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+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: UTF-8
+
+*** 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
+
+
+
+
+
+
+
+                               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_, _Œdogonium_,
+  _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 _Amœba_. 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, amœboid
+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 amœba. 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 amœba (_I_
+  ii).
+
+The succeeding stages are difficult to follow. After repeatedly
+dividing, a large number of these amœba-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_,
+_Glœotrichia_, × 1. _C_, individual of _Glœotrichia_. _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
+_Œdogonium_ and its relatives. There are numerous species of
+_Œdogonium_ 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 _Œdogonium_,
+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 _Œdogonium_. _D_, a similar
+spore germinating. _E_, base of a filament showing the disc (_d_) by
+which it is attached. _F_, another species of _Œdogonium_ 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 _Œdogonium_, 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
+  _Œdogonium_, 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_, _nʹ_, 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 _Œdogonium_ 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 _Œdogonium_ 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_, _Dʹ_, _Cosmarium_. _D_, and _Dʹ_ 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_), × ⅛. _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," × ½. _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_, × ¼. _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_, × ½; _E_, × ¼. _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
+"diœcious."
+
+  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_, _aʹ_, antheridia. _p_, paraphysis.
+_L_, section of a leaf, × 150.]
+
+This moss is diœcious. 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_), × ½. _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 filixfœmina_) (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 diœcious. 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, × ½. _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_), × ½. _x_, fertile part of the leaf. _B_, sporangia of
+_Botrychium_, × 3. _C_, flowering fern (_Osmunda_). _x_, spore-bearing
+leaflets, × ½. _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, × ½. _C_, underground stem, with tubers
+(_o_), × ½. _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_), × ⅓. _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_ ♂). 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, × ½. _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_), × ½. _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 (♂), × ½. _B_, a similar
+branch, with two young female flowers (♀), 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._), × ¼.
+_B_, leaf of _Gingko_, × ½. _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_), × ⅓. _B_, the bulb of the same, × ½. _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,
+× ½. _f_, the filament. _an._ anther. _E_, the gynœcium (pistil), × 1.
+_o_, ovary. _st._ style. _z_, stigma. _F_, a full-grown fruit, × ½.
+_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_, _nʹ_). _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 "_Andrœcium_." 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
+"gynœcium") 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_, × ¼.
+_B_, single flower of Solomon's-seal (_Polygonatum_), × 1. _C_, upper
+part of a plant. _D_, underground stem (rhizome) of Indian cucumber
+root (_Medeola_), × ½. _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_), × ½ (_Iridaceæ_). _B_, the petal-like upper
+part of the pistil, seen from below, and showing a stamen (_an._).
+_st._ the stigma, × ½. _C_, the young fruit, × ½. _D_, section of the
+same, × 1. _E_, diagram of the flower. _F_, part of a plant of the
+so-called "gray moss" (_Tillandsia_), × ½ (_Bromeliaceæ_). _G_, a
+single flower, × 2. _H_, a seed, showing the fine hairs attached to
+it, × 1. _I_, plant of pickerel-weed (_Pontederia_), × ¼
+(_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_), × ½ (_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 diœcious. 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, × ½.
+_B_, leaf of the same plant, × ¼. _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, × ½
+(_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 (_Phœnix 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_). ♂, the male; ♀, the female flowers, × ½. _B_, a single
+male flower, × 2. _C_, a female flower, × 2. _D_, fruiting spike of
+another _Carex_, × ½. _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_),
+× ½. _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, × ½. _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, × ½. _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_), × ½.
+_C_, the column of the same, × 1. _an._ one of the two perfect
+stamens. _st._ sterile, petal-like stamen. _gy._. stigma. _D_,
+_Arethusa_, × ½. _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 gynœcium
+(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, × ½
+(_Alismaceæ_). _B_, section through the gynœcium, 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_,
+× ⅙. _G_, ditch-moss (_Elodea_), with a female flower (_fl._), × ½.
+(_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_), × ½. _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.
+_Fʹ_, four young pollen spores, × 300. _Fʺ_, 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_), × ½. _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 gynœcium 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; ♀, 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_), × ½.
+_E_, seed of white birch, _Betula_ (_Betulaceæ_), × 3. _F_, fruit of
+horn-bean, _Carpinus_ (_Cupuliferæ_), × 1. G, lizard-tail, _Saururus_
+(_Saurureæ_), × ¼. _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_), × ½. _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_),
+× ½. _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 gynœcium
+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_), × ½. _B_, a fruit,
+× 2. _C_, section of the same. _D_, section of a buttercup flower
+(_Ranunculus_), × 1½. _E_, diagram of buttercup flower. _F_, wild
+columbine (_Aquilegia_), × ½. _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_), × ½. _B_, section of the
+flower, × 1. _C_, flower and leaf of tulip-tree, _Liriodendron_
+(_Magnoliaceæ_), × ⅓. _D_, section of a flower, × ½. _E_, a ripe
+fruit, × 1. _F_, diagram of the flower. _G_, flower of the
+sweet-scented shrub, _Calycanthus_ (_Calycanthaceæ_), × ½]
+
+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 diœcious, 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_), × ½. _E_, section of the
+ovary of _D_, × 1. _F_, diagram of the flower. _G_, ripe fruit of
+twin-leaf (_Jeffersonia_), opening by a lid, × ½. _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_), × ½. _B_, a leaf of
+the same, × ⅙. _C_, freshly opened flower, with the large petal-like
+sepals removed, × ½. _p_, petals. _an._ stamens. _st._ stigma. _D_,
+section of the ovary, × 2. _E_, young fruit, × ½. _F_, lotus,
+_Nelumbo_ (_Nelumbieæ_). × ⅙. _G_, a stamen, × 1. _H_, the large
+receptacle, with the separate pistils sunk in its surface, × ½. _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_ (_Rhœadinæ_ 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_ (_Rhœdinæ_). _A_,
+plant of blood-root, _Sanguinaria_ (_Papaveraceæ_), × ⅓. _B_, a single
+flower, × 1. _C_, fruit, × ½. _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_), × ½. _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, × ½. _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_), × ½. _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 _Dionœa_,
+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, × ½. _C_, St. John's-wort
+(_Hypericum_), × ½. _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_), × ½. _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_), × ⅓. _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_), × ½. _B_, a petal, × 1. _C_,
+the young fruit, the styles united in a column, × ½. _D_, the ripe
+fruit, the styles separating to discharge the seeds, × ½. _E_, section
+of a seed, × 2. _F_, wild flax. _Linum_ (_Linaceæ_), × ½. _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_), × ½. _B_, a
+male flower, × 2. _C_, diagram of a perfect flower. _D_, fruit of the
+silver-maple, × ½. _E_, section across the seed, × 2. _F_, embryo
+removed from the seed, × 1. _G_, leaves and flowers of bladder-nut,
+_Staphylea_, (_Sapindaceæ_), × ½. _H_, section of a flower, × 2. _I_,
+diagram of the flower. _J_, flower of buckeye (_Æsculus_), × 1½. _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 diœcious, 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_), × ½. _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_), × ½. _L_,
+single group of flowers, surrounded by the corolla-like involucre,
+× 3. _M_, section of the same, ♂, male flowers; ♀, 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_), × ½.
+_B_, single flower of the same, × 3. _C_, a leaf, showing the
+sheathing base, × ¼. _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_), × ⅓. _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_), × ½. _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_), × ½. _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 monœcious.[13] Whether the begonias
+properly belong with the _Passiflorinæ_ has been questioned.
+
+[13] Monœcious: 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_),
+× ½. _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 (_Œnothera_), 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_), × ½. _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_), × ½. _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, × ½. _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_),
+× ½. _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_), × ½. _K_, a single flower, × 1. _L_, plant
+of pine-sap, _Monotropa_, (_Monotropeæ_), × ½. _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_), × ½.
+_B_, section of a flower, × 1. _C_, diagram of the flower. _D_,
+Moneywort, _Lysimachia_ (_Primulaceæ_), × ½. _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, × ½.]
+
+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_),
+× ½. _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_), × ½. _F_, section of a
+flower, × 1. _G_, flower of wild morning-glory, _Convolvulus_
+(_Convolvulaceæ_), × ½. 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 _Ipomœas_ 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_), × ½.
+_B_, section of a flower, × 2. _C_, nearly ripe fruit, × 1. _D_,
+flowering branch of nightshade, _Solanum_ (_Solaneæ_), × ½. _E_, a
+single flower, × 1. _F_, section of the flower, × 2. _G_, young fruit,
+× 1. _H_, flower of _Petunia_ (_Solaneæ_), × ½. _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_), × ½. _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_), × ½. _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_),
+× ¼. _B_, a single flower, divided lengthwise, × ½. _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_), × ½. _E_, cross-section of the
+ovary, × 3. _F_, flower of fringed gentian, _Gentiana_ (_Gentianaceæ_),
+× ½. _G_, diagram of the flower. _H_, flowering branch of dog-bane,
+_Apocynum_ (_Apocynaceæ_), × ½. _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 (♀). _J_, andrœcium 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
+cœrulea_), × 1. _D_, cross-section of the same. _E_, bedstraw,
+_Galium_ (_Rubiaceæ_), × ½. _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_), × ½. _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_),
+× ¼. _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 diœcious, but oftener monœcious
+(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_), × ⅓. _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."
+
+_Amœba_, 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.
+
+Andrœcium, 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 "_Rhœadinæ_."
+
+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."
+
+Diœcious, 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.
+
+Gynœcium, 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.
+
+_Ipomœa_, 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.
+
+_Œdogonium_, 26-28; Fig. 16.
+  reproduction, 27.
+  fertilization, 28.
+  resting spores, 28.
+
+_Œnothera_. 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.
+
+_Phœnix 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.
+
+_Rhœadinæ_, 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 ***
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+
+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: UTF-8
+
+*** 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
+
+
+
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+
+
+</pre>
+
+
+
+
+<h1><span style="letter-spacing:0.2em;">ELEMENTS</span>
+<br /><br />
+<small>OF</small>
+<br /><br />
+<big><span class="smcap">Structural and Systematic Botany</span></big>,<br />
+<small><br />
+FOR<br />
+<br /></small>
+HIGH SCHOOLS AND ELEMENTARY<br />
+COLLEGE COURSES.</h1>
+
+<p class="title">BY
+<br />
+DOUGLAS HOUGHTON CAMPBELL, <span class="smcap">Ph.D.</span>,<br />
+<span class="smcap">Professor of Botany in the Indiana University.</span></p>
+
+<p class="title">
+BOSTON, U.S.A.:<br />
+PUBLISHED BY GINN &amp;&nbsp;COMPANY.<br />
+1890.
+</p>
+
+
+
+<hr />
+<p class="title"><span class="smcap">Copyright, 1890,<br />By DOUGLAS HOUGHTON CAMPBELL.</span>
+<br /><span class="smcap">All Rights Reserved.</span></p>
+
+<p class="title"><span class="smcap">Typography by J.&nbsp;S. Cushing &amp;&nbsp;Co., Boston, U.S.A.</span></p>
+
+<p class="title"><span class="smcap">Presswork by Ginn &amp;&nbsp;Co., Boston, U.S.A.</span></p>
+
+
+
+<hr />
+<h2><span class="pagenum" title="Page&nbsp;iii">&nbsp;</span><a name="Page_iii" id="Page_iii"></a><a name="PREFACE" id="PREFACE"></a>PREFACE.</h2>
+
+
+<p><span class="smcap">The</span> 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.</p>
+
+<p>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 <i>all</i> 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 <i>introduction</i>, only, to the science.</p>
+
+<p>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<span class="pagenum" title="Page&nbsp;iv">&nbsp;</span><a name="Page_iv" id="Page_iv"></a> only too prevalent idea that the chief aim of
+botany is the ability to run down a plant by means of an &ldquo;Analytical
+Key,&rdquo; 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.</p>
+
+<p>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, <i>e.g.</i>
+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.</p>
+
+<p>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.</p>
+
+<p>The drawings, with very few exceptions, which are duly<span class="pagenum" title="Page&nbsp;v">&nbsp;</span><a name="Page_v" id="Page_v"></a> credited, were
+drawn from nature by the author, and nearly all expressly for this
+work.</p>
+
+<p>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.</p>
+
+<p>The classification adopted is, with slight changes, that given in
+Goebel&#8217;s &ldquo;Outlines of Morphology and Classification&rdquo;; 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 <i>Charace&aelig;</i>, are puzzles to the botanist,
+and at present it is impossible to give them more than a provisional
+place in the system.</p>
+
+<p>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 &ldquo;Analysis&rdquo; of flowers, it will have fulfilled its mission.</p>
+
+<p style="text-align:right; padding-right:2em;">DOUGLAS H. CAMPBELL.</p>
+
+<p class="quotsig"><span class="smcap">Bloomington, Indiana</span>,
+<br />October, 1889.<span class="pagenum" title="Page&nbsp;vi">&nbsp;</span><a name="Page_vi" id="Page_vi"></a></p>
+
+
+
+<hr />
+<h2><span class="pagenum" title="Page&nbsp;vii">&nbsp;</span><a name="Page_vii" id="Page_vii"></a><a name="TABLE_OF_CONTENTS" id="TABLE_OF_CONTENTS"></a>TABLE OF CONTENTS.</h2>
+
+
+<ul class="toc">
+<li>&nbsp;<span class="ralign allsc">PAGE</span></li>
+
+<li><span class="smcap"><a href="#CHAPTER_I">Chapter&nbsp;I.</a>&mdash;Introduction</span><span class="ralign"><a href="#Page_1">1</a></span>
+
+<ul class="subtoc">
+<li>Composition of Matter;</li>
+<li>Biology;</li>
+<li>Botany;</li>
+<li><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Zoology&rsquo;; changed to be consistent with the rest of the book.">Zo&ouml;logy</ins>;</li>
+<li>Departments of Botany;</li>
+<li>Implements and Reagents;</li>
+<li>Collecting Specimens.</li>
+</ul></li>
+
+<li><span class="smcap"><a href="#CHAPTER_II">Chapter&nbsp;II.</a>&mdash;The Cell</span> <span class="ralign"><a href="#Page_6">6</a></span>
+
+<ul class="subtoc">
+<li>Parts of the Cell;</li>
+<li>Formation of New Cells;</li>
+<li>Tissues.</li>
+</ul></li>
+
+<li><span class="smcap"><a href="#CHAPTER_III">Chapter&nbsp;III.</a>&mdash;Classification of Plants</span> <span class="ralign"><a href="#Page_9">9</a></span>
+
+<ul class="subtoc">
+<li><a href="#subk1">Protophytes</a>;</li>
+<li><a href="#slime">Slime-moulds</a>;</li>
+<li><a href="#schizo">Schizophytes</a>;</li>
+<li>Blue-green Slimes, <i>Oscillaria</i>;</li>
+<li>Schizomycetes, <i>Bacteria</i>;</li>
+<li><a href="#green">Green Monads</a>, <i>Euglena</i>, <i>Volvox</i>.</li>
+</ul></li>
+
+<li><span class="smcap"><a href="#CHAPTER_IV">Chapter&nbsp;IV.</a>&mdash;Alg&aelig;</span> <span class="ralign"><a href="#Page_21">21</a></span>
+
+<ul class="subtoc">
+<li>Classification of Alg&aelig;;</li>
+<li><a href="#class1">Green Alg&aelig;</a>;</li>
+<li><a href="#proto"><i>Protococcace&aelig;</i></a>, <i>Protococcus</i>;</li>
+<li><a href="#confer"><i>Confervace&aelig;</i></a>, <i>Cladophora</i>, <i>&#338;dogonium</i>, <i>Coleoch&aelig;te</i>.</li>
+</ul></li>
+
+<li><span class="smcap"><a href="#CHAPTER_V">Chapter&nbsp;V.</a>&mdash;Green Alg&aelig;</span> (<i>Continued</i>) <span class="ralign"><a href="#Page_30">30</a></span>
+
+<ul class="subtoc">
+<li><a href="#pond">Pond-scums</a>, <i>Spirogyra</i>;</li>
+<li><a href="#siphon"><i>Siphone&aelig;</i></a>, <i>Vaucheria</i>;</li>
+<li><a href="#chara"><i>Charace&aelig;</i></a>, <i>Chara</i>.</li>
+</ul></li>
+
+<li><span class="smcap"><a href="#CHAPTER_VI">Chapter&nbsp;VI.</a>&mdash;Brown Seaweeds</span> <span class="ralign"><a href="#Page_41">41</a></span>
+
+<ul class="subtoc">
+<li><i>Diatomace&aelig;</i>;</li>
+<li><a href="#truebr">True Brown Alg&aelig;</a>, <i>Fucus</i>;</li>
+<li>Classification of Brown Alg&aelig;.</li>
+</ul></li>
+
+<li><span class="smcap"><a href="#CHAPTER_VII">Chapter&nbsp;VII.</a>&mdash;Red Alg&aelig;</span> <span class="ralign"><a href="#Page_49">49</a></span>
+
+<ul class="subtoc">
+<li>Structure of Red Alg&aelig;;</li>
+<li><i>Callithamnion</i>;</li>
+<li>Fresh-Water Forms.</li>
+</ul></li>
+</ul>
+
+<div><span class="pagenum" title="Page&nbsp;viii">&nbsp;</span><a name="Page_viii" id="Page_viii"></a></div>
+
+<ul class="toc">
+<li><span class="smcap"><a href="#CHAPTER_VIII">Chapter&nbsp;VIII.</a>&mdash;Fungi</span> <span class="ralign"><a href="#Page_54">54</a></span>
+
+<ul class="subtoc">
+<li><i>Phycomycetes</i>, <i>Mycomycetes</i>;</li>
+<li><a href="#phyco"><i>Phycomycetes</i></a>, Black Moulds, <i>Mucor</i>;</li>
+<li><a href="#rust">White Rusts and Mildews</a>, <i>Cystopus</i>;</li>
+<li><a href="#water">Water Moulds</a>.</li>
+</ul></li>
+
+<li><span class="smcap"><a href="#CHAPTER_IX">Chapter&nbsp;IX.</a>&mdash;True Fungi</span> <span class="ralign"><a href="#Page_63">63</a></span>
+
+<ul class="subtoc">
+<li>Yeast;</li>
+<li><a href="#smuts">Smuts</a>;</li>
+<li><a href="#asco"><i>Ascomycetes</i></a>;</li>
+<li>Dandelion Mildew;</li>
+<li>Cup Fungi, <i>Ascobolus</i>;</li>
+<li><a href="#lichen">Lichens</a>;</li>
+<li>Black Fungi.</li>
+</ul></li>
+
+<li><span class="smcap"><a href="#CHAPTER_X">Chapter&nbsp;X.</a>&mdash;True Fungi</span> (<i>Continued</i>)       <span class="ralign"><a href="#Page_77">77</a></span>
+
+<ul class="subtoc">
+<li><a href="#basid"><i>Basidiomycetes</i></a>;</li>
+<li>Rusts;</li>
+<li><i>Coprinus</i>;</li>
+<li>Classification.</li>
+</ul></li>
+
+<li><span class="smcap"><a href="#CHAPTER_XI">Chapter&nbsp;XI.</a>&mdash;Bryophytes</span> <span class="ralign"><a href="#Page_86">86</a></span>
+
+<ul class="subtoc">
+<li>Classification;</li>
+<li><a href="#liver">Liverworts</a>, <i>Madotheca</i>;</li>
+<li>Classification of Liverworts;</li>
+<li><a href="#moss">Mosses</a>, <i>Funaria</i>;</li>
+<li><a href="#classmoss">Classification of Mosses</a>.</li>
+</ul></li>
+
+<li><span class="smcap"><a href="#CHAPTER_XII">Chapter&nbsp;XII.</a>&mdash;Pteridophytes</span> <span class="ralign"><a href="#Page_102">102</a></span>
+
+<ul class="subtoc">
+<li>Bryophytes and Pteridophytes;</li>
+<li>Germination and Prothallium;</li>
+<li>Structure of Maiden-hair Fern.</li>
+</ul></li>
+
+<li><span class="smcap"><a href="#CHAPTER_XIII">Chapter&nbsp;XIII.</a>&mdash;Classification of Pteridophytes</span> <span class="ralign"><a href="#Page_116">116</a></span>
+
+<ul class="subtoc">
+<li><a href="#ferns">Ferns</a>;</li>
+<li><a href="#horse">Horse-tails</a>;</li>
+<li><a href="#club">Club Mosses</a>.</li>
+</ul></li>
+
+<li><span class="smcap"><a href="#CHAPTER_XIV">Chapter&nbsp;XIV.</a>&mdash;Spermaphytes</span> <span class="ralign"><a href="#Page_128">128</a></span>
+
+<ul class="subtoc">
+<li>General Characteristics;</li>
+<li><a href="#gym">Gymnosperms and Angiosperms</a>, Scotch-pine;</li>
+<li><a href="#classgym">Classification of Gymnosperms</a>.</li>
+</ul></li>
+
+<li><span class="smcap"><a href="#CHAPTER_XV">Chapter&nbsp;XV.</a>&mdash;Spermaphytes</span> (<i>Continued</i>) <span class="ralign"><a href="#Page_143">143</a></span>
+<ul class="subtoc">
+<li>Angiosperms;</li>
+<li>Flowers of Angiosperms;</li>
+<li><a href="#classang">Classification of Angiosperms</a>;</li>
+<li>Monocotyledons, Structure of <i>Erythronium</i>.</li>
+</ul></li>
+
+<li><span class="smcap"><a href="#CHAPTER_XVI">Chapter&nbsp;XVI.</a>&mdash;Classification of Monocotyledons</span> <span class="ralign"><a href="#Page_153">153</a></span>
+
+<ul class="subtoc">
+<li><a href="#lilli"><i>Liliiflor&aelig;</i></a>;</li>
+<li><a href="#enan"><i>Enantioblast&aelig;</i></a>;</li>
+<li><a href="#spad"><i>Spadiciflor&aelig;</i></a>;</li>
+<li><a href="#glum"><i>Glumace&aelig;</i></a>;</li>
+<li><a href="#scit"><i>Scitamine&aelig;</i></a>;</li>
+<li><a href="#gyn"><i>Gynandr&aelig;</i></a>,</li>
+<li><a href="#helo"><i>Helobi&aelig;</i></a>.</li>
+</ul></li>
+
+<li><span class="smcap"><a href="#CHAPTER_XVII">Chapter&nbsp;XVII.</a>&mdash;Dicotyledons</span> <span class="ralign"><a href="#Page_170">170</a></span>
+
+<ul class="subtoc">
+<li>General Characteristics;</li>
+<li>Structure of Shepherd&#8217;s-purse.</li>
+</ul></li>
+</ul>
+<div><span class="pagenum" title="Page&nbsp;ix">&nbsp;</span><a name="Page_ix" id="Page_ix"></a></div>
+<ul class="toc">
+<li><span class="smcap"><a href="#CHAPTER_XVIII">Chapter&nbsp;XVIII.</a>&mdash;Classification of Dicotyledons</span> <span class="ralign"><a href="#Page_181">181</a></span>
+
+<ul class="subtoc">
+<li><i>Choripetal&aelig;</i>: <i>Iuliflor&aelig;</i>;</li>
+<li><i>Centrosperm&aelig;</i>;</li>
+<li><i>Aphanocycl&aelig;</i>;</li>
+<li><i>Eucycl&aelig;</i>;</li>
+<li><i>Tricocc&aelig;</i>;</li>
+<li><i>Calyciflor&aelig;</i>.</li>
+</ul></li>
+
+<li><span class="smcap"><a href="#CHAPTER_XIX">Chapter&nbsp;XIX.</a>&mdash;Classification of Dicotyledons</span> (<i>Continued</i>) <span class="ralign"><a href="#Page_210">210</a></span>
+<ul class="subtoc">
+<li><i>Sympetal&aelig;</i>: <i>Isocarp&aelig;</i>, <i>Bicornes</i>, <i>Primulin&aelig;</i>, <i>Diospyrin&aelig;</i>;</li>
+<li><i>Anisocarp&aelig;</i>, <i>Tubiflor&aelig;</i>, <i>Labiatiflor&aelig;</i>, <i>Contort&aelig;</i>, <i>Campanulin&aelig;</i>,
+<i>Aggregat&aelig;</i>.</li>
+</ul></li>
+
+<li style="margin-bottom:1em;"><span class="smcap"><a href="#CHAPTER_XX">Chapter&nbsp;XX.</a>&mdash;Fertilization of Flowers</span> <span class="ralign"><a href="#Page_225">225</a></span></li>
+
+<li><span class="smcap"><a href="#CHAPTER_XXI">Chapter&nbsp;XXI.</a>&mdash;Histological Methods</span> <span class="ralign"><a href="#Page_230">230</a></span>
+
+<ul class="subtoc">
+<li>Nuclear Division in Wild Onion;</li>
+<li>Methods of Fixing, Staining, and Mounting Permanent Preparations;</li>
+<li>Reference Books.</li>
+</ul></li>
+
+<li><span class="smcap"><a href="#INDEX">Index</a></span> <span class="ralign"><a href="#Page_237">237</a></span></li>
+</ul>
+
+
+
+<hr />
+<h1><span class="pagenum" title="Page&nbsp;1">&nbsp;</span><a name="Page_1" id="Page_1"></a><a name="BOTANY" id="BOTANY"></a><big>BOTANY.</big></h1>
+
+
+
+<hr />
+<h2><a name="CHAPTER_I" id="CHAPTER_I"></a>CHAPTER I.
+<br />
+<small>INTRODUCTION.</small></h2>
+
+
+<p><span class="smcap">All</span> 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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>Investigation has shown that living bodies contain comparatively few
+elements, but these are combined into extraordinarily<span class="pagenum" title="Page&nbsp;2">&nbsp;</span><a name="Page_2" id="Page_2"></a> 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.</p>
+
+<p>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.</p>
+
+<p>The science that treats of living things, irrespective of the
+distinction between plant and animal, is called &ldquo;Biology,&rdquo; but for
+many purposes it is desirable to recognize the distinctions, making
+two departments of Biology,&mdash;Botany, treating of plants; and Zo&ouml;logy,
+of animals. It is with the first of these only that we shall concern
+ourselves here.</p>
+
+<p>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,&mdash;a moss, seaweed, toadstool,&mdash;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&#8217;s
+disposal will permit. Such a study of structure constitutes
+&ldquo;Morphology,&rdquo; which includes two departments,&mdash;gross anatomy, or a
+general study of the parts; and minute anatomy, or &ldquo;Histology,&rdquo; in
+which a microscopic examination is made of the structure of the
+different parts. A special department of Morphology called
+&ldquo;Embryology&rdquo; 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.</p>
+
+<p>From a study of the structure of organisms we get a clue<span class="pagenum" title="Page&nbsp;3">&nbsp;</span><a name="Page_3" id="Page_3"></a> 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 &ldquo;Systematic Botany.&rdquo;</p>
+
+<p>Finally, we may study the functions or workings of an organism: how it
+feeds, breathes, moves, reproduces. This is &ldquo;Physiology,&rdquo; and like
+classification must be preceded by a knowledge of the structures
+concerned.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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.<a name="FNanchor_1_1" id="FNanchor_1_1"></a><a href="#Footnote_1_1" class="fnanchor">[1]</a></p>
+
+<p>In addition to the implements used in studying the gross anatomy, the
+following will be found useful in histological work: 1. a small
+camel&#8217;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.</p>
+
+<p>In addition to these implements, a few reagents may be recommended for
+the simpler histological <span class="pagenum" title="Page&nbsp;4">&nbsp;</span><a name="Page_4" id="Page_4"></a>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.)</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>Most of the lower green plants (<i>alg&aelig;</i>) 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.</p>
+
+<p>Numbers of the most valuable fungi&mdash;<i>i.e.</i> the lower plants that are
+not green&mdash;grow spontaneously on many organic<span class="pagenum" title="Page&nbsp;5">&nbsp;</span><a name="Page_5" id="Page_5"></a> 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.</p>
+
+<p>Mosses, ferns, etc., can be raised with a little care, and of course
+very many flowering plants are readily grown in pots.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+
+
+<hr />
+<h2><span class="pagenum" title="Page&nbsp;6">&nbsp;</span><a name="Page_6" id="Page_6"></a><a name="CHAPTER_II" id="CHAPTER_II"></a>CHAPTER II.
+<br />
+<small>THE CELL.</small></h2>
+
+
+<p><span class="smcap">If</span> we make a thin slice across the stem of a rapidly growing
+plant,&mdash;<i>e.g.</i> geranium, begonia, celery,&mdash;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 &ldquo;cells,&rdquo; and of them the whole
+plant is built up.</p>
+
+<div class="figleft" style="width: 200px;">
+<a name="fig1" id="fig1"></a>
+<img src="images/fig001.png" width="200" height="384" alt="Fig.&nbsp;1." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;1.</span>&mdash;A single cell from a hair on the stamen of the
+common spiderwort (<i>Tradescantia</i>), &times;&nbsp;150. <i>pr.</i> protoplasm; <i>w</i>, cell
+wall; <i>n</i>, nucleus.</p>
+</div>
+
+<blockquote><p>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 (<a href="#fig1">Fig.&nbsp;1</a>). Attached to the base of
+the stamens (<a href="#fig85">Fig.&nbsp;85</a>, <i>B</i>) 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 (<a href="#fig1">Fig.&nbsp;1</a>)
+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 <span class="pagenum" title="Page&nbsp;7">&nbsp;</span><a name="Page_7" id="Page_7"></a>lining of the sac is a roundish body (<i>n</i>),
+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.</p>
+
+<p>The membrane surrounding the cell is known as the cell wall, and in
+young plant cells is always composed of cellulose.</p>
+
+<p>The granular substance lining the cell wall (<a href="#fig1">Fig.&nbsp;1</a>, <i>pr.</i>) is called
+&ldquo;protoplasm,&rdquo; 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.</p></blockquote>
+
+<div class="figcenter" style="width:350px;">
+<a name="fig2" id="fig2"></a>
+<img src="images/fig002.png" width="350" height="222"
+alt="Fig.&nbsp;2." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;2.</span>&mdash;An <i>Am&#339;ba</i>. A cell without a cell wall. <i>n</i>,
+nucleus; <i>v</i>, vacuoles, &times;&nbsp;300.</p>
+</div>
+
+<p>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.</p>
+
+<div class="figcenter" style="width:329px;">
+<a name="fig3" id="fig3"></a>
+<img src="images/fig003.png" width="329" height="450"
+alt="Fig.&nbsp;3." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;3.</span>&mdash;Hairs from the leaf stalk of a wild geranium.
+<i>A</i>, single-celled hair. <i>B</i> and <i>C</i>, hairs consisting of a row of
+cells. The terminal rounded cell secretes a peculiar scented oil that
+gives the plant its characteristic odor. <i>B</i>, &times;&nbsp;50; <i>C</i>, &times;&nbsp;150.</p>
+</div>
+
+<p>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 <a href="#fig2">Figure&nbsp;2</a>. Here we have a mass of protoplasm with a nucleus
+(<i>n</i>) and cavities (vacuoles, <i>v</i>) 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 (<a href="#fig12">Fig.&nbsp;12</a>, <i>B</i>; <a href="#fig16">Fig.&nbsp;16</a>, <i>C</i>) <span class="pagenum" title="Page&nbsp;8">&nbsp;</span><a name="Page_8" id="Page_8"></a>are
+provided with delicate thread-like processes of protoplasm called
+&ldquo;cilia&rdquo; (sing. <i>cilium</i>), which are in active vibration, and propel
+the cell through the water.</p>
+
+<div class="figcenter" style="width:450px;">
+<a name="fig4" id="fig4"></a>
+<img src="images/fig004.png" width="450" height="563"
+alt="Fig.&nbsp;4." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;4.</span>&mdash;<i>A</i>, cross section. <i>B</i>, longitudinal section
+of the leaf stalk of wild geranium, showing its cellular structure.
+<i>Ep.</i> epidermis. <i>h</i>, a hair, &times;&nbsp;50. <i>C</i>, a cell from the prothallium
+(young plant) of a fern, &times;&nbsp;<i>150</i>. The contents of the cell contracted
+by the action of a solution of sugar.</p>
+</div>
+
+<blockquote><p>On placing a cell into a fluid denser than the cell sap (<i>e.g.</i> 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 (<a href="#fig4">Fig.&nbsp;4</a>, <i>C</i>), 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.</p></blockquote>
+
+<p>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 (<a href="#fig3">Fig.&nbsp;3</a>),
+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 (<a href="#fig4">Fig.&nbsp;4</a>, <i>A</i>, <i>B</i>).</p>
+
+
+
+<hr />
+<h2><span class="pagenum" title="Page&nbsp;9">&nbsp;</span><a name="Page_9" id="Page_9"></a><a name="CHAPTER_III" id="CHAPTER_III"></a>CHAPTER III.
+<br />
+<small>CLASSIFICATION OF PLANTS.&mdash;PROTOPHYTES.</small></h2>
+
+
+<p><span class="smcap">For</span> 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.</p>
+
+<p>The following general divisions are usually accepted: I.&nbsp;Sub-kingdom
+(or Branch); II.&nbsp;Class; III.&nbsp;Order; IV.&nbsp;Family; V.&nbsp;Genus; VI.&nbsp;Species.</p>
+
+<p>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 &ldquo;spermaphytes&rdquo; (&ldquo;seed plants&rdquo;).
+They may be divided into two groups (classes), distinguished by
+certain peculiarities in the flowers and seeds. These are named
+respectively &ldquo;gymnosperms&rdquo; and &ldquo;angiosperms,&rdquo; 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 (<i>Abietine&aelig;</i>), including
+the pines and firs. Of the sub-divisions (<i>genera</i>, sing. <i>genus</i>) of
+the fir family, one of the most familiar is the genus <i>Pinus</i>, 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 &ldquo;specific&rdquo; name, <i>strobus</i>.</p>
+
+<p><span class="pagenum" title="Page&nbsp;10">&nbsp;</span><a name="Page_10" id="Page_10"></a>The following table will show more plainly what is meant:</p>
+
+<p class="center" style="margin-top:1em; margin-bottom:2em;">
+Sub-kingdom,<br />
+<i>Spermaphyta</i>.<br />
+<span class="vertical">&nbsp;</span>
+<br />
+<span class="bracketed">Includes all spermaphytes, or seed plants.</span><br />
+<br />
+Class,<br />
+<i>Gymnosperm&aelig;</i>.<br />
+<span class="vertical">&nbsp;</span>
+<br />
+<span class="bracketed">All naked-seeded plants.</span><br />
+<br />
+Order,<br />
+<i>Conifer&aelig;</i>.<br />
+<span class="vertical">&nbsp;</span>
+<br />
+<span class="bracketed">All cone-bearing evergreens.</span><br />
+<br />
+Family,<br />
+<i>Abietine&aelig;</i>.<br />
+<span class="vertical">&nbsp;</span>
+<br />
+<span class="bracketed">Firs, Pines, etc.</span><br />
+<br />
+Genus,<br />
+<i>Pinus</i>.<br />
+<span class="vertical">&nbsp;</span>
+<br />
+<span class="bracketed">Pines.</span><br />
+<br />
+Species,<br />
+<i>Strobus</i>.<br />
+<span class="vertical">&nbsp;</span>
+<br />
+<span class="bracketed">White Pine.</span>
+</p>
+
+
+<h3><span class="pagenum" title="Page&nbsp;11">&nbsp;</span><a name="Page_11" id="Page_11"></a><a name="subk1" id="subk1"></a>SUB-KINGDOM I.
+<br />
+Protophytes.</h3>
+
+<p>The name Protophytes (<i>Protophyta</i>) 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 <span class="pagenum" title="Page&nbsp;12">&nbsp;</span><a name="Page_12" id="Page_12"></a>the slime moulds (<a href="#fig5">Fig.&nbsp;5</a>), <i>Euglena</i> (<a href="#fig9">Fig.&nbsp;9</a>), <i>Volvox</i>
+(<a href="#fig10">Fig.&nbsp;10</a>), and others.</p>
+
+<div class="figcenter" style="width:550px;">
+<a name="fig5" id="fig5"></a>
+<img src="images/fig005.png" width="550" height="431"
+alt="Fig.&nbsp;5." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;5.</span>&mdash;<i>A</i>, a portion of a slime mould growing on a
+bit of rotten wood, &times;&nbsp;3. <i>B</i>, outline of a part of the same, &times;&nbsp;25.
+<i>C</i>, a small portion showing the densely granular character of the
+protoplasm, &times;&nbsp;150. <i>D</i>, a group of spore cases of a slime mould
+(<i>Trichia</i>), of about the natural size. <i>E</i>, two spore cases, &times;&nbsp;5. The
+one at the right has begun to open. <i>F</i>, a thread (capillitium) and
+spores of <i>Trichia</i>, &times;&nbsp;50. <i>G</i>, spores. <i>H</i>, end of the thread, &times;&nbsp;300.
+<i>I</i>, zo&ouml;spores of <i>Trichia</i>, &times;&nbsp;300. <span class="smcap">i</span>, ciliated form; <span class="smcap">ii</span>, am&#339;boid
+forms. <i>n</i>, nucleus. <i>v</i>, contractile vacuole. <i>J</i>, <i>K</i>, sporangia of
+two common slime moulds. <i>J</i>, <i>Stemonitis</i>, &times;&nbsp;2. <i>K</i>, <i>Arcyria</i>, &times;&nbsp;4.</p>
+</div>
+
+<p>Other protophytes, while evidently enough of vegetable nature, are
+nevertheless very different in some respects from the higher plants.</p>
+
+<p>The protophytes may be divided into three classes: I.&nbsp;The slime moulds
+(<i>Myxomycetes</i>); II.&nbsp;The Schizophytes; III.&nbsp;The green monads
+(<i>Volvocine&aelig;</i>).</p>
+
+
+<h4><a name="slime" id="slime"></a>Class I.&mdash;The Slime Moulds.</h4>
+
+<p>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
+(<a href="#fig5">Fig.&nbsp;5</a>, <i>A</i>), 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 <span class="pagenum" title="Page&nbsp;13">&nbsp;</span><a name="Page_13" id="Page_13"></a>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 am&#339;ba. 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.</p>
+
+<p>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 (<i>Trichia</i>) these are round or
+pear-shaped bodies of a yellow color, and about as big as a pin head
+(<a href="#fig5">Fig.&nbsp;5</a>, <i>D</i>), occurring in groups on rotten logs in damp woods.
+Others are stalked (<i>Arcyria</i>, <i>Stemonitis</i>) (<a href="#fig5">Fig.&nbsp;5</a>, <i>J</i>, <i>K</i>), and
+of various colors,&mdash;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.</p>
+
+<blockquote><p>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.</p>
+
+<p>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 (Zo&ouml;spore) with a
+nucleus, and often showing a vacuole (<a href="#fig5">Fig.&nbsp;5</a>, <i>v</i>), 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 (<a href="#fig5">Fig.&nbsp;5</a>, <i>I</i> <span class="smcap">i</span>). Sometimes such
+a cell will be seen to divide into two, <span class="pagenum" title="Page&nbsp;14">&nbsp;</span><a name="Page_14" id="Page_14"></a>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 am&#339;ba (<i>I</i> <span class="smcap">ii</span>).</p></blockquote>
+
+<p>The succeeding stages are difficult to follow. After repeatedly
+dividing, a large number of these am&#339;ba-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.</p>
+
+<blockquote><p>Of the common forms of slime moulds the species of <i>Trichia</i> (Figs.
+<i>D</i>, <i>I</i>) and <i>Physarum</i> 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 &ldquo;moist chamber.&rdquo; 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.</p></blockquote>
+
+
+<h4><a name="schizo" id="schizo"></a><span class="smcap">Class II.</span>&mdash;<i>Schizophytes</i>.</h4>
+
+<p>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 <span class="pagenum" title="Page&nbsp;15">&nbsp;</span><a name="Page_15" id="Page_15"></a>splitting of the cells, whence their
+name. There are two pretty well-marked orders,&mdash;the blue-green slimes
+(<i>Cyanophyce&aelig;</i>) and the bacteria (<i>Schizomycetes</i>). 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.</p>
+
+<p>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.</p>
+
+<div class="figcenter" style="width:284px;">
+<a name="fig6" id="fig6"></a>
+<img src="images/fig006.png" width="284" height="397"
+alt="Fig.&nbsp;6." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;6.</span>&mdash;Blue-green slime (<i>Oscillaria</i>). <i>A</i>, mass of
+filaments of the natural size. <i>B</i>, single filament, &times;&nbsp;300. <i>C</i>, a
+piece of a filament that has become separated. <i>s</i>, sheath, &times;&nbsp;300.</p>
+</div>
+
+<p>As a representative of the group, we will select one of the commonest
+forms (<i>Oscillaria</i>), 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 (<a href="#fig6">Fig.&nbsp;6</a>, <i>a</i>). 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.</p>
+
+<p><span class="pagenum" title="Page&nbsp;16">&nbsp;</span><a name="Page_16" id="Page_16"></a>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.</p>
+
+<blockquote><p>The microscope shows that the filaments of which the mass is composed
+(<a href="#fig6">Fig.&nbsp;6</a>, <i>B</i>) 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.</p>
+
+<p>If the filament is broken, there may generally be detected a delicate,
+colorless sheath that surrounds it, and extends beyond the end cells
+(<a href="#fig6">Fig.&nbsp;6</a>, <i>c</i>). 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.</p></blockquote>
+
+<p>The name &ldquo;oscillaria&rdquo; 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.</p>
+
+<p>The lowest of the <i>Cyanophyce&aelig;</i> 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 (<a href="#fig7">Fig.&nbsp;7</a>, <i>D</i>).</p>
+
+<p>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 (<a href="#fig7">Fig.&nbsp;7</a>,
+<i>A</i>, <i>B</i>). They are sometimes found on <span class="pagenum" title="Page&nbsp;17">&nbsp;</span><a name="Page_17" id="Page_17"></a>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.</p>
+
+<div class="figcenter" style="width:486px;">
+<a name="fig7" id="fig7"></a>
+<img src="images/fig007.png" width="486" height="290"
+alt="Fig.&nbsp;7." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;7.</span>&mdash;Forms of <i>Cyanophyce&aelig;</i>. <i>A</i>, <i>Nostoc</i>. <i>B</i>,
+<i>Gl&#339;otrichia</i>, &times;&nbsp;1. <i>C</i>, individual of <i>Gl&#339;otrichia</i>. <i>D</i>,
+Chro&ouml;coccus. <i>E</i>, <i>Nostoc</i>. <i>F</i>, Oscillaria. <i>G</i>, <i>H</i>, <i>Tolypothrix</i>.
+All &times;&nbsp;300. <i>y</i>, heterocyst. <i>sp.</i> spore.</p>
+</div>
+
+<p>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 (<a href="#fig7">Fig.&nbsp;7</a>, C. <i>sp.</i>). In species where the sheath of the
+filament is well marked (<a href="#fig7">Fig.&nbsp;7</a>, <i>H</i>), groups of cells slip out of the
+sheath, and develop a new one, thus giving rise to a new plant.</p>
+
+<p>The bacteria (<i>Schizomycetes</i>), 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,&mdash;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 <span class="pagenum" title="Page&nbsp;18">&nbsp;</span><a name="Page_18" id="Page_18"></a>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.</p>
+
+<div class="figright" style="width:203px;">
+<a name="fig8" id="fig8"></a>
+<img src="images/fig008.png" width="203" height="400"
+alt="Fig.&nbsp;8." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;8.</span>&mdash;Bacteria.</p>
+</div>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<blockquote><p>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 (<a href="#fig8">Fig.&nbsp;8</a>) recall quite strongly the smaller
+species of oscillaria, and exhibit similar <span class="pagenum" title="Page&nbsp;19">&nbsp;</span><a name="Page_19" id="Page_19"></a>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.</p></blockquote>
+
+<div class="figcenter" style="width:403px;">
+<a name="fig9" id="fig9"></a>
+<img src="images/fig009.png" width="403" height="272"
+alt="Fig.&nbsp;9." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;9.</span>&mdash;<i>Euglena</i>. <i>A</i>, individual in the active
+condition. <i>E</i>, the red &ldquo;eye-spot.&rdquo; <i>c</i>, flagellum. <i>n</i>, nucleus. <i>B</i>,
+resting stage. <i>C</i>, individual dividing, &times;&nbsp;300.</p>
+</div>
+
+<p>Reproduction is for the most part by simple transverse division, as in
+oscillaria; but occasionally spores are produced also.</p>
+
+
+<h4><a name="green" id="green"></a><span class="smcap">Class III.&mdash;Green Monads</span> (<i>Volvocine&aelig;</i>).</h4>
+
+<p>This group of the protophytes is unquestionably closely related to
+certain low animals (<i>Monads</i> or <i>Flagellata</i>), 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.</p>
+
+<p>Of the first group, <i>Euglena</i> (<a href="#fig9">Fig.&nbsp;9</a>), may be selected as a type.</p>
+
+<blockquote><p>This organism is found frequently among other alg&aelig;, 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 (<i>c</i>), by means of which the cell moves. There
+is also to be seen near this end a red speck (<i>e</i>) 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
+(<i>c</i>) 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 (<a href="#fig9">Fig.&nbsp;9</a>,
+<i>B</i>). The contents then divide into two or more parts, which
+afterwards escape as new individuals.</p></blockquote>
+
+<div class="figleft" style="width:246px;">
+<span class="pagenum" title="Page&nbsp;20">&nbsp;</span><a name="Page_20" id="Page_20"></a><a name="fig10" id="fig10"></a>
+<img src="images/fig010.png" width="246" height="248"
+alt="Fig.&nbsp;10." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;10.</span>&mdash;<i>Volvox.</i> <i>A</i>, mature colony, containing
+several smaller ones (<i>x</i>), &times;&nbsp;50. <i>B</i>, Two cells showing the cilia,
+&times;&nbsp;300.</p>
+</div>
+
+<p>Of the forms that are united in colonies<a name="FNanchor_2_2" id="FNanchor_2_2"></a><a href="#Footnote_2_2" class="fnanchor">[2]</a> one of the best known is
+<i>Volvox</i> (<a href="#fig10">Fig.&nbsp;10</a>). 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.</p>
+
+<blockquote><p>The colony (<a href="#fig10">Fig.&nbsp;10</a>, <i>A</i>) 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.&nbsp;<i>B</i>), with the pointed end out. Attached to
+this end are two vibratile filaments (cilia or <i>flagella</i>), and the
+united movements of these cause the rolling motion of the whole
+colony. Usually a number of young colonies (Fig.&nbsp;<i>x</i>) are found within
+the mother colony. These arise by the repeated bipartition of a single
+cell, and escape finally, forming independent colonies.</p>
+
+<p>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.</p></blockquote>
+
+<p>Other forms related to <i>Volvox</i>, and sometimes met with, are
+<i>Gonium</i>, in which there are sixteen cells, forming a flat square;
+<i>Pandorina</i> and <i>Eudorina</i>, with sixteen cells, forming an oval or
+globular colony like <i>Volvox</i>, but much smaller. In all of these the
+structure of the cells is essentially as in <i>Volvox</i>.</p>
+
+
+
+<hr />
+<h2><span class="pagenum" title="Page&nbsp;21">&nbsp;</span><a name="Page_21" id="Page_21"></a><a name="CHAPTER_IV" id="CHAPTER_IV"></a>CHAPTER IV.
+<br />
+<small>SUB-KINGDOM II.
+<br />
+<span class="smcap">Alg&aelig;.</span><a name="FNanchor_3_3" id="FNanchor_3_3"></a><a href="#Footnote_3_3" class="fnanchor">[3]</a></small></h2>
+
+
+<p><span class="smcap">In</span> 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.</p>
+
+<p>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&mdash;I.&nbsp;The Green Alg&aelig; (<i>Chlorophyce&aelig;</i>);
+II.&nbsp;Brown Alg&aelig; (<i>Ph&aelig;ophyce&aelig;</i>); III.&nbsp;Red Alg&aelig; (<i>Rhodophyce&aelig;</i>).</p>
+
+
+<h3><a name="class1" id="class1"></a>Class I.&mdash;Green Alg&aelig;.</h3>
+
+<p>The green alg&aelig; 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.</p>
+
+<p>We may recognize five well-marked orders of the green alg&aelig;&mdash;I.&nbsp;Green
+slimes (<i>Protococcace&aelig;</i>); II.&nbsp;<i>Confervace&aelig;</i>; III.&nbsp;Pond scums
+(<i>Conjugat&aelig;</i>); IV.&nbsp;<i>Siphone&aelig;</i>; V.&nbsp;Stone-worts (<i>Charace&aelig;</i>).</p>
+
+
+<h4><a name="proto" id="proto"></a><span class="pagenum" title="Page&nbsp;22">&nbsp;</span><a name="Page_22" id="Page_22"></a><span class="smcap">Order I.</span>&mdash;<i>Protococcace&aelig;</i>.</h4>
+
+<p>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.</p>
+
+<p>A common representative of the order is the common green slime,
+<i>Protococcus</i> (<a href="#fig11">Fig.&nbsp;11</a>, <i>A</i>, <i>C</i>), 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.</p>
+
+<div class="figcenter" style="width:451px;">
+<a name="fig11" id="fig11"></a>
+<img src="images/fig011.png" width="451" height="308"
+alt="Fig.&nbsp;11." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;11.</span>&mdash;<i>Protococcace&aelig;.</i> <i>A</i>, <i>C</i>, Protococcus. <i>A</i>,
+single cells. <i>B</i>, cells dividing by fission. <i>C</i>, successive steps in
+the process of internal cell division. In <i>C</i> <span class="smcap">iv</span>, the young cells have
+mostly become free. <i>D</i>, a full-grown colony of <i>Pediastrum</i>. <i>E</i>, a
+young colony still surrounded by the membrane of the mother cell. <i>F</i>,
+<i>Scenedesmus</i>. All, &times;&nbsp;300. <i>G</i>, small portion of a young colony of the
+water net (<i>Hydrodictyon</i>), &times;&nbsp;150.</p>
+</div>
+
+<blockquote><p>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 (<a href="#fig11">Fig.&nbsp;11</a>, <i>A</i>) 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 <span class="pagenum" title="Page&nbsp;23">&nbsp;</span><a name="Page_23" id="Page_23"></a>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.</p>
+
+<p>With a little hunting, specimens in various stages of division may be
+found. The division takes place in two ways. In the first (<a href="#fig11">Fig.&nbsp;11</a>,
+<i>B</i>), 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.</p>
+
+<p>The second form of cell division or internal cell division is shown at
+<i>C</i>. 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.</p>
+
+<p>Internal cell division, as we shall see, is found in most plants, but
+only at special times.</p>
+
+<p>Closely resembling <i>Protococcus</i>, and answering quite as well for
+study, are numerous aquatic forms, such as <i>Chlorococcum</i> (<a href="#fig12">Fig.&nbsp;12</a>).
+These are for the most part destitute of a firm cell wall, but are
+imbedded in masses of gelatinous substance like many <i>Cyanophyce&aelig;</i>.
+The chloroplasts are smaller and less distinct than in <i>Protococcus</i>.
+The cells are here oval rather than round, and often show a clear
+space at one end.</p></blockquote>
+
+<div class="figright" style="width:237px;">
+<a name="fig12" id="fig12"></a>
+<img src="images/fig012.png" width="237" height="281"
+alt="Fig.&nbsp;12." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;12.</span>&mdash;<i>Chlorococcum</i>, a plant related to
+<i>Protococcus</i>, but the naked cells are surrounded by a colorless
+gelatinous envelope. <i>A</i>, motionless cells. <i>B</i>, a cell that has
+escaped from its envelope and is ciliated, &times;&nbsp;300.</p>
+</div>
+
+<blockquote><p>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 (<a href="#fig12">Fig.&nbsp;12</a>, <i>B</i>). In this stage
+they closely resemble the individuals of a <i>Volvox</i> colony, or other
+green <i>Flagellata</i>, to which there is little doubt that they are
+related.</p>
+
+<p>There are a number of curious forms common in fresh water that are
+probably related to <i>Protococcus</i>, but differ in having the cells
+united in colonies of definite form. Among the most striking are the
+different species of <i>Pediastrum</i> (<a href="#fig11">Fig.&nbsp;11</a>, <i>D</i>, <i>E</i>), often met with
+in company with <span class="pagenum" title="Page&nbsp;24">&nbsp;</span><a name="Page_24" id="Page_24"></a>other alg&aelig;, 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.</p>
+
+<p>The cells form a flat disc, the outer ones being generally provided
+with a pair of spines.</p>
+
+<p>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 (<a href="#fig11">Fig.&nbsp;11</a>, <i>E</i>).
+Within this membrane the young cells arrange themselves in the form of
+the original colony, and grow together, forming a new colony.</p>
+
+<p>A much larger but rarer form is the water net (<a href="#fig11">Fig.&nbsp;11</a>, <i>G</i>), 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 <i>Scenedesmus</i> (<a href="#fig11">Fig.&nbsp;11</a>, <i>F</i>), of which there are many
+species.</p></blockquote>
+
+
+<h4><a name="confer" id="confer"></a><span class="smcap">Order II.</span>&mdash;<i>Confervace&aelig;</i>.</h4>
+
+<p>Under this head are included a number of forms of which the simplest
+ones approach closely, especially in their younger stages, the
+<i>Protococcace&aelig;</i>. Indeed, some of the so-called <i>Protococcace&aelig;</i> are
+known to be only the early stages of these plants.</p>
+
+<p>A common member of this order is <i>Cladophora</i>, 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.</p>
+
+<blockquote><p>The microscope shows (<a href="#fig13">Fig.&nbsp;13</a>, <i>A</i>) 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.</p>
+
+<p>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 <span class="pagenum" title="Page&nbsp;25">&nbsp;</span><a name="Page_25" id="Page_25"></a>bodies, called &ldquo;pyrenoids.&rdquo; 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&nbsp;cent watery solution of chromic
+acid, then washing thoroughly and staining with borax carmine, the
+nuclei will be made very evident (<a href="#fig13">Fig.&nbsp;13</a>, <i>B</i>). Such preparations may
+be kept permanently in dilute glycerine.</p></blockquote>
+
+<div class="figcenter" style="width:500px;">
+<a name="fig13" id="fig13"></a>
+<img src="images/fig013.png" width="500" height="329"
+alt="Fig.&nbsp;13." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;13.</span>&mdash;<i>Cladophora.</i> <i>A</i>, a fragment of a plant,
+&times;&nbsp;50. <i>B</i>, a single cell treated with chromic acid, and stained with
+alum cochineal. <i>n</i>, nucleus. <i>py.</i> pyrenoid, &times;&nbsp;150. <i>C</i>, three stages
+in the division of a cell. <span class="smcap">i</span>, 1.45&nbsp;p.m.; <span class="smcap">ii</span>, 2.55&nbsp;p.m.; <span class="smcap">iii</span>,
+4.15&nbsp;p.m., &times;&nbsp;150. <i>D</i>, a zo&ouml;spore &times;&nbsp;350.</p>
+</div>
+
+<blockquote><p>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 (<a href="#fig13">Fig.&nbsp;13</a>, <i>C</i>). 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 (<i>C</i> <span class="smcap">iii</span>.) is somewhat contracted,
+but soon becomes closely applied to the new wall. The whole process
+lasts, at ordinary temperatures (20&deg;-25&deg;&nbsp;C.), from three to four
+hours.</p>
+
+<p>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 (zo&ouml;spores) (<a href="#fig13">Fig.&nbsp;13</a>, <i>D</i>), 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
+zo&ouml;spores, from their animal-like movements. They are provided with
+two cilia, closely resembling the motile cells of the <i>Protococcace&aelig;</i>
+and <i>Volvocine&aelig;</i>.<span class="pagenum" title="Page&nbsp;26">&nbsp;</span><a name="Page_26" id="Page_26"></a></p></blockquote>
+
+<p>There are very many examples of these simple <i>Confervace&aelig;</i>, some like
+<i>Conferva</i> being simple rows of cells, others like <i>Stigeoclonium</i>
+(<a href="#fig14">Fig.&nbsp;14</a>, <i>A</i>), <i>Ch&aelig;tophora</i> and <i>Draparnaldia</i> (<a href="#fig14">Fig.&nbsp;14</a>, <i>B</i>, <i>C</i>),
+very much branched. The two latter forms are surrounded by masses of
+transparent jelly, which sometimes reach a length of several
+centimetres.</p>
+
+<div class="figcenter" style="width:404px;">
+<a name="fig14" id="fig14"></a>
+<img src="images/fig014.png" width="404" height="289"
+alt="Fig.&nbsp;14." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;14.</span>&mdash;<i>Confervace&aelig;</i>. <i>A</i>, <i>Stigeoclonium</i>. <i>B</i>,
+<i>Draparnaldia</i>, &times;&nbsp;50. <i>C</i>, a piece of <i>Draparnaldia</i>, &times;&nbsp;2. <i>D</i>, part
+of a filament of <i>Conferva</i>, &times;&nbsp;300.</p>
+</div>
+
+<p>Among the marine forms related to these may be mentioned the sea
+lettuce (<i>Ulva</i>), shown in <a href="#fig15">Figure&nbsp;15</a>. The thin, bright-green,
+leaf-like fronds of this plant are familiar to every seaside student.</p>
+
+<div class="figcenter" style="width:329px;">
+<a name="fig15" id="fig15"></a>
+<img src="images/fig015.png" width="329" height="424"
+alt="Fig.&nbsp;15." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;15.</span>&mdash;A plant of sea lettuce (<i>Ulva</i>). One-half
+natural size.</p>
+</div>
+
+<p>Somewhat higher than <i>Cladophora</i> and its allies, especially in the
+differentiation of the reproductive parts, are the various species of
+<i>&#338;dogonium</i> and its relatives. There are numerous species of
+<i>&#338;dogonium</i> not uncommon in stagnant water growing in company with
+other alg&aelig;, but seldom forming masses by themselves of sufficient size
+to be recognizable to the naked eye.</p>
+
+<blockquote><p>The plant is in structure much like <i>Cladophora</i>, except that it is
+unbranched, and the cells have but a single nucleus (<a href="#fig16">Fig.&nbsp;16</a>, <i>E</i>).
+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.</p>
+
+<p><span class="pagenum" title="Page&nbsp;27">&nbsp;</span><a name="Page_27" id="Page_27"></a>There are two forms of reproduction, non-sexual and sexual. In the
+first the contents of certain cells escape in the form of large
+zo&ouml;spores (<a href="#fig16">Fig.&nbsp;16</a>, <i>C</i>), of oval form, having the smaller end
+colorless and surrounded by a crown of cilia. After a short period of
+active motion, the zo&ouml;spore comes to rest, secretes a cell wall about
+itself, and the transparent end becomes flattened out into a disc
+(<i>E</i>, <i>d</i>), 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 zo&ouml;spores are formed, smaller than the ordinary ones, that
+attach themselves to the filaments bearing the female reproductive
+organ (o&ouml;gonium), and grow into small plants bearing the male organ
+(antheridium), (<a href="#fig16">Fig.&nbsp;16</a>, <i>B</i>).</p></blockquote>
+
+<div class="figcenter" style="width:371px;">
+<a name="fig16" id="fig16"></a>
+<img src="images/fig016.png" width="371" height="488"
+alt="Fig.&nbsp;16." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;16.</span>&mdash;<i>A</i>, portion of a filament of <i>&#338;dogonium</i>,
+with two o&ouml;gonia (<i>og.</i>). The lower one shows the opening. <i>B</i>, a
+similar filament, to which is attached a small male plant with an
+antheridium (<i>an.</i>). <i>C</i>, a zo&ouml;spore of <i>&#338;dogonium</i>. <i>D</i>, a similar
+spore germinating. <i>E</i>, base of a filament showing the disc (<i>d</i>) by
+which it is attached. <i>F</i>, another species of <i>&#338;dogonium</i> with a ripe
+spore (<i>sp.</i>). <i>G</i>, part of a plant of <i>Bulboch&aelig;te</i>. <i>C</i>, <i>D</i>, &times;&nbsp;300;
+the others &times;&nbsp;150.</p>
+</div>
+
+<blockquote><p>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 (<a href="#fig16">Fig.&nbsp;16</a>,
+<i>A</i>, <i>B</i>). 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 &ldquo;o&ouml;gonium.&rdquo; When the egg cell is
+ripe, the o&ouml;gonium opens by means of a little pore at one side
+(<a href="#fig16">Fig.&nbsp;16</a>, <i>A</i>).</p>
+
+<p>In other cells, either of the same filament or else of the small male<span class="pagenum" title="Page&nbsp;28">&nbsp;</span><a name="Page_28" id="Page_28"></a>
+plants already mentioned, small motile cells, called spermatozoids,
+are formed. These are much smaller than the egg cell, and resemble the
+zo&ouml;spores 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 o&ouml;gonium. By careful observation the student may possibly be
+able to follow the spermatozoid into the o&ouml;gonium, 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
+(<a href="#fig16">Fig.&nbsp;16</a>, <i>F</i>). 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.</p></blockquote>
+
+<div class="figcenter" style="width:477px;">
+<a name="fig17" id="fig17"></a>
+<img src="images/fig017.png" width="477" height="315"
+alt="Fig.&nbsp;17." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;17.</span>&mdash;<i>A</i>, plant of <i>Coleoch&aelig;te</i>, &times;&nbsp;50. <i>B</i>, a few
+cells from the margin, with one of the hairs.</p>
+</div>
+
+<p>Much like <i>&#338;dogonium</i>, but differing in being branched, is the genus
+<i>Bulboch&aelig;te</i>, characterized also by hairs swollen at the base, and
+prolonged into a delicate filament (<a href="#fig16">Fig.&nbsp;16</a>, <i>G</i>).</p>
+
+<p>The highest members of the <i>Confervace&aelig;</i> are those of the genus
+<i>Coleoch&aelig;te</i> (<a href="#fig17">Fig.&nbsp;17</a>), 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 alg&aelig; to the
+red. The commonest species form<span class="pagenum" title="Page&nbsp;29">&nbsp;</span><a name="Page_29" id="Page_29"></a> 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.</p>
+
+<blockquote><p>Growing from the upper surface are numerous hairs, consisting of a
+short, sheath-like base, including a very long and delicate filament
+(<a href="#fig17">Fig.&nbsp;17</a>, <i>B</i>). In their methods of reproduction they resemble
+<i>&#338;dogonium</i>, but the reproductive organs are more specialized.</p></blockquote>
+
+
+
+
+<hr />
+<h2><span class="pagenum" title="Page&nbsp;30">&nbsp;</span><a name="Page_30" id="Page_30"></a><a name="CHAPTER_V" id="CHAPTER_V"></a>CHAPTER V.
+<br />
+<small><span class="smcap">Green Alg&aelig;</span>&mdash;<i>Continued</i>.</small></h2>
+
+
+<h4><a name="pond" id="pond"></a><span class="smcap">Order III.&mdash;Pond Scums</span> (<i>Conjugat&aelig;</i>).</h4>
+
+<p><span class="smcap">The</span> <i>Conjugat&aelig;</i>, while in some respects approaching the <i>Confervace&aelig;</i>
+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
+&ldquo;pond scum.&rdquo; The commonest of these pond scums belong to the genus
+<i>Spirogyra</i>, 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.</p>
+
+<div class="figcenter" style="width:618px;">
+<a name="fig18" id="fig18"></a>
+<img src="images/fig018.png" width="618" height="466"
+alt="Fig.&nbsp;18." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;18.</span>&mdash;<i>A</i>, a filament of a common pond scum
+(<i>Spirogyra</i>) separating into two parts. <i>B</i>, a cell undergoing
+division. The cell is seen in optical section, and the chlorophyll
+bands are omitted, <i>n</i>, <i>n&#697;</i>, the two nuclei. <i>C</i>, a complete cell.
+<i>n</i>, nucleus. <i>py.</i> pyrenoid. <i>D</i>, <i>E</i>, successive stages in the
+process of conjugation. <i>G</i>, a ripe spore. <i>H</i>, a form in which
+conjugation takes place between the cells of the same filament. All
+&times;&nbsp;150.</p>
+</div>
+
+<blockquote><p>For microscopical examination the larger species are preferable. When
+one of these is magnified (<a href="#fig18">Fig.&nbsp;18</a>, <i>A</i>, <i>C</i>), 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 (<i>n</i>), 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 <i>Conjugat&aelig;</i>
+are of very peculiar forms. The number of these bands varies much in
+different species of <i>Spirogyra</i>, but is commonly two or three. These
+chloroplasts, like those of other plants, are not noticeably different
+in structure from the ordinary protoplasm, as <span class="pagenum" title="Page&nbsp;31">&nbsp;</span><a name="Page_31" id="Page_31"></a>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 (<a href="#fig18">Fig.&nbsp;18</a>, <i>C</i>, <i>py.</i>). 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 <i>Cladophora</i>, 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;&nbsp;C., or a little lower), the process may be checked.
+The experiment is most conveniently made when <span class="pagenum" title="Page&nbsp;32">&nbsp;</span><a name="Page_32" id="Page_32"></a>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&nbsp;<span class="smcap">p.m.</span>, 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 (<a href="#fig18">Fig.&nbsp;18</a>, <i>B</i>), that finally disappear. At first no
+nucleoli are present in the daughter nuclei, but they appear before
+the division is complete.</p>
+
+<p>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 (<a href="#fig18">Fig.&nbsp;18</a>, <i>A</i>).</p></blockquote>
+
+<p>Spores like those of <i>&#338;dogonium</i> 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.</p>
+
+<blockquote><p>Two filaments lying side by side send out protuberances of the cell
+wall that grow toward each other until they touch (<a href="#fig18">Fig.&nbsp;18</a>, <i>D</i>). 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.</p>
+
+<p>In some species adjoining cells of the same filament become connected,
+the tubes being formed at the end of the cells (<a href="#fig18">Fig.&nbsp;18</a>, <i>H</i>), and the
+cell in which the spore is formed enlarges.</p>
+
+<p>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 <i>&#338;dogonium</i> these require a long period of rest before
+germinating.</p></blockquote>
+
+<div class="figcenter" style="width:321px;">
+<a name="fig19" id="fig19"></a>
+<img src="images/fig019.png" width="321" height="268"
+alt="Fig.&nbsp;19." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;19.</span>&mdash;Forms of <i>Zygnemace&aelig;</i>. <i>A</i>, <i>Zygnema</i>. <i>B</i>,
+<i>C</i>, <i>D</i>, <i>Mesocarpus</i>. All &times;&nbsp;150.</p>
+</div>
+
+<p>There are various genera of the pond scums, differing in the form of
+the chloroplasts and also in the position of the spores. <span class="pagenum" title="Page&nbsp;33">&nbsp;</span><a name="Page_33" id="Page_33"></a>Of these may
+be mentioned <i>Zygnema</i> (<a href="#fig19">Fig.&nbsp;19</a>, <i>A</i>), with two star-shaped
+chloroplasts in each cell, and <i>Mesocarpus</i> (<a href="#fig19">Fig.&nbsp;19</a>, <i>B</i>, <i>D</i>), in
+which the single chloroplast has the form of a thin median plate. (B
+shows the appearance from in front, <i>C</i> from the side, showing the
+thickness of the plate.) <i>Mesocarpus</i> and the allied genera have the
+spore formed between the filaments, the contents of both the uniting
+cells leaving them.</p>
+
+<div class="figcenter" style="width:366px;">
+<a name="fig20" id="fig20"></a>
+<img src="images/fig020.png" width="366" height="272"
+alt="Fig.&nbsp;20." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;20.</span>&mdash;Forms of Desmids. <i>A</i>, <i>B</i>, <i>Closterium</i>.
+<i>C</i>, <i>D</i>, <i>D&#697;</i>, <i>Cosmarium</i>. <i>D</i>, and <i>D&#697;</i> show the process of
+division. <i>E</i>, <i>F</i>, <i>Staurastrum</i>; <i>E</i> seen from the side, <i>F</i> from
+the end.</p>
+</div>
+
+<p>Evidently related to the pond scums, but differing in being for the
+most part strictly unicellular, are the desmids (<a href="#fig20">Fig.&nbsp;20</a>). 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
+(<i>Utricularia</i>) and other fine-leaved aquatics.</p>
+
+<blockquote><p>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, <span class="pagenum" title="Page&nbsp;34">&nbsp;</span><a name="Page_34" id="Page_34"></a>each division having a single large chloroplast of peculiar
+form. The central part of the cell in which the nucleus lies is
+colorless.</p>
+
+<p>Among the commonest forms, often growing with <i>Spirogyra</i>, are various
+species of <i>Closterium</i> (<a href="#fig20">Fig.&nbsp;20</a>, <i>A</i>, <i>B</i>), 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.</p></blockquote>
+
+<p>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.</p>
+
+<p>In their reproduction they closely resemble the pond scums.</p>
+
+
+<h4><a name="siphon" id="siphon"></a><span class="smcap">Order IV.</span>&mdash;<i>Siphone&aelig;</i>.</h4>
+
+<p>The <i>Siphone&aelig;</i> are alg&aelig; occurring both in fresh and salt water, and
+are distinguished from other alg&aelig; 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 <i>Vaucheria</i>, 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 &ldquo;green felts.&rdquo; 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.</p>
+
+<blockquote><p>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 <i>Spirogyra</i> or <i>Cladophora</i>. If we follow it to the tip,
+the contents here will be found to be denser, this being the growing
+point. By careful <span class="pagenum" title="Page&nbsp;35">&nbsp;</span><a name="Page_35" id="Page_35"></a>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 (<i>cl.</i>). and a larger or smaller number of
+small, shining, globular bodies (<i>ol.</i>). 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.</p></blockquote>
+
+<div class="figcenter" style="width:625px;">
+<a name="fig21" id="fig21"></a>
+<img src="images/fig021.png" width="625" height="426"
+alt="Fig.&nbsp;21." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;21.</span>&mdash;<i>A</i>, <i>C</i>, successive stages in the
+development of the sexual organs of a green felt (<i>Vaucheria</i>). <i>an.</i>
+antheridium. <i>og.</i> o&ouml;gonium. <i>D</i>, a ripe o&ouml;gonium. <i>E</i>, the same after
+it has opened. <i>o</i>, the egg cell. <i>F</i>, a ripe spore. <i>G</i>, a species in
+which the sexual organs are borne separately on the main filament.
+<i>A</i>, <i>F</i>, &times;&nbsp;150. <i>G</i>, &times;&nbsp;50. <i>cl.</i> chloroplasts. <i>ol.</i> oil.</p>
+</div>
+
+<blockquote><p>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.</p>
+
+<p>One of the commonest and at the same time most characteristic species
+is <i>Vaucheria racemosa</i> (<a href="#fig21">Fig.&nbsp;21</a>, <i>A</i>, <i>F</i>). 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.</p>
+
+<p><span class="pagenum" title="Page&nbsp;36">&nbsp;</span><a name="Page_36" id="Page_36"></a>The sexual organs are formed on special branches, and their
+arrangement is such as to make the species instantly recognizable.</p>
+
+<p>The first sign of their development is the formation of a short branch
+(<a href="#fig21">Fig.&nbsp;21</a>, <i>A</i>) 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 &ldquo;antheridium,&rdquo; and within are produced, by internal
+division, numerous excessively small spermatozoids.</p>
+
+<p>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
+(<a href="#fig21">Fig.&nbsp;21</a>, <i>B</i>, <i>og.</i>). These are the young o&ouml;gonia, which rapidly
+increase in size, assuming an oval form, and become separated by walls
+from the main branch (<i>C</i>). Unlike the antheridium, the o&ouml;gonia
+contain a great deal of chlorophyll, appearing deep green.</p>
+
+<p>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.</p></blockquote>
+
+<div class="figcenter" style="width:319px;">
+<a name="fig22" id="fig22"></a>
+<img src="images/fig022.png" width="319" height="420"
+alt="Fig.&nbsp;22." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;22.</span>&mdash;<i>A</i>, non-sexual reproduction in <i>Vaucheria
+sessilis</i>. <i>B</i>, non-sexual spore of <i>V.&nbsp;geminata</i>, &times;&nbsp;50.</p>
+</div>
+
+<blockquote><p>The o&ouml;gonia, 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 (<i>D</i>), 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 (<a href="#fig21">Fig.&nbsp;21</a>,
+<i>E</i>, <i>o</i>). Almost as soon as the o&ouml;gonium 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 (<i>F</i>).</p>
+
+<p><span class="pagenum" title="Page&nbsp;37">&nbsp;</span><a name="Page_37" id="Page_37"></a>In some species the sexual organs are borne directly on the filament
+(<a href="#fig21">Fig.&nbsp;21</a>, <i>G</i>).</p>
+
+<p>Large zo&ouml;spores are formed in some of the green felts (<a href="#fig22">Fig.&nbsp;22</a>, <i>A</i>),
+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 zo&ouml;spore, covered with numerous
+short cilia (<i>A</i> <span class="smcap">ii</span>). After a short period of activity, this loses its
+cilia, develops a wall, and begins to grow (<span class="allsc">III, IV</span>). Other species
+(<i>B</i>) 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.</p></blockquote>
+
+
+<h4><a name="chara" id="chara"></a><span class="smcap">Order V.</span>&mdash;<i>Charace&aelig;</i>.</h4>
+
+<p>The <i>Charace&aelig;</i>, or stone-worts, as some of them are called, are so
+very different from the other green alg&aelig; that it is highly probable
+that they should be separated from them.</p>
+
+<p>The type of the order is the genus <i>Chara</i> (<a href="#fig23">Fig.&nbsp;23</a>), 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.</p>
+
+<p>The plant (<a href="#fig23">Fig.&nbsp;23</a>, <i>A</i>) 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.</p>
+
+<p>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 (<a href="#fig23">Fig.&nbsp;23</a>, <i>A</i>, <i>r</i>). The lower of the two
+is globular, and bright scarlet in color; the other, more oval and
+duller.</p>
+
+<p>Examined with a lens the main axis presents a striated appearance. The
+whole plant is harsh to the touch and brittle, <span class="pagenum" title="Page&nbsp;38">&nbsp;</span><a name="Page_38" id="Page_38"></a>owing to the limy
+coating. It is fastened to the ground by fine, colorless hairs, or
+rootlets.</p>
+
+<div class="figcenter" style="width:613px;">
+<a name="fig23" id="fig23"></a>
+<img src="images/fig023.png" width="613" height="486"
+alt="Fig.&nbsp;23." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;23.</span>&mdash;<i>A</i>, plant of a stone-wort (<i>Chara</i>),
+one-half natural size. <i>r</i>, reproductive organs. <i>B</i>, longitudinal
+section through the apex. <i>S</i>, apical cell. <i>x</i>, nodes. <i>y</i>,
+internodes. <i>C</i>, a young leaf. <i>D</i>, cross section of an internode.
+<i>E</i>, of a node of a somewhat older leaf. <i>F</i>, <i>G</i>, young sexual organs
+seen in optical section. <i>o</i>, o&ouml;gonium. <i>An.</i> antheridium. <i>H</i>,
+superficial view. <i>G</i>, <i>I</i>, group of filaments containing
+spermatozoids. <i>J</i>, a small portion of one of these more magnified,
+showing a spermatozoid in each cell. <i>K</i>, free spermatozoids. <i>L</i>, a
+piece of a leaf with ripe o&ouml;gonium (<i>o</i>), and antheridium (<i>An.</i>).
+<i>B</i>, <i>H</i>, &times;&nbsp;150. <i>J</i>, <i>K</i>, &times;&nbsp;300. <i>I</i>, &times;&nbsp;50. <i>L</i>, &times;&nbsp;25.</p>
+</div>
+
+<blockquote><p>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 (<a href="#fig23">Fig.&nbsp;23</a>, <i>B</i>, <i>S</i>). This from
+its position is called the &ldquo;apical cell,&rdquo; 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 (<i>y</i>); the other divides repeatedly,
+forming a node or joint (<i>x</i>).</p>
+
+<p>As the arrangement of these cells is essentially the same in the
+<span class="pagenum" title="Page&nbsp;39">&nbsp;</span><a name="Page_39" id="Page_39"></a>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 <a href="#fig23">Figure&nbsp;23</a>, <i>E</i>.</p>
+
+<p>As the stem grows, a covering is formed over the large internodal cell
+(<i>y</i>) 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 (<i>y</i>) surrounded by the regularly arranged cells of
+the covering or cortex (<a href="#fig23">Fig.&nbsp;23</a>, <i>D</i>).</p>
+
+<p>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 <i>Nitella</i>, where the long internodal
+cells are not covered with a cortex. In <i>Chara</i> they are most evident
+in the root hairs that fasten the plant to the ground.</p>
+
+<p>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 (<a href="#fig23">Fig.&nbsp;23</a>, <i>C</i>). In some species the chloroplasts
+are reddish in the young cells, assuming their green color as the
+cells approach maturity.</p></blockquote>
+
+<p>The plant multiplies non-sexually by means of special branches that
+may become detached, but there are no non-sexual spores formed.</p>
+
+<blockquote><p>The sexual organs have already been noticed arising in pairs at the
+joints of the leaves. The o&ouml;gonium is formed above, the antheridium
+below.</p>
+
+<p>The young o&ouml;gonium (<i>F</i>, <i>O</i>) 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 (<i>G</i>). 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
+o&ouml;gonium (<i>L</i>, <i>O</i>) 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 o&ouml;gonium.</p>
+
+<p>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 <span class="pagenum" title="Page&nbsp;40">&nbsp;</span><a name="Page_40" id="Page_40"></a>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 (<i>G</i>, <i>an.</i>).
+These cells, especially the outer ones, develop a great amount of a
+red pigment, giving the antheridium its characteristic color.</p>
+
+<p>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>I</i>,
+<i>J</i>) composed of a single row of cells, in each of which is formed a
+spermatozoid.</p>
+
+<p>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.</p>
+
+<p>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 (<i>K</i>). To see the
+cilia it is necessary to kill the spermatozoids with iodine or some
+other reagent.</p>
+
+<p>After fertilization the outer cells of the o&ouml;gonium become very hard,
+and the whole falls off, germinating after a sufficient period of
+rest.</p></blockquote>
+
+<p>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.</p>
+
+<p>There are two families of the <i>Charace&aelig;</i>, the <i>Chare&aelig;</i>, of which
+<i>Chara</i> is the type, and the <i>Nitelle&aelig;</i>, represented by various
+species of <i>Nitella</i> and <i>Tolypella</i>. The second family have the
+internodes without any cortex&mdash;that is, consisting of a single long
+cell; and the crown at the top of the o&ouml;gonium is composed of ten
+cells instead of five. They are also destitute of the limy coating of
+the <i>Chare&aelig;</i>.</p>
+
+<p>Both as regards the structure of the plant itself, as well as the
+reproductive organs, especially the very complex antheridium, the
+<i>Charace&aelig;</i> are very widely separated from any other group of plants,
+either above or below them.</p>
+
+
+
+<hr />
+<h2><span class="pagenum" title="Page&nbsp;41">&nbsp;</span><a name="Page_41" id="Page_41"></a><a name="CHAPTER_VI" id="CHAPTER_VI"></a>CHAPTER VI.
+<br />
+<small>THE BROWN ALG&AElig; (<i>Ph&aelig;ophyce&aelig;</i>).</small></h2>
+
+
+<div class="figcenter" style="width:331px;">
+<a name="fig24" id="fig24"></a>
+<img src="images/fig024.png" width="331" height="291"
+alt="Fig.&nbsp;24." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;24.</span>&mdash;Forms of diatoms. <i>A</i>, <i>Pinnularia</i>. <span class="smcap">i</span>, seen
+from above; <span class="smcap">ii</span>, from the side. <i>B</i>, <i>Fragillaria</i> (?). <i>C</i>,
+<i>Navicula</i>. <i>D</i>, <i>F</i>, <i>Eunotia</i>. <i>E</i>, <i>Gomphonema</i>. <i>G</i>, <i>Cocconeis</i>.
+<i>H</i>, <i>Diatoma</i>. All &times;&nbsp;300.</p>
+</div>
+
+<p><span class="smcap">These</span> 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 (<i>Diatomace&aelig;</i>) 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 alg&aelig;, 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 <span class="pagenum" title="Page&nbsp;42">&nbsp;</span><a name="Page_42" id="Page_42"></a>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
+(<a href="#fig25">Fig.&nbsp;25</a>).</p>
+
+<div class="figcenter" style="width:256px;">
+<a name="fig25" id="fig25"></a>
+<img src="images/fig025.png" width="256" height="387"
+alt="Fig.&nbsp;25." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;25.</span>&mdash;Diatoms attached by a gelatinous stalk.
+&times;&nbsp;150</p>
+</div>
+
+<blockquote><p>They are at once distinguished from the desmids by their color, which
+is always some shade of yellowish or reddish brown. The commonest
+forms, <i>e.g.</i> <i>Navicula</i> (<a href="#fig24">Fig.&nbsp;24</a>, <i>C</i>), 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.</p>
+
+<p>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 <i>Pinnularia</i> (<a href="#fig24">Fig.&nbsp;24</a>, <i>A</i> <span class="smcap">ii</span>).</p></blockquote>
+
+<p>Most of the diatoms show movements, swimming slowly or gliding over
+solid substances; but like the movements of <i>Oscillaria</i> and the
+desmids, the movements are not satisfactorily understood, although
+several explanations have been offered.</p>
+
+<p>They resemble somewhat the desmids in their reproduction.</p>
+
+
+<h4><a name="truebr" id="truebr"></a>The True Brown Alg&aelig;.</h4>
+
+<p>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.</p>
+
+<div class="figcenter" style="width:632px;">
+<a name="fig26" id="fig26"></a>
+<img src="images/fig026.png" width="632" height="511"
+alt="Fig.&nbsp;26." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;26.</span>&mdash;<i>A</i>, a branch of common rock weed (<i>Fucus</i>),
+one-half natural size. <i>x</i>, end of a branch bearing conceptacles. <i>B</i>,
+section through a conceptacle containing o&ouml;gonia (<i>og.</i>), &times;&nbsp;25. <i>C</i>,
+<i>E</i>, successive stages in the development of the o&ouml;gonium, &times;&nbsp;150. <i>F</i>,
+<i>G</i>, antheridia. In <i>G</i>, one of the antheridia has discharged the mass
+of spermatozoids (<i>an.</i>), &times;&nbsp;150.</p>
+</div>
+
+<p>One of the commonest forms is the ordinary rock weed (<i>Fucus</i>), which
+covers the rocks of our northeastern coast with a heavy drapery for
+several feet above low-water mark, so that <span class="pagenum" title="Page&nbsp;43">&nbsp;</span><a name="Page_43" id="Page_43"></a>the plants are completely
+exposed as the tide recedes. The commonest species, <i>F.&nbsp;vesiculosus</i>
+(<a href="#fig26">Fig.&nbsp;26</a>, <i>A</i>), 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 <span class="pagenum" title="Page&nbsp;44">&nbsp;</span><a name="Page_44" id="Page_44"></a>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.</p>
+
+<p>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.</p>
+
+<p>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 (<a href="#fig26">Fig.&nbsp;26</a>, <i>A</i>, <i>x</i>) 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 o&ouml;gonia.</p>
+
+<p>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&nbsp;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.</p>
+
+<blockquote><p>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. <span class="pagenum" title="Page&nbsp;45">&nbsp;</span><a name="Page_45" id="Page_45"></a>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.</p>
+
+<p>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, <i>e.g.</i> <i>Ectocarpus</i> and <i>Laminaria</i>
+(<a href="#fig28">Fig.&nbsp;28</a>, <i>A</i>, <i>C</i>), zo&ouml;spores are formed.</p>
+
+<p>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, <i>F.&nbsp;vesiculosus</i>, the
+antheridia and o&ouml;gonia are borne on separate plants; but in others,
+<i>e.g.</i> <i>F.&nbsp;platycarpus</i>, they are both in the same conceptacle.</p>
+
+<p>The walls of the conceptacle (<a href="#fig26">Fig.&nbsp;26</a>, <i>B</i>) 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.</p>
+
+<p>The reproductive bodies arise from the base of these hairs. The
+o&ouml;gonia (<a href="#fig26">Fig.&nbsp;26</a>, <i>C</i>, <i>E</i>) arise as nearly colorless cells, that
+early become divided into two cells, a short basal cell or stalk and a
+larger terminal one, the o&ouml;gonium 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 o&ouml;gonium is of a nearly uniform olive-brown
+tint.</p>
+
+<p>When ripe, the upper part of the o&ouml;gonium dissolves, allowing the
+eight cells, still enclosed in a delicate membrane, to escape
+(<a href="#fig27">Fig.&nbsp;27</a>, <i>H</i>). Finally, the walls separating the inner cells of the
+o&ouml;gonium become also absorbed, as well as the surrounding membrane,
+and the eight egg cells escape into the water (<a href="#fig27">Fig.&nbsp;27</a>, <i>I</i>) as naked
+balls of protoplasm, in which a central nucleus may be dimly seen.</p>
+
+<p>The antheridia (<a href="#fig26">Fig.&nbsp;26</a>, <i>F</i>, <i>G</i>) 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 (<i>G</i>), 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 (<a href="#fig27">Fig.&nbsp;27</a>, <i>K</i>) are oval in form, with two long
+cilia attached to the <span class="pagenum" title="Page&nbsp;46">&nbsp;</span><a name="Page_46" id="Page_46"></a>side where the brown speck, seen while still
+within the antheridium, is conspicuous.</p>
+
+<p>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 o&ouml;gonia, olive. Within a few minutes
+after putting the o&ouml;gonia 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 (<i>J</i>). 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 (<a href="#fig27">Fig.&nbsp;27</a>, <i>M</i>).</p></blockquote>
+
+<div class="figcenter" style="width:399px;">
+<a name="fig27" id="fig27"></a>
+<img src="images/fig027.png" width="399" height="465"
+alt="Fig.&nbsp;27." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;27.</span>&mdash;<i>H</i>, the eight egg cells still surrounded by
+the inner membrane of the o&ouml;gonium. <i>I</i>, the egg cells escaping into
+the water. <i>J</i>, a single egg cell surrounded by spermatozoids. <i>K</i>,
+mass of spermatozoids surrounded by the inner membrane of the
+antheridium. <i>L</i>, spermatozoids. <i>M</i>, young plant. <i>r</i>, the roots.
