of the older trunk is formed.</p>
-
-<p>Next within the bark we find the so-called “woody” portion of the
-twig. This is strong and resistant to both breaking and cutting. The
-microscope shows it to be composed of the ordinary already known woody
-elements,<a name="FNanchor_43_43" id="FNanchor_43_43"></a><a href="#Footnote_43_43" class="fnanchor">[43]</a>
-wood fibers, for strengthening purposes, pitted and spiral vessels as
-conducting tissue; and intermixed with these some living parenchyma
-cells. A cross-section of the stem also shows narrow radial lines
-through the wood. These are pith-rays, composed of vertical plates of
-living parenchyma cells. These cells, unlike the others in the wood,
-are elongated radially, not vertically. The height of the pith-rays
-as well as their thickness varies with the species studied. In the
-older trunk only the outer portion, a few inches in thickness, remains
-light-colored and fresh, and is called sap-wood. The inner wood is
-usually darker and harder, and is termed heart-wood. Living parenchyma
-cells, in general, are present only in the sap-wood, and in this almost
-solely the ascent of sap occurs. Dyestuffs and other substances are
-frequently deposited in the walls of the heart-wood.</p>
-
-<p><span class="pagenum"><a name="Page_382" id="Page_382">[Pg 382]</a></span>
-The third region occupying the center of the twig is the pith. This is
-composed ordinarily of angular, little elongated, parenchyma cells,
-when mature mostly without cell-contents and filled with air. The pith
-region in different trees is quite diversified. It may be hollow,
-chambered, contain scattered thick-walled cells, have woody partitions,
-or rarely be entirely thick-walled.</p>
-
-<p>The nature of the woody ring is rather perplexing at first; but
-its origin is simple. We may conceive that it has developed from a
-stem-type like the sunflower, in which the bundles, though separate,
-are connected by a continuous cambium ring. In the woody twigs the
-numerous bundles are closely packed together, and only separated by
-the primary pith-rays extending from the pith to the cortex. Other
-secondary pith-rays are produced within each bundle, but they usually
-extend only part way from the cortex to the pith. The wood represents
-the xylem of the bundle, and the sieve tubes of the bark, the phloem.</p>
-
-<p><b>744. Growth in thickness.</b>—Although the year’s growth does not
-increase in length after the first season has passed, it does increase
-in diameter very much. From the size of an ordinary little twig it may
-at length become a large tree trunk several feet in thickness. Only a
-portion of the first year’s growth is produced by the growing point.
-All the rest is a product of the cambium, a cylinder of wood being
-added to the exterior of the old wood each season. The cambium, here,
-as in the sunflower, lies between the phloem and the xylem, forming a
-cylinder entirely around the stem. In spring, when active, it becomes
-soft and delicate, thus enabling one to easily strip off the bark from
-some trees, such as willow, etc., at that season.</p>
-
-<p><b>745. Annual rings in woody stems.</b>—The wood produced by the
-cambium each season is not homogeneous throughout, but is usually much
-denser toward the outer part of the yearly cylinder, wood fibers here
-predominating. In the inner portion vessels predominate, giving a much
-more porous effect. The transition from one year’s growth to another is
-very abrupt, giving rise to the appearance of rings in cross-section.
-Since ordinarily in temperate climates but one cylinder of wood is
-added each year, the number of rings will indicate the age of the trunk
-or branch. This is not absolutely accurate, since in some trees under
-certain conditions more than one ring may be produced in a summer. The
-porous part of the ring is often termed “spring wood,” and the denser
-portion “fall wood,” but since growth from the cambium ceases in most
-trees by the middle of July, “summer wood” would be more appropriate
-for the latter. It is mainly the alternation of the cylinders of the
-spring and summer wood that gives the characteristic grain to lumber.
-Pith-rays play an important part in wood graining only in a few woods,
-as, for instance, in quartered oak. The reason for the production of
-porous spring wood and dense summer wood is still one of the unsolved
-problems of botany.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_383" id="Page_383">[Pg 383]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XL" id="CHAPTER_XL">CHAPTER XL.</a><br />
-<span class="h_subtitle">FOLIAGE LEAVES.</span></h3>
-</div>
-
-<h4><a name="XL_1" id="XL_1">I. General Form and Arrangement of Leaves.</a></h4>
-
-<p><b>746. Influence of foliage leaves on the form of the stem.</b>—The
-marked effect which foliage has upon the aspect of the plant or upon
-the landscape is evident to all observers. Perhaps it is usual to
-look upon the stem as having been developed for the display of the
-foliage without taking into account the possibility that the foliage
-may have a great influence upon the form or habit of the stem. It is
-very evident, however, that the foliage exercises a great influence
-on the form of the stem. For example, as trees increase in age and
-size, the development of branches on the interior ceases and some of
-those already formed die, since the dense foliage on the periphery
-of the trees cuts off the necessary light stimulus. The tree,
-therefore, possesses fewer branches and a more open interior. In the
-forest also, the dense foliage above makes possible the shapely,
-clean timber trunks. Note certain trees where by accident, or by
-design, the terminal foliage-bearing branches have been removed that
-foliage-bearing branches may arise in the interior of the tree system.</p>
-
-<p>Without foliage leaves the stems of green plants would develop a very
-different habit from what they do. This development could take place in
-three different directions under the influence of light: (1) The light
-stimulus would induce profuse branching, so that there would be many
-small branches. (2) The stem would develop fewer branches, but they
-would be flattened. (3) Massive trunks with but few or no branches. In
-<span class="pagenum"><a name="Page_384" id="Page_384">[Pg 384]</a></span>
-fact, all these forms are found in certain green stems which do not
-bear leaves. An example of the first is found in asparagus with its
-numerous crowded slender branches. But such forms in our climate are
-rare, since foliage leaves are more efficient. The second and third
-forms are found among cacti, which usually grow in dry regions under
-conditions which would be fatal to ordinary thin foliage leaves.</p>
-
-<p><b>747. Relation of foliage leaves to the stem.</b>—In the study
-of the position of the leaves on the stem we observe two important
-modes of distribution: (1) the distribution along the individual
-stem or branch which bears them, usually classed under the head of
-<i>Phyllotaxy</i>; (2) the distribution of the leaves with reference to the
-plant as a whole.</p>
-
-<p><b>748. Phyllotaxy, or arrangement of leaves.</b>—In examining buds on
-the winter shoots of woody plants, we cannot fail to be impressed with
-some peculiarities in the arrangement of these members on the stem of
-the plant.</p>
-
-<p>In the horse-chestnut, as we have already observed, the leaves are in
-pairs, each one of the pair standing opposite its partner, while the
-pair just below or above stand across the stem at right angles to the
-position of the former pair. In other cases (the common bed-straw) the
-leaves are in whorls, that is, several stand at the same level on the
-axis, distributed around the stem. By far the larger number of plants
-have their leaves arranged alternately. A simple example of alternate
-leaves is presented by the elm, where the leaves stand successively on
-alternate sides of the stem, so that the distance from one leaf to the
-next, as one would measure around the stem, is exactly one half the
-distance around the stem. This arrangement is one half, or the angle of
-divergence of one leaf from the next is one half. In the case of the
-sedges the angle of divergence is less, that is one-third.</p>
-
-<p>By far the larger number of those plants which have the alternate
-arrangement have the leaves set at an angle of divergence represented
-by the fraction two fifths. Other angles of divergence have been
-discovered, and much stress has been laid on what is termed a law in
-the growth of the stem with reference to the position which the leaves
-occupy. Singularly by adding together the numerators and denominators
-of the last two fractions gives the next higher angle of divergence.
-Example:</p>
-
-<table class="lgfnt150" border="0" cellspacing="0" summary=" " cellpadding="0" >
-  <tbody><tr>
-      <td class="tdc bb">1</td>
-      <td class="tdc">&nbsp;+&nbsp;</td>
-      <td class="tdc bb">2</td>
-      <td class="tdc" rowspan="2">&nbsp;=&nbsp;</td>
-      <td class="tdr bb">3</td>
-      <td class="tdc" rowspan="2">;&emsp;&nbsp;</td>
-      <td class="tdc bb">2</td>
-      <td class="tdc">&nbsp;+&nbsp;</td>
-      <td class="tdc bb">3</td>
-      <td class="tdc" rowspan="2">&nbsp;=&nbsp;</td>
-      <td class="tdc bb">5</td>
-      <td class="tdc" rowspan="2">;</td>
-   </tr><tr>
-      <td class="tdc">3</td>
-      <td class="tdc">&nbsp;+&nbsp;</td>
-      <td class="tdc">5</td>
-      <td class="tdr">8</td>
-      <td class="tdc">5</td>
-      <td class="tdc">&nbsp;+&nbsp;</td>
-      <td class="tdc">8</td>
-      <td class="tdr">13</td>
-   </tr>
- </tbody>
-</table>
-
-<p class="no-indent">and so on. There are, however, numerous exceptions to this
-regular arrangement, which have caused some to question the importance of any
-theory like that of the “spiral theory” of growth propounded by Goethe
-and others of his time.
-<span class="pagenum"><a name="Page_385" id="Page_385">[Pg 385]</a></span></p>
-
-<p><b>749. Adaptation in leaf arrangement.</b>—As a result, however, of
-one arrangement or another we see a beautiful adaptation of the plant
-parts to environment, or the influence which environment, especially
-light, has had on the arrangement of the leaves and branches of the
-plant. Access to light and air are of the greatest importance to
-green plants, and one cannot fail to be profoundly impressed with the
-workings of the natural laws in obedience to which the great variety of
-plants have worked out this adaptation in manifold ways.</p>
-
-<p><b>750. Distribution of leaves with reference to the entire
-plant.</b>—In this case, as in the former, we recognize that it is
-primarily a light relation. As the plant becomes larger and more
-branched the lower and inner leaves disappear. The trees and shrubs
-have by far the larger number of leaves on the periphery of the branch
-system. A comparison of different kinds of trees in this respect shows,
-however, that there is great variation. Trees with dense foliage (elm,
-Norway maple, etc.) present numerous leaves on the periphery which
-admit but little light to the interior where leaves are very few or
-wanting. The sugar maple and red maple do not cast such a dense shade
-and there are more leaves in the interior. This is more marked in the
-silver maple, and still more so in the locust (Gleditschia tricanthos).</p>
-
-<p><b>751. Color of foliage leaves.</b>—The great majority of foliage
-leaves are green in color. This we have learned (<a href="#CHAPTER_VII">Chapter VII</a>)
-is due to the presence of a green pigment, chlorophyll, in the chloroplastids
-thickly scattered in the cells of the leaf. We have also learned that
-in the great majority of cases, the light stimulus is necessary for
-the production of chlorophyll green. There are many foliage leaves
-which possess other colors, as red (Rosa rubrifolia), purple (the
-purple barberry, hazel, beech, birch, etc.), yellow (the golden oak,
-elder, etc.); while many others have more or less deep tints of pink,
-red, purple, yellow, when young. All of these leaves, however, possess
-chlorophyll in addition to red, yellow, purple or other pigment.
-These other pigments are sometimes developed in great quantity in the
-cell-sap. They obscure the chlorophyll from view, but do not interfere
-seriously with the action of light and the function of chlorophyll, and
-perhaps in some cases serve as a screen to protect the protoplast.</p>
-
-<p><b>752. Autumn colors.</b>—Foliage leaves of many trees display in
-the autumn gorgeous colors. These colors are principally shades of
-red or yellow, and sometimes purple. The autumn color is more marked
-in some trees than in others. In the red maple, the red and scarlet
-oak, the sourwood, etc., red predominates, though sometimes yellow
-may be present with the red in a single leaf. Sugar maples, poplars,
-hickories, etc., are principally yellow in autumn. The sweet gum has a
-rich variety of color-red, purple, maroon, yellow; sometimes all these
-colors are present on the same tree.
-<span class="pagenum"><a name="Page_386" id="Page_386">[Pg 386]</a></span></p>
-
-<p>The red and purple colors are found suffused in the cell-sap of
-certain cells in the leaf much as we have found it in the cells of
-the red beet. The yellow color is chiefly due to the disappearance
-and degeneration of the chlorophyll while the leaf is in a moribund
-state. A similar phenomenon is seen in the yellowing of crops when
-the soil becomes too wet, or in the blanching of grass when covered
-with a board, or of celery as the earth is ridged up over the leaves
-in late summer and autumn. A number of different theories have been
-advanced to explain autumn coloring, i.e., the appearance of the
-red coloring matter. It has been attributed to the approach of cold
-weather, and this has likely led to the erroneous belief on the part
-of some that it is caused by frost. It very often precedes frost. Some
-have attributed it to the action of the more oblique light rays during
-autumn, and still others to the diminishing water-supply with the
-approach of cool weather. The question is one which has not met as yet
-with a satisfactory solution, and is certainly a very obscure one. It
-is likely that the low temperature or the declining activities of the
-leaf affect certain organic substances in the leaf and give rise to
-the red color, and it is quite certain that in some years the display
-is more brilliant than in others. The color is more striking in some
-regions than in others and the different soil, as well as climate, has
-been supposed to have some influence. The North American forests are
-noted for the brilliant display of autumnal color. This is perhaps due
-to some extent to the great variety or number of species which display
-color. It would seem that there is some specific as well as individual
-peculiarities in certain trees. Some individuals, for example, exhibit
-brilliant colors every autumn, while others near of the same species
-are more subdued.</p>
-
-<p>It has been shown by experiment that when sunlight passes through
-red colors the temperature is slightly increased, and it has been
-suggested that this may be of protection to the living substance which
-has ceased working and is in danger of injury from cold. There does
-not seem to be much ground for this suggestion, however. It certainly
-could not protect the protoplasm of the leaf at night when the cold
-is more intense, and during the day would only aggravate matters
-by supplying an increased amount of heat, since extremes of heat
-and cold in alternation are more harmful to plant life than uniform
-cold. Especially would this be the case in alpine climates where the
-alternation of heat and cold between day and night is extreme, and
-brilliancy of the colors of alpine plants is well known. It seems
-more reasonable to suppose that the red color acts as a screen, as
-the chlorophyll is disappearing, to protect from the injurious action
-of light, certain organic substances which are to be transferred back
-from the leaf to the stem for winter storage. So in the case of many
-stems in the spring or early summer when the young leaves often have
-a reddish color, it is likely that it acts as a screen to protect the
-<span class="pagenum"><a name="Page_387" id="Page_387">[Pg 387]</a></span>
-living substance from the strong light at that season of the year until
-the chlorophyll screen, which is weak in young leaves, becomes darker
-in color and more effective, when the red color often disappears.</p>
-
-<p><b>753. Function of foliage leaves.</b>—In general the function of
-the foliage leaf as an organ of the plant is fivefold (see Chapters
-<a href="#CHAPTER_IV">IV</a>, <a href="#CHAPTER_VII">VII</a>,
-<a href="#CHAPTER_VIII">VIII</a>, <a href="#CHAPTER_XI">XI</a>),
-(1) that of carbon dioxide assimilation or <i>photosynthesis</i>, (2) that
-of transpiration, (3) that of the synthesis of other organic compounds,
-(4) that of respiration, and (5) that of assimilation proper, or the
-making of new living substance. While none of these functions are
-solely carried on in the leaf, it is the chief seat of the first three
-of these processes, its form, position, and structure being especially
-adapted to the purpose. Assimilation proper, as well as respiration,
-probably take place equally in all growing or active parts.</p>
-
-<p><b>754. Parts of the leaf.</b>—All foliage leaves possess a <i>blade</i>
-or <i>lamina</i>, so called because of its <i>expanded</i> and <i>thin</i> character.
-The blade is the essential part. Many leaves, however, are provided
-with a stalk or <i>petiole</i> by which the blade is held out at a greater
-or lesser distance from the stem. Leaves with no petiole are <i>sessile</i>,
-the blade is attached by one end directly on the stem. In some cases
-the base of the blade is wrapped partly around the stem, or in others
-it extends entirely around the stem and is <i>perfoliate</i>. Besides, many
-leaves have short appendages, termed <i>stipules</i>, attached usually on
-opposite sides of the petiole at its junction with the stem. In some
-species of magnolia the stipules are so large that each one envelops
-the entire portion of the bud which has not yet opened. Many leaves
-possess outgrowths in the form of hairs, scales, etc. (<a href="#Page_392">See leaf
-protection</a>.)</p>
-
-<p><b>755. Simple leaves.</b>—Simple leaves are those in which the
-blade is plane along the edge, not divided. The edge may be entire or
-indented (serrate) to a slight extent as in the elm. The form of the
-simple leaf varies greatly but is usually constant for a given species,
-or it may vary in shape in the same species on different parts of the
-plant. Some of the terms applied to the outline of the leaf are ovate,
-oval, elliptical, lanceolate, linear, needle-like, etc., but it is idle
-<span class="pagenum"><a name="Page_388" id="Page_388">[Pg 388]</a></span>
-for one to waste time on matters of minute detail in form until it
-becomes necessary for those in the future who pursue taxonomic work. It
-is evident that a simple leaf, except those of minute size, possesses
-advantages over a divided leaf in the amount of surface it exposes to
-the light. But in other respects it is at a disadvantage, especially
-as it increases in size, since it casts a deeper shade and does not
-admit of such a free circulation of air. It will be found, however, in
-our study of the relation of leaves to light and air that the balance
-between the leaf and its environment is obtained in the relation of the
-leaves to each other.</p>
-
-<p><b>756. Venation of leaves.</b>—A very prominent character of the
-leaf is its “venation.” This is indicated by the presence of numerous
-“veins,” indicated usually by narrow depressed lines on the upper
-surface, and by more or less distinct elevated lines on the under
-surface. There are two general types: (1) In the corn, Smilacina,
-Solomon’s seal, etc., the veins extend lengthwise of the leaf and
-are nearly parallel. Such leaves are said to be <i>parallel-veined</i>.
-It is generally, though not always, a character of monocotyledenous
-plants. (2) In the elm, rose, hawthorn, maple, oak, etc., the veins
-are not all parallel. The larger ones either diverge from the base
-of the blade (palmate leaf, maple), or the midvein extends through
-the middle line of the leaf, while other prominent ones branch off
-from this and extend, nearly parallel, toward the edge of the leaf
-(pinnate venation). The smaller intermediate veins which are also
-very distinct extend irregularly and branch and anastomose in such a
-fashion as to give the figure of a net with very fine meshes. These
-are <i>netted-veined</i> leaves. These are characteristic of most of the
-dicotyledenous plants. It is evident from what has been said of the
-examples cited that there are two types of netted-veined leaves, the
-<i>palmate</i> and <i>pinnate</i>.
-<span class="pagenum"><a name="Page_389" id="Page_389">[Pg 389]</a></span></p>
-
-<p class="blockquot"><span class="smcap">Note.</span> As we have
-already learned in <a href="#CHAPTER_V">Chapter V</a> the veins contain the vascular
-bundles of the leaf. Through them the water and food solutions are distributed
-to all parts of the leaf, and the return current of food material
-elaborated in the leaf moves back through the bast portion into the
-shoot. The veins also possess a small amount of mechanical tissue. This
-forms the framework of the leaf and aids in giving rigidity to the
-leaf and in holding it in the expanded position. The mechanical tissue
-in the framework alone could not support the leaf. Turgescence of the
-mesophyll is needed in addition.</p>
-
-<p><b>757. Cut or lobed leaves.</b>—In many leaves, the indentations
-on the margin are few and deep. Such leaves present several lobes
-the proportionate size of which is dependent upon the depth of the
-indentation or “incision.” Several of the maples, oaks, birches, the
-poison-ivy, thistles, the dandelion, etc., have lobed leaves. Where
-the indentation reaches to or very near the midrib the leaf is said
-to be cut. A study of various leaves will show all gradations from
-simple leaves with plane edges to those which are cut or divided, as in
-compound leaves, and the lobes are often variously indented.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <p>&nbsp;</p>
-    <img src="images/fig433.jpg" alt="" width="200" height="227" />
-    <p class="center">Fig. 433.<br /> Lobed leaves of oak<br /> forming a mosaic.</p>
-   </div>
-  <div class="figsub">
-      <p>&nbsp;</p>
-      <img src="images/fig434.jpg" alt="" width="250" height="215" />
-      <p class="center">Fig. 434.<br /> Twice compound leaf. Leaflets arranged<br />
-           in one plane, but open spaces permit free<br />
-           circulation of air through the large leaf.</p>
-  </div>
-</div>
-
-<p><b>758. Divided, or compound leaves.</b>—The rose, sumac, elder,
-hickory, walnut, locust, pea, clover, American creeper, etc., are
-examples of divided or compound leaves. The former are pinnately
-compound, and the latter are palmately compound. The leaf of the
-honey-locust is twice pinnately compound or bipinnate, and some are
-<span class="pagenum"><a name="Page_390" id="Page_390">[Pg 390]</a></span>
-three times pinnately compound.<a name="FNanchor_44_44" id="FNanchor_44_44"></a><a href="#Footnote_44_44" class="fnanchor">[44]</a>
-It is evident that compound leaves are only extreme forms of lobed or
-cut leaves and that the form of all bears a definite relation to the
-primary venation. There has been a reduction of mesophyll and of the
-area of smaller venation.</p>
-
-<p><b>759.</b> These forms of leaves probably have some definite
-significance. It is not quite clear why they should have developed as
-they have; though it is possible to explain several important relations
-of these forms to their environment. (1) The reduction of the surface
-of the leaf, with the retention of the firmer portions, allows freer
-movement of the air and affords the leaf greater protection from injury
-during violent winds, just as the finely dissected leaves of some
-water plants are less liable to injury from movement of the more dense
-medium in which they live. It is possible that here we may have an
-explanation of one of the factors involved in this reduction of leaf
-surface. (2) In trees with compound leaves, like the hickory, walnut,
-locust, ailanthus, etc., the midvein, and in the case of the Kentucky
-coffee-tree (Gymnocladus) the primary lateral veins also, serve in
-place of terminal branches of the stem. By the increase in the outline
-of the leaf and the reduction of its surface between the larger veins,
-the tree has attained the same leaf development that it would were the
-<span class="pagenum"><a name="Page_391" id="Page_391">[Pg 391]</a></span>
-larger veins replaced by stems bearing simple leaves. The tree as
-it is, however, has the advantage of being able to cast off for the
-winter period a layer of what otherwise would have been a portion of
-the stem system, to retain which through the winter would use more
-energy than with the present reduced stem system, and the stouter
-stem is less liable to dry out. In the case of herbaceous plants, in
-the case of plants like most of the ferns where the stem is on the
-underground rootstock (Pteris), or a very short erect stem, as in the
-Christmas fern, the leaf replaces the aerial stem, and the division (or
-branching, as it is sometimes styled) of the leaf corresponds to the
-branching of the stem. This is more marked in the gigantic exotics like
-Cibotium regale, and in the tree ferns which have quite tall trunks,
-the massive compound leaves replace branches. In the palms and cycads
-are similar examples. Those who choose to observe can doubtless find
-many examples close at hand. (3) While divided leaves have probably not
-been evolved in response to the light relation, still their relation in
-this respect is an important one, since if the leaf with its present
-size were entire, it would cast too dense a shade on other leaves below.</p>
-
-<p><b>760. General structure of the leaf.</b>—The general structure of
-the leaf has been already studied (see Chapters <a href="#CHAPTER_IV">IV</a>,
-<a href="#CHAPTER_V">V</a>, <a href="#CHAPTER_VII">VII</a>). It is
-only necessary to recall the main points. The upper and lower surfaces
-of the leaf are provided with a layer of cells usually devoid of
-chlorophyll. The mesophyll of the leaf consists usually of a layer of
-palisade cells beneath the epidermis, and the remainder consists of
-loose parenchyma with large intercellular spaces. Through the mesophyll
-course the “veins,” or fibrovascular strands, consisting of the xylem
-and phloem portions and serving as conduits for water, salts, and
-foodstuffs. In the epidermis are the stomata, each one protected by
-the two guard cells. The guard cells as well as the mesophyll contain
-chlorophyll. The stomata and the communicating intercellular spaces
-furnish the avenues for the ingress and egress of gases, and for the
-escape of water vapor.</p>
-
-<p><b>761. Protection of leaves.</b>—There are many modifications of
-the general plan of structure in different leaves, many of them being
-adaptations for the protection of the leaf under adverse or trying
-conditions. Many leaves are also capable of assuming certain positions
-which afford them protection. The discussion of this subject may be presented
-under two general heads: Protective modifications; protective positions.
-<span class="pagenum"><a name="Page_392" id="Page_392">[Pg 392]</a></span></p>
-
-<h4><a name="XL_2" id="XL_2">II. Protective Modification of Leaves.</a></h4>
-
-<p><b>762. General directions in which these modifications have taken
-place.</b>—The usual type of foliage leaf selected is that of
-deciduous trees or shrubs or of our common herbs. Such a leaf is
-usually greatly expanded and thin in order to present as great a
-surface as possible in comparison with its mass, since the kind of
-work which the leaf has to do can be more effectually carried on when
-it possesses this form. This form of leaf is best adapted for work in
-regions where there is a medium amount of moisture such as exists in
-the temperate zones. But since there are very great variations in the
-climatic and soil conditions of these regions, and even greater changes
-in desert and arctic regions, the type of leaf described is unsuited
-for all. Its own life would be endangered, and it would also endanger
-the life of the plant. Modifications have therefore taken place to
-meet these conditions, or at least those plants whose leaves have
-become modified in those directions which are suited to the surrounding
-conditions have been able to persist. Excessive cold or heat, drought,
-winds, intense light, rain, etc., are some of the conditions which
-endanger leaves. The protective modifications of leaves may be grouped
-under four general heads: (1) Structural adaptations; (2) Protective
-covering; (3) Reduction of surface; (4) Elimination of the leaf through
-the complete assumption of the leaf function by the stem.</p>
-
-<div class="figcontainer">
-  <a id="FIG_435" name="FIG_435">&nbsp;</a>
-  <div class="figsub">
-    <p>&nbsp;</p>
-    <img src="images/fig435a.jpg" alt="" width="200" height="224" />
-   </div>
-  <div class="figsub">
-      <p>&nbsp;</p>
-      <img src="images/fig435b.jpg" alt="" width="250" height="221" />
-  </div>
-  <div class="blockquot">
-   <p class="center">Fig. 435.</p>
-   <p>Structure of leaf of Lactuca scariola. Upper one grown in sunlight,
-    palisade cells on both sides. Lower one grown in shade, no palisade tissue.</p>
-  </div>
-</div>
-
-<p><b>763.</b> (1) <b>Structural adaptations.</b>—The general structure
-of the leaf presents certain features which are protective. The
-palisade layer of cells found usually beneath the upper epidermis forms
-a compact layer of long cells which not only acts as a light screen
-cutting off a certain amount of the light, since too intense light
-would be harmful; it also aids in lessening the loss of water from the
-upper surface, where radiation is greater. The stomata are usually on
-the under side of aerial leaves, and the mechanism which closes them
-when the leaf is losing too much water is protective. As a protection
-against intense light the number of palisade layers is sometimes
-<span class="pagenum"><a name="Page_393" id="Page_393">[Pg 393]</a></span>
-increased or the cells of this layer are narrow and long. This is often
-beautifully shown when comparing leaves of the same plant grown in
-strong light with those grown in the shade. The compass plant (Lactuca
-scariola) affords an interesting example. The leaves grown in the light
-are usually vertical, so that the light reaches both sides. Such leaves
-often have all of the mesophyll organized into palisade cells (<a href="#FIG_435">fig. 435</a>),
-while leaves grown in the deep shade may have no palisade cells.</p>
-
-<p><b>764.</b> (2) <b>Protective covering.</b>—<i>Epidermis and
-cuticle.</i>—The walls of the epidermal cells are much thickened in some
-plants. Sometimes this thickening occurs in the outer wall, or both
-walls may be thickened. Variation in this respect as well as the extent
-of the thickening occur in different plants and are often correlated
-with the extremes of conditions which they serve to meet. The cuticle,
-a waxy exudation from the thick wall of the epidermis of many leaves,
-also serves as a protection against too great loss of water, or against
-the leaf becoming saturated with water during rains. The cabbage,
-carnation, etc., have a well-developed cuticle. The effect of the
-cuticle in shedding water can be nicely shown by spraying water on a
-cabbage leaf or by immersing it in water. Sunken stomata also retard
-the loss of water vapor.</p>
-
-<p><i>Covers of hair or scales.</i>—In many leaves certain of the cells of the
-epidermis grow out into the form of hairs or scales of various forms,
-<span class="pagenum"><a name="Page_394" id="Page_394">[Pg 394]</a></span>
-and they serve a variety of purposes. When the hairs form a felt-like
-covering as in the common mullein, some antennarias, etc., they lessen
-the loss of water vapor because the air-currents close to the surface
-of the leaf are retarded. Spines (see the thistles, etc.) also afford a
-protection against certain animals.</p>
-
-<p><b>765.</b> (3) <b>Reduction of surface.</b>—Reduction of leaf surface
-is brought about in a variety of ways. There are two general modes:
-(1st) Reduction of surface along with reduction of mass; (2d) Reduction
-of surface inversely as the mass. Examples of the first mode are
-seen in the dissected leaves of many aquatic plants. In this finely
-dissected condition the mass of the leaf substance is much reduced as
-well as the leaf surface, but the leaf is less liable to be injured
-by movement of the water. In addition it has already been pointed out
-that lobed and divided aerial leaves are much less liable to injury
-from violent movements of the air, than if a leaf with the same general
-outline were entire. The needle leaves of the conifers are also
-examples, and they show as well structural provisions for protection
-in the thick, hard cell-walls of the epidermis. To offset the reduced
-surface there are numerous crowded leaves. Reduction of surface
-inversely as the mass, i.e., the mass of the leaf may not be reduced
-at all, or it may be more or less increased. In other words, there is
-less leaf surface in proportion to the mass of leaf substance. It is
-probable in many cases, example: the crowded, overlapping small scale
-leaves of the juniper, arbor-vitæ, cypress, cassiope, pyxidanthera,
-etc., that there has been a reduction in the size of the leaf, and at
-the same time an increase in thickness. This with the crowding together
-of the leaves and their thick cell-walls greatly lessens the radiation
-of moisture and heat, thus protecting the leaves both in dry and cold
-weather. The succulents, like “live-forever,” have a small amount of
-surface in proportion to the mass of the leaf. In the yucca, though the
-leaves are often large, they are very thick and expose a comparatively
-small amount of surface to the dry air and intense sunlight of the
-desert regions. The epidermal covering is also hard and thick. In
-<span class="pagenum"><a name="Page_395" id="Page_395">[Pg 395]</a></span>
-addition, such leaves, as well as those of many succulents, are so
-thick they provide water storage sufficient for the plants, which
-radiate so slowly from their surface.</p>
-
-<div class="figcenter">
-    <img src="images/fig436.jpg" alt="" width="500" height="344" />
-      <p class="center">Fig. 436.<br />
-          A “Phylloclade,” leaves absent, stems<br />
-          broadened to function as leaves, on the<br />
-          edges numerous flowers are borne.</p>
-</div>
-
-<p><b>766.</b> (4) <b>Elimination of the leaf.</b>—Perhaps the most
-striking illustration of the reduction of leaf surface is in those
-cases where the leaf is either completely eliminated as in certain
-euphorbias, or in certain of the cacti where the leaves are thought
-to be reduced to spines. Whether the cactus spine belongs to the
-leaf series or not, the leaf as an organ for assimilation and
-transpiration has been completely eliminated and the same is true in
-the phylloclades. The leaf function has been assumed by the stem. The
-stem in this case contains all the chlorophyll; is bulky, and provides
-water storage.</p>
-
-<h4><a name="XL_3" id="XL_3">III. Protective Positions.</a></h4>
-
-<p><b>767.</b> In many cases the leaves are arranged either in relation
-to the stem, or to each other, or to the ground, in such a way as to
-give protection from too great radiation of heat or moisture. In the
-<span class="pagenum"><a name="Page_396" id="Page_396">[Pg 396]</a></span>
-examples already cited the imbricated leaves of cassiope, pyxidanthera,
-juniper, etc., come also under this head. In the junipers the leaves
-spread out in the summer, while in the winter they are closely
-overlapped. An interesting example of protective position is to be seen
-in the case of the leaves of the white pine. During quite cold winter
-weather the needles are appressed to the stem, and sometimes the trees
-present a striking appearance in contrast with the spreading position
-of the needles in summer. On windy days in winter, the needles turn
-with the wind and become rigid in that position so that they remain in
-a horizontal position for some time, often until the wind dies down,
-or until milder weather. The following day, should there be a cold
-strong wind from the opposite direction, the needles again assume a
-leeward direction. In quiet weather appressed to the stem and in the
-form of a brush there is less radiation of heat than if they diverged.
-In strong winds by turning in the leeward direction the wind is not
-driven between the needle bases and scales. Some plants, especially
-many of those in arctic and alpine regions, have very short stems and
-the leaves are developed near the ground, or the rock. Lying close on
-the ground they do not feel the full force of the drying winds, there
-is less radiation from them, and the radiation of heat from the ground
-protects them. Many plants exhibit movement in response to certain
-stimuli which place them in a position for protection. Some of these
-examples have been discussed under the head of irritability (see
-<a href="#CHAPTER_XIII">Chapter XIII</a>). The night position of leaves and cotyledons
-presented by many plants, but especially by many of the Leguminosæ, is brought
-about by the removal of the light stimulus at evening. In many leaves,
-when the light influence is removed, the influence of growth turns
-the leaves downward, or the cotyledons of some plants upward. In this
-vertical position of the leaf-blade there is less radiation of heat
-during the cool night. The most striking cases of protection movements
-are seen in the sensitive plant. As we have seen, the leaves of mimosa
-close in a vertical position at midday if the light and heat are too
-strong. Excessive transpiration is thus prevented. At night the vertical
-<span class="pagenum"><a name="Page_397" id="Page_397">[Pg 397]</a></span>
-position prevents excessive radiation of heat. The vertical or profile
-position of the leaves of the compass plant already referred to not
-only lessens transpiration, but the intense heat and light of the
-midday sun is avoided. This profile position is characteristic of
-certain plants in the dry regions of Australia, and the topmost leaves
-of tropical forests.</p>
-
-<h4><a name="XL_4" id="XL_4">IV. Relation of Leaves to Light.</a></h4>
-
-<p><b>768.</b> It is very obvious from our study of the function of the
-foliage leaf that its most important relation to environment is that
-which brings it in touch with light and air. It is necessary that light
-penetrate the leaf tissue that the gases of the air and plant may
-readily diffuse and that water vapor may pass out of the leaf. The thin
-expanded leaf-blade is the most economical and efficient organ for leaf
-work. We have seen that leaves respond to fight stimulus in such a way
-as to bring their upper sides usually to face the source of fight, at
-right angles to it or nearly so (<i>heliotropism</i>, see <a href="#CHAPTER_XIII">Chapter XIII</a>).
-How fully this is brought about depends on the kind of plant, as well as on
-other elements of the environment, for as we have seen in our study of
-<span class="pagenum"><a name="Page_398" id="Page_398">[Pg 398]</a></span>
-leaf protection there is danger to some plants in any region, and to
-other plants in certain regions that the intense light and heat may
-harm the protoplast, or the chlorophyll, or both.</p>
-
-<div class="figcenter">
-    <img src="images/fig437.jpg" alt="" width="500" height="392" />
-      <p class="center space-below2">Fig. 437.<br /> Mosaic form by trailing shoots of<br />
-         Panicum variegatum, “ribbon-grass.”</p>
-</div>
-
-<p>The statement that leaves usually face the light at right angles is to
-be taken as a generalized one. The source of the strongest illumination
-varies on different days and again at different times of the day.
-On cloudy days the zenith is the source of strongest illumination.
-The horizontal position of a leaf, where there are no intercepting
-lateral or superior objects would receive its strongest light rays
-perpendicular to its surface. The fact is, however, that leaves on the
-same stem, because of taller or shorter adjacent stems, are so situated
-that the rays of greatest illuminating power are directed at some angle
-between the zenith and horizon. Many leaves, then, which may have
-their upper sides facing the general source of strongest illumination,
-do not necessarily face the sun, and they are thus protected from
-possible injury from intense light and heat because the direct rays of
-sunlight are for the most part oblique. This does not apply, of course,
-to those leaves which “follow the sun” during the day. Their specific
-constitution is such that intense illumination is beneficial.</p>
-
-<p>The leaf is adjusted as well as may be in different species of varying
-constitution, and under different conditions, to a certain balance in
-its relation to the factors concerned. The problem then is to interpret
-from this point of view the positions and grouping of leaves. Because
-of the specific constitution of different plants, and because of a
-great variety of conditions in the environment, we see that it is a
-more or less complex question.</p>
-
-<div class="figcenter">
-    <img  id="FIG_438" src="images/fig438.jpg" alt="" width="400" height="410" />
-      <p class="center space-below2">Fig. 438.<br />
-       Sunflower with young head<br /> turned toward morning sun.</p>
-</div>
-
-<p><b>769. Day and night positions contrasted.</b>—In many plants the
-day and night positions of the leaves are different. At night the
-leaves assume a position more or less vertical, known as the <i>profile</i>
-position. This is generally regarded as a protective position, since
-during the cool of the night the radiation of heat is less than if the
-leaf were in a vertical position. In many of these plants, however, the
-leaves in assuming the night position become closely appressed which
-would also lessen the radiation. This peculiarity of leaves is largely
-<span class="pagenum"><a name="Page_399" id="Page_399">[Pg 399]</a></span>
-possessed by the members of the family Leguminoseæ (clovers, peas,
-beans, etc.), and by the sensitive plants.<a name="FNanchor_45_45" id="FNanchor_45_45"></a><a href="#Footnote_45_45" class="fnanchor">[45]</a>
-But it is also shared by some other plants as well (oxalis, for
-example). The leaves of these plants are usually provided with a
-mechanism which enables them to execute these movements with ease.
-There is a cushion (<i>pulvinus</i>) of tissue at the base of the petiole,
-and in the case of compound leaves, at the base of the pinnæ and
-pinnules which undergoes changes in turgor in its cells. The collapsing
-of the cells by loss of water into the intercellular spaces causes the
-leaf to droop. When the cells regain their turgor by the absorption
-of the water from the intercellular spaces the leaf is raised to the
-horizontal, or day position. The light stimulus induces turgor of the
-pulvinus, the disappearance of the stimulus is accompanied by a loss of
-turgor. It is a remarkable fact that in some sensitive plants, intense
-<span class="pagenum"><a name="Page_400" id="Page_400">[Pg 400]</a></span>
-light stimuli are alarm signals which result in the same movement as if
-the light stimulus were entirely removed. As we know also contact or
-pressure stimulus, or jarring produces the same result in “sensitive”
-plants like mimosa, some species of rubus, etc. In many plants there is
-no well-developed pulvinus, and yet the leaves show similar movements
-in assuming the day and night positions. Examples are seen in the
-sunflower, and in the cotyledons of many plants. A little observation
-will enable any one interested to discover some of these plants.<a name="FNanchor_46_46" id="FNanchor_46_46"></a><a href="#Footnote_46_46" class="fnanchor">[46]</a>
-In these cases the night position is due to epinastic growth, and
-while this influence is not removed during the day the light stimulus
-overcomes it and the leaf is raised to the day position.</p>
-
-<div class="figcenter">
-    <img  id="FIG_439" src="images/fig439.jpg" alt="" width="400" height="380" />
-      <p class="center space-below2">Fig. 439.<br />
-        Same sunflower plant photographed<br /> just at sundown.</p>
-</div>
-
-<p><b>770. Leaves which rotate with the sun.</b>—During the growth period
-the leaves of the sunflower as well as the growing end of the stem
-respond readily to the direct sunlight. The response is so complete
-that during sunny days the leaves toward the growing end of the stem
-are drawn close together in the form of a rosette and the entire
-<span class="pagenum"><a name="Page_401" id="Page_401">[Pg 401]</a></span>
-rosette as well as the end of the stem are turned so that they face the
-sun directly. In the morning under the stimulus of the rising sun the
-rosette is formed and faces the east. All through the day, if the sun
-continues to shine, the leaves follow it, and at sundown the rosette
-faces squarely the western horizon. For a week or more the young
-sunflower head will also face the sun directly and follow it all day as
-surely as the rosette of leaves. At length, a little while before the
-flowers in the head blossom, the head ceases to turn, but the rosette
-of leaves and the stem also, to some extent, continue to turn with the
-sun. When the leaves become mature they also cease to turn. This is
-well shown in all three photographs (figs. <a href="#FIG_438">438</a>-<a href="#FIG_439">439</a>).
-The lower leaves on the stem being older have assumed the fixed horizontal
-position usually characteristic of the plant with cylindrical habit.</p>
-
-<div class="figcenter">
-    <img src="images/fig440.jpg" alt="" width="400" height="366" />
-      <p class="center space-below2">Fig. 440.<br />
-             Same plant a little older when the head<br />
-             does not turn, but the stem and leaves do.</p>
-</div>
-
-<p>It is not true, as is commonly supposed, that the fully opened
-sunflower head turns with the sun. But I have observed young heads
-four or five inches in diameter rotate with the sun all day. This is
-because the growing end of the stem as well as the young head responds
-to the light stimulus. So there is some truth as well as a great deal
-<span class="pagenum"><a name="Page_402" id="Page_402">[Pg 402]</a></span>
-of fiction in the popular belief that the sunflower head follows the
-sun. The young head will follow the sun all day even if all the leaves
-are cut off, and the growing stem will also if all the leaves as well
-as the flower head are cut away. Young seedlings will also turn even if
-the cotyledons and plumule are cut off.</p>
-
-<p>This phenomenon of the rotation of leaves with the sun is much more
-general than one would infer, as may be seen from a little careful
-observation of rapidly growing plants on bright sunny days. In Alabama
-I have observed beautiful rosettes of <i>Cassia marilandica</i> rotate with
-the sun all day. The peculiarity is very striking in the cotton plant,
-especially when the rows extend north and south. In the forenoon or
-afternoon it is most striking as the entire row shows the leaves tilted
-up facing the sun. There are many of our weeds and common flowers of
-field and garden which show this rotation of the leaves. Some of these
-form rotating rosettes; while in others the leaves rotate independently
-as in the sweet clover.</p>
-
-<p><b>771. Fixed position of old leaves.</b>—In many of the cases cited
-in the preceding paragraph, the rotation of the leaf only occurs
-on sunny days. During cloudy days the leaves of the sunflower, for
-example, are in a nearly horizontal position, or the lower ones may
-be somewhat oblique, since the stronger illumination on such a plant
-would be the oblique rays rather than the zenith rays. As the leaves
-reach maturity also the epinastic growth is equalized by hyponastic
-growth so that the growth movements bring the leaf to stand in a nearly
-horizontal position, or that position in which it receives the best
-illumination. In age, then, many leaves have a fixed position and this
-corresponds with the position assumed on cloudy days.</p>
-
-<p><b>772. Position on horizontal stems.</b>—On horizontal stems the
-leaves have a horizontal position, and if such a stem is stood in an
-erect position the appearance is very odd. If the leaf arises directly
-from the horizontal stem, its petiole will be twisted part way around
-in order to bring the face of the leaf uppermost. It is interesting
-to observe the different relation of stem, petiole and blade and the
-<span class="pagenum"><a name="Page_403" id="Page_403">[Pg 403]</a></span>
-amount of twisting as the horizontal stem or vine trails over irregularities
-in the surface, or climbs over and through other vegetation.</p>
-
-<p><b>773. Position of leaflets on divided leaves.</b>—An interesting
-comparison can be made with entire, lobed, divided and dissected
-leaves. The entire leaf usually lies in one plane, since usually the
-problem of adjustment is the same for the entire surface. So the lobes
-of a leaf usually lie all in the same plane as they would if the leaf
-were entire. We find the same is true usually of the compound leaf.
-It forms an incomplete mosaic. Some of the pieces having been removed
-allow much of the light to pass through to leaves beneath. Leaves,
-especially those of some size rarely lie in a flat plane. Some are more
-or less depressed. Some curve downward. Compound leaves often curve
-more or less and the leaflets often droop more or less in a graceful
-fashion. It is interesting, however, that these far separated leaflets
-all lie in the same general plane. This is because the area of the
-leaf, if not too large, makes the problem of position with reference
-to light much the same as if the leaf were entire. The leaflets or
-divisions, though separated, are laminate, and they can work more
-efficiently facing the light. But suppose we extend our observation to
-the finely dissected capillary leaves of some of the parsley family
-(Umbelliferæ), or to the upper leaves of the fennel-leaved thoroughwort
-(Eupatorium fœniculaceum) among the aerial plants, and to Myriophyllum
-among the aquatic plants. The divisions are thread-like or cylindrical.
-One side of the leaflet is just as efficient when presented to the
-light as another. As a result the leaflets are not arranged in the same
-plane, but stand out in many directions.</p>
-
-<p>Occasionally one finds a divided or compound leaf in such a position
-that one portion, because of being shaded above, receives the stronger
-light stimulus from the side, while the other portion is lighted from
-above. If this relation continues throughout the growth-period of the
-leaf the leaflets of one portion may lie in a different plane from
-those of the other portion. In such cases, some of the leaflets are
-permanently twisted to bring them into their proper light relation.
-<span class="pagenum"><a name="Page_404" id="Page_404">[Pg 404]</a></span></p>
-
-<h4><a name="XL_5" id="XL_5">V. Leaf Patterns.</a></h4>
-
-<h5>MOSAICS, OR CLOSE PATTERNS.</h5>
-
-<div class="figcenter">
-    <img  id="FIG_441" src="images/fig441.jpg" alt="" width="600" height="411" />
-  <div class="blockquot">
-      <p class="center">Fig. 441.</p>
-      <p>Fittonia showing leaves arranged to form compact mosaic. The netted
-       venation of the leaf is very distinctly shown in this plant.
-      (Photo by the Author.)</p>
-  </div>
-</div>
-
-<p><b>774.</b> Where the leaves of a plant, or a portion of a plant, are
-approximate and arranged in the form of a pattern, the leaves fitting
-together to form a more or less even and continuous surface, such
-patterns are sometimes termed “mosaics,” since the relation of leaves
-to one another is roughly like the relation of the pieces of a mosaic.
