diff options
Diffstat (limited to 'old')
| -rw-r--r-- | old/20390-8.txt | 11233 | ||||
| -rw-r--r-- | old/20390-8.zip | bin | 0 -> 171764 bytes | |||
| -rw-r--r-- | old/20390.txt | 11233 | ||||
| -rw-r--r-- | old/20390.zip | bin | 0 -> 171633 bytes |
4 files changed, 22466 insertions, 0 deletions
diff --git a/old/20390-8.txt b/old/20390-8.txt new file mode 100644 index 0000000..5129d68 --- /dev/null +++ b/old/20390-8.txt @@ -0,0 +1,11233 @@ +The Project Gutenberg EBook of Elements of Structural and Systematic Botany, by +Douglas Houghton Campbell + +This eBook is for the use of anyone anywhere 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 + + +Title: Elements of Structural and Systematic Botany + For High Schools and Elementary College Courses + +Author: Douglas Houghton Campbell + +Release Date: January 17, 2007 [EBook #20390] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK SYSTEMATIC BOTANY *** + + + + +Produced by Marilynda Fraser-Cunliffe, Laura Wisewell and +the Online Distributed Proofreading Team at +http://www.pgdp.net + + + + + + +--------------------------------------------------------------+ + | | + | Transcriber's note: In this lower-bit text version the male | + | and female symbols have been replaced with [Male] and | + | [Female] respectively. The correct symbols are used in the | + | UTF-8 text and HTML versions of this eBook. | + | | + +--------------------------------------------------------------+ + + + + ELEMENTS + + OF + + STRUCTURAL AND SYSTEMATIC BOTANY, + + + FOR + HIGH SCHOOLS AND ELEMENTARY + COLLEGE COURSES. + + + BY + DOUGLAS HOUGHTON CAMPBELL, PH.D., + PROFESSOR OF BOTANY IN THE INDIANA UNIVERSITY. + + + BOSTON, U.S.A.: + PUBLISHED BY GINN & COMPANY. + 1890. + + + + COPYRIGHT, 1890, + BY DOUGLAS HOUGHTON CAMPBELL. + + ALL RIGHTS RESERVED. + + TYPOGRAPHY BY J. S. CUSHING & CO., BOSTON, U.S.A. + PRESSWORK BY GINN & CO., BOSTON, U.S.A. + + + + +PREFACE. + + +The rapid advances made in the science of botany within the last few +years necessitate changes in the text books in use as well as in +methods of teaching. Having, in his own experience as a teacher, felt +the need of a book different from any now in use, the author has +prepared the present volume with a hope that it may serve the purpose +for which it is intended; viz., an introduction to the study of botany +for use in high schools especially, but sufficiently comprehensive to +serve also as a beginning book in most colleges. + +It does not pretend to be a complete treatise of the whole science, +and this, it is hoped, will be sufficient apology for the absence from +its pages of many important subjects, especially physiological topics. +It was found impracticable to compress within the limits of a book of +moderate size anything like a thorough discussion of even the most +important topics of _all_ the departments of botany. As a thorough +understanding of the structure of any organism forms the basis of all +further intelligent study of the same, it has seemed to the author +proper to emphasize this feature in the present work, which is +professedly an _introduction_, only, to the science. + +This structural work has been supplemented by so much classification +as will serve to make clear the relationships of different groups, and +the principles upon which the classification is based, as well as +enable the student to recognize the commoner types of the different +groups as they are met with. The aim of this book is not, however, +merely the identification of plants. We wish here to enter a strong +protest against the only too prevalent idea that the chief aim of +botany is the ability to run down a plant by means of an "Analytical +Key," the subject being exhausted as soon as the name of the plant is +discovered. A knowledge of the plant itself is far more important than +its name, however desirable it may be to know the latter. + +In selecting the plants employed as examples of the different groups, +such were chosen, as far as possible, as are everywhere common. Of +course this was not always possible, as some important forms, _e.g._ +the red and brown seaweeds, are necessarily not always readily +procurable by all students, but it will be found that the great +majority of the forms used, or closely related ones, are within the +reach of nearly all students; and such directions are given for +collecting and preserving them as will make it possible even for those +in the larger cities to supply themselves with the necessary +materials. Such directions, too, for the manipulation and examination +of specimens are given as will make the book, it is hoped, a +laboratory guide as well as a manual of classification. Indeed, it is +primarily intended that the book should so serve as a help in the +study of the actual specimens. + +Although much can be done in the study, even of the lowest plants, +without microscopic aid other than a hand lens, for a thorough +understanding of the structure of any plant a good compound microscope +is indispensable, and wherever it is possible the student should be +provided with such an instrument, to use this book to the best +advantage. As, however, many are not able to have the use of a +microscope, the gross anatomy of all the forms described has been +carefully treated for the especial benefit of such students. Such +portions of the text, as well as the general discussions, are printed +in ordinary type, while the minute anatomy, and all points requiring +microscopic aid, are discussed in separate paragraphs printed in +smaller type. + +The drawings, with very few exceptions, which are duly credited, were +drawn from nature by the author, and nearly all expressly for this +work. + +A list of the most useful books of reference is appended, all of which +have been more or less consulted in the preparation of the following +pages. + +The classification adopted is, with slight changes, that given in +Goebel's "Outlines of Morphology and Classification"; while, perhaps, +not in all respects entirely satisfactory, it seems to represent more +nearly than any other our present knowledge of the subject. Certain +groups, like the Diatoms and _Characeæ_, are puzzles to the botanist, +and at present it is impossible to give them more than a provisional +place in the system. + +If this volume serves to give the student some comprehension of the +real aims of botanical science, and its claims to be something more +than the "Analysis" of flowers, it will have fulfilled its mission. + +DOUGLAS H. CAMPBELL. + + BLOOMINGTON, INDIANA, + October, 1889. + + + + +TABLE OF CONTENTS. + + + PAGE + CHAPTER I.--INTRODUCTION 1 + + Composition of Matter; Biology; Botany; Zoölogy; Departments + of Botany; Implements and Reagents; Collecting + Specimens. + + + CHAPTER II.--THE CELL 6 + + Parts of the Cell; Formation of New Cells; Tissues. + + + CHAPTER III.--CLASSIFICATION OF PLANTS 9 + + Protophytes; Slime-moulds; Schizophytes; Blue-green Slimes, + _Oscillaria_; Schizomycetes, _Bacteria_; Green Monads, + _Euglena_, _Volvox_. + + + CHAPTER IV.--ALGÆ 21 + + Classification of Algæ; Green Algæ; _Protococcaceæ_, + _Protococcus_; _Confervaceæ_, _Cladophora_, _OEdogonium_, + _Coleochæte_. + + + CHAPTER V.--GREEN ALGÆ (_Continued_) 30 + + Pond-scums, _Spirogyra_; _Siphoneæ_, _Vaucheria_; _Characeæ_, + _Chara_. + + + CHAPTER VI.--BROWN SEAWEEDS 41 + + _Diatomaceæ_; True Brown Algæ, _Fucus_; Classification of + Brown Algæ. + + + CHAPTER VII.--RED ALGÆ 49 + + Structure of Red Algæ; _Callithamnion_; Fresh-Water Forms. + + + CHAPTER VIII.--FUNGI 54 + + _Phycomycetes_, _Mycomycetes_; _Phycomycetes_, Black Moulds, + _Mucor_; White Rusts and Mildews, _Cystopus_; Water Moulds. + + + CHAPTER IX.--TRUE FUNGI 63 + + Yeast; Smuts; _Ascomycetes_; Dandelion Mildew; Cup Fungi, + _Ascobolus_; Lichens; Black Fungi. + + + CHAPTER X.--TRUE FUNGI (_Continued_) 77 + + _Basidiomycetes_; Rusts; _Coprinus_; Classification. + + + CHAPTER XI.--BRYOPHYTES 86 + + Classification; Liverworts, _Madotheca_; Classification of + Liverworts; Mosses, _Funaria_; Classification of Mosses. + + + CHAPTER XII.--PTERIDOPHYTES 102 + + Bryophytes and Pteridophytes; Germination and Prothallium; + Structure of Maiden-hair Fern. + + + CHAPTER XIII.--CLASSIFICATION OF PTERIDOPHYTES 116 + + Ferns; Horse-tails; Club Mosses. + + + CHAPTER XIV.--SPERMAPHYTES 128 + + General Characteristics; Gymnosperms and Angiosperms, + Scotch-pine; Classification of Gymnosperms. + + + CHAPTER XV.--SPERMAPHYTES (_Continued_) 143 + + Angiosperms; Flowers of Angiosperms; Classification of + Angiosperms; Monocotyledons, Structure of _Erythronium_. + + + CHAPTER XVI.--CLASSIFICATION OF MONOCOTYLEDONS 153 + + _Liliifloræ_; _Enantioblastæ_; _Spadicifloræ_; _Glumaceæ_; + _Scitamineæ_; _Gynandræ_, _Helobiæ_. + + + CHAPTER XVII.--DICOTYLEDONS 170 + + General Characteristics; Structure of Shepherd's-purse. + + + CHAPTER XVIII.--CLASSIFICATION OF DICOTYLEDONS 181 + + _Choripetalæ_: _Iulifloræ_; _Centrospermæ_; _Aphanocyclæ_; + _Eucyclæ_; _Tricoccæ_; _Calycifloræ_. + + + CHAPTER XIX.--CLASSIFICATION OF DICOTYLEDONS + (_Continued_) 210 + + _Sympetalæ_: _Isocarpæ_, _Bicornes_, _Primulinæ_, _Diospyrinæ_; + _Anisocarpæ_, _Tubifloræ_, _Labiatifloræ_, _Contortæ_, + _Campanulinæ_, _Aggregatæ_. + + + CHAPTER XX.--FERTILIZATION OF FLOWERS 225 + + + CHAPTER XXI.--HISTOLOGICAL METHODS 230 + + Nuclear Division in Wild Onion; Methods of Fixing, Staining, + and Mounting Permanent Preparations; Reference Books. + + + INDEX 237 + + + + +BOTANY. + + + + +CHAPTER I. + +INTRODUCTION. + + +All matter is composed of certain constituents (about seventy are at +present known), which, so far as the chemist is concerned, are +indivisible, and are known as elements. + +Of the innumerable combinations of these elements, two general classes +may be recognized, organic and inorganic bodies. While it is +impossible, owing to the dependence of all organized matter upon +inorganic matter, to give an absolute definition, we at once recognize +the peculiarities of organic or living bodies as distinguished from +inorganic or non-living ones. All living bodies feed, grow, and +reproduce, these acts being the result of the action of forces +resident within the organism. Inorganic bodies, on the other hand, +remain, as a rule, unchanged so long as they are not acted upon by +external forces. + +All living organisms are dependent for existence upon inorganic +matter, and sooner or later return these elements to the sources +whence they came. Thus, a plant extracts from the earth and air +certain inorganic compounds which are converted by the activity of the +plant into a part of its own substance, becoming thus incorporated +into a living organism. After the plant dies, however, it undergoes +decomposition, and the elements are returned again to the earth and +atmosphere from which they were taken. + +Investigation has shown that living bodies contain comparatively few +elements, but these are combined into extraordinarily complex +compounds. The following elements appear to be essential to all living +bodies: carbon, hydrogen, oxygen, nitrogen, sulphur, potassium. +Besides these there are several others usually present, but not +apparently essential to all organisms. These include phosphorus, iron, +calcium, sodium, magnesium, chlorine, silicon. + +As we examine more closely the structure and functions of organic +bodies, an extraordinary uniformity is apparent in all of them. This +is disguised in the more specialized forms, but in the simpler ones is +very apparent. Owing to this any attempt to separate absolutely the +animal and vegetable kingdoms proves futile. + +The science that treats of living things, irrespective of the +distinction between plant and animal, is called "Biology," but for +many purposes it is desirable to recognize the distinctions, making +two departments of Biology,--Botany, treating of plants; and Zoölogy, +of animals. It is with the first of these only that we shall concern +ourselves here. + +When one takes up a plant his attention is naturally first drawn to +its general appearance and structure, whether it is a complicated one +like one of the flowering plants, or some humbler member of the +vegetable kingdom,--a moss, seaweed, toadstool,--or even some still +simpler plant like a mould, or the apparently structureless green scum +that floats on a stagnant pond. In any case the impulse is to +investigate the form and structure as far as the means at one's +disposal will permit. Such a study of structure constitutes +"Morphology," which includes two departments,--gross anatomy, or a +general study of the parts; and minute anatomy, or "Histology," in +which a microscopic examination is made of the structure of the +different parts. A special department of Morphology called +"Embryology" is often recognized. This embraces a study of the +development of the organism from its earliest stage, and also the +development of its different members. + +From a study of the structure of organisms we get a clue to their +relationships, and upon the basis of such relationships are enabled to +classify them or unite them into groups so as to indicate the degree +to which they are related. This constitutes the division of Botany +usually known as Classification or "Systematic Botany." + +Finally, we may study the functions or workings of an organism: how it +feeds, breathes, moves, reproduces. This is "Physiology," and like +classification must be preceded by a knowledge of the structures +concerned. + +For the study of the gross anatomy of plants the following articles +will be found of great assistance: 1. a sharp knife, and for more +delicate tissues, a razor; 2. a pair of small, fine-pointed scissors; +3. a pair of mounted needles (these can be made by forcing ordinary +sewing needles into handles of pine or other soft wood); 4. a hand +lens; 5. drawing-paper and pencil, and a note book. + +For the study of the lower plants, as well as the histology of the +higher ones, a compound microscope is indispensable. Instruments with +lenses magnifying from about 20 to 500 diameters can be had at a cost +varying from about $20 to $30, and are sufficient for any ordinary +investigations. + +Objects to be studied with the compound microscope are usually +examined by transmitted light, and must be transparent enough to allow +the light to pass through. The objects are placed upon small glass +slips (slides), manufactured for the purpose, and covered with +extremely thin plates of glass, also specially made. If the body to be +examined is a large one, thin slices or sections must be made. This +for most purposes may be done with an ordinary razor. Most plant +tissues are best examined ordinarily in water, though of course +specimens so mounted cannot be preserved for any length of time.[1] + +[1] For the mounting of permanent preparations, see Chapter XIX. + +In addition to the implements used in studying the gross anatomy, the +following will be found useful in histological work: 1. a small +camel's-hair brush for picking up small sections and putting water in +the slides; 2. small forceps for handling delicate objects; 3. +blotting paper for removing superfluous water from the slides and +drawing fluids under the cover glass; 4. pieces of elder or sunflower +pith, for holding small objects while making sections. + +In addition to these implements, a few reagents may be recommended for +the simpler histological work. The most important of these are +alcohol, glycerine, potash (a strong solution of potassium hydrate in +water), iodine (either a little of the commercial tincture of iodine +in water, or, better, a solution of iodine in iodide of potassium), +acetic acid, and some staining fluid. (An aqueous or alcoholic +solution of gentian violet or methyl violet is one of the best.) + +A careful record should be kept by the student of all work done, both +by means of written notes and drawings. For most purposes pencil +drawings are most convenient, and these should be made with a +moderately soft pencil on unruled paper. If it is desired to make the +drawings with ink, a careful outline should first be made with a hard +pencil and this inked over with India-ink or black drawing ink. Ink +drawings are best made upon light bristol board with a hard, +smooth-finished surface. + +When obtainable, the student will do best to work with freshly +gathered specimens; but as these are not always to be had when wanted, +a few words about gathering and preserving material may be of service. + +Most of the lower green plants (_algæ_) may be kept for a long time in +glass jars or other vessels, provided care is taken to remove all +dead specimens at first and to renew the water from time to time. They +usually thrive best in a north window where they get little or no +direct sunshine, and it is well to avoid keeping them too warm. + +Numbers of the most valuable fungi--_i.e._ the lower plants that are +not green--grow spontaneously on many organic substances that are kept +warm and moist. Fresh bread kept moist and covered with a glass will +in a short time produce a varied crop of moulds, and fresh horse +manure kept in the same way serves to support a still greater number +of fungi. + +Mosses, ferns, etc., can be raised with a little care, and of course +very many flowering plants are readily grown in pots. + +Most of the smaller parasitic fungi (rusts, mildews, etc.) may be kept +dry for any length of time, and on moistening with a weak solution of +caustic potash will serve nearly as well as freshly gathered specimens +for most purposes. + +When it is desired to preserve as perfectly as possible the more +delicate plant structures for future study, strong alcohol is the best +and most convenient preserving agent. Except for loss of color it +preserves nearly all plant tissues perfectly. + + + + +CHAPTER II. + +THE CELL. + + +If we make a thin slice across the stem of a rapidly growing +plant,--_e.g._ geranium, begonia, celery,--mount it in water, and +examine it microscopically, it will be found to be made up of numerous +cavities or chambers separated by delicate partitions. Often these +cavities are of sufficient size to be visible to the naked eye, and +examined with a hand lens the section appears like a piece of fine +lace, each mesh being one of the chambers visible when more strongly +magnified. These chambers are known as "cells," and of them the whole +plant is built up. + +[Illustration: FIG. 1.--A single cell from a hair on the stamen of the +common spiderwort (_Tradescantia_), × 150. _pr._ protoplasm; _w_, cell +wall; _n_, nucleus.] + + In order to study the structure of the cell more exactly we will + select such as may be examined without cutting them. A good example + is furnished by the common spiderwort (Fig. 1). Attached to the base + of the stamens (Fig. 85, _B_) are delicate hairs composed of chains + of cells, which may be examined alive by carefully removing a stamen + and placing it in a drop of water under a cover glass. Each cell + (Fig. 1) is an oblong sac, with a delicate colorless wall which + chemical tests show to be composed of cellulose, a substance closely + resembling starch. Within this sac, and forming a lining to it, is + a thin layer of colorless matter containing many fine granules. + Bands and threads of the same substance traverse the cavity of the + cell, which is filled with a deep purple homogeneous fluid. This + fluid, which in most cells is colorless, is called the cell sap, and + is composed mainly of water. Imbedded in the granular lining of the + sac is a roundish body (_n_), which itself has a definite membrane, + and usually shows one or more roundish bodies within, besides an + indistinctly granular appearance. This body is called the nucleus of + the cell, and the small one within it, the nucleolus. + + The membrane surrounding the cell is known as the cell wall, and in + young plant cells is always composed of cellulose. + + The granular substance lining the cell wall (Fig. 1, _pr._) is + called "protoplasm," and with the nucleus constitutes the living + part of the cell. If sufficiently magnified, the granules within the + protoplasm will be seen to be in active streaming motion. This + movement, which is very evident here, is not often so conspicuous, + but still may often be detected without difficulty. + +[Illustration: FIG. 2.--An _Amoeba_. A cell without a cell wall. _n_, +nucleus; _v_, vacuoles, × 300.] + +The cell may be regarded as the unit of organic structure, and of +cells are built up all of the complicated structures of which the +bodies of the highest plants and animals are composed. We shall find +that the cells may become very much modified for various purposes, but +at first they are almost identical in structure, and essentially the +same as the one we have just considered. + +[Illustration: FIG. 3.--Hairs from the leaf stalk of a wild geranium. +_A_, single-celled hair. _B_ and _C_, hairs consisting of a row of +cells. The terminal rounded cell secretes a peculiar scented oil that +gives the plant its characteristic odor. _B_, × 50; _C_, × 150.] + +Very many of the lower forms of life consist of but a single cell +which may occasionally be destitute of a cell wall. Such a form is +shown in Figure 2. Here we have a mass of protoplasm with a nucleus +(_n_) and cavities (vacuoles, _v_) filled with cell sap, but no cell +wall. The protoplasm is in constant movement, and by extensions of a +portion of the mass and contraction of other parts, the whole creeps +slowly along. Other naked cells (Fig. 12, _B_; Fig. 16, _C_) are +provided with delicate thread-like processes of protoplasm called +"cilia" (sing. _cilium_), which are in active vibration, and propel +the cell through the water. + +[Illustration: FIG. 4.--_A_, cross section. _B_, longitudinal section +of the leaf stalk of wild geranium, showing its cellular structure. +_Ep._ epidermis. _h_, a hair, × 50. _C_, a cell from the prothallium +(young plant) of a fern, × _150_. The contents of the cell contracted +by the action of a solution of sugar.] + + On placing a cell into a fluid denser than the cell sap (_e.g._ a + ten-per-cent solution of sugar in water), a portion of the water + will be extracted from the cell, and we shall then see the + protoplasm receding from the wall (Fig. 4, _C_), showing that it is + normally in a state of tension due to pressure from within of the + cell sap. The cell wall shows the same thing though in a less + degree, owing to its being much more rigid than the protoplasmic + lining. It is owing to the partial collapsing of the cells, + consequent on loss of water, that plants wither when the supply of + water is cut off. + +As cells grow, new ones are formed in various ways. If the new cells +remain together, cell aggregates, called tissues, are produced, and +of these tissues are built up the various organs of the higher plants. +The simplest tissues are rows of cells, such as form the hairs +covering the surface of the organs of many flowering plants (Fig. 3), +and are due to a division of the cells in a single direction. If the +divisions take place in three planes, masses of cells, such as make up +the stems, etc., of the higher plants, result (Fig. 4, _A_, _B_). + + + + +CHAPTER III. + +CLASSIFICATION OF PLANTS.--PROTOPHYTES. + + +For the sake of convenience it is desirable to collect into groups +such plants as are evidently related; but as our knowledge of many +forms is still very imperfect, any classification we may adopt must be +to a great extent only provisional, and subject to change at any time, +as new forms are discovered or others become better understood. + +The following general divisions are usually accepted: I. Sub-kingdom +(or Branch); II. Class; III. Order; IV. Family; V. Genus; VI. Species. + +To illustrate: The white pine belongs to the highest great division +(sub-kingdom) of the plant kingdom. The plants of this division all +produce seeds, and hence are called "spermaphytes" ("seed plants"). +They may be divided into two groups (classes), distinguished by +certain peculiarities in the flowers and seeds. These are named +respectively "gymnosperms" and "angiosperms," and to the first our +plant belongs. The gymnosperms may be further divided into several +subordinate groups (orders), one of which, the conifers, or +cone-bearing evergreens, includes our plant. This order includes +several families, among them the fir family (_Abietineæ_), including +the pines and firs. Of the sub-divisions (_genera_, sing. _genus_) of +the fir family, one of the most familiar is the genus _Pinus_, which +embraces all the true pines. Comparing different kinds of pines, we +find that they differ in the form of the cones, arrangement of the +leaves, and other minor particulars. The form we have selected differs +from all other native forms in its cones, and also in having the +leaves in fives, instead of twos or threes, as in most other kinds. +Therefore to distinguish the white pine from all other pines, it is +given a "specific" name, _strobus_. + +The following table will show more plainly what is meant: + + + Sub-kingdom, + _Spermaphyta_. + /--------------------^---------------------\ + Includes all spermaphytes, or seed plants. + + Class, + _Gymnospermæ_. + /------------^------------\ + All naked-seeded plants. + + Order, + _Coniferæ_. + /--------------^--------------\ + All cone-bearing evergreens. + + Family, + _Abietineæ_. + /--------^--------\ + Firs, Pines, etc. + + Genus, + _Pinus_. + /---^---\ + Pines. + + Species, + _Strobus_. + /-----^-----\ + White Pine. + + +SUB-KINGDOM I. + +PROTOPHYTES. + +The name Protophytes (_Protophyta_) has been applied to a large number +of simple plants, which differ a good deal among themselves. Some of +them differ strikingly from the higher plants, and resemble so +remarkably certain low forms of animal life as to be quite +indistinguishable from them, at least in certain stages. Indeed, there +are certain forms that are quite as much animal as vegetable in their +attributes, and must be regarded as connecting the two kingdoms. Such +forms are the slime moulds (Fig. 5), _Euglena_ (Fig. 9), _Volvox_ +(Fig. 10), and others. + +[Illustration: FIG. 5.--_A_, a portion of a slime mould growing on a +bit of rotten wood, × 3. _B_, outline of a part of the same, × 25. +_C_, a small portion showing the densely granular character of the +protoplasm, × 150. _D_, a group of spore cases of a slime mould +(_Trichia_), of about the natural size. _E_, two spore cases, × 5. The +one at the right has begun to open. _F_, a thread (capillitium) and +spores of _Trichia_, × 50. _G_, spores. _H_, end of the thread, × 300. +_I_, zoöspores of _Trichia_, × 300. i, ciliated form; ii, amoeboid +forms. _n_, nucleus. _v_, contractile vacuole. _J_, _K_, sporangia of +two common slime moulds. _J_, _Stemonitis_, × 2. _K_, _Arcyria_, × 4.] + +Other protophytes, while evidently enough of vegetable nature, are +nevertheless very different in some respects from the higher plants. + +The protophytes may be divided into three classes: I. The slime moulds +(_Myxomycetes_); II. The Schizophytes; III. The green monads +(_Volvocineæ_). + + +CLASS I.--THE SLIME MOULDS. + +These curious organisms are among the most puzzling forms with which +the botanist has to do, as they are so much like some of the lowest +forms of animal life as to be scarcely distinguishable from them, and +indeed they are sometimes regarded as animals rather than plants. At +certain stages they consist of naked masses of protoplasm of very +considerable size, not infrequently several centimetres in diameter. +These are met with on decaying logs in damp woods, on rotting leaves, +and other decaying vegetable matter. The commonest ones are bright +yellow or whitish, and form soft, slimy coverings over the substratum +(Fig. 5, _A_), penetrating into its crevices and showing sensitiveness +toward light. The plasmodium, as the mass of protoplasm is called, may +be made to creep upon a slide in the following way: A tumbler is +filled with water and placed in a saucer filled with sand. A strip of +blotting paper about the width of the slide is now placed with one end +in the water, the other hanging over the edge of the glass and against +one side of a slide, which is thus held upright, but must not be +allowed to touch the side of the tumbler. The strip of blotting paper +sucks up the water, which flows slowly down the surface of the slide +in contact with the blotting paper. If now a bit of the substance upon +which the plasmodium is growing is placed against the bottom of the +slide on the side where the stream of water is, the protoplasm will +creep up against the current of water and spread over the slide, +forming delicate threads in which most active streaming movements of +the central granular protoplasm may be seen under the microscope, and +the ends of the branches may be seen to push forward much as we saw in +the amoeba. In order that the experiment may be successful, the whole +apparatus should be carefully protected from the light, and allowed to +stand for several hours. This power of movement, as well as the power +to take in solid food, are eminently animal characteristics, though +the former is common to many plants as well. + +After a longer or shorter time the mass of protoplasm contracts and +gathers into little heaps, each of which develops into a structure +that has no resemblance to any animal, but would be at once placed +with plants. In one common form (_Trichia_) these are round or +pear-shaped bodies of a yellow color, and about as big as a pin head +(Fig. 5, _D_), occurring in groups on rotten logs in damp woods. +Others are stalked (_Arcyria_, _Stemonitis_) (Fig. 5, _J_, _K_), and +of various colors,--red, brown, etc. The outer part of the structure +is a more or less firm wall, which breaks when ripe, discharging a +powdery mass, mixed in most forms with very fine fibres. + + When strongly magnified the fine dust is found to be made up of + innumerable small cells with thick walls, marked with ridges or + processes which differ much in different species. The fibres also + differ much in different genera. Sometimes they are simple, + hair-like threads; in others they are hollow tubes with spiral + thickenings, often very regularly placed, running around their + walls. + + The spores may sometimes be made to germinate by placing them in a + drop of water, and allowing them to remain in a warm place for about + twenty-four hours. If the experiment has been successful, at the end + of this time the spore membrane will have burst, and the contents + escaped in the form of a naked mass of protoplasm (Zoöspore) with a + nucleus, and often showing a vacuole (Fig. 5, _v_), that + alternately becomes much distended, and then disappears entirely. On + first escaping it is usually provided with a long, whip-like + filament of protoplasm, which is in active movement, and by means of + which the cell swims actively through the water (Fig. 5, _I_ i). + Sometimes such a cell will be seen to divide into two, the process + taking but a short time, so that the numbers of these cells under + favorable conditions may become very large. After a time the lash is + withdrawn, and the cell assumes much the form of a small amoeba (_I_ + ii). + +The succeeding stages are difficult to follow. After repeatedly +dividing, a large number of these amoeba-like cells run together, +coalescing when they come in contact, and forming a mass of protoplasm +that grows, and finally assumes the form from which it started. + + Of the common forms of slime moulds the species of _Trichia_ (Figs. + _D_, _I_) and _Physarum_ are, perhaps, the best for studying the + germination, as the spores are larger than in most other forms, and + germinate more readily. The experiment is apt to be most successful + if the spores are sown in a drop of water in which has been infused + some vegetable matter, such as a bit of rotten wood, boiling + thoroughly to kill all germs. A drop of this fluid should be placed + on a perfectly clean cover glass, which it is well to pass once or + twice through a flame, and the spores transferred to this drop with + a needle previously heated. By these precautions foreign germs will + be avoided, which otherwise may interfere seriously with the growth + of the young slime moulds. After sowing the spores in the drop of + culture fluid, the whole should be inverted over a so-called "moist + chamber." This is simply a square of thick blotting paper, in which + an opening is cut small enough to be entirely covered by the cover + glass, but large enough so that the drop in the centre of the cover + glass will not touch the sides of the chamber, but will hang + suspended clear in it. The blotting paper should be soaked + thoroughly in pure water (distilled water is preferable), and then + placed on a slide, covering carefully with the cover glass with the + suspended drop of fluid containing the spores. The whole should be + kept under cover so as to prevent loss of water by evaporation. By + this method the spores may be examined conveniently without + disturbing them, and the whole may be kept as long as desired, so + long as the blotting paper is kept wet, so as to prevent the + suspended drop from drying up. + + +CLASS II.--_Schizophytes_. + +The Schizophytes are very small plants, though not infrequently +occurring in masses of considerable size. They are among the commonest +of all plants, and are found everywhere. They multiply almost entirely +by simple transverse division, or splitting of the cells, whence their +name. There are two pretty well-marked orders,--the blue-green slimes +(_Cyanophyceæ_) and the bacteria (_Schizomycetes_). They are +distinguished, primarily, by the first (with a very few exceptions) +containing chlorophyll (leaf-green), which is entirely absent from +nearly all of the latter. + +The blue-green slimes: These are, with few exceptions, green plants of +simple structure, but possessing, in addition to the ordinary green +pigment (chlorophyll, or leaf-green), another coloring matter, soluble +in water, and usually blue in color, though sometimes yellowish or +red. + +[Illustration: FIG. 6.--Blue-green slime (_Oscillaria_). _A_, mass of +filaments of the natural size. _B_, single filament, × 300. _C_, a +piece of a filament that has become separated. _s_, sheath, × 300.] + +As a representative of the group, we will select one of the commonest +forms (_Oscillaria_), known sometimes as green slime, from forming a +dark blue-green or blackish slimy coat over the mud at the bottom of +stagnant or sluggish water, in watering troughs, on damp rocks, or +even on moist earth. A search in the places mentioned can hardly fail +to secure plenty of specimens for study. If a bit of the slimy mass is +transferred to a china dish, or placed with considerable water on a +piece of stiff paper, after a short time the edge of the mass will +show numerous extremely fine filaments of a dark blue-green color, +radiating in all directions from the mass (Fig. 6, _a_). The filaments +are the individual plants, and possess considerable power of motion, +as is shown by letting the mass remain undisturbed for a day or two, +at the end of which time they will have formed a thin film over the +surface of the vessel in which they are kept; and the radiating +arrangement of the filaments can then be plainly seen. + +If the mass is allowed to dry on the paper, it often leaves a bright +blue stain, due to the blue pigment in the cells of the filament. This +blue color can also be extracted by pulverizing a quantity of the +dried plants, and pouring water over them, the water soon becoming +tinged with a decided blue. If now the water containing the blue +pigment is filtered, and the residue treated with alcohol, the latter +will extract the chlorophyll, becoming colored of a yellow-green. + + The microscope shows that the filaments of which the mass is + composed (Fig. 6, _B_) are single rows of short cylindrical cells of + uniform diameter, except at the end of the filament, where they + usually become somewhat smaller, so that the tip is more or less + distinctly pointed. The protoplasm of the cells has a few small + granules scattered through it, and is colored uniformly of a pale + blue-green. No nucleus can be seen. + + If the filament is broken, there may generally be detected a + delicate, colorless sheath that surrounds it, and extends beyond the + end cells (Fig. 6, _c_). The filament increases in length by the + individual cells undergoing division, this always taking place at + right angles to the axis of the filament. New filaments are produced + simply by the older ones breaking into a number of pieces, each of + which rapidly grows to full size. + +The name "oscillaria" arises from the peculiar oscillating or swinging +movements that the plant exhibits. The most marked movement is a +swaying from side to side, combined with a rotary motion of the free +ends of the filaments, which are often twisted together like the +strands of a rope. If the filaments are entirely free, they may often +be observed to move forward with a slow, creeping movement. Just how +these movements are caused is still a matter of controversy. + +The lowest of the _Cyanophyceæ_ are strictly single-celled, separating +as soon as formed, but cohering usually in masses or colonies by means +of a thick mucilaginous substance that surrounds them (Fig. 7, _D_). + +The higher ones are filaments, in which there may be considerable +differentiation. These often occur in masses of considerable size, +forming jelly-like lumps, which may be soft or quite firm (Fig. 7, +_A_, _B_). They are sometimes found on damp ground, but more commonly +attached to plants, stones, etc., in water. The masses vary in color +from light brown to deep blackish green, and in size from that of a +pin head to several centimetres in diameter. + +[Illustration: FIG. 7.--Forms of _Cyanophyceæ_. _A_, _Nostoc_. _B_, +_Gloeotrichia_, × 1. _C_, individual of _Gloeotrichia_. _D_, +Chroöcoccus. _E_, _Nostoc_. _F_, Oscillaria. _G_, _H_, _Tolypothrix_. +All × 300. _y_, heterocyst. _sp._ spore.] + +In the higher forms special cells called heterocysts are found. They +are colorless, or light yellowish, regularly disposed; but their +function is not known. Besides these, certain cells become +thick-walled, and form resting cells (spores) for the propagation of +the plant (Fig. 7, C. _sp._). In species where the sheath of the +filament is well marked (Fig. 7, _H_), groups of cells slip out of the +sheath, and develop a new one, thus giving rise to a new plant. + +The bacteria (_Schizomycetes_), although among the commonest of +organisms, owing to their excessive minuteness, are difficult to +study, especially for the beginner. They resemble, in their general +structure and methods of reproduction, the blue-green slimes, but are, +with very few exceptions, destitute of chlorophyll, although often +possessing bright pigments,--blue, violet, red, etc. It is one of +these that sometimes forms blood-red spots in flour paste or bits of +bread that have been kept very moist and warm. They are universally +present where decomposition is going on, and are themselves the +principal agents of decay, which is the result of their feeding upon +the substance, as, like all plants without chlorophyll, they require +organic matter for food. Most of the species are very tenacious of +life, and may be completely dried up for a long time without dying, +and on being placed in water will quickly revive. Being so extremely +small, they are readily carried about in the air in their dried-up +condition, and thus fall upon exposed bodies, setting up decomposition +if the conditions are favorable. + +A simple experiment to show this may be performed by taking two test +tubes and partly filling them with an infusion of almost any organic +substance (dried leaves or hay, or a bit of meat will answer). The +fluid should now be boiled so as to kill any germs that may be in it; +and while hot, one of the vessels should be securely stopped up with a +plug of cotton wool, and the other left open. The cotton prevents +access of all solid particles, but allows the air to enter. If proper +care has been taken, the infusion in the closed vessel will remain +unchanged indefinitely; but the other will soon become turbid, and a +disagreeable odor will be given off. Microscopic examination shows the +first to be free from germs of any kind, while the second is swarming +with various forms of bacteria. + +[Illustration: FIG. 8.--Bacteria.] + +These little organisms have of late years attracted the attention of +very many scientists, from the fact that to them is due many, if not +all, contagious diseases. The germs of many such diseases have been +isolated, and experiments prove beyond doubt that these are alone the +causes of the diseases in question. + + If a drop of water containing bacteria is examined, we find them to + be excessively small, many of them barely visible with the strongest + lenses. The larger ones (Fig. 8) recall quite strongly the smaller + species of oscillaria, and exhibit similar movements. Others are so + small as to appear as mere lines and dots, even with the strongest + lenses. Among the common forms are small, nearly globular cells; + oblong, rod-shaped or thread-shaped filaments, either straight or + curved, or even spirally twisted. Frequently they show a quick + movement which is probably in all cases due to cilia, which are, + however, too small to be seen in most cases. + +[Illustration: FIG. 9.--_Euglena_. _A_, individual in the active +condition. _E_, the red "eye-spot." _c_, flagellum. _n_, nucleus. _B_, +resting stage. _C_, individual dividing, × 300.] + +Reproduction is for the most part by simple transverse division, as in +oscillaria; but occasionally spores are produced also. + + +CLASS III.--GREEN MONADS (_Volvocineæ_). + +This group of the protophytes is unquestionably closely related to +certain low animals (_Monads_ or _Flagellata_), with which they are +sometimes united. They are characterized by being actively motile, and +are either strictly unicellular, or the cells are united by a +gelatinous envelope into a colony of definite form. + +Of the first group, _Euglena_ (Fig. 9), may be selected as a type. + + This organism is found frequently among other algæ, and occasionally + forms a green film on stagnant water. It is sometimes regarded as a + plant, sometimes as an animal, and is an elongated, somewhat + worm-like cell without a definite cell wall, so that it can change + its form to some extent. The protoplasm contains oval masses, which + are bright green in color; but the forward pointed end of the cell + is colorless, and has a little depression. At this end there is a + long vibratile protoplasmic filament (_c_), by means of which the + cell moves. There is also to be seen near this end a red speck (_e_) + which is probably sensitive to light. A nucleus can usually be seen + if the cell is first killed with an iodine solution, which often + will render the flagellum (_c_) more evident, this being invisible + while the cell is in motion. The cells multiply by division. + Previous to this the flagellum is withdrawn, and a firm cell wall is + formed about the cell (Fig. 9, _B_). The contents then divide into + two or more parts, which afterwards escape as new individuals. + +Of the forms that are united in colonies[2] one of the best known is +_Volvox_ (Fig. 10). This plant is sometimes found in quiet water, +where it floats on or near the surface as a dark green ball, just +large enough to be seen with the naked eye. They may be kept for some +time in aquaria, and will sometimes multiply rapidly, but are very +susceptible to extremes of temperature, especially of heat. + +[2] The term "colony" is, perhaps, inappropriate, as the whole mass of +cells arises from a single one, and may properly be looked upon as an +individual plant. + +[Illustration: FIG. 10.--_Volvox._ _A_, mature colony, containing +several smaller ones (_x_), × 50. _B_, Two cells showing the cilia, +× 300.] + + The colony (Fig. 10, _A_) is a hollow sphere, the numerous green + cells of which it is composed forming a single layer on the outside. + By killing with iodine, and using a strong lens, each cell is seen + to be somewhat pear-shaped (Fig. _B_), with the pointed end out. + Attached to this end are two vibratile filaments (cilia or + _flagella_), and the united movements of these cause the rolling + motion of the whole colony. Usually a number of young colonies + (Fig. _x_) are found within the mother colony. These arise by the + repeated bipartition of a single cell, and escape finally, forming + independent colonies. + + Another (sexual) form of reproduction occurs, similar to that found + in many higher plants; but as it only occurs at certain seasons, it + is not likely to be met with by the student. + +Other forms related to _Volvox_, and sometimes met with, are +_Gonium_, in which there are sixteen cells, forming a flat square; +_Pandorina_ and _Eudorina_, with sixteen cells, forming an oval or +globular colony like _Volvox_, but much smaller. In all of these the +structure of the cells is essentially as in _Volvox_. + + + + +CHAPTER IV. + +SUB-KINGDOM II. + +ALGÆ.[3] + + +[3] Algæ (sing. _alga_). + +In the second sub-kingdom of plants is embraced an enormous assemblage +of plants, differing widely in size and complexity, and yet showing a +sufficiently complete gradation from the lowest to the highest as to +make it impracticable to make more than one sub-kingdom to include +them. They are nearly all aquatic forms, although many of them will +survive long periods of drying, such forms occurring on moist earth, +rocks, or the trunks of trees, but only growing when there is a +plentiful supply of water. + +All of them possess chlorophyll, which, however, in many forms, is +hidden by the presence of a brown or red pigment. They are ordinarily +divided into three classes--I. The Green Algæ (_Chlorophyceæ_); +II. Brown Algæ (_Phæophyceæ_); III. Red Algæ (_Rhodophyceæ_). + + +CLASS I.--GREEN ALGÆ. + +The green algæ are to be found almost everywhere where there is +moisture, but are especially abundant in sluggish or stagnant fresh +water, being much less common in salt water. They are for the most +part plants of simple structure, many being unicellular, and very few +of them plants of large size. + +We may recognize five well-marked orders of the green algæ--I. Green +slimes (_Protococcaceæ_); II. _Confervaceæ_; III. Pond scums +(_Conjugatæ_); IV. _Siphoneæ_; V. Stone-worts (_Characeæ_). + + +ORDER I.--_Protococcaceæ_. + +The members of this order are minute unicellular plants, growing +either in water or on the damp surfaces of stones, tree trunks, etc. +The plants sometimes grow isolated, but usually the cells are united +more or less regularly into colonies. + +A common representative of the order is the common green slime, +_Protococcus_ (Fig. 11, _A_, _C_), which forms a dark green slimy +coating over stones, tree trunks, flower pots, etc. Owing to their +minute size the structure can only be made out with the microscope. + +[Illustration: FIG. 11.--_Protococcaceæ._ _A_, _C_, Protococcus. _A_, +single cells. _B_, cells dividing by fission. _C_, successive steps in +the process of internal cell division. In _C_ iv, the young cells have +mostly become free. _D_, a full-grown colony of _Pediastrum_. _E_, a +young colony still surrounded by the membrane of the mother cell. _F_, +_Scenedesmus_. All, × 300. _G_, small portion of a young colony of the +water net (_Hydrodictyon_), × 150.] + + Scraping off a little of the material mentioned into a drop of water + upon a slide, and carefully separating it with needles, a cover + glass may be placed over the preparation, and it is ready for + examination. When magnified, the green film is found to be composed + of minute globular cells of varying size, which may in places be + found to be united into groups. With a higher power, each cell + (Fig. 11, _A_) is seen to have a distinct cell wall, within which is + colorless protoplasm. Careful examination shows that the chlorophyll + is confined to several roundish bodies that are not usually in + immediate contact with the wall of the cell. These green masses are + called chlorophyll bodies (chloroplasts). Toward the centre of the + cell, especially if it has first been treated with iodine, the + nucleus may be found. The size of the cells, as well as the number + of chloroplasts, varies a good deal. + + With a little hunting, specimens in various stages of division may + be found. The division takes place in two ways. In the first + (Fig. 11, _B_), known as fission, a wall is formed across the cell, + dividing it into two cells, which may separate immediately or may + remain united until they have undergone further division. In this + case the original cell wall remains as part of the wall of the + daughter cells. Fission is the commonest form of cell multiplication + throughout the vegetable kingdom. + + The second form of cell division or internal cell division is shown + at _C_. Here the protoplasm and nucleus repeatedly divide until a + number of small cells are formed within the old one. These develop + cell walls, and escape by the breaking of the old cell wall, which + is left behind, and takes no part in the process. The cells thus + formed are sometimes provided with two cilia, and are capable of + active movement. + + Internal cell division, as we shall see, is found in most plants, + but only at special times. + + Closely resembling _Protococcus_, and answering quite as well for + study, are numerous aquatic forms, such as _Chlorococcum_ (Fig. 12). + These are for the most part destitute of a firm cell wall, but are + imbedded in masses of gelatinous substance like many _Cyanophyceæ_. + The chloroplasts are smaller and less distinct than in + _Protococcus_. The cells are here oval rather than round, and often + show a clear space at one end. + +[Illustration: FIG. 12.--_Chlorococcum_, a plant related to +_Protococcus_, but the naked cells are surrounded by a colorless +gelatinous envelope. _A_, motionless cells. _B_, a cell that has +escaped from its envelope and is ciliated, × 300.] + + Owing to the absence of a definite membrane, a distinction between + fission and internal cell division can scarcely be made here. Often + the cells escape from the gelatinous envelope, and swim actively by + means of two cilia at the colorless end (Fig. 12, _B_). In this + stage they closely resemble the individuals of a _Volvox_ colony, or + other green _Flagellata_, to which there is little doubt that they + are related. + + There are a number of curious forms common in fresh water that are + probably related to _Protococcus_, but differ in having the cells + united in colonies of definite form. Among the most striking are + the different species of _Pediastrum_ (Fig. 11, _D_, _E_), often met + with in company with other algæ, and growing readily in aquaria when + once established. They are of very elegant shapes, and the number of + cells some multiple of four, usually sixteen. + + The cells form a flat disc, the outer ones being generally provided + with a pair of spines. + + New individuals arise by internal division of the cells, the + contents of each forming as many parts as there are cells in the + whole colony. The young cells now escape through a cleft in the wall + of the mother cell, but are still surrounded by a delicate membrane + (Fig. 11, _E_). Within this membrane the young cells arrange + themselves in the form of the original colony, and grow together, + forming a new colony. + + A much larger but rarer form is the water net (Fig. 11, _G_), in + which the colony has the form of a hollow net, the spaces being + surrounded by long cylindrical cells placed end to end. Other common + forms belong to the genus _Scenedesmus_ (Fig. 11, _F_), of which + there are many species. + + +ORDER II.--_Confervaceæ_. + +Under this head are included a number of forms of which the simplest +ones approach closely, especially in their younger stages, the +_Protococcaceæ_. Indeed, some of the so-called _Protococcaceæ_ are +known to be only the early stages of these plants. + +A common member of this order is _Cladophora_, a coarse-branching +alga, growing commonly in running water, where it forms tufts, +sometimes a metre or more in length. By floating out a little of it in +a saucer, it is easy to see that it is made up of branching filaments. + + The microscope shows (Fig. 13, _A_) that these filaments are rows of + cylindrical cells with thick walls showing evident stratification. + At intervals branches are given off, which may in turn branch, + giving rise to a complicated branching system. These branches begin + as little protuberances of the cell wall at the top of the cell. + They increase rapidly in length, and becoming slightly contracted at + the base, a wall is formed across at this point, shutting it off + from the mother cell. + + The protoplasm lines the wall of the cell, and extends in the form + of thin plates across the cavity of the cell, dividing it up into a + number of irregular chambers. Imbedded in the protoplasm are + numerous flattened chloroplasts, which are so close together as to + make the protoplasm appear almost uniformly green. Within the + chloroplasts are globular, glistening bodies, called "pyrenoids." + The cell has several nuclei, but they are scarcely evident in the + living cell. By placing the cells for a few hours in a one per cent + watery solution of chromic acid, then washing thoroughly and + staining with borax carmine, the nuclei will be made very evident + (Fig. 13, _B_). Such preparations may be kept permanently in dilute + glycerine. + +[Illustration: FIG. 13.--_Cladophora._ _A_, a fragment of a plant, +× 50. _B_, a single cell treated with chromic acid, and stained with +alum cochineal. _n_, nucleus. _py._ pyrenoid, × 150. _C_, three stages +in the division of a cell. i, 1.45 p.m.; ii, 2.55 p.m.; iii, +4.15 p.m., × 150. _D_, a zoöspore × 350.] + + If a mass of actively growing filaments is examined, some of the + cells will probably be found in process of fission. The process is + very simple, and may be easily followed (Fig. 13, _C_). A ridge of + cellulose is formed around the cell wall, projecting inward, and + pushing in the protoplasm as it grows. The process is continued + until the ring closes in the middle, cutting the protoplasmic body + completely in two, and forms a firm membrane across the middle of + the cell. The protoplasm at this stage (_C_ iii.) is somewhat + contracted, but soon becomes closely applied to the new wall. The + whole process lasts, at ordinary temperatures (20°-25° C.), from + three to four hours. + + At certain times, but unfortunately not often to be met with, the + contents of some of the cells form, by internal division, a large + number of small, naked cells (zoöspores) (Fig. 13, _D_), which + escape and swim about actively for a time, and afterwards become + invested with a cell wall, and grow into a new filament. These cells + are called zoöspores, from their animal-like movements. They are + provided with two cilia, closely resembling the motile cells of the + _Protococcaceæ_ and _Volvocineæ_. + +There are very many examples of these simple _Confervaceæ_, some like +_Conferva_ being simple rows of cells, others like _Stigeoclonium_ +(Fig. 14, _A_), _Chætophora_ and _Draparnaldia_ (Fig. 14, _B_, _C_), +very much branched. The two latter forms are surrounded by masses of +transparent jelly, which sometimes reach a length of several +centimetres. + +[Illustration: FIG. 14.--_Confervaceæ_. _A_, _Stigeoclonium_. _B_, +_Draparnaldia_, × 50. _C_, a piece of _Draparnaldia_, × 2. _D_, part +of a filament of _Conferva_, × 300.] + +Among the marine forms related to these may be mentioned the sea +lettuce (_Ulva_), shown in Figure 15. The thin, bright-green, +leaf-like fronds of this plant are familiar to every seaside student. + +[Illustration: FIG. 15.--A plant of sea lettuce (_Ulva_). One-half +natural size.] + +Somewhat higher than _Cladophora_ and its allies, especially in the +differentiation of the reproductive parts, are the various species of +_OEdogonium_ and its relatives. There are numerous species of +_OEdogonium_ not uncommon in stagnant water growing in company with +other algæ, but seldom forming masses by themselves of sufficient size +to be recognizable to the naked eye. + + The plant is in structure much like _Cladophora_, except that it is + unbranched, and the cells have but a single nucleus (Fig. 16, _E_). + Even when not fruiting the filaments may usually be recognized by + peculiar cap-shaped structures at the top of some of the cells. + These arise as the result of certain peculiarities in the process of + cell division, which are too complicated to be explained here. + + There are two forms of reproduction, non-sexual and sexual. In the + first the contents of certain cells escape in the form of large + zoöspores (Fig. 16, _C_), of oval form, having the smaller end + colorless and surrounded by a crown of cilia. After a short period + of active motion, the zoöspore comes to rest, secretes a cell wall + about itself, and the transparent end becomes flattened out into a + disc (_E_, _d_), by which it fastens itself to some object in the + water. The upper part now rapidly elongates, and dividing repeatedly + by cross walls, develops into a filament like the original one. In + many species special zoöspores are formed, smaller than the ordinary + ones, that attach themselves to the filaments bearing the female + reproductive organ (oögonium), and grow into small plants bearing + the male organ (antheridium), (Fig. 16, _B_). + +[Illustration: FIG. 16.--_A_, portion of a filament of _OEdogonium_, +with two oögonia (_og._). The lower one shows the opening. _B_, a +similar filament, to which is attached a small male plant with an +antheridium (_an._). _C_, a zoöspore of _OEdogonium_. _D_, a similar +spore germinating. _E_, base of a filament showing the disc (_d_) by +which it is attached. _F_, another species of _OEdogonium_ with a ripe +spore (_sp._). _G_, part of a plant of _Bulbochæte_. _C_, _D_, × 300; +the others × 150.] + + The sexual reproduction takes place as follows: Certain cells of a + filament become distinguished by their denser contents and by an + increase in size, becoming oval or nearly globular in form (Fig. 16, + _A_, _B_). When fully grown, the contents contract and form a naked + cell, which sometimes shows a clear area at one point on the + surface. This globular mass of protoplasm is the egg cell, or female + cell, and the cell containing it is called the "oögonium." When the + egg cell is ripe, the oögonium opens by means of a little pore at + one side (Fig. 16, _A_). + + In other cells, either of the same filament or else of the small + male plants already mentioned, small motile cells, called + spermatozoids, are formed. These are much smaller than the egg cell, + and resemble the zoöspores in form, but are much smaller, and + without chlorophyll. When ripe they are discharged from the cells in + which they were formed, and enter the oögonium. By careful + observation the student may possibly be able to follow the + spermatozoid into the oögonium, where it enters the egg cell at the + clear spot on its surface. As a result of the entrance of the + spermatozoid (fertilization), the egg cell becomes surrounded by a + thick brown wall, and becomes a resting spore. The spore loses its + green color, and the wall becomes dark colored and differentiated + into several layers, the outer one often provided with spines + (Fig. 16, _F_). As these spores do not germinate for a long time, + the process is only known in a comparatively small number of + species, and can hardly be followed by the ordinary student. + +[Illustration: FIG. 17.--_A_, plant of _Coleochæte_, × 50. _B_, a few +cells from the margin, with one of the hairs.] + +Much like _OEdogonium_, but differing in being branched, is the genus +_Bulbochæte_, characterized also by hairs swollen at the base, and +prolonged into a delicate filament (Fig. 16, _G_). + +The highest members of the _Confervaceæ_ are those of the genus +_Coleochæte_ (Fig. 17), of which there are several species found in +the United States. These show some striking resemblances to the red +seaweeds, and possibly form a transition from the green algæ to the +red. The commonest species form bright-green discs, adhering firmly +to the stems and floating leaves of water lilies and other aquatics. +In aquaria they sometimes attach themselves in large numbers to the +glass sides of the vessel. + + Growing from the upper surface are numerous hairs, consisting of a + short, sheath-like base, including a very long and delicate filament + (Fig. 17, _B_). In their methods of reproduction they resemble + _OEdogonium_, but the reproductive organs are more specialized. + + + + +CHAPTER V. + +GREEN ALGÆ--_Continued_. + + +ORDER III.--POND SCUMS (_Conjugatæ_). + +The _Conjugatæ_, while in some respects approaching the _Confervaceæ_ +in structure, yet differ from them to such an extent in some respects +that their close relationship is doubtful. They are very common and +familiar plants, some of them forming great floating masses upon the +surface of every stagnant pond and ditch, being commonly known as +"pond scum." The commonest of these pond scums belong to the genus +_Spirogyra_, and one of these will illustrate the characteristics of +the order. When in active growth these masses are of a vivid green, +and owing to the presence of a gelatinous coating feel slimy, slipping +through the hands when one attempts to lift them from the water. +Spread out in water, the masses are seen to be composed of slender +threads, often many centimetres in length, and showing no sign of +branching. + +[Illustration: FIG. 18.--_A_, a filament of a common pond scum +(_Spirogyra_) separating into two parts. _B_, a cell undergoing +division. The cell is seen in optical section, and the chlorophyll +bands are omitted, _n_, _n'_, the two nuclei. _C_, a complete cell. +_n_, nucleus. _py._ pyrenoid. _D_, _E_, successive stages in the +process of conjugation. _G_, a ripe spore. _H_, a form in which +conjugation takes place between the cells of the same filament. All +× 150.] + + For microscopical examination the larger species are preferable. + When one of these is magnified (Fig. 18, _A_, _C_), the unbranched + filament is shown to be made up of perfectly cylindrical cells, with + rather delicate walls. The protoplasm is confined to a thin layer + lining the walls, except for numerous fine filaments that radiate + from the centrally placed nucleus (_n_), which thus appears + suspended in the middle of the cell. The nucleus is large and + distinct in the larger species, and has a noticeably large and + conspicuous nucleolus. The most noticeable thing about the cell is + the green spiral bands running around it. These are the + chloroplasts, which in all the _Conjugatæ_ are of very peculiar + forms. The number of these bands varies much in different species of + _Spirogyra_, but is commonly two or three. These chloroplasts, like + those of other plants, are not noticeably different in structure + from the ordinary protoplasm, as is shown by extracting the + chlorophyll, which may be done by placing the plants in alcohol for + a short time. This extracts the chlorophyll, but a microscopic + examination of the decolored cells shows that the bands remain + unchanged, except for the absence of color. These bands are + flattened, with irregularly scalloped margins, and at intervals have + rounded bodies (pyrenoids) imbedded in them (Fig. 18, _C_, _py._). + The pyrenoids, especially when the plant has been exposed to the + light for some time, are surrounded by a circle of small granules, + which become bluish when iodine is applied, showing them to be + starch. (To show the effect of iodine on starch on a large scale, + mix a little flour, which is nearly all starch, with water, and add + a little iodine. The starch will immediately become colored blue, + varying in intensity with the amount of iodine.) The cells divide + much as in _Cladophora_, but the nucleus here takes part in the + process. The division naturally occurs only at night, but by + reducing the temperature at night to near the freezing point (4° C., + or a little lower), the process may be checked. The experiment is + most conveniently made when the temperature out of doors approaches + the freezing point. Then it is only necessary to keep the plants in + a warm room until about 10 P.M., when they may be put out of doors + for the night. On bringing them in in the morning, the division will + begin almost at once, and may be easily studied. The nucleus divides + into two parts, which remain for a time connected by delicate + threads (Fig. 18, _B_), that finally disappear. At first no nucleoli + are present in the daughter nuclei, but they appear before the + division is complete. + + New filaments are formed by the breaking up of the old ones, this + sometimes being very rapid. As the cells break apart, the free ends + bulge strongly, showing the pressure exerted upon the cell wall by + the contents (Fig. 18, _A_). + +Spores like those of _OEdogonium_ are formed, but the process is +somewhat different. It occurs in most species late in the spring, but +may sometimes be met with at other times. The masses of fruiting +plants usually appear brownish colored. If spores have been formed +they can, in the larger species at least, be seen with a hand lens, +appearing as rows of dark-colored specks. + + Two filaments lying side by side send out protuberances of the cell + wall that grow toward each other until they touch (Fig. 18, _D_). At + the point of contact, the wall is absorbed, forming a continuous + channel from one cell to the other. This process usually takes place + in all the cells of the two filaments, so that the two filaments, + connected by tubes at regular intervals, have the form of a ladder. + + In some species adjoining cells of the same filament become + connected, the tubes being formed at the end of the cells (Fig. 18, + _H_), and the cell in which the spore is formed enlarges. + + Soon after the channel is completed, the contents of one cell flow + slowly through it into the neighboring cell, and the protoplasm of + the two fuses into one mass. (The union of the nuclei has also been + observed.) The young spore thus formed contracts somewhat, becoming + oval in form, and soon secretes a thick wall, colorless at first, + but afterwards becoming brown and more or less opaque. The + chlorophyll bands, although much crowded, are at first + distinguishable, but later lose the chlorophyll, and become + unrecognizable. Like the resting spores of _OEdogonium_ these require + a long period of rest before germinating. + +[Illustration: FIG. 19.--Forms of _Zygnemaceæ_. _A_, _Zygnema_. _B_, +_C_, _D_, _Mesocarpus_. All × 150.] + +There are various genera of the pond scums, differing in the form of +the chloroplasts and also in the position of the spores. Of these may +be mentioned _Zygnema_ (Fig. 19, _A_), with two star-shaped +chloroplasts in each cell, and _Mesocarpus_ (Fig. 19, _B_, _D_), in +which the single chloroplast has the form of a thin median plate. (B +shows the appearance from in front, _C_ from the side, showing the +thickness of the plate.) _Mesocarpus_ and the allied genera have the +spore formed between the filaments, the contents of both the uniting +cells leaving them. + +[Illustration: FIG. 20.--Forms of Desmids. _A_, _B_, _Closterium_. +_C_, _D_, _D'_, _Cosmarium_. _D_, and _D'_ show the process of +division. _E_, _F_, _Staurastrum_; _E_ seen from the side, _F_ from +the end.] + +Evidently related to the pond scums, but differing in being for the +most part strictly unicellular, are the desmids (Fig. 20). They are +confined to fresh water, and seldom occur in masses of sufficient size +to be seen with the naked eye, usually being found associated with +pond scums or other filamentous forms. Many of the most beautiful +forms may be obtained by examining the matter adhering to the leaves +and stems of many floating water plants, especially the bladder weed +(_Utricularia_) and other fine-leaved aquatics. + + The desmids include the most beautiful examples of unicellular + plants to be met with, the cells having extremely elegant outlines. + The cell shows a division into two parts, and is often constricted + in the middle, each division having a single large chloroplast of + peculiar form. The central part of the cell in which the nucleus + lies is colorless. + + Among the commonest forms, often growing with _Spirogyra_, are + various species of _Closterium_ (Fig. 20, _A_, _B_), recognizable at + once by their crescent shape. The cell appears bright green, except + at the ends and in the middle. The large chloroplast in each half is + composed of six longitudinal plates, united at the axis of the cell. + Several large pyrenoids are always found, often forming a regular + line through the central axis. At each end of the cell is a vacuole + containing small granules that show an active dancing movement. + +The desmids often have the power of movement, swimming or creeping +slowly over the slide as we examine them, but the mechanism of these +movements is still doubtful. + +In their reproduction they closely resemble the pond scums. + + +ORDER IV.--_Siphoneæ_. + +The _Siphoneæ_ are algæ occurring both in fresh and salt water, and +are distinguished from other algæ by having the form of a tube, +undivided by partition walls, except when reproduction occurs. The +only common representatives of the order in fresh water are those +belonging to the genus _Vaucheria_, but these are to be had almost +everywhere. They usually occur in shallow ditches and ponds, growing +on the bottom, or not infrequently becoming free, and floating where +the water is deeper. They form large, dark green, felted masses, and +are sometimes known as "green felts." Some species grow also on the +wet ground about springs. An examination of one of the masses shows it +to be made up of closely matted, hair-like threads, each of which is +an individual plant. + + In transferring the plants to the slide for microscopic examination, + they must be handled very carefully, as they are very easily + injured. Each thread is a long tube, branching sometimes, but not + divided into cells as in _Spirogyra_ or _Cladophora_. If we follow + it to the tip, the contents here will be found to be denser, this + being the growing point. By careful focusing it is easy to show that + the protoplasm is confined to a thin layer lining the wall, the + central cavity of the tube being filled with cell sap. In the + protoplasm are numerous elongated chloroplasts (_cl._). and a larger + or smaller number of small, shining, globular bodies (_ol._). These + latter are drops of oil, and, when the filaments are injured, + sometimes run together, and form drops of large size. No nucleus can + be seen in the living plant, but by treatment with chromic acid and + staining, numerous very small nuclei may be demonstrated. + +[Illustration: FIG. 21.--_A_, _C_, successive stages in the +development of the sexual organs of a green felt (_Vaucheria_). _an._ +antheridium. _og._ oögonium. _D_, a ripe oögonium. _E_, the same after +it has opened. _o_, the egg cell. _F_, a ripe spore. _G_, a species in +which the sexual organs are borne separately on the main filament. +_A_, _F_, × 150. _G_, × 50. _cl._ chloroplasts. _ol._ oil.] + + When the filaments are growing upon the ground, or at the bottom of + shallow water, the lower end is colorless, and forms a more or less + branching root-like structure, fastening it to the earth. These + rootlets, like the rest of the filament, are undivided by walls. + + One of the commonest and at the same time most characteristic + species is _Vaucheria racemosa_ (Fig. 21, _A_, _F_). The plant + multiplies non-sexually by branches pinched off by a constriction at + the point where they join the main filament, or by the filament + itself becoming constricted and separating into several parts, each + one constituting a new individual. + + The sexual organs are formed on special branches, and their + arrangement is such as to make the species instantly recognizable. + + The first sign of their development is the formation of a short + branch (Fig. 21, _A_) growing out at right angles to the main + filament. This branch becomes club-shaped, and the end somewhat + pointed and more slender, and curves over. This slender, curved + portion is almost colorless, and is soon shut off from the rest of + the branch. It is called an "antheridium," and within are produced, + by internal division, numerous excessively small spermatozoids. + + As the branch grows, its contents become very dense, the oil drops + especially increasing in number and size. About the time that the + antheridium becomes shut off, a circle of buds appears about its + base (Fig. 21, _B_, _og._). These are the young oögonia, which + rapidly increase in size, assuming an oval form, and become + separated by walls from the main branch (_C_). Unlike the + antheridium, the oögonia contain a great deal of chlorophyll, + appearing deep green. + + When ripe, the antheridium opens at the end and discharges the + spermatozoids, which are, however, so very small as scarcely to be + visible except with the strongest lenses. They are little oval + bodies with two cilia, which may sometimes be rendered visible by + staining with iodine. + +[Illustration: FIG. 22.--_A_, non-sexual reproduction in _Vaucheria +sessilis_. _B_, non-sexual spore of _V. geminata_, × 50.] + + The oögonia, which at first are uniformly colored, just before + maturity show a colorless space at the top, from which the + chloroplasts and oil drops have disappeared (_D_), and at the same + time this portion pushes out in the form of a short beak. Soon after + the wall is absorbed at this point, and a portion of the contents is + forced out, leaving an opening, and at the same time the remaining + contents contract to form a round mass, the germ or egg cell + (Fig. 21, _E_, _o_). Almost as soon as the oögonium opens, the + spermatozoids collect about it and enter; but, on account of their + minuteness, it is almost impossible to follow them into the egg + cell, or to determine whether several or only one enter. The + fertilized egg cell becomes almost at once surrounded by a wall, + which rapidly thickens, and forms a resting spore. As the spore + ripens, it loses its green color, becoming colorless, with a few + reddish brown specks scattered through it (_F_). + + In some species the sexual organs are borne directly on the filament + (Fig. 21, _G_). + + Large zoöspores are formed in some of the green felts (Fig. 22, + _A_), and are produced singly in the ends of branches that become + swollen, dark green, and filled with very dense protoplasm. This end + becomes separated by a wall from the rest of the branch, the end + opens, and the contents escape as a very large zoöspore, covered + with numerous short cilia (_A_ ii). After a short period of + activity, this loses its cilia, develops a wall, and begins to grow + (III, IV). Other species (_B_) produce similar spores, which, + however, are not motile, and remain within the mother cell until + they are set free by the decay of its wall. + + +ORDER V.--_Characeæ_. + +The _Characeæ_, or stone-worts, as some of them are called, are so +very different from the other green algæ that it is highly probable +that they should be separated from them. + +The type of the order is the genus _Chara_ (Fig. 23), called +stone-worts from the coating of carbonate of lime found in most of +them, giving them a harsh, stony texture. Several species are common +growing upon the bottom of ponds and slow streams, and range in size +from a few centimetres to a metre or more in height. + +The plant (Fig. 23, _A_) consists of a central jointed axis with +circles of leaves at each joint or node. The distance between the +nodes (internodes) may in the larger species reach a length of several +centimetres. The leaves are slender, cylindrical structures, and like +the stem divided into nodes and internodes, and have at the nodes +delicate leaflets. + +At each joint of the leaf, in fruiting specimens, attached to the +inner side, are borne two small, roundish bodies, in the commoner +species of a reddish color (Fig. 23, _A_, _r_). The lower of the two +is globular, and bright scarlet in color; the other, more oval and +duller. + +Examined with a lens the main axis presents a striated appearance. The +whole plant is harsh to the touch and brittle, owing to the limy +coating. It is fastened to the ground by fine, colorless hairs, or +rootlets. + +[Illustration: FIG. 23.--_A_, plant of a stone-wort (_Chara_), +one-half natural size. _r_, reproductive organs. _B_, longitudinal +section through the apex. _S_, apical cell. _x_, nodes. _y_, +internodes. _C_, a young leaf. _D_, cross section of an internode. +_E_, of a node of a somewhat older leaf. _F_, _G_, young sexual organs +seen in optical section. _o_, oögonium. _An._ antheridium. _H_, +superficial view. _G_, _I_, group of filaments containing +spermatozoids. _J_, a small portion of one of these more magnified, +showing a spermatozoid in each cell. _K_, free spermatozoids. _L_, a +piece of a leaf with ripe oögonium (_o_), and antheridium (_An._). +_B_, _H_, × 150. _J_, _K_, × 300. _I_, × 50. _L_, × 25.] + + By making a series of longitudinal sections with a sharp razor + through the top of the plant, and magnifying sufficiently, it is + found to end in a single, nearly hemispherical cell (Fig. 23, _B_, + _S_). This from its position is called the "apical cell," and from + it are derived all the tissues of the plant. Segments are cut off + from its base, and these divide again into two by a wall parallel to + the first. Of the two cells thus formed one undergoes no further + division and forms the central cell of an internode (_y_); the other + divides repeatedly, forming a node or joint (_x_). + + As the arrangement of these cells is essentially the same in the + leaves and stem, we will examine it in the former, as by cutting + several cross-sections of the whole bunch of young leaves near the + top of the plant, we shall pretty certainly get some sections + through a joint. The arrangement is shown in Figure 23, _E_. + + As the stem grows, a covering is formed over the large internodal + cell (_y_) by the growth of cells from the nodes. These grow both + from above and below, meeting in the middle of the internode and + completely hiding the long axial cell. A section across the + internode shows the large axial cell (_y_) surrounded by the + regularly arranged cells of the covering or cortex (Fig. 23, _D_). + + All the cells contain a layer of protoplasm next the wall with + numerous oval chloroplasts. If the cells are uninjured, they often + show a very marked movement of the protoplasm. These movements are + best seen, however, in forms like _Nitella_, where the long + internodal cells are not covered with a cortex. In _Chara_ they are + most evident in the root hairs that fasten the plant to the ground. + + The growth of the leaves is almost identical with that of the stem, + but the apical growth is limited, and the apical cell becomes + finally very long and pointed (Fig. 23, _C_). In some species the + chloroplasts are reddish in the young cells, assuming their green + color as the cells approach maturity. + +The plant multiplies non-sexually by means of special branches that +may become detached, but there are no non-sexual spores formed. + + The sexual organs have already been noticed arising in pairs at the + joints of the leaves. The oögonium is formed above, the antheridium + below. + + The young oögonium (_F_, _O_) consists of a central cell, below + which is a smaller one surrounded by a circle of five others, which + do not at first project above the central cell, but later completely + envelop it (_G_). Each of these five cells early becomes divided + into an upper and a lower one, the latter becoming twisted as it + elongates, and the central cell later has a small cell cut off from + its base by an oblique wall. The central cell forms the egg cell, + which in the ripe oögonium (_L_, _O_) is surrounded by five, + spirally twisted cells, and crowned by a circle of five smaller + ones, which become of a yellowish color when full grown. They + separate at the time of fertilization to allow the spermatozoids to + enter the oögonium. + + The antheridium consists at first of a basal cell and a terminal + one. The latter, which is nearly globular, divides into eight nearly + similar cells by walls passing through the centre. In each of these + eight cells two walls are next formed parallel to the outer surface, + so that the antheridium (apart from the basal cell) contains + twenty-four cells arranged in three concentric series (_G_, _an._). + These cells, especially the outer ones, develop a great amount of a + red pigment, giving the antheridium its characteristic color. + + The diameter of the antheridium now increases rapidly, and the + central cells separate, leaving a large space within. Of the inner + cells, the second series, while not increasing in diameter, + elongate, assuming an oblong form, and from the innermost are + developed long filaments (_I_, _J_) composed of a single row of + cells, in each of which is formed a spermatozoid. + + The eight outer cells are nearly triangular in outline, fitting + together by deeply indented margins, and having the oblong cells + with the attached filaments upon their inner faces. + + If a ripe antheridium is crushed in a drop of water, after lying a + few minutes the spermatozoids will escape through small openings in + the side of the cells. They are much larger than any we have met + with. Each is a colorless, spiral thread with about three coils, one + end being somewhat dilated with a few granules; the other more + pointed, and bearing two extremely long and delicate cilia (_K_). To + see the cilia it is necessary to kill the spermatozoids with iodine + or some other reagent. + + After fertilization the outer cells of the oögonium become very + hard, and the whole falls off, germinating after a sufficient period + of rest. + +According to the accounts of Pringsheim and others, the young plant +consists at first of a row of elongated cells, upon which a bud is +formed that develops into the perfect plant. + +There are two families of the _Characeæ_, the _Chareæ_, of which +_Chara_ is the type, and the _Nitelleæ_, represented by various +species of _Nitella_ and _Tolypella_. The second family have the +internodes without any cortex--that is, consisting of a single long +cell; and the crown at the top of the oögonium is composed of ten +cells instead of five. They are also destitute of the limy coating of +the _Chareæ_. + +Both as regards the structure of the plant itself, as well as the +reproductive organs, especially the very complex antheridium, the +_Characeæ_ are very widely separated from any other group of plants, +either above or below them. + + + + +CHAPTER VI. + +THE BROWN ALGÆ (_Phæophyceæ_). + + +[Illustration: FIG. 24.--Forms of diatoms. _A_, _Pinnularia_. i, seen +from above; ii, from the side. _B_, _Fragillaria_ (?). _C_, +_Navicula_. _D_, _F_, _Eunotia_. _E_, _Gomphonema_. _G_, _Cocconeis_. +_H_, _Diatoma_. All × 300.] + +These plants are all characterized by the presence of a brown pigment, +in addition to the chlorophyll, which almost entirely conceals the +latter, giving the plants a brownish color, ranging from a light +yellowish brown to nearly black. One order of plants that possibly +belongs here (_Diatomaceæ_) are single celled, but the others are for +the most part large seaweeds. The diatoms, which are placed in this +class simply on account of the color, are probably not closely related +to the other brown algæ, but just where they should be placed is +difficult to say. In some respects they approach quite closely the +desmids, and are not infrequently regarded as related to them. They +are among the commonest of organisms occurring everywhere in stagnant +and running water, both fresh and salt, forming usually, slimy, +yellowish coatings on stones, mud, aquatic plants, etc. Like the +desmids they may be single or united into filaments, and not +infrequently are attached by means of a delicate gelatinous stalk +(Fig. 25). + +[Illustration: FIG. 25.--Diatoms attached by a gelatinous stalk. +× 150] + + They are at once distinguished from the desmids by their color, + which is always some shade of yellowish or reddish brown. The + commonest forms, _e.g._ _Navicula_ (Fig. 24, _C_), are boat-shaped + when seen from above, but there is great variety in this respect. + The cell wall is always impregnated with large amounts of flint, so + that after the cell dies its shape is perfectly preserved, the flint + making a perfect cast of it, looking like glass. These flinty shells + exhibit wonderfully beautiful and delicate markings which are + sometimes so fine as to test the best lenses to make them out. + + This shell is composed of two parts, one shutting over the other + like a pill box and its cover. This arrangement is best seen in such + large forms as _Pinnularia_ (Fig. 24, _A_ ii). + +Most of the diatoms show movements, swimming slowly or gliding over +solid substances; but like the movements of _Oscillaria_ and the +desmids, the movements are not satisfactorily understood, although +several explanations have been offered. + +They resemble somewhat the desmids in their reproduction. + + +THE TRUE BROWN ALGÆ. + +These are all marine forms, many of great size, reaching a length in +some cases of a hundred metres or more, and showing a good deal of +differentiation in their tissues and organs. + +[Illustration: FIG. 26.--_A_, a branch of common rock weed (_Fucus_), +one-half natural size. _x_, end of a branch bearing conceptacles. _B_, +section through a conceptacle containing oögonia (_og._), × 25. _C_, +_E_, successive stages in the development of the oögonium, × 150. _F_, +_G_, antheridia. In _G_, one of the antheridia has discharged the mass +of spermatozoids (_an._), × 150.] + +One of the commonest forms is the ordinary rock weed (_Fucus_), which +covers the rocks of our northeastern coast with a heavy drapery for +several feet above low-water mark, so that the plants are completely +exposed as the tide recedes. The commonest species, _F. vesiculosus_ +(Fig. 26, _A_), is distinguished by the air sacs with which the stems +are provided. The plant is attached to the rock by means of a sort of +disc or root from which springs a stem of tough, leathery texture, and +forking regularly at intervals, so that the ultimate branches are very +numerous, and the plant may reach a length of a metre or more. The +branches are flattened and leaf-like, the centre traversed by a +thickened midrib. The end of the growing branches is occupied by a +transversely elongated pit or depression. The growing point is at the +bottom of this pit, and by a regular forking of the growing point the +symmetrical branching of the plant is brought about. Scattered over +the surface are little circular pits through whose openings protrude +bunches of fine hairs. When wet the plant is flexible and leathery, +but it may become quite dry and hard without suffering, as may be seen +when the plants are exposed to the sun at low tide. + +The air bladders are placed in pairs, for the most part, and buoy up +the plant, bringing it up to the surface when covered with water. + +The interior of the plant is very soft and gelatinous, while the outer +part forms a sort of tough rind of much firmer consistence. The ends +of some of the branches (Fig. 26, _A_, _x_) are usually much swollen, +and the surface covered with little elevations from which may often be +seen protruding clusters of hairs like those arising from the other +parts of the plant. A section through one of these enlarged ends shows +that each elevation corresponds to a cavity situated below it. On some +of the plants these cavities are filled with an orange-yellow mass; in +others there are a number of roundish olive-brown bodies large enough +to be easily seen. The yellow masses are masses of antheridia; the +round bodies, the oögonia. + +If the plants are gathered while wet, and packed so as to prevent +evaporation of the water, they will keep perfectly for several days, +and may readily be shipped for long distances. If they are to be +studied away from the seashore, sections for microscopic examination +should be mounted in salt water (about 3 parts in weight of common +salt to 100 of water). If fresh material is not to be had, dried +specimens or alcoholic material will answer pretty well. + + To study the minute structure of the plant, make a thin + cross-section, and mount in salt water. The inner part or pith is + composed of loosely arranged, elongated cells, placed end to end, + and forming an irregular network, the large spaces between filled + with the mucilaginous substance derived from the altered outer walls + of these cells. This mucilage is hard when dry, but swells up + enormously in water, especially fresh water. The cells grow smaller + and more compact toward the outside of the section, until there are + no spaces of any size between those of the outside or rind. The + cells contain small chloroplasts like those of the higher plants, + but owing to the presence of the brown pigment found in all of the + class, in addition to the chlorophyll, they appear golden brown + instead of green. + + No non-sexual reproductive bodies are known in the rock weeds, + beyond small branches that occur in clusters on the margins of the + main branches, and probably become detached, forming new plants. In + some of the lower forms, however, _e.g._ _Ectocarpus_ and + _Laminaria_ (Fig. 28, _A_, _C_), zoöspores are formed. + + The sexual organs of the rock weed, as we have already seen, are + borne in special cavities (conceptacles) in the enlarged ends of + some of the branches. In the species here figured, _F. vesiculosus_, + the antheridia and oögonia are borne on separate plants; but in + others, _e.g._ _F. platycarpus_, they are both in the same + conceptacle. + + The walls of the conceptacle (Fig. 26, _B_) are composed of closely + interwoven filaments, from which grow inward numerous hairs, filling + up the space within, and often extending out through the opening at + the top. + + The reproductive bodies arise from the base of these hairs. The + oögonia (Fig. 26, _C_, _E_) arise as nearly colorless cells, that + early become divided into two cells, a short basal cell or stalk and + a larger terminal one, the oögonium proper. The latter enlarges + rapidly, and its contents divide into eight parts. The division is + at first indicated by a division of the central portion, which + includes the nucleus, and is colored brown, into two, four, and + finally eight parts, after which walls are formed between these. The + brown color spreads until the whole oögonium is of a nearly uniform + olive-brown tint. + + When ripe, the upper part of the oögonium dissolves, allowing the + eight cells, still enclosed in a delicate membrane, to escape + (Fig. 27, _H_). Finally, the walls separating the inner cells of the + oögonium become also absorbed, as well as the surrounding membrane, + and the eight egg cells escape into the water (Fig. 27, _I_) as + naked balls of protoplasm, in which a central nucleus may be dimly + seen. + + The antheridia (Fig. 26, _F_, _G_) are small oblong cells, at first + colorless, but when ripe containing numerous glistening, reddish + brown dots, each of which is part of a spermatozoid. When ripe, the + contents of the antheridium are forced out into the water (_G_), + leaving the empty outer wall behind, but still surrounded by a thin + membrane. After a few minutes this membrane is dissolved, and the + spermatozoids are set free. These (Fig. 27, _K_) are oval in form, + with two long cilia attached to the side where the brown speck, seen + while still within the antheridium, is conspicuous. + + The act of fertilization may be easily observed by laying fresh + antheridia into a drop of water containing recently discharged egg + cells. To obtain these, all that is necessary is to allow freshly + gathered plants to remain in the air until they are somewhat dry, + when the ripe sexual cells will be discharged from the openings of + the conceptacles, exuding as little drops, those with antheridia + being orange-yellow; the masses of oögonia, olive. Within a few + minutes after putting the oögonia into water, the egg cells may be + seen to escape into the water, when some of the antheridia may be + added. The spermatozoids will be quickly discharged, and collect + immediately in great numbers about the egg cells, to which they + apply themselves closely, often setting them in rotation by the + movements of their cilia, and presenting a most extraordinary + spectacle (_J_). Owing to the small size of the spermatozoids, and + the opacity of the eggs, it is impossible to see whether more than + one spermatozoid penetrates it; but from what is known in other + cases it is not likely. The egg now secretes a wall about itself, + and within a short time begins to grow. It becomes pear-shaped, the + narrow portion becoming attached to the parent plant or to some + other object by means of rootlets, and the upper part grows into the + body of the young plant (Fig. 27, _M_). + +[Illustration: FIG. 27.--_H_, the eight egg cells still surrounded by +the inner membrane of the oögonium. _I_, the egg cells escaping into +the water. _J_, a single egg cell surrounded by spermatozoids. _K_, +mass of spermatozoids surrounded by the inner membrane of the +antheridium. _L_, spermatozoids. _M_, young plant. _r_, the roots. +_K_, × 300; _L_, × 600; the others, × 150.] + +The simpler brown seaweeds, so far as known, multiply only by means of +zoöspores, which may grow directly into new plants, or, as has been +observed in some species, two zoöspores will first unite. A few, like +_Ectocarpus_ (Fig. 28, _A_), are simple, branched filaments, but most +are large plants with complex tissues. Of the latter, a familiar +example is the common kelp, "devil's apron" (_Laminaria_), often three +to four metres in length, with a stout stalk, provided with root-like +organs, by which it is firmly fastened. Above, it expands into a +broad, leaf-like frond, which in some species is divided into strips. +Related to the kelps is the giant kelp of the Pacific (_Macrocystis_), +which is said sometimes to reach a length of three hundred metres. + +[Illustration: FIG. 28.--Forms of brown seaweeds. _A_, _Ectocarpus_, +× 50. Sporangia (_sp._). _B_, a single sporangium, × 150. _C_, kelp +(_Laminaria_), × 1/8. _D_, _E_, gulf weed (_Sargassum_). _D_, one-half +natural size. _E_, natural size. _v_, air bladders. _x_, conceptacle +bearing branches.] + +The highest of the class are the gulf weeds (_Sargassum_), plants of +the warmer seas, but one species of which is found from Cape Cod +southward (Fig. 28, _D_, _E_). These plants possess distinct stems and +leaves, and there are stalked air bladders, looking like berries, +giving the plant a striking resemblance to the higher land plants. + + + + +CHAPTER VII. + +CLASS III.--THE RED ALGÆ (_Rhodophyceæ_). + + +These are among the most beautiful and interesting members of the +plant kingdom, both on account of their beautiful colors and the +exquisitely graceful forms exhibited by many of them. Unfortunately +for inland students they are, with few exceptions, confined to salt +water, and consequently fresh material is not available. Nevertheless, +enough can be done with dried material to get a good idea of their +general appearance, and the fruiting plants can be readily preserved +in strong alcohol. Specimens, simply dried, may be kept for an +indefinite period, and on being placed in water will assume perfectly +the appearance of the living plants. Prolonged exposure, however, to +the action of fresh water extracts the red pigment that gives them +their characteristic color. This pigment is found in the chlorophyll +bodies, and usually quite conceals the chlorophyll, which, however, +becomes evident so soon as the red pigment is removed. + +The red seaweeds differ much in the complexity of the plant body, but +all agree in the presence of the red pigment, and, at least in the +main, in their reproduction. The simpler ones consist of rows of +cells, usually branching like _Cladophora_; others form cell plates +comparable to _Ulva_ (Fig. 30, _C_, _D_); while others, among which is +the well-known Irish moss (_Chondrus_), form plants of considerable +size, with pretty well differentiated tissues. In such forms the outer +cells are smaller and firmer, constituting a sort of rind; while the +inner portions are made up of larger and looser cells, and may be +called the pith. Between these extremes are all intermediate forms. + +They usually grow attached to rocks, shells, wood, or other plants, +such as the kelps and even the larger red seaweeds. They are most +abundant in the warmer seas, but still a considerable number may be +found in all parts of the ocean, even extending into the Arctic +regions. + +[Illustration: FIG. 29.--_A_, a red seaweed (_Callithamnion_), of the +natural size. _B_, a piece of the same, × 50. _t_, tetraspores. _C_ +i-v, successive stages in the development of the tetraspores, × 150. +_D_ I, II young procarps. _tr._ trichogyne. iii, young; iv, ripe spore +fruit. I, III, × 150. iv, × 50. _E_, an antheridium, × 150. _F_, spore +fruit of _Polysiphonia_. The spores are here surrounded by a case, +× 50.] + +The methods of reproduction may be best illustrated by a specific +example, and preferably one of the simpler ones, as these are most +readily studied microscopically. + +The form here illustrated (_Callithamnion_) grows attached to wharves, +etc., below low-water mark, and is extremely delicate, collapsing +completely when removed from the water. The color is a bright rosy +red, and with its graceful form and extreme delicacy it makes one of +the most beautiful of the group. + +If alcoholic material is used, it may be mounted for examination +either in water or very dilute glycerine. + + The plant is composed of much-branched, slender filaments, closely + resembling _Cladophora_ in structure, but with smaller cells + (Fig. 29, _B_). The non-sexual reproduction is by means of special + spores, which from being formed in groups of four, are known as + tetraspores. In the species under consideration the mother cell of + the tetraspores arises as a small bud near the upper end of one of + the ordinary cells (Fig. 29, _C_ i). This bud rapidly increases in + size, assuming an oval form, and becoming cut off from the cell of + the stem (Fig. 29, _C_ ii). The contents now divide into four equal + parts, arranged like the quadrants of a sphere. When ripe, the wall + of the mother cell gives way, and the four spores escape into the + water and give rise to new plants. These spores, it will be noticed, + differ in one important particular from corresponding spores in most + algæ, in being unprovided with cilia, and incapable of spontaneous + movement. + + Occasionally in the same plant that bears tetraspores, but more + commonly in special ones, there are produced the sexual organs, and + subsequently the sporocarps, or fruits, developed from them. The + plants that bear them are usually stouter that the non-sexual ones, + and the masses of ripe carpospores are large enough to be readily + seen with the naked eye. + + If a plant bearing ripe spores is selected, the young stages of the + female organ (procarp) may generally be found by examining the + younger parts of the plant. The procarp arises from a single cell of + the filament. This cell undergoes division by a series of + longitudinal walls into a central cell and about four peripheral + ones (Fig. 29, _D_ i). One of the latter divides next into an upper + and a lower cell, the former growing out into a long, colorless + appendage known as a trichogyne (Fig. 29, _D_, _tr._). + + The antheridia (Fig. 29, _E_) are hemispherical masses of closely + set colorless cells, each of which develops a single spermatozoid + which, like the tetraspores, is destitute of cilia, and is dependent + upon the movement of the water to convey it to the neighborhood of + the procarp. Occasionally one of these spermatozoids may be found + attached to the trichogyne, and in this way fertilization is + effected. Curiously enough, neither the cell which is immediately + fertilized, nor the one beneath it, undergo any further change; but + two of the other peripheral cells on opposite sides of the filament + grow rapidly and develop into large, irregular masses of spores + (Fig. 29, _D_ III, IV). + +While the plant here described may be taken as a type of the group, +it must be borne in mind that many of them differ widely, not only in +the structure of the plant body, but in the complexity of the sexual +organs and spores as well. The tetraspores are often imbedded in the +tissues of the plant, or may be in special receptacles, nor are they +always arranged in the same way as here described, and the same is +true of the carpospores. These latter are in some of the higher forms, +_e.g._ _Polysiphonia_ (Fig. 29, _F_), contained in urn-shaped +receptacles, or they may be buried within the tissues of the plant. + +[Illustration: FIG. 30.--Marine red seaweeds. _A_, _Dasya_. _B_, +_Rhodymenia_ (with smaller algæ attached). _C_, _Grinnellia_. _D_, +_Delesseria_. _A_, _B_, natural size; the others reduced one-half.] + +The fresh-water forms are not common, but may occasionally be met with +in mill streams and other running water, attached to stones and +woodwork, but are much inferior in size and beauty to the marine +species. The red color is not so pronounced, and they are, as a rule, +somewhat dull colored. + +[Illustration: FIG. 31.--Fresh-water red algæ. _A_, _Batrachospermum_, +× about 12. _B_, a branch of the same, × 150. _C_, _Lemanea_, natural +size.] + +The commonest genera are _Batrachospermum_ and _Lemanea_ (Fig. 31). + + + + +CHAPTER VIII. + +SUB-KINGDOM III. + +FUNGI. + + +The name "Fungi" has been given to a vast assemblage of plants, +varying much among themselves, but on the whole of about the same +structural rank as the algæ. Unlike the algæ, however, they are +entirely destitute of chlorophyll, and in consequence are dependent +upon organic matter for food, some being parasites (growing upon +living organisms), others saprophytes (feeding on dead matter). Some +of them show close resemblances in structure to certain algæ, and +there is reason to believe that they are descended from forms that +originally had chlorophyll; others are very different from any green +plants, though more or less evidently related among themselves. +Recognizing then these distinctions, we may make two divisions of the +sub-kingdom: I. The Alga-Fungi (_Phycomycetes_), and II. The True +Fungi (_Mycomycetes_). + + +CLASS I.--_Phycomycetes_. + +These are fungi consisting of long, undivided, often branching tubular +filaments, resembling quite closely those of _Vaucheria_ or other +_Siphoneæ_, but always destitute of any trace of chlorophyll. The +simplest of these include the common moulds (_Mucorini_), one of which +will serve to illustrate the characteristics of the order. + +If a bit of fresh bread, slightly moistened, is kept under a bell jar +or tumbler in a warm room, in the course of twenty-four hours or so it +will be covered with a film of fine white threads, and a little later +will produce a crop of little globular bodies mounted on upright +stalks. These are at first white, but soon become black, and the +filaments bearing them also grow dark-colored. + +These are moulds, and have grown from spores that are in the +atmosphere falling on the bread, which offers the proper conditions +for their growth and multiplication. + +One of the commonest moulds is the one here figured (Fig. 32), and +named _Mucor stolonifer_, from the runners, or "stolons," by which it +spreads from one point to another. As it grows it sends out these +runners along the surface of the bread, or even along the inner +surface of the glass covering it. They fasten themselves at intervals +to the substratum, and send up from these points clusters of short +filaments, each one tipped with a spore case, or "sporangium." + + For microscopical study they are best mounted in dilute glycerine + (about one-quarter glycerine to three-quarters pure water). After + carefully spreading out the specimens in this mixture, allow a drop + of alcohol to fall upon the preparation, and then put on the cover + glass. The alcohol drives out the air, which otherwise interferes + badly with the examination. + + The whole plant consists of a very long, much-branched, but + undivided tubular filament. Where it is in contact with the + substratum, root-like outgrowths are formed, not unlike those + observed in _Vaucheria_. At first the walls are colorless, but later + become dark smoky brown in color. A layer of colorless granular + protoplasm lines the wall, becoming more abundant toward the growing + tips of the branches. The spore cases, "sporangia," arise at the + ends of upright branches (Fig. 32, _C_), which at first are + cylindrical (_a_), but later enlarge at the end (_b_), and become + cut off by a convex wall (_c_). This wall pushes up into the young + sporangium, forming a structure called the "columella." When fully + grown, the sporangium is globular, and appears quite opaque, owing + to the numerous granules in the protoplasm filling the space between + the columella and its outer wall. This protoplasm now divides into a + great number of small oval cells (spores), which rapidly darken, + owing to a thick, black wall formed about each one, and at the same + time the columella and the stalk of the sporangium become + dark-colored. + + When ripe, the wall of the sporangium dissolves, and the spores + (Fig. 32, _E_) are set free. The columella remains unchanged, and + some of the spores often remain sticking to it (Fig. 32, _D_). + +[Illustration: FIG. 32.--_A_, common black mould (_Mucor_), × 5. _B_, +three nearly ripe spore cases, × 25. _C_, development of the spore +cases, i-iv, × 150; v, × 50. _D_, spore case which has discharged its +spores. _E_, spores, × 300. _F_, a form of _Mucor mucedo_, with small +accessory spore cases, × 5. _G_, the spore cases, × 50. _H_, a single +spore case, × 300. _I_, development of the zygospore of a black mould, +× 45 (after De Bary).] + + Spores formed in a manner strongly recalling those of the pond scums + are also known, but only occur after the plants have grown for a + long time, and hence are rarely met with (Fig. 32, _I_). + +Another common mould (_M. mucedo_), often growing in company with the +one described, differs from it mainly in the longer stalk of the +sporangium, which is also smaller, and in not forming runners. This +species sometimes bears clusters of very small sporangia attached to +the middle of the ordinary sporangial filament (Fig. 32, _F_, _H_). +These small sporangia have no columella. + +Other moulds are sometimes met with, parasitic upon the larger species +of _Mucor_. + +Related to the black moulds are the insect moulds (_Entomopthoreæ_), +which attack and destroy insects. The commonest of these attacks the +house flies in autumn, when the flies, thus infested, may often be +found sticking to window panes, and surrounded by a whitish halo of +the spores that have been thrown off by the fungus. + + +ORDER II.--WHITE RUSTS AND MILDEWS (_Peronosporeæ_) + +These are exclusively parasitic fungi, and grow within the tissues of +various flowering plants, sometimes entirely destroying them. + +As a type of this group we will select a very common one (_Cystopus +bliti_), that is always to be found in late summer and autumn growing +on pig weed (_Amarantus_). It forms whitish, blister-like blotches +about the size of a pin head on the leaves and stems, being commonest +on the under side of the leaves (Fig. 33, _A_). In the earlier stages +the leaf does not appear much affected, but later becomes brown and +withered about the blotches caused by the fungus. + + If a thin vertical section of the leaf is made through one of these + blotches, and mounted as described for _Mucor_, the latter is found + to be composed of a mass of spores that have been produced below the + epidermis of the leaf, and have pushed it up by their growth. If the + section is a very thin one, we may be able to make out the structure + of the fungus, and then find it to be composed of irregular, + tubular, much-branched filaments, which, however, are not divided by + cross-walls. These filaments run through the intercellular spaces of + the leaf, and send into the cells little globular suckers, by means + of which the fungus feeds. + + The spores already mentioned are formed at the ends of crowded + filaments, that push up, and finally rupture the epidermis (Fig. 33, + _B_). They are formed by the ends of the filaments swelling up and + becoming constricted, so as to form an oval spore, which is then cut + off by a wall. The portion of the filament immediately below acts in + the same way, and the process is repeated until a chain of half a + dozen or more may be produced, the lowest one being always the last + formed. When ripe, the spores are separated by a thin neck, and + become very easily broken off. + + In order to follow their germination it is only necessary to place a + few leaves with fresh patches of the fungus under a bell jar or + tumbler, inverted over a dish full of water, so as to keep the air + within saturated with moisture, but taking care to keep the leaves + out of the water. After about twenty-four hours, if some of the + spores are scraped off and mounted in water, they will germinate in + the course of an hour or so. The contents divide into about eight + parts, which escape from the top of the spore, which at this time + projects as a little papilla. On escaping, each mass of protoplasm + swims away as a zoöspore, with two extremely delicate cilia. After a + short time it comes to rest, and, after developing a thin cell wall, + germinates by sending out one or two filaments (Fig. 33, _C_, _E_). + +[Illustration: FIG. 33.--_A_, leaf of pig-weed (_Amarantus_), with +spots of white rust (_c_), one-half natural size. _B_, non-sexual +spores (conidia). _C_, the same germinating. _D_, zoöspores. _E_, +germinating zoöspores. _sp._ the spore. _F_, young. _G_, mature sexual +organs. In _G_, the tube may be seen connecting the antheridium +(_an._), with the egg cell (_o_). _H_, a ripe resting spore still +surrounded by the wall of the oögonium. _I_, a part of a filament of +the fungus, showing its irregular form. All × 300.] + + Under normal conditions the spores probably germinate when the + leaves are wet, and the filaments enter the plant through the + breathing pores on the lower surface of the leaves, and spread + rapidly through the intercellular spaces. + + Later on, spores of a very different kind are produced. Unlike those + already studied, they are formed some distance below the epidermis, + and in order to study them satisfactorily, the fungus must be freed + from the host plant. In order to do this, small pieces of the leaf + should be boiled for about a minute in strong caustic potash, and + then treated with acetic or hydrochloric acid. By this means the + tissues of the leaf become so soft as to be readily removed, while + the fungus is but little affected. The preparation should now be + washed and mounted in dilute glycerine. + + The spores (oöspores) are much larger than those first formed, and + possess an outer coat of a dark brown color (Fig. 33, _H_). Each + spore is contained in a large cell, which arises as a swelling of + one of the filaments, and becomes shut off by a wall. At first + (Fig. 33, _F_) its contents are granular, and fill it completely, + but later contract to form a globular mass of protoplasm (G. + _o_), the germ cell or egg cell. The whole is an oögonium, and + differs in no essential respect from that of _Vaucheria_. + + Frequently a smaller cell (antheridium), arising from a neighboring + filament, and in close contact with the oögonium, may be detected + (Fig. 33, _F_, _G_, _an._), and in exceptionally favorable cases a + tube is to be seen connecting it with the germ cell, and by means of + which fertilization is effected. + + After being fertilized, the germ cell secretes a wall, at first thin + and colorless, but later becoming thick and dark-colored on the + outside, and showing a division into several layers, the outermost + of which is dark brown, and covered with irregular reticulate + markings. These spores do not germinate at once, but remain over + winter unchanged. + +[Illustration: FIG. 34.--Fragment of a filament of the white rust of +the shepherd's-purse, showing the suckers (_h_), × 300.] + +It is by no means impossible that sometimes the germ cell may develop +into a spore without being fertilized, as is the case in many of the +water moulds. + +Closely related to the species above described is another one +(_C. candidus_), which attacks shepherd's-purse, radish, and others of +the mustard family, upon which it forms chalky white blotches, and +distorts the diseased parts of the plant very greatly. + + For some reasons this is the best species for study, longitudinal + sections through the stem showing very beautifully the structure of + the fungus, and the penetration of the cells of the host[4] by the + suckers (Fig. 34). + +[4] "Host," the plant or animal upon which a parasite lives. + +[Illustration: FIG. 35.--Non-sexual spores of the vine mildew +(_Peronospora viticola_), × 150.] + +Very similar to the white rusts in most respects, but differing in the +arrangement of the non-sexual spores, are the mildews (_Peronospora_, +_Phytophthora_). These plants form mouldy-looking patches on the +leaves and stems of many plants, and are often very destructive. Among +them are the vine mildew (_Peronospora viticola_) (Fig. 35), the +potato fungus (_Phytophthora infestans_), and many others. + + +ORDER III.--_Saprolegniaceæ_ (WATER MOULDS). + +These plants resemble quite closely the white rusts, and are probably +related to them. They grow on decaying organic matter in water, or +sometimes on living water animals, fish, crustaceans, etc. They may +usually be had for study by throwing into water taken from a stagnant +pond or aquarium, a dead fly or some other insect. After a few days it +will probably be found covered with a dense growth of fine, white +filaments, standing out from it in all directions (Fig. 36, _A_). +Somewhat later, if carefully examined with a lens, little round, white +bodies may be seen scattered among the filaments. + +[Illustration: FIG. 36.--_A_, an insect that has decayed in water, and +become attacked by a water mould (_Saprolegnia_), natural size. _B_, a +ripe zoösporangium, × 100. _C_, the same discharging the spores. _D_, +active. _E_, germinating zoöspores, × 300. _F_, a second sporangium +forming below the empty one. _G_ i-iv, development of the oögonium, +× 100. _H_, ripe oögonium filled with resting spores, × 100.] + + On carefully removing a bit of the younger growth and examining it + microscopically, it is found to consist of long filaments much like + those of _Vaucheria_, but entirely destitute of chlorophyll. In + places these filaments are filled with densely granular protoplasm, + which when highly magnified exhibits streaming movements. The + protoplasm contains a large amount of oil in the form of small, + shining drops. + + In the early stages of its growth the plant multiplies by zoöspores, + produced in great numbers in sporangia at the ends of the branches. + The protoplasm collects here much as we saw in _V. sessilis_, the + end of the filament becoming club-shaped and ending in a short + protuberance (Fig. 36, _B_). This end becomes separated by a wall, + and the contents divide into numerous small cells that sometimes are + naked, and sometimes have a delicate membrane about them. The first + sign of division is the appearance in the protoplasm of delicate + lines dividing it into numerous polygonal areas which soon become + more distinct, and are seen to be distinct cells whose outlines + remain more or less angular on account of the mutual pressure. When + ripe, the end of the sporangium opens, and the contained cells are + discharged (Fig. 36, _C_). In case they have no membrane, they swim + away at once, each being provided with two cilia, and resembling + almost exactly the zoöspores of the white rust (Fig. 36, _D_, _E_). + When the cells are surrounded by a membrane they remain for some + time at rest, but finally the contents escape as a zoöspore, like + those already described. By killing the zoöspores with a little + iodine the granular nature of the protoplasm is made more evident, + and the cilia may be seen. They soon come to rest, and germinate in + the same way as those of the white rusts and mildews. + + As soon as the sporangium is emptied, a new one is formed, either by + the filament growing up through it (Fig. 36, _F_) and the end being + again cut off, or else by a branch budding out just below the base + of the empty sporangium, and growing up by the side of it. + + Besides zoöspores there are also resting spores developed. Oögonia + like those of _Vaucheria_ or the _Peronosporeæ_ are formed usually + after the formation of zoöspores has ceased; but in many cases, + perhaps all, these develop without being fertilized. Antheridia are + often wanting, and even when they are present, it is very doubtful + whether fertilization takes place.[5] + +[5] The antheridia, when present, arise as branches just below the +oögonium, and become closely applied to it, sometimes sending tubes +through its wall, but there has been no satisfactory demonstration of +an actual transfer of the contents of the antheridium to the egg cell. + + The oögonia (Fig. 36, _G_, _H_) arise at the end of the main + filaments, or of short side branches, very much as do the sporangia, + from which they differ at this stage in being of globular form. The + contents contract to form one or several egg cells, naked at first, + but later becoming thick-walled resting spores (_H_). + + + + +CHAPTER IX. + +THE TRUE FUNGI (_Mycomycetes_). + + +The great majority of the plants ordinarily known as _fungi_ are +embraced under this head. While some of the lower forms show +affinities with the _Phycomycetes_, and through them with the algæ, +the greater number differ very strongly from all green plants both in +their habits and in their structure and reproduction. It is a +much-disputed point whether sexual reproduction occurs in any of them, +and it is highly probable that in the great majority, at any rate, the +reproduction is purely non-sexual. + +Probably to be reckoned with the _Mycomycetes_, but of doubtful +affinities, are the small unicellular fungi that are the main causes +of alcoholic fermentation; these are the yeast fungi (_Saccharomycetes_). +They cause the fermentation of beer and wine, as well as the incipient +fermentation in bread, causing it to "rise" by the giving off of +bubbles of carbonic acid gas during the process. + +If a little common yeast is put into water containing starch or sugar, +and kept in a warm place, in a short time bubbles of gas will make +their appearance, and after a little longer time alcohol may be +detected by proper tests; in short, alcoholic fermentation is taking +place in the solution. + + If a little of the fermenting liquid is examined microscopically, it + will be found to contain great numbers of very small, oval cells, + with thin cell walls and colorless contents. A careful examination + with a strong lens (magnifying from 500-1000 diameters) shows that + the protoplasm, in which are granules of varying size, does not fill + the cell completely, but that there are one or more large vacuoles + or spaces filled with colorless cell sap. No nucleus is visible in + the living cell, but it has been shown that a nucleus is present. + + If growth is active, many of the cells will be seen dividing. The + process is somewhat different from ordinary fission and is called + budding (Fig. 37, _B_). A small protuberance appears at the bud or + at the side of the cell, and enlarges rapidly, assuming the form of + the mother cell, from which it becomes completely separated by the + constriction of the base, and may fall off at once, or, as is more + frequently the case, may remain attached for a time, giving rise + itself to other buds, so that not infrequently groups of half a + dozen or more cells are met with (Fig. 37, _B_, _C_). + +[Illustration: FIG. 37.--_A_, single cells of yeast. _B_, _C_, similar +cells, showing the process of budding, × 750.] + +That the yeast cells are the principal agents of alcoholic +fermentation may be shown in much the same way that bacteria are shown +to cause ordinary decomposition. Liquids from which they are excluded +will remain unfermented for an indefinite time. + +There has been much controversy as to the systematic position of the +yeast fungi, which has not yet been satisfactorily settled, the +question being whether they are to be regarded as independent plants +or only one stage in the life history of some higher fungi (possibly +the _Smuts_), which through cultivation have lost the power of +developing further. + + +CLASS I.--THE SMUTS (_Ustillagineæ_). + +The smuts are common and often very destructive parasitic fungi, +living entirely within the tissues of the higher plants. Owing to +this, as well as to the excessively small spores and difficulty in +germinating them, the plants are very difficult of study, except in a +general way, and we will content ourselves with a glance at one of the +common forms, the corn smut (_Ustillago maydis_). This familiar fungus +attacks Indian corn, forming its spores in enormous quantities in +various parts of the diseased plant, but particularly in the flowers +("tassel" and young ear). + + The filaments, which resemble somewhat those of the white rusts, + penetrate all parts of the plant, and as the time approaches for the + formation of the spores, these branch extensively, and at the same + time become soft and mucilaginous (Fig. 38, _B_). The ends of these + short branches enlarge rapidly and become shut off by partitions, + and in each a globular spore (Fig. 38, _C_) is produced. The outer + wall is very dark-colored and provided with short spines. To study + the filaments and spore formation, very thin sections should be made + through the young kernels or other parts in the vicinity, before + they are noticeably distorted by the growth of the spore-bearing + filaments. + +[Illustration: FIG. 38.--_A_, "tassel" of corn attacked by smut +(_Ustillago_). _B_, filaments of the fungus from a thin section of a +diseased grain, showing the beginning of the formation of the spores, +× 300. _C_, ripe spores, × 300.] + +As the spores are forming, an abnormal growth is set up in the cells +of the part attacked, which in consequence becomes enormously enlarged +(Fig. 38, _A_), single grains sometimes growing as large as a walnut. +As the spores ripen, the affected parts, which are at first white, +become a livid gray, due to the black spores shining through the +overlying white tissues. Finally the masses of spores burst through +the overlying cells, appearing like masses of soot, whence the popular +name for the plant. + +The remaining _Mycomycetes_ are pretty readily divisible into two +great classes, based upon the arrangement of the spores. The first of +these is known as the _Ascomycetes_ (Sac fungi), the other the +_Basidiomycetes_ (mushrooms, puff-balls, etc.). + + +CLASS II.--_Ascomycetes_ (SAC FUNGI). + +This class includes a very great number of common plants, all +resembling each other in producing spores in sacs (_asci_, sing. +_ascus_) that are usually oblong in shape, and each containing eight +spores, although the number is not always the same. Besides the spores +formed in these sacs (ascospores), there are other forms produced in +various ways. + +There are two main divisions of the class, the first including only a +few forms, most of which are not likely to be met with by the student. +In these the spore sacs are borne directly upon the filaments without +any protective covering. The only form that is at all common is a +parasitic fungus (_Exoascus_) that attacks peach-trees, causing the +disease of the leaves known as "curl." + +All of the common _Ascomycetes_ belong to the second division, and +have the spore sacs contained in special structures called spore +fruits, that may reach a diameter of several centimetres in a few +cases, though ordinarily much smaller. + +Among the simpler members of this group are the mildews +(_Perisporiaceæ_), mostly parasitic forms, living upon the leaves and +stems of flowering plants, sometimes causing serious injury by their +depredations. They form white or grayish downy films on the surface of +the plant, in certain stages looking like hoar-frost. Being very +common, they may be readily obtained, and are easily studied. One of +the best species for study (_Podosphæra_) grows abundantly on the +leaves of the dandelion, especially when the plants are growing under +unfavorable conditions. The same species is also found on other plants +of the same family. It may be found at almost any time during the +summer; but for studying, the spore fruits material should be +collected in late summer or early autumn. It at first appears as +white, frost-like patches, growing dingier as it becomes older, and +careful scrutiny of the older specimens will show numerous brown or +blackish specks scattered over the patches. These are the spore +fruits. + +[Illustration: FIG. 39.