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TWENTIETH CENTURY TEXT-BOOKS

EDITED BY

A. F. NIGHTINGALE, PH. D.

SUPERINTENDENT OF HIGH SCHOOLS, CHICAGO
AND

CHARLES H. THURBER, A. M.

ASSOCIATE PROFESSOR OF PEDAGOGY IN THE UNIVERSITY
OF CHICAGO

' • '

TWENTIETH CENTURY TEXT-BOOKS

PLANT STRUCTURES

A SECOND BOOK OF BOTANY

JOHN M. COULTER, A.M., PH.D.

HEAD OF DEPARTMENT OF BOTANY
UNIVERSITY OF CHICAGO

NEW YORK
D. APPLETON AND COMPANY

1900

PREFACE

IN the preface to Plant Relations the author gave his
reasons for suggesting that the ecological standpoint is best
adapted for the first contact with plants. It may be, how-
ever, that many teachers will prefer to begin with the mor-
phological standpoint, as given in the present book. Rec-
ognizing this fact, Plant Structures has been made an
independent volume that may precede or follow the other,
or may provide a brief course of botanical study in itself.

Although in the present volume Morphology is the domi-
nant subject, it seems wise to give a somewhat general view
of plants, and therefore Physiology, Ecology, and Taxonomy
are included in a general way. For fear that Physiology
and Ecology may be lost sight of as distinct subjects, and
to introduce important topics not included in the body of
the work, short chapters are devoted to them, which seek
to bring together the main facts, and to call attention to
the larger fields.

This book is not a laboratory guide, but is for reading
and study in connection with laboratory work. An accom-
panying pamphlet for teachers gives helpful suggestions
to those who are not already familiar with its scope and
purpose. It is not expected that all the forms and sub-
jects presented in the text can be included in the labora-
tory exercises, but it is believed that the book will prove a
useful companion in connection with such exercises. It
is very necessary to co-ordinate the results of laboratory
work, to refer to a larger range of material than can be
handled, and to develop some philosophical conception of

yi PREFACE

the plant kingdom. The learning of methods and the
collection of facts are fundamental processes, but they
must be supplemented by information and ideas to be of
most service.

The author does not believe in the use of technical
terms unless absolutely necessary, for they lead frequently
to mistaking definitions of words for knowledge of things.
But it is necessary to introduce the student not merely to
the main facts but also to the literature of botany. Ac-
cordingly, the most commonly used technical terms are
introduced, often two or three for the same thing, but it
is hoped that familiarity with them will enable the student
to read any ordinary botanical text. Care has been taken
to give definitions and derivations, and to call repeated
attention to synonymous terms, so that there may be no
confusion. The chaotic state of morphological terminology
tempted the author to formulate or accept some consistent
scheme of terms ; but it was felt that this would impose
upon the student too great difficulty in reading far more
important current texts.

Chapters I-XII form a connected whole, presenting the
general story of the evolution of plants from the lowest to
the highest. The remaining chapters are supplementary,
and can be used as time or inclination permits, but it is the
judgment of the author that they should be included if
possible. The flower is so conspicuous and important a
feature in connection with the highest plants, that Chapter
XIII seems to be a fitting sequel to the preceding chapters.
It also seems desirable to develop some knowledge of the
great Angiosperm families, as presented in Chapter XIV,
since they are the most conspicuous members of every flora.
In this connection, the author has been in the habit of
directing the examination of characteristic flowers, and of
teaching the use of ordinary taxonomic manuals. Chap-
ter XV deals with anatomical matters, but the structures
included are so bound up with the form and work of plants

rKK,rA\ i'-. Yii

that it seems important to find a place for them even in an
elementary work. The reason for Chapters XVI and XVII
has been stated already, and even if Plant Relations is stud-
ied, Chapter XVII will be useful either as a review or as an
introduction. In the chapter on Plant Physiology the
author has been guided by Xoll's excellent resume in the
"Strasburger " Botany.

The illustrations have been entirely in the charge of
Dr. Otis W. Caldwell, who for several years has conducted
in the University, and in a most efficient way, such labo-
ratory work as this volume implies. Many original illus-
trations have been prepared by Dr. Caldwell and his assist-
ants, and some are credited to Dr. Chamberlain and Dr.
Cowles, of the University, but it is a matter of regret that
pressure of work and time limitation have forbidden a still
greater number. The authors of the original illustrations
are cited, and where illustrations have been obtained else-
where the sources are indicated. The descriptions given
in connection with each illustration are unusually full,
and should be studied carefully, as frequently they contain
important material not included in the text.

The author would again call attention to the fact that
this book is merely intended to serve as a compact supple-
ment to three far more important factors : the teacher, the
laboratory, and field work. Without these it can not serve
its purpose.

JOHX M. COULTER.

THE UXIVKKSITY OF CHICAGO. ^Yocember, 1899.

CONTENTS

CHAPTER PAGE

I. — INTRODUCTION . . 1

II. — THALLOPHYTES : AL.GJE 4

III. — THE EVOLUTION OF SEX 12

IV. — THE GREAT GROUPS OF ALG^E ... . . 17

V. — THALLOPHYTES: FUNGI 48

VI. — THE FOOD OF PLANTS 83

VII. — BRYOPHYTES . . .93

VIII. — THE GREAT GROUPS OF BRYOPHYTES 109

IX. — PTERIDOPHYTES 128

X. — THE GREAT GROUPS OF PTERIDOPHYTES .... 155

XI. — SPERMATOPHYTES : GYMNOSPERMS 171

XII. — SPERMATOPHYTES : ANGIOSPERMS 195

XIIL— THE FLOWER 218

XIV.— MONOCOTYLEDONS AND DICOTYLEDONS 232

XV. — DIFFERENTIATION OF TISSUES 280

XVI. — PLANT PHYSIOLOGY 297

XVII. — PLANT ECOLOGY . . . 311

GLOSSARY . 329

INDEX ' . 337

BOTANY

PART II.— PLANT STRUCTURES

CHAPTER I

INTRODUCTION

1. Differences in structure,— It is evident, even to the
casual observer, that plants differ very much in structure.
They differ not merely in form and size, but also in com-
plexity. Some plants are simple, others are complex, and
the former are regarded as of lower rank.

Beginning with the simplest plants — that is, those of
lowest rank — one can pass by almost insensible grada-
tions to those of highest rank. At certain points -in this
advance notable interruptions of the continuity are dis-
covered, structures, and hence certain habits of work, chang-
ing decidedly, and these breaks enable one to organize the
vast array of plants into groups. Some of the breaks ap-
pear to be more important than others, and opinions may
differ as to those of chief importance, but it is customary
to select three of them as indicating the division of the
plant kingdom into four great groups.

2. The great groups. — The four great groups may be
indicated here, but it must be remembered that their names
mean nothing until plants representing them have been
studied. It Avill be noticed that all the names have the

2 PLANT STRUCTURES

constant termination phytes, which is a Greek word mean-
ing " plants." The prefix in each case is also a Greek word
intended to indicate the kind of plants.

(1) Thallophytes. — The name means "thallus plants,"
but just what a "thallus" is can not well be explained
until some of the plants have been examined. In this
great group are included some of the simplest forms,
known as Algcv and Fungi, the former represented by green
thready growths in fresh water and the great host of sea-
weeds, the latter by moulds, mushrooms, etc.

(2) Bryophytes. — The name means " moss plants," and
suggests very definitely the forms which are included.
Every one knows mosses in a general way, but associated
with them in this great group are the allied liverworts,
which are very common but not so generally known.

(3) Pteridophytes. — The name means " fern plants," and
ferns are well known. Xot all Pteridophytes, however, are
ferns, for associated with them are the horsetails (scouring
rushes) and the club mosses.

(4) Spermatophytes. — The name means " seed plants "-
that is, those plants which produce seeds. In a general
way these are the most familiar plants, and are commonly
spoken of as " flowering plants." They are the highest in
rank and the most conspicuous, and hence have received
much attention. In former times the study of botany in
the schools was restricted to the examination of this one
group, to the entire neglect of the other three great groups.

3. Increasing complexity. — At the very outset it is well
to remember that the Thallophytes contain the simplest
plants — those whose bodies have developed no organs for
special work, and that as one advances through higher
Thallophytes, Bryophytes, and Pteridophytes, there is a con-
stant increase, in the complexity of the plant body, until in
the Spermatophytes it becomes most highly organized, with
numerous structures set apart for special work, just as in the
highest animals limbs, eyes, ears, bones, muscles, nerves, etc.,

INTRODUCTION 3

are set apart for special work. The increasing complexity
is usually spoken of as differentiation — that is, the setting
apart of structures for different kinds of work. Hence the
Bryophytes are said to be more highly differentiated than
the Thallophytes, and the Spermatophytes are regarded as
the most highly differentiated group of plants.

4. Nutrition and reproduction. — However variable plants
may be in complexity, they all do the same general kind of
work. Increasing complexity simply means an attempt to
do this work more effectively. It is plant work that makes
plant structures significant, and hence in this book no at-
tempt will be made to separate them. All the work of
plants may be put under two heads, nutrition and repro-
duction^ the former including all- those processes by which
a plant maintains itself, the latter those processes by which
it produces new plants. In the lowest plants, these two
great kinds of work, or functions, as they are called, are
not set apart in different regions of the body, but usually
the first step toward differentiation is to set apart the re-
productive function from the nutritive, and to develop
special reproductive organs which are entirely distinct from
the general nutritive body.

5. The evolution of plants. — It is generally supposed that
the more complex plants have descended from the simpler
ones ; that the Bryophytes have been derived from the Thallo-
phytes, and so on. All the groups, therefore, are supposed
to be related among themselves in some way, and it is one
of the great problems of botany to discover these relation-
ships. This theory of the relationship of plant groups is
known as the theory of descent, or more generally as evo-
lution. To understand any higher group one must study
the lower ones related to it, and therefore the attempt of
this book will be to trace the evolution of the plant king-
dom, by beginning with the simplest forms and noting the
gradual increase in complexity until the highest forms are
reached,

CHAPTER II

THALLOPHYTES :

6. General characters. — Thallophytes are the simplest of
plants, often so small as to escape general observation, but
sometimes with large bodies. They occur everywhere in
large numbers, and are of special interest as representing
the beginnings of the plant kingdom. In this group also
there are organized all of the principal activities of plants,
so that a study of Thallophytes furnishes a clew to the
structures and functions of the higher, more complex
groups.

The word " thallus " refers to the nutritive body, or
vegetative body, as it is often called. This body does not
differentiate special nutritive organs, such as the leaves and
roots of higher plants, but all of its regions are alike. Its
natural position also is not erect, but prone. AVhile most
Thallophytes have thallus bodies, in some of them, as in
certain marine forms, the nutritive body differentiates into
regions which resemble leaves, stems, and roots ; also cer-
tain Bryophytes have thallus bodies. The thallus body,
therefore^ is not always a distinctive mark of Thallophytes,
but must be supplemented by other characters to determine
the group.

7. Algae and Fungi,— It is convenient to separate Thallo-
phytes into two great divisions, known as AlycB and Fuiiyi.
It should be known that this is a very general division and
not a technical one, for there are groups of Thallophytes
which can not be regarded as strictly either Algae or Fungi,
but for the present these groups may be included,

THALLOPHYTES: ALG.fi 5

The great distinction between these two divisions of
Thallophytes is that the Algae contain chlorophyll and the
Fungi do not. Chlorophyll is the characteristic green color-
ing matter found in plants, the word meaning " leaf green."
It may be thought that to use this coloring material as the
basis of such an important division is somewhat superficial,
but it should be known that the presence of chlorophyll gives
a peculiar power — one which affects the whole structure
of the nutritive body and the habit of life. The presence
of chlorophyll means that the plant can make its own food,
can live independent of other plants and animals. Algae,
therefore, are the independent Thallophytes, so far as their
food is concerned, for they can manufacture it out of the
inorganic materials about them.

The Fungi, on the other hand, contain no chlorophyll,
can not manufacture food from inorganic material, and
hence must obtain it already manufactured by plants or
animals. In this sense they are dependent upon other or-
ganisms, and this dependence has led to great changes in
structure and habit of life.

It is supposed that Fungi have descended from Algae —
that is, that they were once Algae, which gradually acquired
the habit of obtaining food already manufactured, lost their
chlorophyll, and became absolutely dependent and more or
less modified in structure. Fungi may be regarded, there-
fore, as reduced relatives of the Algae, of equal rank so far
as birth and structure go, but of very different habits.

ALG^E

8. General characters. —As already defined, Algae are
Thallophytes which contain chlorophyll, and are therefore
able to manufacture food from inorganic material. They
are known in general as " seaweeds," although there are
fresh-water forms as well as marine. They are exceedingly
variable in size, ranging from forms visible only by means
19

Q PLANT STRUCTURES

of the compound microscope to marine forms with enor-
mously bulky bodies. In general they are hydrophytes — that
is, plants adapted to life in water or in very moist places.
The special interest connected with the group is that it is
supposed to be the ancestral group of the plant kingdom —
the one from which the higher groups have been more or
less directly derived. In this regard they differ from the
Fungi, which are not supposed to be responsible for any
higher groups.

9. The subdivisions. — Although all the Algae contain
chlorophyll, some of them do not appear green. In some
of them another coloring matter is associated with the chlo-
rophyll and may mask it entirely. Advantage is taken of
these color associations to separate Algae into subdivisions.
As these colors are accompanied by constant differences in
structure and work, the distinction on the basis of colors is
more real than it might appear. Upon this basis four sub-
divisions may be made. The constant termination phycece,
which appears in the names, is a Greek word meaning " sea-
weed," which is the common name for Algae ; while the pre-
fix in each case is the Greek name for the color which char-
acterizes the group.

The four subdivisions are as follows : (1) Cyanophycecz,
or " Blue Algae," but usually called " Blue-green Algae," as the
characteristic blue does not entirely mask the green, and
the general tint is bluish-green ; (2) Chlorophycece, or " Green
Algae," in which there is no special coloring matter associ-
ated with the chlorophyll ; (3) Phceophycece, or " Brown
Algae " ; and (4) Rhodophycece, or " Eed Algae."

It should be remarked that probably the Cyanophyceae
do not belong with the other groups, but it is convenient to
present them in this connection.

10. The plant body. — By this phrase is meant the nutri-
tive or vegetative body. There is in plants a unit of struc-
ture known as the cell. The bodies of the simplest plants
consist of but one cell, while the bodies of the most com-

THALLOPHYTES : ALG^E

B-
C

plex plants consist of very many cells. It is necessary to
know something of the ordinary living plant cell before the
bodies of Algae or any other plant bodies can .be under-
stood.

Such a cell if free is approximately spherical in outline,
(Fig. 6), but if pressed upon by contiguous cells may become
variously modified in form
(Fig. 1). Bounding it there
is a thin, elastic wall, com-
posed of a substance called
cellulose. The cell wall,
therefore, forms a delicate
sac, which contains the liv-
ing substance known ^pro-
toplasm. This is the sub-
stance which manifests life,
and is the only substance
in the plant which is alive.
It is the protoplasm which
has organized the cellulose
wall about itself, and which
does all the plant work. It
is a fluid substance which
varies much in its consistence, sometimes being a thin vis-
cous fluid, like the white of an egg, sometimes much more
dense and compactly organized.

The protoplasm of the cell is oTganized into various
structures which are called organs of the cell, each organ
having one or more special functions. One of the most
conspicuous organs of the living cell is the single nucleus, a
comparatively compact and usually spherical protoplasmic
body, and generally centrally placed within the cell (Fig. 1).
All about the nucleus, and filling up the general cavity
within the cell wall, is an organized mass of much thinner
protoplasm, known as cytoplasm. The cytoplasm seems to
form the general background or matrix of the cell, and the

FIG. 1. Cells from a moss leaf, showing
nucleus (B) in which there is a nucle-
olus, cytoplasm (C), and chloroplasts
(A). — CALDWELL.

g PLANT STRUCTURES

nucleus lies imbedded within it (Fig. 1). Every working
cell consists of at least cytoplasm and nucleus. Sometimes
the cellulose wall is absent, and the cell then consists sim-
ply of a nucleus with more or less cytoplasm organized
about it, and is said to be naked.

Another protoplasmic organ of the cell, very conspicuous
among the Algae and other groups, is the plastid. Plastids
are relatively compact bodies, commonly spherical, variable
in number, and lie imbedded in the cytoplasm. There are
various kinds of plastids, the most common being the one
which contains the chlorophyll and hence is stained green.
The chlorophyll-containing plastid is known as the chloro-
plastid, or chloroplast (Fig. 1). An ordinary alga-cell, there-
fore, consists of a cell wall, within which the protoplasm is
organized into cytoplasm, nucleus, and chloroplasts.

The bodies of the simplest Algae consist of one such
cell, and it may be regarded as the simplest form of plant
body. Starting with such forms, one direction of advance
in complexity is to organize several such cells into a loose
row, which resembles a chain (Fig. 4) ; in other forms the
cells in a row become more compacted and flattened, form-
ing a simple filament (Figs. 2, o) ; in still other forms the
original filament puts out branches like itself, producing
a branching filament (Fig. 8). These filamentous bodies
are very characteristic of the Algae.

Starting again with the one-celled body, another line of
advance is for several cells to organize in two directions,
forming a plate of cells. Still another line of advance is for
the cells to organize in three directions, forming a mass of
cells.

The bodies of Algae, therefore, may be said to be one-
celled in the simplest forms, and in the most complex forms
they become filaments, plates, or masses of cells.

11. Reproduction. — In addition to the work of nutrition,
the plant body must organize for reproduction. Just as the
nutritive body begins in the lowest forms with a single cell

THALLOPHYTES: ALGJ5 9

and becomes more complex in the higher forms, so repro-
duction begins in very simple fashion and gradually be-
comes more complex. Two general types of reproduction
are employed by the Algae, and all other plants. They are
as follows :

(1) Vegetative multiplication. — This is the only type of
reproduction employed by the lowest Algae, but it persists
in all higher groups even when the other method has been
introduced. In this type no special reproductive bodies are
formed, but the ordinary vegetative body is used for the
purpose. For example, if the body consists of one cell, that
cell cuts itself into two, each half grows and rounds off as
a distinct cell, and two new bodies appear where there was
one before (Figs. 3, 6). This process of cell division is very
complicated and important, involving a division of nucleus
and cytoplasm so that the new cells may be organized just
as was the old one. Wherever ordinary nutritive cells are
used directly to produce new plant bodies the process is
vegetative multiplication. This method of reproduction may
be indicated by a formula as follows : P — P — P — P — P, in
which P stands for the plant, the formula indicating that
a succession of plants may arise directly from one another
without the interposition of any special structure.

(2) Spores. — Spores are cells which are specially organ-
ized to reproduce, and are not at all concerned in the nutri-
tive work of the plant. Spores are all alike in their power
of reproduction, but they are formed in two very distinct
ways. It must be remembered that these two types of
spores are alike in power but different in origin.

Asexual spores. — These cells are formed by cell divi-
sion. A cell of the plant body is selected for the purpose,
and usually its contents divide and form a variable number
of new cells within the old one (Fig. 2, B). These new cells
are asexual spores, and the cell which has formed them
within itself is known as the mother cell. This peculiar
kind of cell division, which does not involve the wall of the

IQ PLANT STRUCTURES

old cell, is often called internal division, to distinguish it
from fission, which involves the wall of the old cell, and is
the ordinary method of cell division in nutritive cells.

If the mother cell which produces the spores is different
from the other cells of the plant body it is called the sporan-
gium, which means " spore vessel." Often a cell is nutri-
tive for a time and afterward becomes a mother cell, in
which case it is said to function as a sporangium. The wall
of a sporangium usually opens, and the spores are dis-
charged, thus being free to produce new plants. Various
names have been given to asexual spores to indicate certain
peculiarities. As Algae are mostly surrounded by water,
the characteristic asexual spore in the group is one that
can swim by means of minute hair-like processes or cilia,
which have the power of lashing the water (Fig. 7, C).
These ciliated spores are known as zoospores, or "animal-
like spores," referring to their power of locomotion ; some-
times they are called swimming spores, or swarm spores. It
must be remembered that all of these terms refer to the
same thing, a swimming asexual spore.

This method of reproduction may be indicated by a for-
mula as follows : P — o — P — o — P — o — P, which indi-.
cates that new plants are not produced directly from the
old ones, as in vegetative multiplication, but that between
the successive generations there is the asexual spore.

Sexual spores. — These cells are formed by cell union,
two cells fusing together to form the spore. This process
of forming a spore by the fusion of two cells is called the
sexual process, and the two special cells (sexual cells) thus
used are known as gametes (Fig. 2, C, d, e). It must be
noticed that gametes are not spores, for they are not able
alone to produce a new plant ; it is only after two of them
have fused and formed a new cell, the spore, that a plant
can be produced. The spore thus formed does not differ
in its power from the asexual spore, but it differs very
much in its method of origin.

THALLOPHYTES : ALG^E H

The gametes are organized within a mother cell, and if
this cell is distinct from the other cells of the plant it is
called a gametangium, which means " gamete vessel."

This method of reproduction may be indicated by a for-
mula as follows : P = «>o — P = °>o — P = °>o — P,
which indicates that two special cells (gametes) are pro-
duced by the plant, that these two fuse to form one (sexual
spore), which then produces a new plant.

It must not be supposed that if a plant uses one of these
three methods of reproduction (vegetative multiplication,
asexual spores, sexual spores) it does not employ the other
two. All three methods may be employed by the same
plant, so that new plants may arise from it in three differ-
ent ways.

CHAPTER III

THE EVOLUTION OF SEX

12. The general problem. — In the last chapter it was re-
marked that the simplest Algae reproduce only by vegetative
multiplication, the ordinary cell division (fission) of nutri-
tive cells multiplying cells and hence individuals. Among
other low Algae asexual spores are added to fission as a
method of reproduction, the spores being also formed by
cell division, generally internal division. In higher forms
gametes appear, and a new method of reproduction, the
sexual, is added to the other two.

Sexual reproduction is so important a process in all
plants except the lowest, that it is of interest to discover
how it may have originated, and how it developed into its
highest form. Among the Algae the origin and develop-
ment of the sexual process seems to be plainly suggested ;
and as all other plant groups have probably been derived
more or less directly from Algae, what has been accom-
plished for the sexual process in this lowest group was
probably done for the whole plant kingdom.

13. The origin of gametes. — One of the best Algae to
illustrate the possible origin of gametes is a common fresh-
water form known as Ulothrix (Fig. 2). The body consists
of a simple filament composed of a single row of short
cells (Fig. 2, ,4). Each cell contains a nucleus, and a
single large chloroplast which has the form of a thick cyl-
inder investing the rest of the cell contents. Through the
microscope, if the focus is upon the center of the cell,
an optical section of the cylinder is obtained, the chloro-

THE EVOLUTION OF SEX

plast appearing as a thick green mass on each side of the
central nucleus. As no other color appears, it is evident
that Ulothrix is one of the Chlorophycese.

FIG. 2. Ulothrix, a Conferva form. A, base of filament, showing lowest holdfast
cell and five vegetative cells, each with its single conspicuous cylindrical chloro-
plast (seen in section) inclosing a nucleus: B, four cells containing numerous
small zoospores, the others emptied; C, fragment of a filament showing one cell
(a) containing four zoospores, another zoospore (6) displaying four cilia at its
pointed end and just having escaped from its cell, another cell (c) from which
most of the small biciliate gametes have escaped, gametes pairing (d\ and the
resulting zygotes (e) ; D, beginning of new filament from zoospore ; E, feeble
filaments formed by the small zoospores ; F, zygote growing after rest; 6r,
zoospores produced by zygote. — CALDWELL, except F and G, which are after

DODEL-PORT.

The cells are all alike, excepting that the lowest one of
the filament is mostly colorless, and is elongated and more
or less modified to act as a holdfast, anchoring the filament
to some firm support. With this exception the cells are all
nutritive ; but any one of them has the power of organizing
for reproduction. This indicates that at first nutritive and

14- PLANT STKUCTUEES

reproductive cells are not distinctly differentiated, but that
the same cell may be nutritive at one time and reproductive
at another.

In suitable conditions certain cells of the filament will
be observed organizing within themselves new calls by
internal division (Fig. 2, (7, #, b). The method of forma-
tion at once suggests that the new cells are asexual spores,
and the mother cell which produces them is acting as a
sporangium. The spores escape into the water through an
opening formed in the wall of the mother cell, and each is
observed to have four cilia at the pointed end, by means of
which it swims, and hence it is a zoospore or swarm spore.
After swimming about for a time, the zoospores "settle
down," lose the/r cilia, and begin to develop a new filament
like that from which they csme (Fig. 2, D).

Other cells of the same filament also act as mother cells,
but the cells which they produce are more numerous, hence
smaller in size than the zoospores, and they have but two
cilia (Fig. 2, C, c). They also escape into the water and
swim about, except in size and in number of cilia resem-
bling the zoospores. In general they seem to be unable to
act as the zoospores in the formation of new filaments, but
occasionally one of them forms a filament much smaller
than the ordinary one (Fig. 2, E). This indicates that
they may be zoospores reduced in size, and unable to act as
the larger ones. The important fact, however, is that
these smaller swimming cells come together in pairs, each
pair fusing into one cell (Fig. 2, (7, d, e). The cells thus
formed have the power of producing new filaments more or
less directly.

It is evident that this is a sexual act, that the cell pro-
duced by fusion is a sexual spore, that the two cells which
fuse are gametes> and that the mother cell which produces
them acts as a gametangium. Cases of this kind suggest
that the gametes or sex cells have been derived from zoo-
spores, and that asexual spores have given rise to sex cells.

THE EVOLUTION OF SEX 15

The appearance of sex cells (gametes) is but one step in the
evolution of sex. It represents the attainment of sexuality,
but the process becomes much more highly developed.

14. Isogamy. — When gametes first appear, in some such
way as has been described, the two which fuse seem to be
exactly alike. They resemble each other in size and activ-
ity, and in every structure which can be distinguished.
This fact is indicated by the word isogamy, which means
" similar gametes," and those plants whose pairing gametes
are similar, as Ulothrix, are said to be isogamous.

The act of fusing of similar gametes is usually called
conjugation, which means a " yoking together " of similar
bodies. Of course it is a sexual process, but the name is
convenient as indicating not merely the process, but also an
important character of the gametes. The sexual spore
which results from this act of conjugation is called the
zygote or zygospore, meaning " yoked spore."

In isogamy it is evident that while sexuality has been
attained there is no distinction between sexes, as obtains in
the higher plants. It may be called a unisexual condition,
as opposed to a bisexual one. The next problem in the
evolution of sex, therefore, is to discover how a bisexual
condition has been derived from a unisexual or isogamous
one.

15. Heterogamy. — Beginning with isogamous forms, a
series of plants can be selected illustrating how the pairing
gametes gradually became unlike. One of them becomes
less active and larger, until finally it is entirely passive and
very many times larger than its mate (Fig. 7). The other
retains its small size and increases in activity. The pairing
gametes thus become very much differentiated, the larger
passive one being the female gamete, the smaller active one
the male gamete. This condition is indicated by the word
heterogamy, which means " dissimilar gametes," and those
plants whose pairing gametes are dissimilar are said to be
heterogamous.

16 PLANT STRUCTURES

In order to distinguish them the large and passive female
gamete is called the oosphere, which means " egg sphere,"
or it is called the egg ; the small but active male gamete is
variously called the sperniatozoid, the antherozoid, or simply
the sperm. In this book egg and sperm will be used, the
names of similar structures in animals.

In isogamous plants the mother cells (gametangia)
which produce the gametes are alike ; but in heterogamous
plants the gametes are so unlike that the gametangia which
produce them become unlike. Accordingly they have re-
ceived distinctive names, the gametangium which produces
the sperms being called the antheridium, that producing the
egg being called the oogonium (Fig. 10).

The act of fusing of sperm and egg is called fertiliza-
tion, which is the common form of the sexual process. The
sexual spore which results from fertilization is known as the
oospore or " egg-spore," sometimes called the fertilized egg.

It is evident that heterogamous plants are bisexual, and
bisexuality is not only attained among Algae, but it prevails
among all higher plants. Among the lowest forms there is
only vegetative multiplication ; higher forms added sexu-
ality ; then still higher forms became bisexual.

16. Summary. — Isogamous forms produce gametangia,
which produce similar gametes, which by conjugation form
zygotes. Heterogamous forms produce antheridia and
oogonia, which produce sperms and eggs, which by fertiliza-
tion form oospores.

CHAPTER IV

THE GREAT GROUPS OF

17. General characters. — The Algae are distinguished
among Thallophytes by the presence of chlorophyll. It
was stated in a previous chapter that in three of the four
great groups another coloring matter is associated with the
chlorophyll, and that this fact is made the basis of a division
into Blue-green Algae (Cyanophyceae), Green Algae (Chloro-
phyceae), Brown Alga? (Phaeophyceae), and Red Algae (Rhodo-
phyceae), In our limited space it will be impossible to do
more than mention a few representatives of each group,
but they will serve to illustrate the prominent facts.

1. CYANOPHYCEAE (Blue-green Algce]

18. Glceocapsa. — These forms may be found forming
blue-green or olive-green patches on damp tree-trunks, rock,
walls, etc. By means of the microscope these patches are
seen to be composed of multitudes of spherical cells, each
representing a complete Glceocapsa body. One of the pecul-
iarities of the body is that the cell wall becomes mucilagi-
nous, swells, and forms a jelly-like matrix about the work-
ing cell. Each cell divides in the ordinary way, two new
Glceocapsa individuals being formed, this method of vegeta-
tive multiplication being the only form of reproduction
(Fig. 3).

When new cells are formed in this way the swollen
mucilaginous walls are apt to hold them together, so that
presently a number of cells or individuals are found lying

PLANT STRUCTURES

together imbedded in the jelly-like matrix formed by the
wall material (Fig. 3). These imbedded groups of individ-
uals are spoken of as colonies, and as
colonies become large they break up
into new colonies, the individual cells
composing them continuing to divide
and form new individuals. This rep-
resents a very simple life history, in
fact a simpler one could hardly be
imagined.

19. Nostoc. — These forms occur in
jelly-like masses in damp places. If
the jelly be examined it will be found
to contain imbedded in it numerous
cells like those of Glwocapsa, but they
are strung together to form chains of
varying lengths (Fig. 4). The jelly in
which these chains are imbedded is the
same as that found in Glceocapsa, being

formed by the cell walls becoming mucilaginous and swollen.
One notable fact is that all the cells in the chain are not
alike, for at irregu-
lar intervals there oc-
cur larger colorless
cells, an illustration
of the differentiation
of cells. These larger
cells are known as het-
erocysts (Fig. 4, A),
which simply means
"other cells." It is
observed that when
the chain breaks up

into fragments each FIG. 4. Nostoc, & blue-green alga, showing the

frao-TnPTit i<3pnTnr>n<jprl chain-like filaments, and the heterocysts (A)

-0mP°' which determine the breaking up of the chain.

Of the Cells between —CALDWELL.

FIG. 3. Glceocapsa, a blue-
green alga, showing
single cells, and small
groups which have been
formed by division and
are held together by the
enveloping mucilage. —
CALDWELL.

THE GREAT GROUPS OF

two heterocysts. The fragments wriggle out of the jelly
matrix and start new colonies of chains, each cell dividing
to increase the length of the chain. This cell division,
to form new cells, is the characteristic method of repro-
duction.

At the approach of unfavorable conditions certain cells
of the chain become thick-walled and well-protected. These
cells which endure the cold or other hardships, and upon
the return of favorable conditions produce new chains of
cells, are often called spores, but they are better called
" resting cells."

20. Oscillaria. — These forms are found as bluish-green
slippery masses on wet rocks, or on damp soil, or freely
floating. They are simple filaments, composed of very short
flattened cells (Fig. 5), and the name
Oscillaria refers to the fact that they
exhibit a peculiar oscillating move-
ment. These motile filaments are is-
olated, not being held together in a
jelly-like matrix as are the chains of
Nostoc, but the wall develops a cer-
tain amount of mucilage, which gives
the slippery feeling and sometimes
forms a thin mucilaginous sheath
about the row of cells.

The cells of a filament are all alike,
except that the terminal cell has its
free surface rounded. If a filament
breaks, and a new cell surface ex-
posed, it at once becomes rounded.
If a single cell of the filament is

freed from all the rest, both flattened ends become rounded,
and the cell becomes spherical or nearly so. These facts
indicate at least two important things : (1) that the cell
wall is elastic, so that it can be made to change its form,
and (2) that it is pressed upon from within, so that if free

FIG. 5. Oscillaria, a blue-
green alga, showing a
group of filaments (A),
and a single filament
more enlarged (B). —
CALDWEI,L.

20 PLANT STKUCTDKES

it will bulge outward. In all active living cells there is
this pressure upon the wall from within.

Each cell of the Oscillaria filament has the power of
dividing, thus forming new cells and elongating the fila-
ment. A filament may break up into fragments of varying
lengths, and each fragment by cell division organizes a new
filament. Here again reproduction is by means of vegeta-
tive multiplication.

21. Conclusions. — Taking Glwocapsa, Nostoc, and Oscil-
laria as representatives of the group Oyanophyceae, or
" green slimes," we may come to some conclusions concern-
ing the group in general. The plant body is very simple,
consisting of single cells, or chains and filaments of cells.
Although in Nostoc and Oscillaria the cells are organized
into chains and filaments, each cell seems to be able to live
and act independently, and the chain and filament seem to
be little more than colonies of individual cells. In this
sense, all of these plants may be regarded as one-celled.

Differentiation is exhibited in the appearance of hetero-
cysts in Nostoc, peculiar cells which seem to be connected
in some way with the breaking up of filamentous colonies,
although the Oscillaria filament breaks up without them.

The power of motion is also well exhibited by the group,
the free filaments of Oscillaria moving almost continually,
and the imbedded chains of Nostoc at times moving to es-
cape from the restraining mucilage.

The whole group also shows a strong tendency in the
cell-wall material to become converted into mucilage and
much swollen, a tendency which reaches an extreme expres-
sion in such forms as Nostoc and Glwocapsa.

Another distinguishing mark is that reproduction is
exclusively by means of vegetative multiplication, through
ordinary cell division or fission, which takes place very
freely. Individual cells are organized with heavy resistant
walls to enable them to endure the winter or other unfavor-
able conditions, and to start a new series of individuals

THE GREAT GROUPS OF ALG^E

upon the return of favorable conditions. These may 'be
regarded as resting celis. So notable is the fact of repro-
duction by fission that Cyanophyceae are often separated
from the other groups of Algae and spoken of as " Fission
Algae," which put in technical form becomes Schizophyceae.
In this particular, and in several others mentioned above,
they resemble the " Fission Fungi " (Schizomycetes), com-
monly called "bacteria," so closely that they are often
associated with them in a common group called "Fis-
sion plants " (Schizophytes), distinct from the ordinary
Algae and Fungi.

2. CHLOROPHYCE^: (Green Alga).

22. Pleurococcus. — This may be taken as a type of one-
celled Green Algae. It is most commonly found in masses
covering damp tree-trunks, etc., and looking like a green
stain. These fine-
ly granular green
masses are found
to be made up
of multitudes of
spherical cells re-
sembling those of
Gloeocapsa, except
that there is no
blue with the chlo-
rophyll, and the
cells are not im-
bedded in such
jelly-like masses.
The cells may be
solitary, or may
cling together in

colonies of various sizes (Fig. 6). Like Glceocapsa, a cell
divides and forms two new cells, the only reproduction
20

FIG. 6. Pleurococcus, a one-celled green alga : A, show-
ing the adult form with its nucleus ; S, C, D, E,
various stages of division (fission) in producing new
cells ; F, colonies of cells which have remained in
contact. — C \LDWELI,.

22 PLANT STRUCTURES

being of this simple kind. It is evident, therefore, that the
group Chlorophyceae begins with forms just as simple as
are to be found among the Cyanophyceae.

Pleurococcus is used to represent the group of Protococ-
cus forms, one-celled forms which constitute one of the
subdivisions of the Green Algag. It should be said that
Pleurococcus is possibly not a Protococcus form, but may
be a reduced member of some higher group ; but it is so
common, and represents so well a typical one-celled green
alga, that it is used in this connection. It should be
known, also, that while the simplest Protococcus forms re-
produce only by fission, others add to this the other meth-
ods of reproduction.

23. THothrix. — This form was described in § 13. It
is very common in fresh waters, being recognized easily by
its simple filaments composed of short squarish cells, each
cell containing a single conspicuous cylindrical chloroplast
(Fig. 2). This plant uses cell division to multiply the cells
of a filament, and to develop new filaments from fragments
of old ones ; but it also produces asexual spores in the form
of zoospores, and gametes which conjugate and form zygotes.
Both zoospores and zygotes have the power of germination —
that is, the power to begin the development of a new plant.
In the germination of the zygote a new filament is not pro-
duced directly, but there are formed within it zoospores,
each of which produces a new filament (Fig. 2, F, G). All
three kinds of reproduction are represented, therefore, but
the sexual method is the low type called isogamy, the pair-
ing gametes being alike.

Ulothrix is taken as a representative of the Conferva
forms, the most characteristic group of Chlorophyceae.
All the Conferva forms, however, are not isogamous, as will
be illustrated by the next example.

24. Edogonimn. — This is a very common green alga,
found in fresh waters (Fig. 7). The filaments are long and
simple, the lowest cell acting as a holdfast, as in Ulothrix

FIG. 7. Edogoninm nodosiim. a Conferva form : A, portion of a filament showing a
vegetative cell with its nucleus (d), an oogoninm (a) filled by an egg packed with
food material, a second oogonium (c) containing a fertilized egg or oospore as
shown by the heavy wall, and two antheridia (A), each containing two sperms; /?,
another filament showing antheridia (a) from which two sperms (6) have escaped,
a vegetative ceil with its nucleus, and an oogonium which a sperm (c} has entered
and is coming in contact with the egg whose nucleus (d) may be seen; C, a zoo-
spore which has been formed in a vegetative cell, showing the crown of cilia and
the clear apex, as in the sperms; D. a zoospore producing a new filament, putting
out a holdfast at base and elongating: K a further stage of development; F, the
four zoospores formed by the oospore when it germinates. — CALDWELL. except
(7 and F, which are after PRINGSHEIM,

24 PLANT STRUCTURES

(§13). The other cells are longer than in Ulofhrix, each
cell containing a single nucleus and apparently several
chloroplasts, but really there is but one large complex
chloroplast.

The cells of the filament have the power of division,
thus increasing the length of the filament. Any cell also
may act as a sporangium, the contents of a mother cell
organizing a single large asexual spore, which is a zoospore.
The zoospore escapes from the mother cell into the water,
and at its more pointed clear end there is a little crown of
cilia, by means of which it swims about rapidly (Fig. 7, C).
After moving about for a time the zoospore comes to rest,
attaches itself by its clear end to some support, elongates,
begins to divide, and develops a new filament (Fig. 7, Z>, E).

Other cells of the filament become very different from
the ordinary cells, swelling out into globular form (Fig. 7,
A, B), and each such cell organizes within itself a single
large egg (oosphere). As the egg is a female gamete, the
large globular cell which produces it, and which is differen-
tiated from the other cells of the body, is the oogonium.
A perforation in the oogonium wall is formed for the
entrance of sperms.

Other cells in the same filament, or in some other fila-
ment, are observed to differ from the ordinary cells in
being much shorter, as though an ordinary cell had been
divided several times without subsequent elongation (Fig.
7, A, /*, B, a). In each of these short cells one or two
sperms are organized, and therefore each short cell is an
antheridium. When the sperms are set free they are seen
to resemble very small zoospores, having the same little
crown of cilia at one end.

The sperms swim actively about in the vicinity of the
oogonia, and sooner or later one enters the oogonium
through the perforation provided in the wall, and fuses
with the egg (Fig. 7, B, c). As a result of this act of fer-
tilization an oospore is formed, which organizes a firm wall

THE GKEAT GROUPS OF ALG^E

about itself. This firm wall indicates that the oospore is
not to germinate immediately, but is to pass into a resting
condition. Spores which form heavy walls and pass into
the resting con-
dition are often
spoken of as " rest-
ing spores," and it
is very common
for the zygotes
and oospores to
be resting spores.
These resting
spores enable the
plant to endure
through unfavor-
able conditions,
such as failure of
food supply, cold,
drought, etc.
W hen favorable
conditions return,
the protected rest-
ing spore is ready
for germination.

When the
oospore of Edogo-
nium germinates

it does not develop directly into a new filament, but the
contents become organized into four zoospores (Fig. 7, F),
which escape, and each zoospore develops a filament. In
this way each oospore may give rise to four filaments.

It is evident that Edogonium is a heterogamous plant,
and is another one of the Conferva forms. Conferva bodies
are not always simple filaments, as are those of Ulothrix
and Edogonium, but they are sometimes extensively branch-
ing filaments, as in Cladopliora, a green alga very common

FIG. 8. Cladophora, a branching green alga, a very
small part of the plant being shown. The branches
arise at the upper ends of cells, and the cells are
c oen ocy tic . — C ALD WELL .

26 PLANT STRUCTURES

in rivers and lakes (Fig. 8). The cells are long and densely
crowded with chloroplasts ; and in certain cells at the tips
of branches large numbers of zoospores are formed, which
have two cilia at the pointed end, and hence are said to be
biciliate.

25. Vaucheria. — This is one of the most common of the
Green Algas, found in felt-like masses of coarse filaments in
shallow water and on muddy banks, and often called " green

FIG. 9. Vaucheria geminata, a Siphon form, showing a portion of the ccenocytic
body (A) which has sent out a branch at the tip of which a sporangium (B)
formed, within which a large zoospore was organized, and from which (Z>) it is
discharged later as a large multiciliate body (C), which then begins the develop-
ment of a new ccenocytic body (E).— CALDWEI.L.

felt." The filament is very long, and usually branches ex-
tensively, but its great peculiarity is that there is no parti-
tion wall in the whole body, which forms one long continuous
cavity (Figs. 9, 11). This is sometimes spoken of as a one-
celled body, but it is a mistake. Imbedded in the exten-
sive cytoplasm mass, which fills the whole cavity, there are
not only very numerous chloroplasts, but also numerous
nuclei. As has been said, a single nucleus with some cyto-

THE GREAT GKOUPS OF ALG^E 27

plasm organized about it is a cell, whether it has a wall or
not. Therefore the body of Vauclieria is made up of as
many cells as there are nuclei, cells whose protoplasmic
structures have not been kept separate by cell walls. Such
a body, made up of numerous cells, but with no partitions,
is called a cc&nocyte, or it is said to be cwnocytic. Vauclieria
represents a great group of Chlorophyceae whose members
have ccenocytic bodies, and on this account they are called
the Siphon forms.

Vauclieria produces very large zoospores. The tip of a
branch becomes separated from the rest of the body by a
partition and thus acts as a sporangium (Fig. 9, B). In
this improvised sporangium the whole of the contents or-
ganize a single large zoospore, which is ciliated all over,
escapes by squeezing through a perforation in the wall
(Fig. 9, (7), swims about for a time, and finally
develops another Vaucheriabody (Figs. 9, E, 10).
It should be said that this large body, called
a zoospore and acting like one, is really a
mass of small biciliate zoospores, just as the

FIG. 10. A young Vaucheria germinating from a
spore (sp), and showing the holdfast (w).—
After SACHS.

apparently one-celled vegetative body is really composed of
many cells. In this large compound zoospore there are
many nuclei, and in connection with each nucleus two cilia
are developed. Each nucleus with its cytoplasm and two
cilia represents a small biciliate zoospore, such as those of
Cladophora, § 24.

Antheridia and oogonia are also developed. In a com-
mon form these two sex organs appear as short special
branches developed on the side of the large coenocytic body,

PLANT STRUCTURES

and cut off from the general cavity by partition walls (Fig.
11). The oogonium becomes a globular cell, which usually

FIG. 11. Vaucheria sessilis, a Siphon form, show-
ing a portion of the coenocytic body, an an-
theridial branch (A) with an empty anthe-
ridinm (a) at its tip, and an oogouium (S)
containing an oospore (c) and showing the
opening (/) through which the sperms passed
to reach the egg.— CALDWELL.

develops a perforated break for
the entrance of the sperms, and
organizes within itself a single
large egg (Fig. 11, B}. The an-
theridium is a much smaller cell,
within which numerous very small
sperms are formed (Fig. 11, J, a).
The sperms are discharged, swarm
about the oogonium, and finally
one passes through the break and
fuses with the egg, the result be-
ing an oospore. The oospore or-
ganizes a thick wall and becomes
a resting spore.

It is evident that Vaucheria is heterogamous, but all the
other Siphon forms are isogamous, of which Botrydium may
be taken as an illustration (Fig. 12).

26. Spirogyra.— This is one of the commonest of the
" pond scums," occurring in slippery and often frothy
masses of delicate filaments floating in still water or about

FIG. 12. Botrydium, one of the
Siphon forms of green algae,
the whole body containing
one continuous cavity, with
a bulbous, chlorophyll-con-
taining portion, and root-
like branches which pene-
trate the mud in which
the plant grows. — CALD-
WELL.

THE GREAT GROUPS OF ALG^E 29

springs. The filaments are simple, and are not anchored by
a special basal cell, as in Ulothrix and Edogonium. The

FIG. 13. Spirogyra, a Conjugate form, showing one complete cell and portions of
two others. The band-like chloroplasts extend in a spiral from one end of the
cell to the other, in them are imbedded nodule-like bodies ( pyrenoids), and near
the center of the cell the nucleus is swung by radiating strands of cytoplasm. —
CALDWELL.

cells contain remarkable chloroplasts, which are bands pass-
ing spirally about within the cell wall. These bands may

FIG. 14. Spirogyra, showing conjugation : A, conjugating tubes approaching each
other; B, tubes in contact but end walls not absorbed: C, tube complete and con-
tents of one cell passing through; D, a completed zygospore. — CALDWELL.

PLANT STRUCTURES

be solitary or several in a cell, and form very striking and
conspicuous objects (Figs. 13, 14).

Spirogyra and its associates are further peculiar in pro-
ducing no asexual spores, and also in the method of sexual
reproduction. Two adjacent filaments put out tubular
processes toward one another. A cell of one filament sends
out a process which seeks to meet a corresponding process
from a cell of the other filament. When the tips of two
such processes come together, the end walls disappear,

FIG. 15. Spirogyra, showing some common exceptions. At A two cells have been
connected by a tube, but without fusion a zygote has been organized in each cell;
also, the upper cell to the left has attempted to conjugate with the cell to the
right. At B there are cells from three filaments, the cells of the central one hav-
ing conjugated with both of the others.— CALDWELL.

and a continuous tube extending between the two cells is
organized (Figs. 14, 15). When many of the cells of two
parallel filaments become thus united, the appearance is
that of a ladder, with the filaments as the side pieces, and
the connecting tubes as the rounds.

While the connecting tube is being developed the con-
tents of the two cells are organizing, and after the comple-
tion of the tube the contents of one cell pass through and
enter the other cell, fuse with its contents, and a sexual

THE GREAT GROUPS OF ALG^E

spore is organized. As the gametes
look alike, the process is conjuga-
tion, and the sex spore is a zygote,
which, with its heavy wall, is rec-
ognized to be a resting spore. At
the beginning of each growing
season, the well-protected zygotes
which have endured the winter
germinate directly into new Spi-
rogyra filaments.

On account of this peculiar
style of sexual reproduction, in
which gametes are not discharged,
but reach each other through spe-
cial tubes, Spirogyra and its allies
are called Conjugate forms — that
is, forms whose bodies are " yoked
together " during the fusion of the
gametes.

In some of the Conjugate forms
the zygote is formed in the connect-
ing tube (Fig. 16, A), and some-
times zygotes are formed without
conjugation (Fig. 16, B}. Among
the Conjugate forms the Desmids
are of great interest and beauty,
being one-celled, the cells being
organized into two distinct halves
(Fig. 17).

27. Conclusions. — The Green
Algae, as indicated by the illustra-
tions given above, include simple
one-celled forms which reproduce
by fission, but they are chiefly fila-
mentous forms, simple or branching. These filamentous
bodies either have the cells separated from one another

FIG. 16. Two Conjugate forms :
A (Mougeotia), showing for-
mation of zygote in conjuga-
ting tube ; B, C ( Ganatone-
ma), showing formation of
zygote without conjugation.
— After WITTROCK.

32 PLANT STRUCTURES

by walls, or they are coanocytic, as in the Siphon forms.
The characteristic asexual spores are zoospores, but these
may be wanting, as in the Conjugate forms. In addition
to asexual reproduction, both isogamy and heterogamy are
developed, and both zygotes and oospores are resting spores.

FIG. 17. A group of Desmids, one-celled Conjugate forms, showing various pat-
terns, and the cells organized into distinct halves. — After KEBNER.

The Green Algae are of special interest in connection
with the evolution of higher plants, which are supposed to
have been derived from them.

3. PH^OPHYCE^: (Brown Algce)

28. General characters. — The Blue-green Algae and the
Green Algae are characteristic of fresh water, but the Brown
Algae, or " kelps," are almost all marine, being very charac-

THE GREAT GROUPS OF ALGJE

teristic coast forms. All of them are anchored by holdfasts,
which are sometimes highly developed root-like structures ;
and the yellow, brown, or olive-green floating
bodies are buoyed in the water usually by the
aid of floats or air-bladders, which are often
very conspicuous. The kelps are most highly
developed in the colder waters, and form much
of the " wrack," " tangle," etc., of the coasts.
The group is well adapted to
live exposed to waves and cur-
rents with its strong holdfasts,
air-bladders, and tough leathery
bodies. It is what is known as
a specialized group — that is, one
which has become highly organ-
ized for certain special condi-
tions. It is not our
purpose to consider
such a specialized
group in any detail,
as it does not usual-
ly help to explain the
structures of higher
groups.

29. The plant
body. — There is very
great diversity in the
structure of the
plant body. Some
of them, as Ectocar-
pus (Fig. 18), are fil-
amentous forms, like
the Confervas among
the Green Algae, but
others are very much more complex. The thallus of Lam-
inaria is like a huge floating leaf, frequently nine to ten

FIG. 18. A brown alga (Ectocarpus), showing a
body consisting of a simple filament which puts
out branches (A), some sporangia (B) contain-
ing zoospores, and gametangia (C) containing
gametes.— CALD WELL.