-A good illustration of a mosaic is presented by a greenhouse plant
-Fittonia (<a href="#FIG_441">fig. 441</a>). The stems are prostrate and the erect
-branches quite short, but it may have quite a wide system by the spreading of
-the runners; the branches of such a length that the leaves borne near
-the tips all fit together forming a broad surface of leaves so closely
-fitted together often that the stems cannot be seen. The advantage of
-a mosaic over a separate disposition of leaves at somewhat different
-levels is that the leaves do not shade one another. Were all the light
-rays coming down at right angles to the leaves, there would not be
-any shading of the lower ones, but the oblique rays of light would be
-cut off from many of the leaves. In the case of a mosaic all the rays
-of light play upon all the leaves. Some of the mosaics which can be
-observed are as follows:
-<span class="pagenum"><a name="Page_405" id="Page_405">[Pg 405]</a></span></p>
-
-<div class="figcenter">
-    <img src="images/fig442.jpg" alt="" width="400" height="450" />
-      <p class="center">Fig. 442.<br /> Rosette pattern of leaves.</p>
-</div>
-
-<p><b>775. Rosette pattern.</b>—The rosette pattern is presented by
-many plants with “radial” leaves, or leaves which arise in a cluster
-near the surface of the ground, and are thus more or less crowded in
-their arrangement on the stem. The pretty gloxinia often presents fine
-examples of a loose rosette. In the rosette pattern the petioles of
-the lower leaves are longer than the upper ones, and the blade is thus
-carried out beyond the inner leaves. The leaves being so crowded in
-their attachment to the stem lie very nearly in the same plane.</p>
-
-<p><b>776. Vines and climbers.</b>—Some of the most extensive mosaic
-patterns are shown in creeping and climbing vines. A very common
-example is that of the ivies trained on the walls of buildings,
-covering in some instances many square yards of surface. Where the
-vines trail over the ground or clamber over other vegetation, it is
-interesting to observe the various patterns, and the distortion of
-petioles brought about by turning of the leaves. Of examples found in
-greenhouses, the Pellonia is excellent, and the trailing ribbon-grass
-often forms loose mosaics.</p>
-
-<p><b>777. Branch patterns.</b>—These patterns are very common. They
-are often formed in the woods on the ends of branches by the leaves
-adjusting themselves so as to largely avoid shading each other. <a href="#FIG_443">Figure 443</a>
-illustrates one of them from a maple branch. It is interesting to
-note the way in which the leaves fit themselves in the pattern, how in
-some the petioles have elongated, while others have remained short. Of
-course, it should be understood that the pattern is made during the
-growth of the leaves.
-<span class="pagenum"><a name="Page_406" id="Page_406">[Pg 406]</a></span></p>
-
-<div class="figcenter">
-    <img  id="FIG_443" src="images/fig443.jpg" alt="" width="400" height="316" />
-      <p class="center">Fig. 443.<br /> Spray of leaves of striped maple,<br />
-           showing different lengths of leafstalks.</p>
-</div>
-<div class="figcenter">
-    <img src="images/fig444.jpg" alt="" width="400" height="429" />
-      <p class="center">Fig. 444.<br /> Cedar of Lebanon, strong light only<br />
-             from one side of tree (Syria).</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_407" id="Page_407">[Pg 407]</a></span>
-<b>778. The tree pattern.</b>—Mosaics are often formed by the exterior
-foliage on a tree, though they are rarely so regular as some of those
-mentioned above. Still it is common to see in some trees with drooping
-limbs like the elm, beautiful and large mosaics. The weeping elm
-sometimes forms a very close and quite even pattern over the entire
-outer surface. In most trees the leaf arrangement is not such as to
-form large patterns, but is more or less open. While the conifers do
-not form mosaics there are many interesting examples of grouping of
-foliage on branch systems into broadly expanded areas, as seen in the
-branches of white pine trees, especially in the edge of a wood, or as
-seen in the arbor-vitæ.</p>
-
-<h5>OTHER PATTERNS.</h5>
-
-<p><b>779. Imbricate pattern of short stems.</b>—This pattern is quite
-common, and differs from the rosette in that the leaves are distributed
-further apart on the stem so that the central ones are considerably
-higher up than in the mosaic. The lower petioles are longer, as in
-the rosette, so that the outer lower leaves extend further out. Some
-begonias show fine imbricate patterns.</p>
-
-<div class="figcenter">
-    <img src="images/fig445.jpg" alt="" width="400" height="335" />
-      <p class="center">Fig. 445.<br /> Imbricate pattern of leaves;<br /> Begonia.</p>
-</div>
-
-<p><b>780. Spiral patterns.</b>—They are very common on stems of the
-cylindrical type, which are unbranched, or but little branched. The
-sunflower, mullein, chrysanthemum, as it is grown in greenhouses, the
-Easter lily, etc., are examples. The spiral arrangement of the leaves
-provides that each successive leaf on the stem, as one ascends the
-stem, is a little to one side so that it does not cast shade on the leaf
-<span class="pagenum"><a name="Page_408" id="Page_408">[Pg 408]</a></span>
-just below. In some stems, according to the leaf arrangement (or
-phyllotaxy), one would pass several times around in ascending the stem
-before a leaf would be found directly above another, which would be
-such a distance below that it would not be shaded to an appreciable
-extent. Interesting observations can be made on different plants to
-work out the relation of distance of leaves on the stem to length of
-the upper and lower leaves; the number of vertical rows on the stem
-compared to the width of the leaves; and the relation of these facts to
-the problem of light supply. Related to the spiral pattern is that of
-erect stems with opposite leaves. Here each pair is set at right angles
-to the direction of the pair above or below.</p>
-
-<div class="figcenter">
-    <img src="images/fig446.jpg" alt="" width="400" height="383" />
-  <div class="blockquot">
-      <p class="center">Fig. 446.</p>
-      <p>Palm showing radiate arrangement of leaves and the petiole of the
-          leaf functions as stem in lifting leaf to the light.</p>
-  </div>
-</div>
-
-<p><b>781. Radiate pattern.</b>—This pattern is present in many grasses
-and related plants with narrow leaves and short stems. The leaves are
-often very crowded at the base, but by radiating in all directions from
-<span class="pagenum"><a name="Page_409" id="Page_409">[Pg 409]</a></span>
-the horizontal to the vertical, abundant exposure to light is gained
-with little shading. The dragon tree screw-pine, and plants grown in
-greenhouses also illustrate this type. It is also shown in cycads,
-palms, and many ferns, although these have divided leaves.</p>
-
-<div class="figcenter">
-    <img  id="FIG_447" src="images/fig447.jpg" alt="" width="400" height="466" />
-  <div class="blockquot">
-      <p class="center">Fig. 447.</p>
-      <p>Screw-pine (Pandanus) showing prop roots and
-          radiate pattern of leaves.</p>
-  </div>
-</div>
-
-<p><b>782. Compass plants.</b>—These plants with vertical leaf
-arrangement, and exposure of both surfaces to the lateral rays of light
-have been mentioned in other sections (Lactuca scariola).</p>
-
-<p><b>783. Open patterns.</b>—Open patterns are presented by divided or
-“branched” leaves. Where the leaves are very finely dissected, they may
-be clustered in great profusion and yet admit sufficient light for some
-depth below. Where the leaflets are broader, the leaves are likely to
-be fewer in number and so arranged as to admit light to a great depth
-so that successive leaves below on the same or adjacent stems may not
-be too much shaded. On such plants, often the leaves lying next the
-ground are entire or less divided.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_410" id="Page_410">[Pg 410]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XLI" id="CHAPTER_XLI">CHAPTER XLI.</a><br />
-<span class="h_subtitle">THE ROOT.</span></h3>
-</div>
-
-<h4><a name="XLI_1" id="XLI_1">I. Function of Roots.</a></h4>
-
-<p><b>784.</b> The most obvious function of the roots of ordinary
-plants are two: 1st, To furnish anchorage and partial support, and
-2d, absorption of liquid nutriment from the soil. The environmental
-relation of such roots, then, in broad terms, is with the soil. It is
-very clear that in some plants the root serves both functions, while in
-other plants the root may fulfil only one of these requirements.</p>
-
-<p>The problems which the plant has to solve in working out these
-relations are:</p>
-
-<ul class="index">
-<li class="isub1">(1) Permeation of the soil or substratum.</li>
-<li class="isub1">(2) Grappling the substratum.</li>
-<li class="isub1">(3) A congenial moisture or water relation.</li>
-<li class="isub1">(4) Distribution of roots for the purpose of reaching food-laden soil.</li>
-<li class="isub1">(5) Exposure of surface for absorption.</li>
-<li class="isub1">(6) The renewal of the delicate structures for absorption.</li>
-<li class="isub1">(7) Aid in preparation of food from raw material.</li>
-<li class="isub1">(8) The maintenance of the required balance between the environment</li>
-<li class="isub3">as a whole and the increasing or changing requirements of the plant.</li>
-</ul>
-
-<p><b>785.</b> (1) <b>Permeation of the soil or substratum.</b>—The
-fundamental divergence of character in the environmental relations of
-root and stem are manifest as soon as they emerge from the germinating
-seed. Under the influence of the same stimulus (<i>gravity</i>) the root
-<span class="pagenum"><a name="Page_411" id="Page_411">[Pg 411]</a></span>
-shows its geotropic character by growing downward, while the geotropic
-character of the stem is shown in its upward growth.</p>
-
-<p>The medium which the root has to penetrate offers considerable
-resistance, and the form of the root as well as its manner of growth is
-adapted to overcome this difficulty. The slender, conical, penetrating
-root-tip wedges its way between the minute particles of soil or into
-the minute crevices of the rock, while the nutation of the root enables
-it to search for the points of least resistance. The root-tips having
-penetrated the soil, the older portions of the root continue this wedge
-action by growth in diameter, though, of course, elongation of the old
-parts of the root does not take place. It is the widening growth of the
-tapering root that produces the wedge-like action. The crevices of the
-rock are sometimes broadened, but the resistance here is so great, the
-root is often greatly flattened out.</p>
-
-<p><b>786.</b> (2) <b>Grappling the substratum.</b>—The mere penetration
-of a single root into the soil gives it some hold on the soil and it
-offers some resistance to a “pull” since it has wedged its way in
-and the contact of soil particles offers resistance. The root hairs
-formed on the first entering root growing laterally in great numbers
-and applying themselves very closely to the soil particles, increase
-greatly the hold of the plant on the soil, as one can readily see by
-pulling up a young seedling. Lateral roots are soon formed, and as
-these continue to extend and ramify in all directions, the hold is
-increased until in the case of some of the larger plants the resistance
-their hold would offer would equal many tons. Even in some of the
-smaller shrubs and herbs the resistance is considerable, as one can
-easily test by pulling with the hand. To obtain some idea of the amount
-of resistance the roots of these smaller plants offer, they can be
-tested by pulling with the ordinary spring scales.</p>
-
-<p><b>787.</b> (3) <b>A congenial moisture, or water relation.</b>—In
-general, the roots seek those portions of the soil provided with a
-modicum of moisture. Usually a suitable moisture condition is present
-in those portions of the soil containing the plant food. But if
-portions of the soil are too dry and very nearby other portions
-<span class="pagenum"><a name="Page_412" id="Page_412">[Pg 412]</a></span>
-containing moisture, the roots grow mainly into the moist substratum
-(<i>hydrotropism</i>). If the soil is too wet, the roots grow away from it
-to soil with less water, or in some cases will grow to and upon the
-surface of the soil.</p>
-
-<p>The roots need <i>aeration</i>, and where the supply of water is too great,
-the air is shut out, and we know that corn, wheat, and many other
-plants become “sickly” in low and undrained soil in wet seasons. This
-can only be said in the case of our ordinary dry land plants, i.e.,
-those that occupy an intermediate position between <i>water-loving</i>
-plants and <i>dry-conditioned</i> plants. This phase of the subject must be
-reserved for special treatment. (See <a href="#CHAPTER_XLVI">Chapter XLVI</a>.)</p>
-
-<p><b>788.</b> (4) <b>Distribution of roots for the purpose of reaching
-food-laden soil.</b>—This is one of the essential relations of the
-root in the case of the land plant, and probably accounts for the very
-extensive ramification of the roots. To some extent it also explains
-the different root systems in some plants. The pines, spruces, etc.,
-usually grow in regions where the soil is very shallow. The root
-system does not extend deeply into the soil. It spreads laterally and
-extends widely through the shallow surface soil and presents a very
-different aspect from the stem system in the air. The root system of
-the broad-leaved trees usually extends more deeply into the soil, while
-of course, extending laterally to great distances. The hickory, walnut,
-etc., especially have strong tap-roots which extend deeply into the
-soil, and the root system of such a tree is more comparable in aspect,
-if it were entirely uncovered, to the stem system in the air. The
-tap-root is more pronounced in some trees than in others. It may be
-that in the hickory and walnut the deep tap-root is important in
-supplying the tree with water in dry seasons, especially when growing
-on dry, gravelly soil which does not retain moisture on the surface
-nor hold it within two or three feet of the surface. Experiment has
-demonstrated, by pot culture of plants, that where soil rich in plant
-food lies adjacent to poor soil, no matter in what part of the pot the
-rich soil is, the greatest growth and branching of roots is in the rich soil.
-<span class="pagenum"><a name="Page_413" id="Page_413">[Pg 413]</a></span></p>
-
-<p><b>789.</b> (5) <b>Exposure of root surface for absorption.</b>—The
-principal part of root absorption takes place in the young root and
-the root hairs growing near the root-tip. The root-tips and root hairs
-in their relation to the root systems on which they are borne are
-not to be compared morphologically with the leaves and stem system.
-But the root-tips and hairs are absorbing organs of the roots while
-the main root system supports them, brings them into relation with
-the soil and moisture, and conducts food and other substances to and
-from them. One of the important relations of the leaf is that of
-light, and since the source of light is restricted, i.e., it is not
-equally strong from all sides, an expanded and thin leaf-blade is more
-effective than an equal expenditure of plant material in the form of
-thread-like outgrowths. It is different, however, with the plant food
-dissolved in the soil water. It is equally accessible on all sides. A
-greater surface for absorption is exposed with the same expenditure of
-material by multiplication of the organs and a reduction in their size.
-Numerous delicate root hairs present a greater absorbing surface than
-if the same amount of material were massed into leaf-like expansions.
-There is another important advantage also. Its slender roots and
-thread-like root hairs allow greater freedom of circulation of water,
-food solutions, and air than if the absorbing organs of the roots were
-broadly expanded.</p>
-
-<p><b>790.</b> (6) <b>The renewal of the delicate structures for
-absorption.</b>—The delicate root hairs are easily injured. The thin
-cell-walls through which food solutions flow become more or less choked
-by the gradual deposit of substances in solution in the water, and
-continued growth of the root in diameter forms a firmer epidermis and
-cortex through which the solutions taken up by the root hairs would
-pass with difficulty. For this reason new root hairs are constantly
-being formed on the growing root-tip throughout the growing season,
-and in the case of perennial plants, through each season of their growth.</p>
-
-<p><b>791.</b> (7) <b>Aid in preparation of food from raw
-materials.</b>—For most plants the food obtained from the soil is
-already in solution in the soil water. But there are certain substances
-<span class="pagenum"><a name="Page_414" id="Page_414">[Pg 414]</a></span>
-(examples, some of the chemical compounds of potash, phosphoric acid,
-etc.) which are insoluble in water. Certain acids excreted by the
-roots aid in making these substances soluble (see <a href="#CHAPTER_III">Chapter III</a>).
-In a number of plants the roots have become associated with fungus or
-bacterial organisms which assist in the manufacture of nitrogenous food
-substances, or even in the absorption of ordinary food solution from
-the soil, or in making use of the decaying humus of the forest
-(see <a href="#CHAPTER_IX">Chapter IX</a>).</p>
-
-<p><b>792.</b> (8) <b>The maintenance of the required balance between
-the environment and the increasing or changing requirements of the
-plant.</b>—In this matter the entire plant participates. Mention is
-made here only of the general relation which the root sustains to its
-own environment and the increased burden placed upon it by the shoot.
-The increase in the root system keeps pace with the increasing size of
-the stem system. The roots become stronger, their ramifications wider,
-and the number of absorbing rootlets more numerous. The observation
-is sometimes offered that the correlation between the root system of
-a plant, and the form of the stem system and position of the leaves,
-is of such a nature that plants with a tap-root system have their
-leaves so arranged as to shed the water to the center of the system,
-while plants with a fibrous-root system have their leaves so arranged
-as to shed the water outward. In support of this attention is called
-to the radiate type of the leaf system of the dandelion, beet, etc.
-In the second place the imbricate type as manifested in broad-leaved
-trees, and in the overlapping branch systems of many pines, etc. One
-should note, however, that in the former class the leaves are often
-arranged to shed as much water outward as inward. As to the latter
-class, there is need of experiment to determine whether these empirical
-observations are correct, for the following reasons: 1st, Root and leaf
-distribution are governed by other and more important laws, the root
-being influenced by the location of food in the soil which usually
-forms a very thin stratum while the shoot and leaf is mainly influenced
-by light, and root distribution is much wider in a lateral direction
-<span class="pagenum"><a name="Page_415" id="Page_415">[Pg 415]</a></span>
-than that of the branches. 2d, In light rains the leaf surface holds
-back practically all the rain which is then evaporated into the air
-and lost to the root systems. 3d, In heavy and long-continued rains
-the water breaks through the leaf system to such an extent that roots
-under the tree would be as well supplied as those outside, and the
-ground outside being saturated anyway, the roots do not need the
-small additional water which may have been shed outward. 4th, It is
-the habit of plants where left undisturbed (except in rare cases), to
-grow in more or less dense formations or societies. Here there is no
-opportunity for any appreciable centrifugal distribution of rainfall
-and yet the root distribution is practically the same, except that the
-root systems of adjacent plants are interlaced.</p>
-
-<h4><a name="XLI_2" id="XLI_2">II. Kinds of Roots.</a></h4>
-
-<p><b>793. The root system.</b>—From the foregoing, it will be understood
-that the roots of a plant taken together form the <i>root system</i> of that
-plant. In soil-roots in general we usually recognize two kinds of root
-systems.</p>
-
-<p><b>794. The fibrous-root system.</b>—Roots which are composed of
-numerous slender branching roots resembling “fibers,” are termed
-<i>fibrous</i>, or the plant is said to have a <i>fibrous-root system</i>. The
-bean, corn, most grasses, and many other plants have fibrous-root systems.</p>
-
-<p><b>795. The tap-root system.</b>—Plants with a recognizable central
-shaft-like root, more or less thickened and considerably stouter
-than the lateral roots, are said to have <i>tap</i> roots, or they have a
-<i>tap-root system</i>. The dandelion, beet, carrot (see crown tuber) are
-examples. The hickory, walnut, and some other trees have very prominent
-tap-roots when young. The tap-root is maintained in old age, but the
-lateral roots often become finally as large as the tap-root. Besides
-tap-roots and fibrous-roots, which include the larger number, several
-other kinds of roots are to be enumerated.</p>
-
-<p><b>796. Aerial roots.</b>—Aerial roots are most abundantly developed
-in certain tropical plants, especially in the orchids and aroids. Many
-<span class="pagenum"><a name="Page_416" id="Page_416">[Pg 416]</a></span>
-examples of these plants are grown in conservatories. The amount of
-moisture is so great in these tropical regions that the roots are
-abundantly supplied without the soil relation. Certain of the roots
-hang free in the air and are provided with a special sheath of spongy
-tissue called the <i>velamen</i>, through which moisture is absorbed from
-the air. Other roots attach themselves to the trunk or branches of
-the tree on which the orchid is growing, and furnish the support to
-the <i>epiphyte</i>, as such plants are often called. Among the tangle
-of these clinging roots falling leaves are caught. Here they decay
-and nourishing roots grow from the clinging roots into this mass
-of decaying leaves and supply some of the plant food. Aerial roots
-sometimes possess chlorophyll.</p>
-
-<p>There are a number of plants, however, in temperate regions which
-have aerial roots. These are chiefly used to give the stem support as
-it climbs on trees or on walls. They are sometimes called clinging
-roots. A common example is the climbing poison-ivy (Rhus radicans), the
-trumpet creeper, etc. Such aerial roots are called <i>adventitious</i> roots.</p>
-
-<p><b>797. Bracing roots, or prop roots.</b>—These are developed in a
-great variety of plants and serve to brace or prop the plant where
-the fibrous-root system is insufficient to support the heavy shoot
-system, or the shoot system branches so widely props are needed to hold
-up the branches. In the common Indian corn several whorls of bracing
-roots arise from the nodes near the ground and extend outward and
-downward to the ground, though the upper whorls do not always succeed
-in reaching the ground. The screw-pine so common in greenhouses affords
-an excellent example of prop roots. The roots are quite large, and long
-<span class="pagenum"><a name="Page_417" id="Page_417">[Pg 417]</a></span>
-before the root reaches the soil the large root cap is evident. The
-banyan tree of India is a classic example of prop roots for supporting
-the wide-reaching branches. The mangrove in our own subtropical forests
-of Florida is a nearer example.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <img src="images/fig448.jpg" alt="" width="250" height="260" />
-    <p class="center">Fig. 448.<br /> Bracing roots of Indian corn.</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig449.jpg" alt="" width="250" height="244" />
-   <p class="center">Fig. 449.<br  /> Buttresses of silk-cotton tree,<br /> Nassau.</p>
-  </div>
-</div>
-
-<p><b>798. Buttresses</b> are formed at the junction of the root and
-trunk, and therefore are part root and part stem. Splendid examples
-of buttresses are formed on the silk-cotton tree. They are sometimes
-formed on the elm and other trees in low swampy ground.</p>
-
-<p><b>799. Fleshy roots, or root tubers.</b>—These are enlargements of
-the root in the form of tubers, as in the sweet potato, the dahlia,
-etc. They are storage reservoirs for food. Portions of the roots become
-thick and fleshy and contain large quantities of sugar, as in the sweet
-potato, or of <i>inulin</i> (a carbohydrate) in the root tubers of the
-dahlia and other composites.</p>
-
-<p><b>800. Water-roots and roots of water plants.</b>—These are roots
-which are developed in the water, or in the soil. Water-roots are
-<span class="pagenum"><a name="Page_418" id="Page_418">[Pg 418]</a></span>
-sometimes formed on land plants where the root comes in contact with a
-body of water, or a stream. Water-roots usually possess no root hairs,
-or but a few, as can be seen by comparing water-roots with soil-roots,
-or by comparing roots of plants grown in water cultures. The greater
-body of water in contact with the root and the more delicate epidermis
-of the root render less necessary the root hairs. The duck-meats
-(Lemna) are good examples of plants having only water-roots. Other
-aquatic plants like the potamogetons, etc., have true roots which grow
-into the soil and serve to anchor the plant, but they are not developed
-as special organs of absorption, since the stem and leaves largely
-perform this function.</p>
-
-<p><b>801. Holdfasts.</b>—These are organs for anchorage which are not
-true roots. These are especially well developed in some of the algæ
-(Fucus, Laminaria, etc.). They are usually called <i>holdfasts</i>. The
-holdfasts of the larger algæ are mainly for anchoring the plant. They
-do not function as absorbing organs, and the structure is different
-from that of true roots.</p>
-
-<p><b>802. Haustoria or suckers</b> is a name applied to another kind of
-holdfast employed by parasitic plants. In the dodder the haustorium
-penetrates the tissue of the <i>host</i> (the plant on which the parasite
-grows), and besides furnishing a means of attachment, it serves as an
-absorbing organ by means of which the parasite absorbs food from its
-host. The parasitic fungi like the powdery mildews which grow on the
-surface of their hosts have simple haustoria which serve both as organs
-of attachment and absorption, while in the rusts which grow in the
-interior of their hosts the haustoria are merely absorbing organs.</p>
-
-<p><b>803. Rootlets, or rhizoids.</b>—Many of the algæ, liverworts and
-mosses have slender, hair-like organs of attachment and absorption.
-These plants do not have true roots. Because of the slender form and
-small size of these organs, they are called <i>rhizoids</i>, or <i>rootlets</i>.
-In form many of them resemble the root hairs of higher plants.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_419" id="Page_419">[Pg 419]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XLII" id="CHAPTER_XLII">CHAPTER XLII.</a><br />
-<span class="h_subtitle">THE FLORAL SHOOT.</span></h3>
-</div>
-
-<h4><a name="XLII_1" id="XLII_1">I. The Parts of the Flower.</a></h4>
-
-<p>The portion of the stem on which the flowers are borne is the <i>flower</i>
-shoot or axis, or taken together with the flowers, it is known as the
-<i>Flower Cluster</i>.</p>
-
-<p><b>804. The flower.</b>—The flower is best understood by an
-examination, first of one of the types known as a “complete” flower,
-as in the buttercup, the spring-beauty, the blood-root, the apple, the
-rose, etc.</p>
-
-<p>There are two sets of organs or members in the complete flower—(1) the
-floral envelope; (2) the essential or necessary members or organs.</p>
-
-<p>The floral envelope when complete consists of—1st, an outer envelope,
-the <i>calyx</i>, made up of several leaf-like structures (<i>sepals</i>), very
-often possessing chlorophyll, which envelop all the other parts of the
-flower when in bud; 2d, an inner envelope, the <i>corolla</i>, also made up
-of several leaf-like parts (<i>petals</i>), usually bright colored and larger
-than the sepals. The outer and inner floral envelopes are usually in
-whorls (though in close spirals in many of the buttercup family, etc.),
-and for reasons discussed elsewhere (<a href="#CHAPTER_XXXIV">Chapter XXXIV</a>)
-represent leaves. The essential or necessary members of the flower are also usually
-in whorls and likewise represent leaves, but only in rare cases is there
-any suggestion, either in their form or color, of a leaf relationship.
-These members are in two sets: (1) The outer, or <i>andrœcium</i>,
-consisting of a few or many parts (<i>stamens</i>); (2) the inner set, the
-<i>gynœcium</i>, consisting of a few or many parts (<i>carpels</i>).
-<span class="pagenum"><a name="Page_420" id="Page_420">[Pg 420]</a></span></p>
-
-<p><b>805. Purpose of the flower.</b>—While the ultimate purpose of
-all plants is the production of seed or its equivalent through
-which the plant gains distribution and perpetuation, the flower is
-the specialized part of the seed plant which utilizes the food and
-energies contributed by other members of the plant organization for the
-production of seed. In addition to this there are definite functions
-performed by the members of the flower, which come under the general
-head of plant work, or flower work.</p>
-
-<p><b>806. The calyx, or the sepals.</b>—These are chiefly protective,
-affording protection to the young stamens and carpels in the flower
-bud. Where the corolla is absent, sepals are usually present and then
-assume the function of the petals. In a few instances the calyx may
-possibly ultimately join in the formation of the fruit (examples: the
-butternut, walnut, hickory).</p>
-
-<p><b>807. The corolla, or petals.</b>—The petals are partly protective
-in the bud, but their chief function where well developed seems to be
-that of attracting insects, which through their visits to the flower
-aid in “<i>pollination</i>,” especially “<i>cross pollination</i>.”</p>
-
-<p><b>808. The stamens.</b>—The stamens (= microsporophylls) are
-flower organs for the production of <i>pollen</i>, or <i>pollen-spores</i> (=
-microspores). The <i>stalk</i> (not always present) is the <i>filament</i>, the
-<i>anther</i> is borne on the filament when the latter is present. The
-anther consists of the <i>anther sacs</i> or <i>pollen sacs</i> (microsporangium)
-containing the pollen-spores, and the <i>connective</i>, the sterile tissue
-lying between and supporting the anther sac. The stamens are usually
-separate, but sometimes they are united by their filaments, or by their
-anthers. When the pollen is ripe they open by slits or pores and the
-pollen is scattered; or in rarer cases the pollen mass (<i>pollinium</i>) is
-removed through the agency of insects (<a href="#CHAPTER_XLIII">see Insect pollination, Chap. XLIII</a>).</p>
-
-<p><b>809. The pistil.</b>—The pistil consists of the “<i>ovary</i>,” the
-<i>style</i> (not always present), and the <i>stigma</i>. These are well shown in
-a <i>simple pistil</i>, common examples of which are found in the buttercup,
-marsh marigold, the pea, bean, etc. The simple pistil is equivalent to
-a <i>carpel</i> (= macrosporophyll), while the <i>compound pistil</i> consists of
-<span class="pagenum"><a name="Page_421" id="Page_421">[Pg 421]</a></span>
-two or several carpels joined, as in the toothwort, trillium, lily,
-etc. The <i>ovary</i> is the enlarged part which below is attached to
-the receptacle of the flower, and contains within the <i>ovules</i>. The
-<i>style</i>, when present, is a slender elongation of the upper end of
-the ovary. The <i>stigma</i> is supported on the end of the style when the
-latter is present. It is often on a capitate enlargement of the style
-or extends down one side, or when the style is absent it is usually
-seated directly on the upper end of the ovary. The stigmatic surface is
-glutinous or “sticky,” and serves to hold the pollen-spores when they
-come in contact with it.</p>
-
-<p>The <i>ovules</i> are within the ovary and are arranged in different ways
-in different plants. The pollen grain (or better pollen-spore =
-microspore), after it has been transferred to the stigma, “germinates,”
-and the pollen tube grows down through the tissue of the stigma and
-style, or courses down the stylar canal until it reaches the ovule.
-Here it usually enters the ovule (macrosporangium) at the <i>micropyle</i>
-(in some of the ament-bearing plants it enters at the <i>chalaza</i>), and
-the sperm cells are emptied into the embryo sac in the interior of the ovule.</p>
-
-<p><b>810. Fertilization.</b>—One of the sperms unites with the egg
-in the embryo sac. This is <i>fertilization</i>, and from the fertilized
-egg the young embryo is formed still within the ovule. <i>Double
-fertilization</i>,—the other sperm cell sometimes unites with one or both
-of the “polar” nuclei which have united to form the “definitive” or
-“endosperm” nucleus. As a result of fertilization, the embryo plant is
-formed within the ovule, the coats of which enlarge by growth forming
-the seed coats, and altogether forming the seed. (See <a href="#CHAPTER_XXXIV">Chapters XXXIV</a>,
-<a href="#CHAPTER_XXXV">XXXV</a>, <a href="#CHAPTER_XXXVI">XXXVI</a>.)</p>
-
-<h4><a name="XLII_2" id="XLII_2">II. Kinds of Flowers.</a></h4>
-
-<p><b>811. Absence of certain flower parts.</b>—The <i>complete</i> flower
-contains all the four series of parts. When any one of the series of
-parts is lacking, the flower is said to be <i>incomplete</i>. Where only one
-series of the floral envelopes is present the flowers are said to be
-<i>apetalous</i> (the petals are absent), examples: elm, buckwheat, etc.
-<span class="pagenum"><a name="Page_422" id="Page_422">[Pg 422]</a></span>
-Flowers which lack both floral envelopes are <i>naked</i>. When pistils are
-absent but stamens are present the flowers are <i>staminate</i>, whether
-floral envelopes are present or not; and so when stamens are absent and
-pistils present the flower is <i>pistillate</i>. If both stamens and pistils
-are absent the flower is said to be <i>sterile</i> or <i>neutral</i> (snowball,
-marginal or showy flowers in hydrangea). Flowers with both stamens and
-pistils, whether or not they have floral envelopes, are <i>perfect</i> (or
-hermaphrodite), so if only one of these sets of <i>essential organs</i>
-of the flower is present the flower is <i>imperfect</i>, or <i>diclinous</i>.
-Sometimes the imperfect, or diclinous, flowers are on the same plant,
-and the plant is said to be <i>monœcious</i> (of one household). When
-staminate flowers are on certain individual plants, and the pistillate
-flowers of the same species are on other individuals, the plant is
-<i>diœcious</i> (or of two households). When some of the flowers of a plant
-are diclinous and others are perfect, they are said to be <i>polygamous</i>.</p>
-
-<p>Many of these variations relating to the presence or absence of flower
-parts in one way or another contribute to the well-being of the plant.
-Some indicate a division of labor; thus in the neutral flowers of
-certain species of hydrangea or viburnum, the showy petals serve to
-attract insects which aid in the pollination of the fertile flowers. It
-must not be understood, however, that all variations in plants which
-results in new or different forms of flowers is for the good of the
-species. For example, under cultivation the flowers of viburnum and
-hydrangea sometimes are all neutral and showy. While such variations
-sometimes contribute to the happiness of man, the plant has lost the
-power of developing seed. In diclinous flowers cross pollination is
-necessitated.</p>
-
-<p><b>812. Form of the flower.</b>—The flower as a whole has <i>form</i>.
-This is so characteristic that in general all flowers of the different
-individuals of a species are of the same shape, though they may vary
-in size. In general, flowers of closely related plants of different
-species are of the same type as to form, so that often in the shape of
-the flower alone we can see the relationship of kind, though the form
-of the flower is not the most important nor always the sure index of
-<span class="pagenum"><a name="Page_423" id="Page_423">[Pg 423]</a></span>
-kinship. Since many flowers resemble certain familiar objects, names
-are often used which relate to these objects.</p>
-
-<p>Flowers are said to be <i>regular</i>, or <i>irregular</i>. In a regular flower
-all of the parts of a set or series are of the same shape and size,
-while in irregular flowers the parts are of a different shape or size
-in some of the sets. The flowers of the pea family (<i>Papilionaceæ</i>),
-of the mint family (<i>Labiatæ</i>), of the morning glory, larkspur,
-monkshood, etc., are irregular (<a href="#FIG_450">fig. 450</a>). The corolla
-usually gives the characteristic form to the flower, and the name is usually
-applied to the form of the corolla.</p>
-
-<div class="figcenter">
-    <img  id="FIG_450" src="images/fig450.jpg" alt="" width="600" height="232" />
-  <div class="blockquot">
-      <p class="center">Fig. 450.</p>
-      <p>Several forms of flowers. Regular flowers. <i>wh</i>, wheel-shaped
-         corolla; <i>sa</i>, salver-shaped; <i>tub</i>, tubular-shaped. Irregular flowers.
-         <i>pa</i>, butterfly or papilionaceous; <i>per</i>, personate or masked flower;
-         <i>lab</i>, gaping or ringent corolla. The two latter are called bilabiate flowers.</p>
-  </div>
-</div>
-
-<p>Some of the different forms are wheel-shaped or <i>rotate</i> corolla when
-the petals spread out at once like the spokes of a wheel, as in the
-potato, tomato, or bittersweet; <i>salver-shaped</i> when the petals spread
-out at right angles from the end of a corolla tube, as in the phlox;
-<i>bell-shaped</i>, or <i>campanulate</i>, as in the harebell or campanula;
-<i>funnel-shaped</i>, as in the morning glory; <i>tubular</i>, when the ends of
-the petals spread but little or none from the end of the corolla tube,
-as in the turnip flower or in the disk florets of the composites. The
-<i>butterfly</i>, or <i>papilionaceous</i> corolla is peculiar as in the pea
-or bean. The upper petal is the “banner,” the two lateral ones the
-“wings,” and the two lower the “keel.”</p>
-
-<p>The <i>labiate</i> corolla is characteristic of the mint family where the
-<span class="pagenum"><a name="Page_424" id="Page_424">[Pg 424]</a></span>
-gamosepalous corolla is unequally divided, so that the two upper lobes
-are sharply separated from the three lower forming two “lips.” The
-labiate corolla of the toad-flax, or snapdragon is <i>personate</i>, or
-<i>masked</i>, because the lower lip arches upward like a palate and closes
-the entrance to the corolla tube; that of the dead nettle (<i>Lamium</i>) is
-<i>ringent</i> or <i>gaping</i>, because the lips are spread wide apart. In
-some plants the labiate corolla is not very marked and differs but slightly
-from a regular form.</p>
-
-<p>The <i>ligulate</i> or <i>strap-shaped</i> corolla is characteristic of
-the flowers of the dandelion or chicory, or of the ray flowers of other
-composites (<a href="#FIG_451">fig. 451</a>). The lower part of the gamosepalous
-corolla is tubular, and the upper part is strap-shaped, as if that part of the
-tube were split on one side and spread out flat.</p>
-
-<p>These forms of the flower should be studied in appropriate examples.</p>
-
-<p><b>813. Union of flower parts.</b>—In the buttercup flower all the
-parts of each series are separate from one another and from other
-series of parts. Each one is attached to the <i>receptacle</i> of the
-flower, which is a very much shortened portion of the flower axis.
-The calyx being composed of separate and distinct parts is said to be
-<i>polysepalous</i>, and the corolla is likewise <i>polypetalous</i>. The stamens
-are <i>distinct</i>, and the pistils are <i>simple</i>. In many flowers, however,
-there is a greater or lesser <i>union</i> of parts.</p>
-
-<p><b>814. Union of parts of the same series or cycle.</b>—The parts
-<i>coalesce</i>, either slightly or to a great extent. Usually they are not
-so completely coalesced but what the number of parts of the series can
-be determined. Where the sepals are united the calyx is <i>gamosepalous</i>,
-when the petals are united the corolla is <i>gamopetalous</i>.</p>
-
-<p>Union of the sepals or of the corolla is quite common, but union
-of the stamens is rare except in a few families where it is quite
-characteristic. When the stamens are united by their anthers, they
-are <i>syngenœsious</i>. This is the case in most flowers of the composite
-family. When all the stamens are united into one group by their
-filaments, they are <i>monadelphous</i> (one brotherhood), as in
-<span class="pagenum"><a name="Page_425" id="Page_425">[Pg 425]</a></span>
-hollyhock, hibiscus, cotton, marsh-mallow, etc. When they are united
-by their filaments in two groups, they are <i>diadelphous</i> (two
-brotherhoods), as in the pea and most members of the pea family. In
-most species of St. John’s wort (Hypericum), the stamens are united in
-threes (<i>triadelphous</i>).</p>
-
-<p><b>815. The carpels are often united.</b>—The pistil is then said to
-be <i>compound</i>. Where the pistils are consolidated, usually the adjacent
-walls coalesce and thus separate the cavity of each ovary. Each cavity
-in the compound pistil is a <i>locule</i>. In some cases the adjacent walls
-disappear so that there is one common cavity for the compound pistil
-(examples: purslane, chickweeds, pinks, etc.). In a few cases there is a
-false partition (example, in the toothwort and other crucifers). The
-compound pistil is very often lobed slightly, so that the different
-pistils can be discerned. More often the styles or stigmas are
-distinct, and thus indicate the number of pistils united.</p>
-
-<p><b>816. Union of the parts of different series.</b>—While in the
-buttercup and many other flowers, all the different parts are inserted
-on the torus or receptacle, in other flowers one series of parts may
-be joined to another. This is <i>adnation</i> of parts, or the two or more
-series are <i>adnate</i>. In the morning glory the stamens are inserted
-on the inner face of the corolla tube; the same is true in the mint
-family, and there are many other examples. The insertion of parts,
-whether free or adnate, is usually spoken of in reference to their
-relation to the pistil. Thus, in the buttercup the floral envelopes and
-stamens are all free and <i>hypogynous</i>, they are <i>below</i> the pistil.
-The pistil in this case is <i>superior</i>. In the cherry, pear, etc., the
-petals and stamens are borne on the edge of the more or less elevated
-tube of the calyx, and are said to be <i>perigynous</i>, i.e., around the
-pistil. In the cranberry, huckleberry, etc., the calyx is for the
-most part united with the wall of the ovary with the short calyx
-limbs projecting from the upper surface. The petals and stamens are
-inserted on the edge of the calyx above the ovary; they are, therefore,
-<i>epigynous</i>, and the ovary being under the calyx, as it were, is
-<i>inferior</i>.
-<span class="pagenum"><a name="Page_426" id="Page_426">[Pg 426]</a></span></p>
-
-<h4><a name="XLII_3" id="XLII_3">III. Arrangement of Flowers, or Mode of Inflorescence.</a></h4>
-
-<p><b>817. Flowers are solitary or clustered.</b>—<i>Solitary flowers</i>
-are more simple in their arrangement, i.e., it is easier for us to
-determine and name their relation to each other and to other parts of
-the plant. They are either <i>axillary</i>, i.e., on short lateral shoots
-in the axils of ordinary foliage leaves, or they are <i>terminal</i>, i.e.,
-they are borne on the end of the main axis of an ordinary foliage
-shoot. In either case they are so far separated, and the foliage
-leaves are so prominent, they do not form recognizable groups or
-clusters. The manner of arrangement of flowers on the shoot is called
-<i>inflorescence</i>, while the group of flowers so arranged is the
-<i>flower cluster</i>.</p>
-
-<p>Two different modes of inflorescence are usually recognized in
-the arrangement of flowers on the stem. (1) The <i>corymbose</i>, or
-<i>indeterminate inflorescence</i> (also indefinite inflorescence), in
-which the flowers arise from axillary buds, and the terminal bud may
-continue to grow. (2) The <i>cymose</i> or <i>determinate inflorescence</i>
-(also <i>definite inflorescence</i>) in which the flowers arise from terminal
-buds. This arrests the growth of the shoot in length.</p>
-
-<p>There are several advantages to the plant in the different modes of
-inflorescence, chief among which is the massing of the flowers, thus
-increasing the chances for effective pollination.</p>
-
-<p class="center"><b>A. FLOWER CLUSTERS WITH INDETERMINATE<br /> INFLORESCENCE.</b></p>
-
-<p><b>818. The simplest mode of indeterminate inflorescence</b> is where
-the flowers arise in the axils of normal foliage leaves, while the
-terminal bud, as in the florist’s smilax, the bellwort, moneywort,
-apricot, etc., continues to grow. The flowers are <i>solitary</i> and
-<i>axillary</i>. In other cases which are far more numerous, the flowers are
-associated into more or less definite clusters in which are a number
-of recognizable types. The word type used in this sense, it should be
-<span class="pagenum"><a name="Page_427" id="Page_427">[Pg 427]</a></span>
-understood, does not refer to an original structure which is the
-source of others. It merely refers to a mode of inflorescence which we
-attempt to recognize, and about which we group those forms which have
-a resemblance to one another. There are many forms of flower clusters
-which do not conform to any one of our recognized types, and are very
-puzzling. The evolution of the flower clusters has been <i>natural</i>, and
-we cannot make them all conform to an <i>artificial</i> classification.
-These <i>types</i> are named merely as a matter of convenience in the
-expression of our ideas. The types usually recognized are as follows:</p>
-
-<p><b>819. The raceme.</b>—The flower-shoot is more or less elongated,
-and the leaves are reduced to a minute size termed <i>bracts</i>, while the
-flowers on lateral axes are solitary in the axils of the bracts. The
-reduction in the size of the leaves and the somewhat limited growth
-of the shoot in length, makes the flowers more prominent, and brings
-them into closer relation than if they were formed in the axils of
-the leaves on the ordinary foliage shoot. The choke cherry, currant,
-pokeweed, sourwood, etc., are examples of a raceme (fig. 569). In most
-plants with the raceme type, while the inflorescence is indeterminate,
-and the uppermost flowers (those toward the end of the main shoot)
-are younger, still the period of flowering is somewhat restricted
-and the raceme stops growing. In a few plants, however, as in the
-common “shepherd’s-purse,” the raceme continues to grow throughout the
-summer, so that the lower flowers may have ripened their seed while
-the terminal portion of the raceme is still growing and producing
-new flowers. Compound racemes are formed when by branching of the
-flower-shoot there are several racemes in a cluster, as in the false
-Solomon’s seal (Smilacina racemosa).</p>
-
-<p><b>820. The panicle.</b>—The panicle is developed from the raceme type
-by the branching of the lateral flower-axes forming a loose open flower
-cluster, as in the <i>oat</i>.</p>
-
-<p><b>821. The thyrsus</b> is a compact panicle of pyramidal form, as in
-the lilac, horse-chestnut, etc.</p>
-
-<p><b>822. The corymb.</b>—The corymb shows likewise an easy transition
-<span class="pagenum"><a name="Page_428" id="Page_428">[Pg 428]</a></span>
-from the raceme type, by the shortening of the main axis of
-inflorescence, and the lengthening of the lower, lateral flower
-peduncles so that the flower cluster is more or less flattened on
-top. This represents the <i>simple corymb</i>. A <i>compound corymb</i> is one
-in which some of the flower peduncles branch again forming secondary
-corymbs, as in the mountain-ash. It is like a panicle with the lower
-flower stalks elongated.</p>
-
-<p><b>823. The umbel.</b>—The umbel is developed from the raceme, or
-corymb. The main flower-shoot remains very short or undeveloped with
-several flowers on long peduncles arising close together around this
-shortened axis, in the form of a whorl or cluster. Examples are found
-in the milkweed, water pennywort (Hydrocotyle), the oxheart cherry,
-etc. A <i>compound</i> umbel is one in which the peduncles are branched,
-forming secondary umbels, as in the caraway, parsnip, carrot, etc.</p>
-
-<p><b>824. The spike.</b>—In the spike the main axis is long, and the
-solitary flowers in the axils of the bracts are usually sessile, and
-often very much crowded. The plaintain, mullein (<a href="#FIG_422">fig. 422</a>),
-etc., are examples. The spike is a raceme, only the flowers are sessile
-and crowded. In the grasses the flower cluster is branched, and the
-branchlets bearing a few flowers are spikelets.</p>
-
-<p><b>825. The head.</b>—When the flower axis is very much shortened
-and the flowers crowded and sessile or nearly so, forming a globose
-or compressed cluster, it is a <i>head</i> or <i>capitulum</i>. The transition
-is from a spike by the shortening of the main axis, as in the clover,
-button bush (<i>Cephalanthus</i>), etc., or in the shortening of the
-peduncles in an umbel, as in the daisy, dandelion, and other composite
-flowers. In these the head is surrounded by an involucre, which in
-the young head often envelopes the mass of flowers, thus affording
-them protection. In some other composites (Lactuca, for example) the
-involucre affords protection for a longer period, even while the seeds
-are ripening.</p>
-
-<p><b>826. The spadix.</b>—When the main axis of the flower cluster is
-fleshy, the spike or head forms a <i>spadix</i>, as in the Indian turnip,
-the skunk-cabbage, the calla, etc. The spadix is usually more or less
-enclosed in a <i>spathe</i>, a somewhat strap-shaped leaf.</p>
-
-<p><b>827. The catkin.</b>—A spike which is usually caducous, i.e., falls
-<span class="pagenum"><a name="Page_429" id="Page_429">[Pg 429]</a></span>
-away after the maturity of the flower or fruit, is called a catkin,
-or an <i>ament</i>. The flower clusters of the alder, willow, (fig. 555),
-poplar, and the staminate flower clusters of the oak, hickory,
-hazel, birch, etc., are <i>aments</i>. So characteristic is this mode
-of inflorescence that the plants are called <i>amentiferous</i>, or
-<i>amentaceous</i>.</p>
-
-<div class="figcenter">
-    <img  id="FIG_451" src="images/fig451.jpg" alt="" width="400" height="483" />
-  <div class="blockquot">
-      <p class="center">Fig. 451.</p>
-      <p>Head of sunflower showing centripetal inflorescence of tubular
-          flowers. (Photo by the Author.)</p>
-  </div>
-</div>
-
-<p><b>828. Anthesis of flowers with indeterminate inflorescence.</b>—In
-the anthesis of the raceme as well as in other corymbose forms the
-lower (or outer) flowers being older, open first. The opening of the
-flowers then takes place from below, upward; or from the outside,
-inward toward the center of inflorescence. The <i>anthesis</i>, i.e., the
-opening of the flowers of corymbose forms is said to be <i>centripetal</i>,
-i.e., it progresses from outside, inward. The anthesis of the fuller’s
-teazel is peculiar, since it shows both types. There are several
-<span class="pagenum"><a name="Page_430" id="Page_430">[Pg 430]</a></span>
-distinct advantages to the plant where anthesis extends over a period
-of time, as it favors cross pollination, favors the formation of seed
-in case conditions should be unfavorable at one period of anthesis,
-distributes the drain on the plant for food, etc.</p>
-
-<div class="figcenter">
-    <img src="images/fig452.jpg" alt="" width="600" height="312" />
-  <div class="blockquot">
-      <p class="center">Fig. 452.</p>
-      <p class="center">Heads of fuller’s teazel in different stages of flowering.</p>
-  </div>
-</div>
-
-<p class="center"><b>B. FLOWER CLUSTERS WITH DETERMINATE<br /> INFLORESCENCE.</b></p>
-
-<p><b>829. The simplest mode of determinate inflorescence</b> is a plant
-with a solitary terminal flower, as in the hepatica, the tulip,
-etc. The leaves in these two plants are clustered in the form of a
-rosette, and the aerial shoot is naked and bears the single flower at
-its summit. Such a flower-shoot is a <i>scape</i>. As in the case of the
-indeterminate inflorescence, so here the larger number of flower-shoots
-are more complex and specialized, resulting in the evolution of flower
-clusters or masses. Accompanying the association of flowers into
-clusters there has been a reduction in leaf surface on the flower-shoot
-so that the flowers predominate in mass and are more conspicuous. Among
-the recognized modes of determinate inflorescence, the following are
-the chief ones:</p>
-
-<p><b>830. The cyme.</b>—In the cyme the terminal flower on the main axis
-opens first and the remaining flowers are borne on lateral shoots,
-<span class="pagenum"><a name="Page_431" id="Page_431">[Pg 431]</a></span>
-which arise from the axils of leaves or bracts, below. These lateral
-shoots usually branch and elongate so that the terminal flowers on all
-the branches reach nearly the same height as the terminal flower on the
-main shoot, forming a somewhat flattened or convex top of the flower
-cluster. This is illustrated in the basswood flower. The anthesis of
-the cyme is <i>centrifugal</i>, i.e., from the inside outward to the margin.