--_A_, spore-bearing filaments of the dandelion +mildew (_Podosphæra_), × 150. _B_, a germinating spore, × 150. _C-F_, +development of the spore fruit, × 300. _ar._ archicarp. _G_, a ripe +spore fruit, × 150. _H_, the spore sac removed from the spore fruit, +× 150. _I_, spore-bearing filament attacked by another fungus +(_Cicinnobulus_), causing the enlargement of the basal cell, × 150. +_J_, a more advanced stage, × 300. _K_, spores, × 300.] + + For microscopical study, fresh material may be used, or, if + necessary, dried specimens. The latter, before mounting, should be + soaked for a short time in water, to which has been added a few + drops of caustic-potash solution. This will remove the brittleness, + and swell up the dried filaments to their original proportions. A + portion of the plant should be carefully scraped off the leaf on + which it is growing, thoroughly washed in pure water, and + transferred to a drop of water or very dilute glycerine, in which it + should be carefully spread out with needles. If air bubbles + interfere with the examination, they may be driven off with alcohol, + and then the cover glass put on. If the specimen is mounted in + glycerine, it will keep indefinitely, if care is taken to seal it + up. The plant consists of much-interlaced filaments, divided at + intervals by cross-walls.[6] They are nearly colorless, and the + contents are not conspicuous. These filaments send up vertical + branches (Fig. 39, _A_), that become divided into a series of short + cells by means of cross-walls. The cells thus formed are at first + cylindrical, but later bulge out at the sides, becoming broadly + oval, and finally become detached as spores (_conidia_). It is these + spores that give the frosty appearance to the early stages of the + fungus when seen with the naked eye. The spores fall off very easily + when ripe, and germinate quickly in water, sending out two or more + tubes that grow into filaments like those of the parent plant + (Fig. 39, _B_). + +[6] The filaments are attached to the surface of the leaf by suckers, +which are not so readily seen in this species as in some others. A +mildew growing abundantly in autumn on the garden chrysanthemum, +however, shows them very satisfactorily if a bit of the epidermis of a +leaf on which the fungus is just beginning to grow is sliced off with +a sharp razor and mounted in dilute glycerine, or water, removing the +air with alcohol. These suckers are then seen to be globular bodies, +penetrating the outer wall of the cell (Fig. 40). + +[Illustration: FIG. 40.--Chrysanthemum mildew (_Erysiphe_), showing +the suckers (_h_) by which the filaments are attached to the leaf. +_A_, surface view. _B_, vertical section of the leaf, × 300.] + + The spore fruits, as already observed, are formed toward the end of + the season, and, in the species under consideration at least, appear + to be the result of a sexual process. The sexual organs (if they are + really such) are extremely simple, and, owing to their very small + size, are not easily found. They arise as short branches at a point + where two filaments cross; one of them (Fig. 39, _C_, _ar._), the + female cell, or "archicarp," is somewhat larger than the other and + nearly oval in form, and soon becomes separated by a partition from + the filament that bears it. The other branch (antheridium) grows up + in close contact with the archicarp, and like it is shut off by a + partition from its filament. It is more slender than the archicarp, + but otherwise differs little from it. No actual communication can be + shown to be present between the two cells, and it is therefore still + doubtful whether fertilization really takes place. Shortly after + these organs are full-grown, several short branches grow up about + them, and soon completely envelop them (_D_, _E_). These branches + soon grow together, and cross-walls are formed in them, so that the + young spore fruit appears surrounded by a single layer of cells, + sufficiently transparent, however, to allow a view of the interior. + + The antheridium undergoes no further change, but the archicarp soon + divides into two cells,--a small basal one and a larger upper cell. + There next grow from the inner surface of the covering cells, short + filaments, that almost completely fill the space between the + archicarp and the wall. An optical section of such a stage (Fig. 39, + _F_) shows a double wall and the two cells of the archicarp. The + spore fruit now enlarges rapidly, and the outer cells become first + yellow and then dark brown, the walls becoming thicker and harder as + they change color. Sometimes special filaments or appendages grow + out from their outer surfaces, and these are also dark-colored. + Shortly before the fruit is ripe, the upper cell of the archicarp, + which has increased many times in size, shows a division of its + contents into eight parts, each of which develops a wall and becomes + an oval spore. By crushing the ripe spore fruit, these spores still + enclosed in the mother cell (ascus) may be forced out (Fig. 39, + _H_). These spores do not germinate at once, but remain dormant + until the next year. + +[Illustration: FIG. 41.--Forms of mildews (_Erysiphe_). _A_, +_Microsphæra_, a spore fruit, × 150. _B_, cluster of spore sacs of the +same, × 150. _C_, a single appendage, × 300. _D_, end of an appendage +of _Uncinula_, × 300. _E_, appendage of _Phyllactinia_, × 150.] + + Frequently other structures, resembling somewhat the spore fruits, + are found associated with them (Fig. 39, _I_, _K_), and were for a + long time supposed to be a special form of reproductive organ; but + they are now known to belong to another fungus (_Cicinnobulus_), + parasitic upon the mildew. They usually appear at the base of the + chains of conidia, causing the basal cell to enlarge to many times + its original size, and finally kill the young conidia, which shrivel + up. A careful examination reveals the presence of very fine + filaments within those of the mildew, which may be traced up to the + base of the conidial branch, where the receptacle of the parasite is + forming. The spores contained in these receptacles are very small + (Fig. 39, _K_), and when ripe exude in long, worm-shaped masses, if + the receptacle is placed in water. + +The mildews may be divided into two genera: _Podosphæra_, with a +single ascus in the spore fruit; and _Erysiphe_, with two or more. In +the latter the archicarp branches, each branch bearing a spore sac +(Fig. 41, _B_). + +The appendages growing out from the wall of the spore fruit are often +very beautiful in form, and the two genera given above are often +subdivided according to the form of these appendages. + +A common mould closely allied to the mildews is found on various +articles of food when allowed to remain damp, and is also very common +on botanical specimens that have been poorly dried, and hence is often +called "herbarium mould" (_Eurotium herbariorum_). + +[Illustration: FIG. 42.--_A_, spore bearing filament of the herbarium +mould (_Eurotium_), × 150. _B_, _C_, another species showing the way +in which the spores are borne--optical section--× 150. _D_, spore +fruit of the herbarium mould, × 150. _E_, spore sac. _F_, spores, +× 300. _G_, spore-bearing filament of the common blue mould +(_Penicillium_), × 300. _sp._ the spores.] + + The conidia are of a greenish color, and produced on the ends of + upright branches which are enlarged at the end, and from which grow + out little prominences, which give rise to the conidia in the same + way as we have seen in the mildews (Fig. 42, _A_). + + Spore fruits much like those of the mildews are formed later, and + are visible to the naked eye as little yellow grains (Fig. 42, _D_). + These contain numerous very small spore sacs (_E_), each with eight + spores. + +There are numerous common species of _Eurotium_, differing in color +and size, some being yellow or black, and larger than the ordinary +green form. + +Another form, common everywhere on mouldy food of all kinds, as well +as in other situations, is the blue mould (_Penicillium_). This, in +general appearance, resembles almost exactly the herbarium mould, but +is immediately distinguishable by a microscopic examination (Fig. 42, +_G_). + + In studying all of these forms, they may be mounted, as directed for + the black moulds, in dilute glycerine; but must be handled with + great care, as the spores become shaken off with the slightest jar. + +Of the larger _Ascomycetes_, the cup fungi (_Discomycetes_) may be +taken as types. The spore fruit in these forms is often of +considerable size, and, as their name indicates, is open, having the +form of a flat disc or cup. A brief description of a common one will +suffice to give an idea of their structure and development. + +_Ascobolus_ (Fig. 43) is a small, disc-shaped fungus, growing on horse +dung. By keeping some of this covered with a bell jar for a week or +two, so as to retain the moisture, at the end of this time a large +crop of the fungus will probably have made its appearance. The part +visible is the spore fruit (Fig. 43, _A_), of a light brownish color, +and about as big as a pin-head. + + Its development may be readily followed by teasing out in water the + youngest specimens that can be found, taking care to take up a + little of the substratum with it, as the earliest stages are too + small to be visible to the naked eye. The spore fruits arise from + filaments not unlike those of the mildews, and are preceded by the + formation of an archicarp composed of several cells, and readily + seen through the walls of the young fruit (Fig. 43, _B_). In the + study of the early stages, a potash solution will be found useful in + rendering them transparent. + + The young fruit has much the same structure as that of the mildews, + but the spore sacs are much more numerous, and there are special + sterile filaments developed between them. If the young spore fruit + is treated with chlor-iodide of zinc, it is rendered quite + transparent, and the young spore sacs colored a beautiful blue, so + that they are readily distinguishable. + +[Illustration: FIG. 43.--_A_, a small cup fungus (_Ascobolus_), × 5. +_B_, young spore fruit, × 300. _ar._ archicarp. _C_, an older one, +× 150. _ar._ archicarp. _sp._ young spore sacs. _D_, section through a +full-grown spore fruit (partly diagrammatic), × 25. _sp._ spore sacs. +_E_, development of spore sacs and spores: i-iii, × 300; iv, × 150. +_F_, ripe spores. _G_, a sterile filament (paraphysis), × 300. _H_, +large scarlet cup fungus (_Peziza_), natural size.] + + The development of the spore sacs may be traced by carefully + crushing the young spore fruits in water. The young spore sacs + (Fig. 43, _E_ i) are colorless, with granular protoplasm, in which a + nucleus can often be easily seen. The nucleus subsequently divides + repeatedly, until there are eight nuclei, about which the protoplasm + collects to form as many oval masses, each of which develops a wall + and becomes a spore (Figs. ii-iv). These are imbedded in protoplasm, + which is at first granular, but afterwards becomes almost + transparent. As the spores ripen, the wall acquires a beautiful + violet-purple color, changing later to a dark purple-brown, and + marked with irregular longitudinal ridges (Fig. 43, _F_). The + full-grown spore sacs (Fig. 43, _E_, _W_) are oblong in shape, and + attached by a short stalk. The sterile filaments between them often + become curiously enlarged at the end (_G_). As the spore fruit + ripens, it opens at the top, and spreads out so as to expose the + spore sacs as they discharge their contents (Fig. 43, _D_). + +Of the larger cup fungi, those belonging to the genus _Peziza_ +(Fig. 43, _H_) are common, growing on bits of rotten wood on the +ground in woods. They are sometimes bright scarlet or orange-red, and +very showy. Another curious form is the morel (_Morchella_), common in +the spring in dry woods. It is stalked like a mushroom, but the +surface of the conical cap is honeycombed with shallow depressions, +lined with the spore sacs. + + +ORDER _Lichenes_. + +Under the name of lichens are comprised a large number of fungi, +differing a good deal in structure, but most of them not unlike the +cup fungi. They are, with few exceptions, parasitic upon various forms +of algæ, with which they are so intimately associated as to form +apparently a single plant. They grow everywhere on exposed rocks, on +the ground, trunks of trees, fences, etc., and are found pretty much +the world over. Among the commonest of plants are the lichens of the +genus _Parmelia_ (Fig. 44, _A_), growing everywhere on tree trunks, +wooden fences, etc., forming gray, flattened expansions, with much +indented and curled margins. When dry, the plant is quite brittle, but +on moistening becomes flexible, and at the same time more or less +decidedly green in color. The lower surface is white or brown, and +often develops root-like processes by which it is fastened to the +substratum. Sometimes small fragments of the plant become detached in +such numbers as to form a grayish powder over certain portions of it. +These, when supplied with sufficient moisture, will quickly produce +new individuals. + +Not infrequently the spore fruits are to be met with flat discs of a +reddish brown color, two or three millimetres in diameter, and closely +resembling a small cup fungus. They are at first almost closed, but +expand as they mature (Fig. 44, _A_, _ap._). + +[Illustration: FIG. 44.--_A_, a common lichen (_Parmelia_), of the +natural size. _ap._ spore fruit. _B_, section through one of the spore +fruits, × 5. _C_, section through the body of a gelatinous lichen +(_Collema_), showing the _Nostoc_ individuals surrounded by the fungus +filaments, × 300. _D_, a spermagonium of _Collema_, × 25. _E_, a +single _Nostoc_ thread. _F_, spore sacs and paraphyses of _Usnea_, +× 300. _G_, _Protococcus_ cells and fungus filaments of _Usnea_.] + + If a thin vertical section of the plant is made and sufficiently + magnified, it is found to be made up of somewhat irregular, + thick-walled, colorless filaments, divided by cross-walls as in the + other sac-fungi. In the central parts of the plant these are rather + loose, but toward the outside become very closely interwoven and + often grown together, so as to form a tough rind. Among the + filaments of the outer portion are numerous small green cells, that + closer examination shows to be individuals of _Protococcus_, or some + similar green algæ, upon which the lichen is parasitic. These are + sufficiently abundant to form a green line just inside the rind if + the section is examined with a simple lens (Fig. 44, _B_). + + The spore fruits of the lichens resemble in all essential respects + those of the cup fungi, and the spore sacs (Fig. 44, _F_) are much + the same, usually, though not always, containing eight spores, which + are sometimes two-celled. The sterile filaments between the spore + sacs usually have thickened ends, which are dark-colored, and give + the color to the inner surface of the spore fruit. + + In Figure 45, _H_, is shown one of the so-called "_Soredia_,"[7] a + group of the algæ, upon which the lichen is parasitic, surrounded by + some of the filaments, the whole separating spontaneously from the + plant and giving rise to a new one. + +[7] Sing. _soredium_. + +Owing to the toughness of the filaments, the finer structure of the +lichens is often difficult to study, and free use of caustic potash is +necessary to soften and make them manageable. + +[Illustration: FIG. 45.--Forms of lichens. _A_, a branch with lichens +growing upon it, one-half natural size. _B_, _Usnea_, natural size. +_ap._ spore fruit. _C_, _Sticta_, one-half natural size. _D_, +_Peltigera_, one-half natural size. _ap._ spore fruit. _E_, a single +spore fruit, × 2. _F_, _Cladonia_, natural size. _G_, a piece of bark +from a beech, with a crustaceous lichen (_Graphis_) growing upon it, +× 2. _ap._ spore fruit. _H_, _Soredium_ of a lichen, × 300.] + +According to their form, lichens are sometimes divided into the bushy +(fruticose), leafy (frondose), incrusting (crustaceous), and +gelatinous. Of the first, the long gray _Usnea_ (Fig. 45, _A_, _B_), +which drapes the branches of trees in swamps, is a familiar example; +of the second, _Parmelia_, _Sticta_ (Fig. 45, _C_) and _Peltigera_ +(_D_) are types; of the third, _Graphis_ (_G_), common on the trunks +of beech-trees, to which it closely adheres; and of the last, +_Collema_ (Fig. 44, _C_, _D_, _E_), a dark greenish, gelatinous form, +growing on mossy tree trunks, and looking like a colony of _Nostoc_, +which indeed it is, but differing from an ordinary colony in being +penetrated everywhere by the filaments of the fungus growing upon it. + + Not infrequently in this form, as well as in other lichens, special + cavities, known as spermogonia (Fig. 44, _D_), are found, in which + excessively small spores are produced, which have been claimed to + be male reproductive cells, but the latest investigations do not + support this theory. + +[Illustration: FIG. 46.--Branch of a plum-tree attacked by black knot. +Natural size.] + +The last group of the _Ascomycetes_ are the "black fungi," +_Pyrenomycetes_, represented by the black knot of cherry and plum +trees, shown in Figure 46. They are mainly distinguished from the cup +fungi by producing their spore sacs in closed cavities. Some are +parasites; others live on dead wood, leaves, etc., forming very hard +masses, generally black in color, giving them their common name. Owing +to the hardness of the masses, they are very difficult to manipulate; +and, as the structure is not essentially different from that of the +_Discomycetes_, the details will not be entered into here. + +Of the parasitic forms, one of the best known is the "ergot" of rye, +more or less used in medicine. Other forms are known that attack +insects, particularly caterpillars, which are killed by their attacks. + + + + +CHAPTER X. + +FUNGI--_Continued_. + + +CLASS _Basidiomycetes_. + +The _Basidiomycetes_ include the largest and most highly developed of +the fungi, among which are many familiar forms, such as the mushrooms, +toadstools, puff-balls, etc. Besides these large and familiar forms, +there are other simpler and smaller ones that, according to the latest +investigations, are probably related to them, though formerly regarded +as constituting a distinct group. The most generally known of these +lower _Basidiomycetes_ are the so-called rusts. The larger +_Basidiomycetes_ are for the most part saprophytes, living in decaying +vegetable matter, but a few are true parasites upon trees and others +of the flowering plants. + +All of the group are characterized by the production of spores at the +top of special cells known as basidia,[8] the number produced upon a +single basidium varying from a single one to several. + +[8] Sing. _basidium_. + +Of the lower _Basidiomycetes_, the rusts (_Uredineæ_) offer common and +easily procurable forms for study. They are exclusively parasitic in +their habits, growing within the tissues of the higher land plants, +which they often injure seriously. They receive their popular name +from the reddish color of the masses of spores that, when ripe, burst +through the epidermis of the host plant. Like many other fungi, the +rusts have several kinds of spores, which are often produced on +different hosts; thus one kind of wheat rust lives during part of its +life within the leaves of the barberry, where it produces spores quite +different from those upon the wheat; the cedar rust, in the same way, +is found at one time attacking the leaves of the wild crab-apple and +thorn. + +[Illustration: FIG. 47.--_A_, a branch of red cedar attacked by a rust +(_Gymnosporangium_), causing a so-called "cedar apple," × œ. _B_, +spores of the same, one beginning to germinate, × 300. _C_, a spore +that has germinated, each cell producing a short, divided filament +(basidium), which in turn gives rise to secondary spores (_sp._), +× 300. _D_, part of the leaf of a hawthorn attacked by the cluster cup +stage of the same fungus, upper side showing spermogonia, natural +size. _E_, cluster cups (_Roestelia_) of the same fungus, natural +size. _F_, tip of a leaf of the Indian turnip (_Arisæma_), bearing the +cluster cup (_Æcidium_) stage of a rust, × 2. _G_, vertical section +through a young cluster cup. _H_, similar section through a mature +one, × 50. _I_, germinating spores of _H_, × 300. _J_, part of a corn +leaf, with black rust, natural size. _K_, red rust spore of the wheat +rust (_Puccinia graminis_), × 300. _L_, forms of black-rust spores: i, +_Uromyces_; ii, _Puccinia_; iii, _Phragmidium_.] + +The first form met with in most rusts is sometimes called the +"cluster-cup" stage, and in many species is the only stage known. In +Figure 47, _F_, is shown a bit of the leaf of the Indian turnip +(_Arisæma_) affected by one of these "cluster-cup" forms. To the naked +eye, or when slightly magnified, the masses of spores appear as bright +orange spots, mostly upon the lower surface. The affected leaves are +more or less checked in their growth, and the upper surface shows +lighter blotches, corresponding to the areas below that bear the +cluster cups. These at first appear as little elevations of a +yellowish color, and covered with the epidermis; but as the spores +ripen they break through the epidermis, which is turned back around +the opening, the whole forming a little cup filled with a bright +orange red powder, composed of the loose masses of spores. + + Putting a piece of the affected leaf between two pieces of pith so + as to hold it firmly, with a little care thin vertical sections of + the leaf, including one of the cups, may be made, and mounted, + either in water or glycerine, removing the air with alcohol. We find + that the leaf is thickened at this point owing to a diseased growth + of the cells of the leaf, induced by the action of the fungus. The + mass of spores (Fig. 47, _G_) is surrounded by a closely woven mass + of filaments, forming a nearly globular cavity. Occupying the bottom + of the cup are closely set, upright filaments, each bearing a row of + spores, arranged like those of the white rusts, but so closely + crowded as to be flattened at the sides. The outer rows have + thickened walls, and are grown together so as to form the wall of + the cup. + + The spores are filled with granular protoplasm, in which are + numerous drops of orange-yellow oil, to which is principally due + their color. As the spores grow, they finally break the overlying + epidermis, and then become rounded as the pressure from the sides is + relieved. They germinate within a few hours if placed in water, + sending out a tube, into which pass the contents of the spore + (Fig. 47, _I_). + +One of the most noticeable of the rusts is the cedar rust +(_Gymnosporangium_), forming the growths known as "cedar apples," +often met with on the red cedar. These are rounded masses, sometimes +as large as a walnut, growing upon the small twigs of the cedar +(Fig. 47, _A_). This is a morbid growth of the same nature as those +produced by the white rusts and smuts. If one of these cedar apples is +examined in the late autumn or winter, it will be found to have the +surface dotted with little elevations covered by the epidermis, and on +removing this we find masses of forming spores. These rupture the +epidermis early in the spring, and appear then as little spikes of a +rusty red color. If they are kept wet for a few hours, they enlarge +rapidly by the absorption of water, and may reach a length of four or +five centimetres, becoming gelatinous in consistence, and sometimes +almost entirely hiding the surface of the "apple." In this stage the +fungus is extremely conspicuous, and may frequently be met with after +rainy weather in the spring. + + This orange jelly, as shown by the microscope, is made up of + elongated two-celled spores (teleuto spores), attached to long + gelatinous stalks (Fig. 47, _B_). They are thick-walled, and the + contents resemble those of the cluster-cup spores described above. + + To study the earlier stages of germination it is best to choose + specimens in which the masses of spores have not been moistened. By + thoroughly wetting these, and keeping moist, the process of + germination may be readily followed. Many usually begin to grow + within twenty-four hours or less. Each cell of the spore sends out a + tube (Fig. 47, _C_), through an opening in the outer wall, and this + tube rapidly elongates, the spore contents passing into it, until a + short filament (basidium) is formed, which then divides into several + short cells. Each cell develops next a short, pointed process, which + swells up at the end, gradually taking up all the contents of the + cell, until a large oval spore (_sp._) is formed at the tip, + containing all the protoplasm of the cell. + +Experiments have been made showing that these spores do not germinate +upon the cedar, but upon the hawthorn or crab-apple, where they +produce the cluster-cup stage often met with late in the summer. The +affected leaves show bright orange-yellow spots about a centimetre in +diameter (Fig. 47, _D_), and considerably thicker than the other parts +of the leaf. On the upper side of these spots may be seen little black +specks, which microscopic examination shows to be spermogonia, +resembling those of the lichens. Later, on the lower surface, appear +the cluster cups, whose walls are prolonged so that they form little +tubular processes of considerable length (Fig. 47, _E_). + + In most rusts the teleuto spores are produced late in the summer or + autumn, and remain until the following spring before they germinate. + They are very thick-walled, the walls being dark-colored, so that in + mass they appear black, and constitute the "black-rust" stage + (Fig. 47, _J_). Associated with these, but formed earlier, and + germinating immediately, are often to be found large single-celled + spores, borne on long stalks. They are usually oval in form, rather + thin-walled, but the outer surface sometimes provided with little + points. The contents are reddish, so that in mass they appear of the + color of iron rust, and cause the "red rust" of wheat and other + plants, upon which they are growing. + +The classification of the rusts is based mainly upon the size and +shape of the teleuto spores where they are known, as the cluster-cup +and red-rust stages are pretty much the same in all. Of the commoner +genera _Melampsora_, and _Uromyces_ (Fig. 47, _L_ i), have unicellular +teleuto spores; _Puccinia_ (ii) and _Gymnosporangium_, two-celled +spores; _Triphragmium_, three-celled; and _Phragmidium_ (iii), four or +more. + +The rusts are so abundant that a little search can scarcely fail to +find some or all of the stages. The cluster-cup stages are best +examined fresh, or from alcoholic material; the teleuto spores may be +dried without affecting them. + +Probably the best-known member of the group is the wheat rust +(_Puccinia graminis_), which causes so much damage to wheat and +sometimes to other grains. The red-rust stage may be found in early +summer; the black-rust spores in the stubble and dead leaves in the +autumn or spring, forming black lines rupturing the epidermis. + +Probably to be associated with the lower _Basidiomycetes_ are the +large fungi of which _Tremella_ (Fig. 51, _A_) is an example. They are +jelly-like forms, horny and somewhat brittle when dry, but becoming +soft when moistened. They are common, growing on dead twigs, logs, +etc., and are usually brown or orange-yellow in color. + +Of the higher _Basidiomycetes_, the toadstools, mushrooms, etc., are +the highest, and any common form will serve for study. One of the most +accessible and easily studied forms is _Coprinus_, of which there are +several species growing on the excrement of various herbivorous +animals. They not infrequently appear on horse manure that has been +kept covered with a glass for some time, as described for _Ascobolus_. +After two or three weeks some of these fungi are very likely to make +their appearance, and new ones continue to develop for a long time. + +[Illustration: FIG. 48.--_A_, young. _B_, full-grown fruit of a +toadstool (_Coprinus_), × 2. _C_, under side of the cap, showing the +radiating "gills," or spore-bearing plates. _D_, section across one of +the young gills, × 150. _E_, _F_, portions of gills from a nearly ripe +fruit, × 300. _sp._ spores. _x_, sterile cell. In _F_, a basidium is +shown, with the young spores just forming. _G_, _H_, young fruits, +× 50.] + +The first trace of the plant, visible to the naked eye, is a little +downy, white speck, just large enough to be seen. This rapidly +increases in size, becoming oblong in shape, and growing finally +somewhat darker in color; and by the time it reaches a height of a few +millimetres a short stalk becomes perceptible, and presently the whole +assumes the form of a closed umbrella. The top is covered with little +prominences, that diminish in number and size toward the bottom. After +the cap reaches its full size, the stalk begins to grow, slowly at +first, but finally with great rapidity, reaching a height of several +centimetres within a few hours. At the same time that the stalk is +elongating, the cap spreads out, radial clefts appearing on its upper +surface, which flatten out very much as the folds of an umbrella are +stretched as it opens, and the spaces between the clefts appear as +ridges, comparable to the ribs of the umbrella (Fig. 48, _B_). The +under side of the cap has a number of ridges running from the centre +to the margin, and of a black color, due to the innumerable spores +covering their surface (_C_). Almost as soon as the umbrella opens, +the spores are shed, and the whole structure shrivels up and +dissolves, leaving almost no trace behind. + + If we examine microscopically the youngest specimens procurable, + freeing from air with alcohol, and mounting in water or dilute + glycerine, we find it to be a little, nearly globular mass of + colorless filaments, with numerous cross-walls, the whole arising + from similar looser filaments imbedded in the substratum (Fig. 48, + _G_). If the specimen is not too young, a denser central portion can + be made out, and in still older ones (Fig. 48, _H_) this central + mass has assumed the form of a short, thick stalk, crowned by a flat + cap, the whole invested by a loose mass of filaments that merge more + or less gradually into the central portion. By the time the spore + fruit (for this structure corresponds to the spore fruit of the + _Ascomycetes_) reaches a height of two or three millimetres, and is + plainly visible to the naked eye, the cap grows downward at the + margins, so as to almost entirely conceal the stalk. A longitudinal + section of such a stage shows the stalk to be composed of a + small-celled, close tissue becoming looser in the cap, on whose + inner surface the spore-bearing ridges ("gills" or _Lamellæ_) have + begun to develop. Some of these run completely to the edge of the + cap, others only part way. To study their structure, make + cross-sections of the cap of a nearly full-grown, but unopened, + specimen, and this will give numerous sections of the young gills. + We find them to be flat plates, composed within of loosely + interwoven filaments, whose ends stand out at right angles to the + surface of the gills, forming a layer of closely-set upright cells + (basidia) (Fig. 48, _D_). These are at first all alike, but later + some of them become club-shaped, and develop at the end several + (usually four) little points, at the end of which spores are formed + in exactly the same way as we saw in the germinating teleuto spores + of the cedar rust, all the protoplasm of the basidium passing into + the growing spores (Fig. 48, _E_, _F_). The ripe spores (_E_, _sp._) + are oval, and possess a firm, dark outer wall. Occasionally some of + the basidia develop into very large sterile cells (E, _x_), + projecting far beyond the others, and often reaching the neighboring + gill. + +Similar in structure and development to _Coprinus_ are all the large +and common forms; but they differ much in the position of the +spore-bearing tissue, as well as in the form and size of the whole +spore fruit. They are sometimes divided, according to the position of +the spores, into three orders: the closed-fruited (_Angiocarpous_) +forms, the half-closed (_Hemi-angiocarpous_), and the open or +naked-fruited forms (_Gymnocarpous_). + +[Illustration: FIG. 49.--_Basidiomycetes_. _A_, common puff-ball +(_Lycoperdon_). _B_, earth star (_Geaster_). _A_, × Œ. _B_, one-half +natural size.] + +Of the first, the puff-balls (Fig. 49) are common examples. One +species, the giant puff-ball (_Lycoperdon giganteum_), often reaches a +diameter of thirty to forty centimetres. The earth stars (_Geaster_) +have a double covering to the spore fruit, the outer one splitting at +maturity into strips (Fig. 49, _B_). Another pretty and common form is +the little birds'-nest fungus (_Cyathus_), growing on rotten wood or +soil containing much decaying vegetable matter (Fig. 50). + +[Illustration: FIG. 50.--Birds'-nest fungus (_Cyathus_). _A_, young. +_B_, full grown. _C_, section through _B_, showing the "sporangia" +(_sp._). All twice the natural size.] + +In the second order the spores are at first protected, as we have seen +in _Coprinus_, which belongs to this order, but finally become +exposed. Here belong the toadstools and mushrooms (Fig. 51, _B_), the +large shelf-shaped fungi (_Polyporus_), so common on tree trunks and +rotten logs (Fig. 51, _C_, _D_, _E_), and the prickly fungus +(_Hydnum_) (Fig. 51, _G_). + +[Illustration: FIG. 51.--Forms of _Basidiomycetes_. _A_, _Tremella_, +one-half natural size. _B_, _Agaricus_, natural size. _C_, _E_, +_Polyporus_: _C_, × œ; _E_, × Œ. _D_, part of the under surface of +_D_, natural size. _F_, _Clavaria_, a small piece, natural size. _G_, +_Hydnum_, a piece of the natural size.] + +Of the last, or naked-fruited forms, the commonest belong to the +genus _Clavaria_ (Fig. 51, _F_), smooth-branching forms, usually of a +brownish color, bearing the spores directly upon the surface of the +branches. + + + + +CHAPTER XI. + +SUB-KINGDOM IV. + +BRYOPHYTA. + + +The Bryophytes, or mosses, are for the most part land plants, though a +few are aquatic, and with very few exceptions are richly supplied with +chlorophyll. They are for the most part small plants, few of them +being over a few centimetres in height; but, nevertheless, compared +with the plants that we have heretofore studied, quite complex in +their structure. The lowest members of the group are flattened, +creeping plants, or a few of them floating aquatics, without distinct +stem and leaves; but the higher ones have a pretty well-developed +central axis or stem, with simple leaves attached. + +There are two classes--I. Liverworts (_Hepaticæ_), and II. Mosses +(_Musci_). + + +CLASS I.--THE LIVERWORTS. + +One of the commonest of this class, and to be had at any time, is +named _Madotheca_. It is one of the highest of the class, having +distinct stem and leaves. It grows most commonly on the shady side of +tree trunks, being most luxuriant near the ground, where the supply of +moisture is most constant. It also occurs on stones and rocks in moist +places. It closely resembles a true moss in general appearance, and +from the scale-like arrangement of its leaves is sometimes called +"scale moss." + +The leaves (Fig. 52, _A_, _B_) are rounded in outline unequally, +two-lobed, and arranged in two rows on the upper side of the stem, so +closely overlapping as to conceal it entirely. On the under side are +similar but smaller leaves, less regularly disposed. The stems branch +at intervals, the branches spreading out laterally so that the whole +plant is decidedly flattened. On the under side are fine, whitish +hairs, that fasten it to the substratum. If we examine a number of +specimens, especially early in the spring, a difference will be +observed in the plants. Some of them will be found to bear peculiar +structures (Fig. 52, _C_, _D_), in which the spores are produced. +These are called "sporogonia." They are at first globular, but when +ripe open by means of four valves, and discharge a greenish brown mass +of spores. An examination of the younger parts of the same plants will +probably show small buds (Fig. 54, _H_), which contain the female +reproductive organs, from which the sporogonia arise. + +[Illustration: FIG. 52.--_A_, part of a plant of a leafy liverwort +(_Madotheca_), × 2. _B_, part of the same, seen from below, × 4. _C_, +a branch with two open sporogonia (_sp._), × 4. _D_, a single +sporogonium, × 8.] + +On other plants may be found numerous short side branches (Fig. 53, +_B_), with very closely set leaves. If these are carefully separated, +the antheridia can just be seen as minute whitish globules, barely +visible to the naked eye. Plants that, like this one, have the male +and female reproductive organs on distinct plants, are said to be +"dioecious." + + A microscopical examination of the stem and leaves shows their + structure to be very simple. The former is cylindrical, and composed + of nearly uniform elongated cells, with straight cross-walls. The + leaves consist of a single layer of small, roundish cells, which, + like those of the stem, contain numerous rounded chloroplasts, to + which is due their dark green color. + + The tissues are developed from a single apical cell, but it is + difficult to obtain good sections through it. + + The antheridia are borne singly at the bases of the leaves on the + special branches already described (Fig. 53, _A_, _an._). By + carefully dissecting with needles such a branch in a drop of water, + some of the antheridia will usually be detached uninjured, and may + be readily studied, the full-grown ones being just large enough to + be seen with the naked eye. They are globular bodies, attached by a + stalk composed of two rows of cells. The globular portion consists + of a wall of chlorophyll-bearing cells, composed of two layers + below, but single above (Fig. 53, _C_). Within is a mass of + excessively small cells, each of which contains a spermatozoid. In + the young antheridium (_A_, _an._) the wall is single throughout, + and the central cells few in number. To study them in their natural + position, thin longitudinal sections of the antheridial branch + should be made. + +[Illustration: FIG. 53.--_A_, end of a branch from a male plant of +_Madotheca_. The small side branchlets bear the antheridia, × 2. _B_, +two young antheridia (_an._), the upper one seen in optical section, +the lower one from without, × 150. _C_, a ripe antheridium, optical +section, × 50. _D_, sperm cells with young spermatozoids. _E_, ripe +spermatozoids, × 600.] + + When ripe, if brought into water, the antheridium bursts at the top + into a number of irregular lobes that curl back and allow the mass + of sperm cells to escape. The spermatozoids, which are derived + principally from the nucleus of the sperm cells (53, _D_) are so + small as to make a satisfactory examination possible only with very + powerful lenses. The ripe spermatozoid is coiled in a flat spiral + (53, _E_), and has two excessively delicate cilia, visible only + under the most favorable circumstances. + + The female organ in the bryophytes is called an "archegonium," and + differs considerably from anything we have yet studied, but recalls + somewhat the structure of the oögonium of _Chara_. They are found in + groups, contained in little bud-like branches (54, _H_). In order to + study them, a plant should be chosen that has numbers of such buds, + and the smallest that can be found should be used. Those containing + the young archegonia are very small; but after one has been + fertilized, the leaves enclosing it grow much larger, and the bud + becomes quite conspicuous, being surrounded by two or three + comparatively large leaves. By dissecting the young buds, archegonia + in all stages of growth may be found. + +[Illustration: FIG. 54.--_A-D_, development of the archegonium of +_Madotheca_. _B_, surface view, the others in optical section. _o_, +egg cell, × 150. _E_, base of a fertilized archegonium, containing a +young embryo (_em._), × 150. _F_, margin of one of the leaves +surrounding the archegonia. _G_, young sporogonium still surrounded by +the much enlarged base of the archegonium. _h_, neck of the +archegonium. _ar._ abortive archegonia, × 12. _H_, short branch +containing the young sporogonium, × 4.] + + When very young the archegonium is composed of an axial row of three + cells, surrounded by a single outer layer of cells, the upper ones + forming five or six regular rows, which are somewhat twisted + (Fig. 54, _A_, _B_). As it becomes older, the lower part enlarges + slightly, the whole looking something like a long-necked flask (_C_, + _D_). The centre of the neck is occupied by a single row of cells + (canal cells), with more granular contents than the outer cells, the + lowest cell of the row being somewhat larger than the others + (Fig. 54, _C_, _o_). When nearly ripe, the division walls of the + canal cells are absorbed, and the protoplasm of the lowest cell + contracts and forms a globular naked cell, the egg cell (_D_, _o_). + If a ripe archegonium is placed in water, it soon opens at the top, + and the contents of the canal cells are forced out, leaving a clear + channel down to the egg cell. If the latter is not fertilized, the + inner walls of the neck cells turn brown, and the egg cell dies; but + if a spermatozoid penetrates to the egg cell, the latter develops a + wall and begins to grow, forming the embryo or young sporogonium. + +[Illustration: FIG. 55.--Longitudinal section of a nearly full-grown +sporogonium of _Madotheca_, which has not, however, broken through the +overlying cells, × 25. _sp._ cavity in which the spores are formed. +_ar._ abortive archegonium.] + + The first division wall to be formed in the embryo is transverse, + and is followed by vertical ones (Fig. 54, _E_, _em._). As the + embryo enlarges, the walls of the basal part of the archegonium grow + rapidly, so that the embryo remains enclosed in the archegonium + until it is nearly full-grown (Fig. 55). As it increases in size, it + becomes differentiated into three parts: a wedge-shaped base or + "foot" penetrating downward into the upper part of the plant, and + serving to supply the embryo with nourishment; second, a stalk + supporting the third part, the capsule or spore-bearing portion of + the fruit. The capsule is further differentiated into a wall, which + later becomes dark colored, and a central cavity, in which are + developed special cells, some of which by further division into four + parts produce the spores, while the others, elongating enormously, + give rise to special cells, called elaters (Fig. 56, _B_). + +[Illustration: FIG. 56.--Spore (_A_) and two elaters (_B_) of +_Madotheca_, × 300.] + + The ripe spores are nearly globular, contain chlorophyll and drops + of oil, and the outer wall is brown and covered with fine points + (Fig. 56, _A_). The elaters are long-pointed cells, having on the + inner surface of the wall a single or double dark brown spiral band. + These bands are susceptible to changes in moisture, and by their + movements probably assist in scattering the spores after the + sporogonium opens. + +Just before the spores are ripe, the stalk of the sporogonium +elongates rapidly, carrying up the capsule, which breaks through the +archegonium wall, and finally splits into four valves, and discharges +the spores. + +There are four orders of the liverworts represented in the United +States, three of which differ from the one we have studied in being +flattened plants, without distinct stems and leaves,--at least, the +leaves when present are reduced to little scales upon the lower +surface. + +The first order (_Ricciaceæ_) are small aquatic forms, or grow on damp +ground or rotten logs. They are not common forms, and not likely to be +encountered by the student. One of the floating species is shown in +figure 57, _A_. + +The second order, the horned liverworts (_Anthoceroteæ_), are +sometimes to be met with in late summer and autumn, forms growing +mostly on damp ground, and at once recognizable by their long-pointed +sporogonia, which open when ripe by two valves, like a bean pod +(Fig. 57, _B_). + +The third order (_Marchantiaceæ_) includes the most conspicuous +members of the whole class. Some of them, like the common liverwort +(_Marchantia_), shown in Figure 57, _F_, _K_, and the giant liverwort +(Fig. 57, _D_), are large and common forms, growing on the ground in +shady places, the former being often found also in greenhouses. They +are fastened to the ground by numerous fine, silky hairs, and the +tissues are well differentiated, the upper surface of the plant having +a well-marked epidermis, with peculiar breathing pores, large enough +to be seen with the naked eye (Fig. 57, _E_, _J_, _K_) Each of these +is situated in the centre of a little area (Fig. 57, _E_), and beneath +it is a large air space, into which the chlorophyll-bearing cells +(_cl._) of the plant project (_J_). + +The sexual organs are often produced in these forms upon special +branches (_G_), or the antheridia may be sunk in discs on the upper +side of the stem (_D_, _an._). + +[Illustration: FIG. 57.--Forms of liverworts. _A_, _Riccia_, natural +size. _B_, _Anthoceros_ (horned liverwort), natural size. _sp._ +sporogonia. _C_, _Lunularia_, natural size, _x_, buds. _D_, giant +liverwort (_Conocephalus_), natural size. _an._ antheridial disc. _E_, +small piece of the epidermis, showing the breathing pores, × 2. _F_, +common liverwort (_Marchantia_), × 2. _x_, cups containing buds. _G_, +archegonial branch of common liverwort, natural size. _H_, two young +buds from the common liverwort, × 150. _I_, a full-grown bud, × 25. +_J_, vertical section through the body of _Marchantia_, cutting +through a breathing pore (_s_), × 50. _K_, surface view of a breathing +pore, × 150. _L_, a leafy liverwort (_Jungermannia_). _sp._ +sporogonium, × 2.] + +Some forms, like _Marchantia_ and _Lunularia_ (Fig. 57, _C_), produce +little cups (_x_), circular in the first, semicircular in the second, +in which special buds (_H_, _I_) are formed that fall off and produce +new plants. + +The highest of the liverworts (_Jungermanniaceæ_) are, for the most +part, leafy forms like _Madotheca_, and represented by a great many +common forms, growing usually on tree trunks, etc. They are much like +_Madotheca_ in general appearance, but usually very small and +inconspicuous, so as to be easily overlooked, especially as their +color is apt to be brownish, and not unlike that of the bark on which +they grow (Fig. 57, _L_). + + +CLASS II.--THE TRUE MOSSES. + +The true mosses (_Musci_) resemble in many respects the higher +liverworts, such as _Madotheca_ or _Jungermannia_, all of them having +well-marked stems and leaves. The spore fruit is more highly +developed than in the liverworts, but never contains elaters. + +A good idea of the general structure of the higher mosses may be had +from a study of almost any common species. One of the most convenient, +as well as common, forms (_Funaria_) is to be had almost the year +round, and fruits at almost all seasons, except midwinter. It grows in +close patches on the ground in fields, at the bases of walls, +sometimes in the crevices between the bricks of sidewalks, etc. If +fruiting, it may be recognized by the nodding capsule on a long stalk, +that is often more or less twisted, being sensitive to changes in the +moisture of the atmosphere. The plant (Fig. 58, _A_, _B_) has a short +stem, thickly set with relatively large leaves. These are oblong and +pointed, and the centre is traversed by a delicate midrib. The base of +the stem is attached to the ground by numerous fine brown hairs. + +The mature capsule is broadly oval in form (Fig. 58, _C_), and +provided with a lid that falls off when the spores are ripe. While the +capsule is young it is covered by a pointed membranous cap (_B_, +_cal._) that finally falls off. When the lid is removed, a fine fringe +is seen surrounding the opening of the capsule, and serving the same +purpose as the elaters of the liverworts (Fig. 58, _E_). + +[Illustration: FIG. 58.--_A_, fruiting plant of a moss (_Funaria_), +with young sporogonium (_sp._), × 4. B, plant with ripe sporogonium. +_cal_. calyptra, × 2. _C_, sporogonium with calyptra removed. _op._ +lid, × 4. _D_, spores: i, ungerminated; ii-iv, germinating, × 300. +_E_, two teeth from the margin of the capsule, × 50. _F_, epidermal +cells and breathing pore from the surface of the sporogonium, × 150. +_G_, longitudinal section of a young sporogonium, × 12. _sp._ spore +mother cells. _H_, a small portion of _G_, magnified about 300 times. +_sp._ spore mother cells.] + +If the lower part of the stem is carefully examined with a lens, we +may detect a number of fine green filaments growing from it, looking +like the root hairs, except for their color. Sometimes the ground +about young patches of the moss is quite covered by a fine film of +such threads, and looking carefully over it probably very small moss +plants may be seen growing up here and there from it. + +[Illustration: FIG. 59.--Longitudinal section through the summit of a +small male plant of _Funaria_. _a_, _a'_, antheridia. _p_, paraphysis. +_L_, section of a leaf, × 150.] + +This moss is dioecious. The male plants are smaller than the female, +and may be recognized by the bright red antheridia which are formed at +the end of the stem in considerable numbers, and surrounded by a +circle of leaves so that the whole looks something like a flower. +(This is still more evident in some other mosses. See Figure 65, _E_, +_F_.) + + The leaves when magnified are seen to be composed of a single layer + of cells, except the midrib, which is made up of several thicknesses + of elongated cells. Where the leaf is one cell thick, the cells are + oblong in form, becoming narrower as they approach the midrib and + the margin. They contain numerous chloroplasts imbedded in the layer + of protoplasm that lines the wall. The nucleus (Fig. 63, _C_, _n_) + may usually be seen without difficulty, especially if the leaf is + treated with iodine. This plant is one of the best for studying the + division of the chloroplasts, which may usually be found in all + stages of division (Fig. 63, _D_). In the chloroplasts, especially + if the plant has been exposed to light for several hours, will be + found numerous small granules, that assume a bluish tint on the + application of iodine, showing them to be starch grains. If the + plant is kept in the dark for a day or two, these will be absent, + having been used up; but if exposed to the light again, new ones + will be formed, showing that they are formed only under the action + of light. + +[Illustration: FIG. 60.--_A_, _B_, young antheridia of _Funaria_, +optical section, × 150. _C_, two sperm cells of _Atrichum_. _D_, +spermatozoids of _Sphagnum_, × 600.] + + Starch is composed of carbon, hydrogen, and oxygen, and so far as is + known is only produced by chlorophyll-bearing cells, under the + influence of light. The carbon used in the manufacture of starch is + taken from the atmosphere in the form of carbonic acid, so that + green plants serve to purify the atmosphere by the removal of this + substance, which is deleterious to animal life, while at the same + time the carbon, an essential part of all living matter, is combined + in such form as to make it available for the food of other + organisms. + + The marginal cells of the leaf are narrow, and some of them + prolonged into teeth. + + A cross-section of the stem (63, _E_) shows on the outside a single + row of epidermal cells, then larger chlorophyll-bearing cells, and + in the centre a group of very delicate, small, colorless cells, + which in longitudinal section are seen to be elongated, and similar + to those forming the midrib of the leaf. These cells probably serve + for conducting fluids, much as the similar but more perfectly + developed bundles of cells (fibro-vascular bundles) found in the + stems and leaves of the higher plants. + + The root hairs, fastening the plant to the ground, are rows of + cells with brown walls and oblique partitions. They often merge + insensibly into the green filaments (protonema) already noticed. + These latter have usually colorless walls, and more numerous + chloroplasts, looking very much like a delicate specimen of + _Cladophora_ or some similar alga. If a sufficient number of these + filaments is examined, some of them will probably show young moss + plants growing from them (Fig. 63, _A_, _k_), and with a little + patience the leafy plant can be traced back to a little bud + originating as a branch of the filament. Its diameter is at first + scarcely greater than that of the filament, but a series of walls, + close together, are formed, so placed as to cut off a pyramidal cell + at the top, forming the apical cell of the young moss plant. This + apical cell has the form of a three-sided pyramid with the base + upward. From it are developed three series of cells, cut off in + succession from the three sides, and from these cells are derived + all the tissues of the plant which soon becomes of sufficient size + to be easily recognizable. + + The protonemal filaments may be made to grow from almost any part of + the plant by keeping it moist, but grow most abundantly from the + base of the stem. + + The sexual organs are much like those of the liverworts and are + borne at the apex of the stems. + + The antheridia (Figs. 59, 60) are club-shaped bodies with a short + stalk. The upper part consists of a single layer of large + chlorophyll-bearing cells, enclosing a mass of very small, nearly + cubical, colorless, sperm cells each of which contains an + excessively small spermatozoid. + + The young antheridium has an apical cell giving rise to two series + of segments (Fig. 60, _A_), which in the earlier stages are very + plainly marked. + + When ripe the chlorophyll in the outer cells changes color, becoming + red, and if a few such antheridia from a plant that has been kept + rather dry for a day or two, are teased out in a drop of water, they + will quickly open at the apex, the whole mass of sperm cells being + discharged at once. + + Among the antheridia are borne peculiar hairs (Fig. 59, _p_) tipped + by a large globular cell. + +[Illustration: FIG. 61.--_A_, _B_, young; _C_, nearly ripe archegonium +of _Funaria_, optical section, × 150. _D_, upper part of the neck of +_C_, seen from without, showing how it is twisted. _E_, base of a ripe +archegonium. _F_, open apex of the same, × 150. _o_, egg cell. _b_, +ventral canal cell.] + + Owing to their small size the spermatozoids are difficult to see + satisfactorily and other mosses (_e.g._ peat mosses, Figure 64, the + hairy cap moss, Figure 65, _I_), are preferable where obtainable. + The spermatozoids of a peat moss are shown in Figure 60, _D_. Like + all of the bryophytes they have but two cilia. + + The archegonia (Fig. 61) should be looked for in the younger plants + in the neighborhood of those that bear capsules. Like the antheridia + they occur in groups. They closely resemble those of the liverworts, + but the neck is longer and twisted and the base more massive. + Usually but a single one of the group is fertilized. + +[Illustration: FIG. 62.--_A_, young embryo of _Funaria_, still +enclosed within the base of the archegonium, × 300. _B_, an older +embryo freed from the archegonium, × 150. _a_, the apical cell.] + + To study the first division of the embryo, it is usually necessary + to render the archegonium transparent, which may be done by using a + little caustic potash; or letting it lie for a few hours in dilute + glycerine will sometimes suffice. If potash is used it must be + thoroughly washed away, by drawing pure water under the cover glass + with a bit of blotting paper, until every trace of the potash is + removed. The first wall in the embryo is nearly at right angles to + the axis of the archegonium and divides the egg cell into nearly + equal parts. This is followed by nearly vertical walls in each cell + (Fig. 62, _A_). Very soon a two-sided apical cell (Fig. 62, _B_, + _a_) is formed in the upper half of the embryo, which persists until + the embryo has reached a considerable size. As in the liverworts the + young embryo is completely covered by the growing archegonium wall. + + The embryo may be readily removed from the archegonium by adding a + little potash to the water in which it is lying, allowing it to + remain for a few moments and pressing gently upon the cover glass + with a needle. In this way it can be easily forced out of the + archegonium, and then by thoroughly washing away the potash, + neutralizing if necessary with a little acetic acid, very beautiful + preparations may be made. If desired, these may be mounted + permanently in glycerine which, however, must be added very + gradually to avoid shrinking the cells. + +[Illustration: FIG. 63.--_A_, protonema of _Funaria_, with a bud +(_k_), × 50. _B_, outline of a leaf, showing also the thickened +midrib, × 12. _C_, cells of the leaf, × 300. _n_, nucleus. _D_, +chlorophyll granules undergoing division, × 300. _E_, cross-section of +the stem, × 50.] + + For some time the embryo has a nearly cylindrical form, but as it + approaches maturity the differentiation into stalk and capsule + becomes apparent. The latter increases rapidly in diameter, assuming + gradually the oval shape of the full-grown capsule. A longitudinal + section of the nearly ripe capsule (Fig. 58, _G_) shows two distinct + portions; an outer wall of two layers of cells, and an inner mass of + cells in some of which the spores are produced. This inner mass of + cells is continuous with the upper part of the capsule, but + connected with the side walls and bottom by means of slender, + branching filaments of chlorophyll-bearing cells. + + The spores arise from a single layer of cells near the outside of + the inner mass of cells (_G_, _sp._). These cells (_H_, _sp._) are + filled with glistening, granular protoplasm; have a large and + distinct nucleus, and no chlorophyll. They finally become entirely + separated and each one gives rise to four spores which closely + resemble those of the liverworts but are smaller. + + Near the base of the capsule, on the outside, are formed breathing + pores (Fig. 58, _F_) quite similar to those of the higher plants. + + If the spores are kept in water for a few days they will germinate, + bursting the outer brown coat, and the contents protruding through + the opening surrounded by the colorless inner spore membrane. The + protuberance grows rapidly in length and soon becomes separated from + the body of the spore by a wall, and lengthening, more and more, + gives rise to a green filament like those we found attached to the + base of the full-grown plant, and like those giving rise to buds + that develop into leafy plants. + + +CLASSIFICATION OF THE MOSSES. + +The mosses may be divided into four orders: I. The peat mosses +(_Sphagnaceæ_); II. _Andreæaceæ_; III. _Phascaceæ_; IV. The common +mosses (_Bryaceæ_). + +[Illustration: FIG. 64.--_A_, a peat moss (_Sphagnum_), × œ. _B_, a +sporogonium of the same, × 3. _C_, a portion of a leaf, × 150. The +narrow, chlorophyll-bearing cells form meshes, enclosing the large, +colorless empty cells, whose walls are marked with thickened bars, and +contain round openings (_o_).] + +The peat mosses (Fig. 64) are large pale-green mosses, growing often +in enormous masses, forming the foundation of peat-bogs. They are of a +peculiar spongy texture, very light when dry, and capable of absorbing +a great amount of water. They branch (Fig. 64, _A_), the branches +being closely crowded at the top, where the stems continue to grow, +dying away below. + +[Illustration: FIG. 65.--Forms of mosses. _A_, plant of _Phascum_, +× 3. _B_, fruiting plant of _Atrichum_, × 2. _C_, young capsule of +hairy-cap moss (_Polytrichum_), covered by the large, hairy calyptra. +_D_, capsules of _Bartramia_: i, with; ii, without the calyptra. _E_, +upper part of a male plant of _Atrichum_, showing the flower, × 2. +_F_, a male plant of _Mnium_, × 4. _G_, pine-tree moss (_Clemacium_), +× 1. _H_, _Hypnum_, × 1. _I_, ripe capsules of hairy-cap moss: i, +with; ii, without calyptra.] + +The sexual organs are rarely met with, but should be looked for late +in autumn or early spring. The antheridial branches are often +bright-colored, red or yellow, so as to be very conspicuous. The +capsules, which are not often found, are larger than in most of the +common mosses, and quite destitute of a stalk, the apparent stalk +being a prolongation of the axis of the plant in the top of which the +base of the sporogonium is imbedded. The capsule is nearly globular, +opening by a lid at the top (Fig. 64, _B_). + + A microscopical examination of the leaves, which are quite destitute + of a midrib, shows them to be composed of a network of narrow + chlorophyll-bearing cells surrounding much larger empty ones whose + walls are marked with transverse thickenings, and perforated here + and there with large, round holes (Fig. 64, _C_). It is to the + presence of these empty cells that the plant owes its peculiar + spongy texture, the growing plants being fairly saturated with + water. + +The _Andreæaceæ_ are very small, and not at all common. The capsule +splits into four valves, something like a liverwort. + +The _Phascaceæ_ are small mosses growing on the ground or low down on +the trunks of trees, etc. They differ principally from the common +mosses in having the capsule open irregularly and not by a lid. The +commonest forms belong to the genus _Phascum_ (Fig. 65, _A_). + +The vast majority of the mosses the student is likely to meet with +belong to the last order, and agree in the main with the one +described. Some of the commoner forms are shown in Figure 65. + + + + +CHAPTER XII. + +SUB-KINGDOM V. + +PTERIDOPHYTES. + + +If we compare the structure of the sporogonium of a moss or liverwort +with the plant bearing the sexual organs, we find that its tissues are +better differentiated, and that it is on the whole a more complex +structure than the plant that bears it. It, however, remains attached +to the parent plant, deriving its nourishment in part through the +"foot" by means of which it is attached to the plant. + +In the Pteridophytes, however, we find that the sporogonium becomes +very much more developed, and finally becomes entirely detached from +the sexual plant, developing in most cases roots that fasten it to the +ground, after which it may live for many years, and reach a very large +size. + +The sexual plant, which is here called the "prothallium," is of very +simple structure, resembling the lower liverworts usually, and never +reaches more than about a centimetre in diameter, and is often much +smaller than this. + +The common ferns are the types of the sub-kingdom, and a careful study +of any of these will illustrate the principal peculiarities of the +group. The whole plant, as we know it, is really nothing but the +sporogonium, originating from the egg cell in exactly the same way as +the moss sporogonium, and like it gives rise to spores which are +formed upon the leaves. + +The spores may be collected by placing the spore-bearing leaves on +sheets of paper and letting them dry, when the ripe spores will be +discharged covering the paper as a fine, brown powder. If these are +sown on fine, rather closely packed earth, and kept moist and covered +with glass so as to prevent evaporation, within a week or two a fine, +green, moss-like growth will make its appearance, and by the end of +five or six weeks, if the weather is warm, little, flat, heart-shaped +plants of a dark-green color may be seen. These look like small +liverworts, and are the sexual plants (prothallia) of our ferns +(Fig. 66, _F_). Removing one of these carefully, we find on the lower +side numerous fine hairs like those on the lower surface of the +liverworts, which fasten it firmly to the ground. By and by, if our +culture has been successful, we may find attached to some of the +larger of these, little fern plants growing from the under side of the +prothallia, and attached to the ground by a delicate root. As the +little plant becomes larger the prothallium dies, leaving it attached +to the ground as an independent plant, which after a time bears the +spores. + +[Illustration: FIG. 66.--_A_, spore of the ostrich fern (_Onoclea_), +with the outer coat removed. _B_, germinating spore, × 150. _C_, young +prothallium, × 50. _r_, root hair. _sp._ spore membrane. _D_, _E_, +older prothallia. _a_, apical cell, × 150. _F_, a female prothallium, +seen from below, × 12. _ar._ archegonia. _G_, _H_, young archegonia, +in optical section, × 150. _o_, central cell. _b_, ventral canal cell. +_c_, upper canal cell. _I_, a ripe archegonium in the act of opening, +× 150. _o_, egg cell. _J_, a male prothallium, × 50. _an._ antheridia. +_K_, _L_, young antheridia, in optical section, × 300. _M_, ripe +antheridium, × 300. _sp._ sperm cells. _N_, _O_, antheridia that have +partially discharged their contents, × 300. _P_, spermatozoids, killed +with iodine, × 500. _v_, vesicle attached to the hinder end.] + +In choosing spores for germination it is best to select those of large +size and containing abundant chlorophyll, as they germinate more +readily. Especially favorable for this purpose are the spores of the +ostrich fern (_Onoclea struthiopteris_) (Fig. 70, _I_, _J_), or the +sensitive fern (_O. sensibilis_). Another common and readily grown +species is the lady fern (_Asplenium filixfoemina_) (Fig. 70, _H_). The +spores of most ferns retain their vitality for many months, and hence +can be kept dry until wanted. + + The first stages of germination may be readily seen by sowing the + spores in water, where, under favorable circumstances, they will + begin to grow within three or four days. The outer, dry, brown coat + of the spore is first ruptured, and often completely thrown off by + the swelling of the spore contents. Below this is a second colorless + membrane which is also ruptured, but remains attached to the spore. + Through the orifice in the second coat, the inner delicate membrane + protrudes in the form of a nearly colorless papilla which rapidly + elongates and becomes separated from the body of the spore by a + partition, constituting the first root hair (Fig. 66, _B_, _C_, + _r_). The body of the spore containing most of the chlorophyll + elongates more slowly, and divides by a series of transverse walls + so as to form a short row of cells, resembling in structure some of + the simpler algæ (_C_). + + In order to follow the development further, spores must be sown upon + earth, as they do not develop normally in water beyond this stage. + + In studying plants grown on earth, they should be carefully removed + and washed in a drop of water so as to remove, as far as possible, + any adherent particles, and then may be mounted in water for + microscopic examination. + + In most cases, after three or four cross-walls are formed, two walls + arise in the end cell so inclined as to enclose a wedge-shaped cell + (_a_) from which are cut off two series of segments by walls + directed alternately right and left (Fig. 66, _D_, _E_, _a_), the + apical cell growing to its original dimensions after each pair of + segments is cut off. The segments divide by vertical walls in + various directions so that the young plant rapidly assumes the form + of a flat plate of cells attached to the ground by root hairs + developed from the lower surfaces of the cells, and sometimes from + the marginal ones. As the division walls are all vertical, the plant + is nowhere more than one cell thick. The marginal cells of the young + segments divide more rapidly than the inner ones, and soon project + beyond the apical cell which thus comes to lie at the bottom of a + cleft in the front of the plant which in consequence becomes + heart-shaped (_E_, _F_). Sooner or later the apical cell ceases to + form regular segments and becomes indistinguishable from the other + cells. + + In the ostrich fern and lady fern the plants are dioecious. The male + plants (Fig. 66, _J_) are very small, often barely visible to the + naked eye, and when growing thickly form dense, moss-like patches. + They are variable in form, some irregularly shaped, others simple + rows of cells, and some have the heart shape of the larger plants. + +The female plants (Fig. 66, _F_) are always comparatively large and +regularly heart-shaped, occasionally reaching a diameter of nearly or +quite one centimetre, so that they are easily recognizable without +microscopical examination. + + All the cells of the plant except the root hairs contain large and + distinct chloroplasts much like those in the leaves of the moss, and + like them usually to be found in process of division. + + The archegonia arise from cells of the lower surface, just behind + the notch in front (Fig. 66, _F_, _ar._). Previous to their + formation the cells at this point divide by walls parallel to the + surface of the plant, so as to form several layers of cells, and + from the lowest layer of cells the archegonia arise. They resemble + those of the liverworts but are shorter, and the lower part is + completely sunk within the tissues of the plant (Fig. 66, _G_, _I_). + They arise as single surface cells, this first dividing into three + by walls parallel to the outer surface. The lower cell undergoes one + or two divisions, but undergoes no further change; the second cell + (_C_, _o_), becomes the egg cell, and from it is cut off another + cell (_c_), the canal cell of the neck; the uppermost of the three + becomes the neck. There are four rows of neck cells, the two forward + ones being longer than the others, so that the neck is bent + backward. In the full-grown archegonium, there are two canal cells, + the lower one (_H_, _b_) called the ventral canal cell, being + smaller than the other. + + Shortly before the archegonium opens, the canal cells become + disorganized in the same way as in the bryophytes, and the + protoplasm of the central cell contracts to form the egg cell which + shows a large, central nucleus, and in favorable cases, a clear + space at the top called the "receptive spot," as it is here that the + spermatozoid enters. When ripe, if placed in water, the neck cells + become very much distended and finally open widely at the top, the + upper ones not infrequently being detached, and the remains of the + neck cells are forced out (Fig. 66, _I_). + + The antheridia (Fig. 66. _J_, _M_) arise as simple hemispherical + cells, in which two walls are formed (_K_ I, II), the lower + funnel-shaped, the upper hemispherical and meeting the lower one so + as to enclose a central cell (shaded in the figure), from which the + sperm cells arise. Finally, a ring-shaped wall (_L_ iii) is formed, + cutting off a sort of cap cell, so that the antheridium at this + stage consists of a central cell, surrounded by three other cells, + the two lower ring-shaped, the upper disc-shaped. The central cell, + which contains dense, glistening protoplasm, is destitute of + chlorophyll, but the outer cells have a few small chloroplasts. The + former divides repeatedly, until a mass of about thirty-two sperm + cells is formed, each giving rise to a large spirally-coiled + spermatozoid. When ripe, the mass of sperm cells crowds so upon the + outer cells as to render them almost invisible, and as they ripen + they separate by a partial dissolving of the division walls. When + brought into water, the outer cells of the antheridium swell + strongly, and the matter derived from the dissolved walls of the + sperm cells also absorbs water, so that finally the pressure becomes + so great that the wall of the antheridium breaks, and the sperm + cells are forced out by the swelling up of the wall cells (_N_, + _O_). After lying a few moments in the water, the wall of each sperm + cell becomes completely dissolved, and the spermatozoids are + released, and swim rapidly away with a twisting movement. They may + be killed with a little iodine, when each is seen to be a somewhat + flattened band, coiled several times. At the forward end, the coils + are smaller, and there are numerous very long and delicate cilia. At + the hinder end may generally be seen a delicate sac (_P_, _v_), + containing a few small granules, some of which usually show the + reaction of starch, turning blue when iodine is applied. + + In studying the development of the antheridia, it is only necessary + to mount the plants in water and examine them directly; but the + study of the archegonia requires careful longitudinal sections of + the prothallium. To make these, the prothallium should be placed + between small pieces of pith, and the razor must be very sharp. It + may be necessary to use a little potash to make the sections + transparent enough to see the structure, but this must be used + cautiously on account of the great delicacy of the tissues. + + If a plant with ripe archegonia is placed in a drop of water, with + the lower surface uppermost, and at the same time male plants are + put with it, and the whole covered with a cover glass, the + archegonia and antheridia will open simultaneously; and, if examined + with the microscope, we shall see the spermatozoids collect about + the open archegonia, to which they are attracted by the substance + forced out when it opens. With a little patience, one or more may be + seen to enter the open neck through which it forces itself, by a + slow twisting movement, down to the egg cell. In order to make the + experiment successful, the plants should be allowed to become a + little dry, care being taken that no water is poured over them for a + day or two beforehand. + + The first divisions of the fertilized egg cell resemble those in the + moss embryo, except that the first wall is parallel with the + archegonium axis, instead of at right angles to it. Very soon, + however, the embryo becomes very different, four growing points + being established instead of the single one found in the moss + embryo. The two growing points on the side of the embryo nearest the + archegonium neck grow faster than the others, one of these + outstripping the other, and soon becoming recognizable as the first + leaf of the embryo (Fig. 67, _A_, _L_). The other (_r_) is peculiar, + in having its growing point covered by several layers of cells, cut + off from its outer face, a peculiarity which we shall find is + characteristic of the roots of all the higher plants, and, indeed, + this is the first root of the young fern. Of the other two growing + points, the one next the leaf grows slowly, forming a blunt cone + (_st._), and is the apex of the stem. The other (_f_) has no + definite form, and serves merely as an organ of absorption, by means + of which nourishment is supplied to the embryo from the prothallium; + it is known as the foot. + +[Illustration: FIG. 67.--_A_, embryo of the ostrich fern just before +breaking through the prothallium, × 50. _st._ apex of stem. _l_, first +leaf. _r_, first root. _ar._ neck of the archegonium. _B_, young +plant, still attached to the prothallium (_pr._). _C_, underground +stem of the maiden-hair fern (_Adiantum_), with one young leaf, and +the base of an older one, × 1. _D_, three cross-sections of a leaf +stalk: i, nearest the base; iii, nearest the blade of the leaf, +showing the division of the fibro-vascular bundle, × 5. _E_, part of +the blade of the leaf, × œ. _F_, a single spore-bearing leaflet, +showing the edge folded over to cover the sporangia, × 1. _G_, part of +the fibro-vascular bundle of the leaf stalk (cross-section), × 50. +_x_, woody part of the bundle. _y_, bast. _sh._ bundle sheath. _H_, a +small portion of the same bundle, × 150. _I_, stony tissue from the +underground stem, × 150. _J_, sieve tube from the underground stem, +× 300.] + + Up to this point, all the cells of the embryo are much alike, and + the embryo, like that of the bryophytes, is completely surrounded by + the enlarged base of the archegonium (compare Fig. 67, _A_, with + Fig. 55); but before the embryo breaks through the overlying cells a + differentiation of the tissues begins. In the axis of each of the + four divisions the cells divide lengthwise so as to form a + cylindrical mass of narrow cells, not unlike those in the stem of a + moss. Here, however, some of the cells undergo a further change; the + walls thicken in places, and the cells lose their contents, forming + a peculiar conducting tissue (tracheary tissue), found only in the + two highest sub-kingdoms. The whole central cylinder is called a + "fibro-vascular bundle," and in its perfect form, at least, is found + in no plants below the ferns, which are also the first to develop + true roots. + +The young root and leaf now rapidly elongate, and burst through the +overlying cells, the former growing downward and becoming fastened in +the ground, the latter growing upward through the notch in the front +of the prothallium, and increasing rapidly in size (Fig. 67, _B_). The +leaf is more or less deeply cleft, and traversed by veins which are +continuations of the fibro-vascular bundle of the stalk, and +themselves fork once or twice. The surface of the leaf is covered with +a well-developed epidermis, and the cells occupying the space between +the veins contain numerous chloroplasts, so that the little plant is +now quite independent of the prothallium, which has hitherto supported +it. As soon as the fern is firmly established, the prothallium withers +away. + +Comparing this now with the development of the sporogonium in the +bryophytes, it is evident that the young fern is the equivalent of the +sporogonium or spore fruit of the former, being, like it, the direct +product of the fertilized egg cell; and the prothallium represents the +moss or liverwort, upon which are borne the sexual organs. In the +fern, however, the sporogonium becomes entirely independent of the +sexual plant, and does not produce spores until it has reached a large +size, living many years. The sexual stage, on the other hand, is very +much reduced, as we have seen, being so small as to be ordinarily +completely overlooked; but its resemblance to the lower liverworts, +like _Riccia_, or the horned liverworts, is obvious. The terms +oöphyte (egg-bearing plant) and sporophyte (spore-bearing plant, or +sporogonium) are sometimes used to distinguish between the sexual +plant and the spore-bearing one produced from it. + +The common maiden-hair fern (_Adiantum pedatum_) has been selected +here for studying the structure of the full-grown sporophyte, but +almost any other common fern will answer. The maiden-hair fern is +common in rich woods, and may be at once recognized by the form of its +leaves. These arise from a creeping, underground stem (Fig. 67, _C_), +which is covered with brownish scales, and each leaf consists of a +slender stalk, reddish brown or nearly black in color, which divides +into two equal branches at the top. Each of these main branches bears +a row of smaller ones on the outside, and these have a row of delicate +leaflets on each side (Fig. 67, _E_). The stem of the plant is +fastened to the ground by means of numerous stout roots. The youngest +of these, near the growing point of the stem, are unbranched, but the +older ones branch extensively (_C_). + +On breaking the stem across, it is seen to be dark-colored, except in +the centre, which is traversed by a woody cylinder (fibro-vascular +bundle) of a lighter color. This is sometimes circular in sections, +sometimes horse-shoe shaped. Where the stem branches, the bundle of +the branch may be traced back to where it joins that of the main stem. + + A thin cross-section of the stem shows, when magnified, three + regions. First, an outer row of cells, often absent in the older + portions; this is the epidermis. Second, within the epidermis are + several rows of cells similar to the epidermal cells, but somewhat + larger, and like them having dark-brown walls. These merge gradually + into larger cells, with thicker golden brown walls (Fig. 67, _I_). + The latter, if sufficiently magnified, show distinct striation of + the walls, which are often penetrated by deep narrow depressions or + "pits." This thick-walled tissue is called "stony tissue" + (schlerenchyma). All the cells contain numerous granules, which the + iodine test shows to be starch. All of this second region lying + between the epidermis and the fibro-vascular bundle is known as the + ground tissue. The third region (fibro-vascular) is, as we have seen + without the microscope, circular or horse-shoe shaped. It is sharply + separated from the ground tissue by a row of small cells, called the + "bundle sheath." The cross-section of the bundle of the leaf stalk + resembles, almost exactly, that of the stem; and, as it is much + easier to cut, it is to be preferred in studying the arrangement of + the tissues of the bundle (Fig. 67, _G_). Within the bundle sheath + (_sh._) there are two well-marked regions, a central band (_x_) of + large empty cells, with somewhat angular outlines, and distinctly + separated walls; and an outer portion (_y_) filling up the space + between these central cells and the bundle sheath. The central + tissue (_x_) is called the woody tissue (xylem); the outer, the bast + (phloem). The latter is composed of smaller cells of variable form, + and with softer walls than the wood cells. + + A longitudinal section of either the stem or leaf stalk shows that + all the cells are decidedly elongated, especially those of the + fibro-vascular bundle. The xylem (Fig. 68, _C_, _x_) is made up + principally of large empty cells, with pointed ends, whose walls are + marked with closely set, narrow, transverse pits, giving them the + appearance of little ladders, whence they are called "scalariform," + or ladder-shaped markings. These empty cells are known as + "tracheids," and tissue composed of such empty cells, "tracheary + tissue." Besides the tracheids, there are a few small cells with + oblique ends, and with some granular contents. + + The phloem is composed of cells similar to the latter, but there may + also be found, especially in the stem, other larger ones (Fig. 67, + _J_), whose walls are marked with shallow depressions, whose bottoms + are finely pitted. These are the so-called "sieve tubes." + + For microscopical examination, either fresh or alcoholic material + may be used, the sections being mounted in water. Potash will be + found useful in rendering opaque sections transparent. + +The leaves, when young, are coiled up (Fig. 67, _C_), owing to growth +in the earlier stages being greater on the lower than on the upper +side. As the leaf unfolds, the stalk straightens, and the upper +portion (blade) becomes flat. + +The general structure of the leaf stalk may be understood by making a +series of cross-sections at different heights, and examining them with +a hand lens. The arrangement is essentially the same as in the stem. +The epidermis and immediately underlying ground tissue are +dark-colored, but the inner ground tissue is light-colored, and much +softer than the corresponding part of the stem; and some of the outer +cells show a greenish color, due to the presence of chlorophyll. + +The section of the fibro-vascular bundle differs at different heights. +Near the base of the stalk (Fig. _D_ i) it is horseshoe-shaped; but, +if examined higher up, it is found to divide (II, III), one part going +to each of the main branches of the leaf. These secondary bundles +divide further, forming the veins of the leaflets. + +The leaflets (_E_, _F_) are one-sided, the principal vein running +close to the lower edge, and the others branching from it, and forking +as they approach the upper margin, which is deeply lobed, the lobes +being again divided into teeth. The leaflets are very thin and +delicate, with extremely smooth surface, which sheds water perfectly. +If the plant is a large one, some of the leaves will probably bear +spores. The spore-bearing leaves are at once distinguished by having +the middle of each lobe of the leaflets folded over upon the lower +side (_F_). On lifting one of these flaps, numerous little rounded +bodies (spore cases) are seen, whitish when young, but becoming brown +as they ripen. If a leaf with ripe spore cases is placed upon a piece +of paper, as it dries the spores are discharged, covering the paper +with the spores, which look like fine brown powder. + +[Illustration: FIG. 68.--_A_, vertical section of the leaf of the +maiden-hair fern, which has cut across a vein (_f.b._), × 150. _B_, +surface view of the epidermis from the lower surface of a leaf. _f_, +vein. _p_, breathing pore, × 150. _C_, longitudinal section of the +fibro-vascular bundle of the leaf stalk, showing tracheids with +ladder-shaped markings, × 150. _D_, longitudinal section through the +tip of a root, × 150. _a_, apical cell. _Pl._ young fibro-vascular +bundle. _Pb._ young ground tissue. _E_, cross-section of the root, +through the region of the apical cell (_a_), × 150. _F_, cross-section +through a full-grown root, × 25. _r_, root hairs. _G_, the +fibro-vascular bundle of the same, × 150.] + + A microscopical examination of the leaf stalk shows the tissues to + be almost exactly like those of the stem, except the inner ground + tissue, whose cells are thin-walled and colorless (soft tissue or + "parenchyma") instead of stony tissue. The structure of the blade of + the leaf, however, shows a number of peculiarities. Stripping off a + little of the epidermis with a needle, or shaving off a thin slice + with a razor, it may be examined in water, removing the air if + necessary with alcohol. It is composed of a single layer of cells, + of very irregular outline, except where it overlies a vein (Fig. 68, + _B_, _f_). Here the cells are long and narrow, with heavy walls. The + epidermal cells contain numerous chloroplasts, and on the under + surface of the leaf breathing pores (_stomata_, sing. _stoma_), not + unlike those on the capsules of some of the bryophytes. Each + breathing pore consists of two special crescent-shaped epidermal + cells (guard cells), enclosing a central opening or pore + communicating with an air space below. They arise from cells of the + young epidermis that divide by a longitudinal wall, that separates + in the middle, leaving the space between. + +[Illustration: FIG. 69.--_A_, mother cell of the sporangium of the +maiden-hair fern, × 300. _B_, young sporangium, surface view, × 150: +i, from the side; ii, from above. _C-E_, successive stages in the +development of the sporangium seen in optical section, × 150. _F_, +nearly ripe sporangium, × 50: i, from in front; ii, from the side. +_an._ ring. _st._ point of opening. _G_, group of four spores, × 150. +_H_, a single spore, × 300.] + + By holding a leaflet between two pieces of pith, and using a very + sharp razor, cross-sections can be made. Such a section is shown in + Fig. 68, _A_. The epidermis (_e_) bounds the upper and lower + surfaces, and if a vein (_f.b._) is cut across its structure is + found to be like that of the fibro-vascular bundle of the leaf + stalk, but much simplified. + + The ground tissue of the leaf is composed of very loose, thin-walled + cells, containing numerous chloroplasts. Between them are large and + numerous intercellular spaces, filled with air, and communicating + with the breathing pores. These are the principal assimilating cells + of the plant; _i.e._ they are principally concerned in the + absorption and decomposition of carbonic acid from the atmosphere, + and the manufacture of starch. + + The spore cases, or sporangia (Fig. 69), are at first little papillæ + (_A_), arising from the epidermal cells, from which they are early + cut off by a cross-wall. In the upper cell several walls next arise, + forming a short stalk, composed of three rows of cells, and an upper + nearly spherical cell--the sporangium proper. The latter now divides + by four walls (_B_, _C_, i-iv), into a central tetrahedral cell, and + four outer ones. The central cell, whose contents are much denser + than the outer ones, divides again by walls parallel to those first + formed, so that the young sporangium now consists of a central cell, + surrounded by two outer layers of cells. From the central cell a + group of cells is formed by further divisions (_D_), which finally + become entirely separated from each other. The outer cells of the + spore case divide only by walls, at right angles to their outer + surface, so that the wall is never more than two cells thick. Later, + the inner of these two layers becomes disorganized, so that the + central mass of cells floats free in the cavity of the sporangium, + which is now surrounded by but a single layer of cells (_E_). + + Each of the central cells divides into four spores, precisely as in + the bryophytes. The young spores (_G_, _H_) are nearly colorless and + are tetrahedral (like a three-sided pyramid) in form. As they ripen, + chlorophyll is formed in them, and some oil. The wall becomes + differentiated into three layers, the outer opaque and brown, the + two inner more delicate and colorless. + + Running around the outside of the ripe spore case is a single row of + cells (_an._), differing from the others in shape, and having their + inner walls thickened. Near the bottom, two (sometimes four) of + these cells are wider than the others, and their walls are more + strongly thickened. It is at this place (_st._) that the spore case + opens. When the ripe sporangium becomes dry, the ring of thickened + cells (_an._) contracts more strongly than the others, and acts like + a spring pulling the sporangium open and shaking out the spores, + which germinate readily under favorable conditions, and form after a + time the sexual plants (prothallia). + +The roots of the sporophyte arise in large numbers, the youngest being +always nearest the growing point of the stem or larger roots (Fig. 67, +_C_). The growing roots are pointed at the end which is also +light-colored, the older parts becoming dark brown. A cross-section of +the older portions shows a dark-brown ground tissue with a central, +light-colored, circular, fibro-vascular bundle (Fig. 68, _F_). Growing +from its outer surface are numerous brown root hairs (_r_). + + When magnified the walls of all the outer cells (epidermis and + ground tissue) are found to be dark-colored but not very thick, and + the cells are usually filled with starch. There is a bundle sheath + of much-flattened cells separating the fibro-vascular bundle from + the ground tissue. The bundle (Fig. 68, _G_) shows a band of + tracheary tissue in the centre surrounded by colorless cells, all + about alike. + + All of the organs of the fern grow from a definite apical cell, but + it is difficult to study except in the root. + + Selecting a fresh, pretty large root, a series of thin longitudinal + sections should be made either holding the root directly in the + fingers or placing it between pieces of pith. In order to avoid + drying of the sections, as is indeed true in cutting any delicate + tissue, it is a good plan to wet the blade of the razor. If the + section has passed through the apex, it will show the structure + shown in Figure 68, _D_. The apical cell (_a_) is large and + distinct, irregularly triangular in outline. It is really a + triangular pyramid (tetrahedron) with the base upward, which is + shown by making a series of cross-sections through the root tip, and + comparing them with the longitudinal sections. The cross-section of + the apical cell (Fig. _L_) appears also triangular, showing all its + faces to be triangles. Regular series of segments are cut off in + succession from each of the four faces of the apical cell. These + segments undergo regular divisions also, so that very early a + differentiation of the tissues is evident, and the three tissue + systems (epidermal, ground, and fibro-vascular) may be traced + almost to the apex of the root (68, _D_). From the outer series of + segments is derived the peculiar structure (root cap) covering the + delicate growing point and protecting it from injury. + + The apices of the stem and leaves, being otherwise protected, + develop segments only from the sides of the apical cell, the outer + face never having segments cut off from it. + + + + +CHAPTER XIII. + +CLASSIFICATION OF THE PTERIDOPHYTES. + + +There are three well-marked classes of the Pteridophytes: the ferns +(_Filicinæ_); horse-tails (_Equisetinæ_); and the club mosses +(_Lycopodinæ_). + + +CLASS I.--FERNS (_Filicinæ_). + +The ferns constitute by far the greater number of pteridophytes, and +their general structure corresponds with that of the maiden-hair fern +described. There are three orders, of which two, the true ferns +(_Filices_) and the adder-tongues (_Ophioglossaceæ_), are represented +in the United States. A third order, intermediate in some respects +between these two, and called the ringless ferns (_Marattiaceæ_), has +no representatives within our territory. + +The classification is at present based largely upon the characters of +the sporophyte, the sexual plants being still very imperfectly known +in many forms. + +The adder-tongues (_Ophioglossaceæ_) are mostly plants of rather small +size, ranging from about ten to fifty centimetres in height. There are +two genera in the United States, the true adder-tongues +(_Ophioglossum_) and the grape ferns (_Botrychium_). They send up but +one leaf each year, and this in fruiting specimens (Fig. 70, _A_) is +divided into two portions, the spore bearing (_x_) and the green +vegetative part. In _Botrychium_ the leaves are more or less deeply +divided, and the sporangia distinct (Fig. 71, _B_). In _Ophioglossum_ +the sterile division of the leaf is usually smooth and undivided, and +the spore-bearing division forms a sort of spike, and the sporangia +are much less distinct. The sporangia in both differ essentially from +those of the true ferns in not being derived from a single epidermal +cell, but are developed in part from the ground tissue of the leaf. + +[Illustration: FIG. 70.--Forms of ferns. _A_, grape fern +(_Botrychium_), × œ. _x_, fertile part of the leaf. _B_, sporangia of +_Botrychium_, × 3. _C_, flowering fern (_Osmunda_). _x_, spore-bearing +leaflets, × œ. _D_, a sporangium of _Osmunda_, × 25. _r_, ring. _E_, +_Polypodium_, × 1. _F_, brake (_Pteris_), × 1. _G_, shield fern +(_Aspidium_), × 2. _H_, spleen-wort (_Asplenium_), × 2. _I_, ostrich +fern (_Onoclea_), × 1. _J_, the same, with the incurved edges of the +leaflet partially raised so as to show the masses of sporangia +beneath, × 2.] + +In the true ferns (_Filices_), the sporangia resemble those already +described, arising in all (unless possibly _Osmunda_) from a single +epidermal cell. + +One group, the water ferns (_Rhizocarpeæ_), produce two kinds of +spores, large and small. The former produce male, the latter female +prothallia. In both cases the prothallium is small, and often scarcely +protrudes beyond the spore, and may be reduced to a single archegonium +or antheridium (Fig. 71, _B_, _C_) with only one or two cells +representing the vegetative cells of the prothallium (_v_). The water +ferns are all aquatic or semi-aquatic plants, few in number and scarce +or local in their distribution. The commonest are those of the genus +_Marsilia_ (Fig. 71, _A_), looking like a four-leaved clover. Others +(_Salvinia_, _Azolla_) are floating forms (Fig. 71, _D_). + +[Illustration: FIG. 71.--_A_, _Marsilia_, one of the _Rhizocarpeæ_ +(after Underwood). _sp._ the "fruits" containing the sporangia. _B_, a +small spore of _Pilularia_, with the ripe antheridium protruding, +× 180. _C_, male prothallium removed from the spore, × 180. _D_, +_Azolla_ (after Sprague), × 1.] + +Of the true ferns there are a number of families distinguished mainly +by the position of the sporangia, as well as by some differences in +their structure. Of our common ferns, those differing most widely from +the types are the flowering ferns (_Osmunda_), shown in Figure 70, +_C_, _D_. In these the sporangia are large and the ring (_r_) +rudimentary. The leaflets bearing the sporangia are more or less +contracted and covered completely with the sporangia, sometimes all +the leaflets of the spore-bearing leaf being thus changed, sometimes +only a few of them, as in the species figured. + +Our other common ferns have the sporangia in groups (_sori_, sing. +_sorus_) on the backs of the leaves. These sori are of different shape +in different genera, and are usually protected by a delicate +membranous covering (indusium). Illustrations of some of the commonest +genera are shown in Figure 70, _E_, _J_. + + +CLASS II.--HORSE-TAILS (_Equisetinæ_). + +The second class of the pteridophytes includes the horse-tails +(_Equisetinæ_) of which all living forms belong to a single genus +(_Equisetum_). Formerly they were much more numerous than at present, +remains of many different forms being especially abundant in the coal +formations. + +[Illustration: FIG. 72.--_A_, spore-bearing stem of the field +horse-tail (_Equisetum_), × 1. _x_, the spore-bearing cone. _B_, +sterile stem of the same, × œ. _C_, underground stem, with tubers +(_o_), × œ. _D_, cross-section of an aerial stem, × 5. _f.b._ +fibro-vascular bundle. _E_, a single fibro-vascular bundle, × 150. +_tr._ vessels. _F_, a single leaf from the cone, × 5. _G_, the same +cut lengthwise, through a spore sac (_sp._), × 5. _H_, a spore, × 50. +_I_, the same, moistened so that the elaters are coiled up, × 150. +_J_, a male prothallium, × 50. _an._ an antheridium. _K_, +spermatozoids, × 300.] + +One of the commonest forms is the field horse-tail (_Equisetum +arvense_), a very abundant and widely distributed species. It grows in +low, moist ground, and is often found in great abundance growing in +the sand or gravel used as "ballast" for railway tracks. + +The plant sends up branches of two kinds from a creeping underground +stem that may reach a length of a metre or more. This stem (Fig. 72, +_C_) is distinctly jointed, bearing at each joint a toothed sheath, +best seen in the younger portions, as they are apt to be destroyed in +the older parts. Sometimes attached to this are small tubers (_o_) +which are much-shortened branches and under favorable circumstances +give rise to new stems. They have a hard, brown rind, and are composed +within mainly of a firm, white tissue, filled with starch. + +The surface of the stem is marked with furrows, and a section across +it shows that corresponding to these are as many large air spaces that +traverse the stem from joint to joint. From the joints numerous roots, +quite like those of the ferns, arise. + +If the stem is dug up in the late fall or winter, numerous short +branches of a lighter color will be found growing from the joints. +These later grow up above ground into branches of two sorts. Those +produced first (Fig. 72, _A_), in April or May, are stouter than the +others, and nearly destitute of chlorophyll. They are usually twenty +to thirty centimetres in height, of a light reddish brown color, and, +like all the stems, distinctly jointed. The sheaths about the joints +(_L_) are much larger than in the others, and have from ten to twelve +large black teeth at the top. These sheaths are the leaves. At the top +of the branch the joints are very close together, and the leaves of +different form, and closely set so as to form a compact cone (_x_). + +A cross-section of the stem (_D_) shows much the same structure as the +underground stem, but the number of air spaces is larger, and in +addition there is a large central cavity. The fibro-vascular bundles +(_f.b._) are arranged in a circle, alternating with the air channels, +and each one has running through it a small air passage. + +The cone at the top of the branch is made up of closely set, +shield-shaped leaves, which are mostly six-sided, on account of the +pressure. These leaves (_F_, _G_) have short stalks, and are arranged +in circles about the stem. Each one has a number of spore cases +hanging down from the edge, and opening by a cleft on the inner side +(_G_, _sp._). They are filled with a mass of greenish spores that +shake out at the slightest jar when ripe. + +The sterile branches (_B_) are more slender than the spore-bearing +ones, and the sheaths shorter. Surrounding the joints, apparently just +below the sheaths, but really breaking through their bases, are +circles of slender branches resembling the main branch, but more +slender. The sterile branches grow to a height of forty to fifty +centimetres, and from their bushy form the popular name of the plant, +"horse-tail," is taken. The surface of the plant is hard and rough, +due to the presence of great quantities of flint in the epidermis,--a +peculiarity common to all the species. + + The stem is mainly composed of large, thin-walled cells, becoming + smaller as they approach the epidermis. The outer cells of the + ground tissue in the green branches contain chlorophyll, and the + walls of some of them are thickened. The fibro-vascular bundles + differ entirely from those of the ferns. Each bundle is nearly + triangular in section (_E_), with the point inward, and the inner + end occupied by a large air space. The tracheary tissue is only + slightly developed, being represented by a few vessels[9] (_tr._) at + the outer angles of the bundle, and one or two smaller ones close to + the air channel. The rest of the bundle is made up of nearly + uniform, rather thin-walled, colorless cells, some of which, + however, are larger, and have perforated cross-walls, representing + the sieve tubes of the fern bundle. There is no individual bundle + sheath, but the whole circle of bundles has a common outer sheath. + +[9] A vessel differs from a tracheid in being composed of several +cells placed end to end, the partitions being wholly or partially +absorbed, so as to throw the cells into close communication. + + The epidermis is composed of elongated cells whose walls present a + peculiar beaded appearance, due to the deposition of flint within + them. The breathing pores are arranged in vertical lines, and + resemble in general appearance those of the ferns, though differing + in some minor details. Like the other epidermal cells the guard + cells have heavy deposits of flint, which here are in the form of + thick transverse bars. + + The spore cases have thin walls whose cells, shortly before + maturity, develop thickenings upon their walls, which have to do + with the opening of the spore case. The spores (_H_, _I_) are round + cells containing much chlorophyll and provided with four peculiar + appendages called elaters. The elaters are extremely sensitive to + changes in moisture, coiling up tightly when moistened (_I_), but + quickly springing out again when dry (_H_). By dusting a few dry + spores upon a slide, and putting it under the microscope without any + water, the movement may be easily examined. Lightly breathing upon + them will cause the elaters to contract, but in a moment, as soon as + the moisture of the breath has evaporated, they will uncoil with a + quick jerk, causing the spores to move about considerably. + + The fresh spores begin to germinate within about twenty-four hours, + and the early stages, which closely resemble those of the ferns, may + be easily followed by sowing the spores in water. With care it is + possible to get the mature prothallia, which should be treated as + described for the fern prothallia. Under favorable conditions, the + first antheridia are ripe in about five weeks; the archegonia, which + are borne on separate plants, a few weeks later. The antheridia + (Fig. 72, _J_, _an._) are larger than those of the ferns, and the + spermatozoids (_K_) are thicker and with fewer coils, but otherwise + much like fern spermatozoids. + + The archegonia have a shorter neck than those of the ferns, and the + neck is straight. + + Both male and female prothallia are much branched and very irregular + in shape. + +There are a number of common species of _Equisetum_. Some of them, +like the common scouring rush (_E. hiemale_), are unbranched, and the +spores borne at the top of ordinary green branches; others have all +the stems branching like the sterile stems of the field horse-tail, +but produce a spore-bearing cone at the top of some of them. + + +CLASS III.--THE CLUB MOSSES (_Lycopodinæ_). + +The last class of the pteridophytes includes the ground pines, club +mosses, etc., and among cultivated plants numerous species of the +smaller club mosses (_Selaginella_). + +Two orders are generally recognized, although there is some doubt as +to the relationship of the members of the second order. The first +order, the larger club mosses (_Lycopodiaceæ_) is represented in the +northern states by a single genus (_Lycopodium_), of which the common +ground pine (_L. dendroideum_) (Fig. 73) is a familiar species. The +plant grows in the evergreen forests of the northern United States as +well as in the mountains further south, and in the larger northern +cities is often sold in large quantities at the holidays for +decorating. It sends up from a creeping, woody, subterranean stem, +numerous smaller stems which branch extensively, and are thickly set +with small moss-like leaves, the whole looking much like a little +tree. At the ends of some of the branches are small cones (_A_, _x_, +_B_) composed of closely overlapping, scale-like leaves, much as in a +fir cone. Near the base, on the inner surface of each of these scales, +is a kidney-shaped capsule (_C_, _sp._) opening by a cleft along the +upper edge and filled with a mass of fine yellow powder. These +capsules are the spore cases. + +The bases of the upright stems are almost bare, but become covered +with leaves higher up. The leaves are in shape like those of a moss, +but are thicker. The spore-bearing leaves are broader and when +slightly magnified show a toothed margin. + +The stem is traversed by a central fibro-vascular cylinder that +separates easily from the surrounding tissue, owing to the rupture of +the cells of the bundle sheath, this being particularly frequent in +dried specimens. When slightly magnified the arrangement of the +tissues may be seen (Fig. 73, _E_). Within the epidermis is a mass of +ground tissue of firm, woody texture surrounding the central oval or +circular fibro-vascular cylinder. This shows a number of white bars +(xylem) surrounded by a more delicate tissue (phloem). + + On magnifying the section more strongly, the cells of the ground + tissue (_G_) are seen to be oval in outline, with thick striated + walls and small intercellular spaces. Examined in longitudinal + sections they are long and pointed, belonging to the class of cells + known as "fibres." + +[Illustration: FIG. 73.--_A_, a club moss (_Lycopodium_), × 1/3. _x_, +cone. _r_, root. _B_, a cone, × 1. _C_, single scale with sporangium +(_sp._). _D_, spores: i, from above; ii, from below, × 325. _E_, cross +section of stem, × 8. _f.b._ fibro-vascular bundle. _F_, portion of +the fibro-vascular bundle, × 150. _G_, cells of the ground tissue, +× 150.] + + The xylem (_F_, _xy._) of the fibro-vascular bundle is composed of + tracheids, much like those of the ferns; the phloem is composed of + narrow cells, pretty much all alike. + + The spores (_D_) are destitute of chlorophyll and have upon the + outside a network of ridges, except on one side where three straight + lines converge, the spore being slightly flattened between them. + + Almost nothing is known of the prothallia of our native species. + +The second order (_Ligulatæ_) is represented by two very distinct +families: the smaller club mosses (_Selaginelleæ_) and the quill-worts +(_Isoeteæ_). Of the former the majority are tropical, but are common +in greenhouses where they are prized for their delicate moss-like +foliage (Fig. 74, _A_). + +[Illustration: FIG. 74.--_A_, one of the smaller club mosses +(_Selaginella_). _sp._ spore-bearing branch, × 2. _B_, part of a stem, +sending down naked rooting branches (_r_), × 1. _C_, longitudinal +section of a spike, with a single macrosporangium at the base; the +others, microsporangia, × 3. _D_, a scale and microsporangium, × 5. +_E_, young microsporangium, × 150. The shaded cells are the spore +mother cells. _F_, a young macrospore, × 150. _G_, section of the +stem, × 50. _H_, a single fibro-vascular bundle, × 150. _I_, vertical +section of the female prothallium of _Selaginella_, × 50. _ar._ +archegonium. _J_, section of an open archegonium, × 300. _o_, the egg +cell. _K_, microspore, with the contained male prothallium, × 300. +_x_, vegetative cell. _sp._ sperm cells. _L_, young plant, with the +attached macrospore, × 6. _r_, the first root. _l_, the first leaves.] + +The leaves in most species are like those of the larger club mosses, +but more delicate. They are arranged in four rows on the upper side of +the stem, two being larger than the others. The smaller branches grow +out sideways so that the whole branch appears flattened, reminding one +of the habit of the higher liverworts. Special leafless branches (_B_, +_r_) often grow downward from the lower side of the main branches, and +on touching the ground develop roots which fork regularly. + +The sporangia are much like those of the ground pines, and produced +singly at the bases of scale leaves arranged in a spike or cone (_A_, +_sp._), but two kinds of spores, large and small, are formed. In the +species figured the lower sporangium produces four large spores +(macrospores); the others, numerous small spores (microspores). + +Even before the spores are ripe the development of the prothallium +begins, and this is significant, as it shows an undoubted +relationship between these plants and the lowest of the seed plants, +as we shall see when we study that group. + + If ripe spores can be obtained by sowing them upon moist earth, the + young plants will appear in about a month. The microspore (Fig. 74, + _K_) produces a prothallium not unlike that of some of the water + ferns, there being a single vegetative cell (_x_), and the rest of + the prothallium forming a single antheridium. The spermatozoids are + excessively small, and resemble those of the bryophytes. + + The macrospore divides into two cells, a large lower one, and a + smaller upper one. The latter gives rise to a flat disc of cells + producing a number of small archegonia of simple structure (Fig. 74, + _I_, _J_). The lower cell produces later a tissue that serves to + nourish the young embryo. + + The development of the embryo recalls in some particulars that of + the seed plants, and this in connection with the peculiarities of + the sporangia warrants us in regarding the _Ligulatæ_ as the highest + of existing pteridophytes, and to a certain extent connecting them + with the lowest of the spermaphytes. + +Resembling the smaller club mosses in their development, but differing +in some important points, are the quill-worts (_Isoeteæ_). They are +mostly aquatic forms, growing partially or completely submerged, and +look like grasses or rushes. They vary from a few centimetres to half +a metre in height. The stem is very short, and the long cylindrical +leaves closely crowded together. The leaves which are narrow above are +widely expanded and overlapping at the base. The spores are of two +kinds, as in _Selaginella_, but the macrosporangia contain numerous +macrospores. The very large sporangia (_M_, _sp._) are in cavities at +the bases of the leaves, and above each sporangium is a little pointed +outgrowth (ligula), which is also found in the leaves of +_Selaginella_. The quill-worts are not common plants, and owing to +their habits of growth and resemblance to other plants, are likely to +be overlooked unless careful search is made. + + + + +CHAPTER XIV. + +SUB-KINGDOM VI. + +SPERMAPHYTES: PHÆNOGAMS. + + +The last and highest great division of the vegetable kingdom has been +named _Spermaphyta_, "seed plants," from the fact that the structures +known as seeds are peculiar to them. They are also commonly called +flowering plants, though this name might be also appropriately given +to certain of the higher pteridophytes. + +In the seed plants the macrosporangia remain attached to the parent +plant, in nearly all cases, until the archegonia are fertilized and +the embryo plant formed. The outer walls of the sporangium now become +hard, and the whole falls off as a seed. + +In the higher spermaphytes the spore-bearing leaves (sporophylls) +become much modified, and receive special names, those bearing the +microspores being commonly known as stamens; those bearing the +macrospores, carpels or carpophylls. The macrosporangia are also +ordinarily known as "ovules," a name given before it was known that +these were the same as the macrosporangia of the higher pteridophytes. + +In addition to the spore-bearing leaves, those surrounding them may be +much changed in form and brilliantly colored, forming, with the +enclosed sporophylls, the "flower" of the higher spermaphytes. + +As might be expected, the tissues of the higher spermaphytes are the +most highly developed of all plants, though some of them are very +simple. The plants vary extremely in size, the smallest being little +floating plants, less than a millimetre in diameter, while others are +gigantic trees, a hundred metres and more in height. + +There are two classes of the spermaphytes: I., the Gymnosperms, or +naked-seeded ones, in which the ovules (macrosporangia) are borne upon +open carpophylls; and II., Angiosperms, covered-seeded plants, in +which the carpophylls form a closed cavity (ovary) containing the +ovules. + + +CLASS I.--GYMNOSPERMS (_Gymnospermæ_). + +The most familiar of these plants are the common evergreen trees +(conifers), pines, spruces, cedars, etc. A careful study of one of +these will give a good idea of the most important characteristics of +the class, and one of the best for this purpose is the Scotch pine +(_Pinus sylvestris_), which, though a native of Europe, is not +infrequently met with in cultivation in America. If this species +cannot be had by the student, other pines, or indeed almost any other +conifer, will answer. The Scotch pine is a tree of moderate size, +symmetrical in growth when young, with a central main shaft, and +circles of branches at regular intervals; but as it grows older its +growth becomes irregular, and the crown is divided into several main +branches.[10] The trunk and branches are covered with a rough, scaly +bark of a reddish brown color, where it is exposed by the scaling off +of the outer layers. Covering the younger branches, but becoming +thinner on the older ones, are numerous needle-shaped leaves. These +are in pairs, and the base of each pair is surrounded by several dry, +blackish scales. Each pair of leaves is really attached to a very +short side branch, but this is so short as to make the leaves appear +to grow directly from the main branch. Each leaf is about ten +centimetres in length and two millimetres broad. Where the leaves are +in contact they are flattened, but the outer side is rounded, so that +a cross-section is nearly semicircular in outline. With a lens it is +seen that there are five longitudinal lines upon the surface of the +leaf, and careful examination shows rows of small dots corresponding +to these. These dots are the breathing pores. If a cross-section is +even slightly magnified it shows three distinct parts,--a whitish +outer border, a bright green zone, and a central oval, colorless area, +in which, with a little care, may be seen the sections of two +fibro-vascular bundles. In the green zone are sometimes to be seen +colorless spots, sections of resin ducts, containing the resin so +characteristic of the tissues of the conifers. + +[10] In most conifers the symmetrical form of the young tree is +maintained as long as the tree lives. + +The general structure of the stem may be understood by making a series +of cross-sections through branches of different ages. In all, three +regions are distinguishable; viz., an outer region (bark or cortex) +(Fig. 76, _A_, _c_), composed in part of green cells, and, if the +section has been made with a sharp knife, showing a circle of little +openings, from each of which oozes a clear drop of resin. These are +large resin ducts (_r_). The centre is occupied by a soft white tissue +(pith), and the space between the pith and bark is filled by a mass of +woody tissue. Traversing the wood are numerous radiating lines, some +of which run from the bark to the pith, others only part way. These +are called the medullary rays. While in sections from branches of any +age these three regions are recognizable, their relative size varies +extremely. In a section of a twig of the present year the bark and +pith make up a considerable part of the section; but as older branches +are examined, we find a rapid increase in the quantity of wood, while +the thickness of the bark increases but slowly, and the pith scarcely +at all. In the wood, too, each year's growth is marked by a distinct +ring (_A_ i, ii). As the branches grow in diameter the outer bark +becomes split and irregular, and portions die, becoming brown and +hard. + +The tree has a very perfect root system, but different from that of +any pteridophytes. The first root of the embryo persists as the main +or "tap" root of the full-grown tree, and from it branch off the +secondary roots, which in turn give rise to others. + +The sporangia are borne on special scale-like leaves, and arranged +very much as in certain pteridophytes, notably the club mosses; but +instead of large and small spores being produced near together, the +two kinds are borne on special branches, or even on distinct trees +(_e.g._ red cedar). In the Scotch pine the microspores are ripe about +the end of May. The leaves bearing them are aggregated in small cones +("flowers"), crowded about the base of a growing shoot terminating the +branches (Fig. 77, _A_ [Male]). The individual leaves (sporophylls) are +nearly triangular in shape, and attached by the smaller end. On the +lower side of each are borne two sporangia (pollen sacs) (_C_, _sp._), +opening by a longitudinal slit, and filled with innumerable yellow +microspores (pollen spores), which fall out as a shower of yellow dust +if the branch is shaken. + +The macrosporangia (ovules) are borne on similar leaves, known as +carpels, and, like the pollen sacs, borne in pairs, but on the upper +side of the sporophyll instead of the lower. The female flowers appear +when the pollen is ripe. The leaves of which they are composed are +thicker than those of the male flowers, and of a pinkish color. At the +base on the upper side are borne the two ovules (macrosporangia) +(Fig. 77, _E_, _o_), and running through the centre is a ridge that +ends in a little spine or point. + +The ovule-bearing leaf has on the back a scale with fringed edge (_F_, +_sc._), quite conspicuous when the flower is young, but scarcely to be +detected in the older cone. From the female flower is developed the +cone (Fig. 75, _A_), but the process is a slow one, occupying two +years. Shortly after the pollen is shed, the female flowers, which are +at first upright, bend downward, and assume a brownish color, growing +considerably in size for a short time, and then ceasing to grow for +several months. + +[Illustration: FIG. 75.