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CHAPTER VIII

AN INDIVIDUAL PLANT IN ALL OF ITS RELATIONS

FOR the purpose of summarizing the general life-rela-
tions detailed in the preceding chapters, it will be useful to
apply them in the case of a single plant. Taking a com-
mon seed-plant as an illustration, and following its history
from the germination of the seed, certain general facts
become evident in its relations to the external world.

94. Germination of the seed. — The most obvious needs of
the seed for germination are certain amounts of moisture
and heat. In order to secure these to the best advantage,
the seed is usually very definitely related to the soil, either
upon it and covered by moisture and heat-retaining debris,
or embedded in it. Along with the demand for heat and
moisture is one for air (supplying oxygen), which is essen-
tial to life. The relation which germinating seeds need,
therefore, is one which not only secures moisture and heat
advantageously, but permits a free circulation of air.

95. Direction of the root. — The first part of the young
plantlet to emerge from the seed is the tip of the axis
which is to develop the root system. It at once appears to
be very sensitive to the earth influence (geotropism) and
to moisture influence (liydrotropism], for whatever the
direction of emergence from the seed, a curvature is devel-
oped which directs the tip towards and finally into the soil
(see Fig. 143). When the soil is penetrated the primary
root may continue to grow vigorously downward, showing
a strong geotropic tendency, and forming what is known
as the tap-root, from which lateral roots arise, which are

138

AN INDIVIDUAL PLANT IN ALL OF ITS KELATIONS 139

much more influenced in direction by other external
causes, especially the presence of moisture. As a rule,
the soil is not perfectly uniform, and contact with different
substances induces curvatures, and as a result of these and
other causes, the root system may become very intricate,
which is extremely favor-
able for absorbing and
gripping.

96. Direction of the stem.
— As soon as the stem tip
is extricated from the seed,
it exhibits sensitiveness to
the light influence (heliot-
ropism), being guided in
a general way towards the
light (see Fig. 1430).
Direction towards the
light, the source of the in-
fluence, is spoken of as
positive heliotropism, as
distinguished from direc-
tion away from the light,
called negative heliotro-
pism. If the main axis
continues to develop, it
continues to show this posi-
tive heliotropism strongly,
but the branches may show

every variation from positive to transverse heliotropism ;
that is, a direction transverse to the direction of the rays
of light. In some plants certain stems, as stolons, run-
ners, etc., show strong transverse heliotropism, while other
stems, as rootstocks, etc., show a strong transverse geot-
ropism.

97. Direction of foliage leaves. — The general direction of
foliage leaves on an erect stem is transversely heliotropic ;

FIG. 143. Germination of the seed of
arbor- vitae (Thuja). B shows the
emergence of the axis (r) which is to
develop the root, and its turning to-
wards the soil. C shows a later stage,
in which the root (r) has been some-
what developed, and the stem of the
embryo (ft) is developing a curve pre-
paratory to pulling out the seed leaves
(cotyledons). E shows the young plant-
let entirely free from the seed, with its
root (r) extending into the soil, its stem
(K) erect, and its first leaves (c) hori-
zontally spread.— After STRASBURGEK.

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TWENTIETH CENTURY TEXT-BOOKS

EDITED BY

A. F. NIGHTINGALE, PH. D.

SUPERINTENDENT OF HIGH SCHOOLS, CHICAGO

TWENTIETH CENTURY TEXT-BOOKS

PLANT STUDIES

AN ELEMENTARY BOTANY

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

HEAD OF DEPARTMENT OF BOTANY
UNIVERSITY OF CHICAGO

NEW YORK

D. APPLETON AND COMPANY
IQOI

PLANT RELATIONS
Copyright, 1899, by D. Appleton and Company

PLANT STRUCTURES
Copyright, 1899, by D. Appleton and Company

PREFACE

THIS book has been prepared in response to the earnest
solicitation of those schools in which there is not a suffi-
cient allotment of time to permit the development of plant
ecology and morphology, as outlined in Plant Relations and
Plant Structures; and yet which are desirous of imparting
instruction from both points of view. To meet this need —
a temporary one, it is to be hoped, for the study of botany
snould not be limited to one half year — portions of the two
books referred to have been selected and combined, and
together with some new matter have been organized into
this book, under the title Plant Studies.

The book falls naturally into two divisions, the first
fourteen chapters being dominated by Ecology, and repre-
senting the view point of Plant Relations. The remaining
eleven chapters are dominated by Morphology, and present
in much simpler form, especially in the higher groups, the
ideas of Plant Structures. While the author believes that
these two regions of the book are put in proper sequence
for elementary instruction, he is very far from seeking to
impose such an opinion upon teachers, who must use a
sequence adapted to their own convictions and material.
Hence many may prefer to begin with Chapter XV, and re-
turn to the preceding chapters later ; or, what is perhaps

vi PLANT STUDIES

better, they may prefer to combine the two divisions of the
book much more intimately.

In any event, the book is not a laboratory guide, or a
book merely for recitation, but is for reading and study in
connection with laboratory and field-work. The intention
is to present a connected, readable account of some of the
fundamental facts of botany, and to give a certain amount
of information. If it performs no other service in the
schools, however, its purpose will be defeated. It is entire-
ly too compact for any such use, for great subjects, which
should involve a large amount of observation, are often
merely suggested.

It is intended to serve as a supplement to three far more
important factors : (1) the teacher, who must amplify and
suggest at every point ; (2) the laboratory, which must bring
the pupil face to face with plants and their structures;
(3) field-ivork, which must relate the facts observed in the
laboratory to their actual place in Nature, and must bring
new facts to notice which can be observed nowhere else.
Taking the results obtained from these three factors, the
book seeks to organize them, and to suggest explanations.
It seeks to do this in two ways : (1) by means of the text,
which is intended to be clear and untechnical, but compact ;
(2) by means of the illustrations, which must be studied as
carefully as the text, as they are only second in importance
to the actual material. Especially is this true in reference
to the landscapes, many of which can not be made a part of
experience.

My thanks are due to various members of the Depart-
ment of Botany of the university for preparing and select-
ing illustrations. The illustrations of the first fourteen

PREFACE vii

chapters were under the general direction of Dr. Henry C.
Cowles, while those of the remaining chapters were pro-
vided by Dr. Otis W. Caldwell. In this work Dr. Caldwell
had the very efficient assistance of S. M. Coulter, B. A. Gold-
berger, J. G. Land, and A. C. Moore, whose names appear
in connection with the drawings they furnished. Grateful
acknowledgment should also be made to Dr. W. J. Beal,
whose little book entitled Seed Dispersal furnished several
illustrations ; and to Professor George F. Atkinson, whose
excellently illustrated Elementary Botany performed a like
service. Both of these authors are credited in connection
with the illustrations used from their works. The fine
illustrations from Kerner and from Schimper, and from
other authors, will also be recognized ; but their names will
all be found in the legends.

JOHN M. COULTER.
THE UNIVERSITY OF CHICAGO, June, 1900.

CONTENTS

CHAPTER PAOE

I. — INTRODUCTION 1

II. — FOLIAGE LEAVES: THE LIGHT RELATION .... 6

III. — FOLIAGE LEAVES : FUNCTION, STRUCTURE, AND PROTECTION 28

IV.— SHOOTS 53

V.— ROOTS 89

VI. — REPRODUCTIVE ORGANS 109

VII. — FLOWERS AND INSECTS 123

VIII. — AN INDIVIDUAL PLANT IN ALL OF ITS RELATIONS . . 138

IX. — THE STRUGGLE FOR EXISTENCE 142

X. — THE NUTRITION OF PLANTS 149

XL — PLANT SOCIETIES : ECOLOGICAL FACTORS .... 169

XII. — HYDROPHYTE SOCIETIES 177

XIII. — XEROPHYTE SOCIETIES 188

XIV. — MESOPHYTE SOCIETIES 214

XV.— THE PLANT GROUPS 221

XVI. — THALLOPHYTES : ALG^E 224

XVII. — THE GREAT GROUPS OF ALG^E 232

XVIIL— THALLOPHYTES : FUNGI 264

XIX. — BRYOPHYTES (MOSS PLANTS) 299

XX. — THE GREAT GROUPS OF BRYOPHYTES .... 308

XXL — PTERIDOPHYTES (FERN PLANTS) 320

XXII. — THE GREAT GROUPS OF PTERIDOPHYTES .... 334

XXIII. — SPERMATOPHYTES : GYMNOSPERMS 343

XXIV. — SPERMATOPHYTES: ANGIOSPERMS 358

XXV. — MONOCOTYLEDONS AND DICOTYLEDONS .... 376

GLOSSARY 383

INDEX 389

BOTANY

PLANT STUDIES

CHAPTEE I

INTRODUCTION

1. General relations. — Plants form the natural covering
of the earth's surface. So generally is this true that a land
surface without plants seems remarkable. Not only do
plants cover the land, but they abound in waters as well,
both fresh and salt waters. They are wonderfully varied in
size, ranging from huge trees to forms so minute that the
microscope must be used to discover them. They are also
exceedingly variable in form, as may be seen by comparing
trees, lilies, ferns, mosses, mushrooms, lichens, and the
green thready growths (algce) found in water.

2. Plant societies. — One of the most noticeable facts in
reference to plants is that they do not form a monotonous
covering for the earth's surface, but that there are forests in
one place, thickets in another, meadows in another, swamp
growths in another, etc. In this way the general appear-
ance of vegetation is exceedingly varied, and each appear-
ance tells of certain conditions of living. These groups of
plants living together in similar conditions, as trees and
other plants in a forest, or grasses and other plants in a
meadoAV, are known as plant societies. These societies are as

2 PLANT STUDIES

numerous as are the conditions of living, and it may be said
that each society has its own special regulations, which ad-
mit certain plants and exclude others. The study of plant
societies, to determine their conditions of living, is one of
the chief purposes of botanical field work.

3. Plants as living things. — Before engaging in a study
of societies, however, one must discover in a general way
how the individual plant lives, for the plant covering of the
earth's surface is a living one, and plants must always be
thought of as living and at work. They are as much alive
as are animals, and so far as mere living is concerned they
live in much the same way. Nor must it be supposed that
animals move and plants do not, for while more animals than
plants have the power of moving from place to place, some
plants have this power, and those that do not can move cer-
tain parts. The more we know of living things the more is
it evident that life processes are alike in them all, whether
plants or animals. In fact, there are some living things
about which we are uncertain whether to regard them as
plants or animals.

4. The plant body.— Every plant has a body, which may
be alike throughout or may be made up of a number of
different parts. When the green thready plants (algce), so
common in fresh water, are examined, the body looks like
a simple thread, without any special parts ; but the body of
a lily is made up of such dissimilar parts as root, stem,
leaf, and flower (see Figs. 75, 144, 161, 169). The plant
without these special parts is said to be simple, the plant
with them is called complex. The simple plant lives in
the same way and does the same kind of work, so far as
living is concerned, as does the complex plant. The differ-
ence is that in the case of the simple plant its whole body
does every kind of work ; while in the complex plant
different kinds of work are done by different regions of the
body, and these regions come to look unlike when differ-
ent shapes are better suited to different work, as in the

INTRODUCTION 3

case of a leaf and a root, two regions of the body doing
different kinds of work.

5. Plant organs. — These regions of the plant body thus
set apart for special purposes are called organs. The sim-
plest of plants, therefore, do not have distinct organs,
while the complex plants may have several kinds of organs.
All plants are not either very simple or very complex, but
beginning with the simplest plants one may pass to others
not quite so simple, then to others more complex, and so
on gradually until the most complex forms are reached.
This process of becoming more and more complex is known
as differentiation, which simply means the setting apart of
different regions of the body to do different kinds of work.
The advantage of this to the plant becomes plain by using
the common illustration of the difference between a tribe
of savages and a civilized community. The savages all do
the same things, and each savage does everything. In the
civilized community some of the members are farmers,
others bakers, others tailors, others butchers, etc. This is
what is known as " division of labor," and one great advan-
tage it has is that every kind of work is better done. Dif-
ferentiation of organs in a plant means to the plant just
what division of labor means to the community ; it results
in more work, and better work, and new kinds of work.
The very simple plant resembles the savage tribe, the com-
plex plant resembles the civilized community. It must be
understood, however, that in the case of plants the differ-
entiation referred to is one of organs and not of individuals.

6. Plant functions. — Whether plants have many organs,
or few organs, or no organs, it should be remembered that
they are all at work, and are all doing the same essential
things. Although many different kinds of work are being
carried on by plants, they may all be put under two heads,
nutrition and reproduction. Every plant, whether simple
or complex, must care for two things : (1) its own support
(nutrition), and (2) the production of other plants like

4 PLANT STUDIES

itself (reproduction). To the great work of nutrition many
kinds of work contribute, and the same is true of repro-
duction. Nutrition and reproduction, however, are the
two primary kinds of work, and it is interesting to note
that the first advance in the differentiation of a simple
plant body is to separate the nutritive and reproductive
regions. In the complex plants there are nutritive organs
and reproductive organs ; by which is meant that there are
distinct organs which specially contribute to the work of
nutrition, and others which are specially concerned with
the work of reproduction. The different kinds of work are
conveniently spoken of as functions, each organ having one
or more functions.

7. Life-relations. — In its nutritive and reproductive work
the plant is very dependent upon its surroundings. It
must receive material from the outside and get rid of waste
material ; and it must leave its offspring in as favorable
conditions for living as possible. As a consequence, every
organ holds a definite relation to something outside of it-
self, known as its life-relation. For example, green leaves
are definitely related to light, many roots are related to
soil, certain plants are related to abundant water, some
plants are related to other plants or animals (living as
parasites), etc. A plant with several organs, therefore,
may hold a great variety of life-relations, and it is quite a
complex problem for such a plant to adjust all of its parts
properly to their necessary relations. The study of the
life-relations of plants is a division of Botany known as
Ecology, and presents to us many of the most important
problems of plant life.

It must not be supposed that any plant or organ holds
a perfectly simple life-relation, for it is affected by a great
variety of things. A root, for instance, is affected by light,
gravity, moisture, soil material, contact, etc. Every or-
gan, therefore, must adjust itself to a very complex set of
life-relations, and a plant with several organs has so many

INTRODUCTION 5

delicate adjustments to care for that it is really impossi-
ble, as yet, for us to explain why all of its parts are placed
just as they are. In the beginning of the study of plants,
only some of the most prominent functions and life-rela-
tions can be considered. In order to do this, it seems bet-
ter to begin with single organs, and afterwards these can
be put together in the construction of the whole plant.

CHAPTER II

FOLIAGE LEAVES: THE LIGHT-RELATION

8. Definition. — A foliage leaf is the ordinary green leaf,
and is a very important organ in connection with the work
of nutrition. It must not be thought that the work done by
such a leaf cannot be done by green plants which have no
leaves, as the algae, for example. A leaf is simply an or-
gan set apart to do such work better. In studying the
work of a leaf, therefore, we have certain kinds of work
set apart more distinctly than if they were confused with
other kinds. For this reason the leaf is selected as an in-
troduction to some of the important work carried on by
plants, but it must not be forgotten that a plant does not
need leaves to do this work ; they simply enable it to work
more effectively.

9. Position. — It is easily observed that foliage leaves
grow only upon stems, and that the stems which bear them
always expose them to light ; that is, such leaves are aerial
rather than subterranean (see Figs. 1, 75, 174). Many
stems grow underground, and such stems either bear no
foliage leaves, or are so placed that the foliage leaves are
sent above the surface, as in most ferns and many plants of
the early spring (see Figs. 45, 46, 144).

10. Color. — Another fact to be observed is that foliage
leaves have a characteristic green color, a color so universal
that it has come to be associated with plants, and espe-
cially with leaves. It is also evident that this green color
holds some necessary relation to light, for the leaves of
plants grown in the dark, as potatoes sprouting in a cellar,

FOLIAGE LEAVES: THE LIGHT- RELATION 7

do not develop this color. Even when leaves have devel-
oped the green color they lose it if deprived of light, as is
shown by the process of blanching celery, and by the effect
on the color of grass if a board has lain upon it for
some time. It seems plain, therefore, that the green color
found in working foliage leaves depends upon light for its
existence.

We conclude that at least one of the essential life-rela-
tions of a foliage leaf is what may be called the light-rela-
tion. This seems to explain satisfactorily why such leaves
are not developed in a subterranean position, as are many
stems and most roots, and why plants which produce them
do not grow in the dark, as in caverns. The same green,
and hence the same light-relation, is observed in other
parts of the plant as well, and in plants without leaves, the
only difference being that leaves display it most conspicu-
ously. Another indication that the green color is con-
nected with light may be obtained from the fact that it is
found only in the surface region of plants. If one cuts
across a living twig or into a cactus body, the green color
will be seen only in the outer part of the section. The con-
clusion is that the leaf is a special organ for the light-re-
lation. Plants sometimes grow in such situations that it
would be unsafe for them to display leaves, or at least large
leaves. In such a case the work of the leaves can be thrown
upon the stem. A notable illustration of this is the cactus
plant, which produces no foliage leaves, but whose stem dis-
plays the leaf color.

11. An expanded organ. — Another general fact in refer-
ence to the foliage leaf is that in most cases it is an expanded
organ. This means that it has a great amount of surface
exposed in comparison with its mass. As this form is of
such common occurrence it is safe to conclude that it is in
some way related to the work of the leaf, and that whatever
work the leaf does demands an exposure of surface rather
than thickness of body. It is but another step to say that

PLANT STUDIES

the amount of work an active leaf can do will depend in
part upon the amount of surface it exposes.

THE LIGHT-RELATION

12. The general relation. — The ordinary position of the
foliage leaf is more or less horizontal. This enables it to
receive the direct rays of light upon its upper surface. In

this way more rays of
"1 light strike the leaf sur-
face than if it stood ob-
liquely or on edge. It is
often said that leaf blades
are so directed that the
flat surface is at right
angles to the incident
rays of light. While this
may be true of horizon-
tal leaves in a general
way, the observation of
almost any plant will
show that it is a very
general statement, to
which there are numerous
exceptions (see Fig. 1).
Leaves must be arranged
to receive as much light
as possible to help in
their work, but too much
light will destroy the
green substance (chloro-
phyll), which is essential
to the work. The adjust-
ment to light, therefore,
is a delicate one, for
there must be just enough

PIG. 1. The leaves of this plant (Ficus) are
in general horizontal, but it will be seen
that the lower ones are directed down-
ward, and that the leaves become more
horizontal as the stem is ascended. It
will also be seen that the leaves are so
broad that there are few vertical rows.

FOLIAGE LEAVES: THE LIGHT-EELATION 9

and not too much. The danger from too much light is
not the same in the case of all leaves, even on the same
plant, for some are more shaded than others. Leaves also
have a way of protecting themselves from too intense light
by their structure, rather than by a change in their posi-
tion. It is evident, therefore, that the exact position which
any particular leaf holds in relation to light depends upon
many circumstances, and cannot be covered by a general
rule, except that it seeks to get all the light it can without
danger.

13. Fixed position. — Leaves differ very much in the power
of adjusting their position to the direction of the light.

FIG. 2. The day and night positions of the leaves of a member (Amicia) of the pea
family. — After STKASBURGKR.

Most leaves when fully grown are in a fixed position and
cannot change it, however unfavorable it may prove to be,
except as they are blown about. Such leaves are said to
\YAvefixed light positions. This position is determined by
the light conditions that prevailed while the leaf was grow-
ing and able to adjust itself. If these conditions continue,
the resulting fixed position represents the best one that can
be secured under the circumstances. The leaf may not
receive the rays of light directly throughout the whole
period of daylight, but its fixed position is such that it
probably receives more light than it would in any other
position that it could secure.

PLANT STUDIES

14. Motile leaves. — There are leaves, however, which
have no fixed light position, but are so constructed that
they can shift their position as the direction of the light
changes. Such leaves are not in the same position in the

afternoon as in the
forenoon, and their
night position may be
very different from
either (see Figs. 2, 3#,
3£, 4). Some of the
common house plants
show this power. In
the case of the com-
mon Oxalis the night

Fzo. 8a. The day position of the leaves of redbud P0sition <>f the leaves

).— After ARTHUR. is remarkably different

from the position in light.
If such a plant is exposed
to the light in a window and
the positions of the leaves
noted, and then turned
half way around, so as to
bring the other side to the
light, the leaves may be
observed to adjust them-
selves gradually to the
changed light-relations.