-But it is often more or less mixed, since the lateral shoots if they
-bear more than one flower are diminutive cymes and the terminal flower
-opens before the lateral ones. Where the flower cluster is quite large
-and the branching quite extensive, <i>compound cymes</i> are formed, as in
-the dogwood, hydrangea, etc.</p>
-
-<div class="figcenter">
-    <img  id="FIG_453" src="images/fig453.jpg" alt="" width="600" height="265" />
-  <div class="blockquot">
-      <p class="center">Fig. 453.</p>
-      <p>Diagrams of cymose inflorescence. <i>A</i>, dichasium; <i>B</i>, scorpioid
-         cyme; <i>C</i>, helicoid cyme. (After Strasburger.)</p>
-  </div>
-</div>
-
-<p><b>831. The helicoid cyme.</b>—Where successive lateral branching
-takes place, and always continues on the same side a curved flower
-cluster is formed, as in the forget-me-not and most members of the
-borage family. This is known as a <i>helicoid cyme</i> (<a href="#FIG_453">fig. 453, <i>C</i></a>).
-Each new branch becomes in turn the “false” axis bearing a new branch on the
-same side.</p>
-
-<p><b>832. The scorpioid cyme.</b>—<i>A scorpioid cyme</i> (<a href="#FIG_453">fig. 453, <i>B</i></a>)
-is formed where each new branch arises on alternate sides of the “false” axis.</p>
-
-<p><b>833. The forking cyme</b> is where each “false” axis produces two
-branches opposite, so that it represents a false dichotomy (example,
-the flower cluster of chickweed).
-<span class="pagenum"><a name="Page_432" id="Page_432">[Pg 432]</a></span></p>
-
-<p><b>834.</b> Some of these flower clusters are peculiar and it is
-difficult to see how the helicoid, or scorpioid, cymes are of any
-advantage to the plant over a true cyme. The inflorescence of the
-plant being determinate, if the flowering is to be extended over a
-considerable period a peculiar form would necessarily result. In the
-<i>helicoid cyme</i> continued branching takes place on one side, and
-the result in the forget-me-not is a continued inflorescence in its
-effect like that of a continued raceme (compare shepherd’s-purse).
-But we should not expect that all of the complex and specialized
-structures from simple and generalized ones are beneficial to the
-plant. In many plants we recognize evolution in the direction of
-advantageous structures. But since the plant cannot consciously
-evolve these structures, we must also recognize that there may be
-phases of retrogression in which the structures evolved are not so
-beneficial to the plant as the more simple and generalized ones of its
-ancestors. Variation and change do not result in advancing the plant
-or plant structures merely along the lines which will be beneficial.
-The tendency is in all directions. The result in general may be
-diagramed by a tree with divergent and wide-reaching branches. Some die
-out; others remain subordinate or dormant; while still others droop
-downward, showing a retrogression. But in this backward evolution
-they do not return to the condition of their ancestors, nor is the
-same course retraced. A new downward course is followed just as the
-downward-growing branch follows a course of its own, and does not
-return in the trunk.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_433" id="Page_433">[Pg 433]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XLIII" id="CHAPTER_XLIII">CHAPTER XLIII.</a><br />
-<span class="h_subtitle">POLLINATION.</span></h3>
-</div>
-
-<p class="center"><b>Origin of heterospory, and the necessity<br /> for pollination.</b></p>
-
-<p><b>835. Both kinds of sexual organs on the same prothallium.</b>—In
-the ferns, as we have seen, the sexual organs are borne on the
-prothallium, a small, leaf-like, heart-shaped body growing in moist
-situations. In a great many cases both kinds of sexual organs are
-borne on the same prothallium. While it is perhaps not uncommon, in
-some species, that the egg-cell in an archegonium may be fertilized
-by a spermatozoid from an antheridium on the same prothallium, it
-happens many times that it is fertilized by a spermatozoid from another
-prothallium. This may be accomplished in several ways. In the first
-place antheridia are usually found much earlier on the prothallium than
-are the archegonia. When these antheridia are ripe, the spermatozoids
-escape before the archegonia on the same prothallium are mature.</p>
-
-<p><b>836. Cross fertilization in monœcious prothallia.</b>—By swimming
-about in the water or drops of moisture which are at times present in
-these moist situations, these spermatozoids may reach and fertilize
-an egg which is ripe in an archegonium borne on another and older
-prothallium. In this way what is termed cross fertilization is brought
-about nearly as effectually as if the prothallia were diœcious, i.e. if
-the antheridia and archegonia were all borne on separate prothallia.</p>
-
-<p><b>837. Tendency toward diœcious prothallia.</b>—In other cases
-some fern prothallia bear chiefly archegonia, while others bear only
-antheridia. In these cases cross fertilization is enforced because
-of this separation of the sexual organs on different prothallia.
-These different prothallia, the male and female, are largely due to a
-difference in food supply, as has been clearly proven by experiment.</p>
-
-<p><b>838. The two kinds of sexual organs on different prothallia.</b>—In
-the horsetails (equisetum) the separation of the sexual organs on
-different prothallia has become quite constant. Although all the spores
-are alike, so far as we can determine, some produce small male plants
-<span class="pagenum"><a name="Page_434" id="Page_434">[Pg 434]</a></span>
-exclusively, while others produce large female plants, though in some
-cases the latter bear also antheridia. It has been found that when the
-spores are given but little nutriment they form male prothallia, and
-the spores supplied with abundant nutriment form female prothallia.</p>
-
-<p><b>839. Permanent separation of sexes by different amounts of nutriment
-supplied the spores.</b>—This separation of the sexual organs of
-different prothallia, which in most of the ferns, and in equisetum, is
-dependent on the chance supply of nutriment to the germinating spores,
-is made certain when we come to such plants as isoetes and selaginella.
-Here certain of the spores receive more nutriment while they are
-forming than others. In the large sporangia (macrosporangia) only a few
-of the cells of the spore-producing tissue form spores, the remaining
-cells being dissolved to nourish the growing macrospores, which are few
-in number. In the small sporangia (microsporangia) all the cells of the
-spore-producing tissue form spores. Consequently each one has a less
-amount of nutriment, and it is very much smaller, a microspore. The
-sexual nature of the prothallium in selaginella and isoetes, then, is
-predetermined in the spores while they are forming on the sporophyte.
-The microspores are to produce male prothallia, while the macrospores
-are to produce female prothallia.</p>
-
-<p><b>840. Heterospory.</b>—This production of two kinds of spores
-by isoetes, selaginella, and some of the other fern plants is
-<i>heterospory</i>, or such plants are said to be <i>heterosporous</i>.
-Heterospory, then, so far as we know from living forms, has originated
-in the fern group. In all the higher plants, in the gymnosperms and
-angiosperms, it has been perpetuated, the microspores being represented
-by the pollen, while the macrospores are represented by the embryo sac;
-the male organ of the gymnosperms and angiosperms being the antherid
-cell in the pollen or pollen tube, or in some cases perhaps the pollen
-grain itself, and the female organ in the angiosperms perhaps reduced
-to the egg-cell of the embryo sac.</p>
-
-<p><b>841. In the pteridophytes water serves as the medium for conveying
-the sperm cell to the female organ.</b>—In the ferns and their allies,
-as well as in the liverworts and mosses, surface water is a necessary
-medium through which the generative or sperm cell of the male organ,
-the spermatozoid, may reach the germ cell of the female organ. The
-sperm cell is here motile. This is true in a large number of cases
-in the algæ, which are mostly aquatic plants, while in other cases
-currents of water float the sperm cell to the female organ.</p>
-
-<p><b>842. In the higher plants a modification of the prothallium is
-necessary.</b>—As we pass to the gymnosperms and angiosperms,
-however, where the primitive phase (the gametophyte) of the plants
-has become dependent solely on the modern phase (the sporophyte) of
-the plant, surface water no longer serves as the medium through which
-a motile sperm cell reaches the egg-cell to fertilize it. The female
-<span class="pagenum"><a name="Page_435" id="Page_435">[Pg 435]</a></span>
-prothallium, or macrospore, is, in nearly all cases, permanently
-enclosed within the sporangium, so that if there were motile sperm
-cells on the outside of the ovary, they could never reach the egg to
-fertilize it.</p>
-
-<p><b>843.</b> But a modification of the microspore, the pollen tube,
-enables the sperm cell to reach the egg-cell. The tube grows through
-the nucellus, or first through the tissues of the ovary, deriving
-nutriment therefrom.</p>
-
-<p><b>844.</b> But here an important consideration should not escape us.
-The pollen grains (microspores) must in nearly all cases first reach
-the pistil, in order that in the growth of this tube a channel may be
-formed through which the generative cell can make its way to the egg
-cell. The pollen passes from the anther locule, then, to the stigma of
-the ovary. This process is termed <i>pollination</i>.</p>
-
-<p class="center"><b>Pollination.</b></p>
-
-<p><b>845. Self pollination, or close pollination.</b>—Perhaps very few
-of the admirers of the pretty blue violet have ever noticed that there
-are other flowers than those which appeal to us through the beautiful
-colors of the petals. How many have observed that the brightly colored
-flowers of the blue violet rarely “set fruit”? Underneath the soil
-or débris at the foot of the plant are smaller flowers on shorter,
-curved stalks, which do not open. When the anthers dehisce, they are
-lying close upon the stigma of the ovary, and the pollen is deposited
-directly upon the stigma of the same flower. This method of pollination
-is <i>self pollination</i>, or <i>close pollination</i>. These small, closed
-flowers of the violet have been termed “<i>cleistogamous</i>,” because they
-are pollinated while the flower is closed, and fertilization takes
-place as a result.</p>
-
-<p>But self pollination takes place in the case of some open flowers.
-In some cases it takes place by chance, and in other cases by such
-movements of the stamens, or of the flower at the time of the
-dehiscence of the pollen, that it is quite certainly deposited upon the
-stigma of the same flower.</p>
-
-<p><b>846. Wind pollination.</b>—The pine is an example of
-wind-pollinated flowers. Since the pollen floats in the air or
-is carried by the “wind,” such flowers are <i>anemophilous</i>. Other
-anemophilous flowers are found in other conifers, in grasses, sedges,
-many of the ament-bearing trees, and other dicotyledons. Such plants
-produce an abundance of pollen and always in the form of “dust,” so
-that the particles readily separate and are borne on the wind.</p>
-
-<p><b>847. Pollination by insects.</b>—A large number of the plants which
-we have noted as being anemophilous are monœcious or diœcious, i.e. the
-stamens and pistils are borne in separate flowers. The two kinds of
-flowers thus formed, the male and the female, are borne either on the
-same individual (monœcious) or on different individuals (diœcious). In
-<span class="pagenum"><a name="Page_436" id="Page_436">[Pg 436]</a></span>
-such cases cross pollination, i.e. the pollination of the pistil of
-one flower by pollen from another, is sure to take place, if it is
-pollinated at all. Even in monœcious plants cross pollination often
-takes place between flowers of different individuals, so that more
-widely different stocks are united in the fertilized egg, and the
-strain is kept more vigorous than if very close or identical strains
-were united.</p>
-
-<div class="figcenter">
-    <img src="images/fig454.jpg" alt="" width="500" height="507" />
-  <div class="blockquot">
-      <p class="center">Fig. 454.</p>
-      <p>Viola cucullata; blue flowers above, cleistogamous flowers smaller
-             and curved below. Section of pistil at right.</p>
-  </div>
-</div>
-
-<p><b>848.</b> But there are many flowers in which both stamens and
-pistils are present, and yet in which cross pollination is accomplished
-through the agency of insects.</p>
-
-<p><b>859. Pollination of the bluet.</b>—In the pretty bluet the stamens
-and styles of the flowers are of different length as shown in figures
-<a href="#FIG_455">455</a>, <a href="#FIG_456">456</a>. The stamens
-of the long-styled flower are at about the same
-level as the stigma of the short-styled flower, while the stamens of
-<span class="pagenum"><a name="Page_437" id="Page_437">[Pg 437]</a></span>
-the latter are on about the same level as the stigma of the former.
-What does this interesting relation of the stamens and pistils in the
-two different flowers mean? As the butterfly thrusts its “tongue” down
-into the tube of the long-styled flower for the nectar, some of the
-pollen will be rubbed off and adhere to it. When now the butterfly
-visits a short-styled flower this pollen will be in the right position
-to be rubbed off onto the stigma of the short style. The positions
-of the long stamens and long style are such that a similar cross
-pollination will be effected.</p>
-
-<div class="figcenter">
-    <img  id="FIG_455" src="images/fig455.jpg" alt="" width="600" height="259" />
-  <div class="blockquot">
-      <p class="center">Fig. 455.</p>
-      <p>Dichogamous flower of the bluet (Houstonia cœrulea), the long-styled form.</p>
-  </div>
-</div>
-<div class="figcenter">
-    <img  id="FIG_456" src="images/fig456.jpg" alt="" width="600" height="276" />
-  <div class="blockquot">
-      <p class="center">Fig. 456.</p>
-      <p>Dichogamous flower of bluet (Houstonia cœrulea), the short-styled form.</p>
-  </div>
-</div>
-
-<p><b>850. Pollination of the primrose.</b>—In the primroses, of which
-we have examples growing in conservatories, that blossom during the
-winter, we have almost identical examples of the beautiful adaptations
-for cross pollination by insects found in the bluet. The general shape
-<span class="pagenum"><a name="Page_438" id="Page_438">[Pg 438]</a></span>
-of the corolla is the same, but the parts of the flower are in
-fives, instead of in fours as in the bluet. While the pollen of the
-short-styled primulas sometimes must fall on the stigma of the same
-flower, Darwin has found that such pollen is not so potent on the
-stigma of its own flower as on that of another, an additional provision
-which tends to necessitate cross pollination.</p>
-
-<div class="figcenter">
-    <img src="images/fig457.jpg" alt="" width="600" height="257" />
-      <p class="center">Fig. 457.<br /> Dichogamous flowers of primula.</p>
-</div>
-
-<p>In the case of some varieties of pear trees, as the Bartlett, it
-has been found that the flowers remain largely sterile not only to
-their own pollen, or pollen of the flowers on the same tree, but to
-all flowers of that variety. However, they become fertile if cross
-pollinated from a different variety of pear.</p>
-
-<p><b>851. Pollination of the skunk’s cabbage.</b>—In many other flowers
-cross pollination is brought about through the agency of insects,
-where there is a difference in time of the maturing of the stamens and
-pistils of the same flower. The skunk’s cabbage (Spathyema fœtida),
-though repulsive on account of its fetid odor, is nevertheless a very
-interesting plant to study for several reasons. Early in the spring,
-before the leaves appear, and in many cases as soon as the frost is out
-of the hard ground, the hooked beak of the large fleshy spathe of this
-plant pushes its way through the soil.</p>
-
-<p>If we cut away one side of the spathe as shown in <a href="#FIG_459">fig. 459</a>
-we shall have the flowering spadix brought closely to view. In this spadix the
-pistil of each crowded flower has pushed its style through between the
-plates of armor formed by the converging ends of the sepals, and stands
-out alone with the brush-like stigma ready for pollination, while the
-stamens of all the flowers of this spadix are yet hidden beneath. The
-insects which pass from the spadix of one plant to another will, in
-crawling over the projecting stigmas, rub off some of the pollen which
-has been caught while visiting a plant where the stamens are scattering
-their pollen. In this way cross pollination is brought about. Such
-flowers, in which the stigma is prepared for pollination before the
-anthers of the same flower are ripe, are <i>proterogynous</i>.
-<span class="pagenum"><a name="Page_439" id="Page_439">[Pg 439]</a></span></p>
-<p>&nbsp;<span class="pagenum"><a name="Page_440" id="Page_440">[Pg 440]</a></span></p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <p>&nbsp;</p>
-    <img  id="FIG_458" src="images/fig458.jpg" alt="" width="150" height="390" />
-    <p class="center">Fig. 458.<br /> Skunk’s cabbage.</p>
-   </div>
-  <div class="figsub">
-     <p>&nbsp;</p>
-      <img  id="FIG_459" src="images/fig459.jpg" alt="" width="200" height="374" />
-      <p class="center">Fig. 459.<br /> Proterogyny in skunk’s cabbage.<br />
-               (Photograph by the author.)</p>
-  </div>
-  <div class="figsub">
-      <img  id="FIG_460" src="images/fig460.jpg" alt="" width="200" height="350" />
-      <p class="center">Fig. 460.<br /> Skunk’s cabbage;<br /> upper flowers<br /> proterandrous,<br />
-         lower ones<br /> proterogynous.</p>
-  </div>
-</div>
-
-<p>&nbsp;<span class="pagenum"><a name="Page_441" id="Page_441">[Pg 441]</a></span></p>
-<p><span class="pagenum"><a name="Page_442" id="Page_442">[Pg 442]</a></span>
-<b>852.</b> Now if we observe the spadix of another plant we may see a
-condition of things similar to that shown in <a href="#FIG_460">fig. 460</a>.
-In the flowers in the upper part of the spadix here the anthers are wedging their
-way through between the armor-like plates formed by the sepals, while the
-styles of the same flowers are still beneath, and the stigmas are not
-ready for pollination. Such flowers are <i>proterandrous</i>, that is, the
-anthers are ripe before the stigmas of the same flowers are ready for
-pollination. In this spadix the upper flowers are proterandrous, while
-the lower ones are proterogynous, so that it might happen here that
-the lower flowers would be pollinated by the pollen falling on them
-from the stamens of the upper flowers. This would be cross pollination
-so far as the flowers are concerned, but not so far as the plants
-are concerned. In some individuals, however, we find all the flowers
-proterandrous.</p>
-
-<p><b>853. Spiders have discovered this curious relation of the flowers
-and insects.</b>—On several different occasions, while studying
-the adaptations of the flowers of the skunk’s cabbage for cross
-pollination, I was interested to find that the spiders long ago had
-discovered something of the kind, for they spread their nets here to
-catch the unwary but useful insects. I have not seen the net spread
-over the opening in the spathe, but it is spread over the spadix
-within, reaching from tip to tip of either the stigmas, or stamens, or
-both. Behind the spadix crouches the spider-trapper. The insect crawls
-over the edge of the spadix, and plunges unsuspectingly into the dimly
-lighted chamber below, where it becomes entangled in the meshes of the net.</p>
-
-<p>Flowers in which the ripening of the anthers and maturing of the
-stigmas occur at different times are also said to be <i>dichogamous</i>.</p>
-
-<p><b>854. Pollination of jack-in-the-pulpit.</b>—The jack-in-the-pulpit
-(Arisæma triphyllum) has made greater advance in the art of enforcing
-cross pollination. The larger number of plants here are, as we have
-found, diœcious, the staminate flowers being on the spadix of one
-plant, while the pistillate flowers are on the spadix of another. In a
-few plants, however, we find both female and male flowers on the same
-spadix.</p>
-
-<p><b>855.</b> The pretty bell-flower (Campanula rotundifolia) is
-dichogamous and proterandrous (<a href="#FIG_462">fig. 462</a>).
-Many of the composites are also dichogamous.</p>
-
-<p><b>856. Pollination of orchids.</b>—But some of the most marvellous
-adaptations for cross pollination by insects are found in the orchids,
-or members of the orchis family. The larger number of the members of
-this family grow in the tropics. Many of these in the forests are
-supported in lofty trees where they are brought near the sunlight,
-and such are called “epiphytes.” A number of species of orchids are
-distributed in temperate regions.
-<span class="pagenum"><a name="Page_443" id="Page_443">[Pg 443]</a></span></p>
-
-<div class="figcenter">
-    <img src="images/fig461.jpg" alt="" width="400" height="514" />
-      <p class="center">Fig. 461.<br /> A group of jacks.</p>
-</div>
-
-<p><b>857. Cypripedium, or lady-slipper.</b>—One species of the
-lady-slipper is shown in <a href="#FIG_468">fig. 468</a>. The labellum in this
-genus is shaped like a shoe, as one can see by the section of the flower in <a href="#FIG_468">fig. 468</a>.
-The stigma is situated at <i>st</i>, while the anther is situated at <i>a</i>,
-upon the style. The insect enters about the middle of the boat-shaped
-<span class="pagenum"><a name="Page_444" id="Page_444">[Pg 444]</a></span>
-labellum. In going out it passes up and out at the end near the flower
-stalk. In doing this it passes the stigma first and the anther last,
-rubbing against both. The pollen caught on the head of the insect, will
-not touch the stigma of the same flower, but will be in position to
-come in contact with the stigma of the next flower visited.</p>
-
-<div class="figcenter">
-    <img  id="FIG_462" src="images/fig462.jpg" alt="" width="600" height="286" />
-  <div class="blockquot">
-      <p class="center">Fig. 462.</p>
-      <p>Proterandry in the bell-flower (campanula). Left figure shows the
-         syngenœcious stamens surrounding the immature style and stigma. Middle
-         figure shows the immature stigma being pushed through the tube and
-         brushing out the pollen; while in the right-hand figure, after the
-         pollen has disappeared, the lobes of the stigma open out to receive
-         pollen from another flower.</p>
-  </div>
-</div>
-
-<p><b>858. Epipactis.</b>—In epipactis, shown in <a href="#FIG_469">fig. 469</a>,
-the action is similar to that of the blue iris.</p>
-
-<div class="figcenter">
-    <img src="images/fig463.jpg" alt="" width="600" height="218" />
-  <div class="blockquot">
-      <p class="center">Fig. 463.</p>
-      <p>Kalmia latifolia, showing position of anthers before insect visits,
-         and at the right the scattering of the pollen when disturbed by
-         insects. Middle figure section of flower.</p>
-  </div>
-</div>
-
-<p><b>849.</b> In some of the tropical orchids the pollinia are set free
-when the insect touches a certain part of the flower, and are thrown
-in such a way that the disk of the pollinium strikes the insect’s head
-and stands upright. By the time the insect reaches another flower the
-<span class="pagenum"><a name="Page_445" id="Page_445">[Pg 445]</a></span>
-pollinium has bent downward sufficiently to strike against the stigma
-when the insect alights on the labellum. In the mountains of North
-Carolina I have seen a beautiful little orchid, in which, if one
-touches a certain part of the flower with a lead-pencil or other
-suitable object, the pollinium is set free suddenly, turns a complete
-somersault in the air, and lands with the disk sticking to the pencil.
-Many of the orchids grown in conservatories can be used to demonstrate
-some of these peculiar mechanisms.</p>
-
-<div class="figcenter">
-    <img src="images/fig464.jpg" alt="" width="600" height="225" />
-      <p class="center">Fig. 464.<br /> Spray of leaves and flowers of cytisus.</p>
-
-</div>
-<div class="figcenter">
-    <img src="images/fig465.jpg" alt="" width="600" height="258" />
-      <p class="center">Fig. 465.<br /> Flower of cytisus grown in conservatory.<br />
-               Same flower scattering pollen.</p>
-
-</div>
-
-<p><b>860. Pollination of the canna.</b>—In the study of some of the
-marvellous adaptations of flowers for cross pollination one is led to
-inquire if, after all, plants are not intelligent beings, instead of
-mere automatons which respond to various sorts of stimuli. No plant
-has puzzled me so much in this respect as the canna, and any one will
-be well repaid for a study of recently opened flowers, even though it
-may be necessary to rise early in the morning to unravel the mystery,
-before bees or the wind have irritated the labellum. The canna flower
-<span class="pagenum"><a name="Page_446" id="Page_446">[Pg 446]</a></span>
-is a bewildering maze of petals and petal-like members. The calyx
-is green, adherent to the ovary, and the limb divides into three,
-lanceolate lobes. The petals are obovate and spreading, while the
-stamens have all changed to petal-like members, called <i>staminodia</i>.
-Only one still shows its stamen origin, since the anther is seen at one
-side, while the filament is expanded laterally and upwards to form the
-<i>staminodium</i>.</p>
-
-<div class="figcenter">
-    <img src="images/fig466.jpg" alt="" width="500" height="496" />
-  <div class="blockquot">
-      <p class="center">Fig. 466.</p>
-      <p>Spartium, showing the dusting of the pollen through the opening
-         keels on the under side of an insect. (From Kerner and Oliver.)</p>
-  </div>
-</div>
-
-<p><b>861.</b> The ovary has three locules, and the three styles are
-usually united into a long, thin, strap-shaped style, as seen in the
-figure, though in some cases three, nearly distinct, filamentous styles
-are present. The end of this strap-shaped style has a peculiar curve on
-<span class="pagenum"><a name="Page_447" id="Page_447">[Pg 447]</a></span>
-one side, the outline being sometimes like a long narrow letter S. It
-is on the end of this style, and along the crest of this curve, that
-the stigmatic surface lies, so that the pollen must be deposited on the
-stigmatic end or margin in order that fertilization may take place.</p>
-
-<div class="figcenter">
-    <img src="images/fig467.jpg" alt="" width="300" height="421" />
-      <p class="center">Fig. 467.<br /> Cypripedium.</p>
-</div>
-<div class="figcenter">
-    <img  id="FIG_468" src="images/fig468.jpg" alt="" width="600" height="360" />
-  <div class="blockquot">
-      <p class="center">Fig. 468.</p>
-      <p>Section of flower of cypripedium. <i>st</i>, stigma; <i>a</i>, at the left
-         stamen. The insect enters the labellum at the center, passes under and
-         against the stigma, and out through the opening <i>b</i>, where it rubs
-         against the pollen. In passing through another flower this pollen is
-         rubbed off on the stigma.</p>
-  </div>
-</div>
-
-<p><b>862.</b> If we open carefully canna flower buds which are nearly
-ready to open naturally, by unwrapping the folded petals and
-staminodia, we shall see the anther-bearing staminodium is so wrapped
-around the flattened style that the anther lies closely pressed against
-the face of the style, near the margin <i>opposite that on which the
-stigma lies</i>.</p>
-
-<div class="figcenter">
-    <img  id="FIG_469" src="images/fig469.jpg" alt="" width="600" height="260" />
-  <div class="blockquot">
-      <p class="center">Fig. 469.</p>
-      <p>Epipactis with portion of perianth removed to show details. <i>l</i>,
-         labellum; <i>st</i>, stigma; <i>r</i>, rostellum; <i>p</i>, pollinium. When the insect
-         approaches the flower its head strikes the disk of the pollinium and
-         pulls the pollinium out. At this time the pollinium stands up out of
-         the way of the stigma. By the time the insect moves to another flower
-         the pollinia have moved downward so that they are in position to strike
-         the stigma and leave the pollen. At the right is the head of a bee,
-         with two pollinia (<i>a</i>) attached.</p>
-  </div>
-</div>
-
-<p><span class="pagenum"><a name="Page_448" id="Page_448">[Pg 448]</a></span></p>
-
-<div class="figcenter">
-    <img src="images/fig470.jpg" alt="" width="400" height="411" />
-  <div class="blockquot">
-      <p class="center">Fig. 470.</p>
-      <p>Canna flowers with the perianth removed to show the depositing of
-         the pollen on the style by the stamen.</p>
-  </div>
-</div>
-
-<p><b>863.</b> The walls of the anther locules which lie against the style
-become changed to a sticky substance for their entire length, so that
-they cling firmly to the surface of the style and also to the mass of
-pollen within the locules. The result is that when the flower opens,
-and this staminodium unwraps itself from the embrace of the style,
-the mass of pollen is left there deposited, while the empty anther is
-turned around to one side.</p>
-
-<p><b>668.</b> Why does the flower deposit its own pollen on the style?
-Some have regarded this as the act of pollination, and have concluded,
-therefore, that cannas are necessarily self pollinated, and that cross
-pollination does not take place. But why is there such evident care to
-deposit the pollen on the side of the style away from the stigmatic
-margin? If we visit the cannas some morning, when a number of the
-flowers have just opened, and the bumblebees are humming around seeking
-for nectar, we may be able to unlock the secret.</p>
-
-<p><b>864.</b> We see that in a recently opened canna flower, the petal
-which directly faces the style in front stands upward quite close to
-it, so that the flower now is somewhat funnel-shaped. This front petal
-is the <i>labellum</i>, and is the landing place for the bumblebee as he
-alights on the flower. Here he comes humming along and alights on the
-labellum with his head so close to the style that it touches it. But
-just the instant that the bee attempts to crowd down in the flower the
-labellum suddenly bends downward, as shown in <a href="#FIG_468">fig. 468</a>.
-In so doing the head of the bumblebee scrapes against the pollen, bearing some
-of it off. Now while the bee is sipping the nectar it is too far below the
-stigma to deposit any pollen on the latter. When the bumblebee flies to
-another newly opened flower, as it alights, some of the pollen of the
-former flower is brushed on the stigma.</p>
-
-<p><b>865.</b> One can easily demonstrate the sensitiveness of the
-labellum of recently opened canna flowers, if the labellum has not
-already moved down in response to some stimulus. Take a lead-pencil, or
-<span class="pagenum"><a name="Page_449" id="Page_449">[Pg 449]</a></span>
-a knife blade, or even the finger, and touch the upper surface of the
-labellum by thrusting it between the latter and the style. The labellum
-curves quickly downward.</p>
-
-<p><b>866.</b> Sometimes the bumblebees, after sipping the nectar, will
-crawl up over the style in a blundering manner. In this way the flower
-may be pollinated with its own pollen, which is equivalent to self
-pollination. Undoubtedly self pollination does take place often in
-flowers which are adapted, to a greater or less degree, for cross
-pollination by insects.</p>
-
-<div class="figcontainer">
-  <p class="center">Fig. 471. </p>
-  <div class="figsub">
-    <img src="images/fig471a.jpg" alt="" width="250" height="312" />
-    <p class="center">Pollination of the canna flower by bumblebee.</p>
-    </div>
-  <div class="figsub">
-      <img src="images/fig471b.jpg" alt="" width="225" height="311" />
-    <p class="center">Canna flower.<br /> Pollen on style,<br /> stamen at left.</p>
-  </div>
-</div>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_450" id="Page_450">[Pg 450]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XLIV" id="CHAPTER_XLIV">CHAPTER XLIV.</a><br />
-<span class="h_subtitle">THE FRUIT.</span></h3>
-</div>
-
-<h4><a name="XLIV_1" id="XLIV_1">I. Parts of the Fruit.</a></h4>
-
-<p><b>867. After the flower comes the fruit.</b>—With the perfection of
-the fruit the seed is usually formed. This is the end towards which the
-energies of the plant have been directed. While the seed consists only
-of the ripened ovule and the contained embryo, the fruit consists of
-the ripened ovary in addition, and in many cases with other accessory
-parts, as calyx, receptacle, etc., combined with it. The wall of the
-ripened ovary is called a <i>pericarp</i>, and the walls of the ovary form
-the walls of the fruit.</p>
-
-<p><b>868. Pericarp, endocarp, exocarp, etc.</b>—This is the part of the
-fruit which envelops the seed and may consist of the carpels alone, or
-of the carpels and the adherent part of the receptacle, or calyx. In
-many fruits the pericarp shows a differentiation into layers, or zones
-of tissue, as in the cherry, peach, plum, etc. The outer, which is
-here soft and fleshy, is <i>exocarp</i>, while the inner, which is hard, is
-the <i>endocarp</i>. An intermediate layer is sometimes recognized and is
-called <i>mesocarp</i>. In such cases the skin of the fruit is recognized as
-the <i>epicarp</i>. Epicarp and mesocarp are more often taken together as exocarp.</p>
-
-<p>In general fruits are <i>dry</i> or <i>fleshy</i>. Dry fruits may be grouped
-under two heads. Those which open at maturity and scatter the seed are
-<i>dehiscent</i>. Those which do not open are <i>indehiscent</i>.
-<span class="pagenum"><a name="Page_451" id="Page_451">[Pg 451]</a></span></p>
-
-<h4><a name="XLIV_2" id="XLIV_2">II. Indehiscent Fruits.</a></h4>
-
-<p><b>869. The akene.</b>—The thin dry wall of the ovary encloses the
-single seed. It usually does not open and free the seed within. Such a
-fruit is an <i>akene</i>. An <i>akene</i> is a dry, <i>indehiscent</i> fruit.
-All of the crowded but separate pistils in the buttercup flower when ripe make
-a head of akenes, which form the fruit of the buttercup. Other examples
-of akenes are found in other members of the buttercup family, also in
-the composites, etc. The sunflower seed is a good example of an akene.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <p>&nbsp;</p>
-    <img src="images/fig472.jpg" alt="" width="150" height="163" />
-    <p class="center">Fig. 472.<br /> Seed, or akene, of buttercup.</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig473.jpg" alt="" width="300" height="200" />
-      <p class="center">Fig. 473.<br /> Fruit of red oak. An acorn.</p>
-  </div>
-</div>
-
-<p><b>870. The samara.</b>—The winged fruits of the maple, elm, etc.,
-are indehiscent fruits. They are sometimes called key fruits.</p>
-
-<p><b>871. The caryopsis</b> is a dry fruit in which the seed is
-consolidated with the wall of the ovary, as in the wheat, corn, and
-other grasses.</p>
-
-<p><b>872. The schizocarp</b> is a dry fruit consisting of several locules
-(from a <i>syncarpous gynœcium</i>). At maturity the carpels separate from
-each other, but do not themselves dehisce and free the seed, as in the
-carrot family, mallow family.</p>
-
-<p><b>873. The acorn.</b>—The acorn fruit consists of the acorn and
-the “cup” at the base in which the acorn sits. The cup is a curious
-structure, and is supposed to be composed of an involucre of numerous
-small leaves at the base of the pistillate flower, which become
-consolidated into a hard cup-shaped body. When the acorn is ripe it
-easily separates from the cup, but the hard pericarp forming the
-“shell” of the acorn remains closed. Frost may cause it to crack, but
-very often the pericarp is split open at the smaller end by wedge-like
-pressure exerted by the emerging radicle during germination.
-<span class="pagenum"><a name="Page_452" id="Page_452">[Pg 452]</a></span></p>
-
-<div class="figcenter">
-    <img src="images/fig474.jpg" alt="" width="600" height="218" />
-      <p class="center">Fig. 474.<br /> Germinating acorn of white oak.</p>
-</div>
-
-<p><b>874. The hazelnut, chestnut, and beechnut.</b>—In these fruits a
-crown of leaves (involucre) at the base of the flower grows around
-the nut and completely envelops it, forming the husk or burr. When
-the fruit is ripe the nut is easily shelled out from the husk. In the
-beechnut and chestnut the burr dehisces as it dries and allows the nut
-to drop out. But the fruit is not dehiscent, since the pericarp is
-still intact and encloses the seed.</p>
-
-<p><b>875. The hickory-nut, walnut, and butternut.</b>—In these fruits
-the “shuck” of the hickory-nut and the “hull” of the walnut and
-butternut are different from the involucre of the acorn or hazelnut,
-etc. In the hickory-nut the “shuck” probably consists partly of calyx
-and partly of involucral bracts consolidated, probably the calyx part
-predominating. This part of the fruit splits open as it dries and frees
-the “nut,” the pericarp being very hard and indehiscent. In the walnut
-and butternut the “hull” is probably of like origin as the “shuck” of
-the hickory nut, but it does not split open as it ripens. It remains
-fleshy. The walnut and butternut are often called <i>drupes</i> or
-<i>stone-fruits</i>, but the fleshy part of the fruit is not of the same origin
-as the fleshy part of the true drupes, like the cherry, peach, plum, etc.</p>
-
-<h4><a name="XLIV_3" id="XLIV_3">III. Dehiscent Fruits.</a></h4>
-
-<p><b>876. Of the dehiscent fruits</b> several prominent types are
-recognized, and in general they are sometimes called <i>pods</i>. There is a
-<span class="pagenum"><a name="Page_453" id="Page_453">[Pg 453]</a></span>
-single carpel (simple pistil), and the pericarp is dry (gynœcium
-<i>apocarpous</i>); or where there are several carpels united the pistil is
-compound (gynœcium <i>syncarpous</i>).</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <p>&nbsp;</p>
-    <img src="images/fig475.jpg" alt="" width="400" height="141" />
-    <p class="center">Fig. 475.<br /> Diagrams illustrating three types<br />
-        (in cross-section) of the dehiscence<br /> of dry fruits. <i>Loc</i>, loculicidal;<br />
-         <i>Sep</i>, Septicidal, Septifragal.</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig476.jpg" alt="" width="150" height="246" />
-      <p class="center">Fig. 476.<br /> Fruit of sweet pea; a pod.</p>
-  </div>
-</div>
-
-<p><b>877. The capsule.</b>—When the capsule is <i>syncarpous</i> it may
-dehisce in three different ways: 1st. When the carpels split along
-the line of their union with each other longitudinally (<i>septicidal
-dehiscence</i>), as in the azalea or rhododendron. 2d. When the carpels
-<i>split down the middle line</i> (<i>loculicidal dehiscence</i>), as in the
-fruit of the iris, lily, etc. 3d. When the carpels open by pores
-(<i>poricidal dehiscence</i>), as in the poppy. Some syncarpous capsules
-have but one locule, the partitions between the different locules when
-young having disappeared. The “bouncing-bet” is an example, and the
-seeds are attached to a central column in four rows corresponding to
-the four locules present in the young stage.</p>
-
-<p><b>878. A follicle</b> is a capsule with a single carpel which splits
-open along the ventral or upper suture, as in the larkspur, peony.</p>
-
-<p><b>879. The legume, or true pod</b>, is a capsule with a single carpel
-which splits along both sutures, as the pea, bean, etc. As the pod
-ripens and dries, a strong twisting tension is often produced, which
-splits the pod suddenly, scattering the seeds.</p>
-
-<p><b>880. The silique.</b>—In the toothwort, shepherd’s-purse, and
-nearly all of the plants in the mustard family the fruit consists of
-two united carpels, which separate at maturity, leaving the partition
-wall persistent. Such a fruit is a <i>silique</i>; when short it is a
-<i>silicle</i>, or <i>pouch</i>.</p>
-
-<p><b>881. A pyxidium, or pyxis</b>, is a capsule which opens with a lid,
-as in the plantain.
-<span class="pagenum"><a name="Page_454" id="Page_454">[Pg 454]</a></span></p>
-
-<h4><a name="XLIV_4" id="XLIV_4">IV. Fleshy and Juicy Fruits.</a></h4>
-
-<p><b>882. The drupe, or stone-fruit.</b>—In the plum, cherry, peach,
-apricot, etc., the outer portion (exocarp) of the pericarp (ovary)
-becomes fleshy, while the inner portion (endocarp) becomes hard and
-stony, and encloses the seed, or “pit.” Such a fruit is known as a
-drupe, or as a stone-fruit. In the almond the fleshy part of the fruit
-is removed.</p>
-
-<div class="figcenter">
-    <img src="images/fig477.jpg" alt="" width="500" height="351" />
-      <p class="center">Fig. 477.<br /> Drupe, or stone-fruit, of plum.</p>
-</div>
-
-<p><b>883. The raspberry and blackberry.</b>—While these fruits are
-known popularly as “berries,” they are not berries in the technical
-sense. Each ovary, or pericarp, in the flower forms a single small
-fruit, the outer portion being fleshy and the inner stony, just as
-in the cherry or plum. It is a <i>drupelet</i> (little drupe). All of the
-drupelets together make the “berry,” and as they ripen the separate
-drupelets cohere more or less. It is a collection, or aggregation, of
-fruits, and consequently they are sometimes called <i>collective fruits</i>,
-or <i>aggregate fruits</i>. In the raspberry the fruit separates from the
-receptacle, leaving the latter on the stem, while the drupelets of
-the blackberry and dewberry adhere to the receptacle and the latter
-separates from the stem.
-<span class="pagenum"><a name="Page_455" id="Page_455">[Pg 455]</a></span></p>
-
-<p><b>884. The berry.</b>—In the true berry both exocarp (including
-mesocarp) and endocarp are fleshy or juicy. Good examples are found
-in cranberries, huckleberries, gooseberries, currants, snowberries,
-tomatoes, etc. The calyx and wall of the pistil are adnate, and in
-fruit become fleshy so that the seeds are imbedded in the pulpy juice.
-The seeds themselves are more or less stony. In the case of berries,
-as well as in strawberries, raspberries, and blackberries, the fruits
-are eagerly sought by birds and other animals for food. The seeds being
-hard are not digested, but are passed with the other animal excrement
-and thus gain dispersal.</p>
-
-<h4><a name="XLIV_5" id="XLIV_5">V. Reinforced, or Accessory, Fruits.</a></h4>
-
-<p>When the torus (receptacle) is grown to the pericarp in fruit, the
-fruit is said to be <i>reinforced</i>. The torus may enclose the pericarps,
-or the latter may be seated upon the torus.</p>
-
-<div class="figcenter">
-    <img src="images/fig478.jpg" alt="" width="500" height="417" />
-      <p class="center">Fig. 478.<br /> Fruit of raspberry.</p>
-</div>
-
-<p><b>885. In the strawberry</b> the receptacle of the flower becomes
-larger and fleshy, while the “seeds,” which are akenes, are sunk in the
-<span class="pagenum"><a name="Page_456" id="Page_456">[Pg 456]</a></span>
-surface and are hard and stony. The strawberry thus differs from the
-raspberry and blackberry, but like them it is not a true berry.</p>
-
-<p><b>886. The apple, pear, quince, etc.</b>—In the flower the calyx,
-corolla, and stamens are perigynous, i.e., they are seated on the
-margin of the receptacle, or torus, which is elevated around the
-pistils. In fruit the receptacle becomes consolidated with the wall
-of the ovary (with the pericarp). The torus thus <i>reinforces</i> the
-pericarp. The torus and outer portion of the pericarp become fleshy,
-while the inner portion of the pericarp becomes papery and forms the
-“core.” The calyx persists on the free end of the fruit. Such a fruit
-is called a <i>pome</i>. The receptacle, or torus, of the rose-flower,
-closely related to the apple, is instructive when used in comparison.
-The rose-fruit is called a “hip.”</p>
-
-<p><b>887. The pepo.</b>—The fruit of the squash, pumpkin, cucumber,
-etc., is called a <i>pepo</i>. The outer part of the fruit is the receptacle
-(or torus), which is consolidated with the outer part of the
-three-loculed ovary. The calyx, which, with the corolla and stamens,
-was epigynous, falls off from the young fruit.</p>
-
-<h4><a name="XLIV_6" id="XLIV_6">VI. Fruits of Gymnosperms.</a></h4>
-
-<p>The fruits of the gymnosperms differ from nearly all of the angiosperms
-in that the seed formed from the ripened ovule is naked from the first,
-i.e., the ovary, or carpel, does not enclose the seed.</p>
-
-<p><b>888. The cone-fruit</b> is the most prominent fruit of the
-gymnosperms, as can be seen in the cones of various species of pine,
-spruce, balsam, etc.</p>
-
-<p><b>889. Fleshy fruits of the gymnosperms.</b>—Some of the fleshy
-fruits resemble the stone-fruits and berries of the angiosperms. The
-<i>cedar</i> “<i>berries</i>,” for example, are fleshy and contain several seeds.
-But the fleshy part of the fruit is formed, not from pericarp, since
-there is no pericarp, but from the outer portion of the ovules, while
-the inner walls of the ovules form the hard stone surrounding the
-<span class="pagenum"><a name="Page_457" id="Page_457">[Pg 457]</a></span>
-endosperm and embryo. An examination of the pistillate flower of the
-cedar (juniper) shows usually three flask-shaped ovules on the end
-of a fertile shoot subtended by as many bracts (carpels?). The young
-ovules are free, but as they grow they coalesce, and the outer walls
-become fleshy, forming a berry-like fruit with a three-rayed crevice
-at the apex marking the number of ovules. The red fleshy fruit of the
-yew (taxus) resembles a drupe which is open at the apex. The stony
-seed is formed from the single ovule on the fertile shoot, while the
-red cup-shaped fleshy part is formed from the outer integument of the
-ovule. The so-called “aril” of the young ovule is a rudimentary outer
-integument.</p>
-
-<p>The fruit of the maidenhair tree (ginkgo) is about the size of a plum
-and resembles very closely a stone-fruit. But it is merely a ripened
-ovule, the outer layer becoming fleshy while the inner layer becomes
-stony and forms the pit which encloses the embryo and endosperm.