FIG. 18a. A group of brown seaweeds (Laminarias). Note the various habits of
the plant body with its leaf-like thallus and root-like holdfasts.— After KERNER.

THE GREAT GROUPS OF ALG.E

feet long, whose stalk develops root-like holdfasts (Fig. 18a).
The largest body is developed by an Antarctic Laminaria
form, which rises to the surface from a sloping bottom with
a floating thallus six hundred to nine hundred feet long.
Other forms rise from the sea bottom like trees, with
thick trunks, numerous branches, and leaf-like appendages.

The common Fucus,
or " rock weed," is rib-
bon-form and constantly
branches by forking at
the tip (Fig. 19). This
method of branching is
called dichotomous, as dis-
tinct from that in which
branches are put out
from the sides of the axis
(monopodial). The swol-
len air-bladders distrib-
uted throughout the body
are very conspicuous.

The most differenti-
ated thallus is that of
Sargassum (Fig. 20), or
" gulf weed," in which
there are slender branch-
ing stem-like axes bearing
lateral members of various
kinds, some of them like
ordinary foliage leaves ;
others are floats or air-
bladders, which sometimes

resemble clusters of berries ; and other branches bear the
sex organs. All of these structures are but different regions
of a branching thallus. Sargassum forms are often torn
from their anchorage by the waves and carried away from
the coast by currents, collecting in the great sea eddies

FIG. 19. Fragment of a common brown
alga (Fucus), showing the body with
dichotomous branching and bladder-like
air-bladders. — After LUERSSEN.

36 PLANT STRUCTURES

produced by oceanic currents and forming the so-called
"Sargasso seas," as that of the ^North Atlantic.

FIG. 20. A portion of a brown alga (Sargassurri), showing the thallus differentiated
into stem-like and leaf -like portions, and also the bladder-like floats.— After BEN-
NETT and MURRAY.

30. Reproduction. — The two main groups of Brown Algae
differ from each other in their reproduction. One, repre-
sented by the Laminarias and a majority of the forms, pro-
duces zoospores and is isogamous (Fig. 18). The zoospores
and gametes are peculiar in having the two cilia attached
at one side rather than at an end ; and they resemble each
other very closely, except that the gametes fuse in pairs and
form zygotes.

FIG. 21. Sexual reproduction of Fucus, showing the eight eggs (six in sight) dis-
charged from the oogonium and surrounded by a membrane (A), eggs liberated
from the membrane (#), antheridium containing sperms (C), the discharged lat-
erally biciliate sperms (G), and eggs surrounded by swarming sperms (F, H). —
After SI\GRR.

PLANT STRUCTURES

The other group, represented by Fucus (Fig. 21), pro-
duces no asexual spores, but is heterogamous. A single
oogonium usually forms eight eggs (Fig. 21, A), which are
discharged and float freely in the water (Fig. 21, E). The
antheridia (Fig. 21, C) produce numerous minute laterally
biciliate sperms, which are discharged (Fig. 21, G), swim in
great numbers about the large eggs (Fig. 21, F, H), and
finally one fuses with an egg, and an oospore is formed.
As the sperms swarm very actively about the egg and
impinge against it they often set it rotating. Both an-
theridia and oogonia are formed in cavities of the thallus.

4. RHODOPHYCE.E (Red Alga)

31. General characters. — On account of their red colora-
tion these forms are often called Floridea. They are mostly

marine forms, and are
anchored by holdfasts
of various kinds. They
belong to the deepest
waters in which Algae
grow, and it is probable

Ty/tf'&fi: ^^ ^6 r6^ C°l°ring

^~"^™- matter which character-
izes them is associated
with the depth at which
they live. The Red
Algae are also a high-
ly specialized line, and
will be mentioned very
briefly.

32. The plant body.
-The Red Algae, in
general, are more deli-
cate than the Brown

Algae, or kelps, their graceful forms, delicate texture, and
brightly tinted bodies (shades of red, violet, dark purple,

FIG. 22. A red alga (Gigartind), showing
branching habit, and "fruit bodies."—
After SCHENCK.

FIG. 24. A red alga (Dasya), showing a finely divided thallus body. —
CALDWELL.

FIG. 25. A red alga (Jtabdonia), showing holdfasts and branching thallus body

CALDWELL.

FIG. 26. A red alga (Ptilota), whose branching body resembles moss. —
CALDWELL.

THE GKEAT GROUPS OF ALG^E

and reddish-brown) making them very attractive. They
show the greatest variety of forms, branching filaments,
ribbons, and filmy plates prevailing, sometimes branching
very profusely and delicately, and resembling mosses of
fine texture (Figs. 22, 23, 24, 25, 26). The differentiation
of the thallus into root and stem and leaf-like structures
is also common, as in the Brown Algas.

33. Reproduction.— Eed Algae are very peculiar in both
their asexual and sexual reproduction. A sporangium pro-
duces just four asexual spores, but they have no cilia and
no power of motion. They
can not be called zoospores,
therefore, and as each spo- |] J3 j: *

FIG. 27. A red alga ( Callithamnion), show-
ing sporangium (A), and the tetraspores
discharged (B).— After THURET.

FIG. 28. A red alga (Nemation} ; A,
sexual branches, showing antheri-
dia (a), oogonium (o) with its trich-
ogyne (t), to which are attached two
spermatia (s); B, beginning of a
cystocarp (o), the trichogyne (t) still
showing; (7, an almost mature cys-
tocarp (o), with the disorganizing
trichogyne (t).— After VINES.

rangium always produces just
four, they have been called
tetraspores (Fig. 27).

Red Algae are also heterog-
amous, but the sexual process has been so much and so
variously modified that it is very poorly understood. The
antheridia (Fig. 28, A, a) develop sperms which, like the
tetraspores, have no cilia and no power of motion. To dis-

PLANT STRUCTURES

tinguish them from the ciliated sperms, or spermatozoids,
which have the power of locomotion, these motionless male
gametes of the Red Algae are usually called spermatia
(singular, spermatium) (Fig. 28, A, s).

The oogonium is very pe-
culiar, being differentiated
into two regions, a bulbous
base and a hair-like process
(trichogyne)) the whole struc-
ture resembling a flask with a
long, narrow neck, excepting
that it is closed (Fig. 28, A,
o, t). Within the bulbous part
the egg, or its equivalent, is
organized ; a spermatium at-
taches itself to the trichogyne
(Fig. 28, A,s); at the point of
contact the two walls become
perforated, and the contents
of the spermatium thus enter
the trichogyne, and so reach
the bulbous base of the oogo-
nium. The above account rep-
resents the very simplest con-
ditions of the process of fer-
tilization in this group, and
gives no idea of the great and
puzzling complexity exhibited
by the majority of forms.

After fertilization the trich-
ogyne wilts, and the bulbous
base in one way or another
develops a conspicuous struc-
ture called the cystocarp (Figs. 28, 29), which is a case con-
taining asexual spores ; in other words, a spore case, or kind
of sporangium. In the life history of a red alga, there-

FIG. 29. A branch of Polytiphoiria,
one of the red algae, showing the
rows of cells composing the body
(A), small branches or hairs (B).
and a cystocarp (C) with escaping
spores (D) which have no cilia (car-
pospores). — CALDWEI-L.

THE GKEAT GROUPS OF ALG.E

fore, two sorts of asexual spores are produced : (1) the
tetraspores, developed in ordinary sporangia; and (2) the
carpospores, developed in the cystocarp, which has been
produced as the result of fertilization.

OTHER CHLOROPHYLL-CONTAINING THALLOPHYTES

34. Diatoms. — These are peculiar one-celled forms, which
occur in very great abundance in fresh and salt waters.

FIG. 30. A group of Diatoms : c and d, top and side views of the same form; e, colony
of stalked forms attached to an alga;/ and g, top and side views of the form shown
at e; h, a colony; i, a colony, the top and side view shown at A;.— After KEENER.

They are either free-swimming or attached by gelatinous
stalks; solitary, or connected in bands or chains, or im-
bedded in gelatinous tubes or masses. In form they are
rod- shaped, boat-shaped, elliptical, wedge-shaped, straight
or curved (Fig. 30).

PLANT STRUCTURES

The chief peculiarity is that the wall is composed of two
valves, one of which fits into the other like the two parts of
a pill box. This wall is so impregnated with silica that it
is practically indestructible, and siliceous skeletons of dia-
toms are preserved abundantly in certain rock deposits.
They multiply by cell division in a peculiar way, and some
of them have been observed to con-
jugate.

They occur in such numbers in the
ocean that they form a large part of
the free-swimming forms on the sur-
face of the sea, and doubtless showers
of the siliceous skeletons are constant-
ly falling on the sea bottom. There
are certain deposits known as "si-
liceous earths," which are simply
masses of fossil diatoms.

Diatoms have been variously placed
in schemes of classification. Some
have put them among the Brown
Algae because they contain a brown
coloring matter; others have placed
them in the Conjugate forms among
the Green Algae on account of the
occasional conjugation that has been
observed. They are so diiferent from
other forms, however, that it seems
best to keep them separate from all
other Algae.

35. Characeae. — These are common-
ly called " stoneworts," and are often
included as a group of Green Algaa,
as they seem to be Thallophytes, and
have no other coloring matter than

chlorophyll. However, they are so peculiar that they are
better kept by themselves among the Algae. They are such

FIG. 31. A common Chara,
showing tip of main axis.
—After STRASBURGER.

THE GREAT GROUPS OF ALG^E 47

specialized forms, and are so much more highly organized
than all other Algae, that they will be passed over here with
a bare mention. They grow in fresh or brackish waters,
fixed to the bottom, and forming great masses. The cylin-
drical stems are jointed, the joints sending out circles of
branches, which repeat the jointed and branching habit
(Fig. 31).

The walls become incrusted with a deposit of lime,
which makes the plants harsh and brittle, and has sug-
gested the name " stoneworts." In addition to the highly
organized nutritive body, the antheridia and oogonia are
peculiarly complex, being entirely unlike the simple sex
organs of the other Algae.

CHAPTEE V

THALLOPHYTES : FUNGI

36. General characters,— In general, Fungi include Thal-
lophytes which do not contain chlorophyll. From this fact
it follows that they can not manufacture food entirely out
of inorganic material, but are dependent for it upon other
plants or animals. This food is obtained in two general
ways, either (1) directly from the living bodies of plants or
animals, or (2) from dead bodies or the products of living
bodies. In the first case, in which living bodies are at-
tacked, the attacking fungus is called a parasite, and the
plant or animal attacked is called the host. In the second
case, in which living bodies are not attacked, the fungus is
called a saprophyte. Some Fungi can live only as parasites,
or as saprophytes, but some can live in either way.

Fungi form a very large assemblage of plants, much
more numerous than the Algae. As many of the parasites
attack and injure useful plants and animals, producing
many of the so-called " diseases," they are forms of great
interest. Governments and Experiment Stations have ex-
pended a great deal of money in studying the injurious
parasitic Fungi, and in trying to discover some method of
destroying them or of preventing their attacks. Many of
the parasitic forms, however, are harmless ; while many of
the saprophytic forms are decidedly beneficial.

It is generally supposed that the Fungi are derived from

the Algae, having lost their chlorophyll and power of inde^

pendent living. Some of them resemble certain Algae so

closely that the connection seems very plain ; but others

THALLOPHYTES : FUNGI

have been so modified by their parasitic and saprophytic
habits that they have lost all likeness to the Algae, and
their connection with them is very obscure.

37. The plant body, — Discarding certain problematical
forms, to be mentioned later, the bodies of all true Fungi
are organized upon a uniform general plan, to which they
can all be referred (Fig. 32). A set of colorless branching

FIG. 32. A diagrammatic representation of Jfucor, showing the profusely branching
mycelium, and three vertical hyphse (sporophores), sporangia forming on b and c.
— After ZOPP.

filaments, either isolated or interwoven, forms the main
working body, and is called the mycelium. The interweav-
ing may be very loose, the mycelium looking like a delicate
cobweb ; or it may be close and compact, forming a felt-like
mass, as may often be seen in connection with preserved
fruits. The individual threads are called hypJice (singular,
hypha) or liyplial threads. The mycelium is in contact with
its source of food supply, which is called the substratum.

50 PLANT STRUCTURES

From the hyphal threads composing the mycelium verti-
cal ascending branches arise, which are set apart to produce
the asexual spores, which are scattered and produce new
mycelia. These branches are called ascending hyplice or
sporophores, meaning " spore bearers."

Sometimes, especially in the case of parasites, special
descending branches are formed, which penetrate the sub-
stratum or host and absorb the food material. These spe-
cial absorbing branches are called haustoria, meaning " ab-
sorbers."

Such a mycelial body, with its sporophores, and perhaps
haustoria, lies either upon or within a dead substratum in
the case of saprophytes, or upon or within a living plant or
animal in the case of parasites.

38. The subdivisions. — The classification of Fungi is in
confusion on account of lack of knowledge. They are so
much modified by their peculiar life habits that they have
lost or disguised the structures which prove most helpful in
classification among the Algae. Four groups will be pre-
sented, often made to include all the Fungi, but doubtless
they are insufficient and more or less unnatural.

The constant termination of the group names is mycetes,
a Greek word meaning "fungi." The prefix in each case is
intended to indicate some important character of the group.
The names of the four groups to be presented are as follows :
(1) Phycomycetes (" Alga-Fungi "), referring to the fact
that the forms plainly resemble the Algae ; (2) Ascomycetes
(" Ascus-Fungi ") ; (3) JScidiomycetes ("^Ecidium-Fungi ") ;
(4) Basidiomycetes (" Basidium-Fungi "). Just what the
prefixes ascus, cecidiitm, and basidium mean will be ex-
plained in connection with the groups. The last three
groups are often associated together under the name My-
comycetes, meaning " Fungus-Fungi," to distinguish them
from the Phycomycetes, or " Alga-Fungi," referring to the
fact that they do not resemble the Algae, and are only like
themselves.

THALLOPHYTES: FUNGI 5^

One of the ordinary life processes which seems to be
seriously interfered with by the saprophytic and parasitic
habit is the sexual process. At least, while sex organs
and sexual spores are about as evident in Phycomycetes
as in Algae, they are either obscure or wanting in the
Mycomycete groups.

1. PHYCOMYCETES (Alga-Fungi)

39. Saprolegnia. — This is a group of "water-moulds,"
with aquatic habit like the Algae. They live upon the dead
bodies of water pla'nts and animals (Fig. 33), and some-
times attack living fish, one kind being very destructive
to young fish in hatcheries. The hyphae composing the
mycelium are coanocytes, as in the Siphon forms.

Sporangia are organized at the ends of branches by
forming a partition wall separating the cavity of the tip
from the general cavity (Fig. 33, B). The tip becomes
more or less swollen, and within it are formed numerous
biciliate zoospores, which are discharged into the water
(Fig. 33, (7), swim about for a short time, and rapidly form
new mycelia. The process is very suggestive of Cladophora
and Vaucheria. Oogonia and antheridia are also formed
at the ends of the branches (Fig. 33, F), much as in Vau-
cheria. The oogonia are spherical, and form one and some-
times many eggs (Fig. 33, />, E). The antheridia are
formed on branches near the oogonia. An antheridium
comes in contact with an oogonium, and sends out a deli-
cate tube which pierces the oogonium wall (Fig. 33, F).
Through this tube the contents of the antheridium pass,
fuse with the egg, and a heavy-walled oospore or resting
spore is the result.

It is an interesting fact that sometimes the contents of
an antheridium do not enter an oogonium, or antheridia
may not even be formed, and still the egg, without fertiliza-
tion, forms an oospore which can germinate. This peculiar

PLANT STRUCTURES

habit is called parthenogenesis, which means reproduction
by an egg without fertilization.

FIG. 33. A common water mould (Saprolegnia): A, a fly from which mycelial fila-
ments of the parasite are growing; B, tip of a branch organized as a sporangium:
C, sporangium discharging biciliate zoospores; F, oogonium with antheridium in
contact, the tube having penetrated to the egg; D and E, oogonia with several
eggs.— A-C after THURET, D-F after DEBARY.

40. Mucor. — One of the most common of the Mucors, or
" black moulds," forms white furry growths on damp bread,
preserved fruits, manure heaps, etc. It is therefore a
saprophyte, the crenocytic mycelium branching extensively
through the substratum (Fig. 34).

THALLOPHYTES: FUNGI

Erect sporophores arise from it in abundance, and at
the top of each sporophore a globular sporangium is formed,
within which are numerous small asexual spores (Figs. 35,

It is
asex-
are not zoo-
there is no

FIG. 34. Diagram showing mycelium and sporophores of a common Mucor.—
CALDWELL.

36). The sporangium wall bursts (Fig. 37), the light spores
are scattered by the wind, and, falling upon a suitable sub-
stratum, germinate and
form new mycelia.
evident that these
ual spores
spores, for

water medium and swim-
ming is impossible. This
method of transfer being
impossible, the spores are
scattered by currents of
air, and must be corre-
spondingly light and pow-
dery. They are usually
spoken of simply as
" spores," without any
prefix.

FIG. 35. Forming sporangia of Mucor, show-
ing the swollen tip of the sporophore (A),
and a later stage (J5), in which a wall is
formed separating the sporangium from
the rest of the body.— CALDWELL.

54 PLANT STRUCTURES

While the ordinary method of reproduction through the
growing season is by means of these rapidly germinating
spores, in certain conditions a sexual process is observed,
by which a heavy-walled sexual spore is formed as a resting
spore, able to outlive unfavorable conditions. Branches
arise from the hyphae of the mycelium just as in the forma-

FIG. 36. Mature sporangium of Mucor, showing
the wall (A), the numerous spores (C), and
the columella (B)— that is, the partition wall
pushed up into the cavity of the sporangium.
— CALDWELL.

FIG. 37. Bursted sporangium of
Mucor, the ruptured wall not
being shown, and the loose
spores adhering to the colu-
mella.— CALDWELL.

tion of sporophores (Fig. 38). Two contiguous branches
come in contact by their tips (Fig. 38, ^4), the tips are cut
off from the main coenocytic body by partition walls (Fig.
38, #), the walls in contact disorganize, the contents of
the two tip cells fuse, and a heavy-walled sexual spore is
the result (Fig. 38, C). It is evident that the process is
conjugation, suggesting the Conjugate forms among the

THALLOPHYTE8 : FUNGI

Algae ; that the sexual spore is a zygote ; and that' the two
pairing tip cells cut off from the main body by partition
walls are gametarigia. Mucor, therefore, is isogamous.

FIG. 38. Sexual reproduction of Mucor, showing tips of sex branches meeting (A),
the two gametangia cut off by partition walls (B), and the heavy-walled zygote
(f).— CALDWELL.

41. Peronospora. — These are the " downy mildews," very
common parasites on seed plants as hosts, one of the most
common kind attacking grape leaves. The mycelium is cceno-
cytic and entirely internal, ramifying among the tissues
within the leaf, and piercing the living cells with haustoria
which rapidly absorb their contents (Fig. 39). The pres-
ence of the parasite is made known by discolored and

PLANT STRUCTURES

finally deadened spots on the leaves, where the tissues have
been killed.

From this internal mycelium numerous sporophores
arise, coming to the surface of the host and securing the
scattering of their
spores, which fall
upon other leaves
and germinate, the
new mycelia pene-
trating among the
tissues and begin-
ning their ravages.
The sporophores, af-
ter rising above the
surface of the leaf,

branch freely ; and many of them rising near together,
they form little velvety patches on the surface, suggesting
the name " downy mildew."

FIG. 39. A branch of Peronospora in contact with
two cells of a host plant, and sending into them
its large haustoria.— After DEBARY.

FIG. 40. Peronosp&ra, one of the Phycomycetes, shewing at a an oogonium (o) con-
taining an egg, and an antheridium (n) in contact; at b the antheridial tube pene-
trating the oogonium and discharging the contents of the antheridium into the
egg; at c the oogonium containing the oospore or resting spore.— After DEBARY.

In certain conditions special branches arise from the
mycelium, which organize antheridia and oogonia, and
remain within the host (Fig. 40). The oogonium is of the
usual spherical form, organizing a single egg. The an-

THALLOPHYTES: FUNGI 57

theridium comes in contact with the oogonium, puts out a
tube which pierces the oogonium wall and enters the egg,
into which the contents of the an theridium are discharged,
and fertilization is effected. The result is a heavy-walled
oospore. As the oospores are not for immediate germina-
tion, they are not brought to the surface of the host and
scattered, as are the asexual spores. When they are ready
to germinate, the leaves bearing them have perished and
the oospores are liberated.

±2. Conclusions. — The ccenocytic bodies of the whole group
are very suggestive of the Siphon forms among Green Algae,
as is also the method of forming oogonia and antheridia. •

The water-moulds, Saprolegnia and its allies, have re-
tained the aquatic habit of the Algae, and their asexual
spores are zoospores. Such forms as Mucor and Perono-
spora, however, have adapted themselves to terrestrial con-
ditions, zoospores are abandoned, and light spores are de-
veloped which can be carried about by currents of air.

In most of them motile gametes are abandoned. Even
in the heterogamous forms sperms are not organized within
the antheridium, but the contents of the antheridium are
discharged through a tube developed by the wall and pene-
trating the oogonium. It should be said, however, that a
few forms in this group develop sperms, which make them
all the more alga-like.

They are both isogamous and heterogamous, both zygotes
and oospores being resting spores. Taking the characters
all together, it seems reasonably clear that the Phycomycetes
are an assemblage of forms derived from Green Algae (Chlo-
rophyceae) of various kinds.

2. ASCOMYCETES (Ascus- or Sac-Fungi}

43. Mildews. — These are very common parasites, growing
especially upon leaves of seed plants, the mycelium spread-
ing over the surface like a cobweb. A very common mil-

PLANT STKUCTURES

dew, Microsphcera, grows on lilac leaves, which nearly
always show the whitish covering after maturity (Fig. 41).
The branching hyphse show numerous partition walls, and
are not ccenocytic as in the Phycomycetes. Small disk-like
haustoria penetrate into the superficial cells of the host,
anchoring the mycelium and absorbing the cell contents.

Sporophores arise, which form asexual spores in a pe-
culiar way. The end of the sporophore rounds off, almost
separating itself from the part below, and becomes a spore
or spore-like* body. Below this another organizes in the

same way, then another, until
a chain of spores is developed,
easily broken apart and scat-
tered by the wind. Falling
upon other suitable leaves,
they germinate and form new
mycelia, enabling the fungus
to spread rapidly. This meth-
od of cutting a branch into
sections to form spores is
called abstriction, and the
spores formed in this way
are called conidia, or conidi-
ospores (Fig. 43, B).

At certain times the myce-
lium develops special branches
which develop sex organs, but
they are seldom seen and may
not always occur. An oogo-
nium and an antheridium, of
the usual forms, but probably
without organizing gametes,
come into contact, and as a

result an elaborate structure is developed — the ascocarp,
sometimes called the "spore fruit." These ascocarps ap-
pear on the lilac leaves as minute dark dots, each one being

FIG. 41. Lilac leaf covered with mil-
dew (MicroaphoKra), the shaded re-
gions representing the mycelium,
and the black dots the ascocarps. —
CALDWELL.

THALLOPHYTES: FUNGI

a little sphere, which suggested the name Microsphcera
(Fig. 41). The heavy wall of the ascocarp bears beauti-
ful branching hair-like appendages (Fig. 42).

Bursting the wall of this spore fruit several very delicate,
bladder-like sacs are extruded, and through the transparent
wall of each sac there may be
seen several spores (Fig. 42).
The ascocarp, therefore, is
a spore case, just as is the
cystocarp of the Red Algae
(§ 33). The delicate sacs
within are the asci, a word
meaning "sacs," and each
ascus is evidently a mother
cell within which asexual
spores are formed. These
spores are distinguished
from other asexual spores
by the name ascospore.

It is these peculiar moth-
er cells, or asci, which give
name to the group, and an

Ascomycete, Ascus-fungus, or Sac-fungus, is one which pro-
duces spores in asci ; and an ascocarp is a spore case which
contains asci.

In the mildews, therefore, there are two kinds of asexual
spores : (1) conidia, formed from a hyphal branch by abstric-
tion, by which the mycelium may spread rapidly ; and (2)
ascospores, formed in a mother cell and protected by a heavy
case, so that they may bridge over unfavorable conditions,
and may germinate when liberated and form new mycelia.
The resting stage is not a zygote or an oospore, as in the
Algae and Phycomycetes, no sexual spore probably being
formed, but a heavy-walled ascocarp.

44. Other forms. — The mildews have been selected as a
simple illustration of Ascomycetes, but the group is a very

FIG. 42. Ascocarp of the lilac mildew,
showing branching appendages and
two asci protruding from the rup-
tured wall and containing ascospores.
— CALDWELL.

PLANT STRUCTUKES

large one, and contains a great variety of forms. All of
them, however, produce spores in asci, but the asci are not
always inclosed by an ascocarp. Here belong the common
blue mould (Penicillium), found on bread, fruit, etc., in
which stage the branching chains of conidia are very con-
spicuous (Fig. 43); the truffle-fungi, upon whose subter-

Fio. 43. Penicillium, a common mould : A, mycelium with numerous branching
sporophores bearing conidia; B, apex of a sporophore enlarged, showing branch-
ing and chains of conidia.— After BREFELD.

ranean mycelia ascocarps develop which are known as
" truffles " ; the black fungi, which form the diseases known
as " black knot " of the plum and cherry, the " ergot " of
rye (Fig. 44), and many black wart-like growths upon the
bark of trees ; other forms causing " witches'-brooms " (ab-
normal growths on various trees), " peach curl," etc., the
cup-fungi (Figs. 45, 46), and the edible morels (Fig. 47).

THALLOPHYTES : FUNGI

FIG. 45. Two species of cup-fungus
(Peziza).— After LINDAU.

FIG. 44. Head of rye attacked by "er-
got " («), peculiar grain-like masses
replacing the grains of rye ; also a
mass of "ergot" germinating to
form spores (b). — After TULASNE.

FIG. 46. A cup-fungus (Pitya) grow-
ing on a spruce (Picea). — After
REHM.

In some of these forms the ascocarp is completely closed,
as in the lilac mildew ; in others it is flask-shaped ; in
others, as in the cup-fungi, it is like a cup or disk ; but in
all the spores are inclosed by a delicate sac, the ascus.

PLANT STRUCTURES

Here must probably be included the yeast-fungi (Fig.
48), so commonly used to excite alcoholic fermentation.

FIG. 47. The common edible morel (Morchella

esculenta). The structure shown and used

represents the ascocarp, the depressions of

whose surface are lined with asci contain-

• ing ascospores.— After GIBSON.

FIG. 48. Yeast cells, reprodu-
cing by budding, and form-
ing chains.— CALDWELL.

The " yeast cells " seem to be conidia having a peculiar bud-
ding method of multiplication, and the remarkable power
of exciting alcoholic fermentation in sugary solutions.

3. JEciDiOMYCETES (indium- Fung i)

45. General characters. — This is a large group of very
destructive parasites known as " rusts " and " smuts." The
rusts attack particularly the leaves of higher plants, pro-
ducing rusty spots, the wheat rust probably being the best
known. The smuts especially attack the grasses, and are
very injurious to cereals, producing in the heads of oats,
barley, wheat, corn, etc., the disease called smut.

THALLOPHYTES: FUNGI

No indication of a sexual process has been obtained, and
the life histories are so complicated and obscure that the
position of the group is very uncertain. The forms should
probably be included with the Basidiomycetes, but they are
so unlike the ordinary forms of that group that they are
here kept distinct.

Most of the forms are wry polymorphic — that is, a plant
assumes several dissimilar appearances in the course of its
life history. These phases are often so dissimilar that they
have been described as different plants. This polymorphism
is often further complicated by the appearance of different
phases upon entirely different hosts. For example, the
wheat-rust fungus in one stage lives on wheat, and in an-
other on barberry.

46. Wheat rust, — This is one of the few rusts whose life
histories have been traced, and it may be taken as an illus-
tration of the group.

The mycelium of the fungus is found ramifying among
the leaf and stem tissues of the wheat. While the wheat is
growing this mycelium sends to the surface numerous spo-

FIG. 49. Wheat rust, showing sporophores breaking through the tissues of the host
and bearing summer spores (uredospores). — After II. MARSHALL WARD.

rophores, each bearing at its apex a reddish spore (Fig. 49).
As the spores occur in great numbers they form the rusty-
looking lines and spots which give name to the disease.
The spores are scattered by currents of air, and falling upon
other plants, germinate very promptly, thus spreading the

PLANT STRUCTURES

disease with great rapidity (Fig. 50). Once it was thought
that this completed the life cycle, and the fungus received
the name Uredo. When it was known that this is but one

FIG. 50 — Wheat rust, showing a young hypha forcing its way from the surface of a
leaf down among the nutritive cells.— After H. MARSHALL WAIID.

stage in a polymorphic life history it was called the Uredo-
stage, and the spores uredospores, sometimes "summer
spores."

FIG. 51. Wheat rust, showing the winter spores (teleutospores).— After
H. MARSHALL WARD.

Toward the end of the summer the same mycelium
develops sporophores which bear an entirely different kind
of spore (Fig. 51). It is two-celled, with a very heavy black

THALLOPHYTES : FUNGI

wall, and forms what is called the " black rust," which ap-
pears late in the summer on wheat stubble. These spores
are the resting spores, which last through the winter and
germinate in the following spring. They are called teleuto-
spores, meaning the " last spores " of the growing season.
They are also called " winter spores," to distinguish them
from the uredospores or " summer spores." At first this
teleutospore-bearing mycelium was not recognized to be
identical with the uredospore-bearing mycelium, and it was
called Puccinia. This name is now
retained for the whole polymorphous
plant, and wheat rust is Puccinia
graminis. This mycelium on the
wheat, with its summer spores and
winter spores, is but one stage in
the life history of wheat rust.

In the spring the teleutospore
germinates, each cell developing a
small few-celled filament (Fig. 52).
From each cell of the filament a
little branch arises which develops
at its tip a small spore, called a spo-
ridium, which means " spore-like."
This little filament, which is not a
parasite, and which bears sporidia,
is a second phase of the wheat rust,
really the first phase of the growing
season.

The sporidia are scattered, fall
upon barberry leaves, germinate, and
develop a mycelium which spreads

through the leaf. This mycelium produces sporophores
which emerge on the under surface of the leaf in the
form of chains of reddish-yellow conidia (Fig. 53). These
chains of conidia are closely packed in cup-like receptacles,
and these reddish-yellow cup-like masses are often called

FIG. 52. Wheat rust, show-
ing a teleutospore germina-
ting and forming a short fil-
ament, from four of whose
cells a spore branch arises,
the lowest one bearing at
its tip a sporidium.— After
H. MARSHALL WARD.

PLANT STRUCTURES

"cluster-cups." This mycelium on the barberry, bearing
cluster-cups, was thought to be a distinct plant, and was

called ^Ecidium. The
name now is applied to
the cluster-cups, which
are called cecidia, and
the conidia-like spores
which they produce are
known as cecidiospores.

It is the a3cidia which
give name to the group,
and ^Ecidiomycetes are
those Fungi in whose
life history ascidia or
cluster-cups appear.

The aecidiospores are
scattered by the wind,
fall upon the spring
wheat, germinate, and
develop again the myce-
lium which produces the
rust on the wheat, and
so the life cycle is com-
pleted. There are thus
at least three distinct
stages in the life history
of wheat rust. Begin-
ning with the growing
season they are as fol-
lows : (1) The phase bear-
ing the sporidia, which
is not parasitic ; (2) the
aecidium phase, parasitic
on the barberry; (3) the uredo-teleutospore phase, para-
sitic on the wheat.

In this life cycle at least four kinds of asexual spores

THALLOPHYTES : FUNGI

appear : (1) sporidia^ which develop the stage on the barber-
ry ; (2) cecidiospores, which develop the stage on the wheat ;
(3) ttredosporeS) which repeat the mycelium on the wheat ; (4)
teleutospores,v?\iich last through the winter, and in the spring
produce the stage bearing sporidia. It should be said that
there are other spores of this plant produced on the barberry
(Fig. 53), but they are too uncertain to be included here.

The barberry is not absolutely necessary to this life cycle.
In many cases there is no available barberry to act as host,
and the sporidia germinate directly upon the young wheat,
forming the rust-producing mycelium, and the cluster-cup
stage is omitted.

FIG. 54. Two species of "cedar apple" (Gymnosporangium), both on the common
juniper (Junipents Virginiand).—A after FARLOW, B after ENGLER and PRANTL.

47. Other rusts, — Many rusts have life histories similar
to that of the wheat rust, in others one or more of the
stages are omitted. In very few have the stages been con-

PLANT STRUCTURES

nected together, so that a mycelium bearing uredospores is
called a Vredo, one bearing teleutospores a Puccinia, and
one bearing aecidia an ^cidium ; but what forms of Uredo,
Puccinia, and jEcidium belong together in the same life
cycle is very difficult to discover.

Another life cycle which has been discovered is in con-
nection with the " cedar apples " which appear on red
cedar (Fig. 54). In the spring these diseased growths be-
come conspicuous, especially after a rain, when the jelly-
like masses containing the orange-colored spores swell.
This corresponds to the phase which produces rust in
wheat. On the leaves of apple trees, wild crab, hawthorn,
etc., the aecidium stage of the same parasite develops.

4. BASIDIOMYCETES (Basidium-Fungi).
48. General characters. — This group includes the mush-
rooms, toadstools, and puffballs. They are not destructive

parasites, as are many
forms in the preceding
groups, but mostly harm-
less and often useful sap-
rophytes. They must
also be regarded as the
most highly organized of
the Fungi. The popular
distinction between toad-
stools and mushrooms is
not borne out by botan-
ical characters, toadstool
and mushroom being the
same thing botanically,
and forming one group,
puffballs forming an-
other.

As in ^cidiomycetes,

FIG. 55. The common edible mushroom,
Agaricus campestrte.—Afier GIBSON. HO SCXUal prOCCSS has

TIIALLOPTIYTES: FUNGI

been discovered. The life history seems simple, but this
apparent simplicity may represent a very complicated his-
tory. The structure of the common mushroom (Agari-
cux) will serve as an illustration of the group (Fig. 55).

49. A common
mushroom. — The
mycelium, of white
branching threads,
spreads extensively
through the decay-
ing substratum,
and in cultivated
forms is spoken of
as the " spawn."
Upon this myce-
lium little knob-
like protuberances
begin to arise, grow-
ing larger and
larger, until they
are organized into
the so-called
" mushrooms."
The real body of
the plant is the
white thread - like
mycelium, while
the " mushroom "
part seems to rep-
resent a great num-
ber of Sporophores FlG- 56> A common Agrarians : A, section through one
side of pileus, showing sections of the pendent gills;

Organized together s, section of a gill more enlarged, showing the cen-

tral tissue, and the broad border formed by the ba-
sidia : f, still more enlarged section of one side of
a gill, showirg the club-shaped basidia standing at
right angles to the surface, and sending out a pair

to form a single
complex spore-
bearing structure.
The mushroom
23

of small branches, each of which bears a single ba-
sidiospore.— After SACHS.

£ t

T <

THALLOPHYTES : FUNGI

has a stalk-like portion, the stipe, at the base of which the
slender mycelial threads look like white rootlets ; and an
expanded, umbrella-like top called the pileux. From the
under surface of the pileus there hang thin radiating plates,
or gills (Fig. 55). Each gill is a mass of interwoven fila-
ments (hyphae), whose tips turn toward the surface and
form a compact layer of end cells (Fig. 56). These end

FIG. 60. A bracket fungus (Poly]X)ruti) growing on the trunk of a red oak. —
CAT.DWKI.I..

cells, forming the surface of the gill, are club-shaped, and
are called basidia. From the broad end of each basidium
two or four delicate branches arise, each bearing a minute
spore, very much as the sporidia appear in the wheat rust.

Y2 PLANT STRUCTURES

These spores, called basidiospores, shower down from the
gills when ripe, germinate, and produce new mycelia. The
peculiar cell called the basidium gives name to the group
Basidiomycetes.

50. Other forms. — Mushrooms display a great variety of
form and coloration, many of them being very attractive

FIG. 61. A toadstool of the bracket form which has grown about blades of grass
without interfering with their activity.— CALDWELL.

(Figs. 57, 58, 59). The " pore-fungi " have pore-like depres-
sions for their spores, instead of gills, as in the very com-
mon "bracket-fungus" (Polyporus), which forms hard
shell-like outgrowths on tree-trunks and stumps (Figs. 60,

FIG. 62. The common edible Boletus (B. edu- FIG. 63. Another edible Boletus (B. stro-
lls), in which the gills are replaced by bilaceus).— After GIBSON.
pores.— After GIBSON.

FIG. 64. The common edible "coral fun-
gus11 ( Clararia).— After GIBSON.

FUJ. 65. Hydrum repandum, in which gills
are replaced by spinous processes ; edi-
ble.—After GIBSON.

PLANT STRUCTURES

61), and the mushroom-like Boleti (Figs. 62, 63). The
"ear-fungi" form gelatinous, dark-brown, shell-shaped
masses, and the " coral fungi " resemble branching corals
(Fig. 64). The Hydnum forms have spinous processes

instead of gills (Fig.
65). The puffballs or-
ganize globular bodies
(Fig. 66), within which
the spores develop, and
are not liberated until
ripe ; and with them
belong also the "bird's
nest fungus," the "earth
star," the ill-smelling
"stink-horn," etc.

FIG. 66. Puffballs. in which the basidia and
spores are inclosed : edible.— After GIBSON.

OTHER THALLOPHYTES
WITHOUT CHLOROPHYLL

5 1 . Slime - moulds. —
These perplexing forms,
named Myxomycetes, do
not seem to be related
to any group of plants,
and it is a question

whether they are to be regarded as plants or animals. The
working body is a mass of naked protoplasm called a pjfix-
m odium, suggesting the term " slime," and slips along like
a gigantic amoeba. They are common in forests, upon
black soil, fallen leaves, and decaying logs, the slimy yel-
low or orange masses ranging from the size of a pinhead
to as large as a man's hand. They are saprophytic, and
are said to engulf food as do the amo3bas. So suggestive
of certain low animals is this body and food habit that
slime-moulds have also been called Mycetozoa or " fungus-
animals."

THALLOPHYTES : FUNGI Y5

In certain conditions, however, these slimy bodies come
to rest and organize most elaborate and often very beau-
tiful sporangia, full of spores (Fig. 67). These varied
and easily preserved sporangia are used to classify the

FIG. 67. Three common slime moulds (Myxomycetes) on decaying wood: to tin-
left above, groups of the sessile sporangia of Trichia ; to the right above, a group
of the stalked sporangia of Stemonitis, with remnant of old plasmodiuin at base;
below, groups of sporangia of Ilemiarcyria, with a plasmodium mass at upper
left hand.— CALDWKI.L.

forms. Slime-moulds, or " slime-fungi," therefore, seem
to have animal-like bodies which produce plant-like spo-
rangia.

52. Bacteria. — These are the " Fission-Fungi," or Schizo-
mycetes, and are popularly known as " bacteria," " bacilli,"
" microbes," " germs," etc. They are so important and pe-
culiar in their life habits that their study has developed a
special branch of botany, known as " Bacteriology." In
many ways they resemble the Cyanophyceae, or "Fission-
Algae," so closely that they are often associated with them
in classification (see § 21).

FIG. 68. A group of Bacteria, the bodies being black, and bearing motile cilia in
various ways. A , the two to the left the common hay Bacillus (B. mbtilis}, the
one to the right a Spirillum ; B, a Coccus form (Planococcus)\ C, D, E, species of
Pseudomonas : F, G, species of Bacillus, F being that of typhoid fever: ff. Micro-
*inra ; J, K, L, M, species of Spirillum.— After ENGLER and PBANTL.

THALLOPIIYTES : FUNGI 77

They are the smallest known living organisms, the one-
celled form which develops on cooked potatoes, bread, milk,
meat, etc., forming a blood-red stain, having a diameter of
but 0.0005 mm. (-g^fo^ in-)- They are of various forms
(Fig. 68), as Coccus forms, single spherical cells ; Bacterium
forms, short rod-shaped cells ; Bacillus forms, longer rod-
shaped cells ; Leptothrix forms, simple filaments ; Spirillum
forms, spiral filaments, etc.

They multiply by cell division with wonderful rapidity,
and also form resting spores for preservation and distri-
bution. They occur everywhere — in the air, in the water,
in the soil, in the bodies of plants and animals ; many of
them harmless, many of them useful, many of them dan-
gerous.

They are intimately concerned with fermentation and
decay, inducing such changes as the souring of fruit juices,
milk, etc., and the development of pus in wounds. What
is called antiseptic surgery is the use of various means to
exclude bacteria and so prevent inflammation and decay.

The pathogenic forms — that is, those which induce dis-
eases of plants and animals — are of great importance, and
means of making them harmless or destroying them are
being searched for constantly. They are the causes of such
diseases as pear-blight and peach-yellows among plants, and
such human diseases as tuberculosis, cholera, diphtheria,
typhoid fever, etc.

LICHENS

53. General character. — Lichens are abundant every-
where, forming various colored splotches on tree-trunks,
rocks, old boards, etc., and growing also upon the ground
(Figs. 69, 70, 71). They have a general greenish-gray color,
but brighter colors may also be observed.

The great interest connected with Lichens is that they are
not single plants, but each Lichen is formed of a fungus and
an alga, living together so intimately as to appear like a single

TIIALLOPHYTES : FUNGI

plant. In other words, a Lichen is not an individual, but a
tirm of two individuals very unlike each other. This habit

FIG. 70. A common lichen (Pliyscia] growing on bark, showing the spreading thallue
and the numerous dark disks (apothecia) bearing the asci.— OAI.DWET.L.

of living together has been called symbiosis, and the indi-
viduals entering into this relation are called symbionts.

FIG. 71. A common foliose lichen (Paiinelid) growing upon a board, and showing
apothecia.— CALDWEI.I..

PLANT STRUCTURES

If a Lichen be sectioned, the relation between the sym-
bionts will be seen (Fig. 72). The fungus makes the bulk
of the body with its interwoven mycelial threads, in the
meshes of which lie the Algae, sometimes scattered, some-

FIG. 72. Section through thallus of a lichen (Sticta), showing holdfasts (r), lower (t/)
and upper (o) surfaces, fungus hyphae (m), and enmeshed algae (<?). — After SACHS.

times massed. It is these enmeshed Algae, showing through
the transparent mycelium, that give the greenish tint to
the Lichen.

In the case of Lichens the symbionts are thought by
some to be mutually helpful, the alga manufacturing food
for the fungus, and the fungus providing protection and
water containing food materials for the alga. Others do not
recognize any special benefit to the alga, and see in a Lichen
simply a parasitic fungus living on the products of an alga.
In any event the Algae are not destroyed but seem to thrive.
It is discovered that the alga symbiont can live quite inde-

TIIALI.ol'HYTES: FUNGI

pendently of the fungus. In fact, the enmeshed Algae are
often recognized as identical with forms living independ-
ently, those thus used being various Blue-green, Protococ-
cus, and Conferva forms.

On the other hand, the fungus symbiont has become
quite dependent upon the alga, and its germinating spores
do not develop far unless the young mycelium can lay hold
of suitable Alga3. At certain times cup-like or disk-like
bodies appear on the surface of the lichen thallus, with
brown, or black, or more brightly-colored lining (Figs. 70,
71). These bodies are the apothecia, and a section through
them shows that the colored lining is largely made up of
delicate sacs containing spores (Figs. 73, 74). These sacs
are evidently asci, the apothecia correspond to ascocarps,
and the Lichen fungus proves to be an Ascomycete.

Fu;. 73. Section through an apothccium of Anaptycfria, showing stalk of the cup
(m), masses of algal cells (g), outer margin of cup (>•), overlapping edge ((. t), layer
of asci (/n. and massing of hyphae beneath asci (y).— After SACHS.

Certain Ascomycetes, therefore, have learned to use cer-
tain Algae in this peculiar way, and a Lichen is the result.
Some Basidiomycetes have also learned the same habit, and
form Lichens.

Various forms of Lichen bodies can be distinguished as
follows : (1) Crustaceans Lichens, in which the thallus resem-

PLANT STRUCTUKES

bles an incrustation upon its substratum of rock, soil, etc. ;
(2) Foliose Lichens, with flattened, leaf-like, lobed bodies, at-

FIG. 74. Much enlarged section of a portion of the apothecium of Anapttjchia. show-
ing the fungus mycelium \.m), which is massed above (y), just beneath the layer of
asci (1, 2, 3, A), in which spores in various stages of development are .-hown.—
After SACHS.

tached only at the middle or irregularly to the substratum ;
(3) FruticoKf. Lichens, with filamentous bodies branching
like shrubs, either erect, pendulous, or prostrate.

CHAPTER VI

THE FOOD OF PLANTS

54. Introductory. — All plants use the same kind of food,
but the Algae and Fungi suggest that they may have very
different ways of obtaining it. The Algae can manufacture
food from raw material, while the Fungi must obtain it
already manufactured. Between these two extreme condi-
tions there are plants which can manufacture food, and at
the same time have formed the habit of supplementing this
by obtaining elsewhere more or less manufactured food.
Besides this, there are plants which have learned to work
together in the matter of food supply, entering into a con-
dition of symbiosis, as described under the Lichens. These
various habits will be presented here briefly.

oo. Green plants, — The presence of chlorophyll enables
plants to utilize carbon dioxide (C02), a gas present in the
atmosphere and dissolved in waters, and one of the waste
products given off in the respiration of all living organisms.
This gas is absorbed by green plants, its constituent ele-
ments, carbon and oxygen, are dissociated, and with the ele-
ments obtained from absorbed water (H20) are recombined to
form a carbohydrate (sugar, starch, etc.), which is an organ-
ized food. With this as a basis other foods are formed,
and so the plant can live without help from any other
organism.

This process of utilizing carbon dioxide in the formation
of food is not only a wonderful one, but also very important.
It is wonderful, because carbon dioxide and water, both of
them very refractory substances, are broken up at ordinary

84 PLANT STKUCTURES

temperatures and without any special display of energy. It
is important, because the food of all plants and animals de-
pends upon it, as it is the only known process by which inor-
ganic material can be organized.

The process is called photosynthesis, or photosyntax,
words indicating that the presence of light is necessary.
The mechanism on the part of the plant is the chloroplast,
which when exposed to light is able to do this work. The
process is often called " carbon assimilation," " chlorophyll
assimilation," " fixation of carbon," etc. It should be noted
that it is not the chlorophyll which does the work, but the
protoplasmic plastid stained green by the chlorophyll. The
chlorophyll manipulates the light in some way so that the
plastid may obtain from it the energy needed for the work.
Further details concerning it may be obtained by reading
§ 112 of Plant Relations.

It is evident that green plants must expose their chloro-
phyll to the light. For this reason the Algae can not live
in deep waters or in dark places. In the case of the large
marine kelps, although they may be anchored in considera-
ble depth of water, their working bodies are floated up
toward the light by air-bladders. In the case of higher
plants, specially organized chlorophyll-bearing organs, the
foliage leaves, are developed.

56. Saprophytes. — Only cells containing chloroplasts can
live independently. In the higher plants, where bodies be-
come large, many living cells are shut away from the light,
and must depend upon the more superficial green cells for
their food supply. The habit of cells depending upon one
another for food, therefore, is a very common one.

When none of the cells of the plant body contain chloro-
phyll, the whole plant becomes dependent, and must live as
a saprophyte or a parasite. In the case of saprophytes dead
bodies or body products are attacked, and sooner or later all
organic matter is attacked and decomposed by them. The
decomposition is a result of the nutritive processes of plants

THE FOOD OF PLANTS 85

without chlorophyll, and were it not for them "the whole
surface of the earth would be covered with a thick deposit
of the animal and plant remains of the past thousands of
years."

The green plants, therefore, are the manufacturers of
organic material, producing far more than they can use,
while the plants without chlorophyll are the destroyers of
organic material. The chief destroyers are the Bacteria
and ordinary Fungi, but some of the higher plants have
also adopted this method of obtaining food. Many ordinary
green plants have the saprophytic habit of absorbing organic
material from rich humus soil ; and many orchids and heaths
are parasitic, attaching their subterranean parts to those of
other plants, becoming what are called "root parasites."
The cultivated plants, also, may be regarded as partially
saprophytic, in so far as they use the organic material sup-
plied to them in fertilizers.

57. Parasites. — Certain plants without chlorophyll are
not content to obtain organic material from dead bodies,
but attack living ones. As in the case of saprophytes, the
vast majority of plants which have formed this habit are
Bacteria and ordinary Fungi. Parasites are not only modi-
fied in structure in consequence of the absence of chloro-
phyll, but they have developed means of penetrating their
hosts. Many of them have also cultivated a very selective
habit, restricting themselves to certain plants or animals, or
even to certain organs.

The parasitic habit has also been developed by some of
the higher plants, sometimes completely, sometimes par-
tially. Dodder, for example, is completely parasitic at
maturity (Fig. 75), while mistletoe is only partially so,
doing chlorophyll work and also absorbing from the tree
into which it has sent its haustoria.

That saprophytism and parasitism are both habits grad-
ually acquired is inferred from the number of green plants
which have developed them more or less, as a supplement to
24

I'LANT STRUCTURES

the food which they manufacture. The less chlorophyll is
used the less is it developed, and a green plant which is
obtaining the larger amount of its food in a saprophytic

or parasitic way is
on the way to losing
all of its chlorophyll
and becoming a com-
plete saprophyte or
parasite.

Certain of the low-
er Algae are in the
habit of living in the
body cavities of high-
er plants, finding in
such situations the
moisture and protec-
tion which they need.
They may thus have
brought within their
reach some of the
organic products of
the higher plant. If
they can use some of
these, as is very like-
ly, a partially para-
sitic habit is begun,
which may lead to
loss of chlorophyll
and complete para-
sitism.

58. Symbionts. —
The phenomenon of
symbiosis has already

been referred to in connection with Lichens (§ 53). In
its broadest sense the word includes any sort of depend-
ence between living organisms, from the vine and the tree

FIG. 75. A dodder plant parasitic on a willow twig.
The leafless dodder twines about the willow, and
sends out sucking processes which penetrate and
absorb. — After STRASBUBGER.