15. Compass plants. — A
striking illustration of a

special light position is found in the so-called "compass
plants/' The best known of these plants is the rosin-weed
of the prairie region. Growing in situations exposed to
intense light, the leaves are turned edgewise, the flat faces
being turned away from the intense rays of midday, and
directed towards the rays of less intensity ; that is, those of

FIG. 36. The night position of the leaves
of redbud (Cercis). — After ARTHUR.

FOLIAGE LEAVES: THE LIGHT-RELATION

FIG. 4. Two sensitive plants, showing the motile leaves. The plant to the left has its
leaves and numerous leaflets expanded ; the one to the right shows the leaflets
folded together and the leaves drooping. — After KERNER.

the morning and evening (see Fig. 170). As a result, the
apex of the leaf points in a general north or south direction.
It is a significant fact that when the plant grows in shaded
places the leaves do not assume any such position. It
seems evident, therefore, that the position has something
to do with avoiding the danger of too intense light. It

PLANT STUDIES

FIG. 5. The common prickly lettuce (Lactuca
Scariola), showing the leaves standing edge-
wise, and in a general north and south plane.
—After ARTHUR and MACDOUGAL.

must not be supposed
that there is any ac-
curacy in the north or
south direction, as the
edgewise position
seems to be the signifi-
cant one. In the ros-
in-weed probably the
north and south direc-
tion is the prevailing
one ; but in the prickly
lettuce, a very common
weed of waste grounds,
and one of the most
striking of the compass
plants, the edgewise
position is frequently
assumed without any
special reference to the
north or south direc-
tion of the apex (see
Fig. 5).

16. Heliotropism. —
The influence of light
upon the positions of
leaves and other or-
gans is known as lieli-
otropism, and it is one
of the most important
of those external influ-
ences to which plant
organs respond (see
Figs. 6, 43).

It should be under-
stood clearly that this
is but a slight glimpse

FOLIAGE LEAVES: THE LIGHT-EELATION

FIG. 6. These plants are growing near a window. It will be noticed that the stems
bend strongly towards the light, and that the leaves face the light.

of the most obvious relations of foliage leaves to light, and
that the important part which heliotropism plays, not only
in connection with foliage leaves, but also in connection
with other plant organs, is one of the most important and
extensive subjects of plant physiology.

RELATION OF LEAVES TO ONE ANOTHER

A. On erect stems

In view of what has been said, it would seem that the
position of foliage leaves on the stem, and their relation to
one another, must be determined to some extent by the
necessity of a favorable light-relation. It is apparent that
the conditions of the problem are not the same for an erect
as for a horizontal stem.

17. Relation of breadth to number of vertical rows. —
Upon an erect stem it is observed that the leaves are usu-

PLANT STUDIES

ally arranged in a definite number of vertical rows. It is
to the advantage of the plant for these leaves to shade one
another as little as possible. Therefore, the narrower the
leaves, the more numerous may be the vertical rows (see

Figs. 7, 8) ; and
the broader the
leaves the fewer
the vertical rows
(see Fig. 1). A
relation exists,
therefore, be-
tween the breadth
of leaves and the
number of verti-
cal rows, and the
meaning of this
becomes plain
when the light-re-
lation is consid-
ered.

18. Relation of
length to the dis-
tance between
leaves of the same
row. — The leaves
in a vertical row

may be close together or far apart. If they should be close
together and at the same time long, it is evident that they
will shade each other considerably, as the light cannot well
strike in between them and reach the surface of the lower
leaf. Therefore, the closer together the leaves of a verti-
cal row, the shorter are the leaves ; and the farther apart
the leaves of a row, the longer may they be. Short leaves
permit the light to strike between them even if they are
close together on the stem ; and long leaves permit the
same thing only when they are far apart on the stem. A

FIG. 7.

An Easter lily, showing narrow leaves and
numerous vertical rows.

FOLIAGE LEAVES : THE LIGHT-RELATION 15

relation is to be observed, therefore, between the length
of leaves and their distance apart in the same vertical row.
The same kind of relation can be observed in reference
to the breadth of leaves, for if leaves are not only short but
narrow they can stand very close together. It is thus seen
that the length and breadth of leaves, the number of ver-
tical rows on the stem, and the distance between the leaves

FIG. 8. A dragon-tree, showing narrow leaves extending in all directions, and nuraer
ous vertical rows.

of any row, all have to do with the light-relation and are
answers to the problem of shading.

19. Elongation of the lower petioles. — There is still
another common arrangement by which an effective light-
relation is secured by leaves which are broad and placed
close together on the stem. In such a case the stalks
(petioles) of the lower leaves become longer than those
above and thus thrust their blades beyond the shadow (see
Fig. 9). It may be noticed that it is very common to

16 PLANT STUDIES

find the lowest leaves of a plant the largest and with the
longest petioles, even when the leaves are not very close
together on the stem.

It must not be supposed that by any of these devices
shading is absolutely avoided. This is often impossible and
sometimes undesirable. It simply means that by these

FIG. 9. A plant (Saintpaulia) with the lower petioles elongated, thrusting the blades
beyond the shadow of the upper leaves. A loose rosette.

arrangements the most favorable light-relation is sought by
avoiding too great shading.

20. Direction of leaves. — Not only is the position on the
stem to be observed, but the direction of leaves often shows
a definite relation to light. It is a very common thing to
find a plant with a cluster of comparatively large leaves at
or near the base, where they are in no danger of shading
other leaves, and with the stem leaves gradually becoming

FOLIAGE LEAVES : THE LIGHT-RELATION

smaller and less horizontal toward the apex of the stem
(see Figs. 10, 13). The common shepherd's purse and the
mullein may be taken as illustrations. By this arrange-
ment all the leaves are very
completely exposed to the
light.

21. The rosette habit.—
The habit of producing a
cluster or rosette of leaves
at the base of the stem is
called the rosette habit.
Often this rosette of leaves
at the base, frequently lying
flat on the ground or on the
rocks, includes the only fo-
liage leaves the plant pro-
duces. It is evident that a
rosette, in which the leaves
must overlap one another
more or less, is not a very
favorable light arrange-
ment, and therefore it must
be that something is being
provided for besides the
light-relation (see Figs. 11,
12, 13). What this is will
appear later, but even in

this comparatively unfavorable light arrangement, there is
evident adjustment to secure the most light possible under
the circumstances. The lowest leaves of the rosette are
the longest, and the upper (or inner) ones become gradu-
ally shorter, so that all the leaves have at least a part
of the surface exposed to light. The overlapped base of
such leaves is not expanded as much as the exposed apex,
and hence they are mostly narrowed at the base and broad
at the apex. This narrowing at the base is sometimes

FIG. 10. A plant (Echeveria) with fleshy
leaves, showing large horizontal ones
at base, and others becoming smaller
and more directed upward as the
stem is ascended.

PLANT STUDIES

carried so far that most of the part which is covered is
but a stem (petiole) for the upper part (blade) which is
exposed.

In many plants which do not form close rosettes a gen-

FIG. 11. A group of live-for-evers, illustrating the rosette habit and the light-relation.
In the rosettes it will be observed how the leaves are fitted together and diminish
in size inwards, so that excessive shading is avoided. The individual leaves also
become narrower where they overlap, and are broadest where they are exposed to
light. In the background is a plant showing leaves in very definite vertical rows.

eral rosette arrangement of the leaves may be observed by
looking down upon them from above (see Fig. 9), as in some
of the early buttercups which are so low that the large
leaves would seriously shade one another, except that the
lower leaves have longer petioles than the upper, and so
reach beyond the shadow.

FOLIAGE LEAVES: THE LIGHT-RELATION

FIG. 12. Two clumps of rosettes of the house leek (Sempervimim\ the one to the
right showing the compact winter condition, the one to the left with rosettes more
open after being kept indoors for several days.

22. Branched leaves. — Another notable feature of foliage
leaves, which has something to do with the light-relation,
is that on some plants the blade does not consist of one
piece, but is lobed or even broken up into separate pieces.
When the divisions are distinct they are called leaflets, and
every gradation in leaves can be found, from distinct leaf-
lets to lobed leaves, toothed leaves, and finally those whose
margins are not indented at all (entire). This difference
in leaves probably has
more important rea-
sons than the light-
relation, but its sig-
nificance may be ob-
served in this connec-
tion. In those plants
whose leaves are un-
divided, the leaves
generally either di-
minish in size toward
the top of the stem,
or the lower ones de- FlG 13 The leaves of a bellflower (Campanula^

Velop longer petioles. showing the rosette arrangement. The lower

Tn tlii« PPSP +ViP o-Pn petioles are successively longer, carrying their

blades beyond the shadow of the blades above,
eral Outline of the —After KEENER.

<^-=- '••„:-•-•

FIG. 14. A group of leaves, snowing how branched leaves overtop each other without
dangerous shading. It will be seen that the larger blades or less-branched leaves
are towards the bottom of the group.

FOLIAGE LEAVES: THE LIGHT- RELATION 21

plant is conical,, a form very common in herbs with entire
or nearly entire leaves. In plants whose leaf blades are
broken up into leaflets (compound or branched leaves),
however, no such diminution in size toward the top of the
stem is necessary (see Fig. 17), though it may frequently

FIG. 15. A plant showing much-branched leaves, which occur in great profusion with-
out cutting off the light from one another.

occur. When a broad blade is broken up into leaflets
the danger of shading is very much less, as the light can
strike through between the upper leaflets and reach the
leaflets below. On the lower leaves there will be splotches
of light and shadow, but they will shift throughout the
day, so that probably a large part of the leaf will receive
light at some time during the day (see Fig. 14). The

PLANT STUDIES

general outline of such a plant, therefore, is usually not
conical, as in the other case, but cylindrical (see Figs. 4,
15, 16, 22, 45, 83, 96, 161, 174, 178 for branched leaves).

Many other factors enter into the light-relation of foli-
age leaves upon erect stems, but those given may suggest

FIG. 16. A cycad, showing much-branched leaves and palm-like habit.

observation in this direction, and serve to show that the
arrangement of leaves in reference to light depends upon
many things, and is by no means a fixed and indifferent
thing. The study of any growing plant in reference to this
one relation presents a multitude of problems to those who
know how to observe.

B. On horizontal stems

23. Examples of horizontal stems, that is, stems exposed
on one side to the direct light, will be found in the case of
many branches of trees, stems prostrate on the ground, and

FOLIAGE LEAVES: THE LIGHT-RELATION

stems against a support, as the ivies. It is only necessary

to notice how the leaves are adjusted to light on an erect

stem, and then to bend the

stem into a horizontal posi-

tion or against a support, to

realize how unfavorable the

same arrangement would

be, and how many new ad-

justments must be made.

The leaf blades must all be

brought to the light side of

the stem, so far as possible,

and those that belong to

the lower side of the stem

must be fitted into the

spaces left by the leaves

which belong to the upper

side. This may be brought

about by the twisting of

the stem, the twisting of

the petioles, the bending of

the blade on the petiole,

the lengthening of petioles,

or in some other way.

Every horizontal stem has

its own special problems of

leaf adjustment which may

be observed (see Figs. 18,

50).

Sometimes there is not
Space eilOUgh for the full

development of evprv hlarlp
eveiy DlaCle,

and smaller ones are fitted
into the spaces left by the larger ones (see Fig. 21). This
sometimes results in what are called unequally paired leaves,
where opposite leaves develop one large blade and one small
3

FlG. 17. A chrysanthemum, showing
lobed leaves, the rising of the petioles

to adjust the blades to light) and the
general cylindrical habit.

PLANT STUDIES

one. Perhaps the most complete fitting together of leaves
is found in certain ivies, where a regular layer of angular
interlocking leaves is formed, the leaves fitting together like

FIG. 18. A plant (Pellionia) with drooping stems, showing how the leaves are all
brought to the lighted side and fitted together.

the pieces of a mosaic. In fact such an arrangement is
known as the mosaic arrangement, and involves such an
amount of twisting, displacement, elongation of petioles,

PLANT STUDIES

FIG. 20. A spray of maple, showing the adjustment of the leaves in size and position
of blades and length of petioles to secure exposure to light on a horizontal stem. —
After KERNER.

etc., as to give ample evidence of the effort put forth by
plants to secure a favorable light-relation for their foliage

FIG. 21. Two plants showing adjustment of leaves on a horizontal stem. The plant
to the left is nightshade, in which small blades are fitted into spaces left by the
large ones. The plant to the right is Selaginella, in which small leaves are dis-
tributed along the sides of the stem, and others are displayed along the upper sur-
face.—After KEENER.

FOLIAGE LEAVES: THE LIGHT-RELATION

leaves (see Figs. 19, 22). In the case of ordinary shade trees
every direction of branch may be found, and the resulting
adjustment of leaves noted (see Fig. 20).

Looking up into a tree in full foliage, it will be noticed
that the horizontal branches are comparatively bare be-

FIG. 22. A mosaic of fern (Adiantum) leaflets.

neath, while the leaf blades have been carried to the upper
side and have assumed a mosaic arrangement.

Sprays of maidenhair fern (see Fig. 22) show a remark-
able amount of adjustment of the leaflets to the light side.
Another group of fern-plants, known as club-mosses, has
horizontal stems clothed with numerous very small leaves.
These leaves may be seen taking advantage of all the space
on the lighted side (see Fig. 21).

CHAPTER TIT

FOLIAGE LEAVES: FUNCTION, STRUCTURE, AND PROTEC-
TION

A. Functions of foliage leaves

24. Functions in general. — AVe have observed that foliage
leaves are light-related organs, and that this relation is an
important one is evident from the various kinds of adjust-
ment used to secure it. AVe infer, therefore,, that for some
important function of these leaves light is necessary. It
would be hasty to suppose that light is necessary for every
kind of work done by a foliage leaf, for some forms of work
might be carried on by the leaf that light neither helps nor
hinders. Foliage leaves are not confined to one function,
but are concerned in a variety of processes, all of which
have to do with the great work of nutrition. Among the
variety of functions which belong to foliage leaves some of
the most important may be selected for mention. It will
be possible to do little more than indicate these functions
until the plant with all its organs is considered, but some
evidence can be obtained that various processes are taking
place in the foliage leaf.

25. Photosynthesis. — The most important function of the
foliage leaf may be detected by a simple experiment. If
an active leaf or a water plant be submerged in water in a
glass vessel, and exposed to the light, bubbles may be seen
coming from the leaf surface and rising through the water
(see Fig. 23). The water is merely a device by which the

bubbles of gas may be seen. If the leaf is very active the

FOLIAGE LEAVES : FUNCTION, STKUCTUBE, ETC.

bubbles are numerous. That this activity holds a definite
relation to light may be proved by gradually removing the
vessel containing the leaf from the light. As the light
diminishes the bubbles diminish in number, and when a

FIG. 23. An experiment to illustrate the giving off of oxygen in the process of photo-
synthesis.

certain amount of darkness has been reached the bubbles
will cease entirely. If now the vessel be brought back
gradually into the light, the bubbles will reappear, more
and more numerous as the light increases. That this gas
being given off is oxygen may be proved by collecting the

30 PLANT STUDIES

bubbles in a test tube, as in an ordinary chemical experi-
ment for collecting gas over water, and testing it in the
usual way.

Some very important things are learned by this experi-
ment. It is evident that some process is going on within
the leaf which needs light and which results in giving off
oxygen. It is further evident that as oxygen is eliminated,
the process indicated is dealing with substances which
contain more oxygen than is needed. The amount of
oxygen given off may be taken as the measure of the work.
The more oxygen, the more work ; and, as we have observed,
the more light, the more oxygen; and no light, no oxygen.
Therefore, light must be essential to the work of which the
elimination of oxygen is an external indication. That this
process, whatever it may be, is so essentially related to
light, suggests the idea that it is the special process which
demands that the leaf shall be a light-related organ. If so,
it is a dominating kind of work, as 'it chiefly determines
the life-relations of foliage leaves.

The process thus indicated is known as photosynthesis,
and the name suggests that it has to do with the arrange-
ment of material with the help of light. It is really a pro-
cess of food manufacture, by which raw materials are made
into plant food. This process is an exceedingly important
one, for upon it depend the lives of all plants and animals.
The foliage leaves may be considered, therefore, as special
organs of photosynthesis. They are special organs, not ex-
clusive organs, for any green tissue, whether on stem or fruit
or any part of the plant body, may do the same work. It
is at once apparent, also, that during the night the process
of photosynthesis is not going on, and therefore during the
night oxygen is not being given off.

Another part of this process is not so easily observed, but
is so closely related to the elimination of oxygen that it
must be mentioned. Carbon dioxide occurs in the air to
which the foliage leaves are exposed. It is given off from

FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 31

our lungs in breathing, and also comes off from burning
wood or coal. It is a common waste product, being a com-
bination of carbon and oxygen so intimate that the two
elements are separated from one another with great dif-
ficulty. During the process of photosynthesis it has been
discovered that carbon dioxide is being absorbed from the
air by the leaves. As this gas is absorbed chiefly by green
parts and in the light, in just the conditions in which oxy-
gen is being given off, it is natural to connect the two, and
to infer that the process of photosynthesis involves not only
the green color and the light, but also the absorption of
carbon dioxide and the elimination of oxygen.

When we observe that carbon dioxide is a combination
of carbon and oxygen, it seems reasonable to suppose that
the carbon and oxygen are separated from one another in
the plant, and that the carbon is retained and the oxygen
given back to the air. The process of photosynthesis may
be partially defined, therefore, as the breaking up of carbon
dioxide by the green parts of the plants in the presence of
light, the retention of the carbon, and the elimination of
the oxygen. The carbon retained is combined into real
plant food, in a way to be described later. We may con-
sider photosynthesis as the most important function of the
foliage leaf, of which the absorption of carbon dioxide and
the evolution of oxygen are external indications ; and that
light and chlorophyll are in some way essentially connected
with it.

26. Transpiration. — One of the easiest things to observe
in connection with a working leaf is the fact that it gives
off moisture. A simple experiment may demonstrate this.
If a glass vessel (bell jar) be inverted over a small active
plant the moisture is seen to condense on the glass, and
even to trickle down the sides. A still more convenient way
to demonstrate this is to select a single vigorous leaf with
a good petiole ; pass the petiole through a perforated card-
board resting upon a tumbler containing water, and invert

32 PLANT STUDIES

a second tumbler over the blade of the leaf, which projects
above the cardboard (see Fig. 24). It will be observed that
moisture given off from the surface of the working leaf is
condensed on the inner surface of the inverted tumbler.
The cardboard is to shut off evaporation from the water
in the lower tumbler.

When the amount of water given off by a single leaf is
noted, some vague idea may be formed as to the amount of
moisture given off by a great mass of vegetation, such as a
meadow or a forest. It is evident that green plants at
work are contributing a very large amount of moisture to
the air in the form of water vapor, moisture which has been
absorbed by some region of the plant. The foliage leaf,
therefore, may be regarded as an organ of transpiration,
not that the leaves alone are engaged in transpiration, for
many parts of the plant do the same thing, but because the
foliage leaves are the chief seat of transpiration.

The important fact in connection with transpiration is
not that moisture is given off by active foliage leaves,
but that this escaping moisture is the external indication
of some work going on within the leaf. Transpiration,
therefore, may not be regarded so much as work, as the
result, and hence the indication of work. In case the
leaves are submerged, as is true of many plants, it is evi-
dent that transpiration is practically checked, for the
leaves are already bathed with water, and under such cir-
cumstances water vapor is not given off. The same is true
of green water plants without leaves (such as algse). It is
evident that under such circumstances leaf Avork must be
carried on without transpiration.

27. Respiration. — Another kind of work also may be de-
tected in the foliage leaf, but not so easily described. In
fact it escaped the attention of botanists long after they
had discovered photosynthesis and transpiration. It is work
that goes on so long as the leaf is alive, never ceasing day
or night. The external indication of it is the absorption

FIG. 24. Experiment illustrating transpiration.