-The so-called “aril,” or “collar,” at the base of the fruit is the
-rudimentary carpel, which sometimes is more or less completely expanded
-into a true leaf. The fruit of cycas is similar to that of ginkgo, but
-there is no collar at the base. In zamia the fruit is more like a cone,
-the seeds being formed, however, on the under sides of the scales.</p>
-
-<h4><a name="XLIV_7" id="XLIV_7">VII. The “Fruit” of Ferns, Mosses, etc.</a></h4>
-
-<p><b>890. The term “fruit”</b> is often applied in a general or popular
-sense to the groups of spore-producing bodies of ferns (<i>fruit dots</i>,
-or <i>sori</i>), the spore-capsules of mosses and liverworts, and also to
-the fruit-bodies, or spore-bearing parts, of the fungi and algæ.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_458" id="Page_458">[Pg 458]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XLV" id="CHAPTER_XLV">CHAPTER XLV.</a><br />
-<span class="h_subtitle">SEED DISPERSAL.</span></h3>
-</div>
-
-<p><b>891. Means for dissemination of seeds.</b>—During late summer
-or autumn a walk in the woods or afield often convinces us of the
-perfection and variety of means with which plants are provided for the
-dissemination of their seeds, especially when we discover that several
-hundred seeds or fruits of different plants are stealing a ride at
-our expense and annoyance. The hooks and barbs on various seed-pods
-catch into the hairs of passing animals and the seeds may thus be
-transported considerable distances. Among the plants familiar to us,
-which have such contrivances for unlawfully gaining transportation,
-are the beggar-ticks or stick tights, or sometimes called bur-marigold
-(bidens), the tick-treefoil (desmodium), or cockle-bur (xanthium), and
-burdock (arctium).</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-    <p>&nbsp;</p>
-    <img src="images/fig479.jpg" alt="" width="300" height="313" />
-    <p class="center">Fig. 479.<br /> Bur of bidens or bur-marigold,<br />
-                showing barbed seeds.</p>
-   </div>
-  <div class="figsub">
-      <img src="images/fig480.jpg" alt="" width="225" height="305" />
-      <p class="center">Fig. 480.<br /> Seed pod of tick-treefoil (desmodium);<br />
-          at the right some of the hooks<br /> greatly magnified.</p>
-  </div>
-</div>
-
-<p><b>892.</b> Other plants like some of the sedges, etc., living on the
-margins of streams and of lakes, have seeds which are provided with
-floats. The wind or the flowing of the water transports them often to
-distant points.
-<span class="pagenum"><a name="Page_459" id="Page_459">[Pg 459]</a></span></p>
-
-<p><b>893.</b> Many plants possess attractive devices, and offer a
-substantial reward, as a price for the distribution of their seeds.
-Fruits and berries are devoured by birds and other animals; the seeds
-within, often passing unharmed, may be carried long distances. Starchy
-and albuminous seeds and grains are also devoured, and while many
-such seeds are destroyed, others are not injured, and finally are
-lodged in suitable places for growth, often remote from the original
-locality. Thus animals willingly or unwillingly become agents in the
-dissemination of plants over the earth. Man in the development of
-commerce is often responsible for the wide distribution of harmful as
-well as beneficial species.</p>
-
-<div class="figcenter">
-    <img src="images/fig481.jpg" alt="" width="600" height="354" />
-      <p class="center">Fig. 481.<br /> Seeds of geum showing the hooklets<br />
-               where the end of the style is kneed.</p>
-</div>
-
-<p><b>894.</b> Other plants are more independent, and mechanisms are
-employed for violently ejecting seeds from the pod or fruit. The
-unequal tension of the pods of the common vetch (Vicia sativa) when
-drying causes the valves to contract unequally, and on a dry summer day
-the valves twist and pull in opposite directions until they suddenly
-snap apart, and the seeds are thrown forcibly for some distance. In the
-impatiens, or touch-me-not as it is better known, when the pods are
-ripe, often the least touch, or a pinch, or jar, sets the five valves
-free, they coil up suddenly, and the small seeds are thrown for several
-yards in all directions. During autumn, on dry days, the pods of the
-witch hazel contract unequally, and the valves are suddenly spread
-apart, and the seeds are hurled away.</p>
-
-<p>Other plants have seeds provided with tufts of pappus, or hair-like
-masses, or wing-like outgrowths which serve to buoy them up as they are
-<span class="pagenum"><a name="Page_460" id="Page_460">[Pg 460]</a></span>
-whirled along, often miles away. In late spring or early summer the
-pods of the willow burst open, exposing the seeds, each with a tuft of
-white hairs making a mass of soft down. As the delicate hairs dry, they
-straighten out in a loose spreading tuft, which frees the individual
-seeds from the compact mass. Here they are caught by currents of air
-and float off singly or in small clouds.</p>
-
-<div class="figcenter">
-    <img src="images/fig482.jpg" alt="" width="600" height="380" />
-  <div class="blockquot">
-      <p class="center">Fig. 482.</p>
-      <p>Touch-me-not (Impatiens fulva); side and front view of flower below;
-         above unopened pod, and opening to scatter the seed.</p>
-  </div>
-</div>
-
-<p><b>895. The prickly lettuce.</b>—In late summer or early autumn the
-seeds of the prickly lettuce (Lactuca scariola) are caught up from the
-roadsides by the winds, and carried to fields where they are unbidden
-as well as unwelcome guests. This plant is shown in <a href="#FIG_483">fig. 483</a>.</p>
-
-<p><b>896. The wild lettuce.</b>—A related species, the wild lettuce
-(Lactuca canadensis) occurs on roadsides and in the borders of fields,
-and is about one meter in height. The heads of small yellow or purple
-flowers are arranged in a loose or branching panicle. The flowers are
-rather inconspicuous, the rays projecting but little above the apex of
-the enveloping involucral bracts, which closely press together, forming
-a flowerhead more or less flask-shaped.</p>
-
-<div class="figcenter">
-    <img  id="FIG_483" src="images/fig483.jpg" alt="" width="350" height="491" />
-      <p class="center">Fig. 483.<br /> Lactuca scariola.</p>
-</div>
-
-<p>At the time of flowering the involucral bracts spread somewhat at the
-apex, and the tips of the flowers are a little more prominent. As the
-flowers then wither, the bracts press closely together again and the
-head is closed. As the seeds ripen the bracts die, and in drying bend
-outward and downward, around the flower stem below, or they fall away.
-<span class="pagenum"><a name="Page_461" id="Page_461">[Pg 461]</a></span>
-The seeds are thus exposed. The dark brown achenes stand over the
-surface of the receptacle, each one tipped with the long slender
-beak of the ovary. The “pappus,” which is so abundant in many of the
-plants belonging to the composite family, forms here a pencil-like
-tuft at the tip of this long beak. As the involucral bracts dry and
-curve downward, the pappus also dries, and in doing so bends downward
-and stands outward, bristling like the spokes of a small wheel. It is
-an interesting coincidence that this takes place simultaneously with
-the pappus of all the seeds of a head, so that the ends of the pappus
-bristles of adjoining seeds meet, forming a many-sided dome of a
-delicate and beautiful texture. This causes the beaks of the achenes to
-be crowded apart, and with the leverage thus brought to bear upon the
-achenes they are pried off the receptacle. They are thus in a position
-to be wafted away by the gentlest zephyr, and they go sailing away on
-the wind like a miniature parachute. As they come slowly to the ground
-the seed is thus carefully lowered first, so that it touches the ground
-in a position for the end which contains the root of the embryo to come
-in contact with the soil.
-<span class="pagenum"><a name="Page_462" id="Page_462">[Pg 462]</a></span></p>
-
-<p><b>897. The milkweed, or silkweed.</b>—The common milkweed, or
-silkweed (Asclepias cornuti), so abundant in rich grounds, is
-attractive not only because of the peculiar pendent flower clusters,
-but also for the beautiful floats with which it sends its seeds
-skyward, during a puff of wind, to finally lodge on the earth.</p>
-
-<div class="figcenter">
-    <img src="images/fig484.jpg" alt="" width="500" height="442" />
-      <p class="center">Fig. 484.<br /> Milkweed (Asclepias cornuti);<br />
-             dissemination of seed.</p>
-</div>
-
-<p><b>898.</b> The large boat-shaped, tapering pods, in late autumn, are
-packed with oval, flattened, brownish seeds, which overlap each other
-in rows like shingles on a roof. These make a pretty picture as the pod
-in drying splits along the suture on the convex side, and exposes them
-to view. The silky tufts of numerous long, delicate white hairs on the
-inner end of each seed, in drying, bristle out, and thus lift the seeds
-out of their enclosure, where they are caught by the breeze and borne
-away often to a great distance, where they will germinate if conditions
-become favorable, and take their places as contestants in the battle
-for existence.</p>
-
-<p><b>899. The virgin’s bower.</b>—The virgin’s bower (Clematis
-virginiana), too, clambering over fence and shrub, makes a show of
-<span class="pagenum"><a name="Page_463" id="Page_463">[Pg 463]</a></span>
-having transformed its exquisite white flower clusters into
-grayish-white tufts, which scatter in the autumn gusts into hundreds
-of arrow-headed, spiral plumes. The achenes have plumose styles, and
-the spiral form of the plume gives a curious twist to the falling seed
-(<a href="#FIG_485">fig. 485</a>).</p>
-
-<div class="figcenter">
-    <img  id="FIG_485" src="images/fig485.jpg" alt="" width="400" height="450" />
-      <p class="center">Fig. 485.<br /> Seed distribution of virgin’s bower (clematis).</p>
-</div>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_464" id="Page_464">[Pg 464]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XLVI" id="CHAPTER_XLVI">CHAPTER XLVI.</a><br />
-<span class="h_subtitle">VEGETATION IN RELATION TO
-ENVIRONMENT.<a name="FNanchor_47_47" id="FNanchor_47_47"></a><a href="#Footnote_47_47" class="fnanchor">[47]</a></span></h3>
-</div>
-
-<p class="center"><b>I. Factors Influencing Vegetation Types.</b></p>
-
-<p><b>900.</b> All plants are subject to the influence of environment
-from the time the seed begins to germinate until the seed is formed
-again, or until the plant ceases to live. A suitable amount of warmth
-and moisture is necessary that the seed may germinate. Moisture may
-be present, but if it is too cold, germination will not take place.
-So in all the processes of life there are several conditions of the
-environment, or the “outside” of plants, which must be favorable for
-successful growth and reproduction. Not only is this true, but the
-surroundings of plants to a large extent determine the kind of plants
-which can grow in particular localities. It is also evident that the
-reaction of environment on plants has in a large measure caused them
-to take on certain forms and structures which fit them better to exist
-under local conditions. In other cases where plants have varied by
-mutation (<a href="#Page_338">p. 338</a>) some of the new forms may be more suited
-to the conditions of environment than others and they are more apt to survive.
-These conditions of environment acting on the plant are <i>factors</i> which
-have an important determining influence on the existence, habitat,
-habit, and form of the plant. These factors are sometimes spoken of
-as <i>ecological factors</i>, and the study of plants in this relation is
-<span class="pagenum"><a name="Page_465" id="Page_465">[Pg 465]</a></span>
-sometimes spoken of as ecology,<a name="FNanchor_48_48" id="FNanchor_48_48"></a><a href="#Footnote_48_48" class="fnanchor">[48]</a>
-which means a study of plants in their home or a study of the household
-relations of plants. These factors are of three sorts: 1st, physical
-factors; 2d, climatic factors; 3d, biotic factors.</p>
-
-<p><b>901. Physical factors.</b>—Some of these factors are water, light,
-heat, wind, chemical or physical condition of the soil, etc. <i>Water</i>
-is a very important factor for all plants. Even those growing on land
-contain a large percentage of water, which we have seen is rapidly lost
-by transpiration, and unless water is available for root absorption
-the plant soon suffers, and aquatic plants are injured very quickly by
-drying when taken from the water. Excess of soil water is injurious to
-some plants. <i>Light</i> is important in photosynthesis, in determining
-direction of growth as well as in determining the formation of suitable
-leaves in most plants, and has an influence in the structure of the
-leaf according as the light may be strong, weak, etc. <i>Heat</i> has great
-influence on plant growth and on the distribution of plants. The
-growth period for most vegetation begins at 6° C. (= 43° F.), or in
-the tropics at 10°-12° C., but a much higher temperature is usually
-necessary for reproduction. Some arctic algæ, however, fruit at 1.8° C.
-The upper limit favorable for plants in general is 45°-50° C., while
-the optimum temperature is below this. Very high temperatures are
-injurious, and fatal to most plants, but some algæ grow in hot springs
-where the temperature reaches 80°-90° C. Some desert plants are able to
-endure a temperature of 70° C., while some flowering plants of other
-regions are killed at 45° C. Some plants are specifically susceptible
-to cold, but most plants which are injured by freezing suffer because
-the freezing is a drying process of the protoplasm (<a href="#Page_374">see p. 374</a>).
-<i>Wind</i> may serve useful purposes in pollination and in aeration, but severe
-winds injure plants by causing too rapid transpiration, by felling
-trees, by breaking plant parts, by deforming trees and shrubs, and by
-mechanical injuries from “sand-blast.” <i>Ground covers</i> protect plants
-in several ways. Snow during the winter checks radiation of heat from
-the ground so that it does not freeze to so great a depth, and this is
-very important for many trees and shrubs. It also prevents alternate
-<span class="pagenum"><a name="Page_466" id="Page_466">[Pg 466]</a></span>
-freezing and thawing of the ground, which “heaves” some plants from
-the soil. Leaves and other plant remains mulch the soil and check
-evaporation of water. The influence of the <i>chemical condition</i> of the
-soil is very marked in alkaline areas where the concentration of salt
-in the soil permits a very limited range of species. So the physical
-and mechanical conditions of the soil influence plants because the
-moisture content of the ground is so closely dependent on its physical
-condition. Rocky and gravelly soil, other things being equal, is dry.
-Clay is more retentive of moisture than sand, and moisture also varies
-according to the per cent of humus mixed with it, the humus increasing
-the percentage of moisture retained.</p>
-
-<p><b>902. Climatic factors.</b>—These factors are operative over very
-wide areas. There are two climatic factors: rainfall or atmospheric
-moisture, and temperature. A very low annual rainfall in warm or
-tropical countries causes a desert; an abundance of rain permits the
-growth of forests; extreme cold prevents the growth of forests and
-gives us the low vegetation of arctic and alpine regions.</p>
-
-<p><b>903. Biotic factors.</b>—These are animals which act favorably
-in pollination, seed distribution, or unfavorably in destroying or
-injuring plants, and man himself is one of the great agencies in
-checking the growth of some plants while favoring the growth of others.
-Plants also react on themselves in a multitude of ways for good or
-evil. Some are parasites on others; some in symbiosis (<a href="#Page_85">see p. 85</a>)
-aid in providing food; shade plants are protected by those which overtop
-them; mushrooms and other fungi disintegrate dead plants to make humus
-and finally plant food; certain bacteria by nitrification prepare
-nitrates for the higher plants (<a href="#Page_83">see p. 83</a>).</p>
-
-<p class="center"><b>II. Vegetation Types and Structures.</b></p>
-
-<p><b>904. Responsive type of vegetation.</b>—In studying vegetation in
-relation to environment we are more concerned with the form of the
-<span class="pagenum"><a name="Page_467" id="Page_467">[Pg 467]</a></span>
-plants which fits them to exist under the local conditions than we are
-with the classification of plants according to natural relationships.
-Plants may have the same vegetation type, grow side by side, and still
-belong to very different floristic types. For example, the cactus,
-yucca, three-leaved sumac, the sage-brush, etc., have all the same
-general vegetation type and thrive in desert regions. The red oaks, the
-elms, many goldenrods, trillium, etc., have the same general vegetation
-type, but represent very different floristic types. The latter plants
-grow in regions with abundant rainfall throughout the year, where
-the growing season is not very short and temperature conditions are
-moderate. Some goldenrods grow in very sandy soil which dries out
-quickly. These have fleshy or succulent leaves for storing water,
-and while they are of the same floristic type as goldenrods growing
-in other places, the vegetation type is very different. The types of
-vegetation which fit plants for growing in special regions or under
-special conditions, they have taken on in response to the influence
-of the conditions of their environment. While we find all gradations
-between the different types of vegetation, looking at the vegetation
-in a broad way, several types are recognized which were proposed by
-Warming as follows:</p>
-
-<p><b>905. Mesophytes.</b>—These are represented by land plants under
-temperate or moderate climatic and soil conditions. The normal
-land vegetation of our temperate region is composed of mesophytes,
-that is, the plants have mesophytic structures during the growing
-season. The deciduous forests or thickets of trees and shrubs with
-their undergrowth, the meadows, pastures, prairies, weeds, etc., are
-examples. In those portions of the tropics where rainfall is great the
-vegetation is mesophytic the year around.</p>
-
-<p><b>906. Xerophytes.</b>—These are plants which are provided with
-structures which enable them to live under severe conditions of
-dryness, where the air and soil are very dry, as in deserts or
-semideserts, or where the soil is very dry or not retentive of
-moisture, as in very sandy soil which is above ground water, or in
-rocky areas. Since the plants cannot obtain much water from the soil
-<span class="pagenum"><a name="Page_468" id="Page_468">[Pg 468]</a></span>
-they must be provided with structures which will enable them to
-retain the small amount they can absorb from the soil and give it off
-slowly. Otherwise they would dry out by evaporation and die. Some
-of the structures which enable xerophytic plants to withstand the
-conditions of dry climate and soil are lessened leaf surface, increase
-in thickness of leaf, increase in thickness of cuticle, deeply sunken
-stomates, compact growth, also succulent leaves and stems, and in some
-cases loss of the leaf. Evergreens of the north temperate and the
-arctic regions are xerophytes.</p>
-
-<p><b>907. Hydrophytes.</b>—These are plants which grow in fresh water
-or in very damp situations. The leaves of aerial hydrophytes are very
-thin, have a thin cuticle, and lose water easily, so that if the air
-becomes quite dry they are in danger of drying up even though the roots
-may be supplied with an abundance of water. The aquatic plants which
-are entirely submerged have often thin leaves, or very finely divided
-or slender leaves, since these are less liable to be torn by currents
-of water. The stems are slender and especially lack strengthening
-tissue, since the water buoys them up. Removed from the water they
-droop of their own weight, and soon dry up. The stems and leaves have
-large intercellular spaces filled with air which aids in aeration and
-in the diffusion of gases. Some use the term <i>hygrophytes</i>.</p>
-
-<p><b>908. Halophytes.</b>—These are salt-loving plants. They grow in
-salt water, or in salt marshes where the water is brackish, or in
-soil which contains a high per cent of certain salts, for example the
-alkaline soils of the West, especially in the so-called “Bad Lands”
-of Dakota and Nebraska, and in alkaline soils of the Southwest and
-California. These plants are able to withstand a stronger concentration
-of salts in the water than other plants. They are also found in soil
-about salt springs.</p>
-
-<p><b>909. Tropophytes.</b><a name="FNanchor_49_49" id="FNanchor_49_49"></a><a href="#Footnote_49_49" class="fnanchor">[49]</a>—Tropophytes
-are plants which can live as mesophytes during the growing season, and
-then turn to a xerophytic habit in the resting season. Deciduous trees
-and shrubs, and perennial herbs of our temperate regions, are in this
-<span class="pagenum"><a name="Page_469" id="Page_469">[Pg 469]</a></span>
-sense tropophytes, while many are at the same time mesophytes if
-they exist in the portions of the temperate region where rainfall is
-abundant. In the spring and summer they have broad and comparatively
-thin leaves, transpiration goes on rapidly, but there is an abundance
-of moisture in the soil, so that root absorption quickly replaces the
-loss and the plant does not suffer. In the autumn the trees shed their
-leaves, and in this condition with the bare twigs they are able to
-stand the drying effect of the cold and winds of the winter because
-transpiration is now at a minimum, while root absorption is also at a
-minimum because of the cold condition of the soil. Perennial herbs like
-trillium, dentaria, the goldenrods, etc., turn to xerophytic habit by
-the death of their aerial shoots, while the thick underground shoot
-which is also protected by its subterranean habit carries the plant
-through the winter.</p>
-
-<p><b>910.</b> While these different vegetation types are generally
-dominant in certain climatic regions or under certain soil conditions,
-they are not the exclusive vegetation types of the regions. For
-example, in desert or semidesert regions the dominant vegetation
-type is made up of xerophytes. But there is a mesophytic flora even
-in deserts, which appears during the rainy season where temperature
-conditions are favorable for growth. This is sometimes spoken of as the
-rainy-season flora. The plants are annuals and by formation of seed can
-tide over the dry season. So in the region where mesophytes grow there
-are xerophytes, examples being the evergreens like the pines, spruces,
-rhododendrons; or succulent plants like the stonecrop, the purslane,
-etc. Then among hydrophytes the semiaquatics are really xerophytes. The
-roots are in water, and absorption is slow because there are no root
-hairs, or but few, and the aerial parts of the plant are xerophytic.</p>
-
-<p class="center"><b>III. Plant Formations.</b></p>
-
-<p><b>911.</b> The term plant formation is applied to associations of
-plants of the same kind, though there is a great difference in the use
-<span class="pagenum"><a name="Page_470" id="Page_470">[Pg 470]</a></span>
-of the word by different writers which leads to some confusion.<a name="FNanchor_50_50" id="FNanchor_50_50"></a><a href="#Footnote_50_50" class="fnanchor">[50]</a>
-It is sometimes applied to an association of individuals of a species, or
-of several species occupying a rather definite area of ground where the
-soil conditions are not greatly different (individual formation); by
-others it is applied to the plants of a definite physiographic area, as
-a swamp, moor, strand, or beach, bank, rock hill, clay hill, ravine,
-bluff, etc. (principal formation); and in a broad sense it is applied
-to the plants of climatic regions, of those in bodies of water, etc.
-(general formations). Space here is too limited to discuss all these
-kinds of formations, but the nature of the general formations will be
-pointed out. The general formations may be grouped into four divisions:</p>
-
-<ul class="index">
-<li class="isub3">1st. Climatic formations.</li>
-<li class="isub3">2d. Edaphic formations.</li>
-<li class="isub3">3d. Aquatic formations.</li>
-<li class="isub3">4th. Culture formations.</li>
-</ul>
-
-<p><b>912. Climatic formations.</b>—Climatic influences extend over
-wide regions, so that climate controls the general type of vegetation
-of a region. In the sense of control there are two climatic factors,
-temperature and moisture, especially soil moisture. Temperature exerts
-a controlling influence over the vegetation type only where the total
-heat during the period of growth and reproduction is very low. This
-occurs in polar lands and at high elevations where the climate is
-alpine. In the temperate and tropical regions of the globe moisture,
-not heat, controls the general vegetation type. These vegetation types
-in general are coincident with rainfall distribution, and Schimper
-recognizes here three types, which with the arctic-alpine type would
-make four climatic formations as follows:</p>
-
-<p>1st. <i>The woodland formation.</i>—This formation is characterized by
-trees and shrubs, and it is what is called a <i>close</i> formation. By this
-it is meant that so far as the climate is concerned the conditions are
-favorable for the development of trees and shrubs in such abundance
-that they become the dominant vegetation type of the region and grow
-<span class="pagenum"><a name="Page_471" id="Page_471">[Pg 471]</a></span>
-close together. Other plants, as herbs, grasses, etc., occur, but
-they grow as subordinate elements of the general vegetation type, and
-as undergrowth. The land portion of the globe, therefore, outside of
-arctic and alpine regions, where the annual precipitation is 40 to 60
-or more inches, is the area for woodland formation. In some places,
-the eastern part of England, for example, the annual precipitation is
-25 to 30 inches, but the cool temperature permits a forest growth. It
-is true there are places where forests do not grow,—where man cuts
-them down, for example. But if cultivated lands in this region were
-allowed to go to waste, they would in time grow up to forest again.
-So there are swamps where the soil is too wet for trees, or sandy or
-rocky areas where there is not a sufficient amount of soil or water to
-support forest trees. But here it is the soil conditions, not climatic
-conditions, which prevent the development of the forest. But we know
-that swamps are being filled in and the ground gradually becoming
-higher and drier, and that soil is slowly accumulating in rocky areas,
-so that in time if left to natural forces these places would become
-forested. So this area of heavy annual rainfall is a <i>potential</i> forest
-area. These areas are determined by warm currents of moisture-laden
-air from the ocean moving over cooler land areas where the moisture
-is precipitated. In general these areas are along the coasts of great
-continents and on mountains. Therefore the interior of a continent is
-apt to be dry because most of the moisture has been precipitated before
-it reaches the interior. Deserts or steppes are therefore usually near
-the interior of continents. Some exceptions to this general rule are
-found: central South America, which is a region of exceptional rainfall
-because the moisture-laden winds here come from the warmest part of the
-ocean; the desert region west of the Andes mountains, where the winds
-are not favorable; southern California, where the winds come chiefly
-from a cooler portion of the Pacific ocean and move over an area of
-high temperature, etc.</p>
-
-<div class="figcenter">
-    <img src="images/fig486.jpg" alt="" width="500" height="360" />
-  <div class="blockquot">
-      <p class="center">Fig. 486.</p>
-      <p>Typical prairie scene, a few miles west of
-          Lincoln, Nebraska. (Bot. Dept., Univ. Nebraska.)</p>
-  </div>
-</div>
-
-<p>2d. <i>Grassland formation.</i>—Grasses form the dominant vegetation type
-where the annual rainfall is approximately 15 to 25 inches. In true
-<span class="pagenum"><a name="Page_472" id="Page_472">[Pg 472]</a></span>
-grasslands the formation is a close one since
-there is still a sufficient amount of moisture to provide for all
-the plants which can stand on the ground. Yet there is not
-enough moisture to permit the growth of forest as the dominant
-type without aid and protection by man. The so-called prairie
-regions are examples. Trees and shrubs do occur, but they
-cannot compete successfully with the grasses because the climatic
-conditions are favorable for the latter and unfavorable for the
-former. On the border line between forest and prairie the line
-of division is not a clear-cut one because conditions grade from
-one to the other. The two formations are somewhat mixed,
-like the outposts of contending armies, arms of the forest or
-prairie extending out here and there. In the United States the
-prairies extend from Illinois to about the 100th meridian, and
-beyond this to the foothills of the Rockies and southwest to the
-Sonora Nevada desert the region is drier, the rainfall varying
-from 10 to 20 inches. This is the area of the Great Plains,
-and while grasses of the bunch type are dominant, they make
-<span class="pagenum"><a name="Page_473" id="Page_473">[Pg 473]</a></span>
-a more or less open formation because the moisture is not sufficient
-to supply all the plants which could be crowded on the ground, each
-individual tuft needing an area of ground surrounding it on which it
-can draw for moisture. Such a formation is an open one, and in this
-respect is similar to desert formations.</p>
-
-<div class="figcenter">
-    <img src="images/fig487.jpg" alt="" width="600" height="339" />
-  <div class="blockquot">
-      <p class="center">Fig. 487.</p>
-      <p>Winter range in northwestern Nevada, showing open formation; white
-         sage (Eurotia lanata) in foreground, salt-bush (Atriplex confertifolia)
-         and bud-sage (Artemisia spinescens) at base of hill, red sage (Kochia
-         americana) on the higher slope. (After Griffiths, Bull. 38, Bureau
-         Plant Ind., U. S. Dept. Agr.)</p>
-  </div>
-</div>
-
-<p>3d. <i>Desert formations.</i>—These occur where the annual rainfall is
-still lower, 10 to 4 inches or even less, 2 to 3 inches, while in
-one place in Chili it is as low as ½ inch. In the great Sahara desert
-it is about 8 inches, while in the Sonora Nevada desert in the
-southwestern United States it is 4 to 8 inches. Here the formation is
-an open one. In the forest and prairie formations the plants compete
-with each other for occupancy of the ground, since climatic conditions
-are favorable, so that the struggle against climate is not severe.
-But in the desert plants do not compete with each other; since the
-climate is so austere, the struggle is against the climate. Hence
-plants stand at some distance from each other because the roots need
-the moisture from the ground for some distance around them. There is
-not enough moisture for all the plants that begin, and those which get
-<span class="pagenum"><a name="Page_474" id="Page_474">[Pg 474]</a></span>
-the start take the moisture away from the intervening ones, which then
-die. Since the struggle is against the adverse conditions of climate
-and not a competition between plants to occupy the ground, no one
-floristic type dominates as in the case of the grasses and forests of
-the grassland and woodland formations, but grassland and woodland types
-grow together. So we find grasses, trees, and shrubs growing without
-competition in the desert. The dominant vegetation type is xerophytic.</p>
-
-<div class="figcenter">
-    <img src="images/fig488.jpg" alt="" width="600" height="433" />
-      <p class="center">Fig. 488.<br />
-      Northern limit of tree growth, Alaska.<br />
-             (Copyright, 1899, by E. H. Harriman.)</p>
-</div>
-
-<p>4th. <i>Arctic-alpine formation.</i> This formation extends from the limit
-of tree growth to the region of perpetual ice and snow. The forest
-here comes in competition with climate, with the severe cold of the
-long winter night, so that tree growth is limited, and on the border
-line with the woodland formation the trees are stunted, bent to one
-side by the heavy snows, or the tops are killed by the cold wind. The
-arctic zone of plant growth is sometimes spoken of as the “cold waste,”
-since conditions here are somewhat similar to those in the desert, the
-<span class="pagenum"><a name="Page_475" id="Page_475">[Pg 475]</a></span>
-extreme cold exercising a drying effect on vegetation, and the
-vegetation type then is largely xerophytic.</p>
-
-<p><b>913. Edaphic<a name="FNanchor_51_51" id="FNanchor_51_51"></a><a href="#Footnote_51_51" class="fnanchor">[51]</a> formations.</b>—Edaphic
-formations may occur in any of the climatic-formation areas. They are
-controlled by the condition of soil or ground. The condition of the
-soil is unfavorable for the growth of the general vegetation type of
-that region, or is more favorable for another vegetation type, so
-that soil conditions overcome the climatic conditions. These areas
-include swamps, moors, the strand or beach, rocky areas, etc., as well
-as oases in the desert, warm oases in the arctic zone, river bottoms
-in the prairie and plains region, alkaline areas, etc. The edaphic
-formations may be close or open according to the nature of the soil.
-The edaphic formations then are infiltrated in the climatic formations,
-the different vegetation types fitting together like pieces of mosaic,
-which can be seen in some places from a mountain top, or if one could
-take a bird’s-eye view of the landscape or from a balloon.</p>
-
-<p><b>914. Aquatic formations.</b>—These are made up of water plants and
-are of two general kinds: fresh-water plant formations in ponds, lakes,
-streams; and salt-water plant formations in the ocean and inland salt
-seas.</p>
-
-<p><b>915. Culture formations.</b>—Culture formations are largely
-controlled by man, who destroys the climatic or edaphic formation and
-by cultivation protects cultivated types, or by allowing land to go to
-“waste” permits the growth of weeds, though weeds are often abundant
-in the culture areas. In general the culture formations may be grouped
-into two subdivisions: 1st, the vegetation of cultivated places; and
-2d, the vegetation of waste places, as abandoned fields, roadsides, etc.</p>
-
-<p class="center"><b>IV. Plant Societies.</b></p>
-
-<p><b>916. Plant societies</b> are somewhat definite associations of the
-vegetation of an area marked by physiographic conditions. A single
-<span class="pagenum"><a name="Page_476" id="Page_476">[Pg 476]</a></span>
-plant society is nearly if not altogether identical with a “<i>principal
-formation</i>,” but is a more popular expression, and besides includes all
-the plants growing on the area, while in the use of the term “principal
-formation” we have reference mainly to the dominant plants and the most
-conspicuous subordinate species.</p>
-
-<p><b>917. Complex character of plant societies.</b>—In their broadest
-analysis all plant societies are complex. Every plant society has one
-or several dominant species, the individuals of which, because of
-their number and size, give it its peculiar character. The society may
-be so nearly pure that it appears to consist of the individuals of a
-single species. But even in those cases there are small and conspicuous
-plants of other species which occupy spaces between the dominant ones.
-Usually there are several or more kinds in the same society. The larger
-individuals come into competition for first place in regard to ground
-and light, the smaller ones come into competition for the intervening
-spaces for shade, and so on down in the scale of size and shade
-tolerance. Then climbing plants (lianas) and epiphytes (lichens, algæ,
-mosses, ferns, tree orchids, etc.) gain access to light and support by
-growing on other larger and stouter members of the society.</p>
-
-<p>Parasites (dodder, mistletoes, rusts, smuts, mildews, bacteria, etc.)
-are present, either actually or potentially, in all societies, and in
-their methods of obtaining food sap the life and health of their hosts.
-Then come the scavenger members, whose work it is to clean house, as it
-were, the great army of saprophytic fungi (molds, mushrooms, etc.), and
-bacteria ready to lay hold on dead and dying leaves, branches, trunks,
-roots, etc., disintegrate them, and reduce them to humus, where other
-fungi change them into a form in which the larger members of the plant
-society can utilize them as plant food and thus continue the cycle of
-matter through life, death, decay, and into life again. Mycorhiza (see
-<a href="#CHAPTER_IX">Chapter IX</a>) or other forms of mutualistic symbiosis occur
-which make atmospheric nitrogen available for food, or shorten the path from humus
-to available food, or the humus plants feed on the humus directly.
-Nor should we leave out of account the myriads of nitrate and nitrite
-<span class="pagenum"><a name="Page_477" id="Page_477">[Pg 477]</a></span>
-bacteria (see <a href="#CHAPTER_IX">Chapter IX</a>) which make certain substances
-in the soil available to the higher members of the society. Most plant societies
-are also benefited or profoundly influenced in other ways by animals,
-as the flower-visiting insects, birds which feed on injurious insects,
-the worms which mellow up the soil and cover dead organic matter so
-that it may more thoroughly decay. In short, every plant society is
-a great cosmos like the universe itself of which it is a part, where
-multitudinous forms, processes, influences, evolutions, degenerations,
-and regenerations are at work.</p>
-
-<p><b>918. Forest Societies.</b><a name="FNanchor_52_52" id="FNanchor_52_52"></a><a href="#Footnote_52_52" class="fnanchor">[52]</a>—Each
-different climatic belt or region has its characteristic forest.
-For example, the forests of the Hudsonian zone in North America are
-different from those of the Canadian zone, and these in turn different
-from those in the transition zone (mainly in northern United States).
-The forests of the Rocky mountains and of the Pacific coast differ from
-those of the Alleghanian, Carolinian (mainly middle United States)
-or Austroriparian (southern United States) areas. Finally, tropical
-forests are strikingly different from those of other regions. Similar
-variations occur in the forests of other regions of the globe. The
-character of these forests depends largely on climatic factors. The
-character of the forest varies, however, even in the same climatic
-area, dependent on soil conditions, or success in seeding and
-ground-gaining of the different species in competition, etc.</p>
-
-<p><b>919. General structure of the forest.</b>—Structurally the forest
-possesses three subdivisions: the floor, the canopy, and the interior.
-The floor is the surface soil, which holds the rootage of the trees,
-with its covering of leaf-mold and carpet of leaves, mosses, or other
-low, more or less compact vegetation. The canopy is formed by the
-spreading foliage of the tree crowns, which, in a forest of an even
-and regular stand, meet and form a continuous mass of foliage through
-which some light filters down into the interior. Where the stand is
-<span class="pagenum"><a name="Page_478" id="Page_478">[Pg 478]</a></span>
-irregular, i.e., the trees of different heights, the canopy is said to
-be “compound” or “storied.” Where it is uneven, there are open places
-in the canopy which admit more light, in which case the undergrowth
-may be different. The interior of the forest lies between the canopy
-and the floor. It provides for aeration of the floor and interior
-occupants, and also room for the boles or tree trunks (called by
-foresters the wood mass of the forest) which support the canopy and
-provide the channels for communication and food exchange between the
-floor and canopy. The canopy manufactures the carbohydrate food and
-assimilates the mineral and proteid substances absorbed by the roots in
-the soil; and also gets rid of the surplus water needed for conveying
-food materials from the floor to the place where they are elaborated.
-It is the seat where energy is created for work, and also the place for
-seed production.</p>
-
-<div class="figcenter">
-    <img src="images/fig489.jpg" alt="" width="600" height="480" />
-      <p class="center">Fig. 489.<br />
-           Mature forest of redwood (Sequoia sempervirens).<br />
-           (Bureau of Forestry, U. S. Dept. Agr., Bull. 38.)</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_479" id="Page_479">[Pg 479]</a></span>
-<b>920. Longevity of the forest.</b>—The forest is capable of
-self-perpetuation, and, except in case of unusual disaster or the
-action of man, it should live indefinitely. As the old trees die they
-are gradually replaced by younger ones. So while trees may come and
-trees may go, the forest goes on forever.</p>
-
-<p><b>921. Autumn colors.</b>—One of the striking effects produced by
-the deciduous forests is that of the autumn coloring of the leaves.
-It is more pronounced in the forests of the United States than in
-corresponding life zones in the eastern hemisphere because of the
-greater number of species. With the disintegration of the chlorophyll
-bodies, other colors, which in some cases were masked by the green,
-appear. In other cases decomposition products result in the formation
-of other colors, as red, scarlet, yellow, brown, purple, maroon, etc.,
-in different species. These coloring substances to some extent are
-believed to protect the nitrogenous substances in the leaf from injury.
-The colors absorb the sun’s rays, which otherwise might destroy these
-nitrogenous substances before they have passed back through the petiole
-of the leaf into the stem, where they may be stored for food. The
-gorgeous display of color, then, which the leaves of many trees and
-shrubs put on is one of the many useful adaptations of the plants.</p>
-
-<p><b>922. Importance of the forest in the disposal of rainfall.</b>—The
-importance of the forest in disposing of the rainfall is very great.
-The great accumulation of humus on the forest floor holds back the
-water both by absorption and by checking its flow, so that it does not
-immediately flow quickly off the slopes into the drainage system of the
-valley. It percolates into the soil. Much of it is held in the humus
-and soil. What is not retained thus filters slowly through the soil
-and is doled out more gradually into the valley streams and mountain
-tributaries, so that the flood period is extended, and its injury
-lessened or entirely prevented, because the body of water moving at any
-one time is not dangerously high. The winter snow is shaded and in the
-spring melts slowly, and the spring freshets are thus lessened. The
-<span class="pagenum"><a name="Page_480" id="Page_480">[Pg 480]</a></span>
-action of the leaves and humus in retarding the flow of the water
-prevents the washing away of the soil; the roots of trees bind the soil
-also and assist in holding it.</p>
-
-<p><b>923. Absence of forest encourages serious floods.</b>—The great
-floods of the Mississippi and its tributaries are due to the rapidity
-with which heavy rainfall flows from the rolling prairies of the west,
-and from the deforested areas west of the Alleghany system. The serious
-floods in recent years in some of the South Atlantic States are in
-part due to the increasing area of deforestation in the Blue Ridge and
-southern Alleghany system.</p>
-
-<p><b>924. The prairie and plains societies.</b>—These are to be found
-in the grassland formation. In the prairies “meadows” are formed in
-the lower ground near river courses where there is greater moisture
-in soil. The grasses here are principally “sod-formers” which have
-creeping underground stems which mat together, forming a dense sod. On
-the higher and drier ground the “bunch” grasses, like buffalo-grass,
-beard-grass, or broom-sedge, etc., are dominant, and in the drier
-regions as one approaches desert conditions the vegetation gradually
-takes on more the character of the desert, so that in the plains
-sage-brush, the prickly-pear cactus, etc., occur. Besides the dominant
-vegetation of the society there are subordinate species, and the
-societies are especially marked by a spring and autumn flora of
-conspicuous flowering plants which are mixed with the grasses.</p>
-
-<p><b>925. Desert societies.</b>—These are composed of plants which
-possess a form or structure which enables them to exist in a very
-dry climate where the air is very dry and the soil contains but
-little moisture. The true desert plants are perennial. The growth and
-flowering period occurs during the rainy season, or those portions
-of the rainy season when the temperature is favorable, and they rest
-during the very dry season and cold. Characteristic desert plants are
-the cacti with thick succulent green stems or massive trunks, the
-leaves being absent or reduced to mere spines which no longer function
-in photosynthesis; yuccas with thick, narrow and long leaves with a
-firm and thick cuticle; small shrubs or herbs with compact rounded
-habit and small thick gray leaves. All of these structures conserve
-<span class="pagenum"><a name="Page_481" id="Page_481">[Pg 481]</a></span>
-moisture. The mesquite tree is one of the common trees in portions
-of the Sonora Nevada desert. Besides the true desert plants, desert
-societies have a rainy-season flora consisting of annuals, which can
-germinate, vegetate, flower, and seed during the period of rain and
-before the ground moisture has largely disappeared, and these pass the
-resting period in seed.</p>
-
-<div class="figcenter">
-    <img src="images/fig490.jpg" alt="" width="600" height="438" />
-  <div class="blockquot">
-      <p class="center">Fig. 490.</p>
-      <p>Desert vegetation, Arizona, showing large succulent trunks of cactus
-         with shrubs and stunted trees. Open formation. (Photograph by Tuomey.)</p>
-  </div>
-</div>
-<div class="figcenter">
-    <img src="images/fig491.jpg" alt="" width="600" height="436" />
-      <p class="center">Fig. 491.<br /> Polar tundra with scattered flowers, Alaska.<br />
-              (Copyright by E. H. Harriman.)</p>
-</div>
-<div class="figcenter">
-    <img src="images/fig492.jpg" alt="" width="600" height="284" />
-  <div class="blockquot">
-      <p class="center">Fig. 492.</p>
-      <p>Perennial rosette plant from alpine flora of the Andes, showing
-         short stem, rosette of leaves, and large flower. (After Schimper.)</p>
-  </div>
-</div>
-
-<p><b>926. Arctic-alpine societies.</b>—The most striking of the arctic
-plant societies are the “polar tundra,” extensive mats of vegetation
-largely made up of mosses, lichens, etc., only partially decayed
-because of the great cold of the subsoil, and perhaps also because
-of humus acid in the partially decayed vegetation. These tundras
-are brightened by numerous flowering plants which are characterized
-by short stems, a rosette of leaves near the ground, and by large
-bright-colored flowers. Heaths, saxifrages, and dwarf willow abound.
-Alpine plant societies are similar to the arctic, although some of the
-<span class="pagenum"><a name="Page_482" id="Page_482">[Pg 482]</a></span>
-conditions are more severe than in the arctic region. This is
-principally due to the fact that during the summer while the plants are
-growing they are subject to a high temperature during the day and a
-<span class="pagenum"><a name="Page_483" id="Page_483">[Pg 483]</a></span>
-very low temperature at night, whereas during the summer in arctic
-regions while the plants are growing there is continuous warmth for
-growth and continuous light for photosynthesis. Five types of alpine
-plants are recognized by some. 1st. <i>Elfin tree.</i> This type has short,
-gnarled, often horizontal stems, as seen in pines, birches, and other
-trees growing in alpine heights. 2d. <i>The alpine shrubs.</i> In the
-highest alpine belts they are dwarfed and creeping, richly branched and
-spreading close to the ground, while at lower belts they are more like
-lowland shrubs. 3d. <i>The cushion type.</i> The branching is very profuse
-and the branches are short and touch each other on all sides, forming
-compact masses (examples saxifrages, androsace, mosses, etc.). 4th.
-<i>Rosette plants.</i> These are perennial, short stems and very strong
-roots, and play an important part in the alpine meadows. 5th. <i>Alpine
-grasses.</i> These usually have much shorter leaves than grasses of the
-lowlands and consequently form a low sward.</p>
-
-<p><b>927. Edaphic plant societies.</b>—These are equivalent to edaphic
-plant formations, and the vegetation is of course controlled by the
-peculiar conditions of the soil. There are a number of different
-kinds of edaphic plant societies determined by the character of the
-physiographic areas. 1st. <i>Sphagnum moors.</i> These are formed in shallow
-basins originally with more or less water. The growth of the sphagnum
-moss along with other vegetation and its partial decay in the water
-builds up ground rapidly so that in course of time the pond may be
-completely filled in. This filling in proceeds from the shore toward
-the center, and in the early stages of course there would be a pond
-in the center. The partial decay of vegetation creates an excess of
-humus acid which retards absorption by the roots. The conditions are
-such, then, as require aerial structures for retarding the loss of
-water, and plants growing in such moors are usually xerophytes. Some of
-the plants are identical with those growing in the arctic tundra. 2d.
-<i>Sand</i><a name="FNanchor_53_53" id="FNanchor_53_53"></a><a href="#Footnote_53_53" class="fnanchor">[53]</a> <i>strand of beach.</i>
-The quantity of sand with very little or no admixture of humus or plant
-<span class="pagenum"><a name="Page_484" id="Page_484">[Pg 484]</a></span>
-food makes it difficult for plants to obtain a sufficient amount of
-water even where rainfall is abundant. The same may be said of the sand
-dunes farther back from the shore. The plants of these areas are then
-usually xerophytes. Some of the plants accustomed to growing in such
-localities are American sea-rocket, seaside spurge, bugseed, sea-blite,
-sea-purslane, the sandcherry, dwarf willow, marram-grass, certain
-species of beard-grass, etc. 3d. <i>Rocky shores or areas.</i> Here lichens
-and mosses first grow, later to be followed by herbs, grasses, shrubs,
-and trees, as decayed plant remains accumulate in the rock crevices.
-4th. <i>Shores of ponds, or swamp moors.</i> Here the vegetation often
-takes on a zonal arrangement if the ground gradually slopes to the
-shore and out into the pond. In <a href="#FIG_493">Fig. 493</a> is shown zonal
-distribution of plants. The different kinds of plants are drawn into these zones
-by the varying amount of ground water in the soil, or the varying depth
-of the water on the margin of the pond as one proceeds from the land
-towards the deeper water. On the border lines or tension lines between
-the different zones the plants are struggling to occupy here ground
-which is suitable for each adjacent individual formation. Other edaphic
-societies are those of marl ponds, alkaline areas, oases in deserts,
-warm oases in arctic lands, the forested areas along river bottoms in
-prairie or plains regions, etc.
-<span class="pagenum"><a name="Page_485" id="Page_485">[Pg 485]</a></span></p>
-
-<div class="figcenter">
-    <img  id="FIG_493" src="images/fig493.jpg" alt="" width="600" height="311" />
-  <div class="blockquot">
-      <p class="center">Fig. 493.</p>
-      <p>Macrophytes in the upper zone of the photic region. Ascophyllum and
-         Fucus at low tide, Hunter’s Island, New York City. (Photograph by M. A. Howe.)</p>
-  </div>
-</div>
-<div class="figcenter">
-    <img src="images/fig494.jpg" alt="" width="600" height="358" />
-      <p class="center">Fig. 494. <br />
-          Zonal distribution of plants, South Shore, Cayuga Lake.</p>
-</div>
-
-<p><span class="pagenum"><a name="Page_486" id="Page_486">[Pg 486]</a></span>
-<b>928. Aquatic plant societies.</b>—In general we might distinguish
-three kinds, 1st. <i>Fresh-water plant societies</i>, with floating algæ
-like spirogyra, œdogonium, etc., the floating duck-meats, riccias; the
-plants of the lily type with roots and stems attached to the bottom
-and leaves floating on the surface, like the water-lily and certain
-pondweeds, and finally the completely submerged ones like certain
-pondweeds, the bassweed (Chara), etc. 2d. <i>Marine plant societies</i>,
-which are made up mostly of the red and brown algæ or “seaweeds,”
-though some green algæ and flowering plants also occur. 3d. <i>The salt
-marshes</i> where the water is brackish and there is usually a luxuriant
-growth of marsh-grasses.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_487" id="Page_487">[Pg 487]</a></span></p>
-<div class="chapter">
-<h3 class="nobreak"><a name="CHAPTER_XLVII" id="CHAPTER_XLVII">CHAPTER XLVII.</a><br />
-<span class="h_subtitle">CLASSIFICATION OF THE ANGIOSPERMS.</span></h3>
-</div>
-
-<p class="center"><b>Relation of Species, Genus, Family, Order, etc.</b></p>
-
-<p><b>929. Species.</b>—It is not necessary for one to be a botanist in
-order to recognize, during a stroll in the woods where the trillium
-is flowering, that there are many individual plants very like each
-other. They may vary in size, and the parts may differ a little in
-form. When the flowers first open they are usually white, and in age
-they generally become pinkish. In some individuals they are pinkish
-when they first open. Even with these variations, which are trifling
-in comparison with the points of close agreement, we recognize the
-individuals to be of the <i>same kind</i>, just as we recognize the corn
-plants, grown from the seed of an ear of corn, as of the same kind.