--Scotch pine (_Pinus sylvestris_). _A_, a ripe +cone, × œ. _B_, a year-old cone, × 1. _C_, longitudinal section of +_B_. _D_, a single scale of _B_, showing the sporangia (ovules) (_o_), +× 2. _E_, a scale from a ripe cone, with the seeds (_s_), × œ. _F_, +longitudinal section of a ripe seed, × 3. _em._ the embryo. _G_, a +germinating seed, × 2. _r_, the primary root. _H_, longitudinal +section through _G_, showing the first leaves of the young plant still +surrounded by the endosperm, × 4. _I_, an older plant with the leaves +(_l_) withdrawing from the seed coats, × 4. _J_, upper part of a young +plant, showing the circle of primary leaves (cotyledons), × 1. _K_, +section of the same, × 2. _b_, the terminal bud. _L_, cross-section of +the stem of the young plant, × 25. _fb._ a fibro-vascular bundle. _M_, +cross-section of the root, × 25. _x_, wood. _ph._ bast, of the +fibro-vascular bundle.] + +In Figure 75, _B_, is shown such a flower as it appears in the winter +and early spring following. The leaves are thick and fleshy, closely +pressed together, as is seen by dividing the flower lengthwise, and +each leaf ends in a long point (_D_). The ovules are still very small. +As the growth of the tree is resumed in the spring, the flower (cone) +increases rapidly in size and becomes decidedly green in color, the +ovules increasing also very much in size. If a scale from such a cone +is examined about the first of June, the ovules will probably be +nearly full-grown, oval, whitish bodies two to three millimetres in +length. A careful longitudinal section of the scale through the ovule +will show the general structure. Such a section is shown in Figure 77, +_G_. Comparing this with the sporangia of the pteridophytes, the first +difference that strikes us is the presence of an outer coat or +integument (_in._), which is absent in the latter. The single +macrospore (_sp._) is very large and does not lie free in the cavity +of the sporangium, but is in close contact with its wall. It is filled +with a colorless tissue, the prothallium, and if mature, with care it +is possible to see, even with a hand lens, two or more denser oval +bodies (_ar._), the egg cells of the archegonia, which here are very +large. The integument is not entirely closed at the top, but leaves a +little opening through which the pollen spores entered when the flower +was first formed. + +After the archegonia are fertilized the outer parts of the ovule +become hard and brown, and serve to protect the embryo plant, which +reaches a considerable size before the sporangium falls off. As the +walls of the ovule harden, the carpel or leaf bearing it undergoes a +similar change, becoming extremely hard and woody, and as each one +ends in a sharp spine, and they are tightly packed together, it is +almost impossible to separate them. The ripe cone (Fig. 75, _A_) +remains closed during the winter, but in the spring, about the time +the flowers are mature, the scales open spontaneously and discharge +the ripened ovules, now called seeds. Each seed (_E_, _s_) is +surrounded by a membranous envelope derived from the scale to which it +is attached, which becomes easily separated from the seed. The opening +of the cones is caused by drying, and if a number of ripe cones are +gathered in the winter or early spring, and allowed to dry in an +ordinary room, they will in a day or two open, often with a sharp, +crackling sound, and scatter the ripe seeds. + +A section of a ripe seed (_F_) shows the embryo (_em._) surrounded by +a dense, white, starch-bearing tissue derived from the prothallium +cells, and called the "endosperm." This fills up the whole seed which +is surrounded by the hardened shell derived from the integument and +wall of the ovule. The embryo is elongated with a circle of small +leaves at the end away from the opening of the ovule toward which is +directed the root of the embryo. + +The seed may remain unchanged for months, or even years, without +losing its vitality, but if the proper conditions are provided, the +embryo will develop into a new plant. To follow the further growth of +the embryo, the ripe seeds should be planted in good soil and kept +moderately warm and moist. At the end of a week or two some of the +seeds will probably have sprouted. The seed absorbs water, and the +protoplasm of the embryo renews its activity, beginning to feed upon +the nourishing substances in the cells of the endosperm. The embryo +rapidly increases in length, and the root pushes out of the seed +growing rapidly downward and fastening itself in the soil (_G_, _r_). +Cutting the seed lengthwise we find that the leaves have increased +much in length and become green (one of the few cases where +chlorophyll is formed in the absence of light). As these leaves +(called "cotyledons" or seed leaves) increase in length, they +gradually withdraw from the seed whose contents they have exhausted, +and the young plant enters upon an independent existence. + +The young plant has a circle of leaves, about six in number, +surrounding a bud which is the growing point of the stem, and in many +conifers persists as long as the stem grows (Fig. 75, _K_, _b_). A +cross-section of the young stem shows about six separate +fibro-vascular bundles arranged in a circle (_S_, _fb._). The root +shows a central fibro-vascular cylinder surrounded by a dark-colored +ground tissue. Growing from its surface are numerous root hairs +(Fig. 75, _M_). + + For examining the microscopic structure of the pine, fresh material + is for most purposes to be preferred, but alcoholic material will + answer, and as the alcohol hardens the resin, it is for that reason + preferable. + + Cross-sections of the leaf, when sufficiently magnified, show that + the outer colorless border of the section is composed of two parts: + the epidermis of a single row of regular cells with very thick outer + walls, and irregular groups of cells lying below them. These latter + have thick walls appearing silvery and clearer than the epidermal + cells. They vary a good deal, in some leaves being reduced to a + single row, in others forming very conspicuous groups of some size. + The green tissue of the leaf is much more compact than in the fern + we examined, and the cells are more nearly round and the + intercellular spaces smaller. The chloroplasts are numerous and + nearly round in shape. + + Scattered through the green tissue are several resin passages (_r_), + each surrounded by a circle of colorless, thick-walled cells, like + those under the epidermis. At intervals in the latter are + openings--breathing pores--(Fig. 76, _J_), below each of which is an + intercellular space (_i_). They are in structure like those of the + ferns, but the walls of the guard cells are much thickened like the + other epidermal cells. + + Each leaf is traversed by two fibro-vascular bundles of entirely + different structure from those of the ferns. Each is divided into + two nearly equal parts, the wood (_x_) lying toward the inner, flat + side of the leaf, the bast (_T_) toward the outer, convex side. This + type of bundle, called "collateral," is the common form found in the + stems and leaves of seed plants. The cells of the wood or xylem are + rather larger than those of the bast or phloem, and have thicker + walls than any of the phloem cells, except the outermost ones which + are thick-walled fibres like those under the epidermis. Lying + between the bundles are comparatively large colorless cells, and + surrounding the whole central area is a single line of cells that + separates it sharply from the surrounding green tissue. + + In longitudinal sections, the cells, except of the mesophyll (green + tissue) are much elongated. The mesophyll cells, however, are short + and the intercellular spaces much more evident than in the + cross-section. The colorless cells have frequently rounded + depressions or pits upon their walls, and in the fibro-vascular + bundle the difference between the two portions becomes more obvious. + The wood is distinguished by the presence of vessels with close, + spiral or ring-shaped thickenings, while in the phloem are found + sieve tubes, not unlike those in the ferns. + + The fibro-vascular bundles of the stem of the seedling plant show a + structure quite similar to that of the leaf, but very soon a + difference is manifested. Between the two parts of the bundle the + cells continue to divide and add constantly to the size of the + bundle, and at the same time the bundles become connected by a line + of similar growing cells, so that very early we find a ring of + growing cells extending completely around the stem. As the cells in + this ring increase in number, owing to their rapid division, those + on the borders of the ring lose the power of dividing, and gradually + assume the character of the cells on which they border (Fig. 76, + _B_, _cam._). The growth on the inside of the ring is more rapid + than on the outer border, and the ring continues comparatively near + the surface of the stem (Fig. 76, _A_, _cam._). The spaces between + the bundles do not increase materially in breadth, and as the + bundles increase in size become in comparison very small, appearing + in older stems as mere lines between the solid masses of wood that + make up the inner portion of the bundles. These are the primary + medullary rays, and connect the pith in the centre of the stem with + the bark. Later, similar plates of cells are formed, often only a + single cell thick, and appearing when seen in cross-section as a + single row of elongated cells (_C_, _m_). + + As the stem increases in diameter the bundles become broader and + broader toward the outside, and taper to a point toward the centre, + appearing wedge-shaped, the inner ends projecting into the pith. The + outer limits of the bundles are not nearly so distinct, and it is + not easy to tell when the phloem of the bundles ends and the ground + tissue of the bark begins. + + A careful examination of a cross-section of the bark shows first, if + taken from a branch not more than two or three years old, the + epidermis composed of cells not unlike those of the leaf, but whose + walls are usually browner. Underneath are cells with brownish walls, + and often more or less dry and dead. These cells give the brown + color to the bark, and later both epidermis and outer ground tissue + become entirely dead and disappear. The bulk of the ground tissue is + made up of rather large, loose cells, the outer ones containing a + good deal of chlorophyll. Here and there are large resin ducts + (Fig. 76, _H_), appearing in cross-section as oval openings + surrounded by several concentric rows of cells, the innermost + smaller and with denser contents. These secrete the resin that fills + the duct and oozes out when the stem is cut. All of the cells of the + bark contain more or less starch. + + The phloem, when strongly magnified, is seen to be made up of cells + arranged in nearly regular radiating rows. Their walls are not very + thick and the cells are usually somewhat flattened in a radial + direction. + + Some of the cells are larger than the others, and these are found to + be, when examined in longitudinal section, sieve tubes (Fig. 76, + _E_) with numerous lateral sieve plates quite similar to those found + in the stems of ferns. + +[Illustration: FIG. 76.--Scotch pine. _A_, cross-section of a +two-year-old branch, × 3. _p_, pith. _c_, bark. The radiating lines +are medullary rays. _r_, resin ducts. _B_, part of the same, × 150. +_cam._ cambium cells. _x_, tracheids. _C_, cross-section of a +two-year-old branch at the point where the two growth rings join: _I_, +the cells of the first year's growth; _II_, those of the second year. +_m_, a medullary ray, × 150. _D_, longitudinal section of a branch, +showing the form of the tracheids and the bordered pits upon their +walls. _m_, medullary ray, × 150. _E_, part of a sieve tube, × 300. +_F_, cross-section of a tracheid passing through two of the pits in +the wall (_p_), × 300. _G_, longitudinal section of a branch, at right +angles to the medullary rays (_m_). At _y_, the section has passed +through the wall of a tracheid, bearing a row of pits, × 150. _H_, +cross-section of a resin duct, × 150. _I_, cross-section of a leaf, +× 20. _fb._ fibro-vascular bundle. _r_, resin duct. _J_, section of a +breathing pore, × 150. _i_, the air space below it.] + + The growing tissue (cambium), separating the phloem from the wood, + is made up of cells quite like those of the phloem, into which they + insensibly merge, except that their walls are much thinner, as is + always the case with rapidly growing cells. These cells (_B_, + _cam._) are arranged in radial rows and divide, mainly by walls, at + right angles to the radii of the stem. If we examine the inner side + of the ring, the change the cells undergo is more marked. They + become of nearly equal diameter in all directions, and the walls + become woody, showing at the same time distinct stratification (_B_, + _x_). + + On examining the xylem, where two growth rings are in contact, the + reason of the sharply marked line seen when the stem is examined + with the naked eye is obvious. On the inner side of this line (_I_), + the wood cells are comparatively small and much flattened, while the + walls are quite as heavy as those of the much larger cells (_II_) + lying on the outer side of the line. The small cells show the point + where growth ceased at the end of the season, the cells becoming + smaller as growth was feebler. The following year when growth + commenced again, the first wood cells formed by the cambium were + much larger, as growth is most vigorous at this time, and the wood + formed of these larger cells is softer and lighter colored than that + formed of the smaller cells of the autumn growth. + + The wood is mainly composed of tracheids, there being no vessels + formed except the first year. These tracheids are characterized by + the presence of peculiar pits upon their walls, best seen when thin + longitudinal sections are made in a radial direction. These pits + (Fig. 76, _D_, _p_) appear in this view as double circles, but if + cut across, as often happens in a cross-section of the stem, or in a + longitudinal section at right angles to the radius (tangential), + they are seen to be in shape something like an inverted saucer with + a hole through the bottom. They are formed in pairs, one on each + side of the wall of adjacent tracheids, and are separated by a very + delicate membrane (_F_, _p_, _G_, _y_). These "bordered" pits are + very characteristic of the wood of all conifers. + + The structure of the root is best studied in the seedling plant, or + in a rootlet of an older one. The general plan of the root is much + like that of the pteridophytes. The fibro-vascular bundle (Fig. 75, + _M_, _fb._) is of the so-called radial type, there being three xylem + masses (_x_) alternating with as many phloem masses (_ph._) in the + root of the seedling. This regularity becomes destroyed as the root + grows older by the formation of a cambium ring, something like that + in the stem. + + The development of the sporangia is on the whole much like that of + the club mosses, and will not be examined here in detail. The + microspores (pollen spores) are formed in groups of four in + precisely the same way as the spores of the bryophytes and + pteridophytes, and by collecting the male flowers as they begin to + appear in the spring, and crushing the sporangia in water, the + process of division may be seen. For more careful examination they + may be crushed in a mixture of water and acetic acid, to which is + added a little gentian violet. This mixture fixes and stains the + nuclei of the spores, and very instructive preparations may thus be + made.[11] + +[11] See the last chapter for details. + +[Illustration: FIG. 77.--Scotch pine (except _E_ and _F_). _A_, end of +a branch bearing a cluster of male flowers ([Male]), × œ. _B_, a similar +branch, with two young female flowers ([Female]), natural size. _C_, a +scale from a male flower, showing the two sporangia (_sp._); × 5. _D_, +a single ripe pollen spore (microspore), showing the vegetative cell +(_x_), × 150. _E_, a similar scale, from a female flower of the +Austrian pine, seen from within, × 4. _o_, the sporangium (ovule). +_F_, the same, seen from the back, showing the scale (_sc._) attached +to the back. _G_, longitudinal section through a full-grown ovule of +the Scotch pine. _p_, a pollen spore sending down its tube to the +archegonia (_ar._). _sp._ the prothallium (endosperm), filling up the +embryo sac, × 10. _H_, the neck of the archegonium, × 150.] + + The ripe pollen spores (Fig. 77, _D_) are oval cells provided with + a double wall, the outer one giving rise to two peculiar + bladder-like appendages (_z_). Like the microspores of the smaller + club mosses, a small cell is cut off from the body of the spore + (_x_). These pollen spores are carried by the wind to the ovules, + where they germinate. + + The wall of the ripe sporangium or pollen sac is composed of a + single layer of cells in most places, and these cells are provided + with thickened ridges which have to do with opening the pollen sac. + + We have already examined in some detail the structure of the + macrosporangium or ovule. In the full-grown ovule the macrospore, + which in the seed plants is generally known as the "embryo sac," is + completely filled with the prothallium or "endosperm." In the upper + part of the prothallium several large archegonia are formed in much + the same way as in the pteridophytes. The egg cell is very large, + and appears of a yellowish color, and filled with large drops that + give it a peculiar aspect. There is a large nucleus, but it is not + always readily distinguished from the other contents of the egg + cell. The neck of the archegonium is quite long, but does not + project above the surface of the prothallium (Fig. 77, _H_). + +The pollen spores are produced in great numbers, and many of them fall +upon the female flowers, which when ready for pollination have the +scales somewhat separated. The pollen spores now sift down to the base +of the scales, and finally reach the opening of the ovule, where they +germinate. No spermatozoids are produced, the seed plants differing in +this respect from all pteridophytes. The pollen spore bursts its +outer coat, and sends out a tube which penetrates for some distance +into the tissue of the ovule, acting very much as a parasitic fungus +would do, and growing at the expense of the tissue through which it +grows. After a time growth ceases, and is not resumed until the +development of the female prothallium and archegonia is nearly +complete, which does not occur until more than a year from the time +the pollen spore first reaches the ovule. Finally the pollen tube +penetrates down to and through the open neck of the archegonium, until +it comes in contact with the egg cell. These stages can only be seen +by careful sections through a number of ripe ovules, but the track of +the pollen tube is usually easy to follow, as the cells along it are +often brown and apparently dead (Fig. 77, _G_). + + +CLASSIFICATION OF THE GYMNOSPERMS. + +There are three classes of the gymnosperms: I., cycads (_Cycadeæ_); +II., conifers (_Coniferæ_); III., joint firs (_Gnetaceæ_). All of the +gymnosperms of the northern United States belong to the second order, +but representatives of the others are found in the southern and +southwestern states. + +The cycads are palm-like forms having a single trunk crowned by a +circle of compound leaves. Several species are grown for ornament in +conservatories, and a few species occur native in Florida, but +otherwise do not occur within our limits. + +[Illustration: FIG. 78.--Illustrations of gymnosperms. _A_, fruiting +leaf of a cycad (_Cycas_), with macrosporangia (ovules) (_ov._), × Œ. +_B_, leaf of _Gingko_, × œ. _C_, branch of hemlock (_Tsuga_), with a +ripe cone, × 1. _D_, red cedar (_Juniperus_), × 1. _E_, _Arbor-vitæ_ +(_Thuja_), × 1.] + +The spore-bearing leaves usually form cones, recalling somewhat in +structure those of the horse-tails, but one of the commonest +cultivated species (_Cycas revoluta_) bears the ovules, which are very +large, upon leaves that are in shape much like the ordinary ones +(Fig. 78, _A_). + +Of the conifers, there are numerous familiar forms, including all our +common evergreen trees. There are two sub-orders,--the true conifers +and the yews. In the latter there is no true cone, but the ovules are +borne singly at the end of a branch, and the seed in the yew (_Taxus_) +is surrounded by a bright red, fleshy integument. One species of yew, +a low, straggling shrub, occurs sparingly in the northern states, and +is the only representative of the group at the north. The European yew +and the curious Japanese _Gingko_ (Fig. 78, _B_) are sometimes met +with in cultivation. + +Of the true conifers, there are a number of families, based on +peculiarities in the leaves and cones. Some have needle-shaped leaves +and dry cones like the firs, spruces, hemlock (Fig. 78, _C_). Others +have flattened, scale-like leaves, and more or less fleshy cones, like +the red cedar (Fig. 78, _D_) and _Arbor-vitæ_ (_E_). + +A few of the conifers, such as the tamarack or larch (_Larix_) and +cypress (_Taxodium_), lose their leaves in the autumn, and are not, +therefore, properly "evergreen." + +The conifers include some of the most valuable as well as the largest +of trees. Their timber, especially that of some of the pines, is +particularly valuable, and the resin of some of them is also of much +commercial importance. Here belong the giant red-woods (_Sequoia_) of +California, the largest of all American trees. + +The joint firs are comparatively small plants, rarely if ever reaching +the dimensions of trees. They are found in various parts of the world, +but are few in number, and not at all likely to be met with by the +ordinary student. Their flowers are rather more highly differentiated +than those of the other gymnosperms, and are said to show some +approach in structure to those of the angiosperms. + + + + +CHAPTER XV. + +SPERMAPHYTES. + + +CLASS II.--ANGIOSPERMS. + +The angiosperms include an enormous assemblage of plants, all those +ordinarily called "flowering plants" belonging here. There is almost +infinite variety shown in the form and structure of the tissues and +organs, this being particularly the case with the flowers. As already +stated, the ovules, instead of being borne on open carpels, are +enclosed in a cavity formed by a single closed carpel or several +united carpels. To the organ so formed the name "pistil" is usually +applied, and this is known as "simple" or "compound," as it is +composed of one or of two or more carpels. The leaves bearing the +pollen spores are also much modified, and form the so-called +"stamens." In addition to the spore-bearing leaves there are usually +other modified leaves surrounding them, these being often brilliantly +colored and rendering the flower very conspicuous. To these leaves +surrounding the sporophylls, the general name of "perianth" or +"perigone" is given. The perigone has a twofold purpose, serving both +to protect the sporophylls, and, at least in bright-colored flowers, +to attract insects which, as we shall see, are important agents in +transferring pollen from one flower to another. + +When we compare the embryo sac (macrospore) of the angiosperms with +that of the gymnosperms a great difference is noticed, there being +much more difference than between the latter and the higher +pteridophytes. Unfortunately there are very few plants where the +structure of the embryo sac can be readily seen without very skilful +manipulation. + + There are, however, a few plants in which the ovules are very small + and transparent, so that they may be mounted whole and examined + alive. The best plant for this purpose is probably the "Indian pipe" + or "ghost flower," a curious plant growing in rich woods, blossoming + in late summer. It is a parasite or saprophyte, and entirely + destitute of chlorophyll, being pure white throughout. It bears a + single nodding flower at the summit of the stem. (Another species + much like it, but having several brownish flowers, is shown in + Figure 115, _L_.) + + If this plant can be had, the structure of the ovule and embryo sac + may be easily studied, by simply stripping away the tissue bearing + the numerous minute ovules, and mounting a few of them in water, or + water to which a little sugar has been added. + +[Illustration: FIG. 79.--_A_, ripe ovule of _Monotropa uniflora_, in +optical section, × 100. _m_, micropyle. _e_, embryo sac. _B_, the +embryo sac, × 300. At the top is the egg apparatus, consisting of the +two synergidæ (_s_), and the egg cell (_o_). In the centre is the +"endosperm nucleus" (_k_). At the bottom, the "antipodal cells" (_g_).] + + The ovules are attached to a stalk, and each consists of about two + layers of colorless cells enclosing a central, large, oblong cell + (Fig. 79, _A_, _E_), the embryo sac or macrospore. If the ovule is + from a flower that has been open for some time, we shall find in the + centre of the embryo sac a large nucleus (_k_) (or possibly two + which afterward unite into one), and at each end three cells. Those + at the base (_g_) probably represent the prothallium, and those at + the upper end a very rudimentary archegonium, here generally called + the "egg apparatus." + + Of the three cells of the "egg apparatus" the lower (_o_) one is the + egg cell; the others are called "synergidæ." The structure of the + embryo sac and ovules is quite constant among the angiosperms, the + differences being mainly in the shape of the ovules, and the degree + to which its coverings or integuments are developed. + + The pollen spores of many angiosperms will germinate very easily in + a solution of common sugar in water: about fifteen per cent of sugar + is the best. A very good plant for this purpose is the sweet pea, + whose pollen germinates very rapidly, especially in warm weather. + The spores may be sown in a little of the sugar solution in any + convenient vessel, or in a hanging drop suspended in a moist + chamber, as described for germinating the spores of the slime + moulds. The tube begins to develop within a few minutes after the + spores are placed in the solution, and within an hour or so will + have reached a considerable length. Each spore has two nuclei, but + they are less evident here than in some other forms (Fig. 79). + +[Illustration: FIG. 80.--Germinating pollen spores of the sweet pea, +× 200.] + +The upper part of the pistil is variously modified, having either +little papillæ which hold the pollen spores, or are viscid. In either +case the spores germinate when placed upon this receptive part +(stigma) of the pistil, and send their tubes down through the tissues +of the pistil until they reach the ovules, which are fertilized much +as in the gymnosperms. + +The effect of fertilization extends beyond the ovule, the ovary and +often other parts of the flower being affected, enlarging and often +becoming bright-colored and juicy, forming the various fruits of the +angiosperms. These fruits when ripe may be either dry, as in the case +of grains of various kinds, beans, peas, etc.; or the ripe fruit may +be juicy, serving in this way to attract animals of many kinds which +feed on the juicy pulp, and leave the hard seeds uninjured, thus +helping to distribute them. Common examples of these fleshy fruits are +offered by the berries of many plants; apples, melons, cherries, etc., +are also familiar examples. + +The seeds differ a good deal both in regard to size and the degree to +which the embryo is developed at the time the seed ripens. + + +CLASSIFICATION OF THE ANGIOSPERMS. + +The angiosperms are divided into two sub-classes: I. _Monocotyledons_ +and II. _Dicotyledons_. + +The monocotyledons comprise many familiar plants, both ornamental and +useful. They have for the most part elongated, smooth-edged leaves +with parallel veins, and the parts of the flower are in threes in the +majority of them. As their name indicates, there is but one cotyledon +or seed leaf, and the leaves from the first are alternate. As a rule +the embryo is very small and surrounded by abundant endosperm. + +The most thoroughly typical members of the sub-class are the lilies +and their relatives. The one selected for special study here, the +yellow adder-tongue, is very common in the spring; but if not +accessible, almost any liliaceous plant will answer. Of garden +flowers, the tulip, hyacinth, narcissus, or one of the common lilies +may be used; of wild flowers, the various species of _Trillium_ +(Fig. 83, _A_) are common and easily studied forms, but the leaves are +not of the type common to most monocotyledons. + +The yellow adder-tongue (_Erythronium americanum_) (Fig. 81) is one of +the commonest and widespread of wild flowers, blossoming in the +northern states from about the middle of April till the middle of May. +Most of the plants found will not be in flower, and these send up but +a single, oblong, pointed leaf. The flowering plant has two similar +leaves, one of which is usually larger than the other. They seem to +come directly from the ground, but closer examination shows that they +are attached to a stem of considerable length entirely buried in the +ground. This arises from a small bulb (_B_) to whose base numerous +roots (_r_) are attached. Rising from between the leaves is a slender, +leafless stalk bearing a single, nodding flower at the top. + +The leaves are perfectly smooth, dull purplish red on the lower side, +and pale green with purplish blotches above. The epidermis may be very +easily removed, and is perfectly colorless. Examined closely, +longitudinal rows of whitish spots may be detected: these are the +breathing pores. + +[Illustration: FIG. 81.--_A_, plant of the yellow adder-tongue +(_Erythronium americanum_), × 1/3. _B_, the bulb of the same, × œ. _r_, +roots. _C_, section of _B_. _st._ the base of the stem bearing the +bulb for next year (_b_) at its base. _D_, a single petal and stamen, +× œ. _f_, the filament. _an._ anther. _E_, the gynoecium (pistil), × 1. +_o_, ovary. _st._ style. _z_, stigma. _F_, a full-grown fruit, × œ. +_G_, section of a full-grown macrosporangium (ovule), × 25: i, ii, the +two integuments. _sp._ macrospore (embryo sac). _H_, cross-section of +the ripe anther, × 12. _I_, a single pollen spore, × 150, showing the +two nuclei (_n_, _n'_). _J_, a ripe seed, × 2. _K_, the same, in +longitudinal section. _em._ the embryo. _L_, cross-section of the +stem, × 12. _fb._ fibro-vascular bundle. _M_, diagram of the flower.] + +A cross-section of the stem shows numerous whitish areas scattered +through it. These are the fibro-vascular bundles which in the +monocotyledons are of a simple type. The bulb is composed of thick +scales, which are modified leaves, and on cutting it lengthwise, we +shall probably find the young bulb of next year (Fig. _C_, _b_) +already forming inside it, the young bulb arising as a bud at the +base of the stem of the present year. + +The flower is made up of five circles of very much modified leaves, +three leaves in each set. The two outer circles are much alike, but +the three outermost leaves are slightly narrower and strongly tinged +with red on the back, completely concealing the three inner ones +before the flower expands. The latter are pure yellow, except for a +ridge along the back, and a few red specks near the base inside. These +six leaves constitute the perigone of the flower; the three outer are +called sepals, the inner ones petals. + +The next two circles are composed of the sporophylls bearing the +pollen spores.[12] These are the stamens, and taken collectively are +known as the "_Androecium_." Each leaf or stamen consists of two +distinct portions, a delicate stalk or "filament" (_D_, _f_), and the +upper spore-bearing part, the "anther" (_an._). The anther in the +freshly opened flower has a smooth, red surface; but shortly after, +the flower opens, splits along each side, and discharges the pollen +spores. A section across the anther shows it to be composed of four +sporangia or pollen sacs attached to a common central axis +("connective") (Fig. _H_). + +[12] The three outer stamens are shorter than the inner set. + +The central circle of leaves, the carpels (collectively the +"gynoecium") are completely united to form a compound pistil (Fig. 81, +_E_). This shows three distinct portions, the ovule-bearing portion +below (_o_), the "ovary," a stalk above (_st._), the "style," and the +receptive portion (_z_) at the top, the "stigma." Both stigma and +ovary show plainly their compound nature, the former being divided +into three lobes, the latter completely divided into three chambers, +as well as being flattened at the sides with a more or less decided +seam at the three angles. The ovules, which are quite large, are +arranged in two rows in each chamber of the ovary, attached to the +central column ("placenta"). + +The flowers open for several days in succession, but only when the sun +is shining. They are visited by numerous insects which carry the +pollen from one flower to another and deposit it upon the stigma, +where it germinates, and the tube, growing down through the long +style, finally reaches the ovules and fertilizes them. Usually only a +comparatively small number of the seeds mature, there being almost +always a number of imperfect ones in each pod. The pod or fruit (_F_) +is full-grown about a month after the flower opens, and finally +separates into three parts, and discharges the seeds. These are quite +large (Fig. 81, _J_) and covered with a yellowish brown outer coat, +and provided with a peculiar, whitish, spongy appendage attaching it +to the placenta. A longitudinal section of a ripe seed (_K_) shows the +very small, nearly triangular embryo (_em._), while the rest of the +cavity of the seed is filled with a white, starch-bearing tissue, the +endosperm. + +[Illustration: FIG. 82.--_Erythronium_. _A_, a portion of the wall of +the anther, × 150. _B_, a single epidermal cell from the petal, × 150. +_C_, cross-section of a fibro-vascular bundle of the stem, × 150. +_tr._ vessels. _D_, _E_, longitudinal section of the same, showing the +markings of the vessels, × 150. _F_, a bit of the epidermis from the +lower surface of a leaf, showing the breathing pores, × 50. _G_, a +single breathing pore, × 200. _H_, cross-section of a leaf, × 50. +_st._ a breathing pore. _m_, the mesophyll. _fb._ a vein. _I_, +cross-section of a breathing pore, × 200. _J_, young embryo, × 150.] + + A microscopical examination of the tissues of the plant shows them + to be comparatively simple, this being especially the case with the + fibro-vascular system. + + The epidermis of the leaf is readily removed, and examination shows + it to be made up of oblong cells with large breathing pores in + rows. The breathing pores are much larger than any we have yet + seen, and are of the type common to most angiosperms. The ordinary + epidermal cells are quite destitute of chlorophyll, but the two + cells (guard cells) enclosing the breathing pore contain numerous + chloroplasts, and the oblong nuclei of these cells are usually + conspicuous (Fig. 82, _G_). By placing a piece of the leaf between + pieces of pith, and making a number of thin cross-sections at right + angles to the longer axis of the leaf, some of the breathing pores + will probably be cut across, and their structure may be then better + understood. Such a section is shown in Figure 82, _I_. + + The body of the leaf is made up of chlorophyll-bearing cells of + irregular shape and with large air spaces between (_H_, _m_). The + veins traversing this tissue are fibro-vascular bundles of a type + structure similar to that of the stem, which will be described + presently. + + The stem is made up principally of large cells with thin walls, + which in cross-section show numerous small, triangular, + intercellular spaces (_i_) at the angles. These cells contain, + usually, more or less starch. The fibro-vascular bundles (_C_) are + nearly triangular in section, and resemble considerably those of the + field horse-tail, but they are not penetrated by the air channel, + found in the latter. The xylem, as in the pine, is toward the + outside of the stem, but the boundary between xylem and phloem is + not well defined, there being no cambium present. In the xylem are a + number of vessels (_C_, _tr._) at once distinguishable from the + other cells by their definite form, firm walls, and empty cavity. + The vessels in longitudinal sections show spiral and ringed + thickenings. The rest of the xylem cells, as well as those of the + phloem, are not noticeably different from the cells of the ground + tissue, except for their much smaller size, and absence of + intercellular spaces. + + The structure of the leaves of the perigone is much like that of the + green leaves, but the tissues are somewhat reduced. The epidermis of + the outer side of the sepals has breathing pores, but these are + absent from their inner surface, and from both sides of the petals. + The walls of the epidermal cells of the petals are peculiarly + thickened by apparent infoldings of the wall (_B_), and these cells, + as well as those below them, contain small, yellow bodies + (chromoplasts) to which the bright color of the flower is due. The + red specks on the base of the perigone leaves, as well as the red + color of the back of the sepals, the stalk, and leaves are due to a + purplish red cell sap filling the cells at these points. + + The filaments or stalks of the stamens are made up of very delicate + colorless cells, and the centre is traversed by a single + fibro-vascular bundle, which is continued up through the centre of + the anther. To study the latter, thin cross-sections should be made + and mounted in water. Each of the four sporangia, or pollen sacs, is + surrounded on the outside by a wall, consisting of two layers of + cells, becoming thicker in the middle of the section where the + single fibro-vascular bundle is seen (Fig. 81, _H_). On opening, the + cavities of the adjacent sporangia are thrown together. The inner + cells of the wall are marked by thickened bars, much as we saw in + the pine (Fig. 82, _A_), and which, like these, are formed shortly + before the pollen sacs open. The pollen spores (Fig. 81, _I_) are + large, oval cells, having a double wall, the outer one somewhat + heavier than the inner one, but sufficiently transparent to allow a + clear view of the interior, which is filled with very dense, + granular protoplasm in which may be dimly seen two nuclei (_n_, + _ni._), showing that here also there is a division of the spore + contents, although no wall is present. The spores do not germinate + very readily, and are less favorable for this purpose than those of + some other monocotyledons. Among the best for this purpose are the + spiderwort (_Tradescantia_) and _Scilla_. + + Owing to the large size and consequent opacity of the ovules, as + well as to the difficulty of getting the early stages, the + development and finer structure of the ovule will not be discussed + here. The full-grown ovule may be readily sectioned, and a general + idea of its structure obtained. A little potash may be used to + advantage in this study, carefully washing it away when the section + is sufficiently cleared. We find now that the ovule is attached to a + stalk (funiculus) (Fig. 81, _G_, _f_), the body of the ovule being + bent up so as to lie against the stalk. Such an inverted ovule is + called technically, "anatropous." The ovule is much enlarged where + the stalk bends. The upper part of the ovule is on the whole like + that of the pine, but there are two integuments (i, ii) instead of + the single one found in the pine. + + As the seed develops, the embryo sac (_G_, _sp._) enlarges so as to + occupy pretty much the whole space of the seed. At first it is + nearly filled with a fluid, but a layer of cells is formed, lining + the walls, and this thickens until the whole space, except what is + occupied by the small embryo, is filled with them. These are called + the "endosperm cells," but differ from the endosperm cells of the + gymnosperms, in the fact that they are not developed until after + fertilization, and can hardly, therefore, be regarded as + representing the prothallium of the gymnosperms and pteridophytes. + These cells finally form a firm tissue, whose cells are filled with + starch that forms a reserve supply of food for the embryo plant when + the seed germinates. The embryo (Fig. 81, _K_, _em._, Fig. 82, _J_), + even when the seed is ripe, remains very small, and shows scarcely + any differentiation. It is a small, pear-shaped mass of cells, the + smaller end directed toward the upper end of the embryo sac. + +The integuments grow with the embryo sac, and become brown and hard, +forming the shell of the seed. The stalk of the ovule also enlarges, +and finally forms the peculiar, spongy appendage of the seeds already +noticed (Fig. 81, _J_, _K_). + + + + +CHAPTER XVI. + +CLASSIFICATION OF THE MONOCOTYLEDONS. + + +In the following chapter no attempt will be made to give an exhaustive +account of the characteristics of each division of the monocotyledons, +but only such of the most important ones as may serve to supplement +our study of the special one already examined. The classification +here, and this is the case throughout the spermaphytes, is based +mainly upon the characters of the flowers and fruits. + +The classification adopted here is that of the German botanist +Eichler, and seems to the author to accord better with our present +knowledge of the relationships of the groups than do the systems that +are more general in this country. According to Eichler's +classification, the monocotyledons may be divided into seven groups; +viz., I. _Liliifloræ_; II. _Enantioblastæ_; III. _Spadicifloræ_; +IV. _Glumaceæ_; V. _Scitamineæ_; VI. _Gynandræ_; VII. _Helobiæ_. + + +ORDER I.--_Liliifloræ_. + +The plants of this group agree in their general structure with the +adder's-tongue, which is a thoroughly typical representative of the +group; but nevertheless, there is much variation among them in the +details of structure. While most of them are herbaceous forms (dying +down to the ground each year), a few, among which may be mentioned the +yuccas ("bear grass," "Spanish bayonet") of our southern states, +develop a creeping or upright woody stem, increasing in size from year +to year. The herbaceous forms send up their stems yearly from +underground bulbs, tubers, _e.g._ _Trillium_ (Fig. 83, _A_), or +thickened, creeping stems, or root stocks (rhizomes). Good examples of +the last are the Solomon's-seal (Fig. 83, _B_), _Medeola_ (_C_, _D_), +and iris (Fig. 84 _A_). One family, the yams (_Dioscoreæ_), of which +we have one common native species, the wild yam (_Dioscorea villosa_), +have broad, netted-veined leaves and are twining plants, while another +somewhat similar family (_Smilaceæ_) climb by means of tendrils at the +bases of the leaves. Of the latter the "cat-brier" or "green-brier" is +a familiar representative. + +[Illustration: FIG. 83.--Types of _Liliifloræ_. _A_, _Trillium_, × Œ. +_B_, single flower of Solomon's-seal (_Polygonatum_), × 1. _C_, upper +part of a plant. _D_, underground stem (rhizome) of Indian cucumber +root (_Medeola_), × œ. _E_, a rush (_Juncus_), × 1. _F_, a single +flower, × 2. _A-D_, _Liliaceæ_; _E_, _Juncaceæ_.] + +The flowers are for the most part conspicuous, and in plan like that +of the adder's-tongue; but some, like the rushes (Fig. 83, _E_), have +small, inconspicuous flowers; and others, like the yams and smilaxes, +have flowers of two kinds, male and female. + +[Illustration: FIG. 84.--Types of _Liliifloræ_. _A_, flower of the +common blue-flag (_Iris_), × œ (_Iridaceæ_). _B_, the petal-like upper +part of the pistil, seen from below, and showing a stamen (_an._). +_st._ the stigma, × œ. _C_, the young fruit, × œ. _D_, section of the +same, × 1. _E_, diagram of the flower. _F_, part of a plant of the +so-called "gray moss" (_Tillandsia_), × œ (_Bromeliaceæ_). _G_, a +single flower, × 2. _H_, a seed, showing the fine hairs attached to +it, × 1. _I_, plant of pickerel-weed (_Pontederia_), × Œ +(_Pontederiaceæ_). _J_, a single flower, × 1. _K_, section of the +ovary, × 4.] + +The principal family of the _Liliifloræ_ is the _Liliaceæ_, including +some of the most beautiful of all flowers. All of the true lilies +(_Lilium_), as well as the day lilies (_Funkia_, _Hemerocallis_) of +the gardens, tulips, hyacinths, lily-of-the-valley, etc., belong here, +as well as a number of showy wild flowers including several species of +tiger-lilies (_Lilium_), various species of _Trillium_ (Fig. 83, _A_), +Solomon's-seal (_Polygonatum_) (Fig. 83, _B_), bellwort (_Uvularia_), +and others. In all of these, except _Trillium_, the perigone leaves +are colored alike, and the leaves parallel-veined; but in the latter +the sepals are green and the leaves broad and netted-veined. The fruit +of the _Liliaceæ_ may be either a pod, like that of the +adder's-tongue, or a berry, like that of asparagus or Solomon's-seal. + +Differing from the true lilies in having the bases of the perigone +leaves adherent to the surface of the ovary, so that the latter is +apparently below the flower (inferior), and lacking the inner circle +of stamens, is the iris family (_Iridaceæ_), represented by the wild +blue-flag (_Iris versicolor_) (Fig. 84, _A_, _E_), as well as by +numerous cultivated species. In iris the carpels are free above and +colored like the petals (_B_), with the stigma on the under side. Of +garden flowers the gladiolus and crocus are the most familiar +examples, besides the various species of iris; and of wild flowers the +little "blue-eyed grass" (_Sisyrinchium_). + +[Illustration: FIG. 85.--_Enantioblastæ_. _A_, inflorescence of the +common spiderwort (_Tradescantia_), × œ (_Commelyneæ_). _B_, a single +stamen, showing the hairs attached to the filament, × 2. _C_, the +pistil, × 2.] + +The blue pickerel-weed (_Pontederia_) is the type of a family of which +there are few common representatives (Fig. 84, _I_, _K_). + +The last family of the order is the _Bromeliaceæ_, all inhabitants of +the warmer parts of the globe, but represented in the southern states +by several forms, the commonest of which is the so-called "gray moss" +(_Tillandsia_) (Fig. 84, _F_, _H_). Of cultivated plants the pineapple, +whose fruit consists of a fleshy mass made up of the crowded fruits +and the fleshy flower stalks, is the best known. + + +ORDER II.--_Enantioblastæ_. + +The second order of the monocotyledons, _Enantioblastæ_, includes very +few common plants. The most familiar examples are the various species +of _Tradescantia_ (Fig. 88), some of which are native, others exotic. +Of the cultivated forms the commonest is one sometimes called +"wandering-jew," a trailing plant with zigzag stems, and oval, pointed +leaves forming a sheath about each joint. Another common one is the +spiderwort already referred to. In this the leaves are long and +pointed, but also sheathing at the base. When the flowers are showy, +as in these, the sepals and petals are different, the former being +green. The flowers usually open but once, and the petals shrivel up as +the flower fades. There are four families of the order, the spiderwort +belonging to the highest one, _Commelyneæ_. + + +ORDER III.--_Spadicifloræ_. + +The third order of the monocotyledons, _Spadicifloræ_, is a very large +one, and includes the largest and the smallest plants of the whole +sub-class. In all of them the flowers are small and often very +inconspicuous; usually, though not always, the male and female flowers +are separate, and often on different plants. The smallest members of +the group are little aquatics, scarcely visible to the naked eye, and +of extremely simple structure, but nevertheless these little plants +produce true flowers. In marked contrast to these are the palms, some +of which reach a height of thirty metres or more. + +The flowers in most of the order are small and inconspicuous, but +aggregated on a spike (spadix) which may be of very large size. Good +types of the order are the various aroids (_Aroideæ_), of which the +calla (_Richardia_) is a very familiar cultivated example. Of wild +forms the sweet-flag (_Acorus_), Jack-in-the-pulpit (_Arisæma_) +(Fig. 86, _A_, _D_), skunk-cabbage (_Symplocarpus_), and wild calla +may be noted. In _Arisæma_ (Fig. 86, _A_) the flowers are borne only +on the base of the spadix, and the plant is dioecious. The flowers are +of the simplest structure, the female consisting of a single carpel, +and the male of four stamens (_C_, _D_). While the individual flowers +are destitute of a perigone, the whole inflorescence (cluster of +flowers) is surrounded by a large leaf (spathe), which sometimes is +brilliantly colored, this serving to attract insects. The leaves of +the aroids are generally large and sometimes compound, the only +instance of true compound leaves among the monocotyledons (Fig. 86, +_B_). + +[Illustration: FIG. 86.--Types of _Spadicifloræ_. _A_, inflorescence +of Jack-in-the-pulpit (_Arisæma_, _Aroideæ_). The flowers (_fl._) are +at the base of a spike (spadix), surrounded by a sheath (spathe), +which has been cut away on one side in order to show the flowers, × œ. +_B_, leaf of the same plant, × Œ. _C_, vertical section of a female +flower, × 2. _D_, three male flowers, each consisting of four stamens, +× 2. _E_, two plants of a duck-weed (_Lemna_), the one at the left is +in flower, × 4. _F_, another common species. _L_, _Trisulea_, × 1. +_G_, male flower of _E_, × 25. _H_, optical section of the female +flower, showing the single ovule (_ov._), × 25. _I_, part of the +inflorescence of the bur-reed (_Sparganium_), with female flowers, × œ +(_Typhaceæ_). _J_, a single, female flower, × 2. _K_, a ripe fruit, +× 1. _L_, longitudinal section of the same. _M_, two male flowers, +× 1. _N_, a pond-weed (_Potomogeton_), × 1 (_Naiadaceæ_). _O_, a +single flower, × 2. _P_, the same, with the perianth removed, × 2. +_Q_, fruit of the same, × 2.] + +Probably to be regarded as reduced aroids are the duck-weeds +(_Lemnaceæ_) (Fig. 86, _F_, _H_), minute floating plants without any +differentiation of the plant body into stem and leaves. They are +globular or discoid masses of cells, most of them having roots; but +one genus (_Wolffia_) has no roots nor any trace of fibro-vascular +bundles. The flowers are reduced to a single stamen or carpel (Figs. +_E_, _G_, _H_). + +The cat-tail (_Typha_) and bur-reed (_Sparganium_) (Fig. 86, _I_, _L_) +are common representatives of the family _Typhaceæ_, and the +pond-weeds (_Naias_ and _Potomogeton_) are common examples of the +family _Naiadeæ_. These are aquatic plants, completely submerged +(_Naias_), or sometimes partially floating (_Potomogeton_). The latter +genus includes a number of species with leaves varying from linear +(very narrow and pointed) to broadly oval, and are everywhere common +in slow streams. + +The largest members of the group are the screw-pines (_Pandaneæ_) and +the palms (_Palmæ_). These are represented in the United States by +only a few species of the latter family, confined to the southern and +southwestern portions. The palmettoes (_Sabal_ and _Chamærops_) are +the best known. + +Both the palms and screw-pines are often cultivated for ornament, and +as is well known, in the warmer parts of the world the palms are among +the most valuable of all plants. The date palm (_Phoenix dactylifera_) +and the cocoanut (_Cocos nucifera_) are the best known. The apparently +compound ("pinnate" or feather-shaped) leaves of many palms are not +strictly compound; that is, they do not arise from the branching of an +originally single leaf, but are really broad, undivided leaves, which +are closely folded like a fan in the bud, and tear apart along the +folds as the leaf opens. + +Although these plants reach such a great size, an examination of the +stem shows that it is built on much the same plan as that of the other +monocotyledons; that is, the stem is composed of a mass of soft, +ground tissue through which run many small isolated, fibro-vascular +bundles. A good idea of this structure may be had by cutting across a +corn-stalk, which is built on precisely the same pattern. + + +ORDER IV.--_Glumaceæ_. + +The plants of this order resemble each other closely in their habit, +all having long, narrow leaves with sheathing bases that surround the +slender, distinctly jointed stem which frequently has a hard, polished +surface. The flowers are inconspicuous, borne usually in close spikes, +and destitute of a perigone or having this reduced to small scales or +hairs. The flowers are usually surrounded by more or less dry leaves +(glumes, paleæ) which are closely set, so as to nearly conceal the +flowers. The flowers are either hermaphrodite or unisexual. + +[Illustration: FIG. 87.--Types of _Glumaceæ_. _A_, a sedge, _Carex_ +(_Cyperaceæ_). [Male], the male; [Female], the female flowers, × œ. +_B_, a single male flower, × 2. _C_, a female flower, × 2. _D_, +fruiting spike of another _Carex_, × œ. _E_, a single fruit, × 1. _F_, +the same, with the outer envelope removed, and slightly enlarged. _G_, +section of _F_, × 3. _em._ the embryo. _H_, a bulrush, _Scirpus_ +(_Cyperaceæ_), × œ. _I_, a single spikelet, × 2. _J_, a single flower, +× 3. _K_, a spikelet of flowers of the common orchard grass, +_Dactylis_ (_Gramineæ_), × 2. _L_, a single flower, × 2. _M_, the base +of a leaf, showing the split sheath encircling the stem, × 1. _N_, +section of a kernel of corn, showing the embryo (_em._), × 2.] + +There are two well-marked families, the sedges (_Cyperaceæ_) and the +grasses (_Gramineæ_). The former have solid, often triangular stems, +and the sheath at the base of the leaves is not split. The commonest +genera are _Carex_ (Fig. 87, _A_, _G_) and _Cyperus_, of which there +are many common species, differing very little and hard to +distinguish. There are several common species of _Carex_ which blossom +early in the spring, the male flowers being quite conspicuous on +account of the large, yellow anthers. The female flowers are in +similar spikes lower down, where the pollen readily falls upon them, +and is caught by the long stigmas. In some other genera, _e.g._ the +bulrushes (_Scirpus_) (Fig. 87, _H_), the flowers are hermaphrodite, +_i.e._ contain both stamens and pistils. The fruit (Fig. 87, _F_) is +seed-like, but really includes the wall of the ovary as well, which is +grown closely to the enclosed seed. The embryo is small, surrounded by +abundant endosperm (Fig. 87, _G_). Very few of the sedges are of any +economic importance, though one, the papyrus of Egypt, was formerly +much valued for its pith, which was manufactured into paper. + +The second family, the grasses, on the contrary, includes the most +important of all food plants, all of the grains belonging here. They +differ mainly from the sedges in having, generally, hollow, +cylindrical stems, and the sheath of the leaves split down one side; +the leaves are in two rows, while those of the sedges are in three. +The flowers (Fig. 87, _L_) are usually perfect; the stigmas, two in +number and like plumes, so that they readily catch the pollen which is +blown upon them. A few, like the Indian corn, have the flowers +unisexual; the male flowers are at the top of the stem forming the +"tassel," and the female flowers lower down forming the ear. The +"silk" is composed of the enormously lengthened stigmas. The fruits +resemble those of the sedges, but the embryo is usually larger and +placed at one side of the endosperm (_N_, _em._). + +While most of the grasses are comparatively small plants, a few of +them are almost tree-like in their proportions, the species of bamboo +(_Bambusa_) sometimes reaching a height of twenty to thirty metres, +with stems thirty to forty centimetres in diameter. + + +ORDER V.--_Scitamineæ_. + +[Illustration: FIG. 88.--_Scitamineæ_. _A_, upper part of a flowering +plant of Indian shot (_Canna_), much reduced in size (_Cannaceæ_). +_B_, a single flower, × œ. _C_, the single stamen (_an._), and +petal-like pistil (_gy._), × 1. _D_, section of the ovary, × 2. _E_, +diagram of the flower. The place of the missing stamens is indicated +by small circles. _F_, fruit, × œ. _G_, section of an unripe seed. +_em._ embryo. _p_, perisperm, × 2.] + +The plants of this order are all inhabitants of the warmer parts of +the earth, and only a very few occur within the limits of the United +States, and these confined to the extreme south. They are extremely +showy plants, owing to their large leaves and brilliant flowers, and +for this reason are cultivated extensively. Various species of _Canna_ +(Fig. 88) are common in gardens, where they are prized for their +large, richly-colored leaves, and clusters of scarlet, orange, or +yellow flowers. The leafy stems arise from thick tubers or root +stocks, and grow rapidly to a height of two metres or more in the +larger species. The leaves, as in all the order, are very large, and +have a thick midrib with lateral veins running to the margin. The +young leaves are folded up like a trumpet. The flowers are irregular +in form, and in _Canna_ only a single stamen is found; or if more are +present, they are reduced to petal-like rudiments. The single, perfect +stamen (Fig. 88, _C_, _an._) has the filament broad and colored like +the petals, and the anther attached to one side. The pistil (_gy._) is +also petal-like. There are three circles of leaves forming the +perigone, the two outer being more or less membranaceous, and only the +three inner petal-like in texture. The ovary (_o_) is inferior, and +covered on the outside with little papillæ that afterward form short +spines on the outside of the fruit (_F_). + +The seeds are large, but the embryo is very small. A section of a +nearly ripe seed shows the embryo (_em._) occupying the upper part of +the embryo sac which does not nearly fill the seed and contains no +endosperm. The bulk of the seed is derived from the tissue of the body +of the ovule, which in most seeds becomes entirely obliterated by the +growth of the embryo sac. The cells of this tissue become filled with +starch, and serve the same purpose as the endosperm of other seeds. +This tissue is called "perisperm." + +Of food plants belonging to this order, the banana (_Musa_) is much +the most important. Others of more or less value are species of +arrowroot (_Maranta_) and ginger (_Zingiber_). + +There are three families: I. _Musaceæ_ (banana family); +II. _Zingiberaceæ_ (ginger family); and III. _Cannaceæ_ (_Canna_, +_Maranta_). + + +ORDER VI.--_Gynandræ_. + +By far the greater number of the plants of this order belong to the +orchis family (_Orchideæ_), the second family of the order +(_Apostasieæ_), being a small one and unrepresented in the United +States. The orchids are in some respects the most highly specialized +of all flowers, and exhibit wonderful variety in the shape and color +of the flowers, which are often of extraordinary beauty, and show +special contrivances for cross-fertilization that are without parallel +among flowering plants. + +[Illustration: FIG. 89.--_Gynandræ_. _A_, inflorescence of the showy +orchis (_Orchis spectabilis_), × 1 (_Orchideæ_). _B_, a single flower, +with the upper leaves of the perianth turned back to show the column +(_x_). _sp._ the spur attached to the lower petal or lip. _o_, the +ovary, × 1. _C_, the column seen from in front. _an._ the stamen. +_gy._ the stigmatic surface, × 1. _D_, the two pollen masses attached +to a straw, which was inserted into the flower, by means of the viscid +disc (_d_): i, the masses immediately after their withdrawal; ii, iii, +the same a few minutes later, showing the change in position. _E_, +diagram of the flower; the position of the missing stamens indicated +by small circles.] + +The flowers are always more or less bilaterally symmetrical +(zygomorphic). The ovary is inferior, and usually twisted so as to +turn the flower completely around. There are two sets of perigone +leaves, three in each, and these are usually much alike except the +lower (through the twisting of the ovary) of the inner set. This +petal, known as the "lip" or "labellum," is usually larger than the +others, and different in color, as well as being frequently of +peculiar shape. In many of them it is also prolonged backward in a +hollow spur (see Fig. 89, _B_). In all of the orchids except the +lady's-slippers (_Cypripedium_) (Fig. 90, _B_), only one perfect +stamen is developed, and this is united with the three styles to form +a special structure known, as the "column" or "gynostemium" (Fig. 89, +_B_, _C_). The pollen spores are usually aggregated into two or four +waxy masses ("pollinia," sing. pollinium), which usually can only be +removed by the agency of insects upon which all but a very few orchids +are absolutely dependent for the pollination of the flowers. + +[Illustration: FIG. 90.--Forms of _Orchideæ_. _A_, putty-root +(_Aplectrum_), × 1. _B_, yellow lady's-slipper (_Cypripedium_), × œ. +_C_, the column of the same, × 1. _an._ one of the two perfect +stamens. _st._ sterile, petal-like stamen. _gy._. stigma. _D_, +_Arethusa_, × œ. _E_, section of the column, × 1: _an._ stamen. _gy._ +stigma. _F_, the same, seen from in front. _G_, _Habenaria_, × 1. _H_, +_Calopogon_, × 1. In the last the ovary is not twisted, so that the +lip (_L_) lies on the upper side of the flower.] + +In the lady-slippers there are two fertile stamens, and a third +sterile one has the form of a large triangular shield terminating the +column (Fig. 90, _C_, _st._). + +The ovules of the orchids are extremely small, and are only partly +developed at the time the flower opens, the pollen tube growing very +slowly and the ovules maturing as it grows down through the tissues of +the column. The ripe seeds are excessively numerous, but so fine as to +look like dust. + +The orchids are mostly small or moderate-sized plants, few of them +being more than a metre or so in height. All of our native species, +with the exception of a few from the extreme south, grow from fibrous +roots or tubers, but many tropical orchids, as is well known, are +"epiphytes"; that is, they grow upon the trunks and branches of trees. +One genus, _Vanilla_, is a twining epiphyte; the fruit of this plant +furnishes the vanilla of commerce. Aside from this plant, the +economical value of the orchids is small, although a few of them are +used medicinally, but are not specially valuable. + +Of the five thousand species known, the great majority are inhabitants +of the tropics, but nevertheless there are within the United States a +number of very beautiful forms. The largest and showiest are the +lady's-slippers, of which we have six species at the north. The most +beautiful is the showy lady's-slipper (_Cypripedium spectabile_), +whose large, pink and white flowers rival in beauty many of the +choicest tropical orchids. Many of the _Habenarias_, including the +yellow and purple fringed orchids, are strikingly beautiful as are the +_Arethuseæ_ (_Arethusa_, _Pogonia_, _Calopogon_). The last of these +(Fig. 90, _H_) differs from all our other native orchids in having the +ovary untwisted so that the labellum lies on the upper side of the +flower. + +A number of the orchids are saprophytic, growing in soil rich in +decaying vegetable matter, and these forms are often nearly or quite +destitute of chlorophyll, being brownish or yellowish in color, and +with rudimentary leaves. The coral roots (_Corallorhiza_), of which +there are several species, are examples of these, and another closely +related form, the putty-root (_Aplectrum_) (Fig. 90, _A_), has the +flowering stems like those of _Corallorhiza_, but there is a single, +large, plaited leaf sent up later. + + +ORDER VII.--_Helobiæ_. + +The last order of the monocotyledons is composed of marsh or water +plants, some of which recall certain of the dicotyledons. Of the three +families, the first, _Juncagineæ_, includes a few inconspicuous plants +with grass-like or rush-like leaves, and small, greenish or yellowish +flowers (_e.g._ arrow-grass, _Triglochin_). + +The second family (_Alismaceæ_) contains several large and showy +species, inhabitants of marshes. Of these the water-plantain +(_Alisma_), a plant with long-stalked, oval, ribbed leaves, and a +much-branched panicle of small, white flowers, is very common in +marshes and ditches, and the various species of arrowhead +(_Sagittaria_) are among the most characteristic of our marsh plants. +The flowers are unisexual; the female flowers are usually borne at the +base of the inflorescence, and the male flowers above. The gynoecium +(Fig. 91, _B_) consists of numerous, separate carpels attached to a +globular receptacle. The sepals are green and much smaller than the +white petals. The leaves (_F_) are broad, and, besides the thickened, +parallel veins, have numerous smaller ones connecting these. + +[Illustration: FIG. 91.--Types of _Helobiæ_. _A_, inflorescence of +arrowhead (_Sagittaria_), with a single female flower, × œ +(_Alismaceæ_). _B_, section through the gynoecium, showing the numerous +single carpels, × 3. _C_, a ripe fruit, × 3. _D_, a male flower, × 1. +_E_, a single stamen, × 3. _F_, a leaf of _Sagittaria variabilis_, +× 1/6. _G_, ditch-moss (_Elodea_), with a female flower (_fl._), × œ. +(_Hydrocharideæ_). _H_, the flower, × 2. _an._ the rudimentary +stamens. _st._ the stigma. _I_, cross-section of the ovary, × 4. _J_, +male inflorescence of eel-grass (_Vallisneria_), × 1. _K_, a single +expanded male flower, × 12. _st._ the stamen. _L_, a female flower, +× 1. _gy._ the stigma.] + +The last family is the _Hydrocharideæ_. They are submersed aquatics, +or a few of them with long-stalked, floating leaves. Two forms, the +ditch-moss (_Elodea_) (Fig. 91, _G_, _I_) and eel-grass +(_Vallisneria_) are very common in stagnant or slow-running water. In +both of these the plants are completely submersed, but there is a +special arrangement for bringing the flowers to the surface of the +water. Like the arrowhead, the flowers are unisexual, but borne on +different plants. The female flowers (_H_, _L_) are comparatively +large, especially in _Vallisneria_, and are borne on long stalks, by +means of which they reach the surface of the water, where they expand +and are ready for pollination. The male flowers (Fig. 91, _J_, _K_) +are extremely small and borne, many together, surrounded by a +membranous envelope, the whole inflorescence attached by a short +stalk. When the flowers are ready to open, they break away from their +attachment, and the envelope opens, allowing them to escape, and they +immediately rise to the surface where they expand and collect in great +numbers about the open female flowers. Sometimes these are so abundant +during the flowering period (late in summer) that the surface of the +water looks as if flour had been scattered over it. After pollination +is effected, the stem of the female flower coils up like a spring, +drawing the flower beneath the water where the fruit ripens. + +The cells of these plants show very beautifully the circulation of the +protoplasm, the movement being very marked and continuing for a long +time under the microscope. To see this the whole leaf of _Elodea_, or +a section of that of _Vallisneria_, may be used. + + + + +CHAPTER XVII. + +DICOTYLEDONS. + + +The second sub-class of the angiosperms, the dicotyledons, receive +their name from the two opposite seed leaves or cotyledons with which +the young plant is furnished. These leaves are usually quite different +in shape from the other leaves, and not infrequently are very thick +and fleshy, filling nearly the whole seed, as may be seen in a bean or +pea. The number of the dicotyledons is very large, and very much the +greater number of living spermaphytes belong to this group. They +exhibit much greater variety in the structure of the flowers than the +monocotyledons, and the leaves, which in the latter are with few +exceptions quite uniform in structure, show here almost infinite +variety. Thus the leaves may be simple (undivided); _e.g._ oak, apple; +or compound, as in clover, locust, rose, columbine, etc. The leaves +may be stalked or sessile (attached directly to the stem), or even +grown around the stem, as in some honeysuckles. The edges of the +leaves may be perfectly smooth ("entire"), or they may be variously +lobed, notched, or wavy in many ways. As many of the dicotyledons are +trees or shrubs that lose their leaves annually, special leaves are +developed for the protection of the young leaves during the winter. +These have the form of thick scales, and often are provided with +glands secreting a gummy substance which helps render them +water-proof. These scales are best studied in trees with large, winter +buds, such as the horsechestnut (Fig. 92), hickory, lilac, etc. On +removing the hard, scale leaves, the delicate, young leaves, and often +the flowers, may be found within the bud. If we examine a young shoot +of lilac or buckeye, just as the leaves are expanding in the spring, a +complete series of forms may be seen from the simple, external scales, +through immediate forms, to the complete foliage leaf. The veins of +the leaves are almost always much-branched, the veins either being +given off from one main vein or midrib (feather-veined or +pinnate-veined), as in an apple leaf, or there may be a number of +large veins radiating from the base of the leaf, as in the scarlet +geranium or mallow. Such leaves are said to be palmately veined. + +[Illustration: FIG. 92.--End of a branch of a horsechestnut in winter, +showing the buds covered by the thick, brown scale leaves, × 1.] + +Some of them are small herbaceous plants, either upright or prostrate +upon the ground, over which they may creep extensively, becoming +rooted at intervals, as in the white clover, or sending out special +runners, as is seen in the strawberry. Others are woody stemmed +plants, persisting from year to year, and often becoming great trees +that live for hundreds of years. Still others are climbing plants, +either twining their stems about the support, like the morning-glory, +hop, honeysuckle, and many others, or having special organs (tendrils) +by which they fasten themselves to the support. These tendrils +originate in different ways. Sometimes, as in the grape and Virginia +creeper, they are reduced branches, either coiling about the support, +or producing little suckers at their tips by which they cling to walls +or the trunks of trees. Other tendrils, as in the poison ivy and the +true ivy, are short roots that fasten themselves firmly in the +crevices of bark or stones. Still other tendrils, as those of the +sweet-pea and clematis, are parts of the leaf. + +The stems may be modified into thorns for protection, as we see in +many trees and shrubs, and parts of leaves may be similarly changed, +as in the thistle. The underground stems often become much changed, +forming bulbs, tubers, root stocks, etc. much as in the +monocotyledons. These structures are especially found in plants which +die down to the ground each year, and contain supplies of nourishment +for the rapid growth of the annual shoots. + +[Illustration: FIG. 93.--_A_, base of a plant of shepherd's-purse +(_Capsella bursa-pastoris_), × œ. _r_, the main root. _B_, upper part +of the inflorescence, × 1. _C_, two leaves: i, from the upper part; +ii, from the base of the plant, × 1. _D_, a flower, × 3. _E_, the +same, with sepals and petals removed, × 3. _F_, petal. _G_, sepal. +_H_, stamen, × 10. _f_, filament. _an._ anther. _I_, a fruit with one +of the valves removed to show the seeds, × 4. _J_, longitudinal +section of a seed, × 8. _K_, the embryo removed from the seed, × 8. +_l_, the first leaves (cotyledons). _st._ the stem ending in the root. +_L_, cross-section of the stem, × 20. _fb._ fibro-vascular bundle. +_M_, a similar section of the main root, × 15. _N_, diagram of the +flower.] + +The structure of the tissues, and the peculiarities of the flower and +fruit, will be better understood by a somewhat careful examination of +a typical dicotyledon, and a comparison with this of examples of the +principal orders and families. + +One of the commonest of weeds, and at the same time one of the most +convenient plants for studying the characteristics of the +dicotyledons, is the common shepherd's-purse (_Capsella +bursa-pastoris_) (Figs. 93-95). + +The plant grows abundantly in waste places, and is in flower nearly +the year round, sometimes being found in flower in midwinter, after a +week or two of warm weather. It is, however, in best condition for +study in the spring and early summer. The plant may at once be +recognized by the heart-shaped pods and small, white, four-petaled +flowers. The plant begins to flower when very small, but continues to +grow until it forms a much-branching plant, half a metre or more in +height. On pulling up the plant, a large tap-root (Fig. 93, _A_, _r_) +is seen, continuous with the main stem above ground. The first root of +the seedling plant continues here as the main root of the plant, as +was the case with the gymnosperms, but not with the monocotyledons. +From this tap-root other small ones branch off, and these divide +repeatedly, forming a complex root system. The main root is very tough +and hard, owing to the formation of woody tissue in it. A +cross-section slightly magnified (Fig. 93, _M_), shows a round, +opaque, white, central area (_x_), the wood, surrounded by a more +transparent, irregular ring (_ph._), the phloem or bast; and outside +of this is the ground tissue and epidermis. + +The lower leaves are crowded into a rosette, and are larger than those +higher up, from which they differ also in having a stalk (petiole), +while the upper leaves are sessile. The outline of the leaves varies +much in different plants and in different parts of the same plant, +being sometimes almost entire, sometimes divided into lobes almost to +the midrib, and between these extremes all gradations are found. The +larger leaves are traversed by a strong midrib projecting strongly on +the lower side of the leaf, and from this the smaller veins branch. +The upper leaves have frequently two smaller veins starting from the +base of the leaf, and nearly parallel with the midrib (_C_ i). The +surface of the leaves is somewhat roughened with hairs, some of which, +if slightly magnified, look like little white stars. + +Magnifying slightly a thin cross-section of the stem, it shows a +central, ground tissue (pith), whose cells are large enough to be seen +even when very slightly enlarged. Surrounding this is a ring of +fibro-vascular bundles (_L_, _fb._), appearing white and opaque, and +connected by a more transparent tissue. Outside of the ring of +fibro-vascular bundles is the green ground tissue and epidermis. +Comparing this with the section of the seedling pine stem, a +resemblance is at once evident, and this arrangement was also noticed +in the stem of the horse-tail. + +Branches are given off from the main stem, arising at the point where +the leaves join the stem (axils of the leaves), and these may in turn +branch. All the branches terminate finally in an elongated +inflorescence, and the separate flowers are attached to the main axis +of the inflorescence by short stalks. This form of inflorescence is +known technically as a "raceme." Each flower is really a short branch +from which the floral leaves arise in precisely the same way as the +foliage leaves do from the ordinary branches. There are five sets of +floral leaves: I. four outer perigone leaves (sepals) (_F_), small, +green, pointed leaves traversed by three simple veins, and together +forming the calyx; II. four larger, white, inner perigone leaves +(petals) (_G_), broad and slightly notched at the end, and tapering to +the point of attachment. The petals collectively are known as the +"corolla." The veins of the petals fork once; III. and IV. two sets of +stamens (_E_), the outer containing two short, and the inner, four +longer ones arranged in pairs. Each stamen has a slender filament +(_H_, _f_) and a two-lobed anther (_an._). The innermost set consists +of two carpels united into a compound pistil. The ovary is oblong, +slightly flattened so as to be oval in section, and divided into two +chambers. The style is very short and tipped by a round, flattened +stigma. + +The raceme continues to grow for a long time, forming new flowers at +the end, so that all stages of flowers and fruit may often be found in +the same inflorescence. + +The flowers are probably quite independent of insect aid in +pollination, as the stamens are so placed as to almost infallibly shed +their pollen upon the stigma. This fact, probably, accounts for the +inconspicuous character of the flowers. + +After fertilization is effected, and the outer floral leaves fall off, +the ovary rapidly enlarges, and becomes heart-shaped and much +flattened at right angles to the partition. When ripe, each half falls +away, leaving the seeds attached by delicate stalks (funiculi, sing. +funiculus) to the edges of the membranous partition. The seeds are +small, oval bodies with a shining, yellow-brown shell, and with a +little dent at the end where the stalk is attached. Carefully dividing +the seed lengthwise, or crushing it in water so as to remove the +embryo, we find it occupies the whole cavity of the seed, the young +stalk (_st._) being bent down against the back of one of the +cotyledons (_f_). + +[Illustration: FIG. 94.--_A_, cross-section of the stem of the +shepherd's-purse, including a fibro-vascular bundle, × 150. _ep._ +epidermis. _m_, ground tissue. _sh._ bundle sheath. _ph._ phloem. +_xy._ xylem. _tr._ a vessel. _B_, a young root seen in optical +section, × 150. _r_, root cap. _d_, young epidermis. _pb._ ground. +_pl._ young fibro-vascular bundle. _C_ cross section of a small root, +× 150. _fb._ fibro-vascular bundle. _D_, epidermis from the lower side +of the leaf, × 150. _E_, a star-shaped hair from the surface of the +leaf, × 150. _F_, cross-section of a leaf, × 150. _ep._ epidermis. +_m_, ground tissue. _fb._ section of a vein.] + + A microscopic examination of a cross-section of the older root shows + that the central portion is made up of radiating lines of + thick-walled cells (fibres) interspersed with lines of larger, round + openings (vessels). There is a ring of small cambium cells around + this merging into the phloem, which is composed of irregular cells, + with pretty thick, but soft walls. The ground tissue is composed of + large, loose cells, which in the older roots are often ruptured and + partly dried up. The epidermis is usually indistinguishable in the + older roots. To understand the early structure of the roots, the + smallest rootlets obtainable should be selected. The smallest are so + transparent that the tips may be mounted whole in water, and will + show very satisfactorily the arrangement of the young tissues. The + tissues do not here arise from a single, apical cell, as we found in + the pteridophytes, but from a group of cells (the shaded cells in + Fig. 94, _B_). The end of the root, as in the fern, is covered with + a root cap (_r_) composed of successive layers of cells cut off from + the growing point. The rest of the root shows the same division of + the tissues into the primary epidermis (dermatogen) (_d_), young + fibro-vascular cylinder (plerome) (_pl._), and young ground tissue + (periblem) (_pb._). The structure of the older portions of such + a root is not very easy to study, owing to difficulty in making + good cross-sections of so small an object. By using a very + sharp razor, and holding perfectly straight between pieces of pith, + however, satisfactory sections can be made. The cells contain so + much starch as to make them almost opaque, and potash should be used + to clear them. The fibro-vascular bundle is of the radial type, + there being two masses of xylem (_xy._) joined in the middle, and + separating the two phloem masses (_ph._), some of whose cells are + rather thicker walled than the others. The bundle sheath is not so + plain here as in the fern. The ground tissue is composed of + comparatively large cells with thickish, soft walls, that contain + much starch. The epidermis usually dies while the root is still + young. In the larger roots the early formation of the cambium ring, + and the irregular arrangement of the tissues derived from its + growth, soon obliterate all traces of the primitive arrangement of + the tissues. Making a thin cross-section of the stem, and magnifying + strongly, we find bounding the section a single row of epidermal + cells (Fig. 94, _A_, _ep._) whose walls, especially the outer ones, + are strongly thickened. Within these are several rows of thin-walled + ground-tissue cells containing numerous small, round chloroplasts. + The innermost row of these cells (_sh._) are larger and have but + little chlorophyll. This row of cells forms a sheath around the ring + of fibro-vascular bundles very much as is the case in the + horse-tail. The separate bundles are nearly triangular in outline, + the point turned inward, and are connected with each other by masses + of fibrous tissue (_f_), whose thickened walls have a peculiar, + silvery lustre. Just inside of the bundle sheath there is a row of + similar fibres marking the outer limit of the phloem (_ph._). The + rest of the phloem is composed of very small cells. The xylem is + composed of fibrous cells with yellowish walls and numerous large + vessels (_tr._). The central ground tissue (pith) has large, + thin-walled cells with numerous intercellular spaces, as in the stem + of _Erythronium_. Some of these cells contain a few scattered + chloroplasts in the very thin, protoplasmic layer lining their + walls, but the cells are almost completely filled with colorless + cell sap. + + A longitudinal section shows that the epidermal cells are much + elongated, the cells of the ground tissue less so, and in both the + partition walls are straight. In the fibrous cells, both of the + fibro-vascular bundle and those lying between, the end walls are + strongly oblique. The tracheary tissue of the xylem is made up of + small, spirally-marked vessels, and larger ones with thickened + rings or with pits in the walls. The small, spirally-marked vessels + are nearest the centre, and are the first to be formed in the young + bundle. + + The epidermis of the leaves is composed of irregular cells with wavy + outlines like those of the ferns. Breathing pores, of the same type + as those in the ferns and monocotyledons, are found on both + surfaces, but more abundant and more perfectly developed on the + lower surface of the leaf. Owing to their small size they are not + specially favorable for study. The epidermis is sparingly covered + with unicellular hairs, some of which are curiously branched, being + irregularly star-shaped. The walls of these cells are very thick, + and have little protuberances upon the outer surface (Fig. 93, _E_). + + Cross-sections of the leaf may be made between pith as already + directed; or, by folding the leaf carefully several times, the whole + can be easily sectioned. The structure is essentially as in the + adder-tongue, but the epidermal cells appear more irregular, and the + fibro-vascular bundles are better developed. They are like those of + the stem, but somewhat simpler. The xylem lies on the upper side. + + The ground tissue is composed, as in the leaves we have studied, of + chlorophyll-bearing, loose cells, rather more compact upon the upper + side. (In the majority of dicotyledons the upper surface of the + leaves is nearly or quite destitute of breathing pores, and the + cells of the ground tissue below the upper epidermis are closely + packed, forming what is called the "palisade-parenchyma" of the + leaf.) + +[Illustration: FIG. 95.--_A-D_, successive stages in the development +of the flower of _Capsella_, × 50. _A_, surface view. _B-D_, optical +sections. _s_, sepals, _p_, petals. _an._ stamens. _gy._ pistil. _E_, +cross-section of the young anther, × 180. _sp._ spore mother cells. +_F_, cross-section of full-grown anther. _sp._ pollen spores, × 50. +_F'_, four young pollen spores, × 300. _F"_, pollen spores germinating +upon the stigma, × 300. _pt._ pollen tube. _G_, young pistil in +optical section, × 25. H, cross-section of a somewhat older one. _ov._ +ovules. _I-L_, development of the ovule. _sp._ embryo sac +(macrospore). _I-K_, × 150. _L_, × 50. _M_, embryo sac of a full-grown +ovule, × 150. _Sy._ _Synergidæ_. _o_, egg cell. _n_, endosperm +nucleus. _ant._ antipodal cells. _N-Q_, development of the embryo, +× 150. _sus._ suspensor.] + + The shepherd's-purse is an admirable plant for the study of the + development of the flower which is much the same in other + angiosperms. To study this, it is only necessary to teaze out, in a + drop of water, the tip of a raceme, and putting on a cover glass, + examine with a power of from fifty to a hundred diameters. In the + older stages it is best to treat with potash, which will render the + young flowers quite transparent. The young flower (Fig. 95, _A_) is + at first a little protuberance composed of perfectly similar small + cells filled with dense protoplasm. The first of the floral leaves + to appear are the sepals which very early arise as four little buds + surrounding the young flower axis (Fig. 95, _A_, _B_). The stamens + (_C_, _an._) next appear, being at first entirely similar to the + young sepals. The petals do not appear until the other parts of the + flower have reached some size, and the first tracheary tissue + appears in the fibro-vascular bundle of the flower stalk (_D_). The + carpels are more or less united from the first, and form at first a + sort of shallow cup with the edges turned in (_D_, _gy._). This cup + rapidly elongates, and the cavity enlarges, becoming completely + closed at the top where the short style and stigma develop. The + ovules arise in two lines on the inner face of each carpel, and the + tissue which bears them (placenta) grows out into the cavity of the + ovary until the two placentæ meet in the middle and form a partition + completely across the ovary (Fig. 95, _H_). + + The stamens soon show the differentiation into filament and anther, + but the former remains very short until immediately before the + flowers are ready to open. The anther develops four sporangia + (pollen sacs), the process being very similar to that in such + pteridophytes as the club mosses. Each sporangium (Fig. _E_, _F_) + contains a central mass of spore mother cells, and a wall of three + layers of cells. The spore mother cells finally separate, and the + inner layer of the wall cells becomes absorbed much as we saw in + the fern, and the mass of mother cells thus floats free in the + cavity of the sporangium. Each one now divides in precisely the same + way as in the ferns and gymnosperms, into four pollen spores. The + anther opens as described for _Erythronium_. + + By carefully picking to pieces the young ovaries, ovules in all + stages of development may be found, and on account of their small + size and transparency, show beautifully their structure. Being + perfectly transparent, it is only necessary to mount them in water + and cover. + + The young ovule (_I_, _J_) consists of a central, elongated body + (nucellus), having a single layer of cells enclosing a large central + cell (the macrospore or embryo sac) (_sp._). The base of the + nucellus is surrounded by two circular ridges (i, ii) of which the + inner is at first higher than the outer one, but later (_K_, _L_), + the latter grows up above it and completely conceals it as well as + the nucellus. One side of the ovule grows much faster than the + other, so that it is completely bent upon itself, and the opening + between the integuments is brought close to the base of the ovule + (Fig. 95, _L_). This opening is called the "micropyle," and allows + the pollen tube to enter. + + The full-grown embryo sac shows the same structure as that already + described in _Monotropa_ (page 276), but as the walls of the + full-grown ovule are thicker here, its structure is rather difficult + to make out. The ripe stigma is covered with little papillæ + (Fig. 95, _F_) that hold the pollen spores which may be found here + sending out the pollen tube. By carefully opening the ovary and + slightly crushing it in a drop of water, the pollen tube may + sometimes be seen growing along the stalk of the ovule until it + reaches and enters the micropyle. + + To study the embryo a series of young fruits should be selected, and + the ovules carefully dissected out and mounted in water, to which a + little caustic potash has been added. The ovule will be thus + rendered transparent, and by pressing gently on the cover glass with + a needle so as to flatten the ovule slightly, there is usually no + trouble in seeing the embryo lying in the upper part of the embryo + sac, and by pressing more firmly it can often be forced out upon the + slide. The potash should now be removed as completely as possible + with blotting paper, and pure water run under the cover glass. + + The fertilized egg cell first secretes a membrane, and then divides + into a row of cells (_N_) of which the one nearest the micropyle is + often much enlarged. The cell at the other end next enlarges and + becomes divided by walls at right angles to each other into eight + cells. This globular mass of cells, together with the cell next to + it, is the embryo plant, the row of cells to which it is attached + taking no further part in the process, and being known as the + "suspensor." Later the embryo becomes indented above and forms two + lobes (_Q_), which are the beginnings of the cotyledons. The first + root and the stem arise from the cells next the suspensor. + + + + +CHAPTER XVIII. + +CLASSIFICATION OF DICOTYLEDONS. + + +DIVISION I.--_Choripetalæ_. + +Nearly all of the dicotyledons may be placed in one of two great +divisions distinguished by the character of the petals. In the first +group, called _Choripetalæ_, the petals are separate, or in some +degenerate forms entirely absent. As familiar examples of this group, +we may select the buttercup, rose, pink, and many others. + +The second group (_Sympetalæ_ or _Gamopetalæ_) comprises those +dicotyledons whose flowers have the petals more or less completely +united into a tube. The honeysuckles, mints, huckleberry, lilac, etc., +are familiar representatives of the _Sympetalæ_, which includes the +highest of all plants. + +[Illustration: FIG. 96.--Iulifloræ. _A_, male; _B_, female +inflorescence of a willow, _Salix_ (_Amentaceæ_), × œ. _C_, a single +male flower, × 2. _D_, a female flower, × 2. _E_, cross-section of the +ovary, × 8. _F_, an opening fruit. _G_, single seed with its hairy +appendage, × 2.] + +The _Choripetalæ_ may be divided into six groups, including twenty-two +orders. The first group is called _Iulifloræ_, and contains numerous, +familiar plants, mostly trees. In these plants, the flowers are small +and inconspicuous, and usually crowded into dense catkins, as in +willows (Fig. 96) and poplars, or in spikes or heads, as in the +lizard-tail (Fig. 97, _G_), or hop (Fig. 97, _I_). The individual +flowers are very small and simple in structure, being often reduced to +the gynoecium or andræcium, carpels and stamens being almost always in +separate flowers. The outer leaves of the flower (sepals and petals) +are either entirely wanting or much reduced, and never differentiated +into calyx and corolla. + +[Illustration: FIG. 97.--Types of _Iulifloræ_. _A_, branch of hazel, +_Corylus_ (_Cupuliferæ_), × 1. [Male], male; [Female], female +inflorescence. _B_, a single male flower, × 3. _C_, section of the +ovary of a female flower, × 25. _D_, acorn of red oak, _Quercus_ +(_Cupuliferæ_), × œ. _E_, seed of white birch, _Betula_ (_Betulaceæ_), +× 3. _F_, fruit of horn-bean, _Carpinus_ (_Cupuliferæ_), × 1. G, +lizard-tail, _Saururus_ (_Saurureæ_), × Œ. _H_, a single flower, × 2. +_I_, female inflorescence of the hop, _Humulus_ (_Cannabineæ_), × 1. +_J_, a single scale with two flowers, × 1. _K_, a male flower of a +nettle, _Urtica_ (_Urticaceæ_), × 5.] + +In the willows (Fig. 96) the stamens are bright-colored, so that the +flowers are quite showy, and attract numerous insects which visit them +for pollen and nectar, and serve to carry the pollen to the pistillate +flowers, thus insuring their fertilization. In the majority of the +group, however, the flowers are wind-fertilized. An excellent example +of this is seen in the common hazel (Fig. 97, _A_). The male flowers +are produced in great numbers in drooping catkins at the ends of the +branches, shedding the pollen in early spring before the leaves +unfold. The female flowers are produced on the same branches, but +lower down, and in much smaller numbers. The stigmas are long, and +covered with minute hairs that catch the pollen which is shaken out +in clouds every time the plant is shaken by the wind, and falls in a +shower over the stigmas. A similar arrangement is seen in the oaks, +hickories, and walnuts. + +There are three orders of the _Iulifloræ_: _Amentaceæ_, _Piperineæ_, +and _Urticinæ_. The first contains the birches (_Betulaceæ_); oaks, +beeches, hazels, etc. (_Cupuliferæ_); walnuts and hickories +(_Juglandeæ_); willows and poplars (_Salicaceæ_). They are all trees +or shrubs; the fruit is often a nut, and the embryo is very large, +completely filling it. + +The _Piperineæ_ are mostly tropical plants, and include the pepper +plant (_Piper_), as well as other plants with similar properties. Of +our native forms, the only common one is the lizard-tail (_Saururus_), +not uncommon in swampy ground. In these plants, the calyx and corolla +are entirely absent, but the flowers have both carpels and stamens +(Fig. 97, _H_). + +The _Urticinæ_ include, among our common plants, the nettle family +(_Urticaceæ_); plane family (_Plataneæ_), represented by the sycamore +or buttonwood (_Platanus_); the hemp family (_Cannabineæ_); and the +elm family (_Ulmaceæ_). The flowers usually have a calyx, and may +have only stamens or carpels, or both. Sometimes the part of the stem +bearing the flowers may become enlarged and juicy, forming a +fruit-like structure. Well-known examples of this are the fig and +mulberry. + +The second group of the _Choripetalæ_ is called _Centrospermæ_, and +includes but a single order comprising seven families, all of which, +except one (_Nyctagineæ_), are represented by numerous native species. +The latter comprises mostly tropical plants, and is represented in our +gardens by the showy "four-o'clock" (_Mirabilis_). In this plant, as +in most of the order, the corolla is absent, but here the calyx is +large and brightly colored, resembling closely the corolla of a +morning-glory or petunia. The stamens are usually more numerous than +the sepals, and the pistil, though composed of several carpels, has, +as a rule, but a single cavity with the ovules arising from the base, +though sometimes the ovary is several celled. + +[Illustration: FIG. 98.--Types of _Centrospermæ_. _A_, plant of +spring-beauty, _Claytonia_ (_Portulacaceæ_), × œ. _B_, a single +flower, × 1. _C_, fruit, with the sepals removed, × 2. _D_, section of +the seed, showing the curved embryo (_em._), × 5. _E_, single flower +of smart-weed, _Polygonum_ (_Polygonaceæ_), × 2. _F_, the pistil, × 2. +_G_, section of the ovary, showing the single ovule, × 4. _H_, section +of the seed, × 2. _I_, base of the leaf, showing the sheath, × 1. _J_, +flower of pig-weed, _Chenopodium_ (_Chenopodiaceæ_), × 3: i, from +without; ii, in section. _K_, flower of the poke-weed, _Phytolacca_ +(_Phytolaccaceæ_), × 2. _L_, fire-pink, _Silene_ (_Caryophyllaceæ_), +× œ. _M_, a flower with half of the calyx and corolla removed, × 1. +_N_, ripe fruit of mouse-ear chick-weed, _Cerastium_ (_Caryophyllaceæ_), +opening by ten teeth at the summit, × 2. _O_, diagram of the flower +of _Silene_.] + +The first family (_Polygoneæ_) is represented by the various species +of _Polygonum_ (knotgrass, smart-weed, etc.), and among cultivated +plants by the buckwheat (_Fagopyrum_). The goose-foot or pig-weed +(_Chenopodium_) among native plants, and the beet and spinach of the +gardens are examples of the family _Chenopodiaceæ_. Nearly resembling +the last is the amaranth family (_Amarantaceæ_), of which the showy +amaranths and coxcombs of the gardens, and the coarse, green amaranth +or pig-weed are representatives. + +The poke-weed (_Phytolacca_) (Fig. 98, _K_), so conspicuous in autumn +on account of its dark-purple clusters of berries and crimson stalks, +is our only representative of the family _Phytolaccaceæ_. The two +highest families are the purslane family (_Portulacaceæ_) and pink +family (_Caryophylleæ_). These are mostly plants with showy flowers in +which the petals are large and conspicuous, though some of the pink +family, _e.g._ some chick-weeds, have no petals. Of the purslane +family the portulacas of the gardens, and the common purslane or +"pusley," and the spring-beauty (_Claytonia_) (Fig. 98, _A_) are the +commonest examples. The pink family is represented by many common and +often showy plants. The carnation, Japanese pinks, and sweet-william, +all belonging to the genus _Dianthus_, of which there are also two or +three native species, are among the showiest of the family. The genera +_Lychnis_ and _Silene_ (Fig. 98, _L_) also contain very showy species. +Of the less conspicuous genera, the chick-weeds (_Cerastium_ and +_Stellaria_) are the most familiar. + +The third group of the _Choripetalæ_ (the _Aphanocyclæ_) is a very +large one and includes many common plants distributed among five +orders. The lower ones have all the parts of the flower entirely +separate, and often indefinite in number; the higher have the gynoecium +composed of two or more carpels united to form a compound pistil. + +The first order (_Polycarpæ_) includes ten families, of which the +buttercup family (_Ranunculaceæ_) is the most familiar. The plants of +this family show much variation in the details of the flowers, which +are usually showy, but the general plan is much the same. In some of +them, like the anemones (Fig. 99, _A_), clematis, and others, the +corolla is absent, but the sepals are large and brightly colored so as +to appear like petals. In the columbine (_Aquilegia_) (Fig. 99, _F_) +the petals are tubular, forming nectaries, and in the larkspur +(Fig. 99, _T_) one of the sepals is similarly changed. + +Representing the custard-apple family (_Anonaceæ_) is the curious +papaw (_Asimina_), common in many parts of the United States +(Fig. 100, _A_). The family is mainly a tropical one, but this species +extends as far north as southern Michigan. + +[Illustration: FIG. 99.--Types of _Aphanocyclæ_ (_Polycarpæ_), family +_Ranunculaceæ_. _A_, Rue anemone (_Anemonilla_), × œ. _B_, a fruit, +× 2. _C_, section of the same. _D_, section of a buttercup flower +(_Ranunculus_), × 1œ. _E_, diagram of buttercup flower. _F_, wild +columbine (_Aquilegia_), × œ. _G_, one of the spur-shaped petals, × 1. +_H_, the five pistils, × 1. _I_, longitudinal section of the fruit, +× 1. _J_, flower of larkspur (_Delphinium_), × 1. _K_, the four petals +and stamens, after the removal of the five colored and petal-like +sepals, × 1.] + +The magnolia family (_Magnoliaceæ_) has several common members, the +most widely distributed being, perhaps, the tulip-tree (_Liriodendron_) +(Fig. 100, _C_), much valued for its timber. Besides this there are +several species of magnolia, the most northerly species being the +sweet-bay (_Magnolia glauca_) of the Atlantic States, and the +cucumber-tree (_M. acuminata_); the great magnolia (_M. grandiflora_) +is not hardy in the northern states. + +The sweet-scented shrub (_Calycanthus_) (Fig. 100, _G_) is the only +member of the family _Calycanthaceæ_ found within our limits. It grows +wild in the southern states, and is cultivated for its sweet-scented, +dull, reddish flowers. + +[Illustration: FIG. 100.--Types of _Aphanocyclæ_ (_Polycarpæ_). _A_, +branch of papaw, _Asimina_ (_Anonaceæ_), × œ. _B_, section of the +flower, × 1. _C_, flower and leaf of tulip-tree, _Liriodendron_ +(_Magnoliaceæ_), × 1/3. _D_, section of a flower, × œ. _E_, a ripe +fruit, × 1. _F_, diagram of the flower. _G_, flower of the +sweet-scented shrub, _Calycanthus_ (_Calycanthaceæ_), × œ] + +The barberry (_Berberis_) (Fig. 101, _A_) is the type of the family +_Berberideæ_, which also includes the curious mandrake or may-apple +(_Podophyllum_) (Fig. 101, _D_), and the twin-leaf or rheumatism-root +(_Jeffersonia_), whose curious seed vessel is shown in Figure 101, +_G_. The fruit of the barberry and may-apple are edible, but the root +of the latter is poisonous. + +The curious woody twiner, moon-seed (_Menispermum_) (Fig. 101, _I_), +is the sole example in the northern states of the family _Menispermeæ_ +to which it belongs. The flowers are dioecious, and the pistillate +flowers are succeeded by black fruits looking like grapes. The +flattened, bony seed is curiously sculptured, and has the embryo +curled up within it. + +[Illustration: FIG. 101.--Types of _Aphanocyclæ_ (_Polycarpæ_). _A-H_, +_Berberidaceæ_. _A_, flower of barberry (_Berberis_), × 2. _B_, the +same in section. _C_, a stamen, showing the method of opening, × 3. +_D_, flower of may-apple (_Podophyllum_), × œ. _E_, section of the +ovary of _D_, × 1. _F_, diagram of the flower. _G_, ripe fruit of +twin-leaf (_Jeffersonia_), opening by a lid, × œ. _H_, section of +seed, showing the embryo (_em._), × 2. _I_, young leaf and cluster of +male flowers of moon-seed, _Menispermum_ (_Menispermeæ_), × 1. _J_, a +single male flower, × 2. _K_, section of a female flower, × 2. _L_, +ripe seed, × 1. _M_, section of _L_, showing the curved embryo.] + +The last two families of the order, the laurel family (_Laurineæ_) and +the nutmeg family (_Myristicineæ_) are mostly tropical plants, +characterized by the fragrance of the bark, leaves, and fruit. The +former is represented by the sassafras and spice-bush, common +throughout the eastern United States. The latter has no members within +our borders, but is familiar to all through the common nutmeg, which +is the seed of _Myristica fragrans_ of the East Indies. "Mace" is the +"aril" or covering of the seed of the same plant. + +The second order of the _Aphanocyclæ_ comprises a number of aquatic +plants, mostly of large size, and is known as the _Hydropeltidinæ_. +The flowers and leaves are usually very large, the latter usually +nearly round in outline, and frequently with the stalk inserted near +the middle. The leaves of the perigone are numerous, and sometimes +merge gradually into the stamens, as we find in the common white +water-lily (_Castalia_). + +[Illustration: FIG. 102.--Types of _Aphanocyclæ_ (_Hydropeltidinæ_). +_A_, yellow water-lily, _Nymphæa_ (_Nymphæaceæ_), × œ. _B_, a leaf of +the same, × 1/6. _C_, freshly opened flower, with the large petal-like +sepals removed, × œ. _p_, petals. _an._ stamens. _st._ stigma. _D_, +section of the ovary, × 2. _E_, young fruit, × œ. _F_, lotus, +_Nelumbo_ (_Nelumbieæ_). × 1/6. _G_, a stamen, × 1. _H_, the large +receptacle, with the separate pistils sunk in its surface, × œ. _I_, +section of a single pistil, × 2. _ov._ the ovule. _J_, upper part of a +section through the stigma and ovule (_ov._), × 4.] + +There are three families, all represented within the United States. +The first (_Nelumbieæ_) has but a single species, the yellow lotus or +nelumbo (_Nelumbo lutea_), common in the waters of the west and +southwest, but rare eastward (Fig. 101, _F_). In this flower, the end +of the flower axis is much enlarged, looking like the rose of a +watering-pot, and has the large, separate carpels embedded in its +upper surface. When ripe, each forms a nut-like fruit which is edible. +There are but two species of _Nelumbo_ known, the second one +(_N. speciosa_) being a native of southeastern Asia, and probably +found in ancient times in Egypt, as it is represented frequently in +the pictures and carvings of the ancient Egyptians. It differs mainly +from our species in the color of its flowers which are red instead of +yellow. It has recently been introduced into New Jersey where it has +become well established in several localities. + +The second family (_Cabombeæ_) is also represented at the north by but +one species, the water shield (_Brasenia_), not uncommon in marshes. +Its flowers are quite small, of a dull-purple color, and the leaves +oval in outline and centrally peltate, _i.e._ the leaf stalk inserted +in the centre. The whole plant is covered with a transparent +gelatinous coat. + +The third family (_Nymphæaceæ_) includes the common white water-lilies +(_Castalia_) and the yellow water-lilies (_Nymphæa_) (Fig. 102, _A_). +In the latter the petals are small and inconspicuous (Fig. 102, _C_, +_p_), but the sepals are large and showy. In this family the carpels, +instead of being separate, are united into a large compound pistil. +The water-lilies reach their greatest perfection in the tropics, where +they attain an enormous size, the white, blue, or red flowers of some +species being thirty centimetres or more in diameter, and the leaves +of the great _Victoria regia_ of the Amazon reaching two metres or +more in width. + +The third order of the _Aphanocyclæ_ (_Rhoeadinæ_ or _Crucifloræ_) +comprises a number of common plants, principally characterized by +having the parts of the flowers in twos or fours, so that they are +more or less distinctly cross-shaped, whence the name _Crucifloræ_. + +There are four families, of which the first is the poppy family +(_Papaveraceæ_), including the poppies, eschscholtzias, Mexican or +prickly poppy (_Argemone_), etc., of the gardens, and the blood-root +(_Sanguinaria_), celandine poppy (_Stylophorum_), and a few other wild +plants (see Fig. 103, _A-I_). Most of the family have a colored juice +(latex), which is white in the poppy, yellow in celandine and +_Argemone_, and orange-red in the blood-root. From the latex of the +opium poppy the opium of commerce is extracted. + +[Illustration: FIG. 103.--Types of _Aphanocyclæ_ (_Rhoedinæ_). _A_, +plant of blood-root, _Sanguinaria_ (_Papaveraceæ_), × 1/3. _B_, a single +flower, × 1. _C_, fruit, × œ. _D_, section of the seed. _em._ embryo, +× 2. _E_, diagram of the flower. _F_, flower of Dutchman's breeches, +_Dicentra_ (_Fumariaceæ_), × 1. _G_, group of three stamens of the +same, × 2. _H_, one of the inner petals, × 2. _I_, fruit of celandine +poppy, _Stylophorum_ (_Papaveraceæ_), × œ. _J_, flower of mustard, +_Brassica_ (_Cruciferæ_), × 1. _K_, the same, with the petals removed, +× 2. _L_, fruit of the same, × 1.] + +The second family, the fumitories (_Fumariaceæ_) are delicate, smooth +plants, with curious flowers and compound leaves. The garden +bleeding-heart (_Dicentra spectabilis_) and the pretty, wild +_Dicentras_ (Fig. 103, _F_) are familiar to nearly every one. + +Other examples are the mountain fringe (_Adlumia_), a climbing +species, and several species of _Corydalis_, differing mainly from +_Dicentra_ in having the corolla one-sided. + +The mustard family (_Cruciferæ_) comprises by far the greater part of +the order. The shepherd's-purse, already studied, belongs here, and +may be taken as a type of the family. There is great uniformity in all +as regards the flowers, so that the classification is based mainly on +differences in the fruit and seeds. Many of the most valuable garden +vegetables, as well as a few more or less valuable wild plants, are +members of the family, which, however, includes some troublesome +weeds. Cabbages, turnips, radishes, with all their varieties, belong +here, as well as numerous species of wild cresses. A few like the +wall-flower (_Cheiranthus_) and stock (_Matthiola_) are cultivated for +ornament. + +The last family is the caper family (_Capparideæ_), represented by +only a few not common plants. The type of the order is _Capparis_, +whose pickled flower-buds constitute capers. + +The fourth order (_Cistifloræ_) of the _Aphanocyclæ_ is a very large +one, but the majority of the sixteen families included in it are not +represented within our limits. The flowers have the sepals and petals +in fives, the stamens either the same or more numerous. + +[Illustration: FIG. 104.--Types of _Aphanocyclæ_ (_Cistifloræ_). _A_, +flower of wild blue violet, _Viola_ (_Violaceæ_), × 1. _B_, the lower +petal prolonged behind into a sac or spur, × 1. _C_, the stamens, × 2. +_D_, pistil, × 2. _E_, a leaf, × œ. _F_, section of the ovary, × 2. +_G_, the fruit, × 1. _H_, the same after it has opened, × 1. _I_, +diagram of the flower. _J_, flower of mignonette, _Reseda_ +(_Resedaceæ_), × 2. _K_, a petal, × 3. _L_, cross-section of the +ovary, × 3. _M_, fruit, × 1. _N_, plant of sundew, _Drosera_ +(_Droseraceæ_), × œ. _O_, a leaf that has captured a mosquito, × 2. +_P_, flower of another species (_D. filiformis_), × 2. _Q_, +cross-section of the ovary, × 4.] + +Among the commoner members of the order are the mignonettes +(_Resedaceæ_) and the violets (_Violaceæ_), of which the various wild +and cultivated species are familiar plants (Fig. 104, _A_, _M_). The +sundews (_Droseraceæ_) are most extraordinary plants, growing in boggy +land over pretty much the whole world. They are represented in +the United States by several species of sundew (_Drosera_), and the +still more curious Venus's-flytrap (_Dionæa_) of North Carolina. The +leaves of the latter are sensitive, and composed of two parts which +snap together like a steel trap. If an insect lights upon the leaf, +and touches certain hairs upon its upper surface, the two parts snap +together, holding the insect tightly. A digestive fluid is secreted by +glands upon the inner surface of the leaf, and in a short time the +captured insect is actually digested and absorbed by the leaves. The +same process takes place in the sundew (Fig. 104, _N_) where, however, +the mechanism is somewhat different. Here the tentacles, with which +the leaf is studded, secrete a sticky fluid which holds any small +insect that may light upon it. The tentacles now slowly bend inward +and finally the edges of the leaf as well, until the captured insect +is firmly held, when a digestive process, similar to that in _Dionoea_, +takes place. This curious habit is probably to be explained from the +position where the plant grows, the roots being in water where there +does not seem to be a sufficient supply of nitrogenous matter for the +wants of the plant, which supplements the supply from the bodies of +the captured insects. + +[Illustration: FIG. 105.--Types of _Aphanocyclæ_ (_Cistifloræ_). _A_, +_B_, leaves of the pitcher-plant, _Sarracenia_ (_Sarraceniaceæ_). _A_, +from the side; _B_, from in front, × œ. _C_, St. John's-wort +(_Hypericum_), × œ. _D_, a flower, × 1. _E_, the pistil, × 2. _G_, +cross-section of the ovary, × 4. _H_, diagram of the flower.] + +Similar in their habits, but differing much in appearance from the +sundews, are the pitcher-plants (_Sarraceniaceæ_), of which one +species (_Sarracenia purpurea_) is very common in peat bogs throughout +the northern United States. In this species (Fig. 105, _A_, _B_), the +leaves form a rosette, from the centre of which arises in early summer +a tall stalk bearing a single, large, nodding, dark-reddish flower +with a curious umbrella-shaped pistil. The leaf stalk is hollow and +swollen, with a broad wing on one side, and the blade of the leaf +forms a sort of hood at the top. The interior of the pitcher is +covered above with stiff, downward-pointing hairs, while below it is +very smooth. Insects readily enter the pitcher, but on attempting to +get out, the smooth, slippery wall at the bottom, and the stiff, +downward-directed hairs above, prevent their escape, and they fall +into the fluid which fills the bottom of the cup and are drowned, the +leaf absorbing the nitrogenous compounds given off during the process +of decomposition. There are other species common in the southern +states, and a California pitcher-plant (_Darlingtonia_) has a colored +appendage at the mouth of the pitcher which serves to lure insects +into the trap. + +Another family of pitcher-plants (_Nepentheæ_) is found in the warmer +parts of the old world, and some of them are occasionally cultivated +in greenhouses. In these the pitchers are borne at the tips of the +leaves attached to a long tendril. + +Two other families of the order contain familiar native plants, the +rock-rose family (_Cistaceæ_), and the St. John's-worts +(_Hypericaceæ_). The latter particularly are common plants, with +numerous showy yellow flowers, the petals usually marked with black +specks, and the leaves having clear dots scattered through them. The +stamens are numerous, and often in several distinct groups (Fig. 105, +_C_, _D_). + +The last order of the _Aphanocyclæ_ (the _Columniferæ_) has three +families, of which two, the mallows (_Malvaceæ_), and the lindens +(_Tiliaceæ_), include well-known species. Of the former, the various +species of mallows (Fig. 106, _A_) belonging to the genus _Malva_ are +common, as well as some species of _Hibiscus_, including the showy +swamp _Hibiscus_ or rose-mallow (_H. moscheutos_), common in salt +marshes and in the fresh-water marshes of the great lake region. The +hollyhock and shrubby _Althæa_ are familiar cultivated plants of this +order, and the cotton-plant (_Gossypium_) also belongs here. In all of +these the stamens are much branched, and united into a tube enclosing +the style. Most of them are characterized also by the development of +great quantities of a mucilaginous matter within their tissues. + +The common basswood (_Tilia_) is the commonest representative of the +family _Tiliaceæ_ (Fig. 106, _G_). The nearly related European linden, +or lime-tree, is sometimes planted. Its leaves are ordinarily somewhat +smaller than our native species, which it, however, closely resembles. + +[Illustration: FIG. 106.--Types of _Aphanocyclæ_ (_Columniferæ_). _A_, +flower and leaf of the common mallow, _Malva_ (_Malvaceæ_), × œ. _B_, +a flower bud, × 1. _C_, section of a flower, × 2. _D_, the fruit, × 2. +_E_, section of one division of the fruit, with the enclosed seed, +× 3. _em._ the embryo. _F_, diagram of the flower. _G_, leaf and +inflorescence of the basswood, _Tilia_ (_Tiliaceæ_), × 1/3. _br._ a +bract. _H_, a single flower, × 1. _I_, group of stamens, with +petal-like appendage (_x_), × 2. _J_, diagram of the flower.] + +The fourth group of the _Choripetalæ_ is the _Eucyclæ_. The flowers +most commonly have the parts in fives, and the stamens are never more +than twice as many as the sepals. The carpels are usually more or less +completely united into a compound pistil. There are four orders, +comprising twenty-five families. + +[Illustration: FIG. 107.--Types of _Eucyclæ_ (_Gruinales_). _A_, wild +crane's-bill _Geranium_ (_Geraniaceæ_), × œ. _B_, a petal, × 1. _C_, +the young fruit, the styles united in a column, × œ. _D_, the ripe +fruit, the styles separating to discharge the seeds, × œ. _E_, section +of a seed, × 2. _F_, wild flax. _Linum_ (_Linaceæ_), × œ. _G_, a +single flower, × 2. _H_, cross-section of the young fruit, × 3. _I_, +flower. _J_, leaf of wood-sorrel, _Oxalis_ (_Oxalideæ_), × 1. _K_, the +stamens and pistil, × 2. _L_, flower of jewel-weed, _Impatiens_ +(_Balsamineæ_), × 1. _M_, the same, with the parts separated. _p_, +petals. _s_, sepals. _an._ stamens. _gy._ pistil. _N_, fruit, × 1. +_O_, the same, opening. _P_, a seed, × 2.] + +The first order (_Gruinales_) includes six families, consisting for +the most part of plants with conspicuous flowers. Here belong the +geraniums (Fig. 107, _A_), represented by the wild geraniums and +crane's-bill, and the very showy geraniums (_Pelargonium_) of the +gardens. The nasturtiums (_Tropæolum_) represent another family, +mostly tropical, and the wood-sorrels (_Oxalis_) (Fig. 107, _I_) are +common, both wild and cultivated. The most useful member of the order +is unquestionably the common flax (_Linum_), of which there are also +several native species (Fig. 107, _F_). These are types of the flax +family (_Linaceæ_). Linen is the product of the tough, fibrous inner +bark of _L. usitatissimum_, which has been cultivated for its fibre +from time immemorial. The last family is the balsam family +(_Balsamineæ_). The jewel-weed or touch-me-not (_Impatiens_), so +called from the sensitive pods which spring open on being touched, is +very common in moist ground everywhere (Fig. 107, _L-P_). The garden +balsam, or lady's slipper, is a related species (_I. balsamina_). + +[Illustration: FIG. 108.--_Eucyclæ_ (_Terebinthinæ_, _Æsculinæ_). _A_, +leaves and flowers of sugar-maple, _Acer_ (_Aceraceæ_), × œ. _B_, a +male flower, × 2. _C_, diagram of a perfect flower. _D_, fruit of the +silver-maple, × œ. _E_, section across the seed, × 2. _F_, embryo +removed from the seed, × 1. _G_, leaves and flowers of bladder-nut, +_Staphylea_, (_Sapindaceæ_), × œ. _H_, section of a flower, × 2. _I_, +diagram of the flower. _J_, flower of buckeye (_Æsculus_), × 1œ. _K_, +flower of smoke-tree, _Rhus_ (_Anacardiaceæ_), × 3. _L_, the same, in +section.] + +The second order (_Terebinthinæ_) contains but few common plants. +There are six families, mostly inhabitants of the warmer parts of +the world. The best-known members of the order are the orange, lemon, +citron, and their allies. Of our native plants the prickly ash +(_Zanthoxylum_), and the various species of sumach (_Rhus_), are +the best known. In the latter genus belong the poison ivy +(_R. toxicodendron_) and the poison dogwood (_R. venenata_). The +Venetian sumach or smoke-tree (_R. Cotinus_) is commonly planted for +ornament. + +The third order of the _Eucyclæ_, the _Æsculinæ_, embraces six +families, of which three, the horsechestnuts, etc. (_Sapindaceæ_), the +maples (_Aceraceæ_), and the milkworts (_Polygalaceæ_), have several +representatives in the northern United States. Of the first the +buckeye (_Æsculus_) (Fig. 108, _J_) and the bladder-nut (_Staphylea_) +(Fig. 108, _G_) are the commonest native genera, while the +horsechestnut (_Æsculus hippocastanum_) is everywhere planted. + +The various species of maple (_Acer_) are familiar examples of the +_Aceraceæ_ (see Fig. 106, _A_, _F_). + +The fourth and last order of the _Eucyclæ_, the _Frangulinæ_, is +composed mainly of plants with inconspicuous flowers, the stamens as +many as the petals. Not infrequently they are dioecious, or in some, +like the grape, some of the flowers may be unisexual while others are +hermaphrodite (_i.e._ have both stamens and pistil). Among the +commoner plants of the order may be mentioned the spindle-tree, or +burning-bush, as it is sometimes called (_Euonymus_) (Fig. 109, _A_), +and the climbing bitter-sweet (_Celastrus_) (Fig. 109, _D_), belonging +to the family _Celastraceæ_; the holly and black alder, species of +_Ilex_, are examples of the family _Aquifoliaceæ_; the various species +of grape (_Vitis_), the Virginia creeper (_Ampelopsis quinquefolia_), +and one or two other cultivated species of the latter, represent the +vine family (_Vitaceæ_ or _Ampelidæ_), and the buckthorn (_Rhamnus_) +is the type of the _Rhamnaceæ_. + +[Illustration: FIG. 109.--_Eucylæ_ (_Frangulinæ_), _Tricoccæ_. _A_, +flowers of spindle-tree, _Euonymus_, (_Celastraceæ_), × 1. _B_, +cross-section of the ovary, × 2. _C_, diagram of the flower. _D_, leaf +and fruit of bitter-sweet (_Celastrus_), × œ. _E_, fruit opening and +disclosing the seeds. _F_, section of a nearly ripe fruit, showing the +seeds surrounded by the scarlet integument (aril). _em._ the embryo, +× 1. _G_, flower of grape-vine, _Vitis_ (_Vitaceæ_), × 2. The corolla +has fallen off. _H_, vertical section of the pistil, × 2. _I_, nearly +ripe fruits of the frost-grape, × 1. _J_, cross-section of young +fruit, × 2. _K_, a spurge, _Euphorbia_ (_Euphorbiaceæ_), × œ. _L_, +single group of flowers, surrounded by the corolla-like involucre, +× 3. _M_, section of the same, [Male], male flowers; [Female], female +flowers. _N_, a single male flower, × 5. _O_, cross-section of ovary, +× 6. _P_, a seed, × 2. _Q_, longitudinal section of the seed, × 3. +_em._ embryo.] + +The fifth group of the _Choripetalæ_ is a small one, comprising but a +single order (_Tricoccæ_). The flowers are small and inconspicuous, +though sometimes, as in some _Euphorbias_ and the showy _Poinsettia_ +of the greenhouses, the leaves or bracts surrounding the inflorescence +are conspicuously colored, giving the whole the appearance of a large, +showy, single flower. In northern countries the plants are mostly +small weeds, of which the various spurges or _Euphorbias_ are the most +familiar. These plants (Fig. 109, _K_) have the small flowers +surrounded by a cup-shaped involucre (_L_, _M_) so that the whole +inflorescence looks like a single flower. In the spurges, as in the +other members of the order, the flowers are very simple, being often +reduced to a single stamen or pistil (Fig. 109, _M_, _N_). The plants +generally abound in a milky juice which is often poisonous. This juice +in a number of tropical genera is the source of India-rubber. Some +genera like the castor-bean (_Ricinus_) and _Croton_ are cultivated +for their large, showy leaves. + +The water starworts (_Callitriche_), not uncommon in stagnant water, +represent the family _Callitrichaceæ_, and the box (_Buxus_) is the +type of the _Buxaceæ_. + +[Illustration: FIG. 110.--Types of _Calycifloræ_ (_Umbellifloræ_). +_A_, inflorescence of wild parsnip, _Pastinaca_ (_Umbelliferæ_), × œ. +_B_, single flower of the same, × 3. _C_, a leaf, showing the +sheathing base, × Œ. _D_, a fruit, × 2. _E_, cross-section of _D_. +_F_, part of the inflorescence of spikenard, _Aralia_ (_Araliaceæ_), +× 1. _G_, a single flower of the same, × 3. _H_, the fruit, × 2. _I_, +cross-section of the _H_. _J_, inflorescence of dogwood, _Cornus_ +(_Corneæ_). The cluster of flowers is surrounded by four white bracts +(_b_), × 1/3. _K_, a single flower of the same, × 2. _L_, diagram of the +flower. _M_, young fruit of another species (_Cornus stolonifera_) +(red osier), × 2. _N_, cross-section of _M_.] + +The last and highest group of the _Choripetalæ_, the _Calycifloræ_, +embraces a very large assemblage of familiar plants, divided into +eight orders and thirty-two families. With few exceptions, the floral +axis grows up around the ovary, carrying the outer floral leaves above +it, and the ovary appears at the bottom of a cup around whose edge the +other parts of the flower are arranged. Sometimes, as in the fuchsia, +the ovary is grown to the base of the cup or tube, and thus looks as +if it were outside the flower. Such an ovary is said to be "inferior" +in distinction from one that is entirely free from the tube, and thus +is evidently within the flower. The latter is the so-called "superior" +ovary. The carpels are usually united into a compound pistil, but may +be separate, as in the stonecrop (Fig. 111, _E_), or strawberry +(Fig. 114, _C_). + +The first order of the _Calycifloræ_ (_Umbellifloræ_) has the flowers +small, and usually arranged in umbels, _i.e._ several stalked flowers +growing from a common point. The ovary is inferior, and there is a +nectar-secreting disc between the styles and the stamens. Of the three +families, the umbel-worts or _Umbelliferæ_ is the commonest. The +flowers are much alike in all (Fig. 110, _A_, _B_), and nearly all +have large, compound leaves with broad, sheathing bases. The stems are +generally hollow. So great is the uniformity of the flowers and plant, +that the fruit (Fig. 110, _D_) is generally necessary before the plant +can be certainly recognized. This is two-seeded in all, but differs +very much in shape and in the development of oil channels, which +secrete the peculiar oil that gives the characteristic taste to the +fruits of such forms as caraway, coriander, etc. Some of them, like +the wild parsnip, poison hemlock, etc., are violent poisons, while +others like the carrot are perfectly wholesome. + +The wild spikenard (_Aralia_) (Fig. 110, _F_), ginseng, and the true +ivy (_Hedera_) are examples of the _Araliaceæ_, and the various +species of dogwood (_Cornus_) (Fig. 110, _J-N_) represent the dogwood +family (_Corneæ_). + +The second order (_Saxifraginæ_) contains eight families, including a +number of common wild and cultivated plants. The true saxifrages are +represented by several wild and cultivated species of _Saxifraga_, the +little bishop's cap or mitre-wort (_Mitella_) (Fig. 111, _D_), and +others. The wild hydrangea (Fig. 111, _F_) and the showy garden +species represent the family _Hydrangeæ_. In these some of the flowers +are large and showy, but with neither stamens nor pistils (neutral), +while the small, inconspicuous flowers of the central part of the +inflorescence are perfect. In the garden varieties, all of the flowers +are changed, by selection, into the showy, neutral ones. The syringa +or mock orange (_Philadelphus_) (Fig. 111, _I_), the gooseberry, and +currants (_Ribes_) (Fig. 111, _A_), and the stonecrop (_Sedum_) +(Fig. 111, _E_) are types of the families _Philadelpheæ_, _Ribesieæ_, +and _Crassulaceæ_. + +[Illustration: FIG. 111.--_Calycifloræ_ (_Saxifraginæ_): _A_, flowers +and leaves of wild gooseberry, _Ribes_ (_Ribesieæ_), × 1. _B_, +vertical section of the flower, × 2. _C_, diagram of the flower. _D_, +flower of bishop's-cap, _Mitella_ (_Saxifragaceæ_), × 3. _E_, flower +of stonecrop, _Sedum_ (_Crassulaceæ_), × 2. _F_, flowers and leaves of +hydrangea (_Hydrangeæ_), × œ. _n_, neutral flower. _G_, unopened +flower, × 2. _H_, the same, after the petals have fallen away. _I_, +flower of syringa, _Philadelphus_ (_Philadelpheæ_), × 1. _J_, diagram +of the flower.] + +The third order (_Opuntieæ_) has but a single family, the cacti +(_Cactaceæ_). These are strictly American in their distribution, and +inhabit especially the dry plains of the southwest, where they reach +an extraordinary development. They are nearly or quite leafless, and +the fleshy, cylindrical, or flattened stems are usually beset with +stout spines. The flowers (Fig. 112, _A_) are often very showy, so +that many species are cultivated for ornament and are familiar to +every one. The beautiful night-blooming cereus, of which there are +several species, is one of these. A few species of prickly-pear +(_Opuntia_) occur as far north as New York, but most are confined to +the hot, dry plains of the south and southwest. + +[Illustration: FIG. 112.--_Calycifloræ_, _Opuntieæ_ (_Passiflorinæ_). +_A_, flower of a cactus, _Mamillaria_ (_Cactaceæ_) (from "Gray's +Structural Botany"). _B_, leaf and flower of a passion-flower, +_Passiflora_ (_Passifloraceæ_), × œ. _t_, a tendril. _C_, +cross-section of the ovary, × 2. _D_, diagram of the flower.] + +The fourth order (_Passiflorinæ_) are almost without exception +tropical plants, only a very few extending into the southern United +States. The type of the order is the passion-flower (_Passiflora_) +(Fig. 112, _B_), whose numerous species are mostly inhabitants of +tropical America, but a few reach into the United States. The only +other members of the order likely to be met with by the student are +the begonias, of which a great many are commonly cultivated as house +plants on account of their fine foliage and flowers. The leaves are +always one-sided, and the flowers monoecious.[13] Whether the begonias +properly belong with the _Passiflorinæ_ has been questioned. + +[13] Monoecious: having stamens and carpels in different flowers, but +on the same plant. + +[Illustration: FIG. 113.--_Calycifloræ_ (_Myrtifloræ_, _Thymelinæ_). +_A_, flowering branch of moosewood, _Dirca_ (_Thymelæaceæ_), × 1. _B_, +a single flower, × 2. _C_, the same, laid open. _D_, a young flower of +willow herb, _Epilobium_ (_Onagraceæ_), × 1. The pistil (_gy._) is not +yet ready for pollination. _E_, an older flower, with receptive +pistil. _F_, an unopened bud, × 1. _G_, cross-section of the ovary, +× 4. _H_, a young fruit, × 1. _I_, diagram of the flower. _J_, +flowering branch of water milfoil, _Myriophyllum_ (_Haloragidaceæ_), +× œ. _K_, a single leaf, × 1. _L_, female flowers of the same, × 2. +_M_, the fruit, × 2.] + +The fifth order (_Myrtifloræ_) have regular four-parted flowers with +usually eight stamens, but sometimes, through branching of the +stamens, these appear very numerous. The myrtle family, the members of +which are all tropical or sub-tropical, gives name to the order. The +true myrtle (_Myrtus_) is sometimes cultivated for its pretty glossy +green leaves and white flowers, as is also the pomegranate whose +brilliant, scarlet flowers are extremely ornamental. Cloves are the +dried flower-buds of an East-Indian myrtaceous tree (_Caryophyllus_). +In Australia the order includes the giant gum-trees (_Eucalyptus_), +the largest of all known trees, exceeding in size even the giant trees +of California. + +Among the commoner _Myrtifloræ_, the majority belong to the two +families _Onagraceæ_ and _Lythraceæ_. The former includes the evening +primroses (_OEnothera_), willow-herb (_Epilobium_) (Fig. 113, _D_), +and fuchsia; the latter, the purple loosestrife (_Lythrum_) and swamp +loosestrife (_Nesæa_). The water-milfoil (_Myriophyllum_) (Fig. 113, +_J_) is an example of the family _Haloragidaceæ_, and the _Rhexias_ of +the eastern United States represent with us the family _Melastomaceæ_. + +The sixth order of the _Calycifloræ_ is a small one (_Thymelinæ_), +represented in the United States by very few species. The flowers are +four-parted, the calyx resembling a corolla, which is usually absent. +The commonest member of the order is the moosewood (_Dirca_) +(Fig. 113, _A_), belonging to the first of the three families +(_Thymelæaceæ_). Of the second family (_Elæagnaceæ_), the commonest +example is _Shepherdia_, a low shrub having the leaves covered with +curious, scurfy hairs that give them a silvery appearance. The third +family (_Proteaceæ_) has no familiar representatives. + +The seventh order (_Rosifloræ_) includes many well-known plants, all +of which may be united in one family (_Rosaceæ_), with several +sub-families. The flowers are usually five-parted with from five to +thirty stamens, and usually numerous, distinct carpels. In the apple +and pear (Fig. 114, _I_), however, the carpels are more or less grown +together; and in the cherry, peach, etc., there is but a single carpel +giving rise to a single-seeded stone-fruit (drupe) (Fig. 114, _E_, +_H_). In the strawberry (Fig. 114, _A_), rose (_G_), cinquefoil +(_Potentilla_), etc., there are numerous distinct, one-seeded carpels, +and in _Spiræa_ (Fig. 114, _F_) there are five several-seeded carpels, +forming as many dry pods when ripe. The so-called "berry" of the +strawberry is really the much enlarged flower axis, or "receptacle," +in which the little one-seeded fruits are embedded, the latter being +what are ordinarily called the seeds. + +[Illustration: FIG. 114.