34 PLANT STUDIES

of oxygen and the giving out of carbon dioxide. It will be
noted at once that this is exactly the reverse of what takes
place in photosynthesis. During the day, therefore, carbon
dioxide and oxygen are both being absorbed and evolved.
It will also be noted that the taking in of oxygen and the
giving out of carbon dioxide is just the sort of exchange
which takes place in our own respiration. In fact this pro-
cess is also called respiration in plants. It does not depend
upon light, for it goes on in the dark. It does not depend
upon chlorophyll, for it goes on in plants and parts of plants
which are not green. It is not peculiar to leaves, but goes
on in every living part of the plant. A process which goes
on without interruption in all living plants and animals
must be very closely related to their living. We conclude,
therefore, that while photosynthesis is peculiar to green
plants, and only takes place in them when light is present,
respiration is necessary to all plants in all conditions, and
that when it ceases life must soon cease. The fact is,
respiration supplies the energy which enables the living
substance to work.

Once it was thought that plants differ from animals
in the fact that plants absorb carbon dioxide and give off
oxygen, while animals absorb oxygen and give off carbon
dioxide. It is seen now that there is no such difference,
but that respiration (absorption of oxygen and evolution of
carbon dioxide) is common to both plants and animals.
The difference is that green plants have the added work of
photosynthesis.

We may also call the foliage leaf, therefore, an organ cf
respiration, because so much of such work is done by it,
but it must be remembered that respiration is going on in
every living part of the plant.

This by no means completes the list of functions that
might be made out for foliage leaves, but it serves to
indicate both their peculiar work (photosynthesis) and
the fact that they are doing other kinds of work as well.

FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 35

B. Structure of foliage leaves

28. Gross structure, — It is evident that the essential part
of a foliage leaf is its expanded portion or Uade. Often the

leaf is all blade (see Figs. 7,
8, 18) ; frequently there is a
longer or shorter leaf-stalk
(petiole) which helps to put

FIG. 25. Two types of leaf venation. The figure to the left is a leaf of Solomon's
seal (Polygonatum), and shows the principal veins parallel, the very minute cross
veinlets being invisible to the naked eye, being a monocotyl type. The figure to
the right is a leaf of a willow, and shows netted veins, the main central vein (mid-
rib) sending out a series of parallel branches, which are connected with one another
by a network of veinlets, being a dicotyl type.— After ETTINGSHAUSEN.

the blade into better light-relation (see Figs. 1, 9, 17, 20,
26); and sometimes there are little leaf -like appendages (stip-
ules) on the petiole where it joins the stem,, whose func-
tion is not always clear. Upon examining the blade it
is seen to consist of a green substance through which a

PLANT STUDIES

framework of veins is variously arranged. The large veins
which enter the blade send off smaller branches, and these
send off still smaller ones, until the smallest veinlets are

invisible, and the
framework is a
close network of
branching veins.
This is plainly
shown by a "skel-
eton" leaf, one
which has been so
treated that all
the green sub-
stance has disap-
peared, and only
the network of
veins remains. It
will be noticed
that in some
leaves the veins
and veinlets are
very prominent,
in others only
the main veins
are prominent,
while in some it
is hard to detect
any veins (see
Figs. 25, 2G).

29. Significance
of baf veins. — It
is clear that the

framework of veins is doing at least two things for the
blade: (1) it mechanically supports the spread out green sub-
stance ; and (2) it conducts material to and from the green
substance. So complete is the network of veins that this

FIG. 26. A leaf of hawthorn, showing a short petiole, and
a broad toothed blade with a conspicuous network of
veins. Note the relation between the veins end the
teeth. — After STRASBURGER.

FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 37

support and conduction are very perfect (see Fig. 27). It
is also clear that the green substance thus supported and
supplied with material is the important part of the leaf, the
part that demands the light-relation. Study the various
plans of the vein systems in Figs. 3, 9, 13, 18, 19, 20, 21,
25, 26, 51, 70, 76, 82, 83, 92, 161.

FIG. 27. A plant (Fittonia) whose leaves show a network of veins, and also an adjust-
ment to one another to form a mosaic.

30. Epidermis. — If a thick leaf be taken, such as that
of a hyacinth, it will be found possible to peel off from
its surface a delicate transparent skin (epidermis). This
epidermis completely covers the leaf, and generally shows
no green color. It is a protective covering, but at the same
time it must not completely shut off the green substance
beneath from the outside. It is found, therefore, that
three important parts of an ordinary foliage leaf are : (1)

PLANT STUDIES

FIG. 28. Cells of the epidermis
of Maranta, showing the
interlocking walls, and a
stoma (s) with its two guard-
cells.

a network of veins ; (2} a green substance (mesophyll) in

the meshes of the network ; and (3) over all an epidermis.
31. Stomata, — If a compound microscope is used, some

very important additional facts may be discovered. The
thin, transparent epidermis is
found to be made up of a layer of
cells which fit closely together,
sometimes dovetailing with each
other. Curious openings in the
epidermis will also be discovered,
sometimes in very great numbers.
Guarding each opening are two
crescent-shaped cells, known as
guard- cells, and between them a
slit-like opening leads through the
epidermis. The whole apparatus
is known as a stoma (plural
stomata), which really means

" mouth/' of which the guard-cells might be called the

lips (see Figs. 28, 29). Sometimes stomata are found only

on the under side of the leaf, sometimes only

on the upper side, and sometimes on both

sides.

The important fact about stomata is that

the guard-cells can change their shape, and

so regulate the size of the opening. It is not

certain just how the guard-cells change their

shape and just what stomata do for leaves.

They are often called " breathing pores,"

but the name is very inappropriate. Stomata

are not peculiar to the epidermis of foliage

leaves, for they are found in the epidermis

of any green part, as stems, young fruit,

etc. It is evident, therefore, that they hold

an important relation to green tissue which

is covered by epidermis. Also, if we examine

FIG. 29. A single
stoma from the
epidermis of a
lily leaf, show-
ing the two
guard-cells full
of chlorophyll,
and the small
slit-like opening
between.

FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 39

foliage leaves and other green parts of plants which live
submerged in water, we find that the epidermis contains
no stomata. Therefore, stomata hold a definite relation
to green parts covered by epidermis only when this epider-
mis is exposed to the air.

It would seem that the stomata supply open passage-
ways for material from the green tissue through the epider-
mis to the air, or from the air to the green tissue, or both.
It will be remembered, however, that quite a number of
substances are taken into the leaf and given out from it,
so that it is hard to determine whether the stomata are
specially for any one of these movements. For instance,
the leaf gives out moisture in transpiration, oxygen in
photosynthesis, and carbon dioxide in respiration ; while it
takes in carbon dioxide in photosynthesis, and oxygen in
respiration. It is thought stomata specially favor transpira-
tion, and, if so, "breathing pores" is not a happy phrase,
for they certainly assist in the other exchanges.

32. Mesophyll. — If a cross-section be made of an ordi-
nary foliage leaf, such as that of a lily, the three leaf
regions can be seen in their proper relation to each other.
Bounding the section above and below is the layer of trans-
parent epidermal cells, pierced here and there by stomata,
marked by their peculiar guard-cells. Between the epi-
dermal layers is the green tissue, known as the mesophytt,
made up of cells which contain numerous small green
bodies which give color to the whole leaf, and are known as
chlorophyll bodies or chloroplasts.

The mesophyll cells are usually arranged differently in
the upper and lower regions of the leaf. In the upper
region the cells are elongated and stand upright, present-
ing their narrow ends to the upper leaf surface, forming
the palisade tissue. In the lower region the cells are irreg-
ular, and so loosely arranged as to leave passageways for air
between, forming the spongy tissue. The air spaces among
the cells communicate with one another, so that a system of
4

40 PLANT STUDIES

air chambers extends throughout the spongy mesophyll.
It is into this system of air chambers that the stomata
open, and so they are put into direct communication with
the mesophyll or working cells. The peculiar arrangement
of the upper mesophyll, to form the palisade tissue, has to
do with the fact that that surface of the leaf is exposed to
the direct rays of light. This light, so necessary to the
mesophyll, is also dangerous for at least two reasons. If

FIG. 30. 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 (p) and the spongy region (sp) with airspaces among the cells, and two
veins (#) cut across.

the light is too intense it may destroy the chlorophyll, and
the heat may dry out the cells. By presenting only nar-
row ends to this direct light the cells are less exposed to
intense light and heat. Study Fig. 30.

33. Veins. — In the cross-section of the leaf there will
also be seen here and there, embedded in the mesophyll,
the cut ends of the veinlets, made up partly of thick-
walled cells, which hold the leaf in shape and conduct
material to and from the mesophyll (see Fig. 30).

FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 41

C. Leaf protection

34. Need of protection. — Such an important organ as
the leaf, with its delicate active cells well displayed, is ex-
posed to numerous dangers. Chief among these dangers
are intense light, drought, and cold. All leaves are not
exposed to these dangers. For example, plants which grow
in the shade are not in danger from intense light ; many
O.s. water plants are not in danger

from drought ; and plants of
the tropical lowlands are in no

FIG. 31. Sections through leaves of the same plant, showing the effect of exposure to
light upon the structure of the mesophyll. In both cases os indicates upper surface,
and us under surface. In the section at the left the growing leaf was exposed to
direct and intense sunlight, and, as a consequence, all of the mesophyll cells have
assumed the protected or palisade position. In the section at the right the leaf was
grown in the shade, and none of the mesophyll cells have organized in palisade
fashion.— After STAHL.

danger from cold. The danger from all these sources is be-
cause of the large surface with no great thickness of hody,
and the protection against all of them is practically the
same. Most of the forms of protection can be reduced
to two general plans : (1) the development of protective
structures between the endangered mesophyll and the air ;
(2) the diminution of the exposed surface.

35. Protective structures. — The palisade arrangement of
mesophyll may be regarded as an adaptation for protection,

PLANT STUDIES

but it usually occurs, and does not necessarily imply ex-
treme conditions of any kind. However, if the cells of the
palisade tissue are unusually narrow and elongated, or

p—

FIG. 32. Section through a portion of the leaf of the yew (Taxus), showing cuticle
(c), epidermis (e), and the upper portion of the palisade cells (p).

form two or three layers, we might infer the probability of
exposure to intense light or drought. The accompanying
illustration (Fig. 31) shows in a striking way the effect of
light intensity upon the structure of the mesophyll, by
contrasting leaves of the same plant exposed to the extreme
conditions of light and shade.

The most usual structural adaptations, however, are
connected with the epidermis. The outer walls of the epi-
dermal cells may become thickened, sometimes excessively

so; the other epidermal
walls may also become
more or less thickened;
or even what seems to
be more than one epi-
dermal layer is found
protecting the meso-
phyll. If the outer
walls of the epidermal
cells continue to
thicken, the outer re-
gion of the thick wall
loses its structure
and forms the cuticle,
which is one of the

FIG. 33. Section through a portion of the leaf of
carnation, showing the heavy cuticle (cu)
formed by the outer walls of the epidermal
cells (ep). Through the cuticle a passageway
leads to the stoma, whose two guard-cells are
seen lying between the two epidermal cells
shown in the figure. Below the epidermal
cells some of the palisade cells (pal) are shown
containing chloroplasts, and below the stoma
is seen the air chamber into which it opens.

FOLIAGE LEAVES: FUNCTION, STRUCTUKE, ETC. 43

FIG. 34. A hair from the leaf
of Potentilla. It is seen
to grow out from the epi-
dermis.

best protective substances (see Fig.
32). Sometimes this cuticle be-
comes so thick that the passage-
ways through it leading down to
the stomata become regular canals
(see Fig. 33).

Another very common protective
structure upon leaves is to be found
in the great variety of hairs de-
veloped by the epidermis. These
may form but a slightly downy
covering, or the leaf may be cov-
ered by a woolly or felt-like mass
so that the epidermis is entirely
concealed. The common mullein
is a good illustration of a felt-
covered leaf (see Fig. 36). In cold
or dry regions the hairy covering
of leaves is very noticeable, often

giving them a brilliant silky white or bronze look (see
Figs. 34, 35). Sometimes, instead of a hair-like cover-
ing, the epidermis develops scales of various patterns,
often overlapping, and forming an excellent protection
(see Fig. 37). In all these cases it should be remembered
that these hairs and scales may serve other purposes also,
as well as that of protection.

36. Diminution
of exposed surface. —
It will be impossible
to give more than a
few illustrations of
this large subject.

-r -i • FIG. 35. A section through the leaf of bush clover

I Very ary reglO (Lespedeza\ showing upper and lower epidermis,

it has always been palisade cells, and cells of the spongy region.

nntiVpr! tint flip The lower ePidermis Produces numerous hairs

which bend sharply and lie along the leaf surface
leaves are Small and (appressed), forming a close covering.

PLANT STUDIES

FIG. 3G. A branching hair from the leaf of common mullein. The whole plant has a
felt-like covering composed of such hairs.

comparatively thick, although they may be very numerous
(see Figs. 4, 172). In this way each leaf exposes a small

surface to the dry-
ing air and intense
sunlight. In our
southwestern dry
regions the cactus
abounds, plants
which have reduced
their leaves so much
that they are no
longer used for
chlorophyll work,
and are not usually
recognized as leaves.
In their stead the
globular or cylin-
drical or flattened
stems are green and

FIG. 37. A scale from the leaf of Shepherdia. These &

scales overlap and form a complete covering. do leaf Work (FlgS.

FIG. 39. A group of cactus forms (slender cylindrical, columnar,
and globular), all of them spiny and without leaves ; an agave in
front ; clusters of yucca flowers in the background.

FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 47

38, 39, 40, 185, 186, 187, 188). In the same regions the
agaves and yuccas retain their leaves, but they become so
thick that they serve as water reservoirs (see Figs. 38, 39,

FIG. 40. A globular cactus, showing the ribbed stem, the strong spines, and the entire
absence of leaves.

189). In all these cases this reduced surface is supple-
mented by palisade tissue, very thick epidermal walls, and
an abundant cuticle.

37. Rosette arrangement. — The rosette arrangement of
leaves is a very common method of protection used by

48 PLANT STUDIES

small plants growing in exposed situations, as bare rocks
and sandy ground. The cluster of leaves, flat upon the
ground, or nearly so, and more or less overlapping, is very
effectively arranged for resisting intense light or drought
or cold (see Figs. 11, 12, 48).

38. Protective positions. — In other cases, a position is
assumed by the leaves which directs their flat
surfaces so that they are not exposed to the
most intense rays of light. The so-called

FIG. 41. 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 moved together ; and the main leaf-stalk has been directed sharply
downward. The whole change has very much reduced the surface of exposure. —
After DUCHARTRE.

pass plants," already mentioned, are illustrations of this,
the leaves standing edgewise and receiving on their surface
the less intense rays of light (see Figs. 5, 170). In the
dry regions of Australia the leaves on many of the forest
trees and shrubs have this characteristic edgewise position,
known as the profile position, giving to the foliage a very
curious appearance.

Some leaves have the power of shifting their position
according to their needs, directing their flat surfaces to-
ward the light, or more or less inclining them, according

FIG. 42. The telegraph plant (Desmodium gyrcms). Each leaf is made up of three
leaflets, a large terminal one, and a pair of small lateral ones. In the lowest figure
the large leaflets are spread out in their day position ; in the central figure they are
turned sharply downward in their night position. The name of the plant refers to
the peculiar and constant motion of the pair of lateral leaflets, each one of which
describes a curve with a jerking motion, like the second-hand of a watch, as
indicated in the uppermost figure.

PLANT STUDIES

to the danger. Perhaps the most completely adapted
leaves of this kind are those of the "sensitive plants,"
whose leaves respond to various external influences by
changing their positions. The common sensitive plant
abounds in dry regions, and may be taken as a type of
such plants (see Figs. 4, 41, 171). The leaves are divided
into very numerous small leaflets, sometimes very small,
which stretch in pairs along the leaf branches. When
drought approaches, some of the pairs of leaflets fold to-
gether, slightly reduc-
ing the surface expo-
sure. As the drought
continues, more leaflets
fold together, then still
others, until finally all
the leaflets may be
folded together, and the
leaves themselves may

FIG. 43. Cotyledons of squash seedling, show- bend against the stem.

It is like a sailing vessel
gradually taking in sail
as a storm approaches, until finally nothing is exposed,
and the vessel weathers the storm by presenting only bare
poles. Sensitive plants can thus regulate the exposed sur-
face very exactly to the need.

Such motile leaves not only behave in this manner at the
coming of drought, but the positions of the leaflets are
shifted throughout the day in reference to light, and at
night a very characteristic position is assumed (see Figs. 2,
3, 42), once called a " sleeping position." The danger from
night exposure comes from the radiation of heat which
occurs, which may chill the leaves to the danger point.
The night position of the leaflets of Oxalis has been re-
ferred to already (see §14). Similar changes in the direc-
tion of the leaf planes at the coming of night may be
observed in most of the Leguminosce, even the common

ing positions in light (left figure) and in
darkness (right figure). — After ATKINSON.

FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 51

white clover displaying it. It can be observed that the
expanded seed leaves (cotyledons) of many young germinat-
ing plants shift their positions at night (see Fig. 43), often
assuming a vertical position which brings them in contact
with one another, and also covers the stem bud (plumule).

Certain leaves with well-developed
protective structures are able to en-
dure the winter, as in the case of
the so-called evergreens. In the
case of juniper, however, the winter
and summer positions of the leaves
are quite different (see Fig. 44). In
the winter the leaves lie close against
the stem and overlap one another;
while with the coming of warmer
conditions they become widely
spreading.

39. Protection against rain. — It is
also necessary for leaves to avoid
becoming wet by rain. If the water
is allowed to soak in there is danger
of filling the stomata and interfering
with the air exchanges. Hence it
will be noticed that most leaves are
able to shed water, partly by their
positions, partly by their structure.
In many plants the leaves are so ar-
ranged that the water runs off towards the stem and so
reaches the main root system ; in other plants the rain is
shed outwards, as from the eaves of a house.

Some of the structures which prevent the rain from
soaking in are a smooth epidermis, a cuticle layer, waxy
secretions, felt-like coverings, etc. Interesting experi-
ments may be performed with different leaves to test their
power of shedding water. If a gentle spray of water is
allowed to play upon different plants, it will be observed

FIG. 44. Two twigs of juni-
per, showing the effect of
heat and cold upon the
positions of the leaves.
The ordinary protected
winter position of the
leaves is shown by A ;
while in B, in response to
warmer conditions, the
leaves have spread apart
and have become freely ex-
posed.—After WARMING.

52 PLANT STUDIES

that the water glances off at once from the surfaces of
some leaves, runs off more slowly from others, and may be
more or less retained by others.

In this same connection it should be noticed that in
most horizontal leaves the two surfaces differ more or less
in appearance, the upper usually being smoother than the
lower, and the stomata occurring in larger numbers, some-
times exclusively, upon the under surface. While these
differences doubtless have a more important meaning than
protection against wetting, they are also suggestive in this
connection.

CHAPTER IV
SHOOTS

40. General characters. — The term shoot is used to include
both stem and leaves. Among the lower plants, such as
the algae and toadstools, there is no distinct stem and leaf.
In such plants the working body is spoken of as the thallus,
which does the work done by both stem and leaf in the
higher plants. These two kinds of work are separated in
the higher plants, and the shoot is differentiated into stem
and leaves.

41. Life-relation. — In seeking to discover the essential
life-relation of the stem, it is evident that it is not neces-
sarily a light-relation, as in the case of the foliage leaf,
for many stems are subterranean. Also, in general, the
stem is not an expanded organ, as is the ordinary foli-
age leaf. This indicates that whatever may be its essential
life-relation it has little to do with exposure of surface.
It becomes plain that the stem is the great leaf-bearing
organ, and that its life-relation is a leaf-relation. Often
stems branch, and this increases their power of producing
leaves.

In classifying stems, therefore, it seems natural to use
the kind of leaves they bear. From this standpoint there
are three prominent kinds of stems : (1) those bearing foli-
age leaves ; (2) those bearing scaly leaves ; and (3) those
bearing floral leaves. There are some peculiar forms of
stems which do not bear leaves of any kind, but they need

not be included in this general view.

54 PL AST STUDIES

A. Stems 'bearing foliage leaves

42. General character. — As the purpose of this stem is to
display foliage leaves, and as it has been discovered that the
essential life-relation of foliage leaves is the light-relation,
it follows that a stem of this type must be able to relate its
leaves to light. It is, therefore, commonly aerial, and that
it may properly display the leaves it is generally elongated,
with its joints (nodes) bearing the leaves well separated (see
Figs. 1, 4, 18, 20).