-Individuals of the same kind, in this sense, form a <i>species</i>. The
-white wake-robin, then, is a species.</p>
-
-<p>But there are other trilliums which differ greatly from this one. The
-purple trillium (T. erectum) shown in <a href="#FIG_495">fig. 495</a> is very
-different from it. So are a number of others. But the purple trillium
-is a species. It is made up of individuals variable, yet very like one
-another, more so than any one of them is like the white wake-robin.</p>
-
-<p><b>930. Genus.</b>—Yet if we study all parts of the plant, the
-perennial rootstock, the annual shoot, and the parts of the flower, we
-find a great resemblance. In this respect we find that there are
-several species which possess the same general characters. In other
-<span class="pagenum"><a name="Page_488" id="Page_488">[Pg 488]</a></span>
-words, there is a relationship between these different species, a
-relationship which includes more than the individuals of one kind. It
-includes several kinds. Obviously, then, this is a relationship with
-broader limits, and of a higher grade, than that of the individuals
-of a species. The grade next higher than species we call <i>genus</i>.
-Trillium, then, is a genus. Briefly the characters of the genus
-trillium are as follows:</p>
-
-<div class="figcenter">
-    <img  id="FIG_495" src="images/fig495.jpg" alt="" width="300" height="422" />
-      <p class="center">Fig. 495.<br /> Trillium erectum (purple form),<br />
-           two plants from one rootstock.</p>
-</div>
-
-<p><b>931. Genus trillium.</b>—Perianth of six parts: sepals 3,
-herbaceous, persistent; petals colored. Stamens 6 (in two whorls),
-anthers opening inward. Ovary 3-loculed, 3-6-angled; stigmas 3,
-slender, spreading. Herbs with a stout perennial rootstock, with
-fleshy, scale-like leaves, from which the low annual shoot arises,
-bearing a terminal flower and 3 large netted-veined leaves in a whorl.</p>
-
-<p class="blockquot"><i>Note.</i>—In speaking of the genus the present usage
-is to say trillium, but two words are usually employed in speaking of
-the species, as Trillium grandiflorum, T. erectum, etc.</p>
-
-<p><b>932. Genus erythronium.</b>—The yellow adder-tongue, or dogtooth
-violet (Erythronium americanum), shown in <a href="#FIG_496">fig. 496</a>,
-is quite different from any species of trillium. It differs more from any of
-the species of trillium than they do from each other. The perianth is of six
-parts, light yellow, often spotted near the base. Stamens are 6. The ovary is
-obovate, tapering at the base, 3-valved, seeds rather numerous, and the
-style is elongated. The flower stem, or scape, arises from a scaly bulb
-<span class="pagenum"><a name="Page_489" id="Page_489">[Pg 489]</a></span>
-deep in the soil, and is sheathed by two elliptical-lanceolate, mottled
-leaves. The smaller plants have no flower and but one leaf, while the
-bulb is nearer the surface. Each year new bulbs are formed at the end
-of runners from a parent bulb. These runners penetrate each year deeper
-into the soil. The deeper bulbs bear the flower stems.</p>
-
-<p><b>933. Genus lilium.</b>—While the lily differs from either the
-trillium or erythronium, yet we recognize a relationship when we
-compare the perianth of six colored parts, the 6 stamens, and the
-3-sided and long 3-loculed ovary.</p>
-
-<div class="figcenter">
-    <img  id="FIG_496" src="images/fig496.jpg" alt="" width="450" height="425" />
-  <div class="blockquot">
-      <p class="center">Fig. 496.</p>
-      <p>Adder-tongue (erythronium). At left below pistil, and three stamens
-         opposite three parts of the perianth. Bulb at the right.</p>
-  </div>
-</div>
-
-<p><b>934. Family Liliaceæ.</b>—The relationship between genera, as
-between trillium, erythronium, and lilium, brings us to a still higher
-order of relationship, where the limits are broader than in the genus.
-Genera which are thus related make up the <i>family</i>. In the case of
-these genera the family has been named after the lily, and is the lily
-family, or <i>Liliaceæ</i>.</p>
-
-<p><b>935. Order, class, group.</b>—In like manner the lily family, the
-iris family, the amaryllis family, and others which show characters of
-close relationship are united into an <i>order</i> which has broader limits
-<span class="pagenum"><a name="Page_490" id="Page_490">[Pg 490]</a></span>
-than the family. This order is the lily order, or order <i>Liliales</i>. The
-various orders unite to make up the <i>class</i>, and the classes unite to
-form a <i>group</i>.</p>
-
-<p><b>936. Variations in usage of the terms class, order, etc.</b>—Thus,
-according to the system of classification adopted by some, the
-angiosperms form a <i>group</i>. The group angiosperms is then divided into
-two <i>classes</i>, the <i>monocotyledones</i> and <i>dicotyledones</i>. (It
-should be remembered that all systematists do not agree in assigning the
-same grade and limits to the classes, subclasses, etc. For example,
-some treat of the angiosperms as a class, and the monocotyledons
-and dicotyledons as subclasses; while others would divide the
-monocotyledons and dicotyledons into classes, instead of treating each
-one as a class or as a subclass. Systematists differ also in usage as
-to the termination of the ordinal name; for example, some use the word
-<i>Liliales</i> for <i>Liliifloræ</i>, in writing of the order.)</p>
-
-<div class="figcenter">
-    <img  id="FIG_497" src="images/fig497.jpg" alt="" width="600" height="269" />
-  <div class="blockquot">
-      <p class="center">Fig. 497.</p>
-      <p><i>A.</i> Cross-section of the stem of an oak tree thirty-seven years old,
-         showing the annual rings. <i>rm</i>, the medullary rays; <i>m</i>, the pith
-        (medulla).<br />&emsp;<i>B.</i> Cross-section of the stem of a palm tree, showing the
-        scattered bundles.</p>
-  </div>
-</div>
-
-<p><b>937. Monocotyledones.</b>—In the monocotyledons there is a single
-cotyledon on the embryo; the leaves are parallel-veined; the parts
-of the flower are usually in threes; endosperm is usually present in
-the seed; the vascular bundles are usually closed, and are scattered
-irregularly through the stem as shown by a cross-section of the stem
-of a palm (<a href="#FIG_497">fig. 497</a>), or by the arrangement of the bundles in the corn
-stem (<a href="#FIG_57">fig. 57</a>). Thus a single character is not sufficient to show
-<span class="pagenum"><a name="Page_491" id="Page_491">[Pg 491]</a></span>
-relationship in the class (nor is it in orders, nor in many of the
-lower grades), but one must use the sum of several important characters.</p>
-
-<p><b>938. Dicotyledones.</b>—In the dicotyledons there are two
-cotyledons on the embryo; the venation of the leaves is reticulate;
-the endosperm is usually absent in the seed; the parts of the flower
-are frequently in fives; the vascular bundles of the stem are
-generally open and arranged in rings around the stem, as shown in the
-cross-section of the oak (<a href="#FIG_497">fig. 497</a>). There are exceptions
-to all the above characters, and the sum of the characters must be considered,
-just as in the case of the monocotyledons.</p>
-
-<p><b>939. Taxonomy.</b>—This grouping of plants into species, genera,
-families, etc., according to characters and relationships is
-<i>classification</i>, or <i>taxonomy</i>.</p>
-
-<p>To take Trillium grandiflorum for example, its position in the system,
-if all the principal subdivisions should be included in the outline,
-would be indicated as follows:</p>
-
-<ul class="index">
-<li class="isub1">Group, Angiosperms.</li>
-<li class="isub2">Class, Monocotyledones.</li>
-<li class="isub3">Order, Liliales.</li>
-<li class="isub4">Family, Liliaceæ.</li>
-<li class="isub5">Genus, Trillium.</li>
-<li class="isub6">Species, grandiflorum.</li>
-</ul>
-
-<p>In the same way the position of the toothwort would be indicated as
-follows:</p>
-
-<ul class="index">
-<li class="isub1">Group, Angiosperms.</li>
-<li class="isub2">Class, Dicotyledones.</li>
-<li class="isub3">Order, Papaverales.</li>
-<li class="isub4">Family, Cruciferæ.</li>
-<li class="isub5">Genus, Dentaria.</li>
-<li class="isub6">Species, diphylla.</li>
-</ul>
-
-<p>But in giving the technical name of the plant only two of these names
-are used, the genus and species, so that for the toothwort we say
-<i>Dentaria diphylla</i>, and for the white wake-robin we say <i>Trillium
-grandiflorum</i>.</p>
-
-<p><b>940. Kingdom and Subkingdom.</b>—Organic beings form altogether two
-<span class="pagenum"><a name="Page_492" id="Page_492">[Pg 492]</a></span>
-kingdoms, the Animal Kingdom and the Plant Kingdom. The Plant Kingdom
-is then divided into a number of subkingdoms as follows: 1st,
-Subkingdom Thallophyta, the thallus plants, including the Algæ and
-Fungi; 2d, Subkingdom Bryophyta, the moss-like plants, including the
-Liverworts and Mosses; 3d, Subkingdom Pteridophyta, the fern-like
-plants, including Ferns, Lycopods, Equisetum, Isoetes, etc.; 4th,
-Subkingdom Spermatophyta, the seed plants, including Gymnosperms and
-Angiosperms. Subkingdoms are divided into groups of lower order down to
-the classes. So there are subclasses, subfamilies or tribes, subgenera,
-and even subspecies. But taking the principal taxonomic divisions from
-the greater to the lesser rank, the order would be as follows:</p>
-
-<ul class="index">
-<li class="isub1">Plant Kingdom.</li>
-<li class="isub2">Subkingdom, Spermatophyta.</li>
-<li class="isub3">Group (not used in a definite sense).</li>
-<li class="isub4">Class, Gymnospermæ.</li>
-<li class="isub5">Order, Pinales.</li>
-<li class="isub6">Family, Pinaceæ.</li>
-<li class="isub7">Genus, Pinus.</li>
-<li class="isub8">Species, strobus, or, in full,</li>
-<li class="isub1">Pinus strobus, the white pine.</li>
-</ul>
-
-<p class="center"><b>Group Angiospermæ.</b></p>
-
-<p class="center">I. CLASS MONOCOTYLEDONES.</p>
-
-<p><b>941. Order Pandanales.</b>—Aquatic or marsh plants. The cattail
-flags (Typha) and the bur-reeds (Sparganium), each representing a
-family. The name of the order is taken from the tropical genus Pandanus
-(the screw-pine often grown in greenhouses).</p>
-
-<p><b>942. Order Naiadales.</b>—Aquatic or marsh herbs. Three families
-are mentioned here.</p>
-
-<p>The pondweed family (Naiadaceæ), named after one genus, Naias. The
-largest genus is Potamogeton, the species of which are known as
-<span class="pagenum"><a name="Page_493" id="Page_493">[Pg 493]</a></span>
-pondweeds. Ruppia occidentalis occurs in saline ponds in Nebraska, and
-R. maritima along the seacoast and in saline districts in the interior.</p>
-
-<p>The water-plantain family (Alismaceæ) includes the water-plantain
-(Alisma) and the arrow-leaves (Sagittaria).</p>
-
-<p>The tape-grass family (Vallisneriaceæ) includes the tape-grass, or
-eel-grass (the curious Vallisneria spiralis).</p>
-
-<p><b>943. Order Graminales.</b>—Two families.</p>
-
-<p>The grass family (Gramineæ), the grasses and grains.</p>
-
-<p>The sedge family (Cyperaceæ), the sedges.</p>
-
-<p><b>944. Order Palmales</b>, with one family, Palmaceæ, includes the
-palms, abundant in the tropics and extending into Florida. Cultivated
-in greenhouses.</p>
-
-<p><b>945. Order Arales.</b></p>
-
-<p>The arum family (Araceæ). Flowers in a fleshy spadix. Examples: Indian
-turnip (Arisæma), sweet-flag (Acorus), skunk-cabbage (Spathyema).</p>
-
-<p>The duckweed family (Lemnaceæ). (Examples: Lemna, Spirodela, Wolffia.
-<a href="#PARA_51">See paragraphs 51-53</a>.)</p>
-
-<p><b>946. Order Xyridales</b>, from the genus Xyris, the yellow-eyed
-grass family (Xyridaceæ). Species mostly tropical, but a few in North
-America. Other examples are the pipewort family (Eriocaulaceæ, example,
-Eriocaulon septangulare), the pineapple family (Bromeliaceæ, example,
-the pineapple cultivated in Florida); the Florida moss or hanging moss
-(Tillandsia usneoides); the spiderwort family (Commelinaceæ), including
-the spiderwort (Tradescantia, several species in North America); the
-pickerel-weed family (Pontederiaceæ), including the genus Pontederia in
-borders of ponds and streams.</p>
-
-<p><b>947. Order Liliales.</b>—Some of the families are as follows:</p>
-
-<p>The rush family (Juncaceæ, example, Juncus), with many species, plants
-of usually swamp habit.</p>
-
-<p>The lily family (Liliaceæ, examples: Lilium, Allium = Onion,
-Erythronium, Yucca).</p>
-
-<p>The iris family (Iridaceæ, examples: Iris, the blue-flag, fleur-de-lis, etc.).
-<span class="pagenum"><a name="Page_494" id="Page_494">[Pg 494]</a></span></p>
-
-<p>The lily-of-the-valley family (Convallariaceæ, examples:
-lily-of-the-valley, Trillium, etc.)</p>
-
-<p>The amaryllis family (Amaryllidaceæ, examples: Narcissus, the daffodil;
-Cooperia, in southwestern United States).</p>
-
-<p><b>948. Order Scitaminales.</b>—This order includes the large showy
-cultivated Canna of the canna family.</p>
-
-<p><b>949. Order Orchidales.</b> Example, the orchid family (Orchidaceæ)
-with Cypripedium, Orchis, etc.</p>
-
-<p class="center">II. CLASS DICOTYLEDONES.</p>
-
-<p><span class="smcap">Series</span> 1. CHORIPETALÆ. Petals wanting (Apetalæ, or
-Archichlamydæ of some authors), or present and distinct from one
-another (Polypetalæ, or Metachlamydæ).</p>
-
-<p><b>950. Order Casuarinales</b>, confined to tropical seacoasts
-(example, Casuarina).</p>
-
-<p><b>951. Order Piperales</b> includes the lizard’s-tail family
-(Saururaceæ), Saururus cernuus, lizard’s-tail, in the eastern United
-States.</p>
-
-<p><b>952. Order Salicales.</b>—Shrubs or trees, flowers in aments.
-Includes the willows and poplars (Salix and Populus of the willow
-family, Salicaceæ).</p>
-
-<p><b>953. Order Myricales.</b>—Shrubs or small trees. Includes the
-sweet-gale (Myrica gale) in wet places in northern United States and
-British North America, Myrica cerifera forming thickets on sand dunes
-along the Atlantic coast, and the sweet-fern (Comptonia peregrina = C.
-asplenifolia) in the eastern United States in dry soil of hillsides.</p>
-
-<p><b>954. Order Leitneriales.</b>—Shrubs or trees. Includes the
-cork-wood, Leitneria floridana (Leitneriaceæ).</p>
-
-<p><b>955. Order Juglandales.</b>—Trees, staminate flowers in aments. The
-walnut family (Juglandaceæ, examples: walnut, butternut, etc. Juglans;
-hickory, Hicoria = Carya).</p>
-
-<p><b>956. Order Fagales.</b>—Trees and shrubs. Flowers in aments, or the
-pistillate ones with an involucre which forms a cup in fruit, as in the
-acorn of the oak.
-<span class="pagenum"><a name="Page_495" id="Page_495">[Pg 495]</a></span></p>
-
-<p>The birch family (Betulaceæ, examples: Betula, birch; Corylus,
-hazelnut; Alnus, alder, etc.).</p>
-
-<p>The beech family (Fagaceæ = Cupuliferæ, examples: Fagus, beech;
-Castanea, chestnut; Quercus, oak).</p>
-
-<p><b>957. Order Urticales.</b>—Trees, shrubs, or herbs. Examples: the
-elm family (Ulmaceæ), the mulberry family (Moraceæ), and the nettle
-family (Urticaceæ).</p>
-
-<p><b>958. Order Santalales</b>, herbs or shrubs, mostly parasitic.</p>
-
-<p>The mistletoe family (Loranthaceæ), with the American mistletoe
-(Phoradendron flavescens), parasitic on deciduous trees in the South
-Atlantic, Central, and Gulf States (N. J. to Ind. Ter.).</p>
-
-<p>The sandalwood family (Santalaceæ, example, the bastard toad-flax,
-Comandra umbellata), widely distributed in North America.</p>
-
-<p><b>959. Order Aristolochiales.</b>—Herbs or vines with heart-shaped or
-kidney-shaped leaves. The birthwort family (Aristolochiaceæ, example,
-Aristolochia serpentaria, the Virginia snake-root, eastern United
-States; wild ginger, or heart-leaf, Asarum canadense, eastern North
-America.)</p>
-
-<p><b>960. Order Polygonales.</b>—Examples: the buckwheat family
-(Polygonaceæ), including buckwheat (Fagopyrum), and numerous species
-of Polygonum, known as smartweed, water-pepper, tear-thumb, bindweed,
-knotweed, prince’s-feather, etc.</p>
-
-<p><b>961. Order Chenopodiales.</b>—Herbs. There are several families;
-one of the largest is the goosefoot family (Chenopodiaceæ). The genus
-Chenopodium includes many species, known as goosefoot, lamb’s-quarters,
-etc. Here belong also the Russian thistle (Salsola tragus) and the
-saltwort (S. kali). The former is sometimes a troublesome weed in the
-central and western United States, naturalized from Europe. The latter
-occurs along the Atlantic coast on seabeaches. Atriplex occurs in salty
-or alkaline soil, also the glasswort (Salicornia herbacea), the bugseed
-(Corispermum). The pokeweed family (Phytolaccaceæ), the Amaranth family
-(Amaranthaceæ), the purslane family (Portulacaceæ, including the
-<span class="pagenum"><a name="Page_496" id="Page_496">[Pg 496]</a></span>
-purslane or “pursley,” Portulaca oleracea, and the spring-beauty,
-Claytonia virginica), and the pink family (Caryophyllaceæ), belong here.</p>
-
-<p><b>962. Order Ranales.</b>—Herbs, shrubs, or trees. Examples are:</p>
-
-<p>The water-lily family (Nymphæaceæ), with the yellow water-lily (Nymphæa
-advena = Nuphar advena) and the white water-lily (Castalia odorata =
-Nymphæa odorata).</p>
-
-<p>The magnolia family (Magnoliaceæ), including the magnolias
-(Magnolia) and the tulip-tree (Liriodendron). The crowfoot family
-(Ranunculaceæ), with the buttercups, hepatica, clematis, etc.</p>
-
-<p><b>963. Order Papaverales.</b>—Mostly herbs. Examples are:</p>
-
-<p>The poppy family (Papaveraceæ), including the opium or garden poppy
-(Papaver somniferum), the blood-root (Sanguinaria canadensis), the
-Dutchman’s-breeches (Bicuculla cucullaria = Dicentra cucullaria),
-squirrel’s-corn (Bicuculla canadensis = D. canadensis).</p>
-
-<p>The mustard family (Cruciferæ), including the toothwort (Dentaria),
-shepherd’s-purse (Bursa bursa-pastoris = Capsella bursa-pastoris), the
-cabbage, turnip, etc.</p>
-
-<p><b>964. Order Sarraceniales.</b>—Insectivorous plants.</p>
-
-<p>The pitcher-plant family (Sarraceniaceæ). Examples: Sarracenia
-purpurea, the pitcher-plant, in peat-bogs, northern and eastern North
-America.</p>
-
-<p>The sundew family (Droseraceæ). Examples: Drosera rotundifolia, and
-other sundews.</p>
-
-<p><b>965. Order Rosales.</b>—Herbs, shrubs or trees. Seventeen families
-are given in the eastern United States. Examples:</p>
-
-<p>The riverweed family (Podostemaceæ), containing the riverweed
-(Podostemon).</p>
-
-<p>The saxifrage family (Saxifragaceæ), containing a number of species.
-Example, Saxifraga virginiensis.</p>
-
-<p>The gooseberry family (Grossulariaceæ), including the wild and the
-cultivated gooseberry.</p>
-
-<p>The witch-hazel family (Hamamelidaceæ), including the witch-hazel
-(Hamamelis), in eastern North America, and the sweet gum (Liquidambar
-styraciflua).
-<span class="pagenum"><a name="Page_497" id="Page_497">[Pg 497]</a></span></p>
-
-<p>The plane-tree family (Platanaceæ), with the plane-tree, or buttonwood
-(Platanus occidentalis), eastern North America. (Other species occur in
-western United States.)</p>
-
-<p>The rose family (Rosaceæ), including roses, spiræas, raspberries,
-strawberries, the shrubby cinquefoil (Dasiphora fruticosa), etc.</p>
-
-<p>The apple family (Pomaceæ), including the apple, mountain-ash, pear,
-June-berry (or shadbush, also service-berry), the hawthorns (Cratægus).</p>
-
-<p>The plum family (Drupaceæ), including the cherries, plums, peaches, etc.</p>
-
-<p>The pea family (Papilionaceæ), including the pea, bean, clover, vetch,
-lupine, etc., a very large family.</p>
-
-<p><b>966. Order Geraniales.</b>—Herbs, shrubs, or trees. Nine families
-in the eastern United States. Examples:</p>
-
-<p>The geranium family (Geraniaceæ), with the cranesbill (Geranium
-maculatum) and others.</p>
-
-<p>The wood-sorrel family (Oxalidaceæ), with the wood-sorrel (Oxalis
-acetosella) and others.</p>
-
-<p>The flax family (Linaceæ). Example, flax (Linum vulgaris).</p>
-
-<p>The spurge family (Euphorbiaceæ). Plants with a milky juice, and
-curious, degenerate flowers. Examples: the castor-oil plant (Ricinus),
-the spurges (many species of Euphorbia).</p>
-
-<p><b>967. Order Sapindales.</b>—Mostly trees or shrubs. Twelve families
-in the eastern United States. Example:</p>
-
-<p>The sumac family (Anacardiaceæ), containing the sumacs in the genus
-Rhus. Examples: the poison-ivy (R. radicans), a climbing vine, in
-thickets and along fences, in eastern United States. Sometimes
-trained over porches. The poison-oak (R. toxicodendron), a low shrub.
-Poison-sumac or poison-alder (R. vernix = R. venenata), sometimes
-called “thunderwood,” or dogwood, is a large shrub or small tree, very
-poisonous. The smoke-tree (Cotinus cotinoides) belongs to the same
-family, and is often planted as an ornamental tree. The maple family
-(Aceraceæ), including the maples (Acer).
-<span class="pagenum"><a name="Page_498" id="Page_498">[Pg 498]</a></span></p>
-
-<p>The buckeye family (Hippocastanaceæ), including the horse-chestnut
-(Æsculus hippocastanum), much planted as a shade tree along streets.
-Also there are several species of buckeye in the same genus.</p>
-
-<p>The jewelweed family (Balsaminaceæ), including the touch-me-not
-(Impatiens biflora and aurea) in moist places. The garden balsam (Imp.
-balsamea) also belongs here.</p>
-
-<p><b>968. Order Rhamnales.</b>—Shrubs, vines, or small trees. There are
-two families, the buckthorn (Rhamnaceæ), the grape family (Vitaceæ),
-including the grapes (Vitis), the American ivy (Parthenocissus
-quinquefolia = Ampelopsis quinquefolia), in woods and thickets, eastern
-North America, and much planted as a trailer over porches. The Japanese
-ivy (P. tricuspidata = A. veitchii) used as a trailer on the sides of
-buildings belongs here.</p>
-
-<p><b>969. Order Malvales.</b>—Herbs, shrubs, or trees.</p>
-
-<p>The linden family (Tiliaceæ). Example, the basswood or American linden
-(Tilia americana.)</p>
-
-<p>The mallow family (Malvaceæ), including the hollyhock, the mallows,
-rose of Sharon (Hibiscus), etc.</p>
-
-<p><b>970. Order Parietales</b>, with seven families in the eastern United
-States. The St. John’s wort (Hypericum) and the violets each represent
-a family. The violets (Violaceæ) are well-known flowers.</p>
-
-<p><b>971. Order Opuntiales.</b>—These include the cacti (Cactaceæ),
-chiefly growing in the dry or desert regions of America.</p>
-
-<p><b>972. Order Thymeleales</b>, with two families and few species.</p>
-
-<p><b>973. Order Myrtales.</b>—Land, marsh, or aquatic plants. The most
-conspicuous are in the evening primrose family (Onagraceæ), including
-the fireweeds, or willow herbs (Epilobium), and the evening primrose
-(Onagra biennis = Œnothera biennis).</p>
-
-<p><b>974. Order Umbellales.</b>—Herbs, shrubs, or trees, flowers in umbels.
-<span class="pagenum"><a name="Page_499" id="Page_499">[Pg 499]</a></span></p>
-
-<p>The ginseng family (Araliaceæ). This includes the spikenards and
-sarsaparillas in the genus Aralia, and the ginseng (or “sang”), Panax
-quinquefolium.</p>
-
-<p>The carrot family (Umbelliferæ). This family includes the wild carrot
-(Daucus carota), the poison-hemlock (Cicuta), the cultivated carrot and
-parsnip, and a large number of other genera and species.</p>
-
-<p>The dogwood family (Cornaceæ). The flowering dogwood (Cornus florida),
-abundant in eastern North America, is an example.</p>
-
-<p><span class="smcap">Series</span> 2. GAMOPETALÆ (= Sympetalæ or Metachlamydæ). Petals
-partly or wholly united, rarely separate or wanting.</p>
-
-<p><b>975. Order Ericales.</b>—There are six families in eastern United
-States. Examples:</p>
-
-<p>The wintergreen family (Pyrolaceæ), including the shin-leaf (Pyrola
-elliptica).</p>
-
-<p>The Indian-pipe family (Monotropaceæ), with the Indian-pipe (Monotropa
-uniflora) and other humus saprophytes. (<a href="#PARA_182">See paragraphs 182-191</a>.)</p>
-
-<p>The heath family (Ericaceæ). Examples: Labrador tea (Ledum), in bogs
-and swamps in northern North America. The azaleas, with several
-species widely distributed, are beautiful flowering shrubs, and many
-varieties are cultivated. The rhododendrons are larger with larger
-flower clusters, also beautiful flowering shrubs. R. maximum in the
-Alleghany Mountains and vicinity, from Nova Scotia to Ohio and Georgia.
-R. catawbiense, usually at somewhat higher elevations, Virginia to
-Georgia. The mountain laurel (Kalmia latifolia) and other species rival
-the rhododendrons and azaleas in beauty. The trailing arbutus (Epigæa
-repens) in sandy or rocky woods is a well-known small trailing shrub
-in eastern North America. The sourwood (Oxydendrum arboreum) is a tree
-with white racemes of flowers in August, and scarlet leaves in autumn.
-The spring or creeping wintergreen (Gaultheria procumbens) is a small
-shrub with aromatic leaves, and bright red spicy berries.</p>
-
-<p>The huckleberry family (Vaccinaceæ) includes the huckleberries
-<span class="pagenum"><a name="Page_500" id="Page_500">[Pg 500]</a></span>
-(example, Gaylussacia resinosa, the black or high-bush huckleberry,
-eastern United States), the mountain cranberry (Vitis-Idæa vitisidæa
-= Vaccinium vitisidæa) in the northern hemisphere; the bilberries and
-blueberries (of genus Vaccinium); the cranberries (examples: the large
-American cranberry, Oxycoccus macrocarpus and the European cranberry,
-Oxycoccus oxycoccus, in cold bogs of northern North America, the latter
-also in Europe and Asia).</p>
-
-<p><b>976. Order Primulales.</b>—Two families here. The primrose family
-(Primulaceæ) contains the loosestrifes (Steironema), star-flower
-(Trientalis), etc.</p>
-
-<p><b>977. Order Ebenales.</b>—Of the four families, the ebony family
-(Ebenaceæ) contains the well-known persimmon (Diospyros virginiana) and
-the storax family (Styracaceæ) with the silverbell, or snowdrop tree
-(Mohrodendron carolinum).</p>
-
-<p><b>978. Order Gentianales.</b>—Herbs, shrubs, vines, or trees. Six
-families in the United States.</p>
-
-<p>The olive family (Oleaceæ) includes the common lilac (Syringa), the ash
-trees (Fraxinus), the privet (Ligustrum).</p>
-
-<p>The gentian family (Gentianaceæ) among other genera includes the
-gentians (Gentiana).</p>
-
-<p>The milkweed family (Asclepiadaceæ) contains plants mostly with a milky
-juice. Asclepias with many species is one of the most prominent genera.</p>
-
-<p><b>979. Order Polemoniales.</b>—Mostly herbs, rarely shrubs and trees.
-Fifteen families in the eastern United States.</p>
-
-<p>The morning glory family (Convolvulaceæ) includes the bindweeds
-(Convolvulus), the morning glory (Ipomæa), etc.</p>
-
-<p>The dodder family (Cuscutaceæ) includes the dodders, or “love-vines.”
-There are nearly thirty species in the United States. The stems are
-slender and twine around other plants upon which they are parasitic
-(<a href="#PARA_179">see paragraph 179</a>).</p>
-
-<p>The phlox family (Polemoniaceæ). The most prominent genus is Phlox.
-Over forty species occur in North America.</p>
-
-<p>The borage family (Boraginaceæ) includes the heliotrope (Heliotropium),
-the hound’s-tongue (Cynoglossum), the forget-me-not (Myosotis), and others.
-<span class="pagenum"><a name="Page_501" id="Page_501">[Pg 501]</a></span></p>
-
-<p>The vervain family (verbenaceæ) contains the verbenas.</p>
-
-<p>The mint family (Labiatæ) contains the mints (Mentha), skull-cap
-(Scutellaria), dead-nettles (Lamium).</p>
-
-<p>The potato family (Solanaceæ) includes the ground-cherry (Physalis),
-the nightshades (Solanum), the tomato (Lycopersicon), tobacco (Nicotiana).</p>
-
-<p>The figwort family (Scrophulariaceæ) includes the common mullein
-(Verbascum), the monkey-flower (Mimulus), the toad-flax (Linaria),
-turtle’s-head (Chelone), and many other genera and species.</p>
-
-<p>The bladderwort family (Lentibulariaceæ) includes the curious bog or
-aquatic plants with finely dissected leaves, and with bladders in which
-insects are caught (Utricularia).</p>
-
-<p>The trumpet-creeper family (Bignoniaceæ) includes the trumpet-creeper
-(Bignonia), the catalpa tree, and others.</p>
-
-<p><b>980. Order Plantaginales</b> with one family (Plantaginaceæ)
-includes the plantains (Plantago).</p>
-
-<p><b>981. Order Rubiales</b> with three families is represented by the
-madder family (Rubiaceæ) with the bluets (Houstonia), the button-bush
-(Cephalanthus), the partridge-berry (Mitchella), the bedstraws
-(Galium), etc.</p>
-
-<p>The honeysuckle family (Caprifoliaceæ) with the elder (Sambucus), the
-arrowwoods and cranberry trees (Viburnum), the honeysuckles (Lonicera),
-etc.</p>
-
-<p><b>982. Order Valerianales</b> with two families includes the teasel
-family (Dipsacaceæ). Example, Fuller’s teasel (Dipsacus).</p>
-
-<p><b>983. Order Campanulales</b> with five families, the corolla usually
-gamopetalous.</p>
-
-<p>The gourd family (Cucurbitaceæ) includes the pumpkin, squash, melon,
-and a few feral species. Example, the star-cucumber (Sicyos angulatus),
-in moist places in eastern and middle United States.</p>
-
-<p>The bell-flower family (Campanulaceæ) includes the hare-bells or
-bell-flowers (Campanula), the lobelias (example, Lobelia cardinalis,
-the cardinal-flower), etc.
-<span class="pagenum"><a name="Page_502" id="Page_502">[Pg 502]</a></span></p>
-
-<p>The chicory family (Cichoriaceæ) includes the chicory or succory
-(Cichorium intybus, known also as blue-sailors), the oyster-plant or
-salsify (Tragopogon porrifolius), the dandelion (Taraxacum taraxacum =
-T. densleonis), the lettuce (Lactuca), the hawkweed (Hieraceum), and
-others.</p>
-
-<p>The ragweed family (Ambrosiaceæ) includes the ragweeds (Ambrosia), the
-cockle-bur (Xanthium), and others.</p>
-
-<p>The thistle family (Compositæ) includes the thistle (Carduus), asters
-(Aster), goldenrods (Solidago), sunflowers (Helianthus), eupatoriums or
-joepye-weeds, thoroughworts (Eupatorium), cone-flowers or black-eyed
-Susans (Rudbeckia), tickseed (Coreopsis), bur-marigold or beggar-ticks
-or devil’s-bootjack (Bidens), chrysanthemums, etc.</p>
-
-<hr class="chap" />
-<p><span class="pagenum"><a name="Page_503" id="Page_503">[Pg 503]</a></span></p>
-<div class="chapter"><h2 class="nobreak"><a name="INDEX" id="INDEX">INDEX.</a></h2></div>
-
-<ul class="index">
-<li class="isub1">Absorption, <a href="#Page_13">13</a>, <a href="#Page_22">22-28</a></li>
-<li class="isub1">Aceraceæ, <a href="#Page_497">497</a></li>
-<li class="isub1">Acorn, <a href="#Page_451">451</a></li>
-<li class="isub1">Acorus, <a href="#Page_493">493</a></li>
-<li class="isub1">Æcidiomycetes, <a href="#Page_218">218</a></li>
-<li class="isub1">Æcidiospore, <a href="#Page_189">189</a></li>
-<li class="isub1">Æsculus hippocastanum, <a href="#Page_498">498</a></li>
-<li class="isub1">Agaricaceæ, <a href="#Page_199">199</a>, <a href="#Page_219">219</a></li>
-<li class="isub1">Agaricus arvensis, <a href="#Page_206">206</a></li>
-<li class="isub1">Agaricus campestris, <a href="#Page_200">200-207</a></li>
-<li class="isub1">Akene, <a href="#Page_451">451</a></li>
-<li class="isub1">Albumen, <a href="#Page_98">98</a></li>
-<li class="isub1">Albuminous, <a href="#Page_98">98</a>, <a href="#Page_108">108</a></li>
-<li class="isub1">Alder, <a href="#Page_495">495</a></li>
-<li class="isub1">Algæ, <a href="#Page_136">136-176</a></li>
-<li class="isub1">Algæ, absorption by, <a href="#Page_22">22</a></li>
-<li class="isub1">Alismaceæ, <a href="#Page_493">493</a></li>
-<li class="isub1">Alpine formation, <a href="#Page_474">474</a></li>
-<li class="isub1">Alpine plant societies, <a href="#Page_483">483</a></li>
-<li class="isub1">Amanita phalloides, <a href="#Page_207">207</a>, <a href="#Page_208">208</a></li>
-<li class="isub1">Amaranth, <a href="#Page_495">495</a></li>
-<li class="isub1">Amaryllidaceæ, <a href="#Page_494">494</a></li>
-<li class="isub1">Aments, <a href="#Page_429">429</a></li>
-<li class="isub1">American mistletoe, <a href="#Page_495">495</a></li>
-<li class="isub1">Ampelopsis, <a href="#Page_498">498</a></li>
-<li class="isub1">Ancylistales, <a href="#Page_215">215</a></li>
-<li class="isub1">Andreales, <a href="#Page_249">249</a></li>
-<li class="isub1">Andrœcium, <a href="#Page_319">319</a>, <a href="#Page_419">419</a></li>
-<li class="isub1">Anemophilous, <a href="#Page_435">435</a></li>
-<li class="isub1">Angiosperms, morphology of, <a href="#Page_318">318-348</a>;</li>
-<li class="isub3">classification, <a href="#Page_487">487</a></li>
-<li class="isub1">Antheridiophore, <a href="#Page_227">227</a></li>
-<li class="isub1">Antheridium, <a href="#Page_144">144</a>, <a href="#Page_149">149</a>, <a href="#Page_155">155</a>, <a href="#Page_176">176</a>, <a href="#Page_223">223</a>, <a href="#Page_228">228</a>,</li>
-<li class="isub7"><a href="#Page_240">240</a>, <a href="#Page_245">245</a>, <a href="#Page_246">246</a>, <a href="#Page_266">266</a>, <a href="#Page_287">287</a>, <a href="#Page_433">433</a></li>
-<li class="isub1">Anthesis, <a href="#Page_429">429</a></li>
-<li class="isub1">Anthoceros, <a href="#Page_240">240</a>, <a href="#Page_241">241</a></li>
-<li class="isub1">Anthocerotales, <a href="#Page_242">242</a></li>
-<li class="isub1">Anthocerotes, <a href="#Page_242">242</a></li>
-<li class="isub1">Apogamy, <a href="#Page_346">346</a></li>
-<li class="isub1">Apogeotropic (ap″o-ge″o-trop´ic), <a href="#Page_126">126</a></li>
-<li class="isub1">Apogeotropism (ap″o-ge-ot′ro-pism), <a href="#Page_126">126</a></li>
-<li class="isub1">Apple, <a href="#Page_456">456</a>, <a href="#Page_497">497</a></li>
-<li class="isub1">Apple family, <a href="#Page_497">497</a></li>
-<li class="isub1">Aquatic formations, <a href="#Page_475">475</a></li>
-<li class="isub1">Aquatic plant societies, <a href="#Page_486">486</a></li>
-<li class="isub1">Araceæ, <a href="#Page_493">493</a></li>
-<li class="isub1">Archegonia (ar-che-go′ni-a), <a href="#Page_223">223</a>, <a href="#Page_229">229</a>, <a href="#Page_233">233</a>, <a href="#Page_241">241</a>, <a href="#Page_244">244-246</a>,</li>
-<li class="isub7"><a href="#Page_267">267</a>, <a href="#Page_288">288</a>, <a href="#Page_291">291</a>, <a href="#Page_307">307</a>, <a href="#Page_308">308</a></li>
-<li class="isub1">Archegoniophore, <a href="#Page_229">229</a></li>
-<li class="isub1">Archegonium, <a href="#Page_433">433</a></li>
-<li class="isub1">Archesporium (ar″che-spo´ri-um), <a href="#Page_235">235</a></li>
-<li class="isub1">Archidiales, <a href="#Page_249">249</a></li>
-<li class="isub1">Arctic formation, <a href="#Page_481">481</a></li>
-<li class="isub1">Aril, <a href="#Page_457">457</a></li>
-<li class="isub1">Arisæma, <a href="#Page_493">493</a></li>
-<li class="isub1">Arisæma triphyllum, <a href="#Page_442">442</a>, <a href="#Page_443">443</a></li>
-<li class="isub1">Aristolochiales, <a href="#Page_495">495</a></li>
-<li class="isub1">Arrow leaf, <a href="#Page_492">492</a></li>
-<li class="isub1">Arum family, <a href="#Page_493">493</a></li>
-<li class="isub1">Asclepias, <a href="#Page_500">500</a></li>
-<li class="isub1">Asclepias cornuti, <a href="#Page_462">462</a></li>
-<li class="isub1">Ascomycetes (as-co-my-ce′tes), <a href="#Page_195">195-198</a>, <a href="#Page_216">216-218</a></li>
-<li class="isub1">Ascus, <a href="#Page_190">190</a>, <a href="#Page_213">213</a></li>
-<li class="isub1">Ash of plants, <a href="#Page_79">79</a>, <a href="#Page_80">80</a></li>
-<li class="isub1">Ash tree, <a href="#Page_500">500</a></li>
-<li class="isub1">Aspidium acrostichoides, <a href="#Page_253">253</a>, <a href="#Page_257">257</a></li>
-<li class="isub1">Assimilation, <a href="#Page_67">67</a>, <a href="#Page_109">109</a></li>
-<li class="isub1">Aster, <a href="#Page_502">502</a></li>
-<li class="isub1">Atriplex, <a href="#Page_495">495</a></li>
-<li class="isub1">Auriculariales, <a href="#Page_218">218</a></li>
-<li class="isub1">Autotrophic plants, <a href="#Page_85">85</a></li>
-<li class="isub1">Azalea, <a href="#Page_499">499</a></li>
-<li class="isub1">Azolla, <a href="#Page_296">296</a></li>
-
-<li class="ifrst">Bacteria, <a href="#Page_164">164</a>, <a href="#Page_165">165</a></li>
-<li class="isub1">Bacteria, nitrite and nitrate, <a href="#Page_83">83</a>
-      <span class="pagenum"><a name="Page_504" id="Page_504">[Pg 504]</a></span></li>
-<li class="isub1">Bacteriales, <a href="#Page_164">164</a>, <a href="#Page_165">165</a></li>
-<li class="isub1">Bacteroid, <a href="#Page_93">93</a></li>
-<li class="isub1">Bangiales, <a href="#Page_175">175</a></li>
-<li class="isub1">Basidiomycetes (ba-sid″i-o-my-ce′tes), <a href="#Page_199">199-208</a>, <a href="#Page_218">218</a></li>
-<li class="isub1">Basidium, <a href="#Page_201">201</a>, <a href="#Page_213">213</a></li>
-<li class="isub1">Bast, <a href="#Page_50">50-52</a></li>
-<li class="isub1">Batrachospermum, <a href="#Page_171">171-173</a>, <a href="#Page_175">175</a></li>
-<li class="isub1">Bazzania, <a href="#Page_25">25</a></li>
-<li class="isub1">Beard-grasses, <a href="#Page_480">480</a></li>
-<li class="isub1">Bedstraws, <a href="#Page_501">501</a></li>
-<li class="isub1">Beechnut, <a href="#Page_452">452</a></li>
-<li class="isub1">Beet, osmose in, <a href="#Page_15">15</a>, <a href="#Page_16">16</a>, <a href="#Page_17">17</a>, <a href="#Page_18">18</a></li>
-<li class="isub1">Begonia, <a href="#Page_407">407</a></li>
-<li class="isub1">Bellflower, <a href="#Page_501">501</a></li>
-<li class="isub1">Berry, <a href="#Page_454">454</a>, <a href="#Page_455">455</a>, <a href="#Page_456">456</a></li>
-<li class="isub1">Betulaceæ, <a href="#Page_495">495</a></li>
-<li class="isub1">Bicuculla, <a href="#Page_496">496</a></li>
-<li class="isub1">Bidens, <a href="#Page_458">458</a></li>
-<li class="isub1">Bignonia, <a href="#Page_501">501</a></li>
-<li class="isub1">Bilberries, <a href="#Page_500">500</a></li>
-<li class="isub1">Biotic factors, <a href="#Page_466">466</a></li>
-<li class="isub1">Birch, <a href="#Page_495">495</a></li>
-<li class="isub1">Bird’s-nest fungi, <a href="#Page_220">220</a></li>
-<li class="isub1">Blackberry, <a href="#Page_454">454</a></li>
-<li class="isub1">Black fungi, <a href="#Page_198">198</a></li>
-<li class="isub1">Bladderwort, <a href="#Page_501">501</a></li>
-<li class="isub1">Blasia, <a href="#Page_164">164</a>, <a href="#Page_236">236</a></li>
-<li class="isub1">Bloodroot, <a href="#Page_496">496</a></li>
-<li class="isub1">Bluets, <a href="#Page_436">436</a>, <a href="#Page_437">437</a>, <a href="#Page_501">501</a></li>
-<li class="isub1">Boletus, <a href="#Page_209">209</a></li>
-<li class="isub1">Boletus edulis, <a href="#Page_209">209</a></li>
-<li class="isub1">Boraginaceæ, <a href="#Page_500">500</a></li>
-<li class="isub1">Botrychium, <a href="#Page_295">295</a></li>
-<li class="isub1">Botrydiaceæ, <a href="#Page_162">162</a></li>
-<li class="isub1">Botrydium granulatum, <a href="#Page_146">146</a>, <a href="#Page_162">162</a></li>
-<li class="isub1">Broom-sedge, <a href="#Page_480">480</a></li>
-<li class="isub1">Brown algæ, <a href="#Page_167">167-170</a></li>
-<li class="isub1">Bryales, <a href="#Page_349">349</a></li>