--_Calycifloræ_ (_Rosifloræ_). _A_, +inflorescence of strawberry (_Fragaria_), × œ. _B_, a single flower, +× 1. _C_, section of _B_. _D_, floral diagram. _E_, vertical section +of a cherry-flower (_Prunus_), × 1. _F_, vertical section of the +flower of _Spiræa_, × 2. _G_, vertical section of the bud of a wild +rose (_Rosa_), × 1. _H_, vertical section of the young fruit, × 1. +_I_, section of the flower of an apple (_Pyrus_), × 1. _J_, floral +diagram of apple.] + +From the examples given, it will be seen that the order includes not +only some of the most ornamental, cultivated plants, but the majority +of our best fruits. In addition to those already given, may be +mentioned the raspberry, blackberry, quince, plum, and apricot. + +[Illustration: FIG. 115.--_Calycifloræ_ (_Leguminosæ_). _A_, flowers +and leaf of the common pea, _Pisum_ (_Papilionaceæ_), × œ. _t_, +tendril. _st._ stipules. _B_, the petals, separated and displayed, +× 1. _C_, flower, with the calyx and corolla removed, × 1. _D_, a +fruit divided lengthwise, × œ. _E_, the embryo, with one of the +cotyledons removed, × 2. _F_, diagram of the flower. _G_, flower of +red-bud, _Cercis_ (_Cæsalpinaceæ_), × 2. _H_, the same, with calyx and +corolla removed. _I_, inflorescence of the sensitive-brier, +_Schrankia_ (_Mimosaceæ_), × 1. _J_, a single flower, × 2.] + +The last order of the _Calycifloræ_ and the highest of the +_Choripetalæ_ is the order _Leguminosæ_, of which the bean, pea, +clover, and many other common plants are examples. In most of our +common forms the flowers are peculiar in shape, one of the petals +being larger than the others, and covering them in the bud. This +petal is known as the standard. The two lateral petals are known as +the wings, and the two lower and inner are generally grown together +forming what is called the "keel" (Fig. 115, _A_, _B_). The stamens, +ten in number, are sometimes all grown together into a tube, but +generally the upper one is free from the others (Fig. 115, _C_). There +is but one carpel which forms a pod with two valves when ripe +(Fig. 115, _D_). The seeds are large, and the embryo fills the seed +completely. From the peculiar form of the flower, they are known as +_Papilionaceæ_ (_papilio_, a butterfly). Many of the _Papilionaceæ_ +are climbers, either having twining stems, as in the common beans, or +else with part of the leaf changed into a tendril as in the pea +(Fig. 115, _A_), vetch, etc. The leaves are usually compound. + +Of the second family (_Cæsalpineæ_), mainly tropical, the honey locust +(_Gleditschia_) and red-bud (_Cercis_) (Fig. 115, _G_) are the +commonest examples. The flowers differ mainly from the _Papilionaceæ_ +in being less perfectly papilionaceous, and the stamens are almost +entirely distinct (Fig. 115, _H_). The last family (_Mimosaceæ_) is +also mainly tropical. The acacias, sensitive-plant (_Mimosa_), and the +sensitive-brier of the southern United States (_Schrankia_) (Fig. 115, +_I_) represent this family. The flowers are quite different from the +others of the order, being tubular and the petals united, thus +resembling the flowers of the _Sympetalæ_. The leaves of _Mimosa_ and +_Schrankia_ are extraordinarily sensitive, folding up if irritated. + + + + +CHAPTER XIX. + +CLASSIFICATION OF DICOTYLEDONS (_Continued_). + + +DIVISION II.--_Sympetalæ_. + +The _Sympetalæ_ or _Gamopetalæ_ are at once distinguished from the +_Choripetalæ_ by having the petals more or less united, so that the +corolla is to some extent tubular. In the last order of the +_Choripetalæ_ we found a few examples (_Mimosaceæ_) where the same +thing is true, and these form a transition from the _Choripetalæ_ to +the _Sympetalæ_. + +There are two great divisions, _Isocarpæ_ and _Anisocarpæ_. In the +first the carpels are of the same number as the petals and sepals; in +the second fewer. In both cases the carpels are completely united, +forming a single, compound pistil. In the _Isocarpæ_ there are usually +twice as many stamens as petals, occasionally the same number. + +There are three orders of the _Isocarpæ_, viz., _Bicornes_, +_Primulinæ_, and _Diospyrinæ_. The first is a large order with six +families, including many very beautiful plants, and a few of some +economic value. Of the six families, all but one (_Epacrideæ_) are +represented in the United States. Of these the _Pyrolaceæ_ includes +the pretty little pyrolas and prince's-pine (_Chimaphila_) (Fig. 116, +_J_); the _Monotropeæ_ has as its commonest examples, the curious +Indian-pipe (_Monotropa uniflora_), and pine-sap (_M. hypopitys_) +(Fig. 116, _L_). These grow on decaying vegetable matter, and are +quite devoid of chlorophyll, the former species being pure white +throughout (hence a popular name, "ghost flower"); the latter is +yellowish. The magnificent rhododendrons and azaleas (Fig. 116, _F_), +and the mountain laurel (_Kalmia_) (Fig. 116, _I_), belong to the +_Rhodoraceæ_. The heath family (_Ericaceæ_), besides the true heaths +(_Erica_, _Calluna_), includes the pretty trailing-arbutus or +may-flower (_Epigæa_), _Andromeda_, _Oxydendrum_ (Fig. 116, _E_), +wintergreen (_Gaultheria_), etc. The last family is represented by the +cranberry (_Vaccinium_) and huckleberry (_Gaylussacia_). + +[Illustration: FIG. 116.--Types of _Isocarpous sympetalæ_ +(_Bicornes_). _A_, flowers, fruit, and leaves of huckleberry, +_Gaylussacia_ (_Vaccinieæ_), × 1. _B_, vertical section of the flower, +× 3. _C_, a stamen: i, from in front; ii, from the side, × 4. _D_, +cross-section of the young fruit, × 2. _E_, flower of sorrel-tree, +_Oxydendrum_ (_Ericaceæ_), × 2. _F_, flower of azalea (_Rhododendron_), +× œ. _G_, cross-section of the ovary, × 3. _H_, diagram of the flower. +_I_, flower of mountain laurel (_Kalmia_), × 1. _J_, prince's-pine, +_Chimaphila_ (_Pyrolaceæ_), × œ. _K_, a single flower, × 1. _L_, plant +of pine-sap, _Monotropa_, (_Monotropeæ_), × œ. _M_, section of a +flower, × 1.] + +The second order, the primroses (_Primulinæ_), is principally +represented in the cooler parts of the world by the true primrose +family (_Primulaceæ_), of which several familiar plants may be +mentioned. The genus _Primula_ includes the European primrose and +cowslip, as well as two or three small American species, and the +commonly cultivated Chinese primrose. Other genera are _Dodecatheon_, +of which the beautiful shooting-star (_D. Meadia_) (Fig. 117, _A_) is +the best known. Something like this is _Cyclamen_, sometimes +cultivated as a house plant. The moneywort (_Lysimachia nummularia_) +(Fig. 117, _D_), as well as other species, also belongs here. + +[Illustration: FIG. 117.--_Isocarpous sympetalæ_ (_Primulinæ_, +_Diospyrinæ_). _A_, shooting-star, _Dodecatheon_ (_Primulaceæ_), × œ. +_B_, section of a flower, × 1. _C_, diagram of the flower. _D_, +Moneywort, _Lysimachia_ (_Primulaceæ_), × œ. _E_, a perfect flower of +the persimmon, _Diospyros_ (_Ebenaceæ_), × 1. _F_, the same, laid open: +section of the young fruit, × 2. _H_, longitudinal section of a ripe +seed, × 1. _em._ the embryo. _I_, fruit, × œ.] + +The sea-rosemary (_Statice_) and one or two cultivated species of +plumbago are the only members of the plumbago family (_Plumbagineæ_) +likely to be met with. The remaining families of the _Primulinæ_ are +not represented by any common plants. + +The third and last order of the _Isocarpous sympetalæ_ has but a +single common representative in the United States; viz., the persimmon +(_Diospyros_) (Fig. 117, _E_). This belongs to the family _Ebenaceæ_, +to which also belongs the ebony a member of the same genus as the +persimmon, and found in Africa and Asia. + +The second division of the _Sympetalæ_ (the _Anisocarpæ_) has usually +but two or three carpels, never as many as the petals. The stamens are +also never more than five, and very often one or more are abortive. + +[Illustration: FIG. 118.--Types of _Anisocarpous sympetalæ_ +(_Tubifloræ_). _A_, flower and leaves of wild phlox (_Polemoniaceæ_), +× œ. _B_, section of a flower, × 1. _C_, fruit, × 1. _D_, flower of +blue valerian (_Polemonium_), × 1. _E_, flowers and leaf of +water-leaf, _Hydrophyllum_ (_Hydrophyllaceæ_), × œ. _F_, section of a +flower, × 1. _G_, flower of wild morning-glory, _Convolvulus_ +(_Convolvulaceæ_), × œ. One of the bracts surrounding the calyx and +part of the corolla are cut away. _H_, diagram of the flower. _I_, the +fruit of a garden morning-glory, from which the outer wall has fallen, +leaving only the inner membranous partitions, × 1. _J_, a seed, × 1. +_K_, cross-section of a nearly ripe seed, showing the crumpled embryo, +× 2. _L_, an embryo removed from a nearly ripe seed, and spread out; +one of the cotyledons has been partially removed, × 1.] + +The first order (_Tubifloræ_) has, as the name indicates, tubular +flowers which show usually perfect, radial symmetry (_Actinomorphism_). +There are five families, all represented by familiar plants. The first +(_Convolvulaceæ_) has as its type the morning-glory (_Convolvulus_) +(Fig. 118, _G_), and the nearly related _Ipomoeas_ of the gardens. The +curious dodder (_Cuscuta_), whose leafless, yellow stems are sometimes +very conspicuous, twining over various plants, is a member of this +family which has lost its chlorophyll through parasitic habits. The +sweet potato (_Batatas_) is also a member of the morning-glory family. +The numerous species, wild and cultivated, of phlox (Fig. 118, _A_), +and the blue valerian (_Polemonium_) (Fig. 118, _D_), are examples of +the family _Polemoniaceæ_. + +[Illustration: FIG. 119.--_Anisocarpous sympetalæ_ (_Tubifloræ_). _A_, +inflorescence of hound's-tongue, _Cynoglossum_ (_Borragineæ_), × œ. +_B_, section of a flower, × 2. _C_, nearly ripe fruit, × 1. _D_, +flowering branch of nightshade, _Solanum_ (_Solaneæ_), × œ. _E_, a +single flower, × 1. _F_, section of the flower, × 2. _G_, young fruit, +× 1. _H_, flower of _Petunia_ (_Solaneæ_), × œ. _I_, diagram of the +flower.] + +The third family (_Hydrophyllaceæ_) includes several species of +water-leaf (_Hydrophyllum_) (Fig. 118, _E_) and _Phacelia_, among our +wild flowers, and species of _Nemophila_, _Whitlavia_ and others from +the western states, but now common in gardens. + +The Borage family (_Borragineæ_) includes the forget-me-not +(_Myosotis_) and a few pretty wild flowers, _e.g._ the orange-flowered +puccoons (_Lithospermum_); but it also embraces a number of the most +troublesome weeds, among which are the hound's-tongue (_Cynoglossum_) +(Fig. 119, _A_), and the "beggar's-ticks" (_Echinospermum_), whose +prickly fruits (Fig. 119, _C_) become detached on the slightest +provocation, and adhere to whatever they touch with great tenacity. +The flowers in this family are arranged in one-sided inflorescences +which are coiled up at first and straighten as the flowers expand. + +The last family (_Solaneæ_) includes the nightshades (_Solanum_) +(Fig. 119, _D_), to which genus the potato (_S. tuberosum_) and the +egg-plant (_S. Melongena_) also belong. Many of the family contain a +poisonous principle, _e.g._ the deadly nightshade (_Atropa_), tobacco +(_Nicotiana_), stramonium (_Datura_), and others. Of the cultivated +plants, besides those already mentioned, the tomato (_Lycopersicum_), +and various species of _Petunia_ (Fig. 119, _H_), _Solanum_, and +_Datura_ are the commonest. + +The second order of the _Anisocarpæ_ consists of plants whose flowers +usually exhibit very marked, bilateral symmetry (_Zygomorphism_). From +the flower often being two-lipped (see Fig. 120), the name of the +order (_Labiatifloræ_) is derived. + +Of the nine families constituting the order, all but one are +represented within our limits, but the great majority belong to two +families, the mints (_Labiatæ_) and the figworts (_Scrophularineæ_). +The mints are very common and easily recognizable on account of their +square stems, opposite leaves, strongly bilabiate flowers, and the +ovary splitting into four seed-like fruits (Fig. 120, _D_, _F_). + + The great majority of them, too, have the surface covered with + glandular hairs secreting a strong-scented volatile oil, giving the + peculiar odor to these plants. The dead nettle (_Lamium_) (Fig. 120, + _A_) is a thoroughly typical example. The sage, mints, catnip, + thyme, lavender, etc., will recall the peculiarities of the family. + +The stamens are usually four in number through the abortion of one of +them, but sometimes only two perfect stamens are present. + +[Illustration: FIG. 120.--_Anisocarpous sympetalæ_ (_Labiatifloræ_). +_A_, dead nettle, _Lamium_, (_Labiatæ_), × œ. _B_, a single flower, +× 1. _C_, the stamens and pistil, × 1. _D_, cross-section of the +ovary, × 2. _E_, diagram of the flower; the position of the absent +stamen is indicated by the small circle. _F_, fruit of the common +sage, _Salvia_ (_Labiatæ_), × 1. Part of the persistent calyx has been +removed to show the four seed-like fruits, or nutlets. _G_, section of +a nutlet, × 3. The embryo fills the seed completely. _H_, part of an +inflorescence of figwort, _Scrophularia_ (_Scrophularineæ_), × 1. _I_, +cross-section of the young fruit, × 2. _J_, flower of speedwell, +_Veronica_ (_Scrophularineæ_), × 2. _K_, fruit of _Veronica_, × 2. +_L_, cross-section of _K_. _M_, flower of moth-mullein, _Verbascum_ +(_Scrophularineæ_), × œ. _N_, flower of toad-flax, _Linaria_ +(_Scrophularineæ_), × 1. _O_, leaf of bladder-weed, _Utricularia_ +(_Lentibulariaceæ_), × 1. _x_, one of the "traps." _P_, a single trap, +× 5.] + +The _Scrophularineæ_ differ mainly from the _Labiatæ_ in having round +stems, and the ovary not splitting into separate one-seeded fruits. +The leaves are also sometimes alternate. There are generally four +stamens, two long and two short, as in the labiates, but in the +mullein (_Verbascum_) (Fig. 120, _M_), where the flower is only +slightly zygomorphic, there is a fifth rudimentary stamen, while in +others (_e.g._ _Veronica_) (Fig. 120, _J_) there are but two stamens. +Many have large, showy flowers, as in the cultivated foxglove +(_Digitalis_), and the native species of _Gerardia_, mullein, +_Mimulus_, etc., while a few like the figwort, _Scrophularia_ +(Fig. 120, _H_), and speedwells (_Veronica_) have duller-colored or +smaller flowers. + +[Illustration: FIG. 121.--_Anisocarpous sympetalæ_ (_Labiatifloræ_). +_A_, flowering branch of trumpet-creeper, _Tecoma_ (_Bignoniaceæ_), +× Œ. _B_, a single flower, divided lengthwise, × œ. _C_, cross-section +of the ovary, × 2. _D_, diagram of the flower. _E_, flower of vervain, +_Verbena_ (_Verbenæ_), × 2: i, from the side; ii, from in front; iii, +the corolla laid open. _F_, nearly ripe fruit of the same, × 2. _G_, +part of a spike of flowers of the common plantain, _Plantago_ +(_Plantagineæ_), × 1; The upper flowers have the pistils mature, but +the stamens are not yet ripe. _H_, a flower from the upper (younger) +part of the spike. _I_, an older expanded flower, with ripe stamens, +× 3.] + +The curious bladder-weed (_Utricularia_) is the type of the family +_Lentibulariaceæ_, aquatic or semi-aquatic plants which possess +special contrivances for capturing insects or small water animals. +These in the bladder-weed are little sacs (Fig. 120, _P_) which act as +traps from which the animals cannot escape after being captured. There +does not appear to be here any actual digestion, but simply an +absorption of the products of decomposition, as in the pitcher-plant. +In the nearly related land form, _Pinguicula_, however, there is much +the same arrangement as in the sundew. + +The family _Gesneraceæ_ is mainly a tropical one, represented in the +greenhouses by the magnificent _Gloxinia_ and _Achimenes_, but of +native plants there are only a few parasitic forms destitute of +chlorophyll and with small, inconspicuous flowers. The commonest of +these is _Epiphegus_, a much-branched, brownish plant, common in +autumn about the roots of beech-trees upon which it is parasitic, and +whence it derives its common name, "beech-drops." + +The bignonia family (_Bignoniaceæ_) is mainly tropical, but in our +southern states is represented by the showy trumpet-creeper (_Tecoma_) +(Fig. 121, _A_), the catalpa, and _Martynia_. + +The other plants likely to be met with by the student belong either to +the _Verbenaceæ_, represented by the showy verbenas of the gardens, +and our much less showy wild vervains, also belonging to the genus +_Verbena_ (Fig. 121, _E_); or to the plantain family (_Plantagineæ_), +of which the various species of plantain (_Plantago_) are familiar to +every one (Fig. 121, _G_, _I_). The latter seem to be forms in which +the flowers have become inconspicuous, and are wind fertilized, while +probably all of its showy-flowered relatives are dependent on insects +for fertilization. + +The third order (_Contortæ_) of the _Anisocarpæ_ includes five +families, all represented by familiar forms. The first, the olive +family (_Oleaceæ_), besides the olive, contains the lilac and jasmine +among cultivated plants, and the various species of ash (_Fraxinus_), +and the pretty fringe-tree (_Chionanthus_) (Fig. 122, _A_), often +cultivated for its abundant white flowers. The other families are the +_Gentianaceæ_ including the true gentians (_Gentiana_) (Fig. 122, +_F_), the buck-bean (_Menyanthes_), the centauries (_Erythræa_ and +_Sabbatia_), and several other less familiar genera; _Loganiaceæ_, +with the pink-root (_Spigelia_) (Fig. 122, _D_), as the best-known +example; _Apocynaceæ_ including the dog-bane (_Apocynum_) (Fig. 122, +_H_), and in the gardens the oleander and periwinkle (_Vinca_). + +[Illustration: FIG. 122.--_Anisocarpous sympetalæ_ (_Contortæ_). _A_, +flower of fringe-tree, _Chionanthus_ (_Oleaceæ_), × 1. _B_, base of +the flower, with part of the calyx and corolla removed, × 2. _C_, +fruit of white ash, _Fraxinus_ (_Oleaceæ_), × 1. _D_, flower of +pink-root, _Spigelia_ (_Loganiaceæ_), × œ. _E_, cross-section of the +ovary, × 3. _F_, flower of fringed gentian, _Gentiana_ (_Gentianaceæ_), +× œ. _G_, diagram of the flower. _H_, flowering branch of dog-bane, +_Apocynum_ (_Apocynaceæ_), × œ. _I_, vertical section of a flower, +× 2. _J_, bud. _K_, flower of milk-weed, _Asclepias_ (_Asclepiadaceæ_), +× 1. _L_, vertical section through the upper part of the flower, × 2. +_gy._ pistil. _p_, pollen masses. _an._ stamen. _M_, a pair of pollen +masses, × 6. _N_, a nearly ripe seed, × 1.] + +The last family is the milk-weeds (_Asclepiadaceæ_), which have +extremely complicated flowers. Our numerous milk-weeds (Fig. 122, _K_) +are familiar representatives, and exhibit perfectly the peculiarities +of the family. Like the dog-banes, the plants contain a milky juice +which is often poisonous. Besides the true milk-weeds (_Asclepias_), +there are several other genera within the United States, but mostly +southern in their distribution. Many of them are twining plants and +occasionally cultivated for their showy flowers. Of the cultivated +forms, the wax-plant (_Hoya_), and _Physianthus_ are the commonest. + +[Illustration: FIG. 123.--_Anisocarpous sympetalæ_ (_Campanulinæ_). +_A_, vertical section of the bud of American bell-flower, _Campanula_ +(_Campanulaceæ_), × 2. _B_, an expanded flower, × 1. The stamens have +discharged their pollen, and the stigma has opened. _C_, cross-section +of the ovary, × 3. _D_, flower of the Carpathian bell-flower +(_Campanula Carpatica_), × 1. _E_, flower of cardinal-flower, +_Lobelia_ (_Lobeliaceæ_), × 1. _F_, the same, with the corolla and +sepals removed. _an._ the united anthers. _gy._ the tip of the pistil. +_G_, the tip of the pistil, × 2, showing the circle of hairs +surrounding the stigma. _H_, cross-section of the ovary, × 3. _I_, tip +of a branch of cucumber, _Cucurbita_ (_Cucurbitaceæ_), with an +expanded female flower ([Female]). _J_, androecium of a male flower, +showing the peculiar convoluted anthers (_an._), × 2. _K_, +cross-section of the ovary, × 2.] + +The fourth order (_Campanulinæ_) also embraces five families, but of +these only three are represented among our wild plants. The +bell-flowers (_Campanula_) (Fig. 123, _A_, _D_) are examples of the +family _Campanulaceæ_, and numerous species are common, both wild and +cultivated. + +[Illustration: FIG. 124.--_Anisocarpous sympetalæ_ (_Aggregatæ_). _A_, +flowering branch of _Houstonia purpurea_, × 1 (_Rubiaceæ_). _B_, +vertical section of a flower, × 2. _C_, fruit of bluets (_Houstonia +coerulea_), × 1. _D_, cross-section of the same. _E_, bedstraw, +_Galium_ (_Rubiaceæ_), × œ. _F_, a single flower, × 2. _G_, flower of +arrow-wood, _Viburnum_ (_Caprifoliaceæ_), × 2. _H_, the same, divided +vertically. _I_, flowering branch of trumpet honeysuckle, _Lonicera_ +(_Caprifoliaceæ_), × œ. _J_, a single flower, the upper part laid +open, × 1. _K_, diagram of the flower. _L_, part of the inflorescence +of valerian, _Valeriana_, (_Valerianeæ_), × 1. _M_, young; _N_, older +flower, × 2. _O_, cross-section of the young fruit; one division of +the three contains a perfect seed, the others are crowded to one side +by its growth. _P_, inflorescence of teasel, _Dipsacus_ (_Dipsaceæ_), +× Œ. _fl._ flowers. _Q_, a single flower, × 1. _R_, the same, with the +corolla laid open.] + +The various species of _Lobelia_, of which the splendid +cardinal-flower (_L. Cardinalis_) (Fig. 123, _E_) is one of the most +beautiful, represent the very characteristic family _Lobeliaceæ_. +Their milky juice contains more or less marked poisonous properties. +The last family of the order is the gourd family (_Cucurbitaceæ_), +represented by a few wild species, but best known by the many +cultivated varieties of melons, cucumbers, squashes, etc. They are +climbing or running plants, and provided with tendrils. The flowers +are usually unisexual, sometimes dioecious, but oftener monoecious +(Fig. 123, _I_). + +[Illustration: FIG. 125.--_Anisocarpous sympetalæ_ (_Aggregatæ_). +Types of _Compositæ_. _A_, inflorescence of Canada thistle +(_Cirsium_), × 1. _B_, vertical section of _A_. _r_, the receptacle or +enlarged end of the stem, to which the separate flowers are attached. +_C_, a single flower, × 2. _o_, the ovary. _p_, the "pappus" (calyx +lobes). _an._ the united anthers. _D_, the upper part of the stamens +and pistil, × 3: i, from a young flower; ii, from an older one. _an._ +anthers. _gy._ pistil. _E_, ripe fruit, × 1. _F_, inflorescence of +may-weed (_Maruta_). The central part (disc) is occupied by perfect +tubular flowers (_G_), the flowers about the edge (rays) are sterile, +with the corolla much enlarged and white, × 2. _G_, a single flower +from the disc, × 3. _H_, inflorescence of dandelion (_Taraxacum_), the +flowers all alike, with strap-shaped corollas, × 1. _I_, a single +flower, × 2. _c_, the split, strap-shaped corolla. _J_, two ripe +fruits, still attached to the receptacle (_r_). The pappus is raised +on a long stalk, × 1. _K_, a single fruit, × 2.] + +The last and highest order of the _Sympetalæ_, and hence of the +dicotyledons, is known as _Aggregatæ_, from the tendency to have the +flowers densely crowded into a head, which not infrequently is closely +surrounded by bracts so that the whole inflorescence resembles a +single flower. There are six families, five of which have common +representatives, but the last family (_Calycereæ_) has no members +within our limits. + +The lower members of the order, _e.g._ various _Rubiaceæ_ (Fig. 124, +_A_, _E_), have the flowers in loose inflorescences, but as we examine +the higher families, the tendency for the flowers to become crowded +becomes more and more evident, and in the highest of our native forms +_Dipsaceæ_ (Fig. 124, _P_) and _Compositæ_ (Fig. 125) this is very +marked indeed. In the latter family, which is by far the largest of +all the angiosperms, including about ten thousand species, the +differentiation is carried still further. Among our native _Compositæ_ +there are three well-marked types. The first of these may be +represented by the thistles (Fig. 125, _A_). The so-called flower of +the thistle is in reality a close head of small, tubular flowers +(Fig. 125, _C_), each perfect in all respects, having an inferior +one-celled ovary, five stamens with the anthers united, and a +five-parted corolla. The sepals (here called the "pappus") (_p_) have +the form of fine hairs. These little flowers are attached to the +enlarged upper end of the flower stalk (receptacle, _r_), and are +surrounded by closely overlapping bracts or scale leaves which look +like a calyx; the flowers, on superficial examination, appear as +single petals. In other forms like the daisy and may-weed (Fig. 125, +_F_), only the central flowers are perfect, and the edge of the +inflorescence is composed of flowers whose corollas are split and +flattened out, but the stamens and sometimes the pistils are wanting +in these so-called "ray-flowers." In the third group, of which the +dandelion (Fig. 125, _H_), chicory, lettuce, etc., are examples, all +of the flowers have strap-shaped, split corollas, and contain both +stamens and pistils. + +The families of the _Aggregatæ_ are the following: I. _Rubiaceæ_ of +which _Houstonia_ (Fig. 124, _A_), _Galium_ (_E_), _Cephalanthus_ +(button-bush), and _Mitchella_ (partridge-berry) are examples; +II. _Caprifoliaceæ_, containing the honeysuckles (_Lonicera_) +(Fig. 124, _I_), _Viburnum_ (_G_), snowberry (_Symphoricarpus_), and +elder (_Sambucus_); III. _Valerianeæ_, represented by the common +valerian (_Valeriana_) (Fig. 124, _L_); IV. _Dipsaceæ_, of which the +teasel (_Dipsacus_) (Fig. 124, _P_), is the type, and also species of +scabious (_Scabiosa_); V. _Compositæ_ to which the innumerable, +so-called compound flowers, asters, golden-rods, daisies, sunflowers, +etc. belong; VI. _Calycereæ_. + +[Illustration: FIG. 126.--_Aristolochiaceæ_. _A_, plant of wild ginger +(_Asarum_), × 1/3. _B_, vertical section of the flower, × 1. _C_, +diagram of the flower.] + +Besides the groups already mentioned, there are several families of +dicotyledons whose affinities are very doubtful. They are largely +parasitic, _e.g._ mistletoe; or water plants, as the horned pond-weed +(_Ceratophyllum_). One family, the _Aristolochiaceæ_, represented by +the curious "Dutchman's pipe" (_Aristolochia sipho_), a woody twiner +with very large leaves, and the common wild ginger (_Asarum_) +(Fig. 126), do not appear to be in any wise parasitic, but the +structure of their curious flowers differs widely from any other group +of plants. + + + + +CHAPTER XX. + +FERTILIZATION OF FLOWERS. + + +If we compare the flowers of different plants, we shall find almost +infinite variety in structure, and this variation at first appears to +follow no fixed laws; but as we study the matter more thoroughly, we +find that these variations have a deep significance, and almost +without exception have to do with the fertilization of the flower. + +In the simpler flowers, such as those of a grass, sedge, or rush among +the monocotyledons, or an oak, hazel, or plantain, among dicotyledons, +the flowers are extremely inconspicuous and often reduced to the +simplest form. In such plants, the pollen is conveyed from the male +flowers to the female by the wind, and to this end the former are +usually placed above the latter so that these are dusted with the +pollen whenever the plant is shaken by the wind. In these plants, the +male flowers often outnumber the female enormously, and the pollen is +produced in great quantities, and the stigmas are long and often +feathery, so as to catch the pollen readily. This is very beautifully +shown in many grasses. + +If, however, we examine the higher groups of flowering plants, we see +that the outer leaves of the flower become more conspicuous, and that +this is often correlated with the development of a sweet fluid +(nectar) in certain parts of the flower, while the wind-fertilized +flowers are destitute of this as well as of odor. + +If we watch any bright-colored or sweet-scented flower for any length +of time, we shall hardly fail to observe the visits of insects to it, +in search of pollen or honey, and attracted to the flower by its +bright color or sweet perfume. In its visits from flower to flower, +the insect is almost certain to transfer part of the pollen carried +off from one flower to the stigma of another of the same kind, thus +effecting pollination. + +That the fertilization of a flower by pollen from another is +beneficial has been shown by many careful experiments which show that +nearly always--at least in flowers where there are special +contrivances for cross-fertilization--the number of seeds is greater +and the quality better where cross-fertilization has taken place, than +where the flower is fertilized by its own pollen. From these +experiments, as well as from very numerous studies on the structure of +the flower with reference to insect aid in fertilization, we are +justified in the conclusion that all bright-colored flowers are, to a +great extent, dependent upon insect aid for transferring the pollen +from one flower to another, and that many, especially those with +tubular or zygomorphic (bilateral) flowers are perfectly incapable of +self-fertilization. In a few cases snails have been known to be the +conveyers of pollen, and the humming-birds are known in some cases, as +for instance the trumpet-creeper (Fig. 121, _A_), to take the place of +insects.[14] + +[14] In a number of plants with showy flowers, _e.g._ violets, +jewel-weed, small, inconspicuous flowers are also formed, which are +self-fertilizing. These inconspicuous flowers are called +"cleistogamous." + +At first sight it would appear that most flowers are especially +adapted for self-fertilization; but in fact, although stamens and +pistils are in the same flower, there are usually effective +preventives for avoiding self-fertilization. In a few cases +investigated, it has been found that the pollen from the flower will +not germinate upon its own stigma, and in others it seems to act +injuriously. One of the commonest means of avoiding self-fertilization +is the maturing of stamens and pistils at different times. Usually the +stamens ripen first, discharging the pollen and withering before the +stigma is ready to receive it, _e.g._ willow-herb (Fig. 113, _D_), +campanula (Fig. 123, _A_, _D_), and pea; in the two latter, the pollen +is often shed before the flower opens. Not so frequently the stigmas +mature first, as in the plantain (Fig. 121, _G_). + +In many flowers, the stamens, as they ripen, move so as to place +themselves directly before the entrance to the nectary, where they are +necessarily struck by any insect searching for honey; after the pollen +is shed, they move aside or bend downward, and their place is taken by +the pistil, so that an insect which has come from a younger flower +will strike the part of the body previously dusted with pollen against +the stigma, and deposit the pollen upon it. This arrangement is very +beautifully seen in the nasturtium and larkspur (Fig. 99, _J_). + +The tubular flowers of the _Sympetalæ_ are especially adapted for +pollination by insects with long tongues, like the bees and +butterflies, and in most of these flowers the relative position of the +stamens and pistil is such as to ensure cross-fertilization, which in +the majority of them appears to be absolutely dependent upon insect +aid. + +The great orchid family is well known on account of the singular form +and brilliant colors of the flowers which have no equals in these +respects in the whole vegetable kingdom. As might be expected, there +are numerous contrivances for cross-fertilization among them, some of +which are so extraordinary as to be scarcely credible. With few +exceptions the pollen is so placed as to render its removal by insects +necessary. One of the simpler contrivances is readily studied in the +little spring-orchis (Fig. 89) or one of the _Habenarias_ (Fig. 90, +_G_). In the first, the two pollen masses taper below where each is +attached to a viscid disc which is covered by a delicate membrane. +These discs are so placed that when an insect enters the flower and +thrusts its tongue into the spur of the flower, its head is brought +against the membrane covering the discs, rupturing it so as to expose +the disc which adheres firmly to the head or tongue of the insect, +the substance composing the disc hardening like cement on exposure to +the air. As the insect withdraws its tongue, one or both of the pollen +masses are dragged out and carried away. The action of the insect may +be imitated by thrusting a small grass-stalk or some similar body into +the spur of the flower, when on withdrawing it, the two pollen masses +will be removed from the flower. If we now examine these carefully, we +shall see that they change position, being nearly upright at first, +but quickly bending downward and forward (Fig. 89, _D_, ii, iii), so +that on thrusting the stem into another flower the pollen masses +strike against the sticky stigmatic surfaces, and a part of the pollen +is left adhering to them. + +The last arrangement that will be mentioned here is one discovered by +Darwin in a number of very widely separated plants, and to which he +gave the name "heterostylism." Examples of this are the primroses +(_Primula_), loosestrife (_Lythrum_), partridge-berry (_Mitchella_), +pickerel-weed (_Pontederia_), (Fig. 84, _I_), and others. In these +there are two, sometimes three, sets of flowers differing very much in +the relative lengths of stamens and pistil, those with long pistils +having short stamens and _vice versa_. When an insect visits a flower +with short stamens, that part is covered with pollen which in the +short-styled (but long-stamened) flower will strike the stigma, as the +pistil in one flower is almost exactly of the length of the stamens in +the other form. In such flowers as have three forms, _e.g._ +_Pontederia_, each flower has two different lengths of stamens, both +differing from the style of the same flower. Microscopic examination +has shown that there is great variation in the size of the pollen +spores in these plants, the large pollen from the long stamens being +adapted to the long style of the proper flower. + +It will be found that the character of the color of the flower is +related to the insects visiting it. Brilliantly colored flowers are +usually visited by butterflies, bees, and similar day-flying insects. +Flowers opening at night are usually white or pale yellow, colors best +seen at night, and in addition usually are very strongly scented so +as to attract the night-flying moths which usually fertilize them. +Sometimes dull-colored flowers, which frequently have a very offensive +odor, are visited by flies and other carrion-loving insects, which +serve to convey pollen to them. + +Occasionally, flowers in themselves inconspicuous are surrounded by +showy leaves or bracts which take the place of the petals of the +showier flowers in attracting insect visitors. The large dogwood +(Fig. 110, _J_), the calla, and Jack-in-the-pulpit (Fig. 86, _A_) are +illustrations of this. + + + + +CHAPTER XXI. + +HISTOLOGICAL METHODS. + + +In the more exact investigations of the tissues, it is often necessary +to have recourse to other reagents than those we have used hitherto, +in order to bring out plainly the more obscure points of structure. +This is especially the case in studies in cell division in the higher +plants, where the changes in the dividing nucleus are very +complicated. + + For studying these the most favorable examples for ready + demonstration are found in the final division of the pollen spores, + especially of some monocotyledons. An extremely good subject is + offered by the common wild onion (_Allium Canadense_), which flowers + about the last of May. The buds, which are generally partially + replaced by small bulbs, are enclosed in a spathe or sheath which + entirely conceals them. Buds two to three millimetres in length + should be selected, and these opened so as to expose the anthers. + The latter should now be removed to a slide, and carefully crushed + in a drop of dilute acetic acid (one-half acid to one-half + distilled water). This at once fixes the nuclei, and by examining + with a low power, we can determine at once whether or not we have + the right stages. The spore mother cells are recognizable by their + thick transparent walls, and if the desired dividing stages are + present, a drop of staining fluid should be added and allowed to act + for about a minute, the preparation being covered with a cover + glass. After the stain is sufficiently deep, it should be carefully + withdrawn with blotting paper, and pure water run under the cover + glass. + + The best stain for acetic acid preparations is, perhaps, gentian + violet. This is an aniline dye readily soluble in water. For our + purpose, however, it is best to make a concentrated, alcoholic + solution from the dry powder, and dilute this as it is wanted. A + drop of the alcoholic solution is diluted with several times its + volume of weak acetic acid (about two parts of distilled water to + one of the acid), and a drop of this mixture added to the + preparation. In this way the nucleus alone is stained and is + rendered very distinct, appearing of a beautiful violet-blue color. + + If the preparation is to be kept permanently, the acid must all be + washed out, and dilute glycerine run under the cover glass. The + preparation should then be sealed with Canada balsam or some other + cement, but previously all trace of glycerine must be removed from + the slide and upper surface of the cover glass. It is generally best + to gently wipe the edge of the cover glass with a small brush + moistened with alcohol before applying the cement. + +[Illustration: FIG. 127.--_A_, pollen mother cell of the wild onion. +_n_, nucleus. _B-F_, early stages in the division of the nucleus. +_par._ nucleolus; acetic acid, gentian violet, × 350.] + + If the spore mother cells are still quite young, we shall find the + nucleus (Fig. 127, _A_, _n_) comparatively small, and presenting a + granular appearance when strongly magnified. These granules, which + appear isolated, are really parts of filaments or segments, which + are closely twisted together, but scarcely visible in the resting + nucleus. On one side of the nucleus may usually be seen a large + nucleolus (called here, from its lateral position, paranucleus), and + the whole nucleus is sharply separated from the surrounding + protoplasm by a thin but evident membrane. + + The first indication of the approaching division of the nucleus is + an evident increase in size (_B_), and at the same time the colored + granules become larger, and show more clearly that they are in lines + indicating the form of the segments. These granules next become more + or less confluent, and the segments become very evident, appearing + as deeply stained, much-twisted threads filling the nuclear cavity + (Fig. 127, _C_), and about this time the nucleolus disappears. + + The next step is the disappearance of the nuclear membrane so that + the segments lie apparently free in the protoplasm of the cell. They + arrange themselves in a flat plate in the middle of the cell, this + plate appearing, when seen from the side, as a band running across + the middle of the cell. (Fig. 127, _D_, shows this plate as seen + from the side, _E_ seen from above.) + + About the time the nuclear plate is complete, delicate lines may be + detected in the protoplasm converging at two points on opposite + sides of the cell, and forming a spindle-shaped figure with the + nuclear plate occupying its equator. This stage (_D_), is known as + the "nuclear spindle." The segments of the nuclear plate next divide + lengthwise into two similar daughter segments (_F_), and these then + separate, one going to each of the new nuclei. This stage is not + always to be met with, as it seems to be rapidly passed over, but + patient search will generally reveal some nuclei in this condition. + +[Illustration: FIG. 128.--Later stages of nuclear divisions in the +pollen mother cell of wild onion, × 350. All the figures are seen from +the side, except _B_ ii, which is viewed from the pole.] + + Although this is almost impossible to demonstrate, there are + probably as many filaments in the nuclear spindle as there are + segments (in this case about sixteen), and along these the nuclear + segments travel slowly toward the two poles of the spindle + (Fig. 128, _A_, _B_). As the two sets of segments separate, they are + seen to be connected by very numerous, delicate threads, and about + the time the young nuclei reach the poles of the nuclear spindle, + the first trace of the division wall appears in the form of isolated + particles (microsomes), which arise first as thickenings of these + threads in the middle of the cell, and appear in profile as a line + of small granules not at first extending across the cell, but later, + reaching completely across it (Fig. 128, _C_, _E_). These granules + constitute the young cell wall or "cell plate," and finally coalesce + to form a continuous membrane (Fig. 128, _F_). + + The two daughter nuclei pass through the same changes, but in + reverse order that we saw in the mother nucleus previous to the + formation of the nuclear plate, and by the time the partition wall + is complete the nuclei have practically the same structure as the + first stages we examined (Fig. 128, _F_).[15] + +[15] The division is repeated in the same way in each cell so that +ultimately four pollen spores are formed from each of the original +mother cells. + + This complicated process of nuclear division is known technically as + "karyokinesis," and is found throughout the higher animals as well + as plants. + +The simple method of fixing and staining, just described, while giving +excellent results in many cases, is not always applicable, nor as a +rule are the permanent preparations so made satisfactory. For +permanent preparations, strong alcohol (for very delicate tissues, +absolute alcohol, when procurable, is best) is the most convenient +fixing agent, and generally very satisfactory. Specimens may be put +directly into the alcohol, and allowed to stay two or three days, or +indefinitely if not wanted immediately. When alcohol does not give +good results, specimens fixed with chromic or picric acid may +generally be used, and there are other fixing agents which will not be +described here, as they will hardly be used by any except the +professional botanist. Chromic acid is best used in a watery solution +(five per cent chromic acid, ninety-five per cent distilled water). +For most purposes a one per cent solution is best; in this the objects +remain from three or four to twenty-four hours, depending on size, but +are not injured by remaining longer. Picric acid is used as a +saturated solution in distilled water, and the specimen may remain for +about the same length of time as in the chromic acid. After the +specimen is properly fixed it must be thoroughly washed in several +waters, allowing it to remain in the last for twenty-four hours or +more until all trace of the acid has been removed, otherwise there is +usually difficulty in staining. + +As staining agents many colors are used. The most useful are +hæmatoxylin, carmine, and various aniline colors, among which may be +mentioned, besides gentian violet, safranine, Bismarck brown, methyl +violet. Hæmatoxylin and carmine are prepared in various ways, but are +best purchased ready for use, all dealers in microscopic supplies +having them in stock. The aniline colors may be used either dissolved +in alcohol or water, and with all, the best stain, especially of the +nucleus, is obtained by using a very dilute, watery solution, and +allowing the sections to remain for twenty-four hours or so in the +staining mixture. + +Hæmatoxylin and carmine preparations may be mounted either in +glycerine or balsam. (Canada balsam dissolved in chloroform is the +ordinary mounting medium.) In using glycerine it is sometimes +necessary to add the glycerine gradually, allowing the water to slowly +evaporate, as otherwise the specimens will sometimes collapse owing to +the too rapid extraction of the water from the cells. Aniline colors, +as a rule, will not keep in glycerine, the color spreading and finally +fading entirely, so that with most of them the specimens must be +mounted in balsam. + +Glycerine mounts must be closed, which may be done with Canada balsam +as already described. The balsam is best kept in a wide-mouthed +bottle, specially made for the purpose, which has a glass cap covering +the neck, and contains a glass rod for applying the balsam. + +Before mounting in balsam, the specimen must be completely freed from +water by means of absolute alcohol. (Sometimes care must be taken to +bring it gradually into the alcohol to avoid collapsing.[16]) If an +aniline stain has been used, it will not do to let it stay more than a +minute or so in the alcohol, as the latter quickly extracts the stain. +After dehydrating, the specimen should be placed on a clean slide in a +drop of clove oil (bergamot or origanum oil is equally good), which +renders it perfectly transparent, when a drop of balsam should be +dropped upon it, and a perfectly clean cover glass placed over the +preparation. The chloroform in which the balsam is dissolved will soon +evaporate, leaving the object embedded in a transparent film of balsam +between the slide and cover glass. No further treatment is necessary. +For the finer details of nuclear division or similar studies, balsam +mounts are usually preferable. + +[16] For gradual dehydrating, the specimens may be placed +successively in 30 per cent, 50 per cent, 70 per cent, 90 per cent, +and absolute alcohol. + +It is sometimes found necessary in sectioning very small and delicate +organs to embed them in some firm substance which will permit +sectioning, but these processes are too difficult and complicated to +be described here. + + * * * * * + +The following books of reference may be recommended. This list is, of +course, not exhaustive, but includes those works which will probably +be of most value to the general student. + +1. GOEBEL. Outlines of Morphology and Classification. + +2. SACHS. Physiology of Plants. + +3. DE BARY. Comparative Anatomy of Ferns and Phanerogams. + +4. DE BARY. Morphology and Biology of Fungi, Mycetozoa, and Bacteria. + +These four works are translations from the German, and take the +place of Sachs's Text-book of Botany, a very admirable work +published first about twenty years ago, and now somewhat antiquated. +Together they constitute a fairly exhaustive treatise on general +botany.--New York, McMillan & Co. + +5. GRAY. Structural Botany.--New York, Ivison & Co. + +6. GOODALE. Physiological Botany.--New York, Ivison & Co. + +These two books cover somewhat the same ground as 1 and 2, but are +much less exhaustive. + +5. STRASBURGER. Das Botanische Practicum.--Jena. + +Where the student reads German, the original is to be preferred, as +it is much more complete than the translations, which are made from +an abridgment of the original work. This book and the next (7 and 8) +are laboratory manuals, and are largely devoted to methods of work. + +7. ARTHUR, BARNES, and COULTER. Plant Dissection.--Holt & Co., New +York. + +8. WHITMAN. Methods in Microscopic Anatomy and Embryology.--Casino +& Co., Boston. + +For identifying plants the following books may be mentioned:-- + +Green algæ (exclusive of desmids, but including _Cyanophyceæ_ and + _Volvocineæ_). + +WOLLE. Fresh-water Algæ of the United States.--Bethlehem, Penn. + +Desmids. WOLLE. Desmids of the United States.--Bethlehem, Penn. + +The red and brown algæ are partially described in FARLOW'S New England + Algæ. Report of United States Fish Commission, 1879.--Washington. + +The _Characeæ_ are being described by Dr. F. F. ALLEN of New York. The + first part has appeared. + +The literature of the fungi is much scattered. FARLOW and TRELEASE + have prepared a careful index of the American literature on the + subject. + +Mosses. LESQUEREUX and JAMES. Mosses of North America.--Boston, Casino + & Co. + +BARNES. Key to the Genera of Mosses.--Bull. Purdue School of Science, + 1886. + +Pteridophytes. UNDERWOOD. Our Native Ferns and their Allies.--Holt + & Co., New York. + +Spermaphytes. GRAY. Manual of the Botany of the Northern United + States. 6th edition, 1890. This also includes the ferns, and the + liverworts.--New York, Ivison & Co. + +COULTER. Botany of the Rocky Mountains.--New York, Ivison & Co. + +CHAPMAN. Flora of the Southern United States.--New York, 1883. + +WATSON. Botany of California. + + + + +INDEX. + + +_Acacia_, 209. + +_Acer_, _-aceæ_. See "Maple." + +Acetic acid, 3, 59, 98, 138, 230. + +_Achimenes_, 218. + +_Acorus_. See "Sweet-flag." + +Actinomorphic, 213. + +Adder-tongue, 116; Fig. 70. See also "_Erythronium_." + +_Adiantum_. See "Maiden-hair." + +_Adlumia_. See "Mountain-fringe." + +_Æsculinæ_, 199. + +_Æsculus_. See "Buckeye," "Horse-chestnut." + +_Aggregatæ_, 222. + +Alcohol, 5, 31, 55, 83, 230, 233. + +Algæ, 4, 21. + green, 21. + red, 21, 49. + brown, 21, 41. + +Alga-fungi. See "_Phycomycetes_." + +_Alisma_, _-ceæ_. See "Water-plantain." + +_Allium_. See "Wild onion." + +Amaranth, 185. + +_Amarantus_, _-aceæ_. See "Amaranth." + +_Amoeba_, 7; Fig. 2. + +_Ampelidæ_. See "Vine." + +_Ampelopsis_. See "Virginia creeper." + +Anatomy, 3. + gross, Implements for study of, 3. + minute, Implements for study of, 3, 4. + +Anatropous, 151. + +_Andreæaceæ_, 99, 100. + +Androecium, 148. + +_Andromeda_, 211. + +_Anemone_, 185. + +_Angiocarpæ_, 84. + +Angiosperm, 129, 143, 145. + +Aniline colors, 233. + +_Anisocarpæ_, 210, 213. + +_Anonaceæ_. See "Custard-apple." + +Anther, 148, 175, 179. + +Antheridium, 27, 36, 39, 45, 51, 59, 68, 89, 96, 106, 122. + +_Anthoceros_, _Anthoceroteæ_, 91; Fig. 57. + +_Aphanocyclæ_, 185, 196. + +_Aplectrum_, 167; Fig. 90. + +_Apocynum_, _-aceæ_. See "Dog-bane." + +_Apostasieæ_, 164. + +Apple, 145, 171, 206; Fig. 114. + +Apricot, 207. + +_Aquilegia_. See "Columbine." + +_Aralia_, _-aceæ_. See "Spikenard." + +Archegonium, 89, 97, 105, 122, 133, 140, 144. + +Archicarp, 138, 145. + +_Arcyria_, 13; Fig. 5. + +_Arethusa_, _Arethuseæ_, 166; Fig. 90. + +_Argemone_, 191. + +Aril, 189. + +_Arisæma_, 78, 157; Fig. 86. + +_Aristolochia_, _-aceæ_, 224. + +Aroid, _Aroideæ_, 157. + +Arrow-grass, 167. + +Arrowhead, 167; Fig. 91. + +Arrowroot, 163. + +_Asarum_. See "Wild ginger." + +_Asclepias_, _-daceæ_. See "Milk-weed." + +_Ascobolus_, 71-73; Fig. 43. + culture of, 71. + spore fruit, 71. + archicarp, 71. + spore sacs, 72. + +_Ascomycetes_, 65, 66. + +Ascospore, 66. + +Ascus, 66, 69. + +Ash, 218; Fig. 122. + +_Asimina_. See "Papaw." + +_Aspidium_, Fig. 70. + +_Asplenium_, 104; Fig. 70. + +Aster, 224. + +_Atropa_. See "Deadly nightshade." + +Axil, 174. + +Azalea, 210; Fig. 116. + +_Azolla_, 117; Fig. 71. + + +Bacteria, 15, 17, 19; Fig. 8. + +Balsam, _Balsamineæ_, 198. + +Bamboo, 162. + +_Bambusa_. See "Bamboo." + +Banana, 163. + +Barberry, 17, 187; Fig. 101. + +Bark. See "Cortex." + +_Basidiomycetes_, 77. + +Basidium, 77, 80, 83. + +Basswood, 195; Fig. 106. + +Bast. See "Phloem." + +_Batatas_. See "Sweet-potato." + +_Batrachospermum_, 53; Fig. 31. + +Bean, 207, 208. + +Bear-grass. See "_Yucca_." + +Bee, 227, 228. + +Beech, 183. + +Beech-drops, 218. + +Beet, 184. + +Beggar's-ticks, 215. + +Begonia, 3, 205. + +Bell-flower, 220, 226; Fig. 123. + +Bellwort, 156. + +_Berberis_, _-ideæ_. See "Barberry." + +Bergamot oil, 234. + +Berry, 145, 156. + +_Betulaceæ_, 183. + +_Bicornes_, 210. + +_Bignonia_, _-aceæ_, 218. + +Biology, 2. + +Birch, 183. + +Bird's-nest fungus. See "_Cyathus_." + +Bishop's cap, 202; Fig. 111. + +Bismarck brown, 233. + +Bitter-sweet, 199; Fig. 109. + +Black alder, 199. + +Blackberry, 207. + +Black fungi. See "_Pyrenomycetes_." + +Bladder-nut, 199; Fig. 108. + +Bladder-weed, 33, 217; Fig. 120. + +Bleeding-heart. See "_Dicentra_." + +Blood-root, 191; Fig. 103. + +Blue-eyed grass, 156. + +Blue-flag. See "_Iris_." + +Blue-green slime, 15. + +Blue valerian. See "_Polemonium_." + +Borage, 215. + +_Borragineæ_. See "Borage." + +Bordered pits, 138. + +Botany defined, 2. + systematic, 3. + +_Botrychium_. See "Grape fern." + +Box, 201. + +Bract, 199, 222, 229. + +_Brasenia_. See "Water-shield." + +Breathing pore, 91, 99, 113, 130, 147, 150, 177. + +_Bromeliaceæ_, 156. + +Bryophyte, 86. + +Buck-bean, 218. + +Buckeye, 171, 199. + +Buckthorn, 199. + +Buckwheat, 184. + +Budding, 64. + +_Bulbochæte_, 28; Fig. 16. + +Bulb, 146, 153, 172. + +Bulrush, 161; Fig. 87. + +Bundle-sheath, 110, 176. + +Burning-bush. See "Spindle-tree." + +Bur-reed, 159; Fig. 86. + +Buttercup, 181, 185; Fig. 99. + +Butterfly, 227, 228. + +Button-bush, 223. + +Buttonwood. See "Sycamore." + +_Buxus_, _Buxaceæ_. See "Box." + + +Cabbage, 192. + +_Cabombeæ_, 190. + +Cactus, _Cactaceæ_, 203; Fig. 112. + +_Cæsalpineæ_, 210. + +Calcium, 2. + +Calla, 157, 229. + +_Callithamnion_, 50-52; Fig. 29. + general structure, 51. + tetraspores, 51. + procarp, 51. + antheridium, 51. + spores, 52. + +_Callitriche_, _-chaceæ_. See "Water starwort." + +_Calluna_. See "Heath." + +_Calopogon_, 166; Fig. 91. + +_Calycanthus_, _-aceæ_, 187; Fig. 100. + +_Calycereæ_, 223. + +_Calycifloræ_, 200. + +Calyx, 174, 182. + +Cambium, 137-138, 175. + +_Campanula_. See "Bell-flower." + +_Campanulaceæ_, 220. + +_Campanulinæ_, 220. + +Canada balsam, 230-234. + +Canada thistle, 224; Fig. 125. + +_Canna_, _-aceæ_, 162, 163; Fig. 88. + +Caper family, 194. + +_Capparis_, _-ideæ_. See "Caper." + +_Caprifoliaceæ_, 223. + +_Capsella_. See "Shepherd's-purse." + +Caraway, 202. + +Carbon, 2, 95. + +Carbon-dioxides, 95. + +Cardinal-flower. See "Lobelia." + +_Carex_, 161; Fig. 87. + +Carmine, 25, 233. + +Carnation, 185. + +Carpel, 148, 154, 175, 179. + +Carpophyll. See "Carpel." + +Carpospore, 51-53. + +Carrot, 202. + +_Caryophylleæ_. See "Pink." + +_Caryophyllus_. See "Clove." + +_Castalia_, 189. + +Castor-bean, 200. + +Catalpa, 218. + +Cat-brier, 154. + +Catkin, 181. + +Catnip, 215. + +Cat-tail, 159. + +Cedar apple, Cedar rust. See "_Gymnosporangium_." + +_Celastraceæ_, 199. + +_Celastrus_. See "Bitter-sweet." + +Celery, 3. + +Cell, 6. + apical, 38, 96, 105, 115. + division, 23, 31, 229. + row, 8; Fig. 3. + mass, 8; Fig. 4. + sap, 6, 151. + +Cellulose, 3. + +Centaury, 219. + +_Centrospermæ_, 183. + +_Cephalanthus_. See "Button-bush." + +_Cerastium_. See "Chick-weed." + +_Ceratophyllum_. See "Horned pond-weed." + +_Cercis_. See "Red-bud." + +_Chamærops_. See "Palmetto." + +_Chara_, 38-40; Fig. 23. + general structure, 38. + method of growth, 39. + cortex, 39. + non-sexual reproduction, 39. + oögonium, 39. + antheridium, 39, 40. + spermatozoids, 40. + germination, 40. + +_Characeæ_, 21, 37, 40. + +_Chareæ_, 40. + +_Cheiranthus_. See "Wall-flower." + +_Chenopodium_, _-aceæ_. See "Goose-foot." + +Cherry, 15, 206; Fig. 114. + +Chicory, 223. + +Chick-weed, 185; Fig. 98. + +_Chimaphila_. See "Prince's pine." + +_Chionanthus_. See "Fringe-tree." + +Chlorine, 2. + +_Chlorococcum_, 23; Fig. 12. + +Chloroform, 234. + +Chloroplast, 22, 45. + +Chlorophyll, 15. + +Chlorophyll body. See "Chloroplast." + +_Chlorophyceæ_, 21. + +_Chondrus_. See "Irish moss." + +_Choripetalæ_, 181, 208. + +Chromic acid, 25-35, 233. + +Chromoplast, 150. + +_Cicinnobulus_, 69; Fig. 39. + +Cilium, 8. + +Cinquefoil, 206. + +_Cistaceæ_. See "Rock-rose." + +_Cistifloræ_, 192. + +Citron, 196. + +_Citrus_. See "Orange," "Lemon." + +_Cladophora_, 24, 25. + structure of cells, 25. + nuclei, 25. + cell division, 25. + zoöspores, 25. + +Classification, 3-9. + +_Clavaria_, 85; Fig. 51. + +_Claytonia_. See "Spring-beauty." + +Clematis, 185. + +Climbing plants, 171. + +_Closterium_, 33; Fig. 20. + +Clove, 205. + +Clove oil, 234. + +Clover, 207. + +Club moss, 116. + larger, 116. + smaller, 123-126; Fig. 74. + gross anatomy, 125. + spores, 126. + prothallium, 126. + systematic position, 126. + +Cluster-cup, 78. + +_Cocos_. See "Palm-coco," 159. + +_Coleochæte_, 28; Fig. 17. + +Collateral fibro-vascular bundle, 135. + +_Collema_, 76; Fig. 44. + +Columella, 55. + +Columbine, 186; Fig. 99. + +Column, 165. + +_Columniferæ_, 195. + +_Commelyneæ_, 157. + +_Compositæ_, 223, 224. + +Compound flower, 224. + leaf, 159, 170. + +Conceptacle, 45. + +Cone, 131. + +_Conferva_, 26. + +_Confervaceæ_, 21, 24. + +Conidium, 68. + +Conifer, 129, 140, 141. + +_Coniferæ_. See "Conifer." + +_Conjugatæ_, 22-29. + +Connective, 148. + +_Conocephalus_. See "Liverwort, giant." + +_Contortæ_, 218. + +_Convolvulaceæ_, 213. + +_Convolvulus_. See "Morning-glory." + +_Coprinus_, 82-84; Fig. 48. + general structure, 82, 83. + young spore fruit, 83. + gills basidia, 83. + spores, 84. + +Coral root, 167. + +_Corallorhiza_. See "Coral root." + +Coriander, 202. + +Corn, 160, 161. + +_Cornus_, _-aceæ_. See "Dogwood." + +Corolla, 174, 182. + +Cortex, 39, 130. + +_Corydalis_, 192. + +Cotton, 195. + +Cotyledon, 134, 146, 180. + +Cowslip, 211. + +Coxcomb, 185. + +Crab-apple, 77, 80. + +Cranberry, 211. + +_Crassulaceæ_, 203. + +Crane's-bill, 3, 196; Fig. 107. + +Cress, 192. + +_Croton_, 200. + +_Cruciferæ_. See "Mustard family." + +_Crucifloræ_. See "_Rhoeadinæ_." + +Cucumber, 221. + +Cucumber-tree. See "Magnolia." + +_Cucurbitaceæ_. See "Gourd." + +Cup fungi ("_Discomycetes_"), 71. + +_Cupuliferæ_, 183. + +Curl, 66. + +Currant, 203. + +_Cuscuta_. See "Dodder." + +Custard-apple, 186. + +_Cyanophyceæ_. See "Blue-green slime." + +_Cyathus_, 84; Fig. 50. + +_Cycad_, _-eæ_, 140. + +_Cycas revoluta_, 141; Fig. 71. + +_Cyclamen_, 212. + +_Cynoglossum_. See "Hound's-tongue." + +_Cyperaceæ_. See "Sedge." + +_Cyperus_, 161. + +Cypress, 142. + +_Cypripedium_. See "Lady's-slipper." + +_Cystopus_. See also "White rust." + _bliti_, 57; Fig. 33. + general structure, 57. + structure of filaments, 57. + non-sexual spores (conidia), 57. + germination of conidia, 58. + resting spores, 59. + oögonium, 59. + antheridium, 59. + _candidus_, 60; Fig. 34. + + +Daisy, 223. + +Dandelion, 66, 223; Fig. 125. + +_Darlingtonia_, 195. + +_Datura_. See "Stramonium." + +Day lily, 155. + +Deadly nightshade, 215. + +Dead nettle, 215; Fig. 120. + +_Delphinium_. See "Larkspur." + +Dermatogen, 176. + +Desmid, 33, 34; Fig. 20. + +Devil's apron. See "_Laminaria_." + +_Dianthus_. See "Pink." + +_Diatomaceæ_, 41, 42; Figs. 24, 25. + structure, 42. + movements, 42. + reproduction, 42. + +_Dicentra_, 192; Fig. 103. + +Dicotyledon, 145, 170, 181, 225. + +_Digitalis_. See "Foxglove." + +Dioecious, 88. + +_Dionæa_. See "Venus's fly-trap." + +_Dioscoreæ_. See "Yam." + +_Dioscorea villosa_, 154. + +_Diospyros_. See "Persimmon." + +_Diospyrinæ_, 210. + +_Dipsacus_, _-aceæ_. See "Teasel." + +_Dirca_. See "Moosewood." + +Ditch-moss, 167; Fig. 91. + +Dodder, 214. + +_Dodecatheon_. See "Shooting-star." + +Dog-bane, 219; Fig. 122. + +Dogwood, 202, 229; Fig. 110. + +_Draparnaldia_, 26; Fig. 14. + +_Drosera_ _-aceæ_. See "Sun-dew." + +Drupe. See "Stone-fruit." + +Duck-weed, 159; Fig. 86. + +Dutchman's pipe. See "_Aristolochia_." + + +Earth star. See "_Geaster_." + +_Ebenaceæ_ (ebony), 212. + +_Echinospermum_. See "Beggar's-ticks." + +_Ectocarpus_, 45, 47; Fig. 28. + +Eel-grass, 168, 169; Fig. 91. + +Egg apparatus, 144. + +Egg cell, 27, 36, 39, 45, 90, 106, 133, 144. + +Egg-plant, 215. + +Eichler, 153. + +Elater, 91, 122. + +Elder, 224. + +_Elæagnaceæ_, 206. + +Elm, 183. + +_Elodea_. See "Ditch-moss." + +Embryo, 90, 97, 107, 133, 149, 180. + +Embryology, 3. + +Embryo sac, 143, 144, 151. + +_Enantioblastæ_, 153, 156; Fig. 85. + +Endosperm, 133, 146, 152. + +Entire leaves, 170. + +_Entomophthoreæ_, 57. + +_Epacrideæ_, 210. + +Epidermis, 91, 111, 112, 113, 122, 135, 137, 150, 177. + +_Epigæa_. See "Trailing arbutus." + +_Epilobium_. See "Willow-herb." + +_Epiphegus_. See "Beech-drops." + +Epiphyte, 166. + +_Equisetum_, _-tinæ_. See "Horse-tail." + +Ergot, 76. + +_Erica_, _-aceæ_. See "Heath." + +_Erysiphe_, 70. + +_Erythræa_. See "Centaury." + +_Erythronium_, 146-152; Fig. 81. + leaf, 146. + stem, 146. + root, 146. + gross anatomy of stem, 147. + flower, 148. + fruit and seed, 150. + histology of stem, 150. + of leaf, 150. + of flower, 151. + of ovule and seed, 151, 152. + +_Eschscholtzia_, 191. + +_Eucalyptus_, 206. + +_Eucyclæ_, 196, 200. + +_Eudorina_, 20. + +_Euglena_, 11, 19; Fig. 9. + +_Euonymus_. See "Spindle-tree." + +_Euphorbia_, 199; Fig. 109. + +_Eurotium_, 70; Fig. 42. + +Evening primrose, 206. + +_Exoascus_, 66. + + +_Fagopyrum_. See "Buckwheat." + +Feather-veined. See "Pinnate-veined." + +Fern, 5, 102, 104, 116. + flowering, 118; Fig. 70. + lady, 104; Fig. 70. + maiden-hair. See "Maiden-hair fern." + ostrich. See "Ostrich-fern." + sensitive, 104. + true, 117. + water. See "Water-fern." + +Fertilization, 225. + +Fibre, 124, 175, 177. + +Fibro-vascular bundle, 107, 110, 121, 123, 135, 136, 147, 150, 159, 174. + +Fig, 183. + +Figwort, 215, 216; Fig. 120. + +Filament (of stamen), 148, 17. + +_Filices_. See "True ferns." + +_Filicineæ_. See "Fern." + +Fir, 142. + +Fission, 23. + +_Flagellata_, 19. + +Flagellum, 19. + +Flax, 197; Fig. 107. + +Flies, 229. + +Flower, 128, 131. + +Flowering-plant. See "Spermaphyte." + +Forget-me-not, 215. + +Four-o'clock, 183. + +Foxglove, 217. + +_Frangulinæ_, 199. + +_Fraxinus_. See "Ash." + +Fringe-tree, 218; Fig. 122. + +Fruit, 145. + +_Fucaceæ_, 43. + +Fuchsia, 201. + +_Fucus_, 42-46. + _vesiculosus_, 43; Figs. 26, 27. + general structure, 43, 44. + conceptacles, 44. + collecting plants, 44. + cells, 44. + chloroplasts, 44. + oögonium, 45. + _platycarpus_, 45. + antheridium, 45, 46. + fertilization, 46. + germination, 46. + +_Fumariaceæ_. See "Fumitory." + +Fumitory, 192. + +_Funaria_, 93-99; Figs. 58-62. + gross anatomy, 93, 94. + protonema, 93. + "flower," 94. + structure of leaf, 94. + chloroplasts, division of, 95. + formation of starch in chloroplasts, 95. + structure of stem, 96. + root hairs, 96. + buds, 96. + antheridium spermatozoids, 96, 97. + archegonium, 97. + embryo, 98. + capsule and spores, 98, 99. + germination of spores, 99. + +Fungi, culture of, 5, 54. + true. See "_Mycomycetes_." + alga. See "_Phycomycetes_." + +Funiculus, 151, 175. + +_Funkia_. See "Day lily." + + +_Galium_, 223; Fig. 124. + +_Gamopetalæ_. See "_Sympetalæ_." + +_Gaultheria_. See "Wintergreen." + +_Gaylussacia_. See "Huckleberry." + +_Geaster_, 84; Fig. 49. + +Gentian, 218; Fig. 122. + +Gentian violet, 4, 138, 231. + +_Gentiana_, _-aceæ_. See "Gentian." + +_Geranium_, _-aceæ_, 3, 171, 196; Fig. 107. + +_Gerardia_, 217. + +Germ cell. See "Egg cell." + +_Gesneraceæ_, 218. + +Ghost flower. See "Indian-pipe." + +Gill, 83. + +Ginger, 163. + +_Gingko_, 142; Fig. 78. + +_Gleditschia_. See "Honey locust." + +_Gloxinia_, 218. + +_Glumaceæ_, 153, 160; Fig. 87. + +Glume, 162. + +Glycerine, 4, 51, 55, 59, 67, 83, 98, 224, 231, 233. + +_Gnetaceæ_. See "Joint fir." + +Golden-rod, 224. + +_Gonium_, 20. + +Gooseberry, 203; Fig. 111. + +Goose-foot, 184; Fig. 98. + +_Gossypium_. See "Cotton." + +Gourd, 221. + +_Gramineæ_. See "Grass." + +Grape, 171, 199; Fig. 109. + +Grape fern, 116; Fig. 70. + +_Graphis_, 75; Fig. 45. + +Grass, 161, 225; Fig. 87. + +Gray moss. See "_Tillandsia_." + +Green-brier, 154. + +Green-felt. See "_Vaucheria_." + +Green monad, 12, 19. + +Green slime, 21, 22; Fig. 11. + +Ground pine, 123; Fig. 73. + +Ground tissue, 110, 111, 113, 124, 137, 177, 178. + +_Gruinales_, 196. + +Guard cell, 113, 135, 150. + +Gulf weed. See "_Sargassum_." + +Gum. See "_Eucalyptus_." + +_Gymnocarpæ_, 84. + +Gymnosperm, 129, 141. + +_Gymnosporangium_, 79-81; Fig. 47. + cedar apples, 79. + spores, 80. + +_Gynandræ_, 153, 164. + +Gynoecium, 148, 167. + +Gynostemium. See "Column." + + +_Habenaria_, 166, 227; Fig. 90. + +Hæmatoxylin, 233. + +Hair, 8, 177. + +_Haloragidaceæ_, 206. + +Hazel, 182, 183, 225; Fig. 97. + +Head, 181. + +Heath, 211. + +_Helobiæ_, 153, 167. + +_Hemerocallis_. See "Day lily." + +_Hemi-angiocarpæ_, 84. + +Hemlock, 142; Fig. 78. + +Hemp, 183. + +_Hepaticæ_. See "Liverwort." + +Hermaphrodite, 199. + +Heterocyst, 17. + +Heterostylism, 228. + +_Hibiscus_, 195. + +Hickory, 170, 183. + +Holly, 199. + +Hollyhock, 195. + +Honey locust, 209. + +Honeysuckle, 170, 172, 181, 223; Fig. 124. + +Hop, 171, 181; Fig. 97. + +Horned pond-weed, 224. + +Horse-chestnut, 170, 199. + +Horse-tail, 116-120. + field, 120-122; Fig. 72. + stems and tubers, 120. + fertile branches, 120. + leaves, 121. + cone, 121. + stem, 121. + sporangia and spores, 121. + sterile branches, 121. + histology of stem, 121. + of sporangia, 122. + spores, 122. + germination, prothallium, 122. + +Hound's-tongue, 215; Fig. 119. + +_Houstonia_, 223; Fig. 124. + +_Hoya_. See "Wax-plant." + +Huckleberry, 181, 211; Fig. 116. + +Humming-bird, 226. + +Hyacinth, 146. + +_Hydnum_, 84; Fig. 51. + +_Hydrangea_, _-geæ_, 202; Fig. 111. + +_Hydrocharideæ_, 167. + +Hydrogen, 2, 95. + +_Hydropeltidinæ_, 189. + +_Hydrophyllum_, _-aceæ_. See "Water-leaf." + +_Hypericum_, _-aceæ_. See "St. John's-wort." + + +_Ilex_. See "Holly." + +_Impatiens_. See "Jewel-weed," "Balsam." + +India-rubber, 200. + +Indian-pipe, 144, 210; Fig. 79. + +Indian turnip. See "_Arisæma_." + +Indusium, 118. + +Inflorescence, 157. + +Integument, 133, 144, 151, 180. + +Intercellular space, 124, 135, 150. + +Internode, 39. + +Iodine, 4, 22, 31. + +_Ipomoea_, 213. + +_Iridaceæ_, 156. + +Iris, 154, 156; Fig. 84. + +Irish moss, 49. + +_Isocarpæ_, 210, 212. + +_Isoetes_. See "Quill-wort." + +_Iulifloræ_, 181. + +Ivy, 202. + + +Jack-in-the-pulpit. See "_Arisæma_." + +Jasmine, 218. + +_Jeffersonia_. See "Twin-leaf." + +Jewel-weed, 197; Fig. 107. + +Joint fir, 140, 142. + +_Juncagineæ_, 167. + +_Juncus_. See "Rush." + +_Jungermanniaceæ_, 92; Fig. 57. + + +_Kalmia_. See "Mountain laurel." + +Karyokinesis, 233. + +Keel, 208. + +Kelp. See "_Laminaria_." + giant. See "_Macrocystis_." + +Knotgrass. See "_Polygonum_." + + +Labellum. See "Lip." + +_Labiatæ_. See "Mint." + +_Labiatifloræ_, 215. + +Lady's-slipper, 164, 166, 198; Fig. 90. + +Lamella, 83. + +_Laminaria_, 45, 47; Fig. 28. + +_Lamium_. See "Dead nettle." + +Larch. See "Tamarack." + +_Larix_. See "Tamarack." + +Larkspur, 186, 227; Fig. 99. + +Latex, 191. + +Laurel, 188. + +_Laurineæ_. See "Laurel." + +Lavender, 215. + +Leaf-green. See "Chlorophyll." + +Leaf tendril, 171. + +Leaf thorn, 172. + +_Leguminosæ_, 207. + +_Lemanea_, 53; Fig. 31. + +_Lemna_. See "Duck-weed." + +Lemon, 198. + +_Lentibulariaceæ_, 217. + +Lettuce, 223. + +_Lichenes_, 73; Figs. 44, 45. + +Ligula, 127. + +_Ligulatæ_, 125. + +Lilac, 170, 181, 218. + +_Liliaceæ_, 155. + +_Liliifloræ_, 153, 155; Fig. 83. + +_Lilium_. See "Lily." + +Lily, 146, 155. + +Lily-of-the-valley, 155. + +Lime. See "Linden." + +Linden, 195; Fig. 106. + +Linear, 159. + +_Linum_, _-aceæ_. See "Flax." + +Lip, 165. + +_Liriodendron_. See "Tulip-tree." + +_Lithospermum_. See "Puccoon." + +Liverwort, 86. + classification of, 91. + horned. See "_Anthoceroteæ_." + giant, 91; Fig. 57. + +Lizard-tail, 181, 183; Fig. 97. + +_Lobelia_, _-aceæ_. 221; Fig. 123. + +_Loganieæ_, 219. + +_Lonicera_. See "Honeysuckle." + +Loosestrife. See "_Lythrum_." + swamp. See "Nesæa." + +Lotus. See "_Nelumbo_." + +_Lychnis_, 185. + +_Lycoperdon_, 84; Fig. 49. + +_Lycopersicum_. See "Tomato." + +_Lycopodiaceæ_. See "Ground pine." + +_Lycopodinæ_. See "Club moss." + +_Lycopodium_, 123. + _dendroideum_, 123, 124; Fig. 73. + stem and leaves, 123. + cones and sporangia, 123. + gross anatomy, 123. + histology, 124. + spores, 124. + +_Lysimachia_. See "Moneywort." + +_Lythrum_, _-aceæ_, 206, 228. + +Mace, 189. + + +_Macrocystis_, 48. + +Macrospore, 126, 127, 128, 143. + +_Madotheca_, 86-90; Figs. 52-56. + gross anatomy, 86-88. + male and female plants, 87, 88. + histology of leaf and stem, 88. + antheridium, 88, 89. + archegonium, 89, 90. + embryo, 90. + spores and elaters, 90. + +Magnesium, 2. + +_Magnolia_, _-aceæ_, 186. + +Maiden-hair fern, 109-115; Figs. 67-69. + general structure, 109. + gross anatomy of stem, 110. + histology of stem, 110, 111. + gross anatomy of leaf, 111. + histology of leaf, 111, 112. + sporangia, 113, 114. + root, 114, 115. + apical growth of root, 115. + +Mallow, 171, 195; Fig. 106. + +_Malva_, _-aceæ_. See "Mallow." + +_Mamillaria_, Fig. 112. + +Mandrake. See "May-apple." + +Maple, 199; Fig. 108. + +_Maranta_. See "Arrowroot." + +_Marattiaceæ_. See "Ringless ferns." + +_Marchantia_, 91; Fig. 57. + breathing-pores, 91. + sexual organs, 91. + buds, 91. + +_Marchantiaceæ_, 91. + +_Marsilia_, 118; Fig. 71. + +_Martynia_, 218. + +_Matthiola_. See "Stock." + +May-apple, 187; Fig. 101. + +May-weed, 223; Fig. 125. + +_Medeola_, 155; Fig. 83. + +Medullary ray, 130, 137. + +_Melampsora_, 81. + +_Melastomaceæ_, 206. + +Melon, 221. + +_Menispermum_, _-eæ_. See "Moon-seed." + +_Menyanthes_. See "Buck-bean." + +_Mesocarpus_, 33; Fig. 19. + +Mesophyll, 135. + +Methyl-violet, 4, 233. + +Micropyle, 180. + +Microsome, 231. + +Microspore, 126, 128, 131, 138. + +Mignonette, 192; Fig. 104. + +Mildew. See "_Peronospora_," "_Phytophthora_," "_Perisporiaceæ_." + +Milk-weed, 220; Fig. 122. + +Milkwort, 199. + +_Mimosa_. See "Sensitive-plant." + +_Mimosaceæ_, 209, 210. + +_Mimulus_, 217. + +Mint, 181, 215. + +_Mirabilis_. See "Four-o'clock." + +Mistletoe, 224. + +_Mitella_. See "Bishop's cap." + +_Mitchella_. See "Partridge-berry." + +Mitre-wort. See "Bishop's cap." + +Mock-orange. See "_Syringa_." + +Moneywort, 212; Fig. 117. + +Monocotyledon, 146, 153, 225, 229. + +_Monotropa_. See "Indian-pipe," "Pine-sap." + +_Monotropeæ_, 210. + +Moon-seed, 188; Fig. 101. + +Moosewood, 206; Fig. 113. + +_Morchella_. See "Morel." + +Morel, 73. + +Morning-glory, 171, 213; Fig. 118. + +Morphology, 3. + +Moss, 5, 86. + true, 93. + common. See "_Bryaceæ_." + peat. See "_Sphagnaceæ_." + +Moth, 229. + +Mould, black. See "_Mucorini_." + blue. See "_Penicillium_." + herbarium. See "_Eurotium_." + insect. See "_Entomophthoreæ_." + water. See "_Saprolegnia_." + +Mountain-fringe, 192. + +Mountain-laurel, 210; Fig. 116. + +_Mucor_, 55. + mucedo, 56; Fig. 32. + +_Mucor stolonifer_, 55-56. + general structure, 55. + structure of filaments, 55. + spore cases, 55. + sexual spores, 56. + +_Mucorini_, 54. + +Mulberry, 183. + +Mullein, 217; Fig. 120. + +_Musa_, _-aceæ_. See "Banana." + +_Musci_. See "True mosses." + +Mushroom, 82. + +Mustard, 192. + +_Mycomycetes_. See "True fungi." + +_Myosotis_. See "Forget-me-not." + +_Myristica_, _-ineæ_. See "Nutmeg." + +_Myrtifloræ_, 205. + +Myrtle, 205, 206. + +_Myrtus_. See "Myrtle." + +_Myxomycetes_. See "Slime-mould." + + +_Naias_. See "Pond-weed." + +_Naiadeæ_, 159. + +Narcissus, 146. + +Nasturtium, 197, 227. + +_Navicula_, 42; Fig. 24. + +Nectar, 225. + +Nectary, 186. + +Nelumbo, 189, 190; Fig. 101. + +_Nelumbieæ_, 190. + +_Nemophila_, 214. + +_Nepenthes_, _-eæ_. See "Pitcher plant." + +_Nesæa_, 206. + +Nettle. See "_Urticinæ_." + +_Nicotiana_. See "Tobacco." + +Night-blooming cereus, 204. + +Nightshade, 215; Fig. 119. + +_Nitella_, 40. + +_Nitelleæ_, 40. + +Node, 39. + +Nucleus, 7, 31, 231. + +Nuclear division, 7, 31, 231; Figs. 127, 128. + +Nucleolus, 7, 231. + +Nutmeg, 188. + +_Nyctagineæ_, 183. + +_Nymphæa_, 189; Fig. 101. + +_Nymphæaceæ_, 190. + + +Oak, 183, 225; Fig. 97. + +_OEdogonium_, 26-28; Fig. 16. + reproduction, 27. + fertilization, 28. + resting spores, 28. + +_OEnothera_. See "Evening primrose." + +Oil-channel, 202. + +_Oleaceæ_. See "Olive." + +Oleander, 219. + +Olive, 218. + +_Onagraceæ_, 206. + +_Onoclea_, 104; Fig. 70. + +Oögonium, 27, 36, 39, 45, 59, 62. + +Oöphyte, 109. + +Opium--opium poppy, 191. + +_Ophioglosseæ_. See "Adder-tongue." + +_Ophioglossum_, 116. + +_Opuntia_. See "Prickly pear." + +_Opuntieæ_, 203. + +Orange, 198. + +Orchid, 164, 166, 227; Figs. 89, 90. + +_Orchideæ_, 164. + +_Orchis_, 227; Fig. 89. + +Organic bodies, 1. + +Origanum oil, 234. + +_Oscillaria_, 15, 16; Fig. 6. + movements, 15. + color, 16. + structure and reproduction, 16. + +_Osmunda_. See "Flowering-fern." + +Ostrich-fern, 104-109. + germination of spores, 104. + prothallium, 104, 105. + archegonium, 105, 106. + antheridium and spermatozoids, 106. + fertilization, 107. + embryo and young plant, 107, 108. + comparison with sporogonium of bryophytes, 109. + +Ovary, 129, 148, 156, 202. + +Ovule, 129, 131, 144, 148, 151, 179. + +_Oxalis_. See "Wood-sorrel." + +_Oxydendrum_, 211; Fig. 116. + +Oxygen, 2, 95. + + +Palea, 161. + +Palisade parenchyma, 178. + +Palm, 157. + date, 159. + coco, 159. + +_Palmæ_. See "Palm." + +Palmate, 171. + +Palmetto, 159. + +_Pandaneæ_, 159. + +_Papaveraceæ_. See "Poppy." + +Papaw, 186; Fig. 100. + +_Papilionaceæ_, 208. + +Pappus, 223. + +_Papyrus_, 161. + +Paranucleus, 231. + +Parasite, 54. + +Parenchyma. See "Soft tissue." + +_Parmelia_, 73, 75; Fig. 44. + +Partridge-berry, 223, 228. + +_Passiflora_. See "Passion-flower." + +_Passiflorinæ_, 205. + +Passion-flower, 204; Fig. 112. + +Pea, 207, 208; Fig. 115. + +Peach, 206. + +Pear, 206. + +_Pediastrum_, 23; Fig. 11. + +_Pelargonium_, 197. + +Peltate, 190. + +_Peltigera_, 75; Fig. 45. + +_Penicillium_, 71; Fig. 42. + +Pepper, 183. + +Perianth. See "Perigone." + +Periblem, 176. + +Perigone, 143, 148, 151, 170. + +Perisperm, 163. + +_Perisporiaceæ_, 66. + +Periwinkle, 219. + +_Peronospora_, 60; Fig. 35. + +_Peronosporeæ_, 57. + +Persimmon, 212; Fig. 117. + +Petal, 148, 174, 179. + +Petiole, 173. + +Petunia, 215; Fig. 119. + +_Peziza_, 73; Fig. 43. + +_Phacelia_, 214. + +_Phæophyceæ_. See "Brown algæ." + +Phænogam. See "Spermaphyte." + +_Phascum_, _-aceæ_, 99, 101; Fig. 65. + +_Philadelphus_. See "Syringa." + +Phloem, 110, 124, 135, 137, 150, 173, 176. + +_Phlox_, 214; Fig. 118. + +_Phoenix dactylifera_. See "Date-palm." + +Phosphorus, 2. + +_Phragmidium_, 81; Fig. 47. + +_Physarum_, 14. + +_Physianthus_, 220. + +Physiology, 3. + +_Phytolacca_, _-aceæ_. See "Poke-weed." + +_Phytophthora_, 60. + +Pickerel-weed, 156, 228; Fig. 84. + +Picric acid, 156, 233. + +Pig-weed. See "Amaranth." + +Pine, 9, 10, 129, 142. + +Pineapple, 156. + +Pine-sap, 210; Fig. 116. + +_Pinguicula_, 218. + +Pink, 181, 185; Fig. 97. + +Pink-root, 218; Fig. 122. + +Pinnate (leaf), 159. + veined, 171. + +_Pinnularia_, 42; Fig. 24. + +_Pinus sylvestris_. See "Scotch pine." + +_Piper_. See "Pepper." + +_Piperineæ_, 183. + +Pistil, 143, 145, 174. + +Pitcher-plant, 194, 195; Fig. 105. + +Pith, 130, 174, 177. + +Placenta, 148, 179. + +Plane, 183. + +_Plantago_, _-ineæ_. See "Plantain." + +Plantain, 223, 225; Fig. 121. + +Plasmodium, 12. + +_Plataneæ_. See "Plane." + +_Platanus_. See "Sycamore." + +Plerome, 176. + +Plum, 207. + +_Plumbago_, _-ineæ_, 212. + +Pod, 156. + +_Podophyllum_. See "May-apple." + +_Podosphæra_, 66-70; Fig. 39. + general structure, 66. + structure of filaments, 68. + suckers, 68. + conidia, 68. + sexual organs, 68. + spore fruit, 68, 69. + spore sac, 69. + +_Pogonia_, 166. + +_Poinsettia_, 199. + +Poison-dogwood, 198. + +Poison-hemlock, 202. + +Poison-ivy, 171, 198. + +Poke-weed, 185; Fig. 97. + +_Polemonium_, _-aceæ_, 214; Fig. 118. + +Pollinium, 165. + +_Polycarpæ_, 185. + +_Polygala_, _-aceæ_. See "Milkwort." + +_Polygonatum_. See "Solomon's Seal." + +_Polygonum_, _-aceæ_, 184; Fig. 98. + +_Polysiphonia_, 52; Fig. 29. + +Pomegranate, 206. + +Pond-scum, 22, 29, 30. + +Pond-weed, 159; Fig. 86. + +_Pontederia_. See "Pickerel-weed." + +Poplar, 181, 183. + +Poppy, 191. + +_Portulaca_, _-aceæ_. See "Purslane." + +Potash (caustic), 4, 5, 59, 67, 75, 97, 106, 111, 151, 176, 179, 180. + +Potassium, 2. + +Potato, 215. + +Potato-fungus. See "_Phytophthora_." + +_Potentilla_. See "Cinquefoil." + +_Potomogeton_. See "Pond-weed." + +Prickly-ash, 198. + +Prickly fungus. See "_Hydnum_." + +Prickly-pear, 204. + +Prickly-poppy. See "_Argemone_." + +Primrose, 211. + +_Primula_, _-aceæ_. See "Primrose." + +Prince's-pine, 210; Fig. 116. + +Procarp, 51. + +_Proteaceæ_, 205. + +Prothallium, 102, 103, 114, 122, 125, 133, 144, 177. + +_Protococcus_, _-aceæ_, 22, 74; Fig. 11. + +Protophyte, 11. + +Protoplasm, 7. + movements of, 7. + +Pteridophyte, 102, 153. + +_Puccinia_, 81; Fig. 47. See also "Wheat-rust." + +Puccoon, 215. + +Puff-ball. See "_Lycoperdon_." + +Purslane, 185. + +Putty-root. See "_Aplectrum_." + +Pyrenoid, 25, 31. + +_Pyrenomycetes_, 76. + +_Pyrola_, _-aceæ_, 210. + + +Quince, 170. + +Quill-wort, 125, 126; Fig. 74. + + +Raceme, 174. + +Radial fibro-vascular bundles, 138, 176. + +Radish, 192. + +_Ranunculus_, _-aceæ_. See "Buttercup." + +Raspberry, 207. + +Ray-flower, 223. + +Receptacle, 167, 207, 223. + +Receptive spot, 106. + +Red algæ, 21, 49, 52, 53; Figs. 29-31. + +Red-bud, 209; Fig. 115. + +Red cedar, 79, 131, 141; Fig. 78. + +Red-wood, 142. + +Reference-books, 235-236. + +_Reseda_, _-aceæ_. See "Mignonette." + +Resin, 130. + +Resin-duct, 130, 135, 137. + +Resting-spore, 28, 32, 37, 57. + +Rheumatism-root. See "Twin-leaf." + +_Rhexia_, 206. + +_Rhizocarpeæ_. See "Water-fern." + +Rhizoid. See "Root-hair." + +Rhizome. See "Root-stock." + +_Rhododendron_, 210; Fig. 116. + +_Rhodophyceæ_. See "Red algæ." + +_Rhodoraceæ_, 211. + +_Rhoeadinæ_, 190. + +_Rhus_. See "Sumach." + _cotinus_. See "Smoke-tree." + _toxicodendron_. See "Poison-ivy." + _venenata_. See "Poison-dogwood." + +_Ribes_, _-ieæ_, 203; Fig. 111. + +_Ricciaceæ_, 91; Fig. 57. + +_Richardia_. See "Calla." + +_Ricinus_. See "Castor-bean." + +Ringless-fern, 116. + +Rock-rose, 195. + +Rock-weed. See "_Fucus_." + +Root, 102, 104, 114, 173. + +Root-cap, 115, 175. + +Root-hair, 38, 87, 91, 96, 104, 135. + +Root-stock, 154, 172. + +_Rosa_, _-aceæ_. See "Rose." + +Rose, 181, 206; Fig. 114. + +_Rosifloræ_, 206. + +_Rubiaceæ_, 223. + +Rush, 154, 225; Fig. 83. + +Rust, white. See "_Cystopus_." + red. See "_Uredineæ_." + black. See "_Uredineæ_." + + +_Sabal_. See "Palmetto." + +_Sabbatia_. See "Centaury." + +_Saccharomycetes_. See "Yeast." + +Sac fungi. See "_Ascomycetes_." + +Safranine, 233. + +Sage, 215; Fig. 120. + +_Salicineæ_, 183. + +_Salix_. See "Willow." + +_Salvinia_, 118. + +_Sambucus_. See "Elder." + +_Sanguinaria_. See "Blood-root." + +_Sapindaceæ_, 199. + +_Saprolegnia_, _-aceæ_, 60-62; Fig. 36. + zoöspores, 62. + resting spores, 62. + antheridium, 62. + +_Sargassum_, 48; Fig. 28. + +_Sarracenia_, _-aceæ_. See "Pitcher-plant." + +Sassafras, 188. + +_Saururus_. See "Lizard-tail." + +Saxifrage, 202. + +_Saxifraginæ_, 202. + +_Scabiosa_. See "Scabious." + +Scabious, 224. + +Scalariform, 110. + +Scale-leaves, 170. + +_Scenedesmus_, 24; Fig. 11. + +_Schizomycetes_. See "_Bacteria_." + +Schizophytes, 12, 14. + +Schlerenchyma. See "Stony tissue." + +_Schrankia_. See "Sensitive-brier." + +_Scilla_, 151. + +_Scirpus_. See "Bulrush." + +_Scitamineæ_, 153, 162. + +Scotch pine, 129-140; Figs. 75-77. + stems and branches, 129. + leaves, 129, 130. + gross anatomy of stem, 130. + growth-rings, 130. + roots, 131. + sporangia, 131. + cones, 132. + macrospores and prothallium, 133. + ripe cone and seeds, 133. + germination, 134. + young plant, 134. + histology of leaf, 135. + of stem, 136-138. + of root, 138. + microsporangium and pollen spores, 138, 139. + archegonium, 140. + fertilization, 140. + +Scouring-rush, 122. + +_Scrophularia_, _-ineæ_. See "Figwort." + +Sea-lettuce, 26; Fig. 15. + +Sea-rosemary, 212. + +Sea-weed (brown). See "Brown algæ." + (red). See "Red algæ." + +Sedge, 161; Fig. 87. + +_Sedum_. See "Stonecrop." + +Seed, 128, 133, 145, 150. + +Seed-plant. See "Spermaphyte." + +_Selaginella_, _-eæ_. See "Smaller club-moss." + +Sensitive-brier, 209; Fig. 115. + +Sensitive-plant, 209. + +Sepal, 148, 150, 174, 179. + +_Sequoia_. See "Red-wood." + +Sessile leaf, 170. + +_Shepherdia_, 206. + +Shepherd's-purse, 173-180; Figs. 93-95. + gross anatomy of stem, 173. + leaf, 124, 173. + root, 173. + branches, 174. + flower, 174, 175. + fruit and seed, 175. + histology of root, 175, 176. + stem, 177. + leaf, 177, 178. + development of flower, 179. + ovule, 179. + embryo, 180. + +Shooting-star, 212; Fig. 117. + +Sieve-tube, 111, 137. + +_Silene_. See "Catch-fly." + +Silicon, 2. + +Simple leaf, 170. + +_Siphoneæ_, 22, 34. + +_Sisyrinchium_. See "Blue-eyed grass." + +Skunk cabbage, 157. + +Slime mould, 12, 14; Fig. 5. + plasmodium, 12. + movements, 13. + feeding, 13. + spore-cases, 13. + spores, 13. + germination of spores, 14. + +Smart-weed. See "_Polygonum_." + +_Smilaceæ_, 155. + +Smoke-tree, 198. + +Smut, 64, 65. + +Smut-corn. See "_Ustillago_." + +Snowberry, 223. + +Soft-tissue, 112. + +_Solanum_, _-eæ_, 215. + +Solomon's Seal, 154; Fig. 83. + +Soredium, 74. + +Sorus, 118. + +_Spadicifloræ_, 153, 157. + +Spadix, 157. + +Spanish bayonet. See "_Yucca_." + +_Sparganium_. See "Bur-reed." + +Speedwell. See "_Veronica_." + +Spermaphyte, 128-129. + +Spermatozoid, 28, 36, 40, 46, 51, 89, 96, 106, 122. + +Spermagonium, 79, 80. + +_Sphagnum_, _-aceæ_, 99, 100. + sporogonium, 100. + leaf, 100. + +Spice-bush, 188. + +Spiderwort, 6, 151, 157; Fig. 85. + +_Spigelia_. See "Pink-root." + +Spike, 181. + +Spikenard, 202; Fig. 110. + +Spinach, 184. + +Spindle-tree, 199; Fig. 109. + +_Spirogyra_, 30-32; Fig. 18. + structure of cells, 30. + starch, 31. + cell-division, 31. + sexual reproduction, 32. + +Sporangium, 55, 62, 113, 121, 122, 131, 148, 151, 179. + +Spore-case. See "Sporangium." + +Spore-fruit, 51, 66, 69, 70, 73, 83. + +Spore-sac. See "Ascus." + +Sporocarp. See "Spore-fruit." + +Sporogonium, 87, 90, 102, 123. + +Sporophyll, 128, 131, 148. + +Sporophyte, 109. + +Spring-beauty, 185; Fig. 98. + +Spruce, 142. + +Spurge. See "_Euphorbia_." + +Squash, 221. + +Staining agents, 4, 231, 233. + +Stamen, 128, 143, 148, 174, 179. + +Standard, 207. + +_Staphylea_. See "Bladder-nut." + +Starch, 31, 95, 152. + +_Statice_. See "Sea-rosemary." + +_Stellaria_. See "Chick-weed." + +_Stemonitis_, 13; Fig. 5. + +_Sticta_, 75; Fig. 45. + +_Stigeoclonium_, 26; Fig. 14. + +Stigma, 145, 148, 175, 179. + +St. John's-wort, 195; Fig. 105. + +Stock, 192. + +Stoma. See "Breathing-pore." + +Stonecrop, 202; Fig. 113. + +Stone-fruit, 206. + +Stone-wort. See "_Characeæ_." + +Stony-tissue, 110. + +Stramonium, 215. + +Strawberry, 171, 202, 206; Fig. 113. + +Style, 148, 175, 179. + +_Stylophorum_, 187; Fig. 103. + +Sugar, 8, 145. + +Sulphur, 2. + +Sumach, 198; Fig. 108. + +Sun-dew, 192, 193; Fig. 104. + +Sunflower, 224. + +Suspensor, 180. + +Sweet-flag, 157. + +Sweet-potato, 214. + +Sweet-scented shrub. See "_Calycanthus_." + +Sweet-william, 185. + +Sycamore, 183. + +_Sympetalæ_, 210. + +_Symphoricarpus_. See "Snowberry." + +_Symplocarpus_. See "Skunk-cabbage." + +Synergidæ, 144. + +_Syringa_, 199; Fig. 111. See also "Lilac." + + +Tamarack, 142. + +Tap-root, 131, 173. + +_Taraxacum_. See "Dandelion." + +_Taxodium_. See "Cypress." + +_Taxus_. See "Yew." + +Teasel, 224; Fig. 124. + +_Tecoma_. See "Trumpet-creeper." + +Teleuto-spore, 80, 81. + +Tendril, 171. + +_Terebinthinæ_, 198. + +Tetraspore, 51, 52. + +Thistle, 173, 223; Fig. 125. + +Thorn, 172. + +Thyme, 215. + +_Thymeleaceæ_, 206. + +_Thymelinæ_, 206. + +_Tilia_, _-aceæ_. See "Linden." + +_Tillandsia_, 156; Fig. 84. + +Tissue, 8. + +Tissue system, 115. + +Toadstool, 82. + +Tobacco, 215. + +_Tolypella_, 40. + +Tomato, 215. + +Touch-me-not. See "Jewel-weed." + +Tracheary tissue, 110, 121, 177. + +Tracheid, 110, 138. + +_Tradescantia_. See "Spiderwort." + +Trailing arbutus, 211. + +_Tremella_, 81; Fig. 51. + +_Trichia_, 13, 14; Fig. 5. + +Trichogyne, 51. + +_Tricoccæ_, 199. + +_Triglochin_. See "Arrow-grass." + +_Trillium_, 146, 154, 155; Fig. 83. + +_Triphragmium_, 81. + +_Tropæolum_. See "Nasturtium." + +Trumpet-creeper. + +Tuber, 120, 153, 172. + +_Tubifloræ_, 213. + +Tulip, 146. + +Tulip-tree, 187; Fig. 100. + +Turnip, 192. + +Twin-leaf, 187; Fig. 101. + +_Typha_, _-aceæ_. See "Cat-tail." + + +_Ulmaceæ_. See "Elm." + +_Ulva_. See "Sea-lettuce." + +_Umbelliferæ_. See "Umbel-wort." + +Umbel-wort, 202. + +_Umbellifloræ_, 202. + +_Uredineæ_, 77. + +_Uromyces_, 81; Fig. 47. + +_Urticinæ_, 183. + +_Usnea_, 75; Fig. 45. + +_Ustillagineæ_. See "Smut." + +_Ustillago_, 65; Fig. 38. + +_Utricularia_. See "Bladder-weed." + +_Uvularia_. See "Bellwort." + + +_Vaccinium_. See "Cranberry." + +Vacuole, 8. + +Valerian, 224; Fig. 124. + +_Valeriana_, _-eæ_. See "Valerian." + +_Vallisneria_. See "Eel-grass." + +_Vanilla_, 166. + +_Vaucheria_, 34-37; Figs. 21, 22. + structure of plant, 35. + _racemosa_, 35. + non-sexual reproduction, 36. + sexual organs, 36. + fertilization, 36. + resting spores, 37. + +Venus's fly-trap, 192. + +_Verbascum_. See "Mullein." + +_Verbena_, _-aceæ_, 218; Fig. 121. + +_Veronica_, 217; Fig. 120. + +Vervain. See "_Verbena_." + +Vessel, 121, 135, 150, 175, 177. + +_Viburnum_, 223; Fig. 124. + +_Victoria regia_, 190. + +_Vinca_. See "Periwinkle." + +Vine, 199. + +Violet, 192; Fig. 104. + +_Viola_, _-aceæ_. See "Violet." + +Virginia creeper, 171, 199. + +_Vitis_. See "Grape." + +_Vitaceæ_. See "Vine." + +_Volvox_, 12, 20; Fig. 10. + +_Volvocineæ_, 12, 19. + + +Wall-flower, 192. + +Walnut, 183. + +Wandering-Jew, 157. + +Water fern, 117. + +Water-leaf, 214; Fig. 118. + +Water-lily. See "_Nymphæa_," "_Castalia_." + +Water-milfoil, 206; Fig. 113. + +Water mould. See "_Saprolegnia_." + +Water net, 24; Fig. 11. + +Water-plantain, 167. + +Water-shield, 190. + +Water-starwort, 200. + +Wax-plant, 220. + +Wheat, 78. + +Wheat rust, 78, 81; Fig. 47. + +_Whitlavia_, 214. + +Wild ginger, 224; Fig. 126. + +Wild onion, 230. + +Wild parsnip, 202. + +Willow, 181-183; Fig. 96. + +Willow-herb, 206, 226; Fig. 113. + +Wing (of papilionaceous flower), 208. + +Wintergreen, 211. + +_Wolffia_, 159. + +Wood. See "Xylem." + +Wood-sorrel, 197; Fig. 107. + + +Xylem, 110, 124, 135, 150, 173, 176. + + +Yam, 154. + +Yeast, 63, 64; Fig. 37. + cause of fermentation, 63. + reproduction, 64. + systematic position, 64. + +Yew, 141. + +_Yucca_, 153. + + +_Zanthoxylum_. See "Prickly ash." + +_Zingiber_, _-aceæ_. See "Ginger." + +Zoölogy, 2. + +Zoöspore, 25, 37, 58, 62. + +_Zygnema_, 33; Fig. 19. + +Zygomorphy, Zygomorphic, 164, 215, 226. + + + + +NATURAL SCIENCE. + + +_Elements of Physics._ + + A Text-book for High Schools and Academies. By ALFRED P. GAGE, A.M., + Instructor in Physics in the English High School, Boston. 12mo. + 424 pages. Mailing Price, $1.25; Introduction, $1.12; Allowance for + old book, 35 cents. + +This treatise is based upon _the doctrine of the conservation of +energy_, which is made prominent throughout the work. But the leading +feature of the book--one that distinguishes it from all others--is, +that it is strictly _experiment-teaching_ in its method; _i.e._, it +leads the pupil to "read nature in the language of experiment." So far +as practicable, the following plan is adopted: The pupil is expected +to accept as _fact_ only that which he has seen or learned by personal +investigation. He himself performs the larger portion of the +experiments with _simple_ and _inexpensive_ apparatus, such as, in a +majority of cases, is in his power to construct with the aid of +directions given in the book. The experiments given are rather of the +nature of _questions_ than of illustrations, and _precede_ the +statements of principles and laws. Definitions and laws are not given +until the pupil has acquired a knowledge of his subject sufficient to +enable him to construct them for himself. The aim of the book is to +lead the pupil _to observe and to think_. + +C. F. EMERSON, _Prof. of Physics, Dartmouth College_: It takes up the +subject on the right plan, and presents it in a clear, yet scientific, +way. + +WM. NOETLING, _Prof. of Rhetoric, Theory and Practice of Teaching, +State Normal School, Bloomsburg, Pa._: Every page of the book shows +that the author is a _real_ teacher and that he knows how to make +pupils think. I know of no other work on the subject of which this +treats that I can so unreservedly recommend to all wide-awake teachers +as this. + +B. F. WRIGHT, _Supt. of Public Schools, St. Paul, Minn._: I like it +better than any text-book on physics I have seen. + +O. H. ROBERTS, _Prin. of High School, San Jose, Cal._: Gage's Physics +is giving great satisfaction. + + +_Introduction to Physical Science._ + + By A. P. GAGE, Instructor in Physics in the English High School, + Boston, Mass., and Author of _Elements of Physics_, etc. 12mo. + Cloth. viii + 353 pages. With a chart of colors and spectra. Mailing + Price, $1.10; for introduction, $1.00; allowance for an old book in + exchange, 30 cents. + +The great and constantly increasing popularity of Gage's _Elements of +Physics_ has created a demand for an equally good but easier book, on +the same plan, suitable for schools that can give but a limited time +to the study. The _Introduction to Physical Science_ has been prepared +to supply this demand. + +ACCURACY is the prime requisite in scientific text-books. A false +statement is not less false because it is plausible, nor an +inconclusive experiment more satisfactory because it is diverting. In +books of entertainment, such things may be permissible; but in a +text-book, the first essentials are correctness and accuracy. It is +believed that the _Introduction_ will stand the closest expert +scrutiny. Especial care has been taken to restrict the use of +scientific terms, such as _force_, _energy_, _power_, etc., to their +proper significations. Terms like _sound_, _light_, _color_, etc., +which have commonly been applied to both the effect and the agent +producing the effect have been rescued from this ambiguity. + +RECENT ADVANCES in physics have been faithfully recorded, and the +relative practical importance of the various topics has been taken +into account. Among the new features are a full treatment of electric +lighting, and descriptions of storage batteries, methods of +transmitting electric energy, simple and easy methods of making +electrical measurements with inexpensive apparatus, the compound +steam-engine, etc. Static electricity, which is now generally regarded +as of comparatively little importance, is treated briefly; while +dynamic electricity, the most potent and promising physical element of +our modern civilization, is placed in the clearest light of our +present knowledge. + +In INTEREST AND AVAILABILITY the _Introduction_ will, it is believed, +be found no less satisfactory. The wide use of the _Elements_ under +the most varied conditions, and, in particular, the author's own +experience in teaching it, have shown how to improve where improvement +was possible. The style will be found suited to the grades that will +use the book. The experiments are varied, interesting, clear, and of +practical significance, as well as simple in manipulation and ample in +number. Certain subjects that are justly considered difficult and +obscure have been omitted; as, for instance, certain laws relating to +the pressure of gases and the polarization of light. The +_Introduction_ is even more fully illustrated than the _Elements_. + +IN GENERAL. The _Introduction_, like the _Elements_, has this distinct +and distinctive aim,--to elucidate science, instead of "popularizing" +it; to make it liked for its own sake, rather than for its gilding and +coating; and, while teaching the facts, to impart the spirit of +science,--that is to say, the spirit of our civilization and progress. + +GEORGE E. GAY, _Prin. of High School, Malden, Mass._: With the matter, +both the topics and their presentation, I am better pleased than with +any other Physics I have seen. + +R. H. PERKINS, _Supt. of Schools, Chicopee, Mass._: I have no doubt we +can adopt it as early as next month, and use the same to great +advantage in our schools. (_Feb. 6, 1888._) + +MARY E. HILL, _Teacher of Physics, Northfield Seminary, Mass._: I like +the truly scientific method and the clearness with which the subject +is presented. It seems to me admirably adapted to the grade of work +for which it is designed. (_Mar. 5, '88._) + +JOHN PICKARD, _Prin. of Portsmouth High School, N.H._: I like it +exceedingly. It is clear, straightforward, practical, and not too +heavy. + +EZRA BRAINERD, _Pres. and Prof. of Physics, Middlebury College, Vt._: +I have looked it over carefully, and regard it as a much better book +for high schools than the former work. (_Feb. 6, 1888._) + +JAMES A. DE BOER, _Prin. of High School, Montpelier, Vt._: I have not +only examined, but studied it, and consider it superior as a text-book +to any other I have seen. (_Feb. 10, '88._) + +E. B. ROSA, _Teacher of Physics, English and Classical School, +Providence, R.I._: I think it the best thing in that grade published, +and intend to use it another year. (_Feb. 23, '88._) + +G. H. PATTERSON, _Prin. and Prof. of Physics, Berkeley Sch., +Providence, R.I._: A very practical book by a practical teacher. +(_Feb. 2, 1888._) + +GEORGE E. BEERS, _Prin. of Evening High School, Bridgeport, Conn._: +The more I see of Professor Gage's books, the better I like them. They +are popular, and at the same time scientific, plain and simple, full +and complete. (_Feb. 18, 1888._) + +ARTHUR B. CHAFFEE, _Prof. in Franklin College, Ind._: I am very much +pleased with the new book. It will suit the average class better than +the old edition. + +W. D. KERLIN, _Supt. of Public Schools, New Castle, Ind._: I find that +it is the best adapted to the work which we wish to do in our high +school of any book brought to my notice. + +C. A. BRYANT, _Supt. of Schools, Paris, Tex._: It is just the book for +high schools. I shall use it next year. + + +_Introduction to Chemical Science._ + + By R. P. WILLIAMS, Instructor in Chemistry in the English High + School, Boston. 12mo. Cloth. 216 pages. Mailing Price, 90 cents; for + introduction, 80 cents; Allowance for old book in exchange, + 25 cents. + +In a word, this is a working chemistry--brief but adequate. Attention +is invited to a few special features:-- + +1. This book is characterized by directness of treatment, by the +selection, so far as possible, of the most interesting and practical +matter, and by the omission of what is unessential. + +2. Great care has been exercised to combine clearness with accuracy of +statement, both of theories and of facts, and to make the explanations +both lucid and concise. + +3. The three great classes of chemical compounds--acids, bases, and +salts--are given more than usual prominence, and the arrangement and +treatment of the subject-matter relating to them is believed to be a +feature of special merit. + +4. The most important experiments and those best illustrating the +subjects to which they relate, have been selected; but the modes of +experimentation are so simple that most of them can be performed by +the average pupil without assistance from the teacher. + +5. The necessary apparatus and chemicals are less expensive than those +required for any other text-book equally comprehensive. + +6. The special inductive feature of the work consists in calling +attention, by query and suggestion, to the most important phenomena +and inferences. This plan is consistently adhered to. + +7. Though the method is an advanced one, it has been so simplified +that pupils experience no difficulty, but rather an added interest, in +following it; the author himself has successfully employed it in +classes so large that the simplest and most practical plan has been a +necessity. + +8. The book is thought to be comprehensive enough for high schools and +academies, and for a preparatory course in colleges and professional +schools. + +9. Those teachers in particular who have little time to prepare +experiments for pupils, or whose experience in the laboratory has been +limited, will find the simplicity of treatment and of experimentation +well worth their careful consideration. + +Those who try the book find its merits have not been overstated. + +A. B. AUBERT, _Prof. of Chemistry, Maine State College, Orono, Me._: +All the salient points are well explained, the theories are treated of +with great simplicity; it seems as if every student might thoroughly +understand the science of chemistry when taught from such a work. + +H. T. FULLER, _Pres. of Polytechnic Institute, Worcester, Mass._: It +is clear, concise, and suggests the most important and most +significant experiments for illustration of general principles. + +ALFRED S. ROE, _Prin. of High School, Worcester, Mass._: I am very +much pleased with it. I think it the most practical book for actual +work that I have seen. + +FRANK M. GILLEY, _Science Teacher, High School, Chelsea, Mass._: I +have examined the proof-sheets in connection with my class work, and +after comparison with a large number of text-books, feel convinced +that it is superior to any yet published. + +G. S. FELLOWS, _Teacher of Chemistry, High School, Washington, D.C._: +The author's method seems to us the ideal one. Not only are the +theoretical parts rendered clear by experiments performed by the +student himself, but there is a happy blending of theoretical and +applied chemistry as commendable as it is unusual. + +J. I. D. HINES, _Prof. of Chemistry, Cumberland University, Lebanon, +Tenn._: I am very much pleased with it, and think it will give the +student an admirable introduction to the science of chemistry. + +HORACE PHILLIPS, _Prin. of High School, Elkhart, Ind._: My class has +now used it three months. It proves the most satisfactory text-book in +this branch that I have ever used. The cost of apparatus and material +is very small. + +O. S. WESCOTT, _Prin. North Division H. Sch., Chicago_: My chemistry +professor says it is the most satisfactory thing he has seen, and +hopes we may be able to have it in future. + + +_Laboratory Manual of General Chemistry._ + + By R. P. WILLIAMS, Instructor in Chemistry, English High School, + Boston, and author of _Introduction to Chemical Science_. 12mo. + Boards. xvi + 200 pages. Mailing Price, 30 cents; for Introduction, + 25 cents. + +This Manual, prepared especially to accompany the author's +_Introduction to Chemical Science_, but suitable for use with any +text-book of chemistry, gives directions for performing one hundred of +the more important experiments in general chemistry and metal +analysis, with blanks and a model for the same, lists of apparatus and +chemicals, etc. + +The Manual is commended as well-designed, simple, convenient, and +cheap,--a practical book that classes in chemistry need. + +W. M. STINE, _Prof. of Chemistry, Ohio University, Athens, O._: It is +a work that has my heartiest endorsement. I consider it thoroughly +pedagogical in its principles, and its use must certainly give the +student the greatest benefit from his chemical drill. (_Dec. 30, +1888._) + + +_Young's General Astronomy._ + + A Text-book for colleges and technical schools. By CHARLES A. YOUNG, + Ph.D., LL.D., Professor of Astronomy in the College of New Jersey, + and author of _The Sun_, etc. 8vo. viii + 551 pages. Half-morocco. + Illustrated with over 250 cuts and diagrams, and supplemented with + the necessary tables. Introduction Price, $2.25. Allowance for an + old book in exchange, 40 cents. + +The OBJECT of the author has been twofold. First and chiefly, to make +a book adapted for use in the college class-room; and, secondly, to +make one valuable as a permanent storehouse and directory of +information for the student's use after he has finished his prescribed +course. + +The METHOD of treatment corresponds with the object of the book. +Truth, accuracy, and order have been aimed at first, with clearness +and freedom from ambiguity. + +In AMOUNT, the work has been adjusted as closely as possible to the +prevailing courses of study in our colleges. The fine print may be +omitted from the regular lessons and used as collateral reading. It is +important to anything like a complete view of the subject, but not +essential to a course. Some entire chapters can be omitted, if +necessary. + +NEW TOPICS, as indicated above, have received a full share of +attention, and while the book makes no claims to novelty, the name of +the author is a guarantee of much originality both of matter and +manner. + +The book will be found especially well adapted for high school and +academy teachers who desire a work for reference in supplementing +their brief courses. The illustrations are mostly new, and prepared +expressly for this work. The tables in the appendix are from the +latest and most trustworthy sources. A very full and carefully +prepared index will be found at the end. + +The eminence of Professor Young as an original investigator in +astronomy, a lecturer and writer on the subject, and an instructor of +college classes, and his scrupulous care in preparing this volume, led +the publishers to present the work with the highest confidence; and +this confidence has been fully justified by the event. More than one +hundred colleges adopted the work within a year from its publication. + + +_Young's Elements of Astronomy._ + + A Text-Book for use in High Schools and Academies. With a + Uranography. By CHARLES A. YOUNG, Ph.D., LL.D., Professor of + Astronomy in the College of New Jersey (Princeton), and author of _A + General Astronomy_, _The Sun_, etc. 12mo. Half leather. x + 472 + pages, and four star maps. Mailing Price, $1.55; for Introduction, + $1.40; allowance for old book in exchange, 30 cents. + +_Uranography._ + + From Young's Elements of Astronomy. 12mo. Flexible covers. 42 pages, + besides four star maps. By mail, 35 cents; for Introduction, + 30 cents. + +This volume is a new work, and not a mere abridgment of the author's +_General Astronomy_. Much of the material of the larger book has +naturally been incorporated in this, and many of its illustrations are +used; but everything has been worked over, with reference to the high +school course. + +Special attention has been paid to making all statements correct and +accurate _as far as they go_. Many of them are necessarily incomplete, +on account of the elementary character of the work; but it is hoped +that this incompleteness has never been allowed to become untruth, and +that the pupil will not afterwards have to unlearn anything the book +has taught him. + +In the text no mathematics higher than elementary algebra and geometry +is introduced; in the foot-notes and in the Appendix an occasional +trigonometric formula appears, for the benefit of the very +considerable number of high school students who understand such +expressions. This fact should be particularly noted, for it is a +special aim of the book to teach astronomy scientifically without +requiring more knowledge and skill in mathematics than can be expected +of high school pupils. + +Many things of real, but secondary, importance have been treated of in +fine print; and others which, while they certainly ought to be found +within the covers of a high school text-book of astronomy, are not +essential to the course, are relegated to the Appendix. + +A brief URANOGRAPHY is also presented, covering the constellations +visible in the United States, with maps on a scale sufficient for the +easy identification of all the principal stars. It includes also a +list of such telescopic objects in each constellation as are easily +found and lie within the power of a small telescope. + + +_Plant Organization._ + + By R. HALSTED WARD, M.D., F.R.M.S., Professor of Botany in the + Rensselaer Polytechnic Institute, Troy, N.Y. Quarto. 176 pages. + Illustrated. Flexible boards. Mailing Price, 85 cents; for Introd., + 75 cents. + +It consists of a synoptical review of the general structure and +morphology of plants, clearly drawn out according to biological +principles, fully illustrated, and accompanied by a set of blanks for +written exercises by pupils. The plan is designed to encourage close +observation, exact knowledge, and precise statement. + + +_A Primer of Botany._ + + By Mrs. A. A. KNIGHT, of Robinson Seminary, Exeter, N.H. 12mo. + Boards. Illus. vii + 115 pp. Mailing Price, 35 cents; for Introd., + 30 cents. + +This Primer is designed to bring physiological botany to the level of +primary and intermediate grades. + + +_Outlines of Lessons in Botany._ + + For the use of teachers, or mothers studying with their children. By + Miss JANE H. NEWELL. Part I.: From Seed to Leaf. Sq. 16mo. Illus. + 150 pp. Cloth. Mailing Price, 55 cents; for Introd., 50 cents. + +This book aims to give an outline of work for the pupils themselves. +It follows the plan of Gray's _First Lessons_ and _How Plants Grow_, +and is intended to be used with either of these books. + + +_A Reader in Botany._ + + Selected and adapted from well-known Authors. By Miss JANE H. + NEWELL. Part I.: From Seed to Leaf. 12mo. Cloth. vi + 209 pp. + Mailing Price, 70 cents; for Introd., 60 cents. + +This book follows the plan of the editor's _Outlines of Lessons in +Botany_ and Gray's _Lessons_, and treats of Seed-Food, Movements of +Seedlings, Trees in Winter, Climbing Plants, Insectivorous Plants, +Protection of Leaves from the Attacks of Animals, etc. + + +_Little Flower-People._ + + By GERTRUDE ELISABETH HALE. Sq. 12mo. Illus. Cloth. xiii + 85 pp. + Mailing Price, 50 cents; for Introd., 40 cents. + +The aim of this book is to tell some of the most important elementary +facts of plant-life in such a way as to appeal to the child's +imagination and curiosity, and to awaken an observant interest in the +facts themselves. + + + + + +End of the Project Gutenberg EBook of Elements of Structural and Systematic +Botany, by Douglas Houghton Campbell + +*** END OF THIS PROJECT GUTENBERG EBOOK SYSTEMATIC BOTANY *** + +***** This file should be named 20390-8.txt or 20390-8.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/2/0/3/9/20390/ + +Produced by Marilynda Fraser-Cunliffe, Laura Wisewell and +the Online Distributed Proofreading Team at +http://www.pgdp.net + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. Special rules, +set forth in the General Terms of Use part of this license, apply to +copying and distributing Project Gutenberg-tm electronic works to +protect the PROJECT GUTENBERG-tm concept and trademark. Project +Gutenberg is a registered trademark, and may not be used if you +charge for the eBooks, unless you receive specific permission. If you +do not charge anything for copies of this eBook, complying with the +rules is very easy. You may use this eBook for nearly any purpose +such as creation of derivative works, reports, performances and +research. They may be modified and printed and given away--you may do +practically ANYTHING with public domain eBooks. Redistribution is +subject to the trademark license, especially commercial +redistribution. + + + +*** START: FULL LICENSE *** + +THE FULL PROJECT GUTENBERG LICENSE +PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK + +To protect the Project Gutenberg-tm mission of promoting the free +distribution of electronic works, by using or distributing this work +(or any other work associated in any way with the phrase "Project +Gutenberg"), you agree to comply with all the terms of the Full Project +Gutenberg-tm License (available with this file or online at +http://gutenberg.org/license). + + +Section 1. General Terms of Use and Redistributing Project Gutenberg-tm +electronic works + +1.A. By reading or using any part of this Project Gutenberg-tm +electronic work, you indicate that you have read, understand, agree to +and accept all the terms of this license and intellectual property +(trademark/copyright) agreement. If you do not agree to abide by all +the terms of this agreement, you must cease using and return or destroy +all copies of Project Gutenberg-tm electronic works in your possession. +If you paid a fee for obtaining a copy of or access to a Project +Gutenberg-tm electronic work and you do not agree to be bound by the +terms of this agreement, you may obtain a refund from the person or +entity to whom you paid the fee as set forth in paragraph 1.E.8. + +1.B. "Project Gutenberg" is a registered trademark. It may only be +used on or associated in any way with an electronic work by people who +agree to be bound by the terms of this agreement. There are a few +things that you can do with most Project Gutenberg-tm electronic works +even without complying with the full terms of this agreement. See +paragraph 1.C below. There are a lot of things you can do with Project +Gutenberg-tm electronic works if you follow the terms of this agreement +and help preserve free future access to Project Gutenberg-tm electronic +works. See paragraph 1.E below. + +1.C. The Project Gutenberg Literary Archive Foundation ("the Foundation" +or PGLAF), owns a compilation copyright in the collection of Project +Gutenberg-tm electronic works. Nearly all the individual works in the +collection are in the public domain in the United States. If an +individual work is in the public domain in the United States and you are +located in the United States, we do not claim a right to prevent you from +copying, distributing, performing, displaying or creating derivative +works based on the work as long as all references to Project Gutenberg +are removed. Of course, we hope that you will support the Project +Gutenberg-tm mission of promoting free access to electronic works by +freely sharing Project Gutenberg-tm works in compliance with the terms of +this agreement for keeping the Project Gutenberg-tm name associated with +the work. You can easily comply with the terms of this agreement by +keeping this work in the same format with its attached full Project +Gutenberg-tm License when you share it without charge with others. + +1.D. The copyright laws of the place where you are located also govern +what you can do with this work. Copyright laws in most countries are in +a constant state of change. If you are outside the United States, check +the laws of your country in addition to the terms of this agreement +before downloading, copying, displaying, performing, distributing or +creating derivative works based on this work or any other Project +Gutenberg-tm work. The Foundation makes no representations concerning +the copyright status of any work in any country outside the United +States. + +1.E. Unless you have removed all references to Project Gutenberg: + +1.E.1. The following sentence, with active links to, or other immediate +access to, the full Project Gutenberg-tm License must appear prominently +whenever any copy of a Project Gutenberg-tm work (any work on which the +phrase "Project Gutenberg" appears, or with which the phrase "Project +Gutenberg" is associated) is accessed, displayed, performed, viewed, +copied or distributed: + +This eBook is for the use of anyone anywhere 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 + +1.E.2. If an individual Project Gutenberg-tm electronic work is derived +from the public domain (does not contain a notice indicating that it is +posted with permission of the copyright holder), the work can be copied +and distributed to anyone in the United States without paying any fees +or charges. If you are redistributing or providing access to a work +with the phrase "Project Gutenberg" associated with or appearing on the +work, you must comply either with the requirements of paragraphs 1.E.1 +through 1.E.7 or obtain permission for the use of the work and the +Project Gutenberg-tm trademark as set forth in paragraphs 1.E.8 or +1.E.9. + +1.E.3. If an individual Project Gutenberg-tm electronic work is posted +with the permission of the copyright holder, your use and distribution +must comply with both paragraphs 1.E.1 through 1.E.7 and any additional +terms imposed by the copyright holder. Additional terms will be linked +to the Project Gutenberg-tm License for all works posted with the +permission of the copyright holder found at the beginning of this work. + +1.E.4. Do not unlink or detach or remove the full Project Gutenberg-tm +License terms from this work, or any files containing a part of this +work or any other work associated with Project Gutenberg-tm. + +1.E.5. Do not copy, display, perform, distribute or redistribute this +electronic work, or any part of this electronic work, without +prominently displaying the sentence set forth in paragraph 1.E.1 with +active links or immediate access to the full terms of the Project +Gutenberg-tm License. + +1.E.6. You may convert to and distribute this work in any binary, +compressed, marked up, nonproprietary or proprietary form, including any +word processing or hypertext form. However, if you provide access to or +distribute copies of a Project Gutenberg-tm work in a format other than +"Plain Vanilla ASCII" or other format used in the official version +posted on the official Project Gutenberg-tm web site (www.gutenberg.org), +you must, at no additional cost, fee or expense to the user, provide a +copy, a means of exporting a copy, or a means of obtaining a copy upon +request, of the work in its original "Plain Vanilla ASCII" or other +form. Any alternate format must include the full Project Gutenberg-tm +License as specified in paragraph 1.E.1. + +1.E.7. Do not charge a fee for access to, viewing, displaying, +performing, copying or distributing any Project Gutenberg-tm works +unless you comply with paragraph 1.E.8 or 1.E.9. + +1.E.8. You may charge a reasonable fee for copies of or providing +access to or distributing Project Gutenberg-tm electronic works provided +that + +- You pay a royalty fee of 20% of the gross profits you derive from + the use of Project Gutenberg-tm works calculated using the method + you already use to calculate your applicable taxes. The fee is + owed to the owner of the Project Gutenberg-tm trademark, but he + has agreed to donate royalties under this paragraph to the + Project Gutenberg Literary Archive Foundation. Royalty payments + must be paid within 60 days following each date on which you + prepare (or are legally required to prepare) your periodic tax + returns. Royalty payments should be clearly marked as such and + sent to the Project Gutenberg Literary Archive Foundation at the + address specified in Section 4, "Information about donations to + the Project Gutenberg Literary Archive Foundation." + +- You provide a full refund of any money paid by a user who notifies + you in writing (or by e-mail) within 30 days of receipt that s/he + does not agree to the terms of the full Project Gutenberg-tm + License. You must require such a user to return or + destroy all copies of the works possessed in a physical medium + and discontinue all use of and all access to other copies of + Project Gutenberg-tm works. + +- You provide, in accordance with paragraph 1.F.3, a full refund of any + money paid for a work or a replacement copy, if a defect in the + electronic work is discovered and reported to you within 90 days + of receipt of the work. + +- You comply with all other terms of this agreement for free + distribution of Project Gutenberg-tm works. + +1.E.9. If you wish to charge a fee or distribute a Project Gutenberg-tm +electronic work or group of works on different terms than are set +forth in this agreement, you must obtain permission in writing from +both the Project Gutenberg Literary Archive Foundation and Michael +Hart, the owner of the Project Gutenberg-tm trademark. Contact the +Foundation as set forth in Section 3 below. + +1.F. + +1.F.1. Project Gutenberg volunteers and employees expend considerable +effort to identify, do copyright research on, transcribe and proofread +public domain works in creating the Project Gutenberg-tm +collection. Despite these efforts, Project Gutenberg-tm electronic +works, and the medium on which they may be stored, may contain +"Defects," such as, but not limited to, incomplete, inaccurate or +corrupt data, transcription errors, a copyright or other intellectual +property infringement, a defective or damaged disk or other medium, a +computer virus, or computer codes that damage or cannot be read by +your equipment. + +1.F.2. LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the "Right +of Replacement or Refund" described in paragraph 1.F.3, the Project +Gutenberg Literary Archive Foundation, the owner of the Project +Gutenberg-tm trademark, and any other party distributing a Project +Gutenberg-tm electronic work under this agreement, disclaim all +liability to you for damages, costs and expenses, including legal +fees. YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT +LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE +PROVIDED IN PARAGRAPH F3. YOU AGREE THAT THE FOUNDATION, THE +TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE +LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR +INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH +DAMAGE. + +1.F.3. LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a +defect in this electronic work within 90 days of receiving it, you can +receive a refund of the money (if any) you paid for it by sending a +written explanation to the person you received the work from. If you +received the work on a physical medium, you must return the medium with +your written explanation. The person or entity that provided you with +the defective work may elect to provide a replacement copy in lieu of a +refund. If you received the work electronically, the person or entity +providing it to you may choose to give you a second opportunity to +receive the work electronically in lieu of a refund. If the second copy +is also defective, you may demand a refund in writing without further +opportunities to fix the problem. + +1.F.4. Except for the limited right of replacement or refund set forth +in paragraph 1.F.3, this work is provided to you 'AS-IS' WITH NO OTHER +WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO +WARRANTIES OF MERCHANTIBILITY OR FITNESS FOR ANY PURPOSE. + +1.F.5. Some states do not allow disclaimers of certain implied +warranties or the exclusion or limitation of certain types of damages. +If any disclaimer or limitation set forth in this agreement violates the +law of the state applicable to this agreement, the agreement shall be +interpreted to make the maximum disclaimer or limitation permitted by +the applicable state law. The invalidity or unenforceability of any +provision of this agreement shall not void the remaining provisions. + +1.F.6. INDEMNITY - You agree to indemnify and hold the Foundation, the +trademark owner, any agent or employee of the Foundation, anyone +providing copies of Project Gutenberg-tm electronic works in accordance +with this agreement, and any volunteers associated with the production, +promotion and distribution of Project Gutenberg-tm electronic works, +harmless from all liability, costs and expenses, including legal fees, +that arise directly or indirectly from any of the following which you do +or cause to occur: (a) distribution of this or any Project Gutenberg-tm +work, (b) alteration, modification, or additions or deletions to any +Project Gutenberg-tm work, and (c) any Defect you cause. + + +Section 2. Information about the Mission of Project Gutenberg-tm + +Project Gutenberg-tm is synonymous with the free distribution of +electronic works in formats readable by the widest variety of computers +including obsolete, old, middle-aged and new computers. It exists +because of the efforts of hundreds of volunteers and donations from +people in all walks of life. + +Volunteers and financial support to provide volunteers with the +assistance they need, is critical to reaching Project Gutenberg-tm's +goals and ensuring that the Project Gutenberg-tm collection will +remain freely available for generations to come. In 2001, the Project +Gutenberg Literary Archive Foundation was created to provide a secure +and permanent future for Project Gutenberg-tm and future generations. +To learn more about the Project Gutenberg Literary Archive Foundation +and how your efforts and donations can help, see Sections 3 and 4 +and the Foundation web page at http://www.pglaf.org. + + +Section 3. Information about the Project Gutenberg Literary Archive +Foundation + +The Project Gutenberg Literary Archive Foundation is a non profit +501(c)(3) educational corporation organized under the laws of the +state of Mississippi and granted tax exempt status by the Internal +Revenue Service. The Foundation's EIN or federal tax identification +number is 64-6221541. Its 501(c)(3) letter is posted at +http://pglaf.org/fundraising. Contributions to the Project Gutenberg +Literary Archive Foundation are tax deductible to the full extent +permitted by U.S. federal laws and your state's laws. + +The Foundation's principal office is located at 4557 Melan Dr. S. +Fairbanks, AK, 99712., but its volunteers and employees are scattered +throughout numerous locations. Its business office is located at +809 North 1500 West, Salt Lake City, UT 84116, (801) 596-1887, email +business@pglaf.org. Email contact links and up to date contact +information can be found at the Foundation's web site and official +page at http://pglaf.org + +For additional contact information: + Dr. Gregory B. Newby + Chief Executive and Director + gbnewby@pglaf.org + + +Section 4. Information about Donations to the Project Gutenberg +Literary Archive Foundation + +Project Gutenberg-tm depends upon and cannot survive without wide +spread public support and donations to carry out its mission of +increasing the number of public domain and licensed works that can be +freely distributed in machine readable form accessible by the widest +array of equipment including outdated equipment. Many small donations +($1 to $5,000) are particularly important to maintaining tax exempt +status with the IRS. + +The Foundation is committed to complying with the laws regulating +charities and charitable donations in all 50 states of the United +States. Compliance requirements are not uniform and it takes a +considerable effort, much paperwork and many fees to meet and keep up +with these requirements. We do not solicit donations in locations +where we have not received written confirmation of compliance. To +SEND DONATIONS or determine the status of compliance for any +particular state visit http://pglaf.org + +While we cannot and do not solicit contributions from states where we +have not met the solicitation requirements, we know of no prohibition +against accepting unsolicited donations from donors in such states who +approach us with offers to donate. + +International donations are gratefully accepted, but we cannot make +any statements concerning tax treatment of donations received from +outside the United States. U.S. laws alone swamp our small staff. + +Please check the Project Gutenberg Web pages for current donation +methods and addresses. Donations are accepted in a number of other +ways including checks, online payments and credit card donations. +To donate, please visit: http://pglaf.org/donate + + +Section 5. General Information About Project Gutenberg-tm electronic +works. + +Professor Michael S. Hart is the originator of the Project Gutenberg-tm +concept of a library of electronic works that could be freely shared +with anyone. For thirty years, he produced and distributed Project +Gutenberg-tm eBooks with only a loose network of volunteer support. + + +Project Gutenberg-tm eBooks are often created from several printed +editions, all of which are confirmed as Public Domain in the U.S. +unless a copyright notice is included. Thus, we do not necessarily +keep eBooks in compliance with any particular paper edition. + + +Most people start at our Web site which has the main PG search facility: + + http://www.gutenberg.org + +This Web site includes information about Project Gutenberg-tm, +including how to make donations to the Project Gutenberg Literary +Archive Foundation, how to help produce our new eBooks, and how to +subscribe to our email newsletter to hear about new eBooks. diff --git a/old/20390-8.zip b/old/20390-8.zip Binary files differnew file mode 100644 index 0000000..1baea37 --- /dev/null +++ b/old/20390-8.zip diff --git a/old/20390.txt b/old/20390.txt new file mode 100644 index 0000000..ff5c1bc --- /dev/null +++ b/old/20390.txt @@ -0,0 +1,11233 @@ +The Project Gutenberg EBook of Elements of Structural and Systematic Botany, by +Douglas Houghton Campbell + +This eBook is for the use of anyone anywhere 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 + + +Title: Elements of Structural and Systematic Botany + For High Schools and Elementary College Courses + +Author: Douglas Houghton Campbell + +Release Date: January 17, 2007 [EBook #20390] + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK SYSTEMATIC BOTANY *** + + + + +Produced by Marilynda Fraser-Cunliffe, Laura Wisewell and +the Online Distributed Proofreading Team at +http://www.pgdp.net + + + + + + +--------------------------------------------------------------+ + | | + | Transcriber's note: In this lower-bit text version the male | + | and female symbols have been replaced with [Male] and | + | [Female] respectively. The correct symbols are used in the | + | UTF-8 text and HTML versions of this eBook. | + | | + +--------------------------------------------------------------+ + + + + ELEMENTS + + OF + + STRUCTURAL AND SYSTEMATIC BOTANY, + + + FOR + HIGH SCHOOLS AND ELEMENTARY + COLLEGE COURSES. + + + BY + DOUGLAS HOUGHTON CAMPBELL, PH.D., + PROFESSOR OF BOTANY IN THE INDIANA UNIVERSITY. + + + BOSTON, U.S.A.: + PUBLISHED BY GINN & COMPANY. + 1890. + + + + COPYRIGHT, 1890, + BY DOUGLAS HOUGHTON CAMPBELL. + + ALL RIGHTS RESERVED. + + TYPOGRAPHY BY J. S. CUSHING & CO., BOSTON, U.S.A. + PRESSWORK BY GINN & CO., BOSTON, U.S.A. + + + + +PREFACE. + + +The rapid advances made in the science of botany within the last few +years necessitate changes in the text books in use as well as in +methods of teaching. Having, in his own experience as a teacher, felt +the need of a book different from any now in use, the author has +prepared the present volume with a hope that it may serve the purpose +for which it is intended; viz., an introduction to the study of botany +for use in high schools especially, but sufficiently comprehensive to +serve also as a beginning book in most colleges. + +It does not pretend to be a complete treatise of the whole science, +and this, it is hoped, will be sufficient apology for the absence from +its pages of many important subjects, especially physiological topics. +It was found impracticable to compress within the limits of a book of +moderate size anything like a thorough discussion of even the most +important topics of _all_ the departments of botany. As a thorough +understanding of the structure of any organism forms the basis of all +further intelligent study of the same, it has seemed to the author +proper to emphasize this feature in the present work, which is +professedly an _introduction_, only, to the science. + +This structural work has been supplemented by so much classification +as will serve to make clear the relationships of different groups, and +the principles upon which the classification is based, as well as +enable the student to recognize the commoner types of the different +groups as they are met with. The aim of this book is not, however, +merely the identification of plants. We wish here to enter a strong +protest against the only too prevalent idea that the chief aim of +botany is the ability to run down a plant by means of an "Analytical +Key," the subject being exhausted as soon as the name of the plant is +discovered. A knowledge of the plant itself is far more important than +its name, however desirable it may be to know the latter. + +In selecting the plants employed as examples of the different groups, +such were chosen, as far as possible, as are everywhere common. Of +course this was not always possible, as some important forms, _e.g._ +the red and brown seaweeds, are necessarily not always readily +procurable by all students, but it will be found that the great +majority of the forms used, or closely related ones, are within the +reach of nearly all students; and such directions are given for +collecting and preserving them as will make it possible even for those +in the larger cities to supply themselves with the necessary +materials. Such directions, too, for the manipulation and examination +of specimens are given as will make the book, it is hoped, a +laboratory guide as well as a manual of classification. Indeed, it is +primarily intended that the book should so serve as a help in the +study of the actual specimens. + +Although much can be done in the study, even of the lowest plants, +without microscopic aid other than a hand lens, for a thorough +understanding of the structure of any plant a good compound microscope +is indispensable, and wherever it is possible the student should be +provided with such an instrument, to use this book to the best +advantage. As, however, many are not able to have the use of a +microscope, the gross anatomy of all the forms described has been +carefully treated for the especial benefit of such students. Such +portions of the text, as well as the general discussions, are printed +in ordinary type, while the minute anatomy, and all points requiring +microscopic aid, are discussed in separate paragraphs printed in +smaller type. + +The drawings, with very few exceptions, which are duly credited, were +drawn from nature by the author, and nearly all expressly for this +work. + +A list of the most useful books of reference is appended, all of which +have been more or less consulted in the preparation of the following +pages. + +The classification adopted is, with slight changes, that given in +Goebel's "Outlines of Morphology and Classification"; while, perhaps, +not in all respects entirely satisfactory, it seems to represent more +nearly than any other our present knowledge of the subject. Certain +groups, like the Diatoms and _Characeae_, are puzzles to the botanist, +and at present it is impossible to give them more than a provisional +place in the system. + +If this volume serves to give the student some comprehension of the +real aims of botanical science, and its claims to be something more +than the "Analysis" of flowers, it will have fulfilled its mission. + +DOUGLAS H. CAMPBELL. + + BLOOMINGTON, INDIANA, + October, 1889. + + + + +TABLE OF CONTENTS. + + + PAGE + CHAPTER I.