The foliage-bearing stem is generally the most conspicu-
ous part of the plant and gives style to the whole body.
One's impression of the forms of most plants is obtained
from the foliage-bearing stems. Such stems have great
range in size and length of life, from minute size and very
short life to huge trees which may endure for centuries.
Branching is also quite a feature of foliage-bearing stems ;
and when it occurs it is evident that the power of display-
ing foliage is correspondingly increased. Certain promi-
nent types of foliage-bearing stems may be considered.

43. The subterranean type, — It may seem strange to in-
clude any subterranean stem with those that bear foliage,
as such a stem seems to be away from any light-relation.
Ordinarily subterranean stems send foliage-bearing branches
above the surface, and such stems are not to be classed as
foliage-bearing stems. But often the only stem possessed
by the plant is subterranean, and no branches are sent to
the surface. In such cases only foliage leaves appear above
ground, and they come directly from the subterranean stem.
The ordinary ferns furnish a conspicuous illustration of
this habit, all that is seen of them above ground being the
characteristic leaves, the commonly called "stem" being
only the petiole of the leaf (see Figs. 45, 46, 144). Many
seed plants can also be found which show the same habit,
especially those which flower early in the spring. This
cannot be regarded as a very favorable type of stem for

FIG. 45. A fern (Aspidium), showing three large branching leaves coming from a hori-
zontal subterranean stem (rootstock) ; growing leaves are also shown, which are
gradually unrolling. 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 3 represents the under surface of a
portion of the leaf, showing seven groups of spore cases ; at 5 is represented a
section through one of these groups, showing how the spore cases are attached and
protected by a flap ; while at 6 is represented a single spore case opening and dis-
charging its spores, the heavy spring-like ring extending along the back and over
the top. — After WOSSIDLO.
5,

56 PLANT STUDIES

leaf display, and as a rule such stems do not produce
many foliage leaves, but the leaves are apt to be large.

FIG. 46. A common fern, showing the underground stem (rootstock), which sends the
few large foliage leaves above the surface. — After ATKINSON.

The subterranean position is a good one, however, for
purposes of protection against cold or drought, and when
the foliage leaves are killed new ones can be put out by

SHOOTS 57

the protected stem. This position is also taken advantage
of for comparatively safe food storage, and such stems are
apt to become more or less thickened and distorted by this
food deposit.

44. The procumbent type.— In this case the main body
of the stem lies more or less prostrate, although the advanc-
ing tip is usually erect. Such stems may spread in all
directions, and become interwoven into
a mat or carpet. They are found
especially on sterile and exposed soil,

FIG. 47. A strawberry plant, showing a runner which has devel-
oped a new plant, which in turn has sent out another run-
ner.—After SEUBERT.

and there may be an important relation between this fact and
their habit, as there may not be sufficient building material
for erect stems, and the erect position might result in too
much exposure to light, or heat, or wind, etc. Whatever
may be the cause of the procumbent habit, it has its advan-
tages. As compared with the erect stem, there is economy
of building material, for the rigid structures to enable it to
stand upright are not necessary. On the other hand, such
a stem loses in its power to display leaves. Instead of
being free to put out its leaves in every direction, one side
is against the ground, and the space for leaves is diminished
at least one-half. All the leaves it bears are necessarily
directed towards the free side (see Fig. 18).

AVe may be sure, however, that any disadvantage com-
ing from this unfavorable position for leaf display is over-
balanced by advantages in other respects. The position is

PLANT STUDIES

certainly one of protection, and it has a further advantage
in the way of migration and vegetative propagation. As
the stem advances over the ground, roots strike out of the
nodes into the soil. In this way fresh anchorage and new
soil supplies are secured ; the old parts of the stem may

FIG. 48. Two plants of a saxifrage, showing rosette habit, and also the numerous
runners sent out from the base, which strike root at tip and produce new plants.
— After KERNER.

die, but the newer portions have their soil connection and
continue to live. So effective is this habit for this kind of
propagation that plants with erect stems often make use of
it, sending out from near the base special prostrate branches,
which advance over the ground and form new plants.
A very familiar illustration is furnished by the straw-
berry plant, which sends out peculiar naked " runners"
to strike root and form new plants, which then become

SHOOTS

independent plants by the dying of the runners (see Figs.
47, 48).

45. The floating type. — In this case the stems are sus-
tained by water. Numerous illustrations can be found in
small inland lakes and slow-moving streams (see Fig. 49).
Beneath the water these stems often seem quite erect, but

FIG. 49. A submerged plant (Ceratophyllum) with floating stems, showing the stem
joints bearing finely divided leaves.

when taken out they collapse, lacking the buoyant power
of the water. Growing free and more or less upright in
the water, they seem to have all the freedom of erect stems
in displaying foliage leaves, and at the same time they
are not called upon to build rigid structures. Economy
of building material and entire freedom to display foliage
would seem to be a happy combination for plants. It must
be noticed, however, that another very important condition
is introduced. To reach the leaf surfaces the light must
pass through the water, and this diminishes its intensity so

PLANT STUDIES

greatly that the working power of the leaves is reduced.
At no very great depth of water a limit is reached, beyond
which the light is no longer able to be of service to the
leaves in their work. Hence it is that water plants are

restricted to the surface of the
water, or to shoal places ; and in
such places vegetation is very
abundant. Water is so serious
an impediment to light that very
many plants bring their working
leaves to the surface and float
them, as seen in water lilies, thus
obtaining light of undiminished
intensity.

46. The climbing type. — Climb-
ing stems are developed especially
in the tropics, where the vegeta-
tion is so dense and overshadow-
ing that many stems have learned
to climb upon the bodies of other
plants, and so spread their leaves
in better light (see Figs. 50, 55,
98, 199). Great woody vines
fairly interlace the vegetation of
tropical forests, and are known
as "lianas," or "lianes." The
same habit is noticeable, also, in
our temperate vegetation, but it
is by no means so extensively dis-
played as in the tropics. There
are a good many forms of climb-
ing stems. Remembering that
the habit refers to one stem de-

FIG. 50. A vine or liana climbing

the trunk of a tree. The leaves pending Upon another for

are ail adji^ted to face the light mechanical support, we may in-

and to avoid shading one an- r* .

other as far as possible. elude many hedge plants m the

SHOOTS

list of climbers. In this case the stems are too weak to
stand alone, but by interlacing with one another they may
keep an upright position. There are stems, also, which
climb by twining about their support, as the hop vine and

FIG. 51. A cluster of smilax, showing the tendrils which enable it to climb, and also
the prickles. — After KERNER.

morning glory ; others which put out tendrils to grasp the
support (see Figs. 51, 52), as the grapevine and star
cucumber ; and still others which climb by sending out
suckers to act as holdfasts, as the woodbine (see Figs. 53,
54). In all these cases there is an attempt to reach towards

PLANT STUDIES

the light without developing such structures in the stem
as would enable it to stand upright.

47. The erect type. — This type seems altogether the
best adapted for the proper display of foliage leaves. Leaves

FIG. 52. Passion-flower vines climbing supports by means of tendrils, which may be
seen more or less extended or coiled. The two types of leaves upon a single stem
may also be noted.

can be sent out in all directions and carried upward to-
wards the light ; but it is at the expense of developing an
elaborate mechanical system to enable the stem to retain
this position. There is an interesting relation between
these erect bodies and zones of temperature. At high alti-

SHOOTS

FIG. 53. Woodbine (Ampelopsis) in a deciduous forest. The tree trunks are almost
covered by the dense masses of woodbine, whose leaves are adjusted so as to form
compact mosaics. A lower stratum of vegetation is visible, composed of shrubs
and tall herbs, showing that the forest is somewhat open. — After SCHIMPER.

tudes or latitudes the subter-
ranean and prostrate types of
foliage-bearing stems are most
common ; and as one passes to
lower altitudes or latitudes the
erect stems become more nu-
merous and more lofty. Among
stems of the erect type the tree
is the most impressive, and it
has developed into a great vari-
ety of forms or "habits." Any
one recognizes the great differ-
ence in the habits of the pine
and the elm (see Figs. 56,
57, 58, 59), and many of our

FIG. 54. A portion of a woodbine
(Ampelopsis). The stem tendrils
have attached themselves to a
smooth wall by means of disk-like
suckers. — After STRASBURGER.

«. 56. A tree of the pine type (larch), showing the continuous central shaft and
{he horizontal branches, which tend to become more upright towards the top of
the tree. The general outline is distinctly conical. The larch is peculiar among
snch trees in periodically shedding its leaves.

FIG. 57. A pine tree, showing the central shaft and also the bunching of the
needle leaves toward the tips of the branches where there is the best exposure
to light.

SHOOTS

common trees may be known, even at a distance, by their
characteristic habits (see Figs. 60, 61, 62). The difficulty
of the mechanical problems solved by these huge bodies
is very great. They maintain form and position and en-
dure tremendous pressure and strain.

FIG. 58. An elm in its winter condition, showing the absence of a continuous central
shaft, the main stem soon breaking up into branches, and giving a spreading top.
On each side in the background are trees of the pine type, showing the central
shaft and conical outline.

68 PLANT STUDIES

48. Eelation to light. — As stems bearing foliage leaves
hold a special relation to light, it is necessary to speak of
the influence of light upon the direction of growth, an

FIG. 59. An elm in foliage, showing the breaking up of the trunk into branches and
the spreading top.

influence known as heliotropism, already referred to under
foliage leaves. In the case of an erect stem the tendency
is to grow towards the source of light (see Figs. 1, G4).

SHOOTS

This has the general result of placing the leaf blades at
right angles to the rays of light, and in this respect the
heliotropism of the stem aids in securing a favorable leaf
position (see Figs. 63, 630). Prostrate stems are differently
affected by the light, however, being directed transversely
to the rays of light. The same is true of many foliage

FIG. 60. An oak in its winter condition, showing the wide branching. The various
directions of the branches have been determined by the light-relations.

branches, as may be seen by observing almost any tree in
which the lower branches are in the general transverse posi-
tion. These branches generally tend to turn upwards when
they are beyond the region of shading. Subterranean
stems are also mostly horizontal, but they are out of the
influence of light, and under the influence of gravity,
known as geotropism, which guides them into the trans-
verse position. The climbing stem, like the erect one,

PLANT STUDIES

FIG. 61. Cotton woods, in winter condition, on a sand dune, showing the branching
habit, and the tendency to grow in groups.

grows towards the light, while floating stems may be
either erect or transverse.

B. Stems bearing scale leaves

49. General character. — A scale leaf is one which does
not serve as foliage, as it does not develop the necessary
chlorophyll. This means that it does not need such an
exposure of surface, and hence scale leaves are usually much
smaller, and certainly are more inconspicuous than foliage
leaves. A good illustration of scale leaves is furnished by
the ordinary scaly buds of trees, in which the covering of
overlapping scaly leaves i3 very conspicuous (see Fig. 65).
As there is no development of chlorophyll in such leaves,

SHOOTS

they do not need to be exposed to the light. Stems hearing
only scale leaves, therefore, hold no necessary light-relation,
and may be subterranean as well as aerial. For the same

FIG. 62. A group of weeping birches, showing the branching habit and the peculiar
hanging branchlets. The trunks also show the habit of birch bark iii peeling off
in bands around the stem.

reason scale leaves do not need to be separated from one
another, but may overlap, as in the buds referred to.

Sometimes scale leaves occur so intermixed with foliage

FIG. 63. Sunflowers with the upper part of the stem sharply bent towards the light,
giving the leaves better exposure.— After SCHAFPNER.

SHOOTS

leaves that no peculiar stem type is developed. In the
pines scale leaves are found abundantly on the stems which
are developed for foliage purposes. In fact, the main stem
axes of pines bear only scale leaves, while short spur-like
branches bear the characteristic needles, or foliage leaves,
but the form of the
stem is controlled
by the needs of the
foliage. Some very
distinct types of
scale-bearing stems
may be noted.

50. The bud type.
— In this case the
nodes bearing the
leaves remain close
together, not sepa-
rating, as is neces-
sary in ordinary
foliage-bearing
stems, and the
leaves overlap. In
a stem of this char-
acter the later joints
may become sepa-
rated and bear foli-
age leaves, so that

one finds scale leaves below and foliage leaves above on
the same stem axis. This is always true in the case of
branch buds, in which the scale leaves serve the purpose
of protection, and are aerial, not because they need a
light-relation, but because they are protecting young foli-
age leaves which do.

Sometimes the scale leaves of this bud type of stem do
not serve so much for protection as for food storage, and
become fleshy. Ordinary bulbs, such as those of lilies, etc.,

FIG. 63a. Cotyledons of castor-oil bean ; the seedling
to the left showing the ordinary position of the
cotyledons, the one to the right showing the curva-
ture of the stem in response to light from one
side.— After ATKINSON.

PLANT STUDIES

FIG. 64. An araucarian pine, showing the
central shaft, and the regular clusters of
branches spreading in every direction and
bearing numerous small leaves. The low-
ermost branches extend downwards and
are the largest, while those above become
more horizontal and smaller. These dif-
ferences in the size and direction of the
branches secure the largest light expo-
sure.

are of this character ;
and as the main pur-
pose is food storage
the most favorable
position is a subter-
ranean one (see Fig.
66). Sometimes such
scale leaves become
very broad and not
merely overlap but en-
wrap one another, as
in the case of the
onion.

51. The tuber type.
— The ordinary potato
may be taken as an il-
lustration (see Fig.
67). The minute scale
leaves, to be found at
the "eyes" of the
potato, do not overlap,
which means that the
stem joints are farther
apart than in the bud
type. The whole form
of the stem results
from its use as a place
of food storage, and
hence such stems are
generally subterra-
nean. Food storage,
subterranean position,
and reduced scale
leaves are facts which
seem to follow each
other naturally.

SHOOTS

52. The rootstock type, — This is prob-
ably the most common form of subter-
ranean stem. It is elongated, as are foli-
age stems, and hence the scale leaves
are well separated. It is prominently
used for food storage, and is also admirably
adapted for subterranean migration (see
Fig. 68). It can do for the plant, in the
way of migration, what prostrate foliage-
bearing stems do, and is in a more protected
position. Advancing beneath the ground,
it sends up a succession of branches
to the surface. It is a very efficient
method for the "spreading" of plants,
and is extensively used by grasses in cov-
ering areas and forming turf. The persist-
ent continuance of the worst weeds is often
due to this habit (see Figs. 69, 70). It

is impossible

FIG. 65. Branch buds
of elm. Three buds
(K) with their over-
lapping scales are
shown, each just
above the scar (6)
of an old leaf. —
After BEHREN?.

FIG. 66. A bulb, made up of overlap-

ping scales, which are fleshy on an(j vigorous activity,
account of food storage. — After

to remove

all of the

indefinitely

branchin g

rootstocks

from the soil,

and any fragments that remain

are able to send up fresh crops

of aerial branches.

53. Alternation of rest and
activity. — In all of the three
stem types just mentioned, it
is important to note that they
are associated with a remark-
able alternation between rest
From

GRAY.

the branch buds the new leaves

PLANT STUDIES

emerge with
great rapidity,
and trees be-
come covered
with new foliage
in a few days.
From the sub-
terranean stems
the aerial parts
come up so
speedily that the
surface of the
ground seems to
be covered suddenly with young vegetation. This sudden
change from comparative rest to great activity has been
well spoken of as the " awakening" of vegetation.

FIG. 67. A potato plant, showing the subterranean tubers. —
After STRASBURGER.

C. Stems bearing floral leaves

54. The flower. — The so-called
"flowers" which certain plants
produce represent another type of
shoot, being stems with peculiar
leaves. So attractive are flowers
that they have been very much
studied ; and this fact has led
many people to believe that flowers
are the only parts of plants worth
studying. Aside from the fact
that a great many plants do not
produce flowers, even in those
that do the flowers are connected
with only one of the plant pro-
cesses, that of reproduction.
Every one knows that flowers are
exceedingly variable, and names

FIG. 08. The rootstock of Solo-
mon's seal ; from the under side
roots are developed ; and on the
upper side are seen the scars
which mark the positions of the
successive aerial branches which
bear the leaves. The advanc-
ing tip is protected by scales
(forming a bud), and the posi-
tions of previous buds are in-
dicated by groups of ring-like
scars which mark the attach-
ment of former scales. Advanc-
ing in front and dying behind
such a rootstock may give rise
to an indefinite succession of
aerial plants.— After GRAY.

SHOOTS 77

have been given to every kind of variation, so that their
study is often not much more than learning the definitions
of names. However, if we seek to discover the life-rela-
tions of flowers we find that they may be stated very simply.
55. Life-relations. — The flower is to produce seed. It
must not only put itself into proper relation to do this, but

FIG. 69. The rootstock of a rush (Juncus), showing how it advances beneath the
ground and sends above the surface a succession of branches. The breaking up
of such a rootstock only results in so many separate individuals.— After COWLES.

there must also be some arrangement for putting the seeds
into proper conditions for developing new plants. In the
production of seed it is necessary for the flower to secure a
transfer of certain yellowish, powdery bodies which it pro-
duces, known as pollen or pollen-grains, to the organ in
which the seeds are produced, known as the pistil. This
transfer is called pollination. One of the important things,
therefore, in connection with the flower, is for it to put

PLANT STUDIES

FIG. 70. An alpine willow, showing a strong rootstock developing aerial branches
and roots, and capable of long life and extensive migration.— After SCHIMPER.

itself into such relations that it may secure pollination.

Besides pollination,
which is necessary
to the production of
seeds, there must be
an arrangement for
seed distribution.
It is always well for
seeds to be scattered,
so as to be separated
from one another
and from the parent
plant. The two
great external prob-

FIG. 71. A flower of peony, showing the four sets of ° -1

floral organs : k, the sepals, together called the lems in Connection

calyx ; c, the petals, together called the corolla ; with the flower
a, the numerous stamens ; g, the two carpels, /

which contain the ovules.-After STRASBURGER. therefore, are polll-

SHOOTS

nation and seed-distribution.
It is necessary to call attention
to certain peculiar features of
this type of stem.

56. Structures. — The joints
of the stem do not spread
apart, so that the peculiar
leaves are kept close together,
usually forming a rosette-like
cluster (see Fig. 71). These
leaves are of four kinds : the
lowest (outermost) ones (indi-
vidually sepals, collectively
calyx} mostly resemble small
foliage leaves ; the next higher
(inner) set (individually petals,
collectively corolla) are usually
the most conspicuous, delicate
in texture and brightly col-
ored ; the third set (stamens)
produces the pollen ; the
highest (innermost) set (car-
pels) form the pistil and pro-
duce the ovules, which are to
become seeds. These four sets
may not all be present in the
same flower ; the members of
the same set may be more or
less blended with one another,
forming tubes, urns, etc. (see
Figs. 72, 73, 74) ; or the dif-
ferent members may be modi-
fied in the greatest variety of
ways.

Another peculiarity of this
type of stem is that when the

FIG. 72. A group of flowers of the rose
family. The one at the top (Poten-
lilld) shows three broad sepals,
much smaller petals alternating
with them, a group of stamens, and
a large receptacle bearing numer-
ous small carpels. The central one
(Alchemilld) shows the tips of two
small sepals, three larger petals
united below, stamens arising from
the rim of the urn, and a single pe-
culiar pistil. The lowest flower (the
common apple) shows the sepals,
petals, stamens, and three styles,
all arising from the ovary part of
the pistil.— After FOCKE.

PLANT STUDIES

FIG. 73. 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 ; &, a corolla tube split open
and showing the five stamens attached to it near the base ; c, a pistil made up of
two blended carpels, the bulbous base (containing the ovules) being the ovary, the
long stalk-like portion the style, and the knob at the top the stigma. — After
STRASBURGER.

last set of floral leaves (carpels) appear, the growth of the
stem in length is checked and the cluster of floral leaves

a b c d

FIG. 74. A group of flower forms : a, a flower of harebell, showing a bell-shaped
corolla composed of five petals ; 6, a flower of phlox, showing a tubular corolla
with its five petals distinct above and sharply spreading ; c, a flower of dead-nettle,
showing an irregular corolla with its five petals forming two lips above the funnel-
form base ; c?, 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.

SHOOTS 81

appears to be upon the end of the stem axis. It is usual,
also, for the short stem bearing the floral leaves to broaden

FIG. 75. The Star-of -Bethlehem ( Ornithogalum), showing the loose cluster of flowers
at the end of the stem. The leaves and stem arise from a bulb, which produces a
cluster of roots below. — After STRASBURGEB.

at the apex and form what is called a receptacle, upon which
the close set floral leaves stand.