+<i>K</i>, &times;&nbsp;300; <i>L</i>, &times;&nbsp;600; the others, &times;&nbsp;150.</p>
+</div>
+
+<p><span class="pagenum" title="Page&nbsp;47">&nbsp;</span><a name="Page_47" id="Page_47"></a>The simpler brown seaweeds, so far as known, multiply only by means of
+zo&ouml;spores, which may grow directly into new plants, or, as has been
+observed in some species, two zo&ouml;spores will first unite. A few, like
+<i>Ectocarpus</i> (<a href="#fig28">Fig.&nbsp;28</a>, <i>A</i>), are simple, branched filaments, but most
+are large plants with complex tissues. Of the latter, a familiar
+example is the common kelp, &ldquo;devil&#8217;s apron&rdquo; (<i>Laminaria</i>), 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 (<i>Macrocystis</i>),
+which is said sometimes to reach a length of three hundred metres.</p>
+
+<div class="figcenter" style="width:612px;">
+<a name="fig28" id="fig28"></a>
+<img src="images/fig028.png" width="612" height="496"
+alt="Fig.&nbsp;28." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;28.</span>&mdash;Forms of brown seaweeds. <i>A</i>, <i>Ectocarpus</i>,
+&times;&nbsp;50. Sporangia (<i>sp.</i>). <i>B</i>, a single sporangium, &times;&nbsp;150. <i>C</i>, kelp
+(<i>Laminaria</i>), &times;&nbsp;&#8539;. <i>D</i>, <i>E</i>, gulf weed (<i>Sargassum</i>). <i>D</i>, one-half
+natural size. <i>E</i>, natural size. <i>v</i>, air bladders. <i>x</i>, conceptacle
+bearing branches.</p>
+</div>
+
+<p><span class="pagenum" title="Page&nbsp;48">&nbsp;</span><a name="Page_48" id="Page_48"></a>The highest of the class are the gulf weeds (<i>Sargassum</i>), plants of
+the warmer seas, but one species of which is found from Cape Cod
+southward (<a href="#fig28">Fig.&nbsp;28</a>, <i>D</i>, <i>E</i>). 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.</p>
+
+
+
+<hr />
+<h2><a name="CHAPTER_VII" id="CHAPTER_VII"></a>CHAPTER VII.
+<br />
+<small><span class="pagenum" title="Page&nbsp;49">&nbsp;</span><a name="Page_49" id="Page_49"></a><span class="smcap">Class III.&mdash;The Red Alg&aelig;</span> (<i>Rhodophyce&aelig;</i>).</small></h2>
+
+
+<p><span class="smcap">These</span> 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.</p>
+
+<p>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 <i>Cladophora</i>; others form cell plates
+comparable to <i>Ulva</i> (<a href="#fig30">Fig.&nbsp;30</a>, <i>C</i>, <i>D</i>); while others, among which is
+the well-known Irish moss (<i>Chondrus</i>), 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.</p>
+
+<p><span class="pagenum" title="Page&nbsp;50">&nbsp;</span><a name="Page_50" id="Page_50"></a>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.</p>
+
+<div class="figcenter" style="width:545px;">
+<a name="fig29" id="fig29"></a>
+<img src="images/fig029.png" width="545" height="480"
+alt="Fig.&nbsp;29." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;29.</span>&mdash;<i>A</i>, a red seaweed (<i>Callithamnion</i>), of the
+natural size. <i>B</i>, a piece of the same, &times;&nbsp;50. <i>t</i>, tetraspores. <i>C</i>
+<span class="smcap">i&ndash;v</span>, successive stages in the development of the tetraspores, &times;&nbsp;150.
+<i>D</i> <span class="allsc">I, II</span> young procarps. <i>tr.</i> trichogyne. <span class="smcap">iii</span>, young; <span class="smcap">iv</span>, ripe spore
+fruit. <span class="allsc">I, III</span>, &times;&nbsp;150. <span class="smcap">iv</span>, &times;&nbsp;50. <i>E</i>, an antheridium, &times;&nbsp;150. <i>F</i>, spore
+fruit of <i>Polysiphonia</i>. The spores are here surrounded by a case,
+&times;&nbsp;50.</p>
+</div>
+
+<p>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.</p>
+
+<p>The form here illustrated (<i>Callithamnion</i>) 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.</p>
+
+<p><span class="pagenum" title="Page&nbsp;51">&nbsp;</span><a name="Page_51" id="Page_51"></a>If alcoholic material is used, it may be mounted for examination
+either in water or very dilute glycerine.</p>
+
+<blockquote><p>The plant is composed of much-branched, slender filaments, closely
+resembling <i>Cladophora</i> in structure, but with smaller cells (<a href="#fig29">Fig.&nbsp;29</a>,
+<i>B</i>). 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
+(<a href="#fig29">Fig.&nbsp;29</a>, <i>C</i> <span class="smcap">i</span>). This bud rapidly increases in size, assuming an oval
+form, and becoming cut off from the cell of the stem (<a href="#fig29">Fig.&nbsp;29</a>, <i>C</i>
+<span class="smcap">ii</span>). 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 alg&aelig;, in being unprovided
+with cilia, and incapable of spontaneous movement.</p>
+
+<p>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.</p>
+
+<p>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 (<a href="#fig29">Fig.&nbsp;29</a>, <i>D</i>
+<span class="smcap">i</span>). 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 (<a href="#fig29">Fig.&nbsp;29</a>, <i>D</i>, <i>tr.</i>).</p>
+
+<p>The antheridia (<a href="#fig29">Fig.&nbsp;29</a>, <i>E</i>) 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 (<a href="#fig29">Fig.&nbsp;29</a>, <i>D</i> <span class="allsc">III, IV</span>).</p></blockquote>
+
+<p><span class="pagenum" title="Page&nbsp;52">&nbsp;</span><a name="Page_52" id="Page_52"></a>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,
+<i>e.g.</i> <i>Polysiphonia</i> (<a href="#fig29">Fig.&nbsp;29</a>, <i>F</i>), contained in urn-shaped
+receptacles, or they may be buried within the tissues of the plant.</p>
+
+<div class="figcenter" style="width:621px;">
+<a name="fig30" id="fig30"></a>
+<img src="images/fig030.png" width="621" height="522"
+alt="Fig.&nbsp;30." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;30.</span>&mdash;Marine red seaweeds. <i>A</i>, <i>Dasya</i>. <i>B</i>,
+<i>Rhodymenia</i> (with smaller alg&aelig; attached). <i>C</i>, <i>Grinnellia</i>. <i>D</i>,
+<i>Delesseria</i>. <i>A</i>, <i>B</i>, natural size; the others reduced one-half.</p>
+</div>
+
+<p>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 <span class="pagenum" title="Page&nbsp;53">&nbsp;</span><a name="Page_53" id="Page_53"></a>beauty to the marine
+species. The red color is not so pronounced, and they are, as a rule,
+somewhat dull colored.</p>
+
+<div class="figcenter" style="width:438px;">
+<a name="fig31" id="fig31"></a>
+<img src="images/fig031.png" width="438" height="302"
+alt="Fig.&nbsp;31." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;31.</span>&mdash;Fresh-water red alg&aelig;. <i>A</i>, <i>Batrachospermum</i>,
+&times;&nbsp;about&nbsp;12. <i>B</i>, a branch of the same, &times;&nbsp;150. <i>C</i>, <i>Lemanea</i>, natural
+size.</p>
+</div>
+
+<p>The commonest genera are <i>Batrachospermum</i> and <i>Lemanea</i> (<a href="#fig31">Fig.&nbsp;31</a>).</p>
+
+
+<hr />
+<h2><span class="pagenum" title="Page&nbsp;54">&nbsp;</span><a name="Page_54" id="Page_54"></a><a name="CHAPTER_VIII" id="CHAPTER_VIII"></a>CHAPTER VIII.
+<br />
+<small>SUB-KINGDOM III.
+<br />
+<span class="smcap">Fungi.</span></small></h2>
+
+
+<p><span class="smcap">The</span> name &ldquo;Fungi&rdquo; 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 alg&aelig;. Unlike the alg&aelig;, 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 alg&aelig;, 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.&nbsp;The <ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Algo-Fungi&rsquo;; changed to be consistent with the rest of the book.">Alga-Fungi</ins> (<i>Phycomycetes</i>), and
+II.&nbsp;The True Fungi (<i>Mycomycetes</i>).</p>
+
+
+<h4><a name="phyco" id="phyco"></a><span class="smcap">Class I.</span>&mdash;<i>Phycomycetes</i>.</h4>
+
+<p>These are fungi consisting of long, undivided, often branching tubular
+filaments, resembling quite closely those of <i>Vaucheria</i> or other
+<i>Siphone&aelig;</i>, but always destitute of any trace of chlorophyll. The
+simplest of these include the common moulds (<i>Mucorini</i>), one of which
+will serve to illustrate the characteristics of the order.</p>
+
+<p>If a bit of fresh bread, slightly moistened, is kept under a <span class="pagenum" title="Page&nbsp;55">&nbsp;</span><a name="Page_55" id="Page_55"></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.</p>
+
+<p>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.</p>
+
+<p>One of the commonest moulds is the one here figured (<a href="#fig32">Fig.&nbsp;32</a>), and
+named <i>Mucor stolonifer</i>, from the runners, or &ldquo;stolons,&rdquo; 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 &ldquo;sporangium.&rdquo;</p>
+
+<blockquote><p>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.</p>
+
+<p>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
+<i>Vaucheria</i>. 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, &ldquo;sporangia,&rdquo; arise at the ends of upright
+branches (<a href="#fig32">Fig.&nbsp;32</a>, <i>C</i>), which at first are cylindrical (<i>a</i>), but
+later enlarge at the end (<i>b</i>), and become cut off by a convex wall
+(<i>c</i>). This wall pushes up into the young sporangium, forming a
+structure called the &ldquo;columella.&rdquo; 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<span class="pagenum" title="Page&nbsp;56">&nbsp;</span><a name="Page_56" id="Page_56"></a>
+formed about each one, and at the same time the columella and the
+stalk of the sporangium become dark-colored.</p>
+
+<p>When ripe, the wall of the sporangium dissolves, and the spores
+(<a href="#fig32">Fig.&nbsp;32</a>, <i>E</i>) are set free. The columella remains unchanged, and
+some of the spores often remain sticking to it (<a href="#fig32">Fig.&nbsp;32</a>, <i>D</i>).</p></blockquote>
+
+<div class="figcenter" style="width:588px;">
+<a name="fig32" id="fig32"></a>
+<img src="images/fig032.png" width="588" height="463"
+alt="Fig.&nbsp;32." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;32.</span>&mdash;<i>A</i>, common black mould (<i>Mucor</i>), &times;&nbsp;5. <i>B</i>,
+three nearly ripe spore cases, &times;&nbsp;25. <i>C</i>, development of the spore
+cases, <span class="smcap">i&ndash;iv</span>, &times;&nbsp;150; <span class="smcap">v</span>, &times;&nbsp;50. <i>D</i>, spore case which has discharged its
+spores. <i>E</i>, spores, &times;&nbsp;300. <i>F</i>, a form of <i>Mucor mucedo</i>, with small
+accessory spore cases, &times;&nbsp;5. <i>G</i>, the spore cases, &times;&nbsp;50. <i>H</i>, a single
+spore case, &times;&nbsp;300. <i>I</i>, development of the zygospore of a black mould,
+&times;&nbsp;45 (after De Bary).</p>
+</div>
+
+<blockquote><p>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 (<a href="#fig32">Fig.&nbsp;32</a>, <i>I</i>).</p></blockquote>
+
+<p>Another common mould (<i>M.&nbsp;mucedo</i>), 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 <span class="pagenum" title="Page&nbsp;57">&nbsp;</span><a name="Page_57" id="Page_57"></a>sporangial filament (<a href="#fig32">Fig.&nbsp;32</a>, <i>F</i>, <i>H</i>).
+These small sporangia have no columella.</p>
+
+<p>Other moulds are sometimes met with, parasitic upon the larger species
+of <i>Mucor</i>.</p>
+
+<p>Related to the black moulds are the insect moulds (<i>Entomopthore&aelig;</i>),
+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.</p>
+
+
+<h4><a name="rust" id="rust"></a><span class="smcap">Order II.&mdash;White Rusts and Mildews</span> (<i>Peronospore&aelig;</i>)</h4>
+
+<p>These are exclusively parasitic fungi, and grow within the tissues of
+various flowering plants, sometimes entirely destroying them.</p>
+
+<p>As a type of this group we will select a very common one (<i>Cystopus
+bliti</i>), that is always to be found in late summer and autumn growing
+on pig weed (<i>Amarantus</i>). 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 (<a href="#fig33">Fig.&nbsp;33</a>, <i>A</i>). In the earlier stages
+the leaf does not appear much affected, but later becomes brown and
+withered about the blotches caused by the fungus.</p>
+
+<blockquote><p>If a thin vertical section of the leaf is made through one of these
+blotches, and mounted as described for <i>Mucor</i>, 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.</p>
+
+<p>The spores already mentioned are formed at the ends of crowded
+filaments, that push up, and finally rupture the epidermis (<a href="#fig33">Fig.&nbsp;33</a>,
+<i>B</i>). They <span class="pagenum" title="Page&nbsp;58">&nbsp;</span><a name="Page_58" id="Page_58"></a>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.</p>
+
+<p>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
+zo&ouml;spore, 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 (<a href="#fig33">Fig.&nbsp;33</a>, <i>C</i>, <i>E</i>).</p></blockquote>
+
+<div class="figcenter" style="width:538px;">
+<a name="fig33" id="fig33"></a>
+<img src="images/fig033.png" width="538" height="338"
+alt="Fig.&nbsp;33." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;33.</span>&mdash;<i>A</i>, leaf of pig-weed (<i>Amarantus</i>), with
+spots of white rust (<i>c</i>), one-half natural size. <i>B</i>, non-sexual
+spores (conidia). <i>C</i>, the same germinating. <i>D</i>, zo&ouml;spores. <i>E</i>,
+germinating zo&ouml;spores. <i>sp.</i> the spore. <i>F</i>, young. <i>G</i>, mature sexual
+organs. In <i>G</i>, the tube may be seen connecting the antheridium
+(<i>an.</i>), with the egg cell (<i>o</i>). <i>H</i>, a ripe resting spore still
+surrounded by the wall of the o&ouml;gonium. <i>I</i>, a part of a filament of
+the fungus, showing its irregular form. All &times;&nbsp;300.</p>
+</div>
+
+<blockquote><p>Under normal conditions the spores probably germinate when the leaves
+are wet, and the filaments enter the plant through the breathing pores
+on <span class="pagenum" title="Page&nbsp;59">&nbsp;</span><a name="Page_59" id="Page_59"></a>the lower surface of the leaves, and spread rapidly through the
+intercellular spaces.</p>
+
+<p>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.</p>
+
+<p>The spores (o&ouml;spores) are much larger than those first formed, and
+possess an outer coat of a dark brown color (<a href="#fig33">Fig.&nbsp;33</a>, <i>H</i>). 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 (<a href="#fig33">Fig.&nbsp;33</a>, <i>F</i>) its
+contents are granular, and fill it completely, but later contract to
+form a globular mass of protoplasm (G. <i><ins class="correction" title="Transcriber&#8217;s note: Original had a degree-sign here.">o</ins></i>), the germ cell or egg
+cell. The whole is an o&ouml;gonium, and differs in no essential respect
+from that of <i>Vaucheria</i>.</p>
+
+<p>Frequently a smaller cell (antheridium), arising from a neighboring
+filament, and in close contact with the o&ouml;gonium, may be detected
+(<a href="#fig33">Fig.&nbsp;33</a>, <i>F</i>, <i>G</i>, <i>an.</i>), 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.</p>
+
+<p>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.</p></blockquote>
+
+<div class="figcenter" style="width:345px;">
+<a name="fig34" id="fig34"></a>
+<img src="images/fig034.png" width="345" height="166"
+alt="Fig.&nbsp;34." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;34.</span>&mdash;Fragment of a filament of the white rust of
+the shepherd&#8217;s-purse, showing the suckers (<i>h</i>), &times;&nbsp;300.</p>
+</div>
+
+<p>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.</p>
+
+<div class="figleft" style="width:161px;">
+<a name="fig35" id="fig35"></a>
+<img src="images/fig035.png" width="161" height="309"
+alt="Fig.&nbsp;35." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;35.</span>&mdash;Non-sexual spores of the vine mildew
+(<i>Peronospora viticola</i>), &times;&nbsp;150.</p>
+</div>
+
+<p><span class="pagenum" title="Page&nbsp;60">&nbsp;</span><a name="Page_60" id="Page_60"></a>Closely related to the species above described is another one
+(<i>C.&nbsp;candidus</i>), which attacks shepherd&#8217;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.</p>
+
+<blockquote><p>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<a name="FNanchor_4_4" id="FNanchor_4_4"></a><a href="#Footnote_4_4" class="fnanchor">[4]</a> by the
+suckers (<a href="#fig34">Fig.&nbsp;34</a>).</p></blockquote>
+
+<p>Very similar to the white rusts in most respects, but differing in the
+arrangement of the non-sexual spores, are the mildews (<i>Peronospora</i>,
+<i>Phytophthora</i>). 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 (<i>Peronospora viticola</i>) (<a href="#fig35">Fig.&nbsp;35</a>), the
+potato fungus (<i>Phytophthora infestans</i>), and many others.</p>
+
+
+<h4><a name="water" id="water"></a><span class="smcap">Order III.</span>&mdash;<i>Saprolegniace&aelig;</i> (<span class="smcap">Water Moulds</span>).</h4>
+
+<p>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 (<a href="#fig36">Fig.&nbsp;36</a>, <i>A</i>).
+Somewhat <span class="pagenum" title="Page&nbsp;61">&nbsp;</span><a name="Page_61" id="Page_61"></a>later, if carefully examined with a lens, little round, white
+bodies may be seen scattered among the filaments.</p>
+
+<div class="figcenter" style="width:596px;">
+<a name="fig36" id="fig36"></a>
+<img src="images/fig036.png" width="596" height="458"
+alt="Fig.&nbsp;36." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;36.</span>&mdash;<i>A</i>, an insect that has decayed in water, and
+become attacked by a water mould (<i>Saprolegnia</i>), natural size. <i>B</i>, a
+ripe zo&ouml;sporangium, &times;&nbsp;100. <i>C</i>, the same discharging the spores. <i>D</i>,
+active. <i>E</i>, germinating zo&ouml;spores, &times;&nbsp;300. <i>F</i>, a second sporangium
+forming below the empty one. <i>G</i> <span class="smcap">i&ndash;iv</span>, development of the o&ouml;gonium,
+&times;&nbsp;100. <i>H</i>, ripe o&ouml;gonium filled with resting spores, &times;&nbsp;100.</p>
+</div>
+
+<blockquote><p>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 <i>Vaucheria</i>, 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.</p>
+
+<p>In the early stages of its growth the plant multiplies by zo&ouml;spores,
+produced in great numbers in sporangia at the ends of the branches.
+The protoplasm collects here much as we saw in <i>V.&nbsp;sessilis</i>, the end
+of the filament becoming club-shaped and ending in a short
+protuberance (<a href="#fig36">Fig.&nbsp;36</a>, <i>B</i>). 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<span class="pagenum" title="Page&nbsp;62">&nbsp;</span><a name="Page_62" id="Page_62"></a> 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
+(<a href="#fig36">Fig.&nbsp;36</a>, <i>C</i>). In case they have no membrane, they swim away at once,
+each being provided with two cilia, and resembling almost exactly the
+zo&ouml;spores of the white rust (<a href="#fig36">Fig.&nbsp;36</a>, <i>D</i>, <i>E</i>). When the cells are
+surrounded by a membrane they remain for some time at rest, but
+finally the contents escape as a zo&ouml;spore, like those already
+described. By killing the zo&ouml;spores 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.</p>
+
+<p>As soon as the sporangium is emptied, a new one is formed, either by
+the filament growing up through it (<a href="#fig36">Fig.&nbsp;36</a>, <i>F</i>) 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.</p>
+
+<p>Besides zo&ouml;spores there are also resting spores developed. O&ouml;gonia
+like those of <i>Vaucheria</i> or the <i>Peronospore&aelig;</i> are formed usually
+after the formation of zo&ouml;spores 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.<a name="FNanchor_5_5" id="FNanchor_5_5"></a><a href="#Footnote_5_5" class="fnanchor">[5]</a></p>
+
+<p>The o&ouml;gonia (<a href="#fig36">Fig.&nbsp;36</a>, <i>G</i>, <i>H</i>) 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 (<i>H</i>).</p></blockquote>
+
+
+
+<hr />
+<h2><span class="pagenum" title="Page&nbsp;63">&nbsp;</span><a name="Page_63" id="Page_63"></a><a name="CHAPTER_IX" id="CHAPTER_IX"></a>CHAPTER IX.
+<br />
+<small>THE TRUE FUNGI (<i>Mycomycetes</i>).</small></h2>
+
+
+<p><span class="smcap">The</span> great majority of the plants ordinarily known as <i>fungi</i> are
+embraced under this head. While some of the lower forms show
+affinities with the <i>Phycomycetes</i>, and through them with the alg&aelig;,
+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.</p>
+
+<p>Probably to be reckoned with the <i>Mycomycetes</i>, but of doubtful
+affinities, are the small unicellular fungi that are the main causes
+of alcoholic fermentation; these are the yeast fungi
+(<i>Saccharomycetes</i>). They cause the fermentation of beer and wine, as
+well as the incipient fermentation in bread, causing it to &ldquo;rise&rdquo; by
+the giving off of bubbles of carbonic acid gas during the process.</p>
+
+<p>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.</p>
+
+<blockquote><p>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&ndash;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 <span class="pagenum" title="Page&nbsp;64">&nbsp;</span><a name="Page_64" id="Page_64"></a>cell sap. No nucleus is visible in the
+living cell, but it has been shown that a nucleus is present.</p>
+
+<p>If growth is active, many of the cells will be seen dividing. The
+process is somewhat different from ordinary fission and is called
+budding (<a href="#fig37">Fig.&nbsp;37</a>, <i>B</i>). 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 (<a href="#fig37">Fig.&nbsp;37</a>, <i>B</i>, <i>C</i>).</p></blockquote>
+
+<div class="figcenter" style="width:281px;">
+<a name="fig37" id="fig37"></a>
+<img src="images/fig037.png" width="281" height="293"
+alt="Fig.&nbsp;37." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;37.</span>&mdash;<i>A</i>, single cells of yeast. <i>B</i>, <i>C</i>, similar
+cells, showing the process of budding, &times;&nbsp;750.</p>
+</div>
+
+<p>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.</p>
+
+<p>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 <i>Smuts</i>), which through cultivation have lost the power of
+developing further.</p>
+
+
+<h4><a name="smuts" id="smuts"></a><span class="smcap">Class I.&mdash;The Smuts</span> (<i>Ustillagine&aelig;</i>).</h4>
+
+<p>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 <span class="pagenum" title="Page&nbsp;65">&nbsp;</span><a name="Page_65" id="Page_65"></a>(<i>Ustillago maydis</i>). This familiar fungus
+attacks Indian corn, forming its spores in enormous quantities in
+various parts of the diseased plant, but particularly in the flowers
+(&ldquo;tassel&rdquo; and young ear).</p>
+
+<blockquote><p>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 (<a href="#fig38">Fig.&nbsp;38</a>, <i>B</i>). The ends of these
+short branches enlarge rapidly and become shut off by partitions, and
+in each a globular spore (<a href="#fig38">Fig.&nbsp;38</a>, <i>C</i>) 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.</p></blockquote>
+
+<div class="figcenter" style="width:425px;">
+<a name="fig38" id="fig38"></a>
+<img src="images/fig038.png" width="425" height="341"
+alt="Fig.&nbsp;38." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;38.</span>&mdash;<i>A</i>, &ldquo;tassel&rdquo; of corn attacked by smut
+(<i>Ustillago</i>). <i>B</i>, filaments of the fungus from a thin section of a
+diseased grain, showing the beginning of the formation of the spores,
+&times;&nbsp;300. <i>C</i>, ripe spores, &times;&nbsp;300.</p>
+</div>
+
+<p>As the spores are forming, an abnormal growth is set up in the cells
+of the part attacked, which in consequence becomes enormously enlarged
+(<a href="#fig38">Fig.&nbsp;38</a>, <i>A</i>), 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.</p>
+
+<p>The remaining <i>Mycomycetes</i> are pretty readily divisible into two
+great classes, based upon the arrangement of the spores. The first of
+these is known as the <i>Ascomycetes</i> (Sac fungi), the other the
+<i>Basidiomycetes</i> (mushrooms, puff-balls, etc.).</p>
+
+
+<h4><a name="asco" id="asco"></a><span class="pagenum" title="Page&nbsp;66">&nbsp;</span><a name="Page_66" id="Page_66"></a><span class="smcap">Class II.</span>&mdash;<i>Ascomycetes</i> (<span class="smcap">Sac Fungi</span>).</h4>
+
+<p>This class includes a very great number of common plants, all
+resembling each other in producing spores in sacs (<i>asci</i>, sing.
+<i>ascus</i>) 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.</p>
+
+<p>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 (<i>Exoascus</i>) that attacks peach-trees, causing the
+disease of the leaves known as &ldquo;curl.&rdquo;</p>
+
+<p>All of the common <i>Ascomycetes</i> 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.</p>
+
+<p>Among the simpler members of this group are the mildews
+(<i>Perisporiace&aelig;</i>), 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 (<i>Podosph&aelig;ra</i>) 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 <span class="pagenum" title="Page&nbsp;67">&nbsp;</span><a name="Page_67" id="Page_67"></a>will show numerous brown or
+blackish specks scattered over the patches. These are the spore
+fruits.</p>
+
+<div class="figcenter" style="width:623px;">
+<a name="fig39" id="fig39"></a>
+<img src="images/fig039.png" width="623" height="488"
+alt="Fig.&nbsp;39." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;39.</span>&mdash;<i>A</i>, spore-bearing filaments of the dandelion
+mildew (<i>Podosph&aelig;ra</i>), &times;&nbsp;150. <i>B</i>, a germinating spore, &times;&nbsp;150. <i>C&ndash;F</i>,
+development of the spore fruit, &times;&nbsp;300. <i>ar.</i> archicarp. <i>G</i>, a ripe
+spore fruit, &times;&nbsp;150. <i>H</i>, the spore sac removed from the spore fruit,
+&times;&nbsp;150. <i>I</i>, spore-bearing filament attacked by another fungus
+(<i>Cicinnobulus</i>), causing the enlargement of the basal cell, &times;&nbsp;150.
+<i>J</i>, a more advanced stage, &times;&nbsp;300. <i>K</i>, spores, &times;&nbsp;300.</p>
+</div>
+
+<blockquote><p>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 <span class="pagenum" title="Page&nbsp;68">&nbsp;</span><a name="Page_68" id="Page_68"></a>much-interlaced
+filaments, divided at intervals by cross-walls.<a name="FNanchor_6_6" id="FNanchor_6_6"></a><a href="#Footnote_6_6" class="fnanchor">[6]</a> They are nearly
+colorless, and the contents are not conspicuous. These filaments send
+up vertical branches (<a href="#fig39">Fig.&nbsp;39</a>, <i>A</i>), 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 (<i>conidia</i>). 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
+(<a href="#fig39">Fig.&nbsp;39</a>, <i>B</i>).</p></blockquote>
+
+<div class="figcenter" style="width:401px;">
+<a name="fig40" id="fig40"></a>
+<img src="images/fig040.png" width="401" height="284"
+alt="Fig.&nbsp;40." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;40.</span>&mdash;Chrysanthemum mildew (<i>Erysiphe</i>), showing
+the suckers (<i>h</i>) by which the filaments are attached to the leaf.
+<i>A</i>, surface view. <i>B</i>, vertical section of the leaf, &times;&nbsp;300.</p>
+</div>
+
+<blockquote><p>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 (<a href="#fig39">Fig.&nbsp;39</a>, <i>C</i>, <i>ar.</i>), the
+female cell, or &ldquo;archicarp,&rdquo; 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 (<i>D</i>, <i>E</i>). These branches soon grow
+together, and cross-walls are formed in them, so that the young spore
+fruit <span class="pagenum" title="Page&nbsp;69">&nbsp;</span><a name="Page_69" id="Page_69"></a>appears surrounded by a single layer of cells, sufficiently
+transparent, however, to allow a view of the interior.</p>
+
+<p>The antheridium undergoes no further change, but the archicarp soon
+divides into two cells,&mdash;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 (<a href="#fig39">Fig.&nbsp;39</a>,
+<i>F</i>) 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 (<a href="#fig39">Fig.&nbsp;39</a>, <i>H</i>). These spores do
+not germinate at once, but remain dormant until the next year.</p></blockquote>
+
+<div class="figcenter" style="width:502px;">
+<a name="fig41" id="fig41"></a>
+<img src="images/fig041.png" width="502" height="326"
+alt="Fig.&nbsp;41." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;41.</span>&mdash;Forms of mildews (<i>Erysiphe</i>). <i>A</i>,
+<i>Microsph&aelig;ra</i>, a spore fruit, &times;&nbsp;150. <i>B</i>, cluster of spore sacs of the
+same, &times;&nbsp;150. <i>C</i>, a single appendage, &times;&nbsp;300. <i>D</i>, end of an appendage
+of <i>Uncinula</i>, &times;&nbsp;300. <i>E</i>, appendage of <i>Phyllactinia</i>, &times;&nbsp;150.</p>
+</div>
+
+<blockquote><p>Frequently other structures, resembling somewhat the spore fruits, are
+found associated with them (<a href="#fig39">Fig.&nbsp;39</a>, <i>I</i>, <i>K</i>), 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 (<i>Cicinnobulus</i>), 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 <span class="pagenum" title="Page&nbsp;70">&nbsp;</span><a name="Page_70" id="Page_70"></a>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 (<a href="#fig39">Fig.&nbsp;39</a>, <i>K</i>), and when
+ripe exude in long, worm-shaped masses, if the receptacle is placed in
+water.</p></blockquote>
+
+<p>The mildews may be divided into two genera: <i>Podosph&aelig;ra</i>, with a
+single ascus in the spore fruit; and <i>Erysiphe</i>, with two or more. In
+the latter the archicarp branches, each branch bearing a spore sac
+(<a href="#fig41">Fig.&nbsp;41</a>, <i>B</i>).</p>
+
+<p>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.</p>
+
+<p>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 &ldquo;herbarium mould&rdquo; (<i>Eurotium herbariorum</i>).</p>
+
+<div class="figright" style="width:284px;">
+<a name="fig42" id="fig42"></a>
+<img src="images/fig042.png" width="284" height="442"
+alt="Fig.&nbsp;42." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;42.</span>&mdash;<i>A</i>, spore bearing filament of the herbarium
+mould (<i>Eurotium</i>), &times;&nbsp;150. <i>B</i>, <i>C</i>, another species showing the way
+in which the spores are borne&mdash;optical section&mdash;&times;&nbsp;150. <i>D</i>, spore
+fruit of the herbarium mould, &times;&nbsp;150. <i>E</i>, spore sac. <i>F</i>, spores,
+&times;&nbsp;300. <i>G</i>, spore-bearing filament of the common blue mould
+(<i>Penicillium</i>), &times;&nbsp;300. <i>sp.</i> the spores.</p>
+</div>
+
+<blockquote><p>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 (<a href="#fig42">Fig.&nbsp;42</a>, <i>A</i>).</p>
+
+<p>Spore fruits much like those of the mildews are formed later, and are
+visible to the naked eye as little yellow grains (<a href="#fig42">Fig.&nbsp;42</a>, <i>D</i>). These
+contain numerous very small spore sacs (<i>E</i>), each with eight spores.</p></blockquote>
+
+<p><span class="pagenum" title="Page&nbsp;71">&nbsp;</span><a name="Page_71" id="Page_71"></a>There are numerous common species of <i>Eurotium</i>, differing in color
+and size, some being yellow or black, and larger than the ordinary
+green form.</p>
+
+<p>Another form, common everywhere on mouldy food of all kinds, as well
+as in other situations, is the blue mould (<i>Penicillium</i>). This, in
+general appearance, resembles almost exactly the herbarium mould, but
+is immediately distinguishable by a microscopic examination (<a href="#fig42">Fig.&nbsp;42</a>,
+<i>G</i>).</p>
+
+<blockquote><p>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.</p></blockquote>
+
+<p>Of the larger <i>Ascomycetes</i>, the cup fungi (<i>Discomycetes</i>) 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.</p>
+
+<p><i>Ascobolus</i> (<a href="#fig43">Fig.&nbsp;43</a>) 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 (<a href="#fig43">Fig.&nbsp;43</a>, <i>A</i>), of a light brownish color,
+and about as big as a pin-head.</p>
+
+<blockquote><p>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 (<a href="#fig43">Fig.&nbsp;43</a>, <i>B</i>). In the study of the early
+stages, a potash solution will be found useful in rendering them
+transparent.</p>
+
+<p>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 <span class="pagenum" title="Page&nbsp;72">&nbsp;</span><a name="Page_72" id="Page_72"></a>spore sacs colored a beautiful blue, so that they are
+readily distinguishable.</p></blockquote>
+
+<div class="figcenter" style="width:609px;">
+<a name="fig43" id="fig43"></a>
+<img src="images/fig043.png" width="609" height="485"
+alt="Fig.&nbsp;43." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;43.</span>&mdash;<i>A</i>, a small cup fungus (<i>Ascobolus</i>), &times;&nbsp;5.
+<i>B</i>, young spore fruit, &times;&nbsp;300. <i>ar.</i> archicarp. <i>C</i>, an older one,
+&times;&nbsp;150. <i>ar.</i> archicarp. <i>sp.</i> young spore sacs. <i>D</i>, section through a
+full-grown spore fruit (partly diagrammatic), &times;&nbsp;25. <i>sp.</i> spore sacs.
+<i>E</i>, development of spore sacs and spores: <span class="smcap">i&ndash;iii</span>, &times;&nbsp;300; <span class="smcap">iv</span>, &times;&nbsp;150.
+<i>F</i>, ripe spores. <i>G</i>, a sterile filament (paraphysis), &times;&nbsp;300. <i>H</i>,
+large scarlet cup fungus (<i>Peziza</i>), natural size.</p>
+</div>
+
+<blockquote><p>The development of the spore sacs may be traced by carefully crushing
+the young spore fruits in water. The young spore sacs (<a href="#fig43">Fig.&nbsp;43</a>, <i>E</i> <span class="smcap">i</span>)
+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. <span class="smcap">ii&ndash;iv</span>). 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 (<a href="#fig43">Fig.&nbsp;43</a>, <i>F</i>). The full-grown spore sacs (<a href="#fig43">Fig.&nbsp;43</a>, <i>E</i>, <i>W</i>)
+are oblong in shape, and attached by a short stalk. The sterile
+filaments between them often become curiously enlarged at the end
+(<i>G</i>). As the spore fruit ripens, it opens at the top, and <span class="pagenum" title="Page&nbsp;73">&nbsp;</span><a name="Page_73" id="Page_73"></a>spreads out
+so as to expose the spore sacs as they discharge their contents
+(<a href="#fig43">Fig.&nbsp;43</a>, <i>D</i>).</p></blockquote>
+
+<p>Of the larger cup fungi, those belonging to the genus <i>Peziza</i>
+(<a href="#fig43">Fig.&nbsp;43</a>, <i>H</i>) 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 (<i>Morchella</i>), 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.</p>
+
+
+<h4><a name="lichen" id="lichen"></a><span class="smcap">Order</span> <i>Lichenes</i>.</h4>
+
+<p>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 alg&aelig;, 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 <i>Parmelia</i> (<a href="#fig44">Fig.&nbsp;44</a>, <i>A</i>), 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.</p>
+
+<div class="figright" style="width:319px;">
+<a name="fig44" id="fig44"></a>
+<img src="images/fig044.png" width="319" height="459"
+alt="Fig.&nbsp;44." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;44.</span>&mdash;<i>A</i>, a common lichen (<i>Parmelia</i>), of the
+natural size. <i>ap.</i> spore fruit. <i>B</i>, section through one of the spore
+fruits, &times;&nbsp;5. <i>C</i>, section through the body of a gelatinous lichen
+(<i>Collema</i>), showing the <i>Nostoc</i> individuals surrounded by the fungus
+filaments, &times;&nbsp;300. <i>D</i>, a spermagonium of <i>Collema</i>, &times;&nbsp;25. <i>E</i>, a
+single <i>Nostoc</i> thread. <i>F</i>, spore sacs and paraphyses of <i>Usnea</i>,
+&times;&nbsp;300. <i>G</i>, <i>Protococcus</i> cells and fungus filaments of <i>Usnea</i>.</p>
+</div>
+
+<p>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 <span class="pagenum" title="Page&nbsp;74">&nbsp;</span><a name="Page_74" id="Page_74"></a>are at first almost closed, but
+expand as they mature (<a href="#fig44">Fig.&nbsp;44</a>, <i>A</i>, <i>ap.</i>).</p>
+
+<blockquote><p>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 <i>Protococcus</i>, or some similar green alg&aelig;,
+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 (<a href="#fig44">Fig.&nbsp;44</a>, <i>B</i>).</p>
+
+<p>The spore fruits of the lichens resemble in all essential respects
+those of the cup fungi, and the spore sacs (<a href="#fig44">Fig.&nbsp;44</a>, <i>F</i>) 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.</p>
+
+<p>In <a href="#fig45">Figure&nbsp;45</a>, <i>H</i>, is shown one of the so-called &ldquo;<i>Soredia</i>,&rdquo;<a name="FNanchor_7_7" id="FNanchor_7_7"></a><a href="#Footnote_7_7" class="fnanchor">[7]</a> a
+group of the alg&aelig;, upon which the lichen is parasitic, surrounded by
+some of the <span class="pagenum" title="Page&nbsp;75">&nbsp;</span><a name="Page_75" id="Page_75"></a>filaments, the whole separating spontaneously from the
+plant and giving rise to a new one.</p></blockquote>
+
+<p>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.</p>
+
+<div class="figcenter" style="width:625px;">
+<a name="fig45" id="fig45"></a>
+<img src="images/fig045.png" width="625" height="490"
+alt="Fig.&nbsp;45." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;45.</span>&mdash;Forms of lichens. <i>A</i>, a branch with lichens
+growing upon it, one-half natural size. <i>B</i>, <i>Usnea</i>, natural size.
+<i>ap.</i> spore fruit. <i>C</i>, <i>Sticta</i>, one-half natural size. <i>D</i>,
+<i>Peltigera</i>, one-half natural size. <i>ap.</i> spore fruit. <i>E</i>, a single
+spore fruit, &times;&nbsp;2. <i>F</i>, <i>Cladonia</i>, natural size. <i>G</i>, a piece of bark
+from a beech, with a crustaceous lichen (<i>Graphis</i>) growing upon it,
+&times;&nbsp;2. <i>ap.</i> spore fruit. <i>H</i>, <i>Soredium</i> of a lichen, &times;&nbsp;300.</p>
+</div>
+
+<p>According to their form, lichens are sometimes divided into the bushy
+(fruticose), leafy (frondose), incrusting (crustaceous), and
+gelatinous. Of the first, the long gray <i>Usnea</i> (<a href="#fig45">Fig.&nbsp;45</a>, <i>A</i>, <i>B</i>),
+which drapes the branches of trees in swamps, is a familiar example;
+of the second, <i>Parmelia</i>, <i>Sticta</i> (<a href="#fig45">Fig.&nbsp;45</a>, <i>C</i>) and <i>Peltigera</i>
+(<i>D</i>) are types; of the third, <i>Graphis</i> (<i>G</i>), common on the trunks
+of beech-trees, to which it closely adheres; and <span class="pagenum" title="Page&nbsp;76">&nbsp;</span><a name="Page_76" id="Page_76"></a>of the last,
+<i>Collema</i> (<a href="#fig44">Fig.&nbsp;44</a>, <i>C</i>, <i>D</i>, <i>E</i>), a dark greenish, gelatinous form,
+growing on mossy tree trunks, and looking like a colony of <i>Nostoc</i>,
+which indeed it is, but differing from an ordinary colony in being
+penetrated everywhere by the filaments of the fungus growing upon it.</p>
+
+<div class="figleft" style="width:117px;">
+<a name="fig46" id="fig46"></a>
+<img src="images/fig046.png" width="117" height="323"
+alt="Fig.&nbsp;46." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;46.</span>&mdash;Branch of a plum-tree attacked by black knot.
+Natural size.</p>
+</div>
+
+<blockquote><p>Not infrequently in this form, as well as in other lichens, special
+cavities, known as spermogonia (<a href="#fig44">Fig.&nbsp;44</a>, <i>D</i>), 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.</p></blockquote>
+
+<p>The last group of the <i>Ascomycetes</i> are the &ldquo;black fungi,&rdquo;
+<i>Pyrenomycetes</i>, represented by the black knot of cherry and plum
+trees, shown in <a href="#fig46">Figure&nbsp;46</a>. 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
+<i>Discomycetes</i>, the details will not be entered into here.</p>
+
+<p>Of the parasitic forms, one of the best known is the &ldquo;ergot&rdquo; of rye,
+more or less used in medicine. Other forms are known that attack
+insects, particularly caterpillars, which are killed by their attacks.</p>
+
+
+
+<hr />
+<h2><span class="pagenum" title="Page&nbsp;77">&nbsp;</span><a name="Page_77" id="Page_77"></a><a name="CHAPTER_X" id="CHAPTER_X"></a>CHAPTER X.
+<br />
+<small><span class="smcap">Fungi</span>&mdash;<i>Continued</i>.</small></h2>
+
+
+<h4><a name="basid" id="basid"></a><span class="smcap">Class</span> <i>Basidiomycetes</i>.</h4>
+
+<p><span class="smcap">The</span> <i>Basidiomycetes</i> 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 <i>Basidiomycetes</i> are the so-called rusts. The larger
+<i>Basidiomycetes</i> 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.</p>
+
+<p>All of the group are characterized by the production of spores at the
+top of special cells known as basidia,<a name="FNanchor_8_8" id="FNanchor_8_8"></a><a href="#Footnote_8_8" class="fnanchor">[8]</a> the number produced upon a
+single basidium varying from a single one to several.</p>
+
+<p>Of the lower <i>Basidiomycetes</i>, the rusts (<i>Uredine&aelig;</i>) 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 <span class="pagenum" title="Page&nbsp;78">&nbsp;</span><a name="Page_78" id="Page_78"></a>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.</p>
+
+<div class="figcenter" style="width:620px;">
+<a name="fig47" id="fig47"></a>
+<img src="images/fig047.png" width="620" height="479"
+alt="Fig.&nbsp;47." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;47.</span>&mdash;<i>A</i>, a branch of red cedar attacked by a rust
+(<i>Gymnosporangium</i>), causing a so-called &ldquo;cedar apple,&rdquo; &times;&nbsp;&frac12;. <i>B</i>,
+spores of the same, one beginning to germinate, &times;&nbsp;300. <i>C</i>, a spore
+that has germinated, each cell producing a short, divided filament
+(basidium), which in turn gives rise to secondary spores (<i>sp.</i>),
+&times;&nbsp;300. <i>D</i>, part of the leaf of a hawthorn attacked by the cluster cup
+stage of the same fungus, upper side showing spermogonia, natural
+size. <i>E</i>, cluster cups (<i>Roestelia</i>) of the same fungus, natural
+size. <i>F</i>, tip of a leaf of the Indian turnip (<i>Aris&aelig;ma</i>), bearing the
+cluster cup (<i>&AElig;cidium</i>) stage of a rust, &times;&nbsp;2. <i>G</i>, vertical section
+through a young cluster cup. <i>H</i>, similar section through a mature
+one, &times;&nbsp;50. <i>I</i>, germinating spores of <i>H</i>, &times;&nbsp;300. <i>J</i>, part of a corn
+leaf, with black rust, natural size. <i>K</i>, red rust spore of the wheat
+rust (<i>Puccinia graminis</i>), &times;&nbsp;300. <i>L</i>, forms of black-rust spores: <span class="smcap">i</span>,
+<i>Uromyces</i>; <span class="smcap">ii</span>, <i>Puccinia</i>; <span class="smcap">iii</span>, <i>Phragmidium</i>.</p>
+</div>
+
+<p>The first form met with in most rusts is sometimes called the
+&ldquo;cluster-cup&rdquo; stage, and in many species is the only stage known. In
+<a href="#fig47">Figure&nbsp;47</a>, <i>F</i>, is shown a bit of the leaf of the Indian turnip
+(<i>Aris&aelig;ma</i>) affected by one of these &ldquo;cluster-cup&rdquo; forms. To the naked
+eye, or when slightly magnified, <span class="pagenum" title="Page&nbsp;79">&nbsp;</span><a name="Page_79" id="Page_79"></a>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.</p>
+
+<blockquote><p>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 (<a href="#fig47">Fig.&nbsp;47</a>, <i>G</i>) 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.</p>
+
+<p>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 (<a href="#fig47">Fig.&nbsp;47</a>, <i>I</i>).</p></blockquote>
+
+<p>One of the most noticeable of the rusts is the cedar rust
+(<i>Gymnosporangium</i>), forming the growths known as &ldquo;cedar apples,&rdquo;
+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
+(<a href="#fig47">Fig.&nbsp;47</a>, <i>A</i>). 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
+<span class="pagenum" title="Page&nbsp;80">&nbsp;</span><a name="Page_80" id="Page_80"></a>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 &ldquo;apple.&rdquo; In this stage the
+fungus is extremely conspicuous, and may frequently be met with after
+rainy weather in the spring.</p>
+
+<blockquote><p>This orange jelly, as shown by the microscope, is made up of elongated
+two-celled spores (teleuto spores), attached to long gelatinous stalks
+(<a href="#fig47">Fig.&nbsp;47</a>, <i>B</i>). They are thick-walled, and the contents resemble those
+of the cluster-cup spores described above.</p>
+
+<p>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
+(<a href="#fig47">Fig.&nbsp;47</a>, <i>C</i>), 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 (<i>sp.</i>) is formed at the tip, containing all the
+protoplasm of the cell.</p></blockquote>
+
+<p>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 (<a href="#fig47">Fig.&nbsp;47</a>, <i>D</i>), 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 (<a href="#fig47">Fig.&nbsp;47</a>, <i>E</i>).</p>
+
+<blockquote><p>In most rusts the teleuto spores are produced late in the summer or
+autumn, and remain until the following spring before they germinate.
+<span class="pagenum" title="Page&nbsp;81">&nbsp;</span><a name="Page_81" id="Page_81"></a>They are very thick-walled, the walls being dark-colored, so that in
+mass they appear black, and constitute the &ldquo;black-rust&rdquo; stage
+(<a href="#fig47">Fig.&nbsp;47</a>, <i>J</i>). 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 &ldquo;red rust&rdquo; of wheat and other
+plants, upon which they are growing.</p></blockquote>
+
+
+<p>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 <i>Melampsora</i>, and <i>Uromyces</i> (<a href="#fig47">Fig.&nbsp;47</a>, <i>L</i> <span class="smcap">i</span>), have unicellular
+teleuto spores; <i>Puccinia</i> (<span class="smcap">ii</span>) and <i>Gymnosporangium</i>, two-celled
+spores; <i>Triphragmium</i>, three-celled; and <i>Phragmidium</i> (<span class="smcap">iii</span>), four or
+more.</p>
+
+<p>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.</p>
+
+<p>Probably the best-known member of the group is the wheat rust
+(<i>Puccinia graminis</i>), 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.</p>
+
+<p>Probably to be associated with the lower <i>Basidiomycetes</i> are the
+large fungi of which <i>Tremella</i> (<a href="#fig51">Fig.&nbsp;51</a>, <i>A</i>) 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.</p>
+
+<p>Of the higher <i>Basidiomycetes</i>, 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 <i>Coprinus</i>, of which there are
+several species growing on the excrement of various herbivorous
+animals. They not infrequently appear on <span class="pagenum" title="Page&nbsp;82">&nbsp;</span><a name="Page_82" id="Page_82"></a>horse manure that has been
+kept covered with a glass for some time, as described for <i>Ascobolus</i>.
+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.</p>
+
+<div class="figcenter" style="width:572px;">
+<a name="fig48" id="fig48"></a>
+<img src="images/fig048.png" width="572" height="492"
+alt="Fig.&nbsp;48." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;48.</span>&mdash;<i>A</i>, young. <i>B</i>, full-grown fruit of a
+toadstool (<i>Coprinus</i>), &times;&nbsp;2. <i>C</i>, under side of the cap, showing the
+radiating &ldquo;gills,&rdquo; or spore-bearing plates. <i>D</i>, section across one of
+the young gills, &times;&nbsp;150. <i>E</i>, <i>F</i>, portions of gills from a nearly ripe
+fruit, &times;&nbsp;300. <i>sp.</i> spores. <i>x</i>, sterile cell. In <i>F</i>, a basidium is
+shown, with the young spores just forming. <i>G</i>, <i>H</i>, young fruits,
+&times;&nbsp;50.</p>
+</div>
+
+<p>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 <span class="pagenum" title="Page&nbsp;83">&nbsp;</span><a name="Page_83" id="Page_83"></a>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 (<a href="#fig48">Fig.&nbsp;48</a>, <i>B</i>). 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 (<i>C</i>). Almost as soon as the umbrella opens,
+the spores are shed, and the whole structure shrivels up and
+dissolves, leaving almost no trace behind.</p>
+
+
+<div class="figright" style="width:216px;">
+<a name="fig49" id="fig49"></a>
+<img src="images/fig049.png" width="216" height="411"
+alt="Fig.&nbsp;49." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;49.</span>&mdash;<i>Basidiomycetes</i>. <i>A</i>, common puff-ball
+(<i>Lycoperdon</i>). <i>B</i>, earth star (<i>Geaster</i>). <i>A</i>, &times;&nbsp;&frac14;. <i>B</i>, one-half
+natural size.</p>
+</div>
+
+<blockquote><p>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 (<a href="#fig48">Fig.&nbsp;48</a>, <i>G</i>). If
+the specimen is not too young, a denser central portion can be made
+out, and in still older ones (<a href="#fig48">Fig.&nbsp;48</a>, <i>H</i>) 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 <i>Ascomycetes</i>)
+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 (&ldquo;gills&rdquo; or <i>Lamell&aelig;</i>) 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) (<a href="#fig48">Fig.&nbsp;48</a>, <i>D</i>). 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 (<a href="#fig48">Fig.&nbsp;48</a>, <i>E</i>, <i>F</i>). The ripe spores (<i>E</i>,
+<i>sp.</i>) are oval, and possess a firm, dark outer wall. Occasionally
+some of the basidia develop into <span class="pagenum" title="Page&nbsp;84">&nbsp;</span><a name="Page_84" id="Page_84"></a>very large sterile cells (E, <i>x</i>),
+projecting far beyond the others, and often reaching the neighboring
+gill.</p></blockquote>
+
+<p>Similar in structure and development to <i>Coprinus</i> 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 (<i>Angiocarpous</i>)
+forms, the half-closed (<i>Hemi-angiocarpous</i>), and the open or
+naked-fruited forms (<i>Gymnocarpous</i>).</p>
+
+<p>Of the first, the puff-balls (<a href="#fig49">Fig.&nbsp;49</a>) are common examples. One
+species, the giant puff-ball (<i>Lycoperdon giganteum</i>), often reaches a
+diameter of thirty to forty centimetres. The earth stars (<i>Geaster</i>)
+have a double covering to the spore fruit, the outer one splitting at
+maturity into strips (<a href="#fig49">Fig.&nbsp;49</a>, <i>B</i>). Another pretty and common form is
+the little birds&#8217;-nest fungus (<i>Cyathus</i>), growing on rotten wood or
+soil containing much decaying vegetable matter (<a href="#fig50">Fig.&nbsp;50</a>).</p>
+
+<div class="figcenter" style="width:337px;">
+<a name="fig50" id="fig50"></a>
+<img src="images/fig050.png" width="337" height="238"
+alt="Fig.&nbsp;50." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;50.</span>&mdash;Birds&#8217;-nest fungus (<i>Cyathus</i>). <i>A</i>, young.
+<i>B</i>, full grown. <i>C</i>, section through <i>B</i>, showing the &ldquo;sporangia&rdquo;
+(<i>sp.</i>). All twice the natural size.</p>
+</div>
+
+<p>In the second order the spores are at first protected, as we have seen
+in <i>Coprinus</i>, which belongs to this order, but finally <span class="pagenum" title="Page&nbsp;85">&nbsp;</span><a name="Page_85" id="Page_85"></a>become
+exposed. Here belong the toadstools and mushrooms (<a href="#fig51">Fig.&nbsp;51</a>, <i>B</i>), the
+large shelf-shaped fungi (<i>Polyporus</i>), so common on tree trunks and
+rotten logs (<a href="#fig51">Fig.&nbsp;51</a>, <i>C</i>, <i>D</i>, <i>E</i>), and the prickly fungus
+(<i>Hydnum</i>) (<a href="#fig51">Fig.&nbsp;51</a>, <i>G</i>).</p>
+
+<div class="figcenter" style="width:594px;">
+<a name="fig51" id="fig51"></a>
+<img src="images/fig051.png" width="594" height="444"
+alt="Fig.&nbsp;51." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;51.</span>&mdash;Forms of <i>Basidiomycetes</i>. <i>A</i>, <i>Tremella</i>,
+one-half natural size. <i>B</i>, <i>Agaricus</i>, natural size. <i>C</i>, <i>E</i>,
+<i>Polyporus</i>: <i>C</i>, &times;&nbsp;&frac12;; <i>E</i>, &times;&nbsp;&frac14;. <i>D</i>, part of the under surface of
+<i>D</i>, natural size. <i>F</i>, <i>Clavaria</i>, a small piece, natural size. <i>G</i>,
+<i>Hydnum</i>, a piece of the natural size.</p>
+</div>
+
+<p>Of the last, or naked-fruited forms, the commonest belong to the
+genus <i>Clavaria</i> (<a href="#fig51">Fig.&nbsp;51</a>, <i>F</i>), smooth-branching forms, usually of a
+brownish color, bearing the spores directly upon the surface of the
+branches.</p>
+
+
+
+<hr />
+<h2><span class="pagenum" title="Page&nbsp;86">&nbsp;</span><a name="Page_86" id="Page_86"></a><a name="CHAPTER_XI" id="CHAPTER_XI"></a>CHAPTER XI.
+<br />
+<small>SUB-KINGDOM IV.
+<br />
+<span class="smcap">Bryophyta.</span></small></h2>
+
+
+<p><span class="smcap">The</span> 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.</p>
+
+<p>There are two classes&mdash;I.&nbsp;Liverworts (<i>Hepatic&aelig;</i>), and II.&nbsp;Mosses
+(<i>Musci</i>).</p>
+
+
+<h3><a name="liver" id="liver"></a>Class I.&mdash;The Liverworts.</h3>
+
+<p>One of the commonest of this class, and to be had at any time, is
+named <i>Madotheca</i>. 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
+&ldquo;scale moss.&rdquo;</p>
+
+<p><span class="pagenum" title="Page&nbsp;87">&nbsp;</span><a name="Page_87" id="Page_87"></a>The leaves (<a href="#fig52">Fig.&nbsp;52</a>, <i>A</i>, <i>B</i>) 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 (<a href="#fig52">Fig.&nbsp;52</a>, <i>C</i>, <i>D</i>), in which the spores are produced.
+These are called &ldquo;sporogonia.&rdquo; 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 (<a href="#fig54">Fig.&nbsp;54</a>, <i>H</i>), which contain the female
+reproductive organs, from which the sporogonia arise.</p>
+
+<div class="figcenter" style="width:456px;">
+<a name="fig52" id="fig52"></a>
+<img src="images/fig052.png" width="456" height="280"
+alt="Fig.&nbsp;52." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;52.</span>&mdash;<i>A</i>, part of a plant of a leafy liverwort
+(<i>Madotheca</i>), &times;&nbsp;2. <i>B</i>, part of the same, seen from below, &times;&nbsp;4. <i>C</i>,
+a branch with two open sporogonia (<i>sp.</i>), &times;&nbsp;4. <i>D</i>, a single
+sporogonium, &times;&nbsp;8.</p>
+</div>
+
+<p>On other plants may be found numerous short side branches (<a href="#fig53">Fig.&nbsp;53</a>,
+<i>B</i>), 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, <span class="pagenum" title="Page&nbsp;88">&nbsp;</span><a name="Page_88" id="Page_88"></a>like this one, have the male
+and female reproductive organs on distinct plants, are said to be
+&ldquo;di&#339;cious.&rdquo;</p>
+
+<blockquote><p>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.</p>
+
+<p>The tissues are developed from a single apical cell, but it is
+difficult to obtain good sections through it.</p>
+
+<p>The antheridia are borne singly at the bases of the leaves on the
+special branches already described (<a href="#fig53">Fig.&nbsp;53</a>, <i>A</i>, <i>an.</i>). 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 (<a href="#fig53">Fig.&nbsp;53</a>, <i>C</i>). Within is a mass of excessively small cells,
+each of which contains a spermatozoid. In the young antheridium (<i>A</i>,
+<i>an.</i>) 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.</p></blockquote>
+
+<div class="figcenter" style="width:499px;">
+<a name="fig53" id="fig53"></a>
+<img src="images/fig053.png" width="499" height="307"
+alt="Fig.&nbsp;53." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;53.</span>&mdash;<i>A</i>, end of a branch from a male plant of
+<i>Madotheca</i>. The small side branchlets bear the antheridia, &times;&nbsp;2. <i>B</i>,
+two young antheridia (<i>an.</i>), the upper one seen in optical section,
+the lower one from without, &times;&nbsp;150. <i>C</i>, a ripe antheridium, optical
+section, &times;&nbsp;50. <i>D</i>, sperm cells with young spermatozoids. <i>E</i>, ripe
+spermatozoids, &times;&nbsp;600.</p>
+</div>
+
+<blockquote><p>When ripe, if brought into water, the antheridium bursts at the top
+into<span class="pagenum" title="Page&nbsp;89">&nbsp;</span><a name="Page_89" id="Page_89"></a> 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, <i>D</i>) 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, <i>E</i>),
+and has two excessively delicate cilia, visible only under the most
+favorable circumstances.</p>
+
+<p>The female organ in the bryophytes is called an &ldquo;archegonium,&rdquo; and
+differs considerably from anything we have yet studied, but recalls
+somewhat the structure of the o&ouml;gonium of <i>Chara</i>. They are found in
+groups, contained in little bud-like branches (54, <i>H</i>). 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.</p></blockquote>
+
+<div class="figcenter" style="width:479px;">
+<a name="fig54" id="fig54"></a>
+<img src="images/fig054.png" width="479" height="304"
+alt="Fig.&nbsp;54." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;54.</span>&mdash;<i>A&ndash;D</i>, development of the archegonium of
+<i>Madotheca</i>. <i>B</i>, surface view, the others in optical section. <i>o</i>,
+egg cell, &times;&nbsp;150. <i>E</i>, base of a fertilized archegonium, containing a
+young embryo (<i>em.</i>), &times;&nbsp;150. <i>F</i>, margin of one of the leaves
+surrounding the archegonia. <i>G</i>, young sporogonium still surrounded by
+the much enlarged base of the archegonium. <i>h</i>, neck of the
+archegonium. <i>ar.</i> abortive archegonia, &times;&nbsp;12. <i>H</i>, short branch
+containing the young sporogonium, &times;&nbsp;4.</p>
+</div>
+
+<blockquote><p>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 (<a href="#fig54">Fig.&nbsp;54</a>,
+<i>A</i>, <i>B</i>). As it becomes older, the lower part enlarges slightly, the
+whole looking something like a long-necked flask (<i>C</i>, <i>D</i>). The
+centre of the neck is occupied <span class="pagenum" title="Page&nbsp;90">&nbsp;</span><a name="Page_90" id="Page_90"></a>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 (<a href="#fig54">Fig.&nbsp;54</a>, <i>C</i>, <i>o</i>).
+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 (<i>D</i>, <i>o</i>). 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.</p></blockquote>
+
+<div class="figright" style="width:191px;">
+<a name="fig55" id="fig55"></a>
+<img src="images/fig055.png" width="191" height="348"
+alt="Fig.&nbsp;55." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;55.</span>&mdash;Longitudinal section of a nearly full-grown
+sporogonium of <i>Madotheca</i>, which has not, however, broken through the
+overlying cells, &times;&nbsp;25. <i>sp.</i> cavity in which the spores are formed.
+<i>ar.</i> abortive archegonium.</p>
+</div>
+
+<blockquote><p>The first division wall to be formed in the embryo is transverse, and
+is followed by vertical ones (<a href="#fig54">Fig.&nbsp;54</a>, <i>E</i>, <i>em.</i>). 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 (<a href="#fig55">Fig.&nbsp;55</a>). As it increases in size, it becomes
+differentiated into three parts: a wedge-shaped base or &ldquo;foot&rdquo;
+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 (<a href="#fig56">Fig.&nbsp;56</a>, <i>B</i>).</p></blockquote>
+
+<div class="figleft" style="width:129px;">
+<a name="fig56" id="fig56"></a>
+<img src="images/fig056.png" width="129" height="304"
+alt="Fig.&nbsp;56." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;56.</span>&mdash;Spore (<i>A</i>) and two elaters (<i>B</i>) of
+<i>Madotheca</i>, &times;&nbsp;300.</p>
+</div>
+
+<blockquote><p><span class="pagenum" title="Page&nbsp;91">&nbsp;</span><a name="Page_91" id="Page_91"></a>The ripe spores are nearly globular, contain chlorophyll and drops of
+oil, and the outer wall is brown and covered with fine points
+(<a href="#fig56">Fig.&nbsp;56</a>, <i>A</i>). 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.</p></blockquote>
+
+<p>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.</p>
+
+<p>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,&mdash;at least, the
+leaves when present are reduced to little scales upon the lower
+surface.</p>
+
+<p>The first order (<i>Ricciace&aelig;</i>) 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
+<a href="#fig57">figure&nbsp;57</a>, <i>A</i>.</p>
+
+<p>The second order, the horned liverworts (<i>Anthocerote&aelig;</i>), 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
+(<a href="#fig57">Fig.&nbsp;57</a>, <i>B</i>).</p>
+
+<p>The third order (<i>Marchantiace&aelig;</i>) includes the most conspicuous
+members of the whole class. Some of them, like the common liverwort
+(<i>Marchantia</i>), shown in <a href="#fig57">Figure&nbsp;57</a>, <i>F</i>, <i>K</i>, and the giant liverwort
+(<a href="#fig57">Fig.&nbsp;57</a>, <i>D</i>), 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 (<a href="#fig57">Fig.&nbsp;57</a>, <i>E</i>, <i>J</i>, <i>K</i>) Each of these
+is situated in the centre of a little area (<a href="#fig57">Fig.&nbsp;57</a>, <i>E</i>), and beneath
+<span class="pagenum" title="Page&nbsp;92">&nbsp;</span><a name="Page_92" id="Page_92"></a>it is a large air space, into which the chlorophyll-bearing cells
+(<i>cl.</i>) of the plant project (<i>J</i>).</p>
+
+<p>The sexual organs are often produced in these forms upon special
+branches (<i>G</i>), or the antheridia may be sunk in discs on the upper
+side of the stem (<i>D</i>, <i>an.</i>).</p>
+
+<div class="figcenter" style="width:598px;">
+<a name="fig57" id="fig57"></a>
+<img src="images/fig057.png" width="598" height="501"
+alt="Fig.&nbsp;57." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;57.</span>&mdash;Forms of liverworts. <i>A</i>, <i>Riccia</i>, natural
+size. <i>B</i>, <i>Anthoceros</i> (horned liverwort), natural size. <i>sp.</i>
+sporogonia. <i>C</i>, <i>Lunularia</i>, natural size, <i>x</i>, buds. <i>D</i>, giant
+liverwort (<i>Conocephalus</i>), natural size. <i>an.</i> antheridial disc. <i>E</i>,
+small piece of the epidermis, showing the breathing pores, &times;&nbsp;2. <i>F</i>,
+common liverwort (<i>Marchantia</i>), &times;&nbsp;2. <i>x</i>, cups containing buds. <i>G</i>,
+archegonial branch of common liverwort, natural size. <i>H</i>, two young
+buds from the common liverwort, &times;&nbsp;150. <i>I</i>, a full-grown bud, &times;&nbsp;25.
+<i>J</i>, vertical section through the body of <i>Marchantia</i>, cutting
+through a breathing pore (<i>s</i>), &times;&nbsp;50. <i>K</i>, surface view of a breathing
+pore, &times;&nbsp;150. <i>L</i>, a leafy liverwort (<i>Jungermannia</i>). <i>sp.</i>
+sporogonium, &times;&nbsp;2.</p>
+</div>
+
+<p>Some forms, like <i>Marchantia</i> and <i>Lunularia</i> (<a href="#fig57">Fig.&nbsp;57</a>, <i>C</i>), produce
+little cups (<i>x</i>), circular in the first, semicircular in the second,
+in which special buds (<i>H</i>, <i>I</i>) are formed that fall off and produce
+new plants.</p>
+
+<p>The highest of the liverworts (<i>Jungermanniace&aelig;</i>) are, for <span class="pagenum" title="Page&nbsp;93">&nbsp;</span><a name="Page_93" id="Page_93"></a>the most
+part, leafy forms like <i>Madotheca</i>, and represented by a great many
+common forms, growing usually on tree trunks, etc. They are much like
+<i>Madotheca</i> 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 (<a href="#fig57">Fig.&nbsp;57</a>, <i>L</i>).</p>
+
+
+<h3><a name="moss" id="moss"></a>Class II.&mdash;The True Mosses.</h3>
+
+<p>The true mosses (<i>Musci</i>) resemble in many respects the higher
+liverworts, such as <i>Madotheca</i> or <i>Jungermannia</i>, all of them having
+well-marked stems and leaves. The spore fruit is more highly
+developed than in the liverworts, but never contains elaters.</p>
+
+<p>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 (<i>Funaria</i>) 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 (<a href="#fig58">Fig.&nbsp;58</a>, <i>A</i>, <i>B</i>) 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.</p>
+
+<p>The mature capsule is broadly oval in form (<a href="#fig58">Fig.&nbsp;58</a>, <i>C</i>), 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 (<i>B</i>,
+<i>cal.</i>) 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 (<a href="#fig58">Fig.&nbsp;58</a>, <i>E</i>).</p>
+
+<div class="figcenter" style="width:621px;">
+<span class="pagenum" title="Page&nbsp;94">&nbsp;</span><a name="Page_94" id="Page_94"></a><a name="fig58" id="fig58"></a>
+<img src="images/fig058.png" width="621" height="487"
+alt="Fig.&nbsp;58." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;58.</span>&mdash;<i>A</i>, fruiting plant of a moss (<i>Funaria</i>),
+with young sporogonium (<i>sp.</i>), &times;&nbsp;4. B, plant with ripe sporogonium.
+<i>cal</i>. calyptra, &times;&nbsp;2. <i>C</i>, sporogonium with calyptra removed. <i>op.</i>
+lid, &times;&nbsp;4. <i>D</i>, spores: <span class="smcap">i</span>, ungerminated; <span class="smcap">ii&ndash;iv</span>, germinating, &times;&nbsp;300.
+<i>E</i>, two teeth from the margin of the capsule, &times;&nbsp;50. <i>F</i>, epidermal
+cells and breathing pore from the surface of the sporogonium, &times;&nbsp;150.
+<i>G</i>, longitudinal section of a young sporogonium, &times;&nbsp;12. <i>sp.</i> spore
+mother cells. <i>H</i>, a small portion of <i>G</i>, magnified about 300 times.
+<i>sp.</i> spore mother cells.</p>
+</div>
+
+<p>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.</p>
+
+<div class="figcenter" style="width:303px;">
+<a name="fig59" id="fig59"></a>
+<img src="images/fig059.png" width="303" height="393"
+alt="Fig.&nbsp;59." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;59.</span>&mdash;Longitudinal section through the summit of a
+small male plant of <i>Funaria</i>. <i>a</i>, <i>a&#697;</i>, antheridia. <i>p</i>, paraphysis.
+<i>L</i>, section of a leaf, &times;&nbsp;150.</p>
+</div>
+
+<p>This moss is di&#339;cious. 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 <span class="pagenum" title="Page&nbsp;95">&nbsp;</span><a name="Page_95" id="Page_95"></a>looks something like a flower.
+(This is still more evident in some other mosses. See <a href="#fig65">Figure&nbsp;65</a>, <i>E</i>,
+<i>F</i>.)</p>
+
+<blockquote><p>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 (<a href="#fig63">Fig.&nbsp;63</a>, <i>C</i>, <i>n</i>) 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 (<a href="#fig63">Fig.&nbsp;63</a>, <i>D</i>). 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.</p></blockquote>
+
+<div class="figright" style="width:188px;">
+<a name="fig60" id="fig60"></a>
+<img src="images/fig060.png" width="188" height="335"
+alt="Fig.&nbsp;60." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;60.</span>&mdash;<i>A</i>, <i>B</i>, young antheridia of <i>Funaria</i>,
+optical section, &times;&nbsp;150. <i>C</i>, two sperm cells of <i>Atrichum</i>. <i>D</i>,
+spermatozoids of <i>Sphagnum</i>, &times;&nbsp;600.</p>
+</div>
+
+<blockquote><p>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 <span class="pagenum" title="Page&nbsp;96">&nbsp;</span><a name="Page_96" id="Page_96"></a>matter, is combined in
+such form as to make it available for the food of other organisms.</p>
+
+<p>The marginal cells of the leaf are narrow, and some of them prolonged
+into teeth.</p>
+
+<p>A cross-section of the stem (63, <i>E</i>) 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.</p>
+
+<p>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 <i>Cladophora</i> 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 (<a href="#fig63">Fig.&nbsp;63</a>,
+<i>A</i>, <i>k</i>), 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.</p>
+
+<p>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.</p>
+
+<p>The sexual organs are much like those of the liverworts and are borne
+at the apex of the stems.</p>
+
+<p>The antheridia (Figs. <a href="#fig59">59</a>, <a href="#fig60">60</a>) 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.</p>
+
+<p>The young antheridium has an apical cell giving rise to two series of
+segments (<a href="#fig60">Fig.&nbsp;60</a>, <i>A</i>), which in the earlier stages are very plainly
+marked.</p>
+
+<p>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 <span class="pagenum" title="Page&nbsp;97">&nbsp;</span><a name="Page_97" id="Page_97"></a>open at the apex, the whole mass of sperm cells being
+discharged at once.</p>
+
+<p>Among the antheridia are borne peculiar hairs (<a href="#fig59">Fig.&nbsp;59</a>, <i>p</i>) tipped by
+a large globular cell.</p></blockquote>
+
+<div class="figcenter" style="width:417px;">
+<a name="fig61" id="fig61"></a>
+<img src="images/fig061.png" width="417" height="276"
+alt="Fig.&nbsp;61." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;61.</span>&mdash;<i>A</i>, <i>B</i>, young; <i>C</i>, nearly ripe archegonium
+of <i>Funaria</i>, optical section, &times;&nbsp;150. <i>D</i>, upper part of the neck of
+<i>C</i>, seen from without, showing how it is twisted. <i>E</i>, base of a ripe
+archegonium. <i>F</i>, open apex of the same, &times;&nbsp;150. <i>o</i>, egg cell. <i>b</i>,
+ventral canal cell.</p>
+</div>
+
+<blockquote><p>Owing to their small size the spermatozoids are difficult to see
+satisfactorily and other mosses (<i>e.g.</i> peat mosses, <a href="#fig64">Figure&nbsp;64</a>, the
+hairy cap moss, <a href="#fig65">Figure&nbsp;65</a>, <i>I</i>), are preferable where obtainable. The
+spermatozoids of a peat moss are shown in <a href="#fig60">Figure&nbsp;60</a>, <i>D</i>. Like all of
+the bryophytes they have but two cilia.</p>
+
+<p>The archegonia (<a href="#fig61">Fig.&nbsp;61</a>) 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.</p></blockquote>
+
+<div class="figcenter" style="width:338px;">
+<a name="fig62" id="fig62"></a>
+<img src="images/fig062.png" width="338" height="260"
+alt="Fig.&nbsp;62." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;62.</span>&mdash;<i>A</i>, young embryo of <i>Funaria</i>, still
+enclosed within the base of the archegonium, &times;&nbsp;300. <i>B</i>, an older
+embryo freed from the archegonium, &times;&nbsp;150. <i>a</i>, the apical cell.</p>
+</div>
+
+<blockquote><p>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, <span class="pagenum" title="Page&nbsp;98">&nbsp;</span><a name="Page_98" id="Page_98"></a>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
+(<a href="#fig62">Fig.&nbsp;62</a>, <i>A</i>). Very soon a two-sided apical cell (<a href="#fig62">Fig.&nbsp;62</a>, <i>B</i>, <i>a</i>)
+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.</p>
+
+<p>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.</p></blockquote>
+
+<div class="figcenter" style="width:438px;">
+<a name="fig63" id="fig63"></a>
+<img src="images/fig063.png" width="438" height="302"
+alt="Fig.&nbsp;63." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;63.</span>&mdash;<i>A</i>, protonema of <i>Funaria</i>, with a bud
+(<i>k</i>), &times;&nbsp;50. <i>B</i>, outline of a leaf, showing also the thickened
+midrib, &times;&nbsp;12. <i>C</i>, cells of the leaf, &times;&nbsp;300. <i>n</i>, nucleus. <i>D</i>,
+chlorophyll granules undergoing division, &times;&nbsp;300. <i>E</i>, cross-section of
+the stem, &times;&nbsp;50.</p>
+</div>
+
+<blockquote><p>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 (<a href="#fig58">Fig.&nbsp;58</a>, <i>G</i>) 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.</p>
+
+<p>The spores arise from a single layer of cells near the outside of the
+inner mass of cells (<i>G</i>, <i>sp.</i>). These cells (<i>H</i>, <i>sp.</i>) are filled
+with glistening, granular protoplasm; have a large and distinct
+nucleus, and no <span class="pagenum" title="Page&nbsp;99">&nbsp;</span><a name="Page_99" id="Page_99"></a>chlorophyll. They finally become entirely separated
+and each one gives rise to four spores which closely resemble those of
+the liverworts but are smaller.</p>
+
+<p>Near the base of the capsule, on the outside, are formed breathing
+pores (<a href="#fig58">Fig.&nbsp;58</a>, <i>F</i>) quite similar to those of the higher plants.</p>
+
+<p>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.</p></blockquote>
+
+
+<h3><a name="classmoss" id="classmoss"></a>Classification of the Mosses.</h3>
+
+<p>The mosses may be divided into four orders: I.&nbsp;The peat mosses
+(<i>Sphagnace&aelig;</i>); II.&nbsp;<i>Andre&aelig;ace&aelig;</i>; III.&nbsp;<i>Phascace&aelig;</i>; IV.&nbsp;The common
+mosses (<i>Bryace&aelig;</i>).</p>
+
+<div class="figcenter" style="width:457px;">
+<a name="fig64" id="fig64"></a>
+<img src="images/fig064.png" width="457" height="293"
+alt="Fig.&nbsp;64." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;64.</span>&mdash;<i>A</i>, a peat moss (<i>Sphagnum</i>), &times;&nbsp;&frac12;. <i>B</i>, a
+sporogonium of the same, &times;&nbsp;3. <i>C</i>, a portion of a leaf, &times;&nbsp;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 (<i>o</i>).</p>
+</div>
+
+<p>The peat mosses (<a href="#fig64">Fig.&nbsp;64</a>) 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 (<a href="#fig64">Fig.&nbsp;64</a>, <i>A</i>), the branches
+being closely crowded <span class="pagenum" title="Page&nbsp;100">&nbsp;</span><a name="Page_100" id="Page_100"></a>at the top, where the stems continue to grow,
+dying away below.</p>
+
+<div class="figcenter" style="width:577px;">
+<a name="fig65" id="fig65"></a>
+<img src="images/fig065.png" width="577" height="502"
+alt="Fig.&nbsp;65." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;65.</span>&mdash;Forms of mosses. <i>A</i>, plant of <i>Phascum</i>,
+&times;&nbsp;3. <i>B</i>, fruiting plant of <i>Atrichum</i>, &times;&nbsp;2. <i>C</i>, young capsule of
+hairy-cap moss (<i>Polytrichum</i>), covered by the large, hairy calyptra.
+<i>D</i>, capsules of <i>Bartramia</i>: i, with; ii, without the calyptra. <i>E</i>,
+upper part of a male plant of <i>Atrichum</i>, showing the flower, &times;&nbsp;2.
+<i>F</i>, a male plant of <i>Mnium</i>, &times;&nbsp;4. <i>G</i>, pine-tree moss (<i>Clemacium</i>),
+&times;&nbsp;1. <i>H</i>, <i>Hypnum</i>, &times;&nbsp;1. <i>I</i>, ripe capsules of hairy-cap moss: <span class="smcap">i</span>,
+with; <span class="smcap">ii</span>, without calyptra.</p>
+</div>
+
+<p>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 (<a href="#fig64">Fig.&nbsp;64</a>, <i>B</i>).</p>
+
+<blockquote><p><span class="pagenum" title="Page&nbsp;101">&nbsp;</span><a name="Page_101" id="Page_101"></a>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 (<a href="#fig64">Fig.&nbsp;64</a>, <i>C</i>). 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.</p></blockquote>
+
+<p>The <i>Andre&aelig;ace&aelig;</i> are very small, and not at all common. The capsule
+splits into four valves, something like a liverwort.</p>
+
+<p>The <i>Phascace&aelig;</i> 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 <i>Phascum</i> (<a href="#fig65">Fig.&nbsp;65</a>, <i>A</i>).</p>
+
+<p>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 <a href="#fig65">Figure&nbsp;65</a>.</p>
+
+
+
+<hr />
+<h2><span class="pagenum" title="Page&nbsp;102">&nbsp;</span><a name="Page_102" id="Page_102"></a><a name="CHAPTER_XII" id="CHAPTER_XII"></a>CHAPTER XII.
+<br />
+<small>SUB-KINGDOM V.
+<br />
+<span class="smcap">Pteridophytes</span>.</small></h2>
+
+
+<p><span class="smcap">If</span> 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
+&ldquo;foot&rdquo; by means of which it is attached to the plant.</p>
+
+<p>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.</p>
+
+<p>The sexual plant, which is here called the &ldquo;prothallium,&rdquo; 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.</p>
+
+<p>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.</p>
+
+<p>The spores may be collected by placing the spore-bearing leaves on
+sheets of paper and letting them dry, when the ripe <span class="pagenum" title="Page&nbsp;103">&nbsp;</span><a name="Page_103" id="Page_103"></a>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
+(<a href="#fig66">Fig.&nbsp;66</a>, <i>F</i>). Removing one of these carefully, we find on the lower
+side numerous fine hairs like those on the lower <span class="pagenum" title="Page&nbsp;104">&nbsp;</span><a name="Page_104" id="Page_104"></a>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.</p>
+
+<div class="figcenter" style="width:643px;">
+<a name="fig66" id="fig66"></a>
+<img src="images/fig066.png" width="643" height="502"
+alt="Fig.&nbsp;66." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;66.</span>&mdash;<i>A</i>, spore of the ostrich fern (<i>Onoclea</i>),
+with the outer coat removed. <i>B</i>, germinating spore, &times;&nbsp;150. <i>C</i>, young
+prothallium, &times;&nbsp;50. <i>r</i>, root hair. <i>sp.</i> spore membrane. <i>D</i>, <i>E</i>,
+older prothallia. <i>a</i>, apical cell, &times;&nbsp;150. <i>F</i>, a female prothallium,
+seen from below, &times;&nbsp;12. <i>ar.</i> archegonia. <i>G</i>, <i>H</i>, young archegonia,
+in optical section, &times;&nbsp;150. <i>o</i>, central cell. <i>b</i>, ventral canal cell.
+<i>c</i>, upper canal cell. <i>I</i>, a ripe archegonium in the act of opening,
+&times;&nbsp;150. <i>o</i>, egg cell. <i>J</i>, a male prothallium, &times;&nbsp;50. <i>an.</i> antheridia.
+<i>K</i>, <i>L</i>, young antheridia, in optical section, &times;&nbsp;300. <i>M</i>, ripe
+antheridium, &times;&nbsp;300. <i>sp.</i> sperm cells. <i>N</i>, <i>O</i>, antheridia that have
+partially discharged their contents, &times;&nbsp;300. <i>P</i>, spermatozoids, killed
+with iodine, &times;&nbsp;500. <i>v</i>, vesicle attached to the hinder end.</p>
+</div>
+
+<p>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 (<i>Onoclea struthiopteris</i>) (<a href="#fig70">Fig.&nbsp;70</a>, <i>I</i>, <i>J</i>), or the
+sensitive fern (<i>O.&nbsp;sensibilis</i>). Another common and readily grown
+species is the lady fern (<i>Asplenium filixf&#339;mina</i>) (<a href="#fig70">Fig.&nbsp;70</a>, <i>H</i>). The
+spores of most ferns retain their vitality for many months, and hence
+can be kept dry until wanted.</p>
+
+<blockquote><p>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 (<a href="#fig66">Fig.&nbsp;66</a>, <i>B</i>, <i>C</i>, <i>r</i>).