THE FOOD OF PLANTS 87

upon which it climbs, to the alga and fungus GO intimately
associated in a Lichen as to seem a single plant. In a nar-
rower sense it includes only cases in which there is an inti-
mate organic relation between the symbionts. This would
include parasitism, the parasite and host being the sym-
bionts, and the organic relation certainly being intimate.
In a still narrower sense symbiosis includes only those cases
in which the symbionts are mutually helpful. This fact,
however, is very difficult to determine, and opinions vary
widely as to the mutual advantage of the relation. How-
ever large a set of phenomena may be included r ider the
term symbiosis, we use it here in this narrowest sense, which
is often distinguished as mutualism.

(1) Lichens. — The main facts of symbiosis in connection
with Lichens were presented in § 53. That the fungus-
symbiont can not live without the alga has been demon-
strated, but whether the alga-symbiont derives any benefit
from this association is a question in dispute. The latter
can live independently of the former, but enmeshed by the
fungus the alga seems to thrive and to live in situations
which would be impossible to it without the protection and
moisture supplied by the fungus-thallus. Those who lay
stress on the first fact regard the Lichen merely as a pecul-
iar case of parasitism, which has been called heloti*m, or a
condition of slavery, indicating that the alga is enslaved
and even cared for by the fungus for its own use. Those
who see an advantage to the alga in this association regard
a Lichen as an example of mutualism.

It may be of interest to know that artificial Lichens have
been formed, not only by cultivating together spores of a
Lichen-fungus and some Lichen-alga, but also by using
" wild " Algae — that is, Algae which are in the habit of living
independently.

(2) Mycorrhiza. — The name means "root-fungus," and
refers to an association which exists between certain Fungi
of the soil and roots of higher plants, such as orchids, heaths,

FIG. 76. Mycorrhiza: to the left is the tip of a rootlet of beech enmeshed by the
fungus; A, diagram of longitudinal section of an orchid root, showing the cells
of the cortex (p) filled with hyphae; B, part of longitudinal section of orchid root
much enlarged, showing epidermis («), outermost cells of the cortex (p) filled with
hyphal threads, which are sending branches into the adjacent cortical cells (a, i).
—After FRANK.

FIG. 77. Mycorrhiza: A, rootlets of white poplar forming mycorrhiza; B, enlarged
section of single rootlets, showing the hyphae penetrating the cells.— After
KEENER.

THE FOOD OF PLANTS

oaks and their allies, etc. (Figs. 76, 77). The delicate
branching filaments (hyphae) of the fungus spread through
the soil, wrap the rootlets with a mesh of hyphae, and pene-
trate into the cells. It seems 'clear that the fungus obtains
food from the rootlet as a parasite ; but it is also thought
that the hyphal threads, spreading widely through the soil,
are of great service to the host plant
in aiding the rootlets in absorbing.
If this be true, there is mutual ad-
vantage in the association, for the
small amount of nourishment taken
by the fungus is more than compen-
sated by its assistance in absorption.

(3) Root-tubercles. — On the roots
of many legume plants, as clovers,
peas, beans, etc., little wart -like
outgrowths are frequently found,
known as " root-tubercles " (Fig.
78). It is found that these tuber-
cles are caused by certain Bacteria,
which penetrate the roots and in-
duce these excrescent growths. The
tubercles are found to swarm with
Bacteria, which are doubtless ob-
taining food from the roots of the
host. At the same time, these Bac-
teria have the peculiar power of
laying hold of the free nitrogen of
the air circulating in the soil, and
of supplying it to the host plant
in some usable form. Ordinarily
plants can not use free nitrogen,

although it occurs in the air in such abundance, and this
power of these soil Bacteria is peculiarly interesting.

This habit of clover and its allies explains why they are
useful in what is called "restoring the soil." After ordi-

Fio. 78. Root-tubercles on
Vicia Faba.-A.fter NOLL.

PLANT STRUCTURES

nary crops have exhausted the soil of its nitrogen-contain-
ing salts, and it has hecome comparatively sterile, clover is
able to grow by obtaining nitrogen from the air through the
root-tubercles. If the crop of clover be " plowed under,"
nitrogen-containing materials which the clover has organ-
ized will be contributed to the soil, which is thus restored
to a condition which will support the ordinary crops again.
This indicates the significance of a very ordinary " rotation
of crops."

(4) Ant-plants, etc. — In symbiosis one of the symbionts
may be an animal. Certain fresh-water polyps and sponges
become green on account of Alga3 which they harbor with-
in their bodies (Fig. 79). Like
the Lichen -fungus, these ani-
mals use the food manufactured
by the Algae, which in turn find
a congenial situation for living.
By some this would also be re-
garded as a case of helotism,
the animal enslaving the alga.

Very definite arrangements
are made by certain plants for
harboring ants, which in turn
guard them against the attack
of leaf-cutting insects and oth-
er foes. These plants are called
Mynnecophytes, which means
" ant-plants," or myrmecopMlous

plants, which means "plants loving ants." These plants
are mainly in the tropics, and in stem cavities, in hollow
thorns, or elsewhere, they provide dwelling places for tribes
of warlike ants (Fig. 80). In addition to these dwelling
places they provide special kinds of food for the ants.

(5) Flowers and insects. — A very interesting and impor-
tant case of symbiosis is that existing between flowers and
insects. The flowers furnish food to the insects, and the

FIG. 79. A fresh-water polyp (Hy-
dra) attached to a twig and feed-
ing upon algae (C), which may
be seen through the transparent
body wall (B).— CALDWKLL.

THE FOOD OF PLANTS

latter are used by the flowers as agents of pollination. An
account of this relationship is deferred until seed-plants are

FIG. 80. An ant plant (Hydnophytum) from South Java, in which an excrescent
growth provides a habitation for ants.— After SCHIMPER.

considered, or it may be found, with illustrations, in Plant
Relations, Chapter VII.

92 PLANT STRUCTURES

59. Carnivorous plants, — Certain green plants, growing
in situations poor in nitrogen-containing salts, have learned
to supplement the proteids which they manufacture by cap-
turing and digesting insects. The various devices employed
for securing insects have excited great interest, since they
do not seem to be associated with the ordinary idea of plant
activities. Prominent among these forms are the bladder-
worts, pitcher-plants, sundews, Venus's fly-trap, etc. For
further account and illustrations of these plants see Plant
Relations, § 119.

CHAPTER VII

BRYOPHYTES (MOSS PLANTS)

60. Summary from Thallophytes. — Before considering the
second great division of plants it is well to recall the most
important facts connected with the Thallophytes, those
things which may be regarded as the contribution of the
Thallophytes to the evolution of the plant kingdom, and
which are in the background when one enters the region of
the Bryophytes.

(1) Increasing complexity of the body. — Beginning with
single isolated cells, the plant body attains considerable
complexity, in the form of simple or branching filaments,
cell-plates, and cell-masses.

(2) Appearance of spores. — The setting apart of repro-
ductive cells, known as spores, as distinct from nutritive
cells, and of reproductive organs to organize these spores,
represents the first important differentiation of the plant
body into nutritive and reproductive regions.

(3) Differentiation of spores. — After the introduction of
spores they become different in their mode of origin, but
not in their power. The asexual spore, ordinarily formed
by cell division, is followed by the appearance of the sexual
spore, formed by cell union, the act of cell union being
known as the sexual process.

(4) Differentiation of gametes. — At the first appearance
of sex the sexual cells or gametes are alike, but after-
ward they become different in size and activity, the large
passive one being called the egg, the small active one the

94 PLANT STRUCTURES

sperm, the organs producing the two being known as oogo-
nium and antheridium respectively.

(5) Algae the main line. — The Algae, aquatic in habit,
appear to be the Thallophytes which lead to the Bryophytes
and higher groups, the Fungi being regarded as their de-
generate descendants ; and among the Algae the Chloro-
phyceae seem to be most probable ancestors of higher forms.
It should be remembered that among these Green Algae the
ciliated swimming spore (zoospore) is the characteristic
asexual spore, and the sexual spore (zygote or oospore) is
the resting stage of the plant, to carry it over from one
growing season to the next.

61. General characters of Bryophytes.— The name given
to the group means " moss plants," and the Mosses may be
regarded as the most representative forms. Associated
with them in the group, however, are the Liverworts, and
these two groups are plainly distinguished from the Thallo-
phytes below, and from the Pteridophytes above. Starting
with the structures that the Algae have worked out, the
Bryophytes modify them still further, and make their own
contributions to the evolution of the plant kingdom, so
that Bryophytes become much more complex than Thallo-
phytes.

62. Alternation of generations. — Probably the most im-
portant fact connected with the Bryophytes is the distinct
alternation of generations which they exhibit. So impor-
tant is this fact in connection with the development of the
plant kingdom that its general nature must be clearly under-
stood. Probably the clearest definition may be obtained by
tracing in bare outline the life history of an ordinary moss.

Beginning with the asexual spore, which is not ciliated,
as there is no water in which it can swim, we may imagine
that it has been carried by the wind to some spot suitable
for its germination. It develops a branching filamentous
growth which resembles some of the Conferva forms among
the Green Algae (Fig. 81). It is prostrate, and is a regu-

BRYOPIIYTES

lar thallus body, not at all resembling the "moss plant"
of ordinary observation, and is not noticed by those una-
ware of its existence.

Presently one or more buds appear on the sides of this
alga-like body (Fig. 81, V). A bud develops into an erect

FIG. 81. Protonema of moss: A, very young protonema, showing spore (S) which
has germinated it; B, older protonema, showing branching habit, remains of
spore (s), rhizoids (r), and buds (b) of leafy branches (gametophores). — After
MULI.ER and THURGAU.

stalk upon which are numerous small leaves (Figs. 82, 102).
This leafy stalk is the " moss plant " of ordinary observa-
tion, and it will be noticed that it is simply an erect leafy
branch from the prostrate alga-like body.

At the top of this leafy branch sex-organs appear, cor-
responding to the antheridia and oogonia of the Algae, and
within them there are sperms and eggs. A sperm and egg
fuse and an oospore is formed at the summit of the leafy
branch.

The oospore is not a resting spore, but germinates im-
mediately, forming a structure entirely unlike the moss

PLANT STRUCTURES

.rh

FIG. 82. A common moss
(Polytrichum commune),
showing the leafy gameto-
phore with rhizoids (rh),
and two sporophytes (sporo-
gonia), with seta (a), calyp-
tra (c), and operculum (d),
the calyptra having been re-
moved.—After SCHENCK.

plant from which it came. This
new leafy body consists of a slender
stalk bearing at its summit an urn-
like case in which are developed nu-
merous asexual spores (Figs. 82, 107).
This whole structure is often called
the " spore fruit/7 and its stalk is
imbedded at base in the summit of
the leafy branch, thus obtaining firm
anchorage and absorbing what nour-
ishment it needs, but no more a part
of the leafy branch than is a para-
site a part of the host.

When the asexual spores, pro-
duced by the " spore fruit," germi-
nate, they reproduce the alga-like
body with which we began, and the
life cycle is completed.

In examining this life history, it
is apparent that each spore produces
a different structure. The asexual
spore produces the alga-like body
with its erect leafy branch, while
the oospore produces the " spore
fruit" with its leafless stalk and
spore case. These two structures,
one produced by the asexual spore,
the other by the oospore, appear in
alternating succession, and this is
what is meant by alternation of gen-
erations.

These two "generations" differ
strikingly from one another in the
spores which they produce. The
generation composed of alga -like
body and erect leafy branch pro-

BRYOPHYTES 97

duces only sexual spores (oospores), and therefore pro-
duces sex organs and gametes. It is known, therefore,
as the gametophyte — that is, "the gamete plant."

The generation which consists of the "spore fruit "-
that is, leafless stalk and spore case — produces only asexual
spores, and is called the sporophyte — that is, "the spore
plant."

Alternation of generations, therefore, means the alter-
nation of a gametophyte and a sporophyte in completing a
life history. Instead of having the same body produce both
asexual and sexual spores, as in most of the Algae, the two
kinds of spores are separated upon different structures,
known as "generations." It is evident that the gameto-
phyte is the sexual generation, and the sporophyte the
asexual one ; and it should be kept clearly in mind that
the asexual spore always produces the gametophyte, and
the sexual spore the sporophyte. In other words, each
spore produces not its own generation, but the other one.

The relation between the two alternating generations
may be indicated clearly by the following formula, "in
which G and S are used for gametophyte and sporophyte
respectively :

G=g>o— S— o— G=g>o— S— o— G, etc.

The formula indicates that the gametophyte produces
two gametes (sperm and egg), which fuse to form an oospore,
which produces the sporophyte, which produces an asexual
spore, which produces a gametophyte, etc.

That alternation of generations is of great advantage is
evidenced by the fact that it appears in all higher plants.
It must not be supposed that it appears first in the Bryo-
phytes, for its beginnings may be seen among the Thallo-
phytes. The Bryophytes, however, first display it fully
organized and without exception. Just what this alterna-
tion does for plants may not be fully known, but one
advantage seems prominent. By means of it many gameto-
phytes may result from a single oospore ; in other words,

98 PLANT STRUCTURES

it multiplies the product of the sexual spore. A glance at
the formula given above shows that if there were no sporo-
phyte (S) the oospore would produce but one gametophyte
(G). By introducing the sporophyte, however, as many
gametophytes may result from a single oospore as there are
asexual spores produced by the sporophyte, which usually
produces a very great number.

In reference to the sporophytes and gametophytes of
Bryophytes two peculiarities may be mentioned at this
point : (1) the sporophyte is dependent upon the gameto-
phyte for its nourishment, and remains attached to it ;
(2) the gametophyte is the special chlorophyll -generation,
and hence is the more conspicuous. It follows that, in a
general way, the sporophyte of the Bryophytes only pro-
duces spores, while the gametophyte both produces gametes
and does chlorophyll work.

It is important also to note that the protected resting
stage in the life history is not the sexual spore, as in the
Algae, but is the asexual spore in connection with the
sporophyte. These spores have a protecting wall, are
scattered, and may remain for some time without germi-
nation.

If the ordinary terms in reference to Mosses be fitted
to the facts given above, it is evident that the "moss
plant " is the leafy branch of the gametophyte ; that
the " moss fruit " is the sporophyte ; and that the alga-
like part of the gametophyte has escaped attention and
a name.

The names now given to the different structures which
appear in this life history are as follows : The alga-like part
of the gametophyte is the protonema, the leafy branch is
the gametophore ("gamete-bearer") ; the whole sporophyte
is the sporogonium (a name given to this peculiar leafless
sporophyte of Bryophytes), the stalk-like portion is the
seta, the part of it imbedded in the gametophore is the
foot, and the urn-like spore-case is the capsule.

BKYOPHYTES

63. The antheridium. — The male organ of the Bryophytes
is called an antheridium, just as among Thallophytes, but
it has a very different structure. In general among the

Fi«. 83. Sex organs of a common moss (Funaria): the group to the right represents
an antheridium (A) discharging from its apex a mass of sperm mother cells (a), a
single mother cell with its sperm (6), and a single sperm (c), showing body and
two cilia; the group to the left represents an archegonial cluster at summit of
stem (A), showing arche<jonia (a), and paraphyses and leaf sections (6), and also a
single archegonium (B), with venter (b) containing egg and ventral canal cell, and
neck (h) containing the disorganizing axial row (neck canal cells). — Afier SACHS.

Thallophytes it is a single cell (mother cell), and may be
called a simple antheridium, but in the Bryophytes it is a
many-celled organ, and may be regarded as a compound
antheridium. It is usually a stalked, club-shaped, or oval to

100

PLANT STRUCTURES

globular body (Figs. 83, 84, 103). A section through this
body shows it to consist of a single layer of cells, which
forms the wall of the antheridium, and within this a com-
pact mass of small cubical (square in section) cells, within
each one of which there is formed a single sperm (Fig. 84).
These cubical cells are evidently moth-
er cells, and to distinguish them from
others they are called sperm mother cells.
An antheridium, therefore, aside from
its stalk, is a mass of sperm mother
cells surrounded by a wall consisting
of one layer of cells.

The sperm is a very small cell with
two long cilia (Fig. 83). The two
parts are spoken of as "body" and
cilia, and the body may be straight or
somewhat curved. These small bicili-
ate sperms are one of the distinguish-
ing marks of the Bryophytes. The
existence of male gametes in the form
of ciliated sperms indicates that fertil-
ization can take place only in the pres-
ence of water, so that while the plant
has become terrestrial, and its asexual spores have respond-
ed to the new conditions and are no longer ciliated, its
sexual process is conducted as among the Green Algae. It
must not be supposed, however, that any great amount of
water is necessary to enable sperms to swim, even a film
of dew often answering the purpose.

When the mature antheridia are wet they are ruptured
at the apex and discharge the mother cells in a mass (Figs.
83, 105, E), the walls of the mother cells become mucilagi-
nous, and the sperms escaping swim actively about and are
attracted to the organ containing the egg.

64. The archegonium, — This name is given to the female
sex organ, and it is very diiferent from the oogonium of

FIG. 84. Antheridium of
a liverwort in section,
showing single layer
of wall cells surround-
ing the mass of moth-
er cells.— After STBAS-

BURGER.

BRYOPHYTKS

Thallophytes. Instead of being a single mother cell, it is
a many-celled structure, shaped like a flask- (Figs. 83, 98).
The neck of the flask is more or less elongated, and within
the bulbous base (venter) the single egg is organized. The
archegonium, made up of neck and venter, consists mostly
of a single layer of cells. This hollow flask is solid at first,
there being a central vertical row of cells surrounded by
the single layer just referred to. All of the cells of this
axial row, except the lowest one, disorganize and leave a
passageway down through the neck. The lowest one of
the row, which lies in the venter of the archegonium, or-
ganizes the egg. In this way there is formed in the arche-
gonium an open passageway through the neck to the egg
lying in the venter.

To this neck the swimming sperms are attracted, enter
and pass down it, one of them fuses with the egg, and this
act of fertilization results in an oospore.

It is supposed that archegonia have been derived in some
way from oogonia, but. no intermediate stages suggest the
steps. In any event, the presence of the archegonia is one
strong and unvarying distinction between Thallophytes
and Bryophytes. Pteridophytes also have archegonia, and
so characteristic an organ is it that Bryophytes and Pteri-
dophytes are spoken of together as Archegoniates.

65. Germination of the oospore, — The oospore in Bryo-
phytes is not a resting spore, but germinates immediately
by cell division, forming the sporophyte embryo, which
presently develops into the mature sporophyte (Fig. 85, A).
The lower part of the embryo develops downward into the
gametophore, forming the foot, which penetrates and ob-
tains a firm anchorage in the gametophore (Fig. 85, B, C).
The upper part of the embryo develops upward, organizing
the seta and capsule. In true Mosses, when the embryo
becomes too large for the venter of the archegonium in
which it is developing, the archegonium is broken near the
base of the venter and is carried upward perched on the top
25

102

PLANT STRUCTURES

of the capsule like a loose cap or hood, known as the calyp-
tra (Figs. 82, c, 107), which sooner or later falls off. As

stated before, the ma-
ture structure devel-
oped from the oospore
is called a sporogoni-
um, a form of sporo-
phyte peculiar to the
Bryophytes.

66. The sporogonium.
— In its fullest devel-
opment the sporogoni-
um is differentiated
into the three regions,
foot, seta, and capsule
(Figs. 82, 107) ; but in
some forms the seta
may be lacking, and
in others the foot also,
the sporogonium in this
last case being only the
capsule or spore case,
which, after all, is the
essential part of any
sporogonium.

At first the capsule
is solid, and its cells
are all alike. Later a
group of cells within
begins to differ in ap-
pearance from those
about them, being set
apart for the produc-
tion of spores. This

initial group of spore-producing cells is called the arche-
sporium, a word meaning "the beginning of spores." It

FIG. 85. Sporogonium of Fun aria : A, an em-
bryo sporogonium (/,/'), developing within
the venter (6, b) of an archegonium ; B, C,
tips of leafy shoots bearing young sporo-
gonia. pushing up calyptra (c) and archego-
nium neck (h), and sending the foot down
into the apex of the gametophore.— After
GOEBEL.

BRYOPI1YTES 1Q3

does not follow tliat the archesporial cells themselves pro-
duce spores, but that the spores are to appear sooner or
later in their progeny. Usually the archesporial cells
divide and form a larger mass of spore-producing cells.
Such cells are known as sporogenous ("spore-producing")
cells, or the group is spoken of as sporogenous tissue. Spo-
rogenous cells may divide more or less, and the cells of the
last division are mother cells, those which directly produce
the spores. The usual sequence, therefore, is archesporial
cells (archesporium), sporogenous cells, and mother cells ;
but it must be remembered that they all may be referred
to as sporogenous cells.

Each mother cell organizes within itself four spores,
the group being known as a tetrad. In Bryophytes and
the higher groups asexual spores are always produced in
tetrads. After the spores are formed the walls of the
mother cells disorganize, and the spores are left lying loose
in a cavity which was formerly occupied by the sporoge-
nous tissue. All mother cells do not always organize spores.
In. some cases some of them are used up in supplying nour-
ishment to those which form spores. Such mother cells are
said to function as nutritive cells. In other cases, certain
mother cells become much modified in form, being organ-
ized into elongated, spirally-banded cells called elaters (Figs.
97, 101), meaning "drivers" or "hurlers." These elaters
lie among the loose ripe spores, are discharged with them,
and by their jerking movements assist in scattering them.

The cells of the sporogonium which do not enter into
the formation of the archesporium, and are not sporoge-
nous, are said to be sterile, and are often spoken of as
sterile tissue. Every sporogonium, therefore, is made up
of sporogenous tissue and sterile tissue, and the differences
found among the sporogonia of Bryophytes depend upon
the relative display of these two tissues.

The sporogonium is a very important structure from
the standpoint of evolution, for it represents the conspicu-

104

PLANT STRUCTURES

ous part of the higher plants. The "fern plant," and
the herbs, shrubs, and trees among "flowering plants"
correspond to the sporogonmm of Bryophytes, and not to
the leafy branch (gametophore) or "moss plant." Conse-
quently the evolution of the sporogonium through the
Bryophytes is traced with a great deal of interest. It may
be outlined as follows :

In a liverwort called Riccia the simplest sporogonium
is found. It is a globular capsule, without seta or foot

'cot

FIG. 86. Diagrammatic sections of sporogonia of liverworts : A, Riccia, the whole
capsule being archesporium except the sterile wall layer ; B, Marchantia, one
half the capsule being sterile, the archesporium restricted to the other half; D,
Anthoceros, archesporium still more restricted, being dome-shaped and capping a
central sterile tissue, the colnmella (col).— After GOEBET,.

(Fig. 86, ^4). The only sterile tissue is the single layer of
cells forming the wall, all the cells within the wall be-
longing to the archesporium. The ripe sporogonium,
therefore, is nothing but a thin-walled spore case. It is
well to note that the sporophyte thus begins as a spore
case, and that any additional structures that it may de-
velop later are secondary.

In another liverwort (Marchantia) the entire lower half
of the sporogonium is sterile, while in the upper half there

BRYOPHYTES

105

is a single layer of sterile cells as a wall about the arche-
sporium, which is composed of all the remaining cells of the
upper half (Fig. 86, #). It will be noted that the sterile
tissue in this sporogonium has encroached upon the arche-
sporium, which is restricted to one half of the body. In
this case the archesporium has the form of a hemisphere.

In another liverwort (Jungermannia) the archesporium
is still more restricted (Fig. 87). The sterile tissue is organ-

FIG. 87. Diagrammatic section of spo-
rogonium of a Junrjermannia form,
showing differentiation into foot,
seta, and capsule, the archesporium
restricted to upper part of sporoso-
nium.— After GOKBKI,.

FIG. 88. Section through sporogonium of
Sphagnum, showing capsule (k) with
old archeironium neck (ah), calyptra (ca),
dome-shaped mass of sporogenous tissue
(spo), and colnmella («>). also the bulb-
ous foot (spf) imbedded in the pseudo-
podium (ps).— After SCHIMPEK.

ized into a foot and a seta, and the archesporium is a com-
paratively small mass of cells in the upper part of the
sporogonium.

In another liverwort (Antlwceros) the sterile tissue or-
ganizes foot and seta, and the archesporium is still more
restricted (Fig. 86, D). Instead of a solid hemispherical

106

PLANT STRUCTURES

mass, it is a dome-shaped mass, the inner cells of the hemi-
sphere having become sterile. This central group of sterile
cells which is surrounded by the ar-
chesporium is called the columella,
which means "a small column."

In a moss called Sphagnum there
is the same dome-shaped archespori-
um with the columella, as in An-
thoceros, but it is relatively smaller
on account of the more abundant
sterile tissue (Fig. 88).

In the highest Mosses the arche-
sporium becomes very small as com-
pared with the sterile tissue (Fig.
89). A foot, a long seta, and an
elaborate capsule are organized from'
the sterile tissue, while the arche-
sporium is shaped like the walls of
a barrel, as though the dome-shaped
archesporium of Sphagnum or An-
thoceros had become sterile at the
apex. In this way the columella is
continued through the capsule, and
is not capped by the archesporium.

This series indicates that after
the sporogonium begins as a simple
spore case (Riccia), its tendency is
to increase sterile tissue and to re-
strict sporogenous tissue, using the
sterile tissue in the formation of the
organs of the sporogonium body, as

foot, Seta, Capsule Walls, etc.

Among the Green Algae there is
a form known as Coleochcete, whose
bod resembles - those of the sim-

J .^^

plest Liverworts (Fig. 90). u hen

FIG. 89. Young sporogoni-
um of a true moss, show-
ing foot, seta, and young
capsule, in which the ar-
chesporium (darker por-
tion) is barrel -shaped, and
through it the columella is
continuous with the lid. —
After CAMPBELL.

BKYOPIIYTES

107

its oosporcs germinate there is formed a globular mass of
cells, every one of which is a spore mother cell (Fig. 90, C).
If an outer layer of mother cells should become sterile and
form a wall about the others, such a spore case as that of

FIG. W.-Coleocttcete. one of the green algae: A, a portion of the thallns, showing
oogonia with trichogynes (og), antheridia (an), and two enlarged biciliate sperms
(2): B, a fertilized oogonium containing oospore and invested by a tissue (r)
which has developed after fertilization ; C, an oospore which has germinated
and formed a mass of cells (probably a sporophyte), each one of which organizes
a biciliate zoospore (D),— After PRINGSHEIM.

Riccia would be the result (Fig. 86, A). For such reasons
many believe that the Liverworts have been derived from
such forms as Coleochmte.

67. The gametophyte. — Having considered the sporo-
phyte body as represented by the sporogonium, we must
consider the gametophyte body as represented by proto-
nema and leafy branch (gametophore). The gametophyte
results from the germination of an asexual spore, and in
the Mosses it is differentiated into protonema and leafy
gametophore (Figs. 81, 82, 102). Like the sporophyte,

10$ PLANT STRUCTUKES

however, it shows an interesting evolution from its sim-
plest condition in the Liverworts to its most complex con-
dition in the true Mosses.

In the Liverworts the spore develops a flat thallus body,
one plate of cells or more in thickness, which generally
branches dichotomously (see § 29) and forms a more or less
extensive body (Fig. 92). This thallus is the garnet ophyte,
there being no differentiation into protonema and leafy
branch.

In the simpler Liverworts the sex organs (antheridia
and archegoiiia) are scattered over the back of this thallus
(Fig. 92). In other forms they become collected in certain
definite regions of the thallus. In other forms these defi-
nite sexual regions become differentiated from the rest of
the thallus as disks. In other forms these disks, bearing
the sex organs, become short-stalked, and in others long-
stalked, until a regular branch arises from the thallus
body (Figs. 96, 97). This erect branch, bearing the sex or-
gans, is, of course, a gametophore, but it is leafless, the
thallus body doing the chlorophyll work.

In the Sphagnum Mosses the spore develops the same
kind of flat thallus (Fig. 104), but the gametophore be-
comes leafy, sharing the chlorophyll work with the thallus.
In the true Mosses most of the chlorophyll work is done by
the leafy gametophore, and the flat thallus is reduced to
branching filaments (the protonema) (Fig. 102).

The protonema of the true Mosses, therefore, corre-
sponds to the flat thallus of the Liverworts and Sphagnum,
while the leafy branch corresponds to the leafless gameto-
phore found in some Liverworts. It also seems evident
that the gametophore was originally set apart to bear sex
organs, and that the leaves which appear upon it in the
Mosses are subsequent structures.

CHAPTEE VIII

THE GREAT GROUPS OF BRYOPHYTES

HEPATIC^: (Liverworts)

68. General character, — Liverworts live in a variety of
conditions, some floating on the water, many in damp
places, and many on the bark of trees. In general they are
moisture-loving plants (hydrophytes), though some can en-
dure great dryness. The gametophyte body is prostrate,
though there may be erect and leafless gametophores.

This prostrate habit develops a dorsiventral body — that
is, one whose two surfaces (dorsal and ventral) are exposed
to different conditions and become unlike in structure. In
Liverworts the ventral surface is against the substratum,
and puts out numerous hair-like processes (rhizoids) for ab-
sorption and anchorage. The dorsal region is exposed to
the light and its cells develop chlorophyll. If the thallus
is thin, chlorophyll is developed in all the cells ; if it be so
thick that the light is cut off from the ventral cells, the
thallus is differentiated into a green dorsal region doing the
chlorophyll work, and a colorless ventral region producing
absorbing rhizoids. This latter represents a simple differ-
entiation of the nutritive body into working regions, the
ventral region absorbing material and conducting it to the
green dorsal cells which use it in making food.

There seems to have been at least three main lines of
development among Liverworts, each beginning in forms
with a very simple thallus, and developing in different di-
rections. They are briefly indicated as follows :

109

110

PLANT STRUCTURES

69. Harchantia forms. — In this line the simple thallus
gradually "becomes changed into a very complex one. The

thallus retains its simple
outlines; but becomes thick
and differentiated in tissues
(groups of similar cells).
The line may be distin-
guished, therefore, as one
in which the differentia-
tion of the tissues of the
gametophyte is emphasized
(Figs. 91-93). In Mar-
chantia proper the thallus
becomes very complex, and
it may be taken as an illus-
tration.

The thallus is so thick
that there are very distinct
green dorsal and colorless

ventral regions (Fig. 94). The latter puts out numerous
rhizoids and scales from the single layer of epidermal cells.
Above the ventral epidermis are several layers of colorless

FIG. 91. A very small species of Jticcia,
one of the Marchantia forms : A, a
group of thallus bodies slightly en-
larged ; B, section of a thallus, show-
ing rhizoids and two sporogonia im-
bedded and communicating with the
outside by tubular passages in the
thallus.— After STRASBURGER.

FIG. 92. Ricciocarpvs, a Marchantia form, showing numerous rhizoids from ventral
surface, the dichotomous branching, and the position of the sporogonia on the
dorsal surface along the " midribs."— CALDWELL.

FIG. 93. Two common liverworts : to the left is Conocephalus, a Marchantia form,
showing rhizoids, dichotomous branching, and the conspicuous rhombic areas
(areolse) on the dorsal surface; to the right is Anthoceros, with its simple thallus
and pod-like sporogonia. — CALDWELL.

rid

FIG. 94. Cross-sections of thallus of Marchantia: A, section from thicker part of
thallus, where supporting tissue (p) is abundant, and showing lower epidermis
giving rise to rhizoids (h) and plates (J), also chlorophyll tissue (chl) organized
into chambers by partitions (o)\ B, section near margin of thallus more magnified,
showing lower epidermis, two layers of supporting tissue (p) with reticulate walls,
a single chlorophyll chamber with its bounding walls ($) and containing short,
often branching filaments whose cells contain chloroplasts (chl), overarching
upper epidermis (o) pierced by a large chimney-like air-pore (sp). — After GOEBEI-.

FIG. 95. Section through cupule of Marchcmtia, showing wall in which are chloro-
phyll-bearing air-chambers with air-pores, and gemmae (a) in various stages of
development.— After KNY.

FIG. 96. Jfarchanfia poh/morpha : the lower figure represents a gametophyte bear-
ing a mature aiitheridial branch (d), some young antheridial branches, and also
eome cupules with toothed margins, in which the gemmae may be seen ; the
upper figure represents a partial section through the antheridial disk, and shows
antheridia %vithin the antheridial cavities (a, b, c, d, f.f). — After KNY.

THE GREAT GROUPS OF BRYOPHYTES

113

cells more or less modified for conduction. Above these
the dorsal region is organized into a series of large air cham-
bers, into which project chlorophyll-containing cells in the

FIG. 97. Marchantia polymorpha, a common liverwort : 1. thallns. with rhizoide,
bearing a mature archegonial branch (/) and several younger ones (a, b, c, d, e)\
2 and 3, dorsal and ventral views of arcliegonial disk; A and 5, young sporophyte
(sporogonium) embryos; 6. more mature sporogonium still within enlarged venter
of archegoninm; 7, mature sporogonium discharging spores; 8, three spores and
an elater.— After KNY.

form of short branching filaments. Overarching the air
chambers is the dorsal epidermis, and piercing through it
into each air chamber is a conspicuous air pore (Fig. 94, B}.

114

PLANT STKUCTDKES

The air chambers are outlined on the surface as small

rhombic areas (areolce), each containing a single air pore.

Peculiar reproductive bodies are also developed upon

the dorsal surface of Marchantia for vegetative multiplica-

FIG. 98. Marchantia polymorpha : 1, partial section through archegonial disk, show-
ing archegonia with long necks, and venters containing eggs: 9, young archego-
n in m showing axial row; 10, superficial view at later stage; 11. mature archego-
nium, with axial row disorganized and leaving an open passage to the large egg;
12, cross-section of venter; 13, cross-section of neck. — After KNY.

tion. Little cups (citpules] appear, and in them are numer-
ous short-stalked bodies (gemmce), which are round and
flat (biscuit-shaped) and many-celled (Figs. 95, 96). The

THE GREAT GROUPS OF BRYOPHYTES H5

gemmae fall off and develop new thallus bodies, making
rapid multiplication possible.

Marchantia also possess remarkably prominent gameto-
phores, or "sexual branches" as they are often called.
In this case the gametophores are differentiated, one bear-
ing only antheridia (Fig. 96), and known as the "anthe-
ridial branch," the other bearing only archegonia (Figs. 97,
98), and known as the " archegonial branch." The scal-
loped antheridial disk and the star-shaped archegonial disk,
each borne up by the stalk-like garnet oph ore, are seen in the
illustrations. Xot only are the gametophores sexually dif-
ferentiated, but as only one appears on each thallus, the thal-
lus bodies are sexually differentiated. When the two sex
organs appear upon different individuals, the plant is said to
be dioecious, meaning "two households"; when they both
appear upon the same individual, the plant is monwcious,
meaning " one household." Some of the Bryophytes are mo-
noecious, and some of them are dioecious (as Marchantia).

Another distinguishing mark of the line of Marchantia
forms is that the capsule-like sporogonium opens irregu-
larly to discharge its spores (Fig. 97, 7).

70. Jungermaimia forms.— This is the greatest line of
the Liverworts, the forms being much more numerous
than in the other lines. They grow in damp places ; or in
drier situations on rocks, ground, or tree-trunks ; or in the
tropics also on the leaves of forest plants. They are gen-
erally delicate plants, and resemble small Mosses, many of
them doubtless being commonly mistaken for Mosses.

This resemblance to Mosses suggests one of the chief
features of the line. Beginning with a simple thallus, as
in the Marchantia line, the structure of the thallus re-
mains simple, there being no such differentiation of tissues
as in the Marchantia line ; but the form of the thallus
becomes much modified (Figs. 99, 100). Instead of a flat
thallus with even outline, the body is organized into a cen-
tral stem-like axis bearing two rows of small, often crowded

116

PLANT STRUCTURES

leaves. There are really three rows of leaves, but the third
is on the ventral side against the substratum, and is often
so much modified as not to look like the other leaves. In
consequence of this the Jungermannia forms are usually
called "leafy liverworts," to distinguish them from the

FIG. 99. Two liverworts, both Jungermannia forms: to the left is Blasia, which re-
tains the thallus form but has lobed margins; to the right is Scapania, with dis-
tinct leaves and sporogonia (A).— CALDWELL.

other Liverworts, which are "thallose." They are also
often called " scale mosses," on account of their moss-like
appearance and their small scale-like leaves.

The line may be distinguished, therefore, as one in
which the differentiation of the form of the gametophyte
is emphasized. Another distinguishing mark is that the
sporogonium has a prominent seta, and the capsule splits
down into four pieces (valves) when opening to discharge
the spores (Fig. 100, C).

71. Anthoceros forms. — This line contains comparatively
few forms, but they are of great interest, as they are sup-
posed to represent forms which have given rise to the

THE GREAT GKOUPS OF BRYOPHYTES

FIG. 100. Species of Lepidnzia. a genus of leafy liverworts, showing different leaf
forms, and in A and Cthe dehiscence of the sporogonium by four valves. In C
rhizoids are evident; and in B, D, and E the three rows of leaves are seen, the
leaves of the ventral row being comparatively small. — After ENGLER and PRANTL.

Mosses, and possibly to the Pteridophytes also. The
thallus is very simple, being differentiated neither in
structure nor form, as in the two other lines ; but the
26

118

PLANT STRUCTURES

special development has been in connection with the

sporogonium (Figs. 93, 101).

This complex sporogonium (sporophyte) has a large

bulbous foot imbedded in the simple thallus, while

above there arises a long pod-like capsule. The com-
plex walls of this cap-
sule contain chlorophyll
and air pores, so that
the sporogonium is or-
ganized for chlorophyll
work. If the foot could
send absorbing processes
into the soil, this sporo-
phyte could live inde-
pendent of the gameto-
phyte. In opening to
discharge spores the pod-
like capsule splits down
into two valves.

Another peculiarity
of the Anthoceros forms
is in connection with
the antheridia and arch-
egonia. These organs,
instead of growing out
free from the body of the
thallus, as in other Liv-
erworts, are imbedded in
it. The significance of

this peculiarity lies in
the fact t]iat jt j^ a char_
.

acter which belongs to
the Pteridophytes.

The chief direction of development of the three liv-
erwort lines may be summed up briefly as follows : The
Marchantia line has differentiated the structure of the

FIG. 101. Anthoceros gracilis : A, several
gametophytes, on which sporogonia have
developed ; B, an enlarged sporogonium,
showing its elongated character and de-
hiscence by two valves leaving exposed
the slender columella on the surface o^
which are the spores; C, D, E, F, ela-
ters of various forms ; G, spores. — After

THE GEEAT GKOUPS OF BKYOPHYTES

garnet ophyte ; the Jungermannia line has differentiated
the form of the garnet ophyte ; the AntJioceros line has
differentiated the structure of the sporophyte. It should
be remembered that other characters also serve to distin-
guish the lines from one another.

Musci (Mosses)

72. General character. — Mosses are highly specialized
plants, probably derived from Liverworts, the numerous
forms being adapted to all conditions, from submerged to
very dry, being most abundantly displayed in temperate
and arctic regions. Many of them may be dried out com-
pletely and then revived in the presence of moisture, as is
true of many Lichens and Liverworts, with which forms
Mosses are very commonly associated.

They also have great power of vegetative multiplica-
tion, new leafy shoots putting out from old ones and from
the protonema indefinitely, thus forming thick carpets and
masses. Bog mosses often completely fill up bogs or small
ponds and lakes with a dense growth, which dies below
and continues to grow above as long as the conditions are
favorable. These quaking bogs or " mosses," as they are
sometimes called, furnish very treacherous footing unless
rendered firmer by other plants. In these moss-filled bogs
the water and silt shut off the lower strata of moss from
complete disorganization, and they become modified into a
coaly substance called peat, which may accumulate to con-
siderable thickness by the continued upward growth of the
mass of moss.

The gametophyte body is differentiated into two very
distinct regions : (1) the prostrate dorsiventral thallus,
which is called protonema in this group, and which may be
either a broad flat thallus (Fig. 104) or a set of branching
filaments (Figs. 81, 102) ; (2) the erect leafy branch or
gametophore (Fig. 82). This erect branch is said to be

120

PLANT STRUCTURES

radial, in contrast with the dorsiventral thallus, referring
to the fact that it is exposed to similar conditions all
around, and its organs are arranged about a central axis
like the parts of a radiate animal. This position is much

more favorable for the
chlorophyll work than
the dorsiventral posi-
tion, as the special
chlorophyll organs
(leaves) can be spread
out to the light freely
in all directions.

It should be re-
marked that the gam-
etophyte in all groups
of plants is a thallus,
doing its chlorophyll
work, when it does
any, in a dorsiventral
position ; the only ex-
ception being the ra-
dial leafy branch that
arises from the thal-
lus of Mosses. From
Mosses onward the
gametophyte becomes
less conspicuous, so
that the prominent
leafy plants of the
higher groups hold no

relation to the little erect leafy branch of the Mosses,
which is put out by the gametophyte, and which is the
best the gametophyte ever does toward getting into a bet-
ter position for chlorophyll work.

The leafy branch of the Mosses usually becomes inde-
pendent of the thallus by putting out rhizoids at its base

FIG. 102. A moss (Bryum), showing base of a
leafy branch (gametophore) attached to the
protonenia. and having sent out rhizoids. On
the protonemal filament to the right and be-
low is the young bud of another leafy branch.
— MULLER.

THE GREAT GROUPS OF BRYOPHYTES

121

(Fig. 102), the thallus part dying. Sometimes, however,
the filamentous protonema is very persistent, and gives rise
to a perennial succession of leafy branches.

FIG. 103. Tip of leafy branch of a moss (Funaria), bearing a cluster of sex organs,
showing an old antheridium (A), a younger one (B), some of the curious associated
hairs (/>), and leaf sections (I).— After CAMPBELL.

At the summit of the leafy gametophore, either upon
the main axis or upon a lateral branch, the antheridia and
archegonia are borne (Figs. 83, 103). Often the leaves at
the summit become modified in form and arranged to form

122

PLANT STRUCTURES

a rosette, in the center of which are the sex organs. This
rosette is often called the "moss flower," but it holds no
relation to the flower of Seed-plants, and the phrase should
not be used. A rosette may contain but one kind of sex
organ (Figs. 83, 103), or it may contain both kinds, for
Mosses are both dioecious and monoecious. The two prin-
cipal groups are as follows :

73. Sphagnum forms. — These are large and pallid bog
mosses, found abundantly in marshy ground, especially of
temperate and arctic regions, and are conspicuous peat-
formers (Fig. 105, A). The leaves and gametophore axis

are of peculiar struc-
ture to enable them
to suck up and hold
a large amount of wa-
ter. This abundant
water - storage tissue
and the comparative-
ly poor display of
chlorophyll - contain-
ing cells gives the
peculiar pallid ap-
pearance.

They resemble the
Liverworts in the
broad thallus body
of the gametophyte,
from which the large
leafy gametophore
arises (Fig. 104).
They also resemble

Anthoceros forms in the sporogonium, the archesporium
being a dome-shaped mass (Fig. 105, C). On the other
hand, they resemble the true Mosses, not only in the leafy
gametophore, but also in the fact that the capsule opens
at the apex by a circular lid, called the operculum (Fig.

FIG. 104. Thallus body of gametophyte of Sphag-
num, giving rise to rhizoids (f) and buds (k)
which develop into the large leafy branches
(gametophores). — After CAMPBELL.

THE GREAT GROUPS OF BRYOPHYTES

123

105, D), which means a "cover" or "lid." This may
serve to illustrate what is called an "intermediate" or
"transition" type, Sphagnum showing characters which
ally it to Anthcceros forms on the one side, and to true
Mosses on the other.

A peculiar feature of the sporogonium is that it has no
long stalk-like seta, as have the true Mosses, although it
appears to have one. This false appearance arises from the

FIG. 105. Sphagnum : A, a leafy branch (gametophore) bearing four mature sporo-
gonia; B, archegonium in whose venter a young embryo sporophyte (em) is de-
veloping; C, section of a young sporogonium (sporophyte), showing the bulbous
foot (spf) imbedded in the apex of the pseudopodium (ps), the capsule (k), the
columella (co) capped by the dome-shaped archesporium (spo), a portion of the
calyptra (ca), and the old archegonium neck (ah); D, branch bearing mature
sporogonium and showing pseudopodium (ps), capsule (k), and operculum (rf); E,
antberidium discharging sperms; F, a single sperm, showing coiled body and two
cilia. — After SCHIMPER.

fact that the axis of the gametophore is prolonged above
its leafy portion, the prolongation resembling the seta of
an ordinary moss (Fig. 105, D). This prolongation is

124

PLANT STRUCT UKES

called a pseudopodium, or " false stalk," and in the top of
it is imbedded the foot of the sporogonium carrying the
globular capsule (Fig. 105, C).

74. True Mosses. — This immense and most highly organ-
ized Bryophyte group contains the great majority of the
Mosses, which are sometimes called the Bryum forms, to
distinguish them from the Sphagnum forms. They are

FIG. 106. Different stages in the development of the leafy gametophore from the pro-
tonema of a common moss (Funaria): A, the first few cells and a rhizoid (r); J5,
C. later stages, showing apical cell (1) and young leaves (2); D, later stage much
less magnified, showing protonemal filaments and the young gametophore (gam)
—After CAMPBELL.

the representative Bryophytes, the only group vying with
them being the leafy Liverworts, or Jungermannia forms.
They grow in all conditions of moisture, from actual sub-
mergence in water to dry rocks, and they also form exten-
sive peat deposits in bogs.

The thallus body of the gametophyte is made up of
branching filaments (Figs. 81, 102), those exposed to the

THE GREAT GROUPS OF BKYOPHYTES

125

light containing chlorophyll, and those in the substratum
being colorless and acting as rhizoids. The leafy gameto-
phores are often highly organized (Figs. 102, 106), the
leaves and stems showing a certain amount of differentia-
tion of tissues.

It is the sporophyte, however, which shows the great-
est amount of specialization (Fig. 107). The sporogonium

FIG. 107. A common moss (Funaria): in the center is the leafy shoot (gametophore),
with rhizoids, several leaves, and a sporogonium (sporophyte), with a long seta,
capsule, and at its tip the calyptra (col); to the right a capsule with calyptra re-
moved, showing the operculum (o); to the left a young sporogonium pushing up
the calyptra from the leafy shoot.— After CAMPBELL.

has a foot and a long slender seta, but the capsule is espe-
cially complex. The archesporium is reduced to a small
hollow cylinder (Fig. 88), the capsule wall is most elabo-
rately constructed, and the columella runs through the

FIG. 108. Longitudinal section of moss capsule
(Funaria), showing its complex character:
d, operculum; p, peristome: c, c', columel-
la; $, sporogenous tissue; outside of s the
complex wall consisting of layers of cells
and large open spaces (h) traversed by
strands of tissue.— After GOEBEL.

FIG. 110. Sporogonia of Grimmia, from all of
which the operculum has fallen, displaying
the peristome teeth : A, position of the teeth
when dry ; B, position when moist.— After
KEENER.

sin

FIG. 109. Partial longitudinal
section through a moss cap-
sule : A, younger capsule,
showing wall cells (a), cells
of columella (i\ and sporog-
enous cells (su) ; B, some-
what older capsule, a and i
same as before, and sm the
spore mother cells. — After
GOEBEL.

THE GREAT GROUPS OF BRYOPHYTES ^97

center of the capsule to the lid-like operculum (Figs. 108,
109). When the operculum falls off the capsule is left
like an urn full of spores, and at the mouth of the urn
there is usually displayed a set of slender, often very beau-
tiful teeth (Fig. 110), radiating from the circumference to
the center, and called the peristome, meaning "about the
mouth." These teeth are hygroscopic, and by bending
inward and outward help to discharge the spores.

CHAPTER IX

PTERIDOPHYTES (FERN PLANTS)

75. Summary from Bryophytes. — In introducing the Bryo-
phytes a summary from the Thallophytes was given (see §
60), indicating certain important things which that group
has contributed to the evolution of the plant kingdom.
In introducing the Pteridophytes it is well to notice certain
important additions made by the Bryophytes.

(1) Alternation of generations. — The great fact of alter-
nating sexual (gametophyte) and sexless (sporophyte) gen-
erations is first clearly expressed by the Bryophytes, although
its beginnings are to be found among the Thallophytes.
Each generation produces one kind of spore, from which is
developed the other generation.

(2) Gametophyte the chlorophyll generation. — On account
of this fact the food is chiefly manufactured by the gameto-
phyte, which is therefore the more conspicuous generation.
When a moss or a liverwort is spoken of, therefore, the
gametophyte is usually referred to.

(3) Gametophyte and sporophyte not independent. — The
sporophyte is mainly dependent upon the gametophyte for
its nutrition, and remains attached to it, being commonly
called the sporogonium, and its only function is to produce
spores.

(4) Differentiation of tliallus into stem and leaves.—
This appears incompletely in the leafy Liverworts (Junger-
mannia forms) and much more clearly in the erect and
radial leafy branch (gametophore) of the Mosses.

128

PTERIDOPHYTES. 129

(5) Many-celled sex organs. — The antheridia and the
flask-shaped archegonia are very characteristic of Bryo-
phytes as contrasted with Thallophytes.

76. General characters of Pteridophytes.— The name means
"fern plants/'' and the Ferns are the most numerous and the
most representative forms of the group. Associated with
them, however, are the Horsetails (Scouring rushes) and
the Club-mosses. By many the Pteridophytes are thought
to have been derived from such Liverworts as the Antho-
ceros forms, while some think that they may possibly have
been derived directly from the Green Algse. Whatever
their origin, they are very distinct from Bryophytes.

One of the very important facts is the appearance of
the vascular system, which means a "system of vessels,"
organized for conducting material through the plant body.
The appearance of this system marks some such epoch in
the evolution of plants as is marked in animals by the
appearance of the "backbone." As animals are often
grouped as "vertebrates" and "invertebrates," plants are
often grouped as "vascular plants" and "non-vascular
plants," the former being the Pteridophytes and Spermato-
phytes, the latter being the Thallophytes and Bryophytes.
Pteridophytes are of great interest, therefore, as being the
first vascular plants.

77. Alternation of generations. — This alternation con-
tinues in the Pteridophytes, but is even more distinct than
in the Bryophytes, the gametophyte and sporophyte be-
coming independent of one another. An outline of the life
history of an ordinary fern will illustrate this fact, and will
serve also to point out the prominent structures. Upon the
lower surface of the leaves of an ordinary fern dark spots
or lines are often seen. These are found to yield spores,
with which the life history may be begun.