Although many floral stems are produced singly, it is

82 PLANT STUDIES

very common for them to branch, so that the flowers appear
in clusters, sometimes loose and spray-like, sometimes com-
pact (see Figs. 75, 76, 77). For example, the common

FIG. 76. A flower cluster from a walnut tree. — After STRASBURGEK.

dandelion " flower" is really a compact head of flowers.
All of this branching has in view better arrangements for
pollination or for seed-distribution, or for both.

The subject of pollination and seed-distribution will be
considered under the head of reproduction.

SHOOTS

STRUCTURE AND FUNCTION OF THE STEM

57. Stem structure, — The aerial foliage stem is the most
favorable for studying stem structure, as it is not distorted
by its position or by being a depository for food. If an
active twig of an ordinary woody plant be cut across, it will

FIG. 77. Flower clusters of an umbellifer (Sium).— After STRASBTJRGER.

be seen that it is made up of four general regions (see Fig.
78): (1) an outer protecting layer, which may be stripped
off as a thin skin, the epidermis ; (2) within the epider-
mis a zone, generally green, the cortex ; (3) an inner zone
of wood or vessels, known as the vascular region ; (4) a
central pith.

58. Dicotyledons and Conifers. — Sometimes the vessels

PLANT STUDIES

FIG. 78. Section across a young twig of box
elder, showing the four stem regions : e,
epidermis, represented by the heavy bound-
ing line ; c, cortex ; w, vascular cylinder ;
p, pith.

are arranged in a hollow
cylinder, just inside of
the cortex, leaving what
is called pith in the
center (see Fig. 78).
Sometimes the pith dis-
appears in older stems or
parts of stems and leaves
the stem hollow. When
the vessels are arranged
in this way and the stem
lives more than a year, it
can increase in diameter
by adding new vessels
outside of the old. In

the case of trees these additions appear in cross-section like

a series of concentric rings, and as there is usually but one

growth period during the year, they are often called annual

rings (see Fig. 79), and the age of a tree is often estimated

by counting them.

This method of ascer-
taining the age of a

tree is not absolutely

certain, as there may

be more than one

growth period in some

years. In the case of

trees and shrubs the

epidermis is replaced

on the older parts by

layers of cork, which

sometimes becomes

very thick and makes FlG- 79- f*ci™ acro*8 a twig °\ box elder threhe

•* years old, showing three annual rings, or growth

Up the Outer part of rings, in the vascular cylinder. The radiating

What is Commonly lines (m) which cross the vascular region (w)rep-

resent the pith rays, the principal ones extending
Called bark. from the pith to the cortex (c).

SHOOTS

1 i

Stems which increase in diameter mostly belong to the
great groups called Dicotyledons and Conifers. To the
former belong most of our common trees, such as maple,
oak, beech, hickory, etc. (see Figs. 58, 59, 60, 61), as
well as the great majority of common herbs ; to the latter
belong the pines, hemlocks, etc. (see Figs. 56, 57, 64,
193, 194). This annual increase in diameter enables the
tree to put out an increased number of branches and
hence foliage leaves each year, so
that its capacity for leaf work be-
comes greater year after year. A
reason for this is that the stem is
conducting important food sup-
plies to the leaves, and if it in-
creases in diameter it can conduct
more supplies each year and give
work to more leaves.

59. Monocotyledons. — In other
stems, however, the vessels are
arranged differently in the central
region. Instead of forming a hol-
low cylinder enclosing a pith, they
are scattered through the central
region, as may be seen in the cross-
section of a corn-stalk (see Fig.

80). Such stems belong mostly to a great group of plants
known as Monocotyledons, to which belong palms, grasses,
lilies, etc. For the most part such stems do not increase in
diameter, hence there is no branching and no increased
foliage from year to year. A palm well illustrates this
habit, with its columnar, unbranching trunk, and its crown
of foliage leaves, which are about the same in number from
year to year (see Figs. 81, 82).

60. Ferns. — The same is true of the stems of most fern-
plants, as the vessels of the central region are so arranged
that there can be no diameter increase, though the ar-

FIG. 80. A corn-stalk, showing
cross-section and longitudinal
section. The dots represent
the scattered bundles of ves-
sels, which in the longitudinal
section are seen to be long
fiber-like strands.

FIG. 81. A date palm, showing the unbranched columnar trunk covered with old leaf
bases, and with a cluster of huge active leaves at the top, only the lowest portions
of which are shown. Two of the very heavy fruit clusters are also shown.

SHOOTS

rangement is very different from that found in Monocotyle-
dons. It will be noticed how similar in general appearance
is the habit of the tree fern and that of the palm (see Fig.
83).

61. Lower plants. — In the case of moss-plants, and such
algae and fungi as develop stems, the stems are very much

FIG. 82. A palm of the palmetto type (fan palm), with low stem and a crown of large

leaves.

simpler in construction, but they serve the same general
purpose.

62. Conduction by the stem. — Aside from the work of
producing leaves and furnishing mechanical support, the
stem is a great conducting region of the plant. This sub-
ject will be considered in Chapter X., under the general

head of "The Nutrition of Plants."
7

FIG. 83. 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 plants to the
right are bananas (monocotyledons).

CHAPTER V

ROOTS

63. General character. — The root is a third prominent
plant organ, and it presents even a greater variety of rela-
tions than leaf or stem. In whatever relation it is found
it is either an absorbent organ or a holdfast, and very often
both. For such work no light-relation is necessary, as in
the case of foliage leaves ; and there is no leaf-relation, as
in the case of stems. Roots related to the soil may be
taken as an illustration.

It is evident that a soil root anchors the plant in the
soil, and also absorbs water from the soil. If absorption is
considered, it is further evident that the amount of it will
depend in some measure upon the amount of surface which
the roots expose to the soil. We have already noticed that
the foliage leaf has the same problem of exposure, and it
solves it by becoming an expanded organ. The question
may be fairly asked, therefore, why are not roots expanded
organs ? The receiving of rays of light, and the absorbing
of water are very different in their demands. In the former
case a flat surface is demanded, in the latter tubular pro-
cesses. The increase of surface in the root, therefore, is
obtained not by expanding the organ, but by multiplying
it. Besides, to obtain the soil water the roots must burrow
in every direction, and must send out their delicate thread-
like branches to come in contact with as much soil as pos-
sible. Furthermore, in soil roots absorption is not the only
thing to consider, for the roots act as holdfasts and must
grapple the soil. This is certainly done far more effectively

PLANT STUDIES

by numerous thread-like processes spreading in every direc-
tion than by flat, expanded processes.

It should also be noted that as soil roots are subterra-
nean they are used often for the storage of food, as in the
case of many subterranean stems. Certain prominent root
types may be noted as follows :

64. Soil roots. — These roots push into the ground with

great energy,

i / \ u and their ab-

r.i\D\if.t f

sorbing sur-
faces are en-
tirely covered.
Only the young-
est parts of a
root system
absorb actively,
the older parts
transporting
the absorbed
material to the
stem, and help-
ing to grip the
soil. The soil
root is the most
common root
type, being

used by the great majority of seed plants and fern plants,
and among the moss plants the very simple root-like pro-
cesses are mostly soil-related. To such roots the water of
the soil presents itself either as free water — that is, water
that can be drained away — or as films of water adhering to
each soil particle, often called water of adhesion. To come
in contact with this water, not only does the root system
usually branch profusely in every direction, but the youngest
branches develop abundant absorbing hairs, or root hairs
(see Fig. 84), which crowd in among the soil particles and

PIG. 84. Root tips of corn, showing root hairs, their position
in reference to the growing tip, and the effect of the
surrounding medium upon their development : 1, in soil ;
2, in air ; 3, in water.

ROOTS

absorb moisture from them. By these root hairs the absorb-
ing surface, and hence the amount of absorption, is greatly

increased. Individual
root hairs do not last
very long, but new
ones are constantly ap-
pearing just behind the
advancing root tips,
and the old ones are
as constantly disap-
pearing.

(1) Geotropism and
hydrotropism. — Many
outside influences affect
roots in the direction
of their growth, and
as soil roots are espe-
cially favorable for ob-
serving these influ-
ences, two prominent

ones may be mentioned. The influence of gravity, or the
earth influence, is very strong in directing the soil root.

FIG. 85. Apparatus to 8how the response
to water (hydrotropism) upon the part of
roots. The ends -(a) of the box have hooks
for hanging, while the box proper is a cylinder
or trough of wire netting and is filled with
damp sawdust. In the sawdust are planted
peas (y), whose roots (A, z, k, m) first, descend
until they emerge from the damp sawdust,
but soon turn back toward it.— After SACHS.

FIG. 86.

A raspberry plant, whose stem has been bent down to the soil and has
root."— After BEAL.

struck

92 PLANT STUDIES

As is well known, when a seed germinates the tip that is to
develop the root turns towards the earth, even if it has
come from the seed in some other direction. This earth
influence is known as geotropism. Another directing in-
fluence is moisture, or the water influence, known as hydrot-

FIG. 87. A section through the leaf -stalk of a yellow pond-lily (\iiphar), showing the
numerous conspicuous air passages (s) by means of which the parts under water
are aerated ; h, internal hairs projecting into the air passages ; v, the much
reduced and comparatively few vascular bundles.

ropism. By means of this the root is directed towards the
most favorable water supply in the soil.

Ordinarily, geotropism and hydrotropism direct the root
in the same general way, and so reinforce each other ; but
the following experiment may be arranged, which will
separate these two influences. Bore several small holes in
the bottom of a box (such as a cigar box), suspended as in-
dicated in Figure 85, and cover the bottom with blotting
paper. Pass the root tips of several germinated seeds

ROOTS

through the holes, so that the seeds rest on the paper, and
the root tips hang through the holes. If the paper is kept
moist germination will continue, but geotropism will pull
the root tips downwards, and hydrotropism (the moist
paper) will pull them upwards. In this way they will
pursue a devious course, now directed by one influence
and now by the other.

If a root system be examined it will be found that when
there is a main axis (tap
root) it is directed
steadily downwards,
while the branches are
directed differently.
This indicates that all
parts of a root system
are not alike in their
response to these influ-
ences. Several other
influences are also con-
cerned in directing soil
roots, and the path of
any root branch is a
result of all of them.
How variable they are
may be seen by the
numerous directions in
which the branches

travel, and the whole root system preserves the record of
these numerous paths.

(2) The pull on the stem. — Another root property may
be noted in connection with the soil root, namely the pull
on the stem. When a strawberry runner strikes root at
tip (see Fig. 47), the roots, after they obtain anchorage in
the soil, pull the tip a little beneath the surface, as if they
had gripped the soil and then slightly contracted. The
same thing may be observed in the process known as

FIG. 88. A section through the stem of a water-
wort (Elatine), showing the remarkably large
and regularly arranged air passages for root
aeration. The single reduced vascular bundle
is central and connected with the small cor-
tex by thin plates of cells which radiate like
the spokes of a wheel. — After SCHENCK.

PLANT STUDIES

"layering," by which a stem, as a bramble, is bent down
and covered with soil. The covered joints strike root, and
the pulling follows (see Fig. 86). A very plain illustration
of the same fact can be obtained from many crevice plants.
These plants send their root systems into the crevices of
rocks, and spread a rosette of leaves against the rock face.
In the next year a new rosette of leaves, developed further

FIG. 89. Section through the leaf of a qnillwort (Isoetes), showing the four large air
chambers (a), the central vascular region (6), and the very poorly developed
cortex.

up the stem, is also found against the rock face. It is
evident that the stem has been pulled back into the crevice
enough to bring the new leaves against the rock, and this
pulling has been effected by the new roots, which have
laid hold of the crevice soil, or walls.

(3) Soil dangers. — In this connection certain soil dan-
gers and the response of the roots should be noted. The
soil may become poor in water or poor in certain essential
materials, and this results in an extension of the root sys-

KOOTS

tern, as if seeking for water and the essential materials.
Sometimes the root system becomes remarkably extensive,
visiting a large amount of soil in order to procure the
necessary supplies. Sometimes the soil is poor in heat, and
root activity is interfered with. In such cases it is very
common to find the leaves
massed against the soil, thus
slightly checking the loss of
heat.

Most soil roots also need free
air, and when water covers the
soil the supply is cut off. In
many cases there is some way
by which a supply of free air
may be brought down into the
roots from the parts above
water ; sometimes by large air
passages in leaves and stems
(see Figs. 87, 88, 89, 90) ; some-
times by developing special root
structures which rise above the
water level, as prominently
shown by the cypress in the
development of knees. These
knees are outgrowths from roots
beneath the water of the cypress
swamp, and rise above the water level, thus reaching the
air and aerating the root system (see Fig. 91). It has been
shown that if the water rises so high as to flood the knees
for any length of time the trees will die, but it does not
follow that this is the chief reason for their development.

65. Water roots. — A very different type of root is devel-
oped if it is exposed to free water, without any soil relation.
If a stem is floating, clusters of whitish thread-like roots
usually put out from it and dangle in the water. If the water
level sinks so as to bring the tips of these roots to the mucky

FIG. 90. Longitudinal section
through a young quillwort leaf,
showing that the four air cham-
bers shown in Fig. 89 are not con-
tinuous passages, but that there
are four vertical rows of promi-
nent chambers. The plates of
cells separating the chambers in
a vertical row very soon become
dead and full of air. In addition
to the work of aeration these air
chambers are very serviceable in
enabling the leaves to float when
they break off and carry the com-
paratively heavy spore cases.

HOOTS

FIG. 92.

A tropical aroid (Anthurium), showing its large leaves, and bunches of
aerial roots.

soil they usually do not penetrate or enter into any soil re-
lation. Such pure water roots may be found dangling from
the under surface of the common duck weeds, which often
cover the surface of stagnant water with their minute,
green, disk-like bodies.

98 PLANT STUDIES

Plants which ordinarily develop soil roots, if brought
into proper water relations, may develop water roots. For
instance, willows or other stream bank plants may be so
close to the water that some of the root system enters it.
In such cases the numerous clustered roots show their water

FIG. 93. An orchid, showing aerial roots.

character. Sometimes root systems developing in the soil
may enter tile drains, when water roots will develop in such
clusters as to choke the drain. The same bunching of water
roots may be noticed when a hyacinth bulb is grown in a
vessel of water.

66. Air roots. — In certain parts of the tropics the air is
so moist that it is possible for some plants to obtain sum-

ROOTS

cient moisture from this source, without any soil-relation or
water-relation. Among these plants the orchids are most
notable, and they may be observed in almost any green-
house. Clinging to the trunks of trees, usually imitated
in the greenhouse by nests of sticks, they send out long
roots which dangle in the moist air (see Figs. 93, 94).
It is necessary to have some special absorbing and condens-
ing arrangement, and in the
orchids this is usually pro-
vided by the development of
a sponge-like tissue about the
root known as the velamen,
which greedily absorbs the
moisture of the air. Examine
also Figs. 92, 95, 96, 97.

67. Clinging roots. — These
roots are developed to fasten
the plant body to some sup-
port, and do no work of ab-
sorption (see Fig. 98). Very
common illustrations may be
obtained from the ivies, the
trumpet creeper, etc. These
roots cling to various supports,
stone walls, tree trunks, etc.,
by sending minute tendril-
like branches into the crevices. The sea-weeds
develop grasping structures extensively, a large majority
of them being anchored to rocks or to some rigid support
beneath the water, and their bodies floating free. The
root-like processes by which this anchorage is secured are
very prominent in many of the common marine sea-weeds
(see Fig. 162).

68. Prop roots. — Some roots are developed to prop
stems or wide-spreading branches. In swampy ground, or
in tropical forests, it is very common to find the base of

FIG. 94. An orchid, showing aerial
roots and thick leaves.

FIG. 95. Astaghorn fern (Platycerium), an aerial plant of the tropics. About it is a
vine, which shows the leaves adjusted to the lighted side.

PIG. 96. Selaginella, showing dangling aerial roots and finely divided leaves.

FIG. 97. Live oaks, in the Gulf States, upon which are growing masses of long moss
or black moss (Tillandsid), a common aerial plant.

PIG. 98. A tropical forest, showing the cord-like holdfasts developed by certain
lianas, which pass around the tree trunks like tightly bound ropes.— After
KERNEB.

ROOTS

103

tree trunks buttressed by such roots which extend out over
and beneath the surface, and divide the area about the tree
into a series of irregular chambers (see Fig. 100). Some-

FIG. 99. A screw-pine (Pandanus), from the Indian Ocean regioi
prominent prop roots put out near the base.

showing the

times a stem, either inclined or with a poorly developed
primary root system, puts out prop roots which support
it, as in the screw-pine (see Fig. 99). A notable case is
8

106

PLANT STUDIES

that of the banyan tree, whose wide-spreading branches
are supported by prop roots, which are sometimes very
numerous (see Fig. 101). The immense banyans usually

illustrated are
especially culti-
vated as sacred
trees, the prop
roots being as-
sisted in pene-
trating the soil.
There is record
of such a tree in
Ceylon with 350
large and 3,000
small prop roots,
able to cover a
village of 100
huts.

69. Parasites.
— Besides roots
related to soil,
water, air, and
various mechani-
cal supports,
there are others
related to hosts.
A host is a liv-
ing plant or
animal upon
which some
other plant or
animal is living
as a parasite.
The parasite gets its supplies from the host, and must be
related to it properly. If the parasite grows upon the
surface of its host, it must penetrate the body to obtain

FIG. 102. 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.

KOOTS

107

food supplies.
Therefore, pro-
cesses are devel-
oped which pene-
trate and absorb.
The mistletoe and
dodder are seed-
plants which have
this habit, and
both have such
processes (see Figs.
102, 103). This
habit is much more
extensively devel-
oped, however, in
a low group of
plants known as
the fungi. Many
of these parasitic
fungi live upon
plants and animals,
common illustrations being the mildews of lilac leaves and
many other plants, the rust of wheat, the smut of corn, etc.

70. Root structure,
— In the lowest groups
of plants (algae, fungi,
and moss-plants) true
roots are not formed,
but very simple struc-
tures, generally hair-
like (see Fig. 104). In
fern-plants and seed-
plants, however, the
root is a complex
structure, so different
from the root-like pro-

Fio. 103. A section showing the living connection
between dodder and a golden rod upon which it is
growing. The penetrating and absorbing organ (h)
has passed through the cortex (c), the vascular
zone (6), and is disorganizing the pith (p).

FIG. 104. Section through the thallus of a liver-
wort (Marchantia), showing the hair-like pro-
cesses (rhizoids) which come from the under
surface and act as roots in gripping and ab-
sorbing. In the epidermis of the upper surface
a chimney-like opening is seen, leading into
a chamber containing cells with chloroplasts.

108

PLANT STUDIES

cesses of the lower groups that it is regarded as the only
true root. It is quite uniform in structure, consisting of a
tough and fibrous central axis surrounded by a region of
more spongy structure. The tough axis is mostly made
up of vessels, so called because they
conduct material, and is called the
vascular axis. The outer more spongy
region is the cortex, which covers
the vascular axis like a thick skin
(see Fig. 105).

One of the peculiarities of the
root, in which it differs from the
stem, is that the branches come from
the vascular axis and burrow through
the cortex, so that when the latter
is peeled off the branches are left
attached to the axis, and the cortex
shows the holes through which they
passed. It is evident that when such
a root is absorbing, the absorbed ma-
terial (water with various materials
in solution) is received into the

of the cortex the epi- , , . ,

dermis (e) which disap- cortex, through which it must pass
to the vascular axis to be conducted
to the stem.

Another peculiarity of the root
is that it elongates only by growth at the tip, while the
stem usually continues to elongate some distance behind
its growing tip. In the soil this delicate growing tip is
protected by a little cap of cells, known as the root-cap
(see Fig. 105).

FIG. 105. A longitudinal
section through the root
tip of shepherd's purse,
showing the central vas-
cular axis (p!\ surrounded
by the cortex (p), outside

pears in the older parts of
the root, and the promi-
nent root-cap (c).