-<li class="isub1">Buckeye family, <a href="#Page_498">498</a></li>
-<li class="isub1">Buckthorn, <a href="#Page_498">498</a></li>
-<li class="isub1">Buckwheat, <a href="#Page_495">495</a></li>
-<li class="isub1">Buds, winter condition of, <a href="#Page_374">374-377</a></li>
-<li class="isub1">Buffalo-grass, <a href="#Page_480">480</a></li>
-<li class="isub1">Bug seed, <a href="#Page_495">495</a></li>
-<li class="isub1">Bulb, <a href="#Page_372">372</a></li>
-<li class="isub1">Bunch-grasses, <a href="#Page_480">480</a></li>
-<li class="isub1">Butternut, <a href="#Page_452">452</a>, <a href="#Page_494">494</a></li>
-<li class="isub1">Buttonbush, <a href="#Page_501">501</a></li>
-<li class="isub1">Buttonwood, <a href="#Page_497">497</a></li>
-
-<li class="ifrst">Cacti, <a href="#Page_395">395</a>, <a href="#Page_498">498</a></li>
-<li class="isub1">Callithamnion, <a href="#Page_173">173</a></li>
-<li class="isub1">Calyptrogen, <a href="#Page_361">361</a></li>
-<li class="isub1">Cambium, <a href="#Page_50">50</a>, <a href="#Page_52">52</a>, <a href="#Page_358">358</a>, <a href="#Page_363">363</a></li>
-<li class="isub1">Campanula rotundifolia, <a href="#Page_442">442</a>, <a href="#Page_444">444</a>, <a href="#Page_510">510</a></li>
-<li class="isub1">Campanulales, <a href="#Page_501">501</a></li>
-<li class="isub1">Canna, <a href="#Page_445">445-449</a>, <a href="#Page_494">494</a></li>
-<li class="isub1">Capsella bursa-pastoris, <a href="#Page_496">496</a></li>
-<li class="isub1">Capsule, <a href="#Page_453">453</a></li>
-<li class="isub1">Carbohydrate, <a href="#Page_71">71</a>, <a href="#Page_75">75</a>, <a href="#Page_80">80</a>, <a href="#Page_90">90</a></li>
-<li class="isub1">Carbon dioxide, <a href="#Page_62">62-67</a>, <a href="#Page_110">110-113</a></li>
-<li class="isub1">Cardinal-flower, <a href="#Page_501">501</a></li>
-<li class="isub1">Carpogonium, <a href="#Page_172">172</a>, <a href="#Page_176">176</a></li>
-<li class="isub1">Carrot family, <a href="#Page_499">499</a></li>
-<li class="isub1">Caryophyllaceæ, <a href="#Page_496">496</a></li>
-<li class="isub1">Caryopsis, <a href="#Page_451">451</a></li>
-<li class="isub1">Cassia marilandica, <a href="#Page_402">402</a></li>
-<li class="isub1">Cassiope, <a href="#Page_395">395</a></li>
-<li class="isub1">Castalia odorata, <a href="#Page_496">496</a></li>
-<li class="isub1">Castor-oil plant, <a href="#Page_497">497</a></li>
-<li class="isub1">Catalpa, <a href="#Page_501">501</a></li>
-<li class="isub1">Catkin, <a href="#Page_428">428</a></li>
-<li class="isub1">Cattail-flag, <a href="#Page_492">492</a></li>
-<li class="isub1">Caulidium, <a href="#Page_371">371</a></li>
-<li class="isub1">Cedar apples, <a href="#Page_194">194</a></li>
-<li class="isub1">Cell, <a href="#Page_3">3</a>;</li>
-<li class="isub3">artificial <a href="#Page_20">20</a></li>
-<li class="isub1">Cell-sap, <a href="#Page_3">3</a>, <a href="#Page_40">40</a></li>
-<li class="isub1">Ceratopteris thalictroides, <a href="#Page_296">296</a></li>
-<li class="isub1">Chætophora, <a href="#Page_151">151</a>, <a href="#Page_162">162</a></li>
-<li class="isub1">Chætophoraceæ, <a href="#Page_162">162</a></li>
-<li class="isub1">Chara, <a href="#Page_176">176</a></li>
-<li class="isub1">Charales, <a href="#Page_176">176</a></li>
-<li class="isub1">Chemical condition of soil, <a href="#Page_466">466</a></li>
-<li class="isub1">Chemosynthetic assimilation, <a href="#Page_109">109</a></li>
-<li class="isub1">Chenopodiales, <a href="#Page_495">495</a></li>
-<li class="isub1">Chenopods, <a href="#Page_495">495</a></li>
-<li class="isub1">Chestnut, <a href="#Page_452">452</a>, <a href="#Page_494">494</a></li>
-<li class="isub1">Chicory family, <a href="#Page_502">502</a></li>
-<li class="isub1">Chlamydomonas, <a href="#Page_159">159</a>, <a href="#Page_160">160</a></li>
-<li class="isub1">Chlamydospores, <a href="#Page_180">180</a></li>
-<li class="isub1">Chloral hydrate, <a href="#Page_65">65</a>, <a href="#Page_87">87</a></li>
-<li class="isub1">Chlorophyceæ, <a href="#Page_158">158</a></li>
-<li class="isub1">Chlorophyll, <a href="#Page_2">2</a>, <a href="#Page_67">67</a>, <a href="#Page_72">72</a></li>
-<li class="isub1">Chloroplast, <a href="#Page_68">68</a>, <a href="#Page_69">69</a>, <a href="#Page_71">71</a></li>
-<li class="isub1">Christmas fern, <a href="#Page_251">251-253</a></li>
-<li class="isub1">Chromoplast, <a href="#Page_71">71</a></li>
-<li class="isub1">Chromosomes, <a href="#Page_342">342-345</a></li>
-<li class="isub1">Chroococcaceæe, <a href="#Page_163">163</a></li>
-<li class="isub1">Chrysanthemum, <a href="#Page_502">502</a></li>
-<li class="isub1">Chytridiales, <a href="#Page_215">215</a></li>
-<li class="isub1">Cichoriaceæ, <a href="#Page_502">502</a></li>
-<li class="isub1">Cichorium intybus, <a href="#Page_502">502</a></li>
-<li class="isub1">Clavaria botrytes, <a href="#Page_212">212</a></li>
-<li class="isub1">Clavariaceæ, <a href="#Page_210">210</a>, <a href="#Page_219">219</a></li>
-<li class="isub1">Claytonia virginica, <a href="#Page_496">496</a>
-    <span class="pagenum"><a name="Page_505" id="Page_505">[Pg 505]</a></span></li>
-<li class="isub1">Cleistogamous, <a href="#Page_435">435</a></li>
-<li class="isub1">Clematis virginiana, <a href="#Page_462">462</a>, <a href="#Page_463">463</a>, <a href="#Page_496">496</a></li>
-<li class="isub1">Climatic factors, <a href="#Page_466">466</a></li>
-<li class="isub1">Climatic formations, <a href="#Page_470">470</a></li>
-<li class="isub1">Clostridium pasteurianum, <a href="#Page_93">93</a></li>
-<li class="isub1">Clover, <a href="#Page_497">497</a></li>
-<li class="isub1">Club mosses, <a href="#Page_284">284</a>, <a href="#Page_289">289</a></li>
-<li class="isub1">Coccogonales, <a href="#Page_163">163</a></li>
-<li class="isub1">Cocklebur, <a href="#Page_502">502</a></li>
-<li class="isub1">Cold wastes, <a href="#Page_474">474</a></li>
-<li class="isub1">Coleochætaceæ, <a href="#Page_162">162</a></li>
-<li class="isub1">Coleochæte, <a href="#Page_153">153-156</a>, <a href="#Page_226">226</a></li>
-<li class="isub1">Collenchyma, <a href="#Page_356">356</a>, <a href="#Page_363">363</a></li>
-<li class="isub1">Comandra, <a href="#Page_495">495</a></li>
-<li class="isub1">Compass plants, <a href="#Page_409">409</a></li>
-<li class="isub1">Compositæ, <a href="#Page_502">502</a></li>
-<li class="isub1">Comptonia asplenifolia, <a href="#Page_494">494</a></li>
-<li class="isub1">Cone-fruit, <a href="#Page_456">456</a></li>
-<li class="isub1">Confervoideæ, <a href="#Page_162">162</a></li>
-<li class="isub1">Coniferæ, <a href="#Page_316">316</a></li>
-<li class="isub1">Conjugation, <a href="#Page_137">137</a>, <a href="#Page_141">141</a>, <a href="#Page_160">160</a>, <a href="#Page_162">162</a>, <a href="#Page_179">179</a></li>
-<li class="isub1">Convallariaceæ, <a href="#Page_494">494</a></li>
-<li class="isub1">Cooperia, <a href="#Page_494">494</a></li>
-<li class="isub1">Cordyceps, <a href="#Page_218">218</a></li>
-<li class="isub1">Coreopsis, <a href="#Page_502">502</a></li>
-<li class="isub1">Cork, <a href="#Page_357">357</a>, <a href="#Page_363">363</a></li>
-<li class="isub1">Corm, <a href="#Page_373">373</a></li>
-<li class="isub1">Cortex, <a href="#Page_50">50</a></li>
-<li class="isub1">Corymb, <a href="#Page_427">427</a></li>
-<li class="isub1">Cotyledon, <a href="#Page_99">99-101</a></li>
-<li class="isub1">Cranberry, <a href="#Page_500">500</a></li>
-<li class="isub1">Cratægus, <a href="#Page_497">497</a></li>
-<li class="isub1">Crowfoot family, <a href="#Page_496">496</a></li>
-<li class="isub1">Cruciferæ, <a href="#Page_496">496</a></li>
-<li class="isub1">Cryptonemiales, <a href="#Page_175">175</a></li>
-<li class="isub1">Cucurbitaceæ, <a href="#Page_501">501</a></li>
-<li class="isub1">Culture formations, <a href="#Page_470">470</a>, <a href="#Page_475">475</a></li>
-<li class="isub1">Cultures, water, <a href="#Page_28">28</a>, <a href="#Page_29">29</a></li>
-<li class="isub1">Cup fungi, <a href="#Page_199">199</a></li>
-<li class="isub1">Cupuliferæ, <a href="#Page_495">495</a></li>
-<li class="isub1">Cuscuta, <a href="#Page_83">83</a>, <a href="#Page_500">500</a></li>
-<li class="isub1">Cushion type of vegetation, <a href="#Page_483">483</a></li>
-<li class="isub1">Cuticle, <a href="#Page_43">43</a></li>
-<li class="isub1">Cyanophyceæ, <a href="#Page_163">163</a></li>
-<li class="isub1">Cyatheaceæ, <a href="#Page_295">295</a></li>
-<li class="isub1">Cycadales, <a href="#Page_316">316</a></li>
-<li class="isub1">Cycas, <a href="#Page_311">311</a>, <a href="#Page_312">312</a>, <a href="#Page_457">457</a></li>
-<li class="isub1">Cyclosis, <a href="#Page_9">9</a>, <a href="#Page_10">10</a></li>
-<li class="isub1">Cyclosporales, <a href="#Page_171">171</a></li>
-<li class="isub1">Cyme, <a href="#Page_430">430</a>, <a href="#Page_432">432</a></li>
-<li class="isub1">Cyperaceæ, <a href="#Page_493">493</a></li>
-<li class="isub1">Cypripedium, <a href="#Page_443">443</a>, <a href="#Page_447">447</a>, <a href="#Page_494">494</a></li>
-<li class="isub1">Cystocarp, <a href="#Page_174">174</a></li>
-<li class="isub1">Cystopteris bulbifera, <a href="#Page_260">260</a></li>
-<li class="isub1">Cystopus, <a href="#Page_215">215</a></li>
-<li class="isub1">Cytase, <a href="#Page_92">92</a>, <a href="#Page_108">108</a></li>
-<li class="isub1">Cytisus, <a href="#Page_445">445</a></li>
-<li class="isub1">Cytoplasm (cy′to-plasm), <a href="#Page_5">5</a></li>
-
-<li class="ifrst">Dacryomycetales, <a href="#Page_219">219</a></li>
-<li class="isub1">Dahlia, <a href="#Page_108">108</a></li>
-<li class="isub1">Dandelion, <a href="#Page_502">502</a></li>
-<li class="isub1">Dasiphora fruticosa, <a href="#Page_497">497</a></li>
-<li class="isub1">Daucus carota, <a href="#Page_499">499</a></li>
-<li class="isub1">Dehiscence, <a href="#Page_453">453</a></li>
-<li class="isub1">Dentaria, <a href="#Page_322">322-324</a></li>
-<li class="isub1">Dentaria diphylla, <a href="#Page_496">496</a></li>
-<li class="isub1">Dermatogen, <a href="#Page_359">359</a></li>
-<li class="isub1">Desert formation, <a href="#Page_473">473</a></li>
-<li class="isub1">Desert societies, <a href="#Page_480">480</a></li>
-<li class="isub1">Desmodium, <a href="#Page_458">458</a></li>
-<li class="isub1">Desmodium gyrans, <a href="#Page_399">399</a></li>
-<li class="isub1">Diadelphous (di″a-del′phous), <a href="#Page_425">425</a></li>
-<li class="isub1">Diageotropism (di″a-ge-ot′ro-pism), <a href="#Page_126">126</a></li>
-<li class="isub1">Diaheliotropic (di″a-he″li-o-trop′ic), <a href="#Page_127">127</a></li>
-<li class="isub1">Diaheliotropism (di″a-he″li-ot′ro-pism), <a href="#Page_127">127</a></li>
-<li class="isub1">Diastase, <a href="#Page_77">77</a>, <a href="#Page_78">78</a>, <a href="#Page_108">108</a>, <a href="#Page_116">116</a></li>
-<li class="isub1">Diatoms, <a href="#Page_166">166</a></li>
-<li class="isub1">Dichogamous (di-chog′a-mous), <a href="#Page_437">437</a>, <a href="#Page_442">442</a></li>
-<li class="isub1">Dicentra, <a href="#Page_496">496</a></li>
-<li class="isub1">Dicotyledons, <a href="#Page_494">494</a></li>
-<li class="isub1">Dictyophora, <a href="#Page_219">219</a></li>
-<li class="isub1">Diffusion, <a href="#Page_13">13-20</a></li>
-<li class="isub1">Digestion, <a href="#Page_107">107</a>, <a href="#Page_108">108</a>, <a href="#Page_109">109</a></li>
-<li class="isub1">Dimorphism of ferns, <a href="#Page_273">273-280</a></li>
-<li class="isub1">Diœcious, <a href="#Page_435">435</a></li>
-<li class="isub1">Dionæa muscipula, <a href="#Page_133">133</a></li>
-<li class="isub1">Dipodascus, <a href="#Page_216">216</a></li>
-<li class="isub1">Dipsacus, <a href="#Page_501">501</a></li>
-<li class="isub1">Discomycetes, <a href="#Page_217">217</a></li>
-<li class="isub1">Dodder, <a href="#Page_83">83</a>, <a href="#Page_84">84</a>, <a href="#Page_500">500</a></li>
-<li class="isub1">Dogwood, <a href="#Page_499">499</a></li>
-<li class="isub1">Dothidiales, <a href="#Page_218">218</a></li>
-<li class="isub1">Downy mildews, <a href="#Page_185">185</a></li>
-<li class="isub1">Drosera rotundifolia, <a href="#Page_133">133</a>, <a href="#Page_496">496</a></li>
-<li class="isub1">Drupaceæ, <a href="#Page_497">497</a></li>
-<li class="isub1">Drupe, <a href="#Page_454">454</a></li>
-<li class="isub1">Duckweeds, <a href="#Page_26">26</a>, <a href="#Page_28">28</a></li>
-<li class="isub1">Dudresnaya, <a href="#Page_175">175</a></li>
-<li class="isub1">Dunes, <a href="#Page_484">484</a></li>
-
-<li class="ifrst">Ebenales, <a href="#Page_500">500</a>
-     <span class="pagenum"><a name="Page_506" id="Page_506">[Pg 506]</a></span></li>
-<li class="isub1">Ecological factors, <a href="#Page_464">464</a></li>
-<li class="isub1">Ecology (sometimes written œcology), <a href="#Page_464">464</a></li>
-<li class="isub1">Ectocarpus, <a href="#Page_167">167</a></li>
-<li class="isub1">Edaphic formations, <a href="#Page_475">475</a></li>
-<li class="isub1">Elaphomyces, <a href="#Page_217">217</a>, <a href="#Page_218">218</a></li>
-<li class="isub1">Elder, <a href="#Page_501">501</a></li>
-<li class="isub1">Elm family, <a href="#Page_495">495</a></li>
-<li class="isub1">Elodea, <a href="#Page_61">61-63</a></li>
-<li class="isub1">Embryo of ferns, <a href="#Page_269">269-272</a></li>
-<li class="isub1">Embryo sac, <a href="#Page_326">326-328</a></li>
-<li class="isub1">Empusa, <a href="#Page_215">215</a></li>
-<li class="isub1">Endocarp, <a href="#Page_450">450</a></li>
-<li class="isub1">Endomyces, <a href="#Page_216">216</a></li>
-<li class="isub1">Endosperm, <a href="#Page_103">103</a>, <a href="#Page_105">105</a>, <a href="#Page_107">107</a>, <a href="#Page_306">306</a>, <a href="#Page_309">309</a>;</li>
-<li class="isub3">nucleus, <a href="#Page_327">327</a>, <a href="#Page_329">329-334</a></li>
-<li class="isub1">Entomophthorales, <a href="#Page_215">215</a></li>
-<li class="isub1">Enzyme, <a href="#Page_92">92</a>, <a href="#Page_98">98</a>, <a href="#Page_116">116</a>, <a href="#Page_117">117</a></li>
-<li class="isub1">Epidermal system, <a href="#Page_358">358</a></li>
-<li class="isub1">Epidermis, <a href="#Page_358">358</a>, <a href="#Page_359">359</a>, <a href="#Page_363">363</a></li>
-<li class="isub1">Epigæa repens, <a href="#Page_499">499</a></li>
-<li class="isub1">Epigynous, <a href="#Page_425">425</a></li>
-<li class="isub1">Epilobium, <a href="#Page_498">498</a></li>
-<li class="isub1">Epinastic (ep-i-nas′tic), <a href="#Page_129">129</a></li>
-<li class="isub1">Epinasty (ep′i-nas-ty), <a href="#Page_129">129</a></li>
-<li class="isub1">Epipactis, <a href="#Page_444">444</a>, <a href="#Page_447">447</a></li>
-<li class="isub1">Epiphegus, <a href="#Page_84">84</a></li>
-<li class="isub1">Epiphytes, <a href="#Page_416">416</a></li>
-<li class="isub1">Equisetales, <a href="#Page_296">296</a></li>
-<li class="isub1">Equisetineæ, <a href="#Page_296">296</a></li>
-<li class="isub1">Equisetum, <a href="#Page_280">280-283</a></li>
-<li class="isub1">Ericaceæ, <a href="#Page_499">499</a></li>
-<li class="isub1">Ericales, <a href="#Page_499">499</a></li>
-<li class="isub1">Erythronium, <a href="#Page_493">493</a></li>
-<li class="isub1">Etiolated plants (e′ti-o-la″ted), <a href="#Page_68">68</a></li>
-<li class="isub1">Euascomycetes, <a href="#Page_217">217</a></li>
-<li class="isub1">Eubasidiomycetes, <a href="#Page_219">219</a></li>
-<li class="isub1">Eupatorium, <a href="#Page_403">403</a>, <a href="#Page_502">502</a></li>
-<li class="isub1">Euphorbiaceæ, <a href="#Page_497">497</a></li>
-<li class="isub1">Eurotium oryzæ, <a href="#Page_78">78</a></li>
-<li class="isub1">Evening primrose family, <a href="#Page_498">498</a></li>
-<li class="isub1">Exalbuminous, <a href="#Page_108">108</a></li>
-<li class="isub1">Exoascus, <a href="#Page_217">217</a></li>
-<li class="isub1">Exobasidiales, <a href="#Page_219">219</a></li>
-<li class="isub1">Exocarp, <a href="#Page_450">450</a></li>
-
-<li class="ifrst">Fagales, <a href="#Page_494">494</a></li>
-<li class="isub1">Fehling’s solution, <a href="#Page_75">75</a>, <a href="#Page_76">76</a></li>
-<li class="isub1">Ferment, <a href="#Page_98">98</a>, <a href="#Page_108">108</a>, <a href="#Page_116">116</a></li>
-<li class="isub1">Ferns, <a href="#Page_251">251-279</a>, <a href="#Page_292">292</a>, <a href="#Page_457">457</a>;</li>
-<li class="isub3">classification of, <a href="#Page_295">295</a></li>
-<li class="isub1">Fertilization, <a href="#Page_307">307</a>, <a href="#Page_308">308</a>, <a href="#Page_328">328</a>, <a href="#Page_329">329</a>, <a href="#Page_140">140</a>, <a href="#Page_145">145</a>,</li>
-<li class="isub7"><a href="#Page_169">169</a>, <a href="#Page_172">172</a>, <a href="#Page_174">174</a>, <a href="#Page_197">197</a>, <a href="#Page_421">421</a></li>
-<li class="isub1">Fibrovascular bundles, <a href="#Page_49">49-54</a></li>
-<li class="isub1">Figwort family, <a href="#Page_501">501</a></li>
-<li class="isub1">Filicales, <a href="#Page_295">295</a></li>
-<li class="isub1">Filicineæ, <a href="#Page_295">295</a></li>
-<li class="isub1">Fittonia, <a href="#Page_404">404</a></li>
-<li class="isub1">Flagellates, <a href="#Page_83">83</a>, <a href="#Page_165">165</a></li>
-<li class="isub1">Flax, <a href="#Page_497">497</a></li>
-<li class="isub1">Flower cluster, <a href="#Page_419">419</a></li>
-<li class="isub1">Flower, form of, <a href="#Page_422">422</a>;</li>
-<li class="isub3">parts of, <a href="#Page_419">419</a>;</li>
-<li class="isub3">union of parts, <a href="#Page_424">424</a></li>
-<li class="isub1">Flowers, arrangements of, <a href="#Page_426">426</a>;</li>
-<li class="isub3">kinds of, <a href="#Page_421">421</a></li>
-<li class="isub1">Follicle, <a href="#Page_453">453</a></li>
-<li class="isub1">Forest, formations <a href="#Page_471">471</a>;</li>
-<li class="isub3">societies, <a href="#Page_477">477</a></li>
-<li class="isub1">Forests, relation to rainfall, <a href="#Page_479">479</a></li>
-<li class="isub1">Fresh-water societies, <a href="#Page_486">486</a></li>
-<li class="isub1">Frond, <a href="#Page_352">352</a></li>
-<li class="isub1">Fruit, <a href="#Page_450">450-457</a>;</li>
-<li class="isub3">parts of, <a href="#Page_450">450</a></li>
-<li class="isub1">Frullania, <a href="#Page_25">25</a>, <a href="#Page_236">236</a></li>
-<li class="isub1">Fucus, <a href="#Page_168">168-170</a></li>
-<li class="isub1">Fungi, absorption by, <a href="#Page_22">22</a>;</li>
-<li class="isub3">classification of, <a href="#Page_213">213-222</a>;</li>
-<li class="isub3">nutrition of, <a href="#Page_86">86-90</a>;</li>
-<li class="isub3">respiration in, <a href="#Page_115">115</a></li>
-
-<li class="ifrst">Gametangium (gam″et-an′gi-um), <a href="#Page_140">140</a></li>
-<li class="isub1">Gamete (gam′ete), <a href="#Page_138">138</a>, <a href="#Page_139">139</a></li>
-<li class="isub1">Gametophore (gam′et-o-phore), <a href="#Page_230">230</a>, <a href="#Page_248">248</a></li>
-<li class="isub1">Gametophyte (gam′et-o-phyte), <a href="#Page_225">225</a>, <a href="#Page_226">226</a>, <a href="#Page_244">244</a>, <a href="#Page_245">245</a>, <a href="#Page_250">250</a>, <a href="#Page_262">262</a>, <a href="#Page_270">270</a>,</li>
-<li class="isub7"><a href="#Page_283">283</a>, <a href="#Page_292">292</a>, <a href="#Page_294">294</a>, <a href="#Page_305">305</a>, <a href="#Page_314">314</a>, <a href="#Page_317">317</a>,</li>
-<li class="isub7"><a href="#Page_336">336-339</a>, <a href="#Page_340">340-348</a>, <a href="#Page_434">434</a></li>
-<li class="isub1">Gamopetalous (gam″o-pet′a-lous), <a href="#Page_424">424</a></li>
-<li class="isub1">Gamosepalous (gam-o-sep′a-lous), <a href="#Page_424">424</a></li>
-<li class="isub1">Gas in plants, <a href="#Page_60">60-64</a></li>
-<li class="isub1">Gasteromycetes, <a href="#Page_219">219</a></li>
-<li class="isub1">Gemmæ, <a href="#Page_179">179</a>, <a href="#Page_235">235</a></li>
-<li class="isub1">General formations, <a href="#Page_470">470</a></li>
-<li class="isub1">Gentian, <a href="#Page_500">500</a></li>
-<li class="isub1">Geotropism (ge-ot′ro-pism), <a href="#Page_125">125-127</a>, <a href="#Page_410">410</a></li>
-<li class="isub1">Geraniaceæ, <a href="#Page_497">497</a></li>
-<li class="isub1">Geraniales, <a href="#Page_497">497</a></li>
-<li class="isub1">Geranium family, <a href="#Page_497">497</a></li>
-<li class="isub1">Germ, <a href="#Page_459">459</a></li>
-<li class="isub1">Gigartinales, <a href="#Page_175">175</a></li>
-<li class="isub1">Gingko, <a href="#Page_313">313-315</a>, <a href="#Page_457">457</a></li>
-<li class="isub1">Gingkoales, <a href="#Page_316">316</a></li>
-<li class="isub1">Ginseng, <a href="#Page_499">499</a></li>
-<li class="isub1">Glasswort, <a href="#Page_495">495</a></li>
-<li class="isub1">Gleicheniaceæ, <a href="#Page_295">295</a>
-    <span class="pagenum"><a name="Page_507" id="Page_507">[Pg 507]</a></span></li>
-<li class="isub1">Glucose, <a href="#Page_108">108</a>. See sugar.</li>
-<li class="isub1">Gnetales, <a href="#Page_316">316</a></li>
-<li class="isub1">Gonidia, <a href="#Page_118">118</a>, <a href="#Page_143">143</a>, <a href="#Page_172">172</a>, <a href="#Page_174">174</a>, <a href="#Page_178">178-184</a></li>
-<li class="isub1">Gonidiangium (go″nid-an′gi-um), <a href="#Page_178">178</a></li>
-<li class="isub1">Gonidium, <a href="#Page_213">213</a></li>
-<li class="isub1">Gooseberry, <a href="#Page_496">496</a></li>
-<li class="isub1">Goosefoot family, <a href="#Page_495">495</a></li>
-<li class="isub1">Gracilaria, <a href="#Page_173">173</a>, <a href="#Page_174">174</a>, <a href="#Page_175">175</a></li>
-<li class="isub1">Graminales, <a href="#Page_492">492</a></li>
-<li class="isub1">Gramineæ, <a href="#Page_492">492</a></li>
-<li class="isub1">Grape, <a href="#Page_498">498</a></li>
-<li class="isub1">Grass family, <a href="#Page_492">492</a></li>
-<li class="isub1">Grassland formation, <a href="#Page_471">471</a></li>
-<li class="isub1">Green algæ, <a href="#Page_158">158</a></li>
-<li class="isub1">Growth, <a href="#Page_118">118-124</a>, <a href="#Page_380">380</a></li>
-<li class="isub1">Gulfweed, <a href="#Page_170">170</a></li>
-<li class="isub1">Gymnosperms, <a href="#Page_311">311</a>, <a href="#Page_456">456</a></li>
-<li class="isub1">Gymnosporangium, <a href="#Page_194">194</a></li>
-<li class="isub1">Gynœcium, <a href="#Page_320">320</a>, <a href="#Page_419">419</a>, <a href="#Page_451">451</a>, <a href="#Page_452">452</a></li>
-<li class="isub1">Gyrocephalus, <a href="#Page_219">219</a></li>
-
-<li class="ifrst">Halophytes, <a href="#Page_468">468</a></li>
-<li class="isub1">Harpochytrium, <a href="#Page_214">214</a>, <a href="#Page_215">215</a></li>
-<li class="isub1">Haustorium, <a href="#Page_87">87</a>, <a href="#Page_88">88</a></li>
-<li class="isub1">Hawkweed, <a href="#Page_502">502</a></li>
-<li class="isub1">Hawthorn, <a href="#Page_497">497</a></li>
-<li class="isub1">Hazelnut, <a href="#Page_452">452</a>, <a href="#Page_495">495</a></li>
-<li class="isub1">Head, <a href="#Page_428">428</a></li>
-<li class="isub1">Heart-leaf, <a href="#Page_495">495</a></li>
-<li class="isub1">Heath family, <a href="#Page_499">499</a></li>
-<li class="isub1">Heliotrope, <a href="#Page_500">500</a></li>
-<li class="isub1">Heliotropism (he-li-ot′ro-pism), <a href="#Page_127">127-131</a>, <a href="#Page_133">133</a>, <a href="#Page_397">397</a></li>
-<li class="isub1">Helvellales, <a href="#Page_217">217</a></li>
-<li class="isub1">Hemiascomycetes, <a href="#Page_216">216</a></li>
-<li class="isub1">Hemibasidiomycetes, <a href="#Page_218">218</a></li>
-<li class="isub1">Hepaticæ, <a href="#Page_242">242</a></li>
-<li class="isub1">Heterospory (het″er-os′po-ry), <a href="#Page_434">434</a></li>
-<li class="isub1">Heterothallic, <a href="#Page_180">180</a></li>
-<li class="isub1">Heterotrophic plants, <a href="#Page_85">85</a></li>
-<li class="isub1">Hickory, <a href="#Page_494">494</a></li>
-<li class="isub1">Hickory-nut, <a href="#Page_452">452</a></li>
-<li class="isub1">Hilum, <a href="#Page_101">101</a>, <a href="#Page_102">102</a></li>
-<li class="isub1">Hippocastanaceæ, <a href="#Page_498">498</a></li>
-<li class="isub1">Holdfasts, <a href="#Page_418">418</a></li>
-<li class="isub1">Hollyhock, <a href="#Page_498">498</a></li>
-<li class="isub1">Homothallic, <a href="#Page_180">180</a></li>
-<li class="isub1">Honeysuckle, <a href="#Page_501">501</a></li>
-<li class="isub1">Hormogonales, <a href="#Page_163">163</a></li>
-<li class="isub1">Horse-chestnut, <a href="#Page_498">498</a></li>
-<li class="isub1">Horsetails, <a href="#Page_280">280-283</a></li>
-<li class="isub1">Houstonia cœrulea, <a href="#Page_437">437</a></li>
-<li class="isub1">Huckleberry, <a href="#Page_499">499</a></li>
-<li class="isub1">Humus saprophytes, <a href="#Page_85">85</a>, <a href="#Page_91">91</a></li>
-<li class="isub1">Hybridization, <a href="#Page_338">338</a></li>
-<li class="isub1">Hydnaceæ, <a href="#Page_210">210</a>, <a href="#Page_219">219</a></li>
-<li class="isub1">Hydnum coralloides, <a href="#Page_210">210</a></li>
-<li class="isub1">Hydnum repandum, <a href="#Page_211">211</a></li>
-<li class="isub1">Hydrocarbon, <a href="#Page_75">75</a></li>
-<li class="isub1">Hydrodictyaceæ, <a href="#Page_161">161</a></li>
-<li class="isub1">Hydrophytes, <a href="#Page_468">468</a></li>
-<li class="isub1">Hydropterales, <a href="#Page_295">295</a></li>
-<li class="isub1">Hydrotropism (hy-drot′ro′pism), <a href="#Page_133">133</a>, <a href="#Page_134">134</a>, <a href="#Page_412">412</a></li>
-<li class="isub1">Hygrophytes, <a href="#Page_468">468</a></li>
-<li class="isub1">Hymeniales, <a href="#Page_219">219</a></li>
-<li class="isub1">Hymenogastrales, <a href="#Page_219">219</a></li>
-<li class="isub1">Hymenomycetes, <a href="#Page_219">219</a></li>
-<li class="isub1">Hymenomycetineæ, <a href="#Page_219">219</a></li>
-<li class="isub1">Hymenophyllaceæ, <a href="#Page_295">295</a></li>
-<li class="isub1">Hypericum, <a href="#Page_498">498</a></li>
-<li class="isub1">Hypocotyl (hy′po-co″tyl), <a href="#Page_101">101</a></li>
-<li class="isub1">Hypocreales, <a href="#Page_217">217</a></li>
-<li class="isub1">Hypogenous, <a href="#Page_425">425</a></li>
-<li class="isub1">Hyponastic (hy-po-nas′tic), <a href="#Page_129">129</a></li>
-<li class="isub1">Hyponasty (hy′po-nas-ty), <a href="#Page_129">129</a></li>
-<li class="isub1">Hysteriales, <a href="#Page_217">217</a></li>
-
-<li class="ifrst">Impatiens, <a href="#Page_498">498</a></li>
-<li class="isub1">Impatiens fulva, <a href="#Page_460">460</a></li>
-<li class="isub1">Indian-pipe, <a href="#Page_499">499</a></li>
-<li class="isub1">Indian turnip, <a href="#Page_493">493</a></li>
-<li class="isub1">Indusium, <a href="#Page_252">252</a></li>
-<li class="isub1">Inflorescence, <a href="#Page_426">426</a></li>
-<li class="isub1">Insectivorous plants, <a href="#Page_133">133</a>, <a href="#Page_496">496</a></li>
-<li class="isub1">Integument, <a href="#Page_304">304</a></li>
-<li class="isub1">Intramolecular respiration, <a href="#Page_113">113</a>, <a href="#Page_114">114</a></li>
-<li class="isub1">Inulase, <a href="#Page_108">108</a></li>
-<li class="isub1">Inulin, <a href="#Page_108">108</a>, <a href="#Page_417">417</a></li>
-<li class="isub1">Iodine, <a href="#Page_65">65</a></li>
-<li class="isub1">Ipomœa, <a href="#Page_500">500</a></li>
-<li class="isub1">Iridaceæ, <a href="#Page_493">493</a></li>
-<li class="isub1">Iris, <a href="#Page_493">493</a></li>
-<li class="isub1">Irritability, <a href="#Page_125">125-135</a></li>
-<li class="isub1">Isoetales, <a href="#Page_296">296</a></li>
-<li class="isub1">Isoetes, <a href="#Page_289">289-291</a>, <a href="#Page_292">292</a></li>
-<li class="isub1">Isoetineæ, <a href="#Page_296">296</a></li>
-<li class="isub1">Ivy, <a href="#Page_498">498</a></li>
-
-<li class="ifrst">Jack-in-the-pulpit, <a href="#Page_373">373</a></li>
-<li class="isub1">Jewelweed, <a href="#Page_498">498</a></li>
-<li class="isub1">Juglandales, <a href="#Page_494">494</a></li>
-<li class="isub1">June-berry, <a href="#Page_497">497</a></li>
-<li class="isub1">Jungermanniales, <a href="#Page_242">242</a></li>
-
-<li class="ifrst">Kalmia latifolia, <a href="#Page_444">444</a>
-    <span class="pagenum"><a name="Page_508" id="Page_508">[Pg 508]</a></span></li>
-<li class="isub1">Karyokinesis, <a href="#Page_341">341-344</a></li>
-<li class="isub1">Kelps, <a href="#Page_168">168</a></li>
-<li class="isub1">Kingdom, <a href="#Page_492">492</a></li>
-
-<li class="ifrst">Labiatæ, <a href="#Page_423">423</a>, <a href="#Page_501">501</a></li>
-<li class="isub1">Laboulbeniales, <a href="#Page_218">218</a></li>
-<li class="isub1">Labrador tea, <a href="#Page_499">499</a></li>
-<li class="isub1">Lactuca canadensis, <a href="#Page_460">460</a></li>
-<li class="isub1">Lactuca scariola, <a href="#Page_409">409</a>, <a href="#Page_460">460</a>, <a href="#Page_461">461</a></li>
-<li class="isub1">Lagenidium, <a href="#Page_214">214</a>, <a href="#Page_215">215</a></li>
-<li class="isub1">Laminaria, <a href="#Page_168">168</a>, <a href="#Page_169">169</a></li>
-<li class="isub1">Lamium, <a href="#Page_424">424</a>, <a href="#Page_501">501</a></li>
-<li class="isub1">Larch, <a href="#Page_367">367</a></li>
-<li class="isub1">Laurel, <a href="#Page_499">499</a></li>
-<li class="isub1">Leaf patterns, <a href="#Page_404">404</a></li>
-<li class="isub1">Leathesia difformis, <a href="#Page_168">168</a></li>
-<li class="isub1">Leaves, form and arrangement, <a href="#Page_383">383-391</a>;</li>
-<li class="isub3">function of, <a href="#Page_387">387</a>;</li>
-<li class="isub3">protective modifications of, <a href="#Page_392">392</a>;</li>
-<li class="isub3">protective positions, <a href="#Page_395">395</a>;</li>
-<li class="isub3">reduction of surface, <a href="#Page_394">394</a>;</li>
-<li class="isub3">relation to light, <a href="#Page_397">397</a>;</li>
-<li class="isub3">structure of, <a href="#Page_40">40-43</a>, <a href="#Page_131">131</a>, <a href="#Page_391">391</a>, <a href="#Page_393">393</a></li>
-<li class="isub1">Legumes, <a href="#Page_92">92</a>, <a href="#Page_93">93</a>, <a href="#Page_453">453</a></li>
-<li class="isub1">Leguminosæ (= Papilionaceæ), <a href="#Page_396">396</a>, <a href="#Page_399">399</a></li>
-<li class="isub1">Leitneria floridana, <a href="#Page_494">494</a></li>
-<li class="isub1">Leitneriales, <a href="#Page_494">494</a></li>
-<li class="isub1">Lemanea, <a href="#Page_171">171</a>, <a href="#Page_173">173</a>, <a href="#Page_175">175</a>, <a href="#Page_492">492</a></li>
-<li class="isub1">Lemna, <a href="#Page_418">418</a></li>
-<li class="isub1">Lemna trisulca, <a href="#Page_26">26</a>, <a href="#Page_27">27</a></li>
-<li class="isub1">Lenticel, <a href="#Page_357">357</a>, <a href="#Page_358">358</a></li>
-<li class="isub1">Lepiota naucina, <a href="#Page_208">208</a></li>
-<li class="isub1">Lettuce, <a href="#Page_502">502</a></li>
-<li class="isub1">Leucoplast, <a href="#Page_71">71</a></li>
-<li class="isub1">Lichens, <a href="#Page_86">86</a>, <a href="#Page_93">93-95</a>, <a href="#Page_220">220</a>, <a href="#Page_221">221</a></li>
-<li class="isub1">Light, <a href="#Page_465">465</a></li>
-<li class="isub1">Liliaceæ, <a href="#Page_490">490</a>, <a href="#Page_493">493</a></li>
-<li class="isub1">Liliales, <a href="#Page_490">490</a>, <a href="#Page_493">493</a></li>
-<li class="isub1">Lilium, <a href="#Page_489">489-493</a></li>
-<li class="isub1">Linaria vulgaris, <a href="#Page_501">501</a></li>
-<li class="isub1">Linden, <a href="#Page_498">498</a></li>
-<li class="isub1">Linum vulgaris, <a href="#Page_497">497</a></li>
-<li class="isub1">Lipase, <a href="#Page_108">108</a></li>
-<li class="isub1">Liquidambar, <a href="#Page_496">496</a></li>
-<li class="isub1">Liriodendron, <a href="#Page_496">496</a></li>
-<li class="isub1">Live-forever, <a href="#Page_394">394</a></li>
-<li class="isub1">Liverworts, <a href="#Page_222">222-239</a>;</li>
-<li class="isub3">absorption by, <a href="#Page_23">23-25</a>;</li>
-<li class="isub3">classification of, <a href="#Page_242">242</a></li>
-<li class="isub1">Lobelia, <a href="#Page_501">501</a></li>
-<li class="isub1">Lupinus perennis, <a href="#Page_353">353</a></li>
-<li class="isub1">Lycoperdales, <a href="#Page_220">220</a></li>
-<li class="isub1">Lycopodiaceæ, <a href="#Page_296">296</a></li>
-<li class="isub1">Lycopodiales, <a href="#Page_296">296</a></li>
-<li class="isub1">Lycopodiineæ, <a href="#Page_296">296</a></li>
-<li class="isub1">Lycopodium, <a href="#Page_284">284-286</a></li>
-
-<li class="ifrst">Macrosporangium, <a href="#Page_94">94</a>, <a href="#Page_302">302</a>, <a href="#Page_304">304</a>, <a href="#Page_311">311</a>, <a href="#Page_312">312</a>, <a href="#Page_321">321</a></li>
-<li class="isub1">Macrospore, <a href="#Page_287">287</a>, <a href="#Page_290">290</a>, <a href="#Page_326">326-328</a>, <a href="#Page_434">434</a></li>
-<li class="isub1">Magnolia, <a href="#Page_496">496</a></li>
-<li class="isub1">Mallow family, <a href="#Page_498">498</a></li>
-<li class="isub1">Malvales, <a href="#Page_498">498</a></li>
-<li class="isub1">Maple family, <a href="#Page_497">497</a></li>
-<li class="isub1">Marchantia, <a href="#Page_24">24</a>, <a href="#Page_226">226-236</a></li>
-<li class="isub1">Marchantiales, <a href="#Page_242">242</a></li>
-<li class="isub1">Marine plant societies, <a href="#Page_486">486</a></li>
-<li class="isub1">Marratiales, <a href="#Page_295">295</a></li>
-<li class="isub1">Marsilia, <a href="#Page_370">370</a></li>
-<li class="isub1">Marsiliaceæ, <a href="#Page_296">296</a></li>
-<li class="isub1">Matoniaceæ, <a href="#Page_295">295</a></li>
-<li class="isub1">Medicago denticulata, <a href="#Page_92">92</a></li>
-<li class="isub1">Medulla, <a href="#Page_50">50</a></li>
-<li class="isub1">Members of the flower, <a href="#Page_335">335</a></li>
-<li class="isub1">Members of the plant, <a href="#Page_349">349-353</a></li>
-<li class="isub1">Meristem, <a href="#Page_359">359</a></li>
-<li class="isub1">Mesocarp, <a href="#Page_450">450</a></li>
-<li class="isub1">Mesophytes, <a href="#Page_467">467</a></li>
-<li class="isub1">Microsporangia, <a href="#Page_294">294</a>, <a href="#Page_299">299</a></li>
-<li class="isub1">Microspore, <a href="#Page_287">287</a>, <a href="#Page_290">290</a>, <a href="#Page_299">299</a>, <a href="#Page_312">312</a>, <a href="#Page_435">435</a></li>
-<li class="isub1">Microsporophylls, <a href="#Page_299">299</a>, <a href="#Page_320">320</a>, <a href="#Page_420">420</a></li>
-<li class="isub1">Milkweed family, <a href="#Page_500">500</a></li>
-<li class="isub1">Mimosa, <a href="#Page_132">132</a>, <a href="#Page_396">396</a></li>
-<li class="isub1">Mimulus, <a href="#Page_501">501</a></li>
-<li class="isub1">Mint family, <a href="#Page_501">501</a></li>
-<li class="isub1">Mistletoe, <a href="#Page_84">84</a>, <a href="#Page_495">495</a></li>
-<li class="isub1">Mitchella, <a href="#Page_501">501</a></li>
-<li class="isub1">Mixotrophic plants, <a href="#Page_85">85</a></li>
-<li class="isub1">Mnium, <a href="#Page_243">243-246</a></li>
-<li class="isub1">Molds, nutrition of, <a href="#Page_86">86-90</a></li>
-<li class="isub1">Molds, water, <a href="#Page_181">181</a></li>
-<li class="isub1">Monadelphous, <a href="#Page_424">424</a></li>
-<li class="isub1">Monoblepharidales, <a href="#Page_215">215</a></li>
-<li class="isub1">Monoblepharis, <a href="#Page_215">215</a></li>
-<li class="isub1">Monocotyledons, <a href="#Page_490">490</a>, <a href="#Page_492">492</a></li>
-<li class="isub1">Monœcious, <a href="#Page_435">435</a></li>
-<li class="isub1">Monotropa uniflora, <a href="#Page_499">499</a></li>
-<li class="isub1">Morchella, <a href="#Page_198">198</a>, <a href="#Page_199">199</a></li>
-<li class="isub1">Morel, <a href="#Page_198">198</a>, <a href="#Page_199">199</a></li>
-<li class="isub1">Morning-glories, <a href="#Page_500">500</a></li>
-<li class="isub1">Mosaics, <a href="#Page_405">405</a></li>
-<li class="isub1">Mosses, <a href="#Page_243">243-248</a>, <a href="#Page_457">457</a>;</li>
-<li class="isub3">absorption by, <a href="#Page_25">25</a>;</li>
-<li class="isub3">classification of, <a href="#Page_248">248</a></li>
-<li class="isub1">Mucor, <a href="#Page_6">6</a>, <a href="#Page_7">7</a>, <a href="#Page_15">15</a>, <a href="#Page_118">118</a>, <a href="#Page_119">119</a>, <a href="#Page_177">177-180</a>, <a href="#Page_215">215</a></li>
-<li class="isub1">Mucorales, <a href="#Page_215">215</a></li>
-<li class="isub1">Mulberry, <a href="#Page_495">495</a></li>
-<li class="isub1">Mullein, <a href="#Page_366">366</a>, <a href="#Page_394">394</a>, <a href="#Page_501">501</a></li>
-<li class="isub1">Mushrooms, <a href="#Page_199">199-208</a>
-    <span class="pagenum"><a name="Page_509" id="Page_509">[Pg 509]</a></span></li>
-<li class="isub1">Mustard family, <a href="#Page_496">496</a></li>
-<li class="isub1">Mutation, <a href="#Page_338">338</a></li>
-<li class="isub1">Mutualism, <a href="#Page_95">95</a></li>
-<li class="isub1">Mycelium, <a href="#Page_6">6</a>, <a href="#Page_86">86-90</a></li>
-<li class="isub1">Mycetozoa, <a href="#Page_213">213</a>, <a href="#Page_214">214</a></li>
-<li class="isub1">Mycorhiza, <a href="#Page_86">86</a>, <a href="#Page_91">91</a>, <a href="#Page_92">92</a>, <a href="#Page_217">217</a></li>
-<li class="isub1">Myosotis, <a href="#Page_500">500</a></li>
-<li class="isub1">Myrica cerifera, <a href="#Page_494">494</a></li>
-<li class="isub1">Myrica gale, <a href="#Page_494">494</a></li>
-<li class="isub1">Myricales, <a href="#Page_494">494</a></li>
-<li class="isub1">Myriophyllum, <a href="#Page_403">403</a></li>
-<li class="isub1">Myrtales, <a href="#Page_498">498</a></li>
-<li class="isub1">Myxobacteriales, <a href="#Page_165">165</a></li>
-<li class="isub1">Myxomycetes, <a href="#Page_83">83</a>, <a href="#Page_213">213</a>, <a href="#Page_214">214</a></li>
-
-<li class="ifrst">Naiadaceæ, <a href="#Page_492">492</a></li>
-<li class="isub1">Naiadales, <a href="#Page_492">492</a></li>
-<li class="isub1">Naias, <a href="#Page_492">492</a></li>
-<li class="isub1">Nemalion, <a href="#Page_171">171</a>, <a href="#Page_172">172</a>, <a href="#Page_175">175</a></li>
-<li class="isub1">Nemalionales, <a href="#Page_175">175</a></li>
-<li class="isub1">Nettle, <a href="#Page_495">495</a></li>
-<li class="isub1">Nicotiana, <a href="#Page_501">501</a></li>
-<li class="isub1">Nidulariales, <a href="#Page_220">220</a></li>
-<li class="isub1">Nitella, <a href="#Page_8">8</a>, <a href="#Page_9">9</a>, <a href="#Page_176">176</a></li>
-<li class="isub1">Nitrobacter, <a href="#Page_83">83</a></li>
-<li class="isub1">Nitrogen, <a href="#Page_92">92</a>, <a href="#Page_93">93</a></li>
-<li class="isub1">Nitromonas, <a href="#Page_83">83</a></li>
-<li class="isub1">Nostocaceæ, <a href="#Page_164">164</a></li>