--INTRODUCTION 1 + + Composition of Matter; Biology; Botany; Zooelogy; Departments + of Botany; Implements and Reagents; Collecting + Specimens. + + + CHAPTER II.--THE CELL 6 + + Parts of the Cell; Formation of New Cells; Tissues. + + + CHAPTER III.--CLASSIFICATION OF PLANTS 9 + + Protophytes; Slime-moulds; Schizophytes; Blue-green Slimes, + _Oscillaria_; Schizomycetes, _Bacteria_; Green Monads, + _Euglena_, _Volvox_. + + + CHAPTER IV.--ALGAE 21 + + Classification of Algae; Green Algae; _Protococcaceae_, + _Protococcus_; _Confervaceae_, _Cladophora_, _OEdogonium_, + _Coleochaete_. + + + CHAPTER V.--GREEN ALGAE (_Continued_) 30 + + Pond-scums, _Spirogyra_; _Siphoneae_, _Vaucheria_; _Characeae_, + _Chara_. + + + CHAPTER VI.--BROWN SEAWEEDS 41 + + _Diatomaceae_; True Brown Algae, _Fucus_; Classification of + Brown Algae. + + + CHAPTER VII.--RED ALGAE 49 + + Structure of Red Algae; _Callithamnion_; Fresh-Water Forms. + + + CHAPTER VIII.--FUNGI 54 + + _Phycomycetes_, _Mycomycetes_; _Phycomycetes_, Black Moulds, + _Mucor_; White Rusts and Mildews, _Cystopus_; Water Moulds. + + + CHAPTER IX.--TRUE FUNGI 63 + + Yeast; Smuts; _Ascomycetes_; Dandelion Mildew; Cup Fungi, + _Ascobolus_; Lichens; Black Fungi. + + + CHAPTER X.--TRUE FUNGI (_Continued_) 77 + + _Basidiomycetes_; Rusts; _Coprinus_; Classification. + + + CHAPTER XI.--BRYOPHYTES 86 + + Classification; Liverworts, _Madotheca_; Classification of + Liverworts; Mosses, _Funaria_; Classification of Mosses. + + + CHAPTER XII.--PTERIDOPHYTES 102 + + Bryophytes and Pteridophytes; Germination and Prothallium; + Structure of Maiden-hair Fern. + + + CHAPTER XIII.--CLASSIFICATION OF PTERIDOPHYTES 116 + + Ferns; Horse-tails; Club Mosses. + + + CHAPTER XIV.--SPERMAPHYTES 128 + + General Characteristics; Gymnosperms and Angiosperms, + Scotch-pine; Classification of Gymnosperms. + + + CHAPTER XV.--SPERMAPHYTES (_Continued_) 143 + + Angiosperms; Flowers of Angiosperms; Classification of + Angiosperms; Monocotyledons, Structure of _Erythronium_. + + + CHAPTER XVI.--CLASSIFICATION OF MONOCOTYLEDONS 153 + + _Liliiflorae_; _Enantioblastae_; _Spadiciflorae_; _Glumaceae_; + _Scitamineae_; _Gynandrae_, _Helobiae_. + + + CHAPTER XVII.--DICOTYLEDONS 170 + + General Characteristics; Structure of Shepherd's-purse. + + + CHAPTER XVIII.--CLASSIFICATION OF DICOTYLEDONS 181 + + _Choripetalae_: _Iuliflorae_; _Centrospermae_; _Aphanocyclae_; + _Eucyclae_; _Tricoccae_; _Calyciflorae_. + + + CHAPTER XIX.--CLASSIFICATION OF DICOTYLEDONS + (_Continued_) 210 + + _Sympetalae_: _Isocarpae_, _Bicornes_, _Primulinae_, _Diospyrinae_; + _Anisocarpae_, _Tubiflorae_, _Labiatiflorae_, _Contortae_, + _Campanulinae_, _Aggregatae_. + + + CHAPTER XX.--FERTILIZATION OF FLOWERS 225 + + + CHAPTER XXI.--HISTOLOGICAL METHODS 230 + + Nuclear Division in Wild Onion; Methods of Fixing, Staining, + and Mounting Permanent Preparations; Reference Books. + + + INDEX 237 + + + + +BOTANY. + + + + +CHAPTER I. + +INTRODUCTION. + + +All matter is composed of certain constituents (about seventy are at +present known), which, so far as the chemist is concerned, are +indivisible, and are known as elements. + +Of the innumerable combinations of these elements, two general classes +may be recognized, organic and inorganic bodies. While it is +impossible, owing to the dependence of all organized matter upon +inorganic matter, to give an absolute definition, we at once recognize +the peculiarities of organic or living bodies as distinguished from +inorganic or non-living ones. All living bodies feed, grow, and +reproduce, these acts being the result of the action of forces +resident within the organism. Inorganic bodies, on the other hand, +remain, as a rule, unchanged so long as they are not acted upon by +external forces. + +All living organisms are dependent for existence upon inorganic +matter, and sooner or later return these elements to the sources +whence they came. Thus, a plant extracts from the earth and air +certain inorganic compounds which are converted by the activity of the +plant into a part of its own substance, becoming thus incorporated +into a living organism. After the plant dies, however, it undergoes +decomposition, and the elements are returned again to the earth and +atmosphere from which they were taken. + +Investigation has shown that living bodies contain comparatively few +elements, but these are combined into extraordinarily complex +compounds. The following elements appear to be essential to all living +bodies: carbon, hydrogen, oxygen, nitrogen, sulphur, potassium. +Besides these there are several others usually present, but not +apparently essential to all organisms. These include phosphorus, iron, +calcium, sodium, magnesium, chlorine, silicon. + +As we examine more closely the structure and functions of organic +bodies, an extraordinary uniformity is apparent in all of them. This +is disguised in the more specialized forms, but in the simpler ones is +very apparent. Owing to this any attempt to separate absolutely the +animal and vegetable kingdoms proves futile. + +The science that treats of living things, irrespective of the +distinction between plant and animal, is called "Biology," but for +many purposes it is desirable to recognize the distinctions, making +two departments of Biology,--Botany, treating of plants; and Zooelogy, +of animals. It is with the first of these only that we shall concern +ourselves here. + +When one takes up a plant his attention is naturally first drawn to +its general appearance and structure, whether it is a complicated one +like one of the flowering plants, or some humbler member of the +vegetable kingdom,--a moss, seaweed, toadstool,--or even some still +simpler plant like a mould, or the apparently structureless green scum +that floats on a stagnant pond. In any case the impulse is to +investigate the form and structure as far as the means at one's +disposal will permit. Such a study of structure constitutes +"Morphology," which includes two departments,--gross anatomy, or a +general study of the parts; and minute anatomy, or "Histology," in +which a microscopic examination is made of the structure of the +different parts. A special department of Morphology called +"Embryology" is often recognized. This embraces a study of the +development of the organism from its earliest stage, and also the +development of its different members. + +From a study of the structure of organisms we get a clue to their +relationships, and upon the basis of such relationships are enabled to +classify them or unite them into groups so as to indicate the degree +to which they are related. This constitutes the division of Botany +usually known as Classification or "Systematic Botany." + +Finally, we may study the functions or workings of an organism: how it +feeds, breathes, moves, reproduces. This is "Physiology," and like +classification must be preceded by a knowledge of the structures +concerned. + +For the study of the gross anatomy of plants the following articles +will be found of great assistance: 1. a sharp knife, and for more +delicate tissues, a razor; 2. a pair of small, fine-pointed scissors; +3. a pair of mounted needles (these can be made by forcing ordinary +sewing needles into handles of pine or other soft wood); 4. a hand +lens; 5. drawing-paper and pencil, and a note book. + +For the study of the lower plants, as well as the histology of the +higher ones, a compound microscope is indispensable. Instruments with +lenses magnifying from about 20 to 500 diameters can be had at a cost +varying from about $20 to $30, and are sufficient for any ordinary +investigations. + +Objects to be studied with the compound microscope are usually +examined by transmitted light, and must be transparent enough to allow +the light to pass through. The objects are placed upon small glass +slips (slides), manufactured for the purpose, and covered with +extremely thin plates of glass, also specially made. If the body to be +examined is a large one, thin slices or sections must be made. This +for most purposes may be done with an ordinary razor. Most plant +tissues are best examined ordinarily in water, though of course +specimens so mounted cannot be preserved for any length of time.[1] + +[1] For the mounting of permanent preparations, see Chapter XIX. + +In addition to the implements used in studying the gross anatomy, the +following will be found useful in histological work: 1. a small +camel's-hair brush for picking up small sections and putting water in +the slides; 2. small forceps for handling delicate objects; 3. +blotting paper for removing superfluous water from the slides and +drawing fluids under the cover glass; 4. pieces of elder or sunflower +pith, for holding small objects while making sections. + +In addition to these implements, a few reagents may be recommended for +the simpler histological work. The most important of these are +alcohol, glycerine, potash (a strong solution of potassium hydrate in +water), iodine (either a little of the commercial tincture of iodine +in water, or, better, a solution of iodine in iodide of potassium), +acetic acid, and some staining fluid. (An aqueous or alcoholic +solution of gentian violet or methyl violet is one of the best.) + +A careful record should be kept by the student of all work done, both +by means of written notes and drawings. For most purposes pencil +drawings are most convenient, and these should be made with a +moderately soft pencil on unruled paper. If it is desired to make the +drawings with ink, a careful outline should first be made with a hard +pencil and this inked over with India-ink or black drawing ink. Ink +drawings are best made upon light bristol board with a hard, +smooth-finished surface. + +When obtainable, the student will do best to work with freshly +gathered specimens; but as these are not always to be had when wanted, +a few words about gathering and preserving material may be of service. + +Most of the lower green plants (_algae_) may be kept for a long time in +glass jars or other vessels, provided care is taken to remove all +dead specimens at first and to renew the water from time to time. They +usually thrive best in a north window where they get little or no +direct sunshine, and it is well to avoid keeping them too warm. + +Numbers of the most valuable fungi--_i.e._ the lower plants that are +not green--grow spontaneously on many organic substances that are kept +warm and moist. Fresh bread kept moist and covered with a glass will +in a short time produce a varied crop of moulds, and fresh horse +manure kept in the same way serves to support a still greater number +of fungi. + +Mosses, ferns, etc., can be raised with a little care, and of course +very many flowering plants are readily grown in pots. + +Most of the smaller parasitic fungi (rusts, mildews, etc.) may be kept +dry for any length of time, and on moistening with a weak solution of +caustic potash will serve nearly as well as freshly gathered specimens +for most purposes. + +When it is desired to preserve as perfectly as possible the more +delicate plant structures for future study, strong alcohol is the best +and most convenient preserving agent. Except for loss of color it +preserves nearly all plant tissues perfectly. + + + + +CHAPTER II. + +THE CELL. + + +If we make a thin slice across the stem of a rapidly growing +plant,--_e.g._ geranium, begonia, celery,--mount it in water, and +examine it microscopically, it will be found to be made up of numerous +cavities or chambers separated by delicate partitions. Often these +cavities are of sufficient size to be visible to the naked eye, and +examined with a hand lens the section appears like a piece of fine +lace, each mesh being one of the chambers visible when more strongly +magnified. These chambers are known as "cells," and of them the whole +plant is built up. + +[Illustration: FIG. 1.--A single cell from a hair on the stamen of the +common spiderwort (_Tradescantia_), x 150. _pr._ protoplasm; _w_, cell +wall; _n_, nucleus.] + + In order to study the structure of the cell more exactly we will + select such as may be examined without cutting them. A good example + is furnished by the common spiderwort (Fig. 1). Attached to the base + of the stamens (Fig. 85, _B_) are delicate hairs composed of chains + of cells, which may be examined alive by carefully removing a stamen + and placing it in a drop of water under a cover glass. Each cell + (Fig. 1) is an oblong sac, with a delicate colorless wall which + chemical tests show to be composed of cellulose, a substance closely + resembling starch. Within this sac, and forming a lining to it, is + a thin layer of colorless matter containing many fine granules. + Bands and threads of the same substance traverse the cavity of the + cell, which is filled with a deep purple homogeneous fluid. This + fluid, which in most cells is colorless, is called the cell sap, and + is composed mainly of water. Imbedded in the granular lining of the + sac is a roundish body (_n_), which itself has a definite membrane, + and usually shows one or more roundish bodies within, besides an + indistinctly granular appearance. This body is called the nucleus of + the cell, and the small one within it, the nucleolus. + + The membrane surrounding the cell is known as the cell wall, and in + young plant cells is always composed of cellulose. + + The granular substance lining the cell wall (Fig. 1, _pr._) is + called "protoplasm," and with the nucleus constitutes the living + part of the cell. If sufficiently magnified, the granules within the + protoplasm will be seen to be in active streaming motion. This + movement, which is very evident here, is not often so conspicuous, + but still may often be detected without difficulty. + +[Illustration: FIG. 2.--An _Amoeba_. A cell without a cell wall. _n_, +nucleus; _v_, vacuoles, x 300.] + +The cell may be regarded as the unit of organic structure, and of +cells are built up all of the complicated structures of which the +bodies of the highest plants and animals are composed. We shall find +that the cells may become very much modified for various purposes, but +at first they are almost identical in structure, and essentially the +same as the one we have just considered. + +[Illustration: FIG. 3.--Hairs from the leaf stalk of a wild geranium. +_A_, single-celled hair. _B_ and _C_, hairs consisting of a row of +cells. The terminal rounded cell secretes a peculiar scented oil that +gives the plant its characteristic odor. _B_, x 50; _C_, x 150.] + +Very many of the lower forms of life consist of but a single cell +which may occasionally be destitute of a cell wall. Such a form is +shown in Figure 2. Here we have a mass of protoplasm with a nucleus +(_n_) and cavities (vacuoles, _v_) filled with cell sap, but no cell +wall. The protoplasm is in constant movement, and by extensions of a +portion of the mass and contraction of other parts, the whole creeps +slowly along. Other naked cells (Fig. 12, _B_; Fig. 16, _C_) are +provided with delicate thread-like processes of protoplasm called +"cilia" (sing. _cilium_), which are in active vibration, and propel +the cell through the water. + +[Illustration: FIG. 4.--_A_, cross section. _B_, longitudinal section +of the leaf stalk of wild geranium, showing its cellular structure. +_Ep._ epidermis. _h_, a hair, x 50. _C_, a cell from the prothallium +(young plant) of a fern, x _150_. The contents of the cell contracted +by the action of a solution of sugar.] + + On placing a cell into a fluid denser than the cell sap (_e.g._ a + ten-per-cent solution of sugar in water), a portion of the water + will be extracted from the cell, and we shall then see the + protoplasm receding from the wall (Fig. 4, _C_), showing that it is + normally in a state of tension due to pressure from within of the + cell sap. The cell wall shows the same thing though in a less + degree, owing to its being much more rigid than the protoplasmic + lining. It is owing to the partial collapsing of the cells, + consequent on loss of water, that plants wither when the supply of + water is cut off. + +As cells grow, new ones are formed in various ways. If the new cells +remain together, cell aggregates, called tissues, are produced, and +of these tissues are built up the various organs of the higher plants. +The simplest tissues are rows of cells, such as form the hairs +covering the surface of the organs of many flowering plants (Fig. 3), +and are due to a division of the cells in a single direction. If the +divisions take place in three planes, masses of cells, such as make up +the stems, etc., of the higher plants, result (Fig. 4, _A_, _B_). + + + + +CHAPTER III. + +CLASSIFICATION OF PLANTS.--PROTOPHYTES. + + +For the sake of convenience it is desirable to collect into groups +such plants as are evidently related; but as our knowledge of many +forms is still very imperfect, any classification we may adopt must be +to a great extent only provisional, and subject to change at any time, +as new forms are discovered or others become better understood. + +The following general divisions are usually accepted: I. Sub-kingdom +(or Branch); II. Class; III. Order; IV. Family; V. Genus; VI. Species. + +To illustrate: The white pine belongs to the highest great division +(sub-kingdom) of the plant kingdom. The plants of this division all +produce seeds, and hence are called "spermaphytes" ("seed plants"). +They may be divided into two groups (classes), distinguished by +certain peculiarities in the flowers and seeds. These are named +respectively "gymnosperms" and "angiosperms," and to the first our +plant belongs. The gymnosperms may be further divided into several +subordinate groups (orders), one of which, the conifers, or +cone-bearing evergreens, includes our plant. This order includes +several families, among them the fir family (_Abietineae_), including +the pines and firs. Of the sub-divisions (_genera_, sing. _genus_) of +the fir family, one of the most familiar is the genus _Pinus_, which +embraces all the true pines. Comparing different kinds of pines, we +find that they differ in the form of the cones, arrangement of the +leaves, and other minor particulars. The form we have selected differs +from all other native forms in its cones, and also in having the +leaves in fives, instead of twos or threes, as in most other kinds. +Therefore to distinguish the white pine from all other pines, it is +given a "specific" name, _strobus_. + +The following table will show more plainly what is meant: + + + Sub-kingdom, + _Spermaphyta_. + /--------------------^---------------------\ + Includes all spermaphytes, or seed plants. + + Class, + _Gymnospermae_. + /------------^------------\ + All naked-seeded plants. + + Order, + _Coniferae_. + /--------------^--------------\ + All cone-bearing evergreens. + + Family, + _Abietineae_. + /--------^--------\ + Firs, Pines, etc. + + Genus, + _Pinus_. + /---^---\ + Pines. + + Species, + _Strobus_. + /-----^-----\ + White Pine. + + +SUB-KINGDOM I. + +PROTOPHYTES. + +The name Protophytes (_Protophyta_) has been applied to a large number +of simple plants, which differ a good deal among themselves. Some of +them differ strikingly from the higher plants, and resemble so +remarkably certain low forms of animal life as to be quite +indistinguishable from them, at least in certain stages. Indeed, there +are certain forms that are quite as much animal as vegetable in their +attributes, and must be regarded as connecting the two kingdoms. Such +forms are the slime moulds (Fig. 5), _Euglena_ (Fig. 9), _Volvox_ +(Fig. 10), and others. + +[Illustration: FIG. 5.--_A_, a portion of a slime mould growing on a +bit of rotten wood, x 3. _B_, outline of a part of the same, x 25. +_C_, a small portion showing the densely granular character of the +protoplasm, x 150. _D_, a group of spore cases of a slime mould +(_Trichia_), of about the natural size. _E_, two spore cases, x 5. The +one at the right has begun to open. _F_, a thread (capillitium) and +spores of _Trichia_, x 50. _G_, spores. _H_, end of the thread, x 300. +_I_, zooespores of _Trichia_, x 300. i, ciliated form; ii, amoeboid +forms. _n_, nucleus. _v_, contractile vacuole. _J_, _K_, sporangia of +two common slime moulds. _J_, _Stemonitis_, x 2. _K_, _Arcyria_, x 4.] + +Other protophytes, while evidently enough of vegetable nature, are +nevertheless very different in some respects from the higher plants. + +The protophytes may be divided into three classes: I. The slime moulds +(_Myxomycetes_); II. The Schizophytes; III. The green monads +(_Volvocineae_). + + +CLASS I.--THE SLIME MOULDS. + +These curious organisms are among the most puzzling forms with which +the botanist has to do, as they are so much like some of the lowest +forms of animal life as to be scarcely distinguishable from them, and +indeed they are sometimes regarded as animals rather than plants. At +certain stages they consist of naked masses of protoplasm of very +considerable size, not infrequently several centimetres in diameter. +These are met with on decaying logs in damp woods, on rotting leaves, +and other decaying vegetable matter. The commonest ones are bright +yellow or whitish, and form soft, slimy coverings over the substratum +(Fig. 5, _A_), penetrating into its crevices and showing sensitiveness +toward light. The plasmodium, as the mass of protoplasm is called, may +be made to creep upon a slide in the following way: A tumbler is +filled with water and placed in a saucer filled with sand. A strip of +blotting paper about the width of the slide is now placed with one end +in the water, the other hanging over the edge of the glass and against +one side of a slide, which is thus held upright, but must not be +allowed to touch the side of the tumbler. The strip of blotting paper +sucks up the water, which flows slowly down the surface of the slide +in contact with the blotting paper. If now a bit of the substance upon +which the plasmodium is growing is placed against the bottom of the +slide on the side where the stream of water is, the protoplasm will +creep up against the current of water and spread over the slide, +forming delicate threads in which most active streaming movements of +the central granular protoplasm may be seen under the microscope, and +the ends of the branches may be seen to push forward much as we saw in +the amoeba. In order that the experiment may be successful, the whole +apparatus should be carefully protected from the light, and allowed to +stand for several hours. This power of movement, as well as the power +to take in solid food, are eminently animal characteristics, though +the former is common to many plants as well. + +After a longer or shorter time the mass of protoplasm contracts and +gathers into little heaps, each of which develops into a structure +that has no resemblance to any animal, but would be at once placed +with plants. In one common form (_Trichia_) these are round or +pear-shaped bodies of a yellow color, and about as big as a pin head +(Fig. 5, _D_), occurring in groups on rotten logs in damp woods. +Others are stalked (_Arcyria_, _Stemonitis_) (Fig. 5, _J_, _K_), and +of various colors,--red, brown, etc. The outer part of the structure +is a more or less firm wall, which breaks when ripe, discharging a +powdery mass, mixed in most forms with very fine fibres. + + When strongly magnified the fine dust is found to be made up of + innumerable small cells with thick walls, marked with ridges or + processes which differ much in different species. The fibres also + differ much in different genera. Sometimes they are simple, + hair-like threads; in others they are hollow tubes with spiral + thickenings, often very regularly placed, running around their + walls. + + The spores may sometimes be made to germinate by placing them in a + drop of water, and allowing them to remain in a warm place for about + twenty-four hours. If the experiment has been successful, at the end + of this time the spore membrane will have burst, and the contents + escaped in the form of a naked mass of protoplasm (Zooespore) with a + nucleus, and often showing a vacuole (Fig. 5, _v_), that + alternately becomes much distended, and then disappears entirely. On + first escaping it is usually provided with a long, whip-like + filament of protoplasm, which is in active movement, and by means of + which the cell swims actively through the water (Fig. 5, _I_ i). + Sometimes such a cell will be seen to divide into two, the process + taking but a short time, so that the numbers of these cells under + favorable conditions may become very large. After a time the lash is + withdrawn, and the cell assumes much the form of a small amoeba (_I_ + ii). + +The succeeding stages are difficult to follow. After repeatedly +dividing, a large number of these amoeba-like cells run together, +coalescing when they come in contact, and forming a mass of protoplasm +that grows, and finally assumes the form from which it started. + + Of the common forms of slime moulds the species of _Trichia_ (Figs. + _D_, _I_) and _Physarum_ are, perhaps, the best for studying the + germination, as the spores are larger than in most other forms, and + germinate more readily. The experiment is apt to be most successful + if the spores are sown in a drop of water in which has been infused + some vegetable matter, such as a bit of rotten wood, boiling + thoroughly to kill all germs. A drop of this fluid should be placed + on a perfectly clean cover glass, which it is well to pass once or + twice through a flame, and the spores transferred to this drop with + a needle previously heated. By these precautions foreign germs will + be avoided, which otherwise may interfere seriously with the growth + of the young slime moulds. After sowing the spores in the drop of + culture fluid, the whole should be inverted over a so-called "moist + chamber." This is simply a square of thick blotting paper, in which + an opening is cut small enough to be entirely covered by the cover + glass, but large enough so that the drop in the centre of the cover + glass will not touch the sides of the chamber, but will hang + suspended clear in it. The blotting paper should be soaked + thoroughly in pure water (distilled water is preferable), and then + placed on a slide, covering carefully with the cover glass with the + suspended drop of fluid containing the spores. The whole should be + kept under cover so as to prevent loss of water by evaporation. By + this method the spores may be examined conveniently without + disturbing them, and the whole may be kept as long as desired, so + long as the blotting paper is kept wet, so as to prevent the + suspended drop from drying up. + + +CLASS II.--_Schizophytes_. + +The Schizophytes are very small plants, though not infrequently +occurring in masses of considerable size. They are among the commonest +of all plants, and are found everywhere. They multiply almost entirely +by simple transverse division, or splitting of the cells, whence their +name. There are two pretty well-marked orders,--the blue-green slimes +(_Cyanophyceae_) and the bacteria (_Schizomycetes_). They are +distinguished, primarily, by the first (with a very few exceptions) +containing chlorophyll (leaf-green), which is entirely absent from +nearly all of the latter. + +The blue-green slimes: These are, with few exceptions, green plants of +simple structure, but possessing, in addition to the ordinary green +pigment (chlorophyll, or leaf-green), another coloring matter, soluble +in water, and usually blue in color, though sometimes yellowish or +red. + +[Illustration: FIG. 6.--Blue-green slime (_Oscillaria_). _A_, mass of +filaments of the natural size. _B_, single filament, x 300. _C_, a +piece of a filament that has become separated. _s_, sheath, x 300.] + +As a representative of the group, we will select one of the commonest +forms (_Oscillaria_), known sometimes as green slime, from forming a +dark blue-green or blackish slimy coat over the mud at the bottom of +stagnant or sluggish water, in watering troughs, on damp rocks, or +even on moist earth. A search in the places mentioned can hardly fail +to secure plenty of specimens for study. If a bit of the slimy mass is +transferred to a china dish, or placed with considerable water on a +piece of stiff paper, after a short time the edge of the mass will +show numerous extremely fine filaments of a dark blue-green color, +radiating in all directions from the mass (Fig. 6, _a_). The filaments +are the individual plants, and possess considerable power of motion, +as is shown by letting the mass remain undisturbed for a day or two, +at the end of which time they will have formed a thin film over the +surface of the vessel in which they are kept; and the radiating +arrangement of the filaments can then be plainly seen. + +If the mass is allowed to dry on the paper, it often leaves a bright +blue stain, due to the blue pigment in the cells of the filament. This +blue color can also be extracted by pulverizing a quantity of the +dried plants, and pouring water over them, the water soon becoming +tinged with a decided blue. If now the water containing the blue +pigment is filtered, and the residue treated with alcohol, the latter +will extract the chlorophyll, becoming colored of a yellow-green. + + The microscope shows that the filaments of which the mass is + composed (Fig. 6, _B_) are single rows of short cylindrical cells of + uniform diameter, except at the end of the filament, where they + usually become somewhat smaller, so that the tip is more or less + distinctly pointed. The protoplasm of the cells has a few small + granules scattered through it, and is colored uniformly of a pale + blue-green. No nucleus can be seen. + + If the filament is broken, there may generally be detected a + delicate, colorless sheath that surrounds it, and extends beyond the + end cells (Fig. 6, _c_). The filament increases in length by the + individual cells undergoing division, this always taking place at + right angles to the axis of the filament. New filaments are produced + simply by the older ones breaking into a number of pieces, each of + which rapidly grows to full size. + +The name "oscillaria" arises from the peculiar oscillating or swinging +movements that the plant exhibits. The most marked movement is a +swaying from side to side, combined with a rotary motion of the free +ends of the filaments, which are often twisted together like the +strands of a rope. If the filaments are entirely free, they may often +be observed to move forward with a slow, creeping movement. Just how +these movements are caused is still a matter of controversy. + +The lowest of the _Cyanophyceae_ are strictly single-celled, separating +as soon as formed, but cohering usually in masses or colonies by means +of a thick mucilaginous substance that surrounds them (Fig. 7, _D_). + +The higher ones are filaments, in which there may be considerable +differentiation. These often occur in masses of considerable size, +forming jelly-like lumps, which may be soft or quite firm (Fig. 7, +_A_, _B_). They are sometimes found on damp ground, but more commonly +attached to plants, stones, etc., in water. The masses vary in color +from light brown to deep blackish green, and in size from that of a +pin head to several centimetres in diameter. + +[Illustration: FIG. 7.--Forms of _Cyanophyceae_. _A_, _Nostoc_. _B_, +_Gloeotrichia_, x 1. _C_, individual of _Gloeotrichia_. _D_, +Chrooecoccus. _E_, _Nostoc_. _F_, Oscillaria. _G_, _H_, _Tolypothrix_. +All x 300. _y_, heterocyst. _sp._ spore.] + +In the higher forms special cells called heterocysts are found. They +are colorless, or light yellowish, regularly disposed; but their +function is not known. Besides these, certain cells become +thick-walled, and form resting cells (spores) for the propagation of +the plant (Fig. 7, C. _sp._). In species where the sheath of the +filament is well marked (Fig. 7, _H_), groups of cells slip out of the +sheath, and develop a new one, thus giving rise to a new plant. + +The bacteria (_Schizomycetes_), although among the commonest of +organisms, owing to their excessive minuteness, are difficult to +study, especially for the beginner. They resemble, in their general +structure and methods of reproduction, the blue-green slimes, but are, +with very few exceptions, destitute of chlorophyll, although often +possessing bright pigments,--blue, violet, red, etc. It is one of +these that sometimes forms blood-red spots in flour paste or bits of +bread that have been kept very moist and warm. They are universally +present where decomposition is going on, and are themselves the +principal agents of decay, which is the result of their feeding upon +the substance, as, like all plants without chlorophyll, they require +organic matter for food. Most of the species are very tenacious of +life, and may be completely dried up for a long time without dying, +and on being placed in water will quickly revive. Being so extremely +small, they are readily carried about in the air in their dried-up +condition, and thus fall upon exposed bodies, setting up decomposition +if the conditions are favorable. + +A simple experiment to show this may be performed by taking two test +tubes and partly filling them with an infusion of almost any organic +substance (dried leaves or hay, or a bit of meat will answer). The +fluid should now be boiled so as to kill any germs that may be in it; +and while hot, one of the vessels should be securely stopped up with a +plug of cotton wool, and the other left open. The cotton prevents +access of all solid particles, but allows the air to enter. If proper +care has been taken, the infusion in the closed vessel will remain +unchanged indefinitely; but the other will soon become turbid, and a +disagreeable odor will be given off. Microscopic examination shows the +first to be free from germs of any kind, while the second is swarming +with various forms of bacteria. + +[Illustration: FIG. 8.--Bacteria.] + +These little organisms have of late years attracted the attention of +very many scientists, from the fact that to them is due many, if not +all, contagious diseases. The germs of many such diseases have been +isolated, and experiments prove beyond doubt that these are alone the +causes of the diseases in question. + + If a drop of water containing bacteria is examined, we find them to + be excessively small, many of them barely visible with the strongest + lenses. The larger ones (Fig. 8) recall quite strongly the smaller + species of oscillaria, and exhibit similar movements. Others are so + small as to appear as mere lines and dots, even with the strongest + lenses. Among the common forms are small, nearly globular cells; + oblong, rod-shaped or thread-shaped filaments, either straight or + curved, or even spirally twisted. Frequently they show a quick + movement which is probably in all cases due to cilia, which are, + however, too small to be seen in most cases. + +[Illustration: FIG. 9.--_Euglena_. _A_, individual in the active +condition. _E_, the red "eye-spot." _c_, flagellum. _n_, nucleus. _B_, +resting stage. _C_, individual dividing, x 300.] + +Reproduction is for the most part by simple transverse division, as in +oscillaria; but occasionally spores are produced also. + + +CLASS III.--GREEN MONADS (_Volvocineae_). + +This group of the protophytes is unquestionably closely related to +certain low animals (_Monads_ or _Flagellata_), with which they are +sometimes united. They are characterized by being actively motile, and +are either strictly unicellular, or the cells are united by a +gelatinous envelope into a colony of definite form. + +Of the first group, _Euglena_ (Fig. 9), may be selected as a type. + + This organism is found frequently among other algae, and occasionally + forms a green film on stagnant water. It is sometimes regarded as a + plant, sometimes as an animal, and is an elongated, somewhat + worm-like cell without a definite cell wall, so that it can change + its form to some extent. The protoplasm contains oval masses, which + are bright green in color; but the forward pointed end of the cell + is colorless, and has a little depression. At this end there is a + long vibratile protoplasmic filament (_c_), by means of which the + cell moves. There is also to be seen near this end a red speck (_e_) + which is probably sensitive to light. A nucleus can usually be seen + if the cell is first killed with an iodine solution, which often + will render the flagellum (_c_) more evident, this being invisible + while the cell is in motion. The cells multiply by division. + Previous to this the flagellum is withdrawn, and a firm cell wall is + formed about the cell (Fig. 9, _B_). The contents then divide into + two or more parts, which afterwards escape as new individuals. + +Of the forms that are united in colonies[2] one of the best known is +_Volvox_ (Fig. 10). This plant is sometimes found in quiet water, +where it floats on or near the surface as a dark green ball, just +large enough to be seen with the naked eye. They may be kept for some +time in aquaria, and will sometimes multiply rapidly, but are very +susceptible to extremes of temperature, especially of heat. + +[2] The term "colony" is, perhaps, inappropriate, as the whole mass of +cells arises from a single one, and may properly be looked upon as an +individual plant. + +[Illustration: FIG. 10.--_Volvox._ _A_, mature colony, containing +several smaller ones (_x_), x 50. _B_, Two cells showing the cilia, +x 300.] + + The colony (Fig. 10, _A_) is a hollow sphere, the numerous green + cells of which it is composed forming a single layer on the outside. + By killing with iodine, and using a strong lens, each cell is seen + to be somewhat pear-shaped (Fig. _B_), with the pointed end out. + Attached to this end are two vibratile filaments (cilia or + _flagella_), and the united movements of these cause the rolling + motion of the whole colony. Usually a number of young colonies + (Fig. _x_) are found within the mother colony. These arise by the + repeated bipartition of a single cell, and escape finally, forming + independent colonies. + + Another (sexual) form of reproduction occurs, similar to that found + in many higher plants; but as it only occurs at certain seasons, it + is not likely to be met with by the student. + +Other forms related to _Volvox_, and sometimes met with, are +_Gonium_, in which there are sixteen cells, forming a flat square; +_Pandorina_ and _Eudorina_, with sixteen cells, forming an oval or +globular colony like _Volvox_, but much smaller. In all of these the +structure of the cells is essentially as in _Volvox_. + + + + +CHAPTER IV. + +SUB-KINGDOM II. + +ALGAE.[3] + + +[3] Algae (sing. _alga_). + +In the second sub-kingdom of plants is embraced an enormous assemblage +of plants, differing widely in size and complexity, and yet showing a +sufficiently complete gradation from the lowest to the highest as to +make it impracticable to make more than one sub-kingdom to include +them. They are nearly all aquatic forms, although many of them will +survive long periods of drying, such forms occurring on moist earth, +rocks, or the trunks of trees, but only growing when there is a +plentiful supply of water. + +All of them possess chlorophyll, which, however, in many forms, is +hidden by the presence of a brown or red pigment. They are ordinarily +divided into three classes--I. The Green Algae (_Chlorophyceae_); +II. Brown Algae (_Phaeophyceae_); III. Red Algae (_Rhodophyceae_). + + +CLASS I.--GREEN ALGAE. + +The green algae are to be found almost everywhere where there is +moisture, but are especially abundant in sluggish or stagnant fresh +water, being much less common in salt water. They are for the most +part plants of simple structure, many being unicellular, and very few +of them plants of large size. + +We may recognize five well-marked orders of the green algae--I. Green +slimes (_Protococcaceae_); II. _Confervaceae_; III. Pond scums +(_Conjugatae_); IV. _Siphoneae_; V. Stone-worts (_Characeae_). + + +ORDER I.--_Protococcaceae_. + +The members of this order are minute unicellular plants, growing +either in water or on the damp surfaces of stones, tree trunks, etc. +The plants sometimes grow isolated, but usually the cells are united +more or less regularly into colonies. + +A common representative of the order is the common green slime, +_Protococcus_ (Fig. 11, _A_, _C_), which forms a dark green slimy +coating over stones, tree trunks, flower pots, etc. Owing to their +minute size the structure can only be made out with the microscope. + +[Illustration: FIG. 11.--_Protococcaceae._ _A_, _C_, Protococcus. _A_, +single cells. _B_, cells dividing by fission. _C_, successive steps in +the process of internal cell division. In _C_ iv, the young cells have +mostly become free. _D_, a full-grown colony of _Pediastrum_. _E_, a +young colony still surrounded by the membrane of the mother cell. _F_, +_Scenedesmus_. All, x 300. _G_, small portion of a young colony of the +water net (_Hydrodictyon_), x 150.] + + Scraping off a little of the material mentioned into a drop of water + upon a slide, and carefully separating it with needles, a cover + glass may be placed over the preparation, and it is ready for + examination. When magnified, the green film is found to be composed + of minute globular cells of varying size, which may in places be + found to be united into groups. With a higher power, each cell + (Fig. 11, _A_) is seen to have a distinct cell wall, within which is + colorless protoplasm. Careful examination shows that the chlorophyll + is confined to several roundish bodies that are not usually in + immediate contact with the wall of the cell. These green masses are + called chlorophyll bodies (chloroplasts). Toward the centre of the + cell, especially if it has first been treated with iodine, the + nucleus may be found. The size of the cells, as well as the number + of chloroplasts, varies a good deal. + + With a little hunting, specimens in various stages of division may + be found. The division takes place in two ways. In the first + (Fig. 11, _B_), known as fission, a wall is formed across the cell, + dividing it into two cells, which may separate immediately or may + remain united until they have undergone further division. In this + case the original cell wall remains as part of the wall of the + daughter cells. Fission is the commonest form of cell multiplication + throughout the vegetable kingdom. + + The second form of cell division or internal cell division is shown + at _C_. Here the protoplasm and nucleus repeatedly divide until a + number of small cells are formed within the old one. These develop + cell walls, and escape by the breaking of the old cell wall, which + is left behind, and takes no part in the process. The cells thus + formed are sometimes provided with two cilia, and are capable of + active movement. + + Internal cell division, as we shall see, is found in most plants, + but only at special times. + + Closely resembling _Protococcus_, and answering quite as well for + study, are numerous aquatic forms, such as _Chlorococcum_ (Fig. 12). + These are for the most part destitute of a firm cell wall, but are + imbedded in masses of gelatinous substance like many _Cyanophyceae_. + The chloroplasts are smaller and less distinct than in + _Protococcus_. The cells are here oval rather than round, and often + show a clear space at one end. + +[Illustration: FIG. 12.--_Chlorococcum_, a plant related to +_Protococcus_, but the naked cells are surrounded by a colorless +gelatinous envelope. _A_, motionless cells. _B_, a cell that has +escaped from its envelope and is ciliated, x 300.] + + Owing to the absence of a definite membrane, a distinction between + fission and internal cell division can scarcely be made here. Often + the cells escape from the gelatinous envelope, and swim actively by + means of two cilia at the colorless end (Fig. 12, _B_). In this + stage they closely resemble the individuals of a _Volvox_ colony, or + other green _Flagellata_, to which there is little doubt that they + are related. + + There are a number of curious forms common in fresh water that are + probably related to _Protococcus_, but differ in having the cells + united in colonies of definite form. Among the most striking are + the different species of _Pediastrum_ (Fig. 11, _D_, _E_), often met + with in company with other algae, and growing readily in aquaria when + once established. They are of very elegant shapes, and the number of + cells some multiple of four, usually sixteen. + + The cells form a flat disc, the outer ones being generally provided + with a pair of spines. + + New individuals arise by internal division of the cells, the + contents of each forming as many parts as there are cells in the + whole colony. The young cells now escape through a cleft in the wall + of the mother cell, but are still surrounded by a delicate membrane + (Fig. 11, _E_). Within this membrane the young cells arrange + themselves in the form of the original colony, and grow together, + forming a new colony. + + A much larger but rarer form is the water net (Fig. 11, _G_), in + which the colony has the form of a hollow net, the spaces being + surrounded by long cylindrical cells placed end to end. Other common + forms belong to the genus _Scenedesmus_ (Fig. 11, _F_), of which + there are many species. + + +ORDER II.--_Confervaceae_. + +Under this head are included a number of forms of which the simplest +ones approach closely, especially in their younger stages, the +_Protococcaceae_. Indeed, some of the so-called _Protococcaceae_ are +known to be only the early stages of these plants. + +A common member of this order is _Cladophora_, a coarse-branching +alga, growing commonly in running water, where it forms tufts, +sometimes a metre or more in length. By floating out a little of it in +a saucer, it is easy to see that it is made up of branching filaments. + + The microscope shows (Fig. 13, _A_) that these filaments are rows of + cylindrical cells with thick walls showing evident stratification. + At intervals branches are given off, which may in turn branch, + giving rise to a complicated branching system. These branches begin + as little protuberances of the cell wall at the top of the cell. + They increase rapidly in length, and becoming slightly contracted at + the base, a wall is formed across at this point, shutting it off + from the mother cell. + + The protoplasm lines the wall of the cell, and extends in the form + of thin plates across the cavity of the cell, dividing it up into a + number of irregular chambers. Imbedded in the protoplasm are + numerous flattened chloroplasts, which are so close together as to + make the protoplasm appear almost uniformly green. Within the + chloroplasts are globular, glistening bodies, called "pyrenoids." + The cell has several nuclei, but they are scarcely evident in the + living cell. By placing the cells for a few hours in a one per cent + watery solution of chromic acid, then washing thoroughly and + staining with borax carmine, the nuclei will be made very evident + (Fig. 13, _B_). Such preparations may be kept permanently in dilute + glycerine. + +[Illustration: FIG. 13.--_Cladophora._ _A_, a fragment of a plant, +x 50. _B_, a single cell treated with chromic acid, and stained with +alum cochineal. _n_, nucleus. _py._ pyrenoid, x 150. _C_, three stages +in the division of a cell. i, 1.45 p.m.; ii, 2.55 p.m.; iii, +4.15 p.m., x 150. _D_, a zooespore x 350.] + + If a mass of actively growing filaments is examined, some of the + cells will probably be found in process of fission. The process is + very simple, and may be easily followed (Fig. 13, _C_). A ridge of + cellulose is formed around the cell wall, projecting inward, and + pushing in the protoplasm as it grows. The process is continued + until the ring closes in the middle, cutting the protoplasmic body + completely in two, and forms a firm membrane across the middle of + the cell. The protoplasm at this stage (_C_ iii.) is somewhat + contracted, but soon becomes closely applied to the new wall. The + whole process lasts, at ordinary temperatures (20 deg.-25 deg. C.), from + three to four hours. + + At certain times, but unfortunately not often to be met with, the + contents of some of the cells form, by internal division, a large + number of small, naked cells (zooespores) (Fig. 13, _D_), which + escape and swim about actively for a time, and afterwards become + invested with a cell wall, and grow into a new filament. These cells + are called zooespores, from their animal-like movements. They are + provided with two cilia, closely resembling the motile cells of the + _Protococcaceae_ and _Volvocineae_. + +There are very many examples of these simple _Confervaceae_, some like +_Conferva_ being simple rows of cells, others like _Stigeoclonium_ +(Fig. 14, _A_), _Chaetophora_ and _Draparnaldia_ (Fig. 14, _B_, _C_), +very much branched. The two latter forms are surrounded by masses of +transparent jelly, which sometimes reach a length of several +centimetres. + +[Illustration: FIG. 14.--_Confervaceae_. _A_, _Stigeoclonium_. _B_, +_Draparnaldia_, x 50. _C_, a piece of _Draparnaldia_, x 2. _D_, part +of a filament of _Conferva_, x 300.] + +Among the marine forms related to these may be mentioned the sea +lettuce (_Ulva_), shown in Figure 15. The thin, bright-green, +leaf-like fronds of this plant are familiar to every seaside student. + +[Illustration: FIG. 15.--A plant of sea lettuce (_Ulva_). One-half +natural size.] + +Somewhat higher than _Cladophora_ and its allies, especially in the +differentiation of the reproductive parts, are the various species of +_OEdogonium_ and its relatives. There are numerous species of +_OEdogonium_ not uncommon in stagnant water growing in company with +other algae, but seldom forming masses by themselves of sufficient size +to be recognizable to the naked eye. + + The plant is in structure much like _Cladophora_, except that it is + unbranched, and the cells have but a single nucleus (Fig. 16, _E_). + Even when not fruiting the filaments may usually be recognized by + peculiar cap-shaped structures at the top of some of the cells. + These arise as the result of certain peculiarities in the process of + cell division, which are too complicated to be explained here. + + There are two forms of reproduction, non-sexual and sexual. In the + first the contents of certain cells escape in the form of large + zooespores (Fig. 16, _C_), of oval form, having the smaller end + colorless and surrounded by a crown of cilia. After a short period + of active motion, the zooespore comes to rest, secretes a cell wall + about itself, and the transparent end becomes flattened out into a + disc (_E_, _d_), by which it fastens itself to some object in the + water. The upper part now rapidly elongates, and dividing repeatedly + by cross walls, develops into a filament like the original one. In + many species special zooespores are formed, smaller than the ordinary + ones, that attach themselves to the filaments bearing the female + reproductive organ (ooegonium), and grow into small plants bearing + the male organ (antheridium), (Fig. 16, _B_). + +[Illustration: FIG. 16.--_A_, portion of a filament of _OEdogonium_, +with two ooegonia (_og._). The lower one shows the opening. _B_, a +similar filament, to which is attached a small male plant with an +antheridium (_an._). _C_, a zooespore of _OEdogonium_. _D_, a similar +spore germinating. _E_, base of a filament showing the disc (_d_) by +which it is attached. _F_, another species of _OEdogonium_ with a ripe +spore (_sp._). _G_, part of a plant of _Bulbochaete_. _C_, _D_, x 300; +the others x 150.] + + The sexual reproduction takes place as follows: Certain cells of a + filament become distinguished by their denser contents and by an + increase in size, becoming oval or nearly globular in form (Fig. 16, + _A_, _B_). When fully grown, the contents contract and form a naked + cell, which sometimes shows a clear area at one point on the + surface. This globular mass of protoplasm is the egg cell, or female + cell, and the cell containing it is called the "ooegonium." When the + egg cell is ripe, the ooegonium opens by means of a little pore at + one side (Fig. 16, _A_). + + In other cells, either of the same filament or else of the small + male plants already mentioned, small motile cells, called + spermatozoids, are formed. These are much smaller than the egg cell, + and resemble the zooespores in form, but are much smaller, and + without chlorophyll. When ripe they are discharged from the cells in + which they were formed, and enter the ooegonium. By careful + observation the student may possibly be able to follow the + spermatozoid into the ooegonium, where it enters the egg cell at the + clear spot on its surface. As a result of the entrance of the + spermatozoid (fertilization), the egg cell becomes surrounded by a + thick brown wall, and becomes a resting spore. The spore loses its + green color, and the wall becomes dark colored and differentiated + into several layers, the outer one often provided with spines + (Fig. 16, _F_). As these spores do not germinate for a long time, + the process is only known in a comparatively small number of + species, and can hardly be followed by the ordinary student. + +[Illustration: FIG. 17.--_A_, plant of _Coleochaete_, x 50. _B_, a few +cells from the margin, with one of the hairs.] + +Much like _OEdogonium_, but differing in being branched, is the genus +_Bulbochaete_, characterized also by hairs swollen at the base, and +prolonged into a delicate filament (Fig. 16, _G_). + +The highest members of the _Confervaceae_ are those of the genus +_Coleochaete_ (Fig. 17), of which there are several species found in +the United States. These show some striking resemblances to the red +seaweeds, and possibly form a transition from the green algae to the +red. The commonest species form bright-green discs, adhering firmly +to the stems and floating leaves of water lilies and other aquatics. +In aquaria they sometimes attach themselves in large numbers to the +glass sides of the vessel. + + Growing from the upper surface are numerous hairs, consisting of a + short, sheath-like base, including a very long and delicate filament + (Fig. 17, _B_). In their methods of reproduction they resemble + _OEdogonium_, but the reproductive organs are more specialized. + + + + +CHAPTER V. + +GREEN ALGAE--_Continued_. + + +ORDER III.--POND SCUMS (_Conjugatae_). + +The _Conjugatae_, while in some respects approaching the _Confervaceae_ +in structure, yet differ from them to such an extent in some respects +that their close relationship is doubtful. They are very common and +familiar plants, some of them forming great floating masses upon the +surface of every stagnant pond and ditch, being commonly known as +"pond scum." The commonest of these pond scums belong to the genus +_Spirogyra_, and one of these will illustrate the characteristics of +the order. When in active growth these masses are of a vivid green, +and owing to the presence of a gelatinous coating feel slimy, slipping +through the hands when one attempts to lift them from the water. +Spread out in water, the masses are seen to be composed of slender +threads, often many centimetres in length, and showing no sign of +branching. + +[Illustration: FIG. 18.--_A_, a filament of a common pond scum +(_Spirogyra_) separating into two parts. _B_, a cell undergoing +division. The cell is seen in optical section, and the chlorophyll +bands are omitted, _n_, _n'_, the two nuclei. _C_, a complete cell. +_n_, nucleus. _py._ pyrenoid. _D_, _E_, successive stages in the +process of conjugation. _G_, a ripe spore. _H_, a form in which +conjugation takes place between the cells of the same filament. All +x 150.] + + For microscopical examination the larger species are preferable. + When one of these is magnified (Fig. 18, _A_, _C_), the unbranched + filament is shown to be made up of perfectly cylindrical cells, with + rather delicate walls. The protoplasm is confined to a thin layer + lining the walls, except for numerous fine filaments that radiate + from the centrally placed nucleus (_n_), which thus appears + suspended in the middle of the cell. The nucleus is large and + distinct in the larger species, and has a noticeably large and + conspicuous nucleolus. The most noticeable thing about the cell is + the green spiral bands running around it. These are the + chloroplasts, which in all the _Conjugatae_ are of very peculiar + forms. The number of these bands varies much in different species of + _Spirogyra_, but is commonly two or three. These chloroplasts, like + those of other plants, are not noticeably different in structure + from the ordinary protoplasm, as is shown by extracting the + chlorophyll, which may be done by placing the plants in alcohol for + a short time. This extracts the chlorophyll, but a microscopic + examination of the decolored cells shows that the bands remain + unchanged, except for the absence of color. These bands are + flattened, with irregularly scalloped margins, and at intervals have + rounded bodies (pyrenoids) imbedded in them (Fig. 18, _C_, _py._). + The pyrenoids, especially when the plant has been exposed to the + light for some time, are surrounded by a circle of small granules, + which become bluish when iodine is applied, showing them to be + starch. (To show the effect of iodine on starch on a large scale, + mix a little flour, which is nearly all starch, with water, and add + a little iodine. The starch will immediately become colored blue, + varying in intensity with the amount of iodine.) The cells divide + much as in _Cladophora_, but the nucleus here takes part in the + process. The division naturally occurs only at night, but by + reducing the temperature at night to near the freezing point (4 deg. C., + or a little lower), the process may be checked. The experiment is + most conveniently made when the temperature out of doors approaches + the freezing point. Then it is only necessary to keep the plants in + a warm room until about 10 P.M., when they may be put out of doors + for the night. On bringing them in in the morning, the division will + begin almost at once, and may be easily studied. The nucleus divides + into two parts, which remain for a time connected by delicate + threads (Fig. 18, _B_), that finally disappear. At first no nucleoli + are present in the daughter nuclei, but they appear before the + division is complete. + + New filaments are formed by the breaking up of the old ones, this + sometimes being very rapid. As the cells break apart, the free ends + bulge strongly, showing the pressure exerted upon the cell wall by + the contents (Fig. 18, _A_). + +Spores like those of _OEdogonium_ are formed, but the process is +somewhat different. It occurs in most species late in the spring, but +may sometimes be met with at other times. The masses of fruiting +plants usually appear brownish colored. If spores have been formed +they can, in the larger species at least, be seen with a hand lens, +appearing as rows of dark-colored specks. + + Two filaments lying side by side send out protuberances of the cell + wall that grow toward each other until they touch (Fig. 18, _D_). At + the point of contact, the wall is absorbed, forming a continuous + channel from one cell to the other. This process usually takes place + in all the cells of the two filaments, so that the two filaments, + connected by tubes at regular intervals, have the form of a ladder. + + In some species adjoining cells of the same filament become + connected, the tubes being formed at the end of the cells (Fig. 18, + _H_), and the cell in which the spore is formed enlarges. + + Soon after the channel is completed, the contents of one cell flow + slowly through it into the neighboring cell, and the protoplasm of + the two fuses into one mass. (The union of the nuclei has also been + observed.) The young spore thus formed contracts somewhat, becoming + oval in form, and soon secretes a thick wall, colorless at first, + but afterwards becoming brown and more or less opaque. The + chlorophyll bands, although much crowded, are at first + distinguishable, but later lose the chlorophyll, and become + unrecognizable. Like the resting spores of _OEdogonium_ these require + a long period of rest before germinating. + +[Illustration: FIG. 19.--Forms of _Zygnemaceae_. _A_, _Zygnema_. _B_, +_C_, _D_, _Mesocarpus_. All x 150.] + +There are various genera of the pond scums, differing in the form of +the chloroplasts and also in the position of the spores. Of these may +be mentioned _Zygnema_ (Fig. 19, _A_), with two star-shaped +chloroplasts in each cell, and _Mesocarpus_ (Fig. 19, _B_, _D_), in +which the single chloroplast has the form of a thin median plate. (B +shows the appearance from in front, _C_ from the side, showing the +thickness of the plate.) _Mesocarpus_ and the allied genera have the +spore formed between the filaments, the contents of both the uniting +cells leaving them. + +[Illustration: FIG. 20.--Forms of Desmids. _A_, _B_, _Closterium_. +_C_, _D_, _D'_, _Cosmarium_. _D_, and _D'_ show the process of +division. _E_, _F_, _Staurastrum_; _E_ seen from the side, _F_ from +the end.] + +Evidently related to the pond scums, but differing in being for the +most part strictly unicellular, are the desmids (Fig. 20). They are +confined to fresh water, and seldom occur in masses of sufficient size +to be seen with the naked eye, usually being found associated with +pond scums or other filamentous forms. Many of the most beautiful +forms may be obtained by examining the matter adhering to the leaves +and stems of many floating water plants, especially the bladder weed +(_Utricularia_) and other fine-leaved aquatics. + + The desmids include the most beautiful examples of unicellular + plants to be met with, the cells having extremely elegant outlines. + The cell shows a division into two parts, and is often constricted + in the middle, each division having a single large chloroplast of + peculiar form. The central part of the cell in which the nucleus + lies is colorless. + + Among the commonest forms, often growing with _Spirogyra_, are + various species of _Closterium_ (Fig. 20, _A_, _B_), recognizable at + once by their crescent shape. The cell appears bright green, except + at the ends and in the middle. The large chloroplast in each half is + composed of six longitudinal plates, united at the axis of the cell. + Several large pyrenoids are always found, often forming a regular + line through the central axis. At each end of the cell is a vacuole + containing small granules that show an active dancing movement. + +The desmids often have the power of movement, swimming or creeping +slowly over the slide as we examine them, but the mechanism of these +movements is still doubtful. + +In their reproduction they closely resemble the pond scums. + + +ORDER IV.--_Siphoneae_. + +The _Siphoneae_ are algae occurring both in fresh and salt water, and +are distinguished from other algae by having the form of a tube, +undivided by partition walls, except when reproduction occurs. The +only common representatives of the order in fresh water are those +belonging to the genus _Vaucheria_, but these are to be had almost +everywhere. They usually occur in shallow ditches and ponds, growing +on the bottom, or not infrequently becoming free, and floating where +the water is deeper. They form large, dark green, felted masses, and +are sometimes known as "green felts." Some species grow also on the +wet ground about springs. An examination of one of the masses shows it +to be made up of closely matted, hair-like threads, each of which is +an individual plant. + + In transferring the plants to the slide for microscopic examination, + they must be handled very carefully, as they are very easily + injured. Each thread is a long tube, branching sometimes, but not + divided into cells as in _Spirogyra_ or _Cladophora_. If we follow + it to the tip, the contents here will be found to be denser, this + being the growing point. By careful focusing it is easy to show that + the protoplasm is confined to a thin layer lining the wall, the + central cavity of the tube being filled with cell sap. In the + protoplasm are numerous elongated chloroplasts (_cl._). and a larger + or smaller number of small, shining, globular bodies (_ol._). These + latter are drops of oil, and, when the filaments are injured, + sometimes run together, and form drops of large size. No nucleus can + be seen in the living plant, but by treatment with chromic acid and + staining, numerous very small nuclei may be demonstrated. + +[Illustration: FIG. 21.--_A_, _C_, successive stages in the +development of the sexual organs of a green felt (_Vaucheria_). _an._ +antheridium. _og._ ooegonium. _D_, a ripe ooegonium. _E_, the same after +it has opened. _o_, the egg cell. _F_, a ripe spore. _G_, a species in +which the sexual organs are borne separately on the main filament. +_A_, _F_, x 150. _G_, x 50. _cl._ chloroplasts. _ol._ oil.] + + When the filaments are growing upon the ground, or at the bottom of + shallow water, the lower end is colorless, and forms a more or less + branching root-like structure, fastening it to the earth. These + rootlets, like the rest of the filament, are undivided by walls. + + One of the commonest and at the same time most characteristic + species is _Vaucheria racemosa_ (Fig. 21, _A_, _F_). The plant + multiplies non-sexually by branches pinched off by a constriction at + the point where they join the main filament, or by the filament + itself becoming constricted and separating into several parts, each + one constituting a new individual. + + The sexual organs are formed on special branches, and their + arrangement is such as to make the species instantly recognizable. + + The first sign of their development is the formation of a short + branch (Fig. 21, _A_) growing out at right angles to the main + filament. This branch becomes club-shaped, and the end somewhat + pointed and more slender, and curves over. This slender, curved + portion is almost colorless, and is soon shut off from the rest of + the branch. It is called an "antheridium," and within are produced, + by internal division, numerous excessively small spermatozoids. + + As the branch grows, its contents become very dense, the oil drops + especially increasing in number and size. About the time that the + antheridium becomes shut off, a circle of buds appears about its + base (Fig. 21, _B_, _og._). These are the young ooegonia, which + rapidly increase in size, assuming an oval form, and become + separated by walls from the main branch (_C_). Unlike the + antheridium, the ooegonia contain a great deal of chlorophyll, + appearing deep green. + + When ripe, the antheridium opens at the end and discharges the + spermatozoids, which are, however, so very small as scarcely to be + visible except with the strongest lenses. They are little oval + bodies with two cilia, which may sometimes be rendered visible by + staining with iodine. + +[Illustration: FIG. 22.--_A_, non-sexual reproduction in _Vaucheria +sessilis_. _B_, non-sexual spore of _V. geminata_, x 50.] + + The ooegonia, which at first are uniformly colored, just before + maturity show a colorless space at the top, from which the + chloroplasts and oil drops have disappeared (_D_), and at the same + time this portion pushes out in the form of a short beak. Soon after + the wall is absorbed at this point, and a portion of the contents is + forced out, leaving an opening, and at the same time the remaining + contents contract to form a round mass, the germ or egg cell + (Fig. 21, _E_, _o_). Almost as soon as the ooegonium opens, the + spermatozoids collect about it and enter; but, on account of their + minuteness, it is almost impossible to follow them into the egg + cell, or to determine whether several or only one enter. The + fertilized egg cell becomes almost at once surrounded by a wall, + which rapidly thickens, and forms a resting spore. As the spore + ripens, it loses its green color, becoming colorless, with a few + reddish brown specks scattered through it (_F_). + + In some species the sexual organs are borne directly on the filament + (Fig. 21, _G_). + + Large zooespores are formed in some of the green felts (Fig. 22, + _A_), and are produced singly in the ends of branches that become + swollen, dark green, and filled with very dense protoplasm. This end + becomes separated by a wall from the rest of the branch, the end + opens, and the contents escape as a very large zooespore, covered + with numerous short cilia (_A_ ii). After a short period of + activity, this loses its cilia, develops a wall, and begins to grow + (III, IV). Other species (_B_) produce similar spores, which, + however, are not motile, and remain within the mother cell until + they are set free by the decay of its wall. + + +ORDER V.--_Characeae_. + +The _Characeae_, or stone-worts, as some of them are called, are so +very different from the other green algae that it is highly probable +that they should be separated from them. + +The type of the order is the genus _Chara_ (Fig. 23), called +stone-worts from the coating of carbonate of lime found in most of +them, giving them a harsh, stony texture. Several species are common +growing upon the bottom of ponds and slow streams, and range in size +from a few centimetres to a metre or more in height. + +The plant (Fig. 23, _A_) consists of a central jointed axis with +circles of leaves at each joint or node. The distance between the +nodes (internodes) may in the larger species reach a length of several +centimetres. The leaves are slender, cylindrical structures, and like +the stem divided into nodes and internodes, and have at the nodes +delicate leaflets. + +At each joint of the leaf, in fruiting specimens, attached to the +inner side, are borne two small, roundish bodies, in the commoner +species of a reddish color (Fig. 23, _A_, _r_). The lower of the two +is globular, and bright scarlet in color; the other, more oval and +duller. + +Examined with a lens the main axis presents a striated appearance. The +whole plant is harsh to the touch and brittle, owing to the limy +coating. It is fastened to the ground by fine, colorless hairs, or +rootlets. + +[Illustration: FIG. 23.--_A_, plant of a stone-wort (_Chara_), +one-half natural size. _r_, reproductive organs. _B_, longitudinal +section through the apex. _S_, apical cell. _x_, nodes. _y_, +internodes. _C_, a young leaf. _D_, cross section of an internode. +_E_, of a node of a somewhat older leaf. _F_, _G_, young sexual organs +seen in optical section. _o_, ooegonium. _An._ antheridium. _H_, +superficial view. _G_, _I_, group of filaments containing +spermatozoids. _J_, a small portion of one of these more magnified, +showing a spermatozoid in each cell. _K_, free spermatozoids. _L_, a +piece of a leaf with ripe ooegonium (_o_), and antheridium (_An._). +_B_, _H_, x 150. _J_, _K_, x 300. _I_, x 50. _L_, x 25.] + + By making a series of longitudinal sections with a sharp razor + through the top of the plant, and magnifying sufficiently, it is + found to end in a single, nearly hemispherical cell (Fig. 23, _B_, + _S_). This from its position is called the "apical cell," and from + it are derived all the tissues of the plant. Segments are cut off + from its base, and these divide again into two by a wall parallel to + the first. Of the two cells thus formed one undergoes no further + division and forms the central cell of an internode (_y_); the other + divides repeatedly, forming a node or joint (_x_). + + As the arrangement of these cells is essentially the same in the + leaves and stem, we will examine it in the former, as by cutting + several cross-sections of the whole bunch of young leaves near the + top of the plant, we shall pretty certainly get some sections + through a joint. The arrangement is shown in Figure 23, _E_. + + As the stem grows, a covering is formed over the large internodal + cell (_y_) by the growth of cells from the nodes. These grow both + from above and below, meeting in the middle of the internode and + completely hiding the long axial cell. A section across the + internode shows the large axial cell (_y_) surrounded by the + regularly arranged cells of the covering or cortex (Fig. 23, _D_). + + All the cells contain a layer of protoplasm next the wall with + numerous oval chloroplasts. If the cells are uninjured, they often + show a very marked movement of the protoplasm. These movements are + best seen, however, in forms like _Nitella_, where the long + internodal cells are not covered with a cortex. In _Chara_ they are + most evident in the root hairs that fasten the plant to the ground. + + The growth of the leaves is almost identical with that of the stem, + but the apical growth is limited, and the apical cell becomes + finally very long and pointed (Fig. 23, _C_). In some species the + chloroplasts are reddish in the young cells, assuming their green + color as the cells approach maturity. + +The plant multiplies non-sexually by means of special branches that +may become detached, but there are no non-sexual spores formed. + + The sexual organs have already been noticed arising in pairs at the + joints of the leaves. The ooegonium is formed above, the antheridium + below. + + The young ooegonium (_F_, _O_) consists of a central cell, below + which is a smaller one surrounded by a circle of five others, which + do not at first project above the central cell, but later completely + envelop it (_G_). Each of these five cells early becomes divided + into an upper and a lower one, the latter becoming twisted as it + elongates, and the central cell later has a small cell cut off from + its base by an oblique wall. The central cell forms the egg cell, + which in the ripe ooegonium (_L_, _O_) is surrounded by five, + spirally twisted cells, and crowned by a circle of five smaller + ones, which become of a yellowish color when full grown. They + separate at the time of fertilization to allow the spermatozoids to + enter the ooegonium. + + The antheridium consists at first of a basal cell and a terminal + one. The latter, which is nearly globular, divides into eight nearly + similar cells by walls passing through the centre. In each of these + eight cells two walls are next formed parallel to the outer surface, + so that the antheridium (apart from the basal cell) contains + twenty-four cells arranged in three concentric series (_G_, _an._). + These cells, especially the outer ones, develop a great amount of a + red pigment, giving the antheridium its characteristic color. + + The diameter of the antheridium now increases rapidly, and the + central cells separate, leaving a large space within. Of the inner + cells, the second series, while not increasing in diameter, + elongate, assuming an oblong form, and from the innermost are + developed long filaments (_I_, _J_) composed of a single row of + cells, in each of which is formed a spermatozoid. + + The eight outer cells are nearly triangular in outline, fitting + together by deeply indented margins, and having the oblong cells + with the attached filaments upon their inner faces. + + If a ripe antheridium is crushed in a drop of water, after lying a + few minutes the spermatozoids will escape through small openings in + the side of the cells. They are much larger than any we have met + with. Each is a colorless, spiral thread with about three coils, one + end being somewhat dilated with a few granules; the other more + pointed, and bearing two extremely long and delicate cilia (_K_). To + see the cilia it is necessary to kill the spermatozoids with iodine + or some other reagent. + + After fertilization the outer cells of the ooegonium become very + hard, and the whole falls off, germinating after a sufficient period + of rest. + +According to the accounts of Pringsheim and others, the young plant +consists at first of a row of elongated cells, upon which a bud is +formed that develops into the perfect plant. + +There are two families of the _Characeae_, the _Chareae_, of which +_Chara_ is the type, and the _Nitelleae_, represented by various +species of _Nitella_ and _Tolypella_. The second family have the +internodes without any cortex--that is, consisting of a single long +cell; and the crown at the top of the ooegonium is composed of ten +cells instead of five. They are also destitute of the limy coating of +the _Chareae_. + +Both as regards the structure of the plant itself, as well as the +reproductive organs, especially the very complex antheridium, the +_Characeae_ are very widely separated from any other group of plants, +either above or below them. + + + + +CHAPTER VI. + +THE BROWN ALGAE (_Phaeophyceae_). + + +[Illustration: FIG. 24.--Forms of diatoms. _A_, _Pinnularia_. i, seen +from above; ii, from the side. _B_, _Fragillaria_ (?). _C_, +_Navicula_. _D_, _F_, _Eunotia_. _E_, _Gomphonema_. _G_, _Cocconeis_. +_H_, _Diatoma_. All x 300.] + +These plants are all characterized by the presence of a brown pigment, +in addition to the chlorophyll, which almost entirely conceals the +latter, giving the plants a brownish color, ranging from a light +yellowish brown to nearly black. One order of plants that possibly +belongs here (_Diatomaceae_) are single celled, but the others are for +the most part large seaweeds. The diatoms, which are placed in this +class simply on account of the color, are probably not closely related +to the other brown algae, but just where they should be placed is +difficult to say. In some respects they approach quite closely the +desmids, and are not infrequently regarded as related to them. They +are among the commonest of organisms occurring everywhere in stagnant +and running water, both fresh and salt, forming usually, slimy, +yellowish coatings on stones, mud, aquatic plants, etc. Like the +desmids they may be single or united into filaments, and not +infrequently are attached by means of a delicate gelatinous stalk +(Fig. 25). + +[Illustration: FIG. 25.--Diatoms attached by a gelatinous stalk. +x 150] + + They are at once distinguished from the desmids by their color, + which is always some shade of yellowish or reddish brown. The + commonest forms, _e.g._ _Navicula_ (Fig. 24, _C_), are boat-shaped + when seen from above, but there is great variety in this respect. + The cell wall is always impregnated with large amounts of flint, so + that after the cell dies its shape is perfectly preserved, the flint + making a perfect cast of it, looking like glass. These flinty shells + exhibit wonderfully beautiful and delicate markings which are + sometimes so fine as to test the best lenses to make them out. + + This shell is composed of two parts, one shutting over the other + like a pill box and its cover. This arrangement is best seen in such + large forms as _Pinnularia_ (Fig. 24, _A_ ii). + +Most of the diatoms show movements, swimming slowly or gliding over +solid substances; but like the movements of _Oscillaria_ and the +desmids, the movements are not satisfactorily understood, although +several explanations have been offered. + +They resemble somewhat the desmids in their reproduction. + + +THE TRUE BROWN ALGAE. + +These are all marine forms, many of great size, reaching a length in +some cases of a hundred metres or more, and showing a good deal of +differentiation in their tissues and organs. + +[Illustration: FIG. 26.--_A_, a branch of common rock weed (_Fucus_), +one-half natural size. _x_, end of a branch bearing conceptacles. _B_, +section through a conceptacle containing ooegonia (_og._), x 25. _C_, +_E_, successive stages in the development of the ooegonium, x 150. _F_, +_G_, antheridia. In _G_, one of the antheridia has discharged the mass +of spermatozoids (_an._), x 150.] + +One of the commonest forms is the ordinary rock weed (_Fucus_), which +covers the rocks of our northeastern coast with a heavy drapery for +several feet above low-water mark, so that the plants are completely +exposed as the tide recedes. The commonest species, _F. vesiculosus_ +(Fig. 26, _A_), is distinguished by the air sacs with which the stems +are provided. The plant is attached to the rock by means of a sort of +disc or root from which springs a stem of tough, leathery texture, and +forking regularly at intervals, so that the ultimate branches are very +numerous, and the plant may reach a length of a metre or more. The +branches are flattened and leaf-like, the centre traversed by a +thickened midrib. The end of the growing branches is occupied by a +transversely elongated pit or depression. The growing point is at the +bottom of this pit, and by a regular forking of the growing point the +symmetrical branching of the plant is brought about. Scattered over +the surface are little circular pits through whose openings protrude +bunches of fine hairs. When wet the plant is flexible and leathery, +but it may become quite dry and hard without suffering, as may be seen +when the plants are exposed to the sun at low tide. + +The air bladders are placed in pairs, for the most part, and buoy up +the plant, bringing it up to the surface when covered with water. + +The interior of the plant is very soft and gelatinous, while the outer +part forms a sort of tough rind of much firmer consistence. The ends +of some of the branches (Fig. 26, _A_, _x_) are usually much swollen, +and the surface covered with little elevations from which may often be +seen protruding clusters of hairs like those arising from the other +parts of the plant. A section through one of these enlarged ends shows +that each elevation corresponds to a cavity situated below it. On some +of the plants these cavities are filled with an orange-yellow mass; in +others there are a number of roundish olive-brown bodies large enough +to be easily seen. The yellow masses are masses of antheridia; the +round bodies, the ooegonia. + +If the plants are gathered while wet, and packed so as to prevent +evaporation of the water, they will keep perfectly for several days, +and may readily be shipped for long distances. If they are to be +studied away from the seashore, sections for microscopic examination +should be mounted in salt water (about 3 parts in weight of common +salt to 100 of water). If fresh material is not to be had, dried +specimens or alcoholic material will answer pretty well. + + To study the minute structure of the plant, make a thin + cross-section, and mount in salt water. The inner part or pith is + composed of loosely arranged, elongated cells, placed end to end, + and forming an irregular network, the large spaces between filled + with the mucilaginous substance derived from the altered outer walls + of these cells. This mucilage is hard when dry, but swells up + enormously in water, especially fresh water. The cells grow smaller + and more compact toward the outside of the section, until there are + no spaces of any size between those of the outside or rind. The + cells contain small chloroplasts like those of the higher plants, + but owing to the presence of the brown pigment found in all of the + class, in addition to the chlorophyll, they appear golden brown + instead of green. + + No non-sexual reproductive bodies are known in the rock weeds, + beyond small branches that occur in clusters on the margins of the + main branches, and probably become detached, forming new plants. In + some of the lower forms, however, _e.g._ _Ectocarpus_ and + _Laminaria_ (Fig. 28, _A_, _C_), zooespores are formed. + + The sexual organs of the rock weed, as we have already seen, are + borne in special cavities (conceptacles) in the enlarged ends of + some of the branches. In the species here figured, _F. vesiculosus_, + the antheridia and ooegonia are borne on separate plants; but in + others, _e.g._ _F. platycarpus_, they are both in the same + conceptacle. + + The walls of the conceptacle (Fig. 26, _B_) are composed of closely + interwoven filaments, from which grow inward numerous hairs, filling + up the space within, and often extending out through the opening at + the top. + + The reproductive bodies arise from the base of these hairs. The + ooegonia (Fig. 26, _C_, _E_) arise as nearly colorless cells, that + early become divided into two cells, a short basal cell or stalk and + a larger terminal one, the ooegonium proper. The latter enlarges + rapidly, and its contents divide into eight parts. The division is + at first indicated by a division of the central portion, which + includes the nucleus, and is colored brown, into two, four, and + finally eight parts, after which walls are formed between these. The + brown color spreads until the whole ooegonium is of a nearly uniform + olive-brown tint. + + When ripe, the upper part of the ooegonium dissolves, allowing the + eight cells, still enclosed in a delicate membrane, to escape + (Fig. 27, _H_). Finally, the walls separating the inner cells of the + ooegonium become also absorbed, as well as the surrounding membrane, + and the eight egg cells escape into the water (Fig. 27, _I_) as + naked balls of protoplasm, in which a central nucleus may be dimly + seen. + + The antheridia (Fig. 26, _F_, _G_) are small oblong cells, at first + colorless, but when ripe containing numerous glistening, reddish + brown dots, each of which is part of a spermatozoid. When ripe, the + contents of the antheridium are forced out into the water (_G_), + leaving the empty outer wall behind, but still surrounded by a thin + membrane. After a few minutes this membrane is dissolved, and the + spermatozoids are set free. These (Fig. 27, _K_) are oval in form, + with two long cilia attached to the side where the brown speck, seen + while still within the antheridium, is conspicuous. + + The act of fertilization may be easily observed by laying fresh + antheridia into a drop of water containing recently discharged egg + cells. To obtain these, all that is necessary is to allow freshly + gathered plants to remain in the air until they are somewhat dry, + when the ripe sexual cells will be discharged from the openings of + the conceptacles, exuding as little drops, those with antheridia + being orange-yellow; the masses of ooegonia, olive. Within a few + minutes after putting the ooegonia into water, the egg cells may be + seen to escape into the water, when some of the antheridia may be + added. The spermatozoids will be quickly discharged, and collect + immediately in great numbers about the egg cells, to which they + apply themselves closely, often setting them in rotation by the + movements of their cilia, and presenting a most extraordinary + spectacle (_J_). Owing to the small size of the spermatozoids, and + the opacity of the eggs, it is impossible to see whether more than + one spermatozoid penetrates it; but from what is known in other + cases it is not likely. The egg now secretes a wall about itself, + and within a short time begins to grow. It becomes pear-shaped, the + narrow portion becoming attached to the parent plant or to some + other object by means of rootlets, and the upper part grows into the + body of the young plant (Fig. 27, _M_). + +[Illustration: FIG. 27.--_H_, the eight egg cells still surrounded by +the inner membrane of the ooegonium. _I_, the egg cells escaping into +the water. _J_, a single egg cell surrounded by spermatozoids. _K_, +mass of spermatozoids surrounded by the inner membrane of the +antheridium. _L_, spermatozoids. _M_, young plant. _r_, the roots. +_K_, x 300; _L_, x 600; the others, x 150.] + +The simpler brown seaweeds, so far as known, multiply only by means of +zooespores, which may grow directly into new plants, or, as has been +observed in some species, two zooespores will first unite. A few, like +_Ectocarpus_ (Fig. 28, _A_), are simple, branched filaments, but most +are large plants with complex tissues. Of the latter, a familiar +example is the common kelp, "devil's apron" (_Laminaria_), often three +to four metres in length, with a stout stalk, provided with root-like +organs, by which it is firmly fastened. Above, it expands into a +broad, leaf-like frond, which in some species is divided into strips. +Related to the kelps is the giant kelp of the Pacific (_Macrocystis_), +which is said sometimes to reach a length of three hundred metres. + +[Illustration: FIG. 28.--Forms of brown seaweeds. _A_, _Ectocarpus_, +x 50. Sporangia (_sp._). _B_, a single sporangium, x 150. _C_, kelp +(_Laminaria_), x 1/8. _D_, _E_, gulf weed (_Sargassum_). _D_, one-half +natural size. _E_, natural size. _v_, air bladders. _x_, conceptacle +bearing branches.] + +The highest of the class are the gulf weeds (_Sargassum_), plants of +the warmer seas, but one species of which is found from Cape Cod +southward (Fig. 28, _D_, _E_). These plants possess distinct stems and +leaves, and there are stalked air bladders, looking like berries, +giving the plant a striking resemblance to the higher land plants. + + + + +CHAPTER VII. + +CLASS III.--THE RED ALGAE (_Rhodophyceae_). + + +These are among the most beautiful and interesting members of the +plant kingdom, both on account of their beautiful colors and the +exquisitely graceful forms exhibited by many of them. Unfortunately +for inland students they are, with few exceptions, confined to salt +water, and consequently fresh material is not available. Nevertheless, +enough can be done with dried material to get a good idea of their +general appearance, and the fruiting plants can be readily preserved +in strong alcohol. Specimens, simply dried, may be kept for an +indefinite period, and on being placed in water will assume perfectly +the appearance of the living plants. Prolonged exposure, however, to +the action of fresh water extracts the red pigment that gives them +their characteristic color. This pigment is found in the chlorophyll +bodies, and usually quite conceals the chlorophyll, which, however, +becomes evident so soon as the red pigment is removed. + +The red seaweeds differ much in the complexity of the plant body, but +all agree in the presence of the red pigment, and, at least in the +main, in their reproduction. The simpler ones consist of rows of +cells, usually branching like _Cladophora_; others form cell plates +comparable to _Ulva_ (Fig. 30, _C_, _D_); while others, among which is +the well-known Irish moss (_Chondrus_), form plants of considerable +size, with pretty well differentiated tissues. In such forms the outer +cells are smaller and firmer, constituting a sort of rind; while the +inner portions are made up of larger and looser cells, and may be +called the pith. Between these extremes are all intermediate forms. + +They usually grow attached to rocks, shells, wood, or other plants, +such as the kelps and even the larger red seaweeds. They are most +abundant in the warmer seas, but still a considerable number may be +found in all parts of the ocean, even extending into the Arctic +regions. + +[Illustration: FIG. 29.--_A_, a red seaweed (_Callithamnion_), of the +natural size. _B_, a piece of the same, x 50. _t_, tetraspores. _C_ +i-v, successive stages in the development of the tetraspores, x 150. +_D_ I, II young procarps. _tr._ trichogyne. iii, young; iv, ripe spore +fruit. I, III, x 150. iv, x 50. _E_, an antheridium, x 150. _F_, spore +fruit of _Polysiphonia_. The spores are here surrounded by a case, +x 50.] + +The methods of reproduction may be best illustrated by a specific +example, and preferably one of the simpler ones, as these are most +readily studied microscopically. + +The form here illustrated (_Callithamnion_) grows attached to wharves, +etc., below low-water mark, and is extremely delicate, collapsing +completely when removed from the water. The color is a bright rosy +red, and with its graceful form and extreme delicacy it makes one of +the most beautiful of the group. + +If alcoholic material is used, it may be mounted for examination +either in water or very dilute glycerine. + + The plant is composed of much-branched, slender filaments, closely + resembling _Cladophora_ in structure, but with smaller cells + (Fig. 29, _B_). The non-sexual reproduction is by means of special + spores, which from being formed in groups of four, are known as + tetraspores. In the species under consideration the mother cell of + the tetraspores arises as a small bud near the upper end of one of + the ordinary cells (Fig. 29, _C_ i). This bud rapidly increases in + size, assuming an oval form, and becoming cut off from the cell of + the stem (Fig. 29, _C_ ii). The contents now divide into four equal + parts, arranged like the quadrants of a sphere. When ripe, the wall + of the mother cell gives way, and the four spores escape into the + water and give rise to new plants. These spores, it will be noticed, + differ in one important particular from corresponding spores in most + algae, in being unprovided with cilia, and incapable of spontaneous + movement. + + Occasionally in the same plant that bears tetraspores, but more + commonly in special ones, there are produced the sexual organs, and + subsequently the sporocarps, or fruits, developed from them. The + plants that bear them are usually stouter that the non-sexual ones, + and the masses of ripe carpospores are large enough to be readily + seen with the naked eye. + + If a plant bearing ripe spores is selected, the young stages of the + female organ (procarp) may generally be found by examining the + younger parts of the plant. The procarp arises from a single cell of + the filament. This cell undergoes division by a series of + longitudinal walls into a central cell and about four peripheral + ones (Fig. 29, _D_ i). One of the latter divides next into an upper + and a lower cell, the former growing out into a long, colorless + appendage known as a trichogyne (Fig. 29, _D_, _tr._). + + The antheridia (Fig. 29, _E_) are hemispherical masses of closely + set colorless cells, each of which develops a single spermatozoid + which, like the tetraspores, is destitute of cilia, and is dependent + upon the movement of the water to convey it to the neighborhood of + the procarp. Occasionally one of these spermatozoids may be found + attached to the trichogyne, and in this way fertilization is + effected. Curiously enough, neither the cell which is immediately + fertilized, nor the one beneath it, undergo any further change; but + two of the other peripheral cells on opposite sides of the filament + grow rapidly and develop into large, irregular masses of spores + (Fig. 29, _D_ III, IV). + +While the plant here described may be taken as a type of the group, +it must be borne in mind that many of them differ widely, not only in +the structure of the plant body, but in the complexity of the sexual +organs and spores as well. The tetraspores are often imbedded in the +tissues of the plant, or may be in special receptacles, nor are they +always arranged in the same way as here described, and the same is +true of the carpospores. These latter are in some of the higher forms, +_e.g._ _Polysiphonia_ (Fig. 29, _F_), contained in urn-shaped +receptacles, or they may be buried within the tissues of the plant. + +[Illustration: FIG. 30.--Marine red seaweeds. _A_, _Dasya_. _B_, +_Rhodymenia_ (with smaller algae attached). _C_, _Grinnellia_. _D_, +_Delesseria_. _A_, _B_, natural size; the others reduced one-half.] + +The fresh-water forms are not common, but may occasionally be met with +in mill streams and other running water, attached to stones and +woodwork, but are much inferior in size and beauty to the marine +species. The red color is not so pronounced, and they are, as a rule, +somewhat dull colored. + +[Illustration: FIG. 31.--Fresh-water red algae. _A_, _Batrachospermum_, +x about 12. _B_, a branch of the same, x 150. _C_, _Lemanea_, natural +size.] + +The commonest genera are _Batrachospermum_ and _Lemanea_ (Fig. 31). + + + + +CHAPTER VIII. + +SUB-KINGDOM III. + +FUNGI. + + +The name "Fungi" has been given to a vast assemblage of plants, +varying much among themselves, but on the whole of about the same +structural rank as the algae. Unlike the algae, however, they are +entirely destitute of chlorophyll, and in consequence are dependent +upon organic matter for food, some being parasites (growing upon +living organisms), others saprophytes (feeding on dead matter). Some +of them show close resemblances in structure to certain algae, and +there is reason to believe that they are descended from forms that +originally had chlorophyll; others are very different from any green +plants, though more or less evidently related among themselves. +Recognizing then these distinctions, we may make two divisions of the +sub-kingdom: I. The Alga-Fungi (_Phycomycetes_), and II. The True +Fungi (_Mycomycetes_). + + +CLASS I.--_Phycomycetes_. + +These are fungi consisting of long, undivided, often branching tubular +filaments, resembling quite closely those of _Vaucheria_ or other +_Siphoneae_, but always destitute of any trace of chlorophyll. The +simplest of these include the common moulds (_Mucorini_), one of which +will serve to illustrate the characteristics of the order. + +If a bit of fresh bread, slightly moistened, is kept under a bell jar +or tumbler in a warm room, in the course of twenty-four hours or so it +will be covered with a film of fine white threads, and a little later +will produce a crop of little globular bodies mounted on upright +stalks. These are at first white, but soon become black, and the +filaments bearing them also grow dark-colored. + +These are moulds, and have grown from spores that are in the +atmosphere falling on the bread, which offers the proper conditions +for their growth and multiplication. + +One of the commonest moulds is the one here figured (Fig. 32), and +named _Mucor stolonifer_, from the runners, or "stolons," by which it +spreads from one point to another. As it grows it sends out these +runners along the surface of the bread, or even along the inner +surface of the glass covering it. They fasten themselves at intervals +to the substratum, and send up from these points clusters of short +filaments, each one tipped with a spore case, or "sporangium." + + For microscopical study they are best mounted in dilute glycerine + (about one-quarter glycerine to three-quarters pure water). After + carefully spreading out the specimens in this mixture, allow a drop + of alcohol to fall upon the preparation, and then put on the cover + glass. The alcohol drives out the air, which otherwise interferes + badly with the examination. + + The whole plant consists of a very long, much-branched, but + undivided tubular filament. Where it is in contact with the + substratum, root-like outgrowths are formed, not unlike those + observed in _Vaucheria_. At first the walls are colorless, but later + become dark smoky brown in color. A layer of colorless granular + protoplasm lines the wall, becoming more abundant toward the growing + tips of the branches. The spore cases, "sporangia," arise at the + ends of upright branches (Fig. 32, _C_), which at first are + cylindrical (_a_), but later enlarge at the end (_b_), and become + cut off by a convex wall (_c_). This wall pushes up into the young + sporangium, forming a structure called the "columella." When fully + grown, the sporangium is globular, and appears quite opaque, owing + to the numerous granules in the protoplasm filling the space between + the columella and its outer wall. This protoplasm now divides into a + great number of small oval cells (spores), which rapidly darken, + owing to a thick, black wall formed about each one, and at the same + time the columella and the stalk of the sporangium become + dark-colored. + + When ripe, the wall of the sporangium dissolves, and the spores + (Fig. 32, _E_) are set free. The columella remains unchanged, and + some of the spores often remain sticking to it (Fig. 32, _D_). + +[Illustration: FIG. 32.--_A_, common black mould (_Mucor_), x 5. _B_, +three nearly ripe spore cases, x 25. _C_, development of the spore +cases, i-iv, x 150; v, x 50. _D_, spore case which has discharged its +spores. _E_, spores, x 300. _F_, a form of _Mucor mucedo_, with small +accessory spore cases, x 5. _G_, the spore cases, x 50. _H_, a single +spore case, x 300. _I_, development of the zygospore of a black mould, +x 45 (after De Bary).] + + Spores formed in a manner strongly recalling those of the pond scums + are also known, but only occur after the plants have grown for a + long time, and hence are rarely met with (Fig. 32, _I_). + +Another common mould (_M. mucedo_), often growing in company with the +one described, differs from it mainly in the longer stalk of the +sporangium, which is also smaller, and in not forming runners. This +species sometimes bears clusters of very small sporangia attached to +the middle of the ordinary sporangial filament (Fig. 32, _F_, _H_). +These small sporangia have no columella. + +Other moulds are sometimes met with, parasitic upon the larger species +of _Mucor_. + +Related to the black moulds are the insect moulds (_Entomopthoreae_), +which attack and destroy insects. The commonest of these attacks the +house flies in autumn, when the flies, thus infested, may often be +found sticking to window panes, and surrounded by a whitish halo of +the spores that have been thrown off by the fungus. + + +ORDER II.--WHITE RUSTS AND MILDEWS (_Peronosporeae_) + +These are exclusively parasitic fungi, and grow within the tissues of +various flowering plants, sometimes entirely destroying them. + +As a type of this group we will select a very common one (_Cystopus +bliti_), that is always to be found in late summer and autumn growing +on pig weed (_Amarantus_). It forms whitish, blister-like blotches +about the size of a pin head on the leaves and stems, being commonest +on the under side of the leaves (Fig. 33, _A_). In the earlier stages +the leaf does not appear much affected, but later becomes brown and +withered about the blotches caused by the fungus. + + If a thin vertical section of the leaf is made through one of these + blotches, and mounted as described for _Mucor_, the latter is found + to be composed of a mass of spores that have been produced below the + epidermis of the leaf, and have pushed it up by their growth. If the + section is a very thin one, we may be able to make out the structure + of the fungus, and then find it to be composed of irregular, + tubular, much-branched filaments, which, however, are not divided by + cross-walls. These filaments run through the intercellular spaces of + the leaf, and send into the cells little globular suckers, by means + of which the fungus feeds. + + The spores already mentioned are formed at the ends of crowded + filaments, that push up, and finally rupture the epidermis (Fig. 33, + _B_). They are formed by the ends of the filaments swelling up and + becoming constricted, so as to form an oval spore, which is then cut + off by a wall. The portion of the filament immediately below acts in + the same way, and the process is repeated until a chain of half a + dozen or more may be produced, the lowest one being always the last + formed. When ripe, the spores are separated by a thin neck, and + become very easily broken off. + + In order to follow their germination it is only necessary to place a + few leaves with fresh patches of the fungus under a bell jar or + tumbler, inverted over a dish full of water, so as to keep the air + within saturated with moisture, but taking care to keep the leaves + out of the water. After about twenty-four hours, if some of the + spores are scraped off and mounted in water, they will germinate in + the course of an hour or so. The contents divide into about eight + parts, which escape from the top of the spore, which at this time + projects as a little papilla. On escaping, each mass of protoplasm + swims away as a zooespore, with two extremely delicate cilia. After a + short time it comes to rest, and, after developing a thin cell wall, + germinates by sending out one or two filaments (Fig. 33, _C_, _E_). + +[Illustration: FIG. 33.--_A_, leaf of pig-weed (_Amarantus_), with +spots of white rust (_c_), one-half natural size. _B_, non-sexual +spores (conidia). _C_, the same germinating. _D_, zooespores. _E_, +germinating zooespores. _sp._ the spore. _F_, young. _G_, mature sexual +organs. In _G_, the tube may be seen connecting the antheridium +(_an._), with the egg cell (_o_). _H_, a ripe resting spore still +surrounded by the wall of the ooegonium. _I_, a part of a filament of +the fungus, showing its irregular form. All x 300.] + + Under normal conditions the spores probably germinate when the + leaves are wet, and the filaments enter the plant through the + breathing pores on the lower surface of the leaves, and spread + rapidly through the intercellular spaces. + + Later on, spores of a very different kind are produced. Unlike those + already studied, they are formed some distance below the epidermis, + and in order to study them satisfactorily, the fungus must be freed + from the host plant. In order to do this, small pieces of the leaf + should be boiled for about a minute in strong caustic potash, and + then treated with acetic or hydrochloric acid. By this means the + tissues of the leaf become so soft as to be readily removed, while + the fungus is but little affected. The preparation should now be + washed and mounted in dilute glycerine. + + The spores (ooespores) are much larger than those first formed, and + possess an outer coat of a dark brown color (Fig. 33, _H_). Each + spore is contained in a large cell, which arises as a swelling of + one of the filaments, and becomes shut off by a wall. At first + (Fig. 33, _F_) its contents are granular, and fill it completely, + but later contract to form a globular mass of protoplasm (G. + _o_), the germ cell or egg cell. The whole is an ooegonium, and + differs in no essential respect from that of _Vaucheria_. + + Frequently a smaller cell (antheridium), arising from a neighboring + filament, and in close contact with the ooegonium, may be detected + (Fig. 33, _F_, _G_, _an._), and in exceptionally favorable cases a + tube is to be seen connecting it with the germ cell, and by means of + which fertilization is effected. + + After being fertilized, the germ cell secretes a wall, at first thin + and colorless, but later becoming thick and dark-colored on the + outside, and showing a division into several layers, the outermost + of which is dark brown, and covered with irregular reticulate + markings. These spores do not germinate at once, but remain over + winter unchanged. + +[Illustration: FIG. 34.--Fragment of a filament of the white rust of +the shepherd's-purse, showing the suckers (_h_), x 300.] + +It is by no means impossible that sometimes the germ cell may develop +into a spore without being fertilized, as is the case in many of the +water moulds. + +Closely related to the species above described is another one +(_C. candidus_), which attacks shepherd's-purse, radish, and others of +the mustard family, upon which it forms chalky white blotches, and +distorts the diseased parts of the plant very greatly. + + For some reasons this is the best species for study, longitudinal + sections through the stem showing very beautifully the structure of + the fungus, and the penetration of the cells of the host[4] by the + suckers (Fig. 34). + +[4] "Host," the plant or animal upon which a parasite lives. + +[Illustration: FIG. 35.--Non-sexual spores of the vine mildew +(_Peronospora viticola_), x 150.] + +Very similar to the white rusts in most respects, but differing in the +arrangement of the non-sexual spores, are the mildews (_Peronospora_, +_Phytophthora_). These plants form mouldy-looking patches on the +leaves and stems of many plants, and are often very destructive. Among +them are the vine mildew (_Peronospora viticola_) (Fig. 35), the +potato fungus (_Phytophthora infestans_), and many others. + + +ORDER III.--_Saprolegniaceae_ (WATER MOULDS). + +These plants resemble quite closely the white rusts, and are probably +related to them. They grow on decaying organic matter in water, or +sometimes on living water animals, fish, crustaceans, etc. They may +usually be had for study by throwing into water taken from a stagnant +pond or aquarium, a dead fly or some other insect. After a few days it +will probably be found covered with a dense growth of fine, white +filaments, standing out from it in all directions (Fig. 36, _A_). +Somewhat later, if carefully examined with a lens, little round, white +bodies may be seen scattered among the filaments. + +[Illustration: FIG. 36.--_A_, an insect that has decayed in water, and +become attacked by a water mould (_Saprolegnia_), natural size. _B_, a +ripe zooesporangium, x 100. _C_, the same discharging the spores. _D_, +active. _E_, germinating zooespores, x 300. _F_, a second sporangium +forming below the empty one. _G_ i-iv, development of the ooegonium, +x 100. _H_, ripe ooegonium filled with resting spores, x 100.] + + On carefully removing a bit of the younger growth and examining it + microscopically, it is found to consist of long filaments much like + those of _Vaucheria_, but entirely destitute of chlorophyll. In + places these filaments are filled with densely granular protoplasm, + which when highly magnified exhibits streaming movements. The + protoplasm contains a large amount of oil in the form of small, + shining drops. + + In the early stages of its growth the plant multiplies by zooespores, + produced in great numbers in sporangia at the ends of the branches. + The protoplasm collects here much as we saw in _V. sessilis_, the + end of the filament becoming club-shaped and ending in a short + protuberance (Fig. 36, _B_). This end becomes separated by a wall, + and the contents divide into numerous small cells that sometimes are + naked, and sometimes have a delicate membrane about them. The first + sign of division is the appearance in the protoplasm of delicate + lines dividing it into numerous polygonal areas which soon become + more distinct, and are seen to be distinct cells whose outlines + remain more or less angular on account of the mutual pressure. When + ripe, the end of the sporangium opens, and the contained cells are + discharged (Fig. 36, _C_). In case they have no membrane, they swim + away at once, each being provided with two cilia, and resembling + almost exactly the zooespores of the white rust (Fig. 36, _D_, _E_). + When the cells are surrounded by a membrane they remain for some + time at rest, but finally the contents escape as a zooespore, like + those already described. By killing the zooespores with a little + iodine the granular nature of the protoplasm is made more evident, + and the cilia may be seen. They soon come to rest, and germinate in + the same way as those of the white rusts and mildews. + + As soon as the sporangium is emptied, a new one is formed, either by + the filament growing up through it (Fig. 36, _F_) and the end being + again cut off, or else by a branch budding out just below the base + of the empty sporangium, and growing up by the side of it. + + Besides zooespores there are also resting spores developed. Ooegonia + like those of _Vaucheria_ or the _Peronosporeae_ are formed usually + after the formation of zooespores has ceased; but in many cases, + perhaps all, these develop without being fertilized. Antheridia are + often wanting, and even when they are present, it is very doubtful + whether fertilization takes place.[5] + +[5] The antheridia, when present, arise as branches just below the +ooegonium, and become closely applied to it, sometimes sending tubes +through its wall, but there has been no satisfactory demonstration of +an actual transfer of the contents of the antheridium to the egg cell. + + The ooegonia (Fig. 36, _G_, _H_) arise at the end of the main + filaments, or of short side branches, very much as do the sporangia, + from which they differ at this stage in being of globular form. The + contents contract to form one or several egg cells, naked at first, + but later becoming thick-walled resting spores (_H_). + + + + +CHAPTER IX. + +THE TRUE FUNGI (_Mycomycetes_). + + +The great majority of the plants ordinarily known as _fungi_ are +embraced under this head. While some of the lower forms show +affinities with the _Phycomycetes_, and through them with the algae, +the greater number differ very strongly from all green plants both in +their habits and in their structure and reproduction. It is a +much-disputed point whether sexual reproduction occurs in any of them, +and it is highly probable that in the great majority, at any rate, the +reproduction is purely non-sexual. + +Probably to be reckoned with the _Mycomycetes_, but of doubtful +affinities, are the small unicellular fungi that are the main causes +of alcoholic fermentation; these are the yeast fungi (_Saccharomycetes_). +They cause the fermentation of beer and wine, as well as the incipient +fermentation in bread, causing it to "rise" by the giving off of +bubbles of carbonic acid gas during the process. + +If a little common yeast is put into water containing starch or sugar, +and kept in a warm place, in a short time bubbles of gas will make +their appearance, and after a little longer time alcohol may be +detected by proper tests; in short, alcoholic fermentation is taking +place in the solution. + + If a little of the fermenting liquid is examined microscopically, it + will be found to contain great numbers of very small, oval cells, + with thin cell walls and colorless contents. A careful examination + with a strong lens (magnifying from 500-1000 diameters) shows that + the protoplasm, in which are granules of varying size, does not fill + the cell completely, but that there are one or more large vacuoles + or spaces filled with colorless cell sap. No nucleus is visible in + the living cell, but it has been shown that a nucleus is present. + + If growth is active, many of the cells will be seen dividing. The + process is somewhat different from ordinary fission and is called + budding (Fig. 37, _B_). A small protuberance appears at the bud or + at the side of the cell, and enlarges rapidly, assuming the form of + the mother cell, from which it becomes completely separated by the + constriction of the base, and may fall off at once, or, as is more + frequently the case, may remain attached for a time, giving rise + itself to other buds, so that not infrequently groups of half a + dozen or more cells are met with (Fig. 37, _B_, _C_). + +[Illustration: FIG. 37.--_A_, single cells of yeast. _B_, _C_, similar +cells, showing the process of budding, x 750.] + +That the yeast cells are the principal agents of alcoholic +fermentation may be shown in much the same way that bacteria are shown +to cause ordinary decomposition. Liquids from which they are excluded +will remain unfermented for an indefinite time. + +There has been much controversy as to the systematic position of the +yeast fungi, which has not yet been satisfactorily settled, the +question being whether they are to be regarded as independent plants +or only one stage in the life history of some higher fungi (possibly +the _Smuts_), which through cultivation have lost the power of +developing further. + + +CLASS I.--THE SMUTS (_Ustillagineae_). + +The smuts are common and often very destructive parasitic fungi, +living entirely within the tissues of the higher plants. Owing to +this, as well as to the excessively small spores and difficulty in +germinating them, the plants are very difficult of study, except in a +general way, and we will content ourselves with a glance at one of the +common forms, the corn smut (_Ustillago maydis_). This familiar fungus +attacks Indian corn, forming its spores in enormous quantities in +various parts of the diseased plant, but particularly in the flowers +("tassel" and young ear). + + The filaments, which resemble somewhat those of the white rusts, + penetrate all parts of the plant, and as the time approaches for the + formation of the spores, these branch extensively, and at the same + time become soft and mucilaginous (Fig. 38, _B_). The ends of these + short branches enlarge rapidly and become shut off by partitions, + and in each a globular spore (Fig. 38, _C_) is produced. The outer + wall is very dark-colored and provided with short spines. To study + the filaments and spore formation, very thin sections should be made + through the young kernels or other parts in the vicinity, before + they are noticeably distorted by the growth of the spore-bearing + filaments. + +[Illustration: FIG. 38.--_A_, "tassel" of corn attacked by smut +(_Ustillago_). _B_, filaments of the fungus from a thin section of a +diseased grain, showing the beginning of the formation of the spores, +x 300. _C_, ripe spores, x 300.] + +As the spores are forming, an abnormal growth is set up in the cells +of the part attacked, which in consequence becomes enormously enlarged +(Fig. 38, _A_), single grains sometimes growing as large as a walnut. +As the spores ripen, the affected parts, which are at first white, +become a livid gray, due to the black spores shining through the +overlying white tissues. Finally the masses of spores burst through +the overlying cells, appearing like masses of soot, whence the popular +name for the plant. + +The remaining _Mycomycetes_ are pretty readily divisible into two +great classes, based upon the arrangement of the spores. The first of +these is known as the _Ascomycetes_ (Sac fungi), the other the +_Basidiomycetes_ (mushrooms, puff-balls, etc.). + + +CLASS II.--_Ascomycetes_ (SAC FUNGI). + +This class includes a very great number of common plants, all +resembling each other in producing spores in sacs (_asci_, sing. +_ascus_) that are usually oblong in shape, and each containing eight +spores, although the number is not always the same. Besides the spores +formed in these sacs (ascospores), there are other forms produced in +various ways. + +There are two main divisions of the class, the first including only a +few forms, most of which are not likely to be met with by the student. +In these the spore sacs are borne directly upon the filaments without +any protective covering. The only form that is at all common is a +parasitic fungus (_Exoascus_) that attacks peach-trees, causing the +disease of the leaves known as "curl." + +All of the common _Ascomycetes_ belong to the second division, and +have the spore sacs contained in special structures called spore +fruits, that may reach a diameter of several centimetres in a few +cases, though ordinarily much smaller. + +Among the simpler members of this group are the mildews +(_Perisporiaceae_), mostly parasitic forms, living upon the leaves and +stems of flowering plants, sometimes causing serious injury by their +depredations. They form white or grayish downy films on the surface of +the plant, in certain stages looking like hoar-frost. Being very +common, they may be readily obtained, and are easily studied. One of +the best species for study (_Podosphaera_) grows abundantly on the +leaves of the dandelion, especially when the plants are growing under +unfavorable conditions. The same species is also found on other plants +of the same family. It may be found at almost any time during the +summer; but for studying, the spore fruits material should be +collected in late summer or early autumn. It at first appears as +white, frost-like patches, growing dingier as it becomes older, and +careful scrutiny of the older specimens will show numerous brown or +blackish specks scattered over the patches. These are the spore +fruits. + +[Illustration: FIG. 39.