CHAPTER VI

REPRODUCTIVE ORGANS

IT will be remembered that nutrition and reproduction
are the two great functions of plants. In discussing
foliage leaves, stems., and roots, they were used as illustra-
tions of nutritive organs, so far as their external relations
are concerned. We shall now
briefly study the reproductive
organs from the same point
of view, not describing the
processes of reproduction, but
some of the external relations.

71. Vegetative multiplica-
tion.— Among the very lowest
plants, no special organs of
reproduction are developed,
but most plants have them.
There is a kind of reproduc-
tion by which a portion of
the parent body is set apart to
produce a new plant, as when
a strawberry runner produces
a new strawberry plant, or
when a willow twig or a grape
cutting is planted and produces new plants, or when a potato
tuber (a subterranean stem) produces new potato plants, or
when pieces of Begonia leaves are used to start new Begonias.
This is known as vegetative multiplication, a kind of repro-
duction which does not use special reproductive organs.

109

FIG. 106. A group of spores :
spores from a common mold (a
fungus), which are so minute and
light that they are carried about by
the air ; B, two spores from a com-
mon alga (Ulothrix), which can
swim by means of the hair-like
processes ; C', the conspicuous dotted
cell is a spore developed by a com-
mon mildew (a fungus), which is
carried about by currents of air.

110

PLANT STUDIES

72. Spore reproduction. — Besides vegetative multiplica-
tion most plants develop special reproductive bodies,
known as spores, and this kind of reproduction is known
as spore reproduction. These spores are very simple
bodies, but have the power of producing new individuals.
There are two great groups of spores, differing from each
other not at all in their powers, but in the method of their
production by the parent plant. One kind of spore is

produced by dividing
certain organs of the
parent ; in the other
case two special bodies
of the parent blend
together to form the
spore. Although they
are both spores, for
convenience we may
call the first kind
spores (see Figs. 106,
109), and the second
kind eggs (see Fig.
107).* The two special

FIG. 107. Fragments of a common alga (Spi-
rogyra). Portions of two threads are shown,
which have been joined together by the grow-
ing of connecting tubes. In the upper thread
four cells are shown, three of which contain
eggs (z), while the cell marked <?, and its mate
of the other thread each contain a gamete,
the lower one of which will pass through the
tube, blend with the upper one, and form
another egg.

bodies which blend to-
gether to form an egg
are called gametes (see
Figs. 107, 108, 109). These terms are necessary to any
discussion of the external relations. Most plants develop
both spores and eggs, but they are not always equally con-
spicuous. Among the algae, both spores and eggs are prom-
inent ; among certain fungi the same is true, but many
fungi are not known to produce eggs ; among moss-plants
the spores are prominent and abundant, but the egg is
concealed and not generally noticed. What has been said

* It is recognized that this spore is really a fertilized egg, but in
the absence of any accurate simple word, the term egg is used for con-
venience.

REPRODUCTIVE ORGANS

111

of the moss-plants is still more true
of the fern-plants ; while among
the seed-plants certain spores (pol-
len grains) are conspicuous (see
Fig. 110), but the eggs can be ob-
served only by special manipulation
in the laboratory. Seeds are neither
spores nor eggs, but peculiar repro-
ductive bodies which the hidden
egg has helped to produce.

73. Germination. — Spores and
eggs are expected to germinate ;
that is, to begin the development
of a new plant. This germination
needs certain external conditions,
prominent among which are defi-
nite amounts of heat, moisture,
and oxygen, and sometimes light.
Conditions of germination may be
observed most easily in connection
with seeds. It must be understood,
however, that what is called the
germination of seeds is something

very different from the germination
of spores and eggs. In the latter
cases, germination includes the very
beginnings of the young plant. In
the case of a seed, germination begun
by an egg has been checked, and
seed germination is its renewal. In
other words, an egg has germinated
and produced a young plant called
the "embryo," and the germination
of the seed simply consists in the
continued growth and the escape of
this embryo.

FIG. 108. A portion of the
body of a common alga
( (Edogonium), showing
gametes of very unequal size
and activity ; a very large
one (o) is lying in a globular
cell, and a very small one is
entering the cell, another
similar one (s) being just
outside. The two small
gametes have hair-like pro-
cesses and can swim freely.
The small and large gam-
etes unite and form an egg.

FIG. 109. A group of swim-
ming cells : A, a spore of
(Edogonlum (an alga) ;
B, spores of Utothrix (an
alga) ; C, a gamete of
Equisetum (horse-tail or
scouring rush).

112

PLANT STUDIES

FIG. 110. A pollen grain (spore) from the
pine, which develops wings (w) to assist
in its transportation by currents of air.

It is evident that for
the germination of seeds
light is not an essential
condition, for they may
germinate in the light or
hi the dark ; but the need
of heat, moisture, and
oxygen is very apparent.
The amount of heat re-
quired for germination
varies widely with different
seeds, some germinating
at much lower tempera-
tures than others. Every

kind of seed, or spore, or egg has a special temperature

range, below which and above which

it cannot germinate. The two limits

of the range may be called the

lowest and highest points, but be-
tween the two there is a best point

of temperature for germination. The

same general fact is true in reference

to the moisture supply.

74. Dispersal of reproductive bodies.

— Among the most striking external

relations, however, are those con-
nected with the dispersal of spores,

gametes, and seeds. Spores and

seeds must be carried away from the

parent plant, and separated from

each other, out of the reach of

rivalry for nutritive material ; and

gametes must come together and FlG. m. Apodoffireweed

blend to form the eggS. Conspicuous (EpUobium) opening and

among the means of transfer are the exposing its plumed seeds

°. which are transported by

following. the wind.-After BEAL.

KEPRODUCTIVE ORGANS

113

75. Dispersal by locomotion. — The common method of
locomotion is by means of movable hairs (cilia) developed
upon the reproductive body, which propel it through the
water (see Fig. 109).

Swimming spores are
very common among
the algae, and at least
one of the gametes
in algae, moss-plants,
and fern-plants has
the power of swim-
ming by means of
cilia.

76. Dispersal by
water. — It is very
common for repro-
ductive bodies to be
transported by cur-
rents of water. The
spores of many water
plants of all groups,
not constructed for
locomotion, are thus
floated about. This
method of transfer is
also very common -,•
among seeds. Many
seeds are buoyant, or
become so after soak-
ing in water, and
may be carried to
great distances by

currents. For this reason the plants growing upon the
banks or flood-plains of streams may have come from a
wide area. Many seeds can even endure prolonged soak-
ing in sea-water, and then germinate. Darwin estimated

FIG. 112. The upper figure to the left is ar opening
pod of fireweed discharging its plumed seeds.
The lower figure represents the seed-like fruits
of Clematis with their long tail-like plumes. —
After KERNER.

114

PLANT STUDIES

that at least
fourteen per
cent, of the
seeds of any
country can re-
tain their vital-
ity in sea-water
for twenty-
eight days. At
the ordinary
rate of move-
ment of ocean
currents, this
length of time
would permit
such seeds to
be transported
over a thou-
sand miles,
thus making
possible a very great range in distribution.

77. Dispersal of spores by air. — This is one of the most
common methods of transport-
ing spores and seeds. In most
cases spores are sufficiently
small and light to be trans-
ported by the gentlest move-
ments of air. Among the
fungi this is a very common
method of spore dispersal (see
Fig. 106), and it is extensively
used in scattering the spores
of moss-plants, fern-plants (see
Fig. 45), and seed-plants.
Among seed-plants this is one
method of pollination, the

FIG. 113. A ripe dandelion head, showing the mass of
plumes, a few seed-like fruits with their plumes still
attached to the receptacle, and two fallen off.— After
KEENER.

FIG. 114. Seed-like fruits of Senecio
with plumes for dispersal by air.—
After KEBNEK.

REPRODUCTIVE ORGANS

115

FIG. 115. A winged seed of Bignonia.— After STRASBUBGER.

spores called pollen
and occasionally
falling upon the
right spot for
germination.
With such an
agent of transfer
the pollen must
be very light and
powdery, and
also very abun-
dant, for it must
come down al-
most like rain to be

grains being scattered by the wind,

FIG. 117.

Winged fruit of
KEKNEB.

FIG. 116. Winged fruit of maple. — After KERNER.

certain of reaching the right places.
Among the gymiio-
sperms (pines, hem-
locks, etc.) this is the
exclusive method of
pollination, and when a
pine forest is shedding
pollen the air is full of
the spores, which may
be carried to a great
distance before being
deposited. Occasional

Ptelea.— After

116

PLANT STUDIES

FIG. 118. Winged fruit of
Ailanthus. — After KER-

NER.

reports of "showers of sulphur" have
arisen from an especially heavy fall of
pollen that has been carried far from
some gymnosperm forest. In the case
of pines and their near relatives, the
pollen spores are assisted in their dis-
persal through the air by developing a
pair of broad wings from the outer
coat of the spore (see Fig. 110). This
same method of pollination — that is,
carrying the pollen spores by currents
of air — is also used by many mono-
cotyledons, such as grasses ; and by
many dicotyledons, such as our most
common forest trees
(oak, hickory, chest-
nut, etc.).

78. Dispersal of
seeds by air. — Seeds
are very rarely light
enough to be carried
by currents of air
without some special
adaptation. Wings
and plumes of very
many and often very
beautiful patterns
are exceedingly com-
mon in connection
with seeds or seed-
like fruits (see Figs.
115, 116, 117, 118,
119). Wings are de-
veloped by the fruit

FIG. 119. Fruit of basswood (Tilia), showing the
ash, and by the Seeds peculiar wing formed by a leaf.— After KERNER.

REPRODUCTIVE ORGANS

117

FIG. 120. A common tumbleweed ( Cyclolomd).

of pine and catalpa. Plumes and tufts of hairs are devel-
oped by the seed-like fruits of dandelion, thistle, and very
many of their relatives, and by the seeds of the milkweed
(see Figs. Ill, 112, 113, 114). On plains, or level stretches,
where winds are
strong, a curious
habit of seed dis-
persal has been de-
veloped by certain
plants known as
" tumbleweeds " or
"field rollers//
These plants are
profusely branching
annuals with a small

FIG. 121. The 3-valved fruit of violet discharging
root System in a its seeds.-After BEAL.

118

PLANT STUDIES

FIG. 122. A fruit of witch
hazel discharging its
seeds.— After BEAL.

light or sandy soil (see Fig. 120).
When the work of the season is over,
and the absorbing rootlets have
shriveled, the plant is easily blown
from its anchorage by a gust of wind,
and is trundled along the surface like
a light wicker ball, the ripe seed ves-
sels dropping their seeds by the way.
In case of an obstruction, such as a
fence, great masses of these tumble-
weeds may often be seen lodged
against the windward side.

79. Discharge of spores. — In many
plants the distribution of spores and
seeds is not provided for by any of

the methods just mentioned, but the vessels containing

them are so constructed that they are discharged with

more or less violence and are some-
what scattered.

Many spore cases, especially those

of the lower plants, burst irregularly,

and with sufficient violence to throw

out spores. In the liverworts pecu-
liar cells, called elaters or "jumpers,"

are formed among the spores, and

when the wall of the spore case is

ruptured the elaters are liberated,

and by their 'active motion assist in

discharging the spores.

In most of the true mosses the

spore case opens by pushing off a

lid at the apex, which exposes a

delicate fringe of teeth covering the

mouth of the urn-like case. These

teeth bend in and out of the open

spore case as they become moist or

FIG. 123. A pod of wild bean
bursting, the two valves
violently twisting and dis-
charging the seeds.— After
BEAL.

KEPRODTJCTTVE ORGANS

119

dry, and are of considerable service

in the discharge of spores.

In the common ferns a heavy

spring-like ring of cells encircles

the delicate-walled spore case.

When the wall becomes dry and

comparatively brittle the spring

straightens with considerable force,

the delicate wall is suddenly torn

and the spores are discharged (see

Fig. 45).

Even in the case of the pollen-
spores of seed-plants, a special layer

of the wall of the pollen-sac usually

develops as a spring-like layer, which

assists in opening widely the sac
when the wall be-
gins to yield along
the line of break-
ing.

80. Discharge of

seeds. — While seeds are generally carried
away from the parent plant by the agency
of water currents or air currents, as al-
ready noted, or by animals, in some in-
stances there is a mechanical discharge
provided for in the structure of the seed-
case. In such plants as the witch hazel
and violet, the walls of the seed-vessel
press upon the contained seeds, so that
when rupture occurs the seeds are pinched
out, as a moist apple-seed is discharged
by being pressed between the thumb and
finger (see Figs. 121, 122). In the touch-
me-not a strain is developed in the wall
of the seed-vessel, so that at rupture it

FIG. 124. Fruits of Spanish
needle, showing barbed ap-
pendages for grappling.
The figure to the left is one
of the fruits enlarged. —
After KERNEK.

FIG. 125. A fruit of
beggar ticks,
showing the two
barbed append-
ages which lay
hold of animals.
—After BEAL.

120

PLANT STUDIES

suddenly curls up and throws the seeds (see Fig. 123). The
squirting cucumber is so named because it becomes very
much distended with water, which is finally forcibly ejected
along with the mass of seed. An " artillery plant " common

in cultivation discharges its
seeds with considerable vio-
lence ; while the detonations
resulting from the explosions
of the seed-vessels of Hura
crepitans, the " monkey's din-
ner bell/' are often remarked
by travelers in tropical
forests.

81. Dispersal of seeds by animals. — Only a few illustra-
tions can be given of this very large subject. Water birds
are great carriers of seeds which are contained in the mud
clinging to their feet and legs. This mud from the borders
of ponds is usually completely filled with seeds and spores
of various plants. One has no conception of the number
until they are actually com-
puted. The following ex-
tract from Darwin's Origin
of Species illustrates this
point :

FIG. 126. The fruit of carrot, showing
the grappling appendages. — After
BEAL.

FIG. 127. The fruit of cocklebur, showing
the grappling appendages.— After BEAL.

"I took, in February, three
tablespoonfuls of mud from three
different points beneath water,
on the edge of a little pond. This mud when dried weighed only 6f
ounces ; I kept it covered up in my study for six months, pulling up
and counting each plant as it grew ; the plants were of many kinds,
and were altogether 537 in number ; and yet the viscid mud was all
contained in a breakfast cup ! "

Water birds are generally high and strong fliers, and the
seeds and spores may thus be transported to the margins of
distant ponds or lakes, and so very widely dispersed.

In many cases seeds or fruits develop grappling append-

REPRODUCTIVE ORGANS

121

ages of various kinds, which lay hold of animals brushing
past, and so the seeds are dispersed. Common illustrations
are Spanish needles, beggar ticks, stick seeds, burdock, etc.
Study Figs. 124, 125, 126, 127, 128, 129, 130.

FIG. 128. Fruits with grappling appendages. That to the left is agrimony ; that to
the right is Galium.— After KEENER.

In still other cases the fruit becomes pulpy, and attrac-
tive as food to certain birds or mammals. Many of the
seeds (such as those of grapes) may be able to resist the
attacks of the digestive fluids and escape from the alimen-
tary tract in a condition to germinate. As if to attract the
attention of fruit-eating animals, fleshy fruits usually
become brightly col-
ored when ripe, so that
they are plainly seen
in contrast with the
foliage.

82. Dispersal of pol-
len spores by insects.—
The transfer of pollen,
the name applied to FlG- 129- Fruits with Dappling appendages.

. The figure to the left is cocklebur ; that to the

Certain spores Of Seed- right is burdock.-After KEKNER.

122

PLANT STUDIES

plants, is known as pollination, and
the two chief agents of this transfer
are currents of air and insects. In
§77 the transfer by currents of air
was noted, such plants being known
as anemophilous plants. Such plants
seldom produce what are generally
recognized as true flowers. All those
seed-plants which produce more or
less showy flowers, however, are in
some way related to the visits of
insects to bring about pollination,
and are known as entomophilous
plants. This relation between in-
sects and flowers is so important and so extensive that it
will be treated in a separate chapter.

FIG. 130 A head of fruits of
burdocK, showing the
grappling appendages.—
After BEAL.

CHAPTER VII

FLOWERS AND INSECTS

83. Insects as agents of pollination. — The use of insects
as agents of pollen transfer is very extensive, and is the pre-
vailing method of pollination among monocotyledons and
dicotyledons. All ordinary flowers, as usually recognized,
are related in some way to pollination by insects, but it
must not be supposed that they are always successful in
securing it. This mutually helpful relation between flow-
ers and insects is a very wonderful one, and in some cases
it has become so intimate that they cannot exist without
each other. Flowers have been modified in every way to be
adapted to insect visits, and insects have been variously
adapted to flowers.

84. Self-pollination and cross-pollination. — The advantage
of this relation to the flower is to secure pollination. The
pollen may be transferred to the carpel of its own flower,
or to the carpel of some other flower. The former is known
as self -pollination, the latter as cross-pollination. In the
case of cross-pollination the two flowers concerned may be
upon the same plant, or upon different plants, which may
be quite distant from one another. It would seem that
cross-pollination is the preferred method, as flowers are so
commonly arranged to secure it.

85. Advantage to insects. — The advantage of this relation
to the insect is to secure food. This the flower provides
either in the form of nectar or pollen ; and insects visiting
flowers may be divided roughly into the two groups of
nectar-feeding insects, represented by butterflies and moths,

123

124 PLANT STUDIES

and pollen-feeding insects, represented by the numerous
bees and wasps. When pollen is provided as food, the
amount of it is far in excess of the needs of pollination.
The presence of these supplies of food is made known to
the insect by the display of color in connection with the
flowers, by odor, or by form. It should be said that the
attraction of insects by color has been doubted recently, as
certain experiments have suggested that some of the com-
mon flower-visiting insects are color-blind, but remarkably
keen-scented. However this may be for some insects, it
seems to be sufficiently established that many insects rec-
ognize their feeding ground by the display of color.

86. Suitable and unsuitable insects. — It is evident that
all insects desiring nectar or pollen for food are not suit-
able for the work of pollination. For instance, the ordi-
nary ants are fond of such food, but as they walk from plant
to plant the pollen dusted upon them is in great danger of
being brushed off and lost. The most favorable insect is
the flying one, that can pass from flower to flower through
the air. It will be seen, therefore, that the flower must not
only secure the visits of suitable insects, but must guard
against the depredations of unsuitable ones.

87. Danger of self-pollination, — There is still another
problem which insect-pollinating flowers must solve. If
cross-pollination is more advantageous to the plant than
self-pollination, the latter should be prevented so far as
possible. As the stamens and carpels are usually close to-
gether in the same flower, the danger of self-pollination is
constantly present in many flowers. In those plants which
have stamen-producing flowers upon one plant and carpel-
producing flowers upon another, there is no such danger.

88. Problems of pollination. — In most insect-pollinating
flowers, therefore, there are three problems : (1) to prevent
self-pollination, (2) to secure the visits of suitable insects,
and (3) to ward off the visits of unsuitable insects. It
must not be supposed that flowers are uniformly successful

FLOWERS AND INSECTS

125

in solving these problems. They often fail, but succeed
often enough to make the effort worth while.

89. Preventing self-pollination. — It is evident that this
danger arises only in those flowers in which the stamens
and carpels are associ-
ated,, but their separa- ^ " ^ 2
tion in different flowers
may be considered as
one method of prevent-
ing self-pollination. In
order to understand the
various arrangements to
be considered, it is nec-
essary to explain that
the carpel does not re-
ceive the pollen indif-
ferently over its whole
surface. There is one
definite region organ-
ized, known as the
stigma, upon which the
pollen must be deposited
if it is to do its work.
Usually this is at the
most projecting point
of the carpel, very often
at the end of a stalk-
like prolongation from
the ovary (the bulbous
part of the carpel),
known as the style;
sometimes it may run down one side of the style. When
the stigma is ready to receive pollen it has upon it a
sweetish, sticky fluid, which holds and feeds the pollen.
In this condition the stigma is said to be mature ; and the
pollen is mature when it is shedding, that is, ready to fall

FIG. 131. Parts of the flower of rose acacia
(Robiniahispida). In 1 the keel is shown pro-
jecting from the hairy calyx, the other more
showy parts of the corolla having been re-
moved. Within the keel are the stamens
and the carpel, as seen in 3. The keel forms
the natural landing place of a visiting bee,
whose weight depresses the keel and causes
the tip of the style to protrude, as shown in
2. This style tip bears pollen upon it,
caught among the hairs, seen in 3, and as it
strikes the body of the bee some pollen is
brushed off. If the bee has previously visited
another flower and received some pollen, it
will be seen that the stigma, at the very tip
of the style, striking the body first, will very
probably receive some of it. The nectar pit
is shown in 3, at the base of the uppermost
stamen. — After GRAY.