When such a spore germinates it gives rise to a small,
green, heart-shaped thallus, resembling a delicate and sim-
ple liverwort (Fig. Ill, A). Upon this thallus antheridia

130

PLANT STRUCTURES

and archegonia appear, so that it is evidently a gameto-
pliyte. This gametophyte escapes ordinary attention, as it
is usually very small, and lies prostrate upon the substra-
tum. It has received the name prothallium or prothallus,
so that when the term prothallium is used the gametophyte
of Pteridophytes is generally referred to ; j ust as when the
term sporogonium is used the sporophyte of the Bryophytes
is referred to. Within an archegonium borne upon this little
prothallium an oospore is formed. When the oospore ger-

FIG. 111. Prothallmm of a common fern (Aspidium): A, ventral surface, showing
rhizoids (rh), antheridia (an), and archegonia (ar) ; B, ventral surface of an older
gametophyte, showing rhizoids (rh) and young sporophyte with root (w) and leaf
(b).— After SCUENCK.

minates it develops the large leafy plant ordinarily spoken
of as " the fern," with its subterranean stem, from which
roots descend, and from which large branching leaves rise
above the surface of the ground (Fig. Ill, B). It is in
this complex body that the vascular system appears. No
sex organs are developed upon it, but the leaves bear numer-
ous sporangia full of asexual spores. This complex vascular
plant, therefore, is a sporophyte, and corresponds in this
life history to the sporogonium of the Bryophytes. This

PTERIDOPHYTES 131

completes the life cycle, as the asexual spores develop the
prothallium again.

In contrasting this life history with that of Bryophytes
several important differences are discovered. The most
striking one is that the sporophyte has become a large,
leafy, vascular, and independent structure, not at all re-
sembling its representative (the sporogonium) among the
Bryophytes.

Also the gametophyte has become much reduced, as
compared with the gametophytes of the larger Liverworts
and Mosses. It seems to have resumed the simplest liver-
wort form, even the gametophore being suppressed, and
represented, if at all, by a rudiment. The conspicuous
leafy branch of the Mosses, commonly called " the moss
plant," corresponds to nothing in the Pteridophytes, there-
fore, except possibly the rudiment referred to, the prothal-
lium representing only the protonema part of the gameto-
phyte of the true Mosses.

This reduction of the gametophyte seems to be associ-
ated with the fact that the chlorophyll work has been trans-
ferred to the sporophyte, which hereafter remains the
conspicuous generation. The "fern plant" of ordinary
observation, therefore, is the sporophyte ; while the "moss
plant " is a leafy branch of the gametophyte.

Another important contrast indicated is that in Bryo-
phytes the sporophyte is dependent upon the gametophyte
for its nutrition, remaining attached to it ; while in the
Pteridophytes both generations are independent green
plants, the leafy sporophyte remaining attached to the
small gametophyte only while beginning its growth (Fig.
Ill, /y).

Among the Ferns some interesting exceptions to this
method of alternation have been observed. Under certain
conditions a leafy sporophyte may sprout directly from the
prothallium (gametophyte) instead of from an oospore.
This is called apogamy, meaning " without the sexual act."

132 PLANT STIit:CTUKES

Under certain other conditions prothallia are observed to
sprout directly from the leafy sporophyte instead of from
a spore. This is called apospory, meaning "without a
spore."

78. The gametophyte. — The prothallium, like a simple
liverwort, is a dorsiventral body, and puts out numerous

FIG. 112. Stag-horn fern (Platycerium grande), an epiphytic tropical form, showing
the two forms of leaves : a and b, young sterile leaves ; c, leaves bearing spo-
rangia ; d, an old sterile leaf.— CALDWELL.

rhizoids from its ventral surface (Fig. 111). It is so thin
that all the cells contain chlorophyll, and it is usually short-
lived. In rare cases it becomes quite large and permanent,

FIG. 113. Archegonium of P/sri* at the time of fertilization, showing tissue of gam-
etophyte (A), the cells forming the neck (#». the passageway formed by the dis-
organization of the canal cells (V), and the egg (D) lying exposed in the venter.
— CALUWELL.

FIG. 114. Antheridium of Pteris (£). showing wall cells («), opening for escape of
sperm mother cells (e\ escaped mother cells (c), sperms free from mother cells (6),
showing spiral and multiciliate character. — CALDWELL.

134

PLANT STRUCTURES

being a conspicuous object in connection with the sporo-
phyte.

At the bottom of the conspicuous notch in the prothal-
lium is the growing point,
representing the apex of the
plant. This notch is always
a conspicuous feature.

The antheridia and arch-
egonia are usually developed
on the under surface of the
prothallium (Fig. Ill, .1),
and differ from those of all
Bryophytes, except the An-
thoceros forms, in being sunk
in the tissue of the prothal-
lium and opening on the sur-

FIG. 115. Development of gametophytc
of Pteris: the figure to the left shows
the old spore (B), the rhizoid ( O, and
the thallus U); that to the right is
older, showing the same parts, and
also the apical cell (D).— CALDWELL.

FIG. 116. Young gametophytc of Pteris,
showing old spore wall (B), rhizoid*
(Ct). apical cell (D). a young author
idium (K), and an older one in which
sperms have organized (F).—
WELL.

PTEKIDOPHYTES

135

face, more or less of the neck of the archegonium projecting
(Fig. 113). The eggs are not different from those formed
within the archegonia of Bryophytes, but the sperms are
very different. The Bryophyte sperm has a small body and
two long cilia, while the Pteridophyte sperm has a long
spirally coiled body, blunt behind and tapering to a point in
front, where numerous cilia are developed (Fig. 114). It
is, therefore, a large, spirally-coiled, multiciliate sperm, and
is quite characteristic of all Pteridophytes excepting the
Club-mosses. It is evident that a certain amount of water
is necessary for fertilization — in fact, it is needed not only

FIG. 117. Sections of portions of the gainetopliyte ()f Pteris, showing development
of archegonium: A, young stage, showing cells which develop the neck (a), and
the cell from which the egg cell and canal cells develop (6); B, an older stage,
showing neck cells (a), neck canal cell (£>). and cell from which is derived the egg
cell, and the ventral canal cell (c); C, a still older stage, showing increased num-
ber of neck cells (a), two neck canal cells (b), the ventral canal cell (c), and the
cell in which the egg is organized (rf). — CALDWELL.

by the swimming sperm, but also to cause the opening of
the antheridiuin and of the archegonium neck. There
seems to be a relation between the necessity of water for
fertilization and a prostrate, easily moistened gametophyte.
Prothallia are either monoecious or dioecious (see § 69).
When the prothallia are developing (Fig. 115) the anther-

FIG. 118. A fern (Aspidium), showing three large branching leaves coming from a
horizontal subterranean stem (rootstock): young leaves are also shown, which
show circinate vernation. The stem, young leaves, and petioles of the large
leaves are thickly covered with protecting hairs. The stem gives rise to numerous
small roots from its lower surface. The figure marked .} represents the under sur-
face of a portion of the leaf, showing seven sori with shield-like indusia; at ." is
represented a section through a sorns. showing the sporangia attached and pro-
tected by the indusium; while at « is represented a single sporangium opening
and discharging its spores, the heavy annulus extending along the back and over
the top.— After WOSSIDLO,

PTERIDOPHYTES

137

idia begin to appear very early (Fig. 116), and later the
archegonia (Fig. 117). If the prothallium is poorly nour-
ished, only antheridia appear ; it needs to be well developed
and nourished to develop archegonia. There seems to be
a very definite relation, therefore, between nutrition and
the development of the two sex organs, a fact which must
be remembered in connection with certain later develop-
ments.

79. The sporophyte. — This complex body is differentiated
into root, stem, and leaf, and is more highly organized
than any plant body heretofore mentioned (Fig. 118). The
development of this body and its three great working regions
must be considered separately.

(1) Development of embryo. — The oospore, from which
the sporophyte develops, rests in the venter of the arche-
goninm, which at this stage resembles a depression in the

FIG. 119. Embryos of a common fern (Pteris): A, young embryo, showing direction
of basal wall (I), and of second walls (77), which organize quadrants, each of
which subsequently develops into foot (/), root (w), leaf (b). and stem (*); B, an
older embryo, in which the four regions (lettered as in ^4) have developed further,
also showing venter of archegonium (aw), and some tissue of the prothallium (pr).
—A after KIENITZ-GKRLOPP; B after HOPMKISTER.

lower surface of the prothallium (Fig. 119, B). It germi-
nates at once, as in Bryophytes, not being a resting spore
as in Green Algae. The resting stage, as in the Bryophytes,

138 PLANT STRUCTURES

is in connection with the asexual spores, which may be
kept for a long time and then germinated.

The first step in germination is for the oospore to di-
vide into two cells, forming a two-celled embryo. In the
ordinary Ferns this first dividing wall is at right angles to
the surface of the prothallium, and is called the basal wall
(Fig. 119, A). One of the two cells, therefore, is anterior
(toward the notch of the prothallium), and the other is
posterior.

The two cells next divide by forming walls at right
angles to the basal wall, and a four-celled embryo is the
result. This is called the "quadrant stage" of the em-
bryo, as each one of the four cells is like the quadrant of a
sphere.

With the appearance of the quadrant, four body regions,
are organized, each cell by its subsequent divisions giving
rise to a distinct working region (Fig. 119, A). Two of the
cells are inner (away from the substratum) ; also one of the
inner and one of the outer (toward the substratum) cells
are anterior ; while the two other inner and outer cells are
posterior. The anterior outer cell develops the first leaf of
the embryo, generally called the cotyledon (Fig. 119, b) ; the
anterior inner cell develops the stem (Fig. 119, s) ; the pos-
terior outer cell develops the first (primary) root (Fig.
119, w) ; the posterior inner cell develops a special organ
for the use of the embryo, called the foot (Fig. 119, /).
The foot remains in close contact with the prothallium and
absorbs nourishment from it for the young embryo. When
the young sporophyte has developed enough to become in-
dependent the foot disappears. It is therefore spoken of
as a temporary organ of the embryo. It is necessary for the
leaf to emerge from beneath the prothallium, and it may
be seen usually curving upward through the notch. The
other parts remain subterranean.

(2) The root. — The primary root organized by one of
the quadrants of the embryo is a temporary affair (Figs.

PTERIDOPHYTES 139

111, 119), as it is in an unfavorable position in reference to
the dorsiventral stem, which puts out a series of more favor-
ably placed secondary roots into the soil (Fig. 118). The
mature leafy sporophyte, therefore, has neither foot nor
primary root, the product of two of the quadrants of the
embryo having disappeared.

The secondary roots put out by the stem are small, and
do not organize an extensive system, but they are interest-
ing as representing the first appearance of true roots, which
therefore come in with the vascular system. In the lower
groups the root function of absorption is conducted by sim-
ple hair-like processes called rhizoids ; but true roots are
complex in structure and contain vessels.

(3) The stem. — In most of the Ferns the stem is sub-
terranean and dorsiventral (Fig. 118), but in the "tree
ferns " of the tropics it forms an erect, aerial shaft bearing
a crown of leaves (Fig. 120). In the other groups of Pteri-
dophytes there are also aerial stems, both erect and pros-
trate. The stem is complex in structure, the cells being
organized into different " tissue systems," prominent among
which is the vascular system. These tissue systems of vas-
cular plants are described in Chapter XV.

The appearance of the vascular system in connection
with the leafy sporophyte is worthy of note. The leaves
are special organs for chlorophyll work, and must receive
the raw material from air and soil or water. The leaves
of the moss gametophyte are very small and simple affairs,
and can be supplied with material by using very little ap-
paratus. In the leafy sporophyte, however, the leaves are
very prominent structures, capable of doing a great deal
of work. To such working structures material must be
brought rapidly in quantity, and manufactured food ma-
terial must be carried away, and therefore a special con-
ducting apparatus is needed. This is supplied by the vas-
cular system. These vessels extend continuously from root-
tips, through the stem, and out into the leaves, where they

FIG. 120. A group of tropical plants. To the left of the center is a tree fern, with its
slender columnar stem and crown of large leaves. The large-leaved plant* to the
right are bananas (Monocotyledons).-From "Plant Relations."

PTEHIDOPHYTES

141

are spoken of as "leaf veins." Large working leaves and
a vascular system, therefore, belong together and appeal-
together; and1 the vascular plants are also the plants with
leafy sporophytes.

(4) The leaf. — Leaves are devices for spreading out
green tissue to the light, and in the Ferns they are usually
large. There is a stalk-like portion (petiole) which rises
from the subterranean stem, and a broad expanded portion
(blade) exposed to the light and air (Fig. 118). In Ferns
the blade is usually much branched, being cut up into
segments of various sizes and forms.

The essential structure consists of an expansion of
green tissue (mesophyll), through which strands of the
vascular system (veins) branch, forming a supporting
framework, and over all a compact layer of protecting
cells (epidermis). A surface
view of the epidermis shows
that it is pierced by numer-
ous peculiar pores, called
xtnmata, meaning "mouths."
The surface view of a stoma
shows two crescentic cells
(guard cells) in contact at
the ends and leaving be-
tween them a lens-shaped
opening (Fig. 121).

A cross-section through
a leaf gives a good view of
the three regions (Fig. 122).
Above and below is the col-
orless epidermis, pierced
here and there by stomata ;
between the epidermal lay-
ers the cells of the mesophyll are packed : and among
the mesophyll cells there may be seen here and there the
cut ends of the veins. The leaf is usually a dorsiventral

FIG. 121. Some epidermal cells from leaf
of Pleris, showing the interlocking
walls and three stomata, the guard
cells containing chloroplasts.— CAI.D-
WEI.I..

PLANT STRUCTURES

organ, its two surfaces being differently related to light.
To this different relation the mesophyll cells respond in
their arrangement. Those in contact with the upper epi-
dermis become elongated and set endwise close together,
forming the palisade tissue; those below are loosely ar-

Fio. 122. Cross-section through a portion of the leaf of Pteris, showing the heavy-
walled epidermis above and below, two stomata in the lower epidermis (one on
each side of the center) opening into intercellular passages, the mesophyll cells
containing chloroplasts, the upper row arranged in palisade fashion, the other
cells loosely arranged (spongy mesophyll) and leaving large intercellular passages,
and in the center a section of a veinlet (vascular bundle), the xylem being repre-
sented by the central group of heavy-walled cells. — CAI.DWKLL.

ranged, leaving numerous intercellular spaces, forming
the spongy tissue. These spaces form a system of inter-
cellular passageways among the working mesophyll cells,
putting them into communication with the outer air
through the stomata. The freedom of this communication

TTERIDOPHYTES 143

is regulated by the guard cells of the stomata, which come
together or shrink apart as occasion requires, thus dimin-
ishing or enlarging the opening between them. The sto-
mata have well been called "automatic gateways " to the
system of intercellular passageways.

One of the peculiarities of ordinary fern leaves is
that the vein system branches dichotomously, the forking
veins being very conspicuous (Figs. 123-126). Another
fern habit is that the leaves in expanding seem to unroll
from the base, as though they had been rolled from the
apex downward, the apex being in the center of the roll
(Fig. 118). This habit is -spoken of as circinate, from a
word meaning "circle" or "coil," and circinate leaves
when unrolling have a crozier-like tip. The arrangement
of leaves in bud is called vernation (" spring condition "),
and therefore the Ferns are scid to have circinate verna-
tion. The combination of dichotomous venation and cir-
cinate vernation is very characteristic of Ferns.

80. Sporangia. — Among Thallophytes sporangia are usu-
ally simple, mostly consisting of a. single mother cell ; among
Bryophytes simple sporangia do not exist, and in connec-
tion with the usually complex capsule of the sporogonium
the name is dropped ; but among Pteridophytes distinct
sporangia again appear. They are not simple mother cells,
but many-celled bodies. Their structure varies in different
groups of Pteridophytes, but those of ordinary Ferns ma,y
be taken as an illustration.

The sporangia are borne by the leaves, generally upon
the under surface, and are usually closely associated with
the veins and organized into groups of definite form, known
as sori. A sorus may be round or elongated, and is usually
covered by a delicate flap (indushnn) which arises from the
epidermis (Figs. 118, 123, 124). Occasionally the sori are
extended along the under surface of the margin of the leaf,
as in maidenhair fern (Adiantum), and the common brake
(Pteris), in which case they are protected by the inrolled

FIG. 123. Fragrant shield fern (Aspid-
i>/m fragrans), showing general
habit, and to the left (a) the under
surface of a leaflet bearing sori
covered by shield-like indusia.—
After MARION SATTERI.EE.

FIG. 134. The bladder fern ( Oygtopterit >»/!/>-
ifera), showing general habit, and to the
right (a) the under surface of a leaflet,
showing the dichotomous venation, and
five sori protected by pouch-like indusia.
—After MARION SATTERLKE.

PTERIDOPHYTES

145

margin (Figs. 125, 126), which may be called a "false in-
dusium."

It is evident that such leaves are doing two distinct
kinds of work— chlorophyll work and spore formation.
This is true of most of the ordinary Ferns, but some of
them show a tendency to di-
vide the work. Certain leaves,
or certain leaf-branches, pro-
duce spores and do no chloro-
phyll work, while others do
chlorophyll work and produce
no spores. This differentia-
tion in the leaves or leaf-re-
gions is indicated by appro-
priate names. Those leaves
which produce only spores are
called sporophylls, meaning
"spore leaves," while the leaf
branches thus set apart are
called sporophyll branches.
Those leaves which only do
chlorophyll work are called fo-
liage leaves ; and such branch-
es are foliage branches. As
sporophylls are not called upon
for chlorophyll work they often
become much modified, being much more compact, and not
at all resembling the foliage leaves. Such a differentiation
may be seen in the ostrich fern and sensitive fe'Tn ( Onoclea)
(Figs. 127, 128), the climbing fern (Lygodinm), the royal
fern (Osmunda), the moonwort (Botryclihim) (Fig. 129),
and the adder's tongue (Ophioglossum) (Fig. 130).

An ordinary fern sporangium consists of a slender stalk
and a bulbous top which is the spore case (Fig. 118, 6).
This case has a delicate wall formed of a single layer of
cells, and extending around it from the stalk and nearly to

FIG. 125. Leaflets of two common
ferns : A. the common brake
(Pterw): />. maidenhair (Adian-
t a in}: both showing sori borne
at the margin and protected by
the infolded margin, which thus
forms a false indusinm.— CALD-

WEl.L.

146 PLANT STKUCTURES

the stalk again, like a meridian line about a globe, is a row
of peculiar cells with thick walls, forming a heavy ring,
called the annulus. The annulus is like a bent spring,
and when the delicate wall becomes yielding the spring
straightens violently, the wall is torn, and the spores are
discharged with considerable force (Fig. 131). This dis-

FIG. 126. — The pm-ple cliff brake (Pelliea atropiirpnrea\ showing general habit, and
at a a single leaflet showing the dichotomoiis venation and the infolded margin
covering the sori.— After MARION SATTERLEE.

charge of fern spores may be seen by placing some sporangia
upon a moist slide, and under a low power watching them
as they dry and burst.

Within this sporangium the archesporium (see § 66)
consists of a single cell, which by division finally produces

PTERIDOPHYTES

147

numerous mother cells, in each of which a tetrad of spores
is formed. The disorganization of the walls of the mother

FIG. 127. The ostrich fern ( Onodea striithiopteris), showing differentiation of foliage
leaf (a) and sporophyll (6).— After MARION SATTERLKE.

cells sets the spores free in the cavity of the sporangium,
and ready for discharge.

FIG. 128. The sensitive f ern ( Onodea sensibilis), showing differentiation of foliage
leaves and sporophylls.— From "Field, Forest, and Wayside Flowers."

PTEBIDOPHYTE8

149

Among the Bryophytes the sporogenous tissue appears
very early in the development of the sporogonium, the pro-
duction of spores being its only function ; also there is a

*^x^

FIG. 129. A moonwort (Botrychi-
tim), showing the leaf differen-
tiated into foliage and sporophyll
branches.— After STHASBUHGEK.

FIG. 130. The adder's tongue ( Ophiogtoesum
vulgaturri), showing two leaves, each
with a foliage branch and a much longer
sporophyll branch.— After MAKIOX SAT-

150

PLANT STRUCTURES

tendency to restrict the sporogenous tissue and increase the
sterile tissue. It will be observed that with the introduc-
tion of the leafy sporophyte among the Pteridophytes the
sporangia appear much later in its development, sometimes
not appearing for several years, as though they are of

<~cs.

—

-'.CD
.^

FIG. 131. A series showing the dehiscence of a fern sporangium, the rupture of the
wall, the straightening and bending back of the annulus, and the recoil.— After
ATKINSON.

secondary importance as compared with chlorophyll work ;
and that the sporogenous tissue is far more restricted, the
sporangia forming a very small part of the bulk of the
sporophyte body.

PTERIDOPIIYTES 151

81. Heterospory. — This phenomenon appears first among
Pteridophytes, but it is not characteristic of them, being en-
tirely absent from the true Ferns, which far outnumber all
other Pteridophytes. Its chief interest lies in the fact that
it is universal among the Spermatophytes, and that it rep-
resents the change which leads to the appearance of that
high group. It is impossible to understand the greatest
group of plants, therefore, without knowing something
about heterospory. As it begins in simple fashion among
Pteridophytes, and is probably the greatest contribution
they have made to the evolution of the plant kingdom,
unless it be the leafy sporophyte, it is best explained here.

In the ordinary Ferns all the spores in the sporangia
are alike, and when they germinate each spore produces a
prothallium upon which both antheridia and archegonia
appear. It has been remarked, however, that some pro-
thallia are dioecious — that is, some bear only antheridia
and others bear only archegonia. In this case it is evident
that the spores in the sporangium, although they may ap-
pear alike, produce diiferent kinds of prothallia, which
may be called male and female, as each is distinguished by
the sex organ which it produces. As archegonia are only
produced by well-nourished prothallia, it seems fair to sup-
pose that the larger spores will produce female prothallia,
and the smaller ones male prothallia.

This condition of things seems to have developed finally
into a permanent and decided difference in the size of the
spores, some being quite small and others relatively large,
the small ones producing male gametophytes (prothallia
with antheridia), and the large ones female gametophytes
(prothallia with archegonia). When asexual spores differ
thus permanently in size, and give rise to gametophytes of
different sexes, we have the condition called heterospory
("spores different"), and such plants are called heterospo-
rous (Fig. 139). In contrast with heterosporous plants, those
in which the asexual spores appear alike are called homos-

152 PLANT STRUCTURES

porous, or sometimes isosporous, both terms meaning
"spores similar." The corresponding noun form is homos-
pory or isospory. Bryophytes and most Pteridophytes are
homosporous, while some Pteridophytes and all Spermato-
phytes are heterosporous.

It is convenient to distinguish by suitable names the
two kinds of asexual spores produced by the sporangia of
heterosporous plants (Fig. 139). The large ones are called
megaspores, or by some writers macrospores, both terms
meaning "large spores" ; the small ones are called micro-
spores, or "small spores." It should be remembered that
megaspores always produce female gametophytes, and mi-
crospores male gametophytes.

This differentiation does not end with the spores, but
soon involves the sporangia (Fig. 139). Some sporangia
produce only megaspores, and are called megasporangia ;
others produce only microspores, and are called microspo-
rangia. It is important to note that while microsporangia
usually produce numerous microspores, the megasporangia
produce much fewer megaspores, the tendency being to
diminish the number and increase the size, until finally
there are megasporangia which produce but a single large
megaspore.

The differentiation goes still further. If the sporangia
are born upon sporophylls, the sporophylls themselves may
differentiate, some bearing only megasporangia, and others
only microsporangia, the former being called megasporo-
phylls, the latter microsporophylls. In such a case the
sequence is as follows : megasporophylls produce megaspo-
rangia, which produce megaspores, which in germination
produce the female gametophytes (prothallia with archego-
nia) ; while the microsporophylls produce microsporangia,
which produce microspores, which in germination produce
male gametophytes (prothallia with antheridia).

A formula may indicate the life history of a heteros-
porous plant. The formula of homosporous plants with

PTERIDOPHYTES

alternation of generations (Bryophytes and most Pterido-
phytes) was given as follows (§ 62) :

G=8> o— S— o— Gzzg> o— S— o— G=g> o— S, etc.
In the case of heterosporous plants (some Pteridophytes
and all Spermatophytes) it would be modified as follows :

G O^^ O O G O\ n C— — O G O^^ Q ^.4.^

G. — o > 0 — £> — o — G — o> 0 — o — o — G — o > O — £>> etc.

In this case two gametophytes are involved, one pro-
ducing a sperm, the other an egg, which fuse and form the
oospore, which in germination produces the sporophyte,
which produces two kinds of asexual spores (megaspores
and microspores), which in germination produce the two
gametophytes again.

One additional fact connected with heterospory should
be mentioned, and that is the great reduction of the gam-
etophyte. In the homosporous ferns the spore develops
a small but free and independent prothallium which pro-
duces both sex organs. When in heterosporous plants this
work of producing sex organs is divided between two gam-
etophytes they become very much reduced in size and lose
their freedom and independence. They are so small that
they do not escape entirely, if at all, from the embrace of
the spores which produce them, and are mainly dependent
for their nourishment upon the food stored up in the spores
(Figs. 140, 141). As the spore is produced by the sporo-
phyte, heterospory brings about a condition in which the
gametophyte is dependent upon the sporophyte, an exact
reversal of the condition in Bryophytes.

The relative importance of the gametophyte and the
sporophyte throughout the plant kingdom may be roughly
indicated by the accompanying diagram, in which the

shaded part of the parallelogram represents the gameto-
phyte and the unshaded part the sporophyte. Among the

154 PLANT STRUCTURES

lowest plants the gametophyte is represented by the whole
plant structure. When the sporophyte first appears it is
dependent upon the gametophyte (some Thallophytes and
the Bry ophytes), and is relatively inconspicuous. Later
the sporophyte becomes independent (most Pteridophytes),
the gametophyte being relatively inconspicuous. Finally
(heterosporous Pteridophytes) the gametophyte becomes
dependent upon the sporophyte, and in Spermatophytes is
so inconspicuous and concealed that it is only observed by
means of laboratory appliances, while the sporophyte is the
whole plant of ordinary observation.

CHAPTEE X

THE GREAT GROUPS OF PTERIDOPHYTES

82. The great groups. — At least three independent lines
of Pteridophytes are recognized : (1) Filicales (Ferns),
(2) Equisetales (Scouring rushes, Horsetails), and (3) Ly-
copodiales (Club-mosses). The Ferns are much the most
abundant, the Club-mosses are represented by a few hun-
dred forms, while the Horsetails include only about twenty-
five species. These three great groups are so unlike that
they hardly seem to belong together in the same division
of the plant kingdom.

FILICALES (Fern*}

83. General characters.— The Ferns were used in the
preceding chapter as types of Pteridophytes, so that little
need be added. They well deserve to stand as types, as
they contain about four thousand of the four thousand five
hundred species belonging to Pteridophytes. Although
found in considerable numbers in temperate regions, their
chief display is in the tropics, where they form a striking
and characteristic feature of the vegetation. In the trop-
ics not only are great masses of the low forms to be seen,
from those with delicate and filmy moss like leaves to those
with huge leaves, but also tree forms with cylindrical
trunks encased by the rough remnants of fallen leaves and
sometimes rising to a height of thirty-five to forty-five
feet, with a great crown of leaves fifteen to twenty feet
long (Fig. 120).

155

THE GREAT GROUPS OF PTERIDOPHYTES

There are also epiphytic forms (air plants) — that is,
those which perch " upon other plants " but derive no
nourishment from them (Fig. 112). This habit belongs
chiefly to the warm and moist tropics, where the plants
can absorb sufficient moisture from the air without send-
ing roots into the soil. In this way many of the tropical
ferns are found growing upon living and dead trees and
other plants. In the temperate regions the chief epi-
phytes are Lichens, Liverworts, and Mosses, the Ferns be-
ing chiefly found in moist woods and ravines (Fig. 132),
although a number grow in comparatively dry and exposed
situations, sometimes covering extensive areas, as the com-
mon brake (Pteris) (Fig. 125).

The Filicales differ from the other groups of Pterido-
phytes chiefly in having few large leaves, which do chloro-
phyll work and bear sporangia. In a few of them there is a
differentiation of functions in foliage branches and sporo-
phyll branches (Figs. 127-130), but even this is excep-
tional. Another distinction is that the stems are un-
branched.

84. Origin of sporangia. — An important feature in the
Ferns is the origin of the sporangia. In some of them a
sporangium is developed from a single epidermal cell of
the leaf, and is an entirely superficial and generally stalked
affair (Fig. 118, 5) ; in others the sporangium in its devel-
opment involves several epidermal and deeper cells of the
leaf, and is more or less of an imbedded affair. In the first
case the ferns are said to be leptosporangiate ; in the sec-
ond case they are eusporangiate.

The leptosporangiate Ferns are overwhelmingly abun-
dant as compared with the Eusporangiates. Back in the
Coal-measures, however, there was an abundant fern vege-
tation which was probably all eusporangiate. The Lep-
tosporangiates seem to be the modern Ferns, the once
abundant Eusporangiates being represented now in the
temperate regions only by such forms as moon wort (Bo-

158

PLANT STRUCTURES

trycMum) (Fig. 129) and adder's tongue (Opldoglossum)
(Fig. 130). It is important to note, however, that the
Horsetails and Club-mosses are Eusporangiates, as well as
all the Seed-plants.

Another small but interesting group of Ferns includes
the "Water-ferns," floating forms or sometimes on muddy
flats. The common Marsilia may be taken as a type (Fig.

133). The slender creeping stem
sends down numerous roots into
the mucky soil, and at intervals
gives rise to a comparatively large
leaf. This leaf has a long erect
petiole and a blade of four spread-

FIG. 133.— A water-fern (jfarsilia).
showing horizontal stem, with
descending roots, and ascend-
ing leaves ; a, a young leaf
showing circinate vernation :
«,*,sporophyll branches ("spo-
rocarps "). — After BISCHOFF.

FIG. 134. One of the floating water-ferns (Sal-
vinia), showing side view (A) and view from
above (B). The dangling root-like processes
are the modified submerged leaves. In A,
near the top of the cluster of submerged
leaves, some sporophyll branches ("sporo-
carps ") may be seen.— Aft er BISCHOFF.

ing wedge-shaped leaflets like a " four-leaved clover. " The
dichotomous venation and circinate vernation at once sug-
gest the fern alliance. From near the base of the petiole

THE GREAT GROUPS OF PTERIDOPHYTES ^59

another leaf branch arises, in which the blade is modified
as a sporophyll. In this case the sporophyll incloses the
sporangia and becomes hard and nut-like. Another com-
mon form is the floating Salvinia (Fig. 134). The chief
interest lies in the fact that the water-ferns are heteros-
porous. As they are leptosporangiate they are thought
to have been derived from the ordinary leptosporangiate
Ferns, which are homosporous.

Three fern groups are thus outlined : (1) homosporous-
eusporangiate forms, now almost extinct ; (2) homosporous-
leptosporangiate forms, the great overwhelming modern
group, not only of Filicales but also of Pteridophytes, well
called true Ferns, and thought to be derived from the pre-
ceding group ; and (3) heterosporous-leptosporangiate
forms, the water-ferns, thought to be derived from the pre-
ceding group.

EQUISETALES (Horsetails or Scouring ruxlte*}

85. General characters. — The twenty-five forms now rep-
resenting this great group belong to a single genus (Equise-
tum, meaning "horsetail"), but they are but the linger-
ing remnants of an abundant flora which lived in the time
of the Coal-measures, and helped to form the forest vegeta-
tion. The living forms are small and inconspicuous, but
very characteristic in appearance. They grow in moist or
dry places, sometimes in great abundance (Fig. 135).

The stem is slender and conspicuously jointed, the joints
separating easily ; it is also green and fluted with small
longitudinal ridges ; and there is such an abundant deposit
of silica in the epidermis that the plants feel rough. This
last property suggested its former use in scouring, and its
name " scouring rush." At each joint is a sheath of minute
leaves, more or less coalesced, the individual leaves some-
times being indicated only by minute teeth. This arrange-
ment of leaves in a circle about the joint is called the cyclic

FIG. 135. Equisetum arvense, a common horsetail: 1, three fertile shoots rising from
the dorsiventral stem, showing the cycles of coalesced scale-leaves at the joints
and the terminal strobili with numerous sporophylls, that at a being mature; 2,
a sterile shoot from the same stem, showing branching; 3, a single peltate sporo-
phyll bearing sporangia; U, view of sporophyll from beneath, showing dehiscence
of sporangia; 5, 6, 7. spores, showing the unwinding of the outer coat, which aids
in dispersal. — After WOSSIDLO.

THE GREAT GROUPS OF PTERIDOPHYTES

161

arrangement, or sometimes the whorled arrangement, each
such set of leaves being called a cycle or a whorl. These
leaves contain no chlorophyll and have evidently abandoned
chlorophyll work, which is carried on by the green stem.
Such leaves are known as scales, to distinguish them from
foliage leaves. The stem is either simple or profusely
branched (Fig. 135).

86. The strobilus. — One of the distinguishing characters
of the group is that chlorophyll-work and spore-formation
are completely differentiated. Although the foliage leaves

--ar

FIG. 136. Dioecious gametophytes of Eqmsetum : A, the female gametopnyte, show-
ing branching, rhizolds. and an archegonium (ar); B, the male gametophyte,
showing several antheridia ( $ ).— After CAMPBELL.

are reduced to scales, and the chlorophyll-work is done by
the stem, there are well-organized sporophylls. The sporo-
phylls are grouped close together at the end of the stem in
a compact conical cluster which is called a strobilus, the
Latin name for "pine cone," which this cluster of sporo-
phylls resembles (Fig. 135).

Each sporophyll consists of a stalk-like portion and a
shield-like {peltate} top. Beneath the shield hang the

1(52 PLANT STRUCTURES

sporangia, which produce spores of but one kind, hence
these plants are homosporous ; and as the sporangia origi-
nate in eusporangiate fashion, Equisetum has the homospo-
rous-eusporangiate combination shown by one of the Fern
groups. It is interesting to know, however, that some of
the ancient, more highly organized members of this group
were heterosporous, and that the present forms have
dioecious gametophytes (Fig. 136).

LYCOPODIALES (Club-mosses)

87. General characters. — This group is now represented
by about five hundred species, most of which belong to
the two genera Lycopodium and SelagineUa, the latter
being much the larger genus. The plants have slender,
branching, prostrate, or erect stems completely clothed
with small foliage leaves, having a general moss-like
appearance (Fig. 137). Often the erect branches are
terminated by conspicuous conical or cylindrical strobili,
which are the " clubs " that enter into the name " Club-
mosses." There is also a certain kind of resemblance
to miniature pines, so that the name " Ground-pines " is
sometimes used.

Lycopodiales were once much more abundant than now,
and more highly organized, forming a conspicuous part of
the forest vegetation of the Coal-measures.

One of the distinguishing marks of the group is that the
sperm does not resemble that of the other Pteridophytes,
but is of the Bryophyte type (Fig. 140, F). That is, it
consists of a small body with two cilia, instead of a large
spirally coiled body with many cilia. Another distinguish-
ing character is that there is but a single sporangium pro-
duced by each sporophyll (Fig. 137). This is in marked
contrast with the Filicales, whose leaves bear very numer-
ous sporangia, and with the Equisetales, whose sporophylls
bear several sporangia.

THE GREAT GROUPS OF PTERIDOPHYTES

163

FIG. 137. A common club-moss (Lycopodium davatutn): 1, the whole plant, showing
horizontal stem giving rise to roots and to erect branches bearing strobili; 2, a
single sporophyll with its sporangium; 3, spores, much magnified. — After Wos-

8IDLO.

88. Lycopodium. — This genus contains fewer forms than
the other, but they are larger and coarser and more charac-
teristic of the temperate regions, being the ordinary Club-
mosses (Fig. 137). They also more commonly display
conspicuous and distinct strobili, although there is every

164

PLANT STRUCTURES

gradation between ordinary foliage leaves and distinct
sporophylls. '

The sporangia are borne either by distinct sporophyils
or by the ordinary foliage leaves near the summit of the
stem. At the base of each of these leaves, or sporophylls,
on the upper side, is a single sporangium (Fig. 137). The
sporangia are eusporangiate in origin, and as the spores are
all alike, Lycopodiitm has the same homosporous-eusporaii-
giate combination noted in Equisetales and in one of the
groups of Filicales.

89. Selaginella. — This large genus contains the smaller,
more delicate Club-mosses, often being called the " little
Club-mosses." They are especially displayed in the trop-

FIG. 138. Selaginella, showing general spray-like habit, and dangling leafless stems
which strike root (rhizophores).— From "Plant Relations."

ics, and are common in greenhouses as delicate, mossy,
decorative plants (Fig. 138). In general the sporophylls
are not different from the ordinary leaves (Fig. 139), but
sometimes they are modified, though not so distinct as in
certain species of Lycopodium^

THE GREAT GROUPS OF PTERIDOPI1YTE8

165

The solitary sporangium appears in the axils (upper
angles formed by the leaves with the stem) of the leaves
and sporophylls, but arise from the stem instead of the

FIG. 139. Selac/inella Martemii : A, branch bearing strobili; B, a microsporophyll
with a microsporangium, showing microspores through a rupture in the wall; (',
a megasporophyll with a megapporangium ; D, megaspores ; E, microspores. —
CALDWELL.

166

PLANT STRUCTURES

leaf (Fig. 139). This is important as showing that sporan-
gia may be produced by stems as well as by leaves, those
being produced by leaves being called foliar, and those by
stem cauline.

The most important ffact in connection with Selaginella,
however, is that it is heterosporous. Megasporangia, each
usually containing but four megaspores, are found in the
axils of a few of the lower leaves of the strobilus, and more
numerous microsporangia occur in the upper axils, con-
taining very many microspores (Fig. 139). The character
of the gametophytes of heterosporous Pteridophytes may
be well illustrated by those of Selaginella.

The microspore germinates and forms a male gameto-
phyte so small that it is entirely included within the spore

FIG. 140. Male gametophyte of Selaginella: in each case p is the prothallial cell,
the wall cells of the antheridium, s the sperm tissue: F, the biciliate sperms.
After BELAJEFF.

wall (Fig. 140). A single small cell is all that represents
the ordinary cells of the prothallium, while all the rest is
an antheridium, consisting of a wall of a few cells sur-
rounding numerous sperm mother cells. In the presence

THE GREAT GROUPS OF PTERIDOPHYTES

167

of water the antheridium wall breaks down, as also do the
walls of the mother cells, and the small biciliate sperms
are set free.

The much larger megaspores germinate and become
filled with a mass of numerous nutritive cells, representing
the ordinary cells of a prothallium (Fig. 141). The spore
wall is broken by this growing prothallium, a part of which
thus protrudes and becomes exposed, although the main
part of it is still invested by the old megaspore wall. In
this exposed portion
of the female gameto-
phyte the archegonia
appear, and thus be-
come accessible to the
sperms. In the case
of Isoetes (see § 90)
the reduction of the
female gametophyte is
even greater, as it does
not project from the
megaspore wall at all,
and the archegonia
are made accessible
through cracks in the
wall immediately over
them.

The embryo of Se-
laginella is also impor-
tant to consider. Be-
ginning its development in the venter of the archegonium,
it first lies upon the exposed margin of the prothallium,
while the mass of nutritive cells lie deep within the mega-
spore (Fig. 141, emb^ embj. It first develops an elongated
cell, or row of cells, which thrusts the embryo cell deeper
among the nutritive cells. This cell or row of cells, formed
by the embryo to place the real embryo cell in better rela-

FIG. 141. Female gametophyte of a Selaginella :
sjmi, wall of megaspore ; pr, gametophyte ;
ar, an archegonium ; embl and emb%, em-
bryo sporophytes ; et, suspensors ; the gam-
etophyte has developed a few rhizoids. —
After PFEFFER.

168

PLANT STRUCTURES

tion to its food supply, is called the suspensor, and is a
temporary organ of the embryo (Figs. 141, 142, et). At
the end of the suspensor the real embryo develops, and
when its regions become organized it shows the following
parts : (1) a large foot buried among the nutritive cells of
the prothallium and absorbing nourishment ; (2) a root
stretching out toward the substratum ; (3) a stem extend-

FIG. 142. Embryo of Selaginella removed from the gametophyte, showing suspensor
(et), root-tip (w), foot (/), cotyledons (bl), stem-tip (fit), and ligules (lig).— After
PFEFFEB.

ing in the other direction, and bearing just behind its tip
(4) a pair of opposite leaves (cotyledons) (Fig. 142).

As the sporangia of Selaginella are eusporangiate, this
genus has the heterosporous-eusporangiate combination — a
combination not mentioned heretofore, and being of special
interest as it is the combination which belongs to all the
Spermatophytes. For this and other reasons, Selaginella
is one of the Pteridophyte forms which has attracted
special attention, as possibly representing one of the an-
cestral forms of the Seed-plants.

THE GREAT GROUPS OF PTERIDOPHYTES

169

90. Isoetes. — This little group of aquatic plants, known
as " quill worts," is very puzzling as to its relationships
among Pteridophytes. By some it is put with the Ferns,
forming a distinct division of Filicales ; by others it is put

FIG. 143. A common quillwort (Isoetes lacus-
tris), showing cluster of roots dichoto-
mously branching, and cluster of leaves
each enlarged at base and inclosing a sin-
gle sporangium.— After SCHENCK.

FIG. 144. Sperm of Isoetes, show-
ing spiral body and seven long
cilia arising from the beak. —
After BELAJEFP.

with the Club-mosses, and is associated with Selaginella.
It resembles a bunch of fine . grass growing in shoal water
or in mud, but the leaves enlarge at the base and overlap
one another and the very short tuberous stem (Fig. 143).
Within each enlarged leaf base a single sporangium is
formed, and the cluster contains both megasporangia and
microsporangia. The sporangia are eusporangiate, and
therefore Isoetes shares with Selaginella the distinction of

170 PLANT STRUCTURES

having the heterosporous-eusporangiate combination, which
is a feature of the Seed-plants.

The embryo is also peculiar, and is so suggestive of the
embryo of the Monocotyledons (see § 114) among Seed-
plants that some regard it as possibly representing the
ancestral forms of that group, of Spermatophytes. The
peculiarity lies in the fact that at one end of the axis of the
embryo is a root, and at the other the first leaf (cotyledon),
while the stem tip rises as a lateral outgrowth. This is
exactly the distinctive feature of the embryo of Monocoty-
ledons.

The greatest obstacle in the way of associating these
quillworts with the Club-mosses is the fact that their sperms
are of the large and spirally coiled multiciliate type which
belongs to Filicales and Equisetales (Fig. 144), and not at
all the small biciliate type which characterizes the Club-
mosses (Fig. 140). To sum up, the short unbranched stem
with comparatively few large leaves, and the coiled multi-
ciliate sperm, suggest Filicales ; while the solitary spo-
rangia and the heterosporous-eusporangiate character sug-
gest Selaginella.

CHAPTEK XI

SPERMATOPHYTES : GYMNOSPERMS

91. Summary from Pteridophytes. — In considering the
important contributions of Pteridophytes to the evolution
of the plant kingdom the following seem worthy of note :

(1) Prominence of sporophyte and development of vascu-
lar system. — This prominence. is associated with the display
of leaves for chlorophyll work, and the leaves necessitate
the work of conduction, which is arranged for by the vas-
cular system. This fact is true of the whole group.

(2) Differentiation of sporophylls. — The appearance of
sporophylls as distinct from foliage leaves, and their or-
ganization into the cluster known as the strobilus, are facts
of prime importance. This differentiation appears more or
less in all the great groups, but the strobilus is distinct only
in Horsetails and Club-mosses.

(3) Introduction of heterospory and reduction of gameto-
phytes. — Heterospory appears independently in all of the
three great groups — in the water-ferns among the Fili-
cales, in the ancient horsetails among the Equisetales, and
in Selaginella and Isoetes among Lycopodiales. All the
other Pteridophytes, and therefore the great majority of
them, are homosporous. The importance of the appear-
ance of heterospory lies in the fact that it leads to the
development of Spermatophytes, and associated with it is
a great reduction of the gametophytes, which project little,
if at all, from the spores which produce them.

92. Summary of the four groups. — It may be well in this
connection to give certain prominent characters which will

171

PL AST STRUCTURES

serve to distinguish the four great groups of plants. It
must not be supposed that these are the only characters,
or even the most important ones in every case, but they
are convenient for our purpose. Two characters are given
for each of the first three groups — one a positive character
which belongs to it, the other a negative character which
distinguishes it from the group above, and becomes the
positive character of that group.

(1) ThallopJiytes. — Thallus body, but no archegonia.

(2) Bryophytes.— Archegonia, but no vascular system.

(3) Pteridophytes. — Vascular system, but no seeds.

(4) Spermatophytes. — Seeds.

93. General characters of Spermatophytes.— This is the
greatest group of plants in rank and in display. So con-
spicuous are they, and so much do they enter into "our
experience, that they have often been studied as " botany,"
to the exclusion of the other groups. The lower groups
are not meiely necessary to fill out any general view of the
plant kingdom, but they are absolutely essential to an
understanding of the structures of the highest group.

This great dominant group has received a variety of
names. Sometimes they are called Antliopliytes, meaning
"Flowering plants," with the idea that they are distin-
guished by the production of "flowers." A flower is diffi-
cult to define, but in the popular sense all Spermatophytes
do not produce flowers, while in another sense the strobilus
of Pteridophytes is a flower. Hence the flower does not
accurately limit the group, and the name Anthophytes is
not in general use. Much more commonly the group is
called Phanerogams (sometimes corrupted into Phaenogams
or even Phenogams), meaning " evident sexual reproduc-
tion." At the time this name was proposed all the other
groups were called Cryptogams, meaning "hidden sexual
reproduction." It is a curious fact that the names ought
to have been reversed, for sexual reproduction is much more
evident in Cryptogams than in Phanerogams, the mistake

SPERMATOPHYTES : GYMNOSPERMS

arising from the fact that what were supposed to be sexual
organs in Phanerogams have proved not to be such. The
name Phanerogam, therefore, is being generally abandoned ;
but the name Cryptogam is a useful one when the lower
groups are to be referred to ; and the Pteridophytes are
still very frequently called the Vascular Cryptogams. The
most distinguishing mark of the group seems to be the
production of seeds, and hence the name Spermatophytes,
or " Seed-plants," is corning into general use.

The seed can be better defined after its development
has been described, but it results from the fact that in this
group the single megaspore is never discharged from its
megasporangium, but germinates just where it is devel-
oped. The great fact connected with the group, therefore,
is the retention of the megaspore, which results in a seed.
The full meaning of this will appear later.

There are two very independent lines of Seed-plants,
the Gymnosperms and the Angiosperms. The first name
means "naked seeds," referring to the fact that the seeds
are always exposed; the second means " inclosed seeds,"
as the seeds are inclosed in a seed vessel.

GYMNOSPEKMS

94. General characters. — The most familiar Gymnosperms
in temperate regions are the pines, spruces, hemlocks,
cedars, etc., the group so commonly called "evergreens."
It is an ancient tree group, for its representatives were
associated with the giant club-mosses and horsetails in
the forest vegetation of the Coal-measures. Only about
four hundred species exist to-day as a remnant of its for-
mer display, although the pines still form extensive forests.
The group is so diversified in its structure that all forms
can not be included in a single description. The common
pine (Pinus), therefore, will be taken as a type, to show
the general Gymnosperm character.

174 PLANT STRUCTURES

95. The plant body. — The great body of the plant, often
forming a large tree, is the sporophyte ; in fact, the
gametophytes are not visible to ordinary observation. It
should be remembered that the sporophyte is distinctly a
sexless generation, and that it develops no sex organs.
This great sporophyte body is elaborately organized for
nutritive work, with its roots, stems, and leaves. These
organs are very complex in structure, being made up of
various tissue systems that are organized for special kinds
of work. The leaves are the most variable organs, being
differentiated into three distinct kinds — (1) foliage leaves,
(2) scales, and (3) sporophylls.

96. Sporophylls. — The sporophylls are leaves set apart to
produce sporangia, and in the pine they are arranged in
a strobilus, as in the Horsetails and Club-mosses. As
the group is heterosporous, however, there are two kinds
of sporophylls and two kinds of strobili. One kind of
strobilus is made up of megasporophylls bearing mega-
sporangia ; the other is made up of microsporophylls bear-
ing microsporangia. These strobili are often spoken of as
the " flowers " of the pine, but if these are flowers, so are
the strobili of Horsetails and Club-mosses.

97. Microsporophylls. — In the pines the strobilus com-
posed of microsporophylls is comparatively small (Figs.
145, d, 164). Each sporophyll is like a scale leaf, is nar-
rowed at the base, and upon the lower surface are borne
two prominent sporangia, which of course are microspo-
rangia, and contain microspores (Fig. 146).

These structures of Seed-plants all received names
before they were identified with the corresponding struc-
tures of the lower groups. The microsporophyll was called a
stamen, the microsporangia pollen-sacs, and the microspores
pollen grains, or simply pollen. These names are still very
convenient to use in connection with the Spermatophytes,
but it should be remembered that they are simply other
names for structures found in the lower groups.

FIG. 145. Pinus Laricio, showing tip of branch bearing needle-leaves, scale-leaves,
and cones (strobili): a. very young carpellate cones, at time of pollination, borne
at tip of the young shoot upon which new leaves are appearing: b, carpellate cones
one year old; c, carpellate cones two years old, the scales spreading and shedding
the seeds; d, young shoot bearing a cluster of starainate cones.— CALDWBLL.

176

PLANT STRUCTURES

The strobilus composed of microsporophylls may be
called the staminate strobilus — that is, one composed of
stamens ; it is often called the staminate cone, " cone "
being the English translation of the word "strobilus."
Frequently the staminate cone is spoken of as the " male
cone/' as it was once supposed that the stamen is the

FIG. 146. Staminate cone (strobilus) of pine (Pinus): A, section of cone, showing
microsporophylls (stamens) bearing microsporangia; J5, longitudinal section of a
single stamen, showing the large sporangium beneath ; C, cross-section of a sta-
men, showing the two sporangia; D, a single microspore (pollen grain) much en-
larged, showing the two wings, and a male gametophyte of two cells, the lower
and larger (wall cell) developing the pollen tube, the upper and smaller (genera-
tive cell) giving rise to the sperms. — After SCHIMPER.

male organ. This name should, of course, be abandoned,
as the stamen is now known to be a microsporophyll, which
is an organ produced by the sporophyte, which never pro-
duces sex organs. It should be borne distinctly in mind
that the stamen is not a sex organ, for the literature of
botany is full of this old assumption, and the beginner is in

SPERMATOPHYTES : GYMNOSPEKMS

177

danger of becoming confused and of forgetting that pollen
grains are asexual spores.