--_A_, spore-bearing filaments of the dandelion +mildew (_Podosphaera_), x 150. _B_, a germinating spore, x 150. _C-F_, +development of the spore fruit, x 300. _ar._ archicarp. _G_, a ripe +spore fruit, x 150. _H_, the spore sac removed from the spore fruit, +x 150. _I_, spore-bearing filament attacked by another fungus +(_Cicinnobulus_), causing the enlargement of the basal cell, x 150. +_J_, a more advanced stage, x 300. _K_, spores, x 300.] + + For microscopical study, fresh material may be used, or, if + necessary, dried specimens. The latter, before mounting, should be + soaked for a short time in water, to which has been added a few + drops of caustic-potash solution. This will remove the brittleness, + and swell up the dried filaments to their original proportions. A + portion of the plant should be carefully scraped off the leaf on + which it is growing, thoroughly washed in pure water, and + transferred to a drop of water or very dilute glycerine, in which it + should be carefully spread out with needles. If air bubbles + interfere with the examination, they may be driven off with alcohol, + and then the cover glass put on. If the specimen is mounted in + glycerine, it will keep indefinitely, if care is taken to seal it + up. The plant consists of much-interlaced filaments, divided at + intervals by cross-walls.[6] They are nearly colorless, and the + contents are not conspicuous. These filaments send up vertical + branches (Fig. 39, _A_), that become divided into a series of short + cells by means of cross-walls. The cells thus formed are at first + cylindrical, but later bulge out at the sides, becoming broadly + oval, and finally become detached as spores (_conidia_). It is these + spores that give the frosty appearance to the early stages of the + fungus when seen with the naked eye. The spores fall off very easily + when ripe, and germinate quickly in water, sending out two or more + tubes that grow into filaments like those of the parent plant + (Fig. 39, _B_). + +[6] The filaments are attached to the surface of the leaf by suckers, +which are not so readily seen in this species as in some others. A +mildew growing abundantly in autumn on the garden chrysanthemum, +however, shows them very satisfactorily if a bit of the epidermis of a +leaf on which the fungus is just beginning to grow is sliced off with +a sharp razor and mounted in dilute glycerine, or water, removing the +air with alcohol. These suckers are then seen to be globular bodies, +penetrating the outer wall of the cell (Fig. 40). + +[Illustration: FIG. 40.--Chrysanthemum mildew (_Erysiphe_), showing +the suckers (_h_) by which the filaments are attached to the leaf. +_A_, surface view. _B_, vertical section of the leaf, x 300.] + + The spore fruits, as already observed, are formed toward the end of + the season, and, in the species under consideration at least, appear + to be the result of a sexual process. The sexual organs (if they are + really such) are extremely simple, and, owing to their very small + size, are not easily found. They arise as short branches at a point + where two filaments cross; one of them (Fig. 39, _C_, _ar._), the + female cell, or "archicarp," is somewhat larger than the other and + nearly oval in form, and soon becomes separated by a partition from + the filament that bears it. The other branch (antheridium) grows up + in close contact with the archicarp, and like it is shut off by a + partition from its filament. It is more slender than the archicarp, + but otherwise differs little from it. No actual communication can be + shown to be present between the two cells, and it is therefore still + doubtful whether fertilization really takes place. Shortly after + these organs are full-grown, several short branches grow up about + them, and soon completely envelop them (_D_, _E_). These branches + soon grow together, and cross-walls are formed in them, so that the + young spore fruit appears surrounded by a single layer of cells, + sufficiently transparent, however, to allow a view of the interior. + + The antheridium undergoes no further change, but the archicarp soon + divides into two cells,--a small basal one and a larger upper cell. + There next grow from the inner surface of the covering cells, short + filaments, that almost completely fill the space between the + archicarp and the wall. An optical section of such a stage (Fig. 39, + _F_) shows a double wall and the two cells of the archicarp. The + spore fruit now enlarges rapidly, and the outer cells become first + yellow and then dark brown, the walls becoming thicker and harder as + they change color. Sometimes special filaments or appendages grow + out from their outer surfaces, and these are also dark-colored. + Shortly before the fruit is ripe, the upper cell of the archicarp, + which has increased many times in size, shows a division of its + contents into eight parts, each of which develops a wall and becomes + an oval spore. By crushing the ripe spore fruit, these spores still + enclosed in the mother cell (ascus) may be forced out (Fig. 39, + _H_). These spores do not germinate at once, but remain dormant + until the next year. + +[Illustration: FIG. 41.--Forms of mildews (_Erysiphe_). _A_, +_Microsphaera_, a spore fruit, x 150. _B_, cluster of spore sacs of the +same, x 150. _C_, a single appendage, x 300. _D_, end of an appendage +of _Uncinula_, x 300. _E_, appendage of _Phyllactinia_, x 150.] + + Frequently other structures, resembling somewhat the spore fruits, + are found associated with them (Fig. 39, _I_, _K_), and were for a + long time supposed to be a special form of reproductive organ; but + they are now known to belong to another fungus (_Cicinnobulus_), + parasitic upon the mildew. They usually appear at the base of the + chains of conidia, causing the basal cell to enlarge to many times + its original size, and finally kill the young conidia, which shrivel + up. A careful examination reveals the presence of very fine + filaments within those of the mildew, which may be traced up to the + base of the conidial branch, where the receptacle of the parasite is + forming. The spores contained in these receptacles are very small + (Fig. 39, _K_), and when ripe exude in long, worm-shaped masses, if + the receptacle is placed in water. + +The mildews may be divided into two genera: _Podosphaera_, with a +single ascus in the spore fruit; and _Erysiphe_, with two or more. In +the latter the archicarp branches, each branch bearing a spore sac +(Fig. 41, _B_). + +The appendages growing out from the wall of the spore fruit are often +very beautiful in form, and the two genera given above are often +subdivided according to the form of these appendages. + +A common mould closely allied to the mildews is found on various +articles of food when allowed to remain damp, and is also very common +on botanical specimens that have been poorly dried, and hence is often +called "herbarium mould" (_Eurotium herbariorum_). + +[Illustration: FIG. 42.--_A_, spore bearing filament of the herbarium +mould (_Eurotium_), x 150. _B_, _C_, another species showing the way +in which the spores are borne--optical section--x 150. _D_, spore +fruit of the herbarium mould, x 150. _E_, spore sac. _F_, spores, +x 300. _G_, spore-bearing filament of the common blue mould +(_Penicillium_), x 300. _sp._ the spores.] + + The conidia are of a greenish color, and produced on the ends of + upright branches which are enlarged at the end, and from which grow + out little prominences, which give rise to the conidia in the same + way as we have seen in the mildews (Fig. 42, _A_). + + Spore fruits much like those of the mildews are formed later, and + are visible to the naked eye as little yellow grains (Fig. 42, _D_). + These contain numerous very small spore sacs (_E_), each with eight + spores. + +There are numerous common species of _Eurotium_, differing in color +and size, some being yellow or black, and larger than the ordinary +green form. + +Another form, common everywhere on mouldy food of all kinds, as well +as in other situations, is the blue mould (_Penicillium_). This, in +general appearance, resembles almost exactly the herbarium mould, but +is immediately distinguishable by a microscopic examination (Fig. 42, +_G_). + + In studying all of these forms, they may be mounted, as directed for + the black moulds, in dilute glycerine; but must be handled with + great care, as the spores become shaken off with the slightest jar. + +Of the larger _Ascomycetes_, the cup fungi (_Discomycetes_) may be +taken as types. The spore fruit in these forms is often of +considerable size, and, as their name indicates, is open, having the +form of a flat disc or cup. A brief description of a common one will +suffice to give an idea of their structure and development. + +_Ascobolus_ (Fig. 43) is a small, disc-shaped fungus, growing on horse +dung. By keeping some of this covered with a bell jar for a week or +two, so as to retain the moisture, at the end of this time a large +crop of the fungus will probably have made its appearance. The part +visible is the spore fruit (Fig. 43, _A_), of a light brownish color, +and about as big as a pin-head. + + Its development may be readily followed by teasing out in water the + youngest specimens that can be found, taking care to take up a + little of the substratum with it, as the earliest stages are too + small to be visible to the naked eye. The spore fruits arise from + filaments not unlike those of the mildews, and are preceded by the + formation of an archicarp composed of several cells, and readily + seen through the walls of the young fruit (Fig. 43, _B_). In the + study of the early stages, a potash solution will be found useful in + rendering them transparent. + + The young fruit has much the same structure as that of the mildews, + but the spore sacs are much more numerous, and there are special + sterile filaments developed between them. If the young spore fruit + is treated with chlor-iodide of zinc, it is rendered quite + transparent, and the young spore sacs colored a beautiful blue, so + that they are readily distinguishable. + +[Illustration: FIG. 43.--_A_, a small cup fungus (_Ascobolus_), x 5. +_B_, young spore fruit, x 300. _ar._ archicarp. _C_, an older one, +x 150. _ar._ archicarp. _sp._ young spore sacs. _D_, section through a +full-grown spore fruit (partly diagrammatic), x 25. _sp._ spore sacs. +_E_, development of spore sacs and spores: i-iii, x 300; iv, x 150. +_F_, ripe spores. _G_, a sterile filament (paraphysis), x 300. _H_, +large scarlet cup fungus (_Peziza_), natural size.] + + The development of the spore sacs may be traced by carefully + crushing the young spore fruits in water. The young spore sacs + (Fig. 43, _E_ i) are colorless, with granular protoplasm, in which a + nucleus can often be easily seen. The nucleus subsequently divides + repeatedly, until there are eight nuclei, about which the protoplasm + collects to form as many oval masses, each of which develops a wall + and becomes a spore (Figs. ii-iv). These are imbedded in protoplasm, + which is at first granular, but afterwards becomes almost + transparent. As the spores ripen, the wall acquires a beautiful + violet-purple color, changing later to a dark purple-brown, and + marked with irregular longitudinal ridges (Fig. 43, _F_). The + full-grown spore sacs (Fig. 43, _E_, _W_) are oblong in shape, and + attached by a short stalk. The sterile filaments between them often + become curiously enlarged at the end (_G_). As the spore fruit + ripens, it opens at the top, and spreads out so as to expose the + spore sacs as they discharge their contents (Fig. 43, _D_). + +Of the larger cup fungi, those belonging to the genus _Peziza_ +(Fig. 43, _H_) are common, growing on bits of rotten wood on the +ground in woods. They are sometimes bright scarlet or orange-red, and +very showy. Another curious form is the morel (_Morchella_), common in +the spring in dry woods. It is stalked like a mushroom, but the +surface of the conical cap is honeycombed with shallow depressions, +lined with the spore sacs. + + +ORDER _Lichenes_. + +Under the name of lichens are comprised a large number of fungi, +differing a good deal in structure, but most of them not unlike the +cup fungi. They are, with few exceptions, parasitic upon various forms +of algae, with which they are so intimately associated as to form +apparently a single plant. They grow everywhere on exposed rocks, on +the ground, trunks of trees, fences, etc., and are found pretty much +the world over. Among the commonest of plants are the lichens of the +genus _Parmelia_ (Fig. 44, _A_), growing everywhere on tree trunks, +wooden fences, etc., forming gray, flattened expansions, with much +indented and curled margins. When dry, the plant is quite brittle, but +on moistening becomes flexible, and at the same time more or less +decidedly green in color. The lower surface is white or brown, and +often develops root-like processes by which it is fastened to the +substratum. Sometimes small fragments of the plant become detached in +such numbers as to form a grayish powder over certain portions of it. +These, when supplied with sufficient moisture, will quickly produce +new individuals. + +Not infrequently the spore fruits are to be met with flat discs of a +reddish brown color, two or three millimetres in diameter, and closely +resembling a small cup fungus. They are at first almost closed, but +expand as they mature (Fig. 44, _A_, _ap._). + +[Illustration: FIG. 44.--_A_, a common lichen (_Parmelia_), of the +natural size. _ap._ spore fruit. _B_, section through one of the spore +fruits, x 5. _C_, section through the body of a gelatinous lichen +(_Collema_), showing the _Nostoc_ individuals surrounded by the fungus +filaments, x 300. _D_, a spermagonium of _Collema_, x 25. _E_, a +single _Nostoc_ thread. _F_, spore sacs and paraphyses of _Usnea_, +x 300. _G_, _Protococcus_ cells and fungus filaments of _Usnea_.] + + If a thin vertical section of the plant is made and sufficiently + magnified, it is found to be made up of somewhat irregular, + thick-walled, colorless filaments, divided by cross-walls as in the + other sac-fungi. In the central parts of the plant these are rather + loose, but toward the outside become very closely interwoven and + often grown together, so as to form a tough rind. Among the + filaments of the outer portion are numerous small green cells, that + closer examination shows to be individuals of _Protococcus_, or some + similar green algae, upon which the lichen is parasitic. These are + sufficiently abundant to form a green line just inside the rind if + the section is examined with a simple lens (Fig. 44, _B_). + + The spore fruits of the lichens resemble in all essential respects + those of the cup fungi, and the spore sacs (Fig. 44, _F_) are much + the same, usually, though not always, containing eight spores, which + are sometimes two-celled. The sterile filaments between the spore + sacs usually have thickened ends, which are dark-colored, and give + the color to the inner surface of the spore fruit. + + In Figure 45, _H_, is shown one of the so-called "_Soredia_,"[7] a + group of the algae, upon which the lichen is parasitic, surrounded by + some of the filaments, the whole separating spontaneously from the + plant and giving rise to a new one. + +[7] Sing. _soredium_. + +Owing to the toughness of the filaments, the finer structure of the +lichens is often difficult to study, and free use of caustic potash is +necessary to soften and make them manageable. + +[Illustration: FIG. 45.--Forms of lichens. _A_, a branch with lichens +growing upon it, one-half natural size. _B_, _Usnea_, natural size. +_ap._ spore fruit. _C_, _Sticta_, one-half natural size. _D_, +_Peltigera_, one-half natural size. _ap._ spore fruit. _E_, a single +spore fruit, x 2. _F_, _Cladonia_, natural size. _G_, a piece of bark +from a beech, with a crustaceous lichen (_Graphis_) growing upon it, +x 2. _ap._ spore fruit. _H_, _Soredium_ of a lichen, x 300.] + +According to their form, lichens are sometimes divided into the bushy +(fruticose), leafy (frondose), incrusting (crustaceous), and +gelatinous. Of the first, the long gray _Usnea_ (Fig. 45, _A_, _B_), +which drapes the branches of trees in swamps, is a familiar example; +of the second, _Parmelia_, _Sticta_ (Fig. 45, _C_) and _Peltigera_ +(_D_) are types; of the third, _Graphis_ (_G_), common on the trunks +of beech-trees, to which it closely adheres; and of the last, +_Collema_ (Fig. 44, _C_, _D_, _E_), a dark greenish, gelatinous form, +growing on mossy tree trunks, and looking like a colony of _Nostoc_, +which indeed it is, but differing from an ordinary colony in being +penetrated everywhere by the filaments of the fungus growing upon it. + + Not infrequently in this form, as well as in other lichens, special + cavities, known as spermogonia (Fig. 44, _D_), are found, in which + excessively small spores are produced, which have been claimed to + be male reproductive cells, but the latest investigations do not + support this theory. + +[Illustration: FIG. 46.--Branch of a plum-tree attacked by black knot. +Natural size.] + +The last group of the _Ascomycetes_ are the "black fungi," +_Pyrenomycetes_, represented by the black knot of cherry and plum +trees, shown in Figure 46. They are mainly distinguished from the cup +fungi by producing their spore sacs in closed cavities. Some are +parasites; others live on dead wood, leaves, etc., forming very hard +masses, generally black in color, giving them their common name. Owing +to the hardness of the masses, they are very difficult to manipulate; +and, as the structure is not essentially different from that of the +_Discomycetes_, the details will not be entered into here. + +Of the parasitic forms, one of the best known is the "ergot" of rye, +more or less used in medicine. Other forms are known that attack +insects, particularly caterpillars, which are killed by their attacks. + + + + +CHAPTER X. + +FUNGI--_Continued_. + + +CLASS _Basidiomycetes_. + +The _Basidiomycetes_ include the largest and most highly developed of +the fungi, among which are many familiar forms, such as the mushrooms, +toadstools, puff-balls, etc. Besides these large and familiar forms, +there are other simpler and smaller ones that, according to the latest +investigations, are probably related to them, though formerly regarded +as constituting a distinct group. The most generally known of these +lower _Basidiomycetes_ are the so-called rusts. The larger +_Basidiomycetes_ are for the most part saprophytes, living in decaying +vegetable matter, but a few are true parasites upon trees and others +of the flowering plants. + +All of the group are characterized by the production of spores at the +top of special cells known as basidia,[8] the number produced upon a +single basidium varying from a single one to several. + +[8] Sing. _basidium_. + +Of the lower _Basidiomycetes_, the rusts (_Uredineae_) offer common and +easily procurable forms for study. They are exclusively parasitic in +their habits, growing within the tissues of the higher land plants, +which they often injure seriously. They receive their popular name +from the reddish color of the masses of spores that, when ripe, burst +through the epidermis of the host plant. Like many other fungi, the +rusts have several kinds of spores, which are often produced on +different hosts; thus one kind of wheat rust lives during part of its +life within the leaves of the barberry, where it produces spores quite +different from those upon the wheat; the cedar rust, in the same way, +is found at one time attacking the leaves of the wild crab-apple and +thorn. + +[Illustration: FIG. 47.--_A_, a branch of red cedar attacked by a rust +(_Gymnosporangium_), causing a so-called "cedar apple," x 1/2. _B_, +spores of the same, one beginning to germinate, x 300. _C_, a spore +that has germinated, each cell producing a short, divided filament +(basidium), which in turn gives rise to secondary spores (_sp._), +x 300. _D_, part of the leaf of a hawthorn attacked by the cluster cup +stage of the same fungus, upper side showing spermogonia, natural +size. _E_, cluster cups (_Roestelia_) of the same fungus, natural +size. _F_, tip of a leaf of the Indian turnip (_Arisaema_), bearing the +cluster cup (_AEcidium_) stage of a rust, x 2. _G_, vertical section +through a young cluster cup. _H_, similar section through a mature +one, x 50. _I_, germinating spores of _H_, x 300. _J_, part of a corn +leaf, with black rust, natural size. _K_, red rust spore of the wheat +rust (_Puccinia graminis_), x 300. _L_, forms of black-rust spores: i, +_Uromyces_; ii, _Puccinia_; iii, _Phragmidium_.] + +The first form met with in most rusts is sometimes called the +"cluster-cup" stage, and in many species is the only stage known. In +Figure 47, _F_, is shown a bit of the leaf of the Indian turnip +(_Arisaema_) affected by one of these "cluster-cup" forms. To the naked +eye, or when slightly magnified, the masses of spores appear as bright +orange spots, mostly upon the lower surface. The affected leaves are +more or less checked in their growth, and the upper surface shows +lighter blotches, corresponding to the areas below that bear the +cluster cups. These at first appear as little elevations of a +yellowish color, and covered with the epidermis; but as the spores +ripen they break through the epidermis, which is turned back around +the opening, the whole forming a little cup filled with a bright +orange red powder, composed of the loose masses of spores. + + Putting a piece of the affected leaf between two pieces of pith so + as to hold it firmly, with a little care thin vertical sections of + the leaf, including one of the cups, may be made, and mounted, + either in water or glycerine, removing the air with alcohol. We find + that the leaf is thickened at this point owing to a diseased growth + of the cells of the leaf, induced by the action of the fungus. The + mass of spores (Fig. 47, _G_) is surrounded by a closely woven mass + of filaments, forming a nearly globular cavity. Occupying the bottom + of the cup are closely set, upright filaments, each bearing a row of + spores, arranged like those of the white rusts, but so closely + crowded as to be flattened at the sides. The outer rows have + thickened walls, and are grown together so as to form the wall of + the cup. + + The spores are filled with granular protoplasm, in which are + numerous drops of orange-yellow oil, to which is principally due + their color. As the spores grow, they finally break the overlying + epidermis, and then become rounded as the pressure from the sides is + relieved. They germinate within a few hours if placed in water, + sending out a tube, into which pass the contents of the spore + (Fig. 47, _I_). + +One of the most noticeable of the rusts is the cedar rust +(_Gymnosporangium_), forming the growths known as "cedar apples," +often met with on the red cedar. These are rounded masses, sometimes +as large as a walnut, growing upon the small twigs of the cedar +(Fig. 47, _A_). This is a morbid growth of the same nature as those +produced by the white rusts and smuts. If one of these cedar apples is +examined in the late autumn or winter, it will be found to have the +surface dotted with little elevations covered by the epidermis, and on +removing this we find masses of forming spores. These rupture the +epidermis early in the spring, and appear then as little spikes of a +rusty red color. If they are kept wet for a few hours, they enlarge +rapidly by the absorption of water, and may reach a length of four or +five centimetres, becoming gelatinous in consistence, and sometimes +almost entirely hiding the surface of the "apple." In this stage the +fungus is extremely conspicuous, and may frequently be met with after +rainy weather in the spring. + + This orange jelly, as shown by the microscope, is made up of + elongated two-celled spores (teleuto spores), attached to long + gelatinous stalks (Fig. 47, _B_). They are thick-walled, and the + contents resemble those of the cluster-cup spores described above. + + To study the earlier stages of germination it is best to choose + specimens in which the masses of spores have not been moistened. By + thoroughly wetting these, and keeping moist, the process of + germination may be readily followed. Many usually begin to grow + within twenty-four hours or less. Each cell of the spore sends out a + tube (Fig. 47, _C_), through an opening in the outer wall, and this + tube rapidly elongates, the spore contents passing into it, until a + short filament (basidium) is formed, which then divides into several + short cells. Each cell develops next a short, pointed process, which + swells up at the end, gradually taking up all the contents of the + cell, until a large oval spore (_sp._) is formed at the tip, + containing all the protoplasm of the cell. + +Experiments have been made showing that these spores do not germinate +upon the cedar, but upon the hawthorn or crab-apple, where they +produce the cluster-cup stage often met with late in the summer. The +affected leaves show bright orange-yellow spots about a centimetre in +diameter (Fig. 47, _D_), and considerably thicker than the other parts +of the leaf. On the upper side of these spots may be seen little black +specks, which microscopic examination shows to be spermogonia, +resembling those of the lichens. Later, on the lower surface, appear +the cluster cups, whose walls are prolonged so that they form little +tubular processes of considerable length (Fig. 47, _E_). + + In most rusts the teleuto spores are produced late in the summer or + autumn, and remain until the following spring before they germinate. + They are very thick-walled, the walls being dark-colored, so that in + mass they appear black, and constitute the "black-rust" stage + (Fig. 47, _J_). Associated with these, but formed earlier, and + germinating immediately, are often to be found large single-celled + spores, borne on long stalks. They are usually oval in form, rather + thin-walled, but the outer surface sometimes provided with little + points. The contents are reddish, so that in mass they appear of the + color of iron rust, and cause the "red rust" of wheat and other + plants, upon which they are growing. + +The classification of the rusts is based mainly upon the size and +shape of the teleuto spores where they are known, as the cluster-cup +and red-rust stages are pretty much the same in all. Of the commoner +genera _Melampsora_, and _Uromyces_ (Fig. 47, _L_ i), have unicellular +teleuto spores; _Puccinia_ (ii) and _Gymnosporangium_, two-celled +spores; _Triphragmium_, three-celled; and _Phragmidium_ (iii), four or +more. + +The rusts are so abundant that a little search can scarcely fail to +find some or all of the stages. The cluster-cup stages are best +examined fresh, or from alcoholic material; the teleuto spores may be +dried without affecting them. + +Probably the best-known member of the group is the wheat rust +(_Puccinia graminis_), which causes so much damage to wheat and +sometimes to other grains. The red-rust stage may be found in early +summer; the black-rust spores in the stubble and dead leaves in the +autumn or spring, forming black lines rupturing the epidermis. + +Probably to be associated with the lower _Basidiomycetes_ are the +large fungi of which _Tremella_ (Fig. 51, _A_) is an example. They are +jelly-like forms, horny and somewhat brittle when dry, but becoming +soft when moistened. They are common, growing on dead twigs, logs, +etc., and are usually brown or orange-yellow in color. + +Of the higher _Basidiomycetes_, the toadstools, mushrooms, etc., are +the highest, and any common form will serve for study. One of the most +accessible and easily studied forms is _Coprinus_, of which there are +several species growing on the excrement of various herbivorous +animals. They not infrequently appear on horse manure that has been +kept covered with a glass for some time, as described for _Ascobolus_. +After two or three weeks some of these fungi are very likely to make +their appearance, and new ones continue to develop for a long time. + +[Illustration: FIG. 48.--_A_, young. _B_, full-grown fruit of a +toadstool (_Coprinus_), x 2. _C_, under side of the cap, showing the +radiating "gills," or spore-bearing plates. _D_, section across one of +the young gills, x 150. _E_, _F_, portions of gills from a nearly ripe +fruit, x 300. _sp._ spores. _x_, sterile cell. In _F_, a basidium is +shown, with the young spores just forming. _G_, _H_, young fruits, +x 50.] + +The first trace of the plant, visible to the naked eye, is a little +downy, white speck, just large enough to be seen. This rapidly +increases in size, becoming oblong in shape, and growing finally +somewhat darker in color; and by the time it reaches a height of a few +millimetres a short stalk becomes perceptible, and presently the whole +assumes the form of a closed umbrella. The top is covered with little +prominences, that diminish in number and size toward the bottom. After +the cap reaches its full size, the stalk begins to grow, slowly at +first, but finally with great rapidity, reaching a height of several +centimetres within a few hours. At the same time that the stalk is +elongating, the cap spreads out, radial clefts appearing on its upper +surface, which flatten out very much as the folds of an umbrella are +stretched as it opens, and the spaces between the clefts appear as +ridges, comparable to the ribs of the umbrella (Fig. 48, _B_). The +under side of the cap has a number of ridges running from the centre +to the margin, and of a black color, due to the innumerable spores +covering their surface (_C_). Almost as soon as the umbrella opens, +the spores are shed, and the whole structure shrivels up and +dissolves, leaving almost no trace behind. + + If we examine microscopically the youngest specimens procurable, + freeing from air with alcohol, and mounting in water or dilute + glycerine, we find it to be a little, nearly globular mass of + colorless filaments, with numerous cross-walls, the whole arising + from similar looser filaments imbedded in the substratum (Fig. 48, + _G_). If the specimen is not too young, a denser central portion can + be made out, and in still older ones (Fig. 48, _H_) this central + mass has assumed the form of a short, thick stalk, crowned by a flat + cap, the whole invested by a loose mass of filaments that merge more + or less gradually into the central portion. By the time the spore + fruit (for this structure corresponds to the spore fruit of the + _Ascomycetes_) reaches a height of two or three millimetres, and is + plainly visible to the naked eye, the cap grows downward at the + margins, so as to almost entirely conceal the stalk. A longitudinal + section of such a stage shows the stalk to be composed of a + small-celled, close tissue becoming looser in the cap, on whose + inner surface the spore-bearing ridges ("gills" or _Lamellae_) have + begun to develop. Some of these run completely to the edge of the + cap, others only part way. To study their structure, make + cross-sections of the cap of a nearly full-grown, but unopened, + specimen, and this will give numerous sections of the young gills. + We find them to be flat plates, composed within of loosely + interwoven filaments, whose ends stand out at right angles to the + surface of the gills, forming a layer of closely-set upright cells + (basidia) (Fig. 48, _D_). These are at first all alike, but later + some of them become club-shaped, and develop at the end several + (usually four) little points, at the end of which spores are formed + in exactly the same way as we saw in the germinating teleuto spores + of the cedar rust, all the protoplasm of the basidium passing into + the growing spores (Fig. 48, _E_, _F_). The ripe spores (_E_, _sp._) + are oval, and possess a firm, dark outer wall. Occasionally some of + the basidia develop into very large sterile cells (E, _x_), + projecting far beyond the others, and often reaching the neighboring + gill. + +Similar in structure and development to _Coprinus_ are all the large +and common forms; but they differ much in the position of the +spore-bearing tissue, as well as in the form and size of the whole +spore fruit. They are sometimes divided, according to the position of +the spores, into three orders: the closed-fruited (_Angiocarpous_) +forms, the half-closed (_Hemi-angiocarpous_), and the open or +naked-fruited forms (_Gymnocarpous_). + +[Illustration: FIG. 49.--_Basidiomycetes_. _A_, common puff-ball +(_Lycoperdon_). _B_, earth star (_Geaster_). _A_, x 1/4. _B_, one-half +natural size.] + +Of the first, the puff-balls (Fig. 49) are common examples. One +species, the giant puff-ball (_Lycoperdon giganteum_), often reaches a +diameter of thirty to forty centimetres. The earth stars (_Geaster_) +have a double covering to the spore fruit, the outer one splitting at +maturity into strips (Fig. 49, _B_). Another pretty and common form is +the little birds'-nest fungus (_Cyathus_), growing on rotten wood or +soil containing much decaying vegetable matter (Fig. 50). + +[Illustration: FIG. 50.--Birds'-nest fungus (_Cyathus_). _A_, young. +_B_, full grown. _C_, section through _B_, showing the "sporangia" +(_sp._). All twice the natural size.] + +In the second order the spores are at first protected, as we have seen +in _Coprinus_, which belongs to this order, but finally become +exposed. Here belong the toadstools and mushrooms (Fig. 51, _B_), the +large shelf-shaped fungi (_Polyporus_), so common on tree trunks and +rotten logs (Fig. 51, _C_, _D_, _E_), and the prickly fungus +(_Hydnum_) (Fig. 51, _G_). + +[Illustration: FIG. 51.--Forms of _Basidiomycetes_. _A_, _Tremella_, +one-half natural size. _B_, _Agaricus_, natural size. _C_, _E_, +_Polyporus_: _C_, x 1/2; _E_, x 1/4. _D_, part of the under surface of +_D_, natural size. _F_, _Clavaria_, a small piece, natural size. _G_, +_Hydnum_, a piece of the natural size.] + +Of the last, or naked-fruited forms, the commonest belong to the +genus _Clavaria_ (Fig. 51, _F_), smooth-branching forms, usually of a +brownish color, bearing the spores directly upon the surface of the +branches. + + + + +CHAPTER XI. + +SUB-KINGDOM IV. + +BRYOPHYTA. + + +The Bryophytes, or mosses, are for the most part land plants, though a +few are aquatic, and with very few exceptions are richly supplied with +chlorophyll. They are for the most part small plants, few of them +being over a few centimetres in height; but, nevertheless, compared +with the plants that we have heretofore studied, quite complex in +their structure. The lowest members of the group are flattened, +creeping plants, or a few of them floating aquatics, without distinct +stem and leaves; but the higher ones have a pretty well-developed +central axis or stem, with simple leaves attached. + +There are two classes--I. Liverworts (_Hepaticae_), and II. Mosses +(_Musci_). + + +CLASS I.--THE LIVERWORTS. + +One of the commonest of this class, and to be had at any time, is +named _Madotheca_. It is one of the highest of the class, having +distinct stem and leaves. It grows most commonly on the shady side of +tree trunks, being most luxuriant near the ground, where the supply of +moisture is most constant. It also occurs on stones and rocks in moist +places. It closely resembles a true moss in general appearance, and +from the scale-like arrangement of its leaves is sometimes called +"scale moss." + +The leaves (Fig. 52, _A_, _B_) are rounded in outline unequally, +two-lobed, and arranged in two rows on the upper side of the stem, so +closely overlapping as to conceal it entirely. On the under side are +similar but smaller leaves, less regularly disposed. The stems branch +at intervals, the branches spreading out laterally so that the whole +plant is decidedly flattened. On the under side are fine, whitish +hairs, that fasten it to the substratum. If we examine a number of +specimens, especially early in the spring, a difference will be +observed in the plants. Some of them will be found to bear peculiar +structures (Fig. 52, _C_, _D_), in which the spores are produced. +These are called "sporogonia." They are at first globular, but when +ripe open by means of four valves, and discharge a greenish brown mass +of spores. An examination of the younger parts of the same plants will +probably show small buds (Fig. 54, _H_), which contain the female +reproductive organs, from which the sporogonia arise. + +[Illustration: FIG. 52.--_A_, part of a plant of a leafy liverwort +(_Madotheca_), x 2. _B_, part of the same, seen from below, x 4. _C_, +a branch with two open sporogonia (_sp._), x 4. _D_, a single +sporogonium, x 8.] + +On other plants may be found numerous short side branches (Fig. 53, +_B_), with very closely set leaves. If these are carefully separated, +the antheridia can just be seen as minute whitish globules, barely +visible to the naked eye. Plants that, like this one, have the male +and female reproductive organs on distinct plants, are said to be +"dioecious." + + A microscopical examination of the stem and leaves shows their + structure to be very simple. The former is cylindrical, and composed + of nearly uniform elongated cells, with straight cross-walls. The + leaves consist of a single layer of small, roundish cells, which, + like those of the stem, contain numerous rounded chloroplasts, to + which is due their dark green color. + + The tissues are developed from a single apical cell, but it is + difficult to obtain good sections through it. + + The antheridia are borne singly at the bases of the leaves on the + special branches already described (Fig. 53, _A_, _an._). By + carefully dissecting with needles such a branch in a drop of water, + some of the antheridia will usually be detached uninjured, and may + be readily studied, the full-grown ones being just large enough to + be seen with the naked eye. They are globular bodies, attached by a + stalk composed of two rows of cells. The globular portion consists + of a wall of chlorophyll-bearing cells, composed of two layers + below, but single above (Fig. 53, _C_). Within is a mass of + excessively small cells, each of which contains a spermatozoid. In + the young antheridium (_A_, _an._) the wall is single throughout, + and the central cells few in number. To study them in their natural + position, thin longitudinal sections of the antheridial branch + should be made. + +[Illustration: FIG. 53.--_A_, end of a branch from a male plant of +_Madotheca_. The small side branchlets bear the antheridia, x 2. _B_, +two young antheridia (_an._), the upper one seen in optical section, +the lower one from without, x 150. _C_, a ripe antheridium, optical +section, x 50. _D_, sperm cells with young spermatozoids. _E_, ripe +spermatozoids, x 600.] + + When ripe, if brought into water, the antheridium bursts at the top + into a number of irregular lobes that curl back and allow the mass + of sperm cells to escape. The spermatozoids, which are derived + principally from the nucleus of the sperm cells (53, _D_) are so + small as to make a satisfactory examination possible only with very + powerful lenses. The ripe spermatozoid is coiled in a flat spiral + (53, _E_), and has two excessively delicate cilia, visible only + under the most favorable circumstances. + + The female organ in the bryophytes is called an "archegonium," and + differs considerably from anything we have yet studied, but recalls + somewhat the structure of the ooegonium of _Chara_. They are found in + groups, contained in little bud-like branches (54, _H_). In order to + study them, a plant should be chosen that has numbers of such buds, + and the smallest that can be found should be used. Those containing + the young archegonia are very small; but after one has been + fertilized, the leaves enclosing it grow much larger, and the bud + becomes quite conspicuous, being surrounded by two or three + comparatively large leaves. By dissecting the young buds, archegonia + in all stages of growth may be found. + +[Illustration: FIG. 54.--_A-D_, development of the archegonium of +_Madotheca_. _B_, surface view, the others in optical section. _o_, +egg cell, x 150. _E_, base of a fertilized archegonium, containing a +young embryo (_em._), x 150. _F_, margin of one of the leaves +surrounding the archegonia. _G_, young sporogonium still surrounded by +the much enlarged base of the archegonium. _h_, neck of the +archegonium. _ar._ abortive archegonia, x 12. _H_, short branch +containing the young sporogonium, x 4.] + + When very young the archegonium is composed of an axial row of three + cells, surrounded by a single outer layer of cells, the upper ones + forming five or six regular rows, which are somewhat twisted + (Fig. 54, _A_, _B_). As it becomes older, the lower part enlarges + slightly, the whole looking something like a long-necked flask (_C_, + _D_). The centre of the neck is occupied by a single row of cells + (canal cells), with more granular contents than the outer cells, the + lowest cell of the row being somewhat larger than the others + (Fig. 54, _C_, _o_). When nearly ripe, the division walls of the + canal cells are absorbed, and the protoplasm of the lowest cell + contracts and forms a globular naked cell, the egg cell (_D_, _o_). + If a ripe archegonium is placed in water, it soon opens at the top, + and the contents of the canal cells are forced out, leaving a clear + channel down to the egg cell. If the latter is not fertilized, the + inner walls of the neck cells turn brown, and the egg cell dies; but + if a spermatozoid penetrates to the egg cell, the latter develops a + wall and begins to grow, forming the embryo or young sporogonium. + +[Illustration: FIG. 55.--Longitudinal section of a nearly full-grown +sporogonium of _Madotheca_, which has not, however, broken through the +overlying cells, x 25. _sp._ cavity in which the spores are formed. +_ar._ abortive archegonium.] + + The first division wall to be formed in the embryo is transverse, + and is followed by vertical ones (Fig. 54, _E_, _em._). As the + embryo enlarges, the walls of the basal part of the archegonium grow + rapidly, so that the embryo remains enclosed in the archegonium + until it is nearly full-grown (Fig. 55). As it increases in size, it + becomes differentiated into three parts: a wedge-shaped base or + "foot" penetrating downward into the upper part of the plant, and + serving to supply the embryo with nourishment; second, a stalk + supporting the third part, the capsule or spore-bearing portion of + the fruit. The capsule is further differentiated into a wall, which + later becomes dark colored, and a central cavity, in which are + developed special cells, some of which by further division into four + parts produce the spores, while the others, elongating enormously, + give rise to special cells, called elaters (Fig. 56, _B_). + +[Illustration: FIG. 56.--Spore (_A_) and two elaters (_B_) of +_Madotheca_, x 300.] + + The ripe spores are nearly globular, contain chlorophyll and drops + of oil, and the outer wall is brown and covered with fine points + (Fig. 56, _A_). The elaters are long-pointed cells, having on the + inner surface of the wall a single or double dark brown spiral band. + These bands are susceptible to changes in moisture, and by their + movements probably assist in scattering the spores after the + sporogonium opens. + +Just before the spores are ripe, the stalk of the sporogonium +elongates rapidly, carrying up the capsule, which breaks through the +archegonium wall, and finally splits into four valves, and discharges +the spores. + +There are four orders of the liverworts represented in the United +States, three of which differ from the one we have studied in being +flattened plants, without distinct stems and leaves,--at least, the +leaves when present are reduced to little scales upon the lower +surface. + +The first order (_Ricciaceae_) are small aquatic forms, or grow on damp +ground or rotten logs. They are not common forms, and not likely to be +encountered by the student. One of the floating species is shown in +figure 57, _A_. + +The second order, the horned liverworts (_Anthoceroteae_), are +sometimes to be met with in late summer and autumn, forms growing +mostly on damp ground, and at once recognizable by their long-pointed +sporogonia, which open when ripe by two valves, like a bean pod +(Fig. 57, _B_). + +The third order (_Marchantiaceae_) includes the most conspicuous +members of the whole class. Some of them, like the common liverwort +(_Marchantia_), shown in Figure 57, _F_, _K_, and the giant liverwort +(Fig. 57, _D_), are large and common forms, growing on the ground in +shady places, the former being often found also in greenhouses. They +are fastened to the ground by numerous fine, silky hairs, and the +tissues are well differentiated, the upper surface of the plant having +a well-marked epidermis, with peculiar breathing pores, large enough +to be seen with the naked eye (Fig. 57, _E_, _J_, _K_) Each of these +is situated in the centre of a little area (Fig. 57, _E_), and beneath +it is a large air space, into which the chlorophyll-bearing cells +(_cl._) of the plant project (_J_). + +The sexual organs are often produced in these forms upon special +branches (_G_), or the antheridia may be sunk in discs on the upper +side of the stem (_D_, _an._). + +[Illustration: FIG. 57.--Forms of liverworts. _A_, _Riccia_, natural +size. _B_, _Anthoceros_ (horned liverwort), natural size. _sp._ +sporogonia. _C_, _Lunularia_, natural size, _x_, buds. _D_, giant +liverwort (_Conocephalus_), natural size. _an._ antheridial disc. _E_, +small piece of the epidermis, showing the breathing pores, x 2. _F_, +common liverwort (_Marchantia_), x 2. _x_, cups containing buds. _G_, +archegonial branch of common liverwort, natural size. _H_, two young +buds from the common liverwort, x 150. _I_, a full-grown bud, x 25. +_J_, vertical section through the body of _Marchantia_, cutting +through a breathing pore (_s_), x 50. _K_, surface view of a breathing +pore, x 150. _L_, a leafy liverwort (_Jungermannia_). _sp._ +sporogonium, x 2.] + +Some forms, like _Marchantia_ and _Lunularia_ (Fig. 57, _C_), produce +little cups (_x_), circular in the first, semicircular in the second, +in which special buds (_H_, _I_) are formed that fall off and produce +new plants. + +The highest of the liverworts (_Jungermanniaceae_) are, for the most +part, leafy forms like _Madotheca_, and represented by a great many +common forms, growing usually on tree trunks, etc. They are much like +_Madotheca_ in general appearance, but usually very small and +inconspicuous, so as to be easily overlooked, especially as their +color is apt to be brownish, and not unlike that of the bark on which +they grow (Fig. 57, _L_). + + +CLASS II.--THE TRUE MOSSES. + +The true mosses (_Musci_) resemble in many respects the higher +liverworts, such as _Madotheca_ or _Jungermannia_, all of them having +well-marked stems and leaves. The spore fruit is more highly +developed than in the liverworts, but never contains elaters. + +A good idea of the general structure of the higher mosses may be had +from a study of almost any common species. One of the most convenient, +as well as common, forms (_Funaria_) is to be had almost the year +round, and fruits at almost all seasons, except midwinter. It grows in +close patches on the ground in fields, at the bases of walls, +sometimes in the crevices between the bricks of sidewalks, etc. If +fruiting, it may be recognized by the nodding capsule on a long stalk, +that is often more or less twisted, being sensitive to changes in the +moisture of the atmosphere. The plant (Fig. 58, _A_, _B_) has a short +stem, thickly set with relatively large leaves. These are oblong and +pointed, and the centre is traversed by a delicate midrib. The base of +the stem is attached to the ground by numerous fine brown hairs. + +The mature capsule is broadly oval in form (Fig. 58, _C_), and +provided with a lid that falls off when the spores are ripe. While the +capsule is young it is covered by a pointed membranous cap (_B_, +_cal._) that finally falls off. When the lid is removed, a fine fringe +is seen surrounding the opening of the capsule, and serving the same +purpose as the elaters of the liverworts (Fig. 58, _E_). + +[Illustration: FIG. 58.--_A_, fruiting plant of a moss (_Funaria_), +with young sporogonium (_sp._), x 4. B, plant with ripe sporogonium. +_cal_. calyptra, x 2. _C_, sporogonium with calyptra removed. _op._ +lid, x 4. _D_, spores: i, ungerminated; ii-iv, germinating, x 300. +_E_, two teeth from the margin of the capsule, x 50. _F_, epidermal +cells and breathing pore from the surface of the sporogonium, x 150. +_G_, longitudinal section of a young sporogonium, x 12. _sp._ spore +mother cells. _H_, a small portion of _G_, magnified about 300 times. +_sp._ spore mother cells.] + +If the lower part of the stem is carefully examined with a lens, we +may detect a number of fine green filaments growing from it, looking +like the root hairs, except for their color. Sometimes the ground +about young patches of the moss is quite covered by a fine film of +such threads, and looking carefully over it probably very small moss +plants may be seen growing up here and there from it. + +[Illustration: FIG. 59.--Longitudinal section through the summit of a +small male plant of _Funaria_. _a_, _a'_, antheridia. _p_, paraphysis. +_L_, section of a leaf, x 150.] + +This moss is dioecious. The male plants are smaller than the female, +and may be recognized by the bright red antheridia which are formed at +the end of the stem in considerable numbers, and surrounded by a +circle of leaves so that the whole looks something like a flower. +(This is still more evident in some other mosses. See Figure 65, _E_, +_F_.) + + The leaves when magnified are seen to be composed of a single layer + of cells, except the midrib, which is made up of several thicknesses + of elongated cells. Where the leaf is one cell thick, the cells are + oblong in form, becoming narrower as they approach the midrib and + the margin. They contain numerous chloroplasts imbedded in the layer + of protoplasm that lines the wall. The nucleus (Fig. 63, _C_, _n_) + may usually be seen without difficulty, especially if the leaf is + treated with iodine. This plant is one of the best for studying the + division of the chloroplasts, which may usually be found in all + stages of division (Fig. 63, _D_). In the chloroplasts, especially + if the plant has been exposed to light for several hours, will be + found numerous small granules, that assume a bluish tint on the + application of iodine, showing them to be starch grains. If the + plant is kept in the dark for a day or two, these will be absent, + having been used up; but if exposed to the light again, new ones + will be formed, showing that they are formed only under the action + of light. + +[Illustration: FIG. 60.--_A_, _B_, young antheridia of _Funaria_, +optical section, x 150. _C_, two sperm cells of _Atrichum_. _D_, +spermatozoids of _Sphagnum_, x 600.] + + Starch is composed of carbon, hydrogen, and oxygen, and so far as is + known is only produced by chlorophyll-bearing cells, under the + influence of light. The carbon used in the manufacture of starch is + taken from the atmosphere in the form of carbonic acid, so that + green plants serve to purify the atmosphere by the removal of this + substance, which is deleterious to animal life, while at the same + time the carbon, an essential part of all living matter, is combined + in such form as to make it available for the food of other + organisms. + + The marginal cells of the leaf are narrow, and some of them + prolonged into teeth. + + A cross-section of the stem (63, _E_) shows on the outside a single + row of epidermal cells, then larger chlorophyll-bearing cells, and + in the centre a group of very delicate, small, colorless cells, + which in longitudinal section are seen to be elongated, and similar + to those forming the midrib of the leaf. These cells probably serve + for conducting fluids, much as the similar but more perfectly + developed bundles of cells (fibro-vascular bundles) found in the + stems and leaves of the higher plants. + + The root hairs, fastening the plant to the ground, are rows of + cells with brown walls and oblique partitions. They often merge + insensibly into the green filaments (protonema) already noticed. + These latter have usually colorless walls, and more numerous + chloroplasts, looking very much like a delicate specimen of + _Cladophora_ or some similar alga. If a sufficient number of these + filaments is examined, some of them will probably show young moss + plants growing from them (Fig. 63, _A_, _k_), and with a little + patience the leafy plant can be traced back to a little bud + originating as a branch of the filament. Its diameter is at first + scarcely greater than that of the filament, but a series of walls, + close together, are formed, so placed as to cut off a pyramidal cell + at the top, forming the apical cell of the young moss plant. This + apical cell has the form of a three-sided pyramid with the base + upward. From it are developed three series of cells, cut off in + succession from the three sides, and from these cells are derived + all the tissues of the plant which soon becomes of sufficient size + to be easily recognizable. + + The protonemal filaments may be made to grow from almost any part of + the plant by keeping it moist, but grow most abundantly from the + base of the stem. + + The sexual organs are much like those of the liverworts and are + borne at the apex of the stems. + + The antheridia (Figs. 59, 60) are club-shaped bodies with a short + stalk. The upper part consists of a single layer of large + chlorophyll-bearing cells, enclosing a mass of very small, nearly + cubical, colorless, sperm cells each of which contains an + excessively small spermatozoid. + + The young antheridium has an apical cell giving rise to two series + of segments (Fig. 60, _A_), which in the earlier stages are very + plainly marked. + + When ripe the chlorophyll in the outer cells changes color, becoming + red, and if a few such antheridia from a plant that has been kept + rather dry for a day or two, are teased out in a drop of water, they + will quickly open at the apex, the whole mass of sperm cells being + discharged at once. + + Among the antheridia are borne peculiar hairs (Fig. 59, _p_) tipped + by a large globular cell. + +[Illustration: FIG. 61.--_A_, _B_, young; _C_, nearly ripe archegonium +of _Funaria_, optical section, x 150. _D_, upper part of the neck of +_C_, seen from without, showing how it is twisted. _E_, base of a ripe +archegonium. _F_, open apex of the same, x 150. _o_, egg cell. _b_, +ventral canal cell.] + + Owing to their small size the spermatozoids are difficult to see + satisfactorily and other mosses (_e.g._ peat mosses, Figure 64, the + hairy cap moss, Figure 65, _I_), are preferable where obtainable. + The spermatozoids of a peat moss are shown in Figure 60, _D_. Like + all of the bryophytes they have but two cilia. + + The archegonia (Fig. 61) should be looked for in the younger plants + in the neighborhood of those that bear capsules. Like the antheridia + they occur in groups. They closely resemble those of the liverworts, + but the neck is longer and twisted and the base more massive. + Usually but a single one of the group is fertilized. + +[Illustration: FIG. 62.--_A_, young embryo of _Funaria_, still +enclosed within the base of the archegonium, x 300. _B_, an older +embryo freed from the archegonium, x 150. _a_, the apical cell.] + + To study the first division of the embryo, it is usually necessary + to render the archegonium transparent, which may be done by using a + little caustic potash; or letting it lie for a few hours in dilute + glycerine will sometimes suffice. If potash is used it must be + thoroughly washed away, by drawing pure water under the cover glass + with a bit of blotting paper, until every trace of the potash is + removed. The first wall in the embryo is nearly at right angles to + the axis of the archegonium and divides the egg cell into nearly + equal parts. This is followed by nearly vertical walls in each cell + (Fig. 62, _A_). Very soon a two-sided apical cell (Fig. 62, _B_, + _a_) is formed in the upper half of the embryo, which persists until + the embryo has reached a considerable size. As in the liverworts the + young embryo is completely covered by the growing archegonium wall. + + The embryo may be readily removed from the archegonium by adding a + little potash to the water in which it is lying, allowing it to + remain for a few moments and pressing gently upon the cover glass + with a needle. In this way it can be easily forced out of the + archegonium, and then by thoroughly washing away the potash, + neutralizing if necessary with a little acetic acid, very beautiful + preparations may be made. If desired, these may be mounted + permanently in glycerine which, however, must be added very + gradually to avoid shrinking the cells. + +[Illustration: FIG. 63.--_A_, protonema of _Funaria_, with a bud +(_k_), x 50. _B_, outline of a leaf, showing also the thickened +midrib, x 12. _C_, cells of the leaf, x 300. _n_, nucleus. _D_, +chlorophyll granules undergoing division, x 300. _E_, cross-section of +the stem, x 50.] + + For some time the embryo has a nearly cylindrical form, but as it + approaches maturity the differentiation into stalk and capsule + becomes apparent. The latter increases rapidly in diameter, assuming + gradually the oval shape of the full-grown capsule. A longitudinal + section of the nearly ripe capsule (Fig. 58, _G_) shows two distinct + portions; an outer wall of two layers of cells, and an inner mass of + cells in some of which the spores are produced. This inner mass of + cells is continuous with the upper part of the capsule, but + connected with the side walls and bottom by means of slender, + branching filaments of chlorophyll-bearing cells. + + The spores arise from a single layer of cells near the outside of + the inner mass of cells (_G_, _sp._). These cells (_H_, _sp._) are + filled with glistening, granular protoplasm; have a large and + distinct nucleus, and no chlorophyll. They finally become entirely + separated and each one gives rise to four spores which closely + resemble those of the liverworts but are smaller. + + Near the base of the capsule, on the outside, are formed breathing + pores (Fig. 58, _F_) quite similar to those of the higher plants. + + If the spores are kept in water for a few days they will germinate, + bursting the outer brown coat, and the contents protruding through + the opening surrounded by the colorless inner spore membrane. The + protuberance grows rapidly in length and soon becomes separated from + the body of the spore by a wall, and lengthening, more and more, + gives rise to a green filament like those we found attached to the + base of the full-grown plant, and like those giving rise to buds + that develop into leafy plants. + + +CLASSIFICATION OF THE MOSSES. + +The mosses may be divided into four orders: I. The peat mosses +(_Sphagnaceae_); II. _Andreaeaceae_; III. _Phascaceae_; IV. The common +mosses (_Bryaceae_). + +[Illustration: FIG. 64.--_A_, a peat moss (_Sphagnum_), x 1/2. _B_, a +sporogonium of the same, x 3. _C_, a portion of a leaf, x 150. The +narrow, chlorophyll-bearing cells form meshes, enclosing the large, +colorless empty cells, whose walls are marked with thickened bars, and +contain round openings (_o_).] + +The peat mosses (Fig. 64) are large pale-green mosses, growing often +in enormous masses, forming the foundation of peat-bogs. They are of a +peculiar spongy texture, very light when dry, and capable of absorbing +a great amount of water. They branch (Fig. 64, _A_), the branches +being closely crowded at the top, where the stems continue to grow, +dying away below. + +[Illustration: FIG. 65.--Forms of mosses. _A_, plant of _Phascum_, +x 3. _B_, fruiting plant of _Atrichum_, x 2. _C_, young capsule of +hairy-cap moss (_Polytrichum_), covered by the large, hairy calyptra. +_D_, capsules of _Bartramia_: i, with; ii, without the calyptra. _E_, +upper part of a male plant of _Atrichum_, showing the flower, x 2. +_F_, a male plant of _Mnium_, x 4. _G_, pine-tree moss (_Clemacium_), +x 1. _H_, _Hypnum_, x 1. _I_, ripe capsules of hairy-cap moss: i, +with; ii, without calyptra.] + +The sexual organs are rarely met with, but should be looked for late +in autumn or early spring. The antheridial branches are often +bright-colored, red or yellow, so as to be very conspicuous. The +capsules, which are not often found, are larger than in most of the +common mosses, and quite destitute of a stalk, the apparent stalk +being a prolongation of the axis of the plant in the top of which the +base of the sporogonium is imbedded. The capsule is nearly globular, +opening by a lid at the top (Fig. 64, _B_). + + A microscopical examination of the leaves, which are quite destitute + of a midrib, shows them to be composed of a network of narrow + chlorophyll-bearing cells surrounding much larger empty ones whose + walls are marked with transverse thickenings, and perforated here + and there with large, round holes (Fig. 64, _C_). It is to the + presence of these empty cells that the plant owes its peculiar + spongy texture, the growing plants being fairly saturated with + water. + +The _Andreaeaceae_ are very small, and not at all common. The capsule +splits into four valves, something like a liverwort. + +The _Phascaceae_ are small mosses growing on the ground or low down on +the trunks of trees, etc. They differ principally from the common +mosses in having the capsule open irregularly and not by a lid. The +commonest forms belong to the genus _Phascum_ (Fig. 65, _A_). + +The vast majority of the mosses the student is likely to meet with +belong to the last order, and agree in the main with the one +described. Some of the commoner forms are shown in Figure 65. + + + + +CHAPTER XII. + +SUB-KINGDOM V. + +PTERIDOPHYTES. + + +If we compare the structure of the sporogonium of a moss or liverwort +with the plant bearing the sexual organs, we find that its tissues are +better differentiated, and that it is on the whole a more complex +structure than the plant that bears it. It, however, remains attached +to the parent plant, deriving its nourishment in part through the +"foot" by means of which it is attached to the plant. + +In the Pteridophytes, however, we find that the sporogonium becomes +very much more developed, and finally becomes entirely detached from +the sexual plant, developing in most cases roots that fasten it to the +ground, after which it may live for many years, and reach a very large +size. + +The sexual plant, which is here called the "prothallium," is of very +simple structure, resembling the lower liverworts usually, and never +reaches more than about a centimetre in diameter, and is often much +smaller than this. + +The common ferns are the types of the sub-kingdom, and a careful study +of any of these will illustrate the principal peculiarities of the +group. The whole plant, as we know it, is really nothing but the +sporogonium, originating from the egg cell in exactly the same way as +the moss sporogonium, and like it gives rise to spores which are +formed upon the leaves. + +The spores may be collected by placing the spore-bearing leaves on +sheets of paper and letting them dry, when the ripe spores will be +discharged covering the paper as a fine, brown powder. If these are +sown on fine, rather closely packed earth, and kept moist and covered +with glass so as to prevent evaporation, within a week or two a fine, +green, moss-like growth will make its appearance, and by the end of +five or six weeks, if the weather is warm, little, flat, heart-shaped +plants of a dark-green color may be seen. These look like small +liverworts, and are the sexual plants (prothallia) of our ferns +(Fig. 66, _F_). Removing one of these carefully, we find on the lower +side numerous fine hairs like those on the lower surface of the +liverworts, which fasten it firmly to the ground. By and by, if our +culture has been successful, we may find attached to some of the +larger of these, little fern plants growing from the under side of the +prothallia, and attached to the ground by a delicate root. As the +little plant becomes larger the prothallium dies, leaving it attached +to the ground as an independent plant, which after a time bears the +spores. + +[Illustration: FIG. 66.--_A_, spore of the ostrich fern (_Onoclea_), +with the outer coat removed. _B_, germinating spore, x 150. _C_, young +prothallium, x 50. _r_, root hair. _sp._ spore membrane. _D_, _E_, +older prothallia. _a_, apical cell, x 150. _F_, a female prothallium, +seen from below, x 12. _ar._ archegonia. _G_, _H_, young archegonia, +in optical section, x 150. _o_, central cell. _b_, ventral canal cell. +_c_, upper canal cell. _I_, a ripe archegonium in the act of opening, +x 150. _o_, egg cell. _J_, a male prothallium, x 50. _an._ antheridia. +_K_, _L_, young antheridia, in optical section, x 300. _M_, ripe +antheridium, x 300. _sp._ sperm cells. _N_, _O_, antheridia that have +partially discharged their contents, x 300. _P_, spermatozoids, killed +with iodine, x 500. _v_, vesicle attached to the hinder end.] + +In choosing spores for germination it is best to select those of large +size and containing abundant chlorophyll, as they germinate more +readily. Especially favorable for this purpose are the spores of the +ostrich fern (_Onoclea struthiopteris_) (Fig. 70, _I_, _J_), or the +sensitive fern (_O. sensibilis_). Another common and readily grown +species is the lady fern (_Asplenium filixfoemina_) (Fig. 70, _H_). The +spores of most ferns retain their vitality for many months, and hence +can be kept dry until wanted. + + The first stages of germination may be readily seen by sowing the + spores in water, where, under favorable circumstances, they will + begin to grow within three or four days. The outer, dry, brown coat + of the spore is first ruptured, and often completely thrown off by + the swelling of the spore contents. Below this is a second colorless + membrane which is also ruptured, but remains attached to the spore. + Through the orifice in the second coat, the inner delicate membrane + protrudes in the form of a nearly colorless papilla which rapidly + elongates and becomes separated from the body of the spore by a + partition, constituting the first root hair (Fig. 66, _B_, _C_, + _r_). The body of the spore containing most of the chlorophyll + elongates more slowly, and divides by a series of transverse walls + so as to form a short row of cells, resembling in structure some of + the simpler algae (_C_). + + In order to follow the development further, spores must be sown upon + earth, as they do not develop normally in water beyond this stage. + + In studying plants grown on earth, they should be carefully removed + and washed in a drop of water so as to remove, as far as possible, + any adherent particles, and then may be mounted in water for + microscopic examination. + + In most cases, after three or four cross-walls are formed, two walls + arise in the end cell so inclined as to enclose a wedge-shaped cell + (_a_) from which are cut off two series of segments by walls + directed alternately right and left (Fig. 66, _D_, _E_, _a_), the + apical cell growing to its original dimensions after each pair of + segments is cut off. The segments divide by vertical walls in + various directions so that the young plant rapidly assumes the form + of a flat plate of cells attached to the ground by root hairs + developed from the lower surfaces of the cells, and sometimes from + the marginal ones. As the division walls are all vertical, the plant + is nowhere more than one cell thick. The marginal cells of the young + segments divide more rapidly than the inner ones, and soon project + beyond the apical cell which thus comes to lie at the bottom of a + cleft in the front of the plant which in consequence becomes + heart-shaped (_E_, _F_). Sooner or later the apical cell ceases to + form regular segments and becomes indistinguishable from the other + cells. + + In the ostrich fern and lady fern the plants are dioecious. The male + plants (Fig. 66, _J_) are very small, often barely visible to the + naked eye, and when growing thickly form dense, moss-like patches. + They are variable in form, some irregularly shaped, others simple + rows of cells, and some have the heart shape of the larger plants. + +The female plants (Fig. 66, _F_) are always comparatively large and +regularly heart-shaped, occasionally reaching a diameter of nearly or +quite one centimetre, so that they are easily recognizable without +microscopical examination. + + All the cells of the plant except the root hairs contain large and + distinct chloroplasts much like those in the leaves of the moss, and + like them usually to be found in process of division. + + The archegonia arise from cells of the lower surface, just behind + the notch in front (Fig. 66, _F_, _ar._). Previous to their + formation the cells at this point divide by walls parallel to the + surface of the plant, so as to form several layers of cells, and + from the lowest layer of cells the archegonia arise. They resemble + those of the liverworts but are shorter, and the lower part is + completely sunk within the tissues of the plant (Fig. 66, _G_, _I_). + They arise as single surface cells, this first dividing into three + by walls parallel to the outer surface. The lower cell undergoes one + or two divisions, but undergoes no further change; the second cell + (_C_, _o_), becomes the egg cell, and from it is cut off another + cell (_c_), the canal cell of the neck; the uppermost of the three + becomes the neck. There are four rows of neck cells, the two forward + ones being longer than the others, so that the neck is bent + backward. In the full-grown archegonium, there are two canal cells, + the lower one (_H_, _b_) called the ventral canal cell, being + smaller than the other. + + Shortly before the archegonium opens, the canal cells become + disorganized in the same way as in the bryophytes, and the + protoplasm of the central cell contracts to form the egg cell which + shows a large, central nucleus, and in favorable cases, a clear + space at the top called the "receptive spot," as it is here that the + spermatozoid enters. When ripe, if placed in water, the neck cells + become very much distended and finally open widely at the top, the + upper ones not infrequently being detached, and the remains of the + neck cells are forced out (Fig. 66, _I_). + + The antheridia (Fig. 66. _J_, _M_) arise as simple hemispherical + cells, in which two walls are formed (_K_ I, II), the lower + funnel-shaped, the upper hemispherical and meeting the lower one so + as to enclose a central cell (shaded in the figure), from which the + sperm cells arise. Finally, a ring-shaped wall (_L_ iii) is formed, + cutting off a sort of cap cell, so that the antheridium at this + stage consists of a central cell, surrounded by three other cells, + the two lower ring-shaped, the upper disc-shaped. The central cell, + which contains dense, glistening protoplasm, is destitute of + chlorophyll, but the outer cells have a few small chloroplasts. The + former divides repeatedly, until a mass of about thirty-two sperm + cells is formed, each giving rise to a large spirally-coiled + spermatozoid. When ripe, the mass of sperm cells crowds so upon the + outer cells as to render them almost invisible, and as they ripen + they separate by a partial dissolving of the division walls. When + brought into water, the outer cells of the antheridium swell + strongly, and the matter derived from the dissolved walls of the + sperm cells also absorbs water, so that finally the pressure becomes + so great that the wall of the antheridium breaks, and the sperm + cells are forced out by the swelling up of the wall cells (_N_, + _O_). After lying a few moments in the water, the wall of each sperm + cell becomes completely dissolved, and the spermatozoids are + released, and swim rapidly away with a twisting movement. They may + be killed with a little iodine, when each is seen to be a somewhat + flattened band, coiled several times. At the forward end, the coils + are smaller, and there are numerous very long and delicate cilia. At + the hinder end may generally be seen a delicate sac (_P_, _v_), + containing a few small granules, some of which usually show the + reaction of starch, turning blue when iodine is applied. + + In studying the development of the antheridia, it is only necessary + to mount the plants in water and examine them directly; but the + study of the archegonia requires careful longitudinal sections of + the prothallium. To make these, the prothallium should be placed + between small pieces of pith, and the razor must be very sharp. It + may be necessary to use a little potash to make the sections + transparent enough to see the structure, but this must be used + cautiously on account of the great delicacy of the tissues. + + If a plant with ripe archegonia is placed in a drop of water, with + the lower surface uppermost, and at the same time male plants are + put with it, and the whole covered with a cover glass, the + archegonia and antheridia will open simultaneously; and, if examined + with the microscope, we shall see the spermatozoids collect about + the open archegonia, to which they are attracted by the substance + forced out when it opens. With a little patience, one or more may be + seen to enter the open neck through which it forces itself, by a + slow twisting movement, down to the egg cell. In order to make the + experiment successful, the plants should be allowed to become a + little dry, care being taken that no water is poured over them for a + day or two beforehand. + + The first divisions of the fertilized egg cell resemble those in the + moss embryo, except that the first wall is parallel with the + archegonium axis, instead of at right angles to it. Very soon, + however, the embryo becomes very different, four growing points + being established instead of the single one found in the moss + embryo. The two growing points on the side of the embryo nearest the + archegonium neck grow faster than the others, one of these + outstripping the other, and soon becoming recognizable as the first + leaf of the embryo (Fig. 67, _A_, _L_). The other (_r_) is peculiar, + in having its growing point covered by several layers of cells, cut + off from its outer face, a peculiarity which we shall find is + characteristic of the roots of all the higher plants, and, indeed, + this is the first root of the young fern. Of the other two growing + points, the one next the leaf grows slowly, forming a blunt cone + (_st._), and is the apex of the stem. The other (_f_) has no + definite form, and serves merely as an organ of absorption, by means + of which nourishment is supplied to the embryo from the prothallium; + it is known as the foot. + +[Illustration: FIG. 67.--_A_, embryo of the ostrich fern just before +breaking through the prothallium, x 50. _st._ apex of stem. _l_, first +leaf. _r_, first root. _ar._ neck of the archegonium. _B_, young +plant, still attached to the prothallium (_pr._). _C_, underground +stem of the maiden-hair fern (_Adiantum_), with one young leaf, and +the base of an older one, x 1. _D_, three cross-sections of a leaf +stalk: i, nearest the base; iii, nearest the blade of the leaf, +showing the division of the fibro-vascular bundle, x 5. _E_, part of +the blade of the leaf, x 1/2. _F_, a single spore-bearing leaflet, +showing the edge folded over to cover the sporangia, x 1. _G_, part of +the fibro-vascular bundle of the leaf stalk (cross-section), x 50. +_x_, woody part of the bundle. _y_, bast. _sh._ bundle sheath. _H_, a +small portion of the same bundle, x 150. _I_, stony tissue from the +underground stem, x 150. _J_, sieve tube from the underground stem, +x 300.] + + Up to this point, all the cells of the embryo are much alike, and + the embryo, like that of the bryophytes, is completely surrounded by + the enlarged base of the archegonium (compare Fig. 67, _A_, with + Fig. 55); but before the embryo breaks through the overlying cells a + differentiation of the tissues begins. In the axis of each of the + four divisions the cells divide lengthwise so as to form a + cylindrical mass of narrow cells, not unlike those in the stem of a + moss. Here, however, some of the cells undergo a further change; the + walls thicken in places, and the cells lose their contents, forming + a peculiar conducting tissue (tracheary tissue), found only in the + two highest sub-kingdoms. The whole central cylinder is called a + "fibro-vascular bundle," and in its perfect form, at least, is found + in no plants below the ferns, which are also the first to develop + true roots. + +The young root and leaf now rapidly elongate, and burst through the +overlying cells, the former growing downward and becoming fastened in +the ground, the latter growing upward through the notch in the front +of the prothallium, and increasing rapidly in size (Fig. 67, _B_). The +leaf is more or less deeply cleft, and traversed by veins which are +continuations of the fibro-vascular bundle of the stalk, and +themselves fork once or twice. The surface of the leaf is covered with +a well-developed epidermis, and the cells occupying the space between +the veins contain numerous chloroplasts, so that the little plant is +now quite independent of the prothallium, which has hitherto supported +it. As soon as the fern is firmly established, the prothallium withers +away. + +Comparing this now with the development of the sporogonium in the +bryophytes, it is evident that the young fern is the equivalent of the +sporogonium or spore fruit of the former, being, like it, the direct +product of the fertilized egg cell; and the prothallium represents the +moss or liverwort, upon which are borne the sexual organs. In the +fern, however, the sporogonium becomes entirely independent of the +sexual plant, and does not produce spores until it has reached a large +size, living many years. The sexual stage, on the other hand, is very +much reduced, as we have seen, being so small as to be ordinarily +completely overlooked; but its resemblance to the lower liverworts, +like _Riccia_, or the horned liverworts, is obvious. The terms +ooephyte (egg-bearing plant) and sporophyte (spore-bearing plant, or +sporogonium) are sometimes used to distinguish between the sexual +plant and the spore-bearing one produced from it. + +The common maiden-hair fern (_Adiantum pedatum_) has been selected +here for studying the structure of the full-grown sporophyte, but +almost any other common fern will answer. The maiden-hair fern is +common in rich woods, and may be at once recognized by the form of its +leaves. These arise from a creeping, underground stem (Fig. 67, _C_), +which is covered with brownish scales, and each leaf consists of a +slender stalk, reddish brown or nearly black in color, which divides +into two equal branches at the top. Each of these main branches bears +a row of smaller ones on the outside, and these have a row of delicate +leaflets on each side (Fig. 67, _E_). The stem of the plant is +fastened to the ground by means of numerous stout roots. The youngest +of these, near the growing point of the stem, are unbranched, but the +older ones branch extensively (_C_). + +On breaking the stem across, it is seen to be dark-colored, except in +the centre, which is traversed by a woody cylinder (fibro-vascular +bundle) of a lighter color. This is sometimes circular in sections, +sometimes horse-shoe shaped. Where the stem branches, the bundle of +the branch may be traced back to where it joins that of the main stem. + + A thin cross-section of the stem shows, when magnified, three + regions. First, an outer row of cells, often absent in the older + portions; this is the epidermis. Second, within the epidermis are + several rows of cells similar to the epidermal cells, but somewhat + larger, and like them having dark-brown walls. These merge gradually + into larger cells, with thicker golden brown walls (Fig. 67, _I_). + The latter, if sufficiently magnified, show distinct striation of + the walls, which are often penetrated by deep narrow depressions or + "pits." This thick-walled tissue is called "stony tissue" + (schlerenchyma). All the cells contain numerous granules, which the + iodine test shows to be starch. All of this second region lying + between the epidermis and the fibro-vascular bundle is known as the + ground tissue. The third region (fibro-vascular) is, as we have seen + without the microscope, circular or horse-shoe shaped. It is sharply + separated from the ground tissue by a row of small cells, called the + "bundle sheath." The cross-section of the bundle of the leaf stalk + resembles, almost exactly, that of the stem; and, as it is much + easier to cut, it is to be preferred in studying the arrangement of + the tissues of the bundle (Fig. 67, _G_). Within the bundle sheath + (_sh._) there are two well-marked regions, a central band (_x_) of + large empty cells, with somewhat angular outlines, and distinctly + separated walls; and an outer portion (_y_) filling up the space + between these central cells and the bundle sheath. The central + tissue (_x_) is called the woody tissue (xylem); the outer, the bast + (phloem). The latter is composed of smaller cells of variable form, + and with softer walls than the wood cells. + + A longitudinal section of either the stem or leaf stalk shows that + all the cells are decidedly elongated, especially those of the + fibro-vascular bundle. The xylem (Fig. 68, _C_, _x_) is made up + principally of large empty cells, with pointed ends, whose walls are + marked with closely set, narrow, transverse pits, giving them the + appearance of little ladders, whence they are called "scalariform," + or ladder-shaped markings. These empty cells are known as + "tracheids," and tissue composed of such empty cells, "tracheary + tissue." Besides the tracheids, there are a few small cells with + oblique ends, and with some granular contents. + + The phloem is composed of cells similar to the latter, but there may + also be found, especially in the stem, other larger ones (Fig. 67, + _J_), whose walls are marked with shallow depressions, whose bottoms + are finely pitted. These are the so-called "sieve tubes." + + For microscopical examination, either fresh or alcoholic material + may be used, the sections being mounted in water. Potash will be + found useful in rendering opaque sections transparent. + +The leaves, when young, are coiled up (Fig. 67, _C_), owing to growth +in the earlier stages being greater on the lower than on the upper +side. As the leaf unfolds, the stalk straightens, and the upper +portion (blade) becomes flat. + +The general structure of the leaf stalk may be understood by making a +series of cross-sections at different heights, and examining them with +a hand lens. The arrangement is essentially the same as in the stem. +The epidermis and immediately underlying ground tissue are +dark-colored, but the inner ground tissue is light-colored, and much +softer than the corresponding part of the stem; and some of the outer +cells show a greenish color, due to the presence of chlorophyll. + +The section of the fibro-vascular bundle differs at different heights. +Near the base of the stalk (Fig. _D_ i) it is horseshoe-shaped; but, +if examined higher up, it is found to divide (II, III), one part going +to each of the main branches of the leaf. These secondary bundles +divide further, forming the veins of the leaflets. + +The leaflets (_E_, _F_) are one-sided, the principal vein running +close to the lower edge, and the others branching from it, and forking +as they approach the upper margin, which is deeply lobed, the lobes +being again divided into teeth. The leaflets are very thin and +delicate, with extremely smooth surface, which sheds water perfectly. +If the plant is a large one, some of the leaves will probably bear +spores. The spore-bearing leaves are at once distinguished by having +the middle of each lobe of the leaflets folded over upon the lower +side (_F_). On lifting one of these flaps, numerous little rounded +bodies (spore cases) are seen, whitish when young, but becoming brown +as they ripen. If a leaf with ripe spore cases is placed upon a piece +of paper, as it dries the spores are discharged, covering the paper +with the spores, which look like fine brown powder. + +[Illustration: FIG. 68.--_A_, vertical section of the leaf of the +maiden-hair fern, which has cut across a vein (_f.b._), x 150. _B_, +surface view of the epidermis from the lower surface of a leaf. _f_, +vein. _p_, breathing pore, x 150. _C_, longitudinal section of the +fibro-vascular bundle of the leaf stalk, showing tracheids with +ladder-shaped markings, x 150. _D_, longitudinal section through the +tip of a root, x 150. _a_, apical cell. _Pl._ young fibro-vascular +bundle. _Pb._ young ground tissue. _E_, cross-section of the root, +through the region of the apical cell (_a_), x 150. _F_, cross-section +through a full-grown root, x 25. _r_, root hairs. _G_, the +fibro-vascular bundle of the same, x 150.] + + A microscopical examination of the leaf stalk shows the tissues to + be almost exactly like those of the stem, except the inner ground + tissue, whose cells are thin-walled and colorless (soft tissue or + "parenchyma") instead of stony tissue. The structure of the blade of + the leaf, however, shows a number of peculiarities. Stripping off a + little of the epidermis with a needle, or shaving off a thin slice + with a razor, it may be examined in water, removing the air if + necessary with alcohol. It is composed of a single layer of cells, + of very irregular outline, except where it overlies a vein (Fig. 68, + _B_, _f_). Here the cells are long and narrow, with heavy walls. The + epidermal cells contain numerous chloroplasts, and on the under + surface of the leaf breathing pores (_stomata_, sing. _stoma_), not + unlike those on the capsules of some of the bryophytes. Each + breathing pore consists of two special crescent-shaped epidermal + cells (guard cells), enclosing a central opening or pore + communicating with an air space below. They arise from cells of the + young epidermis that divide by a longitudinal wall, that separates + in the middle, leaving the space between. + +[Illustration: FIG. 69.--_A_, mother cell of the sporangium of the +maiden-hair fern, x 300. _B_, young sporangium, surface view, x 150: +i, from the side; ii, from above. _C-E_, successive stages in the +development of the sporangium seen in optical section, x 150. _F_, +nearly ripe sporangium, x 50: i, from in front; ii, from the side. +_an._ ring. _st._ point of opening. _G_, group of four spores, x 150. +_H_, a single spore, x 300.] + + By holding a leaflet between two pieces of pith, and using a very + sharp razor, cross-sections can be made. Such a section is shown in + Fig. 68, _A_. The epidermis (_e_) bounds the upper and lower + surfaces, and if a vein (_f.b._) is cut across its structure is + found to be like that of the fibro-vascular bundle of the leaf + stalk, but much simplified. + + The ground tissue of the leaf is composed of very loose, thin-walled + cells, containing numerous chloroplasts. Between them are large and + numerous intercellular spaces, filled with air, and communicating + with the breathing pores. These are the principal assimilating cells + of the plant; _i.e._ they are principally concerned in the + absorption and decomposition of carbonic acid from the atmosphere, + and the manufacture of starch. + + The spore cases, or sporangia (Fig. 69), are at first little papillae + (_A_), arising from the epidermal cells, from which they are early + cut off by a cross-wall. In the upper cell several walls next arise, + forming a short stalk, composed of three rows of cells, and an upper + nearly spherical cell--the sporangium proper. The latter now divides + by four walls (_B_, _C_, i-iv), into a central tetrahedral cell, and + four outer ones. The central cell, whose contents are much denser + than the outer ones, divides again by walls parallel to those first + formed, so that the young sporangium now consists of a central cell, + surrounded by two outer layers of cells. From the central cell a + group of cells is formed by further divisions (_D_), which finally + become entirely separated from each other. The outer cells of the + spore case divide only by walls, at right angles to their outer + surface, so that the wall is never more than two cells thick. Later, + the inner of these two layers becomes disorganized, so that the + central mass of cells floats free in the cavity of the sporangium, + which is now surrounded by but a single layer of cells (_E_). + + Each of the central cells divides into four spores, precisely as in + the bryophytes. The young spores (_G_, _H_) are nearly colorless and + are tetrahedral (like a three-sided pyramid) in form. As they ripen, + chlorophyll is formed in them, and some oil. The wall becomes + differentiated into three layers, the outer opaque and brown, the + two inner more delicate and colorless. + + Running around the outside of the ripe spore case is a single row of + cells (_an._), differing from the others in shape, and having their + inner walls thickened. Near the bottom, two (sometimes four) of + these cells are wider than the others, and their walls are more + strongly thickened. It is at this place (_st._) that the spore case + opens. When the ripe sporangium becomes dry, the ring of thickened + cells (_an._) contracts more strongly than the others, and acts like + a spring pulling the sporangium open and shaking out the spores, + which germinate readily under favorable conditions, and form after a + time the sexual plants (prothallia). + +The roots of the sporophyte arise in large numbers, the youngest being +always nearest the growing point of the stem or larger roots (Fig. 67, +_C_). The growing roots are pointed at the end which is also +light-colored, the older parts becoming dark brown. A cross-section of +the older portions shows a dark-brown ground tissue with a central, +light-colored, circular, fibro-vascular bundle (Fig. 68, _F_). Growing +from its outer surface are numerous brown root hairs (_r_). + + When magnified the walls of all the outer cells (epidermis and + ground tissue) are found to be dark-colored but not very thick, and + the cells are usually filled with starch. There is a bundle sheath + of much-flattened cells separating the fibro-vascular bundle from + the ground tissue. The bundle (Fig. 68, _G_) shows a band of + tracheary tissue in the centre surrounded by colorless cells, all + about alike. + + All of the organs of the fern grow from a definite apical cell, but + it is difficult to study except in the root. + + Selecting a fresh, pretty large root, a series of thin longitudinal + sections should be made either holding the root directly in the + fingers or placing it between pieces of pith. In order to avoid + drying of the sections, as is indeed true in cutting any delicate + tissue, it is a good plan to wet the blade of the razor. If the + section has passed through the apex, it will show the structure + shown in Figure 68, _D_. The apical cell (_a_) is large and + distinct, irregularly triangular in outline. It is really a + triangular pyramid (tetrahedron) with the base upward, which is + shown by making a series of cross-sections through the root tip, and + comparing them with the longitudinal sections. The cross-section of + the apical cell (Fig. _L_) appears also triangular, showing all its + faces to be triangles. Regular series of segments are cut off in + succession from each of the four faces of the apical cell. These + segments undergo regular divisions also, so that very early a + differentiation of the tissues is evident, and the three tissue + systems (epidermal, ground, and fibro-vascular) may be traced + almost to the apex of the root (68, _D_). From the outer series of + segments is derived the peculiar structure (root cap) covering the + delicate growing point and protecting it from injury. + + The apices of the stem and leaves, being otherwise protected, + develop segments only from the sides of the apical cell, the outer + face never having segments cut off from it. + + + + +CHAPTER XIII. + +CLASSIFICATION OF THE PTERIDOPHYTES. + + +There are three well-marked classes of the Pteridophytes: the ferns +(_Filicinae_); horse-tails (_Equisetinae_); and the club mosses +(_Lycopodinae_). + + +CLASS I.--FERNS (_Filicinae_). + +The ferns constitute by far the greater number of pteridophytes, and +their general structure corresponds with that of the maiden-hair fern +described. There are three orders, of which two, the true ferns +(_Filices_) and the adder-tongues (_Ophioglossaceae_), are represented +in the United States. A third order, intermediate in some respects +between these two, and called the ringless ferns (_Marattiaceae_), has +no representatives within our territory. + +The classification is at present based largely upon the characters of +the sporophyte, the sexual plants being still very imperfectly known +in many forms. + +The adder-tongues (_Ophioglossaceae_) are mostly plants of rather small +size, ranging from about ten to fifty centimetres in height. There are +two genera in the United States, the true adder-tongues +(_Ophioglossum_) and the grape ferns (_Botrychium_). They send up but +one leaf each year, and this in fruiting specimens (Fig. 70, _A_) is +divided into two portions, the spore bearing (_x_) and the green +vegetative part. In _Botrychium_ the leaves are more or less deeply +divided, and the sporangia distinct (Fig. 71, _B_). In _Ophioglossum_ +the sterile division of the leaf is usually smooth and undivided, and +the spore-bearing division forms a sort of spike, and the sporangia +are much less distinct. The sporangia in both differ essentially from +those of the true ferns in not being derived from a single epidermal +cell, but are developed in part from the ground tissue of the leaf. + +[Illustration: FIG. 70.--Forms of ferns. _A_, grape fern +(_Botrychium_), x 1/2. _x_, fertile part of the leaf. _B_, sporangia of +_Botrychium_, x 3. _C_, flowering fern (_Osmunda_). _x_, spore-bearing +leaflets, x 1/2. _D_, a sporangium of _Osmunda_, x 25. _r_, ring. _E_, +_Polypodium_, x 1. _F_, brake (_Pteris_), x 1. _G_, shield fern +(_Aspidium_), x 2. _H_, spleen-wort (_Asplenium_), x 2. _I_, ostrich +fern (_Onoclea_), x 1. _J_, the same, with the incurved edges of the +leaflet partially raised so as to show the masses of sporangia +beneath, x 2.] + +In the true ferns (_Filices_), the sporangia resemble those already +described, arising in all (unless possibly _Osmunda_) from a single +epidermal cell. + +One group, the water ferns (_Rhizocarpeae_), produce two kinds of +spores, large and small. The former produce male, the latter female +prothallia. In both cases the prothallium is small, and often scarcely +protrudes beyond the spore, and may be reduced to a single archegonium +or antheridium (Fig. 71, _B_, _C_) with only one or two cells +representing the vegetative cells of the prothallium (_v_). The water +ferns are all aquatic or semi-aquatic plants, few in number and scarce +or local in their distribution. The commonest are those of the genus +_Marsilia_ (Fig. 71, _A_), looking like a four-leaved clover. Others +(_Salvinia_, _Azolla_) are floating forms (Fig. 71, _D_). + +[Illustration: FIG. 71.--_A_, _Marsilia_, one of the _Rhizocarpeae_ +(after Underwood). _sp._ the "fruits" containing the sporangia. _B_, a +small spore of _Pilularia_, with the ripe antheridium protruding, +x 180. _C_, male prothallium removed from the spore, x 180. _D_, +_Azolla_ (after Sprague), x 1.] + +Of the true ferns there are a number of families distinguished mainly +by the position of the sporangia, as well as by some differences in +their structure. Of our common ferns, those differing most widely from +the types are the flowering ferns (_Osmunda_), shown in Figure 70, +_C_, _D_. In these the sporangia are large and the ring (_r_) +rudimentary. The leaflets bearing the sporangia are more or less +contracted and covered completely with the sporangia, sometimes all +the leaflets of the spore-bearing leaf being thus changed, sometimes +only a few of them, as in the species figured. + +Our other common ferns have the sporangia in groups (_sori_, sing. +_sorus_) on the backs of the leaves. These sori are of different shape +in different genera, and are usually protected by a delicate +membranous covering (indusium). Illustrations of some of the commonest +genera are shown in Figure 70, _E_, _J_. + + +CLASS II.--HORSE-TAILS (_Equisetinae_). + +The second class of the pteridophytes includes the horse-tails +(_Equisetinae_) of which all living forms belong to a single genus +(_Equisetum_). Formerly they were much more numerous than at present, +remains of many different forms being especially abundant in the coal +formations. + +[Illustration: FIG. 72.--_A_, spore-bearing stem of the field +horse-tail (_Equisetum_), x 1. _x_, the spore-bearing cone. _B_, +sterile stem of the same, x 1/2. _C_, underground stem, with tubers +(_o_), x 1/2. _D_, cross-section of an aerial stem, x 5. _f.b._ +fibro-vascular bundle. _E_, a single fibro-vascular bundle, x 150. +_tr._ vessels. _F_, a single leaf from the cone, x 5. _G_, the same +cut lengthwise, through a spore sac (_sp._), x 5. _H_, a spore, x 50. +_I_, the same, moistened so that the elaters are coiled up, x 150. +_J_, a male prothallium, x 50. _an._ an antheridium. _K_, +spermatozoids, x 300.] + +One of the commonest forms is the field horse-tail (_Equisetum +arvense_), a very abundant and widely distributed species. It grows in +low, moist ground, and is often found in great abundance growing in +the sand or gravel used as "ballast" for railway tracks. + +The plant sends up branches of two kinds from a creeping underground +stem that may reach a length of a metre or more. This stem (Fig. 72, +_C_) is distinctly jointed, bearing at each joint a toothed sheath, +best seen in the younger portions, as they are apt to be destroyed in +the older parts. Sometimes attached to this are small tubers (_o_) +which are much-shortened branches and under favorable circumstances +give rise to new stems. They have a hard, brown rind, and are composed +within mainly of a firm, white tissue, filled with starch. + +The surface of the stem is marked with furrows, and a section across +it shows that corresponding to these are as many large air spaces that +traverse the stem from joint to joint. From the joints numerous roots, +quite like those of the ferns, arise. + +If the stem is dug up in the late fall or winter, numerous short +branches of a lighter color will be found growing from the joints. +These later grow up above ground into branches of two sorts. Those +produced first (Fig. 72, _A_), in April or May, are stouter than the +others, and nearly destitute of chlorophyll. They are usually twenty +to thirty centimetres in height, of a light reddish brown color, and, +like all the stems, distinctly jointed. The sheaths about the joints +(_L_) are much larger than in the others, and have from ten to twelve +large black teeth at the top. These sheaths are the leaves. At the top +of the branch the joints are very close together, and the leaves of +different form, and closely set so as to form a compact cone (_x_). + +A cross-section of the stem (_D_) shows much the same structure as the +underground stem, but the number of air spaces is larger, and in +addition there is a large central cavity. The fibro-vascular bundles +(_f.b._) are arranged in a circle, alternating with the air channels, +and each one has running through it a small air passage. + +The cone at the top of the branch is made up of closely set, +shield-shaped leaves, which are mostly six-sided, on account of the +pressure. These leaves (_F_, _G_) have short stalks, and are arranged +in circles about the stem. Each one has a number of spore cases +hanging down from the edge, and opening by a cleft on the inner side +(_G_, _sp._). They are filled with a mass of greenish spores that +shake out at the slightest jar when ripe. + +The sterile branches (_B_) are more slender than the spore-bearing +ones, and the sheaths shorter. Surrounding the joints, apparently just +below the sheaths, but really breaking through their bases, are +circles of slender branches resembling the main branch, but more +slender. The sterile branches grow to a height of forty to fifty +centimetres, and from their bushy form the popular name of the plant, +"horse-tail," is taken. The surface of the plant is hard and rough, +due to the presence of great quantities of flint in the epidermis,--a +peculiarity common to all the species. + + The stem is mainly composed of large, thin-walled cells, becoming + smaller as they approach the epidermis. The outer cells of the + ground tissue in the green branches contain chlorophyll, and the + walls of some of them are thickened. The fibro-vascular bundles + differ entirely from those of the ferns. Each bundle is nearly + triangular in section (_E_), with the point inward, and the inner + end occupied by a large air space. The tracheary tissue is only + slightly developed, being represented by a few vessels[9] (_tr._) at + the outer angles of the bundle, and one or two smaller ones close to + the air channel. The rest of the bundle is made up of nearly + uniform, rather thin-walled, colorless cells, some of which, + however, are larger, and have perforated cross-walls, representing + the sieve tubes of the fern bundle. There is no individual bundle + sheath, but the whole circle of bundles has a common outer sheath. + +[9] A vessel differs from a tracheid in being composed of several +cells placed end to end, the partitions being wholly or partially +absorbed, so as to throw the cells into close communication. + + The epidermis is composed of elongated cells whose walls present a + peculiar beaded appearance, due to the deposition of flint within + them. The breathing pores are arranged in vertical lines, and + resemble in general appearance those of the ferns, though differing + in some minor details. Like the other epidermal cells the guard + cells have heavy deposits of flint, which here are in the form of + thick transverse bars. + + The spore cases have thin walls whose cells, shortly before + maturity, develop thickenings upon their walls, which have to do + with the opening of the spore case. The spores (_H_, _I_) are round + cells containing much chlorophyll and provided with four peculiar + appendages called elaters. The elaters are extremely sensitive to + changes in moisture, coiling up tightly when moistened (_I_), but + quickly springing out again when dry (_H_). By dusting a few dry + spores upon a slide, and putting it under the microscope without any + water, the movement may be easily examined. Lightly breathing upon + them will cause the elaters to contract, but in a moment, as soon as + the moisture of the breath has evaporated, they will uncoil with a + quick jerk, causing the spores to move about considerably. + + The fresh spores begin to germinate within about twenty-four hours, + and the early stages, which closely resemble those of the ferns, may + be easily followed by sowing the spores in water. With care it is + possible to get the mature prothallia, which should be treated as + described for the fern prothallia. Under favorable conditions, the + first antheridia are ripe in about five weeks; the archegonia, which + are borne on separate plants, a few weeks later. The antheridia + (Fig. 72, _J_, _an._) are larger than those of the ferns, and the + spermatozoids (_K_) are thicker and with fewer coils, but otherwise + much like fern spermatozoids. + + The archegonia have a shorter neck than those of the ferns, and the + neck is straight. + + Both male and female prothallia are much branched and very irregular + in shape. + +There are a number of common species of _Equisetum_. Some of them, +like the common scouring rush (_E. hiemale_), are unbranched, and the +spores borne at the top of ordinary green branches; others have all +the stems branching like the sterile stems of the field horse-tail, +but produce a spore-bearing cone at the top of some of them. + + +CLASS III.--THE CLUB MOSSES (_Lycopodinae_). + +The last class of the pteridophytes includes the ground pines, club +mosses, etc., and among cultivated plants numerous species of the +smaller club mosses (_Selaginella_). + +Two orders are generally recognized, although there is some doubt as +to the relationship of the members of the second order. The first +order, the larger club mosses (_Lycopodiaceae_) is represented in the +northern states by a single genus (_Lycopodium_), of which the common +ground pine (_L. dendroideum_) (Fig. 73) is a familiar species. The +plant grows in the evergreen forests of the northern United States as +well as in the mountains further south, and in the larger northern +cities is often sold in large quantities at the holidays for +decorating. It sends up from a creeping, woody, subterranean stem, +numerous smaller stems which branch extensively, and are thickly set +with small moss-like leaves, the whole looking much like a little +tree. At the ends of some of the branches are small cones (_A_, _x_, +_B_) composed of closely overlapping, scale-like leaves, much as in a +fir cone. Near the base, on the inner surface of each of these scales, +is a kidney-shaped capsule (_C_, _sp._) opening by a cleft along the +upper edge and filled with a mass of fine yellow powder. These +capsules are the spore cases. + +The bases of the upright stems are almost bare, but become covered +with leaves higher up. The leaves are in shape like those of a moss, +but are thicker. The spore-bearing leaves are broader and when +slightly magnified show a toothed margin. + +The stem is traversed by a central fibro-vascular cylinder that +separates easily from the surrounding tissue, owing to the rupture of +the cells of the bundle sheath, this being particularly frequent in +dried specimens. When slightly magnified the arrangement of the +tissues may be seen (Fig. 73, _E_). Within the epidermis is a mass of +ground tissue of firm, woody texture surrounding the central oval or +circular fibro-vascular cylinder. This shows a number of white bars +(xylem) surrounded by a more delicate tissue (phloem). + + On magnifying the section more strongly, the cells of the ground + tissue (_G_) are seen to be oval in outline, with thick striated + walls and small intercellular spaces. Examined in longitudinal + sections they are long and pointed, belonging to the class of cells + known as "fibres." + +[Illustration: FIG. 73.--_A_, a club moss (_Lycopodium_), x 1/3. _x_, +cone. _r_, root. _B_, a cone, x 1. _C_, single scale with sporangium +(_sp._). _D_, spores: i, from above; ii, from below, x 325. _E_, cross +section of stem, x 8. _f.b._ fibro-vascular bundle. _F_, portion of +the fibro-vascular bundle, x 150. _G_, cells of the ground tissue, +x 150.] + + The xylem (_F_, _xy._) of the fibro-vascular bundle is composed of + tracheids, much like those of the ferns; the phloem is composed of + narrow cells, pretty much all alike. + + The spores (_D_) are destitute of chlorophyll and have upon the + outside a network of ridges, except on one side where three straight + lines converge, the spore being slightly flattened between them. + + Almost nothing is known of the prothallia of our native species. + +The second order (_Ligulatae_) is represented by two very distinct +families: the smaller club mosses (_Selaginelleae_) and the quill-worts +(_Isoeteae_). Of the former the majority are tropical, but are common +in greenhouses where they are prized for their delicate moss-like +foliage (Fig. 74, _A_). + +[Illustration: FIG. 74.--_A_, one of the smaller club mosses +(_Selaginella_). _sp._ spore-bearing branch, x 2. _B_, part of a stem, +sending down naked rooting branches (_r_), x 1. _C_, longitudinal +section of a spike, with a single macrosporangium at the base; the +others, microsporangia, x 3. _D_, a scale and microsporangium, x 5. +_E_, young microsporangium, x 150. The shaded cells are the spore +mother cells. _F_, a young macrospore, x 150. _G_, section of the +stem, x 50. _H_, a single fibro-vascular bundle, x 150. _I_, vertical +section of the female prothallium of _Selaginella_, x 50. _ar._ +archegonium. _J_, section of an open archegonium, x 300. _o_, the egg +cell. _K_, microspore, with the contained male prothallium, x 300. +_x_, vegetative cell. _sp._ sperm cells. _L_, young plant, with the +attached macrospore, x 6. _r_, the first root. _l_, the first leaves.] + +The leaves in most species are like those of the larger club mosses, +but more delicate. They are arranged in four rows on the upper side of +the stem, two being larger than the others. The smaller branches grow +out sideways so that the whole branch appears flattened, reminding one +of the habit of the higher liverworts. Special leafless branches (_B_, +_r_) often grow downward from the lower side of the main branches, and +on touching the ground develop roots which fork regularly. + +The sporangia are much like those of the ground pines, and produced +singly at the bases of scale leaves arranged in a spike or cone (_A_, +_sp._), but two kinds of spores, large and small, are formed. In the +species figured the lower sporangium produces four large spores +(macrospores); the others, numerous small spores (microspores). + +Even before the spores are ripe the development of the prothallium +begins, and this is significant, as it shows an undoubted +relationship between these plants and the lowest of the seed plants, +as we shall see when we study that group. + + If ripe spores can be obtained by sowing them upon moist earth, the + young plants will appear in about a month. The microspore (Fig. 74, + _K_) produces a prothallium not unlike that of some of the water + ferns, there being a single vegetative cell (_x_), and the rest of + the prothallium forming a single antheridium. The spermatozoids are + excessively small, and resemble those of the bryophytes. + + The macrospore divides into two cells, a large lower one, and a + smaller upper one. The latter gives rise to a flat disc of cells + producing a number of small archegonia of simple structure (Fig. 74, + _I_, _J_). The lower cell produces later a tissue that serves to + nourish the young embryo. + + The development of the embryo recalls in some particulars that of + the seed plants, and this in connection with the peculiarities of + the sporangia warrants us in regarding the _Ligulatae_ as the highest + of existing pteridophytes, and to a certain extent connecting them + with the lowest of the spermaphytes. + +Resembling the smaller club mosses in their development, but differing +in some important points, are the quill-worts (_Isoeteae_). They are +mostly aquatic forms, growing partially or completely submerged, and +look like grasses or rushes. They vary from a few centimetres to half +a metre in height. The stem is very short, and the long cylindrical +leaves closely crowded together. The leaves which are narrow above are +widely expanded and overlapping at the base. The spores are of two +kinds, as in _Selaginella_, but the macrosporangia contain numerous +macrospores. The very large sporangia (_M_, _sp._) are in cavities at +the bases of the leaves, and above each sporangium is a little pointed +outgrowth (ligula), which is also found in the leaves of +_Selaginella_. The quill-worts are not common plants, and owing to +their habits of growth and resemblance to other plants, are likely to +be overlooked unless careful search is made. + + + + +CHAPTER XIV. + +SUB-KINGDOM VI. + +SPERMAPHYTES: PHAENOGAMS. + + +The last and highest great division of the vegetable kingdom has been +named _Spermaphyta_, "seed plants," from the fact that the structures +known as seeds are peculiar to them. They are also commonly called +flowering plants, though this name might be also appropriately given +to certain of the higher pteridophytes. + +In the seed plants the macrosporangia remain attached to the parent +plant, in nearly all cases, until the archegonia are fertilized and +the embryo plant formed. The outer walls of the sporangium now become +hard, and the whole falls off as a seed. + +In the higher spermaphytes the spore-bearing leaves (sporophylls) +become much modified, and receive special names, those bearing the +microspores being commonly known as stamens; those bearing the +macrospores, carpels or carpophylls. The macrosporangia are also +ordinarily known as "ovules," a name given before it was known that +these were the same as the macrosporangia of the higher pteridophytes. + +In addition to the spore-bearing leaves, those surrounding them may be +much changed in form and brilliantly colored, forming, with the +enclosed sporophylls, the "flower" of the higher spermaphytes. + +As might be expected, the tissues of the higher spermaphytes are the +most highly developed of all plants, though some of them are very +simple. The plants vary extremely in size, the smallest being little +floating plants, less than a millimetre in diameter, while others are +gigantic trees, a hundred metres and more in height. + +There are two classes of the spermaphytes: I., the Gymnosperms, or +naked-seeded ones, in which the ovules (macrosporangia) are borne upon +open carpophylls; and II., Angiosperms, covered-seeded plants, in +which the carpophylls form a closed cavity (ovary) containing the +ovules. + + +CLASS I.--GYMNOSPERMS (_Gymnospermae_). + +The most familiar of these plants are the common evergreen trees +(conifers), pines, spruces, cedars, etc. A careful study of one of +these will give a good idea of the most important characteristics of +the class, and one of the best for this purpose is the Scotch pine +(_Pinus sylvestris_), which, though a native of Europe, is not +infrequently met with in cultivation in America. If this species +cannot be had by the student, other pines, or indeed almost any other +conifer, will answer. The Scotch pine is a tree of moderate size, +symmetrical in growth when young, with a central main shaft, and +circles of branches at regular intervals; but as it grows older its +growth becomes irregular, and the crown is divided into several main +branches.[10] The trunk and branches are covered with a rough, scaly +bark of a reddish brown color, where it is exposed by the scaling off +of the outer layers. Covering the younger branches, but becoming +thinner on the older ones, are numerous needle-shaped leaves. These +are in pairs, and the base of each pair is surrounded by several dry, +blackish scales. Each pair of leaves is really attached to a very +short side branch, but this is so short as to make the leaves appear +to grow directly from the main branch. Each leaf is about ten +centimetres in length and two millimetres broad. Where the leaves are +in contact they are flattened, but the outer side is rounded, so that +a cross-section is nearly semicircular in outline. With a lens it is +seen that there are five longitudinal lines upon the surface of the +leaf, and careful examination shows rows of small dots corresponding +to these. These dots are the breathing pores. If a cross-section is +even slightly magnified it shows three distinct parts,--a whitish +outer border, a bright green zone, and a central oval, colorless area, +in which, with a little care, may be seen the sections of two +fibro-vascular bundles. In the green zone are sometimes to be seen +colorless spots, sections of resin ducts, containing the resin so +characteristic of the tissues of the conifers. + +[10] In most conifers the symmetrical form of the young tree is +maintained as long as the tree lives. + +The general structure of the stem may be understood by making a series +of cross-sections through branches of different ages. In all, three +regions are distinguishable; viz., an outer region (bark or cortex) +(Fig. 76, _A_, _c_), composed in part of green cells, and, if the +section has been made with a sharp knife, showing a circle of little +openings, from each of which oozes a clear drop of resin. These are +large resin ducts (_r_). The centre is occupied by a soft white tissue +(pith), and the space between the pith and bark is filled by a mass of +woody tissue. Traversing the wood are numerous radiating lines, some +of which run from the bark to the pith, others only part way. These +are called the medullary rays. While in sections from branches of any +age these three regions are recognizable, their relative size varies +extremely. In a section of a twig of the present year the bark and +pith make up a considerable part of the section; but as older branches +are examined, we find a rapid increase in the quantity of wood, while +the thickness of the bark increases but slowly, and the pith scarcely +at all. In the wood, too, each year's growth is marked by a distinct +ring (_A_ i, ii). As the branches grow in diameter the outer bark +becomes split and irregular, and portions die, becoming brown and +hard. + +The tree has a very perfect root system, but different from that of +any pteridophytes. The first root of the embryo persists as the main +or "tap" root of the full-grown tree, and from it branch off the +secondary roots, which in turn give rise to others. + +The sporangia are borne on special scale-like leaves, and arranged +very much as in certain pteridophytes, notably the club mosses; but +instead of large and small spores being produced near together, the +two kinds are borne on special branches, or even on distinct trees +(_e.g._ red cedar). In the Scotch pine the microspores are ripe about +the end of May. The leaves bearing them are aggregated in small cones +("flowers"), crowded about the base of a growing shoot terminating the +branches (Fig. 77, _A_ [Male]). The individual leaves (sporophylls) are +nearly triangular in shape, and attached by the smaller end. On the +lower side of each are borne two sporangia (pollen sacs) (_C_, _sp._), +opening by a longitudinal slit, and filled with innumerable yellow +microspores (pollen spores), which fall out as a shower of yellow dust +if the branch is shaken. + +The macrosporangia (ovules) are borne on similar leaves, known as +carpels, and, like the pollen sacs, borne in pairs, but on the upper +side of the sporophyll instead of the lower. The female flowers appear +when the pollen is ripe. The leaves of which they are composed are +thicker than those of the male flowers, and of a pinkish color. At the +base on the upper side are borne the two ovules (macrosporangia) +(Fig. 77, _E_, _o_), and running through the centre is a ridge that +ends in a little spine or point. + +The ovule-bearing leaf has on the back a scale with fringed edge (_F_, +_sc._), quite conspicuous when the flower is young, but scarcely to be +detected in the older cone. From the female flower is developed the +cone (Fig. 75, _A_), but the process is a slow one, occupying two +years. Shortly after the pollen is shed, the female flowers, which are +at first upright, bend downward, and assume a brownish color, growing +considerably in size for a short time, and then ceasing to grow for +several months. + +[Illustration: FIG. 75.