+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 alg&aelig;
+(<i>C</i>).</p>
+
+<p>In order to follow the development further, spores must be sown upon
+earth, as they do not develop normally in water beyond this stage.</p>
+
+<p>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.</p>
+
+<p>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
+(<i>a</i>) from which are cut off two series of segments by walls directed
+alternately <span class="pagenum" title="Page&nbsp;105">&nbsp;</span><a name="Page_105" id="Page_105"></a>right and left (<a href="#fig66">Fig.&nbsp;66</a>, <i>D</i>, <i>E</i>, <i>a</i>), 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 (<i>E</i>, <i>F</i>). Sooner or later the
+apical cell ceases to form regular segments and becomes
+indistinguishable from the other cells.</p>
+
+<p>In the ostrich fern and lady fern the plants are di&#339;cious. The male
+plants (<a href="#fig66">Fig.&nbsp;66</a>, <i>J</i>) 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.</p></blockquote>
+
+<p>The female plants (<a href="#fig66">Fig.&nbsp;66</a>, <i>F</i>) 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.</p>
+
+<blockquote><p>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.</p>
+
+<p>The archegonia arise from cells of the lower surface, just behind the
+notch in front (<a href="#fig66">Fig.&nbsp;66</a>, <i>F</i>, <i>ar.</i>). 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 (<a href="#fig66">Fig.&nbsp;66</a>, <i>G</i>, <i>I</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 (<i>C</i>, <i>o</i>), becomes
+the egg cell, and from it is cut off another cell (<i>c</i>), 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 (<i>H</i>, <i>b</i>)
+called the ventral canal cell, being smaller than the other.</p>
+
+<p><span class="pagenum" title="Page&nbsp;106">&nbsp;</span><a name="Page_106" id="Page_106"></a>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 &ldquo;receptive spot,&rdquo; 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 (<a href="#fig66">Fig.&nbsp;66</a>, <i>I</i>).</p>
+
+<p>The antheridia (<a href="#fig66">Fig.&nbsp;66</a>. <i>J</i>, <i>M</i>) arise as simple hemispherical
+cells, in which two walls are formed (<i>K</i> <span class="allsc">I, II</span>), 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 (<i>L</i> <span class="smcap">iii</span>) 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 (<i>N</i>, <i>O</i>). 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
+(<i>P</i>, <i>v</i>), containing a few small granules, some of which usually
+show the reaction of starch, turning blue when iodine is applied.</p>
+
+<p>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 <span class="pagenum" title="Page&nbsp;107">&nbsp;</span><a name="Page_107" id="Page_107"></a>this must be used cautiously on
+account of the great delicacy of the tissues.</p>
+
+<p>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.</p>
+
+<p>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
+(<a href="#fig67">Fig.&nbsp;67</a>, <i>A</i>, <i>L</i>). The other (<i>r</i>) 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 (<i>st.</i>), and is the apex of the
+stem. The other (<i>f</i>) 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.</p></blockquote>
+
+<div class="figcenter" style="width:609px;">
+<a name="fig67" id="fig67"></a>
+<img src="images/fig067.png" width="609" height="507"
+alt="Fig.&nbsp;67." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;67.</span>&mdash;<i>A</i>, embryo of the ostrich fern just before
+breaking through the prothallium, &times;&nbsp;50. <i>st.</i> apex of stem. <i>l</i>, first
+leaf. <i>r</i>, first root. <i>ar.</i> neck of the archegonium. <i>B</i>, young
+plant, still attached to the prothallium (<i>pr.</i>). <i>C</i>, underground
+stem of the maiden-hair fern (<i>Adiantum</i>), with one young leaf, and
+the base of an older one, &times;&nbsp;1. <i>D</i>, three cross-sections of a leaf
+stalk: <span class="smcap">i</span>, nearest the base; <span class="smcap">iii</span>, nearest the blade of the leaf,
+showing the division of the fibro-vascular bundle, &times;&nbsp;5. <i>E</i>, part of
+the blade of the leaf, &times;&nbsp;&frac12;. <i>F</i>, a single spore-bearing leaflet,
+showing the edge folded over to cover the sporangia, &times;&nbsp;1. <i>G</i>, part of
+the fibro-vascular bundle of the leaf stalk (cross-section), &times;&nbsp;50.
+<i>x</i>, woody part of the bundle. <i>y</i>, bast. <i>sh.</i> bundle sheath. <i>H</i>, a
+small portion of the same bundle, &times;&nbsp;150. <i>I</i>, stony tissue from the
+underground stem, &times;&nbsp;150. <i>J</i>, sieve tube from the underground stem,
+&times;&nbsp;300.</p>
+</div>
+
+<blockquote><p>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 <a href="#fig67">Fig.&nbsp;67</a>, <i>A</i>, with <a href="#fig55">Fig.&nbsp;55</a>);
+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 &ldquo;fibro-vascular
+bundle,&rdquo; and in its perfect form, at least, is found in no plants
+below the ferns, which are also the first to develop true roots.</p></blockquote>
+
+<p><span class="pagenum" title="Page&nbsp;108">&nbsp;</span><a name="Page_108" id="Page_108"></a>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 (<a href="#fig67">Fig.&nbsp;67</a>, <i>B</i>). 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
+<span class="pagenum" title="Page&nbsp;109">&nbsp;</span><a name="Page_109" id="Page_109"></a>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.</p>
+
+<p>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 <i>Riccia</i>, or the horned liverworts, is obvious. The terms
+o&ouml;phyte (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.</p>
+
+<p>The common maiden-hair fern (<i>Adiantum pedatum</i>) 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 (<a href="#fig67">Fig.&nbsp;67</a>, <i>C</i>),
+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 (<a href="#fig67">Fig.&nbsp;67</a>, <i>E</i>). 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 (<i>C</i>).</p>
+
+<p>On breaking the stem across, it is seen to be dark-colored, <span class="pagenum" title="Page&nbsp;110">&nbsp;</span><a name="Page_110" id="Page_110"></a>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.</p>
+
+<blockquote><p>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 (<a href="#fig67">Fig.&nbsp;67</a>, <i>I</i>). The latter, if
+sufficiently magnified, show distinct striation of the walls, which
+are often penetrated by deep narrow depressions or &ldquo;pits.&rdquo; This
+thick-walled tissue is called &ldquo;stony tissue&rdquo; (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 &ldquo;bundle sheath.&rdquo; 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 (<a href="#fig67">Fig.&nbsp;67</a>, <i>G</i>).
+Within the bundle sheath (<i>sh.</i>) there are two well-marked regions, a
+central band (<i>x</i>) of large empty cells, with somewhat angular
+outlines, and distinctly separated walls; and an outer portion (<i>y</i>)
+filling up the space between these central cells and the bundle
+sheath. The central tissue (<i>x</i>) 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.</p>
+
+<p>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 (<a href="#fig68">Fig.&nbsp;68</a>, <i>C</i>, <i>x</i>) 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 &ldquo;scalariform,&rdquo; or
+ladder-shaped markings. These empty cells are known as &ldquo;tracheids,&rdquo;
+and tissue composed of such empty cells, &ldquo;tracheary tissue.&rdquo; Besides
+the tracheids, there are a few small cells with oblique ends, and with
+some granular contents.</p>
+
+<p>The phloem is composed of cells similar to the latter, but there may
+also be found, especially in the stem, other larger ones (<a href="#fig67">Fig.&nbsp;67</a>,
+<i>J</i>), whose <span class="pagenum" title="Page&nbsp;111">&nbsp;</span><a name="Page_111" id="Page_111"></a>walls are marked with shallow depressions, whose bottoms
+are finely pitted. These are the so-called &ldquo;sieve tubes.&rdquo;</p>
+
+<p>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.</p></blockquote>
+
+<p>The leaves, when young, are coiled up (<a href="#fig67">Fig.&nbsp;67</a>, <i>C</i>), 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.</p>
+
+<p>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.</p>
+
+<p>The section of the fibro-vascular bundle differs at different heights.
+Near the base of the stalk (Fig.&nbsp;<i>D</i> <span class="smcap">i</span>) it is horseshoe-shaped; but,
+if examined higher up, it is found to divide (<span class="allsc">II, III</span>), one part going
+to each of the main branches of the leaf. These secondary bundles
+divide further, forming the veins of the leaflets.</p>
+
+<p>The leaflets (<i>E</i>, <i>F</i>) 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 (<i>F</i>). 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 <span class="pagenum" title="Page&nbsp;112">&nbsp;</span><a name="Page_112" id="Page_112"></a>upon a piece
+of paper, as it dries the spores are discharged, covering the paper
+with the spores, which look like fine brown powder.</p>
+
+<div class="figcenter" style="width:603px;">
+<a name="fig68" id="fig68"></a>
+<img src="images/fig068.png" width="603" height="502"
+alt="Fig.&nbsp;68." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;68.</span>&mdash;<i>A</i>, vertical section of the leaf of the
+maiden-hair fern, which has cut across a vein (<i>f.b.</i>), &times;&nbsp;150. <i>B</i>,
+surface view of the epidermis from the lower surface of a leaf. <i>f</i>,
+vein. <i>p</i>, breathing pore, &times;&nbsp;150. <i>C</i>, longitudinal section of the
+fibro-vascular bundle of the leaf stalk, showing tracheids with
+ladder-shaped markings, &times;&nbsp;150. <i>D</i>, longitudinal section through the
+tip of a root, &times;&nbsp;150. <i>a</i>, apical cell. <i>Pl.</i> young fibro-vascular
+bundle. <i>Pb.</i> young ground tissue. <i>E</i>, cross-section of the root,
+through the region of the apical cell (<i>a</i>), &times;&nbsp;150. <i>F</i>, cross-section
+through a full-grown root, &times;&nbsp;25. <i>r</i>, root hairs. <i>G</i>, the
+fibro-vascular bundle of the same, &times;&nbsp;150.</p>
+</div>
+
+<blockquote><p>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
+&ldquo;parenchyma&rdquo;) 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 (<a href="#fig68">Fig.&nbsp;68</a>, <i>B</i>,
+<i>f</i>). Here the cells are long and narrow, with heavy <span class="pagenum" title="Page&nbsp;113">&nbsp;</span><a name="Page_113" id="Page_113"></a>walls. The
+epidermal cells contain numerous chloroplasts, and on the under
+surface of the leaf breathing pores (<i>stomata</i>, sing. <i>stoma</i>), 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.</p></blockquote>
+
+<div class="figleft" style="width:273px;">
+<a name="fig69" id="fig69"></a>
+<img src="images/fig069.png" width="273" height="463"
+alt="Fig.&nbsp;69." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;69.</span>&mdash;<i>A</i>, mother cell of the sporangium of the
+maiden-hair fern, &times;&nbsp;300. <i>B</i>, young sporangium, surface view, &times;&nbsp;150:
+<span class="smcap">i</span>, from the side; <span class="smcap">ii</span>, from above. <i>C&ndash;E</i>, successive stages in the
+development of the sporangium seen in optical section, &times;&nbsp;150. <i>F</i>,
+nearly ripe sporangium, &times;&nbsp;50: <span class="smcap">i</span>, from in front; <span class="smcap">ii</span>, from the side.
+<i>an.</i> ring. <i>st.</i> point of opening. <i>G</i>, group of four spores, &times;&nbsp;150.
+<i>H</i>, a single spore, &times;&nbsp;300.</p>
+</div>
+
+<blockquote><p>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
+<a href="#fig68">Fig.&nbsp;68</a>, <i>A</i>. The epidermis (<i>e</i>) bounds the upper and lower surfaces,
+and if a vein (<i>f.b.</i>) is cut across its structure is found to be like
+that of the fibro-vascular bundle of the leaf stalk, but much
+simplified.</p>
+
+<p>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>i.e.</i> they are principally concerned in the absorption and
+decomposition of carbonic acid from the atmosphere, and the
+manufacture of starch.</p>
+
+<p>The spore cases, or sporangia (<a href="#fig69">Fig.&nbsp;69</a>), are at first little papill&aelig;
+(<i>A</i>), 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&mdash;the sporangium proper. The latter now divides
+by four walls (<i>B</i>, <i>C</i>, <span class="smcap">i&ndash;iv</span>), 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 <span class="pagenum" title="Page&nbsp;114">&nbsp;</span><a name="Page_114" id="Page_114"></a>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 (<i>D</i>), 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 (<i>E</i>).</p>
+
+<p>Each of the central cells divides into four spores, precisely as in
+the bryophytes. The young spores (<i>G</i>, <i>H</i>) 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.</p>
+
+<p>Running around the outside of the ripe spore case is a single row of
+cells (<i>an.</i>), 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 (<i>st.</i>) that the spore case opens. When
+the ripe sporangium becomes dry, the ring of thickened cells (<i>an.</i>)
+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).</p></blockquote>
+
+<p>The roots of the sporophyte arise in large numbers, the youngest being
+always nearest the growing point of the stem or larger roots (<a href="#fig67">Fig.&nbsp;67</a>,
+<i>C</i>). 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 (<a href="#fig68">Fig.&nbsp;68</a>, <i>F</i>). Growing
+from its outer surface are numerous brown root hairs (<i>r</i>).</p>
+
+<blockquote><p>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 (<a href="#fig68">Fig.&nbsp;68</a>, <i>G</i>) shows a band of tracheary
+tissue in the centre surrounded by colorless cells, all about alike.</p>
+
+<p><span class="pagenum" title="Page&nbsp;115">&nbsp;</span><a name="Page_115" id="Page_115"></a>All of the organs of the fern grow from a definite apical cell, but it
+is difficult to study except in the root.</p>
+
+<p>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
+<a href="#fig68">Figure&nbsp;68</a>, <i>D</i>. The apical cell (<i>a</i>) 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.&nbsp;<i>L</i>)
+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,
+<i>D</i>). From the outer series of segments is derived the peculiar
+structure (root cap) covering the delicate growing point and
+protecting it from injury.</p>
+
+<p>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.</p></blockquote>
+
+
+
+<hr />
+<h2><span class="pagenum" title="Page&nbsp;116">&nbsp;</span><a name="Page_116" id="Page_116"></a><a name="CHAPTER_XIII" id="CHAPTER_XIII"></a>CHAPTER XIII.
+<br />
+<small>CLASSIFICATION OF THE PTERIDOPHYTES.</small></h2>
+
+
+<p><span class="smcap">There</span> are three well-marked classes of the Pteridophytes: the ferns
+(<i>Filicin&aelig;</i>); horse-tails (<i>Equisetin&aelig;</i>); and the club mosses
+(<i>Lycopodin&aelig;</i>).</p>
+
+
+<h4><a name="ferns" id="ferns"></a><span class="smcap">Class I.&mdash;Ferns</span> (<i>Filicin&aelig;</i>).</h4>
+
+<p>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
+(<i>Filices</i>) and the adder-tongues (<i>Ophioglossace&aelig;</i>), are represented
+in the United States. A third order, intermediate in some respects
+between these two, and called the ringless ferns (<i>Marattiace&aelig;</i>), has
+no representatives within our territory.</p>
+
+<p>The classification is at present based largely upon the characters of
+the sporophyte, the sexual plants being still very imperfectly known
+in many forms.</p>
+
+<p>The adder-tongues (<i>Ophioglossace&aelig;</i>) 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
+(<i>Ophioglossum</i>) and the grape ferns (<i>Botrychium</i>). They send up but
+one leaf each year, and this in fruiting specimens (<a href="#fig70">Fig.&nbsp;70</a>, <i>A</i>) is
+divided into two portions, the spore bearing (<i>x</i>) and the green
+vegetative part. In <i>Botrychium</i> the leaves are more or less deeply
+divided, and the sporangia distinct (<a href="#fig71">Fig.&nbsp;71</a>, <i>B</i>). In <i>Ophioglossum</i>
+the sterile division of the leaf is usually smooth and undivided, and
+the <span class="pagenum" title="Page&nbsp;117">&nbsp;</span><a name="Page_117" id="Page_117"></a>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.</p>
+
+<div class="figcenter" style="width:612px;">
+<a name="fig70" id="fig70"></a>
+<img src="images/fig070.png" width="612" height="490"
+alt="Fig.&nbsp;70." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;70.</span>&mdash;Forms of ferns. <i>A</i>, grape fern
+(<i>Botrychium</i>), &times;&nbsp;&frac12;. <i>x</i>, fertile part of the leaf. <i>B</i>, sporangia of
+<i>Botrychium</i>, &times;&nbsp;3. <i>C</i>, flowering fern (<i>Osmunda</i>). <i>x</i>, spore-bearing
+leaflets, &times;&nbsp;&frac12;. <i>D</i>, a sporangium of <i>Osmunda</i>, &times;&nbsp;25. <i>r</i>, ring. <i>E</i>,
+<i>Polypodium</i>, &times;&nbsp;1. <i>F</i>, brake (<i>Pteris</i>), &times;&nbsp;1. <i>G</i>, shield fern
+(<i>Aspidium</i>), &times;&nbsp;2. <i>H</i>, spleen-wort (<i>Asplenium</i>), &times;&nbsp;2. <i>I</i>, ostrich
+fern (<i>Onoclea</i>), &times;&nbsp;1. <i>J</i>, the same, with the incurved edges of the
+leaflet partially raised so as to show the masses of sporangia
+beneath, &times;&nbsp;2.</p>
+</div>
+
+<p>In the true ferns (<i>Filices</i>), the sporangia resemble those already
+described, arising in all (unless possibly <i>Osmunda</i>) from a single
+epidermal cell.</p>
+
+<p>One group, the water ferns (<i>Rhizocarpe&aelig;</i>), produce two kinds of
+spores, large and small. The former produce male, the latter female
+prothallia. In both cases the prothallium is <span class="pagenum" title="Page&nbsp;118">&nbsp;</span><a name="Page_118" id="Page_118"></a>small, and often scarcely
+protrudes beyond the spore, and may be reduced to a single archegonium
+or antheridium (<a href="#fig71">Fig.&nbsp;71</a>, <i>B</i>, <i>C</i>) with only one or two cells
+representing the vegetative cells of the prothallium (<i>v</i>). 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
+<i>Marsilia</i> (<a href="#fig71">Fig.&nbsp;71</a>, <i>A</i>), looking like a four-leaved clover. Others
+(<i>Salvinia</i>, <i>Azolla</i>) are floating forms (<a href="#fig71">Fig.&nbsp;71</a>, <i>D</i>).</p>
+
+<div class="figcenter" style="width:314px;">
+<a name="fig71" id="fig71"></a>
+<img src="images/fig071.png" width="314" height="486"
+alt="Fig.&nbsp;71." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;71.</span>&mdash;<i>A</i>, <i>Marsilia</i>, one of the <i>Rhizocarpe&aelig;</i>
+(after Underwood). <i>sp.</i> the &ldquo;fruits&rdquo; containing the sporangia. <i>B</i>, a
+small spore of <i>Pilularia</i>, with the ripe antheridium protruding,
+&times;&nbsp;180. <i>C</i>, male prothallium removed from the spore, &times;&nbsp;180. <i>D</i>,
+<i>Azolla</i> (after Sprague), &times;&nbsp;1.</p>
+</div>
+
+<p>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 (<i>Osmunda</i>), shown in <a href="#fig70">Figure&nbsp;70</a>,
+<i>C</i>, <i>D</i>. In these the sporangia are large and the ring (<i>r</i>)
+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.</p>
+
+<p>Our other common ferns have the sporangia in groups (<i>sori</i>, sing.
+<i>sorus</i>) 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 <span class="pagenum" title="Page&nbsp;119">&nbsp;</span><a name="Page_119" id="Page_119"></a>of some of the commonest
+genera are shown in <a href="#fig70">Figure&nbsp;70</a>, <i>E</i>, <i>J</i>.</p>
+
+
+<h4><a name="horse" id="horse"></a><span class="smcap">Class II.&mdash;Horse-tails</span> (<i>Equisetin&aelig;</i>).</h4>
+
+<p>The second class of the pteridophytes includes the horse-tails
+(<i>Equisetin&aelig;</i>) of which all living forms belong to a single genus
+(<i>Equisetum</i>). Formerly they were much more numerous than at present,
+remains of many different forms being especially abundant in the coal
+formations.</p>
+
+<div class="figcenter" style="width:474px;">
+<a name="fig72" id="fig72"></a>
+<img src="images/fig072.png" width="474" height="580"
+alt="Fig.&nbsp;72." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;72.</span>&mdash;<i>A</i>, spore-bearing stem of the field
+horse-tail (<i>Equisetum</i>), &times;&nbsp;1. <i>x</i>, the spore-bearing cone. <i>B</i>,
+sterile stem of the same, &times;&nbsp;&frac12;. <i>C</i>, underground stem, with tubers
+(<i>o</i>), &times;&nbsp;&frac12;. <i>D</i>, cross-section of an aerial stem, &times;&nbsp;5. <i>f.b.</i>
+fibro-vascular bundle. <i>E</i>, a single fibro-vascular bundle, &times;&nbsp;150.
+<i>tr.</i> vessels. <i>F</i>, a single leaf from the cone, &times;&nbsp;5. <i>G</i>, the same
+cut lengthwise, through a spore sac (<i>sp.</i>), &times;&nbsp;5. <i>H</i>, a spore, &times;&nbsp;50.
+<i>I</i>, the same, moistened so that the elaters are coiled up, &times;&nbsp;150.
+<i>J</i>, a male prothallium, &times;&nbsp;50. <i>an.</i> an antheridium. <i>K</i>,
+spermatozoids, &times;&nbsp;300.</p>
+</div>
+
+<p><span class="pagenum" title="Page&nbsp;120">&nbsp;</span><a name="Page_120" id="Page_120"></a>One of the commonest forms is the field horse-tail (<i>Equisetum
+arvense</i>), 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 &ldquo;ballast&rdquo; for railway tracks.</p>
+
+<p>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 (<a href="#fig72">Fig.&nbsp;72</a>,
+<i>C</i>) 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 (<i>o</i>)
+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.</p>
+
+<p>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.</p>
+
+<p>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 (<a href="#fig72">Fig.&nbsp;72</a>, <i>A</i>), 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
+(<i>L</i>) 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 (<i>x</i>).</p>
+
+<p>A cross-section of the stem (<i>D</i>) 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 <span class="pagenum" title="Page&nbsp;121">&nbsp;</span><a name="Page_121" id="Page_121"></a>fibro-vascular bundles
+(<i>f.b.</i>) are arranged in a circle, alternating with the air channels,
+and each one has running through it a small air passage.</p>
+
+<p>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 (<i>F</i>, <i>G</i>) 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
+(<i>G</i>, <i>sp.</i>). They are filled with a mass of greenish spores that
+shake out at the slightest jar when ripe.</p>
+
+<p>The sterile branches (<i>B</i>) 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,
+&ldquo;horse-tail,&rdquo; is taken. The surface of the plant is hard and rough,
+due to the presence of great quantities of flint in the epidermis,&mdash;a
+peculiarity common to all the species.</p>
+
+<blockquote><p>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
+(<i>E</i>), 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<a name="FNanchor_9_9" id="FNanchor_9_9"></a><a href="#Footnote_9_9" class="fnanchor">[9]</a> (<i>tr.</i>) 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 <span class="pagenum" title="Page&nbsp;122">&nbsp;</span><a name="Page_122" id="Page_122"></a>the fern
+bundle. There is no individual bundle sheath, but the whole circle of
+bundles has a common outer sheath.</p>
+
+<p>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.</p>
+
+<p>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 (<i>H</i>, <i>I</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>I</i>), but
+quickly springing out again when dry (<i>H</i>). 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.</p>
+
+<p>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
+(<a href="#fig72">Fig.&nbsp;72</a>, <i>J</i>, <i>an.</i>) are larger than those of the ferns, and the
+spermatozoids (<i>K</i>) are thicker and with fewer coils, but otherwise
+much like fern spermatozoids.</p>
+
+<p>The archegonia have a shorter neck than those of the ferns, and the
+neck is straight.</p>
+
+<p>Both male and female prothallia are much branched and very irregular
+in shape.</p></blockquote>
+
+<p>There are a number of common species of <i>Equisetum</i>. Some of them,
+like the common scouring rush (<i>E.&nbsp;hiemale</i>), 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.</p>
+
+
+<h4><a name="club" id="club"></a><span class="pagenum" title="Page&nbsp;123">&nbsp;</span><a name="Page_123" id="Page_123"></a><span class="smcap">Class III.&mdash;The Club Mosses</span> (<i>Lycopodin&aelig;</i>).</h4>
+
+<p>The last class of the pteridophytes includes the ground pines, club
+mosses, etc., and among cultivated plants numerous species of the
+smaller club mosses (<i>Selaginella</i>).</p>
+
+<p>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 (<i>Lycopodiace&aelig;</i>) is represented in the
+northern states by a single genus (<i>Lycopodium</i>), of which the common
+ground pine (<i>L.&nbsp;dendroideum</i>) (<a href="#fig73">Fig.&nbsp;73</a>) 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 (<i>A</i>, <i>x</i>,
+<i>B</i>) 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 (<i>C</i>, <i>sp.</i>) opening by a cleft along the
+upper edge and filled with a mass of fine yellow powder. These
+capsules are the spore cases.</p>
+
+<p>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.</p>
+
+<p>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 (<a href="#fig73">Fig.&nbsp;73</a>, <i>E</i>). Within the epidermis is a mass of
+ground tissue of firm, woody texture surrounding the central oval or
+circular fibro-vascular<span class="pagenum" title="Page&nbsp;124">&nbsp;</span><a name="Page_124" id="Page_124"></a> cylinder. This shows a number of white bars
+(xylem) surrounded by a more delicate tissue (phloem).</p>
+
+<blockquote><p>On magnifying the section more strongly, the cells of the ground
+tissue (<i>G</i>) 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
+&ldquo;fibres.&rdquo;</p></blockquote>
+
+<div class="figcenter" style="width:453px;">
+<a name="fig73" id="fig73"></a>
+<img src="images/fig073.png" width="453" height="626"
+alt="Fig.&nbsp;73." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;73.</span>&mdash;<i>A</i>, a club moss (<i>Lycopodium</i>), &times;&nbsp;&#8531;. <i>x</i>,
+cone. <i>r</i>, root. <i>B</i>, a cone, &times;&nbsp;1. <i>C</i>, single scale with sporangium
+(<i>sp.</i>). <i>D</i>, spores: <span class="smcap">i</span>, from above; <span class="smcap">ii</span>, from below, &times;&nbsp;325. <i>E</i>, cross
+section of stem, &times;&nbsp;8. <i>f.b.</i> fibro-vascular bundle. <i>F</i>, portion of
+the fibro-vascular bundle, &times;&nbsp;150. <i>G</i>, cells of the ground tissue,
+&times;&nbsp;150.</p>
+</div>
+
+<blockquote><p>The xylem (<i>F</i>, <i>xy.</i>) 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.</p>
+
+<p><span class="pagenum" title="Page&nbsp;125">&nbsp;</span><a name="Page_125" id="Page_125"></a>The spores (<i>D</i>) 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.</p>
+
+<p>Almost nothing is known of the prothallia of our native species.</p></blockquote>
+
+<p>The second order (<i>Ligulat&aelig;</i>) is represented by two very distinct
+families: the smaller club mosses (<i>Selaginelle&aelig;</i>) and the quill-worts
+(<i>Isoete&aelig;</i>). Of the former the majority are tropical, but are common
+in greenhouses where they are prized for their delicate moss-like
+foliage (<a href="#fig74">Fig.&nbsp;74</a>, <i>A</i>).</p>
+
+<div class="figcenter" style="width:586px;">
+<a name="fig74" id="fig74"></a>
+<img src="images/fig074.png" width="586" height="510"
+alt="Fig.&nbsp;74." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;74.</span>&mdash;<i>A</i>, one of the smaller club mosses
+(<i>Selaginella</i>). <i>sp.</i> spore-bearing branch, &times;&nbsp;2. <i>B</i>, part of a stem,
+sending down naked rooting branches (<i>r</i>), &times;&nbsp;1. <i>C</i>, longitudinal
+section of a spike, with a single macrosporangium at the base; the
+others, microsporangia, &times;&nbsp;3. <i>D</i>, a scale and microsporangium, &times;&nbsp;5.
+<i>E</i>, young microsporangium, &times;&nbsp;150. The shaded cells are the spore
+mother cells. <i>F</i>, a young macrospore, &times;&nbsp;150. <i>G</i>, section of the
+stem, &times;&nbsp;50. <i>H</i>, a single fibro-vascular bundle, &times;&nbsp;150. <i>I</i>, vertical
+section of the female prothallium of <i>Selaginella</i>, &times;&nbsp;50. <i>ar.</i>
+archegonium. <i>J</i>, section of an open archegonium, &times;&nbsp;300. <i>o</i>, the egg
+cell. <i>K</i>, microspore, with the contained male prothallium, &times;&nbsp;300.
+<i>x</i>, vegetative cell. <i>sp.</i> sperm cells. <i>L</i>, young plant, with the
+attached macrospore, &times;&nbsp;6. <i>r</i>, the first root. <i>l</i>, the first leaves.</p>
+</div>
+
+<p><span class="pagenum" title="Page&nbsp;126">&nbsp;</span><a name="Page_126" id="Page_126"></a>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 (<i>B</i>,
+<i>r</i>) often grow downward from the lower side of the main branches, and
+on touching the ground develop roots which fork regularly.</p>
+
+<p>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 (<i>A</i>,
+<i>sp.</i>), 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).</p>
+
+<p>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.</p>
+
+<blockquote><p>If ripe spores can be obtained by sowing them upon moist earth, the
+young plants will appear in about a month. The microspore (<a href="#fig74">Fig.&nbsp;74</a>,
+<i>K</i>) produces a prothallium not unlike that of some of the water
+ferns, there being a single vegetative cell (<i>x</i>), and the rest of the
+prothallium forming a single antheridium. The spermatozoids are
+excessively small, and resemble those of the bryophytes.</p>
+
+<p>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 (<a href="#fig74">Fig.&nbsp;74</a>,
+<i>I</i>, <i>J</i>). The lower cell produces later a tissue that serves to
+nourish the young embryo.</p>
+
+<p>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 <i>Ligulat&aelig;</i> as the highest of
+existing pteridophytes, and to a certain extent connecting them with
+the lowest of the spermaphytes.</p></blockquote>
+
+<p>Resembling the smaller club mosses in their development, but differing
+in some important points, are the quill-worts (<i>Isoete&aelig;</i>). They are
+mostly aquatic forms, growing partially <span class="pagenum" title="Page&nbsp;127">&nbsp;</span><a name="Page_127" id="Page_127"></a>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 <i>Selaginella</i>, but the macrosporangia contain numerous
+macrospores. The very large sporangia (<i>M</i>, <i>sp.</i>) 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
+<i>Selaginella</i>. 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.</p>
+
+
+
+<hr />
+<h2><span class="pagenum" title="Page&nbsp;128">&nbsp;</span><a name="Page_128" id="Page_128"></a><a name="CHAPTER_XIV" id="CHAPTER_XIV"></a>CHAPTER XIV.
+<br />
+<small>SUB-KINGDOM VI.
+<br />
+<span class="smcap">Spermaphytes: Ph&aelig;nogams.</span></small></h2>
+
+
+<p><span class="smcap">The</span> last and highest great division of the vegetable kingdom has been
+named <i>Spermaphyta</i>, &ldquo;seed plants,&rdquo; 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.</p>
+
+<p>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.</p>
+
+<p>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 &ldquo;ovules,&rdquo; a name given before it was known that
+these were the same as the macrosporangia of the higher pteridophytes.</p>
+
+<p>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 &ldquo;flower&rdquo; of the higher spermaphytes.</p>
+
+<p>As might be expected, the tissues of the higher spermaphytes are the
+most highly developed of all plants, though <span class="pagenum" title="Page&nbsp;129">&nbsp;</span><a name="Page_129" id="Page_129"></a>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.</p>
+
+<p>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.</p>
+
+
+<h4><a name="gym" id="gym"></a><span class="smcap">Class I.&mdash;Gymnosperms</span> (<i>Gymnosperm&aelig;</i>).</h4>
+
+<p>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
+(<i>Pinus sylvestris</i>), 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.<a name="FNanchor_10_10" id="FNanchor_10_10"></a><a href="#Footnote_10_10" class="fnanchor">[10]</a> 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 <span class="pagenum" title="Page&nbsp;130">&nbsp;</span><a name="Page_130" id="Page_130"></a>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,&mdash;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.</p>
+
+<p>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) (<a href="#fig76">Fig.&nbsp;76</a>, <i>A</i>, <i>c</i>), 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 (<i>r</i>). 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&#8217;s
+growth is marked by a distinct ring (<i>A</i> <span class="smcap">i</span>, <span class="smcap">ii</span>). As the branches grow
+in diameter <span class="pagenum" title="Page&nbsp;131">&nbsp;</span><a name="Page_131" id="Page_131"></a>the outer bark becomes split and irregular, and portions
+die, becoming brown and hard.</p>
+
+<p>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 &ldquo;tap&rdquo; root of the full-grown tree, and from it branch off the
+secondary roots, which in turn give rise to others.</p>
+
+<p>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
+(<i>e.g.</i> red cedar). In the Scotch pine the microspores are ripe about
+the end of May. The leaves bearing them are aggregated in small cones
+(&ldquo;flowers&rdquo;), crowded about the base of a growing shoot terminating the
+branches (<a href="#fig77">Fig.&nbsp;77</a>, <i>A</i> &#9794;). 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) (<i>C</i>, <i>sp.</i>),
+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.</p>
+
+<p>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)
+(<a href="#fig77">Fig.&nbsp;77</a>, <i>E</i>, <i>o</i>), and running through the centre is a ridge that
+ends in a little spine or point.</p>
+
+<p>The ovule-bearing leaf has on the back a scale with fringed edge (<i>F</i>,
+<i>sc.</i>), quite conspicuous when the flower is young, but scarcely to be
+detected in the older cone. From the female flower is developed the
+cone (<a href="#fig75">Fig.&nbsp;75</a>, <i>A</i>), but the process is a <span class="pagenum" title="Page&nbsp;132">&nbsp;</span><a name="Page_132" id="Page_132"></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.</p>
+
+<div class="figcenter" style="width:624px;">
+<a name="fig75" id="fig75"></a>
+<img src="images/fig075.png" width="624" height="462"
+alt="Fig.&nbsp;75." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;75.</span>&mdash;Scotch pine (<i>Pinus sylvestris</i>). <i>A</i>, a ripe
+cone, &times;&nbsp;&frac12;. <i>B</i>, a year-old cone, &times;&nbsp;1. <i>C</i>, longitudinal section of
+<i>B</i>. <i>D</i>, a single scale of <i>B</i>, showing the sporangia (ovules) (<i>o</i>),
+&times;&nbsp;2. <i>E</i>, a scale from a ripe cone, with the seeds (<i>s</i>), &times;&nbsp;&frac12;. <i>F</i>,
+longitudinal section of a ripe seed, &times;&nbsp;3. <i>em.</i> the embryo. <i>G</i>, a
+germinating seed, &times;&nbsp;2. <i>r</i>, the primary root. <i>H</i>, longitudinal
+section through <i>G</i>, showing the first leaves of the young plant still
+surrounded by the endosperm, &times;&nbsp;4. <i>I</i>, an older plant with the leaves
+(<i>l</i>) withdrawing from the seed coats, &times;&nbsp;4. <i>J</i>, upper part of a young
+plant, showing the circle of primary leaves (cotyledons), &times;&nbsp;1. <i>K</i>,
+section of the same, &times;&nbsp;2. <i>b</i>, the terminal bud. <i>L</i>, cross-section of
+the stem of the young plant, &times;&nbsp;25. <i>fb.</i> a fibro-vascular bundle. <i>M</i>,
+cross-section of the root, &times;&nbsp;25. <i>x</i>, wood. <i>ph.</i> bast, of the
+fibro-vascular bundle.</p>
+</div>
+
+<p>In <a href="#fig75">Figure&nbsp;75</a>, <i>B</i>, 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 (<i>D</i>). The ovules are still very small.
+As the growth of the tree is <span class="pagenum" title="Page&nbsp;133">&nbsp;</span><a name="Page_133" id="Page_133"></a>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 <a href="#fig77">Figure&nbsp;77</a>,
+<i>G</i>. Comparing this with the sporangia of the pteridophytes, the first
+difference that strikes us is the presence of an outer coat or
+integument (<i>in.</i>), which is absent in the latter. The single
+macrospore (<i>sp.</i>) 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 (<i>ar.</i>), 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.</p>
+
+<p>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 (<a href="#fig75">Fig.&nbsp;75</a>, <i>A</i>)
+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 (<i>E</i>, <i>s</i>) 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 <span class="pagenum" title="Page&nbsp;134">&nbsp;</span><a name="Page_134" id="Page_134"></a>a day or two open, often with a sharp,
+crackling sound, and scatter the ripe seeds.</p>
+
+<p>A section of a ripe seed (<i>F</i>) shows the embryo (<i>em.</i>) surrounded by
+a dense, white, starch-bearing tissue derived from the prothallium
+cells, and called the &ldquo;endosperm.&rdquo; 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.</p>
+
+<p>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 (<i>G</i>, <i>r</i>).
+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 &ldquo;cotyledons&rdquo; 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.</p>
+
+<p>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 (<a href="#fig75">Fig.&nbsp;75</a>, <i>K</i>, <i>b</i>). A
+cross-section of the young stem shows about six separate
+fibro-vascular bundles arranged in a circle (<i>S</i>, <i>fb.</i>). The root
+shows a central fibro-vascular cylinder surrounded by <span class="pagenum" title="Page&nbsp;135">&nbsp;</span><a name="Page_135" id="Page_135"></a>a dark-colored
+ground tissue. Growing from its surface are numerous root hairs
+(<a href="#fig75">Fig.&nbsp;75</a>, <i>M</i>).</p>
+
+<blockquote><p>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.</p>
+
+<p>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.</p>
+
+<p>Scattered through the green tissue are several resin passages (<i>r</i>),
+each surrounded by a circle of colorless, thick-walled cells, like
+those under the epidermis. At intervals in the latter are
+openings&mdash;breathing pores&mdash;(<a href="#fig76">Fig.&nbsp;76</a>, <i>J</i>), below each of which is an
+intercellular space (<i>i</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.</p>
+
+<p>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 (<i>x</i>) lying toward the inner, flat side
+of the leaf, the bast (<i>T</i>) toward the outer, convex side. This type
+of bundle, called &ldquo;collateral,&rdquo; 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.</p>
+
+<p>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.</p>
+
+<p><span class="pagenum" title="Page&nbsp;136">&nbsp;</span><a name="Page_136" id="Page_136"></a>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, <span class="pagenum" title="Page&nbsp;137">&nbsp;</span><a name="Page_137" id="Page_137"></a>and gradually assume
+the character of the cells on which they border (<a href="#fig76">Fig.&nbsp;76</a>, <i>B</i>,
+<i>cam.</i>). 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 (<a href="#fig76">Fig.&nbsp;76</a>, <i>A</i>, <i>cam.</i>). 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 (<i>C</i>, <i>m</i>).</p>
+
+<p>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.</p>
+
+<p>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 (<a href="#fig76">Fig.&nbsp;76</a>, <i>H</i>),
+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.</p>
+
+<p>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.</p>
+
+<p>Some of the cells are larger than the others, and these are found to
+be, when examined in longitudinal section, sieve tubes (<a href="#fig76">Fig.&nbsp;76</a>, <i>E</i>)
+with numerous lateral sieve plates quite similar to those found in the
+stems of ferns.</p></blockquote>
+
+<div class="figcenter" style="width:639px;">
+<a name="fig76" id="fig76"></a>
+<img src="images/fig076.png" width="639" height="527"
+alt="Fig.&nbsp;76." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;76.</span>&mdash;Scotch pine. <i>A</i>, cross-section of a
+two-year-old branch, &times;&nbsp;3. <i>p</i>, pith. <i>c</i>, bark. The radiating lines
+are medullary rays. <i>r</i>, resin ducts. <i>B</i>, part of the same, &times;&nbsp;150.
+<i>cam.</i> cambium cells. <i>x</i>, tracheids. <i>C</i>, cross-section of a
+two-year-old branch at the point where the two growth rings join: <i>I</i>,
+the cells of the first year&#8217;s growth; <i>II</i>, those of the second year.
+<i>m</i>, a medullary ray, &times;&nbsp;150. <i>D</i>, longitudinal section of a branch,
+showing the form of the tracheids and the bordered pits upon their
+walls. <i>m</i>, medullary ray, &times;&nbsp;150. <i>E</i>, part of a sieve tube, &times;&nbsp;300.
+<i>F</i>, cross-section of a tracheid passing through two of the pits in
+the wall (<i>p</i>), &times;&nbsp;300. <i>G</i>, longitudinal section of a branch, at right
+angles to the medullary rays (<i>m</i>). At <i>y</i>, the section has passed
+through the wall of a tracheid, bearing a row of pits, &times;&nbsp;150. <i>H</i>,
+cross-section of a resin duct, &times;&nbsp;150. <i>I</i>, cross-section of a leaf,
+&times;&nbsp;20. <i>fb.</i> fibro-vascular bundle. <i>r</i>, resin duct. <i>J</i>, section of a
+breathing pore, &times;&nbsp;150. <i>i</i>, the air space below it.</p>
+</div>
+
+<blockquote><p>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 (<i>B</i>, <i>cam.</i>)
+are arranged in radial rows and divide, mainly by walls, at right
+angles to the radii of<span class="pagenum" title="Page&nbsp;138">&nbsp;</span><a name="Page_138" id="Page_138"></a> 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 (<i>B</i>, <i>x</i>).</p>
+
+<p>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>I</i>), the
+wood cells are comparatively small and much flattened, while the walls
+are quite as heavy as those of the much larger cells (<i>II</i>) 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.</p>
+
+<p>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
+(<a href="#fig76">Fig.&nbsp;76</a>, <i>D</i>, <i>p</i>) 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 (<i>F</i>, <i>p</i>, <i>G</i>, <i>y</i>). These &ldquo;bordered&rdquo; pits are very
+characteristic of the wood of all conifers.</p>
+
+<p>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 (<a href="#fig75">Fig.&nbsp;75</a>, <i>M</i>,
+<i>fb.</i>) is of the so-called radial type, there being three xylem masses
+(<i>x</i>) alternating with as many phloem masses (<i>ph.</i>) 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.</p>
+
+<p>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 <span class="pagenum" title="Page&nbsp;139">&nbsp;</span><a name="Page_139" id="Page_139"></a>nuclei of the spores, and very instructive
+preparations may thus be made.<a name="FNanchor_11_11" id="FNanchor_11_11"></a><a href="#Footnote_11_11" class="fnanchor">[11]</a></p></blockquote>
+
+<div class="figcenter" style="width:588px;">
+<a name="fig77" id="fig77"></a>
+<img src="images/fig077.png" width="588" height="495"
+alt="Fig.&nbsp;77." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;77.</span>&mdash;Scotch pine (except <i>E</i> and <i>F</i>). <i>A</i>, end of
+a branch bearing a cluster of male flowers (&#9794;), &times;&nbsp;&frac12;. <i>B</i>, a similar
+branch, with two young female flowers (&#9792;), natural size. <i>C</i>, a scale
+from a male flower, showing the two sporangia (<i>sp.</i>); &times;&nbsp;5. <i>D</i>, a
+single ripe pollen spore (microspore), showing the vegetative cell
+(<i>x</i>), &times;&nbsp;150. <i>E</i>, a similar scale, from a female flower of the
+Austrian pine, seen from within, &times;&nbsp;4. <i>o</i>, the sporangium (ovule).
+<i>F</i>, the same, seen from the back, showing the scale (<i>sc.</i>) attached
+to the back. <i>G</i>, longitudinal section through a full-grown ovule of
+the Scotch pine. <i>p</i>, a pollen spore sending down its tube to the
+archegonia (<i>ar.</i>). <i>sp.</i> the prothallium (endosperm), filling up the
+embryo sac, &times;&nbsp;10. <i>H</i>, the neck of the archegonium, &times;&nbsp;150.</p>
+</div>
+
+<blockquote><p>The ripe pollen spores (<a href="#fig77">Fig.&nbsp;77</a>, <i>D</i>) are oval cells provided with a
+double wall, the outer one giving rise to two peculiar bladder-like
+appendages (<i>z</i>). Like the microspores of the smaller club mosses, a
+small cell is cut off from the body of the spore (<i>x</i>). These pollen
+spores are carried by the wind to the ovules, where they germinate.</p>
+
+<p>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.</p>
+
+<p><span class="pagenum" title="Page&nbsp;140">&nbsp;</span><a name="Page_140" id="Page_140"></a>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 &ldquo;embryo sac,&rdquo; is
+completely filled with the prothallium or &ldquo;endosperm.&rdquo; 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 (<a href="#fig77">Fig.&nbsp;77</a>, <i>H</i>).</p></blockquote>
+
+<p>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 (<a href="#fig77">Fig.&nbsp;77</a>, <i>G</i>).</p>
+
+
+<h3><a name="classgym" id="classgym"></a>Classification of the Gymnosperms.</h3>
+
+<p>There are three classes of the gymnosperms: I., cycads (<i>Cycade&aelig;</i>);
+II., conifers (<i>Conifer&aelig;</i>); III., joint firs (<i>Gnetace&aelig;</i>). All of the
+gymnosperms of the northern United States belong <span class="pagenum" title="Page&nbsp;141">&nbsp;</span><a name="Page_141" id="Page_141"></a>to the second order,
+but representatives of the others are found in the southern and
+southwestern states.</p>
+
+<p>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.</p>
+
+<div class="figcenter" style="width:631px;">
+<a name="fig78" id="fig78"></a>
+<img src="images/fig078.png" width="631" height="492"
+alt="Fig.&nbsp;78." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;78.</span>&mdash;Illustrations of gymnosperms. <i>A</i>, fruiting
+leaf of a cycad (<i>Cycas</i>), with macrosporangia (ovules) (<i>ov.</i>), &times;&nbsp;&frac14;.
+<i>B</i>, leaf of <i>Gingko</i>, &times;&nbsp;&frac12;. <i>C</i>, branch of hemlock (<i>Tsuga</i>), with a
+ripe cone, &times;&nbsp;1. <i>D</i>, red cedar (<i>Juniperus</i>), &times;&nbsp;1. <i>E</i>, <i>Arbor-vit&aelig;</i>
+(<i>Thuja</i>), &times;&nbsp;1.</p>
+</div>
+
+<p>The spore-bearing leaves usually form cones, recalling somewhat in
+structure those of the horse-tails, but one of the commonest
+cultivated species (<i>Cycas revoluta</i>) bears the ovules, which are very
+large, upon leaves that are in shape much like the ordinary ones
+(<a href="#fig78">Fig.&nbsp;78</a>, <i>A</i>).</p>
+
+<p>Of the conifers, there are numerous familiar forms, including all our
+common evergreen trees. There are two sub-orders,&mdash;the true conifers
+and the yews. In the latter there is no true <span class="pagenum" title="Page&nbsp;142">&nbsp;</span><a name="Page_142" id="Page_142"></a>cone, but the ovules are
+borne singly at the end of a branch, and the seed in the yew (<i>Taxus</i>)
+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 <i>Gingko</i> (<a href="#fig78">Fig.&nbsp;78</a>, <i>B</i>) are sometimes met
+with in cultivation.</p>
+
+<p>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 (<a href="#fig78">Fig.&nbsp;78</a>, <i>C</i>). Others
+have flattened, scale-like leaves, and more or less fleshy cones, like
+the red cedar (<a href="#fig78">Fig.&nbsp;78</a>, <i>D</i>) and <i>Arbor-vit&aelig;</i> (<i>E</i>).</p>
+
+<p>A few of the conifers, such as the tamarack or larch (<i>Larix</i>) and
+cypress (<i>Taxodium</i>), lose their leaves in the autumn, and are not,
+therefore, properly &ldquo;evergreen.&rdquo;</p>
+
+<p>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 (<i>Sequoia</i>) of
+California, the largest of all American trees.</p>
+
+<p>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.</p>
+
+
+
+<hr />
+<h2><span class="pagenum" title="Page&nbsp;143">&nbsp;</span><a name="Page_143" id="Page_143"></a><a name="CHAPTER_XV" id="CHAPTER_XV"></a>CHAPTER XV.
+<br />
+<small>SPERMAPHYTES.</small></h2>
+
+
+<h4>Class II.&mdash;Angiosperms.</h4>
+
+<p>The angiosperms include an enormous assemblage of plants, all those
+ordinarily called &ldquo;flowering plants&rdquo; 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 &ldquo;pistil&rdquo; is usually
+applied, and this is known as &ldquo;simple&rdquo; or &ldquo;compound,&rdquo; 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
+&ldquo;stamens.&rdquo; 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 &ldquo;perianth&rdquo; or
+&ldquo;perigone&rdquo; 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.</p>
+
+<p>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.</p>
+
+<div class="figright" style="width:283px;">
+<span class="pagenum" title="Page&nbsp;144">&nbsp;</span><a name="Page_144" id="Page_144"></a><a name="fig79" id="fig79"></a>
+<img src="images/fig079.png" width="283" height="510"
+alt="Fig.&nbsp;79." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;79.</span>&mdash;<i>A</i>, ripe ovule of <i>Monotropa uniflora</i>, in
+optical section, &times;&nbsp;100. <i>m</i>, micropyle. <i>e</i>, embryo sac. <i>B</i>, the
+embryo sac, &times;&nbsp;300. At the top is the egg apparatus, consisting of the
+two synergid&aelig; (<i>s</i>), and the egg cell (<i>o</i>). In the centre is the
+&ldquo;endosperm nucleus&rdquo; (<i>k</i>). At the bottom, the &ldquo;<ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;antipedal&rsquo;.">antipodal</ins>
+cells&rdquo; (<i>g</i>).</p>
+</div>
+
+<blockquote><p>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 &ldquo;Indian pipe&rdquo; or
+&ldquo;ghost flower,&rdquo; 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 <a href="#fig115">Figure&nbsp;115</a>, <i>L</i>.)</p>
+
+<p>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.</p>
+
+<p>The ovules are attached to a stalk, and each consists of about two
+layers of colorless cells enclosing a central, large, oblong cell
+(<a href="#fig79">Fig.&nbsp;79</a>, <i>A</i>, <i>E</i>), 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 (<i>k</i>) (or possibly two which
+afterward unite into one), and at each end three cells. Those at the
+base (<i>g</i>) probably represent the prothallium, and those at the upper
+end a very rudimentary archegonium, here generally called the &ldquo;egg
+apparatus.&rdquo;</p>
+
+<p>Of the three cells of the &ldquo;egg apparatus&rdquo; the lower (<i>o</i>) one is the
+egg cell; the others are called &ldquo;synergid&aelig;.&rdquo; 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.</p>
+
+<p>The pollen spores of many angiosperms will germinate very easily<span class="pagenum" title="Page&nbsp;145">&nbsp;</span><a name="Page_145" id="Page_145"></a> in a
+solution of common sugar in water: about fifteen per&nbsp;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 (<a href="#fig79">Fig.&nbsp;79</a>).</p></blockquote>
+
+<div class="figleft" style="width:198px;">
+<a name="fig80" id="fig80"></a>
+<img src="images/fig080.png" width="198" height="312"
+alt="Fig.&nbsp;80." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;80.</span>&mdash;Germinating pollen spores of the sweet pea,
+&times;&nbsp;200.</p>
+</div>
+
+<p>The upper part of the pistil is variously modified, having either
+little papill&aelig; 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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+
+<h4><a name="classang" id="classang"></a><span class="pagenum" title="Page&nbsp;146">&nbsp;</span><a name="Page_146" id="Page_146"></a>Classification of the Angiosperms.</h4>
+
+<p>The angiosperms are divided into two sub-classes: I.&nbsp;<i>Monocotyledons</i>
+and II.&nbsp;<i>Dicotyledons</i>.</p>
+
+<p>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.</p>
+
+<p>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 <i>Trillium</i>
+(<a href="#fig83">Fig.&nbsp;83</a>, <i>A</i>) are common and easily studied forms, but the leaves are
+not of the type common to most monocotyledons.</p>
+
+<p>The yellow adder-tongue (<i>Erythronium americanum</i>) (<a href="#fig81">Fig.&nbsp;81</a>) 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 (<i>B</i>) to whose base numerous
+roots (<i>r</i>) are attached. Rising from between the leaves is a slender,
+leafless stalk bearing a single, nodding flower at the top.</p>
+
+<p>The leaves are perfectly smooth, dull purplish red on the<span class="pagenum" title="Page&nbsp;147">&nbsp;</span><a name="Page_147" id="Page_147"></a> 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.</p>
+
+<div class="figcenter" style="width:596px;">
+<a name="fig81" id="fig81"></a>
+<img src="images/fig081.png" width="596" height="491"
+alt="Fig.&nbsp;81." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;81.</span>&mdash;<i>A</i>, plant of the yellow adder-tongue
+(<i>Erythronium americanum</i>), &times;&nbsp;&#8531;. <i>B</i>, the bulb of the same, &times;&nbsp;&frac12;. <i>r</i>,
+roots. <i>C</i>, section of <i>B</i>. <i>st.</i> the base of the stem bearing the
+bulb for next year (<i>b</i>) at its base. <i>D</i>, a single petal and stamen,
+&times;&nbsp;&frac12;. <i>f</i>, the filament. <i>an.</i> anther. <i>E</i>, the gyn&#339;cium (pistil), &times;&nbsp;1.
+<i>o</i>, ovary. <i>st.</i> style. <i>z</i>, stigma. <i>F</i>, a full-grown fruit, &times;&nbsp;&frac12;.
+<i>G</i>, section of a full-grown macrosporangium (ovule), &times;&nbsp;25: <span class="smcap">i</span>, <span class="smcap">ii</span>, the
+two integuments. <i>sp.</i> macrospore (embryo sac). <i>H</i>, cross-section of
+the ripe anther, &times;&nbsp;12. <i>I</i>, a single pollen spore, &times;&nbsp;150, showing the
+two nuclei (<i>n</i>, <i>n&#697;</i>). <i>J</i>, a ripe seed, &times;&nbsp;2. <i>K</i>, the same, in
+longitudinal section. <i>em.</i> the embryo. <i>L</i>, cross-section of the
+stem, &times;&nbsp;12. <i>fb.</i> fibro-vascular bundle. <i>M</i>, diagram of the flower.</p>
+</div>
+
+<p>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.&nbsp;<i>C</i>, <i>b</i>)
+already forming inside it, the young <span class="pagenum" title="Page&nbsp;148">&nbsp;</span><a name="Page_148" id="Page_148"></a>bulb arising as a bud at the
+base of the stem of the present year.</p>
+
+<p>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.</p>
+
+<p>The next two circles are composed of the sporophylls bearing the
+pollen spores.<a name="FNanchor_12_12" id="FNanchor_12_12"></a><a href="#Footnote_12_12" class="fnanchor">[12]</a> These are the stamens, and taken collectively are
+known as the &ldquo;<i>Andr&#339;cium</i>.&rdquo; Each leaf or stamen consists of two
+distinct portions, a delicate stalk or &ldquo;filament&rdquo; (<i>D</i>, <i>f</i>), and the
+upper spore-bearing part, the &ldquo;anther&rdquo; (<i>an.</i>). 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
+(&ldquo;connective&rdquo;) (Fig.&nbsp;<i>H</i>).</p>
+
+<p>The central circle of leaves, the carpels (collectively the
+&ldquo;gyn&#339;cium&rdquo;) are completely united to form a compound pistil (<a href="#fig81">Fig.&nbsp;81</a>,
+<i>E</i>). This shows three distinct portions, the ovule-bearing portion
+below (<i>o</i>), the &ldquo;ovary,&rdquo; a stalk above (<i>st.</i>), the &ldquo;style,&rdquo; and the
+receptive portion (<i>z</i>) at the top, the &ldquo;stigma.&rdquo; 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 (&ldquo;placenta&rdquo;).</p>
+
+<p><span class="pagenum" title="Page&nbsp;149">&nbsp;</span><a name="Page_149" id="Page_149"></a>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 (<i>F</i>)
+is full-grown about a month after the flower opens, and finally
+separates into three parts, and discharges the seeds. These are quite
+large (<a href="#fig81">Fig.&nbsp;81</a>, <i>J</i>) and covered with a yellowish brown <span class="pagenum" title="Page&nbsp;150">&nbsp;</span><a name="Page_150" id="Page_150"></a>outer coat,
+and provided with a peculiar, whitish, spongy appendage attaching it
+to the placenta. A longitudinal section of a ripe seed (<i>K</i>) shows the
+very small, nearly triangular embryo (<i>em.</i>), while the rest of the
+cavity of the seed is filled with a white, starch-bearing tissue, the
+endosperm.</p>
+
+<div class="figcenter" style="width:605px;">
+<a name="fig82" id="fig82"></a>
+<img src="images/fig082.png" width="605" height="479"
+alt="Fig.&nbsp;82." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;82.</span>&mdash;<i>Erythronium</i>. <i>A</i>, a portion of the wall of
+the anther, &times;&nbsp;150. <i>B</i>, a single epidermal cell from the petal, &times;&nbsp;150.
+<i>C</i>, cross-section of a fibro-vascular bundle of the stem, &times;&nbsp;150.
+<i>tr.</i> vessels. <i>D</i>, <i>E</i>, longitudinal section of the same, showing the
+markings of the vessels, &times;&nbsp;150. <i>F</i>, a bit of the epidermis from the
+lower surface of a leaf, showing the breathing pores, &times;&nbsp;50. <i>G</i>, a
+single breathing pore, &times;&nbsp;200. <i>H</i>, cross-section of a leaf, &times;&nbsp;50.
+<i>st.</i> a breathing pore. <i>m</i>, the mesophyll. <i>fb.</i> a vein. <i>I</i>,
+cross-section of a breathing pore, &times;&nbsp;200. <i>J</i>, young embryo, &times;&nbsp;150.</p>
+</div>
+
+<blockquote><p>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.</p>
+
+<p>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 (<a href="#fig82">Fig.&nbsp;82</a>, <i>G</i>).
+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 <a href="#fig82">Figure&nbsp;82</a>, <i>I</i>.</p>
+
+<p>The body of the leaf is made up of chlorophyll-bearing cells of
+irregular shape and with large air spaces between (<i>H</i>, <i>m</i>). The
+veins traversing this tissue are fibro-vascular bundles of a type
+structure similar to that of the stem, which will be described
+presently.</p>
+
+<p>The stem is made up principally of large cells with thin walls, which
+in cross-section show numerous small, triangular, intercellular spaces
+(<i>i</i>) at the angles. These cells contain, usually, more or less
+starch. The fibro-vascular bundles (<i>C</i>) 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 (<i>C</i>, <i>tr.</i>) 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.</p>
+
+<p>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
+<span class="pagenum" title="Page&nbsp;151">&nbsp;</span><a name="Page_151" id="Page_151"></a>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 (<i>B</i>), 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.</p>
+
+<p>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 (<a href="#fig81">Fig.&nbsp;81</a>, <i>H</i>). 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
+(<a href="#fig82">Fig.&nbsp;82</a>, <i>A</i>), and which, like these, are formed shortly before the
+pollen sacs open. The pollen spores (<a href="#fig81">Fig.&nbsp;81</a>, <i>I</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 (<i>n</i>, <i>ni.</i>), 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 (<i>Tradescantia</i>)
+and <i>Scilla</i>.</p>
+
+<p>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)
+(<a href="#fig81">Fig.&nbsp;81</a>, <i>G</i>, <i>f</i>), the body of the ovule being bent up so as to lie
+against the stalk. Such an inverted ovule is called technically,
+&ldquo;anatropous.&rdquo; 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 (<span class="smcap">i</span>, <span class="smcap">ii</span>) instead of the single one found in
+the pine.</p>
+
+<p>As the seed develops, the embryo sac (<i>G</i>, <i>sp.</i>) enlarges so as to
+occupy pretty much the whole space of the seed. At first it is nearly
+filled with <span class="pagenum" title="Page&nbsp;152">&nbsp;</span><a name="Page_152" id="Page_152"></a>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 &ldquo;endosperm
+cells,&rdquo; 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 (<a href="#fig81">Fig.&nbsp;81</a>,
+<i>K</i>, <i>em.</i>, <a href="#fig82">Fig.&nbsp;82</a>, <i>J</i>), 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.</p></blockquote>
+
+<p>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 (<a href="#fig81">Fig.&nbsp;81</a>, <i>J</i>, <i>K</i>).</p>
+
+
+
+
+<hr />
+<h2><span class="pagenum" title="Page&nbsp;153">&nbsp;</span><a name="Page_153" id="Page_153"></a><a name="CHAPTER_XVI" id="CHAPTER_XVI"></a>CHAPTER XVI.
+<br />
+<small>CLASSIFICATION OF THE MONOCOTYLEDONS.</small></h2>
+
+
+<p><span class="smcap">In</span> 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.</p>
+
+<p>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&#8217;s
+classification, the monocotyledons may be divided into seven groups;
+viz., I.&nbsp;<i>Liliiflor&aelig;</i>; II.&nbsp;<i>Enantioblast&aelig;</i>; III.&nbsp;<i>Spadiciflor&aelig;</i>;
+IV.&nbsp;<i>Glumace&aelig;</i>; V.&nbsp;<i>Scitamine&aelig;</i>; VI.&nbsp;<i>Gynandr&aelig;</i>; VII.&nbsp;<i>Helobi&aelig;</i>.</p>
+
+
+<h4><a name="lilli" id="lilli"></a><span class="smcap">Order I</span>.&mdash;<i>Liliiflor&aelig;</i>.</h4>
+
+<p>The plants of this group agree in their general structure with the
+adder&#8217;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 (&ldquo;bear grass,&rdquo; &ldquo;Spanish bayonet&rdquo;) 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 <span class="pagenum" title="Page&nbsp;154">&nbsp;</span><a name="Page_154" id="Page_154"></a>yearly from
+underground bulbs, tubers, <i>e.g.</i> <i>Trillium</i> (<a href="#fig83">Fig.&nbsp;83</a>, <i>A</i>), or
+thickened, creeping stems, or root stocks (rhizomes). Good examples of
+the last are the Solomon&#8217;s-seal (<a href="#fig83">Fig.&nbsp;83</a>, <i>B</i>), <i>Medeola</i> (<i>C</i>, <i>D</i>),
+and iris (<a href="#fig84">Fig.&nbsp;84</a> <i>A</i>). One family, the yams (<i>Dioscore&aelig;</i>), of which
+we have one common native species, the wild yam (<i>Dioscorea villosa</i>),
+have broad, netted-veined leaves and are twining plants, while another
+somewhat similar family (<i>Smilace&aelig;</i>) climb by means of tendrils at the
+bases of the leaves. Of the latter the &ldquo;cat-brier&rdquo; or &ldquo;green-brier&rdquo; is
+a familiar representative.</p>
+
+<div class="figcenter" style="width:622px;">
+<a name="fig83" id="fig83"></a>
+<img src="images/fig083.png" width="622" height="484"
+alt="Fig.&nbsp;83." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;83.</span>&mdash;Types of <i>Liliiflor&aelig;</i>. <i>A</i>, <i>Trillium</i>, &times;&nbsp;&frac14;.
+<i>B</i>, single flower of Solomon&#8217;s-seal (<i>Polygonatum</i>), &times;&nbsp;1. <i>C</i>, upper
+part of a plant. <i>D</i>, underground stem (rhizome) of Indian cucumber
+root (<i>Medeola</i>), &times;&nbsp;&frac12;. <i>E</i>, a rush (<i>Juncus</i>), &times;&nbsp;1. <i>F</i>, a single
+flower, &times;&nbsp;2. <i>A&ndash;D</i>, <i>Liliace&aelig;</i>; <i>E</i>, <i>Juncace&aelig;</i>.</p>
+</div>
+
+<p>The flowers are for the most part conspicuous, and in plan like that
+of the adder&#8217;s-tongue; but some, like the rushes (<a href="#fig83">Fig.&nbsp;83</a>, <i>E</i>), have
+small, inconspicuous flowers; and others, like the yams and smilaxes,
+have flowers of two kinds, male and female.</p>
+
+<div class="figcenter" style="width:646px;">
+<span class="pagenum" title="Page&nbsp;155">&nbsp;</span><a name="Page_155" id="Page_155"></a><a name="fig84" id="fig84"></a>
+<img src="images/fig084.png" width="646" height="488"
+alt="Fig.&nbsp;84." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;84.</span>&mdash;Types of <i>Liliiflor&aelig;</i>. <i>A</i>, flower of the
+common blue-flag (<i>Iris</i>), &times;&nbsp;&frac12; (<i>Iridace&aelig;</i>). <i>B</i>, the petal-like upper
+part of the pistil, seen from below, and showing a stamen (<i>an.</i>).
+<i>st.</i> the stigma, &times;&nbsp;&frac12;. <i>C</i>, the young fruit, &times;&nbsp;&frac12;. <i>D</i>, section of the
+same, &times;&nbsp;1. <i>E</i>, diagram of the flower. <i>F</i>, part of a plant of the
+so-called &ldquo;gray moss&rdquo; (<i>Tillandsia</i>), &times;&nbsp;&frac12; (<i>Bromeliace&aelig;</i>). <i>G</i>, a
+single flower, &times;&nbsp;2. <i>H</i>, a seed, showing the fine hairs attached to
+it, &times;&nbsp;1. <i>I</i>, plant of pickerel-weed (<i>Pontederia</i>), &times;&nbsp;&frac14;
+(<i>Pontederiace&aelig;</i>). <i>J</i>, a single flower, &times;&nbsp;1. <i>K</i>, section of the
+ovary, &times;&nbsp;4.</p>
+</div>
+
+<p>The principal family of the <i>Liliiflor&aelig;</i> is the <i>Liliace&aelig;</i>, including
+some of the most beautiful of all flowers. All of the true lilies
+(<i>Lilium</i>), as well as the day lilies (<i>Funkia</i>, <i>Hemerocallis</i>) 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 (<i>Lilium</i>), various species of <i>Trillium</i> (<a href="#fig83">Fig.&nbsp;83</a>, <i>A</i>),
+Solomon&#8217;s-seal (<i>Polygonatum</i>) (<a href="#fig83">Fig.&nbsp;83</a>, <i>B</i>), bellwort (<i>Uvularia</i>),
+and others. In all of these, except <i>Trillium</i>, 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 <i>Liliace&aelig;</i> may be <span class="pagenum" title="Page&nbsp;156">&nbsp;</span><a name="Page_156" id="Page_156"></a>either a pod, like that of the
+adder&#8217;s-tongue, or a berry, like that of asparagus or Solomon&#8217;s-seal.</p>
+
+<div class="figright" style="width:237px;">
+<a name="fig85" id="fig85"></a>
+<img src="images/fig085.png" width="237" height="306"
+alt="Fig.&nbsp;85." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;85.</span>&mdash;<i>Enantioblast&aelig;</i>. <i>A</i>, inflorescence of the
+common spiderwort (<i>Tradescantia</i>), &times;&nbsp;&frac12; (<i>Commelyne&aelig;</i>). <i>B</i>, a single
+stamen, showing the hairs attached to the filament, &times;&nbsp;2. <i>C</i>, the
+pistil, &times;&nbsp;2.</p>
+</div>
+
+<p>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 (<i>Iridace&aelig;</i>), represented by the wild
+blue-flag (<i>Iris versicolor</i>) (<a href="#fig84">Fig.&nbsp;84</a>, <i>A</i>, <i>E</i>), as well as by
+numerous cultivated species. In iris the carpels are free above and
+colored like the petals (<i>B</i>), 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 &ldquo;blue-eyed grass&rdquo; (<i>Sisyrinchium</i>).</p>
+
+<p>The blue pickerel-weed (<i>Pontederia</i>) is the type of a family of which
+there are few common representatives (<a href="#fig84">Fig.&nbsp;84</a>, <i>I</i>, <i>K</i>).</p>
+
+<p>The last family of the order is the <i>Bromeliace&aelig;</i>, 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 &ldquo;gray moss&rdquo;
+(<i><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Tillandsea&rsquo;.">Tillandsia</ins></i>) (<a href="#fig84">Fig.&nbsp;84</a>, <i>F</i>, <i>H</i>). 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.</p>
+
+
+<h4><a name="enan" id="enan"></a><span class="smcap">Order II</span>.&mdash;<i>Enantioblast&aelig;</i>.</h4>
+
+<p>The second order of the monocotyledons, <i>Enantioblast&aelig;</i>, includes very
+few common plants. The most familiar examples <span class="pagenum" title="Page&nbsp;157">&nbsp;</span><a name="Page_157" id="Page_157"></a>are the various species
+of <i>Tradescantia</i> (<a href="#fig88">Fig.&nbsp;88</a>), some of which are native, others exotic.
+Of the cultivated forms the commonest is one sometimes called
+&ldquo;wandering-jew,&rdquo; 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, <i>Commelyne&aelig;</i>.</p>
+
+
+<h4><a name="spad" id="spad"></a><span class="smcap">Order III</span>.&mdash;<i>Spadiciflor&aelig;</i>.</h4>
+
+<p>The third order of the monocotyledons, <i>Spadiciflor&aelig;</i>, 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.</p>
+
+<p>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 (<i>Aroide&aelig;</i>), of which the
+calla (<i>Richardia</i>) is a very familiar cultivated example. Of wild
+forms the sweet-flag (<i>Acorus</i>), Jack-in-the-pulpit (<i>Aris&aelig;ma</i>)
+(<a href="#fig86">Fig.&nbsp;86</a>, <i>A</i>, <i>D</i>), skunk-cabbage (<i>Symplocarpus</i>), and wild calla
+may be noted. In <i>Aris&aelig;ma</i> (<a href="#fig86">Fig.&nbsp;86</a>, <i>A</i>) the flowers are borne only
+on the base of the spadix, and the plant is di&#339;cious. The flowers are
+of the simplest structure, the female consisting of a single carpel,
+and the male of four <span class="pagenum" title="Page&nbsp;158">&nbsp;</span><a name="Page_158" id="Page_158"></a>stamens (<i>C</i>, <i>D</i>). 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 (<a href="#fig86">Fig.&nbsp;86</a>,
+<i>B</i>).</p>
+
+<div class="figcenter" style="width:605px;">
+<a name="fig86" id="fig86"></a>
+<img src="images/fig086.png" width="605" height="492"
+alt="Fig.&nbsp;86." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;86.</span>&mdash;Types of <i>Spadiciflor&aelig;</i>. <i>A</i>, inflorescence
+of Jack-in-the-pulpit (<i>Aris&aelig;ma</i>, <i>Aroide&aelig;</i>). The flowers (<i>fl.</i>) 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, &times;&nbsp;&frac12;.
+<i>B</i>, leaf of the same plant, &times;&nbsp;&frac14;. <i>C</i>, vertical section of a female
+flower, &times;&nbsp;2. <i>D</i>, three male flowers, each consisting of four stamens,
+&times;&nbsp;2. <i>E</i>, two plants of a duck-weed (<i>Lemna</i>), the one at the left is
+in flower, &times;&nbsp;4. <i>F</i>, another common species. <i>L</i>, <i>Trisulea</i>, &times;&nbsp;1.
+<i>G</i>, male flower of <i>E</i>, &times;&nbsp;25. <i>H</i>, optical section of the female
+flower, showing the single ovule (<i>ov.</i>), &times;&nbsp;25. <i>I</i>, part of the
+inflorescence of the bur-reed (<i>Sparganium</i>), with female flowers, &times;&nbsp;&frac12;
+(<i>Typhace&aelig;</i>). <i>J</i>, a single, female flower, &times;&nbsp;2. <i>K</i>, a ripe fruit,
+&times;&nbsp;1. <i>L</i>, longitudinal section of the same. <i>M</i>, two male flowers,
+&times;&nbsp;1. <i>N</i>, a pond-weed (<i>Potomogeton</i>), &times;&nbsp;1 (<i>Naiadace&aelig;</i>). <i>O</i>, a
+single flower, &times;&nbsp;2. <i>P</i>, the same, with the perianth removed, &times;&nbsp;2.
+<i>Q</i>, fruit of the same, &times;&nbsp;2.</p>
+</div>
+
+<p><span class="pagenum" title="Page&nbsp;159">&nbsp;</span><a name="Page_159" id="Page_159"></a>Probably to be regarded as reduced aroids are the duck-weeds
+(<i>Lemnace&aelig;</i>) (<a href="#fig86">Fig.&nbsp;86</a>, <i>F</i>, <i>H</i>), 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 (<i>Wolffia</i>) has no roots nor any trace of fibro-vascular
+bundles. The flowers are reduced to a single stamen or carpel (Figs.
+<i>E</i>, <i>G</i>, <i>H</i>).</p>
+
+<p>The cat-tail (<i>Typha</i>) and bur-reed (<i>Sparganium</i>) (<a href="#fig86">Fig.&nbsp;86</a>, <i>I</i>, <i>L</i>)
+are common representatives of the family <i>Typhace&aelig;</i>, and the
+pond-weeds (<i>Naias</i> and <i>Potomogeton</i>) are common examples of the
+family <i>Naiade&aelig;</i>. These are aquatic plants, completely submerged
+(<i>Naias</i>), or sometimes partially floating (<i>Potomogeton</i>). 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.</p>
+
+<p>The largest members of the group are the screw-pines (<i>Pandane&aelig;</i>) and
+the palms (<i>Palm&aelig;</i>). 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 (<i>Sabal</i> and <i>Cham&aelig;rops</i>) are
+the best known.</p>
+
+<p>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 (<i>Ph&#339;nix dactylifera</i>)
+and the cocoanut (<i>Cocos nucifera</i>) are the best known. The apparently
+compound (&ldquo;pinnate&rdquo; 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.</p>
+
+<p>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 <span class="pagenum" title="Page&nbsp;160">&nbsp;</span><a name="Page_160" id="Page_160"></a>structure may be had by cutting across a
+corn-stalk, which is built on precisely the same pattern.</p>
+
+
+<h4><a name="glum" id="glum"></a><span class="smcap">Order IV</span>.&mdash;<i>Glumace&aelig;</i>.</h4>
+
+<p>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, pale&aelig;) <span class="pagenum" title="Page&nbsp;161">&nbsp;</span><a name="Page_161" id="Page_161"></a>which are closely set, so as to nearly conceal the
+flowers. The flowers are either hermaphrodite or unisexual.</p>
+
+<div class="figcenter" style="width:640px;">
+<a name="fig87" id="fig87"></a>
+<img src="images/fig087.png" width="640" height="493"
+alt="Fig.&nbsp;87." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;87.</span>&mdash;Types of <i>Glumace&aelig;</i>. <i>A</i>, a sedge, <i>Carex</i>
+(<i>Cyperace&aelig;</i>). &#9794;, the male; &#9792;, the female flowers, &times;&nbsp;&frac12;. <i>B</i>, a single
+male flower, &times;&nbsp;2. <i>C</i>, a female flower, &times;&nbsp;2. <i>D</i>, fruiting spike of
+another <i>Carex</i>, &times;&nbsp;&frac12;. <i>E</i>, a single fruit, &times;&nbsp;1. <i>F</i>, the same, with
+the outer envelope removed, and slightly enlarged. <i>G</i>, section of
+<i>F</i>, &times;&nbsp;3. <i>em.</i> the embryo. <i>H</i>, a bulrush, <i>Scirpus</i> (<i>Cyperace&aelig;</i>),
+&times;&nbsp;&frac12;. <i>I</i>, a single spikelet, &times;&nbsp;2. <i>J</i>, a single flower, &times;&nbsp;3. <i>K</i>, a
+spikelet of flowers of the common orchard grass, <i>Dactylis</i>
+(<i>Gramine&aelig;</i>), &times;&nbsp;2. <i>L</i>, a single flower, &times;&nbsp;2. <i>M</i>, the base of a leaf,
+showing the split sheath encircling the stem, &times;&nbsp;1. <i>N</i>, section of a
+kernel of corn, showing the embryo (<i>em.</i>), &times;&nbsp;2.</p>
+</div>
+
+<p>There are two well-marked families, the sedges (<i>Cyperace&aelig;</i>) and the
+grasses (<i>Gramine&aelig;</i>). The former have solid, often triangular stems,
+and the sheath at the base of the leaves is not split. The commonest
+genera are <i>Carex</i> (<a href="#fig87">Fig.&nbsp;87</a>, <i>A</i>, <i>G</i>) and <i>Cyperus</i>, of which there
+are many common species, differing very little and hard to
+distinguish. There are several common species of <i>Carex</i> 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, <i>e.g.</i> the
+bulrushes (<i>Scirpus</i>) (<a href="#fig87">Fig.&nbsp;87</a>, <i>H</i>), the flowers are hermaphrodite,
+<i>i.e.</i> contain both stamens and pistils. The fruit (<a href="#fig87">Fig.&nbsp;87</a>, <i>F</i>) 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 (<a href="#fig87">Fig.&nbsp;87</a>, <i>G</i>). 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.</p>
+
+<p>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 (<a href="#fig87">Fig.&nbsp;87</a>, <i>L</i>) 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
+&ldquo;tassel,&rdquo; and the female flowers lower down forming the ear. The
+&ldquo;silk&rdquo; 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 (<i>N</i>, <i>em.</i>).</p>
+
+<p><span class="pagenum" title="Page&nbsp;162">&nbsp;</span><a name="Page_162" id="Page_162"></a>While most of the grasses are comparatively small plants, a few of
+them are almost tree-like in their proportions, the species of bamboo
+(<i>Bambusa</i>) sometimes reaching a height of twenty to thirty metres,
+with stems thirty to forty centimetres in diameter.</p>
+
+
+<h4><a name="scit" id="scit"></a><span class="smcap">Order V</span>.&mdash;<i>Scitamine&aelig;</i>.</h4>
+
+<div class="figcenter" style="width:635px;">
+<a name="fig88" id="fig88"></a>
+<img src="images/fig088.png" width="635" height="427"
+alt="Fig.&nbsp;88." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;88.</span>&mdash;<i>Scitamine&aelig;</i>. <i>A</i>, upper part of a flowering
+plant of Indian shot (<i>Canna</i>), much reduced in size (<i>Cannace&aelig;</i>).
+<i>B</i>, a single flower, &times;&nbsp;&frac12;. <i>C</i>, the single stamen (<i>an.</i>), and
+petal-like pistil (<i>gy.</i>), &times;&nbsp;1. <i>D</i>, section of the ovary, &times;&nbsp;2. <i>E</i>,
+diagram of the flower. The place of the missing stamens is indicated
+by small circles. <i>F</i>, fruit, &times;&nbsp;&frac12;. <i>G</i>, section of an unripe seed.
+<i>em.</i> embryo. <i>p</i>, perisperm, &times;&nbsp;2.</p>
+</div>
+
+<p>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 <i>Canna</i>
+(<a href="#fig88">Fig.&nbsp;88</a>) are common in gardens, where they are prized for their
+large, richly-colored <span class="pagenum" title="Page&nbsp;163">&nbsp;</span><a name="Page_163" id="Page_163"></a>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 <i>Canna</i> only a single stamen is found; or if more are
+present, they are reduced to petal-like rudiments. The single, perfect
+stamen (<a href="#fig88">Fig.&nbsp;88</a>, <i>C</i>, <i>an.</i>) has the filament broad and colored like
+the petals, and the anther attached to one side. The pistil (<i>gy.</i>) 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 (<i>o</i>) is inferior, and
+covered on the outside with little papill&aelig; that afterward form short
+spines on the outside of the fruit (<i>F</i>).</p>
+
+<p>The seeds are large, but the embryo is very small. A section of a
+nearly ripe seed shows the embryo (<i>em.</i>) 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 &ldquo;perisperm.&rdquo;</p>
+
+<p>Of food plants belonging to this order, the banana (<i>Musa</i>) is much
+the most important. Others of more or less value are species of
+arrowroot (<i>Maranta</i>) and ginger (<i>Zingiber</i>).</p>
+
+<p>There are three families: I.&nbsp;<i>Musace&aelig;</i> (banana family);
+II.&nbsp;<i>Zingiberace&aelig;</i> (ginger family); and III.&nbsp;<i>Cannace&aelig;</i> (<i>Canna</i>,
+<i>Maranta</i>).</p>
+
+
+<h4><a name="gyn" id="gyn"></a><span class="smcap">Order VI</span>.&mdash;<i>Gynandr&aelig;</i>.</h4>
+
+<p>By far the greater number of the plants of this order belong to the
+orchis family (<i>Orchide&aelig;</i>), the second family of the order
+<span class="pagenum" title="Page&nbsp;164">&nbsp;</span><a name="Page_164" id="Page_164"></a>(<i>Apostasie&aelig;</i>), 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.</p>
+
+<div class="figcenter" style="width:537px;">
+<a name="fig89" id="fig89"></a>
+<img src="images/fig089.png" width="537" height="488"
+alt="Fig.&nbsp;89." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;89.</span>&mdash;<i>Gynandr&aelig;</i>. <i>A</i>, inflorescence of the showy
+orchis (<i>Orchis spectabilis</i>), &times;&nbsp;1 (<i>Orchide&aelig;</i>). <i>B</i>, a single flower,
+with the upper leaves of the perianth turned back to show the column
+(<i>x</i>). <i>sp.</i> the spur attached to the lower petal or lip. <i>o</i>, the
+ovary, &times;&nbsp;1. <i>C</i>, the column seen from in front. <i>an.</i> the stamen.
+<i>gy.</i> the stigmatic surface, &times;&nbsp;1. <i>D</i>, the two pollen masses attached
+to a straw, which was inserted into the flower, by means of the viscid
+disc (<i>d</i>): <span class="smcap">i</span>, the masses immediately after their withdrawal; <span class="smcap">ii</span>, <span class="smcap">iii</span>,
+the same a few minutes later, showing the change in position. <i>E</i>,
+diagram of the flower; the position of the missing stamens indicated
+by small circles.</p>
+</div>
+
+<p>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 <span class="pagenum" title="Page&nbsp;165">&nbsp;</span><a name="Page_165" id="Page_165"></a>ovary) of the inner set. This
+petal, known as the &ldquo;lip&rdquo; or &ldquo;labellum,&rdquo; 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 <a href="#fig89">Fig.&nbsp;89</a>, <i>B</i>). In all of the orchids except the
+lady&#8217;s-slippers (<i>Cypripedium</i>) (<a href="#fig90">Fig.&nbsp;90</a>, <i>B</i>), only one perfect
+stamen is developed, and this is united with the three styles to form
+a special structure known, as the &ldquo;column&rdquo; or &ldquo;gynostemium&rdquo; (<a href="#fig89">Fig.&nbsp;89</a>,
+<i>B</i>, <i>C</i>). The pollen spores are usually aggregated into two or four
+waxy masses (&ldquo;pollinia,&rdquo; 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.</p>
+
+<div class="figcenter" style="width:592px;">
+<a name="fig90" id="fig90"></a>
+<img src="images/fig090.png" width="592" height="480"
+alt="Fig.&nbsp;90." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;90.</span>&mdash;Forms of <i>Orchide&aelig;</i>. <i>A</i>, putty-root
+(<i>Aplectrum</i>), &times;&nbsp;1. <i>B</i>, yellow lady&#8217;s-slipper (<i>Cypripedium</i>), &times;&nbsp;&frac12;.