-<li class="isub1">Nucellus, <a href="#Page_304">304</a></li>
-<li class="isub1">Nucleus, <a href="#Page_3">3</a>, <a href="#Page_4">4</a>;</li>
-<li class="isub3">morphology of, <a href="#Page_340">340-345</a></li>
-<li class="isub1">Nuphar advena, <a href="#Page_496">496</a></li>
-<li class="isub1">Nutation, <a href="#Page_123">123</a>, <a href="#Page_124">124</a></li>
-<li class="isub1">Nymphæa odorata, <a href="#Page_496">496</a></li>
-
-<li class="ifrst">Oak, <a href="#Page_495">495</a></li>
-<li class="isub1">Oak family, <a href="#Page_495">495</a></li>
-<li class="isub1">Œdogoniaceæ, <a href="#Page_162">162</a></li>
-<li class="isub1">Œdogonium, <a href="#Page_147">147-151</a>, <a href="#Page_350">350</a></li>
-<li class="isub1">Œnothera biennis, <a href="#Page_498">498</a></li>
-<li class="isub1">Œnothera gigas, <a href="#Page_338">338</a></li>
-<li class="isub1">Œnothera lamarkiana, <a href="#Page_338">338</a></li>
-<li class="isub1">Olpidium, <a href="#Page_214">214</a>, <a href="#Page_215">215</a></li>
-<li class="isub1">Onagar biennis, <a href="#Page_498">498</a></li>
-<li class="isub1">Onagraceæ, <a href="#Page_498">498</a></li>
-<li class="isub1">Onoclea sensibilis, <a href="#Page_254">254</a>, <a href="#Page_273">273-278</a></li>
-<li class="isub1">Oogonium, <a href="#Page_144">144</a>, <a href="#Page_150">150</a>, <a href="#Page_155">155</a></li>
-<li class="isub1">Oomycetes, <a href="#Page_214">214</a>, <a href="#Page_215">215</a></li>
-<li class="isub1">Ophioglossales, <a href="#Page_295">295</a></li>
-<li class="isub1">Ophioglossum, <a href="#Page_295">295</a></li>
-<li class="isub1">Opuntiales, <a href="#Page_498">498</a></li>
-<li class="isub1">Orchidaceæ, <a href="#Page_494">494</a></li>
-<li class="isub1">Orchidales, <a href="#Page_494">494</a></li>
-<li class="isub1">Orchids, <a href="#Page_442">442</a></li>
-<li class="isub1">Oscillatoriaceæ, <a href="#Page_163">163</a></li>
-<li class="isub1">Osmosis, <a href="#Page_13">13-20</a></li>
-<li class="isub1">Osmundaceæ, <a href="#Page_295">295</a></li>
-<li class="isub1">Ostrich fern, <a href="#Page_279">279</a></li>
-<li class="isub1">Ovule, <a href="#Page_302">302</a>, <a href="#Page_321">321</a>, <a href="#Page_334">334</a>, <a href="#Page_421">421</a></li>
-<li class="isub1">Oxalis, <a href="#Page_497">497</a></li>
-<li class="isub1">Oxycoccus, <a href="#Page_500">500</a></li>
-<li class="isub1">Oxydendrum arboreum, <a href="#Page_501">501</a></li>
-<li class="isub1">Oxygen, <a href="#Page_63">63</a>, <a href="#Page_110">110-113</a></li>
-
-<li class="ifrst">Palisade cells, <a href="#Page_41">41</a>, <a href="#Page_43">43</a></li>
-<li class="isub1">Palmaceæ, <a href="#Page_493">493</a></li>
-<li class="isub1">Palmales, <a href="#Page_493">493</a></li>
-<li class="isub1">Palms, <a href="#Page_408">408</a></li>
-<li class="isub1">Pandanales, <a href="#Page_492">492</a></li>
-<li class="isub1">Pandanus, <a href="#Page_492">492</a></li>
-<li class="isub1">Pandorina, <a href="#Page_160">160</a>, <a href="#Page_350">350</a></li>
-<li class="isub1">Panicle, <a href="#Page_427">427</a></li>
-<li class="isub1">Papaverales, <a href="#Page_496">496</a></li>
-<li class="isub1">Papilionaceæ, <a href="#Page_423">423</a>, <a href="#Page_497">497</a></li>
-<li class="isub1">Parasites, <a href="#Page_83">83</a>, <a href="#Page_84">84</a>, <a href="#Page_86">86</a></li>
-<li class="isub1">Parasitic fungi, nutrition of, <a href="#Page_86">86-90</a></li>
-<li class="isub1">Parenchyma, <a href="#Page_50">50</a>, <a href="#Page_356">356</a>, <a href="#Page_363">363</a></li>
-<li class="isub1">Parietales, <a href="#Page_498">498</a></li>
-<li class="isub1">Parkeriaceæ, <a href="#Page_296">296</a></li>
-<li class="isub1">Parmelia, <a href="#Page_96">96</a></li>
-<li class="isub1">Parthenogenesis, <a href="#Page_184">184</a></li>
-<li class="isub1">Partridge-berry, <a href="#Page_501">501</a></li>
-<li class="isub1">Pea, <a href="#Page_497">497</a></li>
-<li class="isub1">Pea family, <a href="#Page_497">497</a></li>
-<li class="isub1">Pear, <a href="#Page_456">456</a></li>
-<li class="isub1">Pediastrum, <a href="#Page_161">161</a></li>
-<li class="isub1">Pellia, <a href="#Page_164">164</a></li>
-<li class="isub1">Pellonia, <a href="#Page_405">405</a></li>
-<li class="isub1">Peltigera, <a href="#Page_94">94</a>, <a href="#Page_95">95</a></li>
-<li class="isub1">Pepo, <a href="#Page_456">456</a></li>
-<li class="isub1">Pericycle, <a href="#Page_360">360</a></li>
-<li class="isub1">Peridineæ, <a href="#Page_166">166</a></li>
-<li class="isub1">Perigynous, <a href="#Page_425">425</a></li>
-<li class="isub1">Perisperm, <a href="#Page_331">331</a>, <a href="#Page_332">332</a></li>
-<li class="isub1">Perisporiales, <a href="#Page_217">217</a></li>
-<li class="isub1">Peronospora, <a href="#Page_183">183</a>, <a href="#Page_215">215</a></li>
-<li class="isub1">Peronosporales, <a href="#Page_215">215</a></li>
-<li class="isub1">Persimmon, <a href="#Page_500">500</a></li>
-<li class="isub1">Pezizales, <a href="#Page_217">217</a></li>
-<li class="isub1">Phacidiales, <a href="#Page_217">217</a></li>
-<li class="isub1">Phæophyceæ, <a href="#Page_167">167</a></li>
-<li class="isub1">Phæosporales, <a href="#Page_171">171</a></li>
-<li class="isub1">Phallales, <a href="#Page_219">219</a></li>
-<li class="isub1">Phloem, <a href="#Page_50">50-52</a>, <a href="#Page_360">360</a>, <a href="#Page_361">361</a>, <a href="#Page_363">363</a></li>
-<li class="isub1">Phlox family, <a href="#Page_500">500</a></li>
-<li class="isub1">Phoradendron flavescens, <a href="#Page_495">495</a></li>
-<li class="isub1">Photosynthesis, <a href="#Page_67">67</a>, <a href="#Page_68">68</a>, <a href="#Page_70">70</a>, <a href="#Page_117">117</a>
-    <span class="pagenum"><a name="Page_510" id="Page_510">[Pg 510]</a></span></li>
-<li class="isub1">Phycomycetes (Phy″co-my-ce′tes), <a href="#Page_214">214</a>, <a href="#Page_215">215</a></li>
-<li class="isub1">Phyllidium, <a href="#Page_371">371</a></li>
-<li class="isub1">Phylloclades, <a href="#Page_373">373</a>, <a href="#Page_395">395</a></li>
-<li class="isub1">Phyllotaxy, <a href="#Page_375">375</a>, <a href="#Page_384">384</a></li>
-<li class="isub1">Physical condition of soil, <a href="#Page_465">465</a></li>
-<li class="isub1">Physical factors, <a href="#Page_465">465</a></li>
-<li class="isub1">Phytolaccaceæ, <a href="#Page_495">495</a></li>
-<li class="isub1">Phytomyxa leguminosarum, <a href="#Page_92">92</a></li>
-<li class="isub1">Phytophthora, <a href="#Page_182">182</a>, <a href="#Page_184">184</a>, <a href="#Page_215">215</a></li>
-<li class="isub1">Pickerel-weed, <a href="#Page_493">493</a></li>
-<li class="isub1">Pilularia, <a href="#Page_296">296</a></li>
-<li class="isub1">Pinales, <a href="#Page_216">216</a></li>
-<li class="isub1">Pine, white, <a href="#Page_297">297-310</a></li>
-<li class="isub1">Piperales, <a href="#Page_494">494</a></li>
-<li class="isub1">Pitcher-plant, <a href="#Page_496">496</a></li>
-<li class="isub1">Pith, <a href="#Page_50">50</a></li>
-<li class="isub1">Plant food, sources of, <a href="#Page_81">81</a></li>
-<li class="isub1">Plant formations, <a href="#Page_496">496</a></li>
-<li class="isub1">Plant substance, analysis of, <a href="#Page_79">79</a>, <a href="#Page_80">80</a></li>
-<li class="isub1">Plantaginales, <a href="#Page_501">501</a></li>
-<li class="isub1">Plantago, <a href="#Page_501">501</a></li>
-<li class="isub1">Plasmolysis (plas-mol′y-sis), <a href="#Page_19">19</a></li>
-<li class="isub1">Plasmopara, <a href="#Page_183">183</a>, <a href="#Page_215">215</a></li>
-<li class="isub1">Plectascales, <a href="#Page_217">217</a></li>
-<li class="isub1">Plectobasidiales, <a href="#Page_220">220</a></li>
-<li class="isub1">Pleurococcaceæ, <a href="#Page_161">161</a></li>
-<li class="isub1">Pleurococcus, <a href="#Page_161">161</a></li>
-<li class="isub1">Plum family, <a href="#Page_497">497</a></li>
-<li class="isub1">Plumule, <a href="#Page_99">99</a></li>
-<li class="isub1">Podostemon, <a href="#Page_496">496</a></li>
-<li class="isub1">Poison-hemlock, <a href="#Page_499">499</a></li>
-<li class="isub1">Poison-ivy, <a href="#Page_497">497</a></li>
-<li class="isub1">Poison-oak, <a href="#Page_497">497</a></li>
-<li class="isub1">Poisonous mushrooms, <a href="#Page_207">207</a>, <a href="#Page_208">208</a></li>
-<li class="isub1">Poison-sumac, <a href="#Page_497">497</a></li>
-<li class="isub1">Pokeweed, <a href="#Page_495">495</a></li>
-<li class="isub1">Polemoneales, <a href="#Page_500">500</a></li>
-<li class="isub1">Pollen grain, <a href="#Page_299">299</a>, <a href="#Page_305">305</a></li>
-<li class="isub1">Pollination, <a href="#Page_303">303</a>, <a href="#Page_304">304</a>, <a href="#Page_420">420</a>, <a href="#Page_430">430</a>, <a href="#Page_433">433-449</a></li>
-<li class="isub1">Pollinium, <a href="#Page_420">420</a></li>
-<li class="isub1">Polygonales, <a href="#Page_495">495</a></li>
-<li class="isub1">Polygonum, <a href="#Page_495">495</a></li>
-<li class="isub1">Polypodiaceæ, <a href="#Page_296">296</a></li>
-<li class="isub1">Polyporaceæ, <a href="#Page_209">209</a>, <a href="#Page_219">219</a></li>
-<li class="isub1">Polyporus, <a href="#Page_209">209</a>, <a href="#Page_210">210</a></li>
-<li class="isub1">Polyporus mollis, <a href="#Page_92">92</a></li>
-<li class="isub1">Polyporus sulphureus, <a href="#Page_209">209</a></li>
-<li class="isub1">Pomaceæ, <a href="#Page_497">497</a></li>
-<li class="isub1">Pondweeds, <a href="#Page_492">492</a></li>
-<li class="isub1">Poppy, <a href="#Page_496">496</a></li>
-<li class="isub1">Porella, <a href="#Page_237">237</a></li>
-<li class="isub1">Portulaca, <a href="#Page_495">495</a></li>
-<li class="isub1">Potamogeton, <a href="#Page_492">492</a></li>
-<li class="isub1">Potato, <a href="#Page_501">501</a></li>
-<li class="isub1">Powdery mildews, <a href="#Page_195">195-198</a>, <a href="#Page_217">217</a></li>
-<li class="isub1">Primrose, <a href="#Page_498">498</a>, <a href="#Page_500">500</a></li>
-<li class="isub1">Primula, <a href="#Page_438">438</a></li>
-<li class="isub1">Primulales, <a href="#Page_500">500</a></li>
-<li class="isub1">Procarp, <a href="#Page_172">172</a>, <a href="#Page_174">174</a>, <a href="#Page_175">175</a></li>
-<li class="isub1">Progeotropism (pro″ge-ot′ro-pism), <a href="#Page_126">126</a></li>
-<li class="isub1">Promycelium (pro″my-ce′li-um), <a href="#Page_192">192</a></li>
-<li class="isub1">Proterandrous, <a href="#Page_441">441</a>, <a href="#Page_442">442</a></li>
-<li class="isub1">Proterandry, <a href="#Page_444">444</a></li>
-<li class="isub1">Proterogenous, <a href="#Page_441">441</a>, <a href="#Page_442">442</a></li>
-<li class="isub1">Proterogeny, <a href="#Page_440">440</a></li>
-<li class="isub1">Prothallium, <a href="#Page_265">265</a>, <a href="#Page_287">287</a>, <a href="#Page_288">288</a>, <a href="#Page_291">291</a>, <a href="#Page_292">292</a>, <a href="#Page_304">304</a>, <a href="#Page_305">305</a>,</li>
-<li class="isub7"><a href="#Page_311">311</a>, <a href="#Page_325">325</a>, <a href="#Page_328">328</a>, <a href="#Page_335">335</a>, <a href="#Page_433">433</a>, <a href="#Page_434">434</a></li>
-<li class="isub1">Protoascales, <a href="#Page_216">216</a></li>
-<li class="isub1">Protoascomycetes, <a href="#Page_216">216</a></li>
-<li class="isub1">Protobasidiomycetes, <a href="#Page_218">218</a></li>
-<li class="isub1">Protococcoideæ, <a href="#Page_158">158</a>, <a href="#Page_162">162</a></li>
-<li class="isub1">Protodiscales, <a href="#Page_217">217</a></li>
-<li class="isub1">Protomyces, <a href="#Page_216">216</a></li>
-<li class="isub1">Protonema (pro″to-ne′ma), <a href="#Page_248">248</a>, <a href="#Page_264">264</a></li>
-<li class="isub1">Protoplasm, <a href="#Page_1">1-12</a>, <a href="#Page_42">42-43</a>, <a href="#Page_342">342</a>;</li>
-<li class="isub3">movement of, <a href="#Page_7">7-11</a></li>
-<li class="isub1">Psilotaceæ, <a href="#Page_296">296</a></li>
-<li class="isub1">Pteridophytes, <a href="#Page_295">295</a>, <a href="#Page_434">434</a></li>
-<li class="isub1">Pteris cretica, <a href="#Page_346">346</a></li>
-<li class="isub1">Puccinia, <a href="#Page_187">187</a></li>
-<li class="isub1">Puff-balls, <a href="#Page_220">220</a></li>
-<li class="isub1">Pumpkin, <a href="#Page_501">501</a></li>
-<li class="isub1">Purslane, <a href="#Page_495">495</a></li>
-<li class="isub1">Pyrenoid, <a href="#Page_2">2</a>, <a href="#Page_3">3</a></li>
-<li class="isub1">Pyrenomycetes, <a href="#Page_217">217</a></li>
-<li class="isub1">Pyrola, <a href="#Page_499">499</a></li>
-<li class="isub1">Pyxidium, <a href="#Page_453">453</a></li>
-
-<li class="ifrst">Quercus, <a href="#Page_495">495</a></li>
-<li class="isub1">Quillworts, <a href="#Page_289">289-291</a></li>
-<li class="isub1">Quince, <a href="#Page_456">456</a></li>
-
-<li class="ifrst">Raceme, <a href="#Page_427">427</a></li>
-<li class="isub1">Radicle, <a href="#Page_99">99</a></li>
-<li class="isub1">Ragweed, <a href="#Page_502">502</a></li>
-<li class="isub1">Rainy-season flora, <a href="#Page_481">481</a></li>
-<li class="isub1">Ranales, <a href="#Page_496">496</a></li>
-<li class="isub1">Ranunculaceæ, <a href="#Page_496">496</a></li>
-<li class="isub1">Raspberry, <a href="#Page_454">454</a>, <a href="#Page_455">455</a></li>
-<li class="isub1">Red algæ, <a href="#Page_171">171</a>, <a href="#Page_174">174</a>;</li>
-<li class="isub3">uses of, <a href="#Page_175">175</a></li>
-<li class="isub1">Reproduction, <a href="#Page_137">137</a>, <a href="#Page_143">143</a>, <a href="#Page_149">149</a>, <a href="#Page_154">154</a>, <a href="#Page_155">155</a>, <a href="#Page_179">179</a>, <a href="#Page_185">185</a>, <a href="#Page_186">186</a></li>
-<li class="isub1">Respiration, <a href="#Page_110">110-116</a>, <a href="#Page_117">117</a></li>
-<li class="isub1">Rhamnales, <a href="#Page_498">498</a>
-    <span class="pagenum"><a name="Page_511" id="Page_511">[Pg 511]</a></span></li>
-<li class="isub1">Rhizoids, <a href="#Page_24">24-26</a></li>
-<li class="isub1">Rhizome, <a href="#Page_354">354</a></li>
-<li class="isub1">Rhizomorph (rhi′zo-morph), <a href="#Page_89">89</a></li>
-<li class="isub1">Rhizophidium, <a href="#Page_214">214</a>, <a href="#Page_215">215</a></li>
-<li class="isub1">Rhizopus, <a href="#Page_177">177-180</a>, <a href="#Page_215">215</a></li>
-<li class="isub1">Rhododendron, <a href="#Page_499">499</a></li>
-<li class="isub1">Rhodomeniales, <a href="#Page_175">175</a></li>
-<li class="isub1">Rhodophyceæ, <a href="#Page_171">171</a></li>
-<li class="isub1">Rhus radicans, <a href="#Page_416">416</a>, <a href="#Page_497">497</a></li>
-<li class="isub1">Riccia, <a href="#Page_23">23</a>, <a href="#Page_164">164</a>, <a href="#Page_222">222-226</a></li>
-<li class="isub1">Ricinus, <a href="#Page_497">497</a></li>
-<li class="isub1">Riverweed, <a href="#Page_496">496</a></li>
-<li class="isub1">Root, function of, <a href="#Page_410">410-418</a></li>
-<li class="isub1">Root hairs, absorption by, <a href="#Page_19">19</a>, <a href="#Page_30">30</a>, <a href="#Page_32">32</a></li>
-<li class="isub1">Root hairs, action on soil, <a href="#Page_82">82</a></li>
-<li class="isub1">Root pressure, <a href="#Page_33">33</a>, <a href="#Page_34">34</a>, <a href="#Page_45">45</a></li>
-<li class="isub1">Root, structure of, <a href="#Page_30">30</a>, <a href="#Page_361">361</a>, <a href="#Page_362">362</a></li>
-<li class="isub1">Root-tubercles, <a href="#Page_92">92</a></li>
-<li class="isub1">Roots, kinds of, <a href="#Page_415">415</a></li>
-<li class="isub1">Rosaceæ, <a href="#Page_497">497</a></li>
-<li class="isub1">Rosales, <a href="#Page_496">496</a></li>
-<li class="isub1">Rose family, <a href="#Page_497">497</a></li>
-<li class="isub1">Rosette, <a href="#Page_405">405</a></li>
-<li class="isub1">Rosette plants, <a href="#Page_483">483</a></li>
-<li class="isub1">Rubiales, <a href="#Page_501">501</a></li>
-<li class="isub1">Rudbeckia, <a href="#Page_502">502</a></li>
-<li class="isub1">Rusts, <a href="#Page_187">187-194</a></li>
-
-<li class="ifrst">Salicaceæ, <a href="#Page_494">494</a></li>
-<li class="isub1">Salix, <a href="#Page_494">494</a></li>
-<li class="isub1">Salsify, <a href="#Page_502">502</a></li>
-<li class="isub1">Salviniaceæ, <a href="#Page_296">296</a></li>
-<li class="isub1">Samara, <a href="#Page_451">451</a></li>
-<li class="isub1">Sandalwood, <a href="#Page_495">495</a></li>
-<li class="isub1">Sanguinaria, <a href="#Page_496">496</a></li>
-<li class="isub1">Santalales, <a href="#Page_495">495</a></li>
-<li class="isub1">Sap, rise of, <a href="#Page_53">53</a>, <a href="#Page_54">54</a></li>
-<li class="isub1">Sapindales, <a href="#Page_497">497</a></li>
-<li class="isub1">Saprolegnia, <a href="#Page_181">181-184</a></li>
-<li class="isub1">Saprolegniales, <a href="#Page_215">215</a></li>
-<li class="isub1">Saprophytes, <a href="#Page_83">83-85</a></li>
-<li class="isub1">Sargassum, <a href="#Page_170">170</a></li>
-<li class="isub1">Sarraceniales, <a href="#Page_496">496</a></li>
-<li class="isub1">Sarsaparilla, <a href="#Page_499">499</a></li>
-<li class="isub1">Saxifrage, <a href="#Page_496">496</a></li>
-<li class="isub1">Schizæaceæ, <a href="#Page_295">295</a></li>
-<li class="isub1">Schizocarp, <a href="#Page_451">451</a></li>
-<li class="isub1">Schizomycetes, <a href="#Page_164">164</a></li>
-<li class="isub1">Schizophyceæ, <a href="#Page_163">163</a></li>
-<li class="isub1">Sclerenchyma, <a href="#Page_356">356-357</a>, <a href="#Page_361">361</a>, <a href="#Page_363">363</a></li>
-<li class="isub1">Scouring rush, <a href="#Page_282">282</a></li>
-<li class="isub1">Screw-pine, <a href="#Page_409">409</a>, <a href="#Page_492">492</a></li>
-<li class="isub1">Scrophulariaceæ, <a href="#Page_501">501</a></li>
-<li class="isub1">Sedge family, <a href="#Page_492">492</a></li>
-<li class="isub1">Seed, dispersal of, <a href="#Page_458">458-463</a></li>
-<li class="isub1">Seed plants, <a href="#Page_338">338</a></li>
-<li class="isub1">Seed, structure of, <a href="#Page_98">98</a>, <a href="#Page_102">102</a></li>
-<li class="isub1">Seedlings, <a href="#Page_97">97-107</a></li>
-<li class="isub1">Seeds, <a href="#Page_330">330-334</a></li>
-<li class="isub1">Selaginella, <a href="#Page_286">286-288</a>, <a href="#Page_292">292</a></li>
-<li class="isub1">Selaginellaceæ, <a href="#Page_296">296</a></li>
-<li class="isub1">Sensitive fern, <a href="#Page_273">273</a></li>
-<li class="isub1">Sensitive plants, <a href="#Page_132">132</a>, <a href="#Page_396">396</a>, <a href="#Page_399">399</a></li>
-<li class="isub1">Sexual organs, <a href="#Page_144">144</a>, <a href="#Page_147">147</a></li>
-<li class="isub1">Shadbush, <a href="#Page_497">497</a></li>
-<li class="isub1">Shepherd’s-purse, <a href="#Page_496">496</a></li>
-<li class="isub1">Shoot, floral, <a href="#Page_419">419</a>, <a href="#Page_432">432</a></li>
-<li class="isub1">Shoots, <a href="#Page_353">353-355</a>;</li>
-<li class="isub3">types of, <a href="#Page_361">361-373</a>;</li>
-<li class="isub3">winter condition of, <a href="#Page_374">374-377</a></li>
-<li class="isub1">Sieve tissue, <a href="#Page_358">358</a>, <a href="#Page_363">363</a></li>
-<li class="isub1">Sieve tubes, <a href="#Page_52">52</a>, <a href="#Page_53">53</a></li>
-<li class="isub1">Silique, <a href="#Page_453">453</a></li>
-<li class="isub1">Silk-cotton tree, <a href="#Page_417">417</a></li>
-<li class="isub1">Silver bell, <a href="#Page_500">500</a></li>
-<li class="isub1">Siphoneæ, <a href="#Page_146">146</a>, <a href="#Page_162">162</a></li>
-<li class="isub1">Skunk’s cabbage, <a href="#Page_439">439-442</a></li>
-<li class="isub1">Slime molds, <a href="#Page_83">83</a></li>
-<li class="isub1">Smoke-tree, <a href="#Page_497">497</a></li>
-<li class="isub1">Societies, <a href="#Page_475">475</a></li>
-<li class="isub1">Solanum, <a href="#Page_501">501</a></li>
-<li class="isub1">Solidago, <a href="#Page_502">502</a></li>
-<li class="isub1">Sourwood, <a href="#Page_499">499</a></li>
-<li class="isub1">Spadix, <a href="#Page_428">428</a></li>
-<li class="isub1">Spartium, <a href="#Page_446">446</a></li>
-<li class="isub1">Spathyema fœtida, <a href="#Page_438">438</a>, <a href="#Page_493">493</a></li>
-<li class="isub1">Spermagonia, <a href="#Page_190">190</a></li>
-<li class="isub1">Spermatophytes, <a href="#Page_338">338</a></li>
-<li class="isub1">Sphacelaria, <a href="#Page_168">168</a></li>
-<li class="isub1">Sphærella lacustris, <a href="#Page_158">158</a>, <a href="#Page_159">159</a></li>
-<li class="isub1">Sphærella nivalis, <a href="#Page_158">158</a>, <a href="#Page_350">350</a></li>
-<li class="isub1">Sphæriales, <a href="#Page_218">218</a></li>
-<li class="isub1">Sphagnales, <a href="#Page_248">248</a></li>
-<li class="isub1">Sphagnum, <a href="#Page_164">164</a></li>
-<li class="isub1">Spiderwort, <a href="#Page_11">11</a>, <a href="#Page_493">493</a></li>
-<li class="isub1">Spike, <a href="#Page_428">428</a></li>
-<li class="isub1">Spirodela polyrhiza, <a href="#Page_27">27</a></li>
-<li class="isub1">Spirogyra, <a href="#Page_1">1-5</a>, <a href="#Page_13">13</a>, <a href="#Page_14">14</a>, <a href="#Page_60">60</a>, <a href="#Page_72">72</a>, <a href="#Page_136">136-140</a>, <a href="#Page_350">350</a></li>
-<li class="isub1">Sporangia, <a href="#Page_178">178-182</a></li>
-<li class="isub1">Sporangium, <a href="#Page_253">253-258</a>, <a href="#Page_281">281</a>, <a href="#Page_290">290</a></li>
-<li class="isub1">Spores, <a href="#Page_225">225</a>, <a href="#Page_256">256-258</a>, <a href="#Page_263">263</a>, <a href="#Page_264">264</a>, <a href="#Page_281">281</a></li>
-<li class="isub1">Sporocarp, <a href="#Page_173">173</a></li>
-<li class="isub1">Sporogonium (spo″ro-go′ni-um), <a href="#Page_224">224</a>, <a href="#Page_231">231</a>, <a href="#Page_233">233</a>, <a href="#Page_234">234</a>, <a href="#Page_237">237</a>, <a href="#Page_238">238</a>,</li>
-<li class="isub7"><a href="#Page_239">239</a>, <a href="#Page_241">241</a>, <a href="#Page_246">246</a>, <a href="#Page_247">247</a>, <a href="#Page_248">248</a>
-    <span class="pagenum"><a name="Page_512" id="Page_512">[Pg 512]</a></span></li>
-<li class="isub1">Sporophyll, <a href="#Page_274">274</a>, <a href="#Page_281">281</a>, <a href="#Page_292">292</a></li>
-<li class="isub1">Sporophyte (spo′ro-phyte), <a href="#Page_225">225</a>, <a href="#Page_226">226</a>, <a href="#Page_232">232</a>, <a href="#Page_234">234</a>, <a href="#Page_237">237-239</a>, <a href="#Page_241">241</a>, <a href="#Page_242">242</a>,</li>
-<li class="isub7"><a href="#Page_250">250</a>, <a href="#Page_261">261</a>, <a href="#Page_268">268</a>, <a href="#Page_270">270</a>, <a href="#Page_283">283</a>, <a href="#Page_292">292</a>, <a href="#Page_294">294</a>, <a href="#Page_314">314</a>,</li>
-<li class="isub7"><a href="#Page_315">315</a>, <a href="#Page_317">317</a>, <a href="#Page_336">336-339</a>, <a href="#Page_340">340-348</a> <a href="#Page_434">434</a></li>
-<li class="isub1">Spurge family, <a href="#Page_497">497</a></li>
-<li class="isub1">Squash, <a href="#Page_501">501</a></li>
-<li class="isub1">Staminodium, <a href="#Page_446">446</a></li>
-<li class="isub1">Starch, formation of, <a href="#Page_68">68</a>, <a href="#Page_70">70-74</a>;</li>
-<li class="isub3">changed to sugar, <a href="#Page_77">77</a>, <a href="#Page_78">78</a>;</li>
-<li class="isub3">translocation of, <a href="#Page_73">73</a>;</li>
-<li class="isub3">digestion of, <a href="#Page_75">75</a></li>
-<li class="isub1">Stems, types of, <a href="#Page_365">365-373</a></li>
-<li class="isub1">Stems, woody, structure of, <a href="#Page_381">381-382</a></li>
-<li class="isub1">Stoma (pl. stomata) (sto′ma-ta), <a href="#Page_42">42-44</a>, <a href="#Page_46">46</a></li>
-<li class="isub1">Strawberry, <a href="#Page_455">455</a>, <a href="#Page_497">497</a></li>
-<li class="isub1">Sugar, test for, <a href="#Page_75">75</a>, <a href="#Page_76">76</a></li>
-<li class="isub1">Sumac, <a href="#Page_497">497</a></li>
-<li class="isub1">Sundew, <a href="#Page_133">133</a>, <a href="#Page_496">496</a></li>
-<li class="isub1">Sunflower, <a href="#Page_399">399-401</a>, <a href="#Page_502">502</a></li>
-<li class="isub1">Sweet gum, <a href="#Page_496">496</a></li>
-<li class="isub1">Symbiosis, <a href="#Page_85">85</a>, <a href="#Page_86">86</a>, <a href="#Page_92">92-95</a></li>
-<li class="isub1">Synergids (syn´er-gids), <a href="#Page_327">327</a>, <a href="#Page_330">330</a></li>
-<li class="isub1">Syngenœsious, <a href="#Page_424">424</a></li>
-<li class="isub1">Synthetic assimilation, <a href="#Page_67">67</a></li>
-
-<li class="ifrst">Tape-grass, <a href="#Page_493">493</a></li>
-<li class="isub1">Taraxacum densleonis, <a href="#Page_502">502</a></li>
-<li class="isub1">Teasel, <a href="#Page_501">501</a></li>
-<li class="isub1">Telegraph-plant, <a href="#Page_399">399</a></li>
-<li class="isub1">Teleutospore, <a href="#Page_188">188</a></li>
-<li class="isub1">Temperature, <a href="#Page_134">134</a>, <a href="#Page_135">135</a>, <a href="#Page_465">465</a></li>
-<li class="isub1">Tetrasporaceæ, <a href="#Page_161">161</a></li>
-<li class="isub1">Tetraspores, <a href="#Page_173">173</a>, <a href="#Page_174">174</a></li>
-<li class="isub1">Thallophytes, <a href="#Page_352">352</a></li>
-<li class="isub1">Thallus, <a href="#Page_352">352</a></li>
-<li class="isub1">Thelephoraceæ, <a href="#Page_219">219</a></li>
-<li class="isub1">Thistle family, <a href="#Page_502">502</a></li>
-<li class="isub1">Thunderwood, <a href="#Page_497">497</a></li>
-<li class="isub1">Thyrsus, <a href="#Page_427">427</a></li>
-<li class="isub1">Tilia, <a href="#Page_498">498</a></li>
-<li class="isub1">Tillandsia, <a href="#Page_493">493</a></li>
-<li class="isub1">Tissue, tensions of, <a href="#Page_57">57-59</a></li>
-<li class="isub1">Tissues, classification of, <a href="#Page_363">363</a>, <a href="#Page_364">364</a>;</li>
-<li class="isub3">kinds of, <a href="#Page_356">356-359</a>;</li>
-<li class="isub3">organization of, <a href="#Page_356">356-362</a></li>
-<li class="isub1">Toad-flax, <a href="#Page_501">501</a></li>
-<li class="isub1">Tomato, <a href="#Page_501">501</a></li>
-<li class="isub1">Tradescantia, <a href="#Page_493">493</a></li>
-<li class="isub1">Tragopogon, <a href="#Page_502">502</a></li>
-<li class="isub1">Trailing arbutus, <a href="#Page_499">499</a></li>
-<li class="isub1">Trametes pini, <a href="#Page_90">90</a></li>
-<li class="isub1">Transpiration, <a href="#Page_35">35-46</a></li>
-<li class="isub1">Tremellales, <a href="#Page_218">218</a>, <a href="#Page_219">219</a></li>
-<li class="isub1">Triadelphous, <a href="#Page_425">425</a></li>
-<li class="isub1">Trillium, <a href="#Page_318">318-322</a>, <a href="#Page_494">494</a></li>
-<li class="isub1">Trumpet-creeper, <a href="#Page_501">501</a></li>
-<li class="isub1">Tuberales, <a href="#Page_217">217</a></li>
-<li class="isub1">Tubers, <a href="#Page_373">373</a></li>
-<li class="isub1">Tundra, <a href="#Page_481">481</a></li>
-<li class="isub1">Turgescence, <a href="#Page_14">14</a>, <a href="#Page_15">15</a></li>
-<li class="isub1">Turgor, <a href="#Page_20">20</a>;</li>
-<li class="isub3">restoration of, <a href="#Page_56">56</a>, <a href="#Page_57">57</a></li>
-<li class="isub1">Typha, <a href="#Page_493">493</a></li>
-
-<li class="ifrst">Ulmaceæ, <a href="#Page_495">495</a></li>
-<li class="isub1">Ulmus americana, <a href="#Page_495">495</a></li>
-<li class="isub1">Ulothrix, <a href="#Page_162">162</a></li>
-<li class="isub1">Ulotrichaceæ, <a href="#Page_162">162</a></li>
-<li class="isub1">Ulvaceæ, <a href="#Page_162">162</a></li>
-<li class="isub1">Umbel, <a href="#Page_428">428</a></li>
-<li class="isub1">Umbellales, <a href="#Page_498">498</a></li>
-<li class="isub1">Uredinales, <a href="#Page_218">218</a></li>
-<li class="isub1">Uredineæ, <a href="#Page_187">187-194</a>, <a href="#Page_218">218</a></li>
-<li class="isub1">Uredospore, <a href="#Page_189">189</a></li>
-<li class="isub1">Uromyces caryophyllinus, <a href="#Page_87">87</a></li>
-<li class="isub1">Urticales, <a href="#Page_495">495</a></li>
-<li class="isub1">Ustilaginales, <a href="#Page_218">218</a></li>
-<li class="isub1">Ustilagineæ, <a href="#Page_218">218</a></li>
-<li class="isub1">Utricularia, <a href="#Page_501">501</a></li>
-
-<li class="ifrst">Vaccinium, <a href="#Page_499">499</a></li>
-<li class="isub1">Vacuoles, <a href="#Page_7">7</a>, <a href="#Page_8">8</a></li>
-<li class="isub1">Valerianales, <a href="#Page_501">501</a></li>
-<li class="isub1">Vallisneria spiralis, <a href="#Page_493">493</a></li>
-<li class="isub1">Variation, <a href="#Page_338">338</a></li>
-<li class="isub1">Vascular tissue, <a href="#Page_358">358</a>, <a href="#Page_363">363</a></li>
-<li class="isub1">Vaucheria, <a href="#Page_142">142-146</a></li>
-<li class="isub1">Vaucheriaceæ, <a href="#Page_162">162</a></li>
-<li class="isub1">Vegetation types, <a href="#Page_464">464</a></li>
-<li class="isub1">Venus fly-trap, <a href="#Page_133">133</a></li>
-<li class="isub1">Verbascum, <a href="#Page_501">501</a></li>
-<li class="isub1">Verbena, <a href="#Page_501">501</a></li>
-<li class="isub1">Vessels, <a href="#Page_52">52</a>, <a href="#Page_53">53</a></li>
-<li class="isub1">Vetch, <a href="#Page_92">92</a>, <a href="#Page_497">497</a></li>
-<li class="isub1">Viburnum, <a href="#Page_501">501</a></li>
-<li class="isub1">Vicia sativa, <a href="#Page_459">459</a></li>
-<li class="isub1">Viola cucullata, <a href="#Page_436">436</a></li>
-<li class="isub1">Violaceæ, <a href="#Page_498">498</a></li>
-<li class="isub1">Virgin’s bower, <a href="#Page_462">462</a>, <a href="#Page_463">463</a></li>
-<li class="isub1">Viscum album, <a href="#Page_84">84</a></li>
-<li class="isub1">Vitaceæ, <a href="#Page_498">498</a></li>
-<li class="isub1">Volvocaceæ, <a href="#Page_158">158</a></li>
-
-<li class="ifrst">Walnut, <a href="#Page_452">452</a>, <a href="#Page_494">494</a></li>
-<li class="isub1">Water, <a href="#Page_465">465</a>;</li>
-<li class="isub3">flow of, in plants, <a href="#Page_53">53</a>, <a href="#Page_54">54</a></li>
-<li class="isub1">Water-lilies, <a href="#Page_496">496</a></li>
-<li class="isub1">Water-plantain, <a href="#Page_493">493</a></li>
-<li class="isub1">White pine, <a href="#Page_396">396</a>
-    <span class="pagenum"><a name="Page_513" id="Page_513">[Pg 513]</a></span></li>
-<li class="isub1">Wild carrot, <a href="#Page_499">499</a></li>
-<li class="isub1">Willow family, <a href="#Page_494">494</a></li>
-<li class="isub1">Wind, <a href="#Page_471">471</a></li>
-<li class="isub1">Wintergreen, <a href="#Page_499">499</a>;</li>
-<li class="isub3">leaf of, <a href="#Page_43">43</a></li>
-<li class="isub1">Witch-hazel, <a href="#Page_496">496</a></li>
-<li class="isub1">Wolffia, <a href="#Page_28">28</a></li>
-<li class="isub1">Woodland formation, <a href="#Page_470">470</a></li>
-
-<li class="ifrst">Xerophytes, <a href="#Page_467">467</a></li>
-<li class="isub1">Xylem, <a href="#Page_50">50</a>, <a href="#Page_52">52</a>, <a href="#Page_360">360</a>, <a href="#Page_361">361</a>, <a href="#Page_363">363</a></li>
-<li class="isub1">Xylogen, <a href="#Page_92">92</a></li>
-<li class="isub1">Xyridales, <a href="#Page_493">493</a></li>
-
-<li class="ifrst">Yeast, <a href="#Page_216">216</a>;</li>
-<li class="isub3">fermentation of, <a href="#Page_115">115</a>, <a href="#Page_116">116</a></li>
-<li class="isub1">Yucca, <a href="#Page_480">480</a>, <a href="#Page_493">493</a></li>
-
-<li class="ifrst">Zamia, <a href="#Page_313">313</a>, <a href="#Page_316">316</a>, <a href="#Page_457">457</a></li>
-<li class="isub1">Zoogonidia, <a href="#Page_143">143</a>, <a href="#Page_149">149</a>, <a href="#Page_178">178-184</a></li>
-<li class="isub1">Zoospore, <a href="#Page_149">149</a>, <a href="#Page_154">154</a></li>
-<li class="isub1">Zygomycetes, <a href="#Page_215">215</a></li>
-<li class="isub1">Zygospore, <a href="#Page_2">2</a>, <a href="#Page_138">138-140</a>, <a href="#Page_157">157</a>, <a href="#Page_160">160</a>, <a href="#Page_179">179</a>, <a href="#Page_180">180</a></li>
-<li class="isub1">Zygote (zy′gote), <a href="#Page_138">138</a>, <a href="#Page_179">179</a></li>
-</ul>
-
-<hr class="full" />
-<div class="chapter">
-<p class="f150 u"><b>TWO NOTABLE NATURE BOOKS.</b></p>
-<p class="f150"><b>FERNS</b></p>
-</div>
-<p class="neg-indent">A Manual for the Northeastern States. By C.
-E. WATERS, Ph.D. (Johns Hopkins). With Analytical Keys Based on
-the Stalks. <i>With over 200 illustrations</i> from original drawings
-and photographs. 362 pp. Square<br /> 8vo. Boxed. $3.00 <i>net</i>. (By mail, $3.34.)</p>
-
-<p>A popular, but thoroughly scientific book, including all the ferns
-in the region covered by Britton’s Manual. Much information is also
-given concerning reproduction and classification, fern photography, etc.</p>
-
-<p>PROF. L. M. UNDERWOOD, OF COLUMBIA:</p>
-<p class="blockquot">“It is really more scientific than one would
-expect from a work of a somewhat popular nature.
-The photographs are very fine, very carefully
-selected and will add much to the text. I do not
-see how they could be much finer.”</p>
-
-<p>THE PLANT WORLD:</p>
-<p class="blockquot">“This book is likely to prove the leading popular
-work on ferns. The majority of the illustrations are from original
-photographs; in respect to this feature, it can be confidently
-asserted that <i>no finer examples of fern photography have ever
-been produced</i>.... May be expected to prove of permanent scientific
-value, as well as to satisfy a want which existing treatises have but
-imperfectly filled.”</p>
-
-<p class="f150 space-above2"><b>MUSHROOMS</b></p>
-
-<p class="neg-indent">Edible, Poisonous Mushrooms, etc. By Prof. GEO. F. ATKINSON,
-of Cornell.</p>
-
-<p>With recipes for cooking by Mrs. S. T. RORER, and the chemistry and
-toxicology of mushrooms, by J. F. CLARK. With 230 illustrations from
-photographs, including fifteen colored plates. 320pp.<br /> 8vo. $3.00 <i>net</i>
-(by mail, $3.23).</p>
-
-<p>Among the additions in this second edition are ten new plates,
-chapters on the “Uses of Mushrooms,” and on the “Cultivation of
-Mushrooms,” illustrated by several flash-light photographs.</p>
-
-<p>EDUCATIONAL REVIEW:</p>
-<p class="blockquot">“It would be difficult to conceive of a more
-attractive and useful book, nor one that is destined to exert a
-greater influence in the study of an important class of plants that
-have been overlooked and avoided simply because of ignorance of their
-qualities, and the want of a suitable book of low price. In addition to
-its general attractiveness and the beauty of its illustrations, it is
-written in a style well calculated to win the merest tyro or the most
-accomplished student of the fungi.... These clear photographs and the
-plain descriptions make the book especially valuable for the amateur
-fungus hunter in picking out the edible from the poisonous species of
-the most common kinds.”</p>
-
-<p>THE PLANT WORLD:</p>
-<p class="blockquot">“This is, without doubt, the most important and
-valuable work of its kind that has appeared in this country in recent
-years.... No student, either amateur or professional, can afford to be
-without it.”</p>
-<hr class="chap" />
-
-<p class="f150"><b>HENRY HOLT AND COMPANY,</b></p>
-<p class="center">NEW YORK.&nbsp; &nbsp;  (xii, ’03).&nbsp; &nbsp;  CHICAGO.</p>
-<hr class="full" />
-
-<div class="chapter"><p class="f120"><b>BRITTON’S MANUAL OF THE FLORA OF<br />
-THE NORTHERN STATES AND CANADA.</b></p></div>
-
-<p class="center">By Director <span class="smcap">N. L. Britton</span>
-of the New York Botanical Garden.<br />
-1080 pp. 8vo. $2.25, net.</p>
-
-<div class="blockquot">
-<p>A comprehensive manual of over a thousand pages, containing about
-4,500 descriptions, probably one-third more than any other. It is
-designed to meet modern requirements and outline modern conceptions of
-the science. It is based on <i>An Illustrated Flora</i>, prepared by Prof.
-Britton in co-operation with Judge Addison Brown. The text has been
-revised and brought up to date, and much of novelty has been added. All
-illustrations are omitted, but specific reference has been made to all
-of the 4,162 figures in the <i>Illustrated Flora</i>.</p>
-
-<p>“It is the most complete and reliable work that ever appeared in
-the form of a flora of this region, and for the first time we have
-a manual in which the plant descriptions are drawn from the plants
-themselves, and do not represent compiled descriptions made by the
-early writers.”—Prof. D. M. Underwood of Columbia.</p>
-
-<p>“This work will at once take its place as the standard manual of
-the region that it covers. It is far superior to any other work of its
-class ever published in America.”—Prof. Conway MacMillan of University
-of Minnesota.</p>
-
-<p>“This book must at once find its way into the schools and
-colleges, to which it may be commended for the students in systematic
-botany.”—Prof. Chas. E. Bessey in “Science.”</p>
-
-<p>“It is nothing if it is not compact; it is nothing if it is not up
-to date; it is nothing if it is not the work of a master. What more can
-be said, save that the more it is used the greater the appreciation by
-the plant-lovers in the region which it covers.”—Prof. Byron D. Halsted
-of Rutgers College.</p>
-
-<p>“The work is well done; and as it is the only volume which gives in
-a way suitable for students the present state of the science, it cannot
-fail to take its place as a standard work.”—Prof. George Macloskie of
-Princeton.</p>
-
-<p>“I regard the book as one that we cannot do without and one that
-will henceforth take its place as a necessary means of determination of
-the plant species within its range.”—Prof. V. M. Spalding of University
-of Michigan.</p>
-
-<p>“An exceedingly valuable contribution to our botanical
-literature.... It is convenient to handle, and the low price will help
-to give it a large circulation.”—Prof. T. J. Burrill of the University
-of Illinois.</p>
-</div>
-
-<table border="0" cellspacing="0" summary=" " cellpadding="0" >
-  <tbody><tr>
-      <td class="tdl" rowspan="2"><span class="lgfnt200">HENRY HOLT &amp; CO.</span></td>
-      <td class="tdl_ws1"><b>29 West 23d Street, New York</b></td>
-   </tr><tr>
-      <td class="tdl_ws1"><b>378 Wabash Avenue, Chicago</b></td>
-   </tr><tr>
-      <td class="tdl" colspan="2"><span class="smcap">viii</span>, ’05</td>
-   </tr>
- </tbody>
-</table>
-
-<hr class="chap" />
-<div class="chapter">
-<p class="f120">CHAMPLIN’S YOUNG FOLKS’</p>
-<p class="f150">Cyclopædia of Natural History</p>
-</div>
-
-<p class="center">By <span class="smcap">J. D. Champlin</span> and
-        <span class="smcap">F. A. Lucas</span></p>
-
-<p class="center">With over 800 illustrations. 725 pp. $2.50</p>
-
-<div class="blockquot">
-<p>A whole “nature library” about animals prepared by experts.