--Scotch pine (_Pinus sylvestris_). _A_, a ripe +cone, x 1/2. _B_, a year-old cone, x 1. _C_, longitudinal section of +_B_. _D_, a single scale of _B_, showing the sporangia (ovules) (_o_), +x 2. _E_, a scale from a ripe cone, with the seeds (_s_), x 1/2. _F_, +longitudinal section of a ripe seed, x 3. _em._ the embryo. _G_, a +germinating seed, x 2. _r_, the primary root. _H_, longitudinal +section through _G_, showing the first leaves of the young plant still +surrounded by the endosperm, x 4. _I_, an older plant with the leaves +(_l_) withdrawing from the seed coats, x 4. _J_, upper part of a young +plant, showing the circle of primary leaves (cotyledons), x 1. _K_, +section of the same, x 2. _b_, the terminal bud. _L_, cross-section of +the stem of the young plant, x 25. _fb._ a fibro-vascular bundle. _M_, +cross-section of the root, x 25. _x_, wood. _ph._ bast, of the +fibro-vascular bundle.] + +In Figure 75, _B_, is shown such a flower as it appears in the winter +and early spring following. The leaves are thick and fleshy, closely +pressed together, as is seen by dividing the flower lengthwise, and +each leaf ends in a long point (_D_). The ovules are still very small. +As the growth of the tree is resumed in the spring, the flower (cone) +increases rapidly in size and becomes decidedly green in color, the +ovules increasing also very much in size. If a scale from such a cone +is examined about the first of June, the ovules will probably be +nearly full-grown, oval, whitish bodies two to three millimetres in +length. A careful longitudinal section of the scale through the ovule +will show the general structure. Such a section is shown in Figure 77, +_G_. Comparing this with the sporangia of the pteridophytes, the first +difference that strikes us is the presence of an outer coat or +integument (_in._), which is absent in the latter. The single +macrospore (_sp._) is very large and does not lie free in the cavity +of the sporangium, but is in close contact with its wall. It is filled +with a colorless tissue, the prothallium, and if mature, with care it +is possible to see, even with a hand lens, two or more denser oval +bodies (_ar._), the egg cells of the archegonia, which here are very +large. The integument is not entirely closed at the top, but leaves a +little opening through which the pollen spores entered when the flower +was first formed. + +After the archegonia are fertilized the outer parts of the ovule +become hard and brown, and serve to protect the embryo plant, which +reaches a considerable size before the sporangium falls off. As the +walls of the ovule harden, the carpel or leaf bearing it undergoes a +similar change, becoming extremely hard and woody, and as each one +ends in a sharp spine, and they are tightly packed together, it is +almost impossible to separate them. The ripe cone (Fig. 75, _A_) +remains closed during the winter, but in the spring, about the time +the flowers are mature, the scales open spontaneously and discharge +the ripened ovules, now called seeds. Each seed (_E_, _s_) is +surrounded by a membranous envelope derived from the scale to which it +is attached, which becomes easily separated from the seed. The opening +of the cones is caused by drying, and if a number of ripe cones are +gathered in the winter or early spring, and allowed to dry in an +ordinary room, they will in a day or two open, often with a sharp, +crackling sound, and scatter the ripe seeds. + +A section of a ripe seed (_F_) shows the embryo (_em._) surrounded by +a dense, white, starch-bearing tissue derived from the prothallium +cells, and called the "endosperm." This fills up the whole seed which +is surrounded by the hardened shell derived from the integument and +wall of the ovule. The embryo is elongated with a circle of small +leaves at the end away from the opening of the ovule toward which is +directed the root of the embryo. + +The seed may remain unchanged for months, or even years, without +losing its vitality, but if the proper conditions are provided, the +embryo will develop into a new plant. To follow the further growth of +the embryo, the ripe seeds should be planted in good soil and kept +moderately warm and moist. At the end of a week or two some of the +seeds will probably have sprouted. The seed absorbs water, and the +protoplasm of the embryo renews its activity, beginning to feed upon +the nourishing substances in the cells of the endosperm. The embryo +rapidly increases in length, and the root pushes out of the seed +growing rapidly downward and fastening itself in the soil (_G_, _r_). +Cutting the seed lengthwise we find that the leaves have increased +much in length and become green (one of the few cases where +chlorophyll is formed in the absence of light). As these leaves +(called "cotyledons" or seed leaves) increase in length, they +gradually withdraw from the seed whose contents they have exhausted, +and the young plant enters upon an independent existence. + +The young plant has a circle of leaves, about six in number, +surrounding a bud which is the growing point of the stem, and in many +conifers persists as long as the stem grows (Fig. 75, _K_, _b_). A +cross-section of the young stem shows about six separate +fibro-vascular bundles arranged in a circle (_S_, _fb._). The root +shows a central fibro-vascular cylinder surrounded by a dark-colored +ground tissue. Growing from its surface are numerous root hairs +(Fig. 75, _M_). + + For examining the microscopic structure of the pine, fresh material + is for most purposes to be preferred, but alcoholic material will + answer, and as the alcohol hardens the resin, it is for that reason + preferable. + + Cross-sections of the leaf, when sufficiently magnified, show that + the outer colorless border of the section is composed of two parts: + the epidermis of a single row of regular cells with very thick outer + walls, and irregular groups of cells lying below them. These latter + have thick walls appearing silvery and clearer than the epidermal + cells. They vary a good deal, in some leaves being reduced to a + single row, in others forming very conspicuous groups of some size. + The green tissue of the leaf is much more compact than in the fern + we examined, and the cells are more nearly round and the + intercellular spaces smaller. The chloroplasts are numerous and + nearly round in shape. + + Scattered through the green tissue are several resin passages (_r_), + each surrounded by a circle of colorless, thick-walled cells, like + those under the epidermis. At intervals in the latter are + openings--breathing pores--(Fig. 76, _J_), below each of which is an + intercellular space (_i_). They are in structure like those of the + ferns, but the walls of the guard cells are much thickened like the + other epidermal cells. + + Each leaf is traversed by two fibro-vascular bundles of entirely + different structure from those of the ferns. Each is divided into + two nearly equal parts, the wood (_x_) lying toward the inner, flat + side of the leaf, the bast (_T_) toward the outer, convex side. This + type of bundle, called "collateral," is the common form found in the + stems and leaves of seed plants. The cells of the wood or xylem are + rather larger than those of the bast or phloem, and have thicker + walls than any of the phloem cells, except the outermost ones which + are thick-walled fibres like those under the epidermis. Lying + between the bundles are comparatively large colorless cells, and + surrounding the whole central area is a single line of cells that + separates it sharply from the surrounding green tissue. + + In longitudinal sections, the cells, except of the mesophyll (green + tissue) are much elongated. The mesophyll cells, however, are short + and the intercellular spaces much more evident than in the + cross-section. The colorless cells have frequently rounded + depressions or pits upon their walls, and in the fibro-vascular + bundle the difference between the two portions becomes more obvious. + The wood is distinguished by the presence of vessels with close, + spiral or ring-shaped thickenings, while in the phloem are found + sieve tubes, not unlike those in the ferns. + + The fibro-vascular bundles of the stem of the seedling plant show a + structure quite similar to that of the leaf, but very soon a + difference is manifested. Between the two parts of the bundle the + cells continue to divide and add constantly to the size of the + bundle, and at the same time the bundles become connected by a line + of similar growing cells, so that very early we find a ring of + growing cells extending completely around the stem. As the cells in + this ring increase in number, owing to their rapid division, those + on the borders of the ring lose the power of dividing, and gradually + assume the character of the cells on which they border (Fig. 76, + _B_, _cam._). The growth on the inside of the ring is more rapid + than on the outer border, and the ring continues comparatively near + the surface of the stem (Fig. 76, _A_, _cam._). The spaces between + the bundles do not increase materially in breadth, and as the + bundles increase in size become in comparison very small, appearing + in older stems as mere lines between the solid masses of wood that + make up the inner portion of the bundles. These are the primary + medullary rays, and connect the pith in the centre of the stem with + the bark. Later, similar plates of cells are formed, often only a + single cell thick, and appearing when seen in cross-section as a + single row of elongated cells (_C_, _m_). + + As the stem increases in diameter the bundles become broader and + broader toward the outside, and taper to a point toward the centre, + appearing wedge-shaped, the inner ends projecting into the pith. The + outer limits of the bundles are not nearly so distinct, and it is + not easy to tell when the phloem of the bundles ends and the ground + tissue of the bark begins. + + A careful examination of a cross-section of the bark shows first, if + taken from a branch not more than two or three years old, the + epidermis composed of cells not unlike those of the leaf, but whose + walls are usually browner. Underneath are cells with brownish walls, + and often more or less dry and dead. These cells give the brown + color to the bark, and later both epidermis and outer ground tissue + become entirely dead and disappear. The bulk of the ground tissue is + made up of rather large, loose cells, the outer ones containing a + good deal of chlorophyll. Here and there are large resin ducts + (Fig. 76, _H_), appearing in cross-section as oval openings + surrounded by several concentric rows of cells, the innermost + smaller and with denser contents. These secrete the resin that fills + the duct and oozes out when the stem is cut. All of the cells of the + bark contain more or less starch. + + The phloem, when strongly magnified, is seen to be made up of cells + arranged in nearly regular radiating rows. Their walls are not very + thick and the cells are usually somewhat flattened in a radial + direction. + + Some of the cells are larger than the others, and these are found to + be, when examined in longitudinal section, sieve tubes (Fig. 76, + _E_) with numerous lateral sieve plates quite similar to those found + in the stems of ferns. + +[Illustration: FIG. 76.--Scotch pine. _A_, cross-section of a +two-year-old branch, x 3. _p_, pith. _c_, bark. The radiating lines +are medullary rays. _r_, resin ducts. _B_, part of the same, x 150. +_cam._ cambium cells. _x_, tracheids. _C_, cross-section of a +two-year-old branch at the point where the two growth rings join: _I_, +the cells of the first year's growth; _II_, those of the second year. +_m_, a medullary ray, x 150. _D_, longitudinal section of a branch, +showing the form of the tracheids and the bordered pits upon their +walls. _m_, medullary ray, x 150. _E_, part of a sieve tube, x 300. +_F_, cross-section of a tracheid passing through two of the pits in +the wall (_p_), x 300. _G_, longitudinal section of a branch, at right +angles to the medullary rays (_m_). At _y_, the section has passed +through the wall of a tracheid, bearing a row of pits, x 150. _H_, +cross-section of a resin duct, x 150. _I_, cross-section of a leaf, +x 20. _fb._ fibro-vascular bundle. _r_, resin duct. _J_, section of a +breathing pore, x 150. _i_, the air space below it.] + + The growing tissue (cambium), separating the phloem from the wood, + is made up of cells quite like those of the phloem, into which they + insensibly merge, except that their walls are much thinner, as is + always the case with rapidly growing cells. These cells (_B_, + _cam._) are arranged in radial rows and divide, mainly by walls, at + right angles to the radii of the stem. If we examine the inner side + of the ring, the change the cells undergo is more marked. They + become of nearly equal diameter in all directions, and the walls + become woody, showing at the same time distinct stratification (_B_, + _x_). + + On examining the xylem, where two growth rings are in contact, the + reason of the sharply marked line seen when the stem is examined + with the naked eye is obvious. On the inner side of this line (_I_), + the wood cells are comparatively small and much flattened, while the + walls are quite as heavy as those of the much larger cells (_II_) + lying on the outer side of the line. The small cells show the point + where growth ceased at the end of the season, the cells becoming + smaller as growth was feebler. The following year when growth + commenced again, the first wood cells formed by the cambium were + much larger, as growth is most vigorous at this time, and the wood + formed of these larger cells is softer and lighter colored than that + formed of the smaller cells of the autumn growth. + + The wood is mainly composed of tracheids, there being no vessels + formed except the first year. These tracheids are characterized by + the presence of peculiar pits upon their walls, best seen when thin + longitudinal sections are made in a radial direction. These pits + (Fig. 76, _D_, _p_) appear in this view as double circles, but if + cut across, as often happens in a cross-section of the stem, or in a + longitudinal section at right angles to the radius (tangential), + they are seen to be in shape something like an inverted saucer with + a hole through the bottom. They are formed in pairs, one on each + side of the wall of adjacent tracheids, and are separated by a very + delicate membrane (_F_, _p_, _G_, _y_). These "bordered" pits are + very characteristic of the wood of all conifers. + + The structure of the root is best studied in the seedling plant, or + in a rootlet of an older one. The general plan of the root is much + like that of the pteridophytes. The fibro-vascular bundle (Fig. 75, + _M_, _fb._) is of the so-called radial type, there being three xylem + masses (_x_) alternating with as many phloem masses (_ph._) in the + root of the seedling. This regularity becomes destroyed as the root + grows older by the formation of a cambium ring, something like that + in the stem. + + The development of the sporangia is on the whole much like that of + the club mosses, and will not be examined here in detail. The + microspores (pollen spores) are formed in groups of four in + precisely the same way as the spores of the bryophytes and + pteridophytes, and by collecting the male flowers as they begin to + appear in the spring, and crushing the sporangia in water, the + process of division may be seen. For more careful examination they + may be crushed in a mixture of water and acetic acid, to which is + added a little gentian violet. This mixture fixes and stains the + nuclei of the spores, and very instructive preparations may thus be + made.[11] + +[11] See the last chapter for details. + +[Illustration: FIG. 77.--Scotch pine (except _E_ and _F_). _A_, end of +a branch bearing a cluster of male flowers ([Male]), x 1/2. _B_, a similar +branch, with two young female flowers ([Female]), natural size. _C_, a +scale from a male flower, showing the two sporangia (_sp._); x 5. _D_, +a single ripe pollen spore (microspore), showing the vegetative cell +(_x_), x 150. _E_, a similar scale, from a female flower of the +Austrian pine, seen from within, x 4. _o_, the sporangium (ovule). +_F_, the same, seen from the back, showing the scale (_sc._) attached +to the back. _G_, longitudinal section through a full-grown ovule of +the Scotch pine. _p_, a pollen spore sending down its tube to the +archegonia (_ar._). _sp._ the prothallium (endosperm), filling up the +embryo sac, x 10. _H_, the neck of the archegonium, x 150.] + + The ripe pollen spores (Fig. 77, _D_) are oval cells provided with + a double wall, the outer one giving rise to two peculiar + bladder-like appendages (_z_). Like the microspores of the smaller + club mosses, a small cell is cut off from the body of the spore + (_x_). These pollen spores are carried by the wind to the ovules, + where they germinate. + + The wall of the ripe sporangium or pollen sac is composed of a + single layer of cells in most places, and these cells are provided + with thickened ridges which have to do with opening the pollen sac. + + We have already examined in some detail the structure of the + macrosporangium or ovule. In the full-grown ovule the macrospore, + which in the seed plants is generally known as the "embryo sac," is + completely filled with the prothallium or "endosperm." In the upper + part of the prothallium several large archegonia are formed in much + the same way as in the pteridophytes. The egg cell is very large, + and appears of a yellowish color, and filled with large drops that + give it a peculiar aspect. There is a large nucleus, but it is not + always readily distinguished from the other contents of the egg + cell. The neck of the archegonium is quite long, but does not + project above the surface of the prothallium (Fig. 77, _H_). + +The pollen spores are produced in great numbers, and many of them fall +upon the female flowers, which when ready for pollination have the +scales somewhat separated. The pollen spores now sift down to the base +of the scales, and finally reach the opening of the ovule, where they +germinate. No spermatozoids are produced, the seed plants differing in +this respect from all pteridophytes. The pollen spore bursts its +outer coat, and sends out a tube which penetrates for some distance +into the tissue of the ovule, acting very much as a parasitic fungus +would do, and growing at the expense of the tissue through which it +grows. After a time growth ceases, and is not resumed until the +development of the female prothallium and archegonia is nearly +complete, which does not occur until more than a year from the time +the pollen spore first reaches the ovule. Finally the pollen tube +penetrates down to and through the open neck of the archegonium, until +it comes in contact with the egg cell. These stages can only be seen +by careful sections through a number of ripe ovules, but the track of +the pollen tube is usually easy to follow, as the cells along it are +often brown and apparently dead (Fig. 77, _G_). + + +CLASSIFICATION OF THE GYMNOSPERMS. + +There are three classes of the gymnosperms: I., cycads (_Cycadeae_); +II., conifers (_Coniferae_); III., joint firs (_Gnetaceae_). All of the +gymnosperms of the northern United States belong to the second order, +but representatives of the others are found in the southern and +southwestern states. + +The cycads are palm-like forms having a single trunk crowned by a +circle of compound leaves. Several species are grown for ornament in +conservatories, and a few species occur native in Florida, but +otherwise do not occur within our limits. + +[Illustration: FIG. 78.--Illustrations of gymnosperms. _A_, fruiting +leaf of a cycad (_Cycas_), with macrosporangia (ovules) (_ov._), x 1/4. +_B_, leaf of _Gingko_, x 1/2. _C_, branch of hemlock (_Tsuga_), with a +ripe cone, x 1. _D_, red cedar (_Juniperus_), x 1. _E_, _Arbor-vitae_ +(_Thuja_), x 1.] + +The spore-bearing leaves usually form cones, recalling somewhat in +structure those of the horse-tails, but one of the commonest +cultivated species (_Cycas revoluta_) bears the ovules, which are very +large, upon leaves that are in shape much like the ordinary ones +(Fig. 78, _A_). + +Of the conifers, there are numerous familiar forms, including all our +common evergreen trees. There are two sub-orders,--the true conifers +and the yews. In the latter there is no true cone, but the ovules are +borne singly at the end of a branch, and the seed in the yew (_Taxus_) +is surrounded by a bright red, fleshy integument. One species of yew, +a low, straggling shrub, occurs sparingly in the northern states, and +is the only representative of the group at the north. The European yew +and the curious Japanese _Gingko_ (Fig. 78, _B_) are sometimes met +with in cultivation. + +Of the true conifers, there are a number of families, based on +peculiarities in the leaves and cones. Some have needle-shaped leaves +and dry cones like the firs, spruces, hemlock (Fig. 78, _C_). Others +have flattened, scale-like leaves, and more or less fleshy cones, like +the red cedar (Fig. 78, _D_) and _Arbor-vitae_ (_E_). + +A few of the conifers, such as the tamarack or larch (_Larix_) and +cypress (_Taxodium_), lose their leaves in the autumn, and are not, +therefore, properly "evergreen." + +The conifers include some of the most valuable as well as the largest +of trees. Their timber, especially that of some of the pines, is +particularly valuable, and the resin of some of them is also of much +commercial importance. Here belong the giant red-woods (_Sequoia_) of +California, the largest of all American trees. + +The joint firs are comparatively small plants, rarely if ever reaching +the dimensions of trees. They are found in various parts of the world, +but are few in number, and not at all likely to be met with by the +ordinary student. Their flowers are rather more highly differentiated +than those of the other gymnosperms, and are said to show some +approach in structure to those of the angiosperms. + + + + +CHAPTER XV. + +SPERMAPHYTES. + + +CLASS II.--ANGIOSPERMS. + +The angiosperms include an enormous assemblage of plants, all those +ordinarily called "flowering plants" belonging here. There is almost +infinite variety shown in the form and structure of the tissues and +organs, this being particularly the case with the flowers. As already +stated, the ovules, instead of being borne on open carpels, are +enclosed in a cavity formed by a single closed carpel or several +united carpels. To the organ so formed the name "pistil" is usually +applied, and this is known as "simple" or "compound," as it is +composed of one or of two or more carpels. The leaves bearing the +pollen spores are also much modified, and form the so-called +"stamens." In addition to the spore-bearing leaves there are usually +other modified leaves surrounding them, these being often brilliantly +colored and rendering the flower very conspicuous. To these leaves +surrounding the sporophylls, the general name of "perianth" or +"perigone" is given. The perigone has a twofold purpose, serving both +to protect the sporophylls, and, at least in bright-colored flowers, +to attract insects which, as we shall see, are important agents in +transferring pollen from one flower to another. + +When we compare the embryo sac (macrospore) of the angiosperms with +that of the gymnosperms a great difference is noticed, there being +much more difference than between the latter and the higher +pteridophytes. Unfortunately there are very few plants where the +structure of the embryo sac can be readily seen without very skilful +manipulation. + + There are, however, a few plants in which the ovules are very small + and transparent, so that they may be mounted whole and examined + alive. The best plant for this purpose is probably the "Indian pipe" + or "ghost flower," a curious plant growing in rich woods, blossoming + in late summer. It is a parasite or saprophyte, and entirely + destitute of chlorophyll, being pure white throughout. It bears a + single nodding flower at the summit of the stem. (Another species + much like it, but having several brownish flowers, is shown in + Figure 115, _L_.) + + If this plant can be had, the structure of the ovule and embryo sac + may be easily studied, by simply stripping away the tissue bearing + the numerous minute ovules, and mounting a few of them in water, or + water to which a little sugar has been added. + +[Illustration: FIG. 79.--_A_, ripe ovule of _Monotropa uniflora_, in +optical section, x 100. _m_, micropyle. _e_, embryo sac. _B_, the +embryo sac, x 300. At the top is the egg apparatus, consisting of the +two synergidae (_s_), and the egg cell (_o_). In the centre is the +"endosperm nucleus" (_k_). At the bottom, the "antipodal cells" (_g_).] + + The ovules are attached to a stalk, and each consists of about two + layers of colorless cells enclosing a central, large, oblong cell + (Fig. 79, _A_, _E_), the embryo sac or macrospore. If the ovule is + from a flower that has been open for some time, we shall find in the + centre of the embryo sac a large nucleus (_k_) (or possibly two + which afterward unite into one), and at each end three cells. Those + at the base (_g_) probably represent the prothallium, and those at + the upper end a very rudimentary archegonium, here generally called + the "egg apparatus." + + Of the three cells of the "egg apparatus" the lower (_o_) one is the + egg cell; the others are called "synergidae." The structure of the + embryo sac and ovules is quite constant among the angiosperms, the + differences being mainly in the shape of the ovules, and the degree + to which its coverings or integuments are developed. + + The pollen spores of many angiosperms will germinate very easily in + a solution of common sugar in water: about fifteen per cent of sugar + is the best. A very good plant for this purpose is the sweet pea, + whose pollen germinates very rapidly, especially in warm weather. + The spores may be sown in a little of the sugar solution in any + convenient vessel, or in a hanging drop suspended in a moist + chamber, as described for germinating the spores of the slime + moulds. The tube begins to develop within a few minutes after the + spores are placed in the solution, and within an hour or so will + have reached a considerable length. Each spore has two nuclei, but + they are less evident here than in some other forms (Fig. 79). + +[Illustration: FIG. 80.--Germinating pollen spores of the sweet pea, +x 200.] + +The upper part of the pistil is variously modified, having either +little papillae which hold the pollen spores, or are viscid. In either +case the spores germinate when placed upon this receptive part +(stigma) of the pistil, and send their tubes down through the tissues +of the pistil until they reach the ovules, which are fertilized much +as in the gymnosperms. + +The effect of fertilization extends beyond the ovule, the ovary and +often other parts of the flower being affected, enlarging and often +becoming bright-colored and juicy, forming the various fruits of the +angiosperms. These fruits when ripe may be either dry, as in the case +of grains of various kinds, beans, peas, etc.; or the ripe fruit may +be juicy, serving in this way to attract animals of many kinds which +feed on the juicy pulp, and leave the hard seeds uninjured, thus +helping to distribute them. Common examples of these fleshy fruits are +offered by the berries of many plants; apples, melons, cherries, etc., +are also familiar examples. + +The seeds differ a good deal both in regard to size and the degree to +which the embryo is developed at the time the seed ripens. + + +CLASSIFICATION OF THE ANGIOSPERMS. + +The angiosperms are divided into two sub-classes: I. _Monocotyledons_ +and II. _Dicotyledons_. + +The monocotyledons comprise many familiar plants, both ornamental and +useful. They have for the most part elongated, smooth-edged leaves +with parallel veins, and the parts of the flower are in threes in the +majority of them. As their name indicates, there is but one cotyledon +or seed leaf, and the leaves from the first are alternate. As a rule +the embryo is very small and surrounded by abundant endosperm. + +The most thoroughly typical members of the sub-class are the lilies +and their relatives. The one selected for special study here, the +yellow adder-tongue, is very common in the spring; but if not +accessible, almost any liliaceous plant will answer. Of garden +flowers, the tulip, hyacinth, narcissus, or one of the common lilies +may be used; of wild flowers, the various species of _Trillium_ +(Fig. 83, _A_) are common and easily studied forms, but the leaves are +not of the type common to most monocotyledons. + +The yellow adder-tongue (_Erythronium americanum_) (Fig. 81) is one of +the commonest and widespread of wild flowers, blossoming in the +northern states from about the middle of April till the middle of May. +Most of the plants found will not be in flower, and these send up but +a single, oblong, pointed leaf. The flowering plant has two similar +leaves, one of which is usually larger than the other. They seem to +come directly from the ground, but closer examination shows that they +are attached to a stem of considerable length entirely buried in the +ground. This arises from a small bulb (_B_) to whose base numerous +roots (_r_) are attached. Rising from between the leaves is a slender, +leafless stalk bearing a single, nodding flower at the top. + +The leaves are perfectly smooth, dull purplish red on the lower side, +and pale green with purplish blotches above. The epidermis may be very +easily removed, and is perfectly colorless. Examined closely, +longitudinal rows of whitish spots may be detected: these are the +breathing pores. + +[Illustration: FIG. 81.--_A_, plant of the yellow adder-tongue +(_Erythronium americanum_), x 1/3. _B_, the bulb of the same, x 1/2. _r_, +roots. _C_, section of _B_. _st._ the base of the stem bearing the +bulb for next year (_b_) at its base. _D_, a single petal and stamen, +x 1/2. _f_, the filament. _an._ anther. _E_, the gynoecium (pistil), x 1. +_o_, ovary. _st._ style. _z_, stigma. _F_, a full-grown fruit, x 1/2. +_G_, section of a full-grown macrosporangium (ovule), x 25: i, ii, the +two integuments. _sp._ macrospore (embryo sac). _H_, cross-section of +the ripe anther, x 12. _I_, a single pollen spore, x 150, showing the +two nuclei (_n_, _n'_). _J_, a ripe seed, x 2. _K_, the same, in +longitudinal section. _em._ the embryo. _L_, cross-section of the +stem, x 12. _fb._ fibro-vascular bundle. _M_, diagram of the flower.] + +A cross-section of the stem shows numerous whitish areas scattered +through it. These are the fibro-vascular bundles which in the +monocotyledons are of a simple type. The bulb is composed of thick +scales, which are modified leaves, and on cutting it lengthwise, we +shall probably find the young bulb of next year (Fig. _C_, _b_) +already forming inside it, the young bulb arising as a bud at the +base of the stem of the present year. + +The flower is made up of five circles of very much modified leaves, +three leaves in each set. The two outer circles are much alike, but +the three outermost leaves are slightly narrower and strongly tinged +with red on the back, completely concealing the three inner ones +before the flower expands. The latter are pure yellow, except for a +ridge along the back, and a few red specks near the base inside. These +six leaves constitute the perigone of the flower; the three outer are +called sepals, the inner ones petals. + +The next two circles are composed of the sporophylls bearing the +pollen spores.[12] These are the stamens, and taken collectively are +known as the "_Androecium_." Each leaf or stamen consists of two +distinct portions, a delicate stalk or "filament" (_D_, _f_), and the +upper spore-bearing part, the "anther" (_an._). The anther in the +freshly opened flower has a smooth, red surface; but shortly after, +the flower opens, splits along each side, and discharges the pollen +spores. A section across the anther shows it to be composed of four +sporangia or pollen sacs attached to a common central axis +("connective") (Fig. _H_). + +[12] The three outer stamens are shorter than the inner set. + +The central circle of leaves, the carpels (collectively the +"gynoecium") are completely united to form a compound pistil (Fig. 81, +_E_). This shows three distinct portions, the ovule-bearing portion +below (_o_), the "ovary," a stalk above (_st._), the "style," and the +receptive portion (_z_) at the top, the "stigma." Both stigma and +ovary show plainly their compound nature, the former being divided +into three lobes, the latter completely divided into three chambers, +as well as being flattened at the sides with a more or less decided +seam at the three angles. The ovules, which are quite large, are +arranged in two rows in each chamber of the ovary, attached to the +central column ("placenta"). + +The flowers open for several days in succession, but only when the sun +is shining. They are visited by numerous insects which carry the +pollen from one flower to another and deposit it upon the stigma, +where it germinates, and the tube, growing down through the long +style, finally reaches the ovules and fertilizes them. Usually only a +comparatively small number of the seeds mature, there being almost +always a number of imperfect ones in each pod. The pod or fruit (_F_) +is full-grown about a month after the flower opens, and finally +separates into three parts, and discharges the seeds. These are quite +large (Fig. 81, _J_) and covered with a yellowish brown outer coat, +and provided with a peculiar, whitish, spongy appendage attaching it +to the placenta. A longitudinal section of a ripe seed (_K_) shows the +very small, nearly triangular embryo (_em._), while the rest of the +cavity of the seed is filled with a white, starch-bearing tissue, the +endosperm. + +[Illustration: FIG. 82.--_Erythronium_. _A_, a portion of the wall of +the anther, x 150. _B_, a single epidermal cell from the petal, x 150. +_C_, cross-section of a fibro-vascular bundle of the stem, x 150. +_tr._ vessels. _D_, _E_, longitudinal section of the same, showing the +markings of the vessels, x 150. _F_, a bit of the epidermis from the +lower surface of a leaf, showing the breathing pores, x 50. _G_, a +single breathing pore, x 200. _H_, cross-section of a leaf, x 50. +_st._ a breathing pore. _m_, the mesophyll. _fb._ a vein. _I_, +cross-section of a breathing pore, x 200. _J_, young embryo, x 150.] + + A microscopical examination of the tissues of the plant shows them + to be comparatively simple, this being especially the case with the + fibro-vascular system. + + The epidermis of the leaf is readily removed, and examination shows + it to be made up of oblong cells with large breathing pores in + rows. The breathing pores are much larger than any we have yet + seen, and are of the type common to most angiosperms. The ordinary + epidermal cells are quite destitute of chlorophyll, but the two + cells (guard cells) enclosing the breathing pore contain numerous + chloroplasts, and the oblong nuclei of these cells are usually + conspicuous (Fig. 82, _G_). By placing a piece of the leaf between + pieces of pith, and making a number of thin cross-sections at right + angles to the longer axis of the leaf, some of the breathing pores + will probably be cut across, and their structure may be then better + understood. Such a section is shown in Figure 82, _I_. + + The body of the leaf is made up of chlorophyll-bearing cells of + irregular shape and with large air spaces between (_H_, _m_). The + veins traversing this tissue are fibro-vascular bundles of a type + structure similar to that of the stem, which will be described + presently. + + The stem is made up principally of large cells with thin walls, + which in cross-section show numerous small, triangular, + intercellular spaces (_i_) at the angles. These cells contain, + usually, more or less starch. The fibro-vascular bundles (_C_) are + nearly triangular in section, and resemble considerably those of the + field horse-tail, but they are not penetrated by the air channel, + found in the latter. The xylem, as in the pine, is toward the + outside of the stem, but the boundary between xylem and phloem is + not well defined, there being no cambium present. In the xylem are a + number of vessels (_C_, _tr._) at once distinguishable from the + other cells by their definite form, firm walls, and empty cavity. + The vessels in longitudinal sections show spiral and ringed + thickenings. The rest of the xylem cells, as well as those of the + phloem, are not noticeably different from the cells of the ground + tissue, except for their much smaller size, and absence of + intercellular spaces. + + The structure of the leaves of the perigone is much like that of the + green leaves, but the tissues are somewhat reduced. The epidermis of + the outer side of the sepals has breathing pores, but these are + absent from their inner surface, and from both sides of the petals. + The walls of the epidermal cells of the petals are peculiarly + thickened by apparent infoldings of the wall (_B_), and these cells, + as well as those below them, contain small, yellow bodies + (chromoplasts) to which the bright color of the flower is due. The + red specks on the base of the perigone leaves, as well as the red + color of the back of the sepals, the stalk, and leaves are due to a + purplish red cell sap filling the cells at these points. + + The filaments or stalks of the stamens are made up of very delicate + colorless cells, and the centre is traversed by a single + fibro-vascular bundle, which is continued up through the centre of + the anther. To study the latter, thin cross-sections should be made + and mounted in water. Each of the four sporangia, or pollen sacs, is + surrounded on the outside by a wall, consisting of two layers of + cells, becoming thicker in the middle of the section where the + single fibro-vascular bundle is seen (Fig. 81, _H_). On opening, the + cavities of the adjacent sporangia are thrown together. The inner + cells of the wall are marked by thickened bars, much as we saw in + the pine (Fig. 82, _A_), and which, like these, are formed shortly + before the pollen sacs open. The pollen spores (Fig. 81, _I_) are + large, oval cells, having a double wall, the outer one somewhat + heavier than the inner one, but sufficiently transparent to allow a + clear view of the interior, which is filled with very dense, + granular protoplasm in which may be dimly seen two nuclei (_n_, + _ni._), showing that here also there is a division of the spore + contents, although no wall is present. The spores do not germinate + very readily, and are less favorable for this purpose than those of + some other monocotyledons. Among the best for this purpose are the + spiderwort (_Tradescantia_) and _Scilla_. + + Owing to the large size and consequent opacity of the ovules, as + well as to the difficulty of getting the early stages, the + development and finer structure of the ovule will not be discussed + here. The full-grown ovule may be readily sectioned, and a general + idea of its structure obtained. A little potash may be used to + advantage in this study, carefully washing it away when the section + is sufficiently cleared. We find now that the ovule is attached to a + stalk (funiculus) (Fig. 81, _G_, _f_), the body of the ovule being + bent up so as to lie against the stalk. Such an inverted ovule is + called technically, "anatropous." The ovule is much enlarged where + the stalk bends. The upper part of the ovule is on the whole like + that of the pine, but there are two integuments (i, ii) instead of + the single one found in the pine. + + As the seed develops, the embryo sac (_G_, _sp._) enlarges so as to + occupy pretty much the whole space of the seed. At first it is + nearly filled with a fluid, but a layer of cells is formed, lining + the walls, and this thickens until the whole space, except what is + occupied by the small embryo, is filled with them. These are called + the "endosperm cells," but differ from the endosperm cells of the + gymnosperms, in the fact that they are not developed until after + fertilization, and can hardly, therefore, be regarded as + representing the prothallium of the gymnosperms and pteridophytes. + These cells finally form a firm tissue, whose cells are filled with + starch that forms a reserve supply of food for the embryo plant when + the seed germinates. The embryo (Fig. 81, _K_, _em._, Fig. 82, _J_), + even when the seed is ripe, remains very small, and shows scarcely + any differentiation. It is a small, pear-shaped mass of cells, the + smaller end directed toward the upper end of the embryo sac. + +The integuments grow with the embryo sac, and become brown and hard, +forming the shell of the seed. The stalk of the ovule also enlarges, +and finally forms the peculiar, spongy appendage of the seeds already +noticed (Fig. 81, _J_, _K_). + + + + +CHAPTER XVI. + +CLASSIFICATION OF THE MONOCOTYLEDONS. + + +In the following chapter no attempt will be made to give an exhaustive +account of the characteristics of each division of the monocotyledons, +but only such of the most important ones as may serve to supplement +our study of the special one already examined. The classification +here, and this is the case throughout the spermaphytes, is based +mainly upon the characters of the flowers and fruits. + +The classification adopted here is that of the German botanist +Eichler, and seems to the author to accord better with our present +knowledge of the relationships of the groups than do the systems that +are more general in this country. According to Eichler's +classification, the monocotyledons may be divided into seven groups; +viz., I. _Liliiflorae_; II. _Enantioblastae_; III. _Spadiciflorae_; +IV. _Glumaceae_; V. _Scitamineae_; VI. _Gynandrae_; VII. _Helobiae_. + + +ORDER I.--_Liliiflorae_. + +The plants of this group agree in their general structure with the +adder's-tongue, which is a thoroughly typical representative of the +group; but nevertheless, there is much variation among them in the +details of structure. While most of them are herbaceous forms (dying +down to the ground each year), a few, among which may be mentioned the +yuccas ("bear grass," "Spanish bayonet") of our southern states, +develop a creeping or upright woody stem, increasing in size from year +to year. The herbaceous forms send up their stems yearly from +underground bulbs, tubers, _e.g._ _Trillium_ (Fig. 83, _A_), or +thickened, creeping stems, or root stocks (rhizomes). Good examples of +the last are the Solomon's-seal (Fig. 83, _B_), _Medeola_ (_C_, _D_), +and iris (Fig. 84 _A_). One family, the yams (_Dioscoreae_), of which +we have one common native species, the wild yam (_Dioscorea villosa_), +have broad, netted-veined leaves and are twining plants, while another +somewhat similar family (_Smilaceae_) climb by means of tendrils at the +bases of the leaves. Of the latter the "cat-brier" or "green-brier" is +a familiar representative. + +[Illustration: FIG. 83.--Types of _Liliiflorae_. _A_, _Trillium_, x 1/4. +_B_, single flower of Solomon's-seal (_Polygonatum_), x 1. _C_, upper +part of a plant. _D_, underground stem (rhizome) of Indian cucumber +root (_Medeola_), x 1/2. _E_, a rush (_Juncus_), x 1. _F_, a single +flower, x 2. _A-D_, _Liliaceae_; _E_, _Juncaceae_.] + +The flowers are for the most part conspicuous, and in plan like that +of the adder's-tongue; but some, like the rushes (Fig. 83, _E_), have +small, inconspicuous flowers; and others, like the yams and smilaxes, +have flowers of two kinds, male and female. + +[Illustration: FIG. 84.--Types of _Liliiflorae_. _A_, flower of the +common blue-flag (_Iris_), x 1/2 (_Iridaceae_). _B_, the petal-like upper +part of the pistil, seen from below, and showing a stamen (_an._). +_st._ the stigma, x 1/2. _C_, the young fruit, x 1/2. _D_, section of the +same, x 1. _E_, diagram of the flower. _F_, part of a plant of the +so-called "gray moss" (_Tillandsia_), x 1/2 (_Bromeliaceae_). _G_, a +single flower, x 2. _H_, a seed, showing the fine hairs attached to +it, x 1. _I_, plant of pickerel-weed (_Pontederia_), x 1/4 +(_Pontederiaceae_). _J_, a single flower, x 1. _K_, section of the +ovary, x 4.] + +The principal family of the _Liliiflorae_ is the _Liliaceae_, including +some of the most beautiful of all flowers. All of the true lilies +(_Lilium_), as well as the day lilies (_Funkia_, _Hemerocallis_) of +the gardens, tulips, hyacinths, lily-of-the-valley, etc., belong here, +as well as a number of showy wild flowers including several species of +tiger-lilies (_Lilium_), various species of _Trillium_ (Fig. 83, _A_), +Solomon's-seal (_Polygonatum_) (Fig. 83, _B_), bellwort (_Uvularia_), +and others. In all of these, except _Trillium_, the perigone leaves +are colored alike, and the leaves parallel-veined; but in the latter +the sepals are green and the leaves broad and netted-veined. The fruit +of the _Liliaceae_ may be either a pod, like that of the +adder's-tongue, or a berry, like that of asparagus or Solomon's-seal. + +Differing from the true lilies in having the bases of the perigone +leaves adherent to the surface of the ovary, so that the latter is +apparently below the flower (inferior), and lacking the inner circle +of stamens, is the iris family (_Iridaceae_), represented by the wild +blue-flag (_Iris versicolor_) (Fig. 84, _A_, _E_), as well as by +numerous cultivated species. In iris the carpels are free above and +colored like the petals (_B_), with the stigma on the under side. Of +garden flowers the gladiolus and crocus are the most familiar +examples, besides the various species of iris; and of wild flowers the +little "blue-eyed grass" (_Sisyrinchium_). + +[Illustration: FIG. 85.--_Enantioblastae_. _A_, inflorescence of the +common spiderwort (_Tradescantia_), x 1/2 (_Commelyneae_). _B_, a single +stamen, showing the hairs attached to the filament, x 2. _C_, the +pistil, x 2.] + +The blue pickerel-weed (_Pontederia_) is the type of a family of which +there are few common representatives (Fig. 84, _I_, _K_). + +The last family of the order is the _Bromeliaceae_, all inhabitants of +the warmer parts of the globe, but represented in the southern states +by several forms, the commonest of which is the so-called "gray moss" +(_Tillandsia_) (Fig. 84, _F_, _H_). Of cultivated plants the pineapple, +whose fruit consists of a fleshy mass made up of the crowded fruits +and the fleshy flower stalks, is the best known. + + +ORDER II.--_Enantioblastae_. + +The second order of the monocotyledons, _Enantioblastae_, includes very +few common plants. The most familiar examples are the various species +of _Tradescantia_ (Fig. 88), some of which are native, others exotic. +Of the cultivated forms the commonest is one sometimes called +"wandering-jew," a trailing plant with zigzag stems, and oval, pointed +leaves forming a sheath about each joint. Another common one is the +spiderwort already referred to. In this the leaves are long and +pointed, but also sheathing at the base. When the flowers are showy, +as in these, the sepals and petals are different, the former being +green. The flowers usually open but once, and the petals shrivel up as +the flower fades. There are four families of the order, the spiderwort +belonging to the highest one, _Commelyneae_. + + +ORDER III.--_Spadiciflorae_. + +The third order of the monocotyledons, _Spadiciflorae_, is a very large +one, and includes the largest and the smallest plants of the whole +sub-class. In all of them the flowers are small and often very +inconspicuous; usually, though not always, the male and female flowers +are separate, and often on different plants. The smallest members of +the group are little aquatics, scarcely visible to the naked eye, and +of extremely simple structure, but nevertheless these little plants +produce true flowers. In marked contrast to these are the palms, some +of which reach a height of thirty metres or more. + +The flowers in most of the order are small and inconspicuous, but +aggregated on a spike (spadix) which may be of very large size. Good +types of the order are the various aroids (_Aroideae_), of which the +calla (_Richardia_) is a very familiar cultivated example. Of wild +forms the sweet-flag (_Acorus_), Jack-in-the-pulpit (_Arisaema_) +(Fig. 86, _A_, _D_), skunk-cabbage (_Symplocarpus_), and wild calla +may be noted. In _Arisaema_ (Fig. 86, _A_) the flowers are borne only +on the base of the spadix, and the plant is dioecious. The flowers are +of the simplest structure, the female consisting of a single carpel, +and the male of four stamens (_C_, _D_). While the individual flowers +are destitute of a perigone, the whole inflorescence (cluster of +flowers) is surrounded by a large leaf (spathe), which sometimes is +brilliantly colored, this serving to attract insects. The leaves of +the aroids are generally large and sometimes compound, the only +instance of true compound leaves among the monocotyledons (Fig. 86, +_B_). + +[Illustration: FIG. 86.--Types of _Spadiciflorae_. _A_, inflorescence +of Jack-in-the-pulpit (_Arisaema_, _Aroideae_). The flowers (_fl._) are +at the base of a spike (spadix), surrounded by a sheath (spathe), +which has been cut away on one side in order to show the flowers, x 1/2. +_B_, leaf of the same plant, x 1/4. _C_, vertical section of a female +flower, x 2. _D_, three male flowers, each consisting of four stamens, +x 2. _E_, two plants of a duck-weed (_Lemna_), the one at the left is +in flower, x 4. _F_, another common species. _L_, _Trisulea_, x 1. +_G_, male flower of _E_, x 25. _H_, optical section of the female +flower, showing the single ovule (_ov._), x 25. _I_, part of the +inflorescence of the bur-reed (_Sparganium_), with female flowers, x 1/2 +(_Typhaceae_). _J_, a single, female flower, x 2. _K_, a ripe fruit, +x 1. _L_, longitudinal section of the same. _M_, two male flowers, +x 1. _N_, a pond-weed (_Potomogeton_), x 1 (_Naiadaceae_). _O_, a +single flower, x 2. _P_, the same, with the perianth removed, x 2. +_Q_, fruit of the same, x 2.] + +Probably to be regarded as reduced aroids are the duck-weeds +(_Lemnaceae_) (Fig. 86, _F_, _H_), minute floating plants without any +differentiation of the plant body into stem and leaves. They are +globular or discoid masses of cells, most of them having roots; but +one genus (_Wolffia_) has no roots nor any trace of fibro-vascular +bundles. The flowers are reduced to a single stamen or carpel (Figs. +_E_, _G_, _H_). + +The cat-tail (_Typha_) and bur-reed (_Sparganium_) (Fig. 86, _I_, _L_) +are common representatives of the family _Typhaceae_, and the +pond-weeds (_Naias_ and _Potomogeton_) are common examples of the +family _Naiadeae_. These are aquatic plants, completely submerged +(_Naias_), or sometimes partially floating (_Potomogeton_). The latter +genus includes a number of species with leaves varying from linear +(very narrow and pointed) to broadly oval, and are everywhere common +in slow streams. + +The largest members of the group are the screw-pines (_Pandaneae_) and +the palms (_Palmae_). These are represented in the United States by +only a few species of the latter family, confined to the southern and +southwestern portions. The palmettoes (_Sabal_ and _Chamaerops_) are +the best known. + +Both the palms and screw-pines are often cultivated for ornament, and +as is well known, in the warmer parts of the world the palms are among +the most valuable of all plants. The date palm (_Phoenix dactylifera_) +and the cocoanut (_Cocos nucifera_) are the best known. The apparently +compound ("pinnate" or feather-shaped) leaves of many palms are not +strictly compound; that is, they do not arise from the branching of an +originally single leaf, but are really broad, undivided leaves, which +are closely folded like a fan in the bud, and tear apart along the +folds as the leaf opens. + +Although these plants reach such a great size, an examination of the +stem shows that it is built on much the same plan as that of the other +monocotyledons; that is, the stem is composed of a mass of soft, +ground tissue through which run many small isolated, fibro-vascular +bundles. A good idea of this structure may be had by cutting across a +corn-stalk, which is built on precisely the same pattern. + + +ORDER IV.--_Glumaceae_. + +The plants of this order resemble each other closely in their habit, +all having long, narrow leaves with sheathing bases that surround the +slender, distinctly jointed stem which frequently has a hard, polished +surface. The flowers are inconspicuous, borne usually in close spikes, +and destitute of a perigone or having this reduced to small scales or +hairs. The flowers are usually surrounded by more or less dry leaves +(glumes, paleae) which are closely set, so as to nearly conceal the +flowers. The flowers are either hermaphrodite or unisexual. + +[Illustration: FIG. 87.--Types of _Glumaceae_. _A_, a sedge, _Carex_ +(_Cyperaceae_). [Male], the male; [Female], the female flowers, x 1/2. +_B_, a single male flower, x 2. _C_, a female flower, x 2. _D_, +fruiting spike of another _Carex_, x 1/2. _E_, a single fruit, x 1. _F_, +the same, with the outer envelope removed, and slightly enlarged. _G_, +section of _F_, x 3. _em._ the embryo. _H_, a bulrush, _Scirpus_ +(_Cyperaceae_), x 1/2. _I_, a single spikelet, x 2. _J_, a single flower, +x 3. _K_, a spikelet of flowers of the common orchard grass, +_Dactylis_ (_Gramineae_), x 2. _L_, a single flower, x 2. _M_, the base +of a leaf, showing the split sheath encircling the stem, x 1. _N_, +section of a kernel of corn, showing the embryo (_em._), x 2.] + +There are two well-marked families, the sedges (_Cyperaceae_) and the +grasses (_Gramineae_). The former have solid, often triangular stems, +and the sheath at the base of the leaves is not split. The commonest +genera are _Carex_ (Fig. 87, _A_, _G_) and _Cyperus_, of which there +are many common species, differing very little and hard to +distinguish. There are several common species of _Carex_ which blossom +early in the spring, the male flowers being quite conspicuous on +account of the large, yellow anthers. The female flowers are in +similar spikes lower down, where the pollen readily falls upon them, +and is caught by the long stigmas. In some other genera, _e.g._ the +bulrushes (_Scirpus_) (Fig. 87, _H_), the flowers are hermaphrodite, +_i.e._ contain both stamens and pistils. The fruit (Fig. 87, _F_) is +seed-like, but really includes the wall of the ovary as well, which is +grown closely to the enclosed seed. The embryo is small, surrounded by +abundant endosperm (Fig. 87, _G_). Very few of the sedges are of any +economic importance, though one, the papyrus of Egypt, was formerly +much valued for its pith, which was manufactured into paper. + +The second family, the grasses, on the contrary, includes the most +important of all food plants, all of the grains belonging here. They +differ mainly from the sedges in having, generally, hollow, +cylindrical stems, and the sheath of the leaves split down one side; +the leaves are in two rows, while those of the sedges are in three. +The flowers (Fig. 87, _L_) are usually perfect; the stigmas, two in +number and like plumes, so that they readily catch the pollen which is +blown upon them. A few, like the Indian corn, have the flowers +unisexual; the male flowers are at the top of the stem forming the +"tassel," and the female flowers lower down forming the ear. The +"silk" is composed of the enormously lengthened stigmas. The fruits +resemble those of the sedges, but the embryo is usually larger and +placed at one side of the endosperm (_N_, _em._). + +While most of the grasses are comparatively small plants, a few of +them are almost tree-like in their proportions, the species of bamboo +(_Bambusa_) sometimes reaching a height of twenty to thirty metres, +with stems thirty to forty centimetres in diameter. + + +ORDER V.--_Scitamineae_. + +[Illustration: FIG. 88.--_Scitamineae_. _A_, upper part of a flowering +plant of Indian shot (_Canna_), much reduced in size (_Cannaceae_). +_B_, a single flower, x 1/2. _C_, the single stamen (_an._), and +petal-like pistil (_gy._), x 1. _D_, section of the ovary, x 2. _E_, +diagram of the flower. The place of the missing stamens is indicated +by small circles. _F_, fruit, x 1/2. _G_, section of an unripe seed. +_em._ embryo. _p_, perisperm, x 2.] + +The plants of this order are all inhabitants of the warmer parts of +the earth, and only a very few occur within the limits of the United +States, and these confined to the extreme south. They are extremely +showy plants, owing to their large leaves and brilliant flowers, and +for this reason are cultivated extensively. Various species of _Canna_ +(Fig. 88) are common in gardens, where they are prized for their +large, richly-colored leaves, and clusters of scarlet, orange, or +yellow flowers. The leafy stems arise from thick tubers or root +stocks, and grow rapidly to a height of two metres or more in the +larger species. The leaves, as in all the order, are very large, and +have a thick midrib with lateral veins running to the margin. The +young leaves are folded up like a trumpet. The flowers are irregular +in form, and in _Canna_ only a single stamen is found; or if more are +present, they are reduced to petal-like rudiments. The single, perfect +stamen (Fig. 88, _C_, _an._) has the filament broad and colored like +the petals, and the anther attached to one side. The pistil (_gy._) is +also petal-like. There are three circles of leaves forming the +perigone, the two outer being more or less membranaceous, and only the +three inner petal-like in texture. The ovary (_o_) is inferior, and +covered on the outside with little papillae that afterward form short +spines on the outside of the fruit (_F_). + +The seeds are large, but the embryo is very small. A section of a +nearly ripe seed shows the embryo (_em._) occupying the upper part of +the embryo sac which does not nearly fill the seed and contains no +endosperm. The bulk of the seed is derived from the tissue of the body +of the ovule, which in most seeds becomes entirely obliterated by the +growth of the embryo sac. The cells of this tissue become filled with +starch, and serve the same purpose as the endosperm of other seeds. +This tissue is called "perisperm." + +Of food plants belonging to this order, the banana (_Musa_) is much +the most important. Others of more or less value are species of +arrowroot (_Maranta_) and ginger (_Zingiber_). + +There are three families: I. _Musaceae_ (banana family); +II. _Zingiberaceae_ (ginger family); and III. _Cannaceae_ (_Canna_, +_Maranta_). + + +ORDER VI.--_Gynandrae_. + +By far the greater number of the plants of this order belong to the +orchis family (_Orchideae_), the second family of the order +(_Apostasieae_), being a small one and unrepresented in the United +States. The orchids are in some respects the most highly specialized +of all flowers, and exhibit wonderful variety in the shape and color +of the flowers, which are often of extraordinary beauty, and show +special contrivances for cross-fertilization that are without parallel +among flowering plants. + +[Illustration: FIG. 89.--_Gynandrae_. _A_, inflorescence of the showy +orchis (_Orchis spectabilis_), x 1 (_Orchideae_). _B_, a single flower, +with the upper leaves of the perianth turned back to show the column +(_x_). _sp._ the spur attached to the lower petal or lip. _o_, the +ovary, x 1. _C_, the column seen from in front. _an._ the stamen. +_gy._ the stigmatic surface, x 1. _D_, the two pollen masses attached +to a straw, which was inserted into the flower, by means of the viscid +disc (_d_): i, the masses immediately after their withdrawal; ii, iii, +the same a few minutes later, showing the change in position. _E_, +diagram of the flower; the position of the missing stamens indicated +by small circles.] + +The flowers are always more or less bilaterally symmetrical +(zygomorphic). The ovary is inferior, and usually twisted so as to +turn the flower completely around. There are two sets of perigone +leaves, three in each, and these are usually much alike except the +lower (through the twisting of the ovary) of the inner set. This +petal, known as the "lip" or "labellum," is usually larger than the +others, and different in color, as well as being frequently of +peculiar shape. In many of them it is also prolonged backward in a +hollow spur (see Fig. 89, _B_). In all of the orchids except the +lady's-slippers (_Cypripedium_) (Fig. 90, _B_), only one perfect +stamen is developed, and this is united with the three styles to form +a special structure known, as the "column" or "gynostemium" (Fig. 89, +_B_, _C_). The pollen spores are usually aggregated into two or four +waxy masses ("pollinia," sing. pollinium), which usually can only be +removed by the agency of insects upon which all but a very few orchids +are absolutely dependent for the pollination of the flowers. + +[Illustration: FIG. 90.--Forms of _Orchideae_. _A_, putty-root +(_Aplectrum_), x 1. _B_, yellow lady's-slipper (_Cypripedium_), x 1/2. +_C_, the column of the same, x 1. _an._ one of the two perfect +stamens. _st._ sterile, petal-like stamen. _gy._. stigma. _D_, +_Arethusa_, x 1/2. _E_, section of the column, x 1: _an._ stamen. _gy._ +stigma. _F_, the same, seen from in front. _G_, _Habenaria_, x 1. _H_, +_Calopogon_, x 1. In the last the ovary is not twisted, so that the +lip (_L_) lies on the upper side of the flower.] + +In the lady-slippers there are two fertile stamens, and a third +sterile one has the form of a large triangular shield terminating the +column (Fig. 90, _C_, _st._). + +The ovules of the orchids are extremely small, and are only partly +developed at the time the flower opens, the pollen tube growing very +slowly and the ovules maturing as it grows down through the tissues of +the column. The ripe seeds are excessively numerous, but so fine as to +look like dust. + +The orchids are mostly small or moderate-sized plants, few of them +being more than a metre or so in height. All of our native species, +with the exception of a few from the extreme south, grow from fibrous +roots or tubers, but many tropical orchids, as is well known, are +"epiphytes"; that is, they grow upon the trunks and branches of trees. +One genus, _Vanilla_, is a twining epiphyte; the fruit of this plant +furnishes the vanilla of commerce. Aside from this plant, the +economical value of the orchids is small, although a few of them are +used medicinally, but are not specially valuable. + +Of the five thousand species known, the great majority are inhabitants +of the tropics, but nevertheless there are within the United States a +number of very beautiful forms. The largest and showiest are the +lady's-slippers, of which we have six species at the north. The most +beautiful is the showy lady's-slipper (_Cypripedium spectabile_), +whose large, pink and white flowers rival in beauty many of the +choicest tropical orchids. Many of the _Habenarias_, including the +yellow and purple fringed orchids, are strikingly beautiful as are the +_Arethuseae_ (_Arethusa_, _Pogonia_, _Calopogon_). The last of these +(Fig. 90, _H_) differs from all our other native orchids in having the +ovary untwisted so that the labellum lies on the upper side of the +flower. + +A number of the orchids are saprophytic, growing in soil rich in +decaying vegetable matter, and these forms are often nearly or quite +destitute of chlorophyll, being brownish or yellowish in color, and +with rudimentary leaves. The coral roots (_Corallorhiza_), of which +there are several species, are examples of these, and another closely +related form, the putty-root (_Aplectrum_) (Fig. 90, _A_), has the +flowering stems like those of _Corallorhiza_, but there is a single, +large, plaited leaf sent up later. + + +ORDER VII.--_Helobiae_. + +The last order of the monocotyledons is composed of marsh or water +plants, some of which recall certain of the dicotyledons. Of the three +families, the first, _Juncagineae_, includes a few inconspicuous plants +with grass-like or rush-like leaves, and small, greenish or yellowish +flowers (_e.g._ arrow-grass, _Triglochin_). + +The second family (_Alismaceae_) contains several large and showy +species, inhabitants of marshes. Of these the water-plantain +(_Alisma_), a plant with long-stalked, oval, ribbed leaves, and a +much-branched panicle of small, white flowers, is very common in +marshes and ditches, and the various species of arrowhead +(_Sagittaria_) are among the most characteristic of our marsh plants. +The flowers are unisexual; the female flowers are usually borne at the +base of the inflorescence, and the male flowers above. The gynoecium +(Fig. 91, _B_) consists of numerous, separate carpels attached to a +globular receptacle. The sepals are green and much smaller than the +white petals. The leaves (_F_) are broad, and, besides the thickened, +parallel veins, have numerous smaller ones connecting these. + +[Illustration: FIG. 91.--Types of _Helobiae_. _A_, inflorescence of +arrowhead (_Sagittaria_), with a single female flower, x 1/2 +(_Alismaceae_). _B_, section through the gynoecium, showing the numerous +single carpels, x 3. _C_, a ripe fruit, x 3. _D_, a male flower, x 1. +_E_, a single stamen, x 3. _F_, a leaf of _Sagittaria variabilis_, +x 1/6. _G_, ditch-moss (_Elodea_), with a female flower (_fl._), x 1/2. +(_Hydrocharideae_). _H_, the flower, x 2. _an._ the rudimentary +stamens. _st._ the stigma. _I_, cross-section of the ovary, x 4. _J_, +male inflorescence of eel-grass (_Vallisneria_), x 1. _K_, a single +expanded male flower, x 12. _st._ the stamen. _L_, a female flower, +x 1. _gy._ the stigma.] + +The last family is the _Hydrocharideae_. They are submersed aquatics, +or a few of them with long-stalked, floating leaves. Two forms, the +ditch-moss (_Elodea_) (Fig. 91, _G_, _I_) and eel-grass +(_Vallisneria_) are very common in stagnant or slow-running water. In +both of these the plants are completely submersed, but there is a +special arrangement for bringing the flowers to the surface of the +water. Like the arrowhead, the flowers are unisexual, but borne on +different plants. The female flowers (_H_, _L_) are comparatively +large, especially in _Vallisneria_, and are borne on long stalks, by +means of which they reach the surface of the water, where they expand +and are ready for pollination. The male flowers (Fig. 91, _J_, _K_) +are extremely small and borne, many together, surrounded by a +membranous envelope, the whole inflorescence attached by a short +stalk. When the flowers are ready to open, they break away from their +attachment, and the envelope opens, allowing them to escape, and they +immediately rise to the surface where they expand and collect in great +numbers about the open female flowers. Sometimes these are so abundant +during the flowering period (late in summer) that the surface of the +water looks as if flour had been scattered over it. After pollination +is effected, the stem of the female flower coils up like a spring, +drawing the flower beneath the water where the fruit ripens. + +The cells of these plants show very beautifully the circulation of the +protoplasm, the movement being very marked and continuing for a long +time under the microscope. To see this the whole leaf of _Elodea_, or +a section of that of _Vallisneria_, may be used. + + + + +CHAPTER XVII. + +DICOTYLEDONS. + + +The second sub-class of the angiosperms, the dicotyledons, receive +their name from the two opposite seed leaves or cotyledons with which +the young plant is furnished. These leaves are usually quite different +in shape from the other leaves, and not infrequently are very thick +and fleshy, filling nearly the whole seed, as may be seen in a bean or +pea. The number of the dicotyledons is very large, and very much the +greater number of living spermaphytes belong to this group. They +exhibit much greater variety in the structure of the flowers than the +monocotyledons, and the leaves, which in the latter are with few +exceptions quite uniform in structure, show here almost infinite +variety. Thus the leaves may be simple (undivided); _e.g._ oak, apple; +or compound, as in clover, locust, rose, columbine, etc. The leaves +may be stalked or sessile (attached directly to the stem), or even +grown around the stem, as in some honeysuckles. The edges of the +leaves may be perfectly smooth ("entire"), or they may be variously +lobed, notched, or wavy in many ways. As many of the dicotyledons are +trees or shrubs that lose their leaves annually, special leaves are +developed for the protection of the young leaves during the winter. +These have the form of thick scales, and often are provided with +glands secreting a gummy substance which helps render them +water-proof. These scales are best studied in trees with large, winter +buds, such as the horsechestnut (Fig. 92), hickory, lilac, etc. On +removing the hard, scale leaves, the delicate, young leaves, and often +the flowers, may be found within the bud. If we examine a young shoot +of lilac or buckeye, just as the leaves are expanding in the spring, a +complete series of forms may be seen from the simple, external scales, +through immediate forms, to the complete foliage leaf. The veins of +the leaves are almost always much-branched, the veins either being +given off from one main vein or midrib (feather-veined or +pinnate-veined), as in an apple leaf, or there may be a number of +large veins radiating from the base of the leaf, as in the scarlet +geranium or mallow. Such leaves are said to be palmately veined. + +[Illustration: FIG. 92.--End of a branch of a horsechestnut in winter, +showing the buds covered by the thick, brown scale leaves, x 1.] + +Some of them are small herbaceous plants, either upright or prostrate +upon the ground, over which they may creep extensively, becoming +rooted at intervals, as in the white clover, or sending out special +runners, as is seen in the strawberry. Others are woody stemmed +plants, persisting from year to year, and often becoming great trees +that live for hundreds of years. Still others are climbing plants, +either twining their stems about the support, like the morning-glory, +hop, honeysuckle, and many others, or having special organs (tendrils) +by which they fasten themselves to the support. These tendrils +originate in different ways. Sometimes, as in the grape and Virginia +creeper, they are reduced branches, either coiling about the support, +or producing little suckers at their tips by which they cling to walls +or the trunks of trees. Other tendrils, as in the poison ivy and the +true ivy, are short roots that fasten themselves firmly in the +crevices of bark or stones. Still other tendrils, as those of the +sweet-pea and clematis, are parts of the leaf. + +The stems may be modified into thorns for protection, as we see in +many trees and shrubs, and parts of leaves may be similarly changed, +as in the thistle. The underground stems often become much changed, +forming bulbs, tubers, root stocks, etc. much as in the +monocotyledons. These structures are especially found in plants which +die down to the ground each year, and contain supplies of nourishment +for the rapid growth of the annual shoots. + +[Illustration: FIG. 93.--_A_, base of a plant of shepherd's-purse +(_Capsella bursa-pastoris_), x 1/2. _r_, the main root. _B_, upper part +of the inflorescence, x 1. _C_, two leaves: i, from the upper part; +ii, from the base of the plant, x 1. _D_, a flower, x 3. _E_, the +same, with sepals and petals removed, x 3. _F_, petal. _G_, sepal. +_H_, stamen, x 10. _f_, filament. _an._ anther. _I_, a fruit with one +of the valves removed to show the seeds, x 4. _J_, longitudinal +section of a seed, x 8. _K_, the embryo removed from the seed, x 8. +_l_, the first leaves (cotyledons). _st._ the stem ending in the root. +_L_, cross-section of the stem, x 20. _fb._ fibro-vascular bundle. +_M_, a similar section of the main root, x 15. _N_, diagram of the +flower.] + +The structure of the tissues, and the peculiarities of the flower and +fruit, will be better understood by a somewhat careful examination of +a typical dicotyledon, and a comparison with this of examples of the +principal orders and families. + +One of the commonest of weeds, and at the same time one of the most +convenient plants for studying the characteristics of the +dicotyledons, is the common shepherd's-purse (_Capsella +bursa-pastoris_) (Figs. 93-95). + +The plant grows abundantly in waste places, and is in flower nearly +the year round, sometimes being found in flower in midwinter, after a +week or two of warm weather. It is, however, in best condition for +study in the spring and early summer. The plant may at once be +recognized by the heart-shaped pods and small, white, four-petaled +flowers. The plant begins to flower when very small, but continues to +grow until it forms a much-branching plant, half a metre or more in +height. On pulling up the plant, a large tap-root (Fig. 93, _A_, _r_) +is seen, continuous with the main stem above ground. The first root of +the seedling plant continues here as the main root of the plant, as +was the case with the gymnosperms, but not with the monocotyledons. +From this tap-root other small ones branch off, and these divide +repeatedly, forming a complex root system. The main root is very tough +and hard, owing to the formation of woody tissue in it. A +cross-section slightly magnified (Fig. 93, _M_), shows a round, +opaque, white, central area (_x_), the wood, surrounded by a more +transparent, irregular ring (_ph._), the phloem or bast; and outside +of this is the ground tissue and epidermis. + +The lower leaves are crowded into a rosette, and are larger than those +higher up, from which they differ also in having a stalk (petiole), +while the upper leaves are sessile. The outline of the leaves varies +much in different plants and in different parts of the same plant, +being sometimes almost entire, sometimes divided into lobes almost to +the midrib, and between these extremes all gradations are found. The +larger leaves are traversed by a strong midrib projecting strongly on +the lower side of the leaf, and from this the smaller veins branch. +The upper leaves have frequently two smaller veins starting from the +base of the leaf, and nearly parallel with the midrib (_C_ i). The +surface of the leaves is somewhat roughened with hairs, some of which, +if slightly magnified, look like little white stars. + +Magnifying slightly a thin cross-section of the stem, it shows a +central, ground tissue (pith), whose cells are large enough to be seen +even when very slightly enlarged. Surrounding this is a ring of +fibro-vascular bundles (_L_, _fb._), appearing white and opaque, and +connected by a more transparent tissue. Outside of the ring of +fibro-vascular bundles is the green ground tissue and epidermis. +Comparing this with the section of the seedling pine stem, a +resemblance is at once evident, and this arrangement was also noticed +in the stem of the horse-tail. + +Branches are given off from the main stem, arising at the point where +the leaves join the stem (axils of the leaves), and these may in turn +branch. All the branches terminate finally in an elongated +inflorescence, and the separate flowers are attached to the main axis +of the inflorescence by short stalks. This form of inflorescence is +known technically as a "raceme." Each flower is really a short branch +from which the floral leaves arise in precisely the same way as the +foliage leaves do from the ordinary branches. There are five sets of +floral leaves: I. four outer perigone leaves (sepals) (_F_), small, +green, pointed leaves traversed by three simple veins, and together +forming the calyx; II. four larger, white, inner perigone leaves +(petals) (_G_), broad and slightly notched at the end, and tapering to +the point of attachment. The petals collectively are known as the +"corolla." The veins of the petals fork once; III. and IV. two sets of +stamens (_E_), the outer containing two short, and the inner, four +longer ones arranged in pairs. Each stamen has a slender filament +(_H_, _f_) and a two-lobed anther (_an._). The innermost set consists +of two carpels united into a compound pistil. The ovary is oblong, +slightly flattened so as to be oval in section, and divided into two +chambers. The style is very short and tipped by a round, flattened +stigma. + +The raceme continues to grow for a long time, forming new flowers at +the end, so that all stages of flowers and fruit may often be found in +the same inflorescence. + +The flowers are probably quite independent of insect aid in +pollination, as the stamens are so placed as to almost infallibly shed +their pollen upon the stigma. This fact, probably, accounts for the +inconspicuous character of the flowers. + +After fertilization is effected, and the outer floral leaves fall off, +the ovary rapidly enlarges, and becomes heart-shaped and much +flattened at right angles to the partition. When ripe, each half falls +away, leaving the seeds attached by delicate stalks (funiculi, sing. +funiculus) to the edges of the membranous partition. The seeds are +small, oval bodies with a shining, yellow-brown shell, and with a +little dent at the end where the stalk is attached. Carefully dividing +the seed lengthwise, or crushing it in water so as to remove the +embryo, we find it occupies the whole cavity of the seed, the young +stalk (_st._) being bent down against the back of one of the +cotyledons (_f_). + +[Illustration: FIG. 94.--_A_, cross-section of the stem of the +shepherd's-purse, including a fibro-vascular bundle, x 150. _ep._ +epidermis. _m_, ground tissue. _sh._ bundle sheath. _ph._ phloem. +_xy._ xylem. _tr._ a vessel. _B_, a young root seen in optical +section, x 150. _r_, root cap. _d_, young epidermis. _pb._ ground. +_pl._ young fibro-vascular bundle. _C_ cross section of a small root, +x 150. _fb._ fibro-vascular bundle. _D_, epidermis from the lower side +of the leaf, x 150. _E_, a star-shaped hair from the surface of the +leaf, x 150. _F_, cross-section of a leaf, x 150. _ep._ epidermis. +_m_, ground tissue. _fb._ section of a vein.] + + A microscopic examination of a cross-section of the older root shows + that the central portion is made up of radiating lines of + thick-walled cells (fibres) interspersed with lines of larger, round + openings (vessels). There is a ring of small cambium cells around + this merging into the phloem, which is composed of irregular cells, + with pretty thick, but soft walls. The ground tissue is composed of + large, loose cells, which in the older roots are often ruptured and + partly dried up. The epidermis is usually indistinguishable in the + older roots. To understand the early structure of the roots, the + smallest rootlets obtainable should be selected. The smallest are so + transparent that the tips may be mounted whole in water, and will + show very satisfactorily the arrangement of the young tissues. The + tissues do not here arise from a single, apical cell, as we found in + the pteridophytes, but from a group of cells (the shaded cells in + Fig. 94, _B_). The end of the root, as in the fern, is covered with + a root cap (_r_) composed of successive layers of cells cut off from + the growing point. The rest of the root shows the same division of + the tissues into the primary epidermis (dermatogen) (_d_), young + fibro-vascular cylinder (plerome) (_pl._), and young ground tissue + (periblem) (_pb._). The structure of the older portions of such + a root is not very easy to study, owing to difficulty in making + good cross-sections of so small an object. By using a very + sharp razor, and holding perfectly straight between pieces of pith, + however, satisfactory sections can be made. The cells contain so + much starch as to make them almost opaque, and potash should be used + to clear them. The fibro-vascular bundle is of the radial type, + there being two masses of xylem (_xy._) joined in the middle, and + separating the two phloem masses (_ph._), some of whose cells are + rather thicker walled than the others. The bundle sheath is not so + plain here as in the fern. The ground tissue is composed of + comparatively large cells with thickish, soft walls, that contain + much starch. The epidermis usually dies while the root is still + young. In the larger roots the early formation of the cambium ring, + and the irregular arrangement of the tissues derived from its + growth, soon obliterate all traces of the primitive arrangement of + the tissues. Making a thin cross-section of the stem, and magnifying + strongly, we find bounding the section a single row of epidermal + cells (Fig. 94, _A_, _ep._) whose walls, especially the outer ones, + are strongly thickened. Within these are several rows of thin-walled + ground-tissue cells containing numerous small, round chloroplasts. + The innermost row of these cells (_sh._) are larger and have but + little chlorophyll. This row of cells forms a sheath around the ring + of fibro-vascular bundles very much as is the case in the + horse-tail. The separate bundles are nearly triangular in outline, + the point turned inward, and are connected with each other by masses + of fibrous tissue (_f_), whose thickened walls have a peculiar, + silvery lustre. Just inside of the bundle sheath there is a row of + similar fibres marking the outer limit of the phloem (_ph._). The + rest of the phloem is composed of very small cells. The xylem is + composed of fibrous cells with yellowish walls and numerous large + vessels (_tr._). The central ground tissue (pith) has large, + thin-walled cells with numerous intercellular spaces, as in the stem + of _Erythronium_. Some of these cells contain a few scattered + chloroplasts in the very thin, protoplasmic layer lining their + walls, but the cells are almost completely filled with colorless + cell sap. + + A longitudinal section shows that the epidermal cells are much + elongated, the cells of the ground tissue less so, and in both the + partition walls are straight. In the fibrous cells, both of the + fibro-vascular bundle and those lying between, the end walls are + strongly oblique. The tracheary tissue of the xylem is made up of + small, spirally-marked vessels, and larger ones with thickened + rings or with pits in the walls. The small, spirally-marked vessels + are nearest the centre, and are the first to be formed in the young + bundle. + + The epidermis of the leaves is composed of irregular cells with wavy + outlines like those of the ferns. Breathing pores, of the same type + as those in the ferns and monocotyledons, are found on both + surfaces, but more abundant and more perfectly developed on the + lower surface of the leaf. Owing to their small size they are not + specially favorable for study. The epidermis is sparingly covered + with unicellular hairs, some of which are curiously branched, being + irregularly star-shaped. The walls of these cells are very thick, + and have little protuberances upon the outer surface (Fig. 93, _E_). + + Cross-sections of the leaf may be made between pith as already + directed; or, by folding the leaf carefully several times, the whole + can be easily sectioned. The structure is essentially as in the + adder-tongue, but the epidermal cells appear more irregular, and the + fibro-vascular bundles are better developed. They are like those of + the stem, but somewhat simpler. The xylem lies on the upper side. + + The ground tissue is composed, as in the leaves we have studied, of + chlorophyll-bearing, loose cells, rather more compact upon the upper + side. (In the majority of dicotyledons the upper surface of the + leaves is nearly or quite destitute of breathing pores, and the + cells of the ground tissue below the upper epidermis are closely + packed, forming what is called the "palisade-parenchyma" of the + leaf.) + +[Illustration: FIG. 95.--_A-D_, successive stages in the development +of the flower of _Capsella_, x 50. _A_, surface view. _B-D_, optical +sections. _s_, sepals, _p_, petals. _an._ stamens. _gy._ pistil. _E_, +cross-section of the young anther, x 180. _sp._ spore mother cells. +_F_, cross-section of full-grown anther. _sp._ pollen spores, x 50. +_F'_, four young pollen spores, x 300. _F"_, pollen spores germinating +upon the stigma, x 300. _pt._ pollen tube. _G_, young pistil in +optical section, x 25. H, cross-section of a somewhat older one. _ov._ +ovules. _I-L_, development of the ovule. _sp._ embryo sac +(macrospore). _I-K_, x 150. _L_, x 50. _M_, embryo sac of a full-grown +ovule, x 150. _Sy._ _Synergidae_. _o_, egg cell. _n_, endosperm +nucleus. _ant._ antipodal cells. _N-Q_, development of the embryo, +x 150. _sus._ suspensor.] + + The shepherd's-purse is an admirable plant for the study of the + development of the flower which is much the same in other + angiosperms. To study this, it is only necessary to teaze out, in a + drop of water, the tip of a raceme, and putting on a cover glass, + examine with a power of from fifty to a hundred diameters. In the + older stages it is best to treat with potash, which will render the + young flowers quite transparent. The young flower (Fig. 95, _A_) is + at first a little protuberance composed of perfectly similar small + cells filled with dense protoplasm. The first of the floral leaves + to appear are the sepals which very early arise as four little buds + surrounding the young flower axis (Fig. 95, _A_, _B_). The stamens + (_C_, _an._) next appear, being at first entirely similar to the + young sepals. The petals do not appear until the other parts of the + flower have reached some size, and the first tracheary tissue + appears in the fibro-vascular bundle of the flower stalk (_D_). The + carpels are more or less united from the first, and form at first a + sort of shallow cup with the edges turned in (_D_, _gy._). This cup + rapidly elongates, and the cavity enlarges, becoming completely + closed at the top where the short style and stigma develop. The + ovules arise in two lines on the inner face of each carpel, and the + tissue which bears them (placenta) grows out into the cavity of the + ovary until the two placentae meet in the middle and form a partition + completely across the ovary (Fig. 95, _H_). + + The stamens soon show the differentiation into filament and anther, + but the former remains very short until immediately before the + flowers are ready to open. The anther develops four sporangia + (pollen sacs), the process being very similar to that in such + pteridophytes as the club mosses. Each sporangium (Fig. _E_, _F_) + contains a central mass of spore mother cells, and a wall of three + layers of cells. The spore mother cells finally separate, and the + inner layer of the wall cells becomes absorbed much as we saw in + the fern, and the mass of mother cells thus floats free in the + cavity of the sporangium. Each one now divides in precisely the same + way as in the ferns and gymnosperms, into four pollen spores. The + anther opens as described for _Erythronium_. + + By carefully picking to pieces the young ovaries, ovules in all + stages of development may be found, and on account of their small + size and transparency, show beautifully their structure. Being + perfectly transparent, it is only necessary to mount them in water + and cover. + + The young ovule (_I_, _J_) consists of a central, elongated body + (nucellus), having a single layer of cells enclosing a large central + cell (the macrospore or embryo sac) (_sp._). The base of the + nucellus is surrounded by two circular ridges (i, ii) of which the + inner is at first higher than the outer one, but later (_K_, _L_), + the latter grows up above it and completely conceals it as well as + the nucellus. One side of the ovule grows much faster than the + other, so that it is completely bent upon itself, and the opening + between the integuments is brought close to the base of the ovule + (Fig. 95, _L_). This opening is called the "micropyle," and allows + the pollen tube to enter. + + The full-grown embryo sac shows the same structure as that already + described in _Monotropa_ (page 276), but as the walls of the + full-grown ovule are thicker here, its structure is rather difficult + to make out. The ripe stigma is covered with little papillae + (Fig. 95, _F_) that hold the pollen spores which may be found here + sending out the pollen tube. By carefully opening the ovary and + slightly crushing it in a drop of water, the pollen tube may + sometimes be seen growing along the stalk of the ovule until it + reaches and enters the micropyle. + + To study the embryo a series of young fruits should be selected, and + the ovules carefully dissected out and mounted in water, to which a + little caustic potash has been added. The ovule will be thus + rendered transparent, and by pressing gently on the cover glass with + a needle so as to flatten the ovule slightly, there is usually no + trouble in seeing the embryo lying in the upper part of the embryo + sac, and by pressing more firmly it can often be forced out upon the + slide. The potash should now be removed as completely as possible + with blotting paper, and pure water run under the cover glass. + + The fertilized egg cell first secretes a membrane, and then divides + into a row of cells (_N_) of which the one nearest the micropyle is + often much enlarged. The cell at the other end next enlarges and + becomes divided by walls at right angles to each other into eight + cells. This globular mass of cells, together with the cell next to + it, is the embryo plant, the row of cells to which it is attached + taking no further part in the process, and being known as the + "suspensor." Later the embryo becomes indented above and forms two + lobes (_Q_), which are the beginnings of the cotyledons. The first + root and the stem arise from the cells next the suspensor. + + + + +CHAPTER XVIII. + +CLASSIFICATION OF DICOTYLEDONS. + + +DIVISION I.--_Choripetalae_. + +Nearly all of the dicotyledons may be placed in one of two great +divisions distinguished by the character of the petals. In the first +group, called _Choripetalae_, the petals are separate, or in some +degenerate forms entirely absent. As familiar examples of this group, +we may select the buttercup, rose, pink, and many others. + +The second group (_Sympetalae_ or _Gamopetalae_) comprises those +dicotyledons whose flowers have the petals more or less completely +united into a tube. The honeysuckles, mints, huckleberry, lilac, etc., +are familiar representatives of the _Sympetalae_, which includes the +highest of all plants. + +[Illustration: FIG. 96.--Iuliflorae. _A_, male; _B_, female +inflorescence of a willow, _Salix_ (_Amentaceae_), x 1/2. _C_, a single +male flower, x 2. _D_, a female flower, x 2. _E_, cross-section of the +ovary, x 8. _F_, an opening fruit. _G_, single seed with its hairy +appendage, x 2.] + +The _Choripetalae_ may be divided into six groups, including twenty-two +orders. The first group is called _Iuliflorae_, and contains numerous, +familiar plants, mostly trees. In these plants, the flowers are small +and inconspicuous, and usually crowded into dense catkins, as in +willows (Fig. 96) and poplars, or in spikes or heads, as in the +lizard-tail (Fig. 97, _G_), or hop (Fig. 97, _I_). The individual +flowers are very small and simple in structure, being often reduced to +the gynoecium or andraecium, carpels and stamens being almost always in +separate flowers. The outer leaves of the flower (sepals and petals) +are either entirely wanting or much reduced, and never differentiated +into calyx and corolla. + +[Illustration: FIG. 97.--Types of _Iuliflorae_. _A_, branch of hazel, +_Corylus_ (_Cupuliferae_), x 1. [Male], male; [Female], female +inflorescence. _B_, a single male flower, x 3. _C_, section of the +ovary of a female flower, x 25. _D_, acorn of red oak, _Quercus_ +(_Cupuliferae_), x 1/2. _E_, seed of white birch, _Betula_ (_Betulaceae_), +x 3. _F_, fruit of horn-bean, _Carpinus_ (_Cupuliferae_), x 1. G, +lizard-tail, _Saururus_ (_Saurureae_), x 1/4. _H_, a single flower, x 2. +_I_, female inflorescence of the hop, _Humulus_ (_Cannabineae_), x 1. +_J_, a single scale with two flowers, x 1. _K_, a male flower of a +nettle, _Urtica_ (_Urticaceae_), x 5.] + +In the willows (Fig. 96) the stamens are bright-colored, so that the +flowers are quite showy, and attract numerous insects which visit them +for pollen and nectar, and serve to carry the pollen to the pistillate +flowers, thus insuring their fertilization. In the majority of the +group, however, the flowers are wind-fertilized. An excellent example +of this is seen in the common hazel (Fig. 97, _A_). The male flowers +are produced in great numbers in drooping catkins at the ends of the +branches, shedding the pollen in early spring before the leaves +unfold. The female flowers are produced on the same branches, but +lower down, and in much smaller numbers. The stigmas are long, and +covered with minute hairs that catch the pollen which is shaken out +in clouds every time the plant is shaken by the wind, and falls in a +shower over the stigmas. A similar arrangement is seen in the oaks, +hickories, and walnuts. + +There are three orders of the _Iuliflorae_: _Amentaceae_, _Piperineae_, +and _Urticinae_. The first contains the birches (_Betulaceae_); oaks, +beeches, hazels, etc. (_Cupuliferae_); walnuts and hickories +(_Juglandeae_); willows and poplars (_Salicaceae_). They are all trees +or shrubs; the fruit is often a nut, and the embryo is very large, +completely filling it. + +The _Piperineae_ are mostly tropical plants, and include the pepper +plant (_Piper_), as well as other plants with similar properties. Of +our native forms, the only common one is the lizard-tail (_Saururus_), +not uncommon in swampy ground. In these plants, the calyx and corolla +are entirely absent, but the flowers have both carpels and stamens +(Fig. 97, _H_). + +The _Urticinae_ include, among our common plants, the nettle family +(_Urticaceae_); plane family (_Plataneae_), represented by the sycamore +or buttonwood (_Platanus_); the hemp family (_Cannabineae_); and the +elm family (_Ulmaceae_). The flowers usually have a calyx, and may +have only stamens or carpels, or both. Sometimes the part of the stem +bearing the flowers may become enlarged and juicy, forming a +fruit-like structure. Well-known examples of this are the fig and +mulberry. + +The second group of the _Choripetalae_ is called _Centrospermae_, and +includes but a single order comprising seven families, all of which, +except one (_Nyctagineae_), are represented by numerous native species. +The latter comprises mostly tropical plants, and is represented in our +gardens by the showy "four-o'clock" (_Mirabilis_). In this plant, as +in most of the order, the corolla is absent, but here the calyx is +large and brightly colored, resembling closely the corolla of a +morning-glory or petunia. The stamens are usually more numerous than +the sepals, and the pistil, though composed of several carpels, has, +as a rule, but a single cavity with the ovules arising from the base, +though sometimes the ovary is several celled. + +[Illustration: FIG. 98.--Types of _Centrospermae_. _A_, plant of +spring-beauty, _Claytonia_ (_Portulacaceae_), x 1/2. _B_, a single +flower, x 1. _C_, fruit, with the sepals removed, x 2. _D_, section of +the seed, showing the curved embryo (_em._), x 5. _E_, single flower +of smart-weed, _Polygonum_ (_Polygonaceae_), x 2. _F_, the pistil, x 2. +_G_, section of the ovary, showing the single ovule, x 4. _H_, section +of the seed, x 2. _I_, base of the leaf, showing the sheath, x 1. _J_, +flower of pig-weed, _Chenopodium_ (_Chenopodiaceae_), x 3: i, from +without; ii, in section. _K_, flower of the poke-weed, _Phytolacca_ +(_Phytolaccaceae_), x 2. _L_, fire-pink, _Silene_ (_Caryophyllaceae_), +x 1/2. _M_, a flower with half of the calyx and corolla removed, x 1. +_N_, ripe fruit of mouse-ear chick-weed, _Cerastium_ (_Caryophyllaceae_), +opening by ten teeth at the summit, x 2. _O_, diagram of the flower +of _Silene_.] + +The first family (_Polygoneae_) is represented by the various species +of _Polygonum_ (knotgrass, smart-weed, etc.), and among cultivated +plants by the buckwheat (_Fagopyrum_). The goose-foot or pig-weed +(_Chenopodium_) among native plants, and the beet and spinach of the +gardens are examples of the family _Chenopodiaceae_. Nearly resembling +the last is the amaranth family (_Amarantaceae_), of which the showy +amaranths and coxcombs of the gardens, and the coarse, green amaranth +or pig-weed are representatives. + +The poke-weed (_Phytolacca_) (Fig. 98, _K_), so conspicuous in autumn +on account of its dark-purple clusters of berries and crimson stalks, +is our only representative of the family _Phytolaccaceae_. The two +highest families are the purslane family (_Portulacaceae_) and pink +family (_Caryophylleae_). These are mostly plants with showy flowers in +which the petals are large and conspicuous, though some of the pink +family, _e.g._ some chick-weeds, have no petals. Of the purslane +family the portulacas of the gardens, and the common purslane or +"pusley," and the spring-beauty (_Claytonia_) (Fig. 98, _A_) are the +commonest examples. The pink family is represented by many common and +often showy plants. The carnation, Japanese pinks, and sweet-william, +all belonging to the genus _Dianthus_, of which there are also two or +three native species, are among the showiest of the family. The genera +_Lychnis_ and _Silene_ (Fig. 98, _L_) also contain very showy species. +Of the less conspicuous genera, the chick-weeds (_Cerastium_ and +_Stellaria_) are the most familiar. + +The third group of the _Choripetalae_ (the _Aphanocyclae_) is a very +large one and includes many common plants distributed among five +orders. The lower ones have all the parts of the flower entirely +separate, and often indefinite in number; the higher have the gynoecium +composed of two or more carpels united to form a compound pistil. + +The first order (_Polycarpae_) includes ten families, of which the +buttercup family (_Ranunculaceae_) is the most familiar. The plants of +this family show much variation in the details of the flowers, which +are usually showy, but the general plan is much the same. In some of +them, like the anemones (Fig. 99, _A_), clematis, and others, the +corolla is absent, but the sepals are large and brightly colored so as +to appear like petals. In the columbine (_Aquilegia_) (Fig. 99, _F_) +the petals are tubular, forming nectaries, and in the larkspur +(Fig. 99, _T_) one of the sepals is similarly changed. + +Representing the custard-apple family (_Anonaceae_) is the curious +papaw (_Asimina_), common in many parts of the United States +(Fig. 100, _A_). The family is mainly a tropical one, but this species +extends as far north as southern Michigan. + +[Illustration: FIG. 99.--Types of _Aphanocyclae_ (_Polycarpae_), family +_Ranunculaceae_. _A_, Rue anemone (_Anemonilla_), x 1/2. _B_, a fruit, +x 2. _C_, section of the same. _D_, section of a buttercup flower +(_Ranunculus_), x 11/2. _E_, diagram of buttercup flower. _F_, wild +columbine (_Aquilegia_), x 1/2. _G_, one of the spur-shaped petals, x 1. +_H_, the five pistils, x 1. _I_, longitudinal section of the fruit, +x 1. _J_, flower of larkspur (_Delphinium_), x 1. _K_, the four petals +and stamens, after the removal of the five colored and petal-like +sepals, x 1.] + +The magnolia family (_Magnoliaceae_) has several common members, the +most widely distributed being, perhaps, the tulip-tree (_Liriodendron_) +(Fig. 100, _C_), much valued for its timber. Besides this there are +several species of magnolia, the most northerly species being the +sweet-bay (_Magnolia glauca_) of the Atlantic States, and the +cucumber-tree (_M. acuminata_); the great magnolia (_M. grandiflora_) +is not hardy in the northern states. + +The sweet-scented shrub (_Calycanthus_) (Fig. 100, _G_) is the only +member of the family _Calycanthaceae_ found within our limits. It grows +wild in the southern states, and is cultivated for its sweet-scented, +dull, reddish flowers. + +[Illustration: FIG. 100.--Types of _Aphanocyclae_ (_Polycarpae_). _A_, +branch of papaw, _Asimina_ (_Anonaceae_), x 1/2. _B_, section of the +flower, x 1. _C_, flower and leaf of tulip-tree, _Liriodendron_ +(_Magnoliaceae_), x 1/3. _D_, section of a flower, x 1/2. _E_, a ripe +fruit, x 1. _F_, diagram of the flower. _G_, flower of the +sweet-scented shrub, _Calycanthus_ (_Calycanthaceae_), x 1/2] + +The barberry (_Berberis_) (Fig. 101, _A_) is the type of the family +_Berberideae_, which also includes the curious mandrake or may-apple +(_Podophyllum_) (Fig. 101, _D_), and the twin-leaf or rheumatism-root +(_Jeffersonia_), whose curious seed vessel is shown in Figure 101, +_G_. The fruit of the barberry and may-apple are edible, but the root +of the latter is poisonous. + +The curious woody twiner, moon-seed (_Menispermum_) (Fig. 101, _I_), +is the sole example in the northern states of the family _Menispermeae_ +to which it belongs. The flowers are dioecious, and the pistillate +flowers are succeeded by black fruits looking like grapes. The +flattened, bony seed is curiously sculptured, and has the embryo +curled up within it. + +[Illustration: FIG. 101.--Types of _Aphanocyclae_ (_Polycarpae_). _A-H_, +_Berberidaceae_. _A_, flower of barberry (_Berberis_), x 2. _B_, the +same in section. _C_, a stamen, showing the method of opening, x 3. +_D_, flower of may-apple (_Podophyllum_), x 1/2. _E_, section of the +ovary of _D_, x 1. _F_, diagram of the flower. _G_, ripe fruit of +twin-leaf (_Jeffersonia_), opening by a lid, x 1/2. _H_, section of +seed, showing the embryo (_em._), x 2. _I_, young leaf and cluster of +male flowers of moon-seed, _Menispermum_ (_Menispermeae_), x 1. _J_, a +single male flower, x 2. _K_, section of a female flower, x 2. _L_, +ripe seed, x 1. _M_, section of _L_, showing the curved embryo.] + +The last two families of the order, the laurel family (_Laurineae_) and +the nutmeg family (_Myristicineae_) are mostly tropical plants, +characterized by the fragrance of the bark, leaves, and fruit. The +former is represented by the sassafras and spice-bush, common +throughout the eastern United States. The latter has no members within +our borders, but is familiar to all through the common nutmeg, which +is the seed of _Myristica fragrans_ of the East Indies. "Mace" is the +"aril" or covering of the seed of the same plant. + +The second order of the _Aphanocyclae_ comprises a number of aquatic +plants, mostly of large size, and is known as the _Hydropeltidinae_. +The flowers and leaves are usually very large, the latter usually +nearly round in outline, and frequently with the stalk inserted near +the middle. The leaves of the perigone are numerous, and sometimes +merge gradually into the stamens, as we find in the common white +water-lily (_Castalia_). + +[Illustration: FIG. 102.--Types of _Aphanocyclae_ (_Hydropeltidinae_). +_A_, yellow water-lily, _Nymphaea_ (_Nymphaeaceae_), x 1/2. _B_, a leaf of +the same, x 1/6. _C_, freshly opened flower, with the large petal-like +sepals removed, x 1/2. _p_, petals. _an._ stamens. _st._ stigma. _D_, +section of the ovary, x 2. _E_, young fruit, x 1/2. _F_, lotus, +_Nelumbo_ (_Nelumbieae_). x 1/6. _G_, a stamen, x 1. _H_, the large +receptacle, with the separate pistils sunk in its surface, x 1/2. _I_, +section of a single pistil, x 2. _ov._ the ovule. _J_, upper part of a +section through the stigma and ovule (_ov._), x 4.] + +There are three families, all represented within the United States. +The first (_Nelumbieae_) has but a single species, the yellow lotus or +nelumbo (_Nelumbo lutea_), common in the waters of the west and +southwest, but rare eastward (Fig. 101, _F_). In this flower, the end +of the flower axis is much enlarged, looking like the rose of a +watering-pot, and has the large, separate carpels embedded in its +upper surface. When ripe, each forms a nut-like fruit which is edible. +There are but two species of _Nelumbo_ known, the second one +(_N. speciosa_) being a native of southeastern Asia, and probably +found in ancient times in Egypt, as it is represented frequently in +the pictures and carvings of the ancient Egyptians. It differs mainly +from our species in the color of its flowers which are red instead of +yellow. It has recently been introduced into New Jersey where it has +become well established in several localities. + +The second family (_Cabombeae_) is also represented at the north by but +one species, the water shield (_Brasenia_), not uncommon in marshes. +Its flowers are quite small, of a dull-purple color, and the leaves +oval in outline and centrally peltate, _i.e._ the leaf stalk inserted +in the centre. The whole plant is covered with a transparent +gelatinous coat. + +The third family (_Nymphaeaceae_) includes the common white water-lilies +(_Castalia_) and the yellow water-lilies (_Nymphaea_) (Fig. 102, _A_). +In the latter the petals are small and inconspicuous (Fig. 102, _C_, +_p_), but the sepals are large and showy. In this family the carpels, +instead of being separate, are united into a large compound pistil. +The water-lilies reach their greatest perfection in the tropics, where +they attain an enormous size, the white, blue, or red flowers of some +species being thirty centimetres or more in diameter, and the leaves +of the great _Victoria regia_ of the Amazon reaching two metres or +more in width. + +The third order of the _Aphanocyclae_ (_Rhoeadinae_ or _Cruciflorae_) +comprises a number of common plants, principally characterized by +having the parts of the flowers in twos or fours, so that they are +more or less distinctly cross-shaped, whence the name _Cruciflorae_. + +There are four families, of which the first is the poppy family +(_Papaveraceae_), including the poppies, eschscholtzias, Mexican or +prickly poppy (_Argemone_), etc., of the gardens, and the blood-root +(_Sanguinaria_), celandine poppy (_Stylophorum_), and a few other wild +plants (see Fig. 103, _A-I_). Most of the family have a colored juice +(latex), which is white in the poppy, yellow in celandine and +_Argemone_, and orange-red in the blood-root. From the latex of the +opium poppy the opium of commerce is extracted. + +[Illustration: FIG. 103.--Types of _Aphanocyclae_ (_Rhoedinae_). _A_, +plant of blood-root, _Sanguinaria_ (_Papaveraceae_), x 1/3. _B_, a single +flower, x 1. _C_, fruit, x 1/2. _D_, section of the seed. _em._ embryo, +x 2. _E_, diagram of the flower. _F_, flower of Dutchman's breeches, +_Dicentra_ (_Fumariaceae_), x 1. _G_, group of three stamens of the +same, x 2. _H_, one of the inner petals, x 2. _I_, fruit of celandine +poppy, _Stylophorum_ (_Papaveraceae_), x 1/2. _J_, flower of mustard, +_Brassica_ (_Cruciferae_), x 1. _K_, the same, with the petals removed, +x 2. _L_, fruit of the same, x 1.] + +The second family, the fumitories (_Fumariaceae_) are delicate, smooth +plants, with curious flowers and compound leaves. The garden +bleeding-heart (_Dicentra spectabilis_) and the pretty, wild +_Dicentras_ (Fig. 103, _F_) are familiar to nearly every one. + +Other examples are the mountain fringe (_Adlumia_), a climbing +species, and several species of _Corydalis_, differing mainly from +_Dicentra_ in having the corolla one-sided. + +The mustard family (_Cruciferae_) comprises by far the greater part of +the order. The shepherd's-purse, already studied, belongs here, and +may be taken as a type of the family. There is great uniformity in all +as regards the flowers, so that the classification is based mainly on +differences in the fruit and seeds. Many of the most valuable garden +vegetables, as well as a few more or less valuable wild plants, are +members of the family, which, however, includes some troublesome +weeds. Cabbages, turnips, radishes, with all their varieties, belong +here, as well as numerous species of wild cresses. A few like the +wall-flower (_Cheiranthus_) and stock (_Matthiola_) are cultivated for +ornament. + +The last family is the caper family (_Capparideae_), represented by +only a few not common plants. The type of the order is _Capparis_, +whose pickled flower-buds constitute capers. + +The fourth order (_Cistiflorae_) of the _Aphanocyclae_ is a very large +one, but the majority of the sixteen families included in it are not +represented within our limits. The flowers have the sepals and petals +in fives, the stamens either the same or more numerous. + +[Illustration: FIG. 104.--Types of _Aphanocyclae_ (_Cistiflorae_). _A_, +flower of wild blue violet, _Viola_ (_Violaceae_), x 1. _B_, the lower +petal prolonged behind into a sac or spur, x 1. _C_, the stamens, x 2. +_D_, pistil, x 2. _E_, a leaf, x 1/2. _F_, section of the ovary, x 2. +_G_, the fruit, x 1. _H_, the same after it has opened, x 1. _I_, +diagram of the flower. _J_, flower of mignonette, _Reseda_ +(_Resedaceae_), x 2. _K_, a petal, x 3. _L_, cross-section of the +ovary, x 3. _M_, fruit, x 1. _N_, plant of sundew, _Drosera_ +(_Droseraceae_), x 1/2. _O_, a leaf that has captured a mosquito, x 2. +_P_, flower of another species (_D. filiformis_), x 2. _Q_, +cross-section of the ovary, x 4.] + +Among the commoner members of the order are the mignonettes +(_Resedaceae_) and the violets (_Violaceae_), of which the various wild +and cultivated species are familiar plants (Fig. 104, _A_, _M_). The +sundews (_Droseraceae_) are most extraordinary plants, growing in boggy +land over pretty much the whole world. They are represented in +the United States by several species of sundew (_Drosera_), and the +still more curious Venus's-flytrap (_Dionaea_) of North Carolina. The +leaves of the latter are sensitive, and composed of two parts which +snap together like a steel trap. If an insect lights upon the leaf, +and touches certain hairs upon its upper surface, the two parts snap +together, holding the insect tightly. A digestive fluid is secreted by +glands upon the inner surface of the leaf, and in a short time the +captured insect is actually digested and absorbed by the leaves. The +same process takes place in the sundew (Fig. 104, _N_) where, however, +the mechanism is somewhat different. Here the tentacles, with which +the leaf is studded, secrete a sticky fluid which holds any small +insect that may light upon it. The tentacles now slowly bend inward +and finally the edges of the leaf as well, until the captured insect +is firmly held, when a digestive process, similar to that in _Dionoea_, +takes place. This curious habit is probably to be explained from the +position where the plant grows, the roots being in water where there +does not seem to be a sufficient supply of nitrogenous matter for the +wants of the plant, which supplements the supply from the bodies of +the captured insects. + +[Illustration: FIG. 105.--Types of _Aphanocyclae_ (_Cistiflorae_). _A_, +_B_, leaves of the pitcher-plant, _Sarracenia_ (_Sarraceniaceae_). _A_, +from the side; _B_, from in front, x 1/2. _C_, St. John's-wort +(_Hypericum_), x 1/2. _D_, a flower, x 1. _E_, the pistil, x 2. _G_, +cross-section of the ovary, x 4. _H_, diagram of the flower.] + +Similar in their habits, but differing much in appearance from the +sundews, are the pitcher-plants (_Sarraceniaceae_), of which one +species (_Sarracenia purpurea_) is very common in peat bogs throughout +the northern United States. In this species (Fig. 105, _A_, _B_), the +leaves form a rosette, from the centre of which arises in early summer +a tall stalk bearing a single, large, nodding, dark-reddish flower +with a curious umbrella-shaped pistil. The leaf stalk is hollow and +swollen, with a broad wing on one side, and the blade of the leaf +forms a sort of hood at the top. The interior of the pitcher is +covered above with stiff, downward-pointing hairs, while below it is +very smooth. Insects readily enter the pitcher, but on attempting to +get out, the smooth, slippery wall at the bottom, and the stiff, +downward-directed hairs above, prevent their escape, and they fall +into the fluid which fills the bottom of the cup and are drowned, the +leaf absorbing the nitrogenous compounds given off during the process +of decomposition. There are other species common in the southern +states, and a California pitcher-plant (_Darlingtonia_) has a colored +appendage at the mouth of the pitcher which serves to lure insects +into the trap. + +Another family of pitcher-plants (_Nepentheae_) is found in the warmer +parts of the old world, and some of them are occasionally cultivated +in greenhouses. In these the pitchers are borne at the tips of the +leaves attached to a long tendril. + +Two other families of the order contain familiar native plants, the +rock-rose family (_Cistaceae_), and the St. John's-worts +(_Hypericaceae_). The latter particularly are common plants, with +numerous showy yellow flowers, the petals usually marked with black +specks, and the leaves having clear dots scattered through them. The +stamens are numerous, and often in several distinct groups (Fig. 105, +_C_, _D_). + +The last order of the _Aphanocyclae_ (the _Columniferae_) has three +families, of which two, the mallows (_Malvaceae_), and the lindens +(_Tiliaceae_), include well-known species. Of the former, the various +species of mallows (Fig. 106, _A_) belonging to the genus _Malva_ are +common, as well as some species of _Hibiscus_, including the showy +swamp _Hibiscus_ or rose-mallow (_H. moscheutos_), common in salt +marshes and in the fresh-water marshes of the great lake region. The +hollyhock and shrubby _Althaea_ are familiar cultivated plants of this +order, and the cotton-plant (_Gossypium_) also belongs here. In all of +these the stamens are much branched, and united into a tube enclosing +the style. Most of them are characterized also by the development of +great quantities of a mucilaginous matter within their tissues. + +The common basswood (_Tilia_) is the commonest representative of the +family _Tiliaceae_ (Fig. 106, _G_). The nearly related European linden, +or lime-tree, is sometimes planted. Its leaves are ordinarily somewhat +smaller than our native species, which it, however, closely resembles. + +[Illustration: FIG. 106.--Types of _Aphanocyclae_ (_Columniferae_). _A_, +flower and leaf of the common mallow, _Malva_ (_Malvaceae_), x 1/2. _B_, +a flower bud, x 1. _C_, section of a flower, x 2. _D_, the fruit, x 2. +_E_, section of one division of the fruit, with the enclosed seed, +x 3. _em._ the embryo. _F_, diagram of the flower. _G_, leaf and +inflorescence of the basswood, _Tilia_ (_Tiliaceae_), x 1/3. _br._ a +bract. _H_, a single flower, x 1. _I_, group of stamens, with +petal-like appendage (_x_), x 2. _J_, diagram of the flower.] + +The fourth group of the _Choripetalae_ is the _Eucyclae_. The flowers +most commonly have the parts in fives, and the stamens are never more +than twice as many as the sepals. The carpels are usually more or less +completely united into a compound pistil. There are four orders, +comprising twenty-five families. + +[Illustration: FIG. 107.--Types of _Eucyclae_ (_Gruinales_). _A_, wild +crane's-bill _Geranium_ (_Geraniaceae_), x 1/2. _B_, a petal, x 1. _C_, +the young fruit, the styles united in a column, x 1/2. _D_, the ripe +fruit, the styles separating to discharge the seeds, x 1/2. _E_, section +of a seed, x 2. _F_, wild flax. _Linum_ (_Linaceae_), x 1/2. _G_, a +single flower, x 2. _H_, cross-section of the young fruit, x 3. _I_, +flower. _J_, leaf of wood-sorrel, _Oxalis_ (_Oxalideae_), x 1. _K_, the +stamens and pistil, x 2. _L_, flower of jewel-weed, _Impatiens_ +(_Balsamineae_), x 1. _M_, the same, with the parts separated. _p_, +petals. _s_, sepals. _an._ stamens. _gy._ pistil. _N_, fruit, x 1. +_O_, the same, opening. _P_, a seed, x 2.] + +The first order (_Gruinales_) includes six families, consisting for +the most part of plants with conspicuous flowers. Here belong the +geraniums (Fig. 107, _A_), represented by the wild geraniums and +crane's-bill, and the very showy geraniums (_Pelargonium_) of the +gardens. The nasturtiums (_Tropaeolum_) represent another family, +mostly tropical, and the wood-sorrels (_Oxalis_) (Fig. 107, _I_) are +common, both wild and cultivated. The most useful member of the order +is unquestionably the common flax (_Linum_), of which there are also +several native species (Fig. 107, _F_). These are types of the flax +family (_Linaceae_). Linen is the product of the tough, fibrous inner +bark of _L. usitatissimum_, which has been cultivated for its fibre +from time immemorial. The last family is the balsam family +(_Balsamineae_). The jewel-weed or touch-me-not (_Impatiens_), so +called from the sensitive pods which spring open on being touched, is +very common in moist ground everywhere (Fig. 107, _L-P_). The garden +balsam, or lady's slipper, is a related species (_I. balsamina_). + +[Illustration: FIG. 108.--_Eucyclae_ (_Terebinthinae_, _AEsculinae_). _A_, +leaves and flowers of sugar-maple, _Acer_ (_Aceraceae_), x 1/2. _B_, a +male flower, x 2. _C_, diagram of a perfect flower. _D_, fruit of the +silver-maple, x 1/2. _E_, section across the seed, x 2. _F_, embryo +removed from the seed, x 1. _G_, leaves and flowers of bladder-nut, +_Staphylea_, (_Sapindaceae_), x 1/2. _H_, section of a flower, x 2. _I_, +diagram of the flower. _J_, flower of buckeye (_AEsculus_), x 11/2. _K_, +flower of smoke-tree, _Rhus_ (_Anacardiaceae_), x 3. _L_, the same, in +section.] + +The second order (_Terebinthinae_) contains but few common plants. +There are six families, mostly inhabitants of the warmer parts of +the world. The best-known members of the order are the orange, lemon, +citron, and their allies. Of our native plants the prickly ash +(_Zanthoxylum_), and the various species of sumach (_Rhus_), are +the best known. In the latter genus belong the poison ivy +(_R. toxicodendron_) and the poison dogwood (_R. venenata_). The +Venetian sumach or smoke-tree (_R. Cotinus_) is commonly planted for +ornament. + +The third order of the _Eucyclae_, the _AEsculinae_, embraces six +families, of which three, the horsechestnuts, etc. (_Sapindaceae_), the +maples (_Aceraceae_), and the milkworts (_Polygalaceae_), have several +representatives in the northern United States. Of the first the +buckeye (_AEsculus_) (Fig. 108, _J_) and the bladder-nut (_Staphylea_) +(Fig. 108, _G_) are the commonest native genera, while the +horsechestnut (_AEsculus hippocastanum_) is everywhere planted. + +The various species of maple (_Acer_) are familiar examples of the +_Aceraceae_ (see Fig. 106, _A_, _F_). + +The fourth and last order of the _Eucyclae_, the _Frangulinae_, is +composed mainly of plants with inconspicuous flowers, the stamens as +many as the petals. Not infrequently they are dioecious, or in some, +like the grape, some of the flowers may be unisexual while others are +hermaphrodite (_i.e._ have both stamens and pistil). Among the +commoner plants of the order may be mentioned the spindle-tree, or +burning-bush, as it is sometimes called (_Euonymus_) (Fig. 109, _A_), +and the climbing bitter-sweet (_Celastrus_) (Fig. 109, _D_), belonging +to the family _Celastraceae_; the holly and black alder, species of +_Ilex_, are examples of the family _Aquifoliaceae_; the various species +of grape (_Vitis_), the Virginia creeper (_Ampelopsis quinquefolia_), +and one or two other cultivated species of the latter, represent the +vine family (_Vitaceae_ or _Ampelidae_), and the buckthorn (_Rhamnus_) +is the type of the _Rhamnaceae_. + +[Illustration: FIG. 109.--_Eucylae_ (_Frangulinae_), _Tricoccae_. _A_, +flowers of spindle-tree, _Euonymus_, (_Celastraceae_), x 1. _B_, +cross-section of the ovary, x 2. _C_, diagram of the flower. _D_, leaf +and fruit of bitter-sweet (_Celastrus_), x 1/2. _E_, fruit opening and +disclosing the seeds. _F_, section of a nearly ripe fruit, showing the +seeds surrounded by the scarlet integument (aril). _em._ the embryo, +x 1. _G_, flower of grape-vine, _Vitis_ (_Vitaceae_), x 2. The corolla +has fallen off. _H_, vertical section of the pistil, x 2. _I_, nearly +ripe fruits of the frost-grape, x 1. _J_, cross-section of young +fruit, x 2. _K_, a spurge, _Euphorbia_ (_Euphorbiaceae_), x 1/2. _L_, +single group of flowers, surrounded by the corolla-like involucre, +x 3. _M_, section of the same, [Male], male flowers; [Female], female +flowers. _N_, a single male flower, x 5. _O_, cross-section of ovary, +x 6. _P_, a seed, x 2. _Q_, longitudinal section of the seed, x 3. +_em._ embryo.] + +The fifth group of the _Choripetalae_ is a small one, comprising but a +single order (_Tricoccae_). The flowers are small and inconspicuous, +though sometimes, as in some _Euphorbias_ and the showy _Poinsettia_ +of the greenhouses, the leaves or bracts surrounding the inflorescence +are conspicuously colored, giving the whole the appearance of a large, +showy, single flower. In northern countries the plants are mostly +small weeds, of which the various spurges or _Euphorbias_ are the most +familiar. These plants (Fig. 109, _K_) have the small flowers +surrounded by a cup-shaped involucre (_L_, _M_) so that the whole +inflorescence looks like a single flower. In the spurges, as in the +other members of the order, the flowers are very simple, being often +reduced to a single stamen or pistil (Fig. 109, _M_, _N_). The plants +generally abound in a milky juice which is often poisonous. This juice +in a number of tropical genera is the source of India-rubber. Some +genera like the castor-bean (_Ricinus_) and _Croton_ are cultivated +for their large, showy leaves. + +The water starworts (_Callitriche_), not uncommon in stagnant water, +represent the family _Callitrichaceae_, and the box (_Buxus_) is the +type of the _Buxaceae_. + +[Illustration: FIG. 110.--Types of _Calyciflorae_ (_Umbelliflorae_). +_A_, inflorescence of wild parsnip, _Pastinaca_ (_Umbelliferae_), x 1/2. +_B_, single flower of the same, x 3. _C_, a leaf, showing the +sheathing base, x 1/4. _D_, a fruit, x 2. _E_, cross-section of _D_. +_F_, part of the inflorescence of spikenard, _Aralia_ (_Araliaceae_), +x 1. _G_, a single flower of the same, x 3. _H_, the fruit, x 2. _I_, +cross-section of the _H_. _J_, inflorescence of dogwood, _Cornus_ +(_Corneae_). The cluster of flowers is surrounded by four white bracts +(_b_), x 1/3. _K_, a single flower of the same, x 2. _L_, diagram of the +flower. _M_, young fruit of another species (_Cornus stolonifera_) +(red osier), x 2. _N_, cross-section of _M_.] + +The last and highest group of the _Choripetalae_, the _Calyciflorae_, +embraces a very large assemblage of familiar plants, divided into +eight orders and thirty-two families. With few exceptions, the floral +axis grows up around the ovary, carrying the outer floral leaves above +it, and the ovary appears at the bottom of a cup around whose edge the +other parts of the flower are arranged. Sometimes, as in the fuchsia, +the ovary is grown to the base of the cup or tube, and thus looks as +if it were outside the flower. Such an ovary is said to be "inferior" +in distinction from one that is entirely free from the tube, and thus +is evidently within the flower. The latter is the so-called "superior" +ovary. The carpels are usually united into a compound pistil, but may +be separate, as in the stonecrop (Fig. 111, _E_), or strawberry +(Fig. 114, _C_). + +The first order of the _Calyciflorae_ (_Umbelliflorae_) has the flowers +small, and usually arranged in umbels, _i.e._ several stalked flowers +growing from a common point. The ovary is inferior, and there is a +nectar-secreting disc between the styles and the stamens. Of the three +families, the umbel-worts or _Umbelliferae_ is the commonest. The +flowers are much alike in all (Fig. 110, _A_, _B_), and nearly all +have large, compound leaves with broad, sheathing bases. The stems are +generally hollow. So great is the uniformity of the flowers and plant, +that the fruit (Fig. 110, _D_) is generally necessary before the plant +can be certainly recognized. This is two-seeded in all, but differs +very much in shape and in the development of oil channels, which +secrete the peculiar oil that gives the characteristic taste to the +fruits of such forms as caraway, coriander, etc. Some of them, like +the wild parsnip, poison hemlock, etc., are violent poisons, while +others like the carrot are perfectly wholesome. + +The wild spikenard (_Aralia_) (Fig. 110, _F_), ginseng, and the true +ivy (_Hedera_) are examples of the _Araliaceae_, and the various +species of dogwood (_Cornus_) (Fig. 110, _J-N_) represent the dogwood +family (_Corneae_). + +The second order (_Saxifraginae_) contains eight families, including a +number of common wild and cultivated plants. The true saxifrages are +represented by several wild and cultivated species of _Saxifraga_, the +little bishop's cap or mitre-wort (_Mitella_) (Fig. 111, _D_), and +others. The wild hydrangea (Fig. 111, _F_) and the showy garden +species represent the family _Hydrangeae_. In these some of the flowers +are large and showy, but with neither stamens nor pistils (neutral), +while the small, inconspicuous flowers of the central part of the +inflorescence are perfect. In the garden varieties, all of the flowers +are changed, by selection, into the showy, neutral ones. The syringa +or mock orange (_Philadelphus_) (Fig. 111, _I_), the gooseberry, and +currants (_Ribes_) (Fig. 111, _A_), and the stonecrop (_Sedum_) +(Fig. 111, _E_) are types of the families _Philadelpheae_, _Ribesieae_, +and _Crassulaceae_. + +[Illustration: FIG. 111.--_Calyciflorae_ (_Saxifraginae_): _A_, flowers +and leaves of wild gooseberry, _Ribes_ (_Ribesieae_), x 1. _B_, +vertical section of the flower, x 2. _C_, diagram of the flower. _D_, +flower of bishop's-cap, _Mitella_ (_Saxifragaceae_), x 3. _E_, flower +of stonecrop, _Sedum_ (_Crassulaceae_), x 2. _F_, flowers and leaves of +hydrangea (_Hydrangeae_), x 1/2. _n_, neutral flower. _G_, unopened +flower, x 2. _H_, the same, after the petals have fallen away. _I_, +flower of syringa, _Philadelphus_ (_Philadelpheae_), x 1. _J_, diagram +of the flower.] + +The third order (_Opuntieae_) has but a single family, the cacti +(_Cactaceae_). These are strictly American in their distribution, and +inhabit especially the dry plains of the southwest, where they reach +an extraordinary development. They are nearly or quite leafless, and +the fleshy, cylindrical, or flattened stems are usually beset with +stout spines. The flowers (Fig. 112, _A_) are often very showy, so +that many species are cultivated for ornament and are familiar to +every one. The beautiful night-blooming cereus, of which there are +several species, is one of these. A few species of prickly-pear +(_Opuntia_) occur as far north as New York, but most are confined to +the hot, dry plains of the south and southwest. + +[Illustration: FIG. 112.--_Calyciflorae_, _Opuntieae_ (_Passiflorinae_). +_A_, flower of a cactus, _Mamillaria_ (_Cactaceae_) (from "Gray's +Structural Botany"). _B_, leaf and flower of a passion-flower, +_Passiflora_ (_Passifloraceae_), x 1/2. _t_, a tendril. _C_, +cross-section of the ovary, x 2. _D_, diagram of the flower.] + +The fourth order (_Passiflorinae_) are almost without exception +tropical plants, only a very few extending into the southern United +States. The type of the order is the passion-flower (_Passiflora_) +(Fig. 112, _B_), whose numerous species are mostly inhabitants of +tropical America, but a few reach into the United States. The only +other members of the order likely to be met with by the student are +the begonias, of which a great many are commonly cultivated as house +plants on account of their fine foliage and flowers. The leaves are +always one-sided, and the flowers monoecious.[13] Whether the begonias +properly belong with the _Passiflorinae_ has been questioned. + +[13] Monoecious: having stamens and carpels in different flowers, but +on the same plant. + +[Illustration: FIG. 113.--_Calyciflorae_ (_Myrtiflorae_, _Thymelinae_). +_A_, flowering branch of moosewood, _Dirca_ (_Thymelaeaceae_), x 1. _B_, +a single flower, x 2. _C_, the same, laid open. _D_, a young flower of +willow herb, _Epilobium_ (_Onagraceae_), x 1. The pistil (_gy._) is not +yet ready for pollination. _E_, an older flower, with receptive +pistil. _F_, an unopened bud, x 1. _G_, cross-section of the ovary, +x 4. _H_, a young fruit, x 1. _I_, diagram of the flower. _J_, +flowering branch of water milfoil, _Myriophyllum_ (_Haloragidaceae_), +x 1/2. _K_, a single leaf, x 1. _L_, female flowers of the same, x 2. +_M_, the fruit, x 2.] + +The fifth order (_Myrtiflorae_) have regular four-parted flowers with +usually eight stamens, but sometimes, through branching of the +stamens, these appear very numerous. The myrtle family, the members of +which are all tropical or sub-tropical, gives name to the order. The +true myrtle (_Myrtus_) is sometimes cultivated for its pretty glossy +green leaves and white flowers, as is also the pomegranate whose +brilliant, scarlet flowers are extremely ornamental. Cloves are the +dried flower-buds of an East-Indian myrtaceous tree (_Caryophyllus_). +In Australia the order includes the giant gum-trees (_Eucalyptus_), +the largest of all known trees, exceeding in size even the giant trees +of California. + +Among the commoner _Myrtiflorae_, the majority belong to the two +families _Onagraceae_ and _Lythraceae_. The former includes the evening +primroses (_OEnothera_), willow-herb (_Epilobium_) (Fig. 113, _D_), +and fuchsia; the latter, the purple loosestrife (_Lythrum_) and swamp +loosestrife (_Nesaea_). The water-milfoil (_Myriophyllum_) (Fig. 113, +_J_) is an example of the family _Haloragidaceae_, and the _Rhexias_ of +the eastern United States represent with us the family _Melastomaceae_. + +The sixth order of the _Calyciflorae_ is a small one (_Thymelinae_), +represented in the United States by very few species. The flowers are +four-parted, the calyx resembling a corolla, which is usually absent. +The commonest member of the order is the moosewood (_Dirca_) +(Fig. 113, _A_), belonging to the first of the three families +(_Thymelaeaceae_). Of the second family (_Elaeagnaceae_), the commonest +example is _Shepherdia_, a low shrub having the leaves covered with +curious, scurfy hairs that give them a silvery appearance. The third +family (_Proteaceae_) has no familiar representatives. + +The seventh order (_Rosiflorae_) includes many well-known plants, all +of which may be united in one family (_Rosaceae_), with several +sub-families. The flowers are usually five-parted with from five to +thirty stamens, and usually numerous, distinct carpels. In the apple +and pear (Fig. 114, _I_), however, the carpels are more or less grown +together; and in the cherry, peach, etc., there is but a single carpel +giving rise to a single-seeded stone-fruit (drupe) (Fig. 114, _E_, +_H_). In the strawberry (Fig. 114, _A_), rose (_G_), cinquefoil +(_Potentilla_), etc., there are numerous distinct, one-seeded carpels, +and in _Spiraea_ (Fig. 114, _F_) there are five several-seeded carpels, +forming as many dry pods when ripe. The so-called "berry" of the +strawberry is really the much enlarged flower axis, or "receptacle," +in which the little one-seeded fruits are embedded, the latter being +what are ordinarily called the seeds. + +[Illustration: FIG. 114.