98. Megasporophylls.— The strobili composed of mega-
sporophylls become much larger than the others, forming

FIG. 147. Pinus sylvestris, showing mature cone partly sectioned, and showing car-
pels (sq, gq1, sq*) with seeds in their axils (g), in which the embryos (em) may be
distinguished; A, a young carpel with two megaspcrangia ; B, an old carpel with
mature seeds (cK), the micropyle being below (M). — After BESSEY.

the well-known cones so characteristic of pines and their
allies (Figs. 145, #, b, c, 163). Each sporophyll is some-
what leaf -like, and at its base upon the upper side are two
megasporangia (Fig. 147). It is these sporangia which are
peculiar in each producing and retaining a solitary large
megaspore. This megaspore resembles a sac-like cavity in

ITS

PLANT STRUCTURES

the body of the sporangium (Fig. 148, d), and was at first
not recognized as being a spore.

These structures had also received names before they
were identified with the corresponding structures of the
lower groups. The megasporophyll was called a carpel,
the megasporangia ovules, and the megaspore an embryo-
sac, because the young embryo was observed to develop
within it (Fig. 147, em).

The strobilus of megasporophylls, therefore, may be
called the carpellate strobilus or carpellate cone. As the
carpel enters into the organization of a structure known as
the pistil, to be described later, the cone is often called
the pistillate cone. As the staminate cone is sometimes
wrongly called a "male cone," so the carpellate cone is
wrongly called a "female cone," the
old idea being that the carpel with
its ovules represented the female sex
organ.

The structure of the megaspo-
rangium, or ovule, must be known.
The main body is the nucellus (Figs.
148, c, 149, nc) ; this sends out from
near its base an outer membrane
(integument) which is distinct above
(Figs. 148 b, 149 i), covering the main
part of the nucellus and projecting
beyond its apex as a prominent neck,

FIG. 148. Diagram of the J "

carpel structures of pine, the passage through which to the apex
showing the heavy scale of t^e nuceHUs is called the micropiile

(A) which bears the /,,,..., ,,N /T,. x 'J

ovule CB), in which are ("little gate") (Fig. 148, a). Cen-
seen the micropyie (a), trally placed within the body of the

integument (6), nucellus ,,

(c), embryo sac or mega- HUCellus IS the COnSplCUOUS Cavity

spore (c?).— CALDWELL. called the embryo-sac (Fig. 148, d),
in reality the retained megaspore.

The relations between integument, micropyie, nucellus,
and embryo-sac should be kept clearly in mind. In the

8PEBMATOPHYTES : GYMNO8PERMS

179

nc—

pine the micropyle is directed downward, toward the base
of the sporophyll (Figs. 147, 148).

99. Female gametophyte. — The female gametophyte is
always produced by the germination of a megaspore, and
therefore it should be
produced by the so-
called embryo-sac with-
in the ovule. This im-
bedded megaspore ger-
minates, just as does
the megaspore of Se-
laginella or Isoetes, by
cell division becoming
filled with a compact
mass of nutritive tissue
representing the ordi-
nary cells of the female
prothallium (Fig. 149,
e). This prothallium
naturally does not
protrude beyond the
boundary of the mega-
spore wall, being com-
pletely surrounded by
the tissues of the
sporangium. It must
be evident that this
gametophyte is abso-
lutely dependent upon
the sporophyte for its
nutrition, and remains
not merely attached to
it, but is actually im-
bedded within its tis-
sues like an internal parasite,
within the ovule, as well as in

FIG. 149. Diagrammatic section through ovule
(megasporangium) of sprnce (Picea), showing
integument (i), nucellns (nc), endosperm or
female gametophyte (e) which fills the large
megaspore imbedded in the nucellus, two
archegonia (a) with short neck (c) and venter
containing the egg (0). and position of ger-
minating pollen grains or microspores (p)
whose tubes (t) penetrate the nucellns tissue
and reach the archegonia. — After SCHIMPER.

So conspicuous a tissue
the seed into which the

180 PLANT STKUCTURES

ovule develops, did not escape early attention, and it was
called endosperm, meaning " within the seed." The endo-
sperm of Gymnosperms, therefore, is the female gameto-
phyte.

At the margin of the endosperm nearest the micropyle
regular flask-shaped archegonia are developed (Fig. 149, a),
making it sure that the endosperm is a female gameto-
phyte. It is evident that the necks of these archegonia
(Fig. 149, c) are shut away from the approach of sperms by
swimming, and that some new method of approach must be
developed.

100. Male gametophyte. — The microspores are developed
in the sporangium in the usual tetrad fashion, and are pro-
duced and scattered in very great abundance. It will be
remembered that the male gametophyte developed by the
microspore of Selaginella is contained entirely within the
spore, and consists of a single ordinary prothallial cell
and one antheridium (see § 89). In the pine it is no bet-
ter developed. One or two small cells appear, which may
be regarded as representing prothallial cells, while the rest
of the gametophyte seems to be a single antheridium (Fig.
146, D). At first this antheridium seems to consist of a
large cell called the wall cell, and a small one called the
generative cell. Sooner or later the generative cell divides
and forms two small cells, one of which divides again and
forms two cells called male cells, which seem to represent
the sperm mother cells of lower plants. The three active
cells of the completed antheridium, therefore, are the wall
cell, with a prominent nucleus, and two small male cells
which are free in the large wall cell.

These sperm mother cells (male cells) do not form
sperms within them, as there is no water connection be-
tween them and the archegonia, and a new method of
transfer is provided. This is done by the wall cell, which
develops a tube, known as the pollen-tube. Into this tube
the male cells enter, and as it penetrates among the cells

SPERMATOPHYTES : GYM^OSPERMS

181

which shut off the archegonia it carries the male cells
along, and so they are brought to the archegonia (Fig. 150).

FIG. 150. Tip of pollen tube of pine,
showing the two male cells (A, B),
two nuclei (C) which accompany
them, and the numerous food
granules (D) : the tip of the tube
is just about to enter the neck of
the archegonium.— CALDWELL.

FIG. 151. Pollen tube passing through the
neck of an archegonium of spruce (Picea),
and containing near its tip the two male
nuclei, which are to be discharged into the
egg whose cytoplasm the tube is just en-
tering.—After STRASBURGEK.

101. Fertilization. — Before fertilization can take place
the pollen-grains (microspores) must be brought as near as
possible to the female gametophyte with its archegonia.
The spores are formed in very great abundance, are dry
and powdery, and are scattered far and wide by the wind.
In the pines and their allies the pollen-grains are winged
(Fig. 146, Z>), so that they are well organized for wind dis-
tribution. This transfer of pollen is called pollination, and
those plants that use the wind as an agent of transfer are
said to be anemophilous, or "wind-loving."

The pollen must reach the ovule, and to insure this it

must fall like rain. To aid in catching the falling pollen

the scale-like carpels of the cone spread apart, the pollen

grains slide down their sloping surfaces and collect in a

182

PLANT STRUCTURES

little drift at the bottom of each carpel, where the ovules
are found (Fig. 147, A, B). The flaring lips of the micro-
pyle roll inward and outward as they are dry or moist, and
by this motion some of the pollen-grains are caught and
pressed down upon the apex of the nucellus.

In this position the pollen-tube develops, crowds its
way among the cells of the nucellus, reaches the wall of
the embryo-sac, and penetrating that, reaches the necks
of the archegonia (Fig. 149, p, t) ; crowding into them
(Fig. 151), the tip of the tube opens, the male cells are

FIG. 152. Fertilization in spruce (PiceaY B is an egg, in the tip of which a pollen
tube (p) has entered and has discharged into the cytoplasm a male nucleus (m),
which is to unite with the egg (female) nucleus (on); C, a later stage in which the
two nuclei are uniting.— After SCHIMPER.

discharged, one male cell fuses with the egg (Fig. 152),
and fertilization is accomplished, an oospore being formed
in the venter of the archegonium.

It will be noticed that the cell which acts as a male
gamete is really the sperm mother cell, which does not
organize a sperm in the absence of a water connection.
This peculiar method of transferring the male cells by
means of a special tube developed by the antheridium is

SPEEMATOPHYTES : GYMNOSPERMS

183

Tfa

called siphonoga-my, which means " sexual reproduction by
means of a tube." So important is this character among
Spermatophytes that some have proposed to call the group
Siphonogams.

102. Development of the embryo. — The oospore Avhen
formed lies at the surface of the endosperm (female gameto-
phyte) nearest to the micropyle. As the endosperm is to
supply nourishment to the em-
bryo, this position is not the

most favorable. Therefore, as
in Selaginella, the oospore first
develops a suspensor, which in
pine and its allies becomes very
long and often tortuous (Fig.
153, A, s). At the tip of the
suspensor the cell or cells (em-
bryo cells) which are to develop
the embryo are carried (Fig. 153,
vl, Jed), and thus become deeply
buried, about centrally placed,
in the endosperm.

Several suspensors may start
from as many archegonia in the
same ovule, and several embryos
may begin to develop, but as a
rule only one survives, and the
solitary completed embryo (Fig.
153, B) lies centrally imbedded

in the endosperm (Fig. 153a). The development of more
than one embryo in a megasporaiigium (ovule) is called
polyembryony, a phenomenon natural to Gymnosperms with
their several archegonia upon a single gametophyte.

103. The seed. — While the embryo is developing some
important changes are taking place in the ovule outside of
the endosperm. The most noteworthy is the change which
transforms the integument into a hard bony covering,

I- a

FIG. 153. Embryos of pine : .1.
very young embryos (kg) at the
tips of long and contorted sus-
pensors (s) ; B, older embryo,
showing attachment to suspen-
sor (s), the extensive root sheath
(wK), root tip (ws), stem tip
(v), and cotyledons (c).— After
STRASBURGER.

184

PLANT STRUCTURES

known as the seed coat, or testa (Fig. 153&). The devel-
opment of this testa hermetically seals the structures with-
in, further development and activity
are checked, and the living cells pass
into the resting condition. This pro-
tected structure with its dormant cells
is the seed.

In a certain sense the seed is a transformed ovule (mega-
sporangium), but this is true only as to its outer configura-

FIG. 153a. Pine seed.

FIG. 154. Pine seedlings, showing the long hypocotyl and the numerous cotyledons,
with the old seed case still attached.— After ATKINSON.

SPERM ATOPHYTES : GYMNOSPERMS

185

tion. If the internal structures be considered it is much
more. It is made up of structures belonging to three gen-
erations, as follows : (1) The old sporophyte is represented
by seed coat and nucellus, (2) the endosperm is a gameto-
phyte, while (3) the embryo is a young sporophyte. It can
hardly be said that the seed is simple in structure, or that
any real conception of it can be obtained without approach-
ing it by way of the lower groups.

The organization of the seed checks the growth of the
embryo, and this development within the seed is known as

FIG. 155. A cycad, showing the palm-like habit, with ranch branched leaves and
scaly stem. — From " Plant Relations."

the intra-seminal development. In this condition the em-
bryo may continue for a very long time, and it is a ques-
tion whether it is death or suspended animation. Is a seed
alive ? is not an easy question to answer, for it may be kept
in a dried-out condition for years, and then when placed
in suitable conditions awaken and put forth a living plant.

SPERMATOPHYTES : GYMNOSPERMS

187

This " awakening " of the seed is spoken of as its " ger-
mination/' but this must not be confused with the germi-
nation of a spore, which is real germination. In the case
of the seed an oospore has germinated and formed an embryo,
which stops growing for a time, and then resumes it. This
resumption of growth is not germination, but is what

FIG. 157. Tip of pollen tube of Cycas revoluta, containing the two spiral, multiciliate
sperms. — After IKENO

happens when a seed is said to "germinate." This second
period of development is known as the extra-seminal, for it
is inaugurated by the escape of the sporophyte from the
seed (Fig. 154).

104. The great groups of Gymnosperms. — There are at
least four living groups of Gymnosperms, and two or three

- ,-_-:- -

FIG. 158. A pine (Pinus) showing the central shaft and also the bunching of the
needle leaves toward the tips of the branches.— From " Plant Relations."

SI'KKMATOIMIVTKS: GYMNOSPERMS

189

extinct ones. The groups differ so widely from one an-
other in habit as to show that Gymnosperms can be very
much diversified. They are all woody forms, but they may
be trailing or straggling
shrubs, gigantic trees, or
high-climbing vines ; and
their leaves may be nee-
dle-like, broad, or "fern-
like." For our purpose it
will be only necessary to
define the two most prom-
inent groups.

105. Cycads. — Cycads
are tropical, fern -like
forms, with large branched
(compound) leaves. The
stem is either a columnar
shaft crowned with a ro-
sette of great branching
leaves, with the general
habit of tree-ferns and
palms (Figs. 155, 156) ;
or they are like great tu-
bers, crowned in the same
way. In ancient times
(the Mesozoic) they were
very abundant, forming
a conspicuous feature of
the vegetation, but now
they are represented only
by about eighty forms
scattered through both
the oriental and occiden-
tal tropics. FIG. 159. The giant redwood (Sequoia gi-

TheV are VerV fern- ffantea) of California : the relative size

J * is indicated by the figure of a man stand-

like in Structure as Well ing at the right.— After WILLIAMSON.

190

PLANT STRUCTURES

as in appearance, but they prod
associated with Spermatophytes,
posed they are Gymnosperms. A

FIG. 160. An araucarian pine (Araucaria),
showing the central shaft, and the regular
cycles of branches spreading in every direc-
tion and bearing numerous small leaves. —
From "Plant Relations."

uce seeds arid must be
and as the seed is ex-
discovery has been made
recently that strikingly
emphasizes their fern-
like structure. In fer-
tilization a pollen-tube
develops, as described
for pine and its allies,
but the male cells
(sperm mother - cells)
which it contains or-
ganize sperms, and
these sperms are of
the coiled multiciliate
type (Fig. 157) charac-
teristic of all the Pter-
idophytes except Club-
mosses. This associa-
tion of the old ciliated
sperm habit with the
new pollen-tube habit
is a very interesting in-
termediate or transition
condition. It should be
said that these sperms
have been actually found
in but two species of
the Cycads, but there
are reasons for suppos-
ing that they may be
found in all. Another
one of the Gymnosperm
groups, represented to-
day only by the com-
monly cultivated maid-

SPERMATOPHYTES : GYMXOSPERMS

191

enhair tree (Oingko), with broad dichotomously veined
leaves, also develops multiciliate sperms.

The testa of the seed, instead of being entirely hard as
described for pine and its allies, develops in two layers, the
inner hard and bony, and the outer pulpy, making the ripe
fruit resemble a plum.

106. Conifers. — This is the great modern Gymnosperm
group, and is characteristic of the temperate regions, where
it forms great forests. Some of the forms are widely dis-
tributed, as the great genus of pines (Pinus) (Fig. 158),
while some are now very much restricted, although for-
merly very widely distributed, as the gigantic redwoods
(Sequoia) of the Pacific slope (Fig. 150). The habit of
the body is quite charac-
teristic, a central shaft
extending continuously to
the very top, while the
lateral branches spread
horizontally, with dimin-
ishing length to the top,
forming a conical outline
(Figs. 160, 162). This
habit of firs, pines, etc.,
gives them an appearance
very distinct from that of
other trees.

Another peculiar fea-
ture is furnished by the
characteristic "needle-
leaves," which seem to be

poorly adapted for foliage. These leaves have small spread
of surface and very heavy protecting walls, and show
adaptation for enduring hard conditions (Fig. 161). As
they have no regular period of falling, the trees are always
clothed with them, and have been called " evergreens."
There are some notable exceptions to this, however, as in

FIG. 161. — Cross-section of a needle-leaf of
pine, showing epidermis (e) in which
there are sunken stomata (.<?/>), heavy-
walled hypodermal tissue (es) which
gives rigidity, the mesophyll region (p)
in which a few resin-ducts (h) are seen,
and the central region (stele) in which
two vascular bundles are developed. —
After SACHS.

FIG. 162. A larch (Larix), showing the continuous central shaft and horizontal
branches, the general outline being distinctly conical. The larch is peculiar
among Conifers in periodically shedding its leaves.— From " Plant Relations."

SPERMATOPHYTE8 : GYMJfQSPEBMS

193

the case of the common larch or tamarack, which sheds
its leaves every season (Fig. 162). There are Conifers,
also, which do not produce needle-leaves, as in the com-
mon arbor-vitae, whose leaves consist of small closely-over-
lapping scale-like bodies
(Fig. 163).

The two types of leaf
arrangement may also be
noted. In most Conifers
the leaves are arranged
along the stem in spiral
fashion, no two leaves
being at the same level.
This is known as the spi-
ral or alternate arrange-
ment. In other forms, as
the cypresses, the leaves
are in cycles, as was men-
tioned in connection with
the Horsetails, the ar-
rangement being known
as the cyclic or whorled.

The character which
gives name to the group
is the "cone" — that is,
the prominent carpellate
cone which becomes so

FIG. 163. Arbor-vitae (Thuja}, showing a
branch with scaly overlapping leaves,
and some carpellate cones (strobili). —
After EICHLER.

conspicuous in connec-
tion with the ripening of
the seeds. These cones
generally ripen dry and

hard (Figs. 145, 147, 163), but sometimes, as in junipers,
they become pulpy (Fig. 164), the whole cone forming the
so-called "berry/'

There are two great groups of Conifers. One, repre-
sented by the pines, has true cones which conceal the

194 PLANT STRUCTUEES

ovules, and the seeds ripen dry. The other, represented
by the yews, has exposed ovules, and the seed either ripens
fleshy or has a fleshy investment.

FIG. 164. The common juniper (Juniperus communis); the branch to the left bearing
staminate etrobili; that to the right bearing stamina tc strobili above and carpel-
late strobili below, which latter have matured into the fleshy, berry-like fniit.
— After BERG and SCHMIDT.

CHAPTER XII

SPERMATOPHYTES : ANGIOSPERMS

107. Summary of Gymnosperms, — Before beginning An-
giosperms it is well to state clearly the characters of Gym-
nosperms which have set them apart as a distinct group of
Spermatophytes, and which serve to contrast them with
Angiosperms.

(1) The microspore (pollen-grain) by wind-pollination
is brought into contact with the megasporangium (ovule),
and there develops the pollen-tube, which penetrates the
nucellus. This contact between pollen and ovule implies
an exposed or naked ovule and hence seed, and therefore
the name " Gymnosperm."

(2) The female gametophyte (endosperm) is well organ-
ized before fertilization.

(3) The female gametophyte produces archegonia.

108. General characters of Angiosperms, — This is the great-
est group of plants, both in numbers and importance, being
estimated to contain about 100,000 species, and forming
the most conspicuous part of the vegetation of the earth.
It is essentially a modern group, replacing the Gymnosperms
which were formerly the dominant Seed-plants, and in the
variety of their display exceeding all other groups. The
name of the group is suggested by the fact that the seeds
are inclosed in a seed case, in contrast with the exposed
seeds of the Gymnosperms.

These are also the true flowering plants, and the ap-
pearance of true flowers means the development of an

195

196

PLANT STRUCTURES

elaborate symbiotic relation between flowers and insects,
through which pollination is secured. In Angiosperms,
therefore, the wind is abandoned as an agent of pollen
transfer and insects are used ; and in passing from Gym-
nosperms to Angiosperms one passes from anemophilous to
entomophilous ("insect-loving") plants. This does not
mean that all Angiosperms are entomophilous, for some are
still wind-pollinated, but that the group is prevailingly ento-
mophilous. This fact, more than anything else, has re-
sulted in a vast variety in the structure of flowers, so char-
acteristic of the group.

109. The plant body. — This of course is a sporophyte,
the gametophytes being minute and concealed, as in Gym-
nosperms. The sporophyte represents the greatest possible
variety in habit, size, and duration, from minute floating
forms to gigantic trees ; herbs, shrubs, trees ; erect, pros-
trate, climbing ; aquatic, terrestrial, epiphytic ; from a few
days to centuries in duration.

Eoots, stems, and leaves are more elaborate and vari-
ously organized for work than in other groups, and the
whole structure represents the high-
est organization the plant body has
,c attained. As in the Gymnosperms,
the leaf is the most variously used
organ, showing at least four distinct
modifications : (1) foliage leaves, (2)
scales, (3) sporophylls, and (4) floral
leaves. The first three are present
in Gymnosperms, and even in Pteri-
dophytes, but floral leaves are pecul-

FIU. 165. stamens of hen- iar to Angiosperms, making the true
bane (Hyotcyamuft) : A, flower, and being associated with en-

front view, showing fila- ^V^l •,

rnent,/) and anther („,; tomophlly.

110. Microsporophylls. — The micro-

JL back view, showing

the connective (c) be-
tween the pollen-sacs.

the connective (c) be- sporopliyll Qf Angiosperms is

-After SCHIMPBR.

definitely known as a " stamen " than

SPERMATOPHYTES : AXGIOSPERMS

19'

that of Gymnosperms, and has lost any semblance to a leaf.
It consists of a stalk-like portion, the filament ; and a
sporangia - bearing portion, the anther (Figs. 165, 167«).

FIG. 166. Cross-section of anther of thorn apple (Datura), .showing the four imbedded
sporangia (a. p) containing microspores?; the pair on each side will merge and
dehisce along the depression between them for the discharge of pollen. — After
FRANK.

The filament may be long or short, slender or broad, or
variously modified, or even wanting. The anther is simply
the region of the sporophyll which bears sporangia, and is

JJIH

FIG. 167. Diagrammatic cross sections of anthers: A, younger stage, showing the
four imbedded sporangia, the contents of two removed, but the other two con-
taining pollen mother cells (pm) surrounded by the tapetum (t); B, an older stage,
in which the microspores (pollen grains) are mature, and the pair of sporangia on
each side are merging together to form a single pollen-sac with longitudinal
dehiscence.— After BAILLON and LI-KKSSKX.

therefore a composite of sporophyll and sporangia and is
often of uncertain limitation. Such a term is convenient,
but is not exact or scientific,
31

198

PLANT STRUCTURES

If a young anther be sectioned transversely four sporan-
gia will be found imbedded beneath the epidermis, a pair
on each side of the axis (Figs. 166, 167). When they reach
maturity, the paired sporangia on each side usually merge to-
gether, forming two spore-containing cavities (Fig. 167, B).
These are generally called " pollen-sacs," and each anther is
said to consist of two pollen-sacs, although each sac is made
up of two merged sporangia, and is not the equivalent of the
pollen-sac in Gymnosperms, which is a single sporangium.

FIG. I67a. Various forms of stamens : A, from Solannm, showing dehiscence by
terminal pores; J5, from Arbutus, showing anthers with terminal pores and
"horns"; C, from Berbens; D, from Atherosperma, showing dehiscence by
uplifted valves; E, from Aquilegia, showing longitudinal dehiscence; F, from
Popowia, showing pollen-sacs near the middle of the stamen. — After ENGLER
and FRANTIC

SPERMATOPIIYTES : ANGIOSPEKMS

199

FIG. 168. Cross - section of
anther of a lily (Butomus),
showing the separating walls
between the members of each
pair of sporangia broken
down at z, forming a con-
tinuous cavity (pollen sac)
which opens by a longitudi-
nal slit.— After SACHS.

The opening of the pollen-sac to discharge its pollen-
grains (microspores) is called dehiscence, which means "a
splitting open," and the methods of
dehiscence are various (Fig. 167$).
By far the most common method
is for the wall of each sac to split
lengthwise (Fig. 168), which is
called longitudinal dehiscence; an-
other is for each sac to open by a
terminal pore (Fig. 1670), in which
case it may be prolonged above into
a tube.

111. Megasporophylls. — These
are the so-called " carpels " of Seed-
plants, and in Angiosperms they
are organized in various ways, but
always so as to inclose the mega-
sporangia (ovules). In the simplest

cases each carpel is independent (Fig. 169, A), and is dif-
ferentiated into three regions : (1) a hollow bulbous base,

which contains the
ovules and is the
real seed case,
known as the
ovary ; (2) sur-
mounting this is a
slender more or less
elongated process,
the style; and (3)
usually at or near
the apex of the style
a special receptive
surface for the pol-
len, the stigma.

In other cases
several carpels to-

FIG. 169. Types of pistils : A, three simple pistils
(apocarpous), each showing ovary and style tipped
with stigma ; B, a compound pistil (syncarpous),
showing ovary (/), separate styles (g), and stigmas
(n) ; C, a compound pistil (syncarpous). showing
ovary (f), single style (g), and stigma (n). — After
BERG and SCHMIDT.

200

PL AST STRUCTURES

gether form a common ovary, while the styles may also
combine to form one style (Fig. 169, C), or they may remain
more or less distinct (Fig. 169, B). Such an ovary may
contain a single chamber, as if the carpels had united edge
to edge (Fig. 170, A) ; or it may contain as many chambers
as there are constituent carpels (Fig. 170, B), as though
each carpel had formed its own ovary before coalescence.
In ordinary phrase an ovary is either " one-celled " or
" several-celled," but as the word " cell " has a very differ-
ent application, the ovary chamber had better be called a
loculus, meaning "a compartment." Ovaries,

FIG. 170. Diagrammatic sections of ovaries: A, cross-section of an ovary with one
loculus and three carpels, the three sets of ovules said to be attached to the wall
(parietal); B, cross-section of an ovary with three loculi and three carpels, the
ovules being in the center (central); C, longitudinal section of B.— After SCHIM-

PER.

therefore, may have one loculus or several loculi. Where
there are several loculi each one usually represents a con-
stituent carpel (Fig. 170, B) ; where there is one loculus
the ovary may comprise one carpel (Fig. 169, ^1), or several
(Fig. 170, .4).

There is a very convenient but not a scientific word,
which stands for any organization of the ovary and the
accompanying parts, and that is pistil. A pistil may be
one carpel (Fig. 169, A), or it may be several carpels or-
ganized together (Fig. 169, B, (7), the former case being a
simple pistil, the latter a compound pistil. In other words,

SPEKMATOPHYTES : AKGlOSPEEMS

201

any organization of carpels which ap-
pears as a single organ with one ovary
is a pistil.

The ovules (megasporangia) are
developed within the ovary (Fig. 170)
either from the carpel wall, when they
tire foliar, or from the stem axis which
ends within the ovary, when they are
cauline (see § 89). They are similar
in structure to those of Gymnosperms,
with integument and micropyle, nu-
cellus, and embryo -sac (megaspore),
except that there are often two integu-
ments, an outer and an inner (Fig.
171).

112. The male gametophyte. — When the pollen-grain
(microspore) germinates there is formed within it the sim-
plest known gametophyte (Fig. 172). Xo trace of the

FKJ. 171. A diagrammatic
section of an ovule of
Angiosperms, showing
outer integument (ai),
inner integument (ii),
micropyle (m), nucellus
(&), and embryo sac or
megaspore (em). — After
SACHS.

FIG. 172. Germination of microspore (pollen grain) in duckweed (Lemna): A, mature
spore with its nucleus; B. nucleus of spore dividing: C, two nuclei resulting from
the division; Z>, a large and small cell following the nuclear division, forming the
two-celled male gametophyte; E, division of smaller cell (generative) to form the
two male cells; F, the two male cells completed and lying near the large tube
nucleus. — CALPWELI..

202

PLANT STRUCTURES

ordinary nutritive cells of the gametophyte remains, and
the whole structure seems to represent a single antherid-
ium. At first it consists of two cells, the large wall cell
and the small free generative cell (Fig. 172, D). Later

the generative cell di-
vides (Fig. 172, E),
either while in the
pollen -grain or after
entrance into the pol-
len-tube, and two male
cells (sperm mother-
cells) are formed (Fig.
172, F), which do not
organize sperms, but
which function direct-
ly as gametes.

When pollination
occurs, and the pollen
has been transferred
from the pollen-sacs
to the stigma, it is de-
tained by the minute
papillae of the stig-
matic surface, which
also excretes a sweet-
ish sticky fluid. This
fluid is a nutrient so-
lution for the micro-
spores, which begin to
put out their tubes.
A pollen-tube pene-
trates through the

FIG. 173. Diagram of a longitudinal section through
a carpel, to illustrate fertilization with all parts
in place : s, stigma ; g. style ; o, ovary ; ai, ii,
outer and inner integuments; n, base of nucel-
lus ; /, funiculus ; b, antipodal cells ; c, endo-
sperm nucleus; k, egg and one synergid; p, pol-
len-tube, having grown from stigma and passed
through the micropyle (m) to the egg.-After stigmatic surface, en-

LUERSSEN. >

ters among the tissues

of the style, which is sometimes very long, slowly or rap-
idly traverses the length of the style supplied with food by

SPERM ATOPIIYTES : ANGIOSPEKMS

203

its cells but not penetrating them, enters the cavity of the
ovary, passes through the micropyle of an ovule, penetrates
the tissues of the nucellus (if any), and finally reaches and
pierces the wall of the embryo-sac, within which is the egg
awaiting fertilization (Fig. 173).

This remarkable ability of the pollen-tube to make its
way through so much tissue, directly to the micropyle of
an inclosed ovule, can only be explained by supposing that
it is under the guidance of some strong attraction.

113. The female gametophyte. — The megaspore (embryo-
sac) occupies the same position in the ovule as in Gymno-
sperms, but its germination is remarkably modified. The
development of the female gametophyte shows two distinct

FIG. 174. Lilium Philadelphicum : to the left a young megasporangium (ovule),
showing integuments ( C). nucellus (A), and megaspore (B) containing a large nu-
cleus. To the right a megaspore whose nucleus is undergoing the first division
in the formation of the gametophyte.— CALDWELL.

periods, separated from one another by the act of fertiliza-
tion. If fertilization is not accomplished the second stage
of the gametophyte is usually not developed.

First period. — The megaspore nucleus divides (Fig.
174), and one nucleus passes to each end of the embryo-

204

PLANT STRUCTURES

sac (Fig. 175, at left). Each of these nuclei dhide (Fig.
175, at right), and two nuclei appear at each end of the
sac (Fig. 175, at middle). Each of the four nuclei divide

FIG. 175. Lilium Phtiadelphicum : to the left is an embryo-sac with a gametophyte
nucleus in each end; to the right these two nuclei are dividing to form the two
nuclei shown in each end of the sac in the middle figure.— CALDWELL.

(Fig. 176, at left), and four nuclei appear at each end (Fig.
176, at middle). When eight nuclei have appeared, nuclear
division stops. Then a remarkable phenomenon occurs.
One nucleus from each end, the two being called "polar
nuclei," moves toward the center of the sac, the two meet
and fuse (Fig. 176, at right, C), and a single large nucleus
is the result.

The three nuclei at the end of the sac nearest the micro-
pyle are organized into cells, each being definitely sur-
rounded by cytoplasm, but there is no wall and the cells
remain naked but distinct. These three cells constitute
the egg-apparatus (Fig. 176, at right, A), the central one,
which usually hangs lower in the sac than the others, being
the egg, the two others being the synergids, or "helpers."
Here, therefore, is an egg without an archegonium, a dis-
tinguishing feature of Angiosperms.

SPERMAT OPLIYTES : ANGIO8PERMS

205

The three nuclei at the other end of the sac are also or-
ganized into cells, and usually have walls. These cells are
known as antipodal cells (Fig. 176, at right,
B). The large nucleus near the center of A

the sac, formed by the fusion of the two / \

FIG. 176. Lilium Philadelphicum, showing last stages of germination of megaspore
before fertilization: the embryo sac to the left contains the pair of nuclei in each
end in a state of division preparatory to the stage represented by the middle figure,
in which there are four nuclei at each end ; the figure to the right shows an embryo-
sac containing a gametophyte about ready for fertilization, with the egg apparatus
(A) composed of the two synergids and egg (central and lower), the three antipo-
dal cells (B), and the two polar nuclei fusing (C) to form the primary endosperm
nucleus. — CALDWELL.

polar nuclei, is known as the primary endosperm nucleus
or the definitive nucleus.

206

PLANT STRUCTURES

FIG. 177. Fertilization in the cotton plant,
a Dicotyledon, showing the pollen tube (P)
passing through the micropyle and con-
taining a single sperm (male cell), and hav-
ing entered the embryo-sac is in contact
with one of the synergids (S) on its way to
the egg (E).— After DUGGAR.

This completes the first
period of gametophyte de-
velopment, and it is ready
for fertilization.

Fertilization. — The
pollen-tube, carrying the
two male cells, has passed
down the style and en-
tered the micropyle (Fig.
173). It then reaches the
wall of the embryo -sac,
pierces it, and is in con-
tact with the egg -appa-
ratus. Usually it passes
along the side of one of
the synergids (Fig. 177),
feeding upon and disor-
ganizing it. When it
comes near the conspicu-
ous nucleus of the egg,
the tip of the tube breaks
and one male cell is dis-
charged into the cyto-
plasm of the egg (Fig.
178). The egg and the
male cell now fuse, and
an oospore, which invests
itself with a wall, is the
result.

Second period. — After
fertilization the gameto-
phyte begins its second
period of development.
The primary endosperm
nucleus begins a series of
divisions, and as a result

SPEKMATOPHYTES : ANGIOSPEKMS

L><>7

the sac becomes more or less filled
with nutritive cells, which are
often organized into a compact
tissue (Fig. 179). These nutri-
tive cells correspond to the endo-
sperm of Gymnosperms, and re-
ceive the same name. In Gymno-
sperms, therefore, the endosperm
(the nutritive body of the female
gametophyte) is mainly formed
before fertilization, while in An-
giosperms it is mainly formed
after fertilization. This means
that in Angiosperms eggs are
formed and fertilization takes
place in a very young gameto-
phyte, while in Gymnosperms and
heterosporous Pteridophytes the
eggs appear much later.

The antipodal cells also proba-
bly represent nutritive cells of the
gametophyte. Sometimes they dis-

FIG. 178. End of embryo-sac of
lily (Lilium Philadelphia/m):
a pollen tube has entered the
sac and has discharged a male
cell, whose nucleus is seen
uniting with the nucleus of
the egg ; near the tip of the
tube is the disorganizing nu-
cleus of one of the synergids.
— CALDWELL.

FIG. 179. One end of the embryo-sac in wake-robin (Trittium). showing endosperm
(shaded cells) in which a young embryo is imbedded. — After ATKINSON.

208

PLANT STRUCTURES

appear very soon after they are formed ; but sometimes
they become very active and even divide and form a con-
siderable amount of tissue, aiding the endosperm in nour-
ishing the young embryo.

114. Development of embryo. — While the endosperm is
forming, the oospore has germinated and the sporophyte
embryo is developing (Fig. 180). Usually a suspensor, more
or less distinct, but never so prominent as in Gymnosperms,

is formed ; at the end of it the
embryo is developed (Fig. 181),
which, when completed, is more
or less surrounded by nourish-
ing endosperm (Fig. 183).

The two groups of Angio-
sperms differ widely in the struc-
ture of the embryo. In Mono-
cotyledons the axis of the em-
bryo develops the root-tip at one
end and the " seed-leaf " (coty-
ledon) at the other, the stem-tip
arising from the side of the axis
as a lateral member (Fig. 182).
This relation of organs recalls
the embryo of Isoetes (see § 90).
Xaturally there can be but one
cotyledon under such circum-
stances, and the group has been
named Monocotyledons.

In Dicotyledons the axis of

the embryo develops the root-tip at one end and the stem-
tip at the other, the cotyledons (usually two) appearing as
a pair of opposite lateral members on either side of the
stem-tip (Fig. 181). This recalls the relation of parts in
the embryo of Selaginella (see § 89). As the cotyledons
are lateral members their number may vary. In Gymno-
sperms, whose embryos are of this type, there are often

FIG. 180. Curved embryo-sac of
arrowhead (Sagittaria), show-
ing in the upper right end a
young embryo, in the other
end the antipodal cells cut off
by a partition, and scattered
through the sac a few free en-
dosperm cells. — After SCHAFF-

NER.

SPERM ATOPHYTE8 : ANGIOSPEKMS

209

several cotyledons in a cycle (Fig. 154) ; and in Dicotyle-
dons there may be one or three cotyledons ; but as a pair
of opposite cotyledons is almost without exception in the
group, it is named Dicotyledons.

The axis of the embryo between the root-tip and the
cotyledons is called the hypocotyl (Figs. 154, 193, 194), which

FIG. 181. Development of embryo of shepherd's purse (Capsella), a Dicotyledon,
beginning with 7, the youngest stage, and following the sequence to VI, the old-
est stage, v represents the stispensor, c the cotyledons, s the stem-tip, w the root,
h the root-cap. Note the root-tip at one end of the axis and the stem-tip at the
other between the cotyledons.— After HANSTEIN.

means " under the cotyledon," a region which shows pecul-
iar activity in connection with the escape of the embryo
from the seed. Formerly it was called either caulide or
radicle, In Dicotyledons the stem-tip between the coty-

210

PLANT STKUCTURES

ledons often organizes the rudiments of subsequent leaves,
forming a little bud which is called the plumule.

Embryos differ much as to com-
pleteness of their development within
the seed. In some plants, especially
those which are parasitic or sapro-
phytic, the embryo is merely a small
mass of cells, without any organiza-
tion of root, stem, or leaf. In many
cases the embryo becomes highly de-
veloped, the endosperm being used
up and the cotyledons stuffed with
food material, the plumule contain-
ing several well - organized young
leaves, and the embryo completely
filling the seed cavity. The com-
mon bean is a good illustration of
this last case, the whole seed within
the integument consisting of the two
large, fleshy cotyledons, between
which lie the hypocotyl and a plu-
mule of several leaves.

115. The seed. — As in Gymno-
sperms, while the processes above
described are taking place within
the ovule, the integument or integu-
ments are becoming transformed into the testa (Fig. 183).
When this hard coat is fully developed, the activities
within cease, and the whole structure passes into that con-
dition of suspended animation which is so little under-
stood, and which may continue for a long time.

The testa is variously developed in seeds, sometimes
being smooth and glistening, sometimes pitted, sometimes
rough with warts or ridges. Sometimes prominent append-
ages are produced which assist in seed-dispersal, as the
wings in Catalpa or Bignonia (Fig. 184), or the tufts of

PIG. 182. Young embryo of
water plantain (Alisma), a
Monocotyledon, the root
being organized at one
end (next the suspensor),
the single cotyledon (C)
at the other, and the stem-
tip arising from a lateral
notch (v). — After HAN-
STEIN.

SPERM ATOPHYTES : ANGIOSPERMS

211

FIG. 183. The two figures to the left are seeds of violet, one showing the black, hard
testa, the other being sectioned and showing testa, endosperm, and imbedded
embryo; the figure to the right is a section of a pepper fruit (Piper), showing
modified ovary wall (po, seed testa (sc), nucellus tissue (p), endosperm (en), and
embryo (em).— After ATKINSON.

hair on the seeds of milkweed, cotton, or fireweed (Fig.
185). For a fuller account of the methods of seed-dispersal
see Plant Relations, Chapter VI.

FIG. 184. A winged seed of Bignonia.— After STRASBURGER.

116. The fruit. — The effect of fertilization is felt beyond
the boundaries of the ovule, which forms the seed. The
ovary is also involved, and becomes more or less modified.
It enlarges more or less, sometimes becoming remarkably
enlarged. It also changes in structure, often becoming
hard or parchment-like. In case it contains several or
numerous seeds, it is organized to open in some way and
discharge them, as in the ordinary pods and capsules (Fig.
185). In case there is but one seed, the modified ovary

212

PLAXT STRUCTURES

wall may invest it as closely as another
integument, and a seed-like fruit is
the result — a fruit which never opens
and is practically a seed. Such a
fruit is known as an akene, and is
very characteristic of the greatest
Angiosperm family, the Composite,
to which sunflowers, asters, golden-
rods, daisies, thistles, dandelions,
etc., belong. Dry fruits which do
not open to discharge the seed often
bear appendages to aid in dispersal
by wind (Figs. 186, 187), or by animals
(Fig. 188).

Capsules, pods, and akenes are said
to be dry fruits, but in many cases
fruits ripen fleshy. In the peach,
plum, cherry, and all ordinary " stone
fruits," the modified ovary wall or-
ganizes two layers, the inner being
very hard, forming the " stone," the
outer being pulpy (Fig. 189), or vari-
ously modified (Fig. 190). In the true berries, as the
grape, currant, tomato, etc., the whole ovary becomes a
thin-skinned pulpy mass in which the seeds are imbedded.

In some cases
the effect of ferti-
lization in chang-
ing structure is
felt beyond the
ovary. In the ap-
ple, pear, quince,
and such fruits,
the pulpy part is
the modifie d

Calyx (one Of the FIQ. 1S6. Winged fruit of maple.— After RERNI;R,

FIG. 1&5. A pod of fireweed
(Epilobium) opening and
exposing its plumed seeds
which are transported by
the wind.— After BKAL.

SPERMATOPIIYTES : ANGIOSPEKMS

213

floral leaves), the ovary and its contained seeds being repre-
sented by the "core." In other cases, the end of the stem
bearing the ovaries (receptacle) becomes enlarged and
pulpy, as in the strawberry (Fig. 191). This effect some-
times involves even
more than the
parts of a single ^j
flower, a whole
flower-cluster,
with its axis and
bracts, becoming j j
an enlarged pulpy
mass, as in the
pineapple (Fig.
192).

The term
"fruit," therefore,

FIG. 187. A ripe dandelion head, showing the mass of
plumes, a few seed-like fruits (akenes) with their
plumes still attached to the receptacle, and two
fallen off.— After KERNEK.

FIG. 188. An akene of beg-
gar ticks, showing the two
barbed appendages which
lay hold of animals.— Af-
ter BEAL.

FIG. 189. To the left a section of a peach (fruit),
showing pulp and stone formed from ovary wall,
and the contained seed (kernel); to the right
the fruit of almond, which ripens dry. — After
GRAY.

214

PLANT STRUCTURES

is a very indefinite one, so far as the structures it includes
are concerned. It is simply an effect which follows fer-
tilization, and involves more or less of the structures adja-

FIG. 190. Fruit of nutmeg (Myristica) : A, section of fruit, showing seed within the
heavy wall ; B, section of seed, showing peculiar convoluted and hard endosperm
(m) in which an embryo (n) is imbedded — After BERG and SCHMIDT.

cent to the seeds. As has been seen, this effect may extend
only to the ovary wall, or it may include the calyx, or it
may be specially directed toward the
receptacle, or it may embrace a whole
flower-cluster. It is what is called a
physiological effect rather than a defi-
nite morphological structure.

117. Germination of the seed.— It
has been pointed out (§ 103) that the
so-called "germination of the seed"
is not true germination like that of
spores. It is the awakening and es-
cape of the young sporophyte, which
has long before passed through its
germination stage.

By various devices seeds are sepa-
rated from the parent plant, are dis-
persed more or less widely, and find

lodgment. If the lodgment is suitable, there are many
devices for burial, such as twisting stalks and awns, bur-

FIG. 191. Fruit of straw-
berry, showing the per-
sistent calyx, and the en-
larged pulpy receptacle
in which numerous sim-
ple and dry fruits (a-
kenes) are imbedded.—
After BAILEY.

SPEKMATOPHYTES : ANGIOSPEKMS

215

rowing animals, etc. The period of rest may be long or
short, but sooner or later, under the influence of moisture,
suitable temperature, and oxygen the quiescent seed begins
to show signs of life.

The sporophyte within begins to grow, and the seed
coat is broken or penetrated through some thin spot or

FIG. 192. Pineapple: A, the cluster of fruits forming the so-called "fruit"; B, single
flower, showing small calyx and more prominent corolla; C, section of flower,
showing the floral organs arising above the ovary (epigynous). — A, B after KOCH;
C after LB MAOUT and DECAISNE.

opening. The root-tip emerges first, is protruded still
farther by the rapid elongation of the hypocotyl, soon
curves toward the earth, penetrates the soil, 'and sending
out rootlets, becomes anchored. After anchorage in the

216

PLANT STRUCTURES

soil, the hypocotyl again rapidly elongates and develops a
strong arch, one of whose limbs is anchored, and the other
is pulling upon the cotyledons (Fig. 193). This pull finally
frees the cotyledons, the hypocotyl straightens, the cotyle-

FIG. 193. Germination of the garden bean, showing the arch of the hypocotyl above
ground, its pull on the seed to extricate the cotyledons and plumule, and the final
straightening of the stem and expansion of the young leaves. — After ATKINSON.

dons are spread out to the air and light, and the young
sporophyte has become independent (Fig. 194).

In the grain of corn and other cereals, so often used in
the laboratory as typical Monocotyledons, but really excep-
tional ones, the embryo escapes easily, as it is placed on
one side of the seed near the surface. The hypocotyl and
stem split the thin covering, and the much-modified cotyle-
don is left within the grain to absorb nourishment.

In some cases the cotyledons do not escape from the
seed, either being distorted with food storage (oak, buck-
eye, etc.), or being retained to absorb nourishment from
the endosperm (palms, grasses, etc.). In such cases the
stem-tip is liberated by the elongation of the petioles of the

SPERMATOPHYTES : AXtHOSPERMS

cotyledons, and the seed coat containing, the cotyledons
remains like a lateral appendage upon the straightened axis.

It is also to be observed in
many cases that the young root
system, after gripping the soil,
contracts, drawing the young
plant deeper into the ground.

118. Summary from Angio-
sperms. — At the beginning of this
chapter (§ 107) the characters of
the Gymnosperms were summar-
ized which distinguished them
from Angiosperms, whose con-
trasting characters may be stated
as follows :

(1) The microspore (pollen-
grain), chiefly by insect pollina-
tion, is brought into contact with
the stigma, which is a receptive
region on the surface of the car-
pel, and there develops the pollen-
tube, which penetrates the style
to reach the ovary cavity which
contains the ovules (megasporan-
gia). The impossibility of con-
tact between pollen and ovule im-
plies inclosed ovules and hence
seeds, and therefore the name
" Angiosperm."

(2) The female gametophyte
is but slightly developed before
fertilization, the egg appearing
very early.

(3) The female gametophyte produces no archegonia,
but a single naked egg.

FIG. 194. Seedling of hazel ( Car-
pinus), showing primary root
(hw) bearing rootlets (sw)
upon which are numerous
root hairs (r), hypocoiyl (h),
cotyledons (c). young stem
(e), and first (I) and second
(I') true leaves. — After SCUIM-

* PEH.

CHAPTEE XIII

THE FLOWER

119. General characters. — In general the flower may be
regarded as a modified branch of the sporophyte stem bear-
ing sporophylls and usually floral leaves. Its representa-
tive among the Pteridophytes and Gymnosperms is the stro-
bilus, which has sporophylls but not floral leaves. Among
Angiosperms it begins in a simple and somewhat indefinite
way, gradually becomes more complex and modified, until
it appears as an elaborate structure very efficient for its
purpose.

This evolution of the flower has proceeded along many
lines, and has resulted in endless diversity of structure.
These diversities are largely used in the classification of
Angiosperms, as it is supposed that near relatives are indi-
cated by similar floral structures, as well as by other fea-
tures. The significance of these diversities is supposed to
be connected with securing proper pollination, chiefly by
insects, and favorable seed distribution.

Although the evolution of flowers has proceeded along
several lines simultaneously, now one feature and now
another being emphasized, it will be clearer to trace some
of the important lines separately.

120. Floral leaves. — In the simplest flowers floral leaves
do not appear, and the flower is represented only by the
sporophylls. Both kinds of sporophylls may be associated,
in which case the flower is said to be perfect (Fig. 195) ; or
they may not both occur in the same flower, in which case
one flower is staminate and the other pistillate (Fig. 196).

218

THE FLOWER

219

When the floral leaves first appear in connection with
the sporophylls they are inconspicuous, scale-like bodies.
In higher forms they become more prominent and inclose

FIG. 195. Lizard's tail (Saururus}: A, tip of branch
bearing leaves and elongated cluster of flowers;
B, a single naked flower from A, showing sta-
mens and four spreading and stigmatic styles;
(7, flower from another species, showing sub-
tending bract, absence of floral leaves, seven
stamens, and a syncarpous pistil ; the flowers
naked and perfect.— After ENGLEK.

FIG. 196. Naked flowers of dif-
ferent willows (Salix), each
from the axil of a bract :
a, b, c, staminate flowers ;
d, e, /, pistillate flowers, the
pistil composed of two car-
pels (syncarpous). — After
WARMING.

FIG. 197. Flower of calamus
(Acorus), showing simple
perianth, stamens, and syn-
carpous pistil: a hypogynous
flower without differentiation
of calyx and corolla.— After
ENGLER.

FIG. 199. Common flax (Linum) :
A. entire flower, showing calyx
and corolla ; B. floral leaves re-
moved, showing stamens and
syucarpous pistil ; C, a mature
capsule splitting open. — After

SCHIMPER.

FIG. 198. Flowers of elm (Vlmns) : A, branch
bearing clusters of flowers and scaly buds ;
B, single flower, showing simple perianth
and stamens, being a stamii ate flower ; C,

flower showing perianth, stamens, and the two divergent styles stigmatic on inner
surface, being a perfect flower; I), section through perfect flower, showing peri-
anth, stamens, and pistil with two loculi each with a single ovule —After ENGLER.

FIG. 200. A flower of peony, showing the four sets of floral organs: k, the sepals, to-
gether called the calyx; c, the petals, together called the corolla; a, the numerous
stamens; g, the two carpels, which contain the ovules.— After STRASBURGEU.

THE FLOWER

221

the young sporophylls, but they are all alike, forming what
is called the perianth (Figs. 197, 198).

In still higher forms the perianth differentiates, the
inner floral leaves become more delicate in texture, larger
and generally brightly colored (Fig. 199, A). The outer
set may remain scale-like, or become like small foliage
leaves. When the dif-
ferentiation of the peri-
anth is distinct, the
outer set of floral leaves
is called the calyx, each
leaf being a sepal ; the
inner set is the corolla,
each leaf being a petal
(Fig. 200). Sometimes,
as in the lily, all the
floral leaves become
uniformly large and
brightly colored, in
which case the term
perianth is retained
(Fig. 201). In other
cases, the calyx may be
the large and colored
set, but whenever there
is a clear distinction
between sets, the outer
is the calyx, the inner
the corolla.