+<i>C</i>, the column of the same, &times;&nbsp;1. <i>an.</i> one of the two perfect
+stamens. <i>st.</i> sterile, petal-like stamen. <i>gy.</i>. stigma. <i>D</i>,
+<i>Arethusa</i>, &times;&nbsp;&frac12;. <i>E</i>, section of the column, &times;&nbsp;1: <i>an.</i> stamen. <i>gy.</i>
+stigma. <i>F</i>, the same, seen from in front. <i>G</i>, <i>Habenaria</i>, &times;&nbsp;1. <i>H</i>,
+<i>Calopogon</i>, &times;&nbsp;1. In the last the ovary is not twisted, so that the
+lip (<i>L</i>) lies on the upper side of the flower.</p>
+</div>
+
+<p><span class="pagenum" title="Page&nbsp;166">&nbsp;</span><a name="Page_166" id="Page_166"></a>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 (<a href="#fig90">Fig.&nbsp;90</a>, <i>C</i>, <i>st.</i>).</p>
+
+<p>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.</p>
+
+<p>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
+&ldquo;epiphytes&rdquo;; that is, they grow upon the trunks and branches of trees.
+One genus, <i>Vanilla</i>, 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.</p>
+
+<p>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&#8217;s-slippers, of which we have six species at the north. The most
+beautiful is the showy lady&#8217;s-slipper (<i>Cypripedium spectabile</i>),
+whose large, pink and white flowers rival in beauty many of the
+choicest tropical orchids. Many of the <i>Habenarias</i>, including the
+yellow and purple fringed orchids, are strikingly beautiful as are the
+<i>Arethuse&aelig;</i> (<i>Arethusa</i>, <i>Pogonia</i>, <i>Calopogon</i>). The last of these
+(<a href="#fig90">Fig.&nbsp;90</a>, <i>H</i>) differs from all our other native orchids in having the
+ovary untwisted so that the labellum lies on the upper side of the
+flower.</p>
+
+<p>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 <span class="pagenum" title="Page&nbsp;167">&nbsp;</span><a name="Page_167" id="Page_167"></a>roots (<i>Corallorhiza</i>), of which
+there are several species, are examples of these, and another closely
+related form, the putty-root (<i>Aplectrum</i>) (<a href="#fig90">Fig.&nbsp;90</a>, <i>A</i>), has the
+flowering stems like those of <i>Corallorhiza</i>, but there is a single,
+large, plaited leaf sent up later.</p>
+
+
+<h4><a name="helo" id="helo"></a><span class="smcap">Order VII</span>.&mdash;<i>Helobi&aelig;</i>.</h4>
+
+<p>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, <i>Juncagine&aelig;</i>, includes a few inconspicuous plants
+with grass-like or rush-like leaves, and small, greenish or yellowish
+flowers (<i>e.g.</i> arrow-grass, <i>Triglochin</i>).</p>
+
+<p>The second family (<i>Alismace&aelig;</i>) contains several large and showy
+species, inhabitants of marshes. Of these the water-plantain
+(<i>Alisma</i>), 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
+(<i>Sagittaria</i>) 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 gyn&#339;cium
+(<a href="#fig91">Fig.&nbsp;91</a>, <i>B</i>) consists of numerous, separate carpels attached to a
+globular receptacle. The sepals are green and much smaller than the
+white petals. The leaves (<i>F</i>) are broad, and, besides the thickened,
+parallel veins, have numerous smaller ones connecting these.</p>
+
+<div class="figcenter" style="width:597px;">
+<a name="fig91" id="fig91"></a>
+<img src="images/fig091.png" width="597" height="513"
+alt="Fig.&nbsp;91." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;91.</span>&mdash;Types of <i>Helobi&aelig;</i>. <i>A</i>, inflorescence of
+arrowhead (<i>Sagittaria</i>), with a single female flower, &times;&nbsp;&frac12;
+(<i>Alismace&aelig;</i>). <i>B</i>, section through the gyn&#339;cium, showing the numerous
+single carpels, &times;&nbsp;3. <i>C</i>, a ripe fruit, &times;&nbsp;3. <i>D</i>, a male flower, &times;&nbsp;1.
+<i>E</i>, a single stamen, &times;&nbsp;3. <i>F</i>, a leaf of <i>Sagittaria variabilis</i>,
+&times;&nbsp;&#8537;. <i>G</i>, ditch-moss (<i>Elodea</i>), with a female flower (<i>fl.</i>), &times;&nbsp;&frac12;.
+(<i>Hydrocharide&aelig;</i>). <i>H</i>, the flower, &times;&nbsp;2. <i>an.</i> the rudimentary
+stamens. <i>st.</i> the stigma. <i>I</i>, cross-section of the ovary, &times;&nbsp;4. <i>J</i>,
+male inflorescence of eel-grass (<i>Vallisneria</i>), &times;&nbsp;1. <i>K</i>, a single
+expanded male flower, &times;&nbsp;12. <i>st.</i> the stamen. <i>L</i>, a female flower,
+&times;&nbsp;1. <i>gy.</i> the stigma.</p>
+</div>
+
+<p>The last family is the <i>Hydrocharide&aelig;</i>. They are submersed aquatics,
+or a few of them with long-stalked, floating leaves. Two forms, the
+ditch-moss (<i>Elodea</i>) (<a href="#fig91">Fig.&nbsp;91</a>, <i>G</i>, <i>I</i>) and eel-grass
+(<i>Vallisneria</i>) 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 (<i>H</i>, <i>L</i>) are comparatively
+large, especially <span class="pagenum" title="Page&nbsp;168">&nbsp;</span><a name="Page_168" id="Page_168"></a>in <i>Vallisneria</i>, 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 (<a href="#fig91">Fig.&nbsp;91</a>, <i>J</i>, <i>K</i>)
+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
+<span class="pagenum" title="Page&nbsp;169">&nbsp;</span><a name="Page_169" id="Page_169"></a>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.</p>
+
+<p>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 <i>Elodea</i>, or
+a section of that of <i>Vallisneria</i>, may be used.</p>
+
+
+
+<hr />
+<h2><span class="pagenum" title="Page&nbsp;170">&nbsp;</span><a name="Page_170" id="Page_170"></a><a name="CHAPTER_XVII" id="CHAPTER_XVII"></a>CHAPTER XVII.
+<br />
+<small>DICOTYLEDONS.</small></h2>
+
+
+<div class="figleft" style="width:113px;">
+<a name="fig92" id="fig92"></a>
+<img src="images/fig092.png" width="113" height="459"
+alt="Fig.&nbsp;92." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;92.</span>&mdash;End of a branch of a horsechestnut in winter,
+showing the buds covered by the thick, brown scale leaves, &times;&nbsp;1.</p>
+</div>
+
+<p style="text-indent:0;"><span class="smcap">The</span> 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); <i>e.g.</i> 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 (&ldquo;entire&rdquo;), 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 (<a href="#fig92">Fig.&nbsp;92</a>), 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 <span class="pagenum" title="Page&nbsp;171">&nbsp;</span><a name="Page_171" id="Page_171"></a>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.</p>
+
+<p>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.</p>
+
+<p><span class="pagenum" title="Page&nbsp;172">&nbsp;</span><a name="Page_172" id="Page_172"></a>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.</p>
+
+<div class="figcenter" style="width:660px;">
+<a name="fig93" id="fig93"></a>
+<img src="images/fig093.png" width="660" height="504"
+alt="Fig.&nbsp;93." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;93.</span>&mdash;<i>A</i>, base of a plant of shepherd&#8217;s-purse
+(<i>Capsella bursa-pastoris</i>), &times;&nbsp;&frac12;. <i>r</i>, the main root. <i>B</i>, upper part
+of the inflorescence, &times;&nbsp;1. <i>C</i>, two leaves: <span class="smcap">i</span>, from the upper part;
+<span class="smcap">ii</span>, from the base of the plant, &times;&nbsp;1. <i>D</i>, a flower, &times;&nbsp;3. <i>E</i>, the
+same, with sepals and petals removed, &times;&nbsp;3. <i>F</i>, petal. <i>G</i>, sepal.
+<i>H</i>, stamen, &times;&nbsp;10. <i>f</i>, filament. <i>an.</i> anther. <i>I</i>, a fruit with one
+of the valves removed to show the seeds, &times;&nbsp;4. <i>J</i>, longitudinal
+section of a seed, &times;&nbsp;8. <i>K</i>, the embryo removed from the seed, &times;&nbsp;8.
+<i>l</i>, the first leaves (cotyledons). <i>st.</i> the stem ending in the root.
+<i>L</i>, cross-section of the stem, &times;&nbsp;20. <i>fb.</i> fibro-vascular bundle.
+<i>M</i>, a similar section of the main root, &times;&nbsp;15. <i>N</i>, diagram of the
+flower.</p>
+</div>
+
+<p>The structure of the tissues, and the peculiarities of the flower and
+fruit, will be better understood by a somewhat careful<span class="pagenum" title="Page&nbsp;173">&nbsp;</span><a name="Page_173" id="Page_173"></a> examination of
+a typical dicotyledon, and a comparison with this of examples of the
+principal orders and families.</p>
+
+<p>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&#8217;s-purse (<i>Capsella
+bursa-pastoris</i>) (Figs.&nbsp;<a href="#fig93">93</a>&ndash;<a href="#fig95">95</a>).</p>
+
+<p>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 (<a href="#fig93">Fig.&nbsp;93</a>, <i>A</i>, <i>r</i>)
+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 (<a href="#fig93">Fig.&nbsp;93</a>, <i>M</i>), shows a round,
+opaque, white, central area (<i>x</i>), the wood, surrounded by a more
+transparent, irregular ring (<i>ph.</i>), the phloem or bast; and outside
+of this is the ground tissue and epidermis.</p>
+
+<p>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<span class="pagenum" title="Page&nbsp;174">&nbsp;</span><a name="Page_174" id="Page_174"></a> branch.
+The upper leaves have frequently two smaller veins starting from the
+base of the leaf, and nearly parallel with the midrib (<i>C</i> <span class="smcap">i</span>). The
+surface of the leaves is somewhat roughened with hairs, some of which,
+if slightly magnified, look like little white stars.</p>
+
+<p>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 (<i>L</i>, <i>fb.</i>), 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.</p>
+
+<p>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 &ldquo;raceme.&rdquo; 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.&nbsp;four outer perigone leaves (sepals) (<i>F</i>), small,
+green, pointed leaves traversed by three simple veins, and together
+forming the calyx; II.&nbsp;four larger, white, inner perigone leaves
+(petals) (<i>G</i>), broad and slightly notched at the end, and tapering to
+the point of attachment. The petals collectively are known as the
+&ldquo;corolla.&rdquo; The veins of the petals fork once; III. and IV. two sets of
+stamens (<i>E</i>), the outer containing two short, and the inner, four
+longer ones arranged in pairs. Each stamen has a slender filament
+(<i>H</i>, <i>f</i>) and a two-lobed anther (<i>an.</i>). The innermost set consists
+of two carpels united into a compound pistil. The ovary is <span class="pagenum" title="Page&nbsp;175">&nbsp;</span><a name="Page_175" id="Page_175"></a>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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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 (<i>st.</i>) being bent down against the back of one of the
+cotyledons (<i>f</i>).</p>
+
+<div class="figcenter" style="width:633px;">
+<a name="fig94" id="fig94"></a>
+<img src="images/fig094.png" width="633" height="479"
+alt="Fig.&nbsp;94." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;94.</span>&mdash;<i>A</i>, cross-section of the stem of the
+shepherd&#8217;s-purse, including a fibro-vascular bundle, &times;&nbsp;150. <i>ep.</i>
+epidermis. <i>m</i>, ground tissue. <i>sh.</i> bundle sheath. <i>ph.</i> phloem.
+<i>xy.</i> xylem. <i>tr.</i> a vessel. <i>B</i>, a young root seen in optical
+section, &times;&nbsp;150. <i>r</i>, root cap. <i>d</i>, young epidermis. <i>pb.</i> ground.
+<i>pl.</i> young fibro-vascular bundle. <i>C</i> cross section of a small root,
+&times;&nbsp;150. <i>fb.</i> fibro-vascular bundle. <i>D</i>, epidermis from the lower side
+of the leaf, &times;&nbsp;150. <i>E</i>, a star-shaped hair from the surface of the
+leaf, &times;&nbsp;150. <i>F</i>, cross-section of a leaf, &times;&nbsp;150. <i>ep.</i> epidermis.
+<i>m</i>, ground tissue. <i>fb.</i> section of a vein.</p>
+</div>
+
+<blockquote><p>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 <a href="#fig94">Fig.&nbsp;94</a>,
+<i>B</i>). The end of the root, as in the fern, is covered with a root cap
+(<i>r</i>) 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 <span class="pagenum" title="Page&nbsp;176">&nbsp;</span><a name="Page_176" id="Page_176"></a>epidermis (dermatogen) (<i>d</i>), young fibro-vascular
+cylinder (plerome) (<i>pl.</i>), and young ground tissue (periblem)
+(<i>pb.</i>). The structure of the older portions of such <ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;as&rsquo;.">a</ins> 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 (<i>xy.</i>) joined in the middle, and separating the two
+phloem masses (<i>ph.</i>), 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 <span class="pagenum" title="Page&nbsp;177">&nbsp;</span><a name="Page_177" id="Page_177"></a>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 (<a href="#fig94">Fig.&nbsp;94</a>, <i>A</i>, <i>ep.</i>) 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 (<i>sh.</i>)
+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 (<i>f</i>), 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 (<i>ph.</i>). 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
+(<i>tr.</i>). The central ground tissue (pith) has large, thin-walled cells
+with numerous intercellular spaces, as in the stem of <i>Erythronium</i>.
+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.</p>
+
+<p>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.</p>
+
+<p>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 (<a href="#fig93">Fig.&nbsp;93</a>, <i>E</i>).</p>
+
+<p>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 <span class="pagenum" title="Page&nbsp;178">&nbsp;</span><a name="Page_178" id="Page_178"></a>better developed. They are like those of
+the stem, but somewhat simpler. The xylem lies on the upper side.</p>
+
+<p>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 &ldquo;palisade-parenchyma&rdquo; of the leaf.)</p></blockquote>
+
+<div class="figcenter" style="width:607px;">
+<a name="fig95" id="fig95"></a>
+<img src="images/fig095.png" width="607" height="500"
+alt="Fig.&nbsp;95." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;95.</span>&mdash;<i>A&ndash;D</i>, successive stages in the development
+of the flower of <i>Capsella</i>, &times;&nbsp;50. <i>A</i>, surface view. <i>B&ndash;D</i>, optical
+sections. <i>s</i>, sepals, <i>p</i>, petals. <i>an.</i> stamens. <i>gy.</i> pistil. <i>E</i>,
+cross-section of the young anther, &times;&nbsp;180. <i>sp.</i> spore mother cells.
+<i>F</i>, cross-section of full-grown anther. <i>sp.</i> pollen spores, &times;&nbsp;50.
+<i>F&#697;</i>, four young pollen spores, &times;&nbsp;300. <i>F&#698;</i>, pollen spores germinating
+upon the stigma, &times;&nbsp;300. <i>pt.</i> pollen tube. <i>G</i>, young pistil in
+optical section, &times;&nbsp;25. H, cross-section of a somewhat older one. <i>ov.</i>
+ovules. <i>I&ndash;L</i>, development of the ovule. <i>sp.</i> embryo sac
+(macrospore). <i>I&ndash;K</i>, &times;&nbsp;150. <i>L</i>, &times;&nbsp;50. <i>M</i>, embryo sac of a full-grown
+ovule, &times;&nbsp;150. <i>Sy.</i> <i>Synergid&aelig;</i>. <i>o</i>, egg cell. <i>n</i>, endosperm
+nucleus. <i>ant.</i> antipodal cells. <i>N&ndash;Q</i>, development of the embryo,
+&times;&nbsp;150. <i>sus.</i> suspensor.</p>
+</div>
+
+<blockquote><p>The shepherd&#8217;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 <span class="pagenum" title="Page&nbsp;179">&nbsp;</span><a name="Page_179" id="Page_179"></a>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 (<a href="#fig95">Fig.&nbsp;95</a>, <i>A</i>) 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 (<a href="#fig95">Fig.&nbsp;95</a>, <i>A</i>, <i>B</i>). The stamens (<i>C</i>, <i>an.</i>) 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 (<i>D</i>). The carpels are more
+or less united from the first, and form at first a sort of shallow cup
+with the edges turned in (<i>D</i>, <i>gy.</i>). 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 placent&aelig; meet in
+the middle and form a partition completely across the ovary (<a href="#fig95">Fig.&nbsp;95</a>,
+<i>H</i>).</p>
+
+<p>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.&nbsp;<i>E</i>, <i>F</i>) 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
+<i>Erythronium</i>.</p>
+
+<p>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.</p>
+
+<p>The young ovule (<i>I</i>, <i>J</i>) consists of a central, elongated body
+(nucellus), having a single layer of cells enclosing a large central
+cell (the macrospore or embryo sac) (<i>sp.</i>). The base of the nucellus
+is surrounded by two circular ridges (<span class="smcap">i</span>, <span class="smcap">ii</span>) of which the inner is at
+first higher than the outer one, but later (<i>K</i>, <i>L</i>), 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 (<a href="#fig95">Fig.&nbsp;95</a>,<span class="pagenum" title="Page&nbsp;180">&nbsp;</span><a name="Page_180" id="Page_180"></a> <i>L</i>). This opening
+is called the &ldquo;micropyle,&rdquo; and allows the pollen tube to enter.</p>
+
+<p>The full-grown embryo sac shows the same structure as that already
+described in <i>Monotropa</i> (page&nbsp;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 papill&aelig; (<a href="#fig95">Fig.&nbsp;95</a>,
+<i>F</i>) 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.</p>
+
+<p>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.</p>
+
+<p>The fertilized egg cell first secretes a membrane, and then divides
+into a row of cells (<i>N</i>) 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 &ldquo;suspensor.&rdquo;
+Later the embryo becomes indented above and forms two lobes (<i>Q</i>),
+which are the beginnings of the cotyledons. The first root and the
+stem arise from the cells next the suspensor.</p></blockquote>
+
+
+
+<hr />
+<h2><span class="pagenum" title="Page&nbsp;181">&nbsp;</span><a name="Page_181" id="Page_181"></a><a name="CHAPTER_XVIII" id="CHAPTER_XVIII"></a>CHAPTER XVIII.
+<br />
+<small>CLASSIFICATION OF DICOTYLEDONS.</small></h2>
+
+<h3><span class="smcap">Division I</span>.&mdash;<i>Choripetal&aelig;</i>.</h3>
+
+<p><span class="smcap">Nearly</span> 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 <i>Choripetal&aelig;</i>, 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.</p>
+
+<div class="figright" style="width:283px;">
+<a name="fig96" id="fig96"></a>
+<img src="images/fig096.png" width="283" height="317"
+alt="Fig.&nbsp;96." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;96.</span>&mdash;Iuliflor&aelig;. <i>A</i>, male; <i>B</i>, female
+inflorescence of a willow, <i>Salix</i> (<i>Amentace&aelig;</i>), &times;&nbsp;&frac12;. <i>C</i>, a single
+male flower, &times;&nbsp;2. <i>D</i>, a female flower, &times;&nbsp;2. <i>E</i>, cross-section of the
+ovary, &times;&nbsp;8. <i>F</i>, an opening fruit. <i>G</i>, single seed with its hairy
+appendage, &times;&nbsp;2.</p>
+</div>
+
+<p>The second group (<i>Sympetal&aelig;</i> or <i>Gamopetal&aelig;</i>) 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 <i>Sympetal&aelig;</i>, which includes the
+highest of all plants.</p>
+
+<p>The <i>Choripetal&aelig;</i> may be divided into six groups, including twenty-two
+orders. The first group is called <i>Iuliflor&aelig;</i>, 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 (<a href="#fig96">Fig.&nbsp;96</a>) and poplars, or in spikes or heads, as in the
+lizard-tail (<a href="#fig97">Fig.&nbsp;97</a>, <i>G</i>), or hop (<a href="#fig97">Fig.&nbsp;97</a>, <i>I</i>). The individual
+flowers are very small <span class="pagenum" title="Page&nbsp;182">&nbsp;</span><a name="Page_182" id="Page_182"></a>and simple in structure, being often reduced to
+the gyn&#339;cium or andr&aelig;cium, 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.</p>
+
+<div class="figcenter" style="width:593px;">
+<a name="fig97" id="fig97"></a>
+<img src="images/fig097.png" width="593" height="474"
+alt="Fig.&nbsp;97." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;97.</span>&mdash;Types of <i>Iuliflor&aelig;</i>. <i>A</i>, branch of hazel,
+<i>Corylus</i> (<i>Cupulifer&aelig;</i>), &times;&nbsp;1. &#9794;, male; &#9792;, female inflorescence. <i>B</i>,
+a single male flower, &times;&nbsp;3. <i>C</i>, section of the ovary of a female
+flower, &times;&nbsp;25. <i>D</i>, acorn of red oak, <i>Quercus</i> (<i>Cupulifer&aelig;</i>), &times;&nbsp;&frac12;.
+<i>E</i>, seed of white birch, <i>Betula</i> (<i>Betulace&aelig;</i>), &times;&nbsp;3. <i>F</i>, fruit of
+horn-bean, <i>Carpinus</i> (<i>Cupulifer&aelig;</i>), &times;&nbsp;1. G, lizard-tail, <i>Saururus</i>
+(<i>Saurure&aelig;</i>), &times;&nbsp;&frac14;. <i>H</i>, a single flower, &times;&nbsp;2. <i>I</i>, female
+inflorescence of the hop, <i>Humulus</i> (<i>Cannabine&aelig;</i>), &times;&nbsp;1. <i>J</i>, a single
+scale with two flowers, &times;&nbsp;1. <i>K</i>, a male flower of a nettle, <i>Urtica</i>
+(<i>Urticace&aelig;</i>), &times;&nbsp;5.</p>
+</div>
+
+<p>In the willows (<a href="#fig96">Fig.&nbsp;96</a>) 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 (<a href="#fig97">Fig.&nbsp;97</a>, <i>A</i>). The male flowers
+are produced in great <span class="pagenum" title="Page&nbsp;183">&nbsp;</span><a name="Page_183" id="Page_183"></a>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.</p>
+
+<p>There are three orders of the <i>Iuliflor&aelig;</i>: <i>Amentace&aelig;</i>, <i>Piperine&aelig;</i>,
+and <i>Urticin&aelig;</i>. The first contains the birches (<i>Betulace&aelig;</i>); oaks,
+beeches, hazels, etc. (<i>Cupulifer&aelig;</i>); walnuts and hickories
+(<i>Juglande&aelig;</i>); willows and poplars (<i>Salicace&aelig;</i>). They are all trees
+or shrubs; the fruit is often a nut, and the embryo is very large,
+completely filling it.</p>
+
+<p>The <i>Piperine&aelig;</i> are mostly tropical plants, and include the pepper
+plant (<i>Piper</i>), as well as other plants with similar properties. Of
+our native forms, the only common one is the lizard-tail (<i>Saururus</i>),
+not uncommon in swampy ground. In these plants, the calyx and corolla
+are entirely absent, but the flowers have both carpels and stamens
+(<a href="#fig97">Fig.&nbsp;97</a>, <i>H</i>).</p>
+
+<p>The <i>Urticin&aelig;</i> include, among our common plants, the nettle family
+(<i>Urticace&aelig;</i>); plane family (<i>Platane&aelig;</i>), represented by the sycamore
+or buttonwood (<i>Platanus</i>); the hemp family (<i>Cannabine&aelig;</i>); and the
+elm family (<i>Ulmace&aelig;</i>). 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.</p>
+
+<p>The second group of the <i>Choripetal&aelig;</i> is called <i>Centrosperm&aelig;</i>, and
+includes but a single order comprising seven families, all of which,
+except one (<i>Nyctagine&aelig;</i>), are represented by numerous native species.
+The latter comprises mostly tropical plants, and is represented in our
+gardens by the showy &ldquo;four-o&#8217;clock&rdquo; (<i>Mirabilis</i>). In this plant, as
+in most of the order, the corolla is absent, but here the calyx is
+large and brightly colored, <span class="pagenum" title="Page&nbsp;184">&nbsp;</span><a name="Page_184" id="Page_184"></a>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.</p>
+
+<div class="figcenter" style="width:631px;">
+<a name="fig98" id="fig98"></a>
+<img src="images/fig098.png" width="631" height="480"
+alt="Fig.&nbsp;98." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;98.</span>&mdash;Types of <i>Centrosperm&aelig;</i>. <i>A</i>, plant of
+spring-beauty, <i>Claytonia</i> (<i>Portulacace&aelig;</i>), &times;&nbsp;&frac12;. <i>B</i>, a single
+flower, &times;&nbsp;1. <i>C</i>, fruit, with the sepals removed, &times;&nbsp;2. <i>D</i>, section of
+the seed, showing the curved embryo (<i>em.</i>), &times;&nbsp;5. <i>E</i>, single flower
+of smart-weed, <i>Polygonum</i> (<i>Polygonace&aelig;</i>), &times;&nbsp;2. <i>F</i>, the pistil, &times;&nbsp;2.
+<i>G</i>, section of the ovary, showing the single ovule, &times;&nbsp;4. <i>H</i>, section
+of the seed, &times;&nbsp;2. <i>I</i>, base of the leaf, showing the sheath, &times;&nbsp;1. <i>J</i>,
+flower of pig-weed, <i>Chenopodium</i> (<i>Chenopodiace&aelig;</i>), &times;&nbsp;3: <span class="smcap">i</span>, from
+without; <span class="smcap">ii</span>, in section. <i>K</i>, flower of the poke-weed, <i>Phytolacca</i>
+(<i>Phytolaccace&aelig;</i>), &times;&nbsp;2. <i>L</i>, fire-pink, <i>Silene</i> (<i>Caryophyllace&aelig;</i>),
+&times;&nbsp;&frac12;. <i>M</i>, a flower with half of the calyx and corolla removed, &times;&nbsp;1.
+<i>N</i>, ripe fruit of mouse-ear chick-weed, <i>Cerastium</i>
+(<i>Caryophyllace&aelig;</i>), opening by ten teeth at the summit, &times;&nbsp;2. <i>O</i>,
+diagram of the flower of <i>Silene</i>.</p>
+</div>
+
+<p>The first family (<i>Polygone&aelig;</i>) is represented by the various species
+of <i>Polygonum</i> (knotgrass, smart-weed, etc.), and among cultivated
+plants by the buckwheat (<i>Fagopyrum</i>). The goose-foot or pig-weed
+(<i>Chenopodium</i>) among native plants, and the beet and spinach of the
+gardens are examples of the family <span class="pagenum" title="Page&nbsp;185">&nbsp;</span><a name="Page_185" id="Page_185"></a><i>Chenopodiace&aelig;</i>. Nearly resembling
+the last is the amaranth family (<i>Amarantace&aelig;</i>), of which the showy
+amaranths and coxcombs of the gardens, and the coarse, green amaranth
+or pig-weed are representatives.</p>
+
+<p>The poke-weed (<i>Phytolacca</i>) (<a href="#fig98">Fig.&nbsp;98</a>, <i>K</i>), so conspicuous in autumn
+on account of its dark-purple clusters of berries and crimson stalks,
+is our only representative of the family <i>Phytolaccace&aelig;</i>. The two
+highest families are the purslane family (<i>Portulacace&aelig;</i>) and pink
+family (<i>Caryophylle&aelig;</i>). These are mostly plants with showy flowers in
+which the petals are large and conspicuous, though some of the pink
+family, <i>e.g.</i> some chick-weeds, have no petals. Of the purslane
+family the portulacas of the gardens, and the common purslane or
+&ldquo;pusley,&rdquo; and the spring-beauty (<i>Claytonia</i>) (<a href="#fig98">Fig.&nbsp;98</a>, <i>A</i>) 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 <i>Dianthus</i>, of which there are also two or
+three native species, are among the showiest of the family. The genera
+<i>Lychnis</i> and <i>Silene</i> (<a href="#fig98">Fig.&nbsp;98</a>, <i>L</i>) also contain very showy species.
+Of the less conspicuous genera, the chick-weeds (<i>Cerastium</i> and
+<i>Stellaria</i>) are the most familiar.</p>
+
+<p>The third group of the <i>Choripetal&aelig;</i> (the <i>Aphanocycl&aelig;</i>) 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 gyn&#339;cium
+composed of two or more carpels united to form a compound pistil.</p>
+
+<p>The first order (<i>Polycarp&aelig;</i>) includes ten families, of which the
+buttercup family (<i><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Rannuculace&aelig;&rsquo;.">Ranunculace&aelig;</ins></i>) 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 (<a href="#fig99">Fig.&nbsp;99</a>, <i>A</i>), clematis,
+and others, the corolla is absent, but the sepals are large and
+brightly colored so as to appear like petals. <span class="pagenum" title="Page&nbsp;186">&nbsp;</span><a name="Page_186" id="Page_186"></a>In the columbine
+(<i>Aquilegia</i>) (<a href="#fig99">Fig.&nbsp;99</a>, <i>F</i>) the petals are tubular, forming
+nectaries, and in the larkspur (<a href="#fig99">Fig.&nbsp;99</a>, <i>T</i>) one of the sepals is
+similarly changed.</p>
+
+<p>Representing the custard-apple family (<i>Anonace&aelig;</i>) is the curious
+papaw (<i>Asimina</i>), common in many parts of the United States
+(<a href="#fig100">Fig.&nbsp;100</a>, <i>A</i>). The family is mainly a tropical one, but this species
+extends as far north as southern Michigan.</p>
+
+<div class="figcenter" style="width:613px;">
+<a name="fig99" id="fig99"></a>
+<img src="images/fig099.png" width="613" height="487"
+alt="Fig.&nbsp;99." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;99.</span>&mdash;Types of <i>Aphanocycl&aelig;</i> (<i>Polycarp&aelig;</i>), family
+<i>Ranunculace&aelig;</i>. <i>A</i>, Rue anemone (<i>Anemonilla</i>), &times;&nbsp;&frac12;. <i>B</i>, a fruit,
+&times;&nbsp;2. <i>C</i>, section of the same. <i>D</i>, section of a buttercup flower
+(<i>Ranunculus</i>), &times;&nbsp;1&frac12;. <i>E</i>, diagram of buttercup flower. <i>F</i>, wild
+columbine (<i>Aquilegia</i>), &times;&nbsp;&frac12;. <i>G</i>, one of the spur-shaped petals, &times;&nbsp;1.
+<i>H</i>, the five pistils, &times;&nbsp;1. <i>I</i>, longitudinal section of the fruit,
+&times;&nbsp;1. <i>J</i>, flower of larkspur (<i>Delphinium</i>), &times;&nbsp;1. <i>K</i>, the four petals
+and stamens, after the removal of the five colored and petal-like
+sepals, &times;&nbsp;1.</p>
+</div>
+
+<p>The magnolia family (<i>Magnoliace&aelig;</i>) has several common members, the
+most widely distributed being, perhaps, the tulip-tree
+(<i>Liriodendron</i>) (<a href="#fig100">Fig.&nbsp;100</a>, <i>C</i>), much valued for its timber. Besides
+this there are several species of magnolia, the most northerly species
+being the sweet-bay (<i>Magnolia <span class="pagenum" title="Page&nbsp;187">&nbsp;</span><a name="Page_187" id="Page_187"></a>glauca</i>) of the Atlantic States, and
+the cucumber-tree (<i>M.&nbsp;acuminata</i>); the great magnolia
+(<i>M.&nbsp;grandiflora</i>) is not hardy in the northern states.</p>
+
+<p>The sweet-scented shrub (<i>Calycanthus</i>) (<a href="#fig100">Fig.&nbsp;100</a>, <i>G</i>) is the only
+member of the family <i>Calycanthace&aelig;</i> found within our limits. It grows
+wild in the southern states, and is cultivated for its sweet-scented,
+dull, reddish flowers.</p>
+
+<div class="figcenter" style="width:578px;">
+<a name="fig100" id="fig100"></a>
+<img src="images/fig100.png" width="578" height="504"
+alt="Fig.&nbsp;100." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;100.</span>&mdash;Types of <i>Aphanocycl&aelig;</i> (<i>Polycarp&aelig;</i>). <i>A</i>,
+branch of papaw, <i>Asimina</i> (<i>Anonace&aelig;</i>), &times;&nbsp;&frac12;. <i>B</i>, section of the
+flower, &times;&nbsp;1. <i>C</i>, flower and leaf of tulip-tree, <i>Liriodendron</i>
+(<i>Magnoliace&aelig;</i>), &times;&nbsp;&#8531;. <i>D</i>, section of a flower, &times;&nbsp;&frac12;. <i>E</i>, a ripe
+fruit, &times;&nbsp;1. <i>F</i>, diagram of the flower. <i>G</i>, flower of the
+sweet-scented shrub, <i>Calycanthus</i> (<i>Calycanthace&aelig;</i>), &times;&nbsp;&frac12;</p>
+</div>
+
+<p>The barberry (<i>Berberis</i>) (<a href="#fig101">Fig.&nbsp;101</a>, <i>A</i>) is the type of the family
+<i>Berberide&aelig;</i>, which also includes the curious mandrake or may-apple
+(<i>Podophyllum</i>) (<a href="#fig101">Fig.&nbsp;101</a>, <i>D</i>), and the twin-leaf or rheumatism-root
+(<i>Jeffersonia</i>), whose curious seed vessel is shown in <a href="#fig101">Figure&nbsp;101</a>,
+<i>G</i>. The fruit of the barberry and may-apple are edible, but the root
+of the latter is poisonous.</p>
+
+<p><span class="pagenum" title="Page&nbsp;188">&nbsp;</span><a name="Page_188" id="Page_188"></a>The curious woody twiner, moon-seed (<i>Menispermum</i>) (<a href="#fig101">Fig.&nbsp;101</a>, <i>I</i>),
+is the sole example in the northern states of the family <i>Menisperme&aelig;</i>
+to which it belongs. The flowers are di&#339;cious, 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.</p>
+
+<div class="figcenter" style="width:603px;">
+<a name="fig101" id="fig101"></a>
+<img src="images/fig101.png" width="603" height="448"
+alt="Fig.&nbsp;101." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;101.</span>&mdash;Types of <i>Aphanocycl&aelig;</i> (<i>Polycarp&aelig;</i>). <i>A&ndash;H</i>,
+<i>Berberidace&aelig;</i>. <i>A</i>, flower of barberry (<i>Berberis</i>), &times;&nbsp;2. <i>B</i>, the
+same in section. <i>C</i>, a stamen, showing the method of opening, &times;&nbsp;3.
+<i>D</i>, flower of may-apple (<i>Podophyllum</i>), &times;&nbsp;&frac12;. <i>E</i>, section of the
+ovary of <i>D</i>, &times;&nbsp;1. <i>F</i>, diagram of the flower. <i>G</i>, ripe fruit of
+twin-leaf (<i>Jeffersonia</i>), opening by a lid, &times;&nbsp;&frac12;. <i>H</i>, section of
+seed, showing the embryo (<i>em.</i>), &times;&nbsp;2. <i>I</i>, young leaf and cluster of
+male flowers of moon-seed, <i>Menispermum</i> (<i>Menisperme&aelig;</i>), &times;&nbsp;1. <i>J</i>, a
+single male flower, &times;&nbsp;2. <i>K</i>, section of a female flower, &times;&nbsp;2. <i>L</i>,
+ripe seed, &times;&nbsp;1. <i>M</i>, section of <i><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;M&rsquo;.">L</ins></i>, showing the curved embryo.</p>
+</div>
+
+<p>The last two families of the order, the laurel family (<i>Laurine&aelig;</i>) and
+the nutmeg family (<i>Myristicine&aelig;</i>) 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 <i>Myristica <span class="pagenum" title="Page&nbsp;189">&nbsp;</span><a name="Page_189" id="Page_189"></a>fragrans</i> of the East Indies. &ldquo;Mace&rdquo; is the
+&ldquo;aril&rdquo; or covering of the seed of the same plant.</p>
+
+<p>The second order of the <i>Aphanocycl&aelig;</i> comprises a number of aquatic
+plants, mostly of large size, and is known as the <i>Hydropeltidin&aelig;</i>.
+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 (<i>Castalia</i>).</p>
+
+<div class="figcenter" style="width:637px;">
+<a name="fig102" id="fig102"></a>
+<img src="images/fig102.png" width="637" height="503"
+alt="Fig.&nbsp;102." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;102.</span>&mdash;Types of <i>Aphanocycl&aelig;</i> (<i>Hydropeltidin&aelig;</i>).
+<i>A</i>, yellow water-lily, <i>Nymph&aelig;a</i> (<i>Nymph&aelig;ace&aelig;</i>), &times;&nbsp;&frac12;. <i>B</i>, a leaf of
+the same, &times;&nbsp;&#8537;. <i>C</i>, freshly opened flower, with the large petal-like
+sepals removed, &times;&nbsp;&frac12;. <i>p</i>, petals. <i>an.</i> stamens. <i>st.</i> stigma. <i>D</i>,
+section of the ovary, &times;&nbsp;2. <i>E</i>, young fruit, &times;&nbsp;&frac12;. <i>F</i>, lotus,
+<i>Nelumbo</i> (<i>Nelumbie&aelig;</i>). &times;&nbsp;&#8537;. <i>G</i>, a stamen, &times;&nbsp;1. <i>H</i>, the large
+receptacle, with the separate pistils sunk in its surface, &times;&nbsp;&frac12;. <i>I</i>,
+section of a single pistil, &times;&nbsp;2. <i>ov.</i> the ovule. <i>J</i>, upper part of a
+section through the stigma and ovule (<i>ov.</i>), &times;&nbsp;4.</p>
+</div>
+
+<p><span class="pagenum" title="Page&nbsp;190">&nbsp;</span><a name="Page_190" id="Page_190"></a>There are three families, all represented within the United States.
+The first (<i>Nelumbie&aelig;</i>) has but a single species, the yellow lotus or
+nelumbo (<i>Nelumbo lutea</i>), common in the waters of the west and
+southwest, but rare eastward (<a href="#fig101">Fig.&nbsp;101</a>, <i>F</i>). 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 <i>Nelumbo</i> known, the second one
+(<i>N.&nbsp;speciosa</i>) 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.</p>
+
+<p>The second family (<i>Cabombe&aelig;</i>) is also represented at the north by but
+one species, the water shield (<i>Brasenia</i>), not uncommon in marshes.
+Its flowers are quite small, of a dull-purple color, and the leaves
+oval in outline and centrally peltate, <i>i.e.</i> the leaf stalk inserted
+in the centre. The whole plant is covered with a transparent
+gelatinous coat.</p>
+
+<p>The third family (<i>Nymph&aelig;ace&aelig;</i>) includes the common white water-lilies
+(<i>Castalia</i>) and the yellow water-lilies (<i>Nymph&aelig;a</i>) (<a href="#fig102">Fig.&nbsp;102</a>, <i>A</i>).
+In the latter the petals are small and inconspicuous (<a href="#fig102">Fig.&nbsp;102</a>, <i>C</i>,
+<i>p</i>), 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 <i>Victoria regia</i> of the Amazon reaching two metres or
+more in width.</p>
+
+<p>The third order of the <i>Aphanocycl&aelig;</i> (<i>Rh&#339;adin&aelig;</i> or <i>Cruciflor&aelig;</i>)
+comprises a number of common plants, <span class="pagenum" title="Page&nbsp;191">&nbsp;</span><a name="Page_191" id="Page_191"></a>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 <i>Cruciflor&aelig;</i>.</p>
+
+<p>There are four families, of which the first is the poppy family
+(<i>Papaverace&aelig;</i>), including the poppies, eschscholtzias, Mexican or
+prickly poppy (<i>Argemone</i>), etc., of the gardens, and the blood-root
+(<i>Sanguinaria</i>), celandine poppy (<i>Stylophorum</i>), and a few other wild
+plants (see <a href="#fig103">Fig.&nbsp;103</a>, <i>A&ndash;I</i>). Most of the family have a colored juice
+(latex), which is white in the poppy, yellow in celandine and
+<i>Argemone</i>, and orange-red in the blood-root. From the latex of the
+opium poppy the opium of commerce is extracted.</p>
+
+<div class="figcenter" style="width:618px;">
+<a name="fig103" id="fig103"></a>
+<img src="images/fig103.png" width="618" height="498"
+alt="Fig.&nbsp;103." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;103.</span>&mdash;Types of <i>Aphanocycl&aelig;</i> (<i>Rh&#339;din&aelig;</i>). <i>A</i>,
+plant of blood-root, <i>Sanguinaria</i> (<i>Papaverace&aelig;</i>), &times;&nbsp;&#8531;. <i>B</i>, a single
+flower, &times;&nbsp;1. <i>C</i>, fruit, &times;&nbsp;&frac12;. <i>D</i>, section of the seed. <i>em.</i> embryo,
+&times;&nbsp;2. <i>E</i>, diagram of the flower. <i>F</i>, flower of Dutchman&#8217;s breeches,
+<i>Dicentra</i> (<i>Fumariace&aelig;</i>), &times;&nbsp;1. <i>G</i>, group of three stamens of the
+same, &times;&nbsp;2. <i>H</i>, one of the inner petals, &times;&nbsp;2. <i>I</i>, fruit of celandine
+poppy, <i>Stylophorum</i> (<i>Papaverace&aelig;</i>), &times;&nbsp;&frac12;. <i>J</i>, flower of mustard,
+<i>Brassica</i> (<i>Crucifer&aelig;</i>), &times;&nbsp;1. <i>K</i>, the same, with the petals removed,
+&times;&nbsp;2. <i>L</i>, fruit of the same, &times;&nbsp;1.</p>
+</div>
+
+<p><span class="pagenum" title="Page&nbsp;192">&nbsp;</span><a name="Page_192" id="Page_192"></a>The second family, the fumitories (<i>Fumariace&aelig;</i>) are delicate, smooth
+plants, with curious flowers and compound leaves. The garden
+bleeding-heart (<i>Dicentra spectabilis</i>) and the pretty, wild
+<i>Dicentras</i> (<a href="#fig103">Fig.&nbsp;103</a>, <i>F</i>) are familiar to nearly every one.</p>
+
+<p>Other examples are the mountain fringe (<i>Adlumia</i>), a climbing
+species, and several species of <i>Corydalis</i>, differing mainly from
+<i>Dicentra</i> in having the corolla one-sided.</p>
+
+<p>The mustard family (<i>Crucifer&aelig;</i>) comprises by far the greater part of
+the order. The shepherd&#8217;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 (<i>Cheiranthus</i>) and stock (<i>Matthiola</i>) are cultivated for
+ornament.</p>
+
+<p>The last family is the caper family (<i>Capparide&aelig;</i>), represented by
+only a few not common plants. The type of the order is <i>Capparis</i>,
+whose pickled flower-buds constitute capers.</p>
+
+<p>The fourth order (<i>Cistiflor&aelig;</i>) of the <i>Aphanocycl&aelig;</i> 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.</p>
+
+<div class="figcenter" style="width:624px;">
+<a name="fig104" id="fig104"></a>
+<img src="images/fig104.png" width="624" height="482"
+alt="Fig.&nbsp;104." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;104.</span>&mdash;Types of <i>Aphanocycl&aelig;</i> (<i>Cistiflor&aelig;</i>). <i>A</i>,
+flower of wild blue violet, <i>Viola</i> (<i>Violace&aelig;</i>), &times;&nbsp;1. <i>B</i>, the lower
+petal prolonged behind into a sac or spur, &times;&nbsp;1. <i>C</i>, the stamens, &times;&nbsp;2.
+<i>D</i>, pistil, &times;&nbsp;2. <i>E</i>, a leaf, &times;&nbsp;&frac12;. <i>F</i>, section of the ovary, &times;&nbsp;2.
+<i>G</i>, the fruit, &times;&nbsp;1. <i>H</i>, the same after it has opened, &times;&nbsp;1. <i>I</i>,
+diagram of the flower. <i>J</i>, flower of mignonette, <i>Reseda</i>
+(<i>Resedace&aelig;</i>), &times;&nbsp;2. <i>K</i>, a petal, &times;&nbsp;3. <i>L</i>, cross-section of the
+ovary, &times;&nbsp;3. <i>M</i>, fruit, &times;&nbsp;1. <i>N</i>, plant of sundew, <i>Drosera</i>
+(<i>Droserace&aelig;</i>), &times;&nbsp;&frac12;. <i>O</i>, a leaf that has captured a mosquito, &times;&nbsp;2.
+<i>P</i>, flower of another species (<i>D.&nbsp;filiformis</i>), &times;&nbsp;2. <i>Q</i>,
+cross-section of the ovary, &times;&nbsp;4.</p>
+</div>
+
+<p>Among the commoner members of the order are the mignonettes
+(<i>Resedace&aelig;</i>) and the violets (<i>Violace&aelig;</i>), of which the various wild
+and cultivated species are familiar plants (<a href="#fig104">Fig.&nbsp;104</a>, <i>A</i>, <i>M</i>). The
+sundews (<i>Droserace&aelig;</i>) are most extraordinary plants, growing in boggy
+land over pretty much <ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;he&rsquo;.">the</ins> whole world. They are represented in
+the United States by several species of sundew (<i>Drosera</i>), and the
+still more curious Venus&#8217;s-flytrap (<i>Dion&aelig;a</i>) of North Carolina. The
+leaves of <span class="pagenum" title="Page&nbsp;193">&nbsp;</span><a name="Page_193" id="Page_193"></a>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 (<a href="#fig104">Fig.&nbsp;104</a>, <i>N</i>) 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
+<span class="pagenum" title="Page&nbsp;194">&nbsp;</span><a name="Page_194" id="Page_194"></a>is firmly held, when a digestive process, similar to that in <i>Dion&#339;a</i>,
+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.</p>
+
+<div class="figcenter" style="width:595px;">
+<a name="fig105" id="fig105"></a>
+<img src="images/fig105.png" width="595" height="391"
+alt="Fig.&nbsp;105." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;105.</span>&mdash;Types of <i>Aphanocycl&aelig;</i> (<i>Cistiflor&aelig;</i>). <i>A</i>,
+<i>B</i>, leaves of the pitcher-plant, <i>Sarracenia</i> (<i>Sarraceniace&aelig;</i>). <i>A</i>,
+from the side; <i>B</i>, from in front, &times;&nbsp;&frac12;. <i>C</i>, St.&nbsp;John&#8217;s-wort
+(<i>Hypericum</i>), &times;&nbsp;&frac12;. <i>D</i>, a flower, &times;&nbsp;1. <i>E</i>, the pistil, &times;&nbsp;2. <i>G</i>,
+cross-section of the ovary, &times;&nbsp;4. <i>H</i>, diagram of the flower.</p>
+</div>
+
+<p>Similar in their habits, but differing much in appearance from the
+sundews, are the pitcher-plants (<i>Sarraceniace&aelig;</i>), of which one
+species (<i>Sarracenia purpurea</i>) is very common in peat bogs throughout
+the northern United States. In this species (<a href="#fig105">Fig.&nbsp;105</a>, <i>A</i>, <i>B</i>), 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 <span class="pagenum" title="Page&nbsp;195">&nbsp;</span><a name="Page_195" id="Page_195"></a>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 (<i>Darlingtonia</i>) has a colored
+appendage at the mouth of the pitcher which serves to lure insects
+into the trap.</p>
+
+<p>Another family of pitcher-plants (<i>Nepenthe&aelig;</i>) 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.</p>
+
+<p>Two other families of the order contain familiar native plants, the
+rock-rose family (<i>Cistace&aelig;</i>), and the St.&nbsp;John&#8217;s-worts
+(<i>Hypericace&aelig;</i>). 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 (<a href="#fig105">Fig.&nbsp;105</a>,
+<i>C</i>, <i>D</i>).</p>
+
+<p>The last order of the <i>Aphanocycl&aelig;</i> (the <i>Columnifer&aelig;</i>) has three
+families, of which two, the mallows (<i>Malvace&aelig;</i>), and the lindens
+(<i>Tiliace&aelig;</i>), include well-known species. Of the former, the various
+species of mallows (<a href="#fig106">Fig.&nbsp;106</a>, <i>A</i>) belonging to the genus <i>Malva</i> are
+common, as well as some species of <i>Hibiscus</i>, including the showy
+swamp <i>Hibiscus</i> or rose-mallow (<i>H.&nbsp;moscheutos</i>), common in salt
+marshes and in the fresh-water marshes of the great lake region. The
+hollyhock and shrubby <i>Alth&aelig;a</i> are familiar cultivated plants of this
+order, and the cotton-plant (<i>Gossypium</i>) 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.</p>
+
+<p>The common basswood (<i>Tilia</i>) is the commonest representative<span class="pagenum" title="Page&nbsp;196">&nbsp;</span><a name="Page_196" id="Page_196"></a> of the
+family <i>Tiliace&aelig;</i> (<a href="#fig106">Fig.&nbsp;106</a>, <i>G</i>). 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.</p>
+
+<div class="figcenter" style="width:617px;">
+<a name="fig106" id="fig106"></a>
+<img src="images/fig106.png" width="617" height="474"
+alt="Fig.&nbsp;106." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;106.</span>&mdash;Types of <i>Aphanocycl&aelig;</i> (<i>Columnifer&aelig;</i>). <i>A</i>,
+flower and leaf of the common mallow, <i>Malva</i> (<i>Malvace&aelig;</i>), &times;&nbsp;&frac12;. <i>B</i>,
+a flower bud, &times;&nbsp;1. <i>C</i>, section of a flower, &times;&nbsp;2. <i>D</i>, the fruit, &times;&nbsp;2.
+<i>E</i>, section of one division of the fruit, with the enclosed seed,
+&times;&nbsp;3. <i>em.</i> the embryo. <i>F</i>, diagram of the flower. <i>G</i>, leaf and
+inflorescence of the basswood, <i>Tilia</i> (<i>Tiliace&aelig;</i>), &times;&nbsp;&#8531;. <i>br.</i> a
+bract. <i>H</i>, a single flower, &times;&nbsp;1. <i>I</i>, group of stamens, with
+petal-like appendage (<i>x</i>), &times;&nbsp;2. <i>J</i>, diagram of the flower.</p>
+</div>
+
+<p>The fourth group of the <i>Choripetal&aelig;</i> is the <i>Eucycl&aelig;</i>. 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.</p>
+
+<div class="figcenter" style="width:619px;">
+<a name="fig107" id="fig107"></a>
+<img src="images/fig107.png" width="619" height="486"
+alt="Fig.&nbsp;107." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;107.</span>&mdash;Types of <i>Eucycl&aelig;</i> (<i>Gruinales</i>). <i>A</i>, wild
+crane&#8217;s-bill <i>Geranium</i> (<i>Geraniace&aelig;</i>), &times;&nbsp;&frac12;. <i>B</i>, a petal, &times;&nbsp;1. <i>C</i>,
+the young fruit, the styles united in a column, &times;&nbsp;&frac12;. <i>D</i>, the ripe
+fruit, the styles separating to discharge the seeds, &times;&nbsp;&frac12;. <i>E</i>, section
+of a seed, &times;&nbsp;2. <i>F</i>, wild flax. <i>Linum</i> (<i>Linace&aelig;</i>), &times;&nbsp;&frac12;. <i>G</i>, a
+single flower, &times;&nbsp;2. <i>H</i>, cross-section of the young fruit, &times;&nbsp;3. <i>I</i>,
+flower. <i>J</i>, leaf of wood-sorrel, <i>Oxalis</i> (<i>Oxalide&aelig;</i>), &times;&nbsp;1. <i>K</i>, the
+stamens and pistil, &times;&nbsp;2. <i>L</i>, flower of jewel-weed, <i>Impatiens</i>
+(<i>Balsamine&aelig;</i>), &times;&nbsp;1. <i>M</i>, the same, with the parts separated. <i>p</i>,
+petals. <i>s</i>, sepals. <i>an.</i> stamens. <i>gy.</i> pistil. <i>N</i>, fruit, &times;&nbsp;1.
+<i>O</i>, the same, opening. <i>P</i>, a seed, &times;&nbsp;2.</p>
+</div>
+
+<p>The first order (<i>Gruinales</i>) includes six families, consisting for
+the most part of plants with conspicuous flowers. Here belong the
+geraniums (<a href="#fig107">Fig.&nbsp;107</a>, <i>A</i>), represented by the wild geraniums and
+crane&#8217;s-bill, and the very showy geraniums <span class="pagenum" title="Page&nbsp;197">&nbsp;</span><a name="Page_197" id="Page_197"></a>(<i>Pelargonium</i>) of the
+gardens. The nasturtiums (<i>Trop&aelig;olum</i>) represent another family,
+mostly tropical, and the wood-sorrels (<i>Oxalis</i>) (<a href="#fig107">Fig.&nbsp;107</a>, <i>I</i>) are
+common, both wild and cultivated. The most useful member of the order
+is unquestionably the common flax (<i>Linum</i>), of which there are also
+several native species (<a href="#fig107">Fig.&nbsp;107</a>, <i>F</i>). These are types of the flax
+family (<i>Linace&aelig;</i>). Linen is the product of the tough, fibrous inner
+bark of <i>L.&nbsp;usitatissimum</i>, which has been cultivated for its fibre
+from time immemorial. The last family is the balsam family
+(<i>Balsamine&aelig;</i>). The jewel-weed or touch-me-not
+(<i><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Impatius&rsquo;.">Impatiens</ins></i>), so called from the sensitive pods which
+spring open on <span class="pagenum" title="Page&nbsp;198">&nbsp;</span><a name="Page_198" id="Page_198"></a>being touched, is very common in moist ground
+everywhere (<a href="#fig107">Fig.&nbsp;107</a>, <i>L&ndash;P</i>). The garden balsam, or lady&#8217;s slipper, is
+a related species (<i>I.&nbsp;balsamina</i>).</p>
+
+<div class="figcenter" style="width:634px;">
+<a name="fig108" id="fig108"></a>
+<img src="images/fig108.png" width="634" height="498"
+alt="Fig.&nbsp;108." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;108.</span>&mdash;<i>Eucycl&aelig;</i> (<i>Terebinthin&aelig;</i>, <i>&AElig;sculin&aelig;</i>). <i>A</i>,
+leaves and flowers of sugar-maple, <i>Acer</i> (<i>Acerace&aelig;</i>), &times;&nbsp;&frac12;. <i>B</i>, a
+male flower, &times;&nbsp;2. <i>C</i>, diagram of a perfect flower. <i>D</i>, fruit of the
+silver-maple, &times;&nbsp;&frac12;. <i>E</i>, section across the seed, &times;&nbsp;2. <i>F</i>, embryo
+removed from the seed, &times;&nbsp;1. <i>G</i>, leaves and flowers of bladder-nut,
+<i>Staphylea</i>, (<i>Sapindace&aelig;</i>), &times;&nbsp;&frac12;. <i>H</i>, section of a flower, &times;&nbsp;2. <i>I</i>,
+diagram of the flower. <i>J</i>, flower of buckeye (<i>&AElig;sculus</i>), &times;&nbsp;1&frac12;. <i>K</i>,
+flower of smoke-tree, <i>Rhus</i> (<i>Anacardiace&aelig;</i>), &times;&nbsp;3. <i>L</i>, the same, in
+section.</p>
+</div>
+
+<p>The second order (<i>Terebinthin&aelig;</i>) 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
+(<i>Zanthoxylum</i>), and the various species of sumach (<i>Rhus</i>), are the
+best known. In the latter genus belong the poison ivy
+(<i>R.&nbsp;toxicodendron</i>) and the poison dogwood (<i>R.&nbsp;venenata</i>). The
+Venetian sumach or smoke-tree (<i>R.&nbsp;Cotinus</i>) is commonly planted for
+ornament.</p>
+
+<p><span class="pagenum" title="Page&nbsp;199">&nbsp;</span><a name="Page_199" id="Page_199"></a>The third order of the <i>Eucycl&aelig;</i>, the <i>&AElig;sculin&aelig;</i>, embraces six
+families, of which three, the horsechestnuts, etc. (<i>Sapindace&aelig;</i>), the
+maples (<i>Acerace&aelig;</i>), and the milkworts (<i>Polygalace&aelig;</i>), have several
+representatives in the northern United States. Of the first the
+buckeye (<i>&AElig;sculus</i>) (<a href="#fig108">Fig.&nbsp;108</a>, <i>J</i>) and the bladder-nut (<i>Staphylea</i>)
+(<a href="#fig108">Fig.&nbsp;108</a>, <i>G</i>) are the commonest native genera, while the
+horsechestnut (<i>&AElig;sculus hippocastanum</i>) is everywhere planted.</p>
+
+<p>The various species of maple (<i>Acer</i>) are familiar examples of the
+<i>Acerace&aelig;</i> (see <a href="#fig106">Fig.&nbsp;106</a>, <i>A</i>, <i>F</i>).</p>
+
+<p>The fourth and last order of the <i>Eucycl&aelig;</i>, the <i>Frangulin&aelig;</i>, is
+composed mainly of plants with inconspicuous flowers, the stamens as
+many as the petals. Not infrequently they are di&#339;cious, or in some,
+like the grape, some of the flowers may be unisexual while others are
+hermaphrodite (<i>i.e.</i> 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 (<i>Euonymus</i>) (<a href="#fig109">Fig.&nbsp;109</a>, <i>A</i>),
+and the climbing bitter-sweet (<i>Celastrus</i>) (<a href="#fig109">Fig.&nbsp;109</a>, <i>D</i>), belonging
+to the family <i>Celastrace&aelig;</i>; the holly and black alder, species of
+<i>Ilex</i>, are examples of the family <i>Aquifoliace&aelig;</i>; the various species
+of grape (<i>Vitis</i>), the Virginia creeper (<i>Ampelopsis quinquefolia</i>),
+and one or two other cultivated species of the latter, represent the
+vine family (<i>Vitace&aelig;</i> or <i>Ampelid&aelig;</i>), and the buckthorn (<i>Rhamnus</i>)
+is the type of the <i>Rhamnace&aelig;</i>.</p>
+
+<div class="figcenter" style="width:614px;">
+<a name="fig109" id="fig109"></a>
+<img src="images/fig109.png" width="614" height="473"
+alt="Fig.&nbsp;109." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;109.</span>&mdash;<i>Eucyl&aelig;</i> (<i>Frangulin&aelig;</i>), <i>Tricocc&aelig;</i>. <i>A</i>,
+flowers of spindle-tree, <i>Euonymus</i>, (<i>Celastrace&aelig;</i>), &times;&nbsp;1. <i>B</i>,
+cross-section of the ovary, &times;&nbsp;2. <i>C</i>, diagram of the flower. <i>D</i>, leaf
+and fruit of bitter-sweet (<i>Celastrus</i>), &times;&nbsp;&frac12;. <i>E</i>, fruit opening and
+disclosing the seeds. <i>F</i>, section of a nearly ripe fruit, showing the
+seeds surrounded by the scarlet integument (aril). <i>em.</i> the embryo,
+&times;&nbsp;1. <i>G</i>, flower of grape-vine, <i>Vitis</i> (<i>Vitace&aelig;</i>), &times;&nbsp;2. The corolla
+has fallen off. <i>H</i>, vertical section of the pistil, &times;&nbsp;2. <i>I</i>, nearly
+ripe fruits of the frost-grape, &times;&nbsp;1. <i>J</i>, cross-section of young
+fruit, &times;&nbsp;2. <i>K</i>, a spurge, <i>Euphorbia</i> (<i>Euphorbiace&aelig;</i>), &times;&nbsp;&frac12;. <i>L</i>,
+single group of flowers, surrounded by the corolla-like involucre,
+&times;&nbsp;3. <i>M</i>, section of the same, &#9794;, male flowers; &#9792;, female flowers.
+<i>N</i>, a single male flower, &times;&nbsp;5. <i>O</i>, cross-section of ovary, &times;&nbsp;6. <i>P</i>,
+a seed, &times;&nbsp;2. <i>Q</i>, longitudinal section of the seed, &times;&nbsp;3. <i>em.</i>
+embryo.</p>
+</div>
+
+<p>The fifth group of the <i>Choripetal&aelig;</i> is a small one, comprising but a
+single order (<i>Tricocc&aelig;</i>). The flowers are small and inconspicuous,
+though sometimes, as in some <i>Euphorbias</i> and the showy <i>Poinsettia</i>
+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 <i>Euphorbias</i> are the most
+familiar. These plants (<a href="#fig109">Fig.&nbsp;109</a>, <i>K</i>) have the small flowers
+surrounded by a cup-shaped involucre (<i>L</i>, <i>M</i>) so that the whole
+inflorescence<span class="pagenum" title="Page&nbsp;200">&nbsp;</span><a name="Page_200" id="Page_200"></a> 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 (<a href="#fig109">Fig.&nbsp;109</a>, <i>M</i>, <i>N</i>). 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 (<i>Ricinus</i>) and <i>Croton</i> are cultivated
+for their large, showy leaves.</p>
+
+<p>The water starworts (<i>Callitriche</i>), not uncommon in stagnant<span class="pagenum" title="Page&nbsp;201">&nbsp;</span><a name="Page_201" id="Page_201"></a> water,
+represent the family <i>Callitrichace&aelig;</i>, and the box (<i>Buxus</i>) is the
+type of the <i>Buxace&aelig;</i>.</p>
+
+<div class="figcenter" style="width:607px;">
+<a name="fig110" id="fig110"></a>
+<img src="images/fig110.png" width="607" height="477"
+alt="Fig.&nbsp;110." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;110.</span>&mdash;Types of <i>Calyciflor&aelig;</i> (<i>Umbelliflor&aelig;</i>).
+<i>A</i>, inflorescence of wild parsnip, <i>Pastinaca</i> (<i>Umbellifer&aelig;</i>), &times;&nbsp;&frac12;.
+<i>B</i>, single flower of the same, &times;&nbsp;3. <i>C</i>, a leaf, showing the
+sheathing base, &times;&nbsp;&frac14;. <i>D</i>, a fruit, &times;&nbsp;2. <i>E</i>, cross-section of <i>D</i>.
+<i>F</i>, part of the inflorescence of spikenard, <i>Aralia</i> (<i>Araliace&aelig;</i>),
+&times;&nbsp;1. <i>G</i>, a single flower of the same, &times;&nbsp;3. <i>H</i>, the fruit, &times;&nbsp;2. <i>I</i>,
+cross-section of the <i>H</i>. <i>J</i>, inflorescence of dogwood, <i>Cornus</i>
+(<i>Corne&aelig;</i>). The cluster of flowers is surrounded by four white bracts
+(<i>b</i>), &times;&nbsp;&#8531;. <i>K</i>, a single flower of the same, &times;&nbsp;2. <i>L</i>, diagram of the
+flower. <i>M</i>, young fruit of another species (<i>Cornus stolonifera</i>)
+(red osier), &times;&nbsp;2. <i>N</i>, cross-section of <i>M</i>.</p>
+</div>
+
+<p>The last and highest group of the <i>Choripetal&aelig;</i>, the <i>Calyciflor&aelig;</i>,
+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 &ldquo;inferior&rdquo;
+<span class="pagenum" title="Page&nbsp;202">&nbsp;</span><a name="Page_202" id="Page_202"></a>in distinction from one that is entirely free from the tube, and thus
+is evidently within the flower. The latter is the so-called &ldquo;superior&rdquo;
+ovary. The carpels are usually united into a compound pistil, but may
+be separate, as in the stonecrop (<a href="#fig111">Fig.&nbsp;111</a>, <i>E</i>), or strawberry
+(<a href="#fig114">Fig.&nbsp;114</a>, <i>C</i>).</p>
+
+<p>The first order of the <i>Calyciflor&aelig;</i> (<i>Umbelliflor&aelig;</i>) has the flowers
+small, and usually arranged in umbels, <i>i.e.</i> 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 <i>Umbellifer&aelig;</i> is the commonest. The
+flowers are much alike in all (<a href="#fig110">Fig.&nbsp;110</a>, <i>A</i>, <i>B</i>), 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 (<a href="#fig110">Fig.&nbsp;110</a>, <i>D</i>) 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.</p>
+
+<p>The wild spikenard (<i>Aralia</i>) (<a href="#fig110">Fig.&nbsp;110</a>, <i>F</i>), ginseng, and the true
+ivy (<i>Hedera</i>) are examples of the <i>Araliace&aelig;</i>, and the various
+species of dogwood (<i>Cornus</i>) (<a href="#fig110">Fig.&nbsp;110</a>, <i>J&ndash;N</i>) represent the dogwood
+family (<i>Corne&aelig;</i>).</p>
+
+<p>The second order (<i>Saxifragin&aelig;</i>) contains eight families, including a
+number of common wild and cultivated plants. The true saxifrages are
+represented by several wild and cultivated species of <i>Saxifraga</i>, the
+little bishop&#8217;s cap or mitre-wort (<i>Mitella</i>) (<a href="#fig111">Fig.&nbsp;111</a>, <i>D</i>), and
+others. The wild hydrangea (<a href="#fig111">Fig.&nbsp;111</a>, <i>F</i>) and the showy garden
+species represent the family <i>Hydrange&aelig;</i>. 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<span class="pagenum" title="Page&nbsp;203">&nbsp;</span><a name="Page_203" id="Page_203"></a> 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 (<i>Philadelphus</i>) (<a href="#fig111">Fig.&nbsp;111</a>, <i>I</i>), the gooseberry, and
+currants (<i>Ribes</i>) (<a href="#fig111">Fig.&nbsp;111</a>, <i>A</i>), and the stonecrop (<i>Sedum</i>)
+(<a href="#fig111">Fig.&nbsp;111</a>, <i>E</i>) are types of the families <i>Philadelphe&aelig;</i>, <i>Ribesie&aelig;</i>,
+and <i>Crassulace&aelig;</i>.</p>
+
+<div class="figcenter" style="width:646px;">
+<a name="fig111" id="fig111"></a>
+<img src="images/fig111.png" width="646" height="482"
+alt="Fig.&nbsp;111." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;111.</span>&mdash;<i>Calyciflor&aelig;</i> (<i>Saxifragin&aelig;</i>): <i>A</i>, flowers
+and leaves of wild gooseberry, <i>Ribes</i> (<i>Ribesie&aelig;</i>), &times;&nbsp;1. <i>B</i>,
+vertical section of the flower, &times;&nbsp;2. <i>C</i>, diagram of the flower. <i>D</i>,
+flower of bishop&#8217;s-cap, <i>Mitella</i> (<i>Saxifragace&aelig;</i>), &times;&nbsp;3. <i>E</i>, flower
+of stonecrop, <i>Sedum</i> (<i>Crassulace&aelig;</i>), &times;&nbsp;2. <i>F</i>, flowers and leaves of
+hydrangea (<i>Hydrange&aelig;</i>), &times;&nbsp;&frac12;. <i>n</i>, neutral flower. <i>G</i>, unopened
+flower, &times;&nbsp;2. <i>H</i>, the same, after the petals have fallen away. <i>I</i>,
+flower of syringa, <i>Philadelphus</i> (<i>Philadelphe&aelig;</i>), &times;&nbsp;1. <i>J</i>, diagram
+of the flower.</p>
+</div>
+
+<p>The third order (<i>Opuntie&aelig;</i>) has but a single family, the cacti
+(<i>Cactace&aelig;</i>). 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 (<a href="#fig112">Fig.&nbsp;112</a>,<span class="pagenum" title="Page&nbsp;204">&nbsp;</span><a name="Page_204" id="Page_204"></a> <i>A</i>) 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
+(<i>Opuntia</i>) occur as far north as New York, but most are confined to
+the hot, dry plains of the south and southwest.</p>
+
+<div class="figcenter" style="width:601px;">
+<a name="fig112" id="fig112"></a>
+<img src="images/fig112.png" width="601" height="495"
+alt="Fig.&nbsp;112." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;112.</span>&mdash;<i>Calyciflor&aelig;</i>, <i>Opuntie&aelig;</i> (<i>Passiflorin&aelig;</i>).
+<i>A</i>, flower of a cactus, <i>Mamillaria</i> (<i>Cactace&aelig;</i>) (from &ldquo;Gray&#8217;s
+Structural Botany&rdquo;). <i>B</i>, leaf and flower of a passion-flower,
+<i>Passiflora</i> (<i>Passiflorace&aelig;</i>), &times;&nbsp;&frac12;. <i>t</i>, a tendril. <i>C</i>,
+cross-section of the ovary, &times;&nbsp;2. <i>D</i>, diagram of the flower.</p>
+</div>
+
+<p>The fourth order (<i>Passiflorin&aelig;</i>) 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 (<i>Passiflora</i>)
+(<a href="#fig112">Fig.&nbsp;112</a>, <i>B</i>), 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 <span class="pagenum" title="Page&nbsp;205">&nbsp;</span><a name="Page_205" id="Page_205"></a>on account of their fine foliage and flowers. The leaves are
+always one-sided, and the flowers mon&#339;cious.<a name="FNanchor_13_13" id="FNanchor_13_13"></a><a href="#Footnote_13_13" class="fnanchor">[13]</a> Whether the begonias
+properly belong with the <i>Passiflorin&aelig;</i> has been questioned.</p>
+
+<div class="figcenter" style="width:590px;">
+<a name="fig113" id="fig113"></a>
+<img src="images/fig113.png" width="590" height="484"
+alt="Fig.&nbsp;113." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;113.</span>&mdash;<i>Calyciflor&aelig;</i> (<i>Myrtiflor&aelig;</i>, <i>Thymelin&aelig;</i>).
+<i>A</i>, flowering branch of moosewood, <i>Dirca</i>
+(<i><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Thymeleace&aelig;&rsquo;.">Thymel&aelig;ace&aelig;</ins></i>), &times;&nbsp;1. <i>B</i>, a single flower, &times;&nbsp;2. <i>C</i>,
+the same, laid open. <i>D</i>, a young flower of willow herb, <i>Epilobium</i>
+(<i>Onagrace&aelig;</i>), &times;&nbsp;1. The pistil (<i>gy.</i>) is not yet ready for
+pollination. <i>E</i>, an older flower, with receptive pistil. <i>F</i>, an
+unopened bud, &times;&nbsp;1. <i>G</i>  , cross-section of the ovary, &times;&nbsp;4. <i>H</i>, a young
+fruit, &times;&nbsp;1. <i>I</i>, diagram of the flower. <i>J</i>, flowering branch of water
+milfoil, <i>Myriophyllum</i> (<i>Haloragidace&aelig;</i>), &times;&nbsp;&frac12;. <i>K</i>, a single leaf,
+&times;&nbsp;1. <i>L</i>, female flowers of the same, &times;&nbsp;2. <i>M</i>, the fruit, &times;&nbsp;2.</p>
+</div>
+
+<p>The fifth order (<i>Myrtiflor&aelig;</i>) 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 (<i>Myrtus</i>) is sometimes cultivated for its pretty glossy
+green leaves and white flowers, as is also <span class="pagenum" title="Page&nbsp;206">&nbsp;</span><a name="Page_206" id="Page_206"></a>the pomegranate whose
+brilliant, scarlet flowers are extremely ornamental. Cloves are the
+dried flower-buds of an East-Indian myrtaceous tree (<i>Caryophyllus</i>).
+In Australia the order includes the giant gum-trees
+(<i><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Encalypus&rsquo;.">Eucalyptus</ins></i>), the largest of all known trees, exceeding
+in size even the giant trees of California.</p>
+
+<p>Among the commoner <i>Myrtiflor&aelig;</i>, the majority belong to the two
+families <i>Onagrace&aelig;</i> and <i>Lythrace&aelig;</i>. The former includes the evening
+primroses (<i>&#338;nothera</i>), willow-herb (<i>Epilobium</i>) (<a href="#fig113">Fig.&nbsp;113</a>, <i>D</i>),
+and fuchsia; the latter, the purple loosestrife (<i>Lythrum</i>) and swamp
+loosestrife (<i>Nes&aelig;a</i>). The water-milfoil (<i>Myriophyllum</i>) (<a href="#fig113">Fig.&nbsp;113</a>,
+<i>J</i>) is an example of the family <i>Haloragidace&aelig;</i>, and the <i>Rhexias</i> of
+the eastern United States represent with us the family <i>Melastomace&aelig;</i>.</p>
+
+<p>The sixth order of the <i>Calyciflor&aelig;</i> is a small one (<i>Thymelin&aelig;</i>),
+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 (<i>Dirca</i>)
+(<a href="#fig113">Fig.&nbsp;113</a>, <i>A</i>), belonging to the first of the three families
+(<i>Thymel&aelig;ace&aelig;</i>). Of the second family (<i>El&aelig;agnace&aelig;</i>), the commonest
+example is <i>Shepherdia</i>, a low shrub having the leaves covered with
+curious, scurfy hairs that give them a silvery appearance. The third
+family (<i>Proteace&aelig;</i>) has no familiar representatives.</p>
+
+<p>The seventh order (<i>Rosiflor&aelig;</i>) includes many well-known plants, all
+of which may be united in one family (<i>Rosace&aelig;</i>), 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 (<a href="#fig114">Fig.&nbsp;114</a>, <i>I</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) (<a href="#fig114">Fig.&nbsp;114</a>, <i>E</i>,
+<i>H</i>). In the strawberry (<a href="#fig114">Fig.&nbsp;114</a>, <i>A</i>), rose (<i>G</i>), cinquefoil
+(<i>Potentilla</i>), etc., there are numerous distinct, one-seeded carpels,
+and in <i>Spir&aelig;a</i> (<a href="#fig114">Fig.&nbsp;114</a>, <i>F</i>) there are five several-seeded carpels,<span class="pagenum" title="Page&nbsp;207">&nbsp;</span><a name="Page_207" id="Page_207"></a>
+forming as many dry pods when ripe. The so-called &ldquo;berry&rdquo; of the
+strawberry is really the much enlarged flower axis, or &ldquo;receptacle,&rdquo;
+in which the little one-seeded fruits are embedded, the latter being
+what are ordinarily called the seeds.</p>
+
+<div class="figcenter" style="width:639px;">
+<a name="fig114" id="fig114"></a>
+<img src="images/fig114.png" width="639" height="484"
+alt="Fig.&nbsp;114." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;114.</span>&mdash;<i>Calyciflor&aelig;</i> (<i>Rosiflor&aelig;</i>). <i>A</i>,
+inflorescence of strawberry (<i>Fragaria</i>), &times;&nbsp;&frac12;. <i>B</i>, a single flower,
+&times;&nbsp;1. <i>C</i>, section of <i>B</i>. <i>D</i>, floral diagram. <i>E</i>, vertical section
+of a cherry-flower (<i>Prunus</i>), &times;&nbsp;1. <i>F</i>, vertical section of the
+flower of <i>Spir&aelig;a</i>, &times;&nbsp;2. <i>G</i>, vertical section of the bud of a wild
+rose (<i>Rosa</i>), &times;&nbsp;1. <i>H</i>, vertical section of the young fruit, &times;&nbsp;1.
+<i>I</i>, section of the flower of an apple (<i>Pyrus</i>), &times;&nbsp;1. <i>J</i>, floral
+diagram of apple.</p>
+</div>
+
+<p>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.</p>
+
+<div class="figcenter" style="width:610px;">
+<a name="fig115" id="fig115"></a>
+<img src="images/fig115.png" width="610" height="489"
+alt="Fig.&nbsp;115." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;115.</span>&mdash;<i>Calyciflor&aelig;</i> (<i>Leguminos&aelig;</i>). <i>A</i>, flowers
+and leaf of the common pea, <i>Pisum</i> (<i>Papilionace&aelig;</i>), &times;&nbsp;&frac12;. <i>t</i>,
+tendril. <i>st.</i> stipules. <i>B</i>, the petals, separated and displayed,
+&times;&nbsp;1. <i>C</i>, flower, with the calyx and corolla removed, &times;&nbsp;1. <i>D</i>, a
+fruit divided lengthwise, &times;&nbsp;&frac12;. <i>E</i>, the embryo, with one of the
+cotyledons removed, &times;&nbsp;2. <i>F</i>, diagram of the flower. <i>G</i>, flower of
+red-bud, <i>Cercis</i> (<i>C&aelig;salpinace&aelig;</i>), &times;&nbsp;2. <i>H</i>, the same, with calyx and
+corolla removed. <i>I</i>, inflorescence of the sensitive-brier,
+<i>Schrankia</i> (<i>Mimosace&aelig;</i>), &times;&nbsp;1. <i>J</i>, a single flower, &times;&nbsp;2.</p>
+</div>
+
+<p>The last order of the <i>Calyciflor&aelig;</i> and the highest of the
+<i>Choripetal&aelig;</i> is the order <i>Leguminos&aelig;</i>, 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,<span class="pagenum" title="Page&nbsp;208">&nbsp;</span><a name="Page_208" id="Page_208"></a> 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 &ldquo;keel&rdquo; (<a href="#fig115">Fig.&nbsp;115</a>, <i>A</i>, <i>B</i>). The stamens,
+ten in number, are sometimes all grown together into a tube, but
+generally the upper one is free from the others (<a href="#fig115">Fig.&nbsp;115</a>, <i>C</i>). There
+is but one carpel which forms a pod with two valves when ripe
+(<a href="#fig115">Fig.&nbsp;115</a>, <i>D</i>). The seeds are large, and the embryo fills the seed
+completely. From the peculiar form of the flower, they are known as
+<i>Papilionace&aelig;</i> (<i>papilio</i>, a butterfly). Many of the <span class="pagenum" title="Page&nbsp;209">&nbsp;</span><a name="Page_209" id="Page_209"></a><i>Papilionace&aelig;</i>
+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
+(<a href="#fig115">Fig.&nbsp;115</a>, <i>A</i>), vetch, etc. The leaves are usually compound.</p>
+
+<p>Of the second family (<i>C&aelig;salpine&aelig;</i>), mainly tropical, the honey locust
+(<i>Gleditschia</i>) and red-bud (<i>Cercis</i>) (<a href="#fig115">Fig.&nbsp;115</a>, <i>G</i>) are the
+commonest examples. The flowers differ mainly from the <i>Papilionace&aelig;</i>
+in being less perfectly papilionaceous, and the stamens are almost
+entirely distinct (<a href="#fig115">Fig.&nbsp;115</a>, <i>H</i>). The last family (<i>Mimosace&aelig;</i>) is
+also mainly tropical. The acacias, sensitive-plant (<i>Mimosa</i>), and the
+sensitive-brier of the southern United States (<i>Schrankia</i>) (<a href="#fig115">Fig.&nbsp;115</a>,
+<i>I</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 <i>Sympetal&aelig;</i>. The leaves of <i>Mimosa</i> and
+<i>Schrankia</i> are extraordinarily sensitive, folding up if irritated.</p>
+
+
+
+
+<hr />
+<h2><span class="pagenum" title="Page&nbsp;210">&nbsp;</span><a name="Page_210" id="Page_210"></a><a name="CHAPTER_XIX" id="CHAPTER_XIX"></a>CHAPTER XIX.
+<br />
+<small>CLASSIFICATION OF DICOTYLEDONS (<i>Continued</i>).
+<br />
+<span class="smcap">Division II</span>.&mdash;<i>Sympetal&aelig;</i>.</small></h2>
+
+<p><span class="smcap">The</span> <i>Sympetal&aelig;</i> or <i>Gamopetal&aelig;</i> are at once distinguished from the
+<i>Choripetal&aelig;</i> by having the petals more or less united, so that the
+corolla is to some extent tubular. In the last order of the
+<i>Choripetal&aelig;</i> we found a few examples (<i>Mimosace&aelig;</i>) where the same
+thing is true, and these form a transition from the <i>Choripetal&aelig;</i> to
+the <i>Sympetal&aelig;</i>.</p>
+
+<p>There are two great divisions, <i>Isocarp&aelig;</i> and <i>Anisocarp&aelig;</i>. 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 <i>Isocarp&aelig;</i> there are usually
+twice as many stamens as petals, occasionally the same number.</p>
+
+<p>There are three orders of the <i>Isocarp&aelig;</i>, viz., <i>Bicornes</i>,
+<i>Primulin&aelig;</i>, and <i>Diospyrin&aelig;</i>. 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 (<i>Epacride&aelig;</i>) are
+represented in the United States. Of these the <i>Pyrolace&aelig;</i> includes
+the pretty little pyrolas and prince&#8217;s-pine (<i>Chimaphila</i>) (<a href="#fig116">Fig.&nbsp;116</a>,
+<i>J</i>); the <i>Monotrope&aelig;</i> has as its commonest examples, the curious
+Indian-pipe (<i>Monotropa uniflora</i>), and pine-sap (<i>M.&nbsp;hypopitys</i>)
+(<a href="#fig116">Fig.&nbsp;116</a>, <i>L</i>). These grow on decaying vegetable matter, and are
+quite devoid of chlorophyll, the former species being pure white
+throughout (hence a popular name, &ldquo;ghost flower&rdquo;); the latter is
+yellowish. The magnificent rhododendrons and azaleas (<a href="#fig116">Fig.&nbsp;116</a>, <i>F</i>),
+and the mountain laurel (<i>Kalmia</i>) (<a href="#fig116">Fig.&nbsp;116</a>, <i>I</i>), belong to the
+<i>Rhodorace&aelig;</i>. <span class="pagenum" title="Page&nbsp;211">&nbsp;</span><a name="Page_211" id="Page_211"></a>The heath family (<i>Ericace&aelig;</i>), besides the true heaths
+(<i>Erica</i>, <i>Calluna</i>), includes the pretty trailing-arbutus or
+may-flower (<i>Epig&aelig;a</i>), <i>Andromeda</i>, <i>Oxydendrum</i> (<a href="#fig116">Fig.&nbsp;116</a>, <i>E</i>),
+wintergreen (<i>Gaultheria</i>), etc. The last family is represented by the
+cranberry (<i>Vaccinium</i>) and huckleberry (<i>Gaylussacia</i>).</p>
+
+<div class="figcenter" style="width:597px;">
+<a name="fig116" id="fig116"></a>
+<img src="images/fig116.png" width="597" height="495"
+alt="Fig.&nbsp;116." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;116.</span>&mdash;Types of <i>Isocarpous sympetal&aelig;</i>
+(<i>Bicornes</i>). <i>A</i>, flowers, fruit, and leaves of huckleberry,
+<i>Gaylussacia</i> (<i>Vaccinie&aelig;</i>), &times;&nbsp;1. <i>B</i>, vertical section of the flower,
+&times;&nbsp;3. <i>C</i>, a stamen: <span class="smcap">i</span>, from in front; <span class="smcap">ii</span>, from the side, &times;&nbsp;4. <i>D</i>,
+cross-section of the young fruit, &times;&nbsp;2. <i>E</i>, flower of sorrel-tree,
+<i>Oxydendrum</i> (<i>Ericace&aelig;</i>), &times;&nbsp;2. <i>F</i>, flower of azalea
+(<i>Rhododendron</i>), &times;&nbsp;&frac12;. <i>G</i>, cross-section of the ovary, &times;&nbsp;3. <i>H</i>,
+diagram of the flower. <i>I</i>, flower of mountain laurel (<i>Kalmia</i>), &times;&nbsp;1.
+<i>J</i>, prince&#8217;s-pine, <i>Chimaphila</i> (<i>Pyrolace&aelig;</i>), &times;&nbsp;&frac12;. <i>K</i>, a single
+flower, &times;&nbsp;1. <i>L</i>, plant of pine-sap, <i>Monotropa</i>, (<i>Monotrope&aelig;</i>), &times;&nbsp;&frac12;.