--_Calyciflorae_ (_Rosiflorae_). _A_, +inflorescence of strawberry (_Fragaria_), x 1/2. _B_, a single flower, +x 1. _C_, section of _B_. _D_, floral diagram. _E_, vertical section +of a cherry-flower (_Prunus_), x 1. _F_, vertical section of the +flower of _Spiraea_, x 2. _G_, vertical section of the bud of a wild +rose (_Rosa_), x 1. _H_, vertical section of the young fruit, x 1. +_I_, section of the flower of an apple (_Pyrus_), x 1. _J_, floral +diagram of apple.] + +From the examples given, it will be seen that the order includes not +only some of the most ornamental, cultivated plants, but the majority +of our best fruits. In addition to those already given, may be +mentioned the raspberry, blackberry, quince, plum, and apricot. + +[Illustration: FIG. 115.--_Calyciflorae_ (_Leguminosae_). _A_, flowers +and leaf of the common pea, _Pisum_ (_Papilionaceae_), x 1/2. _t_, +tendril. _st._ stipules. _B_, the petals, separated and displayed, +x 1. _C_, flower, with the calyx and corolla removed, x 1. _D_, a +fruit divided lengthwise, x 1/2. _E_, the embryo, with one of the +cotyledons removed, x 2. _F_, diagram of the flower. _G_, flower of +red-bud, _Cercis_ (_Caesalpinaceae_), x 2. _H_, the same, with calyx and +corolla removed. _I_, inflorescence of the sensitive-brier, +_Schrankia_ (_Mimosaceae_), x 1. _J_, a single flower, x 2.] + +The last order of the _Calyciflorae_ and the highest of the +_Choripetalae_ is the order _Leguminosae_, of which the bean, pea, +clover, and many other common plants are examples. In most of our +common forms the flowers are peculiar in shape, one of the petals +being larger than the others, and covering them in the bud. This +petal is known as the standard. The two lateral petals are known as +the wings, and the two lower and inner are generally grown together +forming what is called the "keel" (Fig. 115, _A_, _B_). The stamens, +ten in number, are sometimes all grown together into a tube, but +generally the upper one is free from the others (Fig. 115, _C_). There +is but one carpel which forms a pod with two valves when ripe +(Fig. 115, _D_). The seeds are large, and the embryo fills the seed +completely. From the peculiar form of the flower, they are known as +_Papilionaceae_ (_papilio_, a butterfly). Many of the _Papilionaceae_ +are climbers, either having twining stems, as in the common beans, or +else with part of the leaf changed into a tendril as in the pea +(Fig. 115, _A_), vetch, etc. The leaves are usually compound. + +Of the second family (_Caesalpineae_), mainly tropical, the honey locust +(_Gleditschia_) and red-bud (_Cercis_) (Fig. 115, _G_) are the +commonest examples. The flowers differ mainly from the _Papilionaceae_ +in being less perfectly papilionaceous, and the stamens are almost +entirely distinct (Fig. 115, _H_). The last family (_Mimosaceae_) is +also mainly tropical. The acacias, sensitive-plant (_Mimosa_), and the +sensitive-brier of the southern United States (_Schrankia_) (Fig. 115, +_I_) represent this family. The flowers are quite different from the +others of the order, being tubular and the petals united, thus +resembling the flowers of the _Sympetalae_. The leaves of _Mimosa_ and +_Schrankia_ are extraordinarily sensitive, folding up if irritated. + + + + +CHAPTER XIX. + +CLASSIFICATION OF DICOTYLEDONS (_Continued_). + + +DIVISION II.--_Sympetalae_. + +The _Sympetalae_ or _Gamopetalae_ are at once distinguished from the +_Choripetalae_ by having the petals more or less united, so that the +corolla is to some extent tubular. In the last order of the +_Choripetalae_ we found a few examples (_Mimosaceae_) where the same +thing is true, and these form a transition from the _Choripetalae_ to +the _Sympetalae_. + +There are two great divisions, _Isocarpae_ and _Anisocarpae_. In the +first the carpels are of the same number as the petals and sepals; in +the second fewer. In both cases the carpels are completely united, +forming a single, compound pistil. In the _Isocarpae_ there are usually +twice as many stamens as petals, occasionally the same number. + +There are three orders of the _Isocarpae_, viz., _Bicornes_, +_Primulinae_, and _Diospyrinae_. The first is a large order with six +families, including many very beautiful plants, and a few of some +economic value. Of the six families, all but one (_Epacrideae_) are +represented in the United States. Of these the _Pyrolaceae_ includes +the pretty little pyrolas and prince's-pine (_Chimaphila_) (Fig. 116, +_J_); the _Monotropeae_ has as its commonest examples, the curious +Indian-pipe (_Monotropa uniflora_), and pine-sap (_M. hypopitys_) +(Fig. 116, _L_). These grow on decaying vegetable matter, and are +quite devoid of chlorophyll, the former species being pure white +throughout (hence a popular name, "ghost flower"); the latter is +yellowish. The magnificent rhododendrons and azaleas (Fig. 116, _F_), +and the mountain laurel (_Kalmia_) (Fig. 116, _I_), belong to the +_Rhodoraceae_. The heath family (_Ericaceae_), besides the true heaths +(_Erica_, _Calluna_), includes the pretty trailing-arbutus or +may-flower (_Epigaea_), _Andromeda_, _Oxydendrum_ (Fig. 116, _E_), +wintergreen (_Gaultheria_), etc. The last family is represented by the +cranberry (_Vaccinium_) and huckleberry (_Gaylussacia_). + +[Illustration: FIG. 116.--Types of _Isocarpous sympetalae_ +(_Bicornes_). _A_, flowers, fruit, and leaves of huckleberry, +_Gaylussacia_ (_Vaccinieae_), x 1. _B_, vertical section of the flower, +x 3. _C_, a stamen: i, from in front; ii, from the side, x 4. _D_, +cross-section of the young fruit, x 2. _E_, flower of sorrel-tree, +_Oxydendrum_ (_Ericaceae_), x 2. _F_, flower of azalea (_Rhododendron_), +x 1/2. _G_, cross-section of the ovary, x 3. _H_, diagram of the flower. +_I_, flower of mountain laurel (_Kalmia_), x 1. _J_, prince's-pine, +_Chimaphila_ (_Pyrolaceae_), x 1/2. _K_, a single flower, x 1. _L_, plant +of pine-sap, _Monotropa_, (_Monotropeae_), x 1/2. _M_, section of a +flower, x 1.] + +The second order, the primroses (_Primulinae_), is principally +represented in the cooler parts of the world by the true primrose +family (_Primulaceae_), of which several familiar plants may be +mentioned. The genus _Primula_ includes the European primrose and +cowslip, as well as two or three small American species, and the +commonly cultivated Chinese primrose. Other genera are _Dodecatheon_, +of which the beautiful shooting-star (_D. Meadia_) (Fig. 117, _A_) is +the best known. Something like this is _Cyclamen_, sometimes +cultivated as a house plant. The moneywort (_Lysimachia nummularia_) +(Fig. 117, _D_), as well as other species, also belongs here. + +[Illustration: FIG. 117.--_Isocarpous sympetalae_ (_Primulinae_, +_Diospyrinae_). _A_, shooting-star, _Dodecatheon_ (_Primulaceae_), x 1/2. +_B_, section of a flower, x 1. _C_, diagram of the flower. _D_, +Moneywort, _Lysimachia_ (_Primulaceae_), x 1/2. _E_, a perfect flower of +the persimmon, _Diospyros_ (_Ebenaceae_), x 1. _F_, the same, laid open: +section of the young fruit, x 2. _H_, longitudinal section of a ripe +seed, x 1. _em._ the embryo. _I_, fruit, x 1/2.] + +The sea-rosemary (_Statice_) and one or two cultivated species of +plumbago are the only members of the plumbago family (_Plumbagineae_) +likely to be met with. The remaining families of the _Primulinae_ are +not represented by any common plants. + +The third and last order of the _Isocarpous sympetalae_ has but a +single common representative in the United States; viz., the persimmon +(_Diospyros_) (Fig. 117, _E_). This belongs to the family _Ebenaceae_, +to which also belongs the ebony a member of the same genus as the +persimmon, and found in Africa and Asia. + +The second division of the _Sympetalae_ (the _Anisocarpae_) has usually +but two or three carpels, never as many as the petals. The stamens are +also never more than five, and very often one or more are abortive. + +[Illustration: FIG. 118.--Types of _Anisocarpous sympetalae_ +(_Tubiflorae_). _A_, flower and leaves of wild phlox (_Polemoniaceae_), +x 1/2. _B_, section of a flower, x 1. _C_, fruit, x 1. _D_, flower of +blue valerian (_Polemonium_), x 1. _E_, flowers and leaf of +water-leaf, _Hydrophyllum_ (_Hydrophyllaceae_), x 1/2. _F_, section of a +flower, x 1. _G_, flower of wild morning-glory, _Convolvulus_ +(_Convolvulaceae_), x 1/2. One of the bracts surrounding the calyx and +part of the corolla are cut away. _H_, diagram of the flower. _I_, the +fruit of a garden morning-glory, from which the outer wall has fallen, +leaving only the inner membranous partitions, x 1. _J_, a seed, x 1. +_K_, cross-section of a nearly ripe seed, showing the crumpled embryo, +x 2. _L_, an embryo removed from a nearly ripe seed, and spread out; +one of the cotyledons has been partially removed, x 1.] + +The first order (_Tubiflorae_) has, as the name indicates, tubular +flowers which show usually perfect, radial symmetry (_Actinomorphism_). +There are five families, all represented by familiar plants. The first +(_Convolvulaceae_) has as its type the morning-glory (_Convolvulus_) +(Fig. 118, _G_), and the nearly related _Ipomoeas_ of the gardens. The +curious dodder (_Cuscuta_), whose leafless, yellow stems are sometimes +very conspicuous, twining over various plants, is a member of this +family which has lost its chlorophyll through parasitic habits. The +sweet potato (_Batatas_) is also a member of the morning-glory family. +The numerous species, wild and cultivated, of phlox (Fig. 118, _A_), +and the blue valerian (_Polemonium_) (Fig. 118, _D_), are examples of +the family _Polemoniaceae_. + +[Illustration: FIG. 119.--_Anisocarpous sympetalae_ (_Tubiflorae_). _A_, +inflorescence of hound's-tongue, _Cynoglossum_ (_Borragineae_), x 1/2. +_B_, section of a flower, x 2. _C_, nearly ripe fruit, x 1. _D_, +flowering branch of nightshade, _Solanum_ (_Solaneae_), x 1/2. _E_, a +single flower, x 1. _F_, section of the flower, x 2. _G_, young fruit, +x 1. _H_, flower of _Petunia_ (_Solaneae_), x 1/2. _I_, diagram of the +flower.] + +The third family (_Hydrophyllaceae_) includes several species of +water-leaf (_Hydrophyllum_) (Fig. 118, _E_) and _Phacelia_, among our +wild flowers, and species of _Nemophila_, _Whitlavia_ and others from +the western states, but now common in gardens. + +The Borage family (_Borragineae_) includes the forget-me-not +(_Myosotis_) and a few pretty wild flowers, _e.g._ the orange-flowered +puccoons (_Lithospermum_); but it also embraces a number of the most +troublesome weeds, among which are the hound's-tongue (_Cynoglossum_) +(Fig. 119, _A_), and the "beggar's-ticks" (_Echinospermum_), whose +prickly fruits (Fig. 119, _C_) become detached on the slightest +provocation, and adhere to whatever they touch with great tenacity. +The flowers in this family are arranged in one-sided inflorescences +which are coiled up at first and straighten as the flowers expand. + +The last family (_Solaneae_) includes the nightshades (_Solanum_) +(Fig. 119, _D_), to which genus the potato (_S. tuberosum_) and the +egg-plant (_S. Melongena_) also belong. Many of the family contain a +poisonous principle, _e.g._ the deadly nightshade (_Atropa_), tobacco +(_Nicotiana_), stramonium (_Datura_), and others. Of the cultivated +plants, besides those already mentioned, the tomato (_Lycopersicum_), +and various species of _Petunia_ (Fig. 119, _H_), _Solanum_, and +_Datura_ are the commonest. + +The second order of the _Anisocarpae_ consists of plants whose flowers +usually exhibit very marked, bilateral symmetry (_Zygomorphism_). From +the flower often being two-lipped (see Fig. 120), the name of the +order (_Labiatiflorae_) is derived. + +Of the nine families constituting the order, all but one are +represented within our limits, but the great majority belong to two +families, the mints (_Labiatae_) and the figworts (_Scrophularineae_). +The mints are very common and easily recognizable on account of their +square stems, opposite leaves, strongly bilabiate flowers, and the +ovary splitting into four seed-like fruits (Fig. 120, _D_, _F_). + + The great majority of them, too, have the surface covered with + glandular hairs secreting a strong-scented volatile oil, giving the + peculiar odor to these plants. The dead nettle (_Lamium_) (Fig. 120, + _A_) is a thoroughly typical example. The sage, mints, catnip, + thyme, lavender, etc., will recall the peculiarities of the family. + +The stamens are usually four in number through the abortion of one of +them, but sometimes only two perfect stamens are present. + +[Illustration: FIG. 120.--_Anisocarpous sympetalae_ (_Labiatiflorae_). +_A_, dead nettle, _Lamium_, (_Labiatae_), x 1/2. _B_, a single flower, +x 1. _C_, the stamens and pistil, x 1. _D_, cross-section of the +ovary, x 2. _E_, diagram of the flower; the position of the absent +stamen is indicated by the small circle. _F_, fruit of the common +sage, _Salvia_ (_Labiatae_), x 1. Part of the persistent calyx has been +removed to show the four seed-like fruits, or nutlets. _G_, section of +a nutlet, x 3. The embryo fills the seed completely. _H_, part of an +inflorescence of figwort, _Scrophularia_ (_Scrophularineae_), x 1. _I_, +cross-section of the young fruit, x 2. _J_, flower of speedwell, +_Veronica_ (_Scrophularineae_), x 2. _K_, fruit of _Veronica_, x 2. +_L_, cross-section of _K_. _M_, flower of moth-mullein, _Verbascum_ +(_Scrophularineae_), x 1/2. _N_, flower of toad-flax, _Linaria_ +(_Scrophularineae_), x 1. _O_, leaf of bladder-weed, _Utricularia_ +(_Lentibulariaceae_), x 1. _x_, one of the "traps." _P_, a single trap, +x 5.] + +The _Scrophularineae_ differ mainly from the _Labiatae_ in having round +stems, and the ovary not splitting into separate one-seeded fruits. +The leaves are also sometimes alternate. There are generally four +stamens, two long and two short, as in the labiates, but in the +mullein (_Verbascum_) (Fig. 120, _M_), where the flower is only +slightly zygomorphic, there is a fifth rudimentary stamen, while in +others (_e.g._ _Veronica_) (Fig. 120, _J_) there are but two stamens. +Many have large, showy flowers, as in the cultivated foxglove +(_Digitalis_), and the native species of _Gerardia_, mullein, +_Mimulus_, etc., while a few like the figwort, _Scrophularia_ +(Fig. 120, _H_), and speedwells (_Veronica_) have duller-colored or +smaller flowers. + +[Illustration: FIG. 121.--_Anisocarpous sympetalae_ (_Labiatiflorae_). +_A_, flowering branch of trumpet-creeper, _Tecoma_ (_Bignoniaceae_), +x 1/4. _B_, a single flower, divided lengthwise, x 1/2. _C_, cross-section +of the ovary, x 2. _D_, diagram of the flower. _E_, flower of vervain, +_Verbena_ (_Verbenae_), x 2: i, from the side; ii, from in front; iii, +the corolla laid open. _F_, nearly ripe fruit of the same, x 2. _G_, +part of a spike of flowers of the common plantain, _Plantago_ +(_Plantagineae_), x 1; The upper flowers have the pistils mature, but +the stamens are not yet ripe. _H_, a flower from the upper (younger) +part of the spike. _I_, an older expanded flower, with ripe stamens, +x 3.] + +The curious bladder-weed (_Utricularia_) is the type of the family +_Lentibulariaceae_, aquatic or semi-aquatic plants which possess +special contrivances for capturing insects or small water animals. +These in the bladder-weed are little sacs (Fig. 120, _P_) which act as +traps from which the animals cannot escape after being captured. There +does not appear to be here any actual digestion, but simply an +absorption of the products of decomposition, as in the pitcher-plant. +In the nearly related land form, _Pinguicula_, however, there is much +the same arrangement as in the sundew. + +The family _Gesneraceae_ is mainly a tropical one, represented in the +greenhouses by the magnificent _Gloxinia_ and _Achimenes_, but of +native plants there are only a few parasitic forms destitute of +chlorophyll and with small, inconspicuous flowers. The commonest of +these is _Epiphegus_, a much-branched, brownish plant, common in +autumn about the roots of beech-trees upon which it is parasitic, and +whence it derives its common name, "beech-drops." + +The bignonia family (_Bignoniaceae_) is mainly tropical, but in our +southern states is represented by the showy trumpet-creeper (_Tecoma_) +(Fig. 121, _A_), the catalpa, and _Martynia_. + +The other plants likely to be met with by the student belong either to +the _Verbenaceae_, represented by the showy verbenas of the gardens, +and our much less showy wild vervains, also belonging to the genus +_Verbena_ (Fig. 121, _E_); or to the plantain family (_Plantagineae_), +of which the various species of plantain (_Plantago_) are familiar to +every one (Fig. 121, _G_, _I_). The latter seem to be forms in which +the flowers have become inconspicuous, and are wind fertilized, while +probably all of its showy-flowered relatives are dependent on insects +for fertilization. + +The third order (_Contortae_) of the _Anisocarpae_ includes five +families, all represented by familiar forms. The first, the olive +family (_Oleaceae_), besides the olive, contains the lilac and jasmine +among cultivated plants, and the various species of ash (_Fraxinus_), +and the pretty fringe-tree (_Chionanthus_) (Fig. 122, _A_), often +cultivated for its abundant white flowers. The other families are the +_Gentianaceae_ including the true gentians (_Gentiana_) (Fig. 122, +_F_), the buck-bean (_Menyanthes_), the centauries (_Erythraea_ and +_Sabbatia_), and several other less familiar genera; _Loganiaceae_, +with the pink-root (_Spigelia_) (Fig. 122, _D_), as the best-known +example; _Apocynaceae_ including the dog-bane (_Apocynum_) (Fig. 122, +_H_), and in the gardens the oleander and periwinkle (_Vinca_). + +[Illustration: FIG. 122.--_Anisocarpous sympetalae_ (_Contortae_). _A_, +flower of fringe-tree, _Chionanthus_ (_Oleaceae_), x 1. _B_, base of +the flower, with part of the calyx and corolla removed, x 2. _C_, +fruit of white ash, _Fraxinus_ (_Oleaceae_), x 1. _D_, flower of +pink-root, _Spigelia_ (_Loganiaceae_), x 1/2. _E_, cross-section of the +ovary, x 3. _F_, flower of fringed gentian, _Gentiana_ (_Gentianaceae_), +x 1/2. _G_, diagram of the flower. _H_, flowering branch of dog-bane, +_Apocynum_ (_Apocynaceae_), x 1/2. _I_, vertical section of a flower, +x 2. _J_, bud. _K_, flower of milk-weed, _Asclepias_ (_Asclepiadaceae_), +x 1. _L_, vertical section through the upper part of the flower, x 2. +_gy._ pistil. _p_, pollen masses. _an._ stamen. _M_, a pair of pollen +masses, x 6. _N_, a nearly ripe seed, x 1.] + +The last family is the milk-weeds (_Asclepiadaceae_), which have +extremely complicated flowers. Our numerous milk-weeds (Fig. 122, _K_) +are familiar representatives, and exhibit perfectly the peculiarities +of the family. Like the dog-banes, the plants contain a milky juice +which is often poisonous. Besides the true milk-weeds (_Asclepias_), +there are several other genera within the United States, but mostly +southern in their distribution. Many of them are twining plants and +occasionally cultivated for their showy flowers. Of the cultivated +forms, the wax-plant (_Hoya_), and _Physianthus_ are the commonest. + +[Illustration: FIG. 123.--_Anisocarpous sympetalae_ (_Campanulinae_). +_A_, vertical section of the bud of American bell-flower, _Campanula_ +(_Campanulaceae_), x 2. _B_, an expanded flower, x 1. The stamens have +discharged their pollen, and the stigma has opened. _C_, cross-section +of the ovary, x 3. _D_, flower of the Carpathian bell-flower +(_Campanula Carpatica_), x 1. _E_, flower of cardinal-flower, +_Lobelia_ (_Lobeliaceae_), x 1. _F_, the same, with the corolla and +sepals removed. _an._ the united anthers. _gy._ the tip of the pistil. +_G_, the tip of the pistil, x 2, showing the circle of hairs +surrounding the stigma. _H_, cross-section of the ovary, x 3. _I_, tip +of a branch of cucumber, _Cucurbita_ (_Cucurbitaceae_), with an +expanded female flower ([Female]). _J_, androecium of a male flower, +showing the peculiar convoluted anthers (_an._), x 2. _K_, +cross-section of the ovary, x 2.] + +The fourth order (_Campanulinae_) also embraces five families, but of +these only three are represented among our wild plants. The +bell-flowers (_Campanula_) (Fig. 123, _A_, _D_) are examples of the +family _Campanulaceae_, and numerous species are common, both wild and +cultivated. + +[Illustration: FIG. 124.--_Anisocarpous sympetalae_ (_Aggregatae_). _A_, +flowering branch of _Houstonia purpurea_, x 1 (_Rubiaceae_). _B_, +vertical section of a flower, x 2. _C_, fruit of bluets (_Houstonia +coerulea_), x 1. _D_, cross-section of the same. _E_, bedstraw, +_Galium_ (_Rubiaceae_), x 1/2. _F_, a single flower, x 2. _G_, flower of +arrow-wood, _Viburnum_ (_Caprifoliaceae_), x 2. _H_, the same, divided +vertically. _I_, flowering branch of trumpet honeysuckle, _Lonicera_ +(_Caprifoliaceae_), x 1/2. _J_, a single flower, the upper part laid +open, x 1. _K_, diagram of the flower. _L_, part of the inflorescence +of valerian, _Valeriana_, (_Valerianeae_), x 1. _M_, young; _N_, older +flower, x 2. _O_, cross-section of the young fruit; one division of +the three contains a perfect seed, the others are crowded to one side +by its growth. _P_, inflorescence of teasel, _Dipsacus_ (_Dipsaceae_), +x 1/4. _fl._ flowers. _Q_, a single flower, x 1. _R_, the same, with the +corolla laid open.] + +The various species of _Lobelia_, of which the splendid +cardinal-flower (_L. Cardinalis_) (Fig. 123, _E_) is one of the most +beautiful, represent the very characteristic family _Lobeliaceae_. +Their milky juice contains more or less marked poisonous properties. +The last family of the order is the gourd family (_Cucurbitaceae_), +represented by a few wild species, but best known by the many +cultivated varieties of melons, cucumbers, squashes, etc. They are +climbing or running plants, and provided with tendrils. The flowers +are usually unisexual, sometimes dioecious, but oftener monoecious +(Fig. 123, _I_). + +[Illustration: FIG. 125.--_Anisocarpous sympetalae_ (_Aggregatae_). +Types of _Compositae_. _A_, inflorescence of Canada thistle +(_Cirsium_), x 1. _B_, vertical section of _A_. _r_, the receptacle or +enlarged end of the stem, to which the separate flowers are attached. +_C_, a single flower, x 2. _o_, the ovary. _p_, the "pappus" (calyx +lobes). _an._ the united anthers. _D_, the upper part of the stamens +and pistil, x 3: i, from a young flower; ii, from an older one. _an._ +anthers. _gy._ pistil. _E_, ripe fruit, x 1. _F_, inflorescence of +may-weed (_Maruta_). The central part (disc) is occupied by perfect +tubular flowers (_G_), the flowers about the edge (rays) are sterile, +with the corolla much enlarged and white, x 2. _G_, a single flower +from the disc, x 3. _H_, inflorescence of dandelion (_Taraxacum_), the +flowers all alike, with strap-shaped corollas, x 1. _I_, a single +flower, x 2. _c_, the split, strap-shaped corolla. _J_, two ripe +fruits, still attached to the receptacle (_r_). The pappus is raised +on a long stalk, x 1. _K_, a single fruit, x 2.] + +The last and highest order of the _Sympetalae_, and hence of the +dicotyledons, is known as _Aggregatae_, from the tendency to have the +flowers densely crowded into a head, which not infrequently is closely +surrounded by bracts so that the whole inflorescence resembles a +single flower. There are six families, five of which have common +representatives, but the last family (_Calycereae_) has no members +within our limits. + +The lower members of the order, _e.g._ various _Rubiaceae_ (Fig. 124, +_A_, _E_), have the flowers in loose inflorescences, but as we examine +the higher families, the tendency for the flowers to become crowded +becomes more and more evident, and in the highest of our native forms +_Dipsaceae_ (Fig. 124, _P_) and _Compositae_ (Fig. 125) this is very +marked indeed. In the latter family, which is by far the largest of +all the angiosperms, including about ten thousand species, the +differentiation is carried still further. Among our native _Compositae_ +there are three well-marked types. The first of these may be +represented by the thistles (Fig. 125, _A_). The so-called flower of +the thistle is in reality a close head of small, tubular flowers +(Fig. 125, _C_), each perfect in all respects, having an inferior +one-celled ovary, five stamens with the anthers united, and a +five-parted corolla. The sepals (here called the "pappus") (_p_) have +the form of fine hairs. These little flowers are attached to the +enlarged upper end of the flower stalk (receptacle, _r_), and are +surrounded by closely overlapping bracts or scale leaves which look +like a calyx; the flowers, on superficial examination, appear as +single petals. In other forms like the daisy and may-weed (Fig. 125, +_F_), only the central flowers are perfect, and the edge of the +inflorescence is composed of flowers whose corollas are split and +flattened out, but the stamens and sometimes the pistils are wanting +in these so-called "ray-flowers." In the third group, of which the +dandelion (Fig. 125, _H_), chicory, lettuce, etc., are examples, all +of the flowers have strap-shaped, split corollas, and contain both +stamens and pistils. + +The families of the _Aggregatae_ are the following: I. _Rubiaceae_ of +which _Houstonia_ (Fig. 124, _A_), _Galium_ (_E_), _Cephalanthus_ +(button-bush), and _Mitchella_ (partridge-berry) are examples; +II. _Caprifoliaceae_, containing the honeysuckles (_Lonicera_) +(Fig. 124, _I_), _Viburnum_ (_G_), snowberry (_Symphoricarpus_), and +elder (_Sambucus_); III. _Valerianeae_, represented by the common +valerian (_Valeriana_) (Fig. 124, _L_); IV. _Dipsaceae_, of which the +teasel (_Dipsacus_) (Fig. 124, _P_), is the type, and also species of +scabious (_Scabiosa_); V. _Compositae_ to which the innumerable, +so-called compound flowers, asters, golden-rods, daisies, sunflowers, +etc. belong; VI. _Calycereae_. + +[Illustration: FIG. 126.--_Aristolochiaceae_. _A_, plant of wild ginger +(_Asarum_), x 1/3. _B_, vertical section of the flower, x 1. _C_, +diagram of the flower.] + +Besides the groups already mentioned, there are several families of +dicotyledons whose affinities are very doubtful. They are largely +parasitic, _e.g._ mistletoe; or water plants, as the horned pond-weed +(_Ceratophyllum_). One family, the _Aristolochiaceae_, represented by +the curious "Dutchman's pipe" (_Aristolochia sipho_), a woody twiner +with very large leaves, and the common wild ginger (_Asarum_) +(Fig. 126), do not appear to be in any wise parasitic, but the +structure of their curious flowers differs widely from any other group +of plants. + + + + +CHAPTER XX. + +FERTILIZATION OF FLOWERS. + + +If we compare the flowers of different plants, we shall find almost +infinite variety in structure, and this variation at first appears to +follow no fixed laws; but as we study the matter more thoroughly, we +find that these variations have a deep significance, and almost +without exception have to do with the fertilization of the flower. + +In the simpler flowers, such as those of a grass, sedge, or rush among +the monocotyledons, or an oak, hazel, or plantain, among dicotyledons, +the flowers are extremely inconspicuous and often reduced to the +simplest form. In such plants, the pollen is conveyed from the male +flowers to the female by the wind, and to this end the former are +usually placed above the latter so that these are dusted with the +pollen whenever the plant is shaken by the wind. In these plants, the +male flowers often outnumber the female enormously, and the pollen is +produced in great quantities, and the stigmas are long and often +feathery, so as to catch the pollen readily. This is very beautifully +shown in many grasses. + +If, however, we examine the higher groups of flowering plants, we see +that the outer leaves of the flower become more conspicuous, and that +this is often correlated with the development of a sweet fluid +(nectar) in certain parts of the flower, while the wind-fertilized +flowers are destitute of this as well as of odor. + +If we watch any bright-colored or sweet-scented flower for any length +of time, we shall hardly fail to observe the visits of insects to it, +in search of pollen or honey, and attracted to the flower by its +bright color or sweet perfume. In its visits from flower to flower, +the insect is almost certain to transfer part of the pollen carried +off from one flower to the stigma of another of the same kind, thus +effecting pollination. + +That the fertilization of a flower by pollen from another is +beneficial has been shown by many careful experiments which show that +nearly always--at least in flowers where there are special +contrivances for cross-fertilization--the number of seeds is greater +and the quality better where cross-fertilization has taken place, than +where the flower is fertilized by its own pollen. From these +experiments, as well as from very numerous studies on the structure of +the flower with reference to insect aid in fertilization, we are +justified in the conclusion that all bright-colored flowers are, to a +great extent, dependent upon insect aid for transferring the pollen +from one flower to another, and that many, especially those with +tubular or zygomorphic (bilateral) flowers are perfectly incapable of +self-fertilization. In a few cases snails have been known to be the +conveyers of pollen, and the humming-birds are known in some cases, as +for instance the trumpet-creeper (Fig. 121, _A_), to take the place of +insects.[14] + +[14] In a number of plants with showy flowers, _e.g._ violets, +jewel-weed, small, inconspicuous flowers are also formed, which are +self-fertilizing. These inconspicuous flowers are called +"cleistogamous." + +At first sight it would appear that most flowers are especially +adapted for self-fertilization; but in fact, although stamens and +pistils are in the same flower, there are usually effective +preventives for avoiding self-fertilization. In a few cases +investigated, it has been found that the pollen from the flower will +not germinate upon its own stigma, and in others it seems to act +injuriously. One of the commonest means of avoiding self-fertilization +is the maturing of stamens and pistils at different times. Usually the +stamens ripen first, discharging the pollen and withering before the +stigma is ready to receive it, _e.g._ willow-herb (Fig. 113, _D_), +campanula (Fig. 123, _A_, _D_), and pea; in the two latter, the pollen +is often shed before the flower opens. Not so frequently the stigmas +mature first, as in the plantain (Fig. 121, _G_). + +In many flowers, the stamens, as they ripen, move so as to place +themselves directly before the entrance to the nectary, where they are +necessarily struck by any insect searching for honey; after the pollen +is shed, they move aside or bend downward, and their place is taken by +the pistil, so that an insect which has come from a younger flower +will strike the part of the body previously dusted with pollen against +the stigma, and deposit the pollen upon it. This arrangement is very +beautifully seen in the nasturtium and larkspur (Fig. 99, _J_). + +The tubular flowers of the _Sympetalae_ are especially adapted for +pollination by insects with long tongues, like the bees and +butterflies, and in most of these flowers the relative position of the +stamens and pistil is such as to ensure cross-fertilization, which in +the majority of them appears to be absolutely dependent upon insect +aid. + +The great orchid family is well known on account of the singular form +and brilliant colors of the flowers which have no equals in these +respects in the whole vegetable kingdom. As might be expected, there +are numerous contrivances for cross-fertilization among them, some of +which are so extraordinary as to be scarcely credible. With few +exceptions the pollen is so placed as to render its removal by insects +necessary. One of the simpler contrivances is readily studied in the +little spring-orchis (Fig. 89) or one of the _Habenarias_ (Fig. 90, +_G_). In the first, the two pollen masses taper below where each is +attached to a viscid disc which is covered by a delicate membrane. +These discs are so placed that when an insect enters the flower and +thrusts its tongue into the spur of the flower, its head is brought +against the membrane covering the discs, rupturing it so as to expose +the disc which adheres firmly to the head or tongue of the insect, +the substance composing the disc hardening like cement on exposure to +the air. As the insect withdraws its tongue, one or both of the pollen +masses are dragged out and carried away. The action of the insect may +be imitated by thrusting a small grass-stalk or some similar body into +the spur of the flower, when on withdrawing it, the two pollen masses +will be removed from the flower. If we now examine these carefully, we +shall see that they change position, being nearly upright at first, +but quickly bending downward and forward (Fig. 89, _D_, ii, iii), so +that on thrusting the stem into another flower the pollen masses +strike against the sticky stigmatic surfaces, and a part of the pollen +is left adhering to them. + +The last arrangement that will be mentioned here is one discovered by +Darwin in a number of very widely separated plants, and to which he +gave the name "heterostylism." Examples of this are the primroses +(_Primula_), loosestrife (_Lythrum_), partridge-berry (_Mitchella_), +pickerel-weed (_Pontederia_), (Fig. 84, _I_), and others. In these +there are two, sometimes three, sets of flowers differing very much in +the relative lengths of stamens and pistil, those with long pistils +having short stamens and _vice versa_. When an insect visits a flower +with short stamens, that part is covered with pollen which in the +short-styled (but long-stamened) flower will strike the stigma, as the +pistil in one flower is almost exactly of the length of the stamens in +the other form. In such flowers as have three forms, _e.g._ +_Pontederia_, each flower has two different lengths of stamens, both +differing from the style of the same flower. Microscopic examination +has shown that there is great variation in the size of the pollen +spores in these plants, the large pollen from the long stamens being +adapted to the long style of the proper flower. + +It will be found that the character of the color of the flower is +related to the insects visiting it. Brilliantly colored flowers are +usually visited by butterflies, bees, and similar day-flying insects. +Flowers opening at night are usually white or pale yellow, colors best +seen at night, and in addition usually are very strongly scented so +as to attract the night-flying moths which usually fertilize them. +Sometimes dull-colored flowers, which frequently have a very offensive +odor, are visited by flies and other carrion-loving insects, which +serve to convey pollen to them. + +Occasionally, flowers in themselves inconspicuous are surrounded by +showy leaves or bracts which take the place of the petals of the +showier flowers in attracting insect visitors. The large dogwood +(Fig. 110, _J_), the calla, and Jack-in-the-pulpit (Fig. 86, _A_) are +illustrations of this. + + + + +CHAPTER XXI. + +HISTOLOGICAL METHODS. + + +In the more exact investigations of the tissues, it is often necessary +to have recourse to other reagents than those we have used hitherto, +in order to bring out plainly the more obscure points of structure. +This is especially the case in studies in cell division in the higher +plants, where the changes in the dividing nucleus are very +complicated. + + For studying these the most favorable examples for ready + demonstration are found in the final division of the pollen spores, + especially of some monocotyledons. An extremely good subject is + offered by the common wild onion (_Allium Canadense_), which flowers + about the last of May. The buds, which are generally partially + replaced by small bulbs, are enclosed in a spathe or sheath which + entirely conceals them. Buds two to three millimetres in length + should be selected, and these opened so as to expose the anthers. + The latter should now be removed to a slide, and carefully crushed + in a drop of dilute acetic acid (one-half acid to one-half + distilled water). This at once fixes the nuclei, and by examining + with a low power, we can determine at once whether or not we have + the right stages. The spore mother cells are recognizable by their + thick transparent walls, and if the desired dividing stages are + present, a drop of staining fluid should be added and allowed to act + for about a minute, the preparation being covered with a cover + glass. After the stain is sufficiently deep, it should be carefully + withdrawn with blotting paper, and pure water run under the cover + glass. + + The best stain for acetic acid preparations is, perhaps, gentian + violet. This is an aniline dye readily soluble in water. For our + purpose, however, it is best to make a concentrated, alcoholic + solution from the dry powder, and dilute this as it is wanted. A + drop of the alcoholic solution is diluted with several times its + volume of weak acetic acid (about two parts of distilled water to + one of the acid), and a drop of this mixture added to the + preparation. In this way the nucleus alone is stained and is + rendered very distinct, appearing of a beautiful violet-blue color. + + If the preparation is to be kept permanently, the acid must all be + washed out, and dilute glycerine run under the cover glass. The + preparation should then be sealed with Canada balsam or some other + cement, but previously all trace of glycerine must be removed from + the slide and upper surface of the cover glass. It is generally best + to gently wipe the edge of the cover glass with a small brush + moistened with alcohol before applying the cement. + +[Illustration: FIG. 127.--_A_, pollen mother cell of the wild onion. +_n_, nucleus. _B-F_, early stages in the division of the nucleus. +_par._ nucleolus; acetic acid, gentian violet, x 350.] + + If the spore mother cells are still quite young, we shall find the + nucleus (Fig. 127, _A_, _n_) comparatively small, and presenting a + granular appearance when strongly magnified. These granules, which + appear isolated, are really parts of filaments or segments, which + are closely twisted together, but scarcely visible in the resting + nucleus. On one side of the nucleus may usually be seen a large + nucleolus (called here, from its lateral position, paranucleus), and + the whole nucleus is sharply separated from the surrounding + protoplasm by a thin but evident membrane. + + The first indication of the approaching division of the nucleus is + an evident increase in size (_B_), and at the same time the colored + granules become larger, and show more clearly that they are in lines + indicating the form of the segments. These granules next become more + or less confluent, and the segments become very evident, appearing + as deeply stained, much-twisted threads filling the nuclear cavity + (Fig. 127, _C_), and about this time the nucleolus disappears. + + The next step is the disappearance of the nuclear membrane so that + the segments lie apparently free in the protoplasm of the cell. They + arrange themselves in a flat plate in the middle of the cell, this + plate appearing, when seen from the side, as a band running across + the middle of the cell. (Fig. 127, _D_, shows this plate as seen + from the side, _E_ seen from above.) + + About the time the nuclear plate is complete, delicate lines may be + detected in the protoplasm converging at two points on opposite + sides of the cell, and forming a spindle-shaped figure with the + nuclear plate occupying its equator. This stage (_D_), is known as + the "nuclear spindle." The segments of the nuclear plate next divide + lengthwise into two similar daughter segments (_F_), and these then + separate, one going to each of the new nuclei. This stage is not + always to be met with, as it seems to be rapidly passed over, but + patient search will generally reveal some nuclei in this condition. + +[Illustration: FIG. 128.--Later stages of nuclear divisions in the +pollen mother cell of wild onion, x 350. All the figures are seen from +the side, except _B_ ii, which is viewed from the pole.] + + Although this is almost impossible to demonstrate, there are + probably as many filaments in the nuclear spindle as there are + segments (in this case about sixteen), and along these the nuclear + segments travel slowly toward the two poles of the spindle + (Fig. 128, _A_, _B_). As the two sets of segments separate, they are + seen to be connected by very numerous, delicate threads, and about + the time the young nuclei reach the poles of the nuclear spindle, + the first trace of the division wall appears in the form of isolated + particles (microsomes), which arise first as thickenings of these + threads in the middle of the cell, and appear in profile as a line + of small granules not at first extending across the cell, but later, + reaching completely across it (Fig. 128, _C_, _E_). These granules + constitute the young cell wall or "cell plate," and finally coalesce + to form a continuous membrane (Fig. 128, _F_). + + The two daughter nuclei pass through the same changes, but in + reverse order that we saw in the mother nucleus previous to the + formation of the nuclear plate, and by the time the partition wall + is complete the nuclei have practically the same structure as the + first stages we examined (Fig. 128, _F_).[15] + +[15] The division is repeated in the same way in each cell so that +ultimately four pollen spores are formed from each of the original +mother cells. + + This complicated process of nuclear division is known technically as + "karyokinesis," and is found throughout the higher animals as well + as plants. + +The simple method of fixing and staining, just described, while giving +excellent results in many cases, is not always applicable, nor as a +rule are the permanent preparations so made satisfactory. For +permanent preparations, strong alcohol (for very delicate tissues, +absolute alcohol, when procurable, is best) is the most convenient +fixing agent, and generally very satisfactory. Specimens may be put +directly into the alcohol, and allowed to stay two or three days, or +indefinitely if not wanted immediately. When alcohol does not give +good results, specimens fixed with chromic or picric acid may +generally be used, and there are other fixing agents which will not be +described here, as they will hardly be used by any except the +professional botanist. Chromic acid is best used in a watery solution +(five per cent chromic acid, ninety-five per cent distilled water). +For most purposes a one per cent solution is best; in this the objects +remain from three or four to twenty-four hours, depending on size, but +are not injured by remaining longer. Picric acid is used as a +saturated solution in distilled water, and the specimen may remain for +about the same length of time as in the chromic acid. After the +specimen is properly fixed it must be thoroughly washed in several +waters, allowing it to remain in the last for twenty-four hours or +more until all trace of the acid has been removed, otherwise there is +usually difficulty in staining. + +As staining agents many colors are used. The most useful are +haematoxylin, carmine, and various aniline colors, among which may be +mentioned, besides gentian violet, safranine, Bismarck brown, methyl +violet. Haematoxylin and carmine are prepared in various ways, but are +best purchased ready for use, all dealers in microscopic supplies +having them in stock. The aniline colors may be used either dissolved +in alcohol or water, and with all, the best stain, especially of the +nucleus, is obtained by using a very dilute, watery solution, and +allowing the sections to remain for twenty-four hours or so in the +staining mixture. + +Haematoxylin and carmine preparations may be mounted either in +glycerine or balsam. (Canada balsam dissolved in chloroform is the +ordinary mounting medium.) In using glycerine it is sometimes +necessary to add the glycerine gradually, allowing the water to slowly +evaporate, as otherwise the specimens will sometimes collapse owing to +the too rapid extraction of the water from the cells. Aniline colors, +as a rule, will not keep in glycerine, the color spreading and finally +fading entirely, so that with most of them the specimens must be +mounted in balsam. + +Glycerine mounts must be closed, which may be done with Canada balsam +as already described. The balsam is best kept in a wide-mouthed +bottle, specially made for the purpose, which has a glass cap covering +the neck, and contains a glass rod for applying the balsam. + +Before mounting in balsam, the specimen must be completely freed from +water by means of absolute alcohol. (Sometimes care must be taken to +bring it gradually into the alcohol to avoid collapsing.[16]) If an +aniline stain has been used, it will not do to let it stay more than a +minute or so in the alcohol, as the latter quickly extracts the stain. +After dehydrating, the specimen should be placed on a clean slide in a +drop of clove oil (bergamot or origanum oil is equally good), which +renders it perfectly transparent, when a drop of balsam should be +dropped upon it, and a perfectly clean cover glass placed over the +preparation. The chloroform in which the balsam is dissolved will soon +evaporate, leaving the object embedded in a transparent film of balsam +between the slide and cover glass. No further treatment is necessary. +For the finer details of nuclear division or similar studies, balsam +mounts are usually preferable. + +[16] For gradual dehydrating, the specimens may be placed +successively in 30 per cent, 50 per cent, 70 per cent, 90 per cent, +and absolute alcohol. + +It is sometimes found necessary in sectioning very small and delicate +organs to embed them in some firm substance which will permit +sectioning, but these processes are too difficult and complicated to +be described here. + + * * * * * + +The following books of reference may be recommended. This list is, of +course, not exhaustive, but includes those works which will probably +be of most value to the general student. + +1. GOEBEL. Outlines of Morphology and Classification. + +2. SACHS. Physiology of Plants. + +3. DE BARY. Comparative Anatomy of Ferns and Phanerogams. + +4. DE BARY. Morphology and Biology of Fungi, Mycetozoa, and Bacteria. + +These four works are translations from the German, and take the +place of Sachs's Text-book of Botany, a very admirable work +published first about twenty years ago, and now somewhat antiquated. +Together they constitute a fairly exhaustive treatise on general +botany.--New York, McMillan & Co. + +5. GRAY. Structural Botany.--New York, Ivison & Co. + +6. GOODALE. Physiological Botany.--New York, Ivison & Co. + +These two books cover somewhat the same ground as 1 and 2, but are +much less exhaustive. + +5. STRASBURGER. Das Botanische Practicum.--Jena. + +Where the student reads German, the original is to be preferred, as +it is much more complete than the translations, which are made from +an abridgment of the original work. This book and the next (7 and 8) +are laboratory manuals, and are largely devoted to methods of work. + +7. ARTHUR, BARNES, and COULTER. Plant Dissection.--Holt & Co., New +York. + +8. WHITMAN. Methods in Microscopic Anatomy and Embryology.--Casino +& Co., Boston. + +For identifying plants the following books may be mentioned:-- + +Green algae (exclusive of desmids, but including _Cyanophyceae_ and + _Volvocineae_). + +WOLLE. Fresh-water Algae of the United States.--Bethlehem, Penn. + +Desmids. WOLLE. Desmids of the United States.--Bethlehem, Penn. + +The red and brown algae are partially described in FARLOW'S New England + Algae. Report of United States Fish Commission, 1879.--Washington. + +The _Characeae_ are being described by Dr. F. F. ALLEN of New York. The + first part has appeared. + +The literature of the fungi is much scattered. FARLOW and TRELEASE + have prepared a careful index of the American literature on the + subject. + +Mosses. LESQUEREUX and JAMES. Mosses of North America.--Boston, Casino + & Co. + +BARNES. Key to the Genera of Mosses.--Bull. Purdue School of Science, + 1886. + +Pteridophytes. UNDERWOOD. Our Native Ferns and their Allies.--Holt + & Co., New York. + +Spermaphytes. GRAY. Manual of the Botany of the Northern United + States. 6th edition, 1890. This also includes the ferns, and the + liverworts.--New York, Ivison & Co. + +COULTER. Botany of the Rocky Mountains.--New York, Ivison & Co. + +CHAPMAN. Flora of the Southern United States.--New York, 1883. + +WATSON. Botany of California. + + + + +INDEX. + + +_Acacia_, 209. + +_Acer_, _-aceae_. See "Maple." + +Acetic acid, 3, 59, 98, 138, 230. + +_Achimenes_, 218. + +_Acorus_. See "Sweet-flag." + +Actinomorphic, 213. + +Adder-tongue, 116; Fig. 70. See also "_Erythronium_." + +_Adiantum_. See "Maiden-hair." + +_Adlumia_. See "Mountain-fringe." + +_AEsculinae_, 199. + +_AEsculus_. See "Buckeye," "Horse-chestnut." + +_Aggregatae_, 222. + +Alcohol, 5, 31, 55, 83, 230, 233. + +Algae, 4, 21. + green, 21. + red, 21, 49. + brown, 21, 41. + +Alga-fungi. See "_Phycomycetes_." + +_Alisma_, _-ceae_. See "Water-plantain." + +_Allium_. See "Wild onion." + +Amaranth, 185. + +_Amarantus_, _-aceae_. See "Amaranth." + +_Amoeba_, 7; Fig. 2. + +_Ampelidae_. See "Vine." + +_Ampelopsis_. See "Virginia creeper." + +Anatomy, 3. + gross, Implements for study of, 3. + minute, Implements for study of, 3, 4. + +Anatropous, 151. + +_Andreaeaceae_, 99, 100. + +Androecium, 148. + +_Andromeda_, 211. + +_Anemone_, 185. + +_Angiocarpae_, 84. + +Angiosperm, 129, 143, 145. + +Aniline colors, 233. + +_Anisocarpae_, 210, 213. + +_Anonaceae_. See "Custard-apple." + +Anther, 148, 175, 179. + +Antheridium, 27, 36, 39, 45, 51, 59, 68, 89, 96, 106, 122. + +_Anthoceros_, _Anthoceroteae_, 91; Fig. 57. + +_Aphanocyclae_, 185, 196. + +_Aplectrum_, 167; Fig. 90. + +_Apocynum_, _-aceae_. See "Dog-bane." + +_Apostasieae_, 164. + +Apple, 145, 171, 206; Fig. 114. + +Apricot, 207. + +_Aquilegia_. See "Columbine." + +_Aralia_, _-aceae_. See "Spikenard." + +Archegonium, 89, 97, 105, 122, 133, 140, 144. + +Archicarp, 138, 145. + +_Arcyria_, 13; Fig. 5. + +_Arethusa_, _Arethuseae_, 166; Fig. 90. + +_Argemone_, 191. + +Aril, 189. + +_Arisaema_, 78, 157; Fig. 86. + +_Aristolochia_, _-aceae_, 224. + +Aroid, _Aroideae_, 157. + +Arrow-grass, 167. + +Arrowhead, 167; Fig. 91. + +Arrowroot, 163. + +_Asarum_. See "Wild ginger." + +_Asclepias_, _-daceae_. See "Milk-weed." + +_Ascobolus_, 71-73; Fig. 43. + culture of, 71. + spore fruit, 71. + archicarp, 71. + spore sacs, 72. + +_Ascomycetes_, 65, 66. + +Ascospore, 66. + +Ascus, 66, 69. + +Ash, 218; Fig. 122. + +_Asimina_. See "Papaw." + +_Aspidium_, Fig. 70. + +_Asplenium_, 104; Fig. 70. + +Aster, 224. + +_Atropa_. See "Deadly nightshade." + +Axil, 174. + +Azalea, 210; Fig. 116. + +_Azolla_, 117; Fig. 71. + + +Bacteria, 15, 17, 19; Fig. 8. + +Balsam, _Balsamineae_, 198. + +Bamboo, 162. + +_Bambusa_. See "Bamboo." + +Banana, 163. + +Barberry, 17, 187; Fig. 101. + +Bark. See "Cortex." + +_Basidiomycetes_, 77. + +Basidium, 77, 80, 83. + +Basswood, 195; Fig. 106. + +Bast. See "Phloem." + +_Batatas_. See "Sweet-potato." + +_Batrachospermum_, 53; Fig. 31. + +Bean, 207, 208. + +Bear-grass. See "_Yucca_." + +Bee, 227, 228. + +Beech, 183. + +Beech-drops, 218. + +Beet, 184. + +Beggar's-ticks, 215. + +Begonia, 3, 205. + +Bell-flower, 220, 226; Fig. 123. + +Bellwort, 156. + +_Berberis_, _-ideae_. See "Barberry." + +Bergamot oil, 234. + +Berry, 145, 156. + +_Betulaceae_, 183. + +_Bicornes_, 210. + +_Bignonia_, _-aceae_, 218. + +Biology, 2. + +Birch, 183. + +Bird's-nest fungus. See "_Cyathus_." + +Bishop's cap, 202; Fig. 111. + +Bismarck brown, 233. + +Bitter-sweet, 199; Fig. 109. + +Black alder, 199. + +Blackberry, 207. + +Black fungi. See "_Pyrenomycetes_." + +Bladder-nut, 199; Fig. 108. + +Bladder-weed, 33, 217; Fig. 120. + +Bleeding-heart. See "_Dicentra_." + +Blood-root, 191; Fig. 103. + +Blue-eyed grass, 156. + +Blue-flag. See "_Iris_." + +Blue-green slime, 15. + +Blue valerian. See "_Polemonium_." + +Borage, 215. + +_Borragineae_. See "Borage." + +Bordered pits, 138. + +Botany defined, 2. + systematic, 3. + +_Botrychium_. See "Grape fern." + +Box, 201. + +Bract, 199, 222, 229. + +_Brasenia_. See "Water-shield." + +Breathing pore, 91, 99, 113, 130, 147, 150, 177. + +_Bromeliaceae_, 156. + +Bryophyte, 86. + +Buck-bean, 218. + +Buckeye, 171, 199. + +Buckthorn, 199. + +Buckwheat, 184. + +Budding, 64. + +_Bulbochaete_, 28; Fig. 16. + +Bulb, 146, 153, 172. + +Bulrush, 161; Fig. 87. + +Bundle-sheath, 110, 176. + +Burning-bush. See "Spindle-tree." + +Bur-reed, 159; Fig. 86. + +Buttercup, 181, 185; Fig. 99. + +Butterfly, 227, 228. + +Button-bush, 223. + +Buttonwood. See "Sycamore." + +_Buxus_, _Buxaceae_. See "Box." + + +Cabbage, 192. + +_Cabombeae_, 190. + +Cactus, _Cactaceae_, 203; Fig. 112. + +_Caesalpineae_, 210. + +Calcium, 2. + +Calla, 157, 229. + +_Callithamnion_, 50-52; Fig. 29. + general structure, 51. + tetraspores, 51. + procarp, 51. + antheridium, 51. + spores, 52. + +_Callitriche_, _-chaceae_. See "Water starwort." + +_Calluna_. See "Heath." + +_Calopogon_, 166; Fig. 91. + +_Calycanthus_, _-aceae_, 187; Fig. 100. + +_Calycereae_, 223. + +_Calyciflorae_, 200. + +Calyx, 174, 182. + +Cambium, 137-138, 175. + +_Campanula_. See "Bell-flower." + +_Campanulaceae_, 220. + +_Campanulinae_, 220. + +Canada balsam, 230-234. + +Canada thistle, 224; Fig. 125. + +_Canna_, _-aceae_, 162, 163; Fig. 88. + +Caper family, 194. + +_Capparis_, _-ideae_. See "Caper." + +_Caprifoliaceae_, 223. + +_Capsella_. See "Shepherd's-purse." + +Caraway, 202. + +Carbon, 2, 95. + +Carbon-dioxides, 95. + +Cardinal-flower. See "Lobelia." + +_Carex_, 161; Fig. 87. + +Carmine, 25, 233. + +Carnation, 185. + +Carpel, 148, 154, 175, 179. + +Carpophyll. See "Carpel." + +Carpospore, 51-53. + +Carrot, 202. + +_Caryophylleae_. See "Pink." + +_Caryophyllus_. See "Clove." + +_Castalia_, 189. + +Castor-bean, 200. + +Catalpa, 218. + +Cat-brier, 154. + +Catkin, 181. + +Catnip, 215. + +Cat-tail, 159. + +Cedar apple, Cedar rust. See "_Gymnosporangium_." + +_Celastraceae_, 199. + +_Celastrus_. See "Bitter-sweet." + +Celery, 3. + +Cell, 6. + apical, 38, 96, 105, 115. + division, 23, 31, 229. + row, 8; Fig. 3. + mass, 8; Fig. 4. + sap, 6, 151. + +Cellulose, 3. + +Centaury, 219. + +_Centrospermae_, 183. + +_Cephalanthus_. See "Button-bush." + +_Cerastium_. See "Chick-weed." + +_Ceratophyllum_. See "Horned pond-weed." + +_Cercis_. See "Red-bud." + +_Chamaerops_. See "Palmetto." + +_Chara_, 38-40; Fig. 23. + general structure, 38. + method of growth, 39. + cortex, 39. + non-sexual reproduction, 39. + ooegonium, 39. + antheridium, 39, 40. + spermatozoids, 40. + germination, 40. + +_Characeae_, 21, 37, 40. + +_Chareae_, 40. + +_Cheiranthus_. See "Wall-flower." + +_Chenopodium_, _-aceae_. See "Goose-foot." + +Cherry, 15, 206; Fig. 114. + +Chicory, 223. + +Chick-weed, 185; Fig. 98. + +_Chimaphila_. See "Prince's pine." + +_Chionanthus_. See "Fringe-tree." + +Chlorine, 2. + +_Chlorococcum_, 23; Fig. 12. + +Chloroform, 234. + +Chloroplast, 22, 45. + +Chlorophyll, 15. + +Chlorophyll body. See "Chloroplast." + +_Chlorophyceae_, 21. + +_Chondrus_. See "Irish moss." + +_Choripetalae_, 181, 208. + +Chromic acid, 25-35, 233. + +Chromoplast, 150. + +_Cicinnobulus_, 69; Fig. 39. + +Cilium, 8. + +Cinquefoil, 206. + +_Cistaceae_. See "Rock-rose." + +_Cistiflorae_, 192. + +Citron, 196. + +_Citrus_. See "Orange," "Lemon." + +_Cladophora_, 24, 25. + structure of cells, 25. + nuclei, 25. + cell division, 25. + zooespores, 25. + +Classification, 3-9. + +_Clavaria_, 85; Fig. 51. + +_Claytonia_. See "Spring-beauty." + +Clematis, 185. + +Climbing plants, 171. + +_Closterium_, 33; Fig. 20. + +Clove, 205. + +Clove oil, 234. + +Clover, 207. + +Club moss, 116. + larger, 116. + smaller, 123-126; Fig. 74. + gross anatomy, 125. + spores, 126. + prothallium, 126. + systematic position, 126. + +Cluster-cup, 78. + +_Cocos_. See "Palm-coco," 159. + +_Coleochaete_, 28; Fig. 17. + +Collateral fibro-vascular bundle, 135. + +_Collema_, 76; Fig. 44. + +Columella, 55. + +Columbine, 186; Fig. 99. + +Column, 165. + +_Columniferae_, 195. + +_Commelyneae_, 157. + +_Compositae_, 223, 224. + +Compound flower, 224. + leaf, 159, 170. + +Conceptacle, 45. + +Cone, 131. + +_Conferva_, 26. + +_Confervaceae_, 21, 24. + +Conidium, 68. + +Conifer, 129, 140, 141. + +_Coniferae_. See "Conifer." + +_Conjugatae_, 22-29. + +Connective, 148. + +_Conocephalus_. See "Liverwort, giant." + +_Contortae_, 218. + +_Convolvulaceae_, 213. + +_Convolvulus_. See "Morning-glory." + +_Coprinus_, 82-84; Fig. 48. + general structure, 82, 83. + young spore fruit, 83. + gills basidia, 83. + spores, 84. + +Coral root, 167. + +_Corallorhiza_. See "Coral root." + +Coriander, 202. + +Corn, 160, 161. + +_Cornus_, _-aceae_. See "Dogwood." + +Corolla, 174, 182. + +Cortex, 39, 130. + +_Corydalis_, 192. + +Cotton, 195. + +Cotyledon, 134, 146, 180. + +Cowslip, 211. + +Coxcomb, 185. + +Crab-apple, 77, 80. + +Cranberry, 211. + +_Crassulaceae_, 203. + +Crane's-bill, 3, 196; Fig. 107. + +Cress, 192. + +_Croton_, 200. + +_Cruciferae_. See "Mustard family." + +_Cruciflorae_. See "_Rhoeadinae_." + +Cucumber, 221. + +Cucumber-tree. See "Magnolia." + +_Cucurbitaceae_. See "Gourd." + +Cup fungi ("_Discomycetes_"), 71. + +_Cupuliferae_, 183. + +Curl, 66. + +Currant, 203. + +_Cuscuta_. See "Dodder." + +Custard-apple, 186. + +_Cyanophyceae_. See "Blue-green slime." + +_Cyathus_, 84; Fig. 50. + +_Cycad_, _-eae_, 140. + +_Cycas revoluta_, 141; Fig. 71. + +_Cyclamen_, 212. + +_Cynoglossum_. See "Hound's-tongue." + +_Cyperaceae_. See "Sedge." + +_Cyperus_, 161. + +Cypress, 142. + +_Cypripedium_. See "Lady's-slipper." + +_Cystopus_. See also "White rust." + _bliti_, 57; Fig. 33. + general structure, 57. + structure of filaments, 57. + non-sexual spores (conidia), 57. + germination of conidia, 58. + resting spores, 59. + ooegonium, 59. + antheridium, 59. + _candidus_, 60; Fig. 34. + + +Daisy, 223. + +Dandelion, 66, 223; Fig. 125. + +_Darlingtonia_, 195. + +_Datura_. See "Stramonium." + +Day lily, 155. + +Deadly nightshade, 215. + +Dead nettle, 215; Fig. 120. + +_Delphinium_. See "Larkspur." + +Dermatogen, 176. + +Desmid, 33, 34; Fig. 20. + +Devil's apron. See "_Laminaria_." + +_Dianthus_. See "Pink." + +_Diatomaceae_, 41, 42; Figs. 24, 25. + structure, 42. + movements, 42. + reproduction, 42. + +_Dicentra_, 192; Fig. 103. + +Dicotyledon, 145, 170, 181, 225. + +_Digitalis_. See "Foxglove." + +Dioecious, 88. + +_Dionaea_. See "Venus's fly-trap." + +_Dioscoreae_. See "Yam." + +_Dioscorea villosa_, 154. + +_Diospyros_. See "Persimmon." + +_Diospyrinae_, 210. + +_Dipsacus_, _-aceae_. See "Teasel." + +_Dirca_. See "Moosewood." + +Ditch-moss, 167; Fig. 91. + +Dodder, 214. + +_Dodecatheon_. See "Shooting-star." + +Dog-bane, 219; Fig. 122. + +Dogwood, 202, 229; Fig. 110. + +_Draparnaldia_, 26; Fig. 14. + +_Drosera_ _-aceae_. See "Sun-dew." + +Drupe. See "Stone-fruit." + +Duck-weed, 159; Fig. 86. + +Dutchman's pipe. See "_Aristolochia_." + + +Earth star. See "_Geaster_." + +_Ebenaceae_ (ebony), 212. + +_Echinospermum_. See "Beggar's-ticks." + +_Ectocarpus_, 45, 47; Fig. 28. + +Eel-grass, 168, 169; Fig. 91. + +Egg apparatus, 144. + +Egg cell, 27, 36, 39, 45, 90, 106, 133, 144. + +Egg-plant, 215. + +Eichler, 153. + +Elater, 91, 122. + +Elder, 224. + +_Elaeagnaceae_, 206. + +Elm, 183. + +_Elodea_. See "Ditch-moss." + +Embryo, 90, 97, 107, 133, 149, 180. + +Embryology, 3. + +Embryo sac, 143, 144, 151. + +_Enantioblastae_, 153, 156; Fig. 85. + +Endosperm, 133, 146, 152. + +Entire leaves, 170. + +_Entomophthoreae_, 57. + +_Epacrideae_, 210. + +Epidermis, 91, 111, 112, 113, 122, 135, 137, 150, 177. + +_Epigaea_. See "Trailing arbutus." + +_Epilobium_. See "Willow-herb." + +_Epiphegus_. See "Beech-drops." + +Epiphyte, 166. + +_Equisetum_, _-tinae_. See "Horse-tail." + +Ergot, 76. + +_Erica_, _-aceae_. See "Heath." + +_Erysiphe_, 70. + +_Erythraea_. See "Centaury." + +_Erythronium_, 146-152; Fig. 81. + leaf, 146. + stem, 146. + root, 146. + gross anatomy of stem, 147. + flower, 148. + fruit and seed, 150. + histology of stem, 150. + of leaf, 150. + of flower, 151. + of ovule and seed, 151, 152. + +_Eschscholtzia_, 191. + +_Eucalyptus_, 206. + +_Eucyclae_, 196, 200. + +_Eudorina_, 20. + +_Euglena_, 11, 19; Fig. 9. + +_Euonymus_. See "Spindle-tree." + +_Euphorbia_, 199; Fig. 109. + +_Eurotium_, 70; Fig. 42. + +Evening primrose, 206. + +_Exoascus_, 66. + + +_Fagopyrum_. See "Buckwheat." + +Feather-veined. See "Pinnate-veined." + +Fern, 5, 102, 104, 116. + flowering, 118; Fig. 70. + lady, 104; Fig. 70. + maiden-hair. See "Maiden-hair fern." + ostrich. See "Ostrich-fern." + sensitive, 104. + true, 117. + water. See "Water-fern." + +Fertilization, 225. + +Fibre, 124, 175, 177. + +Fibro-vascular bundle, 107, 110, 121, 123, 135, 136, 147, 150, 159, 174. + +Fig, 183. + +Figwort, 215, 216; Fig. 120. + +Filament (of stamen), 148, 17. + +_Filices_. See "True ferns." + +_Filicineae_. See "Fern." + +Fir, 142. + +Fission, 23. + +_Flagellata_, 19. + +Flagellum, 19. + +Flax, 197; Fig. 107. + +Flies, 229. + +Flower, 128, 131. + +Flowering-plant. See "Spermaphyte." + +Forget-me-not, 215. + +Four-o'clock, 183. + +Foxglove, 217. + +_Frangulinae_, 199. + +_Fraxinus_. See "Ash." + +Fringe-tree, 218; Fig. 122. + +Fruit, 145. + +_Fucaceae_, 43. + +Fuchsia, 201. + +_Fucus_, 42-46. + _vesiculosus_, 43; Figs. 26, 27. + general structure, 43, 44. + conceptacles, 44. + collecting plants, 44. + cells, 44. + chloroplasts, 44. + ooegonium, 45. + _platycarpus_, 45. + antheridium, 45, 46. + fertilization, 46. + germination, 46. + +_Fumariaceae_. See "Fumitory." + +Fumitory, 192. + +_Funaria_, 93-99; Figs. 58-62. + gross anatomy, 93, 94. + protonema, 93. + "flower," 94. + structure of leaf, 94. + chloroplasts, division of, 95. + formation of starch in chloroplasts, 95. + structure of stem, 96. + root hairs, 96. + buds, 96. + antheridium spermatozoids, 96, 97. + archegonium, 97. + embryo, 98. + capsule and spores, 98, 99. + germination of spores, 99. + +Fungi, culture of, 5, 54. + true. See "_Mycomycetes_." + alga. See "_Phycomycetes_." + +Funiculus, 151, 175. + +_Funkia_. See "Day lily." + + +_Galium_, 223; Fig. 124. + +_Gamopetalae_. See "_Sympetalae_." + +_Gaultheria_. See "Wintergreen." + +_Gaylussacia_. See "Huckleberry." + +_Geaster_, 84; Fig. 49. + +Gentian, 218; Fig. 122. + +Gentian violet, 4, 138, 231. + +_Gentiana_, _-aceae_. See "Gentian." + +_Geranium_, _-aceae_, 3, 171, 196; Fig. 107. + +_Gerardia_, 217. + +Germ cell. See "Egg cell." + +_Gesneraceae_, 218. + +Ghost flower. See "Indian-pipe." + +Gill, 83. + +Ginger, 163. + +_Gingko_, 142; Fig. 78. + +_Gleditschia_. See "Honey locust." + +_Gloxinia_, 218. + +_Glumaceae_, 153, 160; Fig. 87. + +Glume, 162. + +Glycerine, 4, 51, 55, 59, 67, 83, 98, 224, 231, 233. + +_Gnetaceae_. See "Joint fir." + +Golden-rod, 224. + +_Gonium_, 20. + +Gooseberry, 203; Fig. 111. + +Goose-foot, 184; Fig. 98. + +_Gossypium_. See "Cotton." + +Gourd, 221. + +_Gramineae_. See "Grass." + +Grape, 171, 199; Fig. 109. + +Grape fern, 116; Fig. 70. + +_Graphis_, 75; Fig. 45. + +Grass, 161, 225; Fig. 87. + +Gray moss. See "_Tillandsia_." + +Green-brier, 154. + +Green-felt. See "_Vaucheria_." + +Green monad, 12, 19. + +Green slime, 21, 22; Fig. 11. + +Ground pine, 123; Fig. 73. + +Ground tissue, 110, 111, 113, 124, 137, 177, 178. + +_Gruinales_, 196. + +Guard cell, 113, 135, 150. + +Gulf weed. See "_Sargassum_." + +Gum. See "_Eucalyptus_." + +_Gymnocarpae_, 84. + +Gymnosperm, 129, 141. + +_Gymnosporangium_, 79-81; Fig. 47. + cedar apples, 79. + spores, 80. + +_Gynandrae_, 153, 164. + +Gynoecium, 148, 167. + +Gynostemium. See "Column." + + +_Habenaria_, 166, 227; Fig. 90. + +Haematoxylin, 233. + +Hair, 8, 177. + +_Haloragidaceae_, 206. + +Hazel, 182, 183, 225; Fig. 97. + +Head, 181. + +Heath, 211. + +_Helobiae_, 153, 167. + +_Hemerocallis_. See "Day lily." + +_Hemi-angiocarpae_, 84. + +Hemlock, 142; Fig. 78. + +Hemp, 183. + +_Hepaticae_. See "Liverwort." + +Hermaphrodite, 199. + +Heterocyst, 17. + +Heterostylism, 228. + +_Hibiscus_, 195. + +Hickory, 170, 183. + +Holly, 199. + +Hollyhock, 195. + +Honey locust, 209. + +Honeysuckle, 170, 172, 181, 223; Fig. 124. + +Hop, 171, 181; Fig. 97. + +Horned pond-weed, 224. + +Horse-chestnut, 170, 199. + +Horse-tail, 116-120. + field, 120-122; Fig. 72. + stems and tubers, 120. + fertile branches, 120. + leaves, 121. + cone, 121. + stem, 121. + sporangia and spores, 121. + sterile branches, 121. + histology of stem, 121. + of sporangia, 122. + spores, 122. + germination, prothallium, 122. + +Hound's-tongue, 215; Fig. 119. + +_Houstonia_, 223; Fig. 124. + +_Hoya_. See "Wax-plant." + +Huckleberry, 181, 211; Fig. 116. + +Humming-bird, 226. + +Hyacinth, 146. + +_Hydnum_, 84; Fig. 51. + +_Hydrangea_, _-geae_, 202; Fig. 111. + +_Hydrocharideae_, 167. + +Hydrogen, 2, 95. + +_Hydropeltidinae_, 189. + +_Hydrophyllum_, _-aceae_. See "Water-leaf." + +_Hypericum_, _-aceae_. See "St. John's-wort." + + +_Ilex_. See "Holly." + +_Impatiens_. See "Jewel-weed," "Balsam." + +India-rubber, 200. + +Indian-pipe, 144, 210; Fig. 79. + +Indian turnip. See "_Arisaema_." + +Indusium, 118. + +Inflorescence, 157. + +Integument, 133, 144, 151, 180. + +Intercellular space, 124, 135, 150. + +Internode, 39. + +Iodine, 4, 22, 31. + +_Ipomoea_, 213. + +_Iridaceae_, 156. + +Iris, 154, 156; Fig. 84. + +Irish moss, 49. + +_Isocarpae_, 210, 212. + +_Isoetes_. See "Quill-wort." + +_Iuliflorae_, 181. + +Ivy, 202. + + +Jack-in-the-pulpit. See "_Arisaema_." + +Jasmine, 218. + +_Jeffersonia_. See "Twin-leaf." + +Jewel-weed, 197; Fig. 107. + +Joint fir, 140, 142. + +_Juncagineae_, 167. + +_Juncus_. See "Rush." + +_Jungermanniaceae_, 92; Fig. 57. + + +_Kalmia_. See "Mountain laurel." + +Karyokinesis, 233. + +Keel, 208. + +Kelp. See "_Laminaria_." + giant. See "_Macrocystis_." + +Knotgrass. See "_Polygonum_." + + +Labellum. See "Lip." + +_Labiatae_. See "Mint." + +_Labiatiflorae_, 215. + +Lady's-slipper, 164, 166, 198; Fig. 90. + +Lamella, 83. + +_Laminaria_, 45, 47; Fig. 28. + +_Lamium_. See "Dead nettle." + +Larch. See "Tamarack." + +_Larix_. See "Tamarack." + +Larkspur, 186, 227; Fig. 99. + +Latex, 191. + +Laurel, 188. + +_Laurineae_. See "Laurel." + +Lavender, 215. + +Leaf-green. See "Chlorophyll." + +Leaf tendril, 171. + +Leaf thorn, 172. + +_Leguminosae_, 207. + +_Lemanea_, 53; Fig. 31. + +_Lemna_. See "Duck-weed." + +Lemon, 198. + +_Lentibulariaceae_, 217. + +Lettuce, 223. + +_Lichenes_, 73; Figs. 44, 45. + +Ligula, 127. + +_Ligulatae_, 125. + +Lilac, 170, 181, 218. + +_Liliaceae_, 155. + +_Liliiflorae_, 153, 155; Fig. 83. + +_Lilium_. See "Lily." + +Lily, 146, 155. + +Lily-of-the-valley, 155. + +Lime. See "Linden." + +Linden, 195; Fig. 106. + +Linear, 159. + +_Linum_, _-aceae_. See "Flax." + +Lip, 165. + +_Liriodendron_. See "Tulip-tree." + +_Lithospermum_. See "Puccoon." + +Liverwort, 86. + classification of, 91. + horned. See "_Anthoceroteae_." + giant, 91; Fig. 57. + +Lizard-tail, 181, 183; Fig. 97. + +_Lobelia_, _-aceae_. 221; Fig. 123. + +_Loganieae_, 219. + +_Lonicera_. See "Honeysuckle." + +Loosestrife. See "_Lythrum_." + swamp. See "Nesaea." + +Lotus. See "_Nelumbo_." + +_Lychnis_, 185. + +_Lycoperdon_, 84; Fig. 49. + +_Lycopersicum_. See "Tomato." + +_Lycopodiaceae_. See "Ground pine." + +_Lycopodinae_. See "Club moss." + +_Lycopodium_, 123. + _dendroideum_, 123, 124; Fig. 73. + stem and leaves, 123. + cones and sporangia, 123. + gross anatomy, 123. + histology, 124. + spores, 124. + +_Lysimachia_. See "Moneywort." + +_Lythrum_, _-aceae_, 206, 228. + +Mace, 189. + + +_Macrocystis_, 48. + +Macrospore, 126, 127, 128, 143. + +_Madotheca_, 86-90; Figs. 52-56. + gross anatomy, 86-88. + male and female plants, 87, 88. + histology of leaf and stem, 88. + antheridium, 88, 89. + archegonium, 89, 90. + embryo, 90. + spores and elaters, 90. + +Magnesium, 2. + +_Magnolia_, _-aceae_, 186. + +Maiden-hair fern, 109-115; Figs. 67-69. + general structure, 109. + gross anatomy of stem, 110. + histology of stem, 110, 111. + gross anatomy of leaf, 111. + histology of leaf, 111, 112. + sporangia, 113, 114. + root, 114, 115. + apical growth of root, 115. + +Mallow, 171, 195; Fig. 106. + +_Malva_, _-aceae_. See "Mallow." + +_Mamillaria_, Fig. 112. + +Mandrake. See "May-apple." + +Maple, 199; Fig. 108. + +_Maranta_. See "Arrowroot." + +_Marattiaceae_. See "Ringless ferns." + +_Marchantia_, 91; Fig. 57. + breathing-pores, 91. + sexual organs, 91. + buds, 91. + +_Marchantiaceae_, 91. + +_Marsilia_, 118; Fig. 71. + +_Martynia_, 218. + +_Matthiola_. See "Stock." + +May-apple, 187; Fig. 101. + +May-weed, 223; Fig. 125. + +_Medeola_, 155; Fig. 83. + +Medullary ray, 130, 137. + +_Melampsora_, 81. + +_Melastomaceae_, 206. + +Melon, 221. + +_Menispermum_, _-eae_. See "Moon-seed." + +_Menyanthes_. See "Buck-bean." + +_Mesocarpus_, 33; Fig. 19. + +Mesophyll, 135. + +Methyl-violet, 4, 233. + +Micropyle, 180. + +Microsome, 231. + +Microspore, 126, 128, 131, 138. + +Mignonette, 192; Fig. 104. + +Mildew. See "_Peronospora_," "_Phytophthora_," "_Perisporiaceae_." + +Milk-weed, 220; Fig. 122. + +Milkwort, 199. + +_Mimosa_. See "Sensitive-plant." + +_Mimosaceae_, 209, 210. + +_Mimulus_, 217. + +Mint, 181, 215. + +_Mirabilis_. See "Four-o'clock." + +Mistletoe, 224. + +_Mitella_. See "Bishop's cap." + +_Mitchella_. See "Partridge-berry." + +Mitre-wort. See "Bishop's cap." + +Mock-orange. See "_Syringa_." + +Moneywort, 212; Fig. 117. + +Monocotyledon, 146, 153, 225, 229. + +_Monotropa_. See "Indian-pipe," "Pine-sap." + +_Monotropeae_, 210. + +Moon-seed, 188; Fig. 101. + +Moosewood, 206; Fig. 113. + +_Morchella_. See "Morel." + +Morel, 73. + +Morning-glory, 171, 213; Fig. 118. + +Morphology, 3. + +Moss, 5, 86. + true, 93. + common. See "_Bryaceae_." + peat. See "_Sphagnaceae_." + +Moth, 229. + +Mould, black. See "_Mucorini_." + blue. See "_Penicillium_." + herbarium. See "_Eurotium_." + insect. See "_Entomophthoreae_." + water. See "_Saprolegnia_." + +Mountain-fringe, 192. + +Mountain-laurel, 210; Fig. 116. + +_Mucor_, 55. + mucedo, 56; Fig. 32. + +_Mucor stolonifer_, 55-56. + general structure, 55. + structure of filaments, 55. + spore cases, 55. + sexual spores, 56. + +_Mucorini_, 54. + +Mulberry, 183. + +Mullein, 217; Fig. 120. + +_Musa_, _-aceae_. See "Banana." + +_Musci_. See "True mosses." + +Mushroom, 82. + +Mustard, 192. + +_Mycomycetes_. See "True fungi." + +_Myosotis_. See "Forget-me-not." + +_Myristica_, _-ineae_. See "Nutmeg." + +_Myrtiflorae_, 205. + +Myrtle, 205, 206. + +_Myrtus_. See "Myrtle." + +_Myxomycetes_. See "Slime-mould." + + +_Naias_. See "Pond-weed." + +_Naiadeae_, 159. + +Narcissus, 146. + +Nasturtium, 197, 227. + +_Navicula_, 42; Fig. 24. + +Nectar, 225. + +Nectary, 186. + +Nelumbo, 189, 190; Fig. 101. + +_Nelumbieae_, 190. + +_Nemophila_, 214. + +_Nepenthes_, _-eae_. See "Pitcher plant." + +_Nesaea_, 206. + +Nettle. See "_Urticinae_." + +_Nicotiana_. See "Tobacco." + +Night-blooming cereus, 204. + +Nightshade, 215; Fig. 119. + +_Nitella_, 40. + +_Nitelleae_, 40. + +Node, 39. + +Nucleus, 7, 31, 231. + +Nuclear division, 7, 31, 231; Figs. 127, 128. + +Nucleolus, 7, 231. + +Nutmeg, 188. + +_Nyctagineae_, 183. + +_Nymphaea_, 189; Fig. 101. + +_Nymphaeaceae_, 190. + + +Oak, 183, 225; Fig. 97. + +_OEdogonium_, 26-28; Fig. 16. + reproduction, 27. + fertilization, 28. + resting spores, 28. + +_OEnothera_. See "Evening primrose." + +Oil-channel, 202. + +_Oleaceae_. See "Olive." + +Oleander, 219. + +Olive, 218. + +_Onagraceae_, 206. + +_Onoclea_, 104; Fig. 70. + +Ooegonium, 27, 36, 39, 45, 59, 62. + +Ooephyte, 109. + +Opium--opium poppy, 191. + +_Ophioglosseae_. See "Adder-tongue." + +_Ophioglossum_, 116. + +_Opuntia_. See "Prickly pear." + +_Opuntieae_, 203. + +Orange, 198. + +Orchid, 164, 166, 227; Figs. 89, 90. + +_Orchideae_, 164. + +_Orchis_, 227; Fig. 89. + +Organic bodies, 1. + +Origanum oil, 234. + +_Oscillaria_, 15, 16; Fig. 6. + movements, 15. + color, 16. + structure and reproduction, 16. + +_Osmunda_. See "Flowering-fern." + +Ostrich-fern, 104-109. + germination of spores, 104. + prothallium, 104, 105. + archegonium, 105, 106. + antheridium and spermatozoids, 106. + fertilization, 107. + embryo and young plant, 107, 108. + comparison with sporogonium of bryophytes, 109. + +Ovary, 129, 148, 156, 202. + +Ovule, 129, 131, 144, 148, 151, 179. + +_Oxalis_. See "Wood-sorrel." + +_Oxydendrum_, 211; Fig. 116. + +Oxygen, 2, 95. + + +Palea, 161. + +Palisade parenchyma, 178. + +Palm, 157. + date, 159. + coco, 159. + +_Palmae_. See "Palm." + +Palmate, 171. + +Palmetto, 159. + +_Pandaneae_, 159. + +_Papaveraceae_. See "Poppy." + +Papaw, 186; Fig. 100. + +_Papilionaceae_, 208. + +Pappus, 223. + +_Papyrus_, 161. + +Paranucleus, 231. + +Parasite, 54. + +Parenchyma. See "Soft tissue." + +_Parmelia_, 73, 75; Fig. 44. + +Partridge-berry, 223, 228. + +_Passiflora_. See "Passion-flower." + +_Passiflorinae_, 205. + +Passion-flower, 204; Fig. 112. + +Pea, 207, 208; Fig. 115. + +Peach, 206. + +Pear, 206. + +_Pediastrum_, 23; Fig. 11. + +_Pelargonium_, 197. + +Peltate, 190. + +_Peltigera_, 75; Fig. 45. + +_Penicillium_, 71; Fig. 42. + +Pepper, 183. + +Perianth. See "Perigone." + +Periblem, 176. + +Perigone, 143, 148, 151, 170. + +Perisperm, 163. + +_Perisporiaceae_, 66. + +Periwinkle, 219. + +_Peronospora_, 60; Fig. 35. + +_Peronosporeae_, 57. + +Persimmon, 212; Fig. 117. + +Petal, 148, 174, 179. + +Petiole, 173. + +Petunia, 215; Fig. 119. + +_Peziza_, 73; Fig. 43. + +_Phacelia_, 214. + +_Phaeophyceae_. See "Brown algae." + +Phaenogam. See "Spermaphyte." + +_Phascum_, _-aceae_, 99, 101; Fig. 65. + +_Philadelphus_. See "Syringa." + +Phloem, 110, 124, 135, 137, 150, 173, 176. + +_Phlox_, 214; Fig. 118. + +_Phoenix dactylifera_. See "Date-palm." + +Phosphorus, 2. + +_Phragmidium_, 81; Fig. 47. + +_Physarum_, 14. + +_Physianthus_, 220. + +Physiology, 3. + +_Phytolacca_, _-aceae_. See "Poke-weed." + +_Phytophthora_, 60. + +Pickerel-weed, 156, 228; Fig. 84. + +Picric acid, 156, 233. + +Pig-weed. See "Amaranth." + +Pine, 9, 10, 129, 142. + +Pineapple, 156. + +Pine-sap, 210; Fig. 116. + +_Pinguicula_, 218. + +Pink, 181, 185; Fig. 97. + +Pink-root, 218; Fig. 122. + +Pinnate (leaf), 159. + veined, 171. + +_Pinnularia_, 42; Fig. 24. + +_Pinus sylvestris_. See "Scotch pine." + +_Piper_. See "Pepper." + +_Piperineae_, 183. + +Pistil, 143, 145, 174. + +Pitcher-plant, 194, 195; Fig. 105. + +Pith, 130, 174, 177. + +Placenta, 148, 179. + +Plane, 183. + +_Plantago_, _-ineae_. See "Plantain." + +Plantain, 223, 225; Fig. 121. + +Plasmodium, 12. + +_Plataneae_. See "Plane." + +_Platanus_. See "Sycamore." + +Plerome, 176. + +Plum, 207. + +_Plumbago_, _-ineae_, 212. + +Pod, 156. + +_Podophyllum_. See "May-apple." + +_Podosphaera_, 66-70; Fig. 39. + general structure, 66. + structure of filaments, 68. + suckers, 68. + conidia, 68. + sexual organs, 68. + spore fruit, 68, 69. + spore sac, 69. + +_Pogonia_, 166. + +_Poinsettia_, 199. + +Poison-dogwood, 198. + +Poison-hemlock, 202. + +Poison-ivy, 171, 198. + +Poke-weed, 185; Fig. 97. + +_Polemonium_, _-aceae_, 214; Fig. 118. + +Pollinium, 165. + +_Polycarpae_, 185. + +_Polygala_, _-aceae_. See "Milkwort." + +_Polygonatum_. See "Solomon's Seal." + +_Polygonum_, _-aceae_, 184; Fig. 98. + +_Polysiphonia_, 52; Fig. 29. + +Pomegranate, 206. + +Pond-scum, 22, 29, 30. + +Pond-weed, 159; Fig. 86. + +_Pontederia_. See "Pickerel-weed." + +Poplar, 181, 183. + +Poppy, 191. + +_Portulaca_, _-aceae_. See "Purslane." + +Potash (caustic), 4, 5, 59, 67, 75, 97, 106, 111, 151, 176, 179, 180. + +Potassium, 2. + +Potato, 215. + +Potato-fungus. See "_Phytophthora_." + +_Potentilla_. See "Cinquefoil." + +_Potomogeton_. See "Pond-weed." + +Prickly-ash, 198. + +Prickly fungus. See "_Hydnum_." + +Prickly-pear, 204. + +Prickly-poppy. See "_Argemone_." + +Primrose, 211. + +_Primula_, _-aceae_. See "Primrose." + +Prince's-pine, 210; Fig. 116. + +Procarp, 51. + +_Proteaceae_, 205. + +Prothallium, 102, 103, 114, 122, 125, 133, 144, 177. + +_Protococcus_, _-aceae_, 22, 74; Fig. 11. + +Protophyte, 11. + +Protoplasm, 7. + movements of, 7. + +Pteridophyte, 102, 153. + +_Puccinia_, 81; Fig. 47. See also "Wheat-rust." + +Puccoon, 215. + +Puff-ball. See "_Lycoperdon_." + +Purslane, 185. + +Putty-root. See "_Aplectrum_." + +Pyrenoid, 25, 31. + +_Pyrenomycetes_, 76. + +_Pyrola_, _-aceae_, 210. + + +Quince, 170. + +Quill-wort, 125, 126; Fig. 74. + + +Raceme, 174. + +Radial fibro-vascular bundles, 138, 176. + +Radish, 192. + +_Ranunculus_, _-aceae_. See "Buttercup." + +Raspberry, 207. + +Ray-flower, 223. + +Receptacle, 167, 207, 223. + +Receptive spot, 106. + +Red algae, 21, 49, 52, 53; Figs. 29-31. + +Red-bud, 209; Fig. 115. + +Red cedar, 79, 131, 141; Fig. 78. + +Red-wood, 142. + +Reference-books, 235-236. + +_Reseda_, _-aceae_. See "Mignonette." + +Resin, 130. + +Resin-duct, 130, 135, 137. + +Resting-spore, 28, 32, 37, 57. + +Rheumatism-root. See "Twin-leaf." + +_Rhexia_, 206. + +_Rhizocarpeae_. See "Water-fern." + +Rhizoid. See "Root-hair." + +Rhizome. See "Root-stock." + +_Rhododendron_, 210; Fig. 116. + +_Rhodophyceae_. See "Red algae." + +_Rhodoraceae_, 211. + +_Rhoeadinae_, 190. + +_Rhus_. See "Sumach." + _cotinus_. See "Smoke-tree." + _toxicodendron_. See "Poison-ivy." + _venenata_. See "Poison-dogwood." + +_Ribes_, _-ieae_, 203; Fig. 111. + +_Ricciaceae_, 91; Fig. 57. + +_Richardia_. See "Calla." + +_Ricinus_. See "Castor-bean." + +Ringless-fern, 116. + +Rock-rose, 195. + +Rock-weed. See "_Fucus_." + +Root, 102, 104, 114, 173. + +Root-cap, 115, 175. + +Root-hair, 38, 87, 91, 96, 104, 135. + +Root-stock, 154, 172. + +_Rosa_, _-aceae_. See "Rose." + +Rose, 181, 206; Fig. 114. + +_Rosiflorae_, 206. + +_Rubiaceae_, 223. + +Rush, 154, 225; Fig. 83. + +Rust, white. See "_Cystopus_." + red. See "_Uredineae_." + black. See "_Uredineae_." + + +_Sabal_. See "Palmetto." + +_Sabbatia_. See "Centaury." + +_Saccharomycetes_. See "Yeast." + +Sac fungi. See "_Ascomycetes_." + +Safranine, 233. + +Sage, 215; Fig. 120. + +_Salicineae_, 183. + +_Salix_. See "Willow." + +_Salvinia_, 118. + +_Sambucus_. See "Elder." + +_Sanguinaria_. See "Blood-root." + +_Sapindaceae_, 199. + +_Saprolegnia_, _-aceae_, 60-62; Fig. 36. + zooespores, 62. + resting spores, 62. + antheridium, 62. + +_Sargassum_, 48; Fig. 28. + +_Sarracenia_, _-aceae_. See "Pitcher-plant." + +Sassafras, 188. + +_Saururus_. See "Lizard-tail." + +Saxifrage, 202. + +_Saxifraginae_, 202. + +_Scabiosa_. See "Scabious." + +Scabious, 224. + +Scalariform, 110. + +Scale-leaves, 170. + +_Scenedesmus_, 24; Fig. 11. + +_Schizomycetes_. See "_Bacteria_." + +Schizophytes, 12, 14. + +Schlerenchyma. See "Stony tissue." + +_Schrankia_. See "Sensitive-brier." + +_Scilla_, 151. + +_Scirpus_. See "Bulrush." + +_Scitamineae_, 153, 162. + +Scotch pine, 129-140; Figs. 75-77. + stems and branches, 129. + leaves, 129, 130. + gross anatomy of stem, 130. + growth-rings, 130. + roots, 131. + sporangia, 131. + cones, 132. + macrospores and prothallium, 133. + ripe cone and seeds, 133. + germination, 134. + young plant, 134. + histology of leaf, 135. + of stem, 136-138. + of root, 138. + microsporangium and pollen spores, 138, 139. + archegonium, 140. + fertilization, 140. + +Scouring-rush, 122. + +_Scrophularia_, _-ineae_. See "Figwort." + +Sea-lettuce, 26; Fig. 15. + +Sea-rosemary, 212. + +Sea-weed (brown). See "Brown algae." + (red). See "Red algae." + +Sedge, 161; Fig. 87. + +_Sedum_. See "Stonecrop." + +Seed, 128, 133, 145, 150. + +Seed-plant. See "Spermaphyte." + +_Selaginella_, _-eae_. See "Smaller club-moss." + +Sensitive-brier, 209; Fig. 115. + +Sensitive-plant, 209. + +Sepal, 148, 150, 174, 179. + +_Sequoia_. See "Red-wood." + +Sessile leaf, 170. + +_Shepherdia_, 206. + +Shepherd's-purse, 173-180; Figs. 93-95. + gross anatomy of stem, 173. + leaf, 124, 173. + root, 173. + branches, 174. + flower, 174, 175. + fruit and seed, 175. + histology of root, 175, 176. + stem, 177. + leaf, 177, 178. + development of flower, 179. + ovule, 179. + embryo, 180. + +Shooting-star, 212; Fig. 117. + +Sieve-tube, 111, 137. + +_Silene_. See "Catch-fly." + +Silicon, 2. + +Simple leaf, 170. + +_Siphoneae_, 22, 34. + +_Sisyrinchium_. See "Blue-eyed grass." + +Skunk cabbage, 157. + +Slime mould, 12, 14; Fig. 5. + plasmodium, 12. + movements, 13. + feeding, 13. + spore-cases, 13. + spores, 13. + germination of spores, 14. + +Smart-weed. See "_Polygonum_." + +_Smilaceae_, 155. + +Smoke-tree, 198. + +Smut, 64, 65. + +Smut-corn. See "_Ustillago_." + +Snowberry, 223. + +Soft-tissue, 112. + +_Solanum_, _-eae_, 215. + +Solomon's Seal, 154; Fig. 83. + +Soredium, 74. + +Sorus, 118. + +_Spadiciflorae_, 153, 157. + +Spadix, 157. + +Spanish bayonet. See "_Yucca_." + +_Sparganium_. See "Bur-reed." + +Speedwell. See "_Veronica_." + +Spermaphyte, 128-129. + +Spermatozoid, 28, 36, 40, 46, 51, 89, 96, 106, 122. + +Spermagonium, 79, 80. + +_Sphagnum_, _-aceae_, 99, 100. + sporogonium, 100. + leaf, 100. + +Spice-bush, 188. + +Spiderwort, 6, 151, 157; Fig. 85. + +_Spigelia_. See "Pink-root." + +Spike, 181. + +Spikenard, 202; Fig. 110. + +Spinach, 184. + +Spindle-tree, 199; Fig. 109. + +_Spirogyra_, 30-32; Fig. 18. + structure of cells, 30. + starch, 31. + cell-division, 31. + sexual reproduction, 32. + +Sporangium, 55, 62, 113, 121, 122, 131, 148, 151, 179. + +Spore-case. See "Sporangium." + +Spore-fruit, 51, 66, 69, 70, 73, 83. + +Spore-sac. See "Ascus." + +Sporocarp. See "Spore-fruit." + +Sporogonium, 87, 90, 102, 123. + +Sporophyll, 128, 131, 148. + +Sporophyte, 109. + +Spring-beauty, 185; Fig. 98. + +Spruce, 142. + +Spurge. See "_Euphorbia_." + +Squash, 221. + +Staining agents, 4, 231, 233. + +Stamen, 128, 143, 148, 174, 179. + +Standard, 207. + +_Staphylea_. See "Bladder-nut." + +Starch, 31, 95, 152. + +_Statice_. See "Sea-rosemary." + +_Stellaria_. See "Chick-weed." + +_Stemonitis_, 13; Fig. 5. + +_Sticta_, 75; Fig. 45. + +_Stigeoclonium_, 26; Fig. 14. + +Stigma, 145, 148, 175, 179. + +St. John's-wort, 195; Fig. 105. + +Stock, 192. + +Stoma. See "Breathing-pore." + +Stonecrop, 202; Fig. 113. + +Stone-fruit, 206. + +Stone-wort. See "_Characeae_." + +Stony-tissue, 110. + +Stramonium, 215. + +Strawberry, 171, 202, 206; Fig. 113. + +Style, 148, 175, 179. + +_Stylophorum_, 187; Fig. 103. + +Sugar, 8, 145. + +Sulphur, 2. + +Sumach, 198; Fig. 108. + +Sun-dew, 192, 193; Fig. 104. + +Sunflower, 224. + +Suspensor, 180. + +Sweet-flag, 157. + +Sweet-potato, 214. + +Sweet-scented shrub. See "_Calycanthus_." + +Sweet-william, 185. + +Sycamore, 183. + +_Sympetalae_, 210. + +_Symphoricarpus_. See "Snowberry." + +_Symplocarpus_. See "Skunk-cabbage." + +Synergidae, 144. + +_Syringa_, 199; Fig. 111. See also "Lilac." + + +Tamarack, 142. + +Tap-root, 131, 173. + +_Taraxacum_. See "Dandelion." + +_Taxodium_. See "Cypress." + +_Taxus_. See "Yew." + +Teasel, 224; Fig. 124. + +_Tecoma_. See "Trumpet-creeper." + +Teleuto-spore, 80, 81. + +Tendril, 171. + +_Terebinthinae_, 198. + +Tetraspore, 51, 52. + +Thistle, 173, 223; Fig. 125. + +Thorn, 172. + +Thyme, 215. + +_Thymeleaceae_, 206. + +_Thymelinae_, 206. + +_Tilia_, _-aceae_. See "Linden." + +_Tillandsia_, 156; Fig. 84. + +Tissue, 8. + +Tissue system, 115. + +Toadstool, 82. + +Tobacco, 215. + +_Tolypella_, 40. + +Tomato, 215. + +Touch-me-not. See "Jewel-weed." + +Tracheary tissue, 110, 121, 177. + +Tracheid, 110, 138. + +_Tradescantia_. See "Spiderwort." + +Trailing arbutus, 211. + +_Tremella_, 81; Fig. 51. + +_Trichia_, 13, 14; Fig. 5. + +Trichogyne, 51. + +_Tricoccae_, 199. + +_Triglochin_. See "Arrow-grass." + +_Trillium_, 146, 154, 155; Fig. 83. + +_Triphragmium_, 81. + +_Tropaeolum_. See "Nasturtium." + +Trumpet-creeper. + +Tuber, 120, 153, 172. + +_Tubiflorae_, 213. + +Tulip, 146. + +Tulip-tree, 187; Fig. 100. + +Turnip, 192. + +Twin-leaf, 187; Fig. 101. + +_Typha_, _-aceae_. See "Cat-tail." + + +_Ulmaceae_. See "Elm." + +_Ulva_. See "Sea-lettuce." + +_Umbelliferae_. See "Umbel-wort." + +Umbel-wort, 202. + +_Umbelliflorae_, 202. + +_Uredineae_, 77. + +_Uromyces_, 81; Fig. 47. + +_Urticinae_, 183. + +_Usnea_, 75; Fig. 45. + +_Ustillagineae_. See "Smut." + +_Ustillago_, 65; Fig. 38. + +_Utricularia_. See "Bladder-weed." + +_Uvularia_. See "Bellwort." + + +_Vaccinium_. See "Cranberry." + +Vacuole, 8. + +Valerian, 224; Fig. 124. + +_Valeriana_, _-eae_. See "Valerian." + +_Vallisneria_. See "Eel-grass." + +_Vanilla_, 166. + +_Vaucheria_, 34-37; Figs. 21, 22. + structure of plant, 35. + _racemosa_, 35. + non-sexual reproduction, 36. + sexual organs, 36. + fertilization, 36. + resting spores, 37. + +Venus's fly-trap, 192. + +_Verbascum_. See "Mullein." + +_Verbena_, _-aceae_, 218; Fig. 121. + +_Veronica_, 217; Fig. 120. + +Vervain. See "_Verbena_." + +Vessel, 121, 135, 150, 175, 177. + +_Viburnum_, 223; Fig. 124. + +_Victoria regia_, 190. + +_Vinca_. See "Periwinkle." + +Vine, 199. + +Violet, 192; Fig. 104. + +_Viola_, _-aceae_. See "Violet." + +Virginia creeper, 171, 199. + +_Vitis_. See "Grape." + +_Vitaceae_. See "Vine." + +_Volvox_, 12, 20; Fig. 10. + +_Volvocineae_, 12, 19. + + +Wall-flower, 192. + +Walnut, 183. + +Wandering-Jew, 157. + +Water fern, 117. + +Water-leaf, 214; Fig. 118. + +Water-lily. See "_Nymphaea_," "_Castalia_." + +Water-milfoil, 206; Fig. 113. + +Water mould. See "_Saprolegnia_." + +Water net, 24; Fig. 11. + +Water-plantain, 167. + +Water-shield, 190. + +Water-starwort, 200. + +Wax-plant, 220. + +Wheat, 78. + +Wheat rust, 78, 81; Fig. 47. + +_Whitlavia_, 214. + +Wild ginger, 224; Fig. 126. + +Wild onion, 230. + +Wild parsnip, 202. + +Willow, 181-183; Fig. 96. + +Willow-herb, 206, 226; Fig. 113. + +Wing (of papilionaceous flower), 208. + +Wintergreen, 211. + +_Wolffia_, 159. + +Wood. See "Xylem." + +Wood-sorrel, 197; Fig. 107. + + +Xylem, 110, 124, 135, 150, 173, 176. + + +Yam, 154. + +Yeast, 63, 64; Fig. 37. + cause of fermentation, 63. + reproduction, 64. + systematic position, 64. + +Yew, 141. + +_Yucca_, 153. + + +_Zanthoxylum_. See "Prickly ash." + +_Zingiber_, _-aceae_. See "Ginger." + +Zooelogy, 2. + +Zooespore, 25, 37, 58, 62. + +_Zygnema_, 33; Fig. 19. + +Zygomorphy, Zygomorphic, 164, 215, 226. + + + + +NATURAL SCIENCE. + + +_Elements of Physics._ + + A Text-book for High Schools and Academies. By ALFRED P. GAGE, A.M., + Instructor in Physics in the English High School, Boston. 12mo. + 424 pages. Mailing Price, $1.25; Introduction, $1.12; Allowance for + old book, 35 cents. + +This treatise is based upon _the doctrine of the conservation of +energy_, which is made prominent throughout the work. But the leading +feature of the book--one that distinguishes it from all others--is, +that it is strictly _experiment-teaching_ in its method; _i.e._, it +leads the pupil to "read nature in the language of experiment." So far +as practicable, the following plan is adopted: The pupil is expected +to accept as _fact_ only that which he has seen or learned by personal +investigation. He himself performs the larger portion of the +experiments with _simple_ and _inexpensive_ apparatus, such as, in a +majority of cases, is in his power to construct with the aid of +directions given in the book. The experiments given are rather of the +nature of _questions_ than of illustrations, and _precede_ the +statements of principles and laws. Definitions and laws are not given +until the pupil has acquired a knowledge of his subject sufficient to +enable him to construct them for himself. The aim of the book is to +lead the pupil _to observe and to think_. + +C. F. EMERSON, _Prof. of Physics, Dartmouth College_: It takes up the +subject on the right plan, and presents it in a clear, yet scientific, +way. + +WM. NOETLING, _Prof. of Rhetoric, Theory and Practice of Teaching, +State Normal School, Bloomsburg, Pa._: Every page of the book shows +that the author is a _real_ teacher and that he knows how to make +pupils think. I know of no other work on the subject of which this +treats that I can so unreservedly recommend to all wide-awake teachers +as this. + +B. F. WRIGHT, _Supt. of Public Schools, St. Paul, Minn._: I like it +better than any text-book on physics I have seen. + +O. H. ROBERTS, _Prin. of High School, San Jose, Cal._: Gage's Physics +is giving great satisfaction. + + +_Introduction to Physical Science._ + + By A. P. GAGE, Instructor in Physics in the English High School, + Boston, Mass., and Author of _Elements of Physics_, etc. 12mo. + Cloth. viii + 353 pages. With a chart of colors and spectra. Mailing + Price, $1.10; for introduction, $1.00; allowance for an old book in + exchange, 30 cents. + +The great and constantly increasing popularity of Gage's _Elements of +Physics_ has created a demand for an equally good but easier book, on +the same plan, suitable for schools that can give but a limited time +to the study. The _Introduction to Physical Science_ has been prepared +to supply this demand. + +ACCURACY is the prime requisite in scientific text-books. A false +statement is not less false because it is plausible, nor an +inconclusive experiment more satisfactory because it is diverting. In +books of entertainment, such things may be permissible; but in a +text-book, the first essentials are correctness and accuracy. It is +believed that the _Introduction_ will stand the closest expert +scrutiny. Especial care has been taken to restrict the use of +scientific terms, such as _force_, _energy_, _power_, etc., to their +proper significations. Terms like _sound_, _light_, _color_, etc., +which have commonly been applied to both the effect and the agent +producing the effect have been rescued from this ambiguity. + +RECENT ADVANCES in physics have been faithfully recorded, and the +relative practical importance of the various topics has been taken +into account. Among the new features are a full treatment of electric +lighting, and descriptions of storage batteries, methods of +transmitting electric energy, simple and easy methods of making +electrical measurements with inexpensive apparatus, the compound +steam-engine, etc. Static electricity, which is now generally regarded +as of comparatively little importance, is treated briefly; while +dynamic electricity, the most potent and promising physical element of +our modern civilization, is placed in the clearest light of our +present knowledge. + +In INTEREST AND AVAILABILITY the _Introduction_ will, it is believed, +be found no less satisfactory. The wide use of the _Elements_ under +the most varied conditions, and, in particular, the author's own +experience in teaching it, have shown how to improve where improvement +was possible. The style will be found suited to the grades that will +use the book. The experiments are varied, interesting, clear, and of +practical significance, as well as simple in manipulation and ample in +number. Certain subjects that are justly considered difficult and +obscure have been omitted; as, for instance, certain laws relating to +the pressure of gases and the polarization of light. The +_Introduction_ is even more fully illustrated than the _Elements_. + +IN GENERAL. The _Introduction_, like the _Elements_, has this distinct +and distinctive aim,--to elucidate science, instead of "popularizing" +it; to make it liked for its own sake, rather than for its gilding and +coating; and, while teaching the facts, to impart the spirit of +science,--that is to say, the spirit of our civilization and progress. + +GEORGE E. GAY, _Prin. of High School, Malden, Mass._: With the matter, +both the topics and their presentation, I am better pleased than with +any other Physics I have seen. + +R. H. PERKINS, _Supt. of Schools, Chicopee, Mass._: I have no doubt we +can adopt it as early as next month, and use the same to great +advantage in our schools. (_Feb. 6, 1888._) + +MARY E. HILL, _Teacher of Physics, Northfield Seminary, Mass._: I like +the truly scientific method and the clearness with which the subject +is presented. It seems to me admirably adapted to the grade of work +for which it is designed. (_Mar. 5, '88._) + +JOHN PICKARD, _Prin. of Portsmouth High School, N.H._: I like it +exceedingly. It is clear, straightforward, practical, and not too +heavy. + +EZRA BRAINERD, _Pres. and Prof. of Physics, Middlebury College, Vt._: +I have looked it over carefully, and regard it as a much better book +for high schools than the former work. (_Feb. 6, 1888._) + +JAMES A. DE BOER, _Prin. of High School, Montpelier, Vt._: I have not +only examined, but studied it, and consider it superior as a text-book +to any other I have seen. (_Feb. 10, '88._) + +E. B. ROSA, _Teacher of Physics, English and Classical School, +Providence, R.I._: I think it the best thing in that grade published, +and intend to use it another year. (_Feb. 23, '88._) + +G. H. PATTERSON, _Prin. and Prof. of Physics, Berkeley Sch., +Providence, R.I._: A very practical book by a practical teacher. +(_Feb. 2, 1888._) + +GEORGE E. BEERS, _Prin. of Evening High School, Bridgeport, Conn._: +The more I see of Professor Gage's books, the better I like them. They +are popular, and at the same time scientific, plain and simple, full +and complete. (_Feb. 18, 1888._) + +ARTHUR B. CHAFFEE, _Prof. in Franklin College, Ind._: I am very much +pleased with the new book. It will suit the average class better than +the old edition. + +W. D. KERLIN, _Supt. of Public Schools, New Castle, Ind._: I find that +it is the best adapted to the work which we wish to do in our high +school of any book brought to my notice. + +C. A. BRYANT, _Supt. of Schools, Paris, Tex._: It is just the book for +high schools. I shall use it next year. + + +_Introduction to Chemical Science._ + + By R. P. WILLIAMS, Instructor in Chemistry in the English High + School, Boston. 12mo. Cloth. 216 pages. Mailing Price, 90 cents; for + introduction, 80 cents; Allowance for old book in exchange, + 25 cents. + +In a word, this is a working chemistry--brief but adequate. Attention +is invited to a few special features:-- + +1. This book is characterized by directness of treatment, by the +selection, so far as possible, of the most interesting and practical +matter, and by the omission of what is unessential. + +2. Great care has been exercised to combine clearness with accuracy of +statement, both of theories and of facts, and to make the explanations +both lucid and concise. + +3. The three great classes of chemical compounds--acids, bases, and +salts--are given more than usual prominence, and the arrangement and +treatment of the subject-matter relating to them is believed to be a +feature of special merit. + +4. The most important experiments and those best illustrating the +subjects to which they relate, have been selected; but the modes of +experimentation are so simple that most of them can be performed by +the average pupil without assistance from the teacher. + +5. The necessary apparatus and chemicals are less expensive than those +required for any other text-book equally comprehensive. + +6. The special inductive feature of the work consists in calling +attention, by query and suggestion, to the most important phenomena +and inferences. This plan is consistently adhered to. + +7. Though the method is an advanced one, it has been so simplified +that pupils experience no difficulty, but rather an added interest, in +following it; the author himself has successfully employed it in +classes so large that the simplest and most practical plan has been a +necessity. + +8. The book is thought to be comprehensive enough for high schools and +academies, and for a preparatory course in colleges and professional +schools. + +9. Those teachers in particular who have little time to prepare +experiments for pupils, or whose experience in the laboratory has been +limited, will find the simplicity of treatment and of experimentation +well worth their careful consideration. + +Those who try the book find its merits have not been overstated. + +A. B. AUBERT, _Prof. of Chemistry, Maine State College, Orono, Me._: +All the salient points are well explained, the theories are treated of +with great simplicity; it seems as if every student might thoroughly +understand the science of chemistry when taught from such a work. + +H. T. FULLER, _Pres. of Polytechnic Institute, Worcester, Mass._: It +is clear, concise, and suggests the most important and most +significant experiments for illustration of general principles. + +ALFRED S. ROE, _Prin. of High School, Worcester, Mass._: I am very +much pleased with it. I think it the most practical book for actual +work that I have seen. + +FRANK M. GILLEY, _Science Teacher, High School, Chelsea, Mass._: I +have examined the proof-sheets in connection with my class work, and +after comparison with a large number of text-books, feel convinced +that it is superior to any yet published. + +G. S. FELLOWS, _Teacher of Chemistry, High School, Washington, D.C._: +The author's method seems to us the ideal one. Not only are the +theoretical parts rendered clear by experiments performed by the +student himself, but there is a happy blending of theoretical and +applied chemistry as commendable as it is unusual. + +J. I. D. HINES, _Prof. of Chemistry, Cumberland University, Lebanon, +Tenn._: I am very much pleased with it, and think it will give the +student an admirable introduction to the science of chemistry. + +HORACE PHILLIPS, _Prin. of High School, Elkhart, Ind._: My class has +now used it three months. It proves the most satisfactory text-book in +this branch that I have ever used. The cost of apparatus and material +is very small. + +O. S. WESCOTT, _Prin. North Division H. Sch., Chicago_: My chemistry +professor says it is the most satisfactory thing he has seen, and +hopes we may be able to have it in future. + + +_Laboratory Manual of General Chemistry._ + + By R. P. WILLIAMS, Instructor in Chemistry, English High School, + Boston, and author of _Introduction to Chemical Science_. 12mo. + Boards. xvi + 200 pages. Mailing Price, 30 cents; for Introduction, + 25 cents. + +This Manual, prepared especially to accompany the author's +_Introduction to Chemical Science_, but suitable for use with any +text-book of chemistry, gives directions for performing one hundred of +the more important experiments in general chemistry and metal +analysis, with blanks and a model for the same, lists of apparatus and +chemicals, etc. + +The Manual is commended as well-designed, simple, convenient, and +cheap,--a practical book that classes in chemistry need. + +W. M. STINE, _Prof. of Chemistry, Ohio University, Athens, O._: It is +a work that has my heartiest endorsement. I consider it thoroughly +pedagogical in its principles, and its use must certainly give the +student the greatest benefit from his chemical drill. (_Dec. 30, +1888._) + + +_Young's General Astronomy._ + + A Text-book for colleges and technical schools. By CHARLES A. YOUNG, + Ph.D., LL.D., Professor of Astronomy in the College of New Jersey, + and author of _The Sun_, etc. 8vo. viii + 551 pages. Half-morocco. + Illustrated with over 250 cuts and diagrams, and supplemented with + the necessary tables. Introduction Price, $2.25. Allowance for an + old book in exchange, 40 cents. + +The OBJECT of the author has been twofold. First and chiefly, to make +a book adapted for use in the college class-room; and, secondly, to +make one valuable as a permanent storehouse and directory of +information for the student's use after he has finished his prescribed +course. + +The METHOD of treatment corresponds with the object of the book. +Truth, accuracy, and order have been aimed at first, with clearness +and freedom from ambiguity. + +In AMOUNT, the work has been adjusted as closely as possible to the +prevailing courses of study in our colleges. The fine print may be +omitted from the regular lessons and used as collateral reading. It is +important to anything like a complete view of the subject, but not +essential to a course. Some entire chapters can be omitted, if +necessary. + +NEW TOPICS, as indicated above, have received a full share of +attention, and while the book makes no claims to novelty, the name of +the author is a guarantee of much originality both of matter and +manner. + +The book will be found especially well adapted for high school and +academy teachers who desire a work for reference in supplementing +their brief courses. The illustrations are mostly new, and prepared +expressly for this work. The tables in the appendix are from the +latest and most trustworthy sources. A very full and carefully +prepared index will be found at the end. + +The eminence of Professor Young as an original investigator in +astronomy, a lecturer and writer on the subject, and an instructor of +college classes, and his scrupulous care in preparing this volume, led +the publishers to present the work with the highest confidence; and +this confidence has been fully justified by the event. More than one +hundred colleges adopted the work within a year from its publication. + + +_Young's Elements of Astronomy._ + + A Text-Book for use in High Schools and Academies. With a + Uranography. By CHARLES A. YOUNG, Ph.D., LL.D., Professor of + Astronomy in the College of New Jersey (Princeton), and author of _A + General Astronomy_, _The Sun_, etc. 12mo. Half leather. x + 472 + pages, and four star maps. Mailing Price, $1.55; for Introduction, + $1.40; allowance for old book in exchange, 30 cents. + +_Uranography._ + + From Young's Elements of Astronomy. 12mo. Flexible covers. 42 pages, + besides four star maps. By mail, 35 cents; for Introduction, + 30 cents. + +This volume is a new work, and not a mere abridgment of the author's +_General Astronomy_. Much of the material of the larger book has +naturally been incorporated in this, and many of its illustrations are +used; but everything has been worked over, with reference to the high +school course. + +Special attention has been paid to making all statements correct and +accurate _as far as they go_. Many of them are necessarily incomplete, +on account of the elementary character of the work; but it is hoped +that this incompleteness has never been allowed to become untruth, and +that the pupil will not afterwards have to unlearn anything the book +has taught him. + +In the text no mathematics higher than elementary algebra and geometry +is introduced; in the foot-notes and in the Appendix an occasional +trigonometric formula appears, for the benefit of the very +considerable number of high school students who understand such +expressions. This fact should be particularly noted, for it is a +special aim of the book to teach astronomy scientifically without +requiring more knowledge and skill in mathematics than can be expected +of high school pupils. + +Many things of real, but secondary, importance have been treated of in +fine print; and others which, while they certainly ought to be found +within the covers of a high school text-book of astronomy, are not +essential to the course, are relegated to the Appendix. + +A brief URANOGRAPHY is also presented, covering the constellations +visible in the United States, with maps on a scale sufficient for the +easy identification of all the principal stars. It includes also a +list of such telescopic objects in each constellation as are easily +found and lie within the power of a small telescope. + + +_Plant Organization._ + + By R. HALSTED WARD, M.D., F.R.M.S., Professor of Botany in the + Rensselaer Polytechnic Institute, Troy, N.Y. Quarto. 176 pages. + Illustrated. Flexible boards. Mailing Price, 85 cents; for Introd., + 75 cents. + +It consists of a synoptical review of the general structure and +morphology of plants, clearly drawn out according to biological +principles, fully illustrated, and accompanied by a set of blanks for +written exercises by pupils. The plan is designed to encourage close +observation, exact knowledge, and precise statement. + + +_A Primer of Botany._ + + By Mrs. A. A. KNIGHT, of Robinson Seminary, Exeter, N.H. 12mo. + Boards. Illus. vii + 115 pp. Mailing Price, 35 cents; for Introd., + 30 cents. + +This Primer is designed to bring physiological botany to the level of +primary and intermediate grades. + + +_Outlines of Lessons in Botany._ + + For the use of teachers, or mothers studying with their children. By + Miss JANE H. NEWELL. Part I.: From Seed to Leaf. Sq. 16mo. Illus. + 150 pp. Cloth. Mailing Price, 55 cents; for Introd., 50 cents. + +This book aims to give an outline of work for the pupils themselves. +It follows the plan of Gray's _First Lessons_ and _How Plants Grow_, +and is intended to be used with either of these books. + + +_A Reader in Botany._ + + Selected and adapted from well-known Authors. By Miss JANE H. + NEWELL. Part I.: From Seed to Leaf. 12mo. Cloth. vi + 209 pp. + Mailing Price, 70 cents; for Introd., 60 cents. + +This book follows the plan of the editor's _Outlines of Lessons in +Botany_ and Gray's _Lessons_, and treats of Seed-Food, Movements of +Seedlings, Trees in Winter, Climbing Plants, Insectivorous Plants, +Protection of Leaves from the Attacks of Animals, etc. + + +_Little Flower-People._ + + By GERTRUDE ELISABETH HALE. Sq. 12mo. Illus. Cloth. xiii + 85 pp. + Mailing Price, 50 cents; for Introd., 40 cents. + +The aim of this book is to tell some of the most important elementary +facts of plant-life in such a way as to appeal to the child's +imagination and curiosity, and to awaken an observant interest in the +facts themselves. + + + + + +End of the Project Gutenberg EBook of Elements of Structural and Systematic +Botany, by Douglas Houghton Campbell + +*** END OF THIS PROJECT GUTENBERG EBOOK SYSTEMATIC BOTANY *** + +***** This file should be named 20390.txt or 20390.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/2/0/3/9/20390/ + +Produced by Marilynda Fraser-Cunliffe, Laura Wisewell and +the Online Distributed Proofreading Team at +http://www.pgdp.net + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. Special rules, +set forth in the General Terms of Use part of this license, apply to +copying and distributing Project Gutenberg-tm electronic works to +protect the PROJECT GUTENBERG-tm concept and trademark. Project +Gutenberg is a registered trademark, and may not be used if you +charge for the eBooks, unless you receive specific permission. If you +do not charge anything for copies of this eBook, complying with the +rules is very easy. You may use this eBook for nearly any purpose +such as creation of derivative works, reports, performances and +research. They may be modified and printed and given away--you may do +practically ANYTHING with public domain eBooks. Redistribution is +subject to the trademark license, especially commercial +redistribution. + + + +*** START: FULL LICENSE *** + +THE FULL PROJECT GUTENBERG LICENSE +PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK + +To protect the Project Gutenberg-tm mission of promoting the free +distribution of electronic works, by using or distributing this work +(or any other work associated in any way with the phrase "Project +Gutenberg"), you agree to comply with all the terms of the Full Project +Gutenberg-tm License (available with this file or online at +http://gutenberg.org/license). + + +Section 1. General Terms of Use and Redistributing Project Gutenberg-tm +electronic works + +1.A. By reading or using any part of this Project Gutenberg-tm +electronic work, you indicate that you have read, understand, agree to +and accept all the terms of this license and intellectual property +(trademark/copyright) agreement. If you do not agree to abide by all +the terms of this agreement, you must cease using and return or destroy +all copies of Project Gutenberg-tm electronic works in your possession. +If you paid a fee for obtaining a copy of or access to a Project +Gutenberg-tm electronic work and you do not agree to be bound by the +terms of this agreement, you may obtain a refund from the person or +entity to whom you paid the fee as set forth in paragraph 1.E.8. + +1.B. "Project Gutenberg" is a registered trademark. It may only be +used on or associated in any way with an electronic work by people who +agree to be bound by the terms of this agreement. There are a few +things that you can do with most Project Gutenberg-tm electronic works +even without complying with the full terms of this agreement. See +paragraph 1.C below. There are a lot of things you can do with Project +Gutenberg-tm electronic works if you follow the terms of this agreement +and help preserve free future access to Project Gutenberg-tm electronic +works. See paragraph 1.E below. + +1.C. The Project Gutenberg Literary Archive Foundation ("the Foundation" +or PGLAF), owns a compilation copyright in the collection of Project +Gutenberg-tm electronic works. Nearly all the individual works in the +collection are in the public domain in the United States. If an +individual work is in the public domain in the United States and you are +located in the United States, we do not claim a right to prevent you from +copying, distributing, performing, displaying or creating derivative +works based on the work as long as all references to Project Gutenberg +are removed. Of course, we hope that you will support the Project +Gutenberg-tm mission of promoting free access to electronic works by +freely sharing Project Gutenberg-tm works in compliance with the terms of +this agreement for keeping the Project Gutenberg-tm name associated with +the work. You can easily comply with the terms of this agreement by +keeping this work in the same format with its attached full Project +Gutenberg-tm License when you share it without charge with others. + +1.D. The copyright laws of the place where you are located also govern +what you can do with this work. Copyright laws in most countries are in +a constant state of change. If you are outside the United States, check +the laws of your country in addition to the terms of this agreement +before downloading, copying, displaying, performing, distributing or +creating derivative works based on this work or any other Project +Gutenberg-tm work. The Foundation makes no representations concerning +the copyright status of any work in any country outside the United +States. + +1.E. Unless you have removed all references to Project Gutenberg: + +1.E.1. The following sentence, with active links to, or other immediate +access to, the full Project Gutenberg-tm License must appear prominently +whenever any copy of a Project Gutenberg-tm work (any work on which the +phrase "Project Gutenberg" appears, or with which the phrase "Project +Gutenberg" is associated) is accessed, displayed, performed, viewed, +copied or distributed: + +This eBook is for the use of anyone anywhere 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 + +1.E.2. If an individual Project Gutenberg-tm electronic work is derived +from the public domain (does not contain a notice indicating that it is +posted with permission of the copyright holder), the work can be copied +and distributed to anyone in the United States without paying any fees +or charges. If you are redistributing or providing access to a work +with the phrase "Project Gutenberg" associated with or appearing on the +work, you must comply either with the requirements of paragraphs 1.E.1 +through 1.E.7 or obtain permission for the use of the work and the +Project Gutenberg-tm trademark as set forth in paragraphs 1.E.8 or +1.E.9. + +1.E.3. If an individual Project Gutenberg-tm electronic work is posted +with the permission of the copyright holder, your use and distribution +must comply with both paragraphs 1.E.1 through 1.E.7 and any additional +terms imposed by the copyright holder. Additional terms will be linked +to the Project Gutenberg-tm License for all works posted with the +permission of the copyright holder found at the beginning of this work. + +1.E.4. Do not unlink or detach or remove the full Project Gutenberg-tm +License terms from this work, or any files containing a part of this +work or any other work associated with Project Gutenberg-tm. + +1.E.5. Do not copy, display, perform, distribute or redistribute this +electronic work, or any part of this electronic work, without +prominently displaying the sentence set forth in paragraph 1.E.1 with +active links or immediate access to the full terms of the Project +Gutenberg-tm License. + +1.E.6. You may convert to and distribute this work in any binary, +compressed, marked up, nonproprietary or proprietary form, including any +word processing or hypertext form. However, if you provide access to or +distribute copies of a Project Gutenberg-tm work in a format other than +"Plain Vanilla ASCII" or other format used in the official version +posted on the official Project Gutenberg-tm web site (www.gutenberg.org), +you must, at no additional cost, fee or expense to the user, provide a +copy, a means of exporting a copy, or a means of obtaining a copy upon +request, of the work in its original "Plain Vanilla ASCII" or other +form. Any alternate format must include the full Project Gutenberg-tm +License as specified in paragraph 1.E.1. + +1.E.7. Do not charge a fee for access to, viewing, displaying, +performing, copying or distributing any Project Gutenberg-tm works +unless you comply with paragraph 1.E.8 or 1.E.9. + +1.E.8. You may charge a reasonable fee for copies of or providing +access to or distributing Project Gutenberg-tm electronic works provided +that + +- You pay a royalty fee of 20% of the gross profits you derive from + the use of Project Gutenberg-tm works calculated using the method + you already use to calculate your applicable taxes. The fee is + owed to the owner of the Project Gutenberg-tm trademark, but he + has agreed to donate royalties under this paragraph to the + Project Gutenberg Literary Archive Foundation. Royalty payments + must be paid within 60 days following each date on which you + prepare (or are legally required to prepare) your periodic tax + returns. Royalty payments should be clearly marked as such and + sent to the Project Gutenberg Literary Archive Foundation at the + address specified in Section 4, "Information about donations to + the Project Gutenberg Literary Archive Foundation." + +- You provide a full refund of any money paid by a user who notifies + you in writing (or by e-mail) within 30 days of receipt that s/he + does not agree to the terms of the full Project Gutenberg-tm + License. You must require such a user to return or + destroy all copies of the works possessed in a physical medium + and discontinue all use of and all access to other copies of + Project Gutenberg-tm works. + +- You provide, in accordance with paragraph 1.F.3, a full refund of any + money paid for a work or a replacement copy, if a defect in the + electronic work is discovered and reported to you within 90 days + of receipt of the work. + +- You comply with all other terms of this agreement for free + distribution of Project Gutenberg-tm works. + +1.E.9. If you wish to charge a fee or distribute a Project Gutenberg-tm +electronic work or group of works on different terms than are set +forth in this agreement, you must obtain permission in writing from +both the Project Gutenberg Literary Archive Foundation and Michael +Hart, the owner of the Project Gutenberg-tm trademark. Contact the +Foundation as set forth in Section 3 below. + +1.F. + +1.F.1. Project Gutenberg volunteers and employees expend considerable +effort to identify, do copyright research on, transcribe and proofread +public domain works in creating the Project Gutenberg-tm +collection. Despite these efforts, Project Gutenberg-tm electronic +works, and the medium on which they may be stored, may contain +"Defects," such as, but not limited to, incomplete, inaccurate or +corrupt data, transcription errors, a copyright or other intellectual +property infringement, a defective or damaged disk or other medium, a +computer virus, or computer codes that damage or cannot be read by +your equipment. + +1.F.2. LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the "Right +of Replacement or Refund" described in paragraph 1.F.3, the Project +Gutenberg Literary Archive Foundation, the owner of the Project +Gutenberg-tm trademark, and any other party distributing a Project +Gutenberg-tm electronic work under this agreement, disclaim all +liability to you for damages, costs and expenses, including legal +fees. YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT +LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE +PROVIDED IN PARAGRAPH F3. YOU AGREE THAT THE FOUNDATION, THE +TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE +LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR +INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH +DAMAGE. + +1.F.3. LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a +defect in this electronic work within 90 days of receiving it, you can +receive a refund of the money (if any) you paid for it by sending a +written explanation to the person you received the work from. If you +received the work on a physical medium, you must return the medium with +your written explanation. The person or entity that provided you with +the defective work may elect to provide a replacement copy in lieu of a +refund. If you received the work electronically, the person or entity +providing it to you may choose to give you a second opportunity to +receive the work electronically in lieu of a refund. If the second copy +is also defective, you may demand a refund in writing without further +opportunities to fix the problem. + +1.F.4. Except for the limited right of replacement or refund set forth +in paragraph 1.F.3, this work is provided to you 'AS-IS' WITH NO OTHER +WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO +WARRANTIES OF MERCHANTIBILITY OR FITNESS FOR ANY PURPOSE. + +1.F.5. Some states do not allow disclaimers of certain implied +warranties or the exclusion or limitation of certain types of damages. +If any disclaimer or limitation set forth in this agreement violates the +law of the state applicable to this agreement, the agreement shall be +interpreted to make the maximum disclaimer or limitation permitted by +the applicable state law. The invalidity or unenforceability of any +provision of this agreement shall not void the remaining provisions. + +1.F.6. INDEMNITY - You agree to indemnify and hold the Foundation, the +trademark owner, any agent or employee of the Foundation, anyone +providing copies of Project Gutenberg-tm electronic works in accordance +with this agreement, and any volunteers associated with the production, +promotion and distribution of Project Gutenberg-tm electronic works, +harmless from all liability, costs and expenses, including legal fees, +that arise directly or indirectly from any of the following which you do +or cause to occur: (a) distribution of this or any Project Gutenberg-tm +work, (b) alteration, modification, or additions or deletions to any +Project Gutenberg-tm work, and (c) any Defect you cause. + + +Section 2. Information about the Mission of Project Gutenberg-tm + +Project Gutenberg-tm is synonymous with the free distribution of +electronic works in formats readable by the widest variety of computers +including obsolete, old, middle-aged and new computers. It exists +because of the efforts of hundreds of volunteers and donations from +people in all walks of life. + +Volunteers and financial support to provide volunteers with the +assistance they need, is critical to reaching Project Gutenberg-tm's +goals and ensuring that the Project Gutenberg-tm collection will +remain freely available for generations to come. In 2001, the Project +Gutenberg Literary Archive Foundation was created to provide a secure +and permanent future for Project Gutenberg-tm and future generations. +To learn more about the Project Gutenberg Literary Archive Foundation +and how your efforts and donations can help, see Sections 3 and 4 +and the Foundation web page at http://www.pglaf.org. + + +Section 3. Information about the Project Gutenberg Literary Archive +Foundation + +The Project Gutenberg Literary Archive Foundation is a non profit +501(c)(3) educational corporation organized under the laws of the +state of Mississippi and granted tax exempt status by the Internal +Revenue Service. The Foundation's EIN or federal tax identification +number is 64-6221541. Its 501(c)(3) letter is posted at +http://pglaf.org/fundraising. Contributions to the Project Gutenberg +Literary Archive Foundation are tax deductible to the full extent +permitted by U.S. federal laws and your state's laws. + +The Foundation's principal office is located at 4557 Melan Dr. S. +Fairbanks, AK, 99712., but its volunteers and employees are scattered +throughout numerous locations. Its business office is located at +809 North 1500 West, Salt Lake City, UT 84116, (801) 596-1887, email +business@pglaf.org. Email contact links and up to date contact +information can be found at the Foundation's web site and official +page at http://pglaf.org + +For additional contact information: + Dr. Gregory B. Newby + Chief Executive and Director + gbnewby@pglaf.org + + +Section 4. Information about Donations to the Project Gutenberg +Literary Archive Foundation + +Project Gutenberg-tm depends upon and cannot survive without wide +spread public support and donations to carry out its mission of +increasing the number of public domain and licensed works that can be +freely distributed in machine readable form accessible by the widest +array of equipment including outdated equipment. Many small donations +($1 to $5,000) are particularly important to maintaining tax exempt +status with the IRS. + +The Foundation is committed to complying with the laws regulating +charities and charitable donations in all 50 states of the United +States. Compliance requirements are not uniform and it takes a +considerable effort, much paperwork and many fees to meet and keep up +with these requirements. We do not solicit donations in locations +where we have not received written confirmation of compliance. To +SEND DONATIONS or determine the status of compliance for any +particular state visit http://pglaf.org + +While we cannot and do not solicit contributions from states where we +have not met the solicitation requirements, we know of no prohibition +against accepting unsolicited donations from donors in such states who +approach us with offers to donate. + +International donations are gratefully accepted, but we cannot make +any statements concerning tax treatment of donations received from +outside the United States. U.S. laws alone swamp our small staff. + +Please check the Project Gutenberg Web pages for current donation +methods and addresses. Donations are accepted in a number of other +ways including checks, online payments and credit card donations. +To donate, please visit: http://pglaf.org/donate + + +Section 5. General Information About Project Gutenberg-tm electronic +works. + +Professor Michael S. Hart is the originator of the Project Gutenberg-tm +concept of a library of electronic works that could be freely shared +with anyone. For thirty years, he produced and distributed Project +Gutenberg-tm eBooks with only a loose network of volunteer support. + + +Project Gutenberg-tm eBooks are often created from several printed +editions, all of which are confirmed as Public Domain in the U.S. +unless a copyright notice is included. Thus, we do not necessarily +keep eBooks in compliance with any particular paper edition. + + +Most people start at our Web site which has the main PG search facility: + + http://www.gutenberg.org + +This Web site includes information about Project Gutenberg-tm, +including how to make donations to the Project Gutenberg Literary +Archive Foundation, how to help produce our new eBooks, and how to +subscribe to our email newsletter to hear about new eBooks. diff --git a/old/20390.zip b/old/20390.zip Binary files differnew file mode 100644 index 0000000..9301acd --- /dev/null +++ b/old/20390.zip |