-Scientific facts are presented in simple language, and are enlivened by
-anecdotes, personal experiences, and references to history, art, and
-literature.</p>
-
-<p>The illustrations are not only superior as animal pictures, but are
-genuinely illustrative, since they show the creature in its natural
-surroundings and characteristic action.</p>
-
-<p>Extinct animals are fully treated, because these strange forms are
-fascinating to children, and because they illustrate the derivation of
-such familiar living animals as birds, horses, and dogs.</p>
-
-<p>“A full menagerie of all sorts of animals, with a multitude of
-pictures.... A wonderful exhibition, and the story of each individual
-is interesting and calculated to stimulate the youthful mind in
-research.... Pictures carefully reproduced, so that they represent the
-creatures in their real forms and proportions.”—<i>Brooklyn Eagle.</i></p>
-</div>
-<hr class="r25" />
-
-<p class="f120">CHAMPLIN’S YOUNG FOLKS’</p>
-<p class="f150">Cyclopædia of Literature and Art</p>
-
-<p class="center">With 270 illustrations. 604 pp. 8vo. $2.50</p>
-
-<div class="blockquot">
-<p>Brief accounts of the great books, buildings, statues, pictures,
-operas, symphonies, etc.</p>
-
-<p>“Few poems, plays, novels, pictures, statues, or fictitious
-characters that children—or most of their parents—of our day are likely
-to inquire about will be missed here.... Mr. Champlin’s judgment seems
-unusually sound—will be welcome and useful.”—<i>Nation.</i></p>
-
-<p>“Every schoolboy should have it on his study table.... The range
-of the volume is very wide, for besides those items of classical
-knowledge which constitute the average school encyclopædia, we have
-brief descriptions given of modern books, poems, inventions, pictures,
-and persons about which the lad of the period should be acquainted....
-The pictures in the volume are varied and truly illustrative. Old
-pictures and sculpture are presented in the usual line of drawings, but
-modern scenes and buildings are pictured through excellent half-tone
-reproductions of photographs.”—<i>N. Y. Times Saturday Review.</i></p>
-
-<p class="f120 space-above1">Earlier Volumes of Champlin’s Young Folks’ Cyclopædia.</p>
-<p class="center">With numerous illustrations. 8vo. $2.50 each.</p>
-
-<p class="f120">COMMON THINGS.<span class="ws3">PERSONS and PLACES.</span><br />
-GAMES and SPORTS.</p>
-
-<p class="center space-below1">⁂ <i>12-page circular, with sample pages of Champlin’s Young
-Folks’ Cyclopædias and his other books, free.</i></p>
-</div>
-
-<table border="0" cellspacing="0" summary=" " cellpadding="0" >
-  <tbody><tr>
-      <td class="tdl" rowspan="2"><span class="lgfnt200">HENRY HOLT &amp; CO.</span></td>
-      <td class="tdl_ws1"><b>29 West 23d Street, New York</b></td>
-   </tr><tr>
-      <td class="tdl_ws1"><b>378 Wabash Avenue, Chicago</b></td>
-   </tr><tr>
-      <td class="tdl" colspan="2"><span class="smcap">viii</span>, ’06</td>
-   </tr>
- </tbody>
-</table>
-
-<hr class="chap" />
-<div class="chapter">
-<p class="f150">AMERICAN SCIENCE SERIES</p>
-</div>
-<hr class="r5" />
-
-<p class="center"><i>All prices are</i> NET <i>unless marked</i> RETAIL. <i>Details of the books
-will be found in Henry Holt &amp; Co.’s Educational Catalogue, free on application.</i></p>
-
-<table border="0" cellspacing="0" summary=" " cellpadding="0" >
-  <tbody><tr>
-      <td class="tdl" colspan="2"><b>Physics.</b> By Prof. <span class="smcap">George F. Barker</span>,
-                                  University of Pennsylvania.</td>
-   </tr><tr>
-      <td class="tdl_ws1"><i>Advanced Course.</i> 902 pp. 8vo.</td>
-      <td class="tdr">$3.50</td>
-   </tr><tr>
-      <td class="tdl_space-above1" colspan="2"><b>Chemistry.</b> By Prest. <span class="smcap">Ira Remsen</span>, Johns Hopkins University.</td>
-   </tr><tr>
-      <td class="tdl_ws1">Chemistry. <i>Advanced Course.</i> 850 pp. 8vo.</td>
-      <td class="tdr">2.80</td>
-   </tr><tr>
-      <td class="tdl_ws1">College Chemistry, xx + 669 pp. 8vo.</td>
-      <td class="tdr">2.00</td>
-   </tr><tr>
-      <td class="tdl_ws1">Chemistry. <i>Briefer Course.</i> (<i>New Edition</i>, 1901.) 435 pp. 12mo.</td>
-      <td class="tdr">1.10</td>
-   </tr><tr>
-      <td class="tdl_ws1">Chemistry. <i>Elementary Course.</i> 272 pp. 12mo.</td>
-      <td class="tdr">80c.</td>
-   </tr><tr>
-      <td class="tdl_ws1">Laboratory Manual (<i>to Elementary Course</i>). 196 pp. 12mo.</td>
-      <td class="tdr">40c.</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="2">Chemical Experiments. By Prof. <span class="smcap">Remsen</span> and Dr. <span class="smcap">W. W. Randall</span>.</td>
-   </tr><tr>
-      <td class="tdl_ws1">(<i>For Briefer Course.</i>) <i>No</i> blank pages for notes. 158 pp. 12mo.</td>
-      <td class="tdr">50c.</td>
-   </tr><tr>
-      <td class="tdl_space-above1" colspan="2"><b>Astronomy.</b> By Prof. <span class="smcap">Simon Newcomb</span> of Johns Hopkins and</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="2"><span class="smcap">Edward S. Holden</span>, late Director of the Lick Observatory, California.</td>
-   </tr><tr>
-      <td class="tdl_ws1"><i>Advanced Course.</i> 512 pp. 8vo.</td>
-      <td class="tdr">2.00</td>
-   </tr><tr>
-      <td class="tdl_ws1">The same. <i>Briefer Course.</i> 352 pp. 12mo.</td>
-      <td class="tdr">1.12</td>
-   </tr><tr>
-      <td class="tdl_ws1">The same. <i>Elementary Course.</i> By <span class="smcap">E. S. Holden</span>, 446 pp. 12mo.</td>
-      <td class="tdr">1.20</td>
-   </tr><tr>
-      <td class="tdl_space-above1" colspan="2"><b>Geology.</b> By Profs. <span class="smcap">Thomas C. Chamberlin</span> and <span class="smcap">Rollin D. Salisbury</span>,</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="2">Univ. of Chicago. Vol. I., 684 pp., $4.00. Vol. II. [<i>In press.</i>]</td>
-   </tr><tr>
-      <td class="tdl_space-above1" colspan="2"><b>General Biology.</b> By Prof. <span class="smcap">W. T. Sedgwick</span>, Mass. Institute of Technology,</td>
-   </tr><tr>
-      <td class="tdl_ws1">and Prof. <span class="smcap">E. B. Wilson</span>, Columbia Univ. <i>Revised and Enlarged.</i> 231pp. 8vo.</td>
-      <td class="tdr">1.75</td>
-   </tr><tr>
-      <td class="tdl_space-above1" colspan="2"><b>Botany.</b> By Prof. <span class="smcap">C. E. Bessey</span>, Univ. of Nebraska.</td>
-   </tr><tr>
-      <td class="tdl_ws1"><i>Advanced Course.</i> 611 pp. 8vo.</td>
-      <td class="tdr">2.20</td>
-   </tr><tr>
-      <td class="tdl_ws1">The same. <i>Briefer Course.</i> 356 pp.</td>
-      <td class="tdr">1.12</td>
-   </tr><tr>
-      <td class="tdl_space-above1" colspan="2"><b>Zoology.</b> By Prof. <span class="smcap">A. S. Packard</span>, Jr., Brown University.</td>
-   </tr><tr>
-      <td class="tdl_ws1"><i>Advanced Course.</i> 722 pp. 8vo.</td>
-      <td class="tdr">2.40</td>
-   </tr><tr>
-      <td class="tdl_ws1">The same. <i>Briefer Course.</i> 338 pp.</td>
-      <td class="tdr">1.12</td>
-   </tr><tr>
-      <td class="tdl_ws1">The same. <i>Elementary Course.</i> 290 pp. 12mo.</td>
-      <td class="tdr">80c.</td>
-   </tr><tr>
-      <td class="tdl_space-above1" colspan="2"><b>The Human Body.</b> By <span class="smcap">H. Newell Martin</span>, sometime professor in</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="2"><span class="ws2">the Johns Hopkins University.</span></td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="2"><i>Advanced Course.</i> 685 pp. 8vo. (Copies without</td>
-   </tr><tr>
-      <td class="tdl_ws1"><span class="ws2">chapter on Reproduction sent when specially ordered.)</span></td>
-      <td class="tdr">2.50</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="2">The same. <i>Briefer Course.</i> (<i>Entirely new edition,</i></td>
-   </tr><tr>
-      <td class="tdl_ws1"><span class="ws2">&nbsp;</span><i>revised by Prof. G. Wells Fitz of Harvard.</i>) 408 pp. 12mo.</td>
-      <td class="tdr">1.20</td>
-   </tr><tr>
-      <td class="tdl_ws1">The same. <i>Elementary Course.</i> 261 pp. 12mo.</td>
-      <td class="tdr">75c.</td>
-   </tr><tr>
-      <td class="tdl_ws1">The Human Body and the Effects of Narcotics. 261 pp. 12mo.</td>
-      <td class="tdr">1.20</td>
-   </tr><tr>
-      <td class="tdl_space-above1" colspan="2"><b>Psychology.</b> By Prof. <span class="smcap">William James</span> of Harvard.</td>
-   </tr><tr>
-      <td class="tdl_ws1"><i>Advanced Course.</i> 689 + 704 pp. 8vo. 2vols.</td>
-      <td class="tdr">4.80</td>
-   </tr><tr>
-      <td class="tdl_ws1">The same. <i>Briefer Course.</i> 478 pp. 12mo.</td>
-      <td class="tdr">1.60</td>
-   </tr><tr>
-      <td class="tdl_space-above1" colspan="2"><b>Ethics.</b> By Profs. <span class="smcap">John Dewey</span> and <span class="smcap">James H. Tufts</span>, Chicago University.</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="2"><span class="ws3">(<i>In preparation.</i>)</span></td>
-   </tr><tr>
-      <td class="tdl_space-above1" colspan="2"><b>Political Economy.</b> By the late President <span class="smcap">Francis A. Walker</span>,</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="2"><span class="ws3">Mass. Institute of Technology.</span></td>
-   </tr><tr>
-      <td class="tdl_ws1"><i>Advanced Course.</i> 537 pp. 8vo.</td>
-      <td class="tdr">2.00</td>
-   </tr><tr>
-      <td class="tdl_ws1">The same. <i>Briefer Course.</i> 415 pp. 12mo.</td>
-      <td class="tdr">1.20</td>
-   </tr><tr>
-      <td class="tdl_ws1">The same. <i>Elementary Course.</i> 423 pp. 12mo.</td>
-      <td class="tdr">1.00</td>
-   </tr><tr>
-      <td class="tdl_space-above1" colspan="2"><b>Finance.</b> By Prof. <span class="smcap">Henry Carter Adams</span>, University of Michigan.</td>
-   </tr><tr>
-      <td class="tdl_ws1"><i>Advanced Course.</i> 573 pp. 8vo.</td>
-      <td class="tdr">3.50</td>
-   </tr>
- </tbody>
-</table>
-<p>&nbsp;</p>
-<table border="0" cellspacing="0" summary=" " cellpadding="0" >
-  <tbody><tr>
-      <td class="tdl" rowspan="2"><span class="lgfnt200">HENRY HOLT &amp; CO.</span></td>
-      <td class="tdl_ws1"><b>29 West 23d Street, New York</b></td>
-   </tr><tr>
-      <td class="tdl_ws1"><b>378 Wabash Avenue, Chicago</b></td>
-   </tr><tr>
-      <td class="tdl" colspan="2"><span class="smcap">viii</span>, ’02</td>
-   </tr>
- </tbody>
-</table>
-
-<hr class="chap" />
-<div class="chapter">
-<p class="f200"><b>CHEMISTRY</b></p>
-</div>
-<table border="0" cellspacing="0" summary=" " cellpadding="0" >
-  <tbody><tr>
-      <td class="tdl" colspan="2"><b>Cairns’s Quantitative Chemical Analysis</b></td>
-   </tr><tr>
-      <td class="tdl_ws1">Revised and enlarged by Dr. <span class="smcap">E. Waller</span>. 417 pp. 8vo.</td>
-      <td class="tdr">$2.00,&nbsp;<i>net</i>.</td>
-   </tr><tr>
-      <td class="tdl_space-above1" colspan="2"><b>Cohen’s Physical Chemistry for Biologists</b></td>
-   </tr><tr>
-      <td class="tdl_ws1">Translated by Dr. <span class="smcap">Martin Fischer</span>, Chicago University. 343 pp. 12mo,</td>
-      <td class="tdr">$1.75, <i>net</i>.</td>
-   </tr><tr>
-      <td class="tdl_space-above1" colspan="2"><b>Congdon’s Qualitative Analysis</b></td>
-   </tr><tr>
-      <td class="tdl_ws1">By Prof. <span class="smcap">Ernest A. Congdon</span>, Drexel Institute. 64 pp. <i>Interleaved.</i> 8vo.</td>
-      <td class="tdr">60c., <i>net</i>.</td>
-   </tr><tr>
-      <td class="tdl_space-above1" colspan="2"><b>Nicholson and Avery’s Exercises in Chemistry</b></td>
-   </tr><tr>
-      <td class="tdl_ws1"><p>With Outlines for the Study of Chemistry. To accompany any elementary
-                text. By Prof. <span class="smcap">H. H. Nicholson</span>, University
-                of Nebraska, and Prof. <span class="smcap">Samuel Avery</span>,
-                University of Idaho. 413 pp. 12mo. 60c.,&nbsp;<i>net</i>.</p></td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl_space-above1" colspan="2"><b>Noyes’s (A. A.) General Principles of Physical Science</b></td>
-   </tr><tr>
-      <td class="tdl_ws1"><p>An Introduction to the Study of the Principles of Chemistry. By
-                            Prof. <span class="smcap">A. A. Noyes</span>, Mass. Institute of
-                            Technology. 160 pp. 8vo.&nbsp; $1.50,&nbsp;<i>net</i>.</p></td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl_space-above1" colspan="2"><b>Noyes’s (W. A.) Organic Chemistry</b></td>
-   </tr><tr>
-      <td class="tdl_ws1"><p>By Prof. <span class="smcap">Wm. A. Noyes</span>, Rose Polytechnic
-                          Institute. 534 pp. 12mo.&nbsp; &nbsp; $1.50,&nbsp;<i>net</i>.</p></td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl_space-above1" colspan="2"><b>Qualitative Analysis (Elementary)</b></td>
-   </tr><tr>
-      <td class="tdl_ws1"><span class="ws3">x + 91 pp. 8vo. 80c.,&nbsp;<i>net</i>.</span></td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl_space-above1" colspan="2"><b>Remsen’s Chemistries</b></td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="2">By Pres. <span class="smcap">Ira Remsen</span>, Johns Hopkins. (<i>American Science Series.</i>)</td>
-   </tr><tr>
-      <td class="tdl_ws3"><b>Inorganic Chemistry</b> (<i>Advanced</i>). <span class="smcap">xxii</span> + 853 pp. 8vo.</td>
-      <td class="tdr">$2.80,&nbsp;<i>net</i>.</td>
-   </tr><tr>
-      <td class="tdl_ws3"><b>College Chemistry</b> <span class="smcap">xx</span> + 689 pp. 8vo.</td>
-      <td class="tdr">$2.00,&nbsp;<i>net</i>.</td>
-   </tr><tr>
-      <td class="tdl_ws3"><b>Introduction to Chemistry</b> (<i>Briefer</i>). <span class="smcap">xix</span> + 435 pp. 12mo.</td>
-      <td class="tdr">$1.12,&nbsp;<i>net</i>.</td>
-   </tr><tr>
-      <td class="tdl_ws3"><p>This book is used in hundreds of schools and colleges in this
-                 country. It has passed through several editions in England, and has
-                 been translated into German (being the elementary text-book in the
-                 University of Leipsic), French, and Italian.</p></td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl_ws3"><b>Remsen and Randall’s Experiments</b> (<i>for the “Introduction”</i>).</td>
-      <td class="tdr">50c.,&nbsp;<i>net</i>.</td>
-   </tr><tr>
-      <td class="tdl_ws3"><b>Elements of Chemistry</b> (<i>Elementary</i>). <span class="smcap">x</span> + 272 pp. 12mo.</td>
-      <td class="tdr">80c.,&nbsp;<i>net</i>.</td>
-   </tr><tr>
-      <td class="tdl_ws3"><b>Laboratory Manual</b> (<i>for the “Elements”</i>).</td>
-      <td class="tdr">40c.,&nbsp;<i>net</i>.</td>
-   </tr><tr>
-      <td class="tdl_space-above1"><b>Torrey’s Elementary Chemistry</b> By <span class="smcap">Joseph Torrey</span>, Jr., Harvard. 437 pp. 12mo.</td>
-      <td class="tdr">$1.25,&nbsp;<i>net</i>.</td>
-   </tr><tr>
-      <td class="tdl_space-above1" colspan="2"><b>White’s Qualitative Analysis</b></td>
-   </tr><tr>
-      <td class="tdl_ws1">By Prof. <span class="smcap">John White</span>, Univ. of Nebraska. 96 pp. 8vo.</td>
-      <td class="tdr">80c.,&nbsp;<i>net</i>.</td>
-   </tr><tr>
-      <td class="tdl_space-above1" colspan="2"><b>Woodhull and Van Arsdale’s Chemical Experiments</b></td>
-   </tr><tr>
-      <td class="tdl_ws1">By Prof. <span class="smcap">John F. Woodhull</span> and <span class="smcap">M. B. Van Arsdale</span>,</td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl_ws3">Teachers’ College, New York City. 136 pp. 12mo.</td>
-      <td class="tdr">60c.,&nbsp;<i>net</i>.</td>
-   </tr><tr>
-      <td class="tdl_ws3">Extremely simple experiments in the chemistry of daily life.</td>
-      <td class="tdr"></td>
-   </tr>
- </tbody>
-</table>
-<p>&nbsp;</p>
-<table border="0" cellspacing="0" summary=" " cellpadding="0" >
-  <tbody><tr>
-      <td class="tdl" rowspan="2"><span class="lgfnt200">HENRY HOLT &amp; CO.</span></td>
-      <td class="tdl_ws1"><b>29 West 23d Street, New York</b></td>
-   </tr><tr>
-      <td class="tdl_ws1"><b>378 Wabash Avenue, Chicago</b></td>
-   </tr><tr>
-      <td class="tdl" colspan="2"><span class="smcap">viii</span>, ’05</td>
-   </tr>
- </tbody>
-</table>
-
-<hr class="chap" />
-<div class="chapter">
-<p class="f150 space-above1">CHAMBERLIN &amp; SALISBURY’S</p>
-<p class="f200"><b>GEOLOGY</b></p>
-</div>
-
-<div class="blockquot">
-<p class="neg-indent">By <span class="smcap">Thomas C. Chamberlin</span> and <span class="smcap">Rollin D. Salisbury</span>,
-Professors in the University of Chicago.
-(<i>American Science Series.</i>) 2 vols. 8vo.</p>
-
-<p><i>Vol. I. Geological Processes and their Results.</i> <span class="smcap">xix</span> + 654 pp. $4.00.</p>
-<p><i>Vol. II. Earth History.</i> [<i>In preparation.</i>]</p>
-
-<p>This is a notable scientific work by two of the highest authorities
-on the subject in the United States, and yet written in a style so
-simple that it can be clearly understood by the intelligent reader who
-has had little previous training in the subject.</p>
-
-<p><b>Chas. D. Walcott</b>, <i>Director of U. S. Geological Survey</i>:—I
-am impressed with the admirable plan of the work and with the thorough
-manner in which geological principles and processes and their results
-have been presented. The text is written in an entertaining style
-and is supplemented by admirable illustrations, so that the student
-cannot fail to obtain a clear idea of the nature and work of geological
-agencies, of the present status of the science, and of the spirit which
-actuates the working geologist.</p>
-
-<p><b>Henry S. Williams</b>, <i>Professor in Yale University</i>.—I
-believe it is the best treatise on this part of the subject which we
-have seen in America.</p>
-
-<p><b>R. S. Woodward</b>, <i>Professor in Columbia University</i>:—It is
-admirable for its science, admirable for its literary perfection, and
-admirable for its unequalled illustrations.</p>
-
-<p><b>T. C. Hopkins</b>, <i>Professor in Syracuse University</i>:—It gives
-us the most advanced thought on all the great questions of dynamical
-and structural geology to be found in geological literature.</p>
-
-<p><b>H. Foster Bain</b>, <i>U. S. Geological Survey</i>:—The book is
-pre-eminently a teaching book and I have no doubt that it will at once
-become the standard American text-book on geology.</p>
-
-<p><b>William N. Rice</b>, <i>Professor in Wesleyan University</i>:—The
-book is full of new ideas. It is one of the indispensable books for the
-library of every working geologist and every one who wishes to be an
-up-to-date teacher of geology.</p>
-
-<p><b>T. A. Jaggar, Jr.</b>, <i>Assistant Professor in Harvard
-University</i>:—The book appears to be an excellent statement of modern
-American geology, with abundant new illustrative material, based upon
-the most recent work of government and other surveys. It is especially
-satisfactory to have in hand a geological volume which does not attempt
-to cover the whole field. Modern geology is much too large a subject to
-be condensed into a single volume.</p>
-</div>
-
-<p>&nbsp;</p>
-<table border="0" cellspacing="0" summary=" " cellpadding="0" >
-  <tbody><tr>
-      <td class="tdl" rowspan="2"><span class="lgfnt200">HENRY HOLT &amp; CO.</span></td>
-      <td class="tdl_ws1"><b>29 West 23d Street, New York</b></td>
-   </tr><tr>
-      <td class="tdl_ws1"><b>378 Wabash Avenue, Chicago</b></td>
-   </tr><tr>
-      <td class="tdl" colspan="2"><span class="smcap">viii</span>, ’05</td>
-   </tr>
- </tbody>
-</table>
-
-<hr class="chap" />
-<div class="chapter">
-<p class="f150"><b>THE METRIC SYSTEM.</b></p>
-</div>
-<div class="figcenter">
-    <img src="images/ruler.jpg" alt="" width="600" height="99" />
-    <p class="center">10-centimeter rule.<br />
-                 The upper edge is in millimeters, the lower in
-                 centimeters and half centimeters.</p>
-</div>
-<hr class="r5" />
-<table border="0" cellspacing="0" summary=" " cellpadding="0" >
-  <thead><tr>
-      <th class="tdc"><span class="smcap">Units.</span></th>
-      <th class="tdc" colspan="2"><span class="smcap">The most commonly used divisions and multiples.</span></th>
-  </tr>
-  </thead>
-  <tbody><tr>
-      <td class="tdc" colspan="3">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl" rowspan="6"><span class="smcap">The Meter</span>,<br />&emsp;for <span class="smcap">Length</span></td>
-      <td class="tdc" rowspan="6"><img src="images/cbl-6.jpg" alt="" width="37" height="132" /></td>
-      <td class="tdl"><i>Centimeter</i> (cm), 1/100 meter;</td>
-   </tr><tr>
-      <td class="tdl"><i>Millimeter</i> (mm), 1/1000 meter;</td>
-   </tr><tr>
-      <td class="tdl"><i>Micron</i> (μ), 1/1000 millimeter.</td>
-   </tr><tr>
-      <td class="tdl_ws3">The micron is the unit in micrometry.</td>
-   </tr><tr>
-      <td class="tdl"><i>Kilometer</i>, 1000 meters;</td>
-   </tr><tr>
-      <td class="tdl_ws3">used in measuring roads and other long distances.</td>
-   </tr><tr>
-      <td class="tdl" rowspan="3"><span class="smcap">The Gram</span>,<br />&emsp;for <span class="smcap">Weight</span></td>
-      <td class="tdc" rowspan="3"><img src="images/cbl-3.jpg" alt="" width="16" height="57" /></td>
-      <td class="tdl"><i>Milligram</i> (mg), 1/1000 gram.</td>
-   </tr><tr>
-      <td class="tdl"><i>Kilogram</i>, 1000 grams,</td>
-   </tr><tr>
-      <td class="tdl_ws3">used for ordinary masses, like groceries, etc.</td>
-   </tr><tr>
-      <td class="tdl" rowspan="3"><span class="smcap">The Liter</span>,<br />&emsp;for <span class="smcap">Capacity</span></td>
-      <td class="tdc" rowspan="3"><img src="images/cbl-3.jpg" alt="" width="16" height="57" /></td>
-      <td class="tdl"><i>Cubic Centimeter</i> (cc), 1/1000 liter.</td>
-   </tr><tr>
-      <td class="tdl">This is more common than the correct form,</td>
-   </tr><tr>
-      <td class="tdl_ws1">Milliliter.</td>
-   </tr><tr>
-      <td class="tdl" colspan="3"><i>Divisions</i> of the <i>units</i> are indicated by Latin prefixes:</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="3"><i>deci</i>, 1/10; <i>centi</i>, 1/100; <i>milli</i>, 1/1000.</td>
-   </tr><tr>
-      <td class="tdl" colspan="3"><i>Multiples</i> are designated by Greek prefixes:</td>
-   </tr><tr>
-      <td class="tdl_ws1" colspan="3"><i>deka</i>, 10 times; <i>hecto</i>, 100 times; <i>kilo</i>, 1000 times; <i>myria</i>, 10,000 times.</td>
-   </tr>
- </tbody>
-</table>
-
-<p class="f150 space-above1"><b>TABLE OF METRIC AND ENGLISH MEASURES.</b></p>
-
-<table border="0" cellspacing="0" summary=" " cellpadding="0" >
-  <tbody><tr>
-      <td class="tdl"><span class="smcap">Meter</span></td>
-      <td class="tdl_ws1" colspan="2">= 100&nbsp;centimeters, 1000&nbsp;millimeters, 1,000,000&nbsp;microns, 39.3704&nbsp;inches.</td>
-   </tr><tr>
-      <td class="tdl">Millimeter (mm)</td>
-      <td class="tdl_ws1" colspan="2">= 1000&nbsp;microns, 1/10&nbsp;millimeter, 1/1000&nbsp;meter, 1/25&nbsp;inch, approximately.</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Micron</span> (μ)</td>
-      <td class="tdl_ws1" rowspan="3"  colspan="2">= 1/1000&nbsp;mm, 1/1000000&nbsp;meter (0.000039&nbsp;inch), 1/25000&nbsp;inch, approximately.</td>
-   </tr><tr>
-      <td class="tdl_ws1">(unit of measure in</td>
-   </tr><tr>
-      <td class="tdl_ws1">&nbsp;micrometry)</td>
-   </tr><tr>
-      <td class="tdl">Inch (in.)</td>
-      <td class="tdl_ws1" colspan="2">= 25.399772&nbsp;mm (25.4&nbsp;mm, approx.).</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Liter</span></td>
-      <td class="tdl_ws1" colspan="2">= 1000&nbsp;milliliters or 1000&nbsp;cubic&nbsp;centimeters, 1&nbsp;quart (approx.).</td>
-   </tr><tr>
-      <td class="tdl">Cubic centimeter (cc or cctm)</td>
-      <td class="tdl_ws1" colspan="2">= 1/1000 liter.</td>
-   </tr><tr>
-      <td class="tdl">Fluid ounce (8 fluidrachms)</td>
-      <td class="tdl_ws1" colspan="2">= 29.578 cc (30 cc, approx.).</td>
-   </tr><tr>
-      <td class="tdl"><span class="smcap">Gram</span></td>
-      <td class="tdl_ws1" colspan="2">= 15.432 grains.</td>
-   </tr><tr>
-      <td class="tdl bb"><span class="smcap">Kilogram</span> (kilo)</td>
-      <td class="tdl_ws1 bb" colspan="2">= 2.204 avoirdupois pounds (2⅕ pounds, approx.).</td>
-   </tr><tr>
-      <td class="tdl">Ounce Avoirdupois</td>
-      <td class="tdl_ws1 br" rowspan="2">= 28.349 grams</td>
-      <td class="tdl" rowspan="2">&nbsp;(30 grams, approx.).</td>
-   </tr><tr>
-      <td class="tdl_ws3">(437½&nbsp;grains)</td>
-   </tr><tr>
-      <td class="tdl">Ounce Troy or Apothecaries’</td>
-      <td class="tdl_ws1 br" rowspan="2">= 31.103 grams</td>
-   </tr><tr>
-      <td class="tdl_ws3">(480&nbsp;grains)</td>
-   </tr><tr>
-      <td class="tdc bt" colspan="3">&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-
-<p class="f150 space-above1"><b>TEMPERATURE.</b></p>
-<div class="blockquot">
-<p>To change Centigrade to Fahrenheit: (C. × ⁹/₅) + 32 = F.
-For example, to find the equivalent of 10° Centigrade,</p>
-<p class="center">C. = 10°,  (10° × ⁹/₅) + 32 = 50° F.</p>
-
-<p>To change Fahrenheit to Centigrade: (F. - 32°) × ⁵/₉ = C.
-For example, to reduce 50° Fahrenheit to Centigrade,</p>
-<p class="center">F. = 50°,  and (50° - 32°) × ⁵/₉ = 10° C.;</p>
-
-<p class="no-indent">or - 40° Fahrenheit to Centigrade,</p>
-<p class="center">F. = - 40°,  (- 40° - 32°) = - 72°,</p>
-<p class="no-indent">whence - 72° × ⁵/₉; = - 40° C.</p>
-
-<p class="author">—<i>From “The Microscope” (by S. H. Gage) by permission.</i></p>
-</div>
-<hr class="full" />
-
-<div class="footnotes">
-<p class="f150"><b>Footnotes:</b></p>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_1_1" id="Footnote_1_1"></a><a href="#FNanchor_1_1"><span class="label">[1]</span></a>
-For apparatus, reagents, collection and preservation of material, etc.,
-see Appendix.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_2_2" id="Footnote_2_2"></a><a href="#FNanchor_2_2"><span class="label">[2]</span></a>
-If spirogyra is forming fruit some of the threads will be lying
-parallel in pairs, and connected with short tubes. In some of the cells
-there will be found rounded or oval bodies known as <i>zygospores</i>. These
-may be seen in <a href="#FIG_86">fig. 86</a>, and will be described in another
-part of the book.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_3_3" id="Footnote_3_3"></a><a href="#FNanchor_3_3"><span class="label">[3]</span></a>
-The most suitable preparations of mucor for study are made by growing
-the plant in a nutrient substance which largely consists of gelatine,
-or, better, agar-agar, a gelatinous preparation of certain seaweeds.
-This, after the plant is sown in it, should be poured into sterilised
-shallow glass plates, called Petrie dishes.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_4_4" id="Footnote_4_4"></a><a href="#FNanchor_4_4"><span class="label">[4]</span></a>
-We should note that the coloring matter of the beet resides in the
-cell-sap. It is in these colored cells that we can best see the
-movement take place, since the red color serves to differentiate well
-the moving mass from the cell wall. The protoplasmic membrane at
-several points usually clings tenaciously so that at several places the
-membrane is arched strongly away from the cell wall as shown in <a href="#FIG_24">fig. 24</a>.
-While water is removed from the cell-sap, we note that the coloring
-matter does not escape through the protoplasmic membrane.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_5_5" id="Footnote_5_5"></a><a href="#FNanchor_5_5"><span class="label">[5]</span></a>
-See <a href="#CHAPTER_XXXVIII">Chapter 38</a> for organization of members of the plant body.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_6_6" id="Footnote_6_6"></a><a href="#FNanchor_6_6"><span class="label">[6]</span></a>
-Demonstrations may be made with prepared sections of leaves,</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_7_7" id="Footnote_7_7"></a><a href="#FNanchor_7_7"><span class="label">[7]</span></a>
-This ring and the bundles separate the stem into two regions, an outer
-one composed of large cells with thin walls, known as the cortical
-cells, or collectively the <i>cortex</i>. The inner portion, corresponding
-to what is called the pith, is made up of the same kind of cells and is
-called the <i>medulla</i>, or <i>pith</i>. When the cells of the cortex, as well
-as of the pith, remain thin walled the tissue is called parenchyma.
-Parenchyma belongs to the group of tissues called fundamental.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_8_8" id="Footnote_8_8"></a><a href="#FNanchor_8_8"><span class="label">[8]</span></a>
-In the formation of starch during photosynthesis the separated
-molecules from the carbon dioxide and water unite in such a way that
-carbon, hydrogen, and oxygen are united into a molecule of starch. This
-result is usually represented by the following equation: CO₂ + H₂O =
-CH₂O + O₂. Then by polymerization 6(CH₂O) = C₆H₁₂O₆ = grape sugar.
-Then C₆H₁₂O₆-H₂O = C₆H₁₀O₅ = starch. It is believed, however, that the
-process is much more complicated than this, that several different
-compounds are formed before starch finally appears, and that the
-formula for starch is much higher numerically than is represented by
-C₆H₁₀O₅.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_9_9" id="Footnote_9_9"></a><a href="#FNanchor_9_9"><span class="label">[9]</span></a>
-Paragraphs 156-160 were prepared by Dr. E. J. Durand.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_10_10" id="Footnote_10_10"></a><a href="#FNanchor_10_10"><span class="label">[10]</span></a>
-Make up three stock solutions as follows:</p>
-
-<table border="0" cellspacing="0" summary="Stock Solutions" cellpadding="0" >
-  <tbody><tr>
-      <td class="tdc" colspan="3">(1)</td>
-   </tr><tr>
-      <td class="tdl">Copper sulphate&emsp;&nbsp;</td>
-      <td class="tdr">9</td>
-      <td class="tdr">&nbsp;grams</td>
-   </tr><tr>
-      <td class="tdl">Water</td>
-      <td class="tdr">250</td>
-      <td class="tdl">&nbsp;cc.</td>
-   </tr><tr>
-      <td class="tdc" colspan="3">(2)</td>
-   </tr><tr>
-      <td class="tdl">Caustic potash</td>
-      <td class="tdr">30</td>
-      <td class="tdr">&nbsp;grams</td>
-   </tr><tr>
-      <td class="tdl">Water</td>
-      <td class="tdr">250</td>
-      <td class="tdl">&nbsp;cc.</td>
-   </tr><tr>
-      <td class="tdc" colspan="3">(3)</td>
-   </tr><tr>
-      <td class="tdl">Rochelle salts</td>
-      <td class="tdr">49</td>
-      <td class="tdr">&nbsp;grams</td>
-   </tr><tr>
-      <td class="tdl">Water</td>
-      <td class="tdr">250</td>
-      <td class="tdl">&nbsp;cc.</td>
-   </tr>
- </tbody>
-</table>
-
-<p>For Fehling’s solution take one volume of each of (1), (2), and (3),
-and to the mixture add two volumes of water.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_11_11" id="Footnote_11_11"></a><a href="#FNanchor_11_11"><span class="label">[11]</span></a>
-This solution of taka diastase should be made up cold. If
-it is heated to 60° C. or over it is destroyed.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_12_12" id="Footnote_12_12"></a><a href="#FNanchor_12_12"><span class="label">[12]</span></a>
-Calcium is not essential for the growth of the fungi.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_13_13" id="Footnote_13_13"></a><a href="#FNanchor_13_13"><span class="label">[13]</span></a>
-For example, silicon is used by some plants in strengthening supporting
-tissues. Buckwheat thrives better when supplied with a chloride.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_14_14" id="Footnote_14_14"></a><a href="#FNanchor_14_14"><span class="label">[14]</span></a>
-Evidence points to the belief that certain cells of the host form
-substances which attract, chemitropically, the fungus threads, and that
-in these cells the fungus threads are more abundant than in others.
-Furthermore in the vicinity of the nucleus of the host seems to be the
-place where these activities are more marked.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_15_15" id="Footnote_15_15"></a><a href="#FNanchor_15_15"><span class="label">[15]</span></a>
-In lieu of Arisæma make a practical study of the pea. See paragraph 216<i>a</i>.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_16_16" id="Footnote_16_16"></a><a href="#FNanchor_16_16"><span class="label">[16]</span></a>
-Dissolve a half gram of osmic acid in 50 <i>cc.</i> of water
-and keep tightly corked when not using.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_17_17" id="Footnote_17_17"></a><a href="#FNanchor_17_17"><span class="label">[17]</span></a>
-In Engler &amp; Prantl’s Pflanzenfamilien, Wille uses the term class
-for these principal subdivisions of the algæ. Systematists are not yet
-agreed upon a uniform use of the terms.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_18_18" id="Footnote_18_18"></a><a href="#FNanchor_18_18"><span class="label">[18]</span></a>
-See Bot. Gaz., 17, 389, 1892.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_19_19" id="Footnote_19_19"></a><a href="#FNanchor_19_19"><span class="label">[19]</span></a>
-<b>Class Myxomycetes</b>, or <b>Mycetozoa</b>.—To this
-class belong the “slime molds,” low organisms consisting of masses of
-naked protoplasm which flows among decaying leaves and in decaying
-wood, coming to the surface to fruit. The fruit in many cases resembles
-miniature puff-balls, and these plants were formerly classed with
-the puff-balls. The spores germinate by forming swarm spores which
-unite to form a small plasmodium, which in turn grows to form a large
-plasmodium or protoplasmic mass. It is doubtful if they are any more
-plant than animal organisms. Examples: Trichia, Arcyria, Stemonitis,
-Physarum, Ceratiomyxa, etc., on rotten wood; Plasmodiophora brassicæ
-is a parasite causing club foot of cabbage, radishes, etc. It lives
-within the roots, causing large knots and swellings on the same.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_20_20" id="Footnote_20_20"></a><a href="#FNanchor_20_20"><span class="label">[20]</span></a>
-As suborder in Engler and Prantl.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_21_21" id="Footnote_21_21"></a><a href="#FNanchor_21_21"><span class="label">[21]</span></a>
-As suborder in Engler and Prantl.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_22_22" id="Footnote_22_22"></a><a href="#FNanchor_22_22"><span class="label">[22]</span></a>
-As suborder in Engler and Prantl.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_23_23" id="Footnote_23_23"></a><a href="#FNanchor_23_23"><span class="label">[23]</span></a>
-The Uredinales and Auriculariales in Engler and Prantl are
-placed in order, Auriculariineæ.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_24_24" id="Footnote_24_24"></a><a href="#FNanchor_24_24"><span class="label">[24]</span></a>
- The Uredinales and Auriculariales in Engler and Prantl are
-placed in order, Auriculariineæ.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_25_25" id="Footnote_25_25"></a><a href="#FNanchor_25_25"><span class="label">[25]</span></a>
-May be used as an alternate study for marchantia.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_26_26" id="Footnote_26_26"></a><a href="#FNanchor_26_26"><span class="label">[26]</span></a>
- As subclass in Engler and Prantl.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_27_27" id="Footnote_27_27"></a><a href="#FNanchor_27_27"><span class="label">[27]</span></a>
-As subclass in Engler and Prantl.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_28_28" id="Footnote_28_28"></a><a href="#FNanchor_28_28"><span class="label">[28]</span></a>
-As subclass in Engler and Prantl.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_29_29" id="Footnote_29_29"></a><a href="#FNanchor_29_29"><span class="label">[29]</span></a>
-Called the calyptra.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_30_30" id="Footnote_30_30"></a><a href="#FNanchor_30_30"><span class="label">[30]</span></a>
-As subclass in Engler and Prantl.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_31_31" id="Footnote_31_31"></a><a href="#FNanchor_31_31"><span class="label">[31]</span></a>
-As subclass in Engler and Prantl.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_32_32" id="Footnote_32_32"></a><a href="#FNanchor_32_32"><span class="label">[32]</span></a>
-As subclass in Engler and Prantl.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_33_33" id="Footnote_33_33"></a><a href="#FNanchor_33_33"><span class="label">[33]</span></a>
-As subclass in Engler and Prantl.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_34_34" id="Footnote_34_34"></a><a href="#FNanchor_34_34"><span class="label">[34]</span></a>
-As class Filicales in Engler and Prantl.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_35_35" id="Footnote_35_35"></a><a href="#FNanchor_35_35"><span class="label">[35]</span></a>
-As class Equisetales in Engler and Prantl.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_36_36" id="Footnote_36_36"></a><a href="#FNanchor_36_36"><span class="label">[36]</span></a>
-As class Lycopodiales in Engler and Prantl.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_37_37" id="Footnote_37_37"></a><a href="#FNanchor_37_37"><span class="label">[37]</span></a>
-<b>Suggestions to the teacher.</b>—In the study of the flowering plants
-in the secondary school and in elementary courses three general topics
-are suggested. 1st, the study of the form and members of the plant and
-their arrangement, as in Chapters XXXVIII-XLV. 2d, the study of a few
-plants representative of the more important families, in order that the
-members of the plant, as studied under the first topic, may be seen in
-correlation with the plant as a whole in a number of different types.
-3d, the study of plants in their relation to environment, as in <a href="#CHAPTER_XLVI">Chapter
-XLVI</a>. The first and second topics can be conducted consecutively in the
-classroom and laboratory. The third topic can be studied at opportune
-times during the progress of topics 1 and 2. For example, while
-studying topic 1 excursions can be made to study winter conditions of
-buds, shoots, etc., if in winter period, or the relations of leaves,
-etc., to environment, if in the growing period. While studying topic 2
-excursions can be made to study flower relations, and also vegetation
-relations to environment (see Chapters XLVI-LVII of the author’s
-“College Text-book of Botany”). It is believed that a study of these
-three general topics is of much more value to the beginning student
-than the ordinary plant analysis and determination of species.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_38_38" id="Footnote_38_38"></a><a href="#FNanchor_38_38"><span class="label">[38]</span></a>
-It is interesting to note that in some foliage shoots the stem is
-entirely subterranean. See discussion of the bracken fern and sensitive
-fern in <a href="#CHAPTER_XXXIX">Chapter XXXIX</a>.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_39_39" id="Footnote_39_39"></a><a href="#FNanchor_39_39"><span class="label">[39]</span></a>
-Some fibers occur also very frequently in the Fundamental System,
-forming bundle-sheaths, or strands of mechanical tissue in the cortex.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_40_40" id="Footnote_40_40"></a><a href="#FNanchor_40_40"><span class="label">[40]</span></a>
-Besides these specialized shoots for the storage of food,
-food substances are stored in ordinary shoots. For example, in the
-trunks of many trees starch is stored. With the approach of cold
-weather the starch is converted into oil, in the spring it is converted
-into starch again, and later as the buds begin to grow the starch
-is converted into glucose to be used for food. In many other trees,
-on the other hand, the starch changes to sugar on the approach of
-winter.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_41_41" id="Footnote_41_41"></a><a href="#FNanchor_41_41"><span class="label">[41]</span></a>
-This topic was prepared by Dr. K. M. Wiegand.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_42_42" id="Footnote_42_42"></a><a href="#FNanchor_42_42"><span class="label">[42]</span></a>
-See discussion of Tropophytes in <a href="#CHAPTER_XLVI">Chapter XLVI</a>.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_43_43" id="Footnote_43_43"></a><a href="#FNanchor_43_43"><span class="label">[43]</span></a>
-<a href="#CHAPTER_V">Chapter V</a>, and Organization of Tissues in
-<a href="#CHAPTER_XXXVIII">Chapter XXXVIII</a>.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_44_44" id="Footnote_44_44"></a><a href="#FNanchor_44_44"><span class="label">[44]</span></a>
-Some of the different terms used to express the kinds of
-compound leaves are as follows:</p>
-
-<p><i>Unifoliate</i> (for a single leaflet, as in orange and lemon where
-the compound leaf is greatly reduced and consists of one pinna
-attached to the petiole by a joint). <i>Bifoliate</i> for one with two
-leaflets; <i>trifoliate</i> for one with three leaflets, as in the clover;
-<i>plurifoliate</i> for many leaflets. <i>Odd pinnate</i> for a pinnate leaf with
-one or more pairs of leaflets and one odd leaflet at the end.</p>
-
-<p>So leaves are <i>palmately bifoliate</i>, etc., <i>pinnately bifoliate</i>, etc.
-<i>Decompound</i> leaves are those where they are more than twice compound,
-as <i>ternately decompound</i> in the common meadow rue (Thalictrum).</p>
-
-<p><i>Perfoliate</i> leaves are seen in the bellwort (Uvularia), <i>connate
-perfoliate</i>, as in some of the honeysuckles where the bases of opposite
-leaves are joined together around the stem. <i>Equitant</i> leaves are found
-in the iris, where the leaves fit over one another at the base like a
-saddle.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_45_45" id="Footnote_45_45"></a><a href="#FNanchor_45_45"><span class="label">[45]</span></a>
-The most remarkable case is that of the “telegraph” plant (Desmodium
-gyrans). Aside from the day and night positions which the leaves
-assume, there is a pair of small lateral leaflets to each leaf which
-constantly execute a jerky motion, and swing around in a circle like
-the second hand of a watch.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_46_46" id="Footnote_46_46"></a><a href="#FNanchor_46_46"><span class="label">[46]</span></a>
-Seedlings are usually very sensitive to light and are good
-objects to study.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_47_47" id="Footnote_47_47"></a><a href="#FNanchor_47_47"><span class="label">[47]</span></a>
-For a fuller discussion of this subject by the author see Chapters
-XLVI-LVII of his “College Text-book of Botany” (Henry Holt &amp; Co.).</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_48_48" id="Footnote_48_48"></a><a href="#FNanchor_48_48"><span class="label">[48]</span></a>
-<b>οῖκος</b> = house, and <b>λόγος</b> = discourse.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_49_49" id="Footnote_49_49"></a><a href="#FNanchor_49_49"><span class="label">[49]</span></a>
-Term used by Schimper.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_50_50" id="Footnote_50_50"></a><a href="#FNanchor_50_50"><span class="label">[50]</span></a>
-See the author’s “College Text-book of Botany.” Chapter XLIX.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_51_51" id="Footnote_51_51"></a><a href="#FNanchor_51_51"><span class="label">[51]</span></a>
-<b>ἔδαφος</b> = ground.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_52_52" id="Footnote_52_52"></a><a href="#FNanchor_52_52"><span class="label">[52]</span></a>
-For a full discussion of forest societies see Chapter L in
-the author’s “College Text-book of Botany.”</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a name="Footnote_53_53" id="Footnote_53_53"></a><a href="#FNanchor_53_53"><span class="label">[53]</span></a>
-See Chapter LIV of the author’s “College Text-book of Botany.”</p></div>
-</div>
-
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