+<i>M</i>, section of a flower, &times;&nbsp;1.</p>
+</div>
+
+<p>The second order, the primroses (<i>Primulin&aelig;</i>), is principally
+represented in the cooler parts of the world by the true primrose
+family (<i>Primulace&aelig;</i>), of which several familiar plants may be
+mentioned. The genus <i>Primula</i> includes the European primrose and
+cowslip, as well as two or three small American species, and the
+commonly cultivated Chinese primrose. <span class="pagenum" title="Page&nbsp;212">&nbsp;</span><a name="Page_212" id="Page_212"></a>Other genera are <i>Dodecatheon</i>,
+of which the beautiful shooting-star (<i>D.&nbsp;Meadia</i>) (<a href="#fig117">Fig.&nbsp;117</a>, <i>A</i>) is
+the best known. Something like this is <i>Cyclamen</i>, sometimes
+cultivated as a house plant. The moneywort (<i>Lysimachia nummularia</i>)
+(<a href="#fig117">Fig.&nbsp;117</a>, <i>D</i>), as well as other species, also belongs here.</p>
+
+<div class="figcenter" style="width:614px;">
+<a name="fig117" id="fig117"></a>
+<img src="images/fig117.png" width="614" height="494"
+alt="Fig.&nbsp;117." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;117.</span>&mdash;<i>Isocarpous sympetal&aelig;</i> (<i>Primulin&aelig;</i>,
+<i>Diospyrin&aelig;</i>). <i>A</i>, shooting-star, <i>Dodecatheon</i> (<i>Primulace&aelig;</i>), &times;&nbsp;&frac12;.
+<i>B</i>, section of a flower, &times;&nbsp;1. <i>C</i>, diagram of the flower. <i>D</i>,
+Moneywort, <i>Lysimachia</i> (<i>Primulace&aelig;</i>), &times;&nbsp;&frac12;. <i>E</i>, a perfect flower of
+the persimmon, <i>Diospyros</i> (<i>Ebenace&aelig;</i>), &times;&nbsp;1. <i>F</i>, the same, laid open:
+section of the young fruit, &times;&nbsp;2. <i>H</i>, longitudinal section of a ripe
+seed, &times;&nbsp;1. <i>em.</i> the embryo. <i>I</i>, fruit, &times;&nbsp;&frac12;.</p>
+</div>
+
+<p>The sea-rosemary (<i>Statice</i>) and one or two cultivated species of
+plumbago are the only members of the plumbago family (<i>Plumbagine&aelig;</i>)
+likely to be met with. The remaining families of the <i>Primulin&aelig;</i> are
+not represented by any common plants.</p>
+
+<p>The third and last order of the <i>Isocarpous sympetal&aelig;</i> has but a
+single common representative in the United States; viz., the persimmon
+(<i>Diospyros</i>) (<a href="#fig117">Fig.&nbsp;117</a>, <i>E</i>). This belongs to the family <i>Ebenace&aelig;</i>,
+to which also belongs the ebony <span class="pagenum" title="Page&nbsp;213">&nbsp;</span><a name="Page_213" id="Page_213"></a>a member of the same genus as the
+persimmon, and found in Africa and Asia.</p>
+
+<p>The second division of the <i>Sympetal&aelig;</i> (the <i>Anisocarp&aelig;</i>) 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.</p>
+
+<div class="figcenter" style="width:543px;">
+<a name="fig118" id="fig118"></a>
+<img src="images/fig118.png" width="543" height="486"
+alt="Fig.&nbsp;118." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;118.</span>&mdash;Types of <i>Anisocarpous sympetal&aelig;</i>
+(<i>Tubiflor&aelig;</i>). <i>A</i>, flower and leaves of wild phlox (<i>Polemoniace&aelig;</i>),
+&times;&nbsp;&frac12;. <i>B</i>, section of a flower, &times;&nbsp;1. <i>C</i>, fruit, &times;&nbsp;1. <i>D</i>, flower of
+blue valerian (<i>Polemonium</i>), &times;&nbsp;1. <i>E</i>, flowers and leaf of
+water-leaf, <i>Hydrophyllum</i> (<i>Hydrophyllace&aelig;</i>), &times;&nbsp;&frac12;. <i>F</i>, section of a
+flower, &times;&nbsp;1. <i>G</i>, flower of wild morning-glory, <i>Convolvulus</i>
+(<i>Convolvulace&aelig;</i>), &times;&nbsp;&frac12;. One of the bracts surrounding the calyx and
+part of the corolla are cut away. <i>H</i>, diagram of the flower. <i>I</i>, the
+fruit of a garden morning-glory, from which the outer wall has fallen,
+leaving only the inner membranous partitions, &times;&nbsp;1. <i>J</i>, a seed, &times;&nbsp;1.
+<i>K</i>, cross-section of a nearly ripe seed, showing the crumpled embryo,
+&times;&nbsp;2. <i>L</i>, an embryo removed from a nearly ripe seed, and spread out;
+one of the cotyledons has been partially removed, &times;&nbsp;1.</p>
+</div>
+
+<p>The first order (<i>Tubiflor&aelig;</i>) has, as the name indicates, tubular
+flowers which show usually perfect, radial symmetry
+(<i>Actinomorphism</i>). There are five families, all represented by
+familiar plants. The first (<i>Convolvulace&aelig;</i>) has as its type the
+morning-glory (<i>Convolvulus</i>) (<a href="#fig118">Fig.&nbsp;118</a>, <i>G</i>), and the nearly<span class="pagenum" title="Page&nbsp;214">&nbsp;</span><a name="Page_214" id="Page_214"></a> related
+<i>Ipom&#339;as</i> of the gardens. The curious dodder (<i>Cuscuta</i>), 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 (<i>Batatas</i>) is
+also a member of the morning-glory family. The numerous species, wild
+and cultivated, of phlox (<a href="#fig118">Fig.&nbsp;118</a>, <i>A</i>), and the blue valerian
+(<i>Polemonium</i>) (<a href="#fig118">Fig.&nbsp;118</a>, <i>D</i>), are examples of the family
+<i>Polemoniace&aelig;</i>.</p>
+
+<div class="figcenter" style="width:595px;">
+<a name="fig119" id="fig119"></a>
+<img src="images/fig119.png" width="595" height="505"
+alt="Fig.&nbsp;119." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;119.</span>&mdash;<i>Anisocarpous sympetal&aelig;</i> (<i>Tubiflor&aelig;</i>). <i>A</i>,
+inflorescence of hound&#8217;s-tongue, <i>Cynoglossum</i> (<i>Borragine&aelig;</i>), &times;&nbsp;&frac12;.
+<i>B</i>, section of a flower, &times;&nbsp;2. <i>C</i>, nearly ripe fruit, &times;&nbsp;1. <i>D</i>,
+flowering branch of nightshade, <i>Solanum</i> (<i>Solane&aelig;</i>), &times;&nbsp;&frac12;. <i>E</i>, a
+single flower, &times;&nbsp;1. <i>F</i>, section of the flower, &times;&nbsp;2. <i>G</i>, young fruit,
+&times;&nbsp;1. <i>H</i>, flower of <i>Petunia</i> (<i>Solane&aelig;</i>), &times;&nbsp;&frac12;. <i>I</i>, diagram of the
+flower.</p>
+</div>
+
+<p>The third family (<i>Hydrophyllace&aelig;</i>) includes several species of
+water-leaf (<i>Hydrophyllum</i>) (<a href="#fig118">Fig.&nbsp;118</a>, <i>E</i>) and <i>Phacelia</i>, among our
+wild flowers, and species of <i>Nemophila</i>, <i>Whitlavia</i> and others from
+the western states, but now common in gardens.</p>
+
+<p><span class="pagenum" title="Page&nbsp;215">&nbsp;</span><a name="Page_215" id="Page_215"></a>The Borage family (<i>Borragine&aelig;</i>) includes the forget-me-not
+(<i>Myosotis</i>) and a few pretty wild flowers, <i>e.g.</i> the orange-flowered
+puccoons (<i><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Lithospernum&rsquo;.">Lithospermum</ins></i>); but it also embraces a
+number of the most troublesome weeds, among which are the
+hound&#8217;s-tongue (<i>Cynoglossum</i>) (<a href="#fig119">Fig.&nbsp;119</a>, <i>A</i>), and the
+&ldquo;beggar&#8217;s-ticks&rdquo; (<i><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Echinospernum&rsquo;.">Echinospermum</ins></i>), whose prickly
+fruits (<a href="#fig119">Fig.&nbsp;119</a>, <i>C</i>) 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.</p>
+
+<p>The last family (<i>Solane&aelig;</i>) includes the nightshades (<i>Solanum</i>)
+(<a href="#fig119">Fig.&nbsp;119</a>, <i>D</i>), to which genus the potato (<i>S.&nbsp;tuberosum</i>) and the
+egg-plant (<i>S.&nbsp;Melongena</i>) also belong. Many of the family contain a
+poisonous principle, <i>e.g.</i> the deadly nightshade (<i>Atropa</i>), tobacco
+(<i>Nicotiana</i>), stramonium (<i>Datura</i>), and others. Of the cultivated
+plants, besides those already mentioned, the tomato (<i>Lycopersicum</i>),
+and various species of <i>Petunia</i> (<a href="#fig119">Fig.&nbsp;119</a>, <i>H</i>), <i>Solanum</i>, and
+<i>Datura</i> are the commonest.</p>
+
+<p>The second order of the <i>Anisocarp&aelig;</i> consists of plants whose flowers
+usually exhibit very marked, bilateral symmetry (<i>Zygomorphism</i>). From
+the flower often being two-lipped (see <a href="#fig120">Fig.&nbsp;120</a>), the name of the
+order (<i>Labiatiflor&aelig;</i>) is derived.</p>
+
+<p>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 (<i>Labiat&aelig;</i>) and the figworts (<i>Scrophularine&aelig;</i>).
+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 (<a href="#fig120">Fig.&nbsp;120</a>, <i>D</i>, <i>F</i>).</p>
+
+<blockquote><p>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 (<i>Lamium</i>) (<a href="#fig120">Fig.&nbsp;120</a>,
+<i>A</i>) is a thoroughly typical example. The sage, mints, catnip, thyme,
+lavender, etc., will recall the peculiarities of the family.</p></blockquote>
+
+<p><span class="pagenum" title="Page&nbsp;216">&nbsp;</span><a name="Page_216" id="Page_216"></a>The stamens are usually four in number through the abortion of one of
+them, but sometimes only two perfect stamens are present.</p>
+
+<div class="figcenter" style="width:608px;">
+<a name="fig120" id="fig120"></a>
+<img src="images/fig120.png" width="608" height="477"
+alt="Fig.&nbsp;120." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;120.</span>&mdash;<i>Anisocarpous sympetal&aelig;</i> (<i>Labiatiflor&aelig;</i>).
+<i>A</i>, dead nettle, <i>Lamium</i>, (<i>Labiat&aelig;</i>), &times;&nbsp;&frac12;. <i>B</i>, a single flower,
+&times;&nbsp;1. <i>C</i>, the stamens and pistil, &times;&nbsp;1. <i>D</i>, cross-section of the
+ovary, &times;&nbsp;2. <i>E</i>, diagram of the flower; the position of the absent
+stamen is indicated by the small circle. <i>F</i>, fruit of the common
+sage, <i>Salvia</i> (<i>Labiat&aelig;</i>), &times;&nbsp;1. Part of the persistent calyx has been
+removed to show the four seed-like fruits, or nutlets. <i>G</i>, section of
+a nutlet, &times;&nbsp;3. The embryo fills the seed completely. <i>H</i>, part of an
+inflorescence of figwort, <i>Scrophularia</i> (<i>Scrophularine&aelig;</i>), &times;&nbsp;1. <i>I</i>,
+cross-section of the young fruit, &times;&nbsp;2. <i>J</i>, flower of speedwell,
+<i>Veronica</i> (<i>Scrophularine&aelig;</i>), &times;&nbsp;2. <i>K</i>, fruit of <i>Veronica</i>, &times;&nbsp;2.
+<i>L</i>, cross-section of <i>K</i>. <i>M</i>, flower of moth-mullein, <i>Verbascum</i>
+(<i>Scrophularine&aelig;</i>), &times;&nbsp;&frac12;. <i>N</i>, flower of toad-flax, <i>Linaria</i>
+(<i>Scrophularine&aelig;</i>), &times;&nbsp;1. <i>O</i>, leaf of bladder-weed, <i>Utricularia</i>
+(<i>Lentibulariace&aelig;</i>), &times;&nbsp;1. <i>x</i>, one of the &ldquo;traps.&rdquo; <i>P</i>, a single trap,
+&times;&nbsp;5.</p>
+</div>
+
+<p>The <i>Scrophularine&aelig;</i> differ mainly from the <i>Labiat&aelig;</i> 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 (<i>Verbascum</i>) (<a href="#fig120">Fig.&nbsp;120</a>, <i>M</i>), where the flower is only
+slightly zygomorphic, there is a fifth rudimentary<span class="pagenum" title="Page&nbsp;217">&nbsp;</span><a name="Page_217" id="Page_217"></a> stamen, while in
+others (<i>e.g.</i> <i>Veronica</i>) (<a href="#fig120">Fig.&nbsp;120</a>, <i>J</i>) there are but two stamens.
+Many have large, showy flowers, as in the cultivated foxglove
+(<i>Digitalis</i>), and the native species of <i>Gerardia</i>, mullein,
+<i>Mimulus</i>, etc., while a few like the figwort, <i>Scrophularia</i>
+(<a href="#fig120">Fig.&nbsp;120</a>, <i>H</i>), and speedwells (<i>Veronica</i>) have duller-colored or
+smaller flowers.</p>
+
+<div class="figcenter" style="width:613px;">
+<a name="fig121" id="fig121"></a>
+<img src="images/fig121.png" width="613" height="515"
+alt="Fig.&nbsp;121." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;121.</span>&mdash;<i>Anisocarpous sympetal&aelig;</i> (<i>Labiatiflor&aelig;</i>).
+<i>A</i>, flowering branch of trumpet-creeper, <i>Tecoma</i> (<i>Bignoniace&aelig;</i>),
+&times;&nbsp;&frac14;. <i>B</i>, a single flower, divided lengthwise, &times;&nbsp;&frac12;. <i>C</i>, cross-section
+of the ovary, &times;&nbsp;2. <i>D</i>, diagram of the flower. <i>E</i>, flower of vervain,
+<i>Verbena</i> (<i>Verben&aelig;</i>), &times;&nbsp;2: <span class="smcap">i</span>, from the side; <span class="smcap">ii</span>, from in front; <span class="smcap">iii</span>,
+the corolla laid open. <i>F</i>, nearly ripe fruit of the same, &times;&nbsp;2. <i>G</i>,
+part of a spike of flowers of the common plantain, <i>Plantago</i>
+(<i>Plantagine&aelig;</i>), &times;&nbsp;1; The upper flowers have the pistils mature, but
+the stamens are not yet ripe. <i>H</i>, a flower from the upper (younger)
+part of the spike. <i>I</i>, an older expanded flower, with ripe stamens,
+&times;&nbsp;3.</p>
+</div>
+
+<p>The curious bladder-weed (<i>Utricularia</i>) is the type of the family
+<i>Lentibulariace&aelig;</i>, aquatic or semi-aquatic plants which possess
+special contrivances for capturing insects or small water animals.
+These in the bladder-weed are little sacs (<a href="#fig120">Fig.&nbsp;120</a>,<span class="pagenum" title="Page&nbsp;218">&nbsp;</span><a name="Page_218" id="Page_218"></a> <i>P</i>) 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, <i>Pinguicula</i>, however, there is much
+the same arrangement as in the sundew.</p>
+
+<p>The family <i>Gesnerace&aelig;</i> is mainly a tropical one, represented in the
+greenhouses by the magnificent <i>Gloxinia</i> and <i>Achimenes</i>, but of
+native plants there are only a few parasitic forms destitute of
+chlorophyll and with small, inconspicuous flowers. The commonest of
+these is <i>Epiphegus</i>, 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, &ldquo;beech-drops.&rdquo;</p>
+
+<p>The bignonia family (<i>Bignoniace&aelig;</i>) is mainly tropical, but in our
+southern states is represented by the showy trumpet-creeper (<i>Tecoma</i>)
+(<a href="#fig121">Fig.&nbsp;121</a>, <i>A</i>), the catalpa, and <i>Martynia</i>.</p>
+
+<p>The other plants likely to be met with by the student belong either to
+the <i>Verbenace&aelig;</i>, represented by the showy verbenas of the gardens,
+and our much less showy wild vervains, also belonging to the genus
+<i>Verbena</i> (<a href="#fig121">Fig.&nbsp;121</a>, <i>E</i>); or to the plantain family (<i>Plantagine&aelig;</i>),
+of which the various species of plantain (<i>Plantago</i>) are familiar to
+every one (<a href="#fig121">Fig.&nbsp;121</a>, <i>G</i>, <i>I</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.</p>
+
+<p>The third order (<i>Contort&aelig;</i>) of the <i>Anisocarp&aelig;</i> includes five
+families, all represented by familiar forms. The first, the olive
+family (<i>Oleace&aelig;</i>), besides the olive, contains the lilac and jasmine
+among cultivated plants, and the various species of ash (<i>Fraxinus</i>),
+and the pretty fringe-tree (<i>Chionanthus</i>) (<a href="#fig122">Fig.&nbsp;122</a>, <i>A</i>), often
+cultivated for its abundant white flowers. The other families are the
+<i>Gentianace&aelig;</i> including the true gentians (<i>Gentiana</i>) (<a href="#fig122">Fig.&nbsp;122</a>,
+<i>F</i>), the buck-bean (<i>Menyanthes</i>), the <span class="pagenum" title="Page&nbsp;219">&nbsp;</span><a name="Page_219" id="Page_219"></a>centauries
+(<i><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Eryther&aelig;a&rsquo;.">Erythr&aelig;a</ins></i> and <i>Sabbatia</i>), and several other less
+familiar genera; <i>Loganiace&aelig;</i>, with the pink-root (<i>Spigelia</i>)
+(<a href="#fig122">Fig.&nbsp;122</a>, <i>D</i>), as the best-known example; <i>Apocynace&aelig;</i> including the
+dog-bane (<i>Apocynum</i>) (<a href="#fig122">Fig.&nbsp;122</a>, <i>H</i>), and in the gardens the oleander
+and periwinkle (<i>Vinca</i>).</p>
+
+<div class="figcenter" style="width:552px;">
+<a name="fig122" id="fig122"></a>
+<img src="images/fig122.png" width="552" height="506"
+alt="Fig.&nbsp;122." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;122.</span>&mdash;<i>Anisocarpous sympetal&aelig;</i> (<i>Contort&aelig;</i>). <i>A</i>,
+flower of fringe-tree, <i>Chionanthus</i> (<i>Oleace&aelig;</i>), &times;&nbsp;1. <i>B</i>, base of
+the flower, with part of the calyx and corolla removed, &times;&nbsp;2. <i>C</i>,
+fruit of white ash, <i>Fraxinus</i> (<i>Oleace&aelig;</i>), &times;&nbsp;1. <i>D</i>, flower of
+pink-root, <i>Spigelia</i> (<i>Loganiace&aelig;</i>), &times;&nbsp;&frac12;. <i>E</i>, cross-section of the
+ovary, &times;&nbsp;3. <i>F</i>, flower of fringed gentian, <i>Gentiana</i>
+(<i>Gentianace&aelig;</i>), &times;&nbsp;&frac12;. <i>G</i>, diagram of the flower. <i>H</i>, flowering
+branch of dog-bane, <i>Apocynum</i> (<i>Apocynace&aelig;</i>), &times;&nbsp;&frac12;. <i>I</i>, vertical
+section of a flower, &times;&nbsp;2. <i>J</i>, bud. <i>K</i>, flower of milk-weed,
+<i>Asclepias</i> (<i>Asclepiadace&aelig;</i>), &times;&nbsp;1. <i>L</i>, vertical section through the
+upper part of the flower, &times;&nbsp;2. <i>gy.</i> pistil. <i>p</i>, pollen masses. <i>an.</i>
+stamen. <i>M</i>, a pair of pollen masses, &times;&nbsp;6. <i>N</i>, a nearly ripe seed,
+&times;&nbsp;1.</p>
+</div>
+
+<p>The last family is the milk-weeds (<i>Asclepiadace&aelig;</i>), which have
+extremely complicated flowers. Our numerous milk-weeds (<a href="#fig122">Fig.&nbsp;122</a>, <i>K</i>)
+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.<span class="pagenum" title="Page&nbsp;220">&nbsp;</span><a name="Page_220" id="Page_220"></a> Besides the true milk-weeds (<i>Asclepias</i>),
+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 (<i>Hoya</i>), and <i>Physianthus</i> are the commonest.</p>
+
+<div class="figcenter" style="width:613px;">
+<a name="fig123" id="fig123"></a>
+<img src="images/fig123.png" width="613" height="486"
+alt="Fig.&nbsp;123." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;123.</span>&mdash;<i>Anisocarpous sympetal&aelig;</i> (<i>Campanulin&aelig;</i>).
+<i>A</i>, vertical section of the bud of American bell-flower, <i>Campanula</i>
+(<i>Campanulace&aelig;</i>), &times;&nbsp;2. <i>B</i>, an expanded flower, &times;&nbsp;1. The stamens have
+discharged their pollen, and the stigma has opened. <i>C</i>, cross-section
+of the ovary, &times;&nbsp;3. <i>D</i>, flower of the Carpathian bell-flower
+(<i>Campanula Carpatica</i>), &times;&nbsp;1. <i>E</i>, flower of cardinal-flower,
+<i>Lobelia</i> (<i>Lobeliace&aelig;</i>), &times;&nbsp;1. <i>F</i>, the same, with the corolla and
+sepals removed. <i>an.</i> the united anthers. <i>gy.</i> the tip of the pistil.
+<i>G</i>, the tip of the pistil, &times;&nbsp;2, showing the circle of hairs
+surrounding the stigma. <i>H</i>, cross-section of the ovary, &times;&nbsp;3. <i>I</i>, tip
+of a branch of cucumber, <i>Cucurbita</i> (<i>Cucurbitace&aelig;</i>), with an
+expanded female flower (&#9792;). <i>J</i>, andr&#339;cium of a male flower, showing
+the peculiar convoluted anthers (<i>an.</i>), &times;&nbsp;2. <i>K</i>, cross-section of
+the ovary, &times;&nbsp;2.</p>
+</div>
+
+<p>The fourth order (<i>Campanulin&aelig;</i>) also embraces five families, but of
+these only three are represented among our wild plants. The
+bell-flowers (<i>Campanula</i>) (<a href="#fig123">Fig.&nbsp;123</a>, <i>A</i>, <i>D</i>) are examples <span class="pagenum" title="Page&nbsp;221">&nbsp;</span><a name="Page_221" id="Page_221"></a>of the
+family <i>Campanulace&aelig;</i>, and numerous species are common, both wild and
+cultivated.</p>
+
+<div class="figcenter" style="width:637px;">
+<a name="fig124" id="fig124"></a>
+<img src="images/fig124.png" width="637" height="484"
+alt="Fig.&nbsp;124." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;124.</span>&mdash;<i>Anisocarpous sympetal&aelig;</i> (<i>Aggregat&aelig;</i>). <i>A</i>,
+flowering branch of <i>Houstonia purpurea</i>, &times;&nbsp;1 (<i>Rubiace&aelig;</i>). <i>B</i>,
+vertical section of a flower, &times;&nbsp;2. <i>C</i>, fruit of bluets (<i>Houstonia
+c&#339;rulea</i>), &times;&nbsp;1. <i>D</i>, cross-section of the same. <i>E</i>, bedstraw,
+<i>Galium</i> (<i>Rubiace&aelig;</i>), &times;&nbsp;&frac12;. <i>F</i>, a single flower, &times;&nbsp;2. <i>G</i>, flower of
+arrow-wood, <i>Viburnum</i> (<i>Caprifoliace&aelig;</i>), &times;&nbsp;2. <i>H</i>, the same, divided
+vertically. <i>I</i>, flowering branch of trumpet honeysuckle,
+<i><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Loniccera&rsquo;.">Lonicera</ins></i> (<i>Caprifoliace&aelig;</i>), &times;&nbsp;&frac12;. <i>J</i>, a single flower,
+the upper part laid open, &times;&nbsp;1. <i>K</i>, diagram of the flower. <i>L</i>, part
+of the inflorescence of valerian, <i>Valeriana</i>, (<i>Valeriane&aelig;</i>), &times;&nbsp;1.
+<i>M</i>, young; <i>N</i>, older flower, &times;&nbsp;2. <i>O</i>, 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. <i>P</i>, inflorescence of teasel,
+<i>Dipsacus</i> (<i>Dipsace&aelig;</i>), &times;&nbsp;&frac14;. <i>fl.</i> flowers. <i>Q</i>, a single flower,
+&times;&nbsp;1. <i>R</i>, the same, with the corolla laid open.</p>
+</div>
+
+<p>The various species of <i>Lobelia</i>, of which the splendid
+cardinal-flower (<i>L.&nbsp;Cardinalis</i>) (<a href="#fig123">Fig.&nbsp;123</a>, <i>E</i>) is one of the most
+beautiful, represent the very characteristic family <i>Lobeliace&aelig;</i>.
+Their milky juice contains more or less marked poisonous properties.
+The last family of the order is the gourd family (<i>Cucurbitace&aelig;</i>),
+represented by a few wild species, but best known by the many
+cultivated varieties of melons, cucumbers, <span class="pagenum" title="Page&nbsp;222">&nbsp;</span><a name="Page_222" id="Page_222"></a>squashes, etc. They are
+climbing or running plants, and provided with tendrils. The flowers
+are usually unisexual, sometimes di&#339;cious, but oftener mon&#339;cious
+(<a href="#fig123">Fig.&nbsp;123</a>, <i>I</i>).</p>
+
+<div class="figcenter" style="width:621px;">
+<a name="fig125" id="fig125"></a>
+<img src="images/fig125.png" width="621" height="491"
+alt="Fig.&nbsp;125." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;125.</span>&mdash;<i>Anisocarpous sympetal&aelig;</i> (<i>Aggregat&aelig;</i>).
+Types of <i>Composit&aelig;</i>. <i>A</i>, inflorescence of Canada thistle
+(<i>Cirsium</i>), &times;&nbsp;1. <i>B</i>, vertical section of <i>A</i>. <i>r</i>, the receptacle or
+enlarged end of the stem, to which the separate flowers are attached.
+<i>C</i>, a single flower, &times;&nbsp;2. <i>o</i>, the ovary. <i>p</i>, the &ldquo;pappus&rdquo; (calyx
+lobes). <i>an.</i> the united anthers. <i>D</i>, the upper part of the stamens
+and pistil, &times;&nbsp;3: <span class="smcap">i</span>, from a young flower; <span class="smcap">ii</span>, from an older one. <i>an.</i>
+anthers. <i>gy.</i> pistil. <i>E</i>, ripe fruit, &times;&nbsp;1. <i>F</i>, inflorescence of
+may-weed (<i>Maruta</i>). The central part (disc) is occupied by perfect
+tubular flowers (<i>G</i>), the flowers about the edge (rays) are sterile,
+with the corolla much enlarged and white, &times;&nbsp;2. <i>G</i>, a single flower
+from the disc, &times;&nbsp;3. <i>H</i>, inflorescence of dandelion (<i>Taraxacum</i>), the
+flowers all alike, with strap-shaped corollas, &times;&nbsp;1. <i>I</i>, a single
+flower, &times;&nbsp;2. <i>c</i>, the split, strap-shaped corolla. <i>J</i>, two ripe
+fruits, still attached to the receptacle (<i>r</i>). The pappus is raised
+on a long stalk, &times;&nbsp;1. <i>K</i>, a single fruit, &times;&nbsp;2.</p>
+</div>
+
+<p>The last and highest order of the <i>Sympetal&aelig;</i>, and hence of the
+dicotyledons, is known as <i>Aggregat&aelig;</i>, 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,<span class="pagenum" title="Page&nbsp;223">&nbsp;</span><a name="Page_223" id="Page_223"></a> five of which have common
+representatives, but the last family (<i>Calycere&aelig;</i>) has no members
+within our limits.</p>
+
+<p>The lower members of the order, <i>e.g.</i> various <i>Rubiace&aelig;</i> (<a href="#fig124">Fig.&nbsp;124</a>,
+<i>A</i>, <i>E</i>), 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
+<i>Dipsace&aelig;</i> (<a href="#fig124">Fig.&nbsp;124</a>, <i>P</i>) and <i>Composit&aelig;</i> (<a href="#fig125">Fig.&nbsp;125</a>) 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 <i>Composit&aelig;</i>
+there are three well-marked types. The first of these may be
+represented by the thistles (<a href="#fig125">Fig.&nbsp;125</a>, <i>A</i>). The so-called flower of
+the thistle is in reality a close head of small, tubular flowers
+(<a href="#fig125">Fig.&nbsp;125</a>, <i>C</i>), 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 &ldquo;pappus&rdquo;) (<i>p</i>) have
+the form of fine hairs. These little flowers are attached to the
+enlarged upper end of the flower stalk (receptacle, <i>r</i>), 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 (<a href="#fig125">Fig.&nbsp;125</a>,
+<i>F</i>), 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 &ldquo;ray-flowers.&rdquo; In the third group, of which the
+dandelion (<a href="#fig125">Fig.&nbsp;125</a>, <i>H</i>), chicory, lettuce, etc., are examples, all
+of the flowers have strap-shaped, split corollas, and contain both
+stamens and pistils.</p>
+
+<p>The families of the <i>Aggregat&aelig;</i> are the following: I.&nbsp;<i>Rubiace&aelig;</i> of
+which <i>Houstonia</i> (<a href="#fig124">Fig.&nbsp;124</a>, <i>A</i>), <i>Galium</i> (<i>E</i>), <i>Cephalanthus</i>
+(button-bush), and <i>Mitchella</i> (partridge-berry) are examples;
+II.&nbsp;<i>Caprifoliace&aelig;</i>, containing the honeysuckles (<i>Lonicera</i>)
+(<a href="#fig124">Fig.&nbsp;124</a>, <i>I</i>), <i>Viburnum</i> (<i>G</i>), snowberry (<i>Symphoricarpus</i>), <span class="pagenum" title="Page&nbsp;224">&nbsp;</span><a name="Page_224" id="Page_224"></a>and
+elder (<i>Sambucus</i>); III.&nbsp;<i>Valeriane&aelig;</i>, represented by the common
+valerian (<i>Valeriana</i>) (<a href="#fig124">Fig.&nbsp;124</a>, <i>L</i>); IV.&nbsp;<i>Dipsace&aelig;</i>, of which the
+teasel (<i>Dipsacus</i>) (<a href="#fig124">Fig.&nbsp;124</a>, <i>P</i>), is the type, and also species of
+scabious (<i>Scabiosa</i>); V.&nbsp;<i>Composit&aelig;</i> to which the innumerable,
+so-called compound flowers, asters, golden-rods, daisies, sunflowers,
+etc. belong; VI.&nbsp;<i>Calycere&aelig;</i>.</p>
+
+<div class="figcenter" style="width:383px;">
+<a name="fig126" id="fig126"></a>
+<img src="images/fig126.png" width="383" height="457"
+alt="Fig.&nbsp;126." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;126.</span>&mdash;<i>Aristolochiace&aelig;</i>. <i>A</i>, plant of wild ginger
+(<i>Asarum</i>), &times;&nbsp;&#8531;. <i>B</i>, vertical section of the flower, &times;&nbsp;1. <i>C</i>,
+diagram of the flower.</p>
+</div>
+
+<p>Besides the groups already mentioned, there are several families of
+dicotyledons whose affinities are very doubtful. They are largely
+parasitic, <i>e.g.</i> mistletoe; or water plants, as the horned pond-weed
+(<i>Ceratophyllum</i>). One family, the <i>Aristolochiace&aelig;</i>, represented by
+the curious &ldquo;Dutchman&#8217;s pipe&rdquo; (<i>Aristolochia sipho</i>), a woody twiner
+with very large leaves, and the common wild ginger (<i>Asarum</i>)
+(<a href="#fig126">Fig.&nbsp;126</a>), do not appear to be in any wise parasitic, but the
+structure of their curious flowers differs widely from any other group
+of plants.</p>
+
+
+
+<hr />
+<h2><span class="pagenum" title="Page&nbsp;225">&nbsp;</span><a name="Page_225" id="Page_225"></a><a name="CHAPTER_XX" id="CHAPTER_XX"></a>CHAPTER XX.
+<br />
+<small>FERTILIZATION OF FLOWERS.</small></h2>
+
+
+<p><span class="smcap">If</span> 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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>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<span class="pagenum" title="Page&nbsp;226">&nbsp;</span><a name="Page_226" id="Page_226"></a> 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.</p>
+
+<p>That the fertilization of a flower by pollen from another is
+beneficial has been shown by many careful experiments which show that
+nearly always&mdash;at least in flowers where there are special
+contrivances for cross-fertilization&mdash;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 (<a href="#fig121">Fig.&nbsp;121</a>, <i>A</i>), to take the place of
+insects.<a name="FNanchor_14_14" id="FNanchor_14_14"></a><a href="#Footnote_14_14" class="fnanchor">[14]</a></p>
+
+<p>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, <i>e.g.</i> willow-herb (<a href="#fig113">Fig.&nbsp;113</a>, <i>D</i>),
+campanula (<a href="#fig123">Fig.&nbsp;123</a>, <i>A</i>, <i>D</i>), <span class="pagenum" title="Page&nbsp;227">&nbsp;</span><a name="Page_227" id="Page_227"></a>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 (<a href="#fig121">Fig.&nbsp;121</a>, <i>G</i>).</p>
+
+<p>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 (<a href="#fig99">Fig.&nbsp;99</a>, <i>J</i>).</p>
+
+<p>The tubular flowers of the <i>Sympetal&aelig;</i> 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.</p>
+
+<p>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 (<a href="#fig89">Fig.&nbsp;89</a>) or one of the <i>Habenarias</i> (<a href="#fig90">Fig.&nbsp;90</a>,
+<i>G</i>). 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 <span class="pagenum" title="Page&nbsp;228">&nbsp;</span><a name="Page_228" id="Page_228"></a>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 (<a href="#fig89">Fig.&nbsp;89</a>, <i>D</i>, <span class="smcap">ii</span>, <span class="smcap">iii</span>), 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.</p>
+
+<p>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 &ldquo;heterostylism.&rdquo; Examples of this are the primroses
+(<i>Primula</i>), loosestrife (<i>Lythrum</i>), partridge-berry (<i>Mitchella</i>),
+pickerel-weed (<i>Pontederia</i>), (<a href="#fig84">Fig.&nbsp;84</a>, <i>I</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 <i>vice versa</i>. 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, <i>e.g.</i>
+<i>Pontederia</i>, 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.</p>
+
+<p>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 <span class="pagenum" title="Page&nbsp;229">&nbsp;</span><a name="Page_229" id="Page_229"></a>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.</p>
+
+<p>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
+(<a href="#fig110">Fig.&nbsp;110</a>, <i>J</i>), the calla, and Jack-in-the-pulpit (<a href="#fig86">Fig.&nbsp;86</a>, <i>A</i>) are
+illustrations of this.</p>
+
+
+
+<hr />
+<h2><span class="pagenum" title="Page&nbsp;230">&nbsp;</span><a name="Page_230" id="Page_230"></a><a name="CHAPTER_XXI" id="CHAPTER_XXI"></a>CHAPTER XXI.
+<br />
+<small>HISTOLOGICAL METHODS.</small></h2>
+
+
+<p><span class="smcap">In</span> 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.</p>
+
+<blockquote><p>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 (<i>Allium Canadense</i>), 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.</p>
+
+<p>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.</p>
+
+<p><span class="pagenum" title="Page&nbsp;231">&nbsp;</span><a name="Page_231" id="Page_231"></a>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.</p></blockquote>
+
+<div class="figcenter" style="width:453px;">
+<a name="fig127" id="fig127"></a>
+<img src="images/fig127.png" width="453" height="310"
+alt="Fig.&nbsp;127." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;127.</span>&mdash;<i>A</i>, pollen mother cell of the wild onion.
+<i>n</i>, nucleus. <i>B&ndash;F</i>, early stages in the division of the nucleus.
+<i>par.</i> nucleolus; acetic acid, gentian violet, &times;&nbsp;350.</p>
+</div>
+
+<blockquote><p>If the spore mother cells are still quite young, we shall find the
+nucleus (<a href="#fig127">Fig.&nbsp;127</a>, <i>A</i>, <i>n</i>) 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.</p>
+
+<p>The first indication of the approaching division of the nucleus is an
+evident increase in size (<i>B</i>), 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
+(<a href="#fig127">Fig.&nbsp;127</a>, <i>C</i>), and about this time the nucleolus disappears.</p>
+
+<p>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. (<a href="#fig127">Fig.&nbsp;127</a>, <i>D</i>, shows this plate as seen from the
+side, <i>E</i> seen from above.)</p>
+
+<p><span class="pagenum" title="Page&nbsp;232">&nbsp;</span><a name="Page_232" id="Page_232"></a>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 (<i>D</i>), is known as the
+&ldquo;nuclear spindle.&rdquo; The segments of the nuclear plate next divide
+lengthwise into two similar daughter segments (<i>F</i>), 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.</p></blockquote>
+
+<div class="figcenter" style="width:437px;">
+<a name="fig128" id="fig128"></a>
+<img src="images/fig128.png" width="437" height="311"
+alt="Fig.&nbsp;128." title="" />
+<p class="caption"><span class="smcap">Fig.&nbsp;128.</span>&mdash;Later stages of nuclear divisions in the
+pollen mother cell of wild onion, &times;&nbsp;350. All the figures are seen from
+the side, except <i>B</i> <span class="smcap">ii</span>, which is viewed from the pole.</p>
+</div>
+
+<blockquote><p>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 (<a href="#fig128">Fig.&nbsp;128</a>, <i>A</i>, <i>B</i>). 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 (<a href="#fig128">Fig.&nbsp;128</a>, <i>C</i>, <i>E</i>). These granules constitute the young cell wall
+or &ldquo;cell plate,&rdquo; and finally coalesce to form a continuous membrane
+(<a href="#fig128">Fig.&nbsp;128</a>, <i>F</i>).</p>
+
+<p>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 (<a href="#fig128">Fig.&nbsp;128</a>, <i>F</i>).<a name="FNanchor_15_15" id="FNanchor_15_15"></a><a href="#Footnote_15_15" class="fnanchor">[15]</a></p>
+
+<p><span class="pagenum" title="Page&nbsp;233">&nbsp;</span><a name="Page_233" id="Page_233"></a>This complicated process of nuclear division is known technically as
+&ldquo;karyokinesis,&rdquo; and is found throughout the higher animals as well as
+plants.</p></blockquote>
+
+<p>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&nbsp;cent chromic acid, ninety-five per&nbsp;cent distilled water).
+For most purposes a one per&nbsp;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.</p>
+
+<p>As staining agents many colors are used. The most useful are
+h&aelig;matoxylin, carmine, and various aniline colors, among which may be
+mentioned, besides gentian violet, safranine, Bismarck brown, methyl
+violet. H&aelig;matoxylin 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, <span class="pagenum" title="Page&nbsp;234">&nbsp;</span><a name="Page_234" id="Page_234"></a>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.</p>
+
+<p>H&aelig;matoxylin 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.</p>
+
+<p>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.</p>
+
+<p>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.<a name="FNanchor_16_16" id="FNanchor_16_16"></a><a href="#Footnote_16_16" class="fnanchor">[16]</a>) 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 <span class="pagenum" title="Page&nbsp;235">&nbsp;</span><a name="Page_235" id="Page_235"></a>nuclear division or similar studies, balsam
+mounts are usually preferable.</p>
+
+<p>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.</p>
+
+<hr />
+
+<p>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.</p>
+
+<ul class="books">
+<li>1. <span class="smcap">Goebel</span>. Outlines of Morphology and Classification.</li>
+
+<li>2. <span class="smcap">Sachs</span>. Physiology of Plants.</li>
+
+<li>3. <span class="smcap">De Bary</span>. Comparative Anatomy of Ferns and Phanerogams.</li>
+
+<li>4. <span class="smcap">De Bary</span>. Morphology and Biology of Fungi, Mycetozoa,
+and Bacteria.</li>
+</ul>
+<blockquote class="ads"><p>These four works are translations from the German,
+and take the place of Sachs&#8217;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.&mdash;New
+York, McMillan &amp;&nbsp;Co.</p></blockquote>
+
+<ul class="books">
+<li>5. <span class="smcap">Gray</span>. Structural Botany.&mdash;New York, Ivison &amp;&nbsp;Co.</li>
+
+<li>6. <span class="smcap">Goodale</span>. Physiological Botany.&mdash;New York, Ivison &amp;&nbsp;Co.</li>
+</ul>
+
+<blockquote class="ads"><p>These two books cover somewhat the same ground as
+1 and 2, but are much less exhaustive.</p></blockquote>
+
+<ul class="books">
+<li><ins class="correction" title="Transcriber&#8217;s note: The strange numbering here is as in the original.">5.</ins> <span class="smcap">Strasburger</span>. Das Botanische Practicum.&mdash;Jena.</li>
+</ul>
+
+<blockquote class="ads"><p>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.</p></blockquote>
+
+<ul class="books">
+<li><span class="pagenum" title="Page&nbsp;236">&nbsp;</span><a name="Page_236" id="Page_236"></a>7. <span class="smcap">Arthur, Barnes</span>, and <span class="smcap">Coulter</span>. Plant Dissection.&mdash;Holt
+&amp;&nbsp;Co., New York.</li>
+
+<li>8. <span class="smcap">Whitman</span>. Methods in Microscopic Anatomy and Embryology.&mdash;Casino
+&amp;&nbsp;Co., Boston.</li>
+</ul>
+
+<p>For identifying plants the following books may be mentioned:&mdash;</p>
+
+<ul class="books">
+<li>Green alg&aelig; (exclusive of desmids, but including <i>Cyanophyce&aelig;</i>
+and <i>Volvocine&aelig;</i>).</li>
+
+<li><span class="smcap">Wolle</span>. Fresh-water Alg&aelig; of the United States.&mdash;Bethlehem,
+Penn.</li>
+
+<li>Desmids. <span class="smcap">Wolle</span>. Desmids of the United States.&mdash;Bethlehem,
+Penn.</li>
+
+<li>The red and brown alg&aelig; are partially described in <span class="smcap">Farlow&#8217;s</span>
+New England Alg&aelig;. Report of United States Fish Commission,
+1879.&mdash;Washington.</li>
+
+<li>The <i>Charace&aelig;</i> are being described by Dr.&nbsp;<span class="smcap">F.&nbsp;F. Allen</span> of New
+York. The first part has appeared.</li>
+
+<li>The literature of the fungi is much scattered. <span class="smcap">Farlow</span> and
+<span class="smcap">Trelease</span> have prepared a careful index of the American
+literature on the subject.</li>
+
+<li>Mosses. <span class="smcap">Lesquereux</span> and <span class="smcap">James</span>. Mosses of North America.&mdash;Boston,
+Casino &amp;&nbsp;Co.</li>
+
+<li><span class="smcap">Barnes</span>. Key to the Genera of Mosses.&mdash;Bull. Purdue
+School of Science, 1886.</li>
+
+<li>Pteridophytes. <span class="smcap">Underwood</span>. Our Native Ferns and their
+Allies.&mdash;Holt &amp;&nbsp;Co., New York.</li>
+
+<li>Spermaphytes. <span class="smcap">Gray</span>. Manual of the Botany of the Northern
+United States. 6th edition, 1890. This also includes
+the ferns, and the liverworts.&mdash;New York, Ivison &amp;&nbsp;Co.</li>
+
+<li><span class="smcap">Coulter</span>. Botany of the Rocky Mountains.&mdash;New York,
+Ivison &amp;&nbsp;Co.</li>
+
+<li><span class="smcap">Chapman</span>. Flora of the Southern United States.&mdash;New
+York, 1883.</li>
+
+<li><span class="smcap">Watson</span>. Botany of California.</li>
+</ul>
+
+
+
+<div class="footnotes">
+<h2><a name="FOOTNOTES" id="FOOTNOTES"></a>FOOTNOTES.</h2>
+
+
+<div class="footnote"><p><a name="Footnote_1_1" id="Footnote_1_1"></a><span class="label"><a href="#FNanchor_1_1">[1]</a></span> For the mounting of permanent preparations, see <a href="#CHAPTER_XIX">Chapter&nbsp;XIX</a>.</p></div>
+
+<div class="footnote"><p><a name="Footnote_2_2" id="Footnote_2_2"></a><span class="label"><a href="#FNanchor_2_2">[2]</a></span> The term &ldquo;colony&rdquo; is, perhaps, inappropriate, as the whole mass of
+cells arises from a single one, and may properly be looked upon as an
+individual plant.</p></div>
+
+<div class="footnote"><p><a name="Footnote_3_3" id="Footnote_3_3"></a><span class="label"><a href="#FNanchor_3_3">[3]</a></span> Alg&aelig; (sing. <i>alga</i>).</p></div>
+
+<div class="footnote"><p><a name="Footnote_4_4" id="Footnote_4_4"></a><span class="label"><a href="#FNanchor_4_4">[4]</a></span> &ldquo;Host,&rdquo; the plant or animal upon which a parasite lives.</p></div>
+
+<div class="footnote"><p><a name="Footnote_5_5" id="Footnote_5_5"></a><span class="label"><a href="#FNanchor_5_5">[5]</a></span> The antheridia, when present, arise as branches just below the o&ouml;gonium,
+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.</p></div>
+
+<div class="footnote"><p><a name="Footnote_6_6" id="Footnote_6_6"></a><span class="label"><a href="#FNanchor_6_6">[6]</a></span> 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 (<a href="#fig40">Fig.&nbsp;40</a>).</p></div>
+
+<div class="footnote"><p><a name="Footnote_7_7" id="Footnote_7_7"></a><span class="label"><a href="#FNanchor_7_7">[7]</a></span> Sing. <i>soredium</i>.</p></div>
+
+<div class="footnote"><p><a name="Footnote_8_8" id="Footnote_8_8"></a><span class="label"><a href="#FNanchor_8_8">[8]</a></span> Sing. <i>basidium</i>.</p></div>
+
+<div class="footnote"><p><a name="Footnote_9_9" id="Footnote_9_9"></a><span class="label"><a href="#FNanchor_9_9">[9]</a></span> 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.</p></div>
+
+<div class="footnote"><p><a name="Footnote_10_10" id="Footnote_10_10"></a><span class="label"><a href="#FNanchor_10_10">[10]</a></span> In most conifers the symmetrical form of the young tree is maintained
+as long as the tree lives.</p></div>
+
+<div class="footnote"><p><a name="Footnote_11_11" id="Footnote_11_11"></a><span class="label"><a href="#FNanchor_11_11">[11]</a></span> See the <a href="#CHAPTER_XXI">last chapter</a> for details.</p></div>
+
+<div class="footnote"><p><a name="Footnote_12_12" id="Footnote_12_12"></a><span class="label"><a href="#FNanchor_12_12">[12]</a></span> The three outer stamens are shorter than the inner set.</p></div>
+
+<div class="footnote"><p><a name="Footnote_13_13" id="Footnote_13_13"></a><span class="label"><a href="#FNanchor_13_13">[13]</a></span> Mon&#339;cious: having stamens and carpels in different flowers, but on
+the same plant.</p></div>
+
+<div class="footnote"><p><a name="Footnote_14_14" id="Footnote_14_14"></a><span class="label"><a href="#FNanchor_14_14">[14]</a></span> In a number of plants with showy flowers, <i>e.g.</i> violets, jewel-weed,
+small, inconspicuous flowers are also formed, which are self-fertilizing.
+These inconspicuous flowers are called &ldquo;cleistogamous.&rdquo;</p></div>
+
+<div class="footnote"><p><a name="Footnote_15_15" id="Footnote_15_15"></a><span class="label"><a href="#FNanchor_15_15">[15]</a></span> 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.</p></div>
+
+<div class="footnote"><p><a name="Footnote_16_16" id="Footnote_16_16"></a><span class="label"><a href="#FNanchor_16_16">[16]</a></span> For gradual dehydrating, the specimens may be placed successively in
+30&nbsp;per&nbsp;cent, 50&nbsp;per&nbsp;cent, 70&nbsp;per&nbsp;cent, 90&nbsp;per&nbsp;cent, and absolute alcohol.</p></div>
+</div>
+
+
+
+<hr />
+<h2><span class="pagenum" title="Page&nbsp;237">&nbsp;</span><a name="Page_237" id="Page_237"></a><a name="INDEX" id="INDEX"></a>INDEX.</h2>
+
+
+<table class="az" border="1" summary="Alphabetic jump-table for the index">
+        <tr>
+            <td><a href="#IX_A">A</a></td>
+            <td><a href="#IX_B">B</a></td>
+            <td><a href="#IX_C">C</a></td>
+            <td><a href="#IX_D">D</a></td>
+            <td><a href="#IX_E">E</a></td>
+            <td><a href="#IX_F">F</a></td>
+            <td><a href="#IX_G">G</a></td>
+            <td><a href="#IX_H">H</a></td>
+            <td><a href="#IX_I">I</a></td>
+            <td><a href="#IX_J">J</a></td>
+            <td><a href="#IX_K">K</a></td>
+            <td><a href="#IX_L">L</a></td>
+            <td><a href="#IX_M">M</a></td>
+        </tr>
+        <tr>
+            <td><a href="#IX_N">N</a></td>
+            <td><a href="#IX_O">O</a></td>
+            <td><a href="#IX_P">P</a></td>
+            <td><a href="#IX_Q">Q</a></td>
+            <td><a href="#IX_R">R</a></td>
+            <td><a href="#IX_S">S</a></td>
+            <td><a href="#IX_T">T</a></td>
+            <td><a href="#IX_U">U</a></td>
+            <td><a href="#IX_V">V</a></td>
+            <td><a href="#IX_W">W</a></td>
+            <td><a href="#IX_X">X</a></td>
+            <td><a href="#IX_Y">Y</a></td>
+            <td><a href="#IX_Z">Z</a></td>
+        </tr>
+</table>
+
+
+<ul class="IX">
+<li><i><a name="IX_A" id="IX_A"></a>Acacia</i>, <a href="#Page_209">209</a>.</li>
+<li><i>Acer</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_M">Maple</a>.&rdquo;</li>
+<li>Acetic acid, <a href="#Page_3">3</a>, <a href="#Page_59">59</a>, <a href="#Page_98">98</a>, <a href="#Page_138">138</a>, <a href="#Page_230">230</a>.</li>
+<li><i>Achimenes</i>, <a href="#Page_218">218</a>.</li>
+<li><i>Acorus</i>. See &ldquo;<a href="#IX_S">Sweet-flag</a>.&rdquo;</li>
+<li>Actinomorphic, <a href="#Page_213">213</a>.</li>
+<li>Adder-tongue, <a href="#Page_116">116</a>; <a href="#fig70">Fig.&nbsp;70</a>. See also &ldquo;<i><a href="#IX_E">Erythronium</a></i>.&rdquo;</li>
+<li><i>Adiantum</i>. See &ldquo;<a href="#IX_M">Maiden-hair</a>.&rdquo;</li>
+<li><i>Adlumia</i>. See &ldquo;<a href="#IX_M">Mountain-fringe</a>.&rdquo;</li>
+<li><i>&AElig;sculin&aelig;</i>, <a href="#Page_199">199</a>.</li>
+<li><i>&AElig;sculus</i>. See &ldquo;<a href="#IX_B">Buckeye</a>,&rdquo; &ldquo;<a href="#IX_H">Horse-chestnut</a>.&rdquo;</li>
+<li><i>Aggregat&aelig;</i>, <a href="#Page_222">222</a>.</li>
+<li>Alcohol, <a href="#Page_5">5</a>, <a href="#Page_31">31</a>, <a href="#Page_55">55</a>, <a href="#Page_83">83</a>, <a href="#Page_230">230</a>, <a href="#Page_233">233</a>.</li>
+<li>Alg&aelig;, <a href="#Page_4">4</a>, <a href="#Page_21">21</a>.
+  <ul class="IX">
+  <li>green, <a href="#Page_21">21</a>.</li>
+  <li>red, <a href="#Page_21">21</a>, <a href="#Page_49">49</a>.</li>
+  <li>brown, <a href="#Page_21">21</a>, <a href="#Page_41">41</a>.</li>
+  </ul></li>
+<li>Alga-fungi. See &ldquo;<i><a href="#IX_P">Phycomycetes</a></i>.&rdquo;</li>
+<li><i>Alisma</i>, <i>-ce&aelig;</i>. See &ldquo;<a href="#IX_W">Water-plantain</a>.&rdquo;</li>
+<li><i>Allium</i>. See &ldquo;<a href="#IX_W">Wild onion</a>.&rdquo;</li>
+<li>Amaranth, <a href="#Page_185">185</a>.</li>
+<li><i>Amarantus</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_A">Amaranth</a>.&rdquo;</li>
+<li><i>Am&oelig;ba</i>, <a href="#Page_7">7</a>; <a href="#fig2">Fig.&nbsp;2</a>.</li>
+<li><i>Ampelid&aelig;</i>. See &ldquo;<a href="#IX_V">Vine</a>.&rdquo;</li>
+<li><i>Ampelopsis</i>. See &ldquo;<a href="#IX_V">Virginia creeper</a>.&rdquo;</li>
+<li>Anatomy, <a href="#Page_3">3</a>.
+  <ul class="IX">
+  <li>gross, Implements for study of, <a href="#Page_3">3</a>.</li>
+  <li>minute, Implements for study of, <a href="#Page_3">3</a>, <a href="#Page_4">4</a>.</li>
+  </ul></li>
+<li>Anatropous, <a href="#Page_151">151</a>.</li>
+<li><i>Andre&aelig;ace&aelig;</i>, <a href="#Page_99">99</a>, <a href="#Page_100">100</a>.</li>
+<li>Andr&oelig;cium, <a href="#Page_148">148</a>.</li>
+<li><i>Andromeda</i>, <a href="#Page_211">211</a>.</li>
+<li><i>Anemone</i>, <a href="#Page_185">185</a>.</li>
+<li><i>Angiocarp&aelig;</i>, <a href="#Page_84">84</a>.</li>
+<li>Angiosperm, <a href="#Page_129">129</a>, <a href="#Page_143">143</a>, <a href="#Page_145">145</a>.</li>
+<li>Aniline colors, <a href="#Page_233">233</a>.</li>
+<li><i>Anisocarp&aelig;</i>, <a href="#Page_210">210</a>, <a href="#Page_213">213</a>.</li>
+<li><i>Anonace&aelig;</i>. See &ldquo;<a href="#IX_C">Custard-apple</a>.&rdquo;</li>
+<li>Anther, <a href="#Page_148">148</a>, <a href="#Page_175">175</a>, <a href="#Page_179">179</a>.</li>
+<li>Antheridium, <a href="#Page_27">27</a>, <a href="#Page_36">36</a>, <a href="#Page_39">39</a>, <a href="#Page_45">45</a>, <a href="#Page_51">51</a>, <a href="#Page_59">59</a>, <a href="#Page_68">68</a>, <a href="#Page_89">89</a>, <a href="#Page_96">96</a>, <a href="#Page_106">106</a>, <a href="#Page_122">122</a>.</li>
+<li><i>Anthoceros</i>, <i>Anthocerote&aelig;</i>, <a href="#Page_91">91</a>; <a href="#fig57">Fig.&nbsp;57</a>.</li>
+<li><i>Aphanocycl&aelig;</i>, <a href="#Page_185">185</a>, <a href="#Page_196">196</a>.</li>
+<li><i>Aplectrum</i>, <a href="#Page_167">167</a>; <a href="#fig90">Fig.&nbsp;90</a>.</li>
+<li><i>Apocynum</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_D">Dog-bane</a>.&rdquo;</li>
+<li><i>Apostasie&aelig;</i>, <a href="#Page_164">164</a>.</li>
+<li>Apple, <a href="#Page_145">145</a>, <a href="#Page_171">171</a>, <a href="#Page_206">206</a>; <a href="#fig114">Fig.&nbsp;114</a>.</li>
+<li>Apricot, <a href="#Page_207">207</a>.</li>
+<li><i>Aquilegia</i>. See &ldquo;<a href="#IX_C">Columbine</a>.&rdquo;</li>
+<li><i>Aralia</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_S">Spikenard</a>.&rdquo;</li>
+<li>Archegonium, <a href="#Page_89">89</a>, <a href="#Page_97">97</a>, <a href="#Page_105">105</a>, <a href="#Page_122">122</a>, <a href="#Page_133">133</a>, <a href="#Page_140">140</a>, <a href="#Page_144">144</a>.</li>
+<li>Archicarp, <a href="#Page_138">138</a>, <a href="#Page_145">145</a>.</li>
+<li><i>Arcyria</i>, <a href="#Page_13">13</a>; <a href="#fig5">Fig.&nbsp;5</a>.</li>
+<li><i>Arethusa</i>, <i>Arethuse&aelig;</i>, <a href="#Page_166">166</a>; <a href="#fig90">Fig.&nbsp;90</a>.</li>
+<li><i>Argemone</i>, <a href="#Page_191">191</a>.</li>
+<li>Aril, <a href="#Page_189">189</a>.</li>
+<li><i>Aris&aelig;ma</i>, <a href="#Page_78">78</a>, <a href="#Page_157">157</a>; <a href="#fig86">Fig.&nbsp;86</a>.</li>
+<li><i>Aristolochia</i>, <i>-ace&aelig;</i>, <a href="#Page_224">224</a>.</li>
+<li>Aroid, <i>Aroide&aelig;</i>, <a href="#Page_157">157</a>.</li>
+<li>Arrow-grass, <a href="#Page_167">167</a>.</li>
+<li>Arrowhead, <a href="#Page_167">167</a>; <a href="#fig91">Fig.&nbsp;91</a>.</li>
+<li>Arrowroot, <a href="#Page_163">163</a>.</li>
+<li><i>Asarum</i>. See &ldquo;<a href="#IX_W">Wild ginger</a>.&rdquo;</li>
+<li><i>Asclepias</i>, <i>-dace&aelig;</i>. See &ldquo;<a href="#IX_M">Milk-weed</a>.&rdquo;</li>
+<li><i>Ascobolus</i>, <a href="#Page_71">71</a>&ndash;<a href="#Page_73">73</a>; <a href="#fig43">Fig.&nbsp;43</a>.
+  <ul class="IX">
+  <li>culture of, <a href="#Page_71">71</a>.</li>
+  <li><span class="pagenum" title="Page&nbsp;238">&nbsp;</span><a name="Page_238" id="Page_238"></a>spore fruit, <a href="#Page_71">71</a>.</li>
+  <li>archicarp, <a href="#Page_71">71</a>.</li>
+  <li>spore sacs, <a href="#Page_72">72</a>.</li>
+  </ul></li>
+<li><i>Ascomycetes</i>, <a href="#Page_65">65</a>, <a href="#Page_66">66</a>.</li>
+<li>Ascospore, <a href="#Page_66">66</a>.</li>
+<li>Ascus, <a href="#Page_66">66</a>, <a href="#Page_69">69</a>.</li>
+<li>Ash, <a href="#Page_218">218</a>; <a href="#fig122">Fig.&nbsp;122</a>.</li>
+<li><i>Asimina</i>. See &ldquo;<a href="#IX_P">Papaw</a>.&rdquo;</li>
+<li><i>Aspidium</i>, <a href="#fig70">Fig.&nbsp;70</a>.</li>
+<li><i>Asplenium</i>, <a href="#Page_104">104</a>; <a href="#fig70">Fig.&nbsp;70</a>.</li>
+<li>Aster, <a href="#Page_224">224</a>.</li>
+<li><i>Atropa</i>. See &ldquo;<a href="#IX_D">Deadly nightshade</a>.&rdquo;</li>
+<li>Axil, <a href="#Page_174">174</a>.</li>
+<li>Azalea, <a href="#Page_210">210</a>; <a href="#fig116">Fig.&nbsp;116</a>.</li>
+<li><i>Azolla</i>, <a href="#Page_117">117</a>; <a href="#fig71">Fig.&nbsp;71</a>.</li>
+</ul>
+
+<ul class="IX">
+<li><a name="IX_B" id="IX_B"></a>Bacteria, <a href="#Page_15">15</a>, <a href="#Page_17">17</a>, <a href="#Page_19">19</a>; <a href="#fig8">Fig.&nbsp;8</a>.</li>
+<li>Balsam, <i>Balsamine&aelig;</i>, <a href="#Page_198">198</a>.</li>
+<li>Bamboo, <a href="#Page_162">162</a>.</li>
+<li><i>Bambusa</i>. See &ldquo;<a href="#IX_B">Bamboo</a>.&rdquo;</li>
+<li>Banana, <a href="#Page_163">163</a>.</li>
+<li>Barberry, <a href="#Page_17">17</a>, <a href="#Page_187">187</a>; <a href="#fig101">Fig.&nbsp;101</a>.</li>
+<li>Bark. See &ldquo;<a href="#IX_C">Cortex</a>.&rdquo;</li>
+<li><i>Basidiomycetes</i>, <a href="#Page_77">77</a>.</li>
+<li>Basidium, <a href="#Page_77">77</a>, <a href="#Page_80">80</a>, <a href="#Page_83">83</a>.</li>
+<li>Basswood, <a href="#Page_195">195</a>; <a href="#fig106">Fig.&nbsp;106</a>.</li>
+<li>Bast. See &ldquo;<a href="#IX_P">Phloem</a>.&rdquo;</li>
+<li><i>Batatas</i>. See &ldquo;<a href="#IX_S">Sweet-potato</a>.&rdquo;</li>
+<li><i>Batrachospermum</i>, <a href="#Page_53">53</a>; <a href="#fig31">Fig.&nbsp;31</a>.</li>
+<li>Bean, <a href="#Page_207">207</a>, <a href="#Page_208">208</a>.</li>
+<li>Bear-grass. See &ldquo;<i><a href="#IX_Y">Yucca</a></i>.&rdquo;</li>
+<li>Bee, <a href="#Page_227">227</a>, <a href="#Page_228">228</a>.</li>
+<li>Beech, <a href="#Page_183">183</a>.</li>
+<li>Beech-drops, <a href="#Page_218">218</a>.</li>
+<li>Beet, <a href="#Page_184">184</a>.</li>
+<li>Beggar&#8217;s-ticks, <a href="#Page_215">215</a>.</li>
+<li>Begonia, <a href="#Page_3">3</a>, <a href="#Page_205">205</a>.</li>
+<li>Bell-flower, <a href="#Page_220">220</a>, <a href="#Page_226">226</a>; <a href="#fig123">Fig.&nbsp;123</a>.</li>
+<li>Bellwort, <a href="#Page_156">156</a>.</li>
+<li><i>Berberis</i>, <i>-ide&aelig;</i>. See &ldquo;<a href="#IX_B">Barberry</a>.&rdquo;</li>
+<li>Bergamot oil, <a href="#Page_234">234</a>.</li>
+<li>Berry, <a href="#Page_145">145</a>, <a href="#Page_156">156</a>.</li>
+<li><i>Betulace&aelig;</i>, <a href="#Page_183">183</a>.</li>
+<li><i>Bicornes</i>, <a href="#Page_210">210</a>.</li>
+<li><i>Bignonia</i>, <i>-ace&aelig;</i>, <a href="#Page_218">218</a>.</li>
+<li>Biology, <a href="#Page_2">2</a>.</li>
+<li>Birch, <a href="#Page_183">183</a>.</li>
+<li>Bird&#8217;s-nest fungus. See &ldquo;<i><a href="#IX_C">Cyathus</a></i>.&rdquo;</li>
+<li>Bishop&#8217;s cap, <a href="#Page_202">202</a>; <a href="#fig111">Fig.&nbsp;111</a>.</li>
+<li>Bismarck brown, <a href="#Page_233">233</a>.</li>
+<li>Bitter-sweet, <a href="#Page_199">199</a>; <a href="#fig109">Fig.&nbsp;109</a>.</li>
+<li>Black alder, <a href="#Page_199">199</a>.</li>
+<li>Blackberry, <a href="#Page_207">207</a>.</li>
+<li>Black fungi. See &ldquo;<i><a href="#IX_P">Pyrenomycetes</a></i>.&rdquo;</li>
+<li>Bladder-nut, <a href="#Page_199">199</a>; <a href="#fig108">Fig.&nbsp;108</a>.</li>
+<li>Bladder-weed, <a href="#Page_33">33</a>, <a href="#Page_217">217</a>; <a href="#fig120">Fig.&nbsp;120</a>.</li>
+<li>Bleeding-heart. See &ldquo;<i><a href="#IX_D">Dicentra</a></i>.&rdquo;</li>
+<li>Blood-root, <a href="#Page_191">191</a>; <a href="#fig103">Fig.&nbsp;103</a>.</li>
+<li>Blue-eyed grass, <a href="#Page_156">156</a>.</li>
+<li>Blue-flag. See &ldquo;<i><a href="#IX_I">Iris</a></i>.&rdquo;</li>
+<li>Blue-green slime, <a href="#Page_15">15</a>.</li>
+<li>Blue valerian. See &ldquo;<i><a href="#IX_P">Polemonium</a></i>.&rdquo;</li>
+<li>Borage, <a href="#Page_215">215</a>.</li>
+<li><i>Borragine&aelig;</i>. See &ldquo;<a href="#IX_B">Borage</a>.&rdquo;</li>
+<li>Bordered pits, <a href="#Page_138">138</a>.</li>
+<li>Botany defined, <a href="#Page_2">2</a>.
+  <ul class="IX">
+  <li>systematic, <a href="#Page_3">3</a>.</li>
+  </ul></li>
+<li><i>Botrychium</i>. See &ldquo;<a href="#IX_G">Grape fern</a>.&rdquo;</li>
+<li>Box, <a href="#Page_201">201</a>.</li>
+<li>Bract, <a href="#Page_199">199</a>, <a href="#Page_222">222</a>, <a href="#Page_229">229</a>.</li>
+<li><i>Brasenia</i>. See &ldquo;<a href="#IX_W">Water-shield</a>.&rdquo;</li>
+<li>Breathing pore, <a href="#Page_91">91</a>, <a href="#Page_99">99</a>, <a href="#Page_113">113</a>, <a href="#Page_130">130</a>, <a href="#Page_147">147</a>, <a href="#Page_150">150</a>, <a href="#Page_177">177</a>.</li>
+<li><i>Bromeliace&aelig;</i>, <a href="#Page_156">156</a>.</li>
+<li>Bryophyte, <a href="#Page_86">86</a>.</li>
+<li>Buck-bean, <a href="#Page_218">218</a>.</li>
+<li>Buckeye, <a href="#Page_171">171</a>, <a href="#Page_199">199</a>.</li>
+<li>Buckthorn, <a href="#Page_199">199</a>.</li>
+<li>Buckwheat, <a href="#Page_184">184</a>.</li>
+<li>Budding, <a href="#Page_64">64</a>.</li>
+<li><i>Bulboch&aelig;te</i>, <a href="#Page_28">28</a>; <a href="#fig16">Fig.&nbsp;16</a>.</li>
+<li>Bulb, <a href="#Page_146">146</a>, <a href="#Page_153">153</a>, <a href="#Page_172">172</a>.</li>
+<li>Bulrush, <a href="#Page_161">161</a>; <a href="#fig87">Fig.&nbsp;87</a>.</li>
+<li>Bundle-sheath, <a href="#Page_110">110</a>, <a href="#Page_176">176</a>.</li>
+<li>Burning-bush. See &ldquo;<a href="#IX_S">Spindle-tree</a>.&rdquo;</li>
+<li>Bur-reed, <a href="#Page_159">159</a>; <a href="#fig86">Fig.&nbsp;86</a>.</li>
+<li>Buttercup, <a href="#Page_181">181</a>, <a href="#Page_185">185</a>; <a href="#fig99">Fig.&nbsp;99</a>.</li>
+<li>Butterfly, <a href="#Page_227">227</a>, <a href="#Page_228">228</a>.</li>
+<li>Button-bush, <a href="#Page_223">223</a>.</li>
+<li><span class="pagenum" title="Page&nbsp;239">&nbsp;</span><a name="Page_239" id="Page_239"></a>Buttonwood. See &ldquo;<a href="#IX_S">Sycamore</a>.&rdquo;</li>
+<li><i>Buxus</i>, <i>Buxace&aelig;</i>. See &ldquo;<a href="#IX_B">Box</a>.&rdquo;</li>
+</ul>
+
+<ul class="IX">
+<li><a name="IX_C" id="IX_C"></a>Cabbage, <a href="#Page_192">192</a>.</li>
+<li><i>Cabombe&aelig;</i>, <a href="#Page_190">190</a>.</li>
+<li>Cactus, <i>Cactace&aelig;</i>, <a href="#Page_203">203</a>; <a href="#fig112">Fig.&nbsp;112</a>.</li>
+<li><i>C&aelig;salpine&aelig;</i>, <a href="#Page_210">210</a>.</li>
+<li>Calcium, <a href="#Page_2">2</a>.</li>
+<li>Calla, <a href="#Page_157">157</a>, <a href="#Page_229">229</a>.</li>
+<li><i>Callithamnion</i>, <a href="#Page_50">50</a>&ndash;<a href="#Page_52">52</a>; <a href="#fig29">Fig.&nbsp;29</a>.
+  <ul class="IX">
+  <li>general structure, <a href="#Page_51">51</a>.</li>
+  <li>tetraspores, <a href="#Page_51">51</a>.</li>
+  <li>procarp, <a href="#Page_51">51</a>.</li>
+  <li>antheridium, <a href="#Page_51">51</a>.</li>
+  <li>spores, <a href="#Page_52">52</a>.</li>
+  </ul></li>
+<li><i>Callitriche</i>, <i>-chace&aelig;</i>. See &ldquo;<a href="#IX_W">Water starwort</a>.&rdquo;</li>
+<li><i>Calluna</i>. See &ldquo;<a href="#IX_H">Heath</a>.&rdquo;</li>
+<li><i>Calopogon</i>, <a href="#Page_166">166</a>; <a href="#fig91">Fig.&nbsp;91</a>.</li>
+<li><i>Calycanthus</i>, <i>-ace&aelig;</i>, <a href="#Page_187">187</a>; <a href="#fig100">Fig.&nbsp;100</a>.</li>
+<li><i>Calycere&aelig;</i>, <a href="#Page_223">223</a>.</li>
+<li><i>Calyciflor&aelig;</i>, <a href="#Page_200">200</a>.</li>
+<li>Calyx, <a href="#Page_174">174</a>, <a href="#Page_182">182</a>.</li>
+<li>Cambium, <a href="#Page_137">137</a>&ndash;<a href="#Page_138">138</a>, <a href="#Page_175">175</a>.</li>
+<li><i>Campanula</i>. See &ldquo;<a href="#IX_B">Bell-flower</a>.&rdquo;</li>
+<li><i>Campanulace&aelig;</i>, <a href="#Page_220">220</a>.</li>
+<li><i>Campanulin&aelig;</i>, <a href="#Page_220">220</a>.</li>
+<li>Canada balsam, <a href="#Page_230">230</a>&ndash;<a href="#Page_234">234</a>.</li>
+<li>Canada thistle, <a href="#Page_224">224</a>; <a href="#fig125">Fig.&nbsp;125</a>.</li>
+<li><i>Canna</i>, <i>-ace&aelig;</i>, <a href="#Page_162">162</a>, <a href="#Page_163">163</a>; <a href="#fig88">Fig.&nbsp;88</a>.</li>
+<li>Caper family, <a href="#Page_194">194</a>.</li>
+<li><i>Capparis</i>, <i>-ide&aelig;</i>. See &ldquo;<a href="#IX_C">Caper</a>.&rdquo;</li>
+<li><i>Caprifoliace&aelig;</i>, <a href="#Page_223">223</a>.</li>
+<li><i>Capsella</i>. See &ldquo;<a href="#IX_S">Shepherd&#8217;s-purse</a>.&rdquo;</li>
+<li>Caraway, <a href="#Page_202">202</a>.</li>
+<li>Carbon, <a href="#Page_2">2</a>, <a href="#Page_95">95</a>.</li>
+<li>Carbon-dioxides, <a href="#Page_95">95</a>.</li>
+<li>Cardinal-flower. See &ldquo;<a href="#IX_L">Lobelia</a>.&rdquo;</li>
+<li><i>Carex</i>, <a href="#Page_161">161</a>; <a href="#fig87">Fig.&nbsp;87</a>.</li>
+<li>Carmine, <a href="#Page_25">25</a>, <a href="#Page_233">233</a>.</li>
+<li>Carnation, <a href="#Page_185">185</a>.</li>
+<li>Carpel, <a href="#Page_148">148</a>, <a href="#Page_154">154</a>, <a href="#Page_175">175</a>, <a href="#Page_179">179</a>.</li>
+<li>Carpophyll. See &ldquo;<a href="#IX_C">Carpel</a>.&rdquo;</li>
+<li>Carpospore, <a href="#Page_51">51</a>&ndash;<a href="#Page_53">53</a>.</li>
+<li>Carrot, <a href="#Page_202">202</a>.</li>
+<li><i>Caryophylle&aelig;</i>. See &ldquo;<a href="#IX_P">Pink</a>.&rdquo;</li>
+<li><i>Caryophyllus</i>. See &ldquo;<a href="#IX_C">Clove</a>.&rdquo;</li>
+<li><i>Castalia</i>, <a href="#Page_189">189</a>.</li>
+<li>Castor-bean, <a href="#Page_200">200</a>.</li>
+<li>Catalpa, <a href="#Page_218">218</a>.</li>
+<li>Cat-brier, <a href="#Page_154">154</a>.</li>
+<li>Catkin, <a href="#Page_181">181</a>.</li>
+<li>Catnip, <a href="#Page_215">215</a>.</li>
+<li>Cat-tail, <a href="#Page_159">159</a>.</li>
+<li>Cedar apple, Cedar rust. See &ldquo;<i><a href="#IX_G">Gymnosporangium</a></i>.&rdquo;</li>
+<li><i>Celastrace&aelig;</i>, <a href="#Page_199">199</a>.</li>
+<li><i>Celastrus</i>. See &ldquo;<a href="#IX_B">Bitter-sweet</a>.&rdquo;</li>
+<li>Celery, <a href="#Page_3">3</a>.</li>
+<li>Cell, <a href="#Page_6">6</a>.
+  <ul class="IX">
+  <li>apical, <a href="#Page_38">38</a>, <a href="#Page_96">96</a>, <a href="#Page_105">105</a>, <a href="#Page_115">115</a>.</li>
+  <li>division, <a href="#Page_23">23</a>, <a href="#Page_31">31</a>, <a href="#Page_229">229</a>.</li>
+  <li>row, <a href="#Page_8">8</a>; <a href="#fig3">Fig.&nbsp;3</a>.</li>
+  <li>mass, <a href="#Page_8">8</a>; <a href="#fig4">Fig.&nbsp;4</a>.</li>
+  <li>sap, <a href="#Page_6">6</a>, <a href="#Page_151">151</a>.</li>
+  </ul></li>
+<li>Cellulose, <a href="#Page_3">3</a>.</li>
+<li>Centaury, <a href="#Page_219">219</a>.</li>
+<li><i>Centrosperm&aelig;</i>, <a href="#Page_183">183</a>.</li>
+<li><i>Cephalanthus</i>. See &ldquo;<a href="#IX_B">Button-bush</a>.&rdquo;</li>
+<li><i>Cerastium</i>. See &ldquo;<a href="#IX_C">Chick-weed</a>.&rdquo;</li>
+<li><i>Ceratophyllum</i>. See &ldquo;<a href="#IX_H">Horned pond-weed</a>.&rdquo;</li>
+<li><i>Cercis</i>. See &ldquo;<a href="#IX_R">Red-bud</a>.&rdquo;</li>
+<li><i>Cham&aelig;rops</i>. See &ldquo;<a href="#IX_P">Palmetto</a>.&rdquo;</li>
+<li><i>Chara</i>, <a href="#Page_38">38</a>&ndash;<a href="#Page_40">40</a>; <a href="#fig23">Fig.&nbsp;23</a>.
+  <ul class="IX">
+  <li>general structure, <a href="#Page_38">38</a>.</li>
+  <li>method of growth, <a href="#Page_39">39</a>.</li>
+  <li>cortex, <a href="#Page_39">39</a>.</li>
+  <li>non-sexual reproduction, <a href="#Page_39">39</a>.</li>
+  <li>o&ouml;gonium, <a href="#Page_39">39</a>.</li>
+  <li>antheridium, <a href="#Page_39">39</a>, <a href="#Page_40">40</a>.</li>
+  <li>spermatozoids, <a href="#Page_40">40</a>.</li>
+  <li>germination, <a href="#Page_40">40</a>.</li>
+  </ul></li>
+<li><i>Charace&aelig;</i>, <a href="#Page_21">21</a>, <a href="#Page_37">37</a>, <a href="#Page_40">40</a>.</li>
+<li><i>Chare&aelig;</i>, <a href="#Page_40">40</a>.</li>
+<li><i>Cheiranthus</i>. See &ldquo;<a href="#IX_W">Wall-flower</a>.&rdquo;</li>
+<li><i>Chenopodium</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_G">Goose-foot</a>.&rdquo;</li>
+<li>Cherry, <a href="#Page_15">15</a>, <a href="#Page_206">206</a>; <a href="#fig114">Fig.&nbsp;114</a>.</li>
+<li>Chicory, <a href="#Page_223">223</a>.</li>
+<li><span class="pagenum" title="Page&nbsp;240">&nbsp;</span><a name="Page_240" id="Page_240"></a>Chick-weed, <a href="#Page_185">185</a>; <a href="#fig98">Fig.&nbsp;98</a>.</li>
+<li><i>Chimaphila</i>. See &ldquo;<a href="#IX_P">Prince&#8217;s pine</a>.&rdquo;</li>
+<li><i>Chionanthus</i>. See &ldquo;<a href="#IX_F">Fringe-tree</a>.&rdquo;</li>
+<li>Chlorine, <a href="#Page_2">2</a>.</li>
+<li><i>Chlorococcum</i>, <a href="#Page_23">23</a>; <a href="#fig12">Fig.&nbsp;12</a>.</li>
+<li>Chloroform, <a href="#Page_234">234</a>.</li>
+<li>Chloroplast, <a href="#Page_22">22</a>, <a href="#Page_45">45</a>.</li>
+<li>Chlorophyll, <a href="#Page_15">15</a>.</li>
+<li>Chlorophyll body. See &ldquo;<a href="#IX_C">Chloroplast</a>.&rdquo;</li>
+<li><i>Chlorophyce&aelig;</i>, <a href="#Page_21">21</a>.</li>
+<li><i>Chondrus</i>. See &ldquo;<a href="#IX_I">Irish moss</a>.&rdquo;</li>
+<li><i>Choripetal&aelig;</i>, <a href="#Page_181">181</a>, <a href="#Page_208">208</a>.</li>
+<li>Chromic acid, <a href="#Page_25">25</a>&ndash;<a href="#Page_35">35</a>, <a href="#Page_233">233</a>.</li>
+<li>Chromoplast, <a href="#Page_150">150</a>.</li>
+<li><i>Cicinnobulus</i>, <a href="#Page_69">69</a>; <a href="#fig39">Fig.&nbsp;39</a>.</li>
+<li>Cilium, <a href="#Page_8">8</a>.</li>
+<li>Cinquefoil, <a href="#Page_206">206</a>.</li>
+<li><i>Cistace&aelig;</i>. See &ldquo;<a href="#IX_R">Rock-rose</a>.&rdquo;</li>
+<li><i>Cistiflor&aelig;</i>, <a href="#Page_192">192</a>.</li>
+<li>Citron, <a href="#Page_196">196</a>.</li>
+<li><i>Citrus</i>. See &ldquo;<a href="#IX_O">Orange</a>,&rdquo; &ldquo;<a href="#IX_L">Lemon</a>.&rdquo;</li>
+<li><i>Cladophora</i>, <a href="#Page_24">24</a>, <a href="#Page_25">25</a>.
+  <ul class="IX">
+  <li>structure of cells, <a href="#Page_25">25</a>.</li>
+  <li>nuclei, <a href="#Page_25">25</a>.</li>
+  <li>cell division, <a href="#Page_25">25</a>.</li>
+  <li>zo&ouml;spores, <a href="#Page_25">25</a>.</li>
+  </ul></li>
+<li>Classification, <a href="#Page_3">3</a>&ndash;<a href="#Page_9">9</a>.</li>
+<li><i>Clavaria</i>, <a href="#Page_85">85</a>; <a href="#fig51">Fig.&nbsp;51</a>.</li>
+<li><i>Claytonia</i>. See &ldquo;<a href="#IX_S">Spring-beauty</a>.&rdquo;</li>
+<li>Clematis, <a href="#Page_185">185</a>.</li>
+<li>Climbing plants, <a href="#Page_171">171</a>.</li>
+<li><i>Closterium</i>, <a href="#Page_33">33</a>; <a href="#fig20">Fig.&nbsp;20</a>.</li>
+<li>Clove, <a href="#Page_205">205</a>.</li>
+<li>Clove oil, <a href="#Page_234">234</a>.</li>
+<li>Clover, <a href="#Page_207">207</a>.</li>
+<li>Club moss, <a href="#Page_116">116</a>.
+  <ul class="IX">
+  <li>larger, <a href="#Page_116">116</a>.</li>
+  <li>smaller, <a href="#Page_123">123</a>&ndash;<a href="#Page_126">126</a>; <a href="#fig74">Fig.&nbsp;74</a>.
+    <ul class="IX">
+    <li>gross anatomy, <a href="#Page_125">125</a>.</li>
+    <li>spores, <a href="#Page_126">126</a>.</li>
+    <li>prothallium, <a href="#Page_126">126</a>.</li>
+    <li>systematic position, <a href="#Page_126">126</a>.</li>
+    </ul></li>
+  </ul></li>
+<li>Cluster-cup, <a href="#Page_78">78</a>.</li>
+<li><i>Cocos</i>. See &ldquo;<a href="#IX_P">Palm-coco</a>,&rdquo; <a href="#Page_159">159</a>.</li>
+<li><i>Coleoch&aelig;te</i>, <a href="#Page_28">28</a>; <a href="#fig17">Fig.&nbsp;17</a>.</li>
+<li>Collateral fibro-vascular bundle, <a href="#Page_135">135</a>.</li>
+<li><i>Collema</i>, <a href="#Page_76">76</a>; <a href="#fig44">Fig.&nbsp;44</a>.</li>
+<li>Columella, <a href="#Page_55">55</a>.</li>
+<li>Columbine, <a href="#Page_186">186</a>; <a href="#fig99">Fig.&nbsp;99</a>.</li>
+<li>Column, <a href="#Page_165">165</a>.</li>
+<li><i><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Columinifer&aelig;&rsquo;.">Columnifer&aelig;</ins></i>, <a href="#Page_195">195</a>.</li>
+<li><i>Commelyne&aelig;</i>, <a href="#Page_157">157</a>.</li>
+<li><i>Composit&aelig;</i>, <a href="#Page_223">223</a>, <a href="#Page_224">224</a>.</li>
+<li>Compound flower, <a href="#Page_224">224</a>.