Both floral sets may
not appear, and it has
become the custom to
regard the missing set FIG 201 _An easter.niy. a Monocotyledon,

as the Corolla, SUCh showing perianth (a), stamens (6), stigma (c),

flowers being called flowe^ bu<Yrf)' »nd .\carPel a^rt the. peri'

anth has fallen (/), with its knob-like stigma,
long style, and slender ovary. -CALDW ELL.

222 PLANT STRUCTURES

" without petals." It is not always possible to tell whether
a flower is apetalous — that is, whether it has lost a floral
set which it once had — or is simply one whose perianth has
not yet differentiated, in which case it would be a "primi-
tive type."

The line of evolution, therefore, extends from flowers
without floral leaves, or naked flowers, to those with a dis-
tinctly differentiated calyx and corolla.

121. Spiral to cyclic flowers.— In the simplest flowers the
sporophylls and floral leaves (if any) are distributed about
an elongated axis in a spiral, like a succession of leaves.
That part of the axis which bears the floral organs is for
convenience called the receptacle (Fig. 202). As the recep-

a/ '"' *

FIG. 202. A buttercup (Ranunculus}: a, complete flower, showing sepals, petals, sta-
mens, and head of numerous carpels on a large receptacle; b, section showing
relation of parts; a hypogynous, polypetalous, apocarpous, actinomorphic flower.
—After BAILLON.

tacle is elongated and capable of continued growth, an in-
definite number of each floral organ may appear, especially
of the sporophylls. With the spiral arrangement, there-
fore, there is no definiteness in the number of floral organs ;
there may be one or very many floral leaves, or stamens, or
carpels. The spiral arrangement and indefinite numbers
are features of the ordinary strobilus, and therefore such
flowers are regarded as more primitive than the others.

In higher forms the receptacle becomes shorter, the
spiral more closely coiled, until finally the sets of organs

THE FLO WEE

223

appear to be thrown into rosettes or cycles. This change
does not necessarily affect all the parts simultaneously.
For example, in the common buttercup the sepals and
petals are nearly in cycles, while the carpels are spirally
arranged and indefinitely numerous on the head-like recep-
tacle (Fig. 202). On the other hand, in the common water-

FIG. 203.

Flower of water-lily (Nymphced), showing numerous petals and stamens. —
After CASPARY.

lily the petals and stamens are spiral, and indefinitely re-
peated, while the sepals and carpels are approximately
cyclic (Fig. 203).

Finally, in the highest forms, all the floral organs are
in definite cycles, and there is no indefinite repetition of
any part. All through this evolution from the spiral to the
cyclic arrangement there is constantly appearing a tend-
ency to " settle down " to certain definite numbers. When
the complete cyclic arrangement is finally established these
numbers are established, and they are characteristic of
great groups. In cyclic Monocotyledons there are nearly
always just three organs in each cycle, forming what is
called a trimerous flower (Fig. 204) ; while in cyclic Dicot-

224

PLANT STRUCTURES

yledons the number five prevails, but often four appears,
forming pentamerous or tetramerous flowers (Fig. 199).
This does not mean that there are necessarily just three,
four, or five of each organ in the flower, for there may be
two or more cycles of some one organ. For example, in the
common lily there are six floral leaves in two sets, six sta-
mens in two sets, and three carpels (Fig. 204).

In the cyclic flowers it is also to be noted that each set
alternates with the next set outside (Fig. 204). The petals

are not directly opposite the se-
pals, but are opposite the spaces
between sepals ; the stamens in
turn alternate with the petals ; if
there is a second set of stamens,
it alternates with the outer set,
and so on. If two adjacent sets
are found opposing one another,
it is usually due to the fact that
a set between has disappeared.
For example, if a set of stamens
is opposite the set of petals, either
an outer stamen set or an inner
petal set has disappeared.

This line of evolution, there-
fore, extends from flowers whose
parts are spirally arranged upon
an elongated receptacle and in-
definite in number, to those whose parts are in cycles and
definite in number.

122. Hypogynous to epigynous flowers. — In the simpler
flowers the sepals, petals, and stamens arise from beneath
the ovary (Figs. 197, 202, 205, 1). As in such cases the
ovary or ovaries may be seen distinctly above the origin
(insertion) of the other parts, such a flower is often said to
have a "superior ovary." The more usual term, however,
is hypogynous, meaning in effect "under the ovary," refer-

FIG. 204. Diagram of such a
flower as the lily/showing re-
lation of parts : uppermost
organ is the bract in the axil
of which the flower occurs ;
black dot below indicates po-
sition of stem ; floral parts in
threes and in five alternating
cycles (two stamen scts\ being
a trimerous, pentacyclic flow-
er.— After SCHIMPER.

THE FLOWER

225

ring to the fact that the insertion of the other parts is
under the ovary.

Hypogyny is very largely displayed among flowers, but
there is to be observed a tendency in "some to carry the
insertion of the outer parts higher up. When the outer
parts arise from the rim of an urn-like outgrowth from the

Fi(i. 205. Flowers of Rose family: /, a hypogynous
flower of Potentilla, sepals, petals, and stamens
arising from beneath the head of carpels; 2, a
pi-rigynous flower of Alchemilla, sepals, petals,
and stamens arising from rim of urn-like pro-
longation of the receptacle, which surrounds the
carpel ; 3, an epigynous flower of the common
apple, in which all the parts seem to arise from
the top of the ovary, two of whose loculi are
seen. — After FOCKE.

receptacle, which surrounds the pistil or pistils, the flower
is said to be perigynous (Figs. 205, .2, 206), meaning " around
the pistil." Finally, the insertion is carried above the ovary,
and sepals, petals, and stamens seem to arise from the top
of the ovary (Fig. 205, 3), such a flower being epigynous,
the outer parts appearing "upon the ovary." In such a
case the ovary does not appear within the flower, but below
it (Figs. 205, 252, 261), and the flower is often said to have
an "inferior ovary."

123. Apocarpous to syncarpous flowers. — In the simpler
flowers the carpels are entirely distinct, each carpel organ-

226

PLANT STRUCTURES

izing a simple pistil, a single flower containing as many
pistils as there are carpels, as in the buttercups (Figs.
200, 202). Such a flower is said to be apocarpous, meaning
"carpels separate." There is a very strong tendency,

FIG. 206. Sweet-scented shrub (Calycanthus): A, tip of branch bearing flowers; B,
section through flower, showing numerous floral leaves, stamens, and carpels, and
also the development of the receptacle about the carpels, making a perigynous
flower. — After THIEBAULT.

however, for the carpels of a flower to organize together
and form a single compound pistil. In such a flower there
may be several carpels, but they all appear as one organ
(Figs. 195, C, 197, 198, A 199, B), and the flower is said
to be syncarpous, meaning "carpels together."

124. Polypetalous to sympetalous flowers. — The tendency
for parts of the same set to coalesce is not confined to the
carpels. Sepals often coalesce (Fig. 208), and sometimes
stamens, but the coalescence of petals seems to be more
important. Among the lower forms the petals are entirely
separated (Figs. 199, A, 202, 203, 207), a condition which

THE FLOWER

227

has received a variety of names, but
probably the most common is poly-
petalous, meaning "petals many/'
although eleutheropetalous, meaning
" petals free/' is much more to the
point.

In the highest Angiosperms, how-
ever, the petals are coalesced, form-
ing a more or less tubular organ
(Figs. 208-210). Such flowers are
said to be sympetalous, meaning
"petals united." The words gamo-
petalous and monopetalous are also

much used, but all three words refer to the same condition
of the flower. Often the sympetalous corolla is differenti-

FIG. 207. Flower of straw-
berry, showing sepals, pet-
als, numerous stamens,
and head of carpels ; the
flower is actinomorphic,
hypogynous, and with no
coalescence of parts. — Af-
ter BAILEY.

FIG. 208. A flower of the tobacco plant: a, a complete flower, showing the calyx with
its sepals blended below, the funnelform corolla made up of united petals, and the
stamens just showing at the mouth of the corolla tube; b. a corolla tube split open
and showing the five stamens attached to it near the base; c, a syncarpous pistil
made up of two carpels, showing ovary, style, and stigma.— After STRASBTJRGER.

228

PLANT STRUCTUEES

ated into two regions (Fig. 210, b), a more or less tubular
portion, the tube, and a more or less flaring portion, the limb.

125. Actinomorphic
to zygomorphic flow-
ers. — In the simpler
flowers all the mem-
bers of any one cycle
are alike ; the petals
are all alike, the
stamens are all alike,
etc. Looking at the
center of the flower,
all the parts are re-
peated about it like
the parts of a radi-
ate animal. Such a
flower is actinomor-

phic meaning " ra-
"T . „ , . „
Cliate, and IS Olten

called a ' ' regular

fl » Although

LOWer.

the term actinomor-

phic strictly applies to all the floral organs, it is especially
noteworthy in connection with the corolla, whose changes
will be noted.

FIG. 209. Flower of morning -glory (Ipomced), with
sympetalous corolla split open, showing the five
attached stamens, and the superior ovary with
prominent style and stigma ; the flower is by-
pogynous, sympetalous, and actinomorphic.-
After MEISSNEB.

FIG. 210. A group of sympetalous flower forms: a. a flower of harebell, showing a
bell-shaped corolla; 6, a flower of phlox, showing a tube and spreading limb; c, a
flower of dead-nettle, showing a zygomorphic two-lipped corolla; d, a flower of
toad-flax, showing a two-lipped corolla, and also a spur formed by the base of the
corolla; e, a flower of the snapdragon, showing the two lips of the corolla closed.
— After GRAY.

THE FLOWER

229

In many cases the petals are not all alike, and the radi-
ate character, with its similar parts repeated about a cen-
ter, is lost. In the
common violet, for
example, one of the
petals develops a spur
(Fig. 211) ; in the
sweet pea the petals
are remarkably un-
like, one being broad
and erect, two small-
er and drooping
downward, and the
other two much modi-
fied to form together
a boat-like structure
which incloses the
sporophylls. Such flowers are called zygomorphic., meaning
" yoke-form," and they are often called *•' irregular flowers."

When zygomorphic flowers are also sympetalous the
corolla is often curiously shaped. A very common form

FIG. 211. The pansy ( Viola tricolor): A, section
showing sepals (I, /')• petals (c) one of which
produces a spur (oo. the flower being zygomor-
phic; B, mature fruit (a capsule) and persistent
calyx (£); C, the three boat-shaped valves of
the fruit open, most of the seeds (*) having
been discharged. — After SACHS.

FK;. -21-2. Flower of a mint (Mtut/ta aquaticar. A, the entire flower, showing calyx
of united sepals, unequal petals, stamens, and style with two stigma lobes: B. a
corolla split open, showing petals united and the four stamens attached to the
tube; the flower is sympetalous and zygomorphic.— After WERMING,

230

PLANT STRUCTURES

FIG. 213. Flower of a Labiate ( Teucrium),
showing the calyx of coalesced sepals,
the sympetalous and two-lipped (bilabi-
ate) corolla with three petals (middle one
largest) in the lower lip and two small
ones in the upper, and the stamens and
style emerging through a slit on the up-
per side of the tube; a sympetalous and
zygomorphic flower.— After BIUQUET.

is the bilabiate) or " two-lipped," in which two of the petals
usually organize to form one lip, and the other three form

the other lip (Figs. 210,
c, d, e, 212, 213). The two
lips may be nearly equal,
the upper may stand high
.or overarch the lower, the
lower may project more or
less conspicuously, etc.

126. Inflorescence. —
Very often flowers are soli-
tary, either on the end of
a stem or branch (Figs.
231, 236), or in the axil
of a leaf (Fig. 258). But

such cases grade insensibly into others where a definite
region of the plant is set aside to produce flowers (Figs.
253, 260). Such a region forms what is called the inflo-
rescence. The various ways in which flowers are arranged
in an inflorescence have received technical names, but they
do not enter into our purpose here. They are simply dif-
ferent ways in which plants seek to display their flowers
so as to favor pollination and seed distribution.

There are several tendencies, however, which may be
noted. Some groups incline to loose clusters, either elon-
gated (Fig. 260) or flat-topped (Fig. 253) ; others prefer
large and often solitary flowers (Fig. 258) to a cluster of
smaller ones ; but in the highest groups there is a distinct
tendency to reduce the size of the flowers, increase their
number, and mass them into a compact cluster. This ten-
dency reaches its highest expression in the greatest family
of the Angiosperms, the Compositse, of which the sunflower
or dandelion can be taken as an illustration (Figs. 261, 262),
in which numerous small flowers are closely packed together
in a compact cluster which resembles a single large flower.
It does not follow that all very compact inflorescences in-

THE FLOWEK 231

dicate plants of high rank, for the cat-tail flag (Fig. 221)
and many grasses have very compact inflorescences, and
they are supposed to be plants of low rank. It is to be
noted, however, that the very highest groups have settled
upon this as the best type of inflorescence.

127. Summary, — In tracing the evolution of flowers,
therefore, the following tendencies become evident : (1)
from naked flowers to those with distinct calyx and corolla ;
(2) from spiral arrangement and indefinite numbers to cyclic
arrangement and definite numbers ; (3) from hypogynous
to epigynous flowers ; (4) from apocarpous to syncarpous
pistils ; (5) from polypetalous to sympetalous corollas ; (6)
from actinomorphic or regular to zygomorphic or irregular
flowers ; (7) from loose to compact inflorescences.

These various lines appear in all stages of advancement
in different flowers, so that it would be impossible to deter-
mine the relative rank in all cases. However, if a flower
is naked, spiral, with indefinite numbers, hypogynous, and
apocarpous, it would certainly rank very low. On the con-
trary, the flowers of the Composite have calyx and corolla,
are cyclic, epigynous, syncarpous, sympetalous, often zygo-
morphic, and are in a remarkably compact inflorescence,
indicating the highest possible combination of characters.

128. Flowers and insects. — The adaptations between
flowers and insects, by which the former secure pollination
and the latter food, are endless. Many Angiosperm flowers,
especially those of the lower groups, are still anemophilous,
as are the Gymnosperms, but most of them, by the presence
of color, odor, and nectar, indicate an adaptation to the
visits of insects. This wonderful chapter in the history of
plants will be found discussed, with illustrations, in Plant
Relations, Chapter VII.

CHAPTER XIV

MONOCOTYLEDONS AND DICOTYLEDONS

129. Contrasting characters. — The two great groups of
Angiosperms are quite distinct, aud there is usually no dif-
ficulty in recognizing them. The monocotyledons are
usually regarded as the older and the simpler forms, and
are represented by about twenty thousand species. The
Dicotyledons are much more abundant and diversified, con-
taining about eighty thousand species, and form the domi-
nant vegetation almost everywhere.
The chief contrasting characters
may be stated as follows :

Monocotyledons. — (1) Embryo
with terminal cotyledon and lat-
eral stem-tip. This character is
practically without exception.

(2) Vascular bundles of stem
scattered (Fig. 214). This means
that there is no annual increase in
the diameter of the woody stems,
and no extensive branching, but
to this there are some exceptions.

(3) Leaf veins forming a closed
system (Fig. 215, figure to left).
As a rule there is an evident set

of veins which run approximately parallel, and intricately
branching between them is a system of minute veinlets not
readily seen. The vein system does not end freely in the
232

FIG. 214. Section of stem of
corn, showing the scattered
bundles, indicated by black
dots in cross-section, and by
lines in longitudinal section.
— From " Plant Relations."

MONOCOTYLEDONS AND DICOTYLEDONS 233

margin of the leaf, but forms a ' ' closed venation/' so that
the leaves usually have an even (entire) margin. There

are some notable exceptions
to this character.

(4) Cyclic flowers trim-
erous. The " three-parted "

FIG. 215. Two types of leaf venation: the figure to the left is from Solomon's seal,
a Monocotyledon, and shows the principal veins parallel, the very minute cross
veinlets being invisible to the naked eye; that to the right is from a willow, a
Dicotyledon, and shows netted veins, the main central vein (midrib) sending out
a series of parallel branches, which are connected with one another by a network
of veinlets.— After ETTINGSHAUSEN.

flowers of cyclic Monocotyledons are quite characteristic,
but there are some trimerous Dicotyledons.

Dicotyledons. — (1) Embryo with lateral cotyledons and
terminal stem-tip.

(2) Vascular bundles of stem forming a hollow cylinder
(Fig. 216, w). This means an annual increase in the diam-

234

PLANT STRUCTURES

eter of woody stems (Fig.
217, w), and a possible
increase of the branch
system and foliage dis-
play each year.

(3) Leaf veins form-
ing an open system (Fig.
215, figure to right).
The network of smaller
veinlets between the
larger veins is usually
very evident, especially
on the under surface of
the leaf, suggesting the
name "net- veined"
leaves, in contrast to the " parallel-veined " leaves of Mono-
cotyledons. The vein system ends freely in the margin of
the leaf, forming an "open venation." In consequence of
this, although the leaf _____

rrj

FIG. 216. Section across a young twig of
box elder, showing the four stem regions:
e, epidermis, represented by the heavy
bounding line; c, cortex; w, vascular cyl-
inder; p, pith. — From "Plant Relations/'

may remain entire, it
very commonly be-
comes toothed, lobed,
and divided in various
ways. Two main types
of venation may be
noted, which influence
the form of leaves. In
one case a single very
prominent vein (rib}
runs through the mid-
dle of the blade, and
is called the midrib.
From this all the mi-
nor veins arise as
branches (Figs. 218,
210), and such a leaf

FIG. 217. Section across a twig of box elder
three years old, showing three annual rings,
or growth rings, in the vascular cylinder; the
radiating lines (m) which cross the vascular
region (w) represent the pith rays, the princi-
pal ones extending from the pith to the cor-
tex (c).— From " Plant Relations."

MONOCOTYLEDONS AND DICOTYLEDONS

235

is said to be pinnate or pinnately veined, and inclines to
elongated forms. In the other case several ribs of equal
prominence enter the blade and diverge through it (Fig.
218). Such a leaf is palmate or palmately veined, and in-
clines to broad forms.

(4) Cyclic flowers pentamerous or tetramerous. The
flowers " in fives " are greatly in the majority, but some

FIG. 218. Leaves showing pinnate and palmate branching; the one to the left is from
sumach, that to the right from buckeye.— CALDWELL.

very prominent families have flowers " in fours." There
are also dicotyledonous families with flowers "in threes,"
and some with flowers " in twos."

It should be remembered that no one of the above char-
acters, unless it be the character of the embryo, should be
depended upon absolutely to distinguish these two groups.

236

PLANT STRUCTURES

It is the combination of characters which determines a
group.

MONOCOTYLEDONS

130. Introductory. — This great group gives evidence of
several distinct lines of development, distinguished by what
may be called the working out of different ideas. In this
way numerous families have resulted — that is, groups of

FIG. 219. A leaf of honey locust, to show twice pinnate branching (bipinnate leaf ).—

CALDWELL.

forms which seem to belong together on account of similar
structures. This similarity of structure is taken to mean
relationship. A family, therefore, is made up of a group
of nearly related forms. Opinions may differ as to what
forms are so nearly related that they deserve to consti-
tute a distinct family. A single family of some botanists
may be " split up " into two or more families by others.
Despite this diversity of opinion, most of the families are
fairly well recognized.

MONOCOTYLEDONS AND DICOTYLEDONS 337

Within a family there are smaller groups, indicating
closer relationships, known as genera (singular, genus).
For example, in the great family to which the asters belong,
the different asters resemble one another more than they do
any other members of the family, and hence are grouped
together in a genus Aster. In the same family the golden-
rods are grouped together in the genus Solidago. The
different kinds of Aster or of Solidago are called species
(singular also species). A group of related species, there-
fore, forms a genus ; and a group of related genera forms a
family.

The technical name of a plant is the combination of its
generic and specific names, the former always being written
first. For example, Quercus alba is the name of the com-
mon white oak, Quercus being the name of the genus to
which all oaks belong, and alba the specific name which
distinguishes this oak from other oaks. Xo other names
are necessary, as no two genera of plants can bear the same
name.

In the Monocotyledons about forty families are recog-
nized, containing numerous genera, and among these
genera the twenty thousand species are distributed. It is
evident that it will be impossible to consider such a vast
array of forms, even the families being too numerous to
mention. A few important families will be mentioned,
which will serve to illustrate the group.

131. Pondweeds, — These are submerged aquatics, found
in most fresh waters (some are marine), and are regarded
as among the simplest Monocotyledons. They are slender,
branching herbs, growing under water, but often having
floating leaves, and sending the simple flowers or flower
clusters above the surface for pollination and seed-distri-
bution. The common pondweed (Potamogeton) contains
numerous species (Fig. 220), while Naias (naiads) and
Zannichellia (horned pondweed) are common genera in
ponds and slow waters.

238

1'LANT STKUCTI KKs

The simple character of these forms is indicated by their
aquatic habit and also by their flowers, which are mostly
naked and with few sporophylls. A flower may consist of
a single stamen, or a single carpel ; or there may be several
stamens and carpels associated, but without any coalescence
(Fig. 220, B).

In the same general line with the pondweeds, but with
more complex flowers, are the genera Sagittaria (arrow-

FIQ. 220. Pondweed (Potamogeton): A, branch with cluster (spike) of simple flowers,
showing also the broad floating leaves and the narrow submerged ones; B, a sin-
gle flower, showing" the .inconspicuous perianth lobes (c\ the short stamens (a).
and the two short styles with conspicuous stigmatic surfaces.— A after REICHEN-
BACH; B after LE MAOUT and DECATPNE.

FIG. 221. Cat-tails (Typhd), showing the dense spikes of very simple flowers, each
showing two regions, the lower the pistillate flowers, the upper the staminate.—
From " Field. Forest, and Wayside Flowers."

2-k)

PLANT STRUCTURES

leaf) and Alisma (water-plantain), in which there is a dis-
tinct calyx and corolla. The genus Typlia (cat-tail) is also
an aquatic or marsh form of very simple type, the flow-
ers being in dense
cylindrical clusters
(spikes), the upper
flowers consisting of
stamens, the lower of
carpels, thus forming
two very distinct re-
gions of the spike
(Fig. 221).

132. Grasses.—
This is one of the
largest and probably
one of the most use-
ful groups of plants,
as well as one of the
most peculiar. It is
world-wide in its dis-
tribution, and is re-
markable in its dis-
play of individuals,
often growing so
densely over large
areas as to form a
close turf. If the
grass -like sedges be
associated with them
there are about six
thousand species,
representing nearly
one third of the Mon-
ocotyledons. Here
belong the various
cereals, sugar canes,

FIG. 222. A common meadow grass (Festuca): A,
portion of flower cluster (epikelet), showing the
bracts, in the axils of two of which flowers are
exposed ; B, a single flower with its envelop-
ing bract, showing three stamens, and a pistil
whose ovary bears two style branches with much
branched stigmas.— After STRASBURGER.

MONOCOTYLEDONS AND DICOTYLEDONS

bamboos, and pasture grasses, all of them immensely use-
ful plants.

The flowers are very simple, having no evident perianth
(Fig. 222). Most commonly a flower consists of three sta-
mens, surrounding a single carpel, whose ovary ripens into
the grain, the characteristic seed-like fruit of the group.
The stamens, however, may be of any number from one to
six. The flowers, therefore, are naked, with indefinite num-
bers, and hypogynous, indicating a comparatively simple
type. It is also noteworthy that the group is anemophilous.

One of the noteworthy features of the group is the
prominent development of peculiar leaves (bracts) in con-
nection Avith the flowers. Each flower is completely pro-
tected or even inclosed by one of these bracts, and as the
bracts usually overlap one another the flowers are invisible
until the bracts spread apart and permit the long dangling
stamens to show themselves. These bracts form the so-
called " chaff" of wheat and other cereals, where they
persist and more or less envelop the grain (ripened ovary).
As they are usually called glumes, the grasses and sedges
are said to be ylumaceous plants.

Grasses are not always lowly plants, for in the tropics
the bamboos and canes form growths that may well be
called forests. The grasses constitute the family Graminew,
and the sedges the family Cyperacem.

133. Palms. — More than one thousand species of palms
are grouped in the family Palmacea>. These are the tree
Monocotyledons, and are very characteristic of the tropics,
only the palmetto getting as far north as our Gulf States.
The habit of body is like that of tree-ferns and Cycads, a
tall unbranched columnar trunk bearing at its summit a
crown of huge leaves which are pinnate or palmate in char-
acter, and often splitting so as to appear lobed or compound
(Figs. 223, 224:).

The flower clusters are usually very large (Fig. 223),
and each cluster at first is inclosed in a huge bract, which

FIG. 223. A date palm, showing the unbranched columnar trunk covered with old leaf
bases, and with a cluster of huge pinnate leaves at the top, only the lowest por-
tions of which are shown ; two of the very heavy fruit clusters are also shown.—
From " Plant Relations,11

MONOCOTYLEDONS AND DICOTYLEDONS

24:3

is often hard. Usually a perianth is present, but with no
differentiation of calyx and corolla, and the flower parts are
quite definitely in " threes," so that the cyclic arrangement
with the characteristic Monocotyledon number appears.

FIG. 224. A fan palm, with low stem and crown of large palmate leaves, which have
split so as to appear palmately branched.— From " Plant Relations."

134. Aroids. — This is a group of nearly one thousand
species, most of them belonging to the family Aracece. In
our flora the Indian turnip or Jack-in-the-pulpit (Ariscemd)
(Fig. 225), sweetflag (Acorus), and skunk-cabbage (Symplo-
carpus), may be taken as representatives ; while the culti-
vated Calla-lily is perhaps even better known. The great
display of aroids, however, is in the tropics, where they are
endlessly modified in form and structure, and are erect, or
climbing, or epiphytic.

24:4:

PLANT STRUCTURES

The flowers are usually very simple, often being naked,
with two to nine stamens, and one to four carpels (Fig.

FIG. 225. Jack-in-the-pulpit (Aristema). showing the overarching spathes; in one
case a side view shows the naked tip of the projecting spadix. — After ATKINSON.

197). They are inconspicuous and closely set upon the
lower part of a fleshy axis, which is naked above and often

MONOCOTYLEDONS AND DICOTYLEDONS

245

modified in a remarkable way into a club-shaped or tail-like
often brightly colored affair. This singular flower-cluster
with its fleshy axis is called a spadix. The flowers often
include but one sort of sporophyll, and staminate and
pistillate flowers hold different positions upon the spadix
(Fig. 226).

The spadix is enveloped by a great bract, which sur-
rounds and overarches like a large loose hood, and is called
the spathe. The spathe is exceedingly
variable in form., and is often conspic-
uously colored, forming in the Calla-
lily the conspicuous white part, within
which the spadix may be seen, near the
base of which the flowers are found.
In Jack-in-the-pulpit (Fig. 225) it is
the overarching spathe which suggests
the "pulpit." The spadix and spathe
are the characteristic features of the
group, and the spathe is variously
modified in form, structure, and color
for insect pollination, as is the peri-
anth of other entomophilous groups.

Aroids are further peculiar in hav-
ing broad net-veined leaves of the Di-
cotyledon type. Altogether they form
a remarkably distinct group of Mon-
ocotyledons.

135. Lilies. — The lily and its allies are usually regarded
as the typical Monocotyledon forms. The perianth is
fully developed, and is very conspicuous, either undifferen-
tiated or with distinct calyx and corolla, and the flower is
well organized for insect pollination. The flowers are either
solitary or few in a cluster and correspondingly large, or in
more compact clusters and smaller. In any event, the
perianth is the conspicuous thing, rather than spathes or

glumes.

FIG. 226. Spadix of an
Arum, with spathe re-
moved, showing cluster
of naked pistillate flow-
ers at base, just above
a cluster of staminate
flowers, and the club-
shaped tip of the spa-
dix.— After WOSSIDLO.

246

PLANT STRUCTURES

In the general lily alliance, composed of eight or nine
families, there are more than four thousand species, repre-
senting about one fifth of all the Monocotyledons, and they
are distributed everywhere. They are almost all terrestrial
herbs, and are prominently geophilous ('( earth -lovers")—

that is, they develop
bulbs, rootstocks, etc.,
which enable them to
disappear from above
the surface during un-
favorable conditions
(cold or drought), and
then to reappear rap-
idly upon the return
of favorable conditions
(Figs. 227, 228, 231,
233).

In the regular lily
family (LiUacece) the
flowers are hypogy-
nous and actinomor-
phic (Fig. 231), the
six perianth parts are
mostly alike and some-
times sympetalous (as
in the lily-of-the-val-
ley, hyacinth, easter
lily) (Figs. 201, 229),
the stamens are usu-
ally six (two sets),

and the three carpels are syncarpous (Figs. 204, 230).
This is a higher combination of floral characters than
any of the preceding groups presents. Hypogyny and
actinomorphy are low, but a conspicuous perianth, syn-
carpy, and occasional sympetaly indicate considerable ad-
vancement.

Fi(i. 227. Wake-robin {Trillium}, showing root-
stock, from which two branches arise, each bear-
ing a cycle (whorl) of three leaves and a single
trimerotis flower. — After ATKINSON.

.MONOCOTYLEDONS AND DICOTYLEDONS

24'

In the amaryllis family (AmaryUidacece), a higher fam-
ily of the same general line, represented by species of Nar-
cissus (jonquils, daffodils, etc.), Agave, etc., the flowers
are distinctly epigynous.

FIG. 228. Star-of -Bethlehem (Ornithogalvm) : a, entire plant with tuberous base and
trimerous flowers; b, a single flower; c, portion of flower showing relation of
parts, perianth lobes and stamens arising from beneath the prominent ovary (hy-
pogynons); d, mature fruit; e. section of the syncarpous ovary, showing the three
carpels and loculi.— After SCHIMPER.

In the iris family (frirfacece), the most highly specialized
family of the lily line, and represented by the various spe-

FIG. 25J9. The Japan lily, showing a tubular perianth, the parts of the perianth
distinct above.— From " Field, Forest, and Wayside Flowers."

MONOCOTYLEDONS AND DICOTYLEDONS

249

cies of Iris (flags) (Fig. 232), Crocus, Gladiolus (Figs. 233,
234), etc., the flowers are not only epigynous, but some of
them are zygomorphic.
When a plant has
reached both epigyny
and zygomorphy in its
flowers, it may be re-
garded as of high rank.

130. Orchids.— In
number of species this
(OrcJiidacece) is the
greatest family among
the Monocotyledons,
the species being vari-
ously estimated from
six thousand to ten
thousand, representing
between one third and
one half of all known
Monocotyledons. In display of individuals, however, the
orchids are not to be compared with the grasses, or even
with lilies, for the various species are what are called "rare
plants " — that is, not extensively distributed, and often
very much .restricted. Although there are some beautiful
orchids in temperate regions, as species of Habenaria (rein-
orchis) (Fig. 235), Pogonia, Calopogon, Calypso, Cypripe-
dium (lady-slipper, or moccasin flower) (Fig. 236), etc.,
by far the greatest display and diversity are in the tropics,
where many of them are brilliantly flowered epiphytes
(Fig. 237).

Orchids are the most highly specialized of Monocoty-
ledons, and their brilliant coloration and bizarre forms are
associated with marvelous adaptation for insect visitation
(see Plant Relations, pp. 134, 135). The flowers are epigy-
nous and strongly zygomorphic. One of the petals is re-
markably modified, forming a conspicuous lip which is

FIG. 230. Diagrammatic cross-section of ovary
of Liliitm PhiladelpMcum, showing the three
loculi, in each of which are two ovules (mega-
sporangia): A, ovule; B, integuments; (', nu-
cellus ; I), embryo-sac (megaspore).— CAI.D-
WEI.L.

FIG. 231. The common dog-tooth violet, showing the large mottled leaves and con-
spicuous flowers which are sent rapidly above the surface from the subterranean
bulb (see cut in the left lower corner), also some petals and stamens and the pistil
disst-cted out. — From " Plant Relations."

MONOCOTYLEDONS AND DICOTYLEDONS

251

modified in a great variety of
ways, and a prominent, often
very long, spur, in the bottom of
which nectar is secreted, which
must be reached by the proboscis
of an insect (Fig. 235). The
stamens are reduced to one or
two, and welded with the style

FIG. 232. Flower of flag (Iris),
showing some of the sepals
and petals, one of the three
stamens, and the distinctly in-
ferior ovary, being an epigy-
nons flower. — After GRAT.

FIG. 234. Flower cluster of Gla-
diolus, showing somewhat zygo-
morphic flowers. — CALDWELL.

FIG. 233. Gladiolus, showing tuberous subter-
ranean stem from which roots descend, grass-
like leaves, and somewhat zygomorphic flow-
ers.—After REICHENBACH.

252

PLANT STRUCTURES

and stiginatic surface into an indistinguishable mass in
the center of the flowers. The pollen-grains in each sac
are sticky and cohere in a club-shaped mass (polliniuni).
which is pulled out and carried to another flower bv the

which may be seen in 1 and f ; in
eye of a moth. — After OKAY.

FIG. 235. A flower of an orchid
Ha): at 1 the complete flower is shown,
with three sepals behind and three pet-
als in front, the lowest one of which has
developed a long strap-shaped portion
(lip) and a still longer spur portion, the
opening to which is seen at the base of
the strap, and behind the spur the long
inferior ovary (epigynous character) ;
the two pollen sacs of the single stamen
are seen irt the center of the flower, di-
verging downward, and between them
stretches the stigma surface : the rela-
tion between pollen sacs and stigma sur-
face is shown in 2 ; within each pollen
sac is a mass of sticky pollen (pollini-
um), ending below in a sticky disk,
3 a pollen mass (a) is shown sticking to each

visiting insect. The whole structure indicates a very
highly specialized type, elaborately organized for insect
pollination.

Another interesting epigynous and zygomorphic trop-
ical group, but not so elaborate as the orchids, is repre-
sented by the cannas and bananas (Fig. 120), common in
cultivation as foliage plants, and the aromatic gingers.

From the simple pondweeds to the complex orchids the
evolution of the Monocotyledons has proceeded, and be-
tween them many prominent and successful families have
been worked out.

FIG. 236. A clump of lady-slippers (Cypripedium), showing the habit of the plant
and the general structure of the zygoinorphic flower.— After GIBSON.

254

PLANT STRUCTURES

FIG. 287. A group of orchids (C'attleya), showing the very zygomorphic flowers, the
lip being well shown in the flower to the left (lowest petal).— CALIMVELL.

DICOTYLEDONS

137. Introductory.— Dicotyledons form the greatest group
of plants in rank and in numbers, being the most highly
organized, and containing about eighty thousand species.
They represent the dominant and successful vegetation in
all regions, and are especially in the preponderance in tem-
perate regions. They are herbs, shrubs, and trees, of every
variety of size and habit, and the rich display of leaf forms
is notably conspicuous.

Two great groups of Dicotyledons are recognized, the
Arcliichlamydece and the Sympetalce. In the former there
is either no perianth or its parts are separate (polypeta-
lous) ; in the latter the corolla is sympetalous. The Archi-
chlamydeae are the simpler forms, beginning in as simple a
fashion as do the Monocotyledons ; while the Sympetalae

MONOCOTYLEDONS AND DICOTYLEDONS

255

are evidently derived from them and become the most
highly organized of all plants. The two groups each con-
tain about forty thousand species, but the Archichlamydese
contain about one hundred and sixty families, and the
Sympetalae about fifty.

To present over two hundred families, containing about
eighty thousand species, is clearly impossible, and a very
few of the prominent ones will be selected for illustrations.

A rclt icldamydecf}

138. Poplars and their allies. — This great alliance repre-
sents nearly five thousand species, and seems to form an
isolated group. It is a notable tree assemblage, and appar-
ently the most primitive and ancient group of Dicotyledons,
containing the most important deciduous forest forms of

FIG. 238. An oak in winter condition. — From " Plant Relations.1

256

PLANT STRUCTURES

temperate regions, for here belong the oak (Fig. 238), hick-
ory, walnut, chestnut, beech, poplar, birch, elm (Figs. 198,
239), willow (Fig. 240), etc. The primitive character is in-
dicated not merely by the floral structures, but also by the
general anemophilous habit.

In the poplar (Populus) and its allied form, the willow
(Salix), the flowers are naked and hypogynous (Fig. 196),

FIG. £J(J. An elm in foliage. — From " Plant Rela

MONOCOTYLEDONS AND DICOTYLEDONS

the stamens are indefinite in number (two to thirty), and
the pistil is syncarpous (two carpels). The stamens and

FIG. 240. Flower cluster of willow (aments); that to the left is pistillate, the other
staminate. — After WARMING.

pistils are not only separated in different flowers, but upon
different plants, some plants being staminate and others
pistillate (Fig. 240). The flowers are clustered upon a long
axis, and each one is
protected by a promi-
nent bract. It is these
scaly bracts which
give character to the
cluster, which is called
an ament or catkin,
and the plants which
produce such clusters
are said to be amenta-
ceous. These aments
of poplars, "pussy
willows," and the FIG 241 Amentg of alder ( . ^ branch

with staminate aments (ra), pistillate aments
(m), and a young bud (&); b. pistillate ament at
time of discharging seeds, showing the promi-

alders and birches are
very familiar objects
(Figs. 240, 241).

nent bracts.— After WARMING.

258 PLANT STRUCTURES

The only advanced character in the flowers as described
above is the syncarpous pistil, but in the great allied pepper
family (Piperacece) of the tropics, with its one thousand
species, and most nearly represented in our flora by the

FIG. 242. Ovule of hornbeam (Carpinvf>\ showing chalazogamy: m, the micropyle;
pt, the pollen tube, which may be traced to its entrance into the embryo-sac at. its
antipodal end, and thence upward through the sac toward the egg.— After MARY
EWART.

lizard-tail (Saururus) of the swamps (Fig. 195), the flowers
are not merely naked, but also apocarpous, and the whole
structure is much like that of the simplest Monocotyle-

MONOCOTYLEDONS AND DICOTYLEDONS 259

dons. The peppers seem to represent the simplest of the
Dicotyledons, and this great line may have begun with
some such forms.

A very interesting fact in connection with the fertiliza-
tion of certain amentaceous plants has been discovered.
In birch, alder, walnut, hornbeam, and some others, the
pollen-tube does not enter the ovule by way of the micro-
pyle, but pierces through in the region of the base of the
ovule and so penetrates to the embryo-sac (Fig. 24=2). As
the region of the ovule where integument and nucellus are
not distinguishable is called the chalaza, this phenomenon
is known as chalazoyamy, meaning "fertilization through
the chalaza.'1

139. Buttercups and their allies. — This is a great assem-
blage of terrestrial herbs, including nearly five thousand
species, and is thought by many to be the great stock from
which most of the higher Dicotyledons have been derived.
The alliance includes the water-lilies, buttercups, and pop-
pies, the specialized mustards, and certain notable tree
forms, as magnolias, custard-apples, and the tropical laurels
with one thousand -species represented in our flora only
by the sassafras. Here also is the strange group of " car-
nivorous" plants (Sarracenia, Drosera, Dioncea, etc.). The
group is distinctly entomophilous, in striking contrast with
the preceding one.

Taking the buttercup (Ranunculus) as a type (Fig. 202),
the flower is hypogynous, the calyx and the corolla are dis-
tinctly differentiated and actinomorphic, and adapted for
insect-pollination, but the spiral arrangement and indefinite
numbers are very apparent, notably in connection with the
apocarpous pistils, which are very numerous upon a promi-
nent receptacle, but involving more or less all the parts.
The stamens are also very numerous (Figs. 200, 243, 244).
In the water-lilies the petals and stamens are indefinitely
numerous (Fig. 203), and in the poppies there is no definite
number. In many of the forms, however, in connection

FIG. 243. Marsh marigold (Caltha), a member of the Buttercup family, also showing
floral diagram, in which the floral leaves are five, but the stamens and apocarpous
pistils are indefinitely numerous.— After ATKINSON.

FIG. 244. Zygomorphic flower of larkspur
(Delphinium), with sepals removed, show-
ing two petals with prominent spurs, and
numerous stamens. — After BAILLON.

FIG. 245. Diagram of the zygomorphic
flower of larkspur (Delphinium), show-
ing the spur developed by a sepal and
inclosing the two petal spurs. — After
BAIIJ.ON.

.MONOCOTYLEDONS AND DICOTYLEDONS

261

with one or more of the parts, the Dicotyl number (five)
appears (Figs. 243, 245), but with no special constancy.

In certain. genera of the buttercup family (Ranuncula-
cecc) zygomorphy appears, as in the larkspur (Delphinium)
with its spurred petals and sepals (Figs. 244, 245), and the
monkshood (Aconitum) with its hooded sepal ; and in the

FIG. 246. The common cabbage (Brassicd), a member of the mustard family: A,
flower cluster, showing buds at tip, open flowers below with four spreading petals,
and forming pods below; B, mature pod, with the persistent style; C, pod opening
by two valves, and showing seeds attached to the false partition. — After WARMING.

water-lily family (Nymphaaceci) and poppy family (Papa-
veracece) syncarpy appears. In this alliance, also, belong
the sweet-scented shrubs (Calycanthus), with their perigy-
nous flowers containing numerous parts (Fig. 206).
35

262

PLANT STRUCTURES

FIG. 247. Diagram of crucifer
flower, showing the relations
of parts ; four sepals, four
petals, six stamens, and one
carpel with a false partition.
— After WARMING.

The most specialized large group in this alliance is
the mustard family (Crucifera), with twelve hundred
species, to which belong the mustards, cresses, shep-
herd's purse, peppergrass, radish, cabbage (Fig. 246), etc.
The sepals are four in two sets, the
petals four in one set, the stamens
six with two short ones in an outer
set and four long ones in an inner
set, and one carpel whose ovary be-
comes divided into two loculi by
what is called a "false partition"
(Figs. 246, C, 247), and usually be-
comes an elongated pod (Fig. 246,
A, B). This specialized structure
of the flower distinctly marks the
family, whose name is suggested
by the fact that the four spreading

petals often form a Maltese cross (Fig. 246, A). The pecul-
iar stamen character, four long and two short stamens, is
called tetradynamous ("four strong").

140. Roses. — This family (Rosacem) of one thousand
species is one of the best known and most useful groups of
the temperate regions. In it are such forms as Spircva,
five-finger (Poten-
tilla), strawberry
(Fragaria) (Figs.
191, 207), raspberry
(Fig. 248), and
blackberry (Ru-
bus), rose (Rosa),
hawthorn ( CratcB-
gus), apple, and
pear (Pirus) (Fig.
249), plum, cherry,
almond, and peach
(Primus).

FIG. 248. The common raspberry: the figure to the
left showing flower-stalk, calyx, old stamens
(«). and prominent receptacle, from which the
"fruit" (a cluster of small stone fruits, each
representing a carpel) has been removed. — After
BAILEY,

MONOCOTYLEDONS AND DICOTYLEDONS

263

Many of the true roses have a strong resemblance (Fig.
207) to the buttercups (Ranunculus), with their hypogy-
nous regular flowers, and indefinite number of stamens and
carpels, but the sepals and petals are much more frequently
five, the Dicotyl number being better established. The

FIG. 249. The common pear (Pirus Comments), showing branch with flowers (1), sec-
tion of a flower (2) showing its epigynons character, section of fruit (3) showing
the thickened calyx outside of the ovary or "core" (indicated by dotted outline),
and flower diagram (k) showing all the organs in fives except the stamens. — After

WOSSIDLO.

whole family remains actinomorphic, but perigyny and
epigyny appear in certain forms (Fig. 205), giving rise to
the peculiar fruit (pome) of apples and pears (Fig. 249), in
which the calyx and ovary ripen together. Another spe-
cialized group of roses is that which develops the stone-

264

PI. A NT STRUCTURES

fruits (drupes), as apricots, peaches (Fig. 189), plums,
cherries.

141. Legumes, — This is far the greatest family (Legumi-
nosm) of the Archichlamydeae, containing about seven thou-
sand species, distributed everywhere and of every habit. It
is the -great zygomorphic group of the Archichlamydese,
being elaborately adapted to insect pollination. The more

FIG. 250. A legume plant (Lotus), showing flowering branch (J), a single flower (2)
showing zygomorphic corolla, the cluster of ten stamens (3) which with the carpel
is included in the keel, the solitary carpel (A) which develops into the pod or le-
gume (5), the petals (6) dissected apart and showing standard (a), wings (6), and
the two lower petals (c) which fold together to form the keel, and the floral dia-
gram (7). — After WOSSIDLO.

primitive forms of the Leguminosae, the mimosas, acacias
(Fig. 251), etc., very much resemble true roses and the but-
tercups, with their hypogynous regular flowers and nu-
merous stamens, but the vast majority are Papilio forms
with very irregular (zygomorphic) flowers and few stamens

MONOCOTYLEDONS AND DICOTYLEDONS

265

(Fig. 250). The petals are very dissimilar, the upper one
(standard) being the largest, and erect or spreading, the two
lateral ones (wings) oblique and descending, the two lower
ones coherent by their edges to form a projecting boat-shaped
body (keel], which
incloses the sta-
mens and pistil.
From a fancied re-
semblance to a but-
terfly such flowers
are said to be papil-
ionaceous.

The whole fam-
ily is further char-
acterized by the sin-
gle carpel, which
after fertilization
develops a pod
(Fig. 250, 5), which
often becomes re-
markably large as
compared with the
carpel. It is this
peculiar pod (le-
gume) which has
given to the family
its technical name
LeguminoscB and
the common name
"Legumes."

Well-known members of the family are lupine (Lupi-
nus)9 clover (Tri folium), locust (Robinia), Wistaria, pea
(Pimm), bean (PJiaseolus), tragacanth (Astragalus), vetch
(Vicia), redbud (Cere is), senna (Cassia), honey-locust
(Gleditschid), indigo (Indigofera), sensitive-plants (Acacia,
Mimosa, etc.) (Fig. 251), etc.

FIG. 251. A sensitive-plant (Acacia), showing the
flowers with inconspicuous petals and very nu-
merous stamens, and the pinnately branched sen-
sitive leaves.— After MEYER and SCHUMANN.

266

PLANT STRUCTURES

142. ITmbellifers. — This is the most highly t organized
family ( Umbellifera) of the Archichlamydeas, which may
be said to extend from Peppers to Umbellifers. The Le-
gumes adopt zygomorphy, but remain hypogynous ; and in
some of the Roses epigyny appears ; but the Umbellifers
with their fifteen hundred species are all distinctly epigy-

FIG. 252. The common carrot (Daucus Carota): A. branch bearing the compound
umbels; B, a single epigynous flower, showing inferior ovary, five spreading
petals, five stamens alternating with the petals, and the two styles of the bicarpel-
lary pistil; C, section of flower, showing relation of parts, and also the minute
sepals near the top of the ovary and just beneath the other parts. — After WARMING.

nous (Fig. 252, B, (7), being one of the very few epigy-
nous families among the Archichlamydeae. In addition
to epigyny, the cyclic arrangement and definite Dicotyl
number is established, there being five sepals, five petals,
five stamens, and two carpels, the highest known floral

MONOCOTYLEDONS AND DICOTYLEDONS

267

formula, and one that appears among the highest Sym-
petalse.

The name of the family is suggested by the character-
istic inflorescence, which is also of advanced type. The
flowers are reduced in
size and massed in flat-
topped clusters called
umbels (Figs. 252, A, 253).
The branches of the clus-
ter arise in cycles from
the axis like the braces
of an umbrella. As a re-
sult of the close approxi-
mation of the flowers the
sepals are much reduced
in size and often obsolete
(Fig. 252, 0).

The Umbellifers are
mainly perennial herbs of
the north temperate re-
gions, forming a very dis-
tinct family, and contain-
ing the following familiar
forms : carrot (Daucus)
(Fig. 252), parsnip (Pasti-
naca), hemlock (Conium)
(Fig. 253), pepper-and-
salt (Erigenia), caraway
(Carum), fennel (Fcenic-
ulum), coriander (Cori-
andrum), celery (Api-
11 m), parsley (Petroseli-

\ , AIT rl f fli FIG. 253. Hemlock (Conium), an Umbellifer,

n), etc. All] showing the umbels, with the principal

Umbellifers are the Ara- rays rising from a cycle of bracts (invo-

lucre), and each bearing at its summit a
secondary umbel with its cycle of second-
ary bracts (involucel).— After SCHIMPER.

lias (Araliacea), and the
Dogwoods (Cornacece).

2(58 PLANT STRUCTURES

Sympetalce

143. Introductory. — These are the highest and the most
recent Dicotyledons. While they contain numerous shrubs
and trees in the tropics, they are by no means such a shrub
and tree group in the temperate regions as are the Archi-
chlamydese. The flowers are constantly cyclic, the num-
ber five or four is established, and the corolla is sympeta-
lous, the stamens usually being borne upon its tube (Figs.
208, 209, 212).

There are two well-defined groups of Sympetalae, distin-
guished from one another by the number of cycles and the
number of carpels in the flower. The group containing
the lower forms is pentacyclic, meaning "cycles five," there
being two sets of stamens. In it also there are five carpels,
the floral formula being, Sepals 5, Petals 5, Stamens 5 + 5,
Carpels 5. As the carpels are the same in number as the
other parts, the flowers are called isocarpic, meaning " car-
pels same." The group is named either Pentacydce or Iso-
carpce, and contains about ten families and 4,000 species.

The higher groups, containing about forty families and
36,000 species, is tetr acyclic, meaning " cycles four," and
anisocarpic, meaning "carpels not the same," the floral
formula being, Sepals 5, Petals 5, Stamens 5, Carpels 2.
The group name, therefore, is TetracyclcB or Anisocarpce.

144. Heaths. —The Heath family (Ericacew) and its allies
represent about two thousand species. They are mostly
shrubs, sometimes trailing, and are displayed chiefly in
temperate and arctic or alpine regions, in cold and damp
or dry places, often being prominent vegetation in bogs
and heaths, to which latter they give name (Fig. 254). The
flowers are pentacyclic and isocarpic, as well as mostly hyp-
ogynous and actinomorphic. It is interesting to note that
some forms are not sympetalous, the petals being distinct,
showing a close relationship to the Archichlamydeae. One
of the marked characteristics of the group is the dehiscence

MONOCOTYLEDONS AND DICOTYLEDONS 269

of the pollen-sacs by terminal pores, which are often pro-
longed into tubes (Fig. 255).

FIG. 254. Characteristic heath plants: A, B. C\ Lyonia. showing sympetalous flowers
and single style from the lobed syncarpous ovary; Z>, two forms of Cassiope,
showing trailing habit, small overlapping leaves, and sympetalous flowers, but in
the smaller form the petals are almost distinct. — After DRUDE.