126

PLANT STUDIES

out of the pollen-sacs or to be removed from them. The
devices used by flowers containing both stamens and carpels
to prevent self-pollination are very numerous, but most
of them may be included under the three following heads :
(1) Position. — In these cases the
pollen and stigma are ready at the same
time, but their position in reference to
each other, or in reference to some con-
formation of the flower, makes it un-
likely that the pollen will fall upon the
stigma. The stigma may be placed
above or beyond the pollen sacs, or the
two may be separated by some mechan-
ical obstruction, resulting in much of
the irregularity of flowers.

In the flowers of the rose acacia and
its relatives, the several stamens and
the single carpel are in a cluster, en-
closed in the keel of the flower. The
stigma is at the summit of the style,
and projects somewhat beyond the
pollen-sacs shedding pollen. Also there
is often a rosette of hairs, or bristles,
just beneath the stigma, which acts as
a barrier to the pollen (see Fig. 131).

In the iris, or common flag, each
stamen is in a sort of pocket between
the petal and the petal-like style, while
the stigmatic surface is on the top of a
flap, or shelf, which the style sends out
as a roof to the pocket. With such an
arrangement, it would seem impossible
for the pollen to reach the stigma un-
aided (see Fig. 132).

In the orchids, remarkable for their
strange and beautiful flowers, there are

FIG. 132. A portion of
the flower of an iris,
or flag. The single
stamen shown is
standing between the
petal to the right and
the petal-like style to
the left. Near the
top of this style the
stigmatic shelf is
seen extending to the
right, which must
receive the pollen
upon its upper sur-
face. The nectar
pit is at the junc-
tion of the petal and
stamen. While ob-
taining the nectar the
insect brushes the
pollen-bearing part
of the stamen, and
pollen is lodged upon
its body. In visiting
the next flower and
entering the stamen
chamber the stig-
matic shelf is apt to
be brushed.— After
GRAY.

FLOWEKS AND INSECTS

127

usually two pollen-sacs, and stretched between them is the
stigmatic surface. In this case, however, the pollen grains
are not dry and powdery, but cling together in a mass, and
cannot escape from the sac without being pulled out (see
Fig. 133). The same sort of pollen is developed by the
milkweeds.

(2) Consecutive maturity. — In these cases the pollen and

FIG. 133. A flower of an orchid (Habenaria). At 1 the complete flower is shown,
with three sepals behind, and three petals in front, the lowest one of which has
developed a long strap-shaped portion, and a still longer spur portion, the opening
to which is seen at the base of the strap. At the bottom of this long spur is the
nectar, which is reached by the long proboscis of a moth. The two pollen sacs of
the single stamen are seen in the centre of the flower, diverging downwards, and
between them stretches the stigma surface. The relation between pollen sacs and
stigma surface is more clearly shown in 2. Within each pollen sac is a mass of
sticky pollen, ending below in a sticky disk, which may be seen in 1 and 2. When
the moth thrusts his proboscis into the nectar tube, his head is against the stig-
matic surface and also against the disks. When he removes his head the disks
stick fast and the pollen masses are dragged out. In 3 a pollen mass (a) is
shown sticking to each eye of a moth. Upon visiting another flower these pollen
masses are thrust against the stigmatic surface and pollination is effected. — After
GRAY.

128

PLANT STUDIES

stigma of the same flower are not mature at the same time.
It is evident that this is a very effective method of prevent-
ing self-pollination. When the pollen is being shed the
stigma is not ready to receive, or when the stigma is ready
to receive the pollen is not ready to be shed. In some
cases the pollen is ready first, in other cases the stigma,
the former condition being called protandry, the latter
protogyny. This is a very common method of preventing

self-pollination, and is com-
monly not associated with
irregularity.

The ordinary figwort may
be taken as an example of
protogyny. When the flowers
first open, the style, bearing
the stigma at its tip, is found
protruding from the urn-like
flower, while the four
stamens are curved down
into the tube, and not ready
to shed their pollen. At
some later time the style
bearing the stigma wilts,
and the stamens straighten
up and protrude from the tube. In this way, first the
receptive stigma, and afterwards the shedding pollen-sacs,
occupy the same position.

Protandry is even more common, and many illustrations
can be obtained. For example, the showy flowers of the
common fireweed, or great willow herb, when first opened
display their eight shedding stamens prominently, the style
being sharply curved downward and backward, carrying
the four stigma lobes well out of the way. Later, the
stamens bend away, and the style straightens up and ex-
poses its stigma lobes, now receptive (see Fig. 134).

(3) Difference in pollen. — In these cases there are at

FIG. 134. Flowers of fireweed (Epi-
lobium), showing protandry. In 1 the
stamens are thrust forward, and the
style is sharply turned downward and
backward. In 2 the style is thrust
forward, with its stigmatic branches
spread. An insect in passing from 1
to 2 will almo'st certainly transfer pol-
len from the stamens of 1 to the stig-
mas of 2.— After GRAY.

FLOWERS AND INSECTS

129

least two forms of flowers, which differ from one another
in the relative lengths of their stamens and styles. In the
accompanying illustrations of Houstonia (see Fig. 135) it
is to be noticed that in one flower the stamens are short
and included in the tube, and the style is long and pro-
jecting, with the four stigmas exposed well above the
tube. In the
other flower the
relative lengths
are exactly re-
versed, the
style being
short and in-
cluded in the
tube, and the
stamens long
and projecting.
It appears that
the pollen from
the short sta-
mens is most
effective upon
the stigmas of
the short styles,
and that the
pollen from the
long stamens is
most effective
upon the stig-
mas of the long styles ; and as short stamens and long
styles, or long stamens and short styles, are associated in
the same flower, the pollen must be transferred to some
other flower to find its appropriate stigma. This means
that there is a difference between the pollen of the short
stamens and that of the long ones.

In some cases there are three forms of flowers, as in one

FIG. 135. Flowers of Houstonia, showing two forms of
flowers. In 1 there are short stamens and a long style ;
in 2 long stamens and short style. An insect visiting 1
will receive a band of pollen about the front part of its
body ; upon visiting 2 this band will rub against the
stigmas, and a fresh pollen band will be received upon
the hinder part of the body, which, upon visiting another
flower like No. 1, will brush against the stigmas. —
After GRAY.

130 PLANT STUDIES

of the common loosestrifes. Each flower has stamens of
two lengths, which, with the style, makes possible three
combinations. One flower has short stamens, middle-length
stamens, and long style ; another has short stamens, middle-
length style, and long stamens ; the third has short style,
middle-length stamens, and long stamens. In these cases
also the stigmas are intended to receive pollen from stamens

FIG. 136. Yucca and Pronuba. In the lower figure to the right an opened flower
shows the pendent ovary with the stigma region at its apex. The upper figure to
the right shows the position of Pronuba when collecting pollen. The figure to the
left represents a cluster of capsules of Yucca, which shows the perforations made
by the larvae of Pronuba in escaping. — After RILET and TRELEASE.

of their own length, and a transfer of pollen from flower to
flower is necessary.

90. Self-pollination. — In considering these three general
methods of preventing self-pollination, it must not be sup-
posed that self-pollination is never provided for. It is pro-
vided for more extensively than was once supposed. It is
found that many plants, such as violets, in addition to the
usual showy, insect-pollinated flowers, produce flowers that
are not at all showy, in fact do not open, and are often not
prominently placed. The fact that these flowers are often
closed has suggested for them the name cleistogamous

FLOWERS AND INSECTS 131

flowers. In these flowers self-pollination is a necessity, and
is found to be very effective in producing seed.

91. Yucca and Pronuba. — There can be no doubt, also,
that there is a great deal of self-pollination effected in
flowers adapted for pollination by insects, and that the in-
sects themselves are often responsible for it. But in the
remarkable case of Yucca and Pronuba there is a definite
arrangement for self-pollination by means of an insect (see
Fig. 136). Yucca is a plant of the southwestern arid regions
of North America, and Pronuba is a moth. The plant and
the moth are very dependent upon each other. The bell-
shaped flowers of Yucca hang in great terminal clusters, with
six hanging stamens, and a central ovary ribbed lengthwise,
and with a funnel-shaped opening at its apex, which is the
stigma. The numerous ovules occur in lines beneath the
furrows. During the day the small female Pronuba rests
quietly within the flower, but at dusk becomes very active.
She travels down the stamens, and resting on the open
pollen-sac scoops out the somewhat sticky pollen with her
front legs. Holding the little mass of pollen she runs to
the ovary, stands astride one of the furrows, and pierc-
ing through the wall with her ovipositor, deposits an egg
in an ovule. After depositing several eggs she runs to the
apex of the ovary and begins to crowd the mass of pollen
she has collected into the funnel-like stigma. These actions
are repeated several times, until many eggs are deposited
and repeated pollination has been effected. As a result of
all this the flower is pollinated, and seeds are formed which
develop abundant nourishment for the moth larvae, which
become mature and bore their way out through the wall of
the capsule (Fig. 136).

92. Securing cross-pollination. — In very many ways flow-
ers are adapted to the visits of suitable insects. In ob-
taining nectar or pollen as food, the visiting insect receives
pollen on some part of its body which will be likely to
come in contact with the stigma of the next flower visited.

FIG. 137. A clump of lady-slippers (Cypripedium), showing the habit of the plant
and the general structure of the flower.— After GIBSON.

FLOWERS AND INSECTS

133

Illustrations of this process may be taken from the flowers
already described in connection with the prevention of
self-pollination.

In the flowers of the pea family,, such as the rose acacia
(see Fig. 131), it will be
noticed that the stamens
and pistil are concealed
within the keel, which
forms the natural land-
ing place for the bees
which are used in pol-
lination. This keel is
so inserted that the
weight of the insect de-
presses it,, and the tip
of the style comes in
contact with its body.
Not only does the
stigma strike the body,
but by the glancing
blow the surface of the
style is rubbed against
the insect, and on this
style, below the stigma,
the pollen has been de-
posited and is rubbed
off against the insect.
At the next flower
visited the stigma is
likely to strike the pol-
len obtained from the previous flower, and the style will
deposit a new supply of pollen.

In the flower of the common flag (see Fig. 132) the nectar
is deposited in a pit at the bottom of the chamber formed
by each style and petal. In this chamber the stamen is
found, and more or less roofing it over is the flap, or shelf,

FIG. 138. Flower of Cypripedium, showing the
flap overhanging the opening of the pouch,
into which a bee is crowding its way. The
small figure to the right shows a side view of
the flap ; that to the left a view beneath the
flap, showing the two dark anthers, and be-
tween them, further down (forward), the
stigma surface. — After GIBSON.

134 PLANT STUDIES

upon the upper surface of which the stigma is developed.
As the insect crowds its way into this narrowing chamber,
its body is dusted by the pollen, and as it visits the next
flower and thrusts aside the stigmatic shelf, it is apt to
deposit upon it some of the pollen previously received.

The story of pollination in connection with the orchids
is still more complicated (see Fig. 133). Taking an ordi-
nary orchid for illustration, the details are as follows. Each
of the two pollen masses terminates in a sticky disk or
button ; between them extends the concave stigma sur-
face, at the bottom of which is the opening into the long
tube-like spur in which the nectar is
found. Such a flower is adapted to
the large moths, with long probosces
which can reach the bottom of the
tube. As the moth thrusts its pro-
boscis into the tube, its head touches
the sticky button on each side, so that
when it flies away these buttons stick
to its head, sometimes directly to its

FiG.139. A bee imprisoned d th u are t

in the pouch (partly cut *

away) of Cypripedium. out. These masses are then carried

-After GIBSON. to the next flower an(} are thrust

against the stigma in the attempt to get the nectar.

In the lady-slipper (Cypripedium), another orchid, the
flowers have a conspicuous pouch (see Fig. 137), in which
the nectar is secreted. A peculiar structure, like a flap,
overhangs the opening of the pouch, beneath which are the
two anthers, and between them the stigmatic surface (see
Fig. 138). Into the pouch a bee crowds its way and be-
comes imprisoned (see Fig. 139). The nectar which the
bee obtains is in the bottom of the pouch (see Fig. 140).
When escaping, the bee moves towards the opening over-
hung by the flap and rubs first against the stigmatic sur-
face (see Fig. 141), and then against the anthers, receiving
pollen on its back (see Fig. 142). A visit to another flower

FLOWERS AND INSECTS

135

FIG. 140. A bee obtaining nectar in the pouch of
Cypripedium. — After GIBSON.

will result in rubbing some of the pollen upon the stigma,
and in receiving more pollen for another flower.

In cases of protandry, as the common fig wort, flowers
in the two condi-
tions will be visited
by the pollinating
insect, and as the
shedding stamens
and receptive stig-
mas occupy the
same relative posi-
tion, the pollen
from one flower
will be carried to the stigma of another. It is evident that
exactly the same methods prevail in the case of protogyny,
as the fire weed (see Fig. 134).

The Houstonia (see Fig. 135), in which there are sta-
mens and styles of different lengths, is visited by insects

whose bodies fill
the tube and pro-
trude above it. In
visiting flowers of
both kinds, one re-
gion of the body
receives pollen
from the short sta-
mens, and another
region from the
long stamens. In
this way the insect
will carry about two bands of pollen, which come in con-
tact with the corresponding stigmas. When there are three
forms of flowers, as mentioned in the case of one of the
loosestrifes, the insect receives three pollen bands, one for
each of the three sets of stigmas.

93. Warding off unsuitable insects. — Prominent among

FIG. 141. A bee escaping from the pouch of Cypri-
pedium, and coming in contact with the stigma.
Advancing a little further the bee will come in con-
tact with the anthers and receive pollen. — After
GIBSON.

136

PLANT STUDIES

the unsuitable insects, which Kerner calls " unbidden
guests," are ants, and adaptations for reducing their visits
to a minimum may be taken as illustrations.

(1) Hairs. — A common device for turning back ants,
and other creeping insects, is a barrier of hair on the stem,
or in the flower cluster, or in the flower.

(2) Glandular secretions. — In some cases a sticky
secretion is exuded from the surface of plants, which

effectively stops
the smaller creep-
ing insects. In
certain species of
catch-fly a sticky
ring girdles each

<J°int °f the stem*
(3) Isolation.-

The leaves of cer-
tain plants form
water reservoirs
about the stem.
To ascend such a
stern, therefore, a
creeping insect
must cross a series
of such reservoirs.
Teasel furnishes a
common illustration, the opposite leaves being united at
the base and forming a series of cups. More extensive
water reservoirs are found in Bilbergia, sometimes called
"traveler's tree," whose great flower clusters are pro-
tected by large reservoirs formed by the rosettes of leaves,
which creeping insects cannot cross.

(4) Latex. — This is a milky secretion found in some
plants, as in milkweeds. Caoutchouc is a latex secretion
of certain tropical trees. When latex is exposed to the
air it stiffens immediately, becoming sticky and finally

FIG. 142. A bee escaping from the pouch of Cypri-
pedium, and rubbing against an anther.— After
GIBSON.

FLOWEKS AND INSECTS 137

hard. In the flower clusters of many latex-secreting
plants the epidermis of the stem is very smooth and deli-
cate, and easily pierced by the claws of ants and other
creeping insects who seek to maintain footing on the
smooth surface. Wherever the epidermis is pierced the
latex gushes out, and by its stiffening and hardening glues
the insect fast.

(5) Protective forms. — In some cases the structure of
the flower prevents the access of small creeping insects to
the pollen or to the nectar. In the common snapdragon
the two lips are firmly closed (see Fig. 74), and they can be
forced apart only by some heavy insect, as the bumble-bee,
alighting upon the projecting lower lip, all lighter insects
being excluded. In many species of Pentstemon, one of
the stamens does not develop pollen sacs, but lies like a bar
across the mouth of the pit in which the nectar is secreted.
Through the crevices left by this bar the thin proboscis of
a moth or butterfly can pass, but not the whole body of a
creeping insect. Very numerous adaptations of this kind
may be observed in different flowers.

(6) Protective closure. — Certain flowers are closed at
certain hours of the day, when there is the chief danger
from creeping insects. For instance, the evening prim-
roses open at dusk, after the deposit of dew, when ants are
not abroad ; and at the same time they secure the visits of
moths, which are night-fliers.

Numerous other adaptations to hinder the visits of
unsuitable insects may be observed, but those given will
serve as illustrations.

CHAPTER VIII

AN INDIVIDUAL PLANT IN ALL OF ITS RELATIONS

FOE the purpose of summarizing the general life-rela-
tions detailed in the preceding chapters, it will be useful to
apply them in the case of a single plant. Taking a com-
mon seed-plant as an illustration, and following its history
from the germination of the seed, certain general facts
become evident in its relations to the external world.

95. Direction of the root. — The first part of the young
plantlet to emerge from the seed is the tip of the axis
which is to develop the root system. It at once appears to
be very sensitive to the earth influence (geotropism) and
to moisture influence (hydrotropism), for whatever the
direction of emergence from the seed, a curvature is devel-
oped which directs the tip towards and finally into the soil
(see Fig. 143). When the soil is penetrated the primary
root may continue to grow vigorously downward, showing
a strong geotropic tendency, and forming what is known
as the tap-root, from which lateral roots arise, which are

138

AN INDIVIDUAL PLANT IN ALL OF ITS EELATIONS 139

97. Direction of foliage leaves. — The general direction of
foliage leaves on an erect stem is transversely heliotropic ;

FIG. 143. Germination of the seed of
arbor- vitae (Thuja). B shows the
emergence of the axis (?•) which is to
develop the root, and its turning to-
wards the soil. C shows a later stage,
in which the root (r) has been some-
what developed, and the stem of the
embryo (7t) is developing a curve pre-
paratory to pulling out the seed leaves
(cotyledons). E shows the young plant-
let entirely free from the seed, with its
root (r) extending into the soil, its stem
(h) erect, and its first leaves (c} hori-
zontally spread. — After STRASBURGEK.

140

PLANT STUDIES

if necessary, the parts of the leaf or the stem itself twisting
to allow the blade to assume this position. The danger of
the leaves shading one another is reduced to a minimum by
the elongation of internodes, the spiral arrangement, short-
ening and changing direction upwards, or lobing.

This outlines the general nutritive relations, the roots

FIG. 143a. Germination of the garden bean, showing the arch of the seedling stem
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.

and leaves being favorably placed for absorption, and the
latter also favorably placed for photosynthesis.

98. Placing of flowers. — The purposes of the flower seem
to be served best by exposed positions, and consequently
flowers mostly appear at the extremities of stems and
branches, a position evidently favorable to pollination and
seed dispersal. The flowers thus exposed are very com-
monly massed, or, if not, the single flower is apt to be large
and conspicuous. The various devices for protecting nec-
tar and pollen against too great moisture, and the more

AN INDIVIDUAL PLANT IN ALL OF ITS RELATIONS 141

delicate structures against chill ; for securing the visits of
suitable insects, and warding off unsuitable insects ; and
for dispersing the seeds, need not be repeated.

99. Branch buds. — If the plant under examination be a
tree or shrub, branch buds will be observed to develop at
the end of the growing season (see Fig. 65). This device
for protecting growing tips through a season of dangerous
cold is very familiar to those living in the temperate
regions. The internodes do not elongate, hence the leaves
overlap ; they develop little or no chlorophyll, and become
scales. The protection afforded by these overlapping
scales is often increased by the development of hairs, or
by the secretion of mucilage or gum.

CHAPTER IX

THE STRUGGLE FOB EXISTENCE

100. Definition. — The phrase "struggle for existence"
has come to mean, so far as plants are concerned, that it is
usually impossible for them to secure ideal relations, and
that they must encounter unfavorable conditions. The
proper light and heat relations may be difficult to obtain,
and also the proper relations to food material. It often
happens, also, that conditions once fairly favorable may be-
come unfavorable. Also, multitudes of plants are trying
to take possession of the same conditions. All this leads
to the so-called "struggle," and vastly more plants fail
than succeed. Before considering the organization of plant
societies, it will be helpful to consider some of the possible
changes in conditions, and the effect on plants.