+  <ul class="IX">
+  <li>leaf, <a href="#Page_159">159</a>, <a href="#Page_170">170</a>.</li>
+  </ul></li>
+<li>Conceptacle, <a href="#Page_45">45</a>.</li>
+<li>Cone, <a href="#Page_131">131</a>.</li>
+<li><i>Conferva</i>, <a href="#Page_26">26</a>.</li>
+<li><i>Confervace&aelig;</i>, <a href="#Page_21">21</a>, <a href="#Page_24">24</a>.</li>
+<li>Conidium, <a href="#Page_68">68</a>.</li>
+<li>Conifer, <a href="#Page_129">129</a>, <a href="#Page_140">140</a>, <a href="#Page_141">141</a>.</li>
+<li><i>Conifer&aelig;</i>. See &ldquo;<a href="#IX_C">Conifer</a>.&rdquo;</li>
+<li><i>Conjugat&aelig;</i>, <a href="#Page_22">22</a>&ndash;<a href="#Page_29">29</a>.</li>
+<li>Connective, <a href="#Page_148">148</a>.</li>
+<li><i>Conocephalus</i>. See &ldquo;<a href="#IX_L">Liverwort, giant</a>.&rdquo;</li>
+<li><i>Contort&aelig;</i>, <a href="#Page_218">218</a>.</li>
+<li><i>Convolvulace&aelig;</i>, <a href="#Page_213">213</a>.</li>
+<li><i>Convolvulus</i>. See &ldquo;<a href="#IX_M">Morning-glory</a>.&rdquo;</li>
+<li><i>Coprinus</i>, <a href="#Page_82">82</a>&ndash;<a href="#Page_84">84</a>; <a href="#fig48">Fig.&nbsp;48</a>.
+  <ul class="IX">
+  <li>general structure, <a href="#Page_82">82</a>, <a href="#Page_83">83</a>.</li>
+  <li>young spore fruit, <a href="#Page_83">83</a>.</li>
+  <li>gills basidia, <a href="#Page_83">83</a>.</li>
+  <li>spores, <a href="#Page_84">84</a>.</li>
+  </ul></li>
+<li>Coral root, <a href="#Page_167">167</a>.</li>
+<li><i>Corallorhiza</i>. See &ldquo;<a href="#IX_C">Coral root</a>.&rdquo;</li>
+<li>Coriander, <a href="#Page_202">202</a>.</li>
+<li>Corn, <a href="#Page_160">160</a>, <a href="#Page_161">161</a>.</li>
+<li><i>Cornus</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_D">Dogwood</a>.&rdquo;</li>
+<li>Corolla, <a href="#Page_174">174</a>, <a href="#Page_182">182</a>.</li>
+<li>Cortex, <a href="#Page_39">39</a>, <a href="#Page_130">130</a>.</li>
+<li><i>Corydalis</i>, <a href="#Page_192">192</a>.</li>
+<li>Cotton, <a href="#Page_195">195</a>.</li>
+<li>Cotyledon, <a href="#Page_134">134</a>, <a href="#Page_146">146</a>, <a href="#Page_180">180</a>.</li>
+<li>Cowslip, <a href="#Page_211">211</a>.</li>
+<li>Coxcomb, <a href="#Page_185">185</a>.</li>
+<li>Crab-apple, <a href="#Page_77">77</a>, <a href="#Page_80">80</a>.</li>
+<li>Cranberry, <a href="#Page_211">211</a>.</li>
+<li><i>Crassulace&aelig;</i>, <a href="#Page_203">203</a>.</li>
+<li>Crane&#8217;s-bill, <a href="#Page_3">3</a>, <a href="#Page_196">196</a>; <a href="#fig107">Fig.&nbsp;107</a>.</li>
+<li>Cress, <a href="#Page_192">192</a>.</li>
+<li><span class="pagenum" title="Page&nbsp;241">&nbsp;</span><a name="Page_241" id="Page_241"></a><i>Croton</i>, <a href="#Page_200">200</a>.</li>
+<li><i>Crucifer&aelig;</i>. See &ldquo;<a href="#IX_M">Mustard family</a>.&rdquo;</li>
+<li><i>Cruciflor&aelig;</i>. See &ldquo;<i><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Rhocadin&aelig;&rsquo;."><a href="#IX_R">Rh&oelig;adin&aelig;</a></ins></i>.&rdquo;</li>
+<li>Cucumber, <a href="#Page_221">221</a>.</li>
+<li>Cucumber-tree. See &ldquo;<a href="#IX_M">Magnolia</a>.&rdquo;</li>
+<li><i>Cucurbitace&aelig;</i>. See &ldquo;<a href="#IX_G">Gourd</a>.&rdquo;</li>
+<li>Cup fungi (&ldquo;<i>Discomycetes</i>&rdquo;), <a href="#Page_71">71</a>.</li>
+<li><i>Cupulifer&aelig;</i>, <a href="#Page_183">183</a>.</li>
+<li>Curl, <a href="#Page_66">66</a>.</li>
+<li>Currant, <a href="#Page_203">203</a>.</li>
+<li><i>Cuscuta</i>. See &ldquo;<a href="#IX_D">Dodder</a>.&rdquo;</li>
+<li>Custard-apple, <a href="#Page_186">186</a>.</li>
+<li><i>Cyanophyce&aelig;</i>. See &ldquo;<a href="#IX_B">Blue-green slime</a>.&rdquo;</li>
+<li><i>Cyathus</i>, <a href="#Page_84">84</a>; <a href="#fig50">Fig.&nbsp;50</a>.</li>
+<li><i>Cycad</i>, <i>-e&aelig;</i>, <a href="#Page_140">140</a>.</li>
+<li><i>Cycas revoluta</i>, <a href="#Page_141">141</a>; <a href="#fig71">Fig.&nbsp;71</a>.</li>
+<li><i>Cyclamen</i>, <a href="#Page_212">212</a>.</li>
+<li><i>Cynoglossum</i>. See &ldquo;<a href="#IX_H">Hound&#8217;s-tongue</a>.&rdquo;</li>
+<li><i>Cyperace&aelig;</i>. See &ldquo;<a href="#IX_S">Sedge</a>.&rdquo;</li>
+<li><i>Cyperus</i>, <a href="#Page_161">161</a>.</li>
+<li>Cypress, <a href="#Page_142">142</a>.</li>
+<li><i>Cypripedium</i>. See &ldquo;<a href="#IX_L">Lady&#8217;s-slipper</a>.&rdquo;</li>
+<li><i>Cystopus</i>. See also &ldquo;<a href="#IX_W">White rust</a>.&rdquo;
+  <ul class="IX">
+  <li><i>bliti</i>, <a href="#Page_57">57</a>; <a href="#fig33">Fig.&nbsp;33</a>.</li>
+  <li>general structure, <a href="#Page_57">57</a>.</li>
+  <li>structure of filaments, <a href="#Page_57">57</a>.</li>
+  <li>non-sexual spores (conidia), <a href="#Page_57">57</a>.</li>
+  <li>germination of conidia, <a href="#Page_58">58</a>.</li>
+  <li>resting spores, <a href="#Page_59">59</a>.</li>
+  <li>o&ouml;gonium, <a href="#Page_59">59</a>.</li>
+  <li>antheridium, <a href="#Page_59">59</a>.</li>
+  <li><i>candidus</i>, <a href="#Page_60">60</a>; <a href="#fig34">Fig.&nbsp;34</a>.</li>
+  </ul></li>
+</ul>
+
+<ul class="IX">
+<li><a name="IX_D" id="IX_D"></a>Daisy, <a href="#Page_223">223</a>.</li>
+<li>Dandelion, <a href="#Page_66">66</a>, <a href="#Page_223">223</a>; <a href="#fig125">Fig.&nbsp;125</a>.</li>
+<li><i>Darlingtonia</i>, <a href="#Page_195">195</a>.</li>
+<li><i>Datura</i>. See &ldquo;<a href="#IX_S">Stramonium</a>.&rdquo;</li>
+<li>Day lily, <a href="#Page_155">155</a>.</li>
+<li>Deadly nightshade, <a href="#Page_215">215</a>.</li>
+<li>Dead nettle, <a href="#Page_215">215</a>; <a href="#fig120">Fig.&nbsp;120</a>.</li>
+<li><i>Delphinium</i>. See &ldquo;<a href="#IX_L">Larkspur</a>.&rdquo;</li>
+<li>Dermatogen, <a href="#Page_176">176</a>.</li>
+<li>Desmid, <a href="#Page_33">33</a>, <a href="#Page_34">34</a>; <a href="#fig20">Fig.&nbsp;20</a>.</li>
+<li>Devil&#8217;s apron. See &ldquo;<i><a href="#IX_L">Laminaria</a></i>.&rdquo;</li>
+<li><i>Dianthus</i>. See &ldquo;<a href="#IX_P">Pink</a>.&rdquo;</li>
+<li><i>Diatomace&aelig;</i>, <a href="#Page_41">41</a>, <a href="#Page_42">42</a>; Figs. <a href="#fig24">24</a>, <a href="#fig25">25</a>.
+  <ul class="IX">
+  <li>structure, <a href="#Page_42">42</a>.</li>
+  <li>movements, <a href="#Page_42">42</a>.</li>
+  <li>reproduction, <a href="#Page_42">42</a>.</li>
+  </ul></li>
+<li><i>Dicentra</i>, <a href="#Page_192">192</a>; <a href="#fig103">Fig.&nbsp;103</a>.</li>
+<li>Dicotyledon, <a href="#Page_145">145</a>, <a href="#Page_170">170</a>, <a href="#Page_181">181</a>, <a href="#Page_225">225</a>.</li>
+<li><i>Digitalis</i>. See &ldquo;<a href="#IX_F">Foxglove</a>.&rdquo;</li>
+<li>Di&oelig;cious, <a href="#Page_88">88</a>.</li>
+<li><i>Dion&aelig;a</i>. See &ldquo;<a href="#IX_V">Venus&#8217;s fly-trap</a>.&rdquo;</li>
+<li><i>Dioscore&aelig;</i>. See &ldquo;<a href="#IX_Y">Yam</a>.&rdquo;</li>
+<li><i><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Diascorea&rsquo;.">Dioscorea</ins> villosa</i>, <a href="#Page_154">154</a>.</li>
+<li><i>Diospyros</i>. See &ldquo;<a href="#IX_P">Persimmon</a>.&rdquo;</li>
+<li><i>Diospyrin&aelig;</i>, <a href="#Page_210">210</a>.</li>
+<li><i>Dipsacus</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_T">Teasel</a>.&rdquo;</li>
+<li><i>Dirca</i>. See &ldquo;<ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Moose-wood&rsquo;; changed to be consistent with the rest of the book."><a href="#IX_M">Moosewood</a></ins>.&rdquo;</li>
+<li>Ditch-moss, <a href="#Page_167">167</a>; <a href="#fig91">Fig.&nbsp;91</a>.</li>
+<li>Dodder, <a href="#Page_214">214</a>.</li>
+<li><i>Dodecatheon</i>. See &ldquo;<a href="#IX_S">Shooting-star</a>.&rdquo;</li>
+<li>Dog-bane, <a href="#Page_219">219</a>; <a href="#fig122">Fig.&nbsp;122</a>.</li>
+<li>Dogwood, <a href="#Page_202">202</a>, <a href="#Page_229">229</a>; <a href="#fig110">Fig.&nbsp;110</a>.</li>
+<li><i><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Drapernaldia&rsquo;.">Draparnaldia</ins></i>, <a href="#Page_26">26</a>; <a href="#fig14">Fig.&nbsp;14</a>.</li>
+<li><i>Drosera</i> <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_S">Sun-dew</a>.&rdquo;</li>
+<li>Drupe. See &ldquo;<a href="#IX_S">Stone-fruit</a>.&rdquo;</li>
+<li>Duck-weed, <a href="#Page_159">159</a>; <a href="#fig86">Fig.&nbsp;86</a>.</li>
+<li>Dutchman&#8217;s pipe. See &ldquo;<i><a href="#IX_A">Aristolochia</a></i>.&rdquo;</li>
+</ul>
+
+<ul class="IX">
+<li><a name="IX_E" id="IX_E"></a>Earth star. See &ldquo;<i><a href="#IX_G">Geaster</a></i>.&rdquo;</li>
+<li><i>Ebenace&aelig;</i> (ebony), <a href="#Page_212">212</a>.</li>
+<li><i>Echinospermum</i>. See &ldquo;<a href="#IX_B">Beggar&#8217;s-ticks</a>.&rdquo;</li>
+<li><i>Ectocarpus</i>, <a href="#Page_45">45</a>, <a href="#Page_47">47</a>; <a href="#fig28">Fig.&nbsp;28</a>.</li>
+<li>Eel-grass, <a href="#Page_168">168</a>, <a href="#Page_169">169</a>; <a href="#fig91">Fig.&nbsp;91</a>.</li>
+<li>Egg apparatus, <a href="#Page_144">144</a>.</li>
+<li>Egg cell, <a href="#Page_27">27</a>, <a href="#Page_36">36</a>, <a href="#Page_39">39</a>, <a href="#Page_45">45</a>, <a href="#Page_90">90</a>, <a href="#Page_106">106</a>, <a href="#Page_133">133</a>, <a href="#Page_144">144</a>.</li>
+<li>Egg-plant, <a href="#Page_215">215</a>.</li>
+<li>Eichler, <a href="#Page_153">153</a>.</li>
+<li>Elater, <a href="#Page_91">91</a>, <a href="#Page_122">122</a>.</li>
+<li>Elder, <a href="#Page_224">224</a>.</li>
+<li><i>El&aelig;agnace&aelig;</i>, <a href="#Page_206">206</a>.</li>
+<li>Elm, <a href="#Page_183">183</a>.</li>
+<li><i>Elodea</i>. See &ldquo;<a href="#IX_D">Ditch-moss</a>.&rdquo;</li>
+<li>Embryo, <a href="#Page_90">90</a>, <a href="#Page_97">97</a>, <a href="#Page_107">107</a>, <a href="#Page_133">133</a>, <a href="#Page_149">149</a>, <a href="#Page_180">180</a>.</li>
+<li>Embryology, <a href="#Page_3">3</a>.</li>
+<li>Embryo sac, <a href="#Page_143">143</a>, <a href="#Page_144">144</a>, <a href="#Page_151">151</a>.</li>
+<li><span class="pagenum" title="Page&nbsp;242">&nbsp;</span><a name="Page_242" id="Page_242"></a><i>Enantioblast&aelig;</i>, <a href="#Page_153">153</a>, <a href="#Page_156">156</a>; <a href="#fig85">Fig.&nbsp;85</a>.</li>
+<li>Endosperm, <a href="#Page_133">133</a>, <a href="#Page_146">146</a>, <a href="#Page_152">152</a>.</li>
+<li>Entire leaves, <a href="#Page_170">170</a>.</li>
+<li><i>Entomophthore&aelig;</i>, <a href="#Page_57">57</a>.</li>
+<li><i>Epacride&aelig;</i>, <a href="#Page_210">210</a>.</li>
+<li>Epidermis, <a href="#Page_91">91</a>, <a href="#Page_111">111</a>, <a href="#Page_112">112</a>, <a href="#Page_113">113</a>, <a href="#Page_122">122</a>, <a href="#Page_135">135</a>, <a href="#Page_137">137</a>, <a href="#Page_150">150</a>, <a href="#Page_177">177</a>.</li>
+<li><i>Epig&aelig;a</i>. See &ldquo;<a href="#IX_T">Trailing arbutus</a>.&rdquo;</li>
+<li><i>Epilobium</i>. See &ldquo;<a href="#IX_W">Willow-herb</a>.&rdquo;</li>
+<li><i>Epiphegus</i>. See &ldquo;<a href="#IX_B">Beech-drops</a>.&rdquo;</li>
+<li>Epiphyte, <a href="#Page_166">166</a>.</li>
+<li><i>Equisetum</i>, <i>-tin&aelig;</i>. See &ldquo;<a href="#IX_H">Horse-tail</a>.&rdquo;</li>
+<li>Ergot, <a href="#Page_76">76</a>.</li>
+<li><i>Erica</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_H">Heath</a>.&rdquo;</li>
+<li><i>Erysiphe</i>, <a href="#Page_70">70</a>.</li>
+<li><i>Erythr&aelig;a</i>. See &ldquo;<a href="#IX_C">Centaury</a>.&rdquo;</li>
+<li><i>Erythronium</i>, <a href="#Page_146">146</a>&ndash;<a href="#Page_152">152</a>; <a href="#fig81">Fig.&nbsp;81</a>.
+  <ul class="IX">
+  <li>leaf, <a href="#Page_146">146</a>.</li>
+  <li>stem, <a href="#Page_146">146</a>.</li>
+  <li>root, <a href="#Page_146">146</a>.</li>
+  <li>gross anatomy of stem, <a href="#Page_147">147</a>.</li>
+  <li>flower, <a href="#Page_148">148</a>.</li>
+  <li>fruit and seed, <a href="#Page_150">150</a>.</li>
+  <li>histology of stem, <a href="#Page_150">150</a>.</li>
+  <li>of leaf, <a href="#Page_150">150</a>.</li>
+  <li>of flower, <a href="#Page_151">151</a>.</li>
+  <li>of ovule and seed, <a href="#Page_151">151</a>, <a href="#Page_152">152</a>.</li>
+  </ul></li>
+<li><i>Eschscholtzia</i>, <a href="#Page_191">191</a>.</li>
+<li><i>Eucalyptus</i>, <a href="#Page_206">206</a>.</li>
+<li><i>Eucycl&aelig;</i>, <a href="#Page_196">196</a>, <a href="#Page_200">200</a>.</li>
+<li><i>Eudorina</i>, <a href="#Page_20">20</a>.</li>
+<li><i>Euglena</i>, <a href="#Page_11">11</a>, <a href="#Page_19">19</a>; <a href="#fig9">Fig.&nbsp;9</a>.</li>
+<li><i>Euonymus</i>. See &ldquo;<a href="#IX_S">Spindle-tree</a>.&rdquo;</li>
+<li><i>Euphorbia</i>, <a href="#Page_199">199</a>; <a href="#fig109">Fig.&nbsp;109</a>.</li>
+<li><i>Eurotium</i>, <a href="#Page_70">70</a>; <a href="#fig42">Fig.&nbsp;42</a>.</li>
+<li>Evening primrose, <a href="#Page_206">206</a>.</li>
+<li><i>Exoascus</i>, <a href="#Page_66">66</a>.</li>
+</ul>
+
+<ul class="IX">
+<li><i><a name="IX_F" id="IX_F"></a>Fagopyrum</i>. See &ldquo;<a href="#IX_B">Buckwheat</a>.&rdquo;</li>
+<li>Feather-veined. See &ldquo;<a href="#IX_P">Pinnate-veined</a>.&rdquo;</li>
+<li>Fern, <a href="#Page_5">5</a>, <a href="#Page_102">102</a>, <a href="#Page_104">104</a>, <a href="#Page_116">116</a>.
+  <ul class="IX">
+  <li>flowering, <a href="#Page_118">118</a>; <a href="#fig70">Fig.&nbsp;70</a>.</li>
+  <li>lady, <a href="#Page_104">104</a>; <a href="#fig70">Fig.&nbsp;70</a>.</li>
+  <li>maiden-hair. See &ldquo;<a href="#IX_M">Maiden-hair fern</a>.&rdquo;</li>
+  <li>ostrich. See &ldquo;<a href="#IX_O">Ostrich-fern</a>.&rdquo;</li>
+  <li>sensitive, <a href="#Page_104">104</a>.</li>
+  <li>true, <a href="#Page_117">117</a>.</li>
+  <li>water. See &ldquo;<a href="#IX_W">Water-fern</a>.&rdquo;</li>
+  </ul></li>
+<li>Fertilization, <a href="#Page_225">225</a>.</li>
+<li>Fibre, <a href="#Page_124">124</a>, <a href="#Page_175">175</a>, <a href="#Page_177">177</a>.</li>
+<li>Fibro-vascular bundle, <a href="#Page_107">107</a>, <a href="#Page_110">110</a>, <a href="#Page_121">121</a>, <a href="#Page_123">123</a>, <a href="#Page_135">135</a>, <a href="#Page_136">136</a>, <a href="#Page_147">147</a>, <a href="#Page_150">150</a>, <a href="#Page_159">159</a>, <a href="#Page_174">174</a>.</li>
+<li>Fig, <a href="#Page_183">183</a>.</li>
+<li>Figwort, <a href="#Page_215">215</a>, <a href="#Page_216">216</a>; <a href="#fig120">Fig.&nbsp;120</a>.</li>
+<li>Filament (of stamen), <a href="#Page_148">148</a>, <a href="#Page_17">17</a>.</li>
+<li><i>Filices</i>. See &ldquo;<a href="#IX_T">True ferns</a>.&rdquo;</li>
+<li><i>Filicine&aelig;</i>. See &ldquo;<a href="#IX_F">Fern</a>.&rdquo;</li>
+<li>Fir, <a href="#Page_142">142</a>.</li>
+<li>Fission, <a href="#Page_23">23</a>.</li>
+<li><i>Flagellata</i>, <a href="#Page_19">19</a>.</li>
+<li>Flagellum, <a href="#Page_19">19</a>.</li>
+<li>Flax, <a href="#Page_197">197</a>; <a href="#fig107">Fig.&nbsp;107</a>.</li>
+<li>Flies, <a href="#Page_229">229</a>.</li>
+<li>Flower, <a href="#Page_128">128</a>, <a href="#Page_131">131</a>.</li>
+<li>Flowering-plant. See &ldquo;<a href="#IX_S">Spermaphyte</a>.&rdquo;</li>
+<li>Forget-me-not, <a href="#Page_215">215</a>.</li>
+<li>Four-o&#8217;clock, <a href="#Page_183">183</a>.</li>
+<li>Foxglove, <a href="#Page_217">217</a>.</li>
+<li><i>Frangulin&aelig;</i>, <a href="#Page_199">199</a>.</li>
+<li><i>Fraxinus</i>. See &ldquo;<a href="#IX_A">Ash</a>.&rdquo;</li>
+<li>Fringe-tree, <a href="#Page_218">218</a>; <a href="#fig122">Fig.&nbsp;122</a>.</li>
+<li>Fruit, <a href="#Page_145">145</a>.</li>
+<li><i>Fucace&aelig;</i>, <a href="#Page_43">43</a>.</li>
+<li>Fuchsia, <a href="#Page_201">201</a>.</li>
+<li><i>Fucus</i>, <a href="#Page_42">42</a>&ndash;<a href="#Page_46">46</a>.
+  <ul class="IX">
+  <li><i>vesiculosus</i>, <a href="#Page_43">43</a>; Figs. <a href="#fig26">26</a>, <a href="#fig27">27</a>.</li>
+  <li>general structure, <a href="#Page_43">43</a>, <a href="#Page_44">44</a>.</li>
+  <li>conceptacles, <a href="#Page_44">44</a>.</li>
+  <li>collecting plants, <a href="#Page_44">44</a>.</li>
+  <li>cells, <a href="#Page_44">44</a>.</li>
+  <li>chloroplasts, <a href="#Page_44">44</a>.</li>
+  <li>o&ouml;gonium, <a href="#Page_45">45</a>.</li>
+  <li><i>platycarpus</i>, <a href="#Page_45">45</a>.</li>
+  <li>antheridium, <a href="#Page_45">45</a>, <a href="#Page_46">46</a>.</li>
+  <li>fertilization, <a href="#Page_46">46</a>.</li>
+  <li>germination, <a href="#Page_46">46</a>.</li>
+  </ul></li>
+<li><i>Fumariace&aelig;</i>. See &ldquo;<a href="#IX_F">Fumitory</a>.&rdquo;</li>
+<li>Fumitory, <a href="#Page_192">192</a>.</li>
+<li><span class="pagenum" title="Page&nbsp;243">&nbsp;</span><a name="Page_243" id="Page_243"></a><i>Funaria</i>, <a href="#Page_93">93</a>&ndash;<a href="#Page_99">99</a>; Figs. <a href="#fig58">58</a>&ndash;<a href="#fig62">62</a>.
+  <ul class="IX">
+  <li>gross anatomy, <a href="#Page_93">93</a>, <a href="#Page_94">94</a>.</li>
+  <li>protonema, <a href="#Page_93">93</a>.</li>
+  <li>&ldquo;flower,&rdquo; <a href="#Page_94">94</a>.</li>
+  <li>structure of leaf, <a href="#Page_94">94</a>.</li>
+  <li>chloroplasts, division of, <a href="#Page_95">95</a>.</li>
+  <li>formation of starch in chloroplasts, <a href="#Page_95">95</a>.</li>
+  <li>structure of stem, <a href="#Page_96">96</a>.</li>
+  <li>root hairs, <a href="#Page_96">96</a>.</li>
+  <li>buds, <a href="#Page_96">96</a>.</li>
+  <li>antheridium spermatozoids, <a href="#Page_96">96</a>, <a href="#Page_97">97</a>.</li>
+  <li>archegonium, <a href="#Page_97">97</a>.</li>
+  <li>embryo, <a href="#Page_98">98</a>.</li>
+  <li>capsule and spores, <a href="#Page_98">98</a>, <a href="#Page_99">99</a>.</li>
+  <li>germination of spores, <a href="#Page_99">99</a>.</li>
+  </ul></li>
+<li>Fungi, culture of, <a href="#Page_5">5</a>, <a href="#Page_54">54</a>.
+  <ul class="IX">
+  <li>true. See &ldquo;<i><a href="#IX_M">Mycomycetes</a></i>.&rdquo;</li>
+  <li>alga. See &ldquo;<i><a href="#IX_P">Phycomycetes</a></i>.&rdquo;</li>
+  </ul></li>
+<li>Funiculus, <a href="#Page_151">151</a>, <a href="#Page_175">175</a>.</li>
+<li><i>Funkia</i>. See &ldquo;<a href="#IX_D">Day lily</a>.&rdquo;</li>
+</ul>
+
+<ul class="IX">
+<li><i><a name="IX_G" id="IX_G"></a>Galium</i>, <a href="#Page_223">223</a>; <a href="#fig124">Fig.&nbsp;124</a>.</li>
+<li><i>Gamopetal&aelig;</i>. See &ldquo;<i><a href="#IX_S">Sympetal&aelig;</a></i>.&rdquo;</li>
+<li><i>Gaultheria</i>. See &ldquo;<a href="#IX_W">Wintergreen</a>.&rdquo;</li>
+<li><i>Gaylussacia</i>. See &ldquo;<a href="#IX_H">Huckleberry</a>.&rdquo;</li>
+<li><i>Geaster</i>, <a href="#Page_84">84</a>; <a href="#fig49">Fig.&nbsp;49</a>.</li>
+<li>Gentian, <a href="#Page_218">218</a>; <a href="#fig122">Fig.&nbsp;122</a>.</li>
+<li>Gentian violet, <a href="#Page_4">4</a>, <a href="#Page_138">138</a>, <a href="#Page_231">231</a>.</li>
+<li><i>Gentiana</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_G">Gentian</a>.&rdquo;</li>
+<li><i>Geranium</i>, <i>-ace&aelig;</i>, <a href="#Page_3">3</a>, <a href="#Page_171">171</a>, <a href="#Page_196">196</a>; <a href="#fig107">Fig.&nbsp;107</a>.</li>
+<li><i>Gerardia</i>, <a href="#Page_217">217</a>.</li>
+<li>Germ cell. See &ldquo;<a href="#IX_E">Egg cell</a>.&rdquo;</li>
+<li><i>Gesnerace&aelig;</i>, <a href="#Page_218">218</a>.</li>
+<li>Ghost flower. See &ldquo;<a href="#IX_I">Indian-pipe</a>.&rdquo;</li>
+<li>Gill, <a href="#Page_83">83</a>.</li>
+<li>Ginger, <a href="#Page_163">163</a>.</li>
+<li><i>Gingko</i>, <a href="#Page_142">142</a>; <a href="#fig78">Fig.&nbsp;78</a>.</li>
+<li><i>Gleditschia</i>. See &ldquo;<a href="#IX_H">Honey locust</a>.&rdquo;</li>
+<li><i>Gloxinia</i>, <a href="#Page_218">218</a>.</li>
+<li><i>Glumace&aelig;</i>, <a href="#Page_153">153</a>, <a href="#Page_160">160</a>; <a href="#fig87">Fig.&nbsp;87</a>.</li>
+<li>Glume, <a href="#Page_162">162</a>.</li>
+<li>Glycerine, <a href="#Page_4">4</a>, <a href="#Page_51">51</a>, <a href="#Page_55">55</a>, <a href="#Page_59">59</a>, <a href="#Page_67">67</a>, <a href="#Page_83">83</a>, <a href="#Page_98">98</a>, <a href="#Page_224">224</a>, <a href="#Page_231">231</a>, <a href="#Page_233">233</a>.</li>
+<li><i>Gnetace&aelig;</i>. See &ldquo;<a href="#IX_J">Joint fir</a>.&rdquo;</li>
+<li>Golden-rod, <a href="#Page_224">224</a>.</li>
+<li><i>Gonium</i>, <a href="#Page_20">20</a>.</li>
+<li>Gooseberry, <a href="#Page_203">203</a>; <a href="#fig111">Fig.&nbsp;111</a>.</li>
+<li>Goose-foot, <a href="#Page_184">184</a>; <a href="#fig98">Fig.&nbsp;98</a>.</li>
+<li><i>Gossypium</i>. See &ldquo;<a href="#IX_C">Cotton</a>.&rdquo;</li>
+<li>Gourd, <a href="#Page_221">221</a>.</li>
+<li><i>Gramine&aelig;</i>. See &ldquo;<a href="#IX_G">Grass</a>.&rdquo;</li>
+<li>Grape, <a href="#Page_171">171</a>, <a href="#Page_199">199</a>; <a href="#fig109">Fig.&nbsp;109</a>.</li>
+<li>Grape fern, <a href="#Page_116">116</a>; <a href="#fig70">Fig.&nbsp;70</a>.</li>
+<li><i>Graphis</i>, <a href="#Page_75">75</a>; <a href="#fig45">Fig.&nbsp;45</a>.</li>
+<li>Grass, <a href="#Page_161">161</a>, <a href="#Page_225">225</a>; <a href="#fig87">Fig.&nbsp;87</a>.</li>
+<li>Gray moss. See &ldquo;<i><a href="#IX_T">Tillandsia</a></i>.&rdquo;</li>
+<li>Green-brier, <a href="#Page_154">154</a>.</li>
+<li>Green-felt. See &ldquo;<i><a href="#IX_V">Vaucheria</a></i>.&rdquo;</li>
+<li>Green monad, <a href="#Page_12">12</a>, <a href="#Page_19">19</a>.</li>
+<li>Green slime, <a href="#Page_21">21</a>, <a href="#Page_22">22</a>; <a href="#fig11">Fig.&nbsp;11</a>.</li>
+<li>Ground pine, <a href="#Page_123">123</a>; <a href="#fig73">Fig.&nbsp;73</a>.</li>
+<li>Ground tissue, <a href="#Page_110">110</a>, <a href="#Page_111">111</a>, <a href="#Page_113">113</a>, <a href="#Page_124">124</a>, <a href="#Page_137">137</a>, <a href="#Page_177">177</a>, <a href="#Page_178">178</a>.</li>
+<li><i>Gruinales</i>, <a href="#Page_196">196</a>.</li>
+<li>Guard cell, <a href="#Page_113">113</a>, <a href="#Page_135">135</a>, <a href="#Page_150">150</a>.</li>
+<li>Gulf weed. See &ldquo;<i><a href="#IX_S">Sargassum</a></i>.&rdquo;</li>
+<li>Gum. See &ldquo;<i><a href="#IX_E">Eucalyptus</a></i>.&rdquo;</li>
+<li><i>Gymnocarp&aelig;</i>, <a href="#Page_84">84</a>.</li>
+<li>Gymnosperm, <a href="#Page_129">129</a>, <a href="#Page_141">141</a>.</li>
+<li><i>Gymnosporangium</i>, <a href="#Page_79">79</a>&ndash;<a href="#Page_81">81</a>; <a href="#fig47">Fig.&nbsp;47</a>.
+  <ul class="IX">
+  <li>cedar apples, <a href="#Page_79">79</a>.</li>
+  <li>spores, <a href="#Page_80">80</a>.</li>
+  </ul></li>
+<li><i>Gynandr&aelig;</i>, <a href="#Page_153">153</a>, <a href="#Page_164">164</a>.</li>
+<li>Gyn&oelig;cium, <a href="#Page_148">148</a>, <a href="#Page_167">167</a>.</li>
+<li>Gynostemium. See &ldquo;<a href="#IX_C">Column</a>.&rdquo;</li>
+</ul>
+
+<ul class="IX">
+<li><i><a name="IX_H" id="IX_H"></a>Habenaria</i>, <a href="#Page_166">166</a>, <a href="#Page_227">227</a>; <a href="#fig90">Fig.&nbsp;90</a>.</li>
+<li>H&aelig;matoxylin, <a href="#Page_233">233</a>.</li>
+<li>Hair, <a href="#Page_8">8</a>, <a href="#Page_177">177</a>.</li>
+<li><i>Haloragidace&aelig;</i>, <a href="#Page_206">206</a>.</li>
+<li>Hazel, <a href="#Page_182">182</a>, <a href="#Page_183">183</a>, <a href="#Page_225">225</a>; <a href="#fig97">Fig.&nbsp;97</a>.</li>
+<li>Head, <a href="#Page_181">181</a>.</li>
+<li>Heath, <a href="#Page_211">211</a>.</li>
+<li><i>Helobi&aelig;</i>, <a href="#Page_153">153</a>, <a href="#Page_167">167</a>.</li>
+<li><i>Hemerocallis</i>. See &ldquo;<a href="#IX_D">Day lily</a>.&rdquo;</li>
+<li><i>Hemi-angiocarp&aelig;</i>, <a href="#Page_84">84</a>.</li>
+<li>Hemlock, <a href="#Page_142">142</a>; <a href="#fig78">Fig.&nbsp;78</a>.</li>
+<li>Hemp, <a href="#Page_183">183</a>.</li>
+<li><i>Hepatic&aelig;</i>. See &ldquo;<a href="#IX_L">Liverwort</a>.&rdquo;</li>
+<li><span class="pagenum" title="Page&nbsp;244">&nbsp;</span><a name="Page_244" id="Page_244"></a>Hermaphrodite, <a href="#Page_199">199</a>.</li>
+<li>Heterocyst, <a href="#Page_17">17</a>.</li>
+<li>Heterostylism, <a href="#Page_228">228</a>.</li>
+<li><i>Hibiscus</i>, <a href="#Page_195">195</a>.</li>
+<li>Hickory, <a href="#Page_170">170</a>, <a href="#Page_183">183</a>.</li>
+<li>Holly, <a href="#Page_199">199</a>.</li>
+<li>Hollyhock, <a href="#Page_195">195</a>.</li>
+<li>Honey locust, <a href="#Page_209">209</a>.</li>
+<li>Honeysuckle, <a href="#Page_170">170</a>, <a href="#Page_172">172</a>, <a href="#Page_181">181</a>, <a href="#Page_223">223</a>; <a href="#fig124">Fig.&nbsp;124</a>.</li>
+<li>Hop, <a href="#Page_171">171</a>, <a href="#Page_181">181</a>; <a href="#fig97">Fig.&nbsp;97</a>.</li>
+<li>Horned pond-weed, <a href="#Page_224">224</a>.</li>
+<li>Horse-chestnut, <a href="#Page_170">170</a>, <a href="#Page_199">199</a>.</li>
+<li>Horse-tail, <a href="#Page_116">116</a>&ndash;<a href="#Page_120">120</a>.
+  <ul class="IX">
+  <li>field, <a href="#Page_120">120</a>&ndash;<a href="#Page_122">122</a>; <a href="#fig72">Fig.&nbsp;72</a>.</li>
+  <li>stems and tubers, <a href="#Page_120">120</a>.</li>
+  <li>fertile branches, <a href="#Page_120">120</a>.</li>
+  <li>leaves, <a href="#Page_121">121</a>.</li>
+  <li>cone, <a href="#Page_121">121</a>.</li>
+  <li>stem, <a href="#Page_121">121</a>.</li>
+  <li>sporangia and spores, <a href="#Page_121">121</a>.</li>
+  <li>sterile branches, <a href="#Page_121">121</a>.</li>
+  <li>histology of stem, <a href="#Page_121">121</a>.
+    <ul class="IX">
+    <li>of sporangia, <a href="#Page_122">122</a>.</li>
+    </ul></li>
+  <li>spores, <a href="#Page_122">122</a>.</li>
+  <li>germination, prothallium, <a href="#Page_122">122</a>.</li>
+  </ul></li>
+<li>Hound&#8217;s-tongue, <a href="#Page_215">215</a>; <a href="#fig119">Fig.&nbsp;119</a>.</li>
+<li><i>Houstonia</i>, <a href="#Page_223">223</a>; <a href="#fig124">Fig.&nbsp;124</a>.</li>
+<li><i>Hoya</i>. See &ldquo;<a href="#IX_W">Wax-plant</a>.&rdquo;</li>
+<li>Huckleberry, <a href="#Page_181">181</a>, <a href="#Page_211">211</a>; <a href="#fig116">Fig.&nbsp;116</a>.</li>
+<li>Humming-bird, <a href="#Page_226">226</a>.</li>
+<li>Hyacinth, <a href="#Page_146">146</a>.</li>
+<li><i>Hydnum</i>, <a href="#Page_84">84</a>; <a href="#fig51">Fig.&nbsp;51</a>.</li>
+<li><i>Hydrangea</i>, <i>-ge&aelig;</i>, <a href="#Page_202">202</a>; <a href="#fig111">Fig.&nbsp;111</a>.</li>
+<li><i>Hydrocharide&aelig;</i>, <a href="#Page_167">167</a>.</li>
+<li>Hydrogen, <a href="#Page_2">2</a>, <a href="#Page_95">95</a>.</li>
+<li><i>Hydropeltidin&aelig;</i>, <a href="#Page_189">189</a>.</li>
+<li><i>Hydrophyllum</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_W">Water-leaf</a>.&rdquo;</li>
+<li><i>Hypericum</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_S">St.&nbsp;John&#8217;s-wort</a>.&rdquo;</li>
+</ul>
+
+<ul class="IX">
+<li><i><a name="IX_I" id="IX_I"></a>Ilex</i>. See &ldquo;<a href="#IX_H">Holly</a>.&rdquo;</li>
+<li><i>Impatiens</i>. See &ldquo;<a href="#IX_J">Jewel-weed</a>,&rdquo; &ldquo;<a href="#IX_B">Balsam</a>.&rdquo;</li>
+<li>India-rubber, <a href="#Page_200">200</a>.</li>
+<li>Indian-pipe, <a href="#Page_144">144</a>, <a href="#Page_210">210</a>; <a href="#fig79">Fig.&nbsp;79</a>.</li>
+<li>Indian turnip. See &ldquo;<i><a href="#IX_A">Aris&aelig;ma</a></i>.&rdquo;</li>
+<li>Indusium, <a href="#Page_118">118</a>.</li>
+<li>Inflorescence, <a href="#Page_157">157</a>.</li>
+<li>Integument, <a href="#Page_133">133</a>, <a href="#Page_144">144</a>, <a href="#Page_151">151</a>, <a href="#Page_180">180</a>.</li>
+<li>Intercellular space, <a href="#Page_124">124</a>, <a href="#Page_135">135</a>, <a href="#Page_150">150</a>.</li>
+<li>Internode, <a href="#Page_39">39</a>.</li>
+<li>Iodine, <a href="#Page_4">4</a>, <a href="#Page_22">22</a>, <a href="#Page_31">31</a>.</li>
+<li><i>Ipom&oelig;a</i>, <a href="#Page_213">213</a>.</li>
+<li><i>Iridace&aelig;</i>, <a href="#Page_156">156</a>.</li>
+<li>Iris, <a href="#Page_154">154</a>, <a href="#Page_156">156</a>; <a href="#fig84">Fig.&nbsp;84</a>.</li>
+<li>Irish moss, <a href="#Page_49">49</a>.</li>
+<li><i>Isocarp&aelig;</i>, <a href="#Page_210">210</a>, <a href="#Page_212">212</a>.</li>
+<li><i>Isoetes</i>. See &ldquo;<a href="#IX_Q">Quill-wort</a>.&rdquo;</li>
+<li><i>Iuliflor&aelig;</i>, <a href="#Page_181">181</a>.</li>
+<li>Ivy, <a href="#Page_202">202</a>.</li>
+</ul>
+
+<ul class="IX">
+<li><a name="IX_J" id="IX_J"></a>Jack-in-the-pulpit. See &ldquo;<i><a href="#IX_A">Aris&aelig;ma</a></i>.&rdquo;</li>
+<li>Jasmine, <a href="#Page_218">218</a>.</li>
+<li><i>Jeffersonia</i>. See &ldquo;<a href="#IX_T">Twin-leaf</a>.&rdquo;</li>
+<li>Jewel-weed, <a href="#Page_197">197</a>; <a href="#fig107">Fig.&nbsp;107</a>.</li>
+<li>Joint fir, <a href="#Page_140">140</a>, <a href="#Page_142">142</a>.</li>
+<li><i>Juncagine&aelig;</i>, <a href="#Page_167">167</a>.</li>
+<li><i>Juncus</i>. See &ldquo;<a href="#IX_R">Rush</a>.&rdquo;</li>
+<li><i>Jungermanniace&aelig;</i>, <a href="#Page_92">92</a>; <a href="#fig57">Fig.&nbsp;57</a>.</li>
+</ul>
+
+<ul class="IX">
+<li><i><a name="IX_K" id="IX_K"></a>Kalmia</i>. See &ldquo;<a href="#IX_M">Mountain laurel</a>.&rdquo;</li>
+<li>Karyokinesis, <a href="#Page_233">233</a>.</li>
+<li>Keel, <a href="#Page_208">208</a>.</li>
+<li>Kelp. See &ldquo;<i><a href="#IX_L">Laminaria</a></i>.&rdquo;
+  <ul class="IX">
+  <li>giant. See &ldquo;<i><a href="#IX_M">Macrocystis</a></i>.&rdquo;</li>
+  </ul></li>
+<li>Knotgrass. See &ldquo;<i><a href="#IX_P">Polygonum</a></i>.&rdquo;</li>
+</ul>
+
+<ul class="IX">
+<li><a name="IX_L" id="IX_L"></a>Labellum. See &ldquo;<a href="#IX_L">Lip</a>.&rdquo;</li>
+<li><i>Labiat&aelig;</i>. See &ldquo;<a href="#IX_M">Mint</a>.&rdquo;</li>
+<li><i>Labiatiflor&aelig;</i>, <a href="#Page_215">215</a>.</li>
+<li>Lady&#8217;s-slipper, <a href="#Page_164">164</a>, <a href="#Page_166">166</a>, <a href="#Page_198">198</a>; <a href="#fig90">Fig.&nbsp;90</a>.</li>
+<li>Lamella, <a href="#Page_83">83</a>.</li>
+<li><i>Laminaria</i>, <a href="#Page_45">45</a>, <a href="#Page_47">47</a>; <a href="#fig28">Fig.&nbsp;28</a>.</li>
+<li><i>Lamium</i>. See &ldquo;<a href="#IX_D">Dead nettle</a>.&rdquo;</li>
+<li>Larch. See &ldquo;<a href="#IX_T">Tamarack</a>.&rdquo;</li>
+<li><i>Larix</i>. See &ldquo;<a href="#IX_T">Tamarack</a>.&rdquo;</li>
+<li>Larkspur, <a href="#Page_186">186</a>, <a href="#Page_227">227</a>; <a href="#fig99">Fig.&nbsp;99</a>.</li>
+<li>Latex, <a href="#Page_191">191</a>.</li>
+<li><span class="pagenum" title="Page&nbsp;245">&nbsp;</span><a name="Page_245" id="Page_245"></a>Laurel, <a href="#Page_188">188</a>.</li>
+<li><i>Laurine&aelig;</i>. See &ldquo;<a href="#IX_L">Laurel</a>.&rdquo;</li>
+<li>Lavender, <a href="#Page_215">215</a>.</li>
+<li>Leaf-green. See &ldquo;<a href="#IX_C">Chlorophyll</a>.&rdquo;</li>
+<li>Leaf tendril, <a href="#Page_171">171</a>.</li>
+<li>Leaf thorn, <a href="#Page_172">172</a>.</li>
+<li><i>Leguminos&aelig;</i>, <a href="#Page_207">207</a>.</li>
+<li><i>Lemanea</i>, <a href="#Page_53">53</a>; <a href="#fig31">Fig.&nbsp;31</a>.</li>
+<li><i>Lemna</i>. See &ldquo;<a href="#IX_D">Duck-weed</a>.&rdquo;</li>
+<li>Lemon, <a href="#Page_198">198</a>.</li>
+<li><i>Lentibulariace&aelig;</i>, <a href="#Page_217">217</a>.</li>
+<li>Lettuce, <a href="#Page_223">223</a>.</li>
+<li><i>Lichenes</i>, <a href="#Page_73">73</a>; Figs. <a href="#fig44">44</a>, <a href="#fig45">45</a>.</li>
+<li>Ligula, <a href="#Page_127">127</a>.</li>
+<li><i>Ligulat&aelig;</i>, <a href="#Page_125">125</a>.</li>
+<li>Lilac, <a href="#Page_170">170</a>, <a href="#Page_181">181</a>, <a href="#Page_218">218</a>.</li>
+<li><i>Liliace&aelig;</i>, <a href="#Page_155">155</a>.</li>
+<li><i>Liliiflor&aelig;</i>, <a href="#Page_153">153</a>, <a href="#Page_155">155</a>; <a href="#fig83">Fig.&nbsp;83</a>.</li>
+<li><i>Lilium</i>. See &ldquo;<a href="#IX_L">Lily</a>.&rdquo;</li>
+<li>Lily, <a href="#Page_146">146</a>, <a href="#Page_155">155</a>.</li>
+<li>Lily-of-the-valley, <a href="#Page_155">155</a>.</li>
+<li>Lime. See &ldquo;<a href="#IX_L">Linden</a>.&rdquo;</li>
+<li>Linden, <a href="#Page_195">195</a>; <a href="#fig106">Fig.&nbsp;106</a>.</li>
+<li>Linear, <a href="#Page_159">159</a>.</li>
+<li><i>Linum</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_F">Flax</a>.&rdquo;</li>
+<li>Lip, <a href="#Page_165">165</a>.</li>
+<li><i>Liriodendron</i>. See &ldquo;<a href="#IX_T">Tulip-tree</a>.&rdquo;</li>
+<li><i>Lithospermum</i>. See &ldquo;<a href="#IX_P">Puccoon</a>.&rdquo;</li>
+<li>Liverwort, <a href="#Page_86">86</a>.
+  <ul class="IX">
+  <li>classification of, <a href="#Page_91">91</a>.</li>
+  <li>horned. See &ldquo;<i><a href="#IX_A">Anthocerote&aelig;</a></i>.&rdquo;</li>
+  <li>giant, <a href="#Page_91">91</a>; <a href="#fig57">Fig.&nbsp;57</a>.</li>
+  </ul></li>
+<li>Lizard-tail, <a href="#Page_181">181</a>, <a href="#Page_183">183</a>; <a href="#fig97">Fig.&nbsp;97</a>.</li>
+<li><i>Lobelia</i>, <i>-ace&aelig;</i>. 221; <a href="#fig123">Fig.&nbsp;123</a>.</li>
+<li><i>Loganie&aelig;</i>, <a href="#Page_219">219</a>.</li>
+<li><i>Lonicera</i>. See &ldquo;<a href="#IX_H">Honeysuckle</a>.&rdquo;</li>
+<li>Loosestrife. See &ldquo;<i><a href="#IX_L">Lythrum</a></i>.&rdquo;
+  <ul class="IX">
+  <li>swamp. See &ldquo;<a href="#IX_N">Nes&aelig;a</a>.&rdquo;</li>
+  </ul></li>
+<li>Lotus. See &ldquo;<i><a href="#IX_N">Nelumbo</a></i>.&rdquo;</li>
+<li><i>Lychnis</i>, <a href="#Page_185">185</a>.</li>
+<li><i>Lycoperdon</i>, <a href="#Page_84">84</a>; <a href="#fig49">Fig.&nbsp;49</a>.</li>
+<li><i>Lycopersicum</i>. See &ldquo;<a href="#IX_T">Tomato</a>.&rdquo;</li>
+<li><i>Lycopodiace&aelig;</i>. See &ldquo;<a href="#IX_G">Ground pine</a>.&rdquo;</li>
+<li><i>Lycopodin&aelig;</i>. See &ldquo;<a href="#IX_C">Club moss</a>.&rdquo;</li>
+<li><i>Lycopodium</i>, <a href="#Page_123">123</a>.
+  <ul class="IX">
+  <li><i>dendroideum</i>, <a href="#Page_123">123</a>, <a href="#Page_124">124</a>; <a href="#fig73">Fig.&nbsp;73</a>.</li>
+  <li>stem and leaves, <a href="#Page_123">123</a>.</li>
+  <li>cones and sporangia, <a href="#Page_123">123</a>.</li>
+  <li>gross anatomy, <a href="#Page_123">123</a>.</li>
+  <li>histology, <a href="#Page_124">124</a>.</li>
+  <li>spores, <a href="#Page_124">124</a>.</li>
+  </ul></li>
+<li><i>Lysimachia</i>. See &ldquo;<a href="#IX_M">Moneywort</a>.&rdquo;</li>
+<li><i>Lythrum</i>, <i>-ace&aelig;</i>, <a href="#Page_206">206</a>, <a href="#Page_228">228</a>.</li>
+<li>Mace, <a href="#Page_189">189</a>.</li>
+</ul>
+
+<ul class="IX">
+<li><i><a name="IX_M" id="IX_M"></a>Macrocystis</i>, <a href="#Page_48">48</a>.</li>
+<li>Macrospore, <a href="#Page_126">126</a>, <a href="#Page_127">127</a>, <a href="#Page_128">128</a>, <a href="#Page_143">143</a>.</li>
+<li><i>Madotheca</i>, <a href="#Page_86">86</a>&ndash;<a href="#Page_90">90</a>; Figs. <a href="#fig52">52</a>&ndash;<a href="#fig56">56</a>.
+  <ul class="IX">
+  <li>gross anatomy, <a href="#Page_86">86</a>&ndash;<a href="#Page_88">88</a>.</li>
+  <li>male and female plants, <a href="#Page_87">87</a>, <a href="#Page_88">88</a>.</li>
+  <li>histology of leaf and stem, <a href="#Page_88">88</a>.</li>
+  <li>antheridium, <a href="#Page_88">88</a>, <a href="#Page_89">89</a>.</li>
+  <li>archegonium, <a href="#Page_89">89</a>, <a href="#Page_90">90</a>.</li>
+  <li>embryo, <a href="#Page_90">90</a>.</li>
+  <li>spores and elaters, <a href="#Page_90">90</a>.</li>
+  </ul></li>
+<li>Magnesium, <a href="#Page_2">2</a>.</li>
+<li><i>Magnolia</i>, <i>-ace&aelig;</i>, <a href="#Page_186">186</a>.</li>
+<li>Maiden-hair fern, <a href="#Page_109">109</a>&ndash;<a href="#Page_115">115</a>; Figs. <a href="#fig67">67</a>&ndash;<a href="#fig69">69</a>.
+  <ul class="IX">
+  <li>general structure, <a href="#Page_109">109</a>.</li>
+  <li>gross anatomy of stem, <a href="#Page_110">110</a>.</li>
+  <li>histology of stem, <a href="#Page_110">110</a>, <a href="#Page_111">111</a>.</li>
+  <li>gross anatomy of leaf, <a href="#Page_111">111</a>.</li>
+  <li>histology of leaf, <a href="#Page_111">111</a>, <a href="#Page_112">112</a>.</li>
+  <li>sporangia, <a href="#Page_113">113</a>, <a href="#Page_114">114</a>.</li>
+  <li>root, <a href="#Page_114">114</a>, <a href="#Page_115">115</a>.</li>
+  <li>apical growth of root, <a href="#Page_115">115</a>.</li>
+  </ul></li>
+<li>Mallow, <a href="#Page_171">171</a>, <a href="#Page_195">195</a>; <a href="#fig106">Fig.&nbsp;106</a>.</li>
+<li><i>Malva</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_M">Mallow</a>.&rdquo;</li>
+<li><i>Mamillaria</i>, <a href="#fig112">Fig.&nbsp;112</a>.</li>
+<li>Mandrake. See &ldquo;<a href="#IX_M">May-apple</a>.&rdquo;</li>
+<li>Maple, <a href="#Page_199">199</a>; <a href="#fig108">Fig.&nbsp;108</a>.</li>
+<li><i>Maranta</i>. See &ldquo;<a href="#IX_A">Arrowroot</a>.&rdquo;</li>
+<li><i>Marattiace&aelig;</i>. See &ldquo;<a href="#IX_R">Ringless ferns</a>.&rdquo;</li>
+<li><i>Marchantia</i>, <a href="#Page_91">91</a>; <a href="#fig57">Fig.&nbsp;57</a>.
+  <ul class="IX">
+  <li>breathing-pores, <a href="#Page_91">91</a>.</li>
+  <li>sexual organs, <a href="#Page_91">91</a>.</li>
+  <li>buds, <a href="#Page_91">91</a>.</li>
+  </ul></li>
+<li><i>Marchantiace&aelig;</i>, <a href="#Page_91">91</a>.</li>
+<li><i>Marsilia</i>, <a href="#Page_118">118</a>; <a href="#fig71">Fig.&nbsp;71</a>.</li>
+<li><span class="pagenum" title="Page&nbsp;246">&nbsp;</span><a name="Page_246" id="Page_246"></a><i>Martynia</i>, <a href="#Page_218">218</a>.</li>
+<li><i>Matthiola</i>. See &ldquo;<a href="#IX_S">Stock</a>.&rdquo;</li>
+<li>May-apple, <a href="#Page_187">187</a>; <a href="#fig101">Fig.&nbsp;101</a>.</li>
+<li>May-weed, <a href="#Page_223">223</a>; <a href="#fig125">Fig.&nbsp;125</a>.</li>
+<li><i>Medeola</i>, <a href="#Page_155">155</a>; <a href="#fig83">Fig.&nbsp;83</a>.</li>
+<li>Medullary ray, <a href="#Page_130">130</a>, <a href="#Page_137">137</a>.</li>
+<li><i>Melampsora</i>, <a href="#Page_81">81</a>.</li>
+<li><i>Melastomace&aelig;</i>, <a href="#Page_206">206</a>.</li>
+<li>Melon, <a href="#Page_221">221</a>.</li>
+<li><i><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Menispernum&rsquo;.">Menispermum</ins></i>, <i>-e&aelig;</i>. See &ldquo;<a href="#IX_M">Moon-seed</a>.&rdquo;</li>
+<li><i>Menyanthes</i>. See &ldquo;<a href="#IX_B">Buck-bean</a>.&rdquo;</li>
+<li><i>Mesocarpus</i>, <a href="#Page_33">33</a>; <a href="#fig19">Fig.&nbsp;19</a>.</li>
+<li>Mesophyll, <a href="#Page_135">135</a>.</li>
+<li>Methyl-violet, <a href="#Page_4">4</a>, <a href="#Page_233">233</a>.</li>
+<li>Micropyle, <a href="#Page_180">180</a>.</li>
+<li>Microsome, <a href="#Page_231">231</a>.</li>
+<li>Microspore, <a href="#Page_126">126</a>, <a href="#Page_128">128</a>, <a href="#Page_131">131</a>, <a href="#Page_138">138</a>.</li>
+<li>Mignonette, <a href="#Page_192">192</a>; <a href="#fig104">Fig.&nbsp;104</a>.</li>
+<li>Mildew. See &ldquo;<i><a href="#IX_P">Peronospora</a></i>,&rdquo; &ldquo;<i><a href="#IX_P">Phytophthora</a></i>,&rdquo; &ldquo;<i><a href="#IX_P">Perisporiace&aelig;</a></i>.&rdquo;</li>
+<li>Milk-weed, <a href="#Page_220">220</a>; <a href="#fig122">Fig.&nbsp;122</a>.</li>
+<li><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Milk-wort&rsquo;; changed to be consistent with the rest of the book.">Milkwort</ins>, <a href="#Page_199">199</a>.</li>
+<li><i>Mimosa</i>. See &ldquo;<a href="#IX_S">Sensitive-plant</a>.&rdquo;</li>
+<li><i>Mimosace&aelig;</i>, <a href="#Page_209">209</a>, <a href="#Page_210">210</a>.</li>
+<li><i>Mimulus</i>, <a href="#Page_217">217</a>.</li>
+<li>Mint, <a href="#Page_181">181</a>, <a href="#Page_215">215</a>.</li>
+<li><i>Mirabilis</i>. See &ldquo;<a href="#IX_F">Four-o&#8217;clock</a>.&rdquo;</li>
+<li>Mistletoe, <a href="#Page_224">224</a>.</li>
+<li><i>Mitella</i>. See &ldquo;<a href="#IX_B">Bishop&#8217;s cap</a>.&rdquo;</li>
+<li><i>Mitchella</i>. See &ldquo;<a href="#IX_P">Partridge-berry</a>.&rdquo;</li>
+<li>Mitre-wort. See &ldquo;<a href="#IX_B">Bishop&#8217;s cap</a>.&rdquo;</li>
+<li>Mock-orange. See &ldquo;<i><a href="#IX_S">Syringa</a></i>.&rdquo;</li>
+<li>Moneywort, <a href="#Page_212">212</a>; <a href="#fig117">Fig.&nbsp;117</a>.</li>
+<li>Monocotyledon, <a href="#Page_146">146</a>, <a href="#Page_153">153</a>, <a href="#Page_225">225</a>, <a href="#Page_229">229</a>.</li>
+<li><i>Monotropa</i>. See &ldquo;<a href="#IX_I">Indian-pipe</a>,&rdquo; &ldquo;<a href="#IX_P">Pine-sap</a>.&rdquo;</li>
+<li><i>Monotrope&aelig;</i>, <a href="#Page_210">210</a>.</li>
+<li>Moon-seed, <a href="#Page_188">188</a>; <a href="#fig101">Fig.&nbsp;101</a>.</li>
+<li><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Moose-wood&rsquo;; changed to be consistent with the rest of the book.">Moosewood</ins>, <a href="#Page_206">206</a>; <a href="#fig113">Fig.&nbsp;113</a>.</li>
+<li><i>Morchella</i>. See &ldquo;<a href="#IX_M">Morel</a>.&rdquo;</li>
+<li>Morel, <a href="#Page_73">73</a>.</li>
+<li>Morning-glory, <a href="#Page_171">171</a>, <a href="#Page_213">213</a>; <a href="#fig118">Fig.&nbsp;118</a>.</li>
+<li>Morphology, <a href="#Page_3">3</a>.</li>
+<li>Moss, <a href="#Page_5">5</a>, <a href="#Page_86">86</a>.
+  <ul class="IX">
+  <li>true, <a href="#Page_93">93</a>.</li>
+  <li>common. See &ldquo;<i><a href="#IX_B">Bryace&aelig;</a></i>.&rdquo;</li>
+  <li>peat. See &ldquo;<i><a href="#IX_S">Sphagnace&aelig;</a></i>.&rdquo;</li>
+  </ul></li>
+<li>Moth, <a href="#Page_229">229</a>.</li>
+<li>Mould, black. See &ldquo;<i><a href="#IX_M">Mucorini</a></i>.&rdquo;
+  <ul class="IX">
+  <li>blue. See &ldquo;<i><a href="#IX_P">Penicillium</a></i>.&rdquo;</li>
+  <li>herbarium. See &ldquo;<i><a href="#IX_E">Eurotium</a></i>.&rdquo;</li>
+  <li>insect. See &ldquo;<i><a href="#IX_E">Entomophthore&aelig;</a></i>.&rdquo;</li>
+  <li>water. See &ldquo;<i><a href="#IX_S">Saprolegnia</a></i>.&rdquo;</li>
+  </ul></li>
+<li>Mountain-fringe, <a href="#Page_192">192</a>.</li>
+<li>Mountain-laurel, <a href="#Page_210">210</a>; <a href="#fig116">Fig.&nbsp;116</a>.</li>
+<li><i>Mucor</i>, <a href="#Page_55">55</a>.
+  <ul class="IX">
+  <li>mucedo, <a href="#Page_56">56</a>; <a href="#fig32">Fig.&nbsp;32</a>.</li>
+  </ul></li>
+<li><i>Mucor stolonifer</i>, <a href="#Page_55">55</a>&ndash;<a href="#Page_56">56</a>.
+  <ul class="IX">
+  <li>general structure, <a href="#Page_55">55</a>.</li>
+  <li>structure of filaments, <a href="#Page_55">55</a>.</li>
+  <li>spore cases, <a href="#Page_55">55</a>.</li>
+  <li>sexual spores, <a href="#Page_56">56</a>.</li>
+  </ul></li>
+<li><i>Mucorini</i>, <a href="#Page_54">54</a>.</li>
+<li>Mulberry, <a href="#Page_183">183</a>.</li>
+<li>Mullein, <a href="#Page_217">217</a>; <a href="#fig120">Fig.&nbsp;120</a>.</li>
+<li><i>Musa</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_B">Banana</a>.&rdquo;</li>
+<li><i>Musci</i>. See &ldquo;<a href="#IX_T">True mosses</a>.&rdquo;</li>
+<li>Mushroom, <a href="#Page_82">82</a>.</li>
+<li>Mustard, <a href="#Page_192">192</a>.</li>
+<li><i>Mycomycetes</i>. See &ldquo;<a href="#IX_T">True fungi</a>.&rdquo;</li>
+<li><i>Myosotis</i>. See &ldquo;<a href="#IX_F">Forget-me-not</a>.&rdquo;</li>
+<li><i>Myristica</i>, <i>-ine&aelig;</i>. See &ldquo;<a href="#IX_N">Nutmeg</a>.&rdquo;</li>
+<li><i>Myrtiflor&aelig;</i>, <a href="#Page_205">205</a>.</li>
+<li>Myrtle, <a href="#Page_205">205</a>, <a href="#Page_206">206</a>.</li>
+<li><i>Myrtus</i>. See &ldquo;<a href="#IX_M">Myrtle</a>.&rdquo;</li>
+<li><i>Myxomycetes</i>. See &ldquo;<a href="#IX_S">Slime-mould</a>.&rdquo;</li>
+</ul>
+
+<ul class="IX">
+<li><i><a name="IX_N" id="IX_N"></a>Naias</i>. See &ldquo;<a href="#IX_P">Pond-weed</a>.&rdquo;</li>
+<li><i>Naiade&aelig;</i>, <a href="#Page_159">159</a>.</li>
+<li>Narcissus, <a href="#Page_146">146</a>.</li>
+<li>Nasturtium, <a href="#Page_197">197</a>, <a href="#Page_227">227</a>.</li>
+<li><i>Navicula</i>, <a href="#Page_42">42</a>; <a href="#fig24">Fig.&nbsp;24</a>.</li>
+<li>Nectar, <a href="#Page_225">225</a>.</li>
+<li>Nectary, <a href="#Page_186">186</a>.</li>
+<li>Nelumbo, <a href="#Page_189">189</a>, <a href="#Page_190">190</a>; <a href="#fig101">Fig.&nbsp;101</a>.</li>
+<li><i>Nelumbie&aelig;</i>, <a href="#Page_190">190</a>.</li>
+<li><i>Nemophila</i>, <a href="#Page_214">214</a>.</li>
+<li><i>Nepenthes</i>, <i>-e&aelig;</i>. See &ldquo;<a href="#IX_P">Pitcher plant</a>.&rdquo;</li>
+<li><i>Nes&aelig;a</i>, <a href="#Page_206">206</a>.</li>
+<li><span class="pagenum" title="Page&nbsp;247">&nbsp;</span><a name="Page_247" id="Page_247"></a>Nettle. See &ldquo;<i><a href="#IX_U">Urticin&aelig;</a></i>.&rdquo;</li>
+<li><i>Nicotiana</i>. See &ldquo;<a href="#IX_T">Tobacco</a>.&rdquo;</li>
+<li>Night-blooming cereus, <a href="#Page_204">204</a>.</li>
+<li>Nightshade, <a href="#Page_215">215</a>; <a href="#fig119">Fig.&nbsp;119</a>.</li>
+<li><i>Nitella</i>, <a href="#Page_40">40</a>.</li>
+<li><i>Nitelle&aelig;</i>, <a href="#Page_40">40</a>.</li>
+<li>Node, <a href="#Page_39">39</a>.</li>
+<li>Nucleus, <a href="#Page_7">7</a>, <a href="#Page_31">31</a>, <a href="#Page_231">231</a>.</li>
+<li>Nuclear division, <a href="#Page_7">7</a>, <a href="#Page_31">31</a>, <a href="#Page_231">231</a>; Figs. <a href="#fig127">127</a>, <a href="#fig128">128</a>.</li>
+<li>Nucleolus, <a href="#Page_7">7</a>, <a href="#Page_231">231</a>.</li>
+<li>Nutmeg, <a href="#Page_188">188</a>.</li>
+<li><i>Nyctagine&aelig;</i>, <a href="#Page_183">183</a>.</li>
+<li><i>Nymph&aelig;a</i>, <a href="#Page_189">189</a>; <a href="#fig101">Fig.&nbsp;101</a>.</li>
+<li><i>Nymph&aelig;ace&aelig;</i>, <a href="#Page_190">190</a>.</li>
+</ul>
+
+<ul class="IX">
+<li><a name="IX_O" id="IX_O"></a>Oak, <a href="#Page_183">183</a>, <a href="#Page_225">225</a>; <a href="#fig97">Fig.&nbsp;97</a>.</li>
+<li><i>&OElig;dogonium</i>, <a href="#Page_26">26</a>&ndash;<a href="#Page_28">28</a>; <a href="#fig16">Fig.&nbsp;16</a>.
+  <ul class="IX">
+  <li>reproduction, <a href="#Page_27">27</a>.</li>
+  <li>fertilization, <a href="#Page_28">28</a>.</li>
+  <li>resting spores, <a href="#Page_28">28</a>.</li>
+  </ul></li>
+<li><i>&OElig;nothera</i>. See &ldquo;<a href="#IX_E">Evening primrose</a>.&rdquo;</li>
+<li>Oil-channel, <a href="#Page_202">202</a>.</li>
+<li><i>Oleace&aelig;</i>. See &ldquo;<a href="#IX_O">Olive</a>.&rdquo;</li>
+<li>Oleander, <a href="#Page_219">219</a>.</li>
+<li>Olive, <a href="#Page_218">218</a>.</li>
+<li><i>Onagrace&aelig;</i>, <a href="#Page_206">206</a>.</li>
+<li><i>Onoclea</i>, <a href="#Page_104">104</a>; <a href="#fig70">Fig.&nbsp;70</a>.</li>
+<li>O&ouml;gonium, <a href="#Page_27">27</a>, <a href="#Page_36">36</a>, <a href="#Page_39">39</a>, <a href="#Page_45">45</a>, <a href="#Page_59">59</a>, <a href="#Page_62">62</a>.</li>
+<li>O&ouml;phyte, <a href="#Page_109">109</a>.</li>
+<li>Opium--opium poppy, <a href="#Page_191">191</a>.</li>
+<li><i>Ophioglosse&aelig;</i>. See &ldquo;<a href="#IX_A">Adder-tongue</a>.&rdquo;</li>
+<li><i>Ophioglossum</i>, <a href="#Page_116">116</a>.</li>
+<li><i>Opuntia</i>. See &ldquo;<a href="#IX_P">Prickly pear</a>.&rdquo;</li>
+<li><i>Opuntie&aelig;</i>, <a href="#Page_203">203</a>.</li>
+<li>Orange, <a href="#Page_198">198</a>.</li>
+<li>Orchid, <a href="#Page_164">164</a>, <a href="#Page_166">166</a>, <a href="#Page_227">227</a>; Figs. <a href="#fig89">89</a>, <a href="#fig90">90</a>.</li>
+<li><i>Orchide&aelig;</i>, <a href="#Page_164">164</a>.</li>
+<li><i>Orchis</i>, <a href="#Page_227">227</a>; <a href="#fig89">Fig.&nbsp;89</a>.</li>
+<li>Organic bodies, <a href="#Page_1">1</a>.</li>
+<li>Origanum oil, <a href="#Page_234">234</a>.</li>
+<li><i>Oscillaria</i>, <a href="#Page_15">15</a>, <a href="#Page_16">16</a>; <a href="#fig6">Fig.&nbsp;6</a>.
+  <ul class="IX">
+  <li>movements, <a href="#Page_15">15</a>.</li>
+  <li>color, <a href="#Page_16">16</a>.</li>
+  <li>structure and reproduction, <a href="#Page_16">16</a>.</li>
+  </ul></li>
+<li><i>Osmunda</i>. See &ldquo;<a href="#IX_F">Flowering-fern</a>.&rdquo;</li>
+<li>Ostrich-fern, <a href="#Page_104">104</a>&ndash;<a href="#Page_109">109</a>.
+  <ul class="IX">
+  <li>germination of spores, <a href="#Page_104">104</a>.</li>
+  <li>prothallium, <a href="#Page_104">104</a>, <a href="#Page_105">105</a>.</li>
+  <li>archegonium, <a href="#Page_105">105</a>, <a href="#Page_106">106</a>.</li>
+  <li>antheridium and spermatozoids, <a href="#Page_106">106</a>.</li>
+  <li>fertilization, <a href="#Page_107">107</a>.</li>
+  <li>embryo and young plant, <a href="#Page_107">107</a>, <a href="#Page_108">108</a>.</li>
+  <li>comparison with sporogonium of bryophytes, <a href="#Page_109">109</a>.</li>
+  </ul></li>
+<li>Ovary, <a href="#Page_129">129</a>, <a href="#Page_148">148</a>, <a href="#Page_156">156</a>, <a href="#Page_202">202</a>.</li>
+<li>Ovule, <a href="#Page_129">129</a>, <a href="#Page_131">131</a>, <a href="#Page_144">144</a>, <a href="#Page_148">148</a>, <a href="#Page_151">151</a>, <a href="#Page_179">179</a>.</li>
+<li><i>Oxalis</i>. See &ldquo;<a href="#IX_W">Wood-sorrel</a>.&rdquo;</li>
+<li><i>Oxydendrum</i>, <a href="#Page_211">211</a>; <a href="#fig116">Fig.&nbsp;116</a>.</li>
+<li>Oxygen, <a href="#Page_2">2</a>, <a href="#Page_95">95</a>.</li>
+</ul>
+
+<ul class="IX">
+<li><a name="IX_P" id="IX_P"></a>Palea, <a href="#Page_161">161</a>.</li>
+<li>Palisade parenchyma, <a href="#Page_178">178</a>.</li>
+<li>Palm, <a href="#Page_157">157</a>.
+  <ul class="IX">
+  <li>date, <a href="#Page_159">159</a>.</li>
+  <li>coco, <a href="#Page_159">159</a>.</li>
+  </ul></li>
+<li><i>Palm&aelig;</i>. See &ldquo;<a href="#IX_P">Palm</a>.&rdquo;</li>
+<li>Palmate, <a href="#Page_171">171</a>.</li>
+<li>Palmetto, <a href="#Page_159">159</a>.</li>
+<li><i>Pandane&aelig;</i>, <a href="#Page_159">159</a>.</li>
+<li><i>Papaverace&aelig;</i>. See &ldquo;<a href="#IX_P">Poppy</a>.&rdquo;</li>
+<li>Papaw, <a href="#Page_186">186</a>; <a href="#fig100">Fig.&nbsp;100</a>.</li>
+<li><i>Papilionace&aelig;</i>, <a href="#Page_208">208</a>.</li>
+<li>Pappus, <a href="#Page_223">223</a>.</li>
+<li><i>Papyrus</i>, <a href="#Page_161">161</a>.</li>
+<li>Paranucleus, <a href="#Page_231">231</a>.</li>
+<li>Parasite, <a href="#Page_54">54</a>.</li>
+<li>Parenchyma. See &ldquo;<a href="#IX_S">Soft tissue</a>.&rdquo;</li>
+<li><i>Parmelia</i>, <a href="#Page_73">73</a>, <a href="#Page_75">75</a>; <a href="#fig44">Fig.&nbsp;44</a>.</li>
+<li>Partridge-berry, <a href="#Page_223">223</a>, <a href="#Page_228">228</a>.</li>
+<li><i>Passiflora</i>. See &ldquo;<a href="#IX_P">Passion-flower</a>.&rdquo;</li>
+<li><i>Passiflorin&aelig;</i>, <a href="#Page_205">205</a>.</li>
+<li>Passion-flower, <a href="#Page_204">204</a>; <a href="#fig112">Fig.&nbsp;112</a>.</li>
+<li>Pea, <a href="#Page_207">207</a>, <a href="#Page_208">208</a>; <a href="#fig115">Fig.&nbsp;115</a>.</li>
+<li>Peach, <a href="#Page_206">206</a>.</li>
+<li>Pear, <a href="#Page_206">206</a>.</li>
+<li><i>Pediastrum</i>, <a href="#Page_23">23</a>; <a href="#fig11">Fig.&nbsp;11</a>.</li>
+<li><i>Pelargonium</i>, <a href="#Page_197">197</a>.</li>
+<li>Peltate, <a href="#Page_190">190</a>.</li>
+<li><span class="pagenum" title="Page&nbsp;248">&nbsp;</span><a name="Page_248" id="Page_248"></a><i>Peltigera</i>, <a href="#Page_75">75</a>; <a href="#fig45">Fig.&nbsp;45</a>.</li>
+<li><i>Penicillium</i>, <a href="#Page_71">71</a>; <a href="#fig42">Fig.&nbsp;42</a>.</li>
+<li>Pepper, <a href="#Page_183">183</a>.</li>
+<li>Perianth. See &ldquo;<a href="#IX_P">Perigone</a>.&rdquo;</li>
+<li>Periblem, <a href="#Page_176">176</a>.</li>
+<li>Perigone, <a href="#Page_143">143</a>, <a href="#Page_148">148</a>, <a href="#Page_151">151</a>, <a href="#Page_170">170</a>.</li>
+<li>Perisperm, <a href="#Page_163">163</a>.</li>
+<li><i>Perisporiace&aelig;</i>, <a href="#Page_66">66</a>.</li>
+<li>Periwinkle, <a href="#Page_219">219</a>.</li>
+<li><i>Peronospora</i>, <a href="#Page_60">60</a>; <a href="#fig35">Fig.&nbsp;35</a>.</li>
+<li><i>Peronospore&aelig;</i>, <a href="#Page_57">57</a>.</li>
+<li>Persimmon, <a href="#Page_212">212</a>; <a href="#fig117">Fig.&nbsp;117</a>.</li>
+<li>Petal, <a href="#Page_148">148</a>, <a href="#Page_174">174</a>, <a href="#Page_179">179</a>.</li>
+<li>Petiole, <a href="#Page_173">173</a>.</li>
+<li>Petunia, <a href="#Page_215">215</a>; <a href="#fig119">Fig.&nbsp;119</a>.</li>
+<li><i>Peziza</i>, <a href="#Page_73">73</a>; <a href="#fig43">Fig.&nbsp;43</a>.</li>
+<li><i>Phacelia</i>, <a href="#Page_214">214</a>.</li>
+<li><i>Ph&aelig;ophyce&aelig;</i>. See &ldquo;<a href="#IX_B">Brown alg&aelig;</a>.&rdquo;</li>
+<li>Ph&aelig;nogam. See &ldquo;<a href="#IX_S">Spermaphyte</a>.&rdquo;</li>
+<li><i>Phascum</i>, <i>-ace&aelig;</i>, <a href="#Page_99">99</a>, <a href="#Page_101">101</a>; <a href="#fig65">Fig.&nbsp;65</a>.</li>
+<li><i>Philadelphus</i>. See &ldquo;<a href="#IX_S">Syringa</a>.&rdquo;</li>
+<li>Phloem, <a href="#Page_110">110</a>, <a href="#Page_124">124</a>, <a href="#Page_135">135</a>, <a href="#Page_137">137</a>, <a href="#Page_150">150</a>, <a href="#Page_173">173</a>, <a href="#Page_176">176</a>.</li>
+<li><i>Phlox</i>, <a href="#Page_214">214</a>; <a href="#fig118">Fig.&nbsp;118</a>.</li>
+<li><i>Ph&oelig;nix dactylifera</i>. See &ldquo;<a href="#IX_D">Date-palm</a>.&rdquo;</li>
+<li>Phosphorus, <a href="#Page_2">2</a>.</li>
+<li><i>Phragmidium</i>, <a href="#Page_81">81</a>; <a href="#fig47">Fig.&nbsp;47</a>.</li>
+<li><i>Physarum</i>, <a href="#Page_14">14</a>.</li>
+<li><i>Physianthus</i>, <a href="#Page_220">220</a>.</li>
+<li>Physiology, <a href="#Page_3">3</a>.</li>
+<li><i>Phytolacca</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_P">Poke-weed</a>.&rdquo;</li>
+<li><i>Phytophthora</i>, <a href="#Page_60">60</a>.</li>
+<li>Pickerel-weed, <a href="#Page_156">156</a>, <a href="#Page_228">228</a>; <a href="#fig84">Fig.&nbsp;84</a>.</li>
+<li>Picric acid, <a href="#Page_156">156</a>, <a href="#Page_233">233</a>.</li>
+<li>Pig-weed. See &ldquo;<a href="#IX_A">Amaranth</a>.&rdquo;</li>
+<li>Pine, <a href="#Page_9">9</a>, <a href="#Page_10">10</a>, <a href="#Page_129">129</a>, <a href="#Page_142">142</a>.</li>
+<li><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Pine-apple&rsquo;; changed to be consistent with the rest of the book.">Pineapple</ins>, <a href="#Page_156">156</a>.</li>
+<li>Pine-sap, <a href="#Page_210">210</a>; <a href="#fig116">Fig.&nbsp;116</a>.</li>
+<li><i>Pinguicula</i>, <a href="#Page_218">218</a>.</li>
+<li>Pink, <a href="#Page_181">181</a>, <a href="#Page_185">185</a>; <a href="#fig97">Fig.&nbsp;97</a>.</li>
+<li>Pink-root, <a href="#Page_218">218</a>; <a href="#fig122">Fig.&nbsp;122</a>.</li>
+<li>Pinnate (leaf), <a href="#Page_159">159</a>.
+  <ul class="IX">
+  <li>veined, <a href="#Page_171">171</a>.</li>
+  </ul></li>
+<li><i>Pinnularia</i>, <a href="#Page_42">42</a>; <a href="#fig24">Fig.&nbsp;24</a>.</li>
+<li><i>Pinus sylvestris</i>. See &ldquo;<a href="#IX_S">Scotch pine</a>.&rdquo;</li>
+<li><i>Piper</i>. See &ldquo;<a href="#IX_P">Pepper</a>.&rdquo;</li>
+<li><i>Piperine&aelig;</i>, <a href="#Page_183">183</a>.</li>
+<li>Pistil, <a href="#Page_143">143</a>, <a href="#Page_145">145</a>, <a href="#Page_174">174</a>.</li>
+<li>Pitcher-plant, <a href="#Page_194">194</a>, <a href="#Page_195">195</a>; <a href="#fig105">Fig.&nbsp;105</a>.</li>
+<li>Pith, <a href="#Page_130">130</a>, <a href="#Page_174">174</a>, <a href="#Page_177">177</a>.</li>
+<li>Placenta, <a href="#Page_148">148</a>, <a href="#Page_179">179</a>.</li>
+<li>Plane, <a href="#Page_183">183</a>.</li>
+<li><i>Plantago</i>, <i>-ine&aelig;</i>. See &ldquo;<a href="#IX_P">Plantain</a>.&rdquo;</li>
+<li>Plantain, <a href="#Page_223">223</a>, <a href="#Page_225">225</a>; <a href="#fig121">Fig.&nbsp;121</a>.</li>
+<li>Plasmodium, <a href="#Page_12">12</a>.</li>
+<li><i>Platane&aelig;</i>. See &ldquo;<a href="#IX_P">Plane</a>.&rdquo;</li>
+<li><i>Platanus</i>. See &ldquo;<a href="#IX_S">Sycamore</a>.&rdquo;</li>
+<li>Plerome, <a href="#Page_176">176</a>.</li>
+<li>Plum, <a href="#Page_207">207</a>.</li>
+<li><i>Plumbago</i>, <i>-ine&aelig;</i>, <a href="#Page_212">212</a>.</li>
+<li>Pod, <a href="#Page_156">156</a>.</li>
+<li><i>Podophyllum</i>. See &ldquo;<a href="#IX_M">May-apple</a>.&rdquo;</li>
+<li><i>Podosph&aelig;ra</i>, <a href="#Page_66">66</a>&ndash;<a href="#Page_70">70</a>; <a href="#fig39">Fig.&nbsp;39</a>.