Common representatives of the family are as follows :
huckleberry (Gaylussacia), cranberry and blueberry ( Vac-
cinium), bearberry (Arctostaphylos), trailing arbutus (Epi-

270

PLANT STRUCTURES

gcea), wintergreen (Gaultheria), heather (Calluna), moun-
tain laurel (Ealmia), Azalea, Rhododendron (Fig. 256),
Indian pipe (Monotropa), etc.

FIG. 255. Flowers of heath plants (Erica}, showing complete flowers (A), the sta-
mens with " two-horned " anthers which discharge pollen through terminal pores,
and the lobed syncarpous ovary with single style and prominent terminal stigma
(B, C, D).— After DRUDE.

145. Convolvulus forms, — The well-known morning-glory
(Tpomcea) (Fig. 209) may be taken as a type of the Convol-

MONOCOTYLEDONS AND DICOTYLEDONS

2T1

vulus family (Convolvulacece). Allied with it are Polemo-
nium and Phlox (Fig. 210, b) (Polemoniacece}, the gentians
(Gentianacece), and the dog-banes (Apocynacece) (Fig. 257).
It is here that the regular sympetalous flower reaches its
highest expression in the form of conspicuous tubes, fun-

FIG 256. A cluster of Rhododendron flowers.— After HOOKER.

nels (Fig. 258), trumpets, etc. The flowers are tetracyclic
and anisocarpic, besides being hypogynous and actinomor-
phic. These regular tubular forms represent about five
thousand species, and contain many of the best-known
flowers.

272

PLANT STRUCTURES

146. Labiates. — This great family (LaUatce) and its alli-
ances represent more than ten thousand species. The con-
spicuous feature is the
zygomorphic flower, dif-
fering in this regard from
the Convolvulus forms,
which they resemble in
being tetracyclic and ani-
socarpic, as well as hypogy-
nous. The irregularity
consists in organizing the
mouth of the sympetalous
corolla into two "lips,"
resulting in the labiate or

FIG. 257. A common dogbane (Apoc-ynuin). — Froir

Flowers.'"

" P'ield, Forest. ;ind Wayside

FIG. 258. The hedge bindweed ( Convolvulus), showing the twining habit and the con-
spicuous funnelform corollas.— From " Field, Forest, and Wayside Flowers."

274

PLANT STKUCTUEES

bilabiate structure (Fig. 210, c, d, e), and suggesting the
name of the dominant family. The upper lip usually con-
tains two petals, and the lower three ; the two lips are some-
times widely separated, and sometimes in close contact, and
differ widely in relative prominence.

Associated with zygomorphy in this group is a frequent
reduction in the number of stamens, which are often four
(Fig. 212) or two. The whole structure is highly special-
ized for the visits of insects, and this great zygomorphic
alliance holds the same
relative position among
Sympetalae as is held
by the zygomorphic Le-
gumes among Archi-
chlamydeae.

In the mint family,
as the Labiates are often
called, there are about
two thousand seven hun-
dred species, including
mint (Mentlia) (Fig.
212), dittany (Cunila),
hyssop (Hyssopus), mar-
joram (Origanum),

FIG. 259. Flowers of dead nettle (La-
mium) : A, entire bilabiate flower ;
B, section of flower, showing rela-
tion of parts.— After WARMING,

FIG. 260. A labiate plant ( Teucrium), show-
ing branch with flower clusters (4), and
side view of a few flowers (B), showing
their bilabiate character. — After BRIQUET.

MONOCOTYLEDONS AND DICOTYLEDONS 275

thyme (Thymus), balm (Melissa), sage (Salvia), catnip
(Nepeta), skullcap (Scutellaria), horehound (Marrubium),
lavender (Lavandula), rosemary (Rosmarinus) , dead nettle
(Lamium) (Fig. 269), Teucrium (Figs. 213, 260), etc., a
remarkable series of aromatic forms.

Allied is the Xightshade family (Solanacece) , with fif-
teen hundred species, containing such common forms as
the nightshades and potato (Solatium), tomato (Ly coper -
sicum), tobacco (Nicotiana) (Fig. 208), etc., in which the
corolla is actinomorphic or nearly so ; also the great Fig-
wort family (Scroplmlariacece), with two thousand species,
represented' by mullein ( Verbascum), snapdragon (Antir-
rhinum) (Fig. 210, e), toad-flax (Linaria) (Fig. 210, d),
Pentstemon, speedwell ( Veronica), Gerardia, painted cup
(Castilleia) , etc.; also the Verbena family ( Verbenacece) ,
with over seven hundred species ; and the two hundred
plantains (Plant aginacetB), etc.

147. Composites. — This greatest and ranking family
( Composite) of Angiosperms is estimated to contain at least
twelve thousand species, containing more than one seventh
of all known Dicotyledons and more than one tenth of all
Seed-plants. Xot only is it the greatest family, but it is
the youngest. Composites are distributed everywhere, but
are most numerous in temperate regions, and are mostly
herbs.

The name of the family suggests the most conspicuous
feature — namely, the remarkably complete organization of
the numerous small flowers into a compact head which
resembles a single flower, formerly called a "compound
flower." Taking the head of an Arnica as a type (Fig.
261), the outermost set of organs consists of more or less
leaf -like bracts or scales (involucre), which resemble sepals ;
within these is a circle of flowers with conspicuous yellow
corollas (rays), which are zygomorphic, being split above
the tubular base and flattened into a strap-shaped body,
and much resembling petals (Fig. 261, A, D) ; within the

FIG. 261. Flowers of Arnica: A, lower part of stem, and upper part bearing a
head, in. which are seen the conspicuous rays and the disk; D, single ray flower,
showing the corolla, tubular at base and strap-shaped above, the two-parted style,
the tuft of pappus hairs, and the inferior ovary which develops into a seed-like
fruit (akene); E. single disk flower, showing tubular corolla with spreading limb,
the two-parted style emerging from the top of the stamen tube, the prominent
pappus, and the inferior ovary or akene; C, a single stamen. — After HOFFMAN.
276

MONOCOTYLEDONS AND DICOTYLEDONS

277

ray-flowers is the broad expanse supplied by a very much
broadened axis, and known as the disk (Fig. 261, A), which
is closely packed with very numerous small and regular
tubular flowers, known as disk-floivers (Fig. 261, e).

FIG. 262. The common dandelion ( Taraxacum): 1, two flower stalks; in one the head
is closed, showing the double involucre, the inner erect, the outer reftexed, in the
other the head open, showing that all the flowers are strap-shaped; 2, a single
flower showing inferior ovary, pappus, corolla, stamen tube, and two-parted style;
3, a mature akene; It, a head from which all but one of the akenes have been re-
moved, showing the pitted receptacle and the prominent pappus beak. — After
STRASBURGER.

The division of labor among the flowers of a single head
is plainly marked, and sometimes it becomes quite com-
plex. The closely packed flowers have resulted in modify-
ing the sepals extremely. Sometimes they disappear en-

278

PLANT STRUCTURES

tirely ; sometimes they become a tuft of delicate hairs, as
in Arnica (Fig. 261, />, E), thistle (Cnicus), and dandelion
(Taraxacum) (Fig. 263), surmounting the seed-like akene
and aiding in its transportation through the air ; sometimes
they are converted into two or more tooth-like and often

FIG. 263. Flowers of dandelion, showing action of style in removing pollen from the
stamen tube: 1, style having elongated through the tube and carrying pollen; 2,
style branches beginning to recurve; 3, style branches completely recurved. —
From " Field, Forest, and Wayside Flowers."

barbed processes arising from the akene, as in tickseed
(Coreopsis) and beggar-ticks (Fig. 188) or Spanish needles
(Bidens), to lay hold of passing animals ; sometimes they
become beautifully plumose bristles, as in the blazing star
(Liatris) ; sometimes they simply form a more or less con-
spicuous cup or set of scales crowning the akene. In all
of these modifications the calyx is called pappus.

The stamens within the corolla are organized into a
tube by their coalescent anthers (Fig. 263), and discharge
their pollen within, which is carried to the surface of the

MONOCOTYLEDONS AND DICOTYLEDONS 279

head and exposed by the swab-like rising of the style (Fig.
#63). The head is thus smeared with pollen, and visiting
insects can not fail to distribute it over the head or carry
it to some other head.

In the dandelion and its allies the flowers of the disk
are like the ray-flowers, the corolla being zygomorphic and
strap-shaped (Figs. 262, 263).

The combination of characters is sympetalous, tetracyc-
lic, and anisocarpic flowers, which are epigynous and often
zygomorphic, with stamens organized into a tube and calyx
modified into a pappus, and numerous flowers organized
into a compact involucrate head in which there is more or
less division of labor. There is no group of plants that
shows such high organization, and the Composite seem to
deserve the distinction of the highest family of the plant
kingdom.

The well-known forms are too numerous to mention,
but among them, in addition to those already mentioned,
there are iron-weed ( Vernonia), Aster, daisy (Bellis),
goldenrod (Solidago), rosin-weed and compass-plant (Silph-
ium), sunflower (Helianthus), Chrysanthemum, ragweed
(Ambrosia), cocklebur (Xanthium), ox-eye daisy (Leucan-
themum), tansy (Tanacetum), wormwood and sage-brush
(Artemisia), lettuce (Lactuca), etc.

CHAPTEE XV

DIFFERENTIATION OF TISSUES

148. Introductory. — Among the simplest Thallophytes
the cells forming the body are practically all alike, both as
to form and work. What one cell does all do, and there
is very little dependence of cells upon one another. As
plant bodies become larger this condition of things can not
continue, as all of the cells can not be put into the same
relations. In such a body certain cells can be related to
the external food supply only through other cells, and the
body becomes differentiated. In fact, the relating of cells
to one another and to the external food-supply makes large
bodies possible.

The first differentiation of the plant body is that which
separates nutritive cells from reproductive cells, and this is
accomplished quite completely among the Thallophytes.
The differentiation of the tissues of the nutritive body,
however, is that which specially concerns us in this chapter.

A tissue is an aggregation of similar cells doing similar
work. Among the Thallophytes the nutritive body is prac-
tically one tissue, although in some of the larger Thallo-
phytes the outer and the inner cells differ somewhat. This
primitive tissue is composed of cells with thin walls and
active protoplasm, and is called parenchyma, meaning
"parent tissue."

Among the Bryophytes, in the leafy gametophore and

in the sporogonium, there is often developed considerable

dissimilarity among the cells forming the nutritive body,

but the cells may all still be regarded as parenchyma. It

380

DIFFEKENTIATION OF TISSUES 281

is in the sporophyte of the Pteridophytes and Spermato-
phytes that this differentiation of tissues becomes extreme,
and tissues are organized which differ decidedly from
parenchyma. This differentiation means division of labor,
and the more highly organized the body the more tissues
there are.

All the other tissues are derived from parenchyma, and
as the work of nutrition and of reproduction is always
retained by the parenchyma cells, the derived tissues are
for mechanical rather
than for vital purposes.
There is a long list of
these derived and me-
chanical tissues, some of
them being of general
occurrence, and others
more restricted, and
there is every gradation

between them and the FIG. 264. Parenchyma and sclerenchyma from

parenchyma from which the 8tem of pteris> in cross-section.-CHAM-

f J BEKLAIN.

they have come. We

shall note only a few which are distinctly differentiated

and which are common to all vascular plants.

149. Parenchyma. — The parenchyma of the vascular plants,
is typically made up of cells which have thin walls and whose
three dimensions are approximately equal (Figs. 264, 265),
though sometimes they are elongated. Until abandoned,
such cells contain very active protoplasm, and it is in them
that nutritive work and cell division are carried on. So
long as these cells retain the power of cell division the
tissue is called meristein, or it is said to be meristematic,
from a Greek word meaning "to divide." When the cells
stop dividing, the tissue is said to be permanent. The
growing points of organs, as stems, roots, and leaves, are
composed of parenchyma which is meristematic (Figs. 266,
274), and meristem occurs wherever growth is going on.

282

PLANT STRUCTURES

150. Mestome and stereome. — When the plant body be-
comes complex a conductive system is necessary, so that
the different regions of the body may be put into communi-
cation. The material absorbed
by the roots must be carried to
the leaves, and the food manu-
factured in the leaves must
be carried to regions of growth
and storage. This business of
transportation is provided for
by the specially organized ves-
sels referred to in preceding
chapters, and all conducting tis-
sue, of whatever kind, is spoken
of collectively as mestome.

If a complex body is to main-
tain its form, and especially if
it is to stand upright and be-
come large, it must develop
structures rigid enough to fur-
nish mechanical support. All
the tissues which serve this pur-
pose are collectively known as
stereome.

The sporophyte body of
Pteridophytes and Spermato-
phytes, therefore, is mostly

made up of living and working parenchyma, which is
traversed by mechanical mestome and stereome.

151. Dicotyl and Conifer stems. — The stems of these two
groups are so nearly alike in general plan that they may
be considered together. In fact, the resemblances were
once thought to be so important that these two groups
were put together and kept distinct from Monocotyledons ;
but this was before the gametophyte structures were
known to bear very different testimony.

FIG. 265. Same tissues as in pre-
ceding figure, in longitudinal sec-
tion, the parenchyma showing
nuclei.— CHAMBERLAIN.

DIFFERENTIATION OF TISSUES

283

At the apex of the growing stem there is a group of
active meristem cells, from which all the tissues are de-
rived (Fig. 266). This group is known as the apical group.
Below the apical group the tissues and regions of the stem
begin to appear, and still farther down they hecome dis-
tinctly differentiated, passing into permanent tissue, the
apical group by its
divisions continually
adding to them and
increasing the stem
in length.

Just behind the
apical group, the
cells begin to give the
appearance of being
organized into three
great embryonic re-
gions, the cells still
remaining meristem-
atic (Fig. 266). At
the surface there is a
single layer of cells
distinct from those

within, known as the dermatogen, or "skin-producer," as
farther down, where it becomes permanent tissue, it is the
epidermis. In the center of the embryonic region there
is organized a solid cylinder of cells, distinct from those
around it, and called the plerome, meaning uthat which
fills up." Farther down, where the plerome passes into
permanent tissue, it is called the central cylinder or stele
("column"). Between the plerome and dermatogen is
a tissue region called the periblem, meaning "that which
is put around," and when it becomes permanent tissue it
is called the cortex, meaning "bark " or "rind."

Putting these facts together, the general statement is
that at the apex there is the apical group of meristem cells ;

FIG. 266. Section through growing point of stem of
Hippuris : below the growing point, composed
of a uniform meristem tissue, the three embry-
onic regions are outlined, showing the dermato-
gen (d, d), the central plerome (p, p), and be-
tween them the periblem. — After DK BARY.

PLANT STRUCTURES

below them are the three embryonic regions, dermatogen,
periblem, and plerome ; and farther below these three
regions pass into permanent tissue, organizing the epider-
mis, cortex, and stele. The three embryonic regions are
usually not so distinct in the Conifer stem as in the Dico-
tyl stem, but both stems have epidermis, cortex, and stele.
Epidermis. — The epidermis is a protective layer, whose
cells do not become so much modified but that they may
be regarded as parenchyma. It gives rise also to super-
ficial parts, as hairs, etc. In the case of trees, the epidermis
does not usually keep up with the increasing diameter, and
disappears. This puts the work of protection upon the
cortex, which organizes a superficial tissue called cork, a
prominent part of the structure known as bark.

Cortex. — The cortex is characterized by containing
much active parenchyma, or primitive tissue, being the
chief seat of the life activities of the stem. Its superficial
cells, at least, contain chlorophyll and do chlorophyll work,
while its deeper cells are usually temporary storage places
for food. The cortex is also char-
acterized by the development of
stereome, or rigid tissues for me-
chanical support. The stereome
may brace the epidermis, forming
the Jiypodermis ; or it may form
bands and strands within the cor-
tex ; in fact, its amount and ar-
rangement differ widely in differ-
ent plants.

The two principal stereome tis-
sues are collenchyma and scleretir
chyma, meaning " sheath-tissue "
and " hard-tissue " respectively.
In collenchyma the cells are thick-
ened at the angles and have very elastic walls (Fig. 267),
making the tissue well adapted for parts which are growing

FIG. 267. Some collenchyma
cells from the stem of a com-
mon dock (Rumex), showing
the cells thickened at the
angles.— CHAMBERLAIN.

DIFFERENTIATION OF TISSUES

285

in length. The chief mechanical tissue for parts which
have stopped growing in length is sclerenchyma (Figs. 264,
265). The cells are thick-walled, and usually elongated
and with tapering ends, including the so-called "fibers."

FIG. 268. Sections through an open collateral vascular bundle from a sunflower stem;
A, cross- section; B. longitudinal section; the letters in both referring to the same
structures; M, pith; JT, xylem, containing spiral (s, s') and pitted (t, t') vessels;
C, cambium; P, phloem, containing sieve vessels ($b); b, a mass of bast fibers or
sclerenchyma; ic, pith rays between the bundles; e, the bundle sheath: It, cor-
tex.—After VINES.

Stele. — The characteristic feature of the stele or central
cylinder is the development of the mestome or vascular

286

PLANT STRUCTURES

tissues, of which there are two prominent kinds. The
tracheary vessels are for water conduction, and are cells
with heavy walls and usually large diameter (Fig. 268).
The thickening of the walls is not uniform, giving them a
very characteristic appearance, the thickening taking the
form of spiral bands, rings, or reticulations (Fig. 268, B).
Often the reticulation has such close meshes that the cell
wall has the appearance of being covered with thin spots,
and such cells are called " pitted vessels." The vessels with
spirals and rings are usually much smaller in diameter than
the pitted ones. The true tracheary cells are more or less
elongated and without tapering ends, fitting end to end
and forming a continuous longitudinal series, suggesting a
trachea, and hence the name. In the Conifers there are

no true tracheary cells, as in
the Dicotyledons, except a few
small spiral vessels which are
formed at first in the young
stele, but the tracheary tissue
is made up of tracheids, mean-
ing "trachea -like," differing
from tracheae or true tracheary
vessels in having tapering ends
and in not forming a continu-
ous series (Fig. 269). The walls
of these tracheids are " pitted"
in a way which is characteristic
of Gymnosperms, the "pits"
appearing as two concentric
rings, called "bordered pits."

The other prominent mes-
tome tissue developed in the
stele is the sieve vessels, for the
conduction of organized food, chiefly proteids (Fig. 268).
Sieve cells are so named because in their walls special areas
are organized which are perforated like the lid of a pepper-

Fio. 269. Tracheids from wood of
pine, showing tapering ends and
bordered pit?.— CHAMBERLAIN.

DIFFERENTIATION OF TISSUES 287

box or a "sieve." These perforated areas are the sieve-
plates, and through them the vessels communicate with
one another and with the adjacent tissue.

The tracheary and sieve vessels occur in separate
strands, the tracheary strand being called xylem (" wood "),
the sieve strand phloem ("bark "). A xylem and a phloem
strand are usually organized together to form a vascular
bundle, and it is these fiber-like bundles which are found
traversing the stems of all vascular plants and appearing
conspicuously as the veins of leaves. Among the Dicotyls
and Conifers the vascular bundles appear in the stele in
such a way as to outline a hollow cylinder (Fig. 216), the
xylem of each bundle being toward the center, the phloem
toward the circumference of the stem. The undifferenti-
ated parenchyma of the sfcele which the vascular cylinder
incloses is called the pith. In older parts of the stem the
pith is often abandoned by the activities of the plant, and
either remains as a dead spongy tissue, or disappears en-
tirely, leaving a hollow stem. Between the bundles form-
ing the vascular cylinder there is also undifferentiated
parenchyma, and as it seems to extend from the pith out
between the bundles like "rays from the sun," the rays
are called pith rays.

Such vascular bundles as described above, in which the
xylem and phloem strands are " side-by-side " upon the same
radius, are called collateral (Fig. 270). One of the pecul-
iarities of the collateral bundles of Dicotyls and Conifers,
however, is that when the two strands of each bundle are
organized some meristem is left between them. This means
that between the strands the work of forming new cells can
go on. Such bundles are said to be open ; and the open
collateral bundle is characteristic of the stems of the Dico-
tyls and Conifers.

The meristem between the xylem and phloem of the
open bundle is called cambium (Figs. 268, 270). The cam-
bium also extends across the pith rays between the bundles,

288

PLANT STRUCTURES

connecting the cambium in the bundles, and thus forming
a camHum cylinder, which separates the xylem and phloem
of the vascular cylinder. This cambium continues the f or-

FIG. 270. Cross-section of open collateral vascular bundle from stem of castor-oil
plant (Ricinus), showing pith cells (m), xylem containing spiral (t) and pitted (g)
vessels, cambium of bundle (c) and of pith rays (cb), phloem containing sieve ves-
sels («/), three bundles of bast fibers or sclerenchyma (6). the bundle sheath con-
taining starch grains, and outside of it parenchyma of the cortex (r). — After SACHS.

mation of xylem tissue on the one side and phloem tissue
on the other in the bundles, and new parenchyma between
the bundles, and so the stem increases in diameter. If the
stem lives from year to year the addition made by the cam-
bium each season is marked off from that of the previous
season, giving rise to the so-called growth rings or annual
rings, so conspicuous a feature of the cross-section of tree

DIFFERENTIATION OF TISSUES 289

trunks (Fig. 217). This continuous addition to the vessels
increases the capacity of the stem for conduction, and per-
mits the further extension of branches and a larger display
of leaves.

The annual additions to the xylem are added to the in-
creasing mass of wood. The older portions of the xylem
mass are gradually abandoned by the ascending water
("sap"), often change in color, and form the heart-wood.
The younger portion, through which the sap is moving, is
the sap-wood. It is evident, however, that the annual ad-
ditions to the phloem are not in a position for permanency.
The new phloem is deposited inside of the old, and this, to-
gether with the new xylem, presses upon the old phloem,
which becomes ruptured in various ways, and rapidly or
very gradually peels off, being constantly renewed from
within. It is the protecting layers of cork (see this section
under Cortex), the old phloem, and the new phloem down
to the cambium, which constitute the so-called bark of
trees, a structure .exceedingly complex and extremely vari-
able in different trees.

The stele also frequently develops stereome tissue in the
form of sclerenchyma. These thick-walled fibers are often
closely associated with one or both of the vascular strands
of the bundles (Fig. 270), and lead to the old name fibro-
vascular bundles.

To sum up, the stems of Dicotyledons and Conifers are
characterized by the development of a vascular cylinder, in
which the bundles are collateral and open, permitting
increase in diameter, extension of the branch system, and
a continuous increase in leaf display.

152. Monocotyl steins. — In the stems of Monocotyledons
there is the same apical development and differentiation
(Fig. 266). The characteristic difference from the Dicotyl
and Conifer type, just described, is in connection with the
development of the vascular bundles in the stele. Instead
of outlining a hollow cylinder, the bundles are scattered

290

PLANT STRUCTURES

through the stele (Fig. 214). This lack of regularity would
interfere with the organization of a cambium cylinder, and
we find the bundles collateral but closed — that is, with no
meristem left between the xylem and phloem (Fig. 271).

FIG. 271. Cross-section of a closed collateral bundle from the stem of corn, showing
the xylem with annular (r), spiral (s), and pitted (g) vessels; the phloem contain-
ing sieve vessels (v), and separated from the xylem hy no intervening cambium;
both xylem and phloem surrounded by a mass of sclerenchyma (fibers); and in-
vesting vessels and fibers the parenchyma (p) of the pith-like tissue through
which the bundles are distributed. — After SACHS.

This lack of cambium means that stems living for sev-
eral years do not increase in diameter, but become columnar

DIFFERENTIATION OF TISSUES

291

shafts, as in the palm, rather than much elongated cones.
It also means lack of ability to develop an extending branch
system or to display more numerous leaves each year. The
palm may be taken as a typical result of such a structure,
with its columnar and unbranched trunk, and its foliage
crown containing about the same number of leaves each year.

The lack of regular arrangement of the bundles also
prevents the outlining of a pith region or the organization
of definite pith rays. The failure to increase in diameter
also precludes the necessity of bark, with its protective cork
constantly renewed, and its sloughing-off phloem.

To sum up, the stems of the Monocotyledons are
characterized by the vascular bundles not developing a
cylinder or any regular arrangement, and by collateral and
closed bundles, which do not permit increase in diameter,
or a branch system, or increase in leaf display.

153. Pteridophyte stems. — The stems of Pteridophytes
are quite different from those of Spermatophytes. While
the large Club -mosses (Lyco-
podium] and Isoetes usually
have an apical group of meris-
tem cells, as among the Seed-
plants, the smaller Club-mosses
(Selaginella), Ferns, and Horse-
tails usually have a single api-
cal cell, whose divisions give
rise to all the cells of the stem.
Generally also a dermatogen is
not organized, and in such
cases there is no true epidermis,
the cortex developing the ex-
ternal protective tissue. In the cortex there is usually an
extensive development of stereome, in the form of scleren-
chyma (Fig. 272), the stele furnishing little or none, and
the vascular bundles not adding much to the rigidity, as
they do in the Seed-plants,

FIG. 272. Diagram of tissues in crops-
section of stem of a fern (Pteris),
showing two masses of scleren
chyma (st), between and about
which are vascular bundles. —
CHAMBERLAIN.

292 PLANT STRUCTURES

In Equisetum and Isoetes the vascular bundles may be
said to be collateral, as in the Seed-plants, but the charac-
teristic Pteridophyte type is very different. In fact, the
vascular masses can hardly be compared with the bundles
of the Seed-plants, although they are called bundles for
convenience. In the stele one or more of these bundles
are organized (Fig. 272), the tracheary vessels (xylem) being
in the center and completely invested by the sieve vessels

FIG. 273. Cross-section of concentric vascular bundle of a fern (Pteris): the single
row of shaded cells investing the others is the bundle sheath; the large and heavy-
walled cells within constitute the xylem; and between the xylem and the bundle
ehealh is the phloem. — CHAMBERLAIN.

(phloem). This is called the concentric bundle (Fig. 273),
as distinguished from the collateral bundles of Seed-plants,
and is characteristic of Pteridophyte stems.

DIFFERENTIATION OF TISSUES

293

154. Roots. — True roots appear only in connection with
the vascular plants (Pteridophytes and Spermatophytes) ;
and in all of them the structure is essentially the same,
and quite different from stem structure. A single ap-
ical cell (in most Pteridophytes) (Fig. 274) or an apical
group (in Spermatophytes) usually gives rise to the three
embryonic regions — dermatogen, periblem, and plerome
(Fig. 275).

A fourth region, how-
ever, peculiar to root, is
usually added. The apical

FIG. 274. Section through root-tip of
Pteris: the cell with a nucleus is the
single apical cell, which in front has
cut off cells which organize the root-
cap. — CHAMBERLAIN.

Fi<i. 275. A longitudinal section through
the root - tip of shepherd's purse,
showing the plerome (pi), surround-
ed by the periblem (/», outside of
periblem the epidermis (e) which
disappears in the older parts of the
root, and the prominent root-cap (c).
—From "Plant Relations."

cell or group cuts off a tis-
sue in front of itself (Fig.
274), known as the calyptrogen, or "cap producer." for it
organizes the root-cap, which protects the delicate meri-
stem of-the growing point.

Another striking feature is that in the stele there is
organized a single solid vascular cylinder, forming a tough
central axis (Fig. 277), from which the usually well-devel-
oped cortex can be peeled off as a thick rind. In this vas-
cular axis, which is called " a bundle " for convenience but
does not represent the bundle of Seed-plant stems, the ar-
rangement of the xylem and phloem is entirely unlike that
37

294

PLANT STRUCTURES

FIG. 276. Cross-section of the vascular axis of a root, showing radiate type of bundle
the xylem (p) and phloem (ph) alternating. — After SACHS.

found in stems. The xylem is in the center and sends out
a few radiating arms, between which are strands of phloem,

forming the so-called
radiate bundle (Fig. 276).
This arrangement brings
the tracheary vessels
(xylem) to the surface of
the bundle region, which
is not true of either the
concentric or collateral
bundle. This seems to
be associated with the
fact that the xylem is to
receive and conduct the

FIG. 277. Endogenous origin of root branch- water absorbed from the
es, showing them (») arising from the cen- -i T- i ^ i .,

tral axis (/) and breaking through the

cortex (r).-After VINES. that this characteristic

DIFFERENTIATION OF TISSUES

295

bundle structure of the root appears only in young and
active roots. In older ones certain secondary changes take
place which obscure the structure and result in a resem-
blance to the stem.

The origin of branches in roots is also peculiar. In
stems branches originate at the surface, involving epi-
dermis, cortex, and vascular bundles, such an origin being
called exogenous ("produced outside7'); but in roots
branches originate on the vascular cylinder, burrow through
the cortex, and emerge at the surface (Fig. 277). If the
cortex be stripped off from a root with branches, the
branches are left attached to the woody axis, and the cor-
tex is found pierced with holes made by the burrowing
branches. Such an origin is called endogenous, meaning
" produced within."

To sum up the peculiarities of the root, it may be said
to develop a root-cap, to have a solid vascular cylinder in
which the xylem and phloem are arranged to form a bundle
of the radiate type, and to branch endogenously.

FIG. 2~8. A section through the leaf of lily, showing upper epidermis (ue), lower epi-
dermis (le) with its stomata (st). mesophyll (dotted cells) composed of the palisade
region (/>) and the spongy region <'/?/?) with air spaces among the cells, and two
veins (v) cut across. — From "Plant Relations.'"

296 PLANT STRUCTURES

155. Leaves. — Leaves usually develop from an apical
region in the- same general way as do stems and roots,
modified by their common dorsiventral character. Com-
paring the leaf of an ordinary seed-plant with its stem, it
will be noted that the three regions are represented (Fig.
278) : (1) the epidermis ; (2) the cortex, represented by
the mesophyll ; (3) the stele, represented by the veins.

In the case of collateral bundles, where in the stem the
xylem is always toward the center and the phloem is toward
the circumference, in the leaves the xylem is toward the
upper and the phloem toward the lower surface.

CHAPTER XVI

PLANT PHYSIOLOGY

156. Introductory. — Plants may be studied from several
points of view, each of which has resulted in a distinct
division of Botany. The study of the forms of plants and
their structure is MORPHOLOGY, and it is this phase of Bot-
any which has been chiefly considered in the previous chap-
ters. The study of plants at work is PHYSIOLOGY, and as
structure is simply preparation for work, the preceding
chapters have contained some Physiology, chiefly in refer-
ence to nutrition and reproduction. The study of the clas-
sification of plants is TAXONOMY, and in the preceding
pages the larger groups have been outlined. The study of
plants as to their external relations is ECOLOGY, a subject
which will be presented in the following chapter, and which
is the chief subject of Plant Relations. The study of the
diseases of plants and their remedies is PATHOLOGY ; their
study in relation to the interests of man is ECONOMIC
BOTAXV.

Besides these general subjects, which apply to all plants,
the different groups form the subjects of special study. The
study of the Morphology, Physiology, or Taxonomy of the
Bacteria is Bacteriology ; of the Algae, Algology ; of the
Fungi, Mycology ; of the Bryophytes, Bryology ; of the
fossil plants, Palceobotany or Palwophytology, etc.

In the present chapter it is the purpose to give a very
brief outline of the great subject of Plant Physiology, not
with the expectation of presenting its facts adequately, but
with the hope that the important field thus presented may

297

298 PLA.NT STRUCT! KKS

attract to further study. It is merely the opening of a door
to catch a fleeting glimpse.

A common division of the subject presents it under five
heads : (1) Stability of form, (2) ^Nutrition, (3) Respira-
tion, (4) Movement, (5) Reproduction.

STABILITY OF FORM

157. Turgidity. — It is a remarkable fact that plants and
parts of plants composed entirely of cells with very thin and
delicate walls are rigid enough to maintain their form.
It has already been noted (see § 20) that such active cells
exert an internal pressure upon their walls. This seems to
be due to the active absorption of liquid, which causes the
very elastic walls to stretch, as in the "blowing up " of a
bladder. In this way each gorged and distended cell be-
comes comparatively rigid, and the mass of cells retains its
form. It seems evident that the active protoplasm greedily
pulls liquid through the wall and does not let it escape so
easily. If for any reason the protoplasm of a gorged cell
loses its hold upon the contained liquid the cell collapses.

158. Tension of tissues. — The rigidity which comes to
active parenchyma cells through their turgidity is increased
by the tensions developed by adjacent tissues. For exam-
ple, the internal and external tissues of a stem are apt to
increase in volume at different rates ; the faster will pull
upon the slower, and the slower will resist, and thus be-
tween the two a tension is developed which helps to keep
them rigid. This is strikingly shown by splitting a dande-
lion stem, when the inner tissue, relieved somewhat from
the resistance of the outer, elongates and causes the strip
to become strongly curved outward or even coiled. Experi-
ments with strips from active twigs, including the pith,
will usually demonstrate the same curve outward. Tension
of tissues is chiefly developed, of course, where elongation
is taking place.

PLANT PHYSIOLOGY 299

159. Stereome. — When growth is completed, cell walls
lose their elasticity, turgidity becomes less, and therefore
tensions diminish, ard rigidity is supplied by special ster-
eome tissues, chief among which is sclerenchyma. An-
other stereome tissue is collenchyma, which on account of
its elastic walls can be used to supplement turgidity and
tension where elongation is still going on. For a fuller
account of stereome tissues see 8 150.

160. Food. — Plant food must contain carbon (C), hydro-
gen (H), oxygen (0), and nitrogen (N), and also more
or less of other elements, notably sulphur, phosphorus,
potassium, calcium, magnesium, and iron. In the case
of green plants these elements are obtained from inor-
ganic compounds and food is manufactured ; while plants
without chlorophyll obtain their food already organized.
The sources of these elements for green plants are as
follows: Carbon from carbon dioxide (C02) of the air;
hydrogen and oxygen from water (H20) ; and nitrogen
and the other elements from their various salts which
occur in the soil and are dissolved in the water which
enters the plant.

All of these substances must present themselves to
plants in the form of a gas or a liquid, as they must pass
through cell walls ; and the processes of absorption have
to do with the taking in of the gas carbon dioxide and of
water in which the necessary salts are dissolved.

161. Absorption. — Green plants alone will be considered,
as the unusual methods of securing food have been men-
tioned in Chapter VII. For convenience also, only terres-
trial green plants will be referred to, as it is simple to
modify the processes to the aquatic habit, where the sur-
rounding water supplies what is obtained by land plants
from both air and soil.

300 PLANT STRUCTURES

In such plants the carbon dioxide is absorbed directly
from the air by the foliage leaves, whose expanse of surface
is as important for this purpose as for exposing chlorophyll
to light. When the work of foliage leaves is mentioned it
must always be understood that it applies as well to any
green tissue displayed by the plant.

The water, with its dissolved salts, is absorbed from the
soil by the roots. Only the youngest parts of the root-
system can absorb, and the absorbing capacity of these
parts is usually vastly increased by the development of
numerous root hairs, just behind the growing tip (Fig. 194).
These root hairs are ephemeral, new ones being continu-
ally put out as the tip advances, and the older ones disap-
pearing. They come in very close contact with the soil
particles, and "suck in" the water which invests each
particle as a film.

162. Transfer of water. — The water and its dissolved salts
absorbed by the root-system must be transferred to the foli-
age leaves, where they are to be used, along with the carbon
dioxide, in the manufacture of food.

Having entered the epidermis of the absorbing rootlets
the water passes on to the cortex, and traversing it enters
the xylem system of the central axis. In some way this
transfer is accompanied by pressure, known as root pres-
sure, which becomes very evident when an active stem is
cut off near the ground. The stump is said to "bleed,"
and sends out water ("sap") as if there were a force
pump in the root-system. This root pressure doubtless
helps to lift the water through the xylem of the root into
the stem, and in low plants may possibly be able to send it
to the leaves, but for most plants this is not possible.

When the water enters the xylem of the root it is in a
continuous system of vessels which extends through the
stem and out into the leaves. The movement of the ab-
sorbed water through the xylem is called the transpiration
current, or very commonly the "ascent of sap." An ex-

i'LANT PHYSIOLOGY

periment demonstrating this ascent of sap and its route
through the xylem will be found described in Plant Rela-
tions, p. 151. How it is that the transpiration current
moves through the xylem is not certainly known.

163. Transpiration. — When the water carrying dissolved
salts reaches the mesophyll cells, some of the water and all
of the salts are retained for food manufacture. However,
much more water enters the leaves than is needed for food,
this excess having been used for carrying soil salts. When
the soil salts have reached their destination the excess of
water is evaporated from the leaf surface, the process being
called transpiration. For an experiment demonstrating
transpiration see Plant Relations, § 26.

This transpiration is regulated according to the needs
of the plant. If the water is abundant, transpiration is
encouraged ; if the water supply is low, transpiration is
checked. One of the chief ways of regulating is by means
of the very small but exceedingly numerous stomata (see §
79 [4]), whose guard cells become turgid or collapse and so
determine the size of the opening between them. It has
been estimated that a leaf of an ordinary sunflower contains
about thirteen million stomata, but the number varies widely
in different plants. In ordinary dorsiventral leaves the sto-
mata are much more abundant upon the lower surface than
upon the upper, from which they may be lacking entirely.
In erect leaves they are distributed equally upon both sur-
faces ; in floating leaves they occur only upon the upper
surface ; in submerged leaves they are lacking entirely.

The amount of water thus evaporated from active
leaves is very great. It is estimated that the leaves of a
sunflower as high as a man evaporate about one quart of
water in a warm day ; and that an average oak tree in its
five active months evaporates about twenty-eight thousand
gallons. If these figures be applied to a meadow or a
forest the result may indicate the large importance of this
process.

302 PLANT STKU'TtkKS

164. Photosynthesis. — This is the process by which car-
bon dioxide and water are "broken up," their elements
recombined to form a carbohydrate, and some oxygen given
oif as a waste product, the mechanism being the chloroplasts
and light. It has been sufficiently described in § 55, and
also in Plant Relations, pp. 28 and 150.

165. Formation of proteids.— The carbohydrates formed
by photosynthesis, such as starch, sugar, etc., contain car-
bon, hydrogen, and oxygen. Out of them the living cells
must organize proteids, and in the reconstruction nitrogen
and sulphur, and sometimes phosphorus, are added. This
work goes on both in green cells and other living cells, as
it does not seem to be entirely dependent upon chloroplasts
and light.

166. Transfer of carbohydrates and proteids, — These two
forms of food having been manufactured, they must be
carried to the regions of growth or storage. In order to be
transported they must be in soluble form, and if not already
soluble they must be digested, insoluble starch being con-
verted into soluble sugar, etc. In these digested forms
they are transported to regions where work is going on,
and there they are assimilated — that is, transformed into
the enormously complex working substance protoplasm ;
or they are transported to regions of storage and there they
are reconverted into insoluble storage forms, as starch, etc.

These foods pass through both the cortex and phloem
in every direction, but the long-distance transfer of pro-
teids, as from leaves to roots, seems to be mainly through
the sieve vessels.

BESPIRATION

167. Respiration. — This is an essential process in plants
as well as in animals, and is really the phenomenon of
"breathing." The external indication of the process is
the absorption of oxygen and the giving out of carbon di-
oxide ; and it goes on in all organs, day and night. AVhen

PLANT I'liYSlOLOdY

it ceases death ensues sooner or later. By this process
energy, stored up by the processes of nutrition, is liberated,
and with this liberated energy the plant works. It may be
said that oxygen seems to have the power of arousing pro-
toplasm to activity.

It is not sufficient for the air containing oxygen to come
in contact merely with the outer surface of a complex plant,
as its absorption and transfer would be too slow. There
must be an "internal atmosphere" in contact with the
living cells. This is provided for by the intercellular
spaces, which form a labyrinthine system of passageways,
opening at the surface through stomata and lenticels (pores
through bark). In this internal atmosphere the exchange
of oxygen and carbon dioxide is effected, the oxygen being
renewed by diffusion from the outside, and the carbon
dioxide finally escaping by diffusion to the outside.

MOVEMENT

168. Introductory.— In addition to movements of mate-
rial, as described above, plants execute movements depend-
ent upon the activity of protoplasm, which result in change
of position. Naked masses of protoplasm, as the plas-
modium of slime-moulds (see § 51), advance with a sliding,
snail-like movement upon surfaces ; zoospores and ciliated
sperms swim freely about by means of motile cilia ; while
many low plants, as Bacteria (§52), Diatoms (§34), Oscil-
laria (§ 20), etc., have the power of locomotion.

When the protoplasm is confined within rigid walls and
tissues, as in most plants, the power of locomotion usually
disappears, and the plants are fixed ; but within active cells
the protoplasm continues to move, streaming back and
forth and about within the confines of the cell.

In the case of complex plants, however, another kind
of movement is apparent, by which parts are moved and
variously directed, sometimes slowly, sometimes with great

;>Q4 PLANT STRUCTUKKS

rapidity. In these cases the part concerned develops a
curvature, and by various curvatures it attains its ultimate
position. These curvatures are not necessarily permanent,
for a perfectly straight stem results from a series of cur-
vatures near its apex. Curvatures may be developed by
unequal growth on the two sides of an organ, or by unequal
turgidity of the cells of the two sides, or by the unequal
power of the cell walls to absorb water.

169. Hygroscopic movements. — These movements are only
exhibited by dry tissues, and hence are not the direct result
of the activity of protoplasm. The dry walls absorb mois-
ture and swell up, and if this absorption of moisture and
its evaporation is unequal on two sides of an organ a curva-
ture will result. In this way many seed vessels are rup-
tured, the sporangia of ferns are opened, the operculum of
mosses is lifted off by the peristome, the hair-like pappus
of certain Composites is spread or collapsed, certain seeds
are dispersed and buried, etc. One of the peculiarities of
this hygroscopic power of certain cells is that the result
may be obtained through the absorption of the moisture of
the air, and the hygroscopic awns of certain fruits have
been used in the manufacture of rough hygrometers
(" measures of moisture ").

170. Growth movements. — Growth itself is a great physi-
ological subject, but certain movements which accompany
it are referred to here. Two kinds of growth movements
are apparent.

One may be called nutation, by which is meant that the
growing tip of an organ does not advance in a straight
line, but bends now toward one side, now toward the other.
In this way the tip describes a curve, which may be a
circle, or an ellipse of varying breadth ; but as the tip is
advancing all the time, the real curve described is a spiral
with circular or elliptical cross-section. The sweep of a
young hop-vine in search of support, or of various tendrils,
may be taken as extreme illustrations, but in most cases

PLANT PHYSIOLOGY 395

the nutation of growing tips only becomes apparent through
prolonged experiment.

The other prominent growth movement is that which
places organs in proper relations for their work, sending
roots into the soil and stems into the air, and directing
leaf planes in various ways. For example, in the germina-
tion of an ordinary seed, in whatever direction the parts
emerge the root curves toward the soil, the stem turns
upward, and the cotyledons spread out horizontally.

The movement of nutation seems to be due largely to
internal causes, while the movements which direct organs
tire due largely to external causes known as stimuli. Some
of the prominent stimuli concerned in directing organs are
as follows :

Heliotropism. — In this case the stimulus is light, and
under its influence aerial parts are largely directed. Plants
growing in a window furnish plain illustration of helio-
tropism. In general the stems and petioles curve toward
the light, showing positive heliotropism (Fig. 279) ; the
leaf blades are directed at right angles to the rays of light,
showing trans verve heliotropism ; while if there are hold-
fasts or aerial roots they are directed away from the light,
showing negative heliotropism. The thallus bodies of ferns,
liverworts, etc., are transversely heliotropic, as ordinary
leaves, a position best related to chlorophyll work. If the
light is too intense, leaves may assume an edgewise or pro-
file position, a condition well illustrated by the so-called
"compass plants." (See Plant Relations, p. 10.)

Geotropism. — In this case the stimulus is gravity, and
its influence in directing the parts of plants is very great.
All upward growing plants, as ordinary stems, some leaves,
etc., are negatively geotropic, growing away from the center
of gravity. Tap-roots are notable illustrations of positive
geotropism, growing toward the source of gravity with con-
siderable force. Lateral branches from a main or tap-root,
however, tire usually transversely yeotrupic.

FIG. 279. Sunflower stems with the upper part of the stem sharply bent toward the
light, giving the leaves better exposure, the stem showing positive heliotropism. -
After SCHAFFNEK.

PLANT PHYSIOLOGY 397

That these influences in directing are very real is testi-
fied to by the fact that when the organs are turned aside
from their proper direction they will curve toward it and
overcome a good deal of resistance to regain it. Although
these curvatures are mainly developed in growing parts,
even mature parts which have been displaced may be
brought back into position. For example, when the stems
of certain plants, notably the grasses, have been prostrated
by wind, etc., they often can resume the erect position under
the influence of negative geotropism, a very strong and even
angular curvature being developed at certain joints.

Hydrotropism. — The influence of moisture is very strong
in directing certain organs, notably absorbing systems.
Roots often wander widely and in every direction under
the guidance of hydrotropism, even against the geotropic
influence. Ordinarily geotropism and hydrotropism act in
the same direction, but it is interesting to dissociate them
so that they may " pull " against one another. For such
an experiment see Plant Relations, p. 91.

Other stimuli. — Other outside stimuli which have a
directive influence upon organs are chemical substances
(chemotropism), such as direct sperms to the proper female
organ ; heat (thermotropism) ; water currents (rheotropism) ;
mechanical contact, etc. The most noteworthy illus-
trations of the effect of contact are furnished by tendril-
climbers. When a nutating tendril comes in contact with
a support a sharp curvature is developed which grasps it.
In many cases the irritable response goes further, the ten-
dril between the plant axis and the support developing a
spiral coil.

171. Irritable movements.— The great majority of plants
can execute movements only in connection with growth, as
described in the preceding section, and when mature their
parts are fixed and incapable of further adjustment. Cer-
tain plants, however, have developed the power of moving
mature parts, the motile part always being a leaf, such as

308

•LANT STRUCTURES

foliage leaf, stamen, etc. It is interesting to note tliat these
movements have been cultivated by but few families, nota-
ble among them being the Legumes (§ 141).

These movements of mature organs, some of which arc
very rapid, are due to changes in the turgidity of cells. As
already mentioned (§ 157), turgid cells are inflated and
rigid, and when turgidity ceases the cells collapse and the
tissue becomes flaccid. A. special organ for varying tur-
gidity, known as the pulvinus, is usually associated with
the motile leaves and leaflets. The pulvinus is practically
a mass of parenchyma cells, whose turgidity is made to vary
by various causes, and leaf -movement is the result.

The causes which induce some movements are unknown,
as in the case of Desmodium gyrans (see Plant Relation*,
p. 49), whose small lateral leaflets uninterruptedly de-
scribe circles, completing a cycle in one to three minutes.

In other cases the inciting cause is the change from light
to dark, the leaves assuming at night a very dif-
ferent position from that during the day. Dur-
ing the day the leaflets are spread out freely,

FIG. 280. A leaf of a sensitive plant in two conditions: in the figure to the left the leaf
is fully expanded, with its four main divisions and numerous leaflets well spread;
in the figure to the right is shown the same leaf after it has been " shocked " by
a sudden touch, or by sudden heat, or in some other way; the leaflets have been
thrown together forward and upward, the four main divisions have been movod
together, and the main leaf-stalk has been directed sharply downward. — After

DUCHARTRE.

PLANT PHYSIOLOGY 309

while at night they droop and usually fold together (see
Plant Relations, pp. 9, 10). These are the so-called nycti-
tropic movements or " night movements/' which maybe ob-
served in many of the Legumes, as clover, locust, bean, etc.
In still other cases, mechanical irritation induces move-
ment, as sudden contact, heat, injury, etc. Some of the
"carnivorous plants " are notable illustrations of this, es-
pecially Dioncva, which snaps its leaves shut like a steel
trap when touched (see Plant Relations, p. 161). Among
the most irritable of plants are the so-called "sensitive
plants," species of Mimosa, Acacia, etc., all of them Le-
gumes. The most commonly cultivated sensitive plant is
Mimosa pudica (Fig. 280), whose sensitiveness to contact
and rapidity of response are remarkable (see Plant Rela-
tions, p. 48).

REPBODUCTION

172. Reproduction. — The important function of repro-
duction has been considered in connection with the various
plant groups. Among the lowest plants the only method
of reproduction is cell division, which in the complex
forms results in growth. In the more complex plants va-
rious outgrowths or portions of the body, as gemmae, buds,
bulbs, tubers, various branch modifications, etc., furnish
means of propagation. All of these methods are included
under the head of vegetative multiplication, as the plants
are propagated by ordinary vegetative tissues.

AVhen a special cell is organized for reproduction, dis-
tinct from the vegetative cells, it is called a spore, and re-
production by spores is introduced. The first spores devel-
oped seem to have been those produced by the division of
the contents of a mother cell, and are called asexual spores.
These spores are scattered in various ways — by swimming
(zoospores), by floating, by the wind, by insects.

Another type of spore is the sexual spore, formed by
the union of two sexual cells called gametes. The gametes
38

310 PLANT STRUCT UKES

seem to have been derived from asexual spores. At first
the pairing gametes are alike, but later they become differ-
entiated into sperms or male cells, and eggs or female cells.

With the establishment of alternation of generations,
the asexual spores are restricted to the sporophyte, and the
gametes to the gametophyte. With the further introduction
of heterospory, the male and the female gametes are sepa-
rated upon different gametophytes, which become much
reduced.

With the reduction of the megaspores to one in a spo-
rangium (ovule), and its retention, the seed is organized,
and the elaborate scheme of insect-pollination is developed.

CHAPTEE XVII

PLANT ECOLOGY

173. Introductory, — Ecology has to do with the external
relations of plants, and forms the principal subject of the
volume entitled Plant Relations, which should be consulted
for fuller descriptions and illustrations. It treats of the
adjustment of plants and their organs to their physical
surroundings, and also their relations with one another
and with animals, and has sometimes been called " plant
sociology."

LIFE RELATIONS

174. Foliage leaves. — The life relation essential to foliage
leaves is the relation to light. This is shown by their
positions and forms, as well as by their behavior when
deprived of light. This light relation suggests the answer
to very many questions concerning leaves. It is not very
important to know the names of different forms and differ-
ent arrangements of leaves, but it is important to observe
that these forms and arrangements are in response to the
light relation.

In general a leaf adjusts its own position and its relation
to its fellows so as to receive the greatest amount of light.
Upon erect stems the leaves occur in vertical rows which
are uniformly spaced about the circumference. If these
rows are numerous the leaves are narrow ; if they are few
the leaves are usually broad. If broad leaves were associ-
ated with numerous rows there would be excessive shading ;

312 PLANT STKUCTURES

if narrow leaves were associated with few rows there would
be waste of space.

It is very common to observe the lower leaves of a stem
long-petioled, those above short-petioled, and so on until
the uppermost have sessile blades, thus thrusting the blades
of lower leaves beyond the shadow of the upper leaves.
There may also be a gradual change in the size and direc-
tion of the leaves, the lower ones being relatively large and
horizontal, and the upper ones gradually smaller and more
directed upward. In the case of branched (compound)
leaves the reduction in the size of the upper leaves is not
so necessary, as the light strikes between the upper leaflets
and reaches those below.

On stems exposed to light only or chiefly on one side,
the leaf blades are thrown to the lighted side in a variety
of ways. In ivies, many prostrate stems, horizontal branches
of trees, etc., the leaves brought to the lighted side are
observed to form regular mosaics, each leaf interfering
with its neighbor as little as possible.

There is often need of protection against too intense
light, against chill, against rain, etc., which is provided
for in a great variety of ways. Coverings of hairs or scales,
the profile position, the temporary shifting of position,
rolling up or folding, reduction in size, etc., are some of
the common methods of protection.

175. Shoots. — The stem is an organ which is mostly
related to the leaves it bears, the stem with its leaves being
the shoot. In the foliage-bearing stems the leaves must be
displayed to the light and air. Such stems may be sub-
terranean, prostrate, floating, climbing, or erect, and all of
these positions have their advantages and disadvantages,
the erect type being the most favorable for foliage display.

In stems which bear scale leaves no light relation is
necessary, so that such shoots may be and often are sub-
terranean, and the leaves may overlap, as in scaly buds
and bulbs. The subterranean position is very favorable

PLANT ECOLOGY 313

for food storage, and such shoots often become modified as
food depositories, as in bulbs, tubers, rootstocks, etc. In
the scaly buds the structure is used for protection rather
than storage.

The stem bearing floral leaves is the shoot ordinarily
called "the flower," whose structure and work have been
sufficiently described. Its adjustments have in view polli-
nation and seed dispersal, two very great ecological sub-
jects full of interesting details.

176. Roots. — Eoots are absorbent organs or holdfasts or
both, and they enter into a variety of relations. Most
common is the soil relation, and the energetic way in
which such roots penetrate the soil, and search in every
direction for water and absorb it, proves them to be highly
organized members. Then there are roots related to free
water, and others to air, each with its appropriate struc-
ture. More mechanical are the clinging roots (ivies, etc.),
and prop roots (screw pines, banyans, etc.), but their adap-
tation to the peculiar service they render is none the less
interesting.

The above statements concerning leaves, shoots, and
roots should be applied with necessary modifications to the
lower plants which do not produce such organs. The
light relation and its demands are no less real among the
Algae than among Spermatophytes, as well as relations to
air, soil, water, mechanical support, etc.

PLANT SOCIETIES

177. Introductory. — Plants are not scattered at hap-
hazard over the surface of the earth, but are organized
into definite communities. These communities are deter-
mined by the conditions of living — conditions which admit
some plants and forbid others. Such an association of
plants living together in similar conditions is a plant so-
ciety. Closely related plants do not usually live together

314 PLANT STRUCTURES

iu the same society, as their rivalry is too intense ; but
each society is usually made up of unrelated plants which
can make use of the same conditions.

There are numerous factors which combine to deter-
mine societies, and it is known as yet only in a vague way
how they operate.

178. Ecological factors. — Water.— This is a very impor-
tant factor in the organization of societies, which are usu-
ally local associations. Taking plants altogether, the
amount of water to which they are exposed varies from
complete submergence to perpetual drought, but within
this range plants vary widely as to the amount of water
necessary for living.

Heat. — In considering the general distribution of plants
over the surface of the earth, great zones of plants are out-
lined by zones of temperature ; but in the organization of
local societies in any given area the temperature condi-
tions are nearly uniform. Usually plants work only at
temperatures between 32° and 122° Fahr., but for each
plant there is its own range of temperature, sometimes
extensive, sometimes restricted. Even in plant societies,
however, the effect of the heat factor may be noted in the
succession of plants through the working season, spring
plants being very different from summer and autumn
plants.

Soil. — The great importance of this factor is evident,
even in water plants, for the soil of the drainage area deter-
mines the materials carried by the water. Soil is to be
considered both as to its chemical composition and its
physical properties, the latter chiefly in reference to its
disposition toward water. Soils vary greatly in the power
of receiving and retaining water, sand having a high recep-
tive and low retentive power, and clay just the reverse,
and these factors have large effect upon vegetation.

Light. — All green plants can not receive the same amount
of light. Hence some of them have learned to live with a

PLANT ECOLOGY

less amount than others, and are " shade plants " as dis-
tinct from " light plants." In forests and thickets many
of these shade plants are to be seen, which would find an
exposed situation hard to endure. In almost every society,
therefore, plants are arranged in strata, dependent upon
the amount of light they receive, and the number of these
strata and the plants characterizing each stratum are im-
portant factors to note.

Wind. — This is an important factor in regions where
there are strong prevailing winds. Wind has a drying
effect and increases the transpiration of plants, tending to
impoverish them in water. In such conditions only those
plants can live which are well adapted to regulate tran-
spiration.

The above five factors are among the most important,
but no single factor determines a society. As each factor
has a large possible range, the combinations of factors may
be very numerous, and it is these combinations which de-
termine societies. For convenience, however, societies are
usually grouped on the basis of the water factor, at least
three great groups being recognized.

179. Hydrophyte societies.— These are societies of water
plants, the water factor being so conspicuous that the
plants are either submerged or standing in water. A plant
completely exposed to water, submerged, or floating, may
be taken to illustrate the usual adaptations. The epi-
dermal walls are thin, so that water may be absorbed
through the whole surface ; hence the root system is very
commonly reduced or even wanting ; and hence the water-
conducting tissues (xylem) are feebly developed. The tis-
sues for mechanical support (stereome) are feebly devel-
oped, the plant being sustained by the buoyant power of
water. Such a plant, although maintaining its form in
water, collapses upon removal. Very common also is the
development of conspicuous air passages for internal aera-
tion and for increasing buoyancy ; and sometimes a special

316 PLANT STRUCTURES

buoyancy is provided for by the development of bladder-
like floats.

Conspicuous among hydrophyte societies may be men-
tioned the following : (1) Free-swimming societies, in which
the plants are entirely sustained by water, and are free to
move either by locomotion or by water currents. Here
belong the " plankton societies," consisting of minute
plants and animals invisible to the naked eye, conspicuous
among the plants being the diatoms ; also the " pond so-
cieties," composed of algae, duckweeds, etc., which float in
stagnant or slow-moving waters.

(2) Pondweed societies, in which the plants are an-
chored, but their bodies are submerged or floating. Here
belong the " rock societies," consisting of plants anchored
to some firm support under water, the most conspicuous
forms being the numerous fresh-water and marine algae,
among which there are often elaborate systems of holdfasts
and floats. The "loose-soil societies" are distinguished
by imbedding their roots or root-like processes in the mucky
soil of the bottom (Figs. 281, 2S2). The water lilies with
their broad floating leaves, the pondweeds or pickerel weeds
with their narrow submerged leaves, are conspicuous illus-
trations, associated with which are algae, mosses, water
ferns, etc.

(3) Swamp societies, in which the plants are rooted in
water, or in soil rich in water, but the leaf-bearing stems
rise above the surface. The conspicuous swamp societies
are "reed swamps," characterized by bulrushes, cat-tails
and reed-grasses (Figs. 283, 284), tall wand-like Monocoty-
ledons, usually forming a fringe about the shallow margins
of small lakes and ponds; " swamp-moors," the ordinary
swamps, marshes, bogs, etc., and dominated by coarse
sedges and grasses (Fig. 282) ; " swamp-thickets," consist-
ing of willows, alders, birches, etc. ; " sphagnum-moors," in
which sphagnummoss predominates, and is accompanied by
numerous peculiar orchids, heaths, carnivorous plants, etc. ;

PLANT ECOLOGY

319

"swamp-forests," which are largely coniferous, tamarack
(larch), pine, hemlock, etc., prevailing.

180. Xerophyte societies. — These societies are exposed to
the other extreme of the water factor, and are composed
of plants adapted to dry air and soil. To meet these

320

PLANT STRUCTURES

drought conditions numerous adaptations have been de-
veloped and are very characteristic of xerophytic plants.
Some of the conspicuous adaptations are as follows : peri-

odic reduction of surface, annuals bridging over a period
of drought in the form of seeds, geophilous plants also dis-
appearing from the surface and persisting in subterranean

324 PLANT STRUCTURES

parts, deciduous trees and shrubs dropping their leaves,
etc. ; temporary reduction of surface, the leaves rolling up
or folding together in various ways ; profile position, the
leaves standing edgewise and not exposing their flat sur-
faces to the most intense light ; motile leaves which can
shift their position to suit their needs ; small leaves, a very
characteristic feature of xerophytic plants ; coverings of
hair ; dwarf growth ; anatomical adaptations, such as
cuticle, palisade tissue, etc. Probably the most conspicu-
ous adaptation, however, is the organization of "water-
reservoirs," which collect and retain the scanty water sup-
ply, doling it out as the plant needs it.

Some of the prominent societies are as follows : "rock-
societies " composed of plants living upon exposed rock sur-
faces, walls, fences, etc., notably lichens and mosses ;
"sand societies," including beaches, dunes, and sandy
fields ; " shrubby heaths," characterized by heath plants ;
"plains," the great areas of dry air and wind developed in
the interiors of continents; "cactus deserts," still more
arid areas of the Mexican region, where the cactus, agave,
yucca, etc., have learned to live by means of the most ex-
treme xerophytic modifications ; " tropical deserts," where
xerophytic conditions reach their extreme in the combina-
tion of maximum heat and minimum water ; " xerophyte
thickets," the most impenetrable of all thicket-growths,
represented by the " chaparral " of the Southwest, and the
"bush" and "scrub" of Africa and Australia; "xero-
phyte forests," also notably coniferous. (See Figs. 285,
286, 287.)

181. Mesophyte societies. — Mesophytes make up the com-
mon vegetation, the conditions of moisture being medium,
and the soil fertile. This is the normal plant condition,
and is the arable condition — that is, best adapted for the
plants which man seeks to cultivate. If a hydrophytic
area is to be cultivated, it is drained and made mesophytic ;
if a xerophytic area is to be cultivated, it is irrigated and

PLANT ECOLOGY 327

made mesopliytic. As contrasted with hydrophyte and xero-
phyte societies, the mesophyte societies are far richer in
leaf forms and in general luxuriance. The artificial soci-
eties which have been formed under the influence of man,
through the introduction of weeds and culture plants, are
all mesophytic.

Among the mesophyte grass and herb societies are the
'•arctic and alpine carpets," so characteristic of high lati-
tudes and altitudes where the conditions forbid trees, shrubs,
or even tall herbs ; " meadows," areas dominated by grasses,
the prairies being the greatest meadows, where grasses and
flowering herbs are richly displayed ; " pastures," drier and
more open than meadows.

Among the woody mesophyte societies are the " thick-
ets," composed of willow, alder, birch, hazel, etc., either
pure or forming a jungle of mixed shrubs, brambles, and
tall herbs ; " deciduous forests," the glory of the temperate
regions, rich in forms and foliage display, with annual fall
of leaves, and exhibiting the remarkable and conspicuous
phenomenon of autumnal coloration ; " rainy tropical for-
ests," in the region of trade winds, heavy rainfalls, and
great heat, where the world's vegetation reaches its climax,
and where in a saturated atmosphere gigantic jungles are
developed, composed of trees of various heights, shrubs of
all sizes, tall and low herbs, all bound together in an inex-
tricable tangle by great vines or lianas, and covered by a
luxuriant growth of numerous epiphytes. (See Figs. 288,
289.)

GLOSSARY

[The definitions of a glossary are often unsatisfactory. It is much better to con-
sult the fuller explanations of the text by means of the index. The following glos-
sary includes only frequently recurring technical terms. Those which are found only
in reasonably close association with their explanation are omitted. The number fol-
lowing each definition refers to the page where the term will be found most fully
defined.]

ACTINOMORPHIC : applied to a flower in which the parts in each set are

similar; regular. 228.

A KENE : a one-seeded fruit which ripens dry and seed-like. 212.
ALTERNATION OF GENERATIONS : the alternation of gametophyte and

sporophyte in a life history. 94.
AXEMOPHILOUS : applied to flowers or plants which use the wind as agent

of pollination. 181.
AN*SOCARPIC : applied to a flower whose carpels are fewer than the other

floral organs. 268.

ANTHER : the sporangium-bearing part of a stamen. 197.
ANTHERIDIUM : the male organ, producing sperms. 16.
ANTIPODAL CELLS : in Angiosperms the cells of the female gametophyte

at the opposite end of the embryo-sac from the egg-apparatus.

205.

APETALOUS : applied to a flower with no petals. 221.
ApocAKi'ors: applied to a flower whose carpels are free from one an-
other. 226.
ARCHEGONIUM : the femnle, egg-producing organ of Bryophytes. Pteri-

dophytes, and Gymnosperms. 100.
ABCHESPOEIDM : the first cell or group of cells in the spore-producing

series. 102.

Asi OCARP: a special case containing asci. 58.
ASCOSI'ORE : a spore formed within an ascus. 59.
Asrrs: a delicate sac (mother-cell) within which ascospores develop.

59.
ASEXUAL SPORE : one produced usually by cell-division, at least not by

cell-union. 9.

329

330 GLOSSARY

CALYX : the outer set of floral leaves. 221.

CAPSULE : in Bryophytes the spore-vessel ; in Angiosperms a dry fruit

which opens to discharge its seeds. 98, 211.
CARPEL : the megasporophyll of Spermatophytes. 178.
CHLOROPHYLL : the green coloring matter of plants. 5.
CHLOROPLAST : the protoplasmic body within the cell which is stained

green by chlorophyll. 7.
COLUMELLA : in Bryophytes the sterile tissue of the sporogonium which

is surrounded by the sporogenous tissue. 106.
CONIDIUM : an asexual spore formed by cutting off the tip of the sporo-

phore, or by the division of hyphae. 58.
CONJUGATION : the union of similar gametes. 15.
COROLLA : the inner set of floral leaves. 221.

COTYLEDON : the first leaf developed by an embryo sporophyte. 138.
CYCLIC : applied to an arrangement of leaves or floral parts in which

two or more appear upon the axis at the same level, forming a cycle,

or whorl, or verticil. 159.

DEHISCENCE : the opening of an organ to discharge its contents, as in
sporangia, pollen-sacs, capsules, etc. 199.

DICHOTOMOUS : applied to a style of branching in which the tip of the
axis forks. 35.

DKECIOUS : applied to plants in which the two sex-organs are upon dif-
ferent individuals. 115.

DORSIVENTRAL : applied to a body whose two surfaces are differently
exposed, as an ordinary thallus or leaf. 109.

EGG : the female gamete. 16.

EGG-APPARATUS : in Angiosperms the group of three cells in the embryo-
sac composed of the egg and the two synergids. 204.
ELATER : in Liverworts a spore-mother-cell peculiarly modified to aid

in scattering the spores. 103.
EMBRYO : a plant in the earliest stages of its development from the

spore. 137.
EMBRYO-SAC : the megaspore of Spermatophytes. which later contains

the embryo. 178.
ENDOSPERM : the nourishing tissue developed within the embryo-sac, and

thought to represent the female gametophyte. 180.
ENDOSPERM NUCLEUS : the nucleus of the embryo-sac which gives rise to

the endosperm. 205.
ENTOMOPHILOUS : applied to flowers or plants which use insects as agents

of pollination. 196.

GLOSSARY 331

EPIGYNOUS : applied to a flower whose outer parts appear to arise from

the top of the ovary. 225.
EUSPORANGIATE : applied to those Pteridophytes and Spermatophytes

whose sporangia develop from a group of epidermal and deeper

cells. 157.

FAMILY : a group of related plants, usually comprising several genera,

236.

FERTILIZATION : the union of sperm and egg. 16.
FILAMENT : the stalk-like part of a stamen. 197.
FISSION : cell - division which includes the wall of the old cell.

10.
FOOT : in Bryophytes the part of the sporogonium imbedded in the

gametophore ; in Pteridophytes an organ of the sporophyte embryo

to absorb from the gametophyte. 98, 138.

GAMETANGIUM : the organ within which gametes are produced. 11.

GAMETE : a sexual cell, which by union with another produces a sexual
spore. 10.

GAMETOPHORE : a special branch which bears sex organs. 98.

GAMETOPHYTE : in alternation of generations, the generation which bears
the sex organs. 97.

GENERATIVE CELL : in Spermatophytes the cell of the male gameto-
phyte (within the pollen grain) which gives rise to the male
cells. 180.

GENUS : a group of very closely related plants, usually comprising sev-
eral species. 237.

HAUSTORIUM : a special organ of a parasite (usually a fungus) for ab-
sorption. 50.

PIETEROGAMOUS : applied to plants whose pairing gametes are un-
like. 15.

HETEROSPOROUS : applied to those higher plants whose sporophyte pro-
duces two forms of asexual spores. 151.

HOMOSPOROUS : applied to those plants whose sporophyte produces simi-
lar asexual spores. 151.

HOST : a plant or animal attacked by a parasite. 48.

HYPHA : an individual filament of a mycelium. 49.

HYPOCOTYL : the axis of the embryo sporophyte between the root-tip and
the cotyledons. 209.

HYPOGYNOUS : applied to a flower whose outer parts arise from beneath
the ovary. 224.

332 GLOSSARY

INDUSIUM : in Ferns a flap-like membrane protecting a sorus. 143.

INFLORESCENCE : a flower-cluster. 230.

INSERTION : the point of origin of an organ. 224.

INTEGUMENT : in Spermatophytes a membrane investing the nucellus.

178.
INVOLUCRE : a cycle or rosette of bracts beneath a flower-cluster, as iu

Umbellifers and Composites. ~7~>.
ISOCARPIC : applied to a flower whose carpels equal in number the other

floral organs. 268.
ISOGAMOUS : applied to plants whose pairing gametes are similar. 15.

LEPTOSPORANGIATE : applied to those Ferns whose sporangia develop
from a single epidermal cell. 157.

MALE CELL : in Sperm atophytes the fertilizing cell conducted by the

pollen-tube to the egg. 180.

MEGASPORANGIUM : a sporangium which produces only megaspores. 152.
MEGASPORE : in heterosporous plants the large spore which produces a

female gametophyte. 152.
MEGASPOROPHYLL : a sporophyll which produces only megasporangia.

152.
MESOPHYLL : the tissue of a leaf between the two epidermal layers which

usually contains chloroplasts. 141.
MICROSPORANGIUM : a sporangium which produces only microspores.

152.
MICROSPORE : in heterosporous plants the small spore which produces a

male gametophyte. 152.
MICROSPOROPHYLL : a sporophyll which produces only microsporangia.

152.
MICROPYLE: the passageway to the nucellus left by the integument.

178.
MONCECIOUS : applied to plants in which the two sex organs are upon

the same individual. 115.
MONOPODIAL : applied to a style of branching in which the branches

arise from the side of the axis. 35.

MOTHER CELL : usually a cell which produces new cells by internal divi-
sion. 9.
MYCELIUM : the mat of filaments which composes the working body of

a fungus. 49.

NAKED FLOWER : one with no floral leaves. 222.
NUCELLUS : the main bodv of the ovule. 178.

GLOSSARY 333

OOGONIUM : the female, egg-producing organ of Thallophytes. 16.

OOSPHERE : the female gamete, or egg. 16.

OOSPORE : the sexual spore resulting from fertilization. 16.

OVARY : in Angiosperms the bulbous part of the pistil, which contains

the ovules. 199.
OvrLE : the megasporangium of Spermatophytes. 178.

PAPPUS : the modified calyx of the Composites. 278.

PARASITE : a plant which obtains food by attacking living plants or ani-
mals. 48.

PENTACYCLIC : applied to a flower whose four floral organs are in five
cycles, the stamens being in two cycles. 268.

PERIANTH : the set of floral leaves when not differentiated into calyx
and corolla. 221.

PERIGYNOUS : applied to a flower whose outer parts arise from a cup
surrounding the ovary. 225.

PETAL : one of the floral leaves which make up the corolla. 221.

PHOTOSYNTHESIS : the process by which chloroplasts, aided by light,
manufacture carbohydrates from carbon dioxide and water. 84.

PISTIL : the central organ of the flower, composed of one or more car-
pels. 200.

PISTILLATE : applied to flowers with carpels but no stamens. 218.

POLLEN : the microspores of Spermatophytes. 174.

POLLEN-TUBE : the tube developed from .the wall of the pollen grain
which penetrates to the egg and conducts the male cells. 180.

POLLINATION : the transfer of pollen from anther to ovule (in Gymno-
sperms) or stigma (in Angiosperms). 181.

POLYPETALOUS : applied to flowers whose petals are free from one an-
other. 227.

PROTHALLIUM : the gametophyte of Ferns. 130.

PROTONEMA : the thallus portion of the gametophyte of Mosses. 98.

RADIAL : applied to a body with uniform exposure of surface, and pro-
ducing similar organs about a common center. 120.

RECEPTACLE : in Angiosperms that part of the stem which is more or
less modified to support the parts of the flower. 222.

RHIZOID : a hair-like process developed by the lower plants and by inde-
pendent gametophytes to act as a holdfast or absorbing organ, or
both. 109.

SAPROPHYTE : a plant which obtains food from the dead bodies or body
products of plants or animals. 48.

334 GLOSSARY

SCALE : a leaf without chlorophyll, and usually reduced in size.
161.

SEPAL : one of the floral leaves which make up the calyx. 221.

SETA : in Bryophytes the stalk-like portion of the sporogonium. 98.

SEXUAL SPORE : one produced by the union of gametes. 10.

SPECIES : plants so nearly alike that they all might have come from a
single parent. 237.

SPERM : the male gamete. 16.

SPIRAL : applied to an arrangement of leaves or floral parts in which
no two appear upon the axis at the same level ; often called alter-
nate. 193.

SPORANGIUM : the organ within which asexual spores are produced (ex-
cept in Bryophytes). 10.

SPORE : a cell set apart for reproduction. 9.

SPOROGONIUM : the leafless sporophyte of Bryophytes. 98.

SPOROPHORE : a special branch bearing asexual spores. 49.

SPOROPHYLL : a leaf set apart to produce sporangia. 145.

SPOROPHYTE : in alternation of generations, the generation which pro-
duces the asexual spores. 97.

STAMEN : the microsporophyll of Spermatophytes. 174.

STAMINATE : applied to a flower with stamens but no carpels. 218.

STIGMA : in Angiosperms that portion of the carpel (usually of the style)
prepared to receive pollen. 199.

STOMA (pi. STOMATA) : an epidermal organ for regulating the communi-
cation between green tissue and the air. 141.

STROBILUS : a cone-like cluster of sporophylls. 161.

STYLE : the stalk-like prolongation from the ovary which bears the
stigma. 199.

SUSPENSOR : in heterosporous plants an organ of the sporophyte embryo
which places it in a more favorable position in reference to food
supply. 168.

SYMBIONT: an organism which enters into the condition of symbio-
sis. 79.

SYMBIOSIS : usually applied to the condition in which two different
organisms live together in intimate and mutually helpful rela-
tions. 79.

SYMPETALOUS : applied to a flower whose petals have coalesced.
227.

SYNCARPOUS : applied to a flower whose carpels have coalesced.
226.

SYNERGID : in Angiosperms one of the pair of cells associated with the
egg to form the egg-apparatus. 204.

GLOSSARY 335

TESTA : the hard coat of the seed. 184.

TETRACYCLIC : applied to a flower whose four floral organs are in four

cycles. 268.
TETRAD : a group of four spores produced by a mother-cell. 103.

ZOOSPORE : a motile asexual spore. 10.

ZYGOMORPHIC : applied to a flower in which the parts in one or more

sets are not similar ; irregular. 229.
ZYGOTE : the sexual spore resulting from conjugation. 15.

INDEX

[The italicized numbers indicate that, the subject is illustrated upon the page cited.
In such case the subject may be referred to only in the illustration, or it may bn
referred to also in the text.]

Absorption, 299.
Acacia, 265.
Aconitum, 261.
Acorus, 219. 243.
Actinomorphy, 228.
Adder's tongue : see Ophioglossmn.
Adiantum, 143, 145.
^Ecidiomycetes, 50, 62.
yEcidiospore, 66.
^Ecldium, 66.
Agaricus, 68, 69.
Agave, 247.
Air pore : see Stoma.
Akene, 212, 213. 814, 276, 177.
Alchemilla, 225.
Alder : see Alnus.
Algae, 4, 5, 17.
Alisma, 210, 240.
Almond : see Prunus.
Alnus. 257.

Alternation of generations, 94, 129.
Amanita, 70.
Amaryllidaceae, 247.
Amaryllis family: see Amarylli-
daceae.

Ambrosia, 279.
Ament, 257.
Anaptychiii. Hi. ,s' .'.

Anemophilous, 181.
Angiosperms, 173, 195, 217.
Anisocarpae, 268.
Annulus, 136, 146, 150.
Anther, 106, 197, 199.
Antheridium, 16, 99, 100, 11J, 121.

i,:.;. 134. 161, 166.
Antherozoid, 16.

Anthoceros, 104, 105, 111. 116. 118
Anthophytes, 172.
Antipodal cells, 202, 205, 208.
Antirrhinum, 228, 275.
Ant-plants, 90. 91.
Apical cell, 134.
Apical group. -'$.:.
Apium, 267.
Apocarpy, 199. 222, 225.
Apocynaceae. 271.
Apocynum, 272.
Apogamy, 131.
Apospory, 132.
Apothecium, 79, 81. $ .'.
Apple : see Pirus.
Aquilegia, 198.
Araceae, 243.
Araliaceae, 267.
Araucaria, 190.
Arbor vitae: see Thuja.
Arbutus, 198 : see Epigjea.
Archegoniates, 101.
337

338

INDEX

Archegonium, 99, 100, US, 114, 133,

135, 161, 167, 179.
Archesporiuin, 102, 104, 105, 146.
Archichlamydeae, 255.
Arctostaphylos, 269.
Areolae, 111, 114.
Arisasma, 243, 244.
Arnica, 275, 276, 278.
Aroids, 243.
Artemisia, 279.
Arum, 245.
Ascocarp, 58, 59.
Ascomycetes, 50, 57.
Ascospore, 59.
Ascus, 59.
Asexual spore, 9.
Aspidium, 130, 136, 144.
Assimilation, 302.
Aster, 279.
Astragalus, 265.
Atherosperma, 198.
Azalea, 270.

Bacillus, 76.

Bacteria, 21, 75. 76.

Balm : see Melissa.

Banana, 140.

Bark, 284, 289.

Basidiomycetes, 50, 68.

Basidiospore, 69, 72.

Basidium, 69, 71.

Bean : see Phaseolus.

Bearberry : see Arctostaphylos.

Beech, 256.

Bellis, 279.

Berberis, 198.

Bidens, 278.

Beggar-ticks, 213.

Bignonia, 211.

Birch, 256.

Blackberry : see Rubus.

Black knot, 60.
Black mould, 52.
Blasia, 116.

Blueberry : see Vaccinium.
Blue-green algae, 6, 17.
Blue mould, 60.
Boletus, 73, 74.
Botrychium, 145, 149.
Botrydium, 28.
Box elder, 234.
Bracket fungus, 72.
Brake : see Pteris.
Brassica, 2 61.
Bryophytes, 2, 93, 172.
Brown algae, 6, 32.
Bryum, 120, 124.
Buckeye, 235.
Butomus, 199.

Buttercup : see Ranunculus.
Buttercup family : see Ranuncu-
laceae.

Cabbage : see Brassica.

Calamus : see Acorus.

Calla-lily, 243.

Callithamnion, 43.

Callophyllis, 39.

Calluna, 270.

Calopogon, 249.

Caltha, 260.

Calycanthus, 226, 261.

Calypso, 249.

Calyptra, 102, 125.

Calyptrogen, 293.

Calyx, 220, 221.

Cambium, 285, 287, 288.

Capsella, 209, 293.

Capsule, 98, 123, 125, 126, 211,

Caraway : see Carum.

Carbohydrate, 302.

Carbon dioxide, 83.

INDEX

339

Carnivorous plants, 92.

Carpel, 111, 178, 199, 219, 220.

Carpinus, 217, 258.

Carpospore, 44i 45.

Carrot : see Daucus.

Carum, 267.

Cassia, 265.

Cassiope, 269.

Castilleia, 275.

Catkin, 257.

Catnip : see Nepeta.

Cat-tail: see Typha.

Cattleya, 254.

Caulicle, 209.

Cauline, 166.

Cedar apple, 67, 68.

Celery : see Apium.

Cell, 6, 7.

Cellulose, 7.

Cercis, 265.

Chalazogamy, 258, 259.

Characeae, 46.

Chemotropism, 307.

Cherry : see Prunus.

Chestnut, 256.

Chlorophyceae, 6, 21.

Chlorophyll, 5, 83.

Chloroplast, 7, 8.

Chrysanthemum, 279.

Cilia, 10.

Circinate, 136, 143.

Cladophora, 25.

Clavaria, 13.

Climbing fern : see Lygodium.

Closed bundle, 290.

Clover : see Trifolium.

Club mosses, 162.

Cnicus, 278.

Cocklebur : see Xanthium.

Ccenocyte, 27.

Coleochaete, 106. 101.

Collateral bundle, 287.

Collenchyma, 284.

Columella, 104, 105, 106, 126.

Compass plant : see Silphium.

Composite, 275.

Composites, 275, 216, 211, 218.

Concentric bundle, 292.

Conferva forms, 22.

Conidia, 58, 60.

Conifers, 191, 282.

Conium, 261.

Conjugate forms, 31.

Conjugation, 15.

Connective, 196.

Conocephalus, 111.

Convolvulaceae, 271.

Convolvulus forms, 270.

Convolvulus, 273.

Coprinus, 70.

Coral fungus, 13, 74.

Coreopsis, 278.

Coriandrum, 267.

Cork, 284.

Corn, 216, 282, 290.

Cornacese, 267.

Corolla, 220, 221.

Cortex, 283, 284, 288.

Cotton, 206.

Cotyledon, 137, 138, 168, 184, $09,

210, 216, 211.

Cranberry: see Vaccinium.
Cratsegus, 262.
Crocus, 249.
Crucifer, 262.
Cruciferae, 262.
Cryptogams, 172.
Cunila, 274.
Cup fungus, 60, 61.
Cupule, 112, 114.
Cyanophyceae, 6, 17.
Cycads, 185, 186, 181, 189.
Cyclic, 159, 193.
Cyperaceae, 241.

340

INDEX

Cypripedium, 249, 253.
Cystocarp, 43, 44.
Cystopteris, 78, 144.
Cytoplasm, 7.

Daisy: see Bellis.

Dandelion : see Taraxacum.

Dasya, 40.

Datura, 197.

Daucus, 266, 267.

Dead-nettle, 228.

Definitive nucleus : see Endosperm

nucleus.

Dehiscence, l'J8, 1!M).
Delphinium, 260, 261.
Dermatogen, 283.
Desmids, 31, 32.
Desmodium, 308.
Diatoms, 45.
Dichotomous, 35.
Dicotyledons, 208, 233, 254, 282.
Differentiation, 3, 280.
Dogbane: see Apocynum.
Dog-tooth violet : see Erythronium.
Dogwood family : see Cornacea\
Dorsiventral. 109.
Downy mildew, 55.
Drupe, 264.
Digestion, 302.
Dioecious, 115.
Disk, 276, 277.
Dodder, 86.

Ear-fungus, 74.
Easter lily, 221.
Ecology, 297, 311.
Economic botany, 297.
Ectocarpus, 33.
Edogonium, 22, £8.
Egg, 16. 202, 204, 205, 206.

Egg-apparatus, 204, 205, 206.

Elater, 103, 113, 118.

Elm : see Ulmus.

Embryo, 137, 167, 168, 170, 183, 207,

208, 209, 210, 211.
Embryo-sac, 178, 179, 201, 203, 208.
Endosperm, 179, 180, 207, 208, 211.
Endosperm nucleus, 202, 205.
Entomophilous, 196.
Epidermis, 141, 142, 191, 283, 284,

295.

Epigaaa, 269.
Epigyny, 224, MS.
Epilobium, 212.
Epiphyte, 157.
Equisetales, 159.
Equisetum, 159, 160, 161.
Ergot, 60. 61.
Erica, 270.
Ericaceae. 268.
Erigenia, 267.
Erythronium. 250.
Eusporangiate. 157.
Evolution, 3.

Fennel : see Foeniculum.

Ferns, 155, 156.

Fertilization, 16, 181, 206, 207.

Festuca, 2jQ.

Figwort family: see Scrophula-

riaceae.

Filament, 8. 196, 197.
Filicales, 155.
Fireweed : see Epilobium.
Fission. 10.
Flax : see Linum.
Floral leaves. 218.
Florideae, 38.
Flower, 218.
Flowering plants, 172.
Fcenk-ulum, 267.

INDEX

341

Foliar, 166.

Food, 83, 299.

Foot, 98, 102, 137, 138, 168.

Fragaria, 214, 227, 262.

Fruit, 211, 21$, 213, 214,215.

Fucus, 35, 37.

Funaria, 99, 102, 121, 124, 125, 126.

Fungi, 4, 48.

Gametangiura, 11.

Gamete, 10, 12.

Gametophore, 98, 112, 120, 124.

Gametophyte, 97, 107, 132, 134, 161,

166, 167, 176, 179, 180, 201, 203,

204, 205.
Gaultheria, 270.
Gaylussacia, 269.
Gemma, 112, 114.
Generative cell, 180, 201.
Gentianaceae, 271.
Geophilous, 246.
Geotropism, 305.
Gerardia, 275.
Germination, 187, 214.
Gigartina, 38.
Gills, 71.
Ginkgo, 191.
Gladiolus, 249, 251.
Gleditschia, 236, 265.
Glceocapsa, 17, 18.
Glume, 241.

Goldenrod : see Solidago.
Gonatonema, 31.
Gramineae, 241.
Green algne, 6. 21.
Green plants, 83.
Green slimes, 20.
Grimmia, 126.
Growth movement, 304.
Growth ring, 234.
Grain, 241.

Grasses, 240.

Grass family : see Grarnineae.
Gymnosperms, 171, 173, 195.
Gymnosporangium, 67.

Habenaria, 249, 252.

Harebell, 228.

Haustoria, 50.

Hazel : see Carpinus.

Heart-wood, 289.

Heat, 314.

Heath family : see Ericaceae.

Heaths, 268, 269, 270.

Helianthus, 279, 285, 306.

Heliotropism, 305.

Hemiarcyria, 75.

Hemlock : see Conium.

Henbane : see Hyoscyamus.

Hepaticae, 109.

Heterocyst, 18.

Heterogamy, 15.

Heterospory, 151.

Hickory, 256.

Hippuris, 283.

Homospory, 151.

Honey locust : see Gleditschia.

Horehound : see Marrubium.

Hornbeam : see Carpinus.

Horsetail, 159.

Host, 48.

Huckleberry: see Gaylussacia.

Hydnum, 73, 74.

Hydra, 90.

Hydrophytes, 6, 315.

Hydrophytum, 91.

Hydrotropism, 307.

Hygroscopic movement, 304.

Hyoscyamus, 196.

Hypha, 49.

Hypocotyl, 184, 209, 216, 217.

342

INDEX

Hypodermis, 284.
Hypogyny, 224, 225.
Hyssopus, 274.

Indigo : see Indigofera.

Indigofera, 265.

Iiidusium, 136, 143, 144.

Inflorescence, 230.

Insects and flowers, 90.

Integument, 178, 179, 201, 202,

Involucre, 267, 275, 277.

Ipoinoea, 228, 270.

Iridaceae, 247.

Iris, 248, 251.

Iris family : see Iridaceae.

Irritable movement, 307. -

Isocarpa?, 268.

Isoetes, 169.

Isogamy, 15.

Japan lily, 21$.

Jungermannia, 105, 115, 116, 117.

Juniper, 194-

Kalmia, 270.

Labiatae, 272.

Labiates, 272.

Lactuca, 279.

Lam in aria. 33, 34-

Lamium, 274, 275.

Larch : see Larix.

Larix, 192.

Larkspur : see Delphinium.

Laurel : see Kalmia.

Lavandula, 275.

Leaf, 141. 142, 295, 296, 311.

Legumes, 250, 251, 264.

Leguminosa?, 264.

Lemna, 201.

Lepidozia, 117.

Leptosporangiate, 157.

Lettuce : see Lactuca.

Leucanthemum, 279.

Liatris, 278.

Lichens, 77, 78, 79, 87.

Life relations, 311.

Light, 314.

Ligule. 168.

Liliacea% 246.

Lilies, 245.

Lilium, 203, 204, 205, 207, 224, 249,

295.

Lily: see Lilium.
Lily family : see Liliaceae.
Linaria, '228, 275.
Linum, 220.
Liverworts, 109.
Loculus, 200.
Locust : see Robinia.
Lotus, 264.
Lupinus, 265.
Lycopersicum, 275.
Lycopodiales, 162.
Lycopodiurn, 162, 163.
Lygodium, 145.
Lyonia, 269.

Macrospore, 152.

Maidenhair fern : see Adiantum.

Male cell, 180, 181, 201, 206, 207.

Maple, 212.

Marasmius, 70.

Marchantia, 104, HO, 111, 112, 113,

114.

Marguerite: see Leucanthemum.
Marjoram : see Origanum.
Marrubium, 275.
Marsh marigold : see Caltha.

INDEX

343

Marsilia, 158.

Mega-sporangium, 152, 177, 179.
Megaspore, 152, 165, 167, 179, 201,

203.

Megasporophyll, 152, 165, 177, 199.
Melissa, 275.
Mentha, 229, 274.
Meristem, 281.

Mesophyll, 141, 142, 191, 295.
Mesophytes, 324.
Mestome, 282.

Micropyle, 178, 201, 202, 206.
Microspira, 76.
Microspha?ra, 58.
Microsporangium, 152, 176, 197.
Microspore, 152, 165, 166, 179, 197,

201.
Microsporophyll, 152, 165, 174,196,

198.

Midrib, 234.
Mildews, 57.
Mimosa, 265, 808, 309.
Mint : see Mentha.
Mint family : see Labiatas.
Monocotyledons, 208, 232, 236, 289.
Monoecious, 115.
Monopodial, 35.
Monotropa, 270.
Moon wort: see Botrychium.
Morels, 60, 62.

Morning-glory : see Ipomoea.
Morphology, 297.
Mosses, 93, 119, 124.
Mother cell, 9.
Mougeotia, 31.
Movement, 303.
Mucor, 49, 52, 53, 54, 55.
Mullein : see Verbascum.
Musci, 119.
Mushrooms, 68.

Mustard family : see Cruciferae.
Mycelium, 49.

Mycoinycetes, 50.
Mycorrhiza, 87, 88.
Myristica, 214.
Myrmecophytes, 90, 91.
Myxomycetes, 74, 75.

Naias, 237.
Narcissus, 247.
Nemalion, 43.
Nepeta, 275.
Nicotiana, 227, 275.
Nightshade family : see Solanacea?.
Nostoc, 18.

Nucellus, 178, 179, 201, 202, 203.
Nucleus, 7.
Nutation, 304.
Nutmeg, 214.
Nutrition, 3, 299.
Nyctitropic movement, 309.
Nymphaeaceae, 261.

Oak, 255, 256.

CEdogonium : see Edogonium.
Onoclea, 145, 147, 148.
Oogonium, 16.
Oosphere, 16.
Oospore, 16, 101.
Open bundle, 287.
Operculum, 122, 125.
Ophioglossum, 145, 149.
Orchidacea3, 249.
Orchids, 249, 252. 253, 254.
Orchid family : see Orchidacea?.
Origanum, 274.
Ornithogalum, 247.
Oscillaria, 19.
Osmunda, 145. 156.
Ostrich fern : see Onoclea.
Ovary, 199, 200, 202.
Ovule, 178, 179, 201, 203.

344

INDEX

Palisade tissue, 142, 295.

Palmaceae, 241.

Palm family : see Palmaceae.

Palms, 241, 242, 243.

Papaveraceae, 261.

Pappus, 276, 277, 278.

Parasites, 48, 85.

Parenchyma, 280, 281, 282, 288.

Parmelia, 79.

Parsley: see Petroselinum.

Parsley family : see Umbellifera3.

Parsnip : see Pastinaca.

Parthenogenesis, 52.

Pastinaca, 267.

Pathology, 297.

Pea : see Pisum.

Peach : see Prunus.

Peach curl, 60.

Pea family : see Leguminosae.

Pear : see Pirus.

Peat, 119.

Pellasa, 146.

Penicillium, 60.

Pentacycla?, 268.

Pentstemon, 275.

Peony, 220.

Pepper, 211, 258.

Pepper family : see PiperaceaB.

Perianth, 219, 220, 221.

Periblem, 288.

Perigyny, 225, 226.

Peristome, 126, 127.

Peronospora, 55, 56.

Petal, 220, 221.

Petiole, 141.

Petroselinura, 267.

Phaeophyceae, 6, 32.

Phanerogams, 172.

Phaseolus, 216, 265.

Phloem, 285, 287, 288, 290, 292, 29+

Phlox, 228, 271.

Photosyntax, 84.

Photosynthesis, 84, 302.

Phycomycetes, 50, 51.

Physcia, 79.

Physiology, 297.

Picea, 179, 181, 182.

Pileus, 71.

Pine : see Pin us.

Pineapple, 215.

Pinus, 173, 175, 176, 177, 178, 181,

183, 184, 188, 191, 286.
PiperaceaB, 258.
Pirus, 225, 262, 263.
Pistil, 199, 200, 219, 220.
Pisum, 265.
Pith, 285, 287, 288.
Planococcus, 76.
Plantaginaceae, 275.
Plant body, 6.
Plant societies, 313.
Plasmodium, 74, 75.
Plastid, 7, 8.
Platycerium, 182.
Plerome, 283.
Pleurococcus, 21.
Plum : see Prunus.
Plumule, 210.
Pod, 211, 212.
Pogonia, 249.
Polemoniaceae, 271.
Polemonium, 271.
Pollen, 174, 176, 197,201.
Pollen-tube, 179, 180, 181, 187, 202,

206. 207.
Pollination, 181.
Polyembryony, 183.
Polymorphism, 63.
Polypetaly, 226.
Polyporus, 71, 72.
Polysiphonia, 44-
Polytrichum, 96.

INDEX

345

Pome, 263.

Pondweeds, 237.

Poplars, 255.

Popowia, 198.

Poppy, 261.

Poppy family : see Papaveraceae.

Populus, 256.

Pore-fungus, 72.

Potamogeton, 237, 238.

Potato : see Solanuin.

Potentilla, 225, 262.

Proteid, 302.

Prothallium, 130, 132, 134.

Protococcus forms, 22.

Protonema, 95, 98.

Protoplasm, 7.

Prunus, 218, 262.

Pseudomonas, 76.

Pseudopodium, 105, 123, 124.

Pteridophytes, 2, 128, 172, 291.

Pteris, 133, 134, 135, 137, 141, 142,

143, 145, 281, 291, 292, 293.
Ptilota, 42.

Puccinia, 63, 64, 65, 66.
Puff-balls, 68, 74.
Pulvinus, 308.

Quillwort : see Isoetes.

Rabdonia, 41.
Radiate bundle, 294.
Radicle, 209.
Radish, 120.

Ragweed : see Ambrosia.
Ranunculaceae, 261.
Ranunculus, 222, 259.
Raspberry : see Rubus.
Rays, 275, 276.
Receptacle. 222,
Red algae, 6, 38.

Redbud : see Cercis.

Redwood : see Sequoia.

Reproduction, 3, 8, 309.

Respiration, 302.

Rheotropism, 307.

Rhizoid, 109, 110, 134.

Rhizophores, 164.

Rhododendron, 270, 271.

Rhodophyceae, 6, 38.

Riccia, 104, 110.

Ricciocarpus, 110.

Ricinus. 288.

Robinia, 265.

Root, 138, 217, 293, 294, 313.

Root-cap, 293.

Root-fungus, 87, 88.

Root-hairs, 217, 300.

Root-pressure, 300.

Root-tubercles, 89.

Rosaceae, 262.

Rose family : see Rosaceae.

Rosin- weed : see Silphium.

Rosmarinus, 275.

Royal fern : see Osmunda.

Rubus, 262.

Rumex, 284.

Rust, 62, 63, 64, 65, 66.

Sac-fungi, 57.
Sage : see Salvia.
Sage-brush : see Artemisia.
Sagittaria, 208, 338.
Salix, 219, 233, 256, 257.
Salvia, 275.
Salvinia, 158.
Saprolegnia, 51. 52.
Saprophyte, 48, 84.
Sap-wood, 289.
Sargassum. 35. 36.
Saururus, 219, 258.
Scales, 161.

346

INDEX

Scapania, 116.
Schizomycetes, 21.
Schizophytes, 21.
Sclerenchyma, 281, 282, 284, 285,

288, 290, 291.
Scouring rush, 159.
Scrophulariacea?, 275.
Scutellaria, 275.
Sedge family : see Cyperaceas.
Seed, 183, 184, 210, 811, 212, 214.
Selaginella, 162, 164. 165, 166, 168.
Sensitive fern : see Onoclea.
Sensitive-plant : see Acacia.
Sepal, 220, 221.
Sequoia, 189.
Seta, 98, 125.
Sex, 12.

Sexual spore, 10.
Shepherd's purse : see Capsella.
Shield fern : see Aspidium.
Shoot, 312.

Sieve vessels, 285, 286.
Silphium, 279.
Siphon forms, 27.
Siphonogams, 183.
Siphonogamy, 183.
Slime moulds, 74, 75.
Smut, 62.

Snapdragon : see Antirrhinum.
Soil, 314.
Solanaceae, 275.
Solanum, 198, 275.
Solidago, 279.
Solomon's seal, 233.
Sorus, 136, 143, 144.
Spadix, 244, 245.
Spathe, 244, 245.
Sperm, 16, 100, 133, 135, 162, 166,

169, 187, 190.
Spermatia, 43, 44.
Spermatophytes, 2, 171, 172.
Spermatozoid, 16.

Sperm mother cell, 100.

Sphagnum, 105, 106, 122, 123.

Spike, 240.

Spiraa, 262.

Spiral, 193.

Spirillum, 76.

Spirogyra, 28, 29, 30.

Spongy tissue, 142.

Sporangium, 10, 136, 143, 145, 150,

157, 163, 179.
Spore, 9.
Sporidium, 65.
Sporogenous tissue, 103.
Sporogonium, 98, 102, 104, 105, 106,

125, 126.

Sporophore, 49, 50.
Sporophyll, 145, 147, 148, 149, 174,

176.

Sporophyte, 97, 102, 137.
Spruce : see Picea.
Stability of form, 298.
Stamen, 174, 176, 196, 198, 219,

220.

Stele, 191, 283, 285.
Stem, 139, 282, 289, 291, 312.
Stemonitis, 75.
Stereome, 282, 299.
Sterile tissue, 103.
Sticta, 80.
Stigma, 199, 202.
Stomata, 141, 142, 191, 295, 301.
Strawberry: see Fragaria.
Strobilus, 160, 161, 163, 165, 174,

175, 176, 193, 194.
Style, 199, 202.
Substratum, 49.
Sumach, 235.

Sunflower : see Helianthus.
Suspensor, 167, 168, 183, 209,

210.

Symbiont, 79, 86.
Symbiosis, 79, 86.

INDEX

347

Sympetalae, 268.
Sym petaly, 226, 227.
Symplocarpus, 243.
Syncarpy, 199, 219, 225.
Synergid, 202, 204, 205, 206.

Tanacetum, 279.
Tansy: see Tanacetum.
Taraxacum, 213, 277, 278.
Taxonomy, 297.
Teleutospore, 64, 65.
Tension of tissues, 298.
Testa, 184, 211.
Tetracyclae, 268.
Tetrad, 103.
Tetraspore, 43.
Teucrium, 230, 274, 275.
Thallophytes, 2, 4, 172.
Thermotropism, 307.
Thistle : see Cnicus.
Thorn apple : see Datura.
Thuja, 193.
Thymus, 274.
Tickseed : see Coreopsis.
Tissues, 280.
Toad-flax : see Linaria.
Toadstools, 68.
Tobacco : see Nicotiana.
Tomato : see Lycopersicum.
Tracheae, 285, 286.
Tracheids, 286.
Transfer of water, 300.
Transpiration, 301.
Tree fern, 140.
Trichia, 75.
Trichogyne, 43, 44.
Trillium, 207, 246, 265.
Truffles, 60.
Turgid ity, 298.
Typha, 239, 240.

Umbel, 266, 267.
Umbelliferae, 266.
Umbellifers, 266.
Ulmus, 210, 256.
Ulothrix, 12, 13, 22.
Uredo, 64.
Uredospore, 63, 64.

Vaccinium, 269.

Vascular bundle, 232, 234, 287, 291.

Vascular cylinder, 234, 287.

Vascular system, 129, 139.

Vaucheria, 26, 27, 28.

Vegetative multiplication, 9.

Veins, 141, 142.

Venation, 233.

Verbascum, 275.

Verbenaceae, 275.

Vernation, 143.

Vernonia, 279.

Veronica, 275.

Vicia, 265.

Violet, 211, 229.

Wall cell, 180.

Walnut, 256.

Water, 83, 314.

Water ferns, 158.

Water-lily, 223, 261.

Water-lily family : see Nymphaea-

cese.

Water moulds, 51.
Wheat rust, 63, 64, 65, 66.
Willow : see Salix.
Wind, 315.
Wintergreen : see Gaultheria.

348

Wistaria, 265.
Witches'-broora, 60.
Wormwood : see Artemisia.

Xanthium, 279.

Xerophytes, 319.

Xylem, 285, 287, 288, 290,

INDEX

Yeast, 62.

Zannichellia, 237.
Zoospore, 10.
Zygomorphy, 228,
Zygospore, 15.
Zygote, 15.

THE END

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