+  <ul class="IX">
+  <li>general structure, <a href="#Page_66">66</a>.</li>
+  <li>structure of filaments, <a href="#Page_68">68</a>.</li>
+  <li>suckers, <a href="#Page_68">68</a>.</li>
+  <li>conidia, <a href="#Page_68">68</a>.</li>
+  <li>sexual organs, <a href="#Page_68">68</a>.</li>
+  <li>spore fruit, <a href="#Page_68">68</a>, <a href="#Page_69">69</a>.</li>
+  <li>spore sac, <a href="#Page_69">69</a>.</li>
+  </ul></li>
+<li><i>Pogonia</i>, <a href="#Page_166">166</a>.</li>
+<li><i>Poinsettia</i>, <a href="#Page_199">199</a>.</li>
+<li>Poison-dogwood, <a href="#Page_198">198</a>.</li>
+<li>Poison-hemlock, <a href="#Page_202">202</a>.</li>
+<li>Poison-ivy, <a href="#Page_171">171</a>, <a href="#Page_198">198</a>.</li>
+<li>Poke-weed, <a href="#Page_185">185</a>; <a href="#fig97">Fig.&nbsp;97</a>.</li>
+<li><i>Polemonium</i>, <i>-ace&aelig;</i>, <a href="#Page_214">214</a>; <a href="#fig118">Fig.&nbsp;118</a>.</li>
+<li>Pollinium, <a href="#Page_165">165</a>.</li>
+<li><i>Polycarp&aelig;</i>, <a href="#Page_185">185</a>.</li>
+<li><i>Polygala</i>, <i>-ace&aelig;</i>. See &ldquo;<ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Milk-wort&rsquo;; changed to be consistent with the rest of the book."><a href="#IX_M">Milkwort</a></ins>.&rdquo;</li>
+<li><i>Polygonatum</i>. See &ldquo;<a href="#IX_S">Solomon&#8217;s Seal</a>.&rdquo;</li>
+<li><i>Polygonum</i>, <i>-ace&aelig;</i>, <a href="#Page_184">184</a>; <a href="#fig98">Fig.&nbsp;98</a>.</li>
+<li><i>Polysiphonia</i>, <a href="#Page_52">52</a>; <a href="#fig29">Fig.&nbsp;29</a>.</li>
+<li>Pomegranate, <a href="#Page_206">206</a>.</li>
+<li>Pond-scum, <a href="#Page_22">22</a>, <a href="#Page_29">29</a>, <a href="#Page_30">30</a>.</li>
+<li>Pond-weed, <a href="#Page_159">159</a>; <a href="#fig86">Fig.&nbsp;86</a>.</li>
+<li><i>Pontederia</i>. See &ldquo;<a href="#IX_P">Pickerel-weed</a>.&rdquo;</li>
+<li>Poplar, <a href="#Page_181">181</a>, <a href="#Page_183">183</a>.</li>
+<li>Poppy, <a href="#Page_191">191</a>.</li>
+<li><i>Portulaca</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_P">Purslane</a>.&rdquo;</li>
+<li><span class="pagenum" title="Page&nbsp;249">&nbsp;</span><a name="Page_249" id="Page_249"></a>Potash (caustic), <a href="#Page_4">4</a>, <a href="#Page_5">5</a>, <a href="#Page_59">59</a>, <a href="#Page_67">67</a>, <a href="#Page_75">75</a>, <a href="#Page_97">97</a>, <a href="#Page_106">106</a>, <a href="#Page_111">111</a>, <a href="#Page_151">151</a>, <a href="#Page_176">176</a>, <a href="#Page_179">179</a>, <a href="#Page_180">180</a>.</li>
+<li>Potassium, <a href="#Page_2">2</a>.</li>
+<li>Potato, <a href="#Page_215">215</a>.</li>
+<li>Potato-fungus. See &ldquo;<i><a href="#IX_P">Phytophthora</a></i>.&rdquo;</li>
+<li><i>Potentilla</i>. See &ldquo;<a href="#IX_C">Cinquefoil</a>.&rdquo;</li>
+<li><i>Potomogeton</i>. See &ldquo;<a href="#IX_P">Pond-weed</a>.&rdquo;</li>
+<li>Prickly-ash, <a href="#Page_198">198</a>.</li>
+<li>Prickly fungus. See &ldquo;<i><a href="#IX_H">Hydnum</a></i>.&rdquo;</li>
+<li>Prickly-pear, <a href="#Page_204">204</a>.</li>
+<li>Prickly-poppy. See &ldquo;<i><a href="#IX_A">Argemone</a></i>.&rdquo;</li>
+<li>Primrose, <a href="#Page_211">211</a>.</li>
+<li><i>Primula</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_P">Primrose</a>.&rdquo;</li>
+<li>Prince&#8217;s-pine, <a href="#Page_210">210</a>; <a href="#fig116">Fig.&nbsp;116</a>.</li>
+<li>Procarp, <a href="#Page_51">51</a>.</li>
+<li><i>Proteace&aelig;</i>, <a href="#Page_205">205</a>.</li>
+<li>Prothallium, <a href="#Page_102">102</a>, <a href="#Page_103">103</a>, <a href="#Page_114">114</a>, <a href="#Page_122">122</a>, <a href="#Page_125">125</a>, <a href="#Page_133">133</a>, <a href="#Page_144">144</a>, <a href="#Page_177">177</a>.</li>
+<li><i>Protococcus</i>, <i>-ace&aelig;</i>, <a href="#Page_22">22</a>, <a href="#Page_74">74</a>; <a href="#fig11">Fig.&nbsp;11</a>.</li>
+<li>Protophyte, <a href="#Page_11">11</a>.</li>
+<li>Protoplasm, <a href="#Page_7">7</a>.
+  <ul class="IX">
+  <li>movements of, <a href="#Page_7">7</a>.</li>
+  </ul></li>
+<li>Pteridophyte, <a href="#Page_102">102</a>, <a href="#Page_153">153</a>.</li>
+<li><i>Puccinia</i>, <a href="#Page_81">81</a>; <a href="#fig47">Fig.&nbsp;47</a>. See also &ldquo;<a href="#IX_W">Wheat-rust</a>.&rdquo;</li>
+<li>Puccoon, <a href="#Page_215">215</a>.</li>
+<li>Puff-ball. See &ldquo;<i><a href="#IX_L">Lycoperdon</a></i>.&rdquo;</li>
+<li>Purslane, <a href="#Page_185">185</a>.</li>
+<li>Putty-root. See &ldquo;<i><a href="#IX_A">Aplectrum</a></i>.&rdquo;</li>
+<li>Pyrenoid, <a href="#Page_25">25</a>, <a href="#Page_31">31</a>.</li>
+<li><i>Pyrenomycetes</i>, <a href="#Page_76">76</a>.</li>
+<li><i>Pyrola</i>, <i>-ace&aelig;</i>, <a href="#Page_210">210</a>.</li>
+</ul>
+
+<ul class="IX">
+<li><a name="IX_Q" id="IX_Q"></a>Quince, <a href="#Page_170">170</a>.</li>
+<li>Quill-wort, <a href="#Page_125">125</a>, <a href="#Page_126">126</a>; <a href="#fig74">Fig.&nbsp;74</a>.</li>
+</ul>
+
+<ul class="IX">
+<li><a name="IX_R" id="IX_R"></a>Raceme, <a href="#Page_174">174</a>.</li>
+<li>Radial fibro-vascular bundles, <a href="#Page_138">138</a>, <a href="#Page_176">176</a>.</li>
+<li>Radish, <a href="#Page_192">192</a>.</li>
+<li><i>Ranunculus</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_B">Buttercup</a>.&rdquo;</li>
+<li>Raspberry, <a href="#Page_207">207</a>.</li>
+<li>Ray-flower, <a href="#Page_223">223</a>.</li>
+<li>Receptacle, <a href="#Page_167">167</a>, <a href="#Page_207">207</a>, <a href="#Page_223">223</a>.</li>
+<li>Receptive spot, <a href="#Page_106">106</a>.</li>
+<li>Red alg&aelig;, <a href="#Page_21">21</a>, <a href="#Page_49">49</a>, <a href="#Page_52">52</a>, <a href="#Page_53">53</a>; Figs. <a href="#fig29">29</a>&ndash;<a href="#fig31">31</a>.</li>
+<li>Red-bud, <a href="#Page_209">209</a>; <a href="#fig115">Fig.&nbsp;115</a>.</li>
+<li>Red cedar, <a href="#Page_79">79</a>, <a href="#Page_131">131</a>, <a href="#Page_141">141</a>; <a href="#fig78">Fig.&nbsp;78</a>.</li>
+<li>Red-wood, <a href="#Page_142">142</a>.</li>
+<li>Reference-books, <a href="#Page_235">235</a>&ndash;<a href="#Page_236">236</a>.</li>
+<li><i>Reseda</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_M">Mignonette</a>.&rdquo;</li>
+<li>Resin, <a href="#Page_130">130</a>.</li>
+<li>Resin-duct, <a href="#Page_130">130</a>, <a href="#Page_135">135</a>, <a href="#Page_137">137</a>.</li>
+<li>Resting-spore, <a href="#Page_28">28</a>, <a href="#Page_32">32</a>, <a href="#Page_37">37</a>, <a href="#Page_57">57</a>.</li>
+<li>Rheumatism-root. See &ldquo;<a href="#IX_T">Twin-leaf</a>.&rdquo;</li>
+<li><i>Rhexia</i>, <a href="#Page_206">206</a>.</li>
+<li><i>Rhizocarpe&aelig;</i>. See &ldquo;<a href="#IX_W">Water-fern</a>.&rdquo;</li>
+<li>Rhizoid. See &ldquo;<a href="#IX_R">Root-hair</a>.&rdquo;</li>
+<li>Rhizome. See &ldquo;<a href="#IX_R">Root-stock</a>.&rdquo;</li>
+<li><i>Rhododendron</i>, <a href="#Page_210">210</a>; <a href="#fig116">Fig.&nbsp;116</a>.</li>
+<li><i>Rhodophyce&aelig;</i>. See &ldquo;<a href="#IX_R">Red alg&aelig;</a>.&rdquo;</li>
+<li><i>Rhodorace&aelig;</i>, <a href="#Page_211">211</a>.</li>
+<li><i>Rh&oelig;adin&aelig;</i>, <a href="#Page_190">190</a>.</li>
+<li><i>Rhus</i>. See &ldquo;<a href="#IX_S">Sumach</a>.&rdquo;
+  <ul class="IX">
+  <li><i>cotinus</i>. See &ldquo;<a href="#IX_S">Smoke-tree</a>.&rdquo;</li>
+  <li><i><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;toxiocodendron&rsquo;.">toxicodendron</ins></i>. See &ldquo;<a href="#IX_P">Poison-ivy</a>.&rdquo;</li>
+  <li><i>venenata</i>. See &ldquo;<a href="#IX_P">Poison-dogwood</a>.&rdquo;</li>
+  </ul></li>
+<li><i>Ribes</i>, <i>-ie&aelig;</i>, <a href="#Page_203">203</a>; <a href="#fig111">Fig.&nbsp;111</a>.</li>
+<li><i>Ricciace&aelig;</i>, <a href="#Page_91">91</a>; <a href="#fig57">Fig.&nbsp;57</a>.</li>
+<li><i>Richardia</i>. See &ldquo;<a href="#IX_C">Calla</a>.&rdquo;</li>
+<li><i>Ricinus</i>. See &ldquo;<a href="#IX_C">Castor-bean</a>.&rdquo;</li>
+<li>Ringless-fern, <a href="#Page_116">116</a>.</li>
+<li>Rock-rose, <a href="#Page_195">195</a>.</li>
+<li>Rock-weed. See &ldquo;<i><a href="#IX_F">Fucus</a></i>.&rdquo;</li>
+<li>Root, <a href="#Page_102">102</a>, <a href="#Page_104">104</a>, <a href="#Page_114">114</a>, <a href="#Page_173">173</a>.</li>
+<li>Root-cap, <a href="#Page_115">115</a>, <a href="#Page_175">175</a>.</li>
+<li>Root-hair, <a href="#Page_38">38</a>, <a href="#Page_87">87</a>, <a href="#Page_91">91</a>, <a href="#Page_96">96</a>, <a href="#Page_104">104</a>, <a href="#Page_135">135</a>.</li>
+<li>Root-stock, <a href="#Page_154">154</a>, <a href="#Page_172">172</a>.</li>
+<li><i>Rosa</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_R">Rose</a>.&rdquo;</li>
+<li>Rose, <a href="#Page_181">181</a>, <a href="#Page_206">206</a>; <a href="#fig114">Fig.&nbsp;114</a>.</li>
+<li><i>Rosiflor&aelig;</i>, <a href="#Page_206">206</a>.</li>
+<li><i>Rubiace&aelig;</i>, <a href="#Page_223">223</a>.</li>
+<li>Rush, <a href="#Page_154">154</a>, <a href="#Page_225">225</a>; <a href="#fig83">Fig.&nbsp;83</a>.</li>
+<li>Rust, white. See &ldquo;<i><a href="#IX_C">Cystopus</a></i>.&rdquo;
+  <ul class="IX">
+  <li>red. See &ldquo;<i><a href="#IX_U">Uredine&aelig;</a></i>.&rdquo;</li>
+  <li>black. See &ldquo;<i><a href="#IX_U">Uredine&aelig;</a></i>.&rdquo;</li>
+  </ul></li>
+</ul>
+
+<ul class="IX">
+<li><i><a name="IX_S" id="IX_S"></a>Sabal</i>. See &ldquo;<a href="#IX_P">Palmetto</a>.&rdquo;</li>
+<li><i>Sabbatia</i>. See &ldquo;<a href="#IX_C">Centaury</a>.&rdquo;</li>
+<li><span class="pagenum" title="Page&nbsp;250">&nbsp;</span><a name="Page_250" id="Page_250"></a><i>Saccharomycetes</i>. See &ldquo;<a href="#IX_Y">Yeast</a>.&rdquo;</li>
+<li>Sac fungi. See &ldquo;<i><a href="#IX_A">Ascomycetes</a></i>.&rdquo;</li>
+<li>Safranine, <a href="#Page_233">233</a>.</li>
+<li>Sage, <a href="#Page_215">215</a>; <a href="#fig120">Fig.&nbsp;120</a>.</li>
+<li><i>Salicine&aelig;</i>, <a href="#Page_183">183</a>.</li>
+<li><i>Salix</i>. See &ldquo;<a href="#IX_W">Willow</a>.&rdquo;</li>
+<li><i>Salvinia</i>, <a href="#Page_118">118</a>.</li>
+<li><i>Sambucus</i>. See &ldquo;<a href="#IX_E">Elder</a>.&rdquo;</li>
+<li><i>Sanguinaria</i>. See &ldquo;<a href="#IX_B">Blood-root</a>.&rdquo;</li>
+<li><i>Sapindace&aelig;</i>, <a href="#Page_199">199</a>.</li>
+<li><i>Saprolegnia</i>, <i>-ace&aelig;</i>, <a href="#Page_60">60</a>&ndash;<a href="#Page_62">62</a>; <a href="#fig36">Fig.&nbsp;36</a>.
+  <ul class="IX">
+  <li>zo&ouml;spores, <a href="#Page_62">62</a>.</li>
+  <li>resting spores, <a href="#Page_62">62</a>.</li>
+  <li>antheridium, <a href="#Page_62">62</a>.</li>
+  </ul></li>
+<li><i>Sargassum</i>, <a href="#Page_48">48</a>; <a href="#fig28">Fig.&nbsp;28</a>.</li>
+<li><i>Sarracenia</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_P">Pitcher-plant</a>.&rdquo;</li>
+<li>Sassafras, <a href="#Page_188">188</a>.</li>
+<li><i>Saururus</i>. See &ldquo;<a href="#IX_L">Lizard-tail</a>.&rdquo;</li>
+<li>Saxifrage, <a href="#Page_202">202</a>.</li>
+<li><i>Saxifragin&aelig;</i>, <a href="#Page_202">202</a>.</li>
+<li><i>Scabiosa</i>. See &ldquo;<a href="#IX_S">Scabious</a>.&rdquo;</li>
+<li>Scabious, <a href="#Page_224">224</a>.</li>
+<li>Scalariform, <a href="#Page_110">110</a>.</li>
+<li>Scale-leaves, <a href="#Page_170">170</a>.</li>
+<li><i>Scenedesmus</i>, <a href="#Page_24">24</a>; <a href="#fig11">Fig.&nbsp;11</a>.</li>
+<li><i>Schizomycetes</i>. See &ldquo;<i><a href="#IX_B">Bacteria</a></i>.&rdquo;</li>
+<li>Schizophytes, <a href="#Page_12">12</a>, <a href="#Page_14">14</a>.</li>
+<li>Schlerenchyma. See &ldquo;<a href="#IX_S">Stony tissue</a>.&rdquo;</li>
+<li><i>Schrankia</i>. See &ldquo;<a href="#IX_S">Sensitive-brier</a>.&rdquo;</li>
+<li><i>Scilla</i>, <a href="#Page_151">151</a>.</li>
+<li><i>Scirpus</i>. See &ldquo;<a href="#IX_B">Bulrush</a>.&rdquo;</li>
+<li><i>Scitamine&aelig;</i>, <a href="#Page_153">153</a>, <a href="#Page_162">162</a>.</li>
+<li>Scotch pine, <a href="#Page_129">129</a>&ndash;<a href="#Page_140">140</a>; Figs. <a href="#fig75">75</a>&ndash;<a href="#fig77">77</a>.
+  <ul class="IX">
+  <li>stems and branches, <a href="#Page_129">129</a>.</li>
+  <li>leaves, <a href="#Page_129">129</a>, <a href="#Page_130">130</a>.</li>
+  <li>gross anatomy of stem, <a href="#Page_130">130</a>.</li>
+  <li>growth-rings, <a href="#Page_130">130</a>.</li>
+  <li>roots, <a href="#Page_131">131</a>.</li>
+  <li>sporangia, <a href="#Page_131">131</a>.</li>
+  <li>cones, <a href="#Page_132">132</a>.</li>
+  <li>macrospores and prothallium, <a href="#Page_133">133</a>.</li>
+  <li>ripe cone and seeds, <a href="#Page_133">133</a>.</li>
+  <li>germination, <a href="#Page_134">134</a>.</li>
+  <li>young plant, <a href="#Page_134">134</a>.</li>
+  <li>histology of leaf, <a href="#Page_135">135</a>.
+    <ul class="IX">
+    <li>of stem, <a href="#Page_136">136</a>&ndash;<a href="#Page_138">138</a>.</li>
+    <li>of root, <a href="#Page_138">138</a>.</li>
+    </ul></li>
+  <li>microsporangium and pollen spores, <a href="#Page_138">138</a>, <a href="#Page_139">139</a>.</li>
+  <li>archegonium, <a href="#Page_140">140</a>.</li>
+  <li>fertilization, <a href="#Page_140">140</a>.</li>
+  </ul></li>
+<li>Scouring-rush, <a href="#Page_122">122</a>.</li>
+<li><i>Scrophularia</i>, <i>-ine&aelig;</i>. See &ldquo;<a href="#IX_F">Figwort</a>.&rdquo;</li>
+<li>Sea-lettuce, <a href="#Page_26">26</a>; <a href="#fig15">Fig.&nbsp;15</a>.</li>
+<li>Sea-rosemary, <a href="#Page_212">212</a>.</li>
+<li>Sea-weed (brown). See &ldquo;<a href="#IX_B">Brown alg&aelig;</a>.&rdquo;
+  <ul class="IX">
+  <li>(red). See &ldquo;<a href="#IX_R">Red alg&aelig;</a>.&rdquo;</li>
+  </ul></li>
+<li>Sedge, <a href="#Page_161">161</a>; <a href="#fig87">Fig.&nbsp;87</a>.</li>
+<li><i>Sedum</i>. See &ldquo;<ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Stone-crop&rsquo;; changed to be consistent with the rest of the book."><a href="#IX_S">Stonecrop</a></ins>.&rdquo;</li>
+<li>Seed, <a href="#Page_128">128</a>, <a href="#Page_133">133</a>, <a href="#Page_145">145</a>, <a href="#Page_150">150</a>.</li>
+<li>Seed-plant. See &ldquo;<a href="#IX_S">Spermaphyte</a>.&rdquo;</li>
+<li><i>Selaginella</i>, <i>-e&aelig;</i>. See &ldquo;<a href="#IX_S">Smaller club-moss</a>.&rdquo;</li>
+<li>Sensitive-brier, <a href="#Page_209">209</a>; <a href="#fig115">Fig.&nbsp;115</a>.</li>
+<li>Sensitive-plant, <a href="#Page_209">209</a>.</li>
+<li>Sepal, <a href="#Page_148">148</a>, <a href="#Page_150">150</a>, <a href="#Page_174">174</a>, <a href="#Page_179">179</a>.</li>
+<li><i>Sequoia</i>. See &ldquo;<a href="#IX_R">Red-wood</a>.&rdquo;</li>
+<li>Sessile leaf, <a href="#Page_170">170</a>.</li>
+<li><i>Shepherdia</i>, <a href="#Page_206">206</a>.</li>
+<li>Shepherd&#8217;s-purse, <a href="#Page_173">173</a>&ndash;<a href="#Page_180">180</a>; Figs. <a href="#fig93">93</a>&ndash;<a href="#fig95">95</a>.
+  <ul class="IX">
+  <li>gross anatomy of stem, <a href="#Page_173">173</a>.
+    <ul class="IX">
+    <li>leaf, <a href="#Page_124">124</a>, <a href="#Page_173">173</a>.</li>
+    <li>root, <a href="#Page_173">173</a>.</li>
+    </ul></li>
+  <li>branches, <a href="#Page_174">174</a>.</li>
+  <li>flower, <a href="#Page_174">174</a>, <a href="#Page_175">175</a>.</li>
+  <li>fruit and seed, <a href="#Page_175">175</a>.</li>
+  <li>histology of root, <a href="#Page_175">175</a>, <a href="#Page_176">176</a>.
+    <ul class="IX">
+    <li>stem, <a href="#Page_177">177</a>.</li>
+    <li>leaf, <a href="#Page_177">177</a>, <a href="#Page_178">178</a>.</li>
+    </ul></li>
+  <li>development of flower, <a href="#Page_179">179</a>.
+    <ul class="IX">
+    <li>ovule, <a href="#Page_179">179</a>.</li>
+    <li>embryo, <a href="#Page_180">180</a>.</li>
+    </ul></li>
+  </ul></li>
+<li>Shooting-star, <a href="#Page_212">212</a>; <a href="#fig117">Fig.&nbsp;117</a>.</li>
+<li>Sieve-tube, <a href="#Page_111">111</a>, <a href="#Page_137">137</a>.</li>
+<li><i>Silene</i>. See &ldquo;<a href="#IX_C">Catch-fly</a>.&rdquo;</li>
+<li>Silicon, <a href="#Page_2">2</a>.</li>
+<li>Simple leaf, <a href="#Page_170">170</a>.</li>
+<li><span class="pagenum" title="Page&nbsp;251">&nbsp;</span><a name="Page_251" id="Page_251"></a><i>Siphone&aelig;</i>, <a href="#Page_22">22</a>, <a href="#Page_34">34</a>.</li>
+<li><i>Sisyrinchium</i>. See &ldquo;<a href="#IX_B">Blue-eyed grass</a>.&rdquo;</li>
+<li>Skunk cabbage, <a href="#Page_157">157</a>.</li>
+<li>Slime mould, <a href="#Page_12">12</a>, <a href="#Page_14">14</a>; <a href="#fig5">Fig.&nbsp;5</a>.
+  <ul class="IX">
+  <li>plasmodium, <a href="#Page_12">12</a>.</li>
+  <li>movements, <a href="#Page_13">13</a>.</li>
+  <li>feeding, <a href="#Page_13">13</a>.</li>
+  <li>spore-cases, <a href="#Page_13">13</a>.</li>
+  <li>spores, <a href="#Page_13">13</a>.</li>
+  <li>germination of spores, <a href="#Page_14">14</a>.</li>
+  </ul></li>
+<li>Smart-weed. See &ldquo;<i><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Polygonium&rsquo;."><a href="#IX_P">Polygonum</a></ins></i>.&rdquo;</li>
+<li><i>Smilace&aelig;</i>, <a href="#Page_155">155</a>.</li>
+<li>Smoke-tree, <a href="#Page_198">198</a>.</li>
+<li>Smut, <a href="#Page_64">64</a>, <a href="#Page_65">65</a>.</li>
+<li>Smut-corn. See &ldquo;<i><a href="#IX_U">Ustillago</a></i>.&rdquo;</li>
+<li><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Snow-berry&rsquo;; changed to be consistent with the rest of the book.">Snowberry</ins>, <a href="#Page_223">223</a>.</li>
+<li>Soft-tissue, <a href="#Page_112">112</a>.</li>
+<li><i>Solanum</i>, <i>-e&aelig;</i>, <a href="#Page_215">215</a>.</li>
+<li>Solomon&#8217;s Seal, <a href="#Page_154">154</a>; <a href="#fig83">Fig.&nbsp;83</a>.</li>
+<li>Soredium, <a href="#Page_74">74</a>.</li>
+<li>Sorus, <a href="#Page_118">118</a>.</li>
+<li><i>Spadiciflor&aelig;</i>, <a href="#Page_153">153</a>, <a href="#Page_157">157</a>.</li>
+<li>Spadix, <a href="#Page_157">157</a>.</li>
+<li>Spanish bayonet. See &ldquo;<i><a href="#IX_Y">Yucca</a></i>.&rdquo;</li>
+<li><i>Sparganium</i>. See &ldquo;<a href="#IX_B">Bur-reed</a>.&rdquo;</li>
+<li>Speedwell. See &ldquo;<i><a href="#IX_V">Veronica</a></i>.&rdquo;</li>
+<li>Spermaphyte, <a href="#Page_128">128</a>&ndash;<a href="#Page_129">129</a>.</li>
+<li>Spermatozoid, <a href="#Page_28">28</a>, <a href="#Page_36">36</a>, <a href="#Page_40">40</a>, <a href="#Page_46">46</a>, <a href="#Page_51">51</a>, <a href="#Page_89">89</a>, <a href="#Page_96">96</a>, <a href="#Page_106">106</a>, <a href="#Page_122">122</a>.</li>
+<li><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Spermogonium&rsquo;.">Spermagonium</ins>, <a href="#Page_79">79</a>, <a href="#Page_80">80</a>.</li>
+<li><i>Sphagnum</i>, <i>-ace&aelig;</i>, <a href="#Page_99">99</a>, <a href="#Page_100">100</a>.
+  <ul class="IX">
+  <li>sporogonium, <a href="#Page_100">100</a>.</li>
+  <li>leaf, <a href="#Page_100">100</a>.</li>
+  </ul></li>
+<li>Spice-bush, <a href="#Page_188">188</a>.</li>
+<li>Spiderwort, <a href="#Page_6">6</a>, <a href="#Page_151">151</a>, <a href="#Page_157">157</a>; <a href="#fig85">Fig.&nbsp;85</a>.</li>
+<li><i>Spigelia</i>. See &ldquo;<a href="#IX_P">Pink-root</a>.&rdquo;</li>
+<li>Spike, <a href="#Page_181">181</a>.</li>
+<li>Spikenard, <a href="#Page_202">202</a>; <a href="#fig110">Fig.&nbsp;110</a>.</li>
+<li>Spinach, <a href="#Page_184">184</a>.</li>
+<li>Spindle-tree, <a href="#Page_199">199</a>; <a href="#fig109">Fig.&nbsp;109</a>.</li>
+<li><i>Spirogyra</i>, <a href="#Page_30">30</a>&ndash;<a href="#Page_32">32</a>; <a href="#fig18">Fig.&nbsp;18</a>.
+  <ul class="IX">
+  <li>structure of cells, <a href="#Page_30">30</a>.</li>
+  <li>starch, <a href="#Page_31">31</a>.</li>
+  <li>cell-division, <a href="#Page_31">31</a>.</li>
+  <li>sexual reproduction, <a href="#Page_32">32</a>.</li>
+  </ul></li>
+<li>Sporangium, <a href="#Page_55">55</a>, <a href="#Page_62">62</a>, <a href="#Page_113">113</a>, <a href="#Page_121">121</a>, <a href="#Page_122">122</a>, <a href="#Page_131">131</a>, <a href="#Page_148">148</a>, <a href="#Page_151">151</a>, <a href="#Page_179">179</a>.</li>
+<li>Spore-case. See &ldquo;<a href="#IX_S">Sporangium</a>.&rdquo;</li>
+<li>Spore-fruit, <a href="#Page_51">51</a>, <a href="#Page_66">66</a>, <a href="#Page_69">69</a>, <a href="#Page_70">70</a>, <a href="#Page_73">73</a>, <a href="#Page_83">83</a>.</li>
+<li>Spore-sac. See &ldquo;<a href="#IX_A">Ascus</a>.&rdquo;</li>
+<li>Sporocarp. See &ldquo;<a href="#IX_S">Spore-fruit</a>.&rdquo;</li>
+<li>Sporogonium, <a href="#Page_87">87</a>, <a href="#Page_90">90</a>, <a href="#Page_102">102</a>, <a href="#Page_123">123</a>.</li>
+<li>Sporophyll, <a href="#Page_128">128</a>, <a href="#Page_131">131</a>, <a href="#Page_148">148</a>.</li>
+<li>Sporophyte, <a href="#Page_109">109</a>.</li>
+<li>Spring-beauty, <a href="#Page_185">185</a>; <a href="#fig98">Fig.&nbsp;98</a>.</li>
+<li>Spruce, <a href="#Page_142">142</a>.</li>
+<li>Spurge. See &ldquo;<i><a href="#IX_E">Euphorbia</a></i>.&rdquo;</li>
+<li>Squash, <a href="#Page_221">221</a>.</li>
+<li>Staining agents, <a href="#Page_4">4</a>, <a href="#Page_231">231</a>, <a href="#Page_233">233</a>.</li>
+<li>Stamen, <a href="#Page_128">128</a>, <a href="#Page_143">143</a>, <a href="#Page_148">148</a>, <a href="#Page_174">174</a>, <a href="#Page_179">179</a>.</li>
+<li>Standard, <a href="#Page_207">207</a>.</li>
+<li><i>Staphylea</i>. See &ldquo;<a href="#IX_B">Bladder-nut</a>.&rdquo;</li>
+<li>Starch, <a href="#Page_31">31</a>, <a href="#Page_95">95</a>, <a href="#Page_152">152</a>.</li>
+<li><i>Statice</i>. See &ldquo;<a href="#IX_S">Sea-rosemary</a>.&rdquo;</li>
+<li><i>Stellaria</i>. See &ldquo;<a href="#IX_C">Chick-weed</a>.&rdquo;</li>
+<li><i>Stemonitis</i>, <a href="#Page_13">13</a>; <a href="#fig5">Fig.&nbsp;5</a>.</li>
+<li><i>Sticta</i>, <a href="#Page_75">75</a>; <a href="#fig45">Fig.&nbsp;45</a>.</li>
+<li><i>Stigeoclonium</i>, <a href="#Page_26">26</a>; <a href="#fig14">Fig.&nbsp;14</a>.</li>
+<li>Stigma, <a href="#Page_145">145</a>, <a href="#Page_148">148</a>, <a href="#Page_175">175</a>, <a href="#Page_179">179</a>.</li>
+<li>St.&nbsp;John&#8217;s-wort, <a href="#Page_195">195</a>; <a href="#fig105">Fig.&nbsp;105</a>.</li>
+<li>Stock, <a href="#Page_192">192</a>.</li>
+<li>Stoma. See &ldquo;<a href="#IX_B">Breathing-pore</a>.&rdquo;</li>
+<li><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Stone-crop&rsquo;; changed to be consistent with the rest of the book.">Stonecrop</ins>, <a href="#Page_202">202</a>; <a href="#fig113">Fig.&nbsp;113</a>.</li>
+<li>Stone-fruit, <a href="#Page_206">206</a>.</li>
+<li>Stone-wort. See &ldquo;<i><a href="#IX_C">Charace&aelig;</a></i>.&rdquo;</li>
+<li>Stony-tissue, <a href="#Page_110">110</a>.</li>
+<li>Stramonium, <a href="#Page_215">215</a>.</li>
+<li>Strawberry, <a href="#Page_171">171</a>, <a href="#Page_202">202</a>, <a href="#Page_206">206</a>; <a href="#fig113">Fig.&nbsp;113</a>.</li>
+<li>Style, <a href="#Page_148">148</a>, <a href="#Page_175">175</a>, <a href="#Page_179">179</a>.</li>
+<li><i>Stylophorum</i>, <a href="#Page_187">187</a>; <a href="#fig103">Fig.&nbsp;103</a>.</li>
+<li>Sugar, <a href="#Page_8">8</a>, <a href="#Page_145">145</a>.</li>
+<li>Sulphur, <a href="#Page_2">2</a>.</li>
+<li>Sumach, <a href="#Page_198">198</a>; <a href="#fig108">Fig.&nbsp;108</a>.</li>
+<li>Sun-dew, <a href="#Page_192">192</a>, <a href="#Page_193">193</a>; <a href="#fig104">Fig.&nbsp;104</a>.</li>
+<li><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Sun-flower&rsquo;; changed to be consistent with the rest of the book.">Sunflower</ins>, <a href="#Page_224">224</a>.</li>
+<li>Suspensor, <a href="#Page_180">180</a>.</li>
+<li>Sweet-flag, <a href="#Page_157">157</a>.</li>
+<li>Sweet-potato, <a href="#Page_214">214</a>.</li>
+<li>Sweet-scented shrub. See &ldquo;<i><a href="#IX_C">Calycanthus</a></i>.&rdquo;</li>
+<li><span class="pagenum" title="Page&nbsp;252">&nbsp;</span><a name="Page_252" id="Page_252"></a>Sweet-william, <a href="#Page_185">185</a>.</li>
+<li>Sycamore, <a href="#Page_183">183</a>.</li>
+<li><i>Sympetal&aelig;</i>, <a href="#Page_210">210</a>.</li>
+<li><i>Symphoricarpus</i>. See &ldquo;<ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Snow-berry&rsquo;; changed to be consistent with the rest of the book."><a href="#IX_S">Snowberry</a></ins>.&rdquo;</li>
+<li><i>Symplocarpus</i>. See &ldquo;<a href="#IX_S">Skunk-cabbage</a>.&rdquo;</li>
+<li>Synergid&aelig;, <a href="#Page_144">144</a>.</li>
+<li><i>Syringa</i>, <a href="#Page_199">199</a>; <a href="#fig111">Fig.&nbsp;111</a>. See also &ldquo;<a href="#IX_L">Lilac</a>.&rdquo;</li>
+</ul>
+
+<ul class="IX">
+<li><a name="IX_T" id="IX_T"></a>Tamarack, <a href="#Page_142">142</a>.</li>
+<li>Tap-root, <a href="#Page_131">131</a>, <a href="#Page_173">173</a>.</li>
+<li><i>Taraxacum</i>. See &ldquo;<a href="#IX_D">Dandelion</a>.&rdquo;</li>
+<li><i>Taxodium</i>. See &ldquo;<a href="#IX_C">Cypress</a>.&rdquo;</li>
+<li><i>Taxus</i>. See &ldquo;<a href="#IX_Y">Yew</a>.&rdquo;</li>
+<li>Teasel, <a href="#Page_224">224</a>; <a href="#fig124">Fig.&nbsp;124</a>.</li>
+<li><i>Tecoma</i>. See &ldquo;<a href="#IX_T">Trumpet-creeper</a>.&rdquo;</li>
+<li>Teleuto-spore, <a href="#Page_80">80</a>, <a href="#Page_81">81</a>.</li>
+<li>Tendril, <a href="#Page_171">171</a>.</li>
+<li><i>Terebinthin&aelig;</i>, <a href="#Page_198">198</a>.</li>
+<li>Tetraspore, <a href="#Page_51">51</a>, <a href="#Page_52">52</a>.</li>
+<li>Thistle, <a href="#Page_173">173</a>, <a href="#Page_223">223</a>; <a href="#fig125">Fig.&nbsp;125</a>.</li>
+<li>Thorn, <a href="#Page_172">172</a>.</li>
+<li>Thyme, <a href="#Page_215">215</a>.</li>
+<li><i>Thymeleace&aelig;</i>, <a href="#Page_206">206</a>.</li>
+<li><i><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Thymeline&aelig;&rsquo;.">Thymelin&aelig;</ins></i>, <a href="#Page_206">206</a>.</li>
+<li><i>Tilia</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_L">Linden</a>.&rdquo;</li>
+<li><i>Tillandsia</i>, <a href="#Page_156">156</a>; <a href="#fig84">Fig.&nbsp;84</a>.</li>
+<li>Tissue, <a href="#Page_8">8</a>.</li>
+<li>Tissue system, <a href="#Page_115">115</a>.</li>
+<li>Toadstool, <a href="#Page_82">82</a>.</li>
+<li>Tobacco, <a href="#Page_215">215</a>.</li>
+<li><i>Tolypella</i>, <a href="#Page_40">40</a>.</li>
+<li>Tomato, <a href="#Page_215">215</a>.</li>
+<li>Touch-me-not. See &ldquo;<a href="#IX_J">Jewel-weed</a>.&rdquo;</li>
+<li>Tracheary tissue, <a href="#Page_110">110</a>, <a href="#Page_121">121</a>, <a href="#Page_177">177</a>.</li>
+<li>Tracheid, <a href="#Page_110">110</a>, <a href="#Page_138">138</a>.</li>
+<li><i>Tradescantia</i>. See &ldquo;<a href="#IX_S">Spiderwort</a>.&rdquo;</li>
+<li>Trailing arbutus, <a href="#Page_211">211</a>.</li>
+<li><i>Tremella</i>, <a href="#Page_81">81</a>; <a href="#fig51">Fig.&nbsp;51</a>.</li>
+<li><i>Trichia</i>, <a href="#Page_13">13</a>, <a href="#Page_14">14</a>; <a href="#fig5">Fig.&nbsp;5</a>.</li>
+<li>Trichogyne, <a href="#Page_51">51</a>.</li>
+<li><i>Tricocc&aelig;</i>, <a href="#Page_199">199</a>.</li>
+<li><i>Triglochin</i>. See &ldquo;<a href="#IX_A">Arrow-grass</a>.&rdquo;</li>
+<li><i>Trillium</i>, <a href="#Page_146">146</a>, <a href="#Page_154">154</a>, <a href="#Page_155">155</a>; <a href="#fig83">Fig.&nbsp;83</a>.</li>
+<li><i>Triphragmium</i>, <a href="#Page_81">81</a>.</li>
+<li><i>Trop&aelig;olum</i>. See &ldquo;<a href="#IX_N">Nasturtium</a>.&rdquo;</li>
+<li>Trumpet-creeper.</li>
+<li>Tuber, <a href="#Page_120">120</a>, <a href="#Page_153">153</a>, <a href="#Page_172">172</a>.</li>
+<li><i>Tubiflor&aelig;</i>, <a href="#Page_213">213</a>.</li>
+<li>Tulip, <a href="#Page_146">146</a>.</li>
+<li>Tulip-tree, <a href="#Page_187">187</a>; <a href="#fig100">Fig.&nbsp;100</a>.</li>
+<li>Turnip, <a href="#Page_192">192</a>.</li>
+<li>Twin-leaf, <a href="#Page_187">187</a>; <a href="#fig101">Fig.&nbsp;101</a>.</li>
+<li><i>Typha</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_C">Cat-tail</a>.&rdquo;</li>
+</ul>
+
+<ul class="IX">
+<li><i><a name="IX_U" id="IX_U"></a>Ulmace&aelig;</i>. See &ldquo;<a href="#IX_E">Elm</a>.&rdquo;</li>
+<li><i>Ulva</i>. See &ldquo;<a href="#IX_S">Sea-lettuce</a>.&rdquo;</li>
+<li><i>Umbellifer&aelig;</i>. See &ldquo;<a href="#IX_U">Umbel-wort</a>.&rdquo;</li>
+<li>Umbel-wort, <a href="#Page_202">202</a>.</li>
+<li><i>Umbelliflor&aelig;</i>, <a href="#Page_202">202</a>.</li>
+<li><i>Uredine&aelig;</i>, <a href="#Page_77">77</a>.</li>
+<li><i>Uromyces</i>, <a href="#Page_81">81</a>; <a href="#fig47">Fig.&nbsp;47</a>.</li>
+<li><i>Urticin&aelig;</i>, <a href="#Page_183">183</a>.</li>
+<li><i>Usnea</i>, <a href="#Page_75">75</a>; <a href="#fig45">Fig.&nbsp;45</a>.</li>
+<li><i>Ustillagine&aelig;</i>. See &ldquo;<a href="#IX_S">Smut</a>.&rdquo;</li>
+<li><i>Ustillago</i>, <a href="#Page_65">65</a>; <a href="#fig38">Fig.&nbsp;38</a>.</li>
+<li><i>Utricularia</i>. See &ldquo;<a href="#IX_B">Bladder-weed</a>.&rdquo;</li>
+<li><i>Uvularia</i>. See &ldquo;<a href="#IX_B">Bellwort</a>.&rdquo;</li>
+</ul>
+
+<ul class="IX">
+<li><i><a name="IX_V" id="IX_V"></a>Vaccinium</i>. See &ldquo;<a href="#IX_C">Cranberry</a>.&rdquo;</li>
+<li>Vacuole, <a href="#Page_8">8</a>.</li>
+<li>Valerian, <a href="#Page_224">224</a>; <a href="#fig124">Fig.&nbsp;124</a>.</li>
+<li><i>Valeriana</i>, <i>-e&aelig;</i>. See &ldquo;<a href="#IX_V">Valerian</a>.&rdquo;</li>
+<li><i>Vallisneria</i>. See &ldquo;<a href="#IX_E">Eel-grass</a>.&rdquo;</li>
+<li><i>Vanilla</i>, <a href="#Page_166">166</a>.</li>
+<li><i>Vaucheria</i>, <a href="#Page_34">34</a>&ndash;<a href="#Page_37">37</a>; Figs. <a href="#fig21">21</a>, <a href="#fig22">22</a>.
+  <ul class="IX">
+  <li>structure of plant, <a href="#Page_35">35</a>.</li>
+  <li><i>racemosa</i>, <a href="#Page_35">35</a>.</li>
+  <li>non-sexual reproduction, <a href="#Page_36">36</a>.</li>
+  <li>sexual organs, <a href="#Page_36">36</a>.</li>
+  <li>fertilization, <a href="#Page_36">36</a>.</li>
+  <li>resting spores, <a href="#Page_37">37</a>.</li>
+  </ul></li>
+<li>Venus&#8217;s fly-trap, <a href="#Page_192">192</a>.</li>
+<li><i>Verbascum</i>. See &ldquo;<a href="#IX_M">Mullein</a>.&rdquo;</li>
+<li><i>Verbena</i>, <i>-ace&aelig;</i>, <a href="#Page_218">218</a>; <a href="#fig121">Fig.&nbsp;121</a>.</li>
+<li><i>Veronica</i>, <a href="#Page_217">217</a>; <a href="#fig120">Fig.&nbsp;120</a>.</li>
+<li><ins class="correction" title="Transcriber&#8217;s note: Original read &lsquo;Vervein&rsquo;.">Vervain</ins>. See &ldquo;<i><a href="#IX_V">Verbena</a></i>.&rdquo;</li>
+<li>Vessel, <a href="#Page_121">121</a>, <a href="#Page_135">135</a>, <a href="#Page_150">150</a>, <a href="#Page_175">175</a>, <a href="#Page_177">177</a>.</li>
+<li><i>Viburnum</i>, <a href="#Page_223">223</a>; <a href="#fig124">Fig.&nbsp;124</a>.</li>
+<li><i>Victoria regia</i>, <a href="#Page_190">190</a>.</li>
+<li><span class="pagenum" title="Page&nbsp;253">&nbsp;</span><a name="Page_253" id="Page_253"></a><i>Vinca</i>. See &ldquo;<a href="#IX_P">Periwinkle</a>.&rdquo;</li>
+<li>Vine, <a href="#Page_199">199</a>.</li>
+<li>Violet, <a href="#Page_192">192</a>; <a href="#fig104">Fig.&nbsp;104</a>.</li>
+<li><i>Viola</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_V">Violet</a>.&rdquo;</li>
+<li>Virginia creeper, <a href="#Page_171">171</a>, <a href="#Page_199">199</a>.</li>
+<li><i>Vitis</i>. See &ldquo;<a href="#IX_G">Grape</a>.&rdquo;</li>
+<li><i>Vitace&aelig;</i>. See &ldquo;<a href="#IX_V">Vine</a>.&rdquo;</li>
+<li><i>Volvox</i>, <a href="#Page_12">12</a>, <a href="#Page_20">20</a>; <a href="#fig10">Fig.&nbsp;10</a>.</li>
+<li><i>Volvocine&aelig;</i>, <a href="#Page_12">12</a>, <a href="#Page_19">19</a>.</li>
+</ul>
+
+<ul class="IX">
+<li><a name="IX_W" id="IX_W"></a>Wall-flower, <a href="#Page_192">192</a>.</li>
+<li>Walnut, <a href="#Page_183">183</a>.</li>
+<li>Wandering-Jew, <a href="#Page_157">157</a>.</li>
+<li>Water fern, <a href="#Page_117">117</a>.</li>
+<li>Water-leaf, <a href="#Page_214">214</a>; <a href="#fig118">Fig.&nbsp;118</a>.</li>
+<li>Water-lily. See &ldquo;<i><a href="#IX_N">Nymph&aelig;a</a></i>,&rdquo; &ldquo;<i><a href="#IX_C">Castalia</a></i>.&rdquo;</li>
+<li>Water-milfoil, <a href="#Page_206">206</a>; <a href="#fig113">Fig.&nbsp;113</a>.</li>
+<li>Water mould. See &ldquo;<i><a href="#IX_S">Saprolegnia</a></i>.&rdquo;</li>
+<li>Water net, <a href="#Page_24">24</a>; <a href="#fig11">Fig.&nbsp;11</a>.</li>
+<li>Water-plantain, <a href="#Page_167">167</a>.</li>
+<li>Water-shield, <a href="#Page_190">190</a>.</li>
+<li>Water-starwort, <a href="#Page_200">200</a>.</li>
+<li>Wax-plant, <a href="#Page_220">220</a>.</li>
+<li>Wheat, <a href="#Page_78">78</a>.</li>
+<li>Wheat rust, <a href="#Page_78">78</a>, <a href="#Page_81">81</a>; <a href="#fig47">Fig.&nbsp;47</a>.</li>
+<li><i>Whitlavia</i>, <a href="#Page_214">214</a>.</li>
+<li>Wild ginger, <a href="#Page_224">224</a>; <a href="#fig126">Fig.&nbsp;126</a>.</li>
+<li>Wild onion, <a href="#Page_230">230</a>.</li>
+<li>Wild parsnip, <a href="#Page_202">202</a>.</li>
+<li>Willow, <a href="#Page_181">181</a>&ndash;<a href="#Page_183">183</a>; <a href="#fig96">Fig.&nbsp;96</a>.</li>
+<li>Willow-herb, <a href="#Page_206">206</a>, <a href="#Page_226">226</a>; <a href="#fig113">Fig.&nbsp;113</a>.</li>
+<li>Wing (of papilionaceous flower), <a href="#Page_208">208</a>.</li>
+<li>Wintergreen, <a href="#Page_211">211</a>.</li>
+<li><i>Wolffia</i>, <a href="#Page_159">159</a>.</li>
+<li>Wood. See &ldquo;<a href="#IX_X">Xylem</a>.&rdquo;</li>
+<li>Wood-sorrel, <a href="#Page_197">197</a>; <a href="#fig107">Fig.&nbsp;107</a>.</li>
+</ul>
+
+<ul class="IX">
+<li><a name="IX_X" id="IX_X"></a>Xylem, <a href="#Page_110">110</a>, <a href="#Page_124">124</a>, <a href="#Page_135">135</a>, <a href="#Page_150">150</a>, <a href="#Page_173">173</a>, <a href="#Page_176">176</a>.</li>
+</ul>
+
+<ul class="IX">
+<li><a name="IX_Y" id="IX_Y"></a>Yam, <a href="#Page_154">154</a>.</li>
+<li>Yeast, <a href="#Page_63">63</a>, <a href="#Page_64">64</a>; <a href="#fig37">Fig.&nbsp;37</a>.
+  <ul class="IX">
+  <li>cause of fermentation, <a href="#Page_63">63</a>.</li>
+  <li>reproduction, <a href="#Page_64">64</a>.</li>
+  <li>systematic position, <a href="#Page_64">64</a>.</li>
+  </ul></li>
+<li>Yew, <a href="#Page_141">141</a>.</li>
+<li><i>Yucca</i>, <a href="#Page_153">153</a>.</li>
+</ul>
+
+<ul class="IX">
+<li><i><a name="IX_Z" id="IX_Z"></a>Zanthoxylum</i>. See &ldquo;<a href="#IX_P">Prickly ash</a>.&rdquo;</li>
+<li><i>Zingiber</i>, <i>-ace&aelig;</i>. See &ldquo;<a href="#IX_G">Ginger</a>.&rdquo;</li>
+<li>Zo&ouml;logy, <a href="#Page_2">2</a>.</li>
+<li>Zo&ouml;spore, <a href="#Page_25">25</a>, <a href="#Page_37">37</a>, <a href="#Page_58">58</a>, <a href="#Page_62">62</a>.</li>
+<li><i>Zygnema</i>, <a href="#Page_33">33</a>; <a href="#fig19">Fig.&nbsp;19</a>.</li>
+<li>Zygomorphy, Zygomorphic, <a href="#Page_164">164</a>, <a href="#Page_215">215</a>, <a href="#Page_226">226</a>.</li>
+</ul>
+
+
+
+
+<hr />
+<h2><a name="NATURAL_SCIENCE" id="NATURAL_SCIENCE"></a>NATURAL SCIENCE.</h2>
+
+
+<h3 class="ads">Elements of Physics.</h3>
+
+<blockquote class="ads"><p>A Text-book for High Schools and Academies. By <span class="smcap">Alfred P. Gage</span>, A.M.,
+Instructor in Physics in the English High School, Boston. 12mo.
+424&nbsp;pages. Mailing Price, $1.25; Introduction, $1.12; Allowance for
+old book, 35&nbsp;cents.</p></blockquote>
+
+<p class="dc"><span class="dropcap">T</span><span class="smcap">his</span> treatise is based upon <i>the doctrine of the conservation of
+energy</i>, which is made prominent throughout the work. But the leading
+feature of the book&mdash;one that distinguishes it from all others&mdash;is,
+that it is strictly <i>experiment-teaching</i> in its method; <i>i.e.</i>, it
+leads the pupil to &ldquo;read nature in the language of experiment.&rdquo; So far
+as practicable, the following plan is adopted: The pupil is expected
+to accept as <i>fact</i> only that which he has seen or learned by personal
+investigation. He himself performs the larger portion of the
+experiments with <i>simple</i> and <i>inexpensive</i> 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 <i>questions</i> than of illustrations, and <i>precede</i> 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 <i>to observe and to think</i>.</p>
+
+<p class="comment"><b>C.&nbsp;F. Emerson</b>, <i>Prof. of Physics, Dartmouth College</i>: It takes up the
+subject on the right plan, and presents it in a clear, yet scientific,
+way.</p>
+
+<p class="comment"><b>Wm. Noetling</b>, <i>Prof. of Rhetoric, Theory and Practice of Teaching,
+State Normal School, Bloomsburg, Pa.</i>: Every page of the book shows
+that the author is a <i>real</i> 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.</p>
+
+<p class="comment"><b>B.&nbsp;F. Wright</b>, <i>Supt. of Public Schools, St.&nbsp;Paul, Minn.</i>: I like it
+better than any text-book on physics I have seen.</p>
+
+<p class="comment"><b>O.&nbsp;H. Roberts</b>, <i>Prin. of High School, San Jose, Cal.</i>: Gage&#8217;s Physics
+is giving great satisfaction.</p>
+
+
+<h3 class="ads">Introduction to Physical Science.</h3>
+
+<blockquote class="ads"><p>By <span class="smcap">A.&nbsp;P. Gage</span>, Instructor in Physics in the English High School,
+Boston, Mass., and Author of <i>Elements of Physics</i>, etc. 12mo. Cloth.
+viii&nbsp;+&nbsp;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&nbsp;cents.</p></blockquote>
+
+<p class="dc"><span class="dropcap">T</span><span class="smcap">he</span> great and constantly increasing popularity of Gage&#8217;s <i>Elements of
+Physics</i> 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 <i>Introduction to Physical Science</i> has been prepared
+to supply this demand.</p>
+
+<p><b>Accuracy</b> 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 <i>Introduction</i> will stand the closest expert
+scrutiny. Especial care has been taken to restrict the use of
+scientific terms, such as <i>force</i>, <i>energy</i>, <i>power</i>, etc., to their
+proper significations. Terms like <i>sound</i>, <i>light</i>, <i>color</i>, etc.,
+which have commonly been applied to both the effect and the agent
+producing the effect have been rescued from this ambiguity.</p>
+
+<p><b>Recent Advances</b> 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.</p>
+
+<p>In <b>Interest and Availability</b> the <i>Introduction</i> will, it is believed,
+be found no less satisfactory. The wide use of the <i>Elements</i> under
+the most varied conditions, and, in particular, the author&#8217;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
+<i>Introduction</i> is even more fully illustrated than the <i>Elements</i>.</p>
+
+<p><b>In General.</b> The <i>Introduction</i>, like the <i>Elements</i>, has this distinct
+and distinctive aim,&mdash;to elucidate science, instead of &ldquo;popularizing&rdquo;
+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,&mdash;that is to say, the spirit of our civilization and progress.</p>
+
+<p class="comment"><b>George E. Gay</b>, <i>Prin. of High School, Malden, Mass.</i>: With the matter,
+both the topics and their presentation, I am better pleased than with
+any other Physics I have seen.</p>
+
+<p class="comment"><b>R.&nbsp;H. Perkins</b>, <i>Supt. of Schools, Chicopee, Mass.</i>: I have no doubt we
+can adopt it as early as next month, and use the same to great
+advantage in our schools. (<i>Feb.&nbsp;6, 1888.</i>)</p>
+
+<p class="comment"><b>Mary E. Hill</b>, <i>Teacher of Physics, Northfield Seminary, Mass.</i>: 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. (<i>Mar.&nbsp;5, &#8217;88.</i>)</p>
+
+<p class="comment"><b>John Pickard</b>, <i>Prin. of Portsmouth High School, N.H.</i>: I like it
+exceedingly. It is clear, straightforward, practical, and not too
+heavy.</p>
+
+<p class="comment"><b>Ezra Brainerd</b>, <i>Pres. and Prof. of Physics, Middlebury College, Vt.</i>:
+I have looked it over carefully, and regard it as a much better book
+for high schools than the former work. (<i>Feb.&nbsp;6, 1888.</i>)</p>
+
+<p class="comment"><b>James A. De Boer</b>, <i>Prin. of High School, Montpelier, Vt.</i>: I have not
+only examined, but studied it, and consider it superior as a text-book
+to any other I have seen. (<i>Feb.&nbsp;10, &#8217;88.</i>)</p>
+
+<p class="comment"><b>E.&nbsp;B. Rosa</b>, <i>Teacher of Physics, English and Classical School,
+Providence, R.I.</i>: I think it the best thing in that grade published,
+and intend to use it another year. (<i>Feb.&nbsp;23, &#8217;88.</i>)</p>
+
+<p class="comment"><b>G.&nbsp;H. Patterson</b>, <i>Prin. and Prof. of Physics, Berkeley Sch.,
+Providence, R.I.</i>: A very practical book by a practical teacher.
+(<i>Feb.&nbsp;2, 1888.</i>)</p>
+
+<p class="comment"><b>George E. Beers</b>, <i>Prin. of Evening High School, Bridgeport, Conn.</i>:
+The more I see of Professor Gage&#8217;s books, the better I like them. They
+are popular, and at the same time scientific, plain and simple, full
+and complete. (<i>Feb.&nbsp;18, 1888.</i>)</p>
+
+<p class="comment"><b>Arthur B. Chaffee</b>, <i>Prof. in Franklin College, Ind.</i>: I am very much
+pleased with the new book. It will suit the average class better than
+the old edition.</p>
+
+<p class="comment"><b>W.&nbsp;D. Kerlin</b>, <i>Supt. of Public Schools, New Castle, Ind.</i>: 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.</p>
+
+<p class="comment"><b>C.&nbsp;A. Bryant</b>, <i>Supt. of Schools, Paris, Tex.</i>: It is just the book for
+high schools. I shall use it next year.</p>
+
+
+<h3 class="ads">Introduction to Chemical Science.</h3>
+
+<blockquote class="ads"><p>By <span class="smcap">R.&nbsp;P. Williams</span>, Instructor in Chemistry in the English High School,
+Boston. 12mo. Cloth. 216&nbsp;pages. Mailing Price, 90&nbsp;cents; for
+introduction, 80&nbsp;cents; Allowance for old book in exchange, 25&nbsp;cents.</p></blockquote>
+
+<p class="dc"><span class="dropcap">I</span><span class="smcap">n</span> a word, this is a working chemistry&mdash;brief but adequate. Attention
+is invited to a few special features:&mdash;</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>3. The three great classes of chemical compounds&mdash;acids, bases, and
+salts&mdash;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.</p>
+
+<p>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.</p>
+
+<p>5. The necessary apparatus and chemicals are less expensive than those
+required for any other text-book equally comprehensive.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>8. The book is thought to be comprehensive enough for high schools and
+academies, and for a preparatory course in colleges and professional
+schools.</p>
+
+<p>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.</p>
+
+<p>Those who try the book find its merits have not been overstated.</p>
+
+<p class="comment"><b>A.&nbsp;B. Aubert</b>, <i>Prof. of Chemistry, Maine State College, Orono, Me.</i>:
+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.</p>
+
+<p class="comment"><b>H.&nbsp;T. Fuller</b>, <i>Pres. of Polytechnic Institute, Worcester, Mass.</i>: It
+is clear, concise, and suggests the most important and most
+significant experiments for illustration of general principles.</p>
+
+<p class="comment"><b>Alfred S. Roe</b>, <i>Prin. of High School, Worcester, Mass.</i>: I am very
+much pleased with it. I think it the most practical book for actual
+work that I have seen.</p>
+
+<p class="comment"><b>Frank M. Gilley</b>, <i>Science Teacher, High School, Chelsea, Mass.</i>: 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.</p>
+
+<p class="comment"><b>G.&nbsp;S. Fellows</b>, <i>Teacher of Chemistry, High School, Washington, D.C.</i>:
+The author&#8217;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.</p>
+
+<p class="comment"><b>J.&nbsp;I.&nbsp;D. Hines</b>, <i>Prof. of Chemistry, Cumberland University, Lebanon,
+Tenn.</i>: I am very much pleased with it, and think it will give the
+student an admirable introduction to the science of chemistry.</p>
+
+<p class="comment"><b>Horace Phillips</b>, <i>Prin. of High School, Elkhart, Ind.</i>: 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.</p>
+
+<p class="comment"><b>O.&nbsp;S. Wescott</b>, <i>Prin. North Division H. Sch., Chicago</i>: My chemistry
+professor says it is the most satisfactory thing he has seen, and
+hopes we may be able to have it in future.</p>
+
+
+<h3 class="ads">Laboratory Manual of General Chemistry.</h3>
+
+<blockquote class="ads"><p>By <span class="smcap">R.&nbsp;P. Williams</span>, Instructor in Chemistry, English High School,
+Boston, and author of <i>Introduction to Chemical Science</i>. 12mo.
+Boards. xvi&nbsp;+&nbsp;200 pages. Mailing Price, 30&nbsp;cents; for Introduction,
+25&nbsp;cents.</p></blockquote>
+
+<p class="dc"><span class="dropcap">T</span><span class="smcap">his</span> Manual, prepared especially to accompany the author&#8217;s
+<i>Introduction to Chemical Science</i>, 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.</p>
+
+<p>The Manual is commended as well-designed, simple, convenient, and
+cheap,&mdash;a practical book that classes in chemistry need.</p>
+
+<p class="comment"><b>W.&nbsp;M. Stine</b>, <i>Prof. of Chemistry, Ohio University, Athens, O.</i>: 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. (<i>Dec.&nbsp;30,
+1888.</i>)</p>
+
+
+<h3 class="ads">Young&#8217;s General Astronomy.</h3>
+
+<blockquote class="ads"><p>A Text-book for colleges and technical schools. By <span class="smcap">Charles A. Young</span>,
+Ph.D., LL.D., Professor of Astronomy in the College of New Jersey, and
+author of <i>The Sun</i>, etc. 8vo. viii&nbsp;+&nbsp;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&nbsp;cents.</p></blockquote>
+
+<p class="dc"><span class="dropcap">T</span><span class="smcap">he</span> <b>object</b> 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&#8217;s use after he has finished his prescribed
+course.</p>
+
+<p>The <b>method</b> of treatment corresponds with the object of the book.
+Truth, accuracy, and order have been aimed at first, with clearness
+and freedom from ambiguity.</p>
+
+<p>In <b>amount</b>, 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.</p>
+
+<p><b>New topics</b>, 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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+
+<h3 class="ads">Young&#8217;s Elements of Astronomy.</h3>
+
+<blockquote class="ads"><p>A Text-Book for use in High Schools and Academies. With a Uranography.
+By <span class="smcap">Charles A. Young</span>, Ph.D., LL.D., Professor of Astronomy in the
+College of New Jersey (Princeton), and author of <i>A General
+Astronomy</i>, <i>The Sun</i>, etc. 12mo. Half leather. x&nbsp;+&nbsp;472 pages, and
+four star maps. Mailing Price, $1.55; for Introduction, $1.40;
+allowance for old book in exchange, 30&nbsp;cents.</p></blockquote>
+
+<h4 style="text-align:left; font-style:italic; font-variant:normal; margin-top:0.5em; margin-bottom:0.5em;">Uranography.</h4>
+
+<blockquote class="ads"><p>From Young&#8217;s Elements of Astronomy. 12mo. Flexible covers. 42&nbsp;pages,
+besides four star maps. By mail, 35&nbsp;cents; for Introduction, 30&nbsp;cents.</p></blockquote>
+
+<p class="dc"><span class="dropcap">T</span><span class="smcap">his</span> volume is a new work, and not a mere abridgment of the author&#8217;s
+<i>General Astronomy</i>. 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.</p>
+
+<p>Special attention has been paid to making all statements correct and
+accurate <i>as far as they go</i>. 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.</p>
+
+<p>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.</p>
+
+<p>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.</p>
+
+<p>A brief <b>Uranography</b> 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.</p>
+
+
+<h3 class="ads">Plant Organization.</h3>
+
+<blockquote class="ads"><p>By <span class="smcap">R. Halsted Ward</span>, M.D., F.R.M.S., Professor of Botany in the
+Rensselaer Polytechnic Institute, Troy, N.Y. Quarto. 176&nbsp;pages.
+Illustrated. Flexible boards. Mailing Price, 85&nbsp;cents; for Introd.,
+75&nbsp;cents.</p></blockquote>
+
+<p class="dc"><span class="dropcap">I</span><span class="smcap">t</span> 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.</p>
+
+
+<h3 class="ads">A Primer of Botany.</h3>
+
+<blockquote class="ads"><p>By Mrs.&nbsp;<span class="smcap">A.&nbsp;A. Knight</span>, of Robinson Seminary, Exeter, N.H. 12mo. Boards.
+Illus. vii&nbsp;+&nbsp;115 pp. Mailing Price, 35&nbsp;cents; for Introd., 30&nbsp;cents.</p></blockquote>
+
+<p class="dc"><span class="dropcap">T</span><span class="smcap">his</span> Primer is designed to bring physiological botany to the level of
+primary and intermediate grades.</p>
+
+
+<h3 class="ads">Outlines of Lessons in Botany.</h3>
+
+<blockquote class="ads"><p>For the use of teachers, or mothers studying with their children. By
+Miss <span class="smcap">Jane H. Newell</span>. Part I.: From Seed to Leaf. Sq. 16mo. Illus.
+150&nbsp;pp. Cloth. Mailing Price, 55&nbsp;cents; for Introd., 50&nbsp;cents.</p></blockquote>
+
+<p class="dc"><span class="dropcap">T</span><span class="smcap">his</span> book aims to give an outline of work for the pupils themselves.
+It follows the plan of Gray&#8217;s <i>First Lessons</i> and <i>How Plants Grow</i>,
+and is intended to be used with either of these books.</p>
+
+
+<h3 class="ads">A Reader in Botany.</h3>
+
+<blockquote class="ads"><p>Selected and adapted from well-known Authors. By Miss <span class="smcap">Jane H. Newell</span>.
+Part I.: From Seed to Leaf. 12mo. Cloth. vi&nbsp;+&nbsp;209 pp. Mailing Price,
+70&nbsp;cents; for Introd., 60&nbsp;cents.</p></blockquote>
+
+<p class="dc"><span class="dropcap">T</span><span class="smcap">his</span> book follows the plan of the editor&#8217;s <i>Outlines of Lessons in
+Botany</i> and Gray&#8217;s <i>Lessons</i>, and treats of Seed-Food, Movements of
+Seedlings, Trees in Winter, Climbing Plants, Insectivorous Plants,
+Protection of Leaves from the Attacks of Animals, etc.</p>
+
+
+<h3 class="ads">Little Flower-People.</h3>
+
+<blockquote class="ads"><p>By <span class="smcap">Gertrude Elisabeth Hale</span>. Sq. 12mo. Illus. Cloth. xiii&nbsp;+&nbsp;85 pp.
+Mailing Price, 50&nbsp;cents; for Introd., 40&nbsp;cents.</p></blockquote>
+
+<p class="dc"><span class="dropcap">T</span><span class="smcap">he</span> 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&#8217;s
+imagination and curiosity, and to awaken an observant interest in the
+facts themselves.</p>
+
+
+
+
+
+
+
+
+<pre>
+
+
+
+
+
+End of the Project Gutenberg EBook of Elements of Structural and Systematic
+Botany, by Douglas Houghton Campbell
+
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+</pre>
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+</body>
+</html>
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@@ -0,0 +1,11 @@
+This eBook, including all associated images, markup, improvements,
+metadata, and any other content or labor, has been confirmed to be
+in the PUBLIC DOMAIN IN THE UNITED STATES.
+
+Procedures for determining public domain status are described in
+the "Copyright How-To" at https://www.gutenberg.org.
+
+No investigation has been made concerning possible copyrights in
+jurisdictions other than the United States. Anyone seeking to utilize
+this eBook outside of the United States should confirm copyright
+status under the laws that apply to them.
diff --git a/README.md b/README.md
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+++ b/README.md
@@ -0,0 +1,2 @@
+Project Gutenberg (https://www.gutenberg.org) public repository for
+eBook #20390 (https://www.gutenberg.org/ebooks/20390)
diff --git a/old/20390-8.txt b/old/20390-8.txt
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+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 _Charace�_, 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; Zo�logy; 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.--ALG�                                                 21
+
+  Classification of Alg�; Green Alg�; _Protococcace�_,
+  _Protococcus_; _Confervace�_, _Cladophora_, _OEdogonium_,
+  _Coleoch�te_.
+
+
+  CHAPTER V.--GREEN ALG� (_Continued_)                              30
+
+  Pond-scums, _Spirogyra_; _Siphone�_, _Vaucheria_; _Charace�_,
+  _Chara_.
+
+
+  CHAPTER VI.--BROWN SEAWEEDS                                       41
+
+  _Diatomace�_; True Brown Alg�, _Fucus_; Classification of
+  Brown Alg�.
+
+
+  CHAPTER VII.--RED ALG�                                            49
+
+  Structure of Red Alg�; _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
+
+  _Liliiflor�_; _Enantioblast�_; _Spadiciflor�_; _Glumace�_;
+  _Scitamine�_; _Gynandr�_, _Helobi�_.
+
+
+  CHAPTER XVII.--DICOTYLEDONS                                      170
+
+  General Characteristics; Structure of Shepherd's-purse.
+
+
+  CHAPTER XVIII.--CLASSIFICATION OF DICOTYLEDONS                   181
+
+  _Choripetal�_: _Iuliflor�_; _Centrosperm�_; _Aphanocycl�_;
+  _Eucycl�_; _Tricocc�_; _Calyciflor�_.
+
+
+  CHAPTER XIX.--CLASSIFICATION OF DICOTYLEDONS
+  (_Continued_)                                                    210
+
+  _Sympetal�_: _Isocarp�_, _Bicornes_, _Primulin�_, _Diospyrin�_;
+  _Anisocarp�_, _Tubiflor�_, _Labiatiflor�_, _Contort�_,
+  _Campanulin�_, _Aggregat�_.
+
+
+  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 Zo�logy,
+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 (_alg�_) 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_), נ150. _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, נ300.]
+
+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_, נ50; _C_, נ150.]
+
+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, נ50. _C_, a cell from the prothallium
+(young plant) of a fern, נ_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 (_Abietine�_), 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,
+                        _Gymnosperm�_.
+                 /------------^------------\
+                   All naked-seeded plants.
+
+                            Order,
+                         _Conifer�_.
+               /--------------^--------------\
+                 All cone-bearing evergreens.
+
+                           Family,
+                         _Abietine�_.
+                     /--------^--------\
+                      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, נ3. _B_, outline of a part of the same, נ25.
+_C_, a small portion showing the densely granular character of the
+protoplasm, נ150. _D_, a group of spore cases of a slime mould
+(_Trichia_), of about the natural size. _E_, two spore cases, נ5. The
+one at the right has begun to open. _F_, a thread (capillitium) and
+spores of _Trichia_, נ50. _G_, spores. _H_, end of the thread, נ300.
+_I_, zo�spores of _Trichia_, נ300. i, ciliated form; ii, amoeboid
+forms. _n_, nucleus. _v_, contractile vacuole. _J_, _K_, sporangia of
+two common slime moulds. _J_, _Stemonitis_, נ2. _K_, _Arcyria_, נ4.]
+
+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
+(_Volvocine�_).
+
+
+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 (Zo�spore) 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
+(_Cyanophyce�_) 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, נ300. _C_, a
+piece of a filament that has become separated. _s_, sheath, נ300.]
+
+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 _Cyanophyce�_ 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 _Cyanophyce�_. _A_, _Nostoc_. _B_,
+_Gloeotrichia_, נ1. _C_, individual of _Gloeotrichia_. _D_,
+Chro�coccus. _E_, _Nostoc_. _F_, Oscillaria. _G_, _H_, _Tolypothrix_.
+All נ300. _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, נ300.]
+
+Reproduction is for the most part by simple transverse division, as in
+oscillaria; but occasionally spores are produced also.
+
+
+CLASS III.--GREEN MONADS (_Volvocine�_).
+
+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 alg�, 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_), נ50. _B_, Two cells showing the cilia,
+נ300.]
+
+  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.
+
+ALG�.[3]
+
+
+[3] Alg� (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 Alg� (_Chlorophyce�_);
+II.�Brown Alg� (_Ph�ophyce�_); III.�Red Alg� (_Rhodophyce�_).
+
+
+CLASS I.--GREEN ALG�.
+
+The green alg� 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 alg�--I.�Green
+slimes (_Protococcace�_); II.�_Confervace�_; III.�Pond scums
+(_Conjugat�_); IV.�_Siphone�_; V.�Stone-worts (_Charace�_).
+
+
+ORDER I.--_Protococcace�_.
+
+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.--_Protococcace�._ _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, נ300. _G_, small portion of a young colony of the
+water net (_Hydrodictyon_), נ150.]
+
+  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 _Cyanophyce�_.
+  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, נ300.]
+
+  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 alg�, 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.--_Confervace�_.
+
+Under this head are included a number of forms of which the simplest
+ones approach closely, especially in their younger stages, the
+_Protococcace�_. Indeed, some of the so-called _Protococcace�_ 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,
+נ50. _B_, a single cell treated with chromic acid, and stained with
+alum cochineal. _n_, nucleus. _py._ pyrenoid, נ150. _C_, three stages
+in the division of a cell. i, 1.45�p.m.; ii, 2.55�p.m.; iii,
+4.15�p.m., נ150. _D_, a zo�spore נ350.]
+
+  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 (zo�spores) (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 zo�spores, from their animal-like movements. They are
+  provided with two cilia, closely resembling the motile cells of the
+  _Protococcace�_ and _Volvocine�_.
+
+There are very many examples of these simple _Confervace�_, some like
+_Conferva_ being simple rows of cells, others like _Stigeoclonium_
+(Fig.�14, _A_), _Ch�tophora_ 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.--_Confervace�_. _A_, _Stigeoclonium_. _B_,
+_Draparnaldia_, נ50. _C_, a piece of _Draparnaldia_, נ2. _D_, part
+of a filament of _Conferva_, נ300.]
+
+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 alg�, 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
+  zo�spores (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 zo�spore 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 zo�spores are formed, smaller than the ordinary
+  ones, that attach themselves to the filaments bearing the female
+  reproductive organ (o�gonium), 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 o�gonia (_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 zo�spore 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 _Bulboch�te_. _C_, _D_, נ300;
+the others נ150.]
+
+  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 "o�gonium." When the
+  egg cell is ripe, the o�gonium 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 zo�spores 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 o�gonium. By careful
+  observation the student may possibly be able to follow the
+  spermatozoid into the o�gonium, 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 _Coleoch�te_, נ50. _B_, a few
+cells from the margin, with one of the hairs.]
+
+Much like _OEdogonium_, but differing in being branched, is the genus
+_Bulboch�te_, characterized also by hairs swollen at the base, and
+prolonged into a delicate filament (Fig.�16, _G_).
+
+The highest members of the _Confervace�_ are those of the genus
+_Coleoch�te_ (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 alg� 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 ALG�--_Continued_.
+
+
+ORDER III.--POND SCUMS (_Conjugat�_).
+
+The _Conjugat�_, while in some respects approaching the _Confervace�_
+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
+נ150.]
+
+  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 _Conjugat�_ 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 _Zygnemace�_. _A_, _Zygnema_. _B_,
+_C_, _D_, _Mesocarpus_. All נ150.]
+
+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.--_Siphone�_.
+
+The _Siphone�_ are alg� occurring both in fresh and salt water, and
+are distinguished from other alg� 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._ o�gonium. _D_, a ripe o�gonium. _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_, נ150. _G_, נ50. _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 o�gonia, which
+  rapidly increase in size, assuming an oval form, and become
+  separated by walls from the main branch (_C_). Unlike the
+  antheridium, the o�gonia 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_, נ50.]
+
+  The o�gonia, 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 o�gonium 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 zo�spores 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 zo�spore, 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.--_Charace�_.
+
+The _Charace�_, or stone-worts, as some of them are called, are so
+very different from the other green alg� 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_, o�gonium. _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 o�gonium (_o_), and antheridium (_An._).
+_B_, _H_, נ150. _J_, _K_, נ300. _I_, נ50. _L_, נ25.]
+
+  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 o�gonium is formed above, the antheridium
+  below.
+
+  The young o�gonium (_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 o�gonium (_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 o�gonium.
+
+  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 o�gonium 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 _Charace�_, the _Chare�_, of which
+_Chara_ is the type, and the _Nitelle�_, 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 o�gonium is composed of ten
+cells instead of five. They are also destitute of the limy coating of
+the _Chare�_.
+
+Both as regards the structure of the plant itself, as well as the
+reproductive organs, especially the very complex antheridium, the
+_Charace�_ are very widely separated from any other group of plants,
+either above or below them.
+
+
+
+
+CHAPTER VI.
+
+THE BROWN ALG� (_Ph�ophyce�_).
+
+
+[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 נ300.]
+
+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 (_Diatomace�_) 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 alg�, 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.
+נ150]
+
+  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 ALG�.
+
+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 o�gonia (_og._), נ25. _C_,
+_E_, successive stages in the development of the o�gonium, נ150. _F_,
+_G_, antheridia. In _G_, one of the antheridia has discharged the mass
+of spermatozoids (_an._), נ150.]
+
+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 o�gonia.
+
+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_), zo�spores 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 o�gonia 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
+  o�gonia (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 o�gonium 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 o�gonium is of a nearly uniform
+  olive-brown tint.
+
+  When ripe, the upper part of the o�gonium 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
+  o�gonium 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 o�gonia, olive. Within a few
+  minutes after putting the o�gonia 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 o�gonium. _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_, נ300; _L_, נ600; the others, נ150.]
+
+The simpler brown seaweeds, so far as known, multiply only by means of
+zo�spores, which may grow directly into new plants, or, as has been
+observed in some species, two zo�spores 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_,
+נ50. Sporangia (_sp._). _B_, a single sporangium, נ150. _C_, kelp
+(_Laminaria_), נ1/8. _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 ALG� (_Rhodophyce�_).
+
+
+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, נ50. _t_, tetraspores. _C_
+i-v, successive stages in the development of the tetraspores, נ150.
+_D_ I, II young procarps. _tr._ trichogyne. iii, young; iv, ripe spore
+fruit. I, III, נ150. iv, נ50. _E_, an antheridium, נ150. _F_, spore
+fruit of _Polysiphonia_. The spores are here surrounded by a case,
+נ50.]
+
+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
+  alg�, 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 alg� 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 alg�. _A_, _Batrachospermum_,
+נabout�12. _B_, a branch of the same, נ150. _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 alg�. Unlike the alg�, 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 alg�, 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
+_Siphone�_, 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_), נ5. _B_,
+three nearly ripe spore cases, נ25. _C_, development of the spore
+cases, i-iv, נ150; v, נ50. _D_, spore case which has discharged its
+spores. _E_, spores, נ300. _F_, a form of _Mucor mucedo_, with small
+accessory spore cases, נ5. _G_, the spore cases, נ50. _H_, a single
+spore case, נ300. _I_, development of the zygospore of a black mould,
+נ45 (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 (_Entomopthore�_),
+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 (_Peronospore�_)
+
+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 zo�spore, 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_, zo�spores. _E_,
+germinating zo�spores. _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 o�gonium. _I_, a part of a filament of
+the fungus, showing its irregular form. All נ300.]
+
+  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 (o�spores) 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 o�gonium, 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 o�gonium, 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_), נ300.]
+
+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_), נ150.]
+
+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.--_Saprolegniace�_ (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 zo�sporangium, נ100. _C_, the same discharging the spores. _D_,
+active. _E_, germinating zo�spores, נ300. _F_, a second sporangium
+forming below the empty one. _G_ i-iv, development of the o�gonium,
+נ100. _H_, ripe o�gonium filled with resting spores, נ100.]
+
+  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 zo�spores,
+  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 zo�spores 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 zo�spore, like
+  those already described. By killing the zo�spores 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 zo�spores there are also resting spores developed. O�gonia
+  like those of _Vaucheria_ or the _Peronospore�_ are formed usually
+  after the formation of zo�spores 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
+o�gonium, 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 o�gonia (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 alg�,
+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, נ750.]
+
+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 (_Ustillagine�_).
+
+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,
+נ300. _C_, ripe spores, נ300.]
+
+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
+(_Perisporiace�_), 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 (_Podosph�ra_) 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 (_Podosph�ra_), נ150. _B_, a germinating spore, נ150. _C-F_,
+development of the spore fruit, נ300. _ar._ archicarp. _G_, a ripe
+spore fruit, נ150. _H_, the spore sac removed from the spore fruit,
+נ150. _I_, spore-bearing filament attacked by another fungus
+(_Cicinnobulus_), causing the enlargement of the basal cell, נ150.
+_J_, a more advanced stage, נ300. _K_, spores, נ300.]
+
+  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, נ300.]
+
+  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_,
+_Microsph�ra_, a spore fruit, נ150. _B_, cluster of spore sacs of the
+same, נ150. _C_, a single appendage, נ300. _D_, end of an appendage
+of _Uncinula_, נ300. _E_, appendage of _Phyllactinia_, נ150.]
+
+  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: _Podosph�ra_, 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_), נ150. _B_, _C_, another species showing the way
+in which the spores are borne--optical section--נ150. _D_, spore
+fruit of the herbarium mould, נ150. _E_, spore sac. _F_, spores,
+נ300. _G_, spore-bearing filament of the common blue mould
+(_Penicillium_), נ300. _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_), נ5.
+_B_, young spore fruit, נ300. _ar._ archicarp. _C_, an older one,
+נ150. _ar._ archicarp. _sp._ young spore sacs. _D_, section through a
+full-grown spore fruit (partly diagrammatic), נ25. _sp._ spore sacs.
+_E_, development of spore sacs and spores: i-iii, נ300; iv, נ150.
+_F_, ripe spores. _G_, a sterile filament (paraphysis), נ300. _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 alg�, 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, נ5. _C_, section through the body of a gelatinous lichen
+(_Collema_), showing the _Nostoc_ individuals surrounded by the fungus
+filaments, נ300. _D_, a spermagonium of _Collema_, נ25. _E_, a
+single _Nostoc_ thread. _F_, spore sacs and paraphyses of _Usnea_,
+נ300. _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 alg�, 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 alg�, 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, נ2. _F_, _Cladonia_, natural size. _G_, a piece of bark
+from a beech, with a crustaceous lichen (_Graphis_) growing upon it,
+נ2. _ap._ spore fruit. _H_, _Soredium_ of a lichen, נ300.]
+
+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 (_Uredine�_) 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," נ�. _B_,
+spores of the same, one beginning to germinate, נ300. _C_, a spore
+that has germinated, each cell producing a short, divided filament
+(basidium), which in turn gives rise to secondary spores (_sp._),
+נ300. _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 (_Aris�ma_), bearing the
+cluster cup (_�cidium_) stage of a rust, נ2. _G_, vertical section
+through a young cluster cup. _H_, similar section through a mature
+one, נ50. _I_, germinating spores of _H_, נ300. _J_, part of a corn
+leaf, with black rust, natural size. _K_, red rust spore of the wheat
+rust (_Puccinia graminis_), נ300. _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
+(_Aris�ma_) 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_), נ2. _C_, under side of the cap, showing the
+radiating "gills," or spore-bearing plates. _D_, section across one of
+the young gills, נ150. _E_, _F_, portions of gills from a nearly ripe
+fruit, נ300. _sp._ spores. _x_, sterile cell. In _F_, a basidium is
+shown, with the young spores just forming. _G_, _H_, young fruits,
+נ50.]
+
+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 _Lamell�_) 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_, נ�. _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_, נ�; _E_, נ�. _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 (_Hepatic�_), 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_), נ2. _B_, part of the same, seen from below, נ4. _C_,
+a branch with two open sporogonia (_sp._), נ4. _D_, a single
+sporogonium, נ8.]
+
+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, נ2. _B_,
+two young antheridia (_an._), the upper one seen in optical section,
+the lower one from without, נ150. _C_, a ripe antheridium, optical
+section, נ50. _D_, sperm cells with young spermatozoids. _E_, ripe
+spermatozoids, נ600.]
+
+  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 o�gonium 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, נ150. _E_, base of a fertilized archegonium, containing a
+young embryo (_em._), נ150. _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, נ12. _H_, short branch
+containing the young sporogonium, נ4.]
+
+  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, נ25. _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_, נ300.]
+
+  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 (_Ricciace�_) 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 (_Anthocerote�_), 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 (_Marchantiace�_) 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, נ2. _F_,
+common liverwort (_Marchantia_), נ2. _x_, cups containing buds. _G_,
+archegonial branch of common liverwort, natural size. _H_, two young
+buds from the common liverwort, נ150. _I_, a full-grown bud, נ25.
+_J_, vertical section through the body of _Marchantia_, cutting
+through a breathing pore (_s_), נ50. _K_, surface view of a breathing
+pore, נ150. _L_, a leafy liverwort (_Jungermannia_). _sp._
+sporogonium, נ2.]
+
+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 (_Jungermanniace�_) 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._), נ4. B, plant with ripe sporogonium.
+_cal_. calyptra, נ2. _C_, sporogonium with calyptra removed. _op._
+lid, נ4. _D_, spores: i, ungerminated; ii-iv, germinating, נ300.
+_E_, two teeth from the margin of the capsule, נ50. _F_, epidermal
+cells and breathing pore from the surface of the sporogonium, נ150.
+_G_, longitudinal section of a young sporogonium, נ12. _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, נ150.]
+
+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, נ150. _C_, two sperm cells of _Atrichum_. _D_,
+spermatozoids of _Sphagnum_, נ600.]
+
+  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, נ150. _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, נ150. _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, נ300. _B_, an older
+embryo freed from the archegonium, נ150. _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_), נ50. _B_, outline of a leaf, showing also the thickened
+midrib, נ12. _C_, cells of the leaf, נ300. _n_, nucleus. _D_,
+chlorophyll granules undergoing division, נ300. _E_, cross-section of
+the stem, נ50.]
+
+  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
+(_Sphagnace�_); II.�_Andre�ace�_; III.�_Phascace�_; IV.�The common
+mosses (_Bryace�_).
+
+[Illustration: FIG.�64.--_A_, a peat moss (_Sphagnum_), נ�. _B_, a
+sporogonium of the same, נ3. _C_, a portion of a leaf, נ150. 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_,
+נ3. _B_, fruiting plant of _Atrichum_, נ2. _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, נ2.
+_F_, a male plant of _Mnium_, נ4. _G_, pine-tree moss (_Clemacium_),
+נ1. _H_, _Hypnum_, נ1. _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 _Andre�ace�_ are very small, and not at all common. The capsule
+splits into four valves, something like a liverwort.
+
+The _Phascace�_ 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, נ150. _C_, young
+prothallium, נ50. _r_, root hair. _sp._ spore membrane. _D_, _E_,
+older prothallia. _a_, apical cell, נ150. _F_, a female prothallium,
+seen from below, נ12. _ar._ archegonia. _G_, _H_, young archegonia,
+in optical section, נ150. _o_, central cell. _b_, ventral canal cell.
+_c_, upper canal cell. _I_, a ripe archegonium in the act of opening,
+נ150. _o_, egg cell. _J_, a male prothallium, נ50. _an._ antheridia.
+_K_, _L_, young antheridia, in optical section, נ300. _M_, ripe
+antheridium, נ300. _sp._ sperm cells. _N_, _O_, antheridia that have
+partially discharged their contents, נ300. _P_, spermatozoids, killed
+with iodine, נ500. _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 alg� (_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, נ50. _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, נ1. _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, נ5. _E_, part of
+the blade of the leaf, נ�. _F_, a single spore-bearing leaflet,
+showing the edge folded over to cover the sporangia, נ1. _G_, part of
+the fibro-vascular bundle of the leaf stalk (cross-section), נ50.
+_x_, woody part of the bundle. _y_, bast. _sh._ bundle sheath. _H_, a
+small portion of the same bundle, נ150. _I_, stony tissue from the
+underground stem, נ150. _J_, sieve tube from the underground stem,
+נ300.]
+
+  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
+o�phyte (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._), נ150. _B_,
+surface view of the epidermis from the lower surface of a leaf. _f_,
+vein. _p_, breathing pore, נ150. _C_, longitudinal section of the
+fibro-vascular bundle of the leaf stalk, showing tracheids with
+ladder-shaped markings, נ150. _D_, longitudinal section through the
+tip of a root, נ150. _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_), נ150. _F_, cross-section
+through a full-grown root, נ25. _r_, root hairs. _G_, the
+fibro-vascular bundle of the same, נ150.]
+
+  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, נ300. _B_, young sporangium, surface view, נ150:
+i, from the side; ii, from above. _C-E_, successive stages in the
+development of the sporangium seen in optical section, נ150. _F_,
+nearly ripe sporangium, נ50: i, from in front; ii, from the side.
+_an._ ring. _st._ point of opening. _G_, group of four spores, נ150.
+_H_, a single spore, נ300.]
+
+  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 papill�
+  (_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
+(_Filicin�_); horse-tails (_Equisetin�_); and the club mosses
+(_Lycopodin�_).
+
+
+CLASS I.--FERNS (_Filicin�_).
+
+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 (_Ophioglossace�_), are represented
+in the United States. A third order, intermediate in some respects
+between these two, and called the ringless ferns (_Marattiace�_), 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 (_Ophioglossace�_) 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_), נ�. _x_, fertile part of the leaf. _B_, sporangia of
+_Botrychium_, נ3. _C_, flowering fern (_Osmunda_). _x_, spore-bearing
+leaflets, נ�. _D_, a sporangium of _Osmunda_, נ25. _r_, ring. _E_,
+_Polypodium_, נ1. _F_, brake (_Pteris_), נ1. _G_, shield fern
+(_Aspidium_), נ2. _H_, spleen-wort (_Asplenium_), נ2. _I_, ostrich
+fern (_Onoclea_), נ1. _J_, the same, with the incurved edges of the
+leaflet partially raised so as to show the masses of sporangia
+beneath, נ2.]
+
+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 (_Rhizocarpe�_), 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 _Rhizocarpe�_
+(after Underwood). _sp._ the "fruits" containing the sporangia. _B_, a
+small spore of _Pilularia_, with the ripe antheridium protruding,
+נ180. _C_, male prothallium removed from the spore, נ180. _D_,
+_Azolla_ (after Sprague), נ1.]
+
+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 (_Equisetin�_).
+
+The second class of the pteridophytes includes the horse-tails
+(_Equisetin�_) 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_), נ1. _x_, the spore-bearing cone. _B_,
+sterile stem of the same, נ�. _C_, underground stem, with tubers
+(_o_), נ�. _D_, cross-section of an aerial stem, נ5. _f.b._
+fibro-vascular bundle. _E_, a single fibro-vascular bundle, נ150.
+_tr._ vessels. _F_, a single leaf from the cone, נ5. _G_, the same
+cut lengthwise, through a spore sac (_sp._), נ5. _H_, a spore, נ50.
+_I_, the same, moistened so that the elaters are coiled up, נ150.
+_J_, a male prothallium, נ50. _an._ an antheridium. _K_,
+spermatozoids, נ300.]
+
+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 (_Lycopodin�_).
+
+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 (_Lycopodiace�_) 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_), נ1/3. _x_,
+cone. _r_, root. _B_, a cone, נ1. _C_, single scale with sporangium
+(_sp._). _D_, spores: i, from above; ii, from below, נ325. _E_, cross
+section of stem, נ8. _f.b._ fibro-vascular bundle. _F_, portion of
+the fibro-vascular bundle, נ150. _G_, cells of the ground tissue,
+נ150.]
+
+  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 (_Ligulat�_) is represented by two very distinct
+families: the smaller club mosses (_Selaginelle�_) and the quill-worts
+(_Isoete�_). 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, נ2. _B_, part of a stem,
+sending down naked rooting branches (_r_), נ1. _C_, longitudinal
+section of a spike, with a single macrosporangium at the base; the
+others, microsporangia, נ3. _D_, a scale and microsporangium, נ5.
+_E_, young microsporangium, נ150. The shaded cells are the spore
+mother cells. _F_, a young macrospore, נ150. _G_, section of the
+stem, נ50. _H_, a single fibro-vascular bundle, נ150. _I_, vertical
+section of the female prothallium of _Selaginella_, נ50. _ar._
+archegonium. _J_, section of an open archegonium, נ300. _o_, the egg
+cell. _K_, microspore, with the contained male prothallium, נ300.
+_x_, vegetative cell. _sp._ sperm cells. _L_, young plant, with the
+attached macrospore, נ6. _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 _Ligulat�_ 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 (_Isoete�_). 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: PH�NOGAMS.
+
+
+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 (_Gymnosperm�_).
+
+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, נ�. _B_, a year-old cone, נ1. _C_, longitudinal section of
+_B_. _D_, a single scale of _B_, showing the sporangia (ovules) (_o_),
+נ2. _E_, a scale from a ripe cone, with the seeds (_s_), נ�. _F_,
+longitudinal section of a ripe seed, נ3. _em._ the embryo. _G_, a
+germinating seed, נ2. _r_, the primary root. _H_, longitudinal
+section through _G_, showing the first leaves of the young plant still
+surrounded by the endosperm, נ4. _I_, an older plant with the leaves
+(_l_) withdrawing from the seed coats, נ4. _J_, upper part of a young
+plant, showing the circle of primary leaves (cotyledons), נ1. _K_,
+section of the same, נ2. _b_, the terminal bud. _L_, cross-section of
+the stem of the young plant, נ25. _fb._ a fibro-vascular bundle. _M_,
+cross-section of the root, נ25. _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, נ3. _p_, pith. _c_, bark. The radiating lines
+are medullary rays. _r_, resin ducts. _B_, part of the same, נ150.
+_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, נ150. _D_, longitudinal section of a branch,
+showing the form of the tracheids and the bordered pits upon their
+walls. _m_, medullary ray, נ150. _E_, part of a sieve tube, נ300.
+_F_, cross-section of a tracheid passing through two of the pits in
+the wall (_p_), נ300. _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, נ150. _H_,
+cross-section of a resin duct, נ150. _I_, cross-section of a leaf,
+נ20. _fb._ fibro-vascular bundle. _r_, resin duct. _J_, section of a
+breathing pore, נ150. _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]), נ�. _B_, a similar
+branch, with two young female flowers ([Female]), natural size. _C_, a
+scale from a male flower, showing the two sporangia (_sp._); נ5. _D_,
+a single ripe pollen spore (microspore), showing the vegetative cell
+(_x_), נ150. _E_, a similar scale, from a female flower of the
+Austrian pine, seen from within, נ4. _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, נ10. _H_, the neck of the archegonium, נ150.]
+
+  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 (_Cycade�_);
+II., conifers (_Conifer�_); III., joint firs (_Gnetace�_). 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._), נ�.
+_B_, leaf of _Gingko_, נ�. _C_, branch of hemlock (_Tsuga_), with a
+ripe cone, נ1. _D_, red cedar (_Juniperus_), נ1. _E_, _Arbor-vit�_
+(_Thuja_), נ1.]
+
+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-vit�_ (_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, נ100. _m_, micropyle. _e_, embryo sac. _B_, the
+embryo sac, נ300. At the top is the egg apparatus, consisting of the
+two synergid� (_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 "synergid�." 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,
+נ200.]
+
+The upper part of the pistil is variously modified, having either
+little papill� 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_), נ1/3. _B_, the bulb of the same, נ�. _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,
+נ�. _f_, the filament. _an._ anther. _E_, the gynoecium (pistil), נ1.
+_o_, ovary. _st._ style. _z_, stigma. _F_, a full-grown fruit, נ�.
+_G_, section of a full-grown macrosporangium (ovule), נ25: i, ii, the
+two integuments. _sp._ macrospore (embryo sac). _H_, cross-section of
+the ripe anther, נ12. _I_, a single pollen spore, נ150, showing the
+two nuclei (_n_, _n'_). _J_, a ripe seed, נ2. _K_, the same, in
+longitudinal section. _em._ the embryo. _L_, cross-section of the
+stem, נ12. _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, נ150. _B_, a single epidermal cell from the petal, נ150.
+_C_, cross-section of a fibro-vascular bundle of the stem, נ150.
+_tr._ vessels. _D_, _E_, longitudinal section of the same, showing the
+markings of the vessels, נ150. _F_, a bit of the epidermis from the
+lower surface of a leaf, showing the breathing pores, נ50. _G_, a
+single breathing pore, נ200. _H_, cross-section of a leaf, נ50.
+_st._ a breathing pore. _m_, the mesophyll. _fb._ a vein. _I_,
+cross-section of a breathing pore, נ200. _J_, young embryo, נ150.]
+
+  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.�_Liliiflor�_; II.�_Enantioblast�_; III.�_Spadiciflor�_;
+IV.�_Glumace�_; V.�_Scitamine�_; VI.�_Gynandr�_; VII.�_Helobi�_.
+
+
+ORDER I.--_Liliiflor�_.
+
+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 (_Dioscore�_), 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 (_Smilace�_) 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 _Liliiflor�_. _A_, _Trillium_, נ�.
+_B_, single flower of Solomon's-seal (_Polygonatum_), נ1. _C_, upper
+part of a plant. _D_, underground stem (rhizome) of Indian cucumber
+root (_Medeola_), נ�. _E_, a rush (_Juncus_), נ1. _F_, a single
+flower, נ2. _A-D_, _Liliace�_; _E_, _Juncace�_.]
+
+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 _Liliiflor�_. _A_, flower of the
+common blue-flag (_Iris_), נ� (_Iridace�_). _B_, the petal-like upper
+part of the pistil, seen from below, and showing a stamen (_an._).
+_st._ the stigma, נ�. _C_, the young fruit, נ�. _D_, section of the
+same, נ1. _E_, diagram of the flower. _F_, part of a plant of the
+so-called "gray moss" (_Tillandsia_), נ� (_Bromeliace�_). _G_, a
+single flower, נ2. _H_, a seed, showing the fine hairs attached to
+it, נ1. _I_, plant of pickerel-weed (_Pontederia_), נ�
+(_Pontederiace�_). _J_, a single flower, נ1. _K_, section of the
+ovary, נ4.]
+
+The principal family of the _Liliiflor�_ is the _Liliace�_, 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 _Liliace�_ 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 (_Iridace�_), 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.--_Enantioblast�_. _A_, inflorescence of the
+common spiderwort (_Tradescantia_), נ� (_Commelyne�_). _B_, a single
+stamen, showing the hairs attached to the filament, נ2. _C_, the
+pistil, נ2.]
+
+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 _Bromeliace�_, 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.--_Enantioblast�_.
+
+The second order of the monocotyledons, _Enantioblast�_, 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, _Commelyne�_.
+
+
+ORDER III.--_Spadiciflor�_.
+
+The third order of the monocotyledons, _Spadiciflor�_, 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 (_Aroide�_), of which the
+calla (_Richardia_) is a very familiar cultivated example. Of wild
+forms the sweet-flag (_Acorus_), Jack-in-the-pulpit (_Aris�ma_)
+(Fig.�86, _A_, _D_), skunk-cabbage (_Symplocarpus_), and wild calla
+may be noted. In _Aris�ma_ (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 _Spadiciflor�_. _A_, inflorescence
+of Jack-in-the-pulpit (_Aris�ma_, _Aroide�_). 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, נ�.
+_B_, leaf of the same plant, נ�. _C_, vertical section of a female
+flower, נ2. _D_, three male flowers, each consisting of four stamens,
+נ2. _E_, two plants of a duck-weed (_Lemna_), the one at the left is
+in flower, נ4. _F_, another common species. _L_, _Trisulea_, נ1.
+_G_, male flower of _E_, נ25. _H_, optical section of the female
+flower, showing the single ovule (_ov._), נ25. _I_, part of the
+inflorescence of the bur-reed (_Sparganium_), with female flowers, נ�
+(_Typhace�_). _J_, a single, female flower, נ2. _K_, a ripe fruit,
+נ1. _L_, longitudinal section of the same. _M_, two male flowers,
+נ1. _N_, a pond-weed (_Potomogeton_), נ1 (_Naiadace�_). _O_, a
+single flower, נ2. _P_, the same, with the perianth removed, נ2.
+_Q_, fruit of the same, נ2.]
+
+Probably to be regarded as reduced aroids are the duck-weeds
+(_Lemnace�_) (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 _Typhace�_, and the
+pond-weeds (_Naias_ and _Potomogeton_) are common examples of the
+family _Naiade�_. 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 (_Pandane�_) and
+the palms (_Palm�_). 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 _Cham�rops_) 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.--_Glumace�_.
+
+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, pale�) which are closely set, so as to nearly conceal the
+flowers. The flowers are either hermaphrodite or unisexual.
+
+[Illustration: FIG.�87.--Types of _Glumace�_. _A_, a sedge, _Carex_
+(_Cyperace�_). [Male], the male; [Female], the female flowers, נ�.
+_B_, a single male flower, נ2. _C_, a female flower, נ2. _D_,
+fruiting spike of another _Carex_, נ�. _E_, a single fruit, נ1. _F_,
+the same, with the outer envelope removed, and slightly enlarged. _G_,
+section of _F_, נ3. _em._ the embryo. _H_, a bulrush, _Scirpus_
+(_Cyperace�_), נ�. _I_, a single spikelet, נ2. _J_, a single flower,
+נ3. _K_, a spikelet of flowers of the common orchard grass,
+_Dactylis_ (_Gramine�_), נ2. _L_, a single flower, נ2. _M_, the base
+of a leaf, showing the split sheath encircling the stem, נ1. _N_,
+section of a kernel of corn, showing the embryo (_em._), נ2.]
+
+There are two well-marked families, the sedges (_Cyperace�_) and the
+grasses (_Gramine�_). 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.--_Scitamine�_.
+
+[Illustration: FIG.�88.--_Scitamine�_. _A_, upper part of a flowering
+plant of Indian shot (_Canna_), much reduced in size (_Cannace�_).
+_B_, a single flower, נ�. _C_, the single stamen (_an._), and
+petal-like pistil (_gy._), נ1. _D_, section of the ovary, נ2. _E_,
+diagram of the flower. The place of the missing stamens is indicated
+by small circles. _F_, fruit, נ�. _G_, section of an unripe seed.
+_em._ embryo. _p_, perisperm, נ2.]
+
+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 papill� 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.�_Musace�_ (banana family);
+II.�_Zingiberace�_ (ginger family); and III.�_Cannace�_ (_Canna_,
+_Maranta_).
+
+
+ORDER VI.--_Gynandr�_.
+
+By far the greater number of the plants of this order belong to the
+orchis family (_Orchide�_), the second family of the order
+(_Apostasie�_), 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.--_Gynandr�_. _A_, inflorescence of the showy
+orchis (_Orchis spectabilis_), נ1 (_Orchide�_). _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, נ1. _C_, the column seen from in front. _an._ the stamen.
+_gy._ the stigmatic surface, נ1. _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 _Orchide�_. _A_, putty-root
+(_Aplectrum_), נ1. _B_, yellow lady's-slipper (_Cypripedium_), נ�.
+_C_, the column of the same, נ1. _an._ one of the two perfect
+stamens. _st._ sterile, petal-like stamen. _gy._. stigma. _D_,
+_Arethusa_, נ�. _E_, section of the column, נ1: _an._ stamen. _gy._
+stigma. _F_, the same, seen from in front. _G_, _Habenaria_, נ1. _H_,
+_Calopogon_, נ1. 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
+_Arethuse�_ (_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.--_Helobi�_.
+
+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, _Juncagine�_, 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 (_Alismace�_) 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 _Helobi�_. _A_, inflorescence of
+arrowhead (_Sagittaria_), with a single female flower, נ�
+(_Alismace�_). _B_, section through the gynoecium, showing the numerous
+single carpels, נ3. _C_, a ripe fruit, נ3. _D_, a male flower, נ1.
+_E_, a single stamen, נ3. _F_, a leaf of _Sagittaria variabilis_,
+נ1/6. _G_, ditch-moss (_Elodea_), with a female flower (_fl._), נ�.
+(_Hydrocharide�_). _H_, the flower, נ2. _an._ the rudimentary
+stamens. _st._ the stigma. _I_, cross-section of the ovary, נ4. _J_,
+male inflorescence of eel-grass (_Vallisneria_), נ1. _K_, a single
+expanded male flower, נ12. _st._ the stamen. _L_, a female flower,
+נ1. _gy._ the stigma.]
+
+The last family is the _Hydrocharide�_. 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, נ1.]
+
+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_), נ�. _r_, the main root. _B_, upper part
+of the inflorescence, נ1. _C_, two leaves: i, from the upper part;
+ii, from the base of the plant, נ1. _D_, a flower, נ3. _E_, the
+same, with sepals and petals removed, נ3. _F_, petal. _G_, sepal.
+_H_, stamen, נ10. _f_, filament. _an._ anther. _I_, a fruit with one
+of the valves removed to show the seeds, נ4. _J_, longitudinal
+section of a seed, נ8. _K_, the embryo removed from the seed, נ8.
+_l_, the first leaves (cotyledons). _st._ the stem ending in the root.
+_L_, cross-section of the stem, נ20. _fb._ fibro-vascular bundle.
+_M_, a similar section of the main root, נ15. _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, נ150. _ep._
+epidermis. _m_, ground tissue. _sh._ bundle sheath. _ph._ phloem.
+_xy._ xylem. _tr._ a vessel. _B_, a young root seen in optical
+section, נ150. _r_, root cap. _d_, young epidermis. _pb._ ground.
+_pl._ young fibro-vascular bundle. _C_ cross section of a small root,
+נ150. _fb._ fibro-vascular bundle. _D_, epidermis from the lower side
+of the leaf, נ150. _E_, a star-shaped hair from the surface of the
+leaf, נ150. _F_, cross-section of a leaf, נ150. _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_, נ50. _A_, surface view. _B-D_, optical
+sections. _s_, sepals, _p_, petals. _an._ stamens. _gy._ pistil. _E_,
+cross-section of the young anther, נ180. _sp._ spore mother cells.
+_F_, cross-section of full-grown anther. _sp._ pollen spores, נ50.
+_F'_, four young pollen spores, נ300. _F"_, pollen spores germinating
+upon the stigma, נ300. _pt._ pollen tube. _G_, young pistil in
+optical section, נ25. H, cross-section of a somewhat older one. _ov._
+ovules. _I-L_, development of the ovule. _sp._ embryo sac
+(macrospore). _I-K_, נ150. _L_, נ50. _M_, embryo sac of a full-grown
+ovule, נ150. _Sy._ _Synergid�_. _o_, egg cell. _n_, endosperm
+nucleus. _ant._ antipodal cells. _N-Q_, development of the embryo,
+נ150. _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 placent� 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 papill�
+  (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.--_Choripetal�_.
+
+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 _Choripetal�_, 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 (_Sympetal�_ or _Gamopetal�_) 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 _Sympetal�_, which includes the
+highest of all plants.
+
+[Illustration: FIG.�96.--Iuliflor�. _A_, male; _B_, female
+inflorescence of a willow, _Salix_ (_Amentace�_), נ�. _C_, a single
+male flower, נ2. _D_, a female flower, נ2. _E_, cross-section of the
+ovary, נ8. _F_, an opening fruit. _G_, single seed with its hairy
+appendage, נ2.]
+
+The _Choripetal�_ may be divided into six groups, including twenty-two
+orders. The first group is called _Iuliflor�_, 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 andr�cium, 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 _Iuliflor�_. _A_, branch of hazel,
+_Corylus_ (_Cupulifer�_), נ1. [Male], male; [Female], female
+inflorescence. _B_, a single male flower, נ3. _C_, section of the
+ovary of a female flower, נ25. _D_, acorn of red oak, _Quercus_
+(_Cupulifer�_), נ�. _E_, seed of white birch, _Betula_ (_Betulace�_),
+נ3. _F_, fruit of horn-bean, _Carpinus_ (_Cupulifer�_), נ1. G,
+lizard-tail, _Saururus_ (_Saurure�_), נ�. _H_, a single flower, נ2.
+_I_, female inflorescence of the hop, _Humulus_ (_Cannabine�_), נ1.
+_J_, a single scale with two flowers, נ1. _K_, a male flower of a
+nettle, _Urtica_ (_Urticace�_), נ5.]
+
+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 _Iuliflor�_: _Amentace�_, _Piperine�_,
+and _Urticin�_. The first contains the birches (_Betulace�_); oaks,
+beeches, hazels, etc. (_Cupulifer�_); walnuts and hickories
+(_Juglande�_); willows and poplars (_Salicace�_). They are all trees
+or shrubs; the fruit is often a nut, and the embryo is very large,
+completely filling it.
+
+The _Piperine�_ 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 _Urticin�_ include, among our common plants, the nettle family
+(_Urticace�_); plane family (_Platane�_), represented by the sycamore
+or buttonwood (_Platanus_); the hemp family (_Cannabine�_); and the
+elm family (_Ulmace�_). 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 _Choripetal�_ is called _Centrosperm�_, and
+includes but a single order comprising seven families, all of which,
+except one (_Nyctagine�_), 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 _Centrosperm�_. _A_, plant of
+spring-beauty, _Claytonia_ (_Portulacace�_), נ�. _B_, a single
+flower, נ1. _C_, fruit, with the sepals removed, נ2. _D_, section of
+the seed, showing the curved embryo (_em._), נ5. _E_, single flower
+of smart-weed, _Polygonum_ (_Polygonace�_), נ2. _F_, the pistil, נ2.
+_G_, section of the ovary, showing the single ovule, נ4. _H_, section
+of the seed, נ2. _I_, base of the leaf, showing the sheath, נ1. _J_,
+flower of pig-weed, _Chenopodium_ (_Chenopodiace�_), נ3: i, from
+without; ii, in section. _K_, flower of the poke-weed, _Phytolacca_
+(_Phytolaccace�_), נ2. _L_, fire-pink, _Silene_ (_Caryophyllace�_),
+נ�. _M_, a flower with half of the calyx and corolla removed, נ1.
+_N_, ripe fruit of mouse-ear chick-weed, _Cerastium_ (_Caryophyllace�_),
+opening by ten teeth at the summit, נ2. _O_, diagram of the flower
+of _Silene_.]
+
+The first family (_Polygone�_) 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 _Chenopodiace�_. Nearly resembling
+the last is the amaranth family (_Amarantace�_), 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 _Phytolaccace�_. The two
+highest families are the purslane family (_Portulacace�_) and pink
+family (_Caryophylle�_). 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 _Choripetal�_ (the _Aphanocycl�_) 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 (_Polycarp�_) includes ten families, of which the
+buttercup family (_Ranunculace�_) 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 (_Anonace�_) 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 _Aphanocycl�_ (_Polycarp�_), family
+_Ranunculace�_. _A_, Rue anemone (_Anemonilla_), נ�. _B_, a fruit,
+נ2. _C_, section of the same. _D_, section of a buttercup flower
+(_Ranunculus_), נ1�. _E_, diagram of buttercup flower. _F_, wild
+columbine (_Aquilegia_), נ�. _G_, one of the spur-shaped petals, נ1.
+_H_, the five pistils, נ1. _I_, longitudinal section of the fruit,
+נ1. _J_, flower of larkspur (_Delphinium_), נ1. _K_, the four petals
+and stamens, after the removal of the five colored and petal-like
+sepals, נ1.]
+
+The magnolia family (_Magnoliace�_) 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 _Calycanthace�_ 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 _Aphanocycl�_ (_Polycarp�_). _A_,
+branch of papaw, _Asimina_ (_Anonace�_), נ�. _B_, section of the
+flower, נ1. _C_, flower and leaf of tulip-tree, _Liriodendron_
+(_Magnoliace�_), נ1/3. _D_, section of a flower, נ�. _E_, a ripe
+fruit, נ1. _F_, diagram of the flower. _G_, flower of the
+sweet-scented shrub, _Calycanthus_ (_Calycanthace�_), נ�]
+
+The barberry (_Berberis_) (Fig.�101, _A_) is the type of the family
+_Berberide�_, 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 _Menisperme�_
+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 _Aphanocycl�_ (_Polycarp�_). _A-H_,
+_Berberidace�_. _A_, flower of barberry (_Berberis_), נ2. _B_, the
+same in section. _C_, a stamen, showing the method of opening, נ3.
+_D_, flower of may-apple (_Podophyllum_), נ�. _E_, section of the
+ovary of _D_, נ1. _F_, diagram of the flower. _G_, ripe fruit of
+twin-leaf (_Jeffersonia_), opening by a lid, נ�. _H_, section of
+seed, showing the embryo (_em._), נ2. _I_, young leaf and cluster of
+male flowers of moon-seed, _Menispermum_ (_Menisperme�_), נ1. _J_, a
+single male flower, נ2. _K_, section of a female flower, נ2. _L_,
+ripe seed, נ1. _M_, section of _L_, showing the curved embryo.]
+
+The last two families of the order, the laurel family (_Laurine�_) and
+the nutmeg family (_Myristicine�_) 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 _Aphanocycl�_ comprises a number of aquatic
+plants, mostly of large size, and is known as the _Hydropeltidin�_.
+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 _Aphanocycl�_ (_Hydropeltidin�_).
+_A_, yellow water-lily, _Nymph�a_ (_Nymph�ace�_), נ�. _B_, a leaf of
+the same, נ1/6. _C_, freshly opened flower, with the large petal-like
+sepals removed, נ�. _p_, petals. _an._ stamens. _st._ stigma. _D_,
+section of the ovary, נ2. _E_, young fruit, נ�. _F_, lotus,
+_Nelumbo_ (_Nelumbie�_). נ1/6. _G_, a stamen, נ1. _H_, the large
+receptacle, with the separate pistils sunk in its surface, נ�. _I_,
+section of a single pistil, נ2. _ov._ the ovule. _J_, upper part of a
+section through the stigma and ovule (_ov._), נ4.]
+
+There are three families, all represented within the United States.
+The first (_Nelumbie�_) 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 (_Cabombe�_) 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 (_Nymph�ace�_) includes the common white water-lilies
+(_Castalia_) and the yellow water-lilies (_Nymph�a_) (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 _Aphanocycl�_ (_Rhoeadin�_ or _Cruciflor�_)
+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 _Cruciflor�_.
+
+There are four families, of which the first is the poppy family
+(_Papaverace�_), 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 _Aphanocycl�_ (_Rhoedin�_). _A_,
+plant of blood-root, _Sanguinaria_ (_Papaverace�_), נ1/3. _B_, a single
+flower, נ1. _C_, fruit, נ�. _D_, section of the seed. _em._ embryo,
+נ2. _E_, diagram of the flower. _F_, flower of Dutchman's breeches,
+_Dicentra_ (_Fumariace�_), נ1. _G_, group of three stamens of the
+same, נ2. _H_, one of the inner petals, נ2. _I_, fruit of celandine
+poppy, _Stylophorum_ (_Papaverace�_), נ�. _J_, flower of mustard,
+_Brassica_ (_Crucifer�_), נ1. _K_, the same, with the petals removed,
+נ2. _L_, fruit of the same, נ1.]
+
+The second family, the fumitories (_Fumariace�_) 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 (_Crucifer�_) 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 (_Capparide�_), represented by
+only a few not common plants. The type of the order is _Capparis_,
+whose pickled flower-buds constitute capers.
+
+The fourth order (_Cistiflor�_) of the _Aphanocycl�_ 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 _Aphanocycl�_ (_Cistiflor�_). _A_,
+flower of wild blue violet, _Viola_ (_Violace�_), נ1. _B_, the lower
+petal prolonged behind into a sac or spur, נ1. _C_, the stamens, נ2.
+_D_, pistil, נ2. _E_, a leaf, נ�. _F_, section of the ovary, נ2.
+_G_, the fruit, נ1. _H_, the same after it has opened, נ1. _I_,
+diagram of the flower. _J_, flower of mignonette, _Reseda_
+(_Resedace�_), נ2. _K_, a petal, נ3. _L_, cross-section of the
+ovary, נ3. _M_, fruit, נ1. _N_, plant of sundew, _Drosera_
+(_Droserace�_), נ�. _O_, a leaf that has captured a mosquito, נ2.
+_P_, flower of another species (_D.�filiformis_), נ2. _Q_,
+cross-section of the ovary, נ4.]
+
+Among the commoner members of the order are the mignonettes
+(_Resedace�_) and the violets (_Violace�_), of which the various wild
+and cultivated species are familiar plants (Fig.�104, _A_, _M_). The
+sundews (_Droserace�_) 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 (_Dion�a_) 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 _Aphanocycl�_ (_Cistiflor�_). _A_,
+_B_, leaves of the pitcher-plant, _Sarracenia_ (_Sarraceniace�_). _A_,
+from the side; _B_, from in front, נ�. _C_, St.�John's-wort
+(_Hypericum_), נ�. _D_, a flower, נ1. _E_, the pistil, נ2. _G_,
+cross-section of the ovary, נ4. _H_, diagram of the flower.]
+
+Similar in their habits, but differing much in appearance from the
+sundews, are the pitcher-plants (_Sarraceniace�_), 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 (_Nepenthe�_) 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 (_Cistace�_), and the St.�John's-worts
+(_Hypericace�_). 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 _Aphanocycl�_ (the _Columnifer�_) has three
+families, of which two, the mallows (_Malvace�_), and the lindens
+(_Tiliace�_), 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 _Alth�a_ 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 _Tiliace�_ (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 _Aphanocycl�_ (_Columnifer�_). _A_,
+flower and leaf of the common mallow, _Malva_ (_Malvace�_), נ�. _B_,
+a flower bud, נ1. _C_, section of a flower, נ2. _D_, the fruit, נ2.
+_E_, section of one division of the fruit, with the enclosed seed,
+נ3. _em._ the embryo. _F_, diagram of the flower. _G_, leaf and
+inflorescence of the basswood, _Tilia_ (_Tiliace�_), נ1/3. _br._ a
+bract. _H_, a single flower, נ1. _I_, group of stamens, with
+petal-like appendage (_x_), נ2. _J_, diagram of the flower.]
+
+The fourth group of the _Choripetal�_ is the _Eucycl�_. 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 _Eucycl�_ (_Gruinales_). _A_, wild
+crane's-bill _Geranium_ (_Geraniace�_), נ�. _B_, a petal, נ1. _C_,
+the young fruit, the styles united in a column, נ�. _D_, the ripe
+fruit, the styles separating to discharge the seeds, נ�. _E_, section
+of a seed, נ2. _F_, wild flax. _Linum_ (_Linace�_), נ�. _G_, a
+single flower, נ2. _H_, cross-section of the young fruit, נ3. _I_,
+flower. _J_, leaf of wood-sorrel, _Oxalis_ (_Oxalide�_), נ1. _K_, the
+stamens and pistil, נ2. _L_, flower of jewel-weed, _Impatiens_
+(_Balsamine�_), נ1. _M_, the same, with the parts separated. _p_,
+petals. _s_, sepals. _an._ stamens. _gy._ pistil. _N_, fruit, נ1.
+_O_, the same, opening. _P_, a seed, נ2.]
+
+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 (_Trop�olum_) 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 (_Linace�_). 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
+(_Balsamine�_). 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.--_Eucycl�_ (_Terebinthin�_, _�sculin�_). _A_,
+leaves and flowers of sugar-maple, _Acer_ (_Acerace�_), נ�. _B_, a
+male flower, נ2. _C_, diagram of a perfect flower. _D_, fruit of the
+silver-maple, נ�. _E_, section across the seed, נ2. _F_, embryo
+removed from the seed, נ1. _G_, leaves and flowers of bladder-nut,
+_Staphylea_, (_Sapindace�_), נ�. _H_, section of a flower, נ2. _I_,
+diagram of the flower. _J_, flower of buckeye (_�sculus_), נ1�. _K_,
+flower of smoke-tree, _Rhus_ (_Anacardiace�_), נ3. _L_, the same, in
+section.]
+
+The second order (_Terebinthin�_) 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 _Eucycl�_, the _�sculin�_, embraces six
+families, of which three, the horsechestnuts, etc. (_Sapindace�_), the
+maples (_Acerace�_), and the milkworts (_Polygalace�_), have several
+representatives in the northern United States. Of the first the
+buckeye (_�sculus_) (Fig.�108, _J_) and the bladder-nut (_Staphylea_)
+(Fig.�108, _G_) are the commonest native genera, while the
+horsechestnut (_�sculus hippocastanum_) is everywhere planted.
+
+The various species of maple (_Acer_) are familiar examples of the
+_Acerace�_ (see Fig.�106, _A_, _F_).
+
+The fourth and last order of the _Eucycl�_, the _Frangulin�_, 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 _Celastrace�_; the holly and black alder, species of
+_Ilex_, are examples of the family _Aquifoliace�_; 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 (_Vitace�_ or _Ampelid�_), and the buckthorn (_Rhamnus_)
+is the type of the _Rhamnace�_.
+
+[Illustration: FIG.�109.--_Eucyl�_ (_Frangulin�_), _Tricocc�_. _A_,
+flowers of spindle-tree, _Euonymus_, (_Celastrace�_), נ1. _B_,
+cross-section of the ovary, נ2. _C_, diagram of the flower. _D_, leaf
+and fruit of bitter-sweet (_Celastrus_), נ�. _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,
+נ1. _G_, flower of grape-vine, _Vitis_ (_Vitace�_), נ2. The corolla
+has fallen off. _H_, vertical section of the pistil, נ2. _I_, nearly
+ripe fruits of the frost-grape, נ1. _J_, cross-section of young
+fruit, נ2. _K_, a spurge, _Euphorbia_ (_Euphorbiace�_), נ�. _L_,
+single group of flowers, surrounded by the corolla-like involucre,
+נ3. _M_, section of the same, [Male], male flowers; [Female], female
+flowers. _N_, a single male flower, נ5. _O_, cross-section of ovary,
+נ6. _P_, a seed, נ2. _Q_, longitudinal section of the seed, נ3.
+_em._ embryo.]
+
+The fifth group of the _Choripetal�_ is a small one, comprising but a
+single order (_Tricocc�_). 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 _Callitrichace�_, and the box (_Buxus_) is the
+type of the _Buxace�_.
+
+[Illustration: FIG.�110.--Types of _Calyciflor�_ (_Umbelliflor�_).
+_A_, inflorescence of wild parsnip, _Pastinaca_ (_Umbellifer�_), נ�.
+_B_, single flower of the same, נ3. _C_, a leaf, showing the
+sheathing base, נ�. _D_, a fruit, נ2. _E_, cross-section of _D_.
+_F_, part of the inflorescence of spikenard, _Aralia_ (_Araliace�_),
+נ1. _G_, a single flower of the same, נ3. _H_, the fruit, נ2. _I_,
+cross-section of the _H_. _J_, inflorescence of dogwood, _Cornus_
+(_Corne�_). The cluster of flowers is surrounded by four white bracts
+(_b_), נ1/3. _K_, a single flower of the same, נ2. _L_, diagram of the
+flower. _M_, young fruit of another species (_Cornus stolonifera_)
+(red osier), נ2. _N_, cross-section of _M_.]
+
+The last and highest group of the _Choripetal�_, the _Calyciflor�_,
+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 _Calyciflor�_ (_Umbelliflor�_) 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 _Umbellifer�_ 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 _Araliace�_, and the various
+species of dogwood (_Cornus_) (Fig.�110, _J-N_) represent the dogwood
+family (_Corne�_).
+
+The second order (_Saxifragin�_) 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 _Hydrange�_. 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 _Philadelphe�_, _Ribesie�_,
+and _Crassulace�_.
+
+[Illustration: FIG.�111.--_Calyciflor�_ (_Saxifragin�_): _A_, flowers
+and leaves of wild gooseberry, _Ribes_ (_Ribesie�_), נ1. _B_,
+vertical section of the flower, נ2. _C_, diagram of the flower. _D_,
+flower of bishop's-cap, _Mitella_ (_Saxifragace�_), נ3. _E_, flower
+of stonecrop, _Sedum_ (_Crassulace�_), נ2. _F_, flowers and leaves of
+hydrangea (_Hydrange�_), נ�. _n_, neutral flower. _G_, unopened
+flower, נ2. _H_, the same, after the petals have fallen away. _I_,
+flower of syringa, _Philadelphus_ (_Philadelphe�_), נ1. _J_, diagram
+of the flower.]
+
+The third order (_Opuntie�_) has but a single family, the cacti
+(_Cactace�_). 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.--_Calyciflor�_, _Opuntie�_ (_Passiflorin�_).
+_A_, flower of a cactus, _Mamillaria_ (_Cactace�_) (from "Gray's
+Structural Botany"). _B_, leaf and flower of a passion-flower,
+_Passiflora_ (_Passiflorace�_), נ�. _t_, a tendril. _C_,
+cross-section of the ovary, נ2. _D_, diagram of the flower.]
+
+The fourth order (_Passiflorin�_) 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 _Passiflorin�_ has been questioned.
+
+[13] Monoecious: having stamens and carpels in different flowers, but
+on the same plant.
+
+[Illustration: FIG.�113.--_Calyciflor�_ (_Myrtiflor�_, _Thymelin�_).
+_A_, flowering branch of moosewood, _Dirca_ (_Thymel�ace�_), נ1. _B_,
+a single flower, נ2. _C_, the same, laid open. _D_, a young flower of
+willow herb, _Epilobium_ (_Onagrace�_), נ1. The pistil (_gy._) is not
+yet ready for pollination. _E_, an older flower, with receptive
+pistil. _F_, an unopened bud, נ1. _G_, cross-section of the ovary,
+נ4. _H_, a young fruit, נ1. _I_, diagram of the flower. _J_,
+flowering branch of water milfoil, _Myriophyllum_ (_Haloragidace�_),
+נ�. _K_, a single leaf, נ1. _L_, female flowers of the same, נ2.
+_M_, the fruit, נ2.]
+
+The fifth order (_Myrtiflor�_) 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 _Myrtiflor�_, the majority belong to the two
+families _Onagrace�_ and _Lythrace�_. The former includes the evening
+primroses (_OEnothera_), willow-herb (_Epilobium_) (Fig.�113, _D_),
+and fuchsia; the latter, the purple loosestrife (_Lythrum_) and swamp
+loosestrife (_Nes�a_). The water-milfoil (_Myriophyllum_) (Fig.�113,
+_J_) is an example of the family _Haloragidace�_, and the _Rhexias_ of
+the eastern United States represent with us the family _Melastomace�_.
+
+The sixth order of the _Calyciflor�_ is a small one (_Thymelin�_),
+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
+(_Thymel�ace�_). Of the second family (_El�agnace�_), 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 (_Proteace�_) has no familiar representatives.
+
+The seventh order (_Rosiflor�_) includes many well-known plants, all
+of which may be united in one family (_Rosace�_), 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 _Spir�a_ (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.--_Calyciflor�_ (_Rosiflor�_). _A_,
+inflorescence of strawberry (_Fragaria_), נ�. _B_, a single flower,
+נ1. _C_, section of _B_. _D_, floral diagram. _E_, vertical section
+of a cherry-flower (_Prunus_), נ1. _F_, vertical section of the
+flower of _Spir�a_, נ2. _G_, vertical section of the bud of a wild
+rose (_Rosa_), נ1. _H_, vertical section of the young fruit, נ1.
+_I_, section of the flower of an apple (_Pyrus_), נ1. _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.--_Calyciflor�_ (_Leguminos�_). _A_, flowers
+and leaf of the common pea, _Pisum_ (_Papilionace�_), נ�. _t_,
+tendril. _st._ stipules. _B_, the petals, separated and displayed,
+נ1. _C_, flower, with the calyx and corolla removed, נ1. _D_, a
+fruit divided lengthwise, נ�. _E_, the embryo, with one of the
+cotyledons removed, נ2. _F_, diagram of the flower. _G_, flower of
+red-bud, _Cercis_ (_C�salpinace�_), נ2. _H_, the same, with calyx and
+corolla removed. _I_, inflorescence of the sensitive-brier,
+_Schrankia_ (_Mimosace�_), נ1. _J_, a single flower, נ2.]
+
+The last order of the _Calyciflor�_ and the highest of the
+_Choripetal�_ is the order _Leguminos�_, 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
+_Papilionace�_ (_papilio_, a butterfly). Many of the _Papilionace�_
+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 (_C�salpine�_), mainly tropical, the honey locust
+(_Gleditschia_) and red-bud (_Cercis_) (Fig.�115, _G_) are the
+commonest examples. The flowers differ mainly from the _Papilionace�_
+in being less perfectly papilionaceous, and the stamens are almost
+entirely distinct (Fig.�115, _H_). The last family (_Mimosace�_) 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 _Sympetal�_. The leaves of _Mimosa_ and
+_Schrankia_ are extraordinarily sensitive, folding up if irritated.
+
+
+
+
+CHAPTER XIX.
+
+CLASSIFICATION OF DICOTYLEDONS (_Continued_).
+
+
+DIVISION II.--_Sympetal�_.
+
+The _Sympetal�_ or _Gamopetal�_ are at once distinguished from the
+_Choripetal�_ by having the petals more or less united, so that the
+corolla is to some extent tubular. In the last order of the
+_Choripetal�_ we found a few examples (_Mimosace�_) where the same
+thing is true, and these form a transition from the _Choripetal�_ to
+the _Sympetal�_.
+
+There are two great divisions, _Isocarp�_ and _Anisocarp�_. 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 _Isocarp�_ there are usually
+twice as many stamens as petals, occasionally the same number.
+
+There are three orders of the _Isocarp�_, viz., _Bicornes_,
+_Primulin�_, and _Diospyrin�_. 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 (_Epacride�_) are
+represented in the United States. Of these the _Pyrolace�_ includes
+the pretty little pyrolas and prince's-pine (_Chimaphila_) (Fig.�116,
+_J_); the _Monotrope�_ 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
+_Rhodorace�_. The heath family (_Ericace�_), besides the true heaths
+(_Erica_, _Calluna_), includes the pretty trailing-arbutus or
+may-flower (_Epig�a_), _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 sympetal�_
+(_Bicornes_). _A_, flowers, fruit, and leaves of huckleberry,
+_Gaylussacia_ (_Vaccinie�_), נ1. _B_, vertical section of the flower,
+נ3. _C_, a stamen: i, from in front; ii, from the side, נ4. _D_,
+cross-section of the young fruit, נ2. _E_, flower of sorrel-tree,
+_Oxydendrum_ (_Ericace�_), נ2. _F_, flower of azalea (_Rhododendron_),
+נ�. _G_, cross-section of the ovary, נ3. _H_, diagram of the flower.
+_I_, flower of mountain laurel (_Kalmia_), נ1. _J_, prince's-pine,
+_Chimaphila_ (_Pyrolace�_), נ�. _K_, a single flower, נ1. _L_, plant
+of pine-sap, _Monotropa_, (_Monotrope�_), נ�. _M_, section of a
+flower, נ1.]
+
+The second order, the primroses (_Primulin�_), is principally
+represented in the cooler parts of the world by the true primrose
+family (_Primulace�_), 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 sympetal�_ (_Primulin�_,
+_Diospyrin�_). _A_, shooting-star, _Dodecatheon_ (_Primulace�_), נ�.
+_B_, section of a flower, נ1. _C_, diagram of the flower. _D_,
+Moneywort, _Lysimachia_ (_Primulace�_), נ�. _E_, a perfect flower of
+the persimmon, _Diospyros_ (_Ebenace�_), נ1. _F_, the same, laid open:
+section of the young fruit, נ2. _H_, longitudinal section of a ripe
+seed, נ1. _em._ the embryo. _I_, fruit, נ�.]
+
+The sea-rosemary (_Statice_) and one or two cultivated species of
+plumbago are the only members of the plumbago family (_Plumbagine�_)
+likely to be met with. The remaining families of the _Primulin�_ are
+not represented by any common plants.
+
+The third and last order of the _Isocarpous sympetal�_ has but a
+single common representative in the United States; viz., the persimmon
+(_Diospyros_) (Fig.�117, _E_). This belongs to the family _Ebenace�_,
+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 _Sympetal�_ (the _Anisocarp�_) 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 sympetal�_
+(_Tubiflor�_). _A_, flower and leaves of wild phlox (_Polemoniace�_),
+נ�. _B_, section of a flower, נ1. _C_, fruit, נ1. _D_, flower of
+blue valerian (_Polemonium_), נ1. _E_, flowers and leaf of
+water-leaf, _Hydrophyllum_ (_Hydrophyllace�_), נ�. _F_, section of a
+flower, נ1. _G_, flower of wild morning-glory, _Convolvulus_
+(_Convolvulace�_), נ�. 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, נ1. _J_, a seed, נ1.
+_K_, cross-section of a nearly ripe seed, showing the crumpled embryo,
+נ2. _L_, an embryo removed from a nearly ripe seed, and spread out;
+one of the cotyledons has been partially removed, נ1.]
+
+The first order (_Tubiflor�_) 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
+(_Convolvulace�_) 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 _Polemoniace�_.
+
+[Illustration: FIG.�119.--_Anisocarpous sympetal�_ (_Tubiflor�_). _A_,
+inflorescence of hound's-tongue, _Cynoglossum_ (_Borragine�_), נ�.
+_B_, section of a flower, נ2. _C_, nearly ripe fruit, נ1. _D_,
+flowering branch of nightshade, _Solanum_ (_Solane�_), נ�. _E_, a
+single flower, נ1. _F_, section of the flower, נ2. _G_, young fruit,
+נ1. _H_, flower of _Petunia_ (_Solane�_), נ�. _I_, diagram of the
+flower.]
+
+The third family (_Hydrophyllace�_) 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 (_Borragine�_) 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 (_Solane�_) 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 _Anisocarp�_ 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 (_Labiatiflor�_) 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 (_Labiat�_) and the figworts (_Scrophularine�_).
+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 sympetal�_ (_Labiatiflor�_).
+_A_, dead nettle, _Lamium_, (_Labiat�_), נ�. _B_, a single flower,
+נ1. _C_, the stamens and pistil, נ1. _D_, cross-section of the
+ovary, נ2. _E_, diagram of the flower; the position of the absent
+stamen is indicated by the small circle. _F_, fruit of the common
+sage, _Salvia_ (_Labiat�_), נ1. Part of the persistent calyx has been
+removed to show the four seed-like fruits, or nutlets. _G_, section of
+a nutlet, נ3. The embryo fills the seed completely. _H_, part of an
+inflorescence of figwort, _Scrophularia_ (_Scrophularine�_), נ1. _I_,
+cross-section of the young fruit, נ2. _J_, flower of speedwell,
+_Veronica_ (_Scrophularine�_), נ2. _K_, fruit of _Veronica_, נ2.
+_L_, cross-section of _K_. _M_, flower of moth-mullein, _Verbascum_
+(_Scrophularine�_), נ�. _N_, flower of toad-flax, _Linaria_
+(_Scrophularine�_), נ1. _O_, leaf of bladder-weed, _Utricularia_
+(_Lentibulariace�_), נ1. _x_, one of the "traps." _P_, a single trap,
+נ5.]
+
+The _Scrophularine�_ differ mainly from the _Labiat�_ 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 sympetal�_ (_Labiatiflor�_).
+_A_, flowering branch of trumpet-creeper, _Tecoma_ (_Bignoniace�_),
+נ�. _B_, a single flower, divided lengthwise, נ�. _C_, cross-section
+of the ovary, נ2. _D_, diagram of the flower. _E_, flower of vervain,
+_Verbena_ (_Verben�_), נ2: i, from the side; ii, from in front; iii,
+the corolla laid open. _F_, nearly ripe fruit of the same, נ2. _G_,
+part of a spike of flowers of the common plantain, _Plantago_
+(_Plantagine�_), נ1; 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,
+נ3.]
+
+The curious bladder-weed (_Utricularia_) is the type of the family
+_Lentibulariace�_, 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 _Gesnerace�_ 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 (_Bignoniace�_) 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 _Verbenace�_, 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 (_Plantagine�_),
+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 (_Contort�_) of the _Anisocarp�_ includes five
+families, all represented by familiar forms. The first, the olive
+family (_Oleace�_), 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
+_Gentianace�_ including the true gentians (_Gentiana_) (Fig.�122,
+_F_), the buck-bean (_Menyanthes_), the centauries (_Erythr�a_ and
+_Sabbatia_), and several other less familiar genera; _Loganiace�_,
+with the pink-root (_Spigelia_) (Fig.�122, _D_), as the best-known
+example; _Apocynace�_ including the dog-bane (_Apocynum_) (Fig.�122,
+_H_), and in the gardens the oleander and periwinkle (_Vinca_).
+
+[Illustration: FIG.�122.--_Anisocarpous sympetal�_ (_Contort�_). _A_,
+flower of fringe-tree, _Chionanthus_ (_Oleace�_), נ1. _B_, base of
+the flower, with part of the calyx and corolla removed, נ2. _C_,
+fruit of white ash, _Fraxinus_ (_Oleace�_), נ1. _D_, flower of
+pink-root, _Spigelia_ (_Loganiace�_), נ�. _E_, cross-section of the
+ovary, נ3. _F_, flower of fringed gentian, _Gentiana_ (_Gentianace�_),
+נ�. _G_, diagram of the flower. _H_, flowering branch of dog-bane,
+_Apocynum_ (_Apocynace�_), נ�. _I_, vertical section of a flower,
+נ2. _J_, bud. _K_, flower of milk-weed, _Asclepias_ (_Asclepiadace�_),
+נ1. _L_, vertical section through the upper part of the flower, נ2.
+_gy._ pistil. _p_, pollen masses. _an._ stamen. _M_, a pair of pollen
+masses, נ6. _N_, a nearly ripe seed, נ1.]
+
+The last family is the milk-weeds (_Asclepiadace�_), 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 sympetal�_ (_Campanulin�_).
+_A_, vertical section of the bud of American bell-flower, _Campanula_
+(_Campanulace�_), נ2. _B_, an expanded flower, נ1. The stamens have
+discharged their pollen, and the stigma has opened. _C_, cross-section
+of the ovary, נ3. _D_, flower of the Carpathian bell-flower
+(_Campanula Carpatica_), נ1. _E_, flower of cardinal-flower,
+_Lobelia_ (_Lobeliace�_), נ1. _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, נ2, showing the circle of hairs
+surrounding the stigma. _H_, cross-section of the ovary, נ3. _I_, tip
+of a branch of cucumber, _Cucurbita_ (_Cucurbitace�_), with an
+expanded female flower ([Female]). _J_, androecium of a male flower,
+showing the peculiar convoluted anthers (_an._), נ2. _K_,
+cross-section of the ovary, נ2.]
+
+The fourth order (_Campanulin�_) 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 _Campanulace�_, and numerous species are common, both wild and
+cultivated.
+
+[Illustration: FIG.�124.--_Anisocarpous sympetal�_ (_Aggregat�_). _A_,
+flowering branch of _Houstonia purpurea_, נ1 (_Rubiace�_). _B_,
+vertical section of a flower, נ2. _C_, fruit of bluets (_Houstonia
+coerulea_), נ1. _D_, cross-section of the same. _E_, bedstraw,
+_Galium_ (_Rubiace�_), נ�. _F_, a single flower, נ2. _G_, flower of
+arrow-wood, _Viburnum_ (_Caprifoliace�_), נ2. _H_, the same, divided
+vertically. _I_, flowering branch of trumpet honeysuckle, _Lonicera_
+(_Caprifoliace�_), נ�. _J_, a single flower, the upper part laid
+open, נ1. _K_, diagram of the flower. _L_, part of the inflorescence
+of valerian, _Valeriana_, (_Valeriane�_), נ1. _M_, young; _N_, older
+flower, נ2. _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_ (_Dipsace�_),
+נ�. _fl._ flowers. _Q_, a single flower, נ1. _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 _Lobeliace�_.
+Their milky juice contains more or less marked poisonous properties.
+The last family of the order is the gourd family (_Cucurbitace�_),
+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 sympetal�_ (_Aggregat�_).
+Types of _Composit�_. _A_, inflorescence of Canada thistle
+(_Cirsium_), נ1. _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, נ2. _o_, the ovary. _p_, the "pappus" (calyx
+lobes). _an._ the united anthers. _D_, the upper part of the stamens
+and pistil, נ3: i, from a young flower; ii, from an older one. _an._
+anthers. _gy._ pistil. _E_, ripe fruit, נ1. _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, נ2. _G_, a single flower
+from the disc, נ3. _H_, inflorescence of dandelion (_Taraxacum_), the
+flowers all alike, with strap-shaped corollas, נ1. _I_, a single
+flower, נ2. _c_, the split, strap-shaped corolla. _J_, two ripe
+fruits, still attached to the receptacle (_r_). The pappus is raised
+on a long stalk, נ1. _K_, a single fruit, נ2.]
+
+The last and highest order of the _Sympetal�_, and hence of the
+dicotyledons, is known as _Aggregat�_, 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 (_Calycere�_) has no members
+within our limits.
+
+The lower members of the order, _e.g._ various _Rubiace�_ (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
+_Dipsace�_ (Fig.�124, _P_) and _Composit�_ (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 _Composit�_
+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 _Aggregat�_ are the following: I.�_Rubiace�_ of
+which _Houstonia_ (Fig.�124, _A_), _Galium_ (_E_), _Cephalanthus_
+(button-bush), and _Mitchella_ (partridge-berry) are examples;
+II.�_Caprifoliace�_, containing the honeysuckles (_Lonicera_)
+(Fig.�124, _I_), _Viburnum_ (_G_), snowberry (_Symphoricarpus_), and
+elder (_Sambucus_); III.�_Valeriane�_, represented by the common
+valerian (_Valeriana_) (Fig.�124, _L_); IV.�_Dipsace�_, of which the
+teasel (_Dipsacus_) (Fig.�124, _P_), is the type, and also species of
+scabious (_Scabiosa_); V.�_Composit�_ to which the innumerable,
+so-called compound flowers, asters, golden-rods, daisies, sunflowers,
+etc. belong; VI.�_Calycere�_.
+
+[Illustration: FIG.�126.--_Aristolochiace�_. _A_, plant of wild ginger
+(_Asarum_), נ1/3. _B_, vertical section of the flower, נ1. _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 _Aristolochiace�_, 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 _Sympetal�_ 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, נ350.]
+
+  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, נ350. 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
+h�matoxylin, carmine, and various aniline colors, among which may be
+mentioned, besides gentian violet, safranine, Bismarck brown, methyl
+violet. H�matoxylin 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.
+
+H�matoxylin 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 alg� (exclusive of desmids, but including _Cyanophyce�_ and
+  _Volvocine�_).
+
+WOLLE. Fresh-water Alg� of the United States.--Bethlehem, Penn.
+
+Desmids. WOLLE. Desmids of the United States.--Bethlehem, Penn.
+
+The red and brown alg� are partially described in FARLOW'S New England
+  Alg�. Report of United States Fish Commission, 1879.--Washington.
+
+The _Charace�_ 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_, _-ace�_. 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."
+
+_�sculin�_, 199.
+
+_�sculus_. See "Buckeye," "Horse-chestnut."
+
+_Aggregat�_, 222.
+
+Alcohol, 5, 31, 55, 83, 230, 233.
+
+Alg�, 4, 21.
+  green, 21.
+  red, 21, 49.
+  brown, 21, 41.
+
+Alga-fungi. See "_Phycomycetes_."
+
+_Alisma_, _-ce�_. See "Water-plantain."
+
+_Allium_. See "Wild onion."
+
+Amaranth, 185.
+
+_Amarantus_, _-ace�_. See "Amaranth."
+
+_Amoeba_, 7; Fig.�2.
+
+_Ampelid�_. See "Vine."
+
+_Ampelopsis_. See "Virginia creeper."
+
+Anatomy, 3.
+  gross, Implements for study of, 3.
+  minute, Implements for study of, 3, 4.
+
+Anatropous, 151.
+
+_Andre�ace�_, 99, 100.
+
+Androecium, 148.
+
+_Andromeda_, 211.
+
+_Anemone_, 185.
+
+_Angiocarp�_, 84.
+
+Angiosperm, 129, 143, 145.
+
+Aniline colors, 233.
+
+_Anisocarp�_, 210, 213.
+
+_Anonace�_. See "Custard-apple."
+
+Anther, 148, 175, 179.
+
+Antheridium, 27, 36, 39, 45, 51, 59, 68, 89, 96, 106, 122.
+
+_Anthoceros_, _Anthocerote�_, 91; Fig.�57.
+
+_Aphanocycl�_, 185, 196.
+
+_Aplectrum_, 167; Fig.�90.
+
+_Apocynum_, _-ace�_. See "Dog-bane."
+
+_Apostasie�_, 164.
+
+Apple, 145, 171, 206; Fig.�114.
+
+Apricot, 207.
+
+_Aquilegia_. See "Columbine."
+
+_Aralia_, _-ace�_. See "Spikenard."
+
+Archegonium, 89, 97, 105, 122, 133, 140, 144.
+
+Archicarp, 138, 145.
+
+_Arcyria_, 13; Fig.�5.
+
+_Arethusa_, _Arethuse�_, 166; Fig.�90.
+
+_Argemone_, 191.
+
+Aril, 189.
+
+_Aris�ma_, 78, 157; Fig.�86.
+
+_Aristolochia_, _-ace�_, 224.
+
+Aroid, _Aroide�_, 157.
+
+Arrow-grass, 167.
+
+Arrowhead, 167; Fig.�91.
+
+Arrowroot, 163.
+
+_Asarum_. See "Wild ginger."
+
+_Asclepias_, _-dace�_. 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, _Balsamine�_, 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_, _-ide�_. See "Barberry."
+
+Bergamot oil, 234.
+
+Berry, 145, 156.
+
+_Betulace�_, 183.
+
+_Bicornes_, 210.
+
+_Bignonia_, _-ace�_, 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.
+
+_Borragine�_. 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.
+
+_Bromeliace�_, 156.
+
+Bryophyte, 86.
+
+Buck-bean, 218.
+
+Buckeye, 171, 199.
+
+Buckthorn, 199.
+
+Buckwheat, 184.
+
+Budding, 64.
+
+_Bulboch�te_, 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_, _Buxace�_. See "Box."
+
+
+Cabbage, 192.
+
+_Cabombe�_, 190.
+
+Cactus, _Cactace�_, 203; Fig.�112.
+
+_C�salpine�_, 210.
+
+Calcium, 2.
+
+Calla, 157, 229.
+
+_Callithamnion_, 50-52; Fig.�29.
+  general structure, 51.
+  tetraspores, 51.
+  procarp, 51.
+  antheridium, 51.
+  spores, 52.
+
+_Callitriche_, _-chace�_. See "Water starwort."
+
+_Calluna_. See "Heath."
+
+_Calopogon_, 166; Fig.�91.
+
+_Calycanthus_, _-ace�_, 187; Fig.�100.
+
+_Calycere�_, 223.
+
+_Calyciflor�_, 200.
+
+Calyx, 174, 182.
+
+Cambium, 137-138, 175.
+
+_Campanula_. See "Bell-flower."
+
+_Campanulace�_, 220.
+
+_Campanulin�_, 220.
+
+Canada balsam, 230-234.
+
+Canada thistle, 224; Fig.�125.
+
+_Canna_, _-ace�_, 162, 163; Fig.�88.
+
+Caper family, 194.
+
+_Capparis_, _-ide�_. See "Caper."
+
+_Caprifoliace�_, 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.
+
+_Caryophylle�_. 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_."
+
+_Celastrace�_, 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.
+
+_Centrosperm�_, 183.
+
+_Cephalanthus_. See "Button-bush."
+
+_Cerastium_. See "Chick-weed."
+
+_Ceratophyllum_. See "Horned pond-weed."
+
+_Cercis_. See "Red-bud."
+
+_Cham�rops_. See "Palmetto."
+
+_Chara_, 38-40; Fig.�23.
+  general structure, 38.
+  method of growth, 39.
+  cortex, 39.
+  non-sexual reproduction, 39.
+  o�gonium, 39.
+  antheridium, 39, 40.
+  spermatozoids, 40.
+  germination, 40.
+
+_Charace�_, 21, 37, 40.
+
+_Chare�_, 40.
+
+_Cheiranthus_. See "Wall-flower."
+
+_Chenopodium_, _-ace�_. 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."
+
+_Chlorophyce�_, 21.
+
+_Chondrus_. See "Irish moss."
+
+_Choripetal�_, 181, 208.
+
+Chromic acid, 25-35, 233.
+
+Chromoplast, 150.
+
+_Cicinnobulus_, 69; Fig.�39.
+
+Cilium, 8.
+
+Cinquefoil, 206.
+
+_Cistace�_. See "Rock-rose."
+
+_Cistiflor�_, 192.
+
+Citron, 196.
+
+_Citrus_. See "Orange," "Lemon."
+
+_Cladophora_, 24, 25.
+  structure of cells, 25.
+  nuclei, 25.
+  cell division, 25.
+  zo�spores, 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.
+
+_Coleoch�te_, 28; Fig.�17.
+
+Collateral fibro-vascular bundle, 135.
+
+_Collema_, 76; Fig.�44.
+
+Columella, 55.
+
+Columbine, 186; Fig.�99.
+
+Column, 165.
+
+_Columnifer�_, 195.
+
+_Commelyne�_, 157.
+
+_Composit�_, 223, 224.
+
+Compound flower, 224.
+  leaf, 159, 170.
+
+Conceptacle, 45.
+
+Cone, 131.
+
+_Conferva_, 26.
+
+_Confervace�_, 21, 24.
+
+Conidium, 68.
+
+Conifer, 129, 140, 141.
+
+_Conifer�_. See "Conifer."
+
+_Conjugat�_, 22-29.
+
+Connective, 148.
+
+_Conocephalus_. See "Liverwort, giant."
+
+_Contort�_, 218.
+
+_Convolvulace�_, 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_, _-ace�_. 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.
+
+_Crassulace�_, 203.
+
+Crane's-bill, 3, 196; Fig.�107.
+
+Cress, 192.
+
+_Croton_, 200.
+
+_Crucifer�_. See "Mustard family."
+
+_Cruciflor�_. See "_Rhoeadin�_."
+
+Cucumber, 221.
+
+Cucumber-tree. See "Magnolia."
+
+_Cucurbitace�_. See "Gourd."
+
+Cup fungi ("_Discomycetes_"), 71.
+
+_Cupulifer�_, 183.
+
+Curl, 66.
+
+Currant, 203.
+
+_Cuscuta_. See "Dodder."
+
+Custard-apple, 186.
+
+_Cyanophyce�_. See "Blue-green slime."
+
+_Cyathus_, 84; Fig.�50.
+
+_Cycad_, _-e�_, 140.
+
+_Cycas revoluta_, 141; Fig.�71.
+
+_Cyclamen_, 212.
+
+_Cynoglossum_. See "Hound's-tongue."
+
+_Cyperace�_. 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.
+  o�gonium, 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."
+
+_Diatomace�_, 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.
+
+_Dion�a_. See "Venus's fly-trap."
+
+_Dioscore�_. See "Yam."
+
+_Dioscorea villosa_, 154.
+
+_Diospyros_. See "Persimmon."
+
+_Diospyrin�_, 210.
+
+_Dipsacus_, _-ace�_. 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_ _-ace�_. See "Sun-dew."
+
+Drupe. See "Stone-fruit."
+
+Duck-weed, 159; Fig.�86.
+
+Dutchman's pipe. See "_Aristolochia_."
+
+
+Earth star. See "_Geaster_."
+
+_Ebenace�_ (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.
+
+_El�agnace�_, 206.
+
+Elm, 183.
+
+_Elodea_. See "Ditch-moss."
+
+Embryo, 90, 97, 107, 133, 149, 180.
+
+Embryology, 3.
+
+Embryo sac, 143, 144, 151.
+
+_Enantioblast�_, 153, 156; Fig.�85.
+
+Endosperm, 133, 146, 152.
+
+Entire leaves, 170.
+
+_Entomophthore�_, 57.
+
+_Epacride�_, 210.
+
+Epidermis, 91, 111, 112, 113, 122, 135, 137, 150, 177.
+
+_Epig�a_. See "Trailing arbutus."
+
+_Epilobium_. See "Willow-herb."
+
+_Epiphegus_. See "Beech-drops."
+
+Epiphyte, 166.
+
+_Equisetum_, _-tin�_. See "Horse-tail."
+
+Ergot, 76.
+
+_Erica_, _-ace�_. See "Heath."
+
+_Erysiphe_, 70.
+
+_Erythr�a_. 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.
+
+_Eucycl�_, 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."
+
+_Filicine�_. 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.
+
+_Frangulin�_, 199.
+
+_Fraxinus_. See "Ash."
+
+Fringe-tree, 218; Fig.�122.
+
+Fruit, 145.
+
+_Fucace�_, 43.
+
+Fuchsia, 201.
+
+_Fucus_, 42-46.
+  _vesiculosus_, 43; Figs. 26, 27.
+  general structure, 43, 44.
+  conceptacles, 44.
+  collecting plants, 44.
+  cells, 44.
+  chloroplasts, 44.
+  o�gonium, 45.
+  _platycarpus_, 45.
+  antheridium, 45, 46.
+  fertilization, 46.
+  germination, 46.
+
+_Fumariace�_. 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.
+
+_Gamopetal�_. See "_Sympetal�_."
+
+_Gaultheria_. See "Wintergreen."
+
+_Gaylussacia_. See "Huckleberry."
+
+_Geaster_, 84; Fig.�49.
+
+Gentian, 218; Fig.�122.
+
+Gentian violet, 4, 138, 231.
+
+_Gentiana_, _-ace�_. See "Gentian."
+
+_Geranium_, _-ace�_, 3, 171, 196; Fig.�107.
+
+_Gerardia_, 217.
+
+Germ cell. See "Egg cell."
+
+_Gesnerace�_, 218.
+
+Ghost flower. See "Indian-pipe."
+
+Gill, 83.
+
+Ginger, 163.
+
+_Gingko_, 142; Fig.�78.
+
+_Gleditschia_. See "Honey locust."
+
+_Gloxinia_, 218.
+
+_Glumace�_, 153, 160; Fig.�87.
+
+Glume, 162.
+
+Glycerine, 4, 51, 55, 59, 67, 83, 98, 224, 231, 233.
+
+_Gnetace�_. See "Joint fir."
+
+Golden-rod, 224.
+
+_Gonium_, 20.
+
+Gooseberry, 203; Fig.�111.
+
+Goose-foot, 184; Fig.�98.
+
+_Gossypium_. See "Cotton."
+
+Gourd, 221.
+
+_Gramine�_. 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_."
+
+_Gymnocarp�_, 84.
+
+Gymnosperm, 129, 141.
+
+_Gymnosporangium_, 79-81; Fig.�47.
+  cedar apples, 79.
+  spores, 80.
+
+_Gynandr�_, 153, 164.
+
+Gynoecium, 148, 167.
+
+Gynostemium. See "Column."
+
+
+_Habenaria_, 166, 227; Fig.�90.
+
+H�matoxylin, 233.
+
+Hair, 8, 177.
+
+_Haloragidace�_, 206.
+
+Hazel, 182, 183, 225; Fig.�97.
+
+Head, 181.
+
+Heath, 211.
+
+_Helobi�_, 153, 167.
+
+_Hemerocallis_. See "Day lily."
+
+_Hemi-angiocarp�_, 84.
+
+Hemlock, 142; Fig.�78.
+
+Hemp, 183.
+
+_Hepatic�_. 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_, _-ge�_, 202; Fig.�111.
+
+_Hydrocharide�_, 167.
+
+Hydrogen, 2, 95.
+
+_Hydropeltidin�_, 189.
+
+_Hydrophyllum_, _-ace�_. See "Water-leaf."
+
+_Hypericum_, _-ace�_. 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 "_Aris�ma_."
+
+Indusium, 118.
+
+Inflorescence, 157.
+
+Integument, 133, 144, 151, 180.
+
+Intercellular space, 124, 135, 150.
+
+Internode, 39.
+
+Iodine, 4, 22, 31.
+
+_Ipomoea_, 213.
+
+_Iridace�_, 156.
+
+Iris, 154, 156; Fig.�84.
+
+Irish moss, 49.
+
+_Isocarp�_, 210, 212.
+
+_Isoetes_. See "Quill-wort."
+
+_Iuliflor�_, 181.
+
+Ivy, 202.
+
+
+Jack-in-the-pulpit. See "_Aris�ma_."
+
+Jasmine, 218.
+
+_Jeffersonia_. See "Twin-leaf."
+
+Jewel-weed, 197; Fig.�107.
+
+Joint fir, 140, 142.
+
+_Juncagine�_, 167.
+
+_Juncus_. See "Rush."
+
+_Jungermanniace�_, 92; Fig.�57.
+
+
+_Kalmia_. See "Mountain laurel."
+
+Karyokinesis, 233.
+
+Keel, 208.
+
+Kelp. See "_Laminaria_."
+  giant. See "_Macrocystis_."
+
+Knotgrass. See "_Polygonum_."
+
+
+Labellum. See "Lip."
+
+_Labiat�_. See "Mint."
+
+_Labiatiflor�_, 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.
+
+_Laurine�_. See "Laurel."
+
+Lavender, 215.
+
+Leaf-green. See "Chlorophyll."
+
+Leaf tendril, 171.
+
+Leaf thorn, 172.
+
+_Leguminos�_, 207.
+
+_Lemanea_, 53; Fig.�31.
+
+_Lemna_. See "Duck-weed."
+
+Lemon, 198.
+
+_Lentibulariace�_, 217.
+
+Lettuce, 223.
+
+_Lichenes_, 73; Figs. 44, 45.
+
+Ligula, 127.
+
+_Ligulat�_, 125.
+
+Lilac, 170, 181, 218.
+
+_Liliace�_, 155.
+
+_Liliiflor�_, 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_, _-ace�_. See "Flax."
+
+Lip, 165.
+
+_Liriodendron_. See "Tulip-tree."
+
+_Lithospermum_. See "Puccoon."
+
+Liverwort, 86.
+  classification of, 91.
+  horned. See "_Anthocerote�_."
+  giant, 91; Fig.�57.
+
+Lizard-tail, 181, 183; Fig.�97.
+
+_Lobelia_, _-ace�_. 221; Fig.�123.
+
+_Loganie�_, 219.
+
+_Lonicera_. See "Honeysuckle."
+
+Loosestrife. See "_Lythrum_."
+  swamp. See "Nes�a."
+
+Lotus. See "_Nelumbo_."
+
+_Lychnis_, 185.
+
+_Lycoperdon_, 84; Fig.�49.
+
+_Lycopersicum_. See "Tomato."
+
+_Lycopodiace�_. See "Ground pine."
+
+_Lycopodin�_. 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_, _-ace�_, 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_, _-ace�_, 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_, _-ace�_. See "Mallow."
+
+_Mamillaria_, Fig.�112.
+
+Mandrake. See "May-apple."
+
+Maple, 199; Fig.�108.
+
+_Maranta_. See "Arrowroot."
+
+_Marattiace�_. See "Ringless ferns."
+
+_Marchantia_, 91; Fig.�57.
+  breathing-pores, 91.
+  sexual organs, 91.
+  buds, 91.
+
+_Marchantiace�_, 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.
+
+_Melastomace�_, 206.
+
+Melon, 221.
+
+_Menispermum_, _-e�_. 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_," "_Perisporiace�_."
+
+Milk-weed, 220; Fig.�122.
+
+Milkwort, 199.
+
+_Mimosa_. See "Sensitive-plant."
+
+_Mimosace�_, 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."
+
+_Monotrope�_, 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 "_Bryace�_."
+  peat. See "_Sphagnace�_."
+
+Moth, 229.
+
+Mould, black. See "_Mucorini_."
+  blue. See "_Penicillium_."
+  herbarium. See "_Eurotium_."
+  insect. See "_Entomophthore�_."
+  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_, _-ace�_. See "Banana."
+
+_Musci_. See "True mosses."
+
+Mushroom, 82.
+
+Mustard, 192.
+
+_Mycomycetes_. See "True fungi."
+
+_Myosotis_. See "Forget-me-not."
+
+_Myristica_, _-ine�_. See "Nutmeg."
+
+_Myrtiflor�_, 205.
+
+Myrtle, 205, 206.
+
+_Myrtus_. See "Myrtle."
+
+_Myxomycetes_. See "Slime-mould."
+
+
+_Naias_. See "Pond-weed."
+
+_Naiade�_, 159.
+
+Narcissus, 146.
+
+Nasturtium, 197, 227.
+
+_Navicula_, 42; Fig.�24.
+
+Nectar, 225.
+
+Nectary, 186.
+
+Nelumbo, 189, 190; Fig.�101.
+
+_Nelumbie�_, 190.
+
+_Nemophila_, 214.
+
+_Nepenthes_, _-e�_. See "Pitcher plant."
+
+_Nes�a_, 206.
+
+Nettle. See "_Urticin�_."
+
+_Nicotiana_. See "Tobacco."
+
+Night-blooming cereus, 204.
+
+Nightshade, 215; Fig.�119.
+
+_Nitella_, 40.
+
+_Nitelle�_, 40.
+
+Node, 39.
+
+Nucleus, 7, 31, 231.
+
+Nuclear division, 7, 31, 231; Figs. 127, 128.
+
+Nucleolus, 7, 231.
+
+Nutmeg, 188.
+
+_Nyctagine�_, 183.
+
+_Nymph�a_, 189; Fig.�101.
+
+_Nymph�ace�_, 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.
+
+_Oleace�_. See "Olive."
+
+Oleander, 219.
+
+Olive, 218.
+
+_Onagrace�_, 206.
+
+_Onoclea_, 104; Fig.�70.
+
+O�gonium, 27, 36, 39, 45, 59, 62.
+
+O�phyte, 109.
+
+Opium--opium poppy, 191.
+
+_Ophioglosse�_. See "Adder-tongue."
+
+_Ophioglossum_, 116.
+
+_Opuntia_. See "Prickly pear."
+
+_Opuntie�_, 203.
+
+Orange, 198.
+
+Orchid, 164, 166, 227; Figs. 89, 90.
+
+_Orchide�_, 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.
+
+_Palm�_. See "Palm."
+
+Palmate, 171.
+
+Palmetto, 159.
+
+_Pandane�_, 159.
+
+_Papaverace�_. See "Poppy."
+
+Papaw, 186; Fig.�100.
+
+_Papilionace�_, 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."
+
+_Passiflorin�_, 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.
+
+_Perisporiace�_, 66.
+
+Periwinkle, 219.
+
+_Peronospora_, 60; Fig.�35.
+
+_Peronospore�_, 57.
+
+Persimmon, 212; Fig.�117.
+
+Petal, 148, 174, 179.
+
+Petiole, 173.
+
+Petunia, 215; Fig.�119.
+
+_Peziza_, 73; Fig.�43.
+
+_Phacelia_, 214.
+
+_Ph�ophyce�_. See "Brown alg�."
+
+Ph�nogam. See "Spermaphyte."
+
+_Phascum_, _-ace�_, 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_, _-ace�_. 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."
+
+_Piperine�_, 183.
+
+Pistil, 143, 145, 174.
+
+Pitcher-plant, 194, 195; Fig.�105.
+
+Pith, 130, 174, 177.
+
+Placenta, 148, 179.
+
+Plane, 183.
+
+_Plantago_, _-ine�_. See "Plantain."
+
+Plantain, 223, 225; Fig.�121.
+
+Plasmodium, 12.
+
+_Platane�_. See "Plane."
+
+_Platanus_. See "Sycamore."
+
+Plerome, 176.
+
+Plum, 207.
+
+_Plumbago_, _-ine�_, 212.
+
+Pod, 156.
+
+_Podophyllum_. See "May-apple."
+
+_Podosph�ra_, 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_, _-ace�_, 214; Fig.�118.
+
+Pollinium, 165.
+
+_Polycarp�_, 185.
+
+_Polygala_, _-ace�_. See "Milkwort."
+
+_Polygonatum_. See "Solomon's Seal."
+
+_Polygonum_, _-ace�_, 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_, _-ace�_. 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_, _-ace�_. See "Primrose."
+
+Prince's-pine, 210; Fig.�116.
+
+Procarp, 51.
+
+_Proteace�_, 205.
+
+Prothallium, 102, 103, 114, 122, 125, 133, 144, 177.
+
+_Protococcus_, _-ace�_, 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_, _-ace�_, 210.
+
+
+Quince, 170.
+
+Quill-wort, 125, 126; Fig.�74.
+
+
+Raceme, 174.
+
+Radial fibro-vascular bundles, 138, 176.
+
+Radish, 192.
+
+_Ranunculus_, _-ace�_. See "Buttercup."
+
+Raspberry, 207.
+
+Ray-flower, 223.
+
+Receptacle, 167, 207, 223.
+
+Receptive spot, 106.
+
+Red alg�, 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_, _-ace�_. See "Mignonette."
+
+Resin, 130.
+
+Resin-duct, 130, 135, 137.
+
+Resting-spore, 28, 32, 37, 57.
+
+Rheumatism-root. See "Twin-leaf."
+
+_Rhexia_, 206.
+
+_Rhizocarpe�_. See "Water-fern."
+
+Rhizoid. See "Root-hair."
+
+Rhizome. See "Root-stock."
+
+_Rhododendron_, 210; Fig.�116.
+
+_Rhodophyce�_. See "Red alg�."
+
+_Rhodorace�_, 211.
+
+_Rhoeadin�_, 190.
+
+_Rhus_. See "Sumach."
+  _cotinus_. See "Smoke-tree."
+  _toxicodendron_. See "Poison-ivy."
+  _venenata_. See "Poison-dogwood."
+
+_Ribes_, _-ie�_, 203; Fig.�111.
+
+_Ricciace�_, 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_, _-ace�_. See "Rose."
+
+Rose, 181, 206; Fig.�114.
+
+_Rosiflor�_, 206.
+
+_Rubiace�_, 223.
+
+Rush, 154, 225; Fig.�83.
+
+Rust, white. See "_Cystopus_."
+  red. See "_Uredine�_."
+  black. See "_Uredine�_."
+
+
+_Sabal_. See "Palmetto."
+
+_Sabbatia_. See "Centaury."
+
+_Saccharomycetes_. See "Yeast."
+
+Sac fungi. See "_Ascomycetes_."
+
+Safranine, 233.
+
+Sage, 215; Fig.�120.
+
+_Salicine�_, 183.
+
+_Salix_. See "Willow."
+
+_Salvinia_, 118.
+
+_Sambucus_. See "Elder."
+
+_Sanguinaria_. See "Blood-root."
+
+_Sapindace�_, 199.
+
+_Saprolegnia_, _-ace�_, 60-62; Fig.�36.
+  zo�spores, 62.
+  resting spores, 62.
+  antheridium, 62.
+
+_Sargassum_, 48; Fig.�28.
+
+_Sarracenia_, _-ace�_. See "Pitcher-plant."
+
+Sassafras, 188.
+
+_Saururus_. See "Lizard-tail."
+
+Saxifrage, 202.
+
+_Saxifragin�_, 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."
+
+_Scitamine�_, 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_, _-ine�_. See "Figwort."
+
+Sea-lettuce, 26; Fig.�15.
+
+Sea-rosemary, 212.
+
+Sea-weed (brown). See "Brown alg�."
+  (red). See "Red alg�."
+
+Sedge, 161; Fig.�87.
+
+_Sedum_. See "Stonecrop."
+
+Seed, 128, 133, 145, 150.
+
+Seed-plant. See "Spermaphyte."
+
+_Selaginella_, _-e�_. 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.
+
+_Siphone�_, 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_."
+
+_Smilace�_, 155.
+
+Smoke-tree, 198.
+
+Smut, 64, 65.
+
+Smut-corn. See "_Ustillago_."
+
+Snowberry, 223.
+
+Soft-tissue, 112.
+
+_Solanum_, _-e�_, 215.
+
+Solomon's Seal, 154; Fig.�83.
+
+Soredium, 74.
+
+Sorus, 118.
+
+_Spadiciflor�_, 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_, _-ace�_, 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 "_Charace�_."
+
+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.
+
+_Sympetal�_, 210.
+
+_Symphoricarpus_. See "Snowberry."
+
+_Symplocarpus_. See "Skunk-cabbage."
+
+Synergid�, 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.
+
+_Terebinthin�_, 198.
+
+Tetraspore, 51, 52.
+
+Thistle, 173, 223; Fig.�125.
+
+Thorn, 172.
+
+Thyme, 215.
+
+_Thymeleace�_, 206.
+
+_Thymelin�_, 206.
+
+_Tilia_, _-ace�_. 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.
+
+_Tricocc�_, 199.
+
+_Triglochin_. See "Arrow-grass."
+
+_Trillium_, 146, 154, 155; Fig.�83.
+
+_Triphragmium_, 81.
+
+_Trop�olum_. See "Nasturtium."
+
+Trumpet-creeper.
+
+Tuber, 120, 153, 172.
+
+_Tubiflor�_, 213.
+
+Tulip, 146.
+
+Tulip-tree, 187; Fig.�100.
+
+Turnip, 192.
+
+Twin-leaf, 187; Fig.�101.
+
+_Typha_, _-ace�_. See "Cat-tail."
+
+
+_Ulmace�_. See "Elm."
+
+_Ulva_. See "Sea-lettuce."
+
+_Umbellifer�_. See "Umbel-wort."
+
+Umbel-wort, 202.
+
+_Umbelliflor�_, 202.
+
+_Uredine�_, 77.
+
+_Uromyces_, 81; Fig.�47.
+
+_Urticin�_, 183.
+
+_Usnea_, 75; Fig.�45.
+
+_Ustillagine�_. See "Smut."
+
+_Ustillago_, 65; Fig.�38.
+
+_Utricularia_. See "Bladder-weed."
+
+_Uvularia_. See "Bellwort."
+
+
+_Vaccinium_. See "Cranberry."
+
+Vacuole, 8.
+
+Valerian, 224; Fig.�124.
+
+_Valeriana_, _-e�_. 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_, _-ace�_, 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_, _-ace�_. See "Violet."
+
+Virginia creeper, 171, 199.
+
+_Vitis_. See "Grape."
+
+_Vitace�_. See "Vine."
+
+_Volvox_, 12, 20; Fig.�10.
+
+_Volvocine�_, 12, 19.
+
+
+Wall-flower, 192.
+
+Walnut, 183.
+
+Wandering-Jew, 157.
+
+Water fern, 117.
+
+Water-leaf, 214; Fig.�118.
+
+Water-lily. See "_Nymph�a_," "_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_, _-ace�_. See "Ginger."
+
+Zo�logy, 2.
+
+Zo�spore, 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
+
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+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  |
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+  | UTF-8 text and HTML versions of this eBook.                  |
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+  +--------------------------------------------------------------+
+
+
+
+                               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 ***
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