101. Decrease of water. — This is probably the most com-
mon factor to fluctuate in the environment of a plant.
Along the borders of streams and ponds, and in swampy
places, the variation in the water is very noticeable, but the
same thing is true of soils in general. However, the change
chiefly referred to is that which is permanent, and which
compels plants not merely to tide over a drought, but to
face a permanent decrease in the water supply.

Around the margins of ponds are very commonly seen
fringes of such plants as bulrushes, cat-tail flags, reed-
grasses, etc., standing in shoal water. As these plants
grow close together, silt from the land is entangled by them,
and presently it accumulates to such an extent that there
is no more standing water, and the water supply for the
142

THE STRUGGLE FOR EXISTENCE 143

bulrushes and their associates has permanently decreased
below the favorable amount. In this way certain lake
margins gradually encroach upon the water, and in so
doing the water supply is permanently diminished for many
plants. By the same process, smaller lakelets are gradually
being converted into bogs, and the bogs in turn into drier
ground, and these unfavorable changes in water supply are
a menace to many plants.

The operations of man, also, have been very effective in
diminishing the water supply for plants. Drainage, which
is so extensively practiced, while it may make the water-
supply more favorable for the plants which man desires, cer-
tainly makes it very unfavorable for many other plants.
The clearing of forests has a similar result. The forest
soil is receptive and retentive in reference to water, and is
somewhat like a great sponge, steadily supplying the streams
which drain it. The removal of the forest destroys much
of this power. The water is not held and gradually doled
out, but rushes off in a flood ; hence, the streams which
drain the cleared area are alternately flooded and dried up.
This results in a much less total supply of water available
for the use of plants.

102. Decrease of light. — It is very common to observe
tall, rank vegetation shading lower forms, and seriously
interfering with the light supply. If the rank vegetation
is rather temporary, the low plants may learn to precede or
follow it, and so avoid the shading ; but if the over-shading
vegetation is a forest growth, shading becomes permanent.
In the case of deciduous trees, which drop their leaves at the
close of the growing season and put out a fresh crop in the
spring, there is an interval in the early spring, before the
leaves are fully developed, during which low plants may
secure a good exposure to light (see Fig. 144). In such
places one finds an abundance of " spring flowers," but later
in the season the low plants become very scarce. This
effective over-shading is not common to all forests, for

FIG. 144. A common spring plant (dog-tooth violet) which grows in deciduous
forests. The large mottled leaves and the conspicuous flowers are sent rapidly
above the surface from the subterranean bulb (see cut in the left lower corner),
where are also seen dissected out some petals and stamens and the pistil.

THE STRUGGLE FOR EXISTENCE 145

there are "light forests/' such as the oak forest, which
permit much low vegetation, as well as the shade forests,
such as beech forests, which permit very little.

In the forest regions of the tropics, however, the shad-
ing is permanent, since there is no annual fall of leaves.
In such conditions the climbing habit has been extensively
cultivated.

103. Change in temperature. — In regions outside of the
tropics the annual change of temperature is a very im-
portant factor in the life of plants, and they have provided
for it in one way or another. In tracing the history of
plants, however, back into what are called " geological
times/' we discover that there have been relatively per-
manent changes in temperature. Now and then glacial
conditions prevailed, during which regions before temperate
or even tropical were subjected to arctic conditions. It is
very evident that such permanent changes of temperature
must have had an immense influence upon plant life.

104. Change in soil composition. — One of the most ex-
tensive agencies in changing the compositions of soils in
certain regions has been the movement of glaciers of conti-
nental extent, which have deposited soil material over very
extensive areas. Areas within reach of occasional floods,
also, may have the soil much changed in character by the
new deposits. Shifting dunes are billow-like masses of
sand, developed and kept in motion by strong prevailing
winds, and often encroach upon other areas. Besides these
changes in the character of soil by natural agencies, the
various operations of man have been influential. Clearing,
draining, fertilizing, all change the character of the soil,
both in its chemical composition and its physical properties.

105. Devastating animals. — The ravages of animals form
an important factor in the life of many plants. For example,
grazing animals are wholesale destroyers of vegetation, and
may seriously affect the plant life of an area. The various
leaf feeders among insects have frequently done a vast

14:6 PLANT STUDIES

amount of damage to plants. Many burrowing animals
attack subterranean parts of plants, and interfere seriously
with their occupation of an area.

Various protective adaptations against such attacks have
been pointed out, but this subject probably has been much
exaggerated. The occurrence of hairs, prickles, thorns,
and spiny growths upon many plants may discourage the
attacks of animals, but it would be rash to assume that
these protections have been developed because of the danger
of such attacks. One of the families of plants most com-
pletely protected in this way is the great cactus family,
chiefly inhabiting the arid regions of southwestern United
States and Mexico. In such a region succulent vegetation
is at a premium, and it is doubtless true that the armor of
thorns and bristles reduces the amount of destruction.

In addition to armor, the acrid or bitter secretions of
certain plants or certain parts of plants would have a
tendency to ward off the attacks of animals.

106. Plant rivalry, — It is evident that there must be
rivalry among plants in occupying an area, and that those
plants which can most nearly utilize identical conditions
will be the most intense rivals. For example, a great many
young oaks may start up over an area, and it is evident
that the individuals must come into sharp competition with
one another, and that but few of them succeed in establish-
ing themselves permanently. This is rivalry between in-
dividuals of the same kind ; but some other kind of trees,
as the beech, may come into competition with the oak, and
another form of rivalry will appear.

As a consequence of plant rivalry, the different plants
which finally succeed in taking possession of an area are
apt to be dissimilar, and a plant society is usually made up
of plants which represent wTidely different regions of the
plant kingdom. It is sometimes said that any well de-
veloped plant society is an epitome of the plant kingdom.

A familiar illustration of plant rivalry may be observed

THE STRUGGLE FOR EXISTENCE 147

in the case of what are called " weeds. " Every one is fa-
miliar with the fact that if cultivated ground is neglected
these undesirable plants will invade it vigorously and seri-
ously affect the development of plants under cultivation.

107. Adaptation. — When the changes mentioned above
occur in the environment of plants to such an extent as
to make the conditions for living very unfavorable, one
of three things is likely to occur, adaptation, migration,
or destruction.

The change in conditions may come slowly enough, and
certain plants may be able to endure it long enough to
adjust themselves to it. Such an adjustment may involve
changes in structure, and probably no plants are plastic
enough to adjust themselves to extreme and sudden changes
which are to be comparatively permanent. There are
plants, such as the common cress, which may be called
amphibious, which can live in the water or out of it without
change of structure, but this is endurance rather than
adaptation. Many plants, however, can pass slowly into
different conditions, such as drier soil, denser shade, etc.,
and corresponding changes in their structure may be noted.
Very often, however, such plants are given no opportunity
to adjust themselves to the new conditions, as the area is
apt to be invaded by plants already better adapted. While
adaptation may be regarded as a real result of changed con-
ditions, it would seem to be by no means the common one.

108. Migration. — This is a very common result of
changed conditions. Plants migrate as truly as animals,
though, of course, their migration is from generation to
generation. It is evident, however, that migration cannot
be universal, for barriers of various kinds may forbid it.
In general, these barriers represent unfavorable conditions
for living. If a plant area with good soil is surrounded by
a sterile area, the latter would form an efficient barrier to
migration from the former. Plants of the lowlands could
not cross mountains to escape from unfavorable conditions.

148 PLANT STUDIES

To make migration possible, therefore, it is necessary for
the conditions to be favorable for the migrating plants in
some direction. In the case of bulrushes, cat-tail flags,
etc., growing in the shoal water of a lake margin, the
building up of soil about them results in unfavorable con-
ditions. As a consequence, they migrate further into the
lake. If the lake happens to be a small one, the filling up
process may finally obliterate it, and a time will come when
such forms as bulrushes and flags will find it impossible to
migrate.

In glacial times very many arctic plants migrated south-
ward, especially along the mountain systems, and many
alpine plants moved to lower ground. When warmer con-
ditions returned, many plants that had been driven south
returned towards the north, and the arctic and alpine plants
retreated to the north and up the mountains. The history
of plants is full of migrations, compelled by changed con-
ditions and permitted in various directions. It must be
remembered, also, that migrations often result in changes
of structure.

109. Destruction, — Probably this is by far the most com-
mon result of greatly changed conditions. Even if plants
adapt themselves to changed conditions, or migrate, their
structure may be so changed that they will seem like quite
different plants. In this way old forms gradually disappear
and new ones take their places.

CHAPTER X

THE NUTRITION OF PLANTS

110. Physiology. — In the previous chapters plants have
been considered in reference to their surroundings. It
was observed that various organs of nutrition hold certain
life-relations, but it is essential to discover what these rela-
tions mean to the life of the plant. The study of plants
from the standpoint of their life-relations has been called
Ecology ; the study of the life-processes of plants is called
Physiology. These two points of view may be illustrated
by comparing them to two points of view for the study of
man. Man may be studied in reference to his relation to
his fellow-men and to the character of the country in which
he lives ; or his bodily processes may be studied, such as
digestion, circulation, respiration, etc. The former cor-
responds to Ecology, the latter is Physiology.

All of the ecological relations that have been mentioned
find their meaning in the physiology of the plant, for life-
relations have in view life-processes. The subject of plant
physiology is a very complex one, and it would be impossi-
ble in an elementary work to present more than a few very
general facts. Certain facts in reference to plant move-
ments, an important physiological subject, have been men-
tioned in connection with life-relations, but it seems neces-
sary to make some special mention of nutrition.

111. Significance of chlorophyll. — Probably the most im-
portant fact to observe in reference to the nutrition of
plants is that some plants are green or have green parts,
while others, such as toadstools, do not show this green

149

150 PLANT STUDIES

color. It has been stated that this green color is due to
the presence of a coloring matter known as chlorophyll
(see §12). The two groups may be spoken of, therefore,
as (1) green plants and (2) plants without chlorophyll.
The presence of chlorophyll makes it possible for the plants
containing it to manufacture their own food out of such
materials as water, soil material, and gases. For this
reason, green plants may be entirely independent of all
other living things, so far as their food supply is concerned.

Plants without chlorophyll, however, are unable to
manufacture food out of such materials, and must obtain
it already manufactured in the bodies of other plants or
animals. For this reason, they are dependent upon other
living things for their food supply, just as are animals. It
is evident that plants without chlorophyll may obtain this
food supply either from the living bodies of plants and ani-
mals, in which case they are called parasites, or they may
obtain it from the substances derived from the bodies of
plants and animals, in which case they are called sapro-
phytes. For example, the rust which attacks the wheat,
and is found upon the leaves and stems of the living plant ;
is a parasite, while the mould which often develops on stale
bread is a saprophyte. Some plants without chlorophyll
can live either as parasites or saprophytes, while others are
always one or the other. By far the largest number of
parasites and saprophytes belong to the group of low plants
called fungi, and when fungi are referred to, it must be
understood that it means the greatest group of plants with-
out chlorophyll.

112. Photosynthesis. — The nutritive processes in green
plants are the same as in other plants, and in addition there
is in green plants the peculiar process known as photosyn-
thesis (see §25). In plants with foliage leaves, these are
the chief organs for this work. It must be remembered,
however, that leaves are not necessary for photosynthesis,
for plants without leaves, such as algae, perform it. The

THE NUTKITION OF PLANTS 151

essential thing is green tissue exposed to light, but in this
brief account an ordinary leafy plant growing in the soil
will be considered.

As the leaves are the active structures in the work of
photosynthesis, the raw materials necessary must be brought
to them. In a general way, these materials are carbon di-
oxide and water. The gas exists diifused through the
atmosphere, and so is in contact with the leaves. It also
occurs dissolved in the water of the soil, but the gas used
is absorbed from the air by the leaves. The supply of
water, on the other hand, in soil-related plants, is obtained
from the soil. The root system absorbs this water, which
then ascends the stem and is distributed to the leaves.

(1) Ascent of water. — The water does not move up-
wards through all parts of the stem, but is restricted to a
certain definite region. This region is easily recognized as
the woody part of stems. Sometimes separate strands of
wood, looking like fibers, may be seen running lengthwise
through the stem ; sometimes the fibrous strands are packed
so close together that they form a compact woody mass, as
in shrubs and trees. In the case of most trees new wood is
made each year, through which the water moves. Hence
the very common distinction is made between sap-wood,
through which the water is moving, and heart-wood, which
the water current has abandoned. Just how the water
ascends through these woody fibers, especially in tall trees,
is a matter of much discussion, and cannot be regarded as
definitely known. In any event, it should be remembered
that these woody fibers are not like the open veins and
arteries of animal bodies, and no "circulation" is possible.
These same woody strands are seen branching throughout
the leaves, forming the so-called vein system, and it is evi-
dent, therefore, that they form a continuous route from
roots to leaves.

It is easy to demonstrate the ascent of water in the
stem, and the path it takes, by a simple experiment. If
11

152 PLANT STUDIES

an active stem be cut and plunged into water stained with
an aniline color called eosin,* the ascending water will stain
its pathway. After some time sections through the stem
will show that the water has traveled upwards through it,
and the stain will point out the region of the stem used in
the movement.

In general, therefore, the carbon dioxide is absorbed
directly from the air by the leaves, and the water is ab-
sorbed by the root from the soil, and moves upwards through
the stem into the leaves. An interesting fact about these
raw materials is that they are very common waste products.
They are waste products because in most life-processes they
cannot be taken to pieces and used. The fact that they

can be used in photosynthesis

^9K *&S&s®&&^==^r~ shows that it is a very re-
Jy* ®® ^J markable life process.

(2) Chloroplasts. — Having
obtained some knowledge of

the raw materials used in

photosynthesis, and their

PIG. 145. Some mesophyll cells from J

the leaf of Fittonia, showing chloro- SOUrCCS, it IS necessary to

Plasts- consider the plant machinery

arranged for the work. In the working leaf cells it is
discovered that the color is due to the presence of very
small green bodies, known as chlorophyll bodies or cliloro-
plasts (see Fig. 145). These consist of the living substance,
known as protoplasm, and the green stain called chloro-
phyll ; therefore, each chloroplast is a living body (plastid)
stained green. It is in these chloroplasts that the work of
photosynthesis is done. In order that they may work it
is necessary for them to obtain a supply of energy from
some outside source, and the source used in nature is sun-
light. The green stain (chlorophyll) seems to be used in
absorbing the necessary energy from sunlight, and the

* The commoner grades of red ink are usually solutions of eosin.

THE NUTRITION OF PLANTS 153

plastid uses this energy in the work of photosynthesis. It
is evident, therefore, that photosynthesis goes on only in
the sunlight, and is suspended entirely at night. It is
found that any intense light can be used as a substitute
for sunlight, and plants have been observed to carry on
the work of photosynthesis in the presence of electric
light.

(3) Result of photosynthesis. — The result of this work
can be stated only in a very general way. Carbon dioxide
is composed of two elements, carbon and oxygen, in the
proportion one part of carbon to two parts of oxygen.
Water is also composed of two elements, hydrogen and oxy-
gen. In photosynthesis the elements composing these sub-
stances are separated from one another, and recombined in
a new way. In the process a certain amount of oxygen is
liberated, just as much as was in the carbon dioxide, and a
new substance is formed, known as a carbohydrate. The
oxygen set free escapes from the plant, and may be re-
garded as waste product in the process of photosynthesis.
It will be remembered that the external changes in this
process are the absorption of carbon dioxide and the giving
off of oxygen (see §25).

(4) Carbohydrates and proteids. — The carbohydrate
formed is an organic substance ; that is, a substance made
in nature only by life processes. It is the same kind of
substance as sugar or starch, and all are known as carbohy-
drates ; that is, substances composed of carbon, and of hy-
drogen and oxygen in the same proportion as in water.
The work of photosynthesis, therefore, is to form carbohy-
drates. The carbohydrates, such as sugar and starch, rep-
resent but one type of food material. Proteids represent
another prominent type, substances which contain carbon,
hydrogen, and oxygen, as do carbohydrates, but which also
contain other elements, notably nitrogen, sulphur, and
phosphorus. The white of an egg may be taken as an ex-
ample of proteids. They seem to be made from the carbo-

154 PLANT STUDIES

hydrates, the nitrogen, sulphur, and other necessary
additional elements being obtained from soil substances
dissolved in the water which is absorbed and conveyed
to the leaves.

113. Transpiration. — The water which is absorbed by the
roots and passes to the leaves is much more abundant than
is needed in the process of photosynthesis. It should be re-
membered that the water is not only used as a raw material
for food manufacture, but also acts as a solvent of the soil
materials and carries them into the plant. The water in
excess of the small amount used in food manufacture is
given off from the plant in the form of water vapor, the
process being already referred to as transpiration (see §26).

114. Digestion. — Carbohydrates and proteids may be re-
garded as prominent types of plant food which green
plants are able to manufacture. These foods are trans-
ported through the plant to regions where work is going on,
and if there is a greater supply of food than is needed for
the working regions, the excess is stored up in some part
of the plant. As a rule, green plants are able to manufac-
ture much more food than they use, and it is upon this ex-
cess that other plants and animals live. In the transfer of
foods through the plant certain changes are often neces-
sary. For example, starch is insoluble, and hence cannot
be carried about in solution. It is necessary to transform
it into sugar, which is soluble. These changes, made to
facilitate the transfer of foods, represent digestion.

115. Assimilation. — When food in some form has reached
a working region, it is organized into the living substance
of the plant, known as protoplasm, and the protoplasm
builds the plant structure. This process of organizing the
food into the living substance is known as assimilation.

116. Respiration. — The formation of foods, their diges-
tion and assimilation are all preparatory to the process of
respiration, which may be called the use of assimilated
food. The whole working power of the plant depends

THE NUTRITION OF PLANTS

155

upon respiration, which means the absorption of oxygen by
the protoplasm, the breaking down of protoplasm, and the
giving off of carbon dioxide and water as wastes. The im-

FIG. 146. The common Northern pitcher plant. The hollow leaves, each with a hood
and a wing, form a rosette, from the center of which arise the flower stalks. —
After KERNER.

portance of this process may be realized when it is remem-
bered that there is the same need in our own living, as it
is essential for us also to "breathe in" oxygen, and as a
result we "breathe out" carbon dioxide and water. This
breaking down or "oxidizing" of protoplasm releases the

156

PLANT STUDIES

power by which, the work of the plant is carried on (see

§27).

117. Summary of life-processes. — To summarize the nu-
tritive life-processes in green plants, therefore, photosyn-
thesis manufactures carbohydrates,
the materials used being carbon
dioxide and water, the work being
done by the chloroplast with the
aid of light ; the manufacture of
proteids uses these carbohydrates,
and also substances containing
nitrogen, sulphur, etc.; digestion
puts the insoluble carbohydrates
and the proteids into a soluble
form for transfer through the
plant; assimilation converts this
food material into the living sub-
stance of the plant, protoplasm ;
respiration is the oxidizing of the
protoplasm which enables the
plant to work, oxygen being ab-
sorbed, and carbon dioxide and
water vapor being given off in
the process.

118. Plants without chlorophyll.
— Remembering the life-processes
described under green plants, it is
evident that plants without chlo-

™Phy" ™* d° .*e work of

and winged pitcher, and the photosynthesis. This means that
overarching hood with transiu- th cannot manufacture carbo-

cent spots. — After KEKNEK. rf

hydrates, and that they must de-
pend upon other plants or animals for this important food.
Mushrooms, puff-balls, molds, mildews, rusts, dodder,
corpse plants, beech drops, etc., may be taken as illustra-
tions of such plants.

THE NUTRITION OF PLANTS 157

119. Saprophytes. — In the case of saprophytes dead bodies
or body products are attacked, and sooner or later all or-
ganic matter is attacked and decomposed by them. The de-
composition is a result of the nutritive processes of plants
without chlorophyll, and were it not for them " the whole sur-
face 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 or-
ganic 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 ordi-
nary Fungi, but some of the higher plants have also adopt-
ed this method of obtaining food. Many ordinary green
plants have the saprophytic habit of absorbing organic ma-
terial 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."

120. 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. 148), 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

158

PLANT STUDIES

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.

121. Symbionts. —
The phenomenon of
symbiosis will be re-
ferred to more fully in connection with Lichens (§ 194).
In its broadest sense the word includes any sort of depend-
ence between living organisms, from the vine and the tree

FIG. 148. 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 STRASBURGER.

THE NUTRITION OF PLANTS

upon which it climbs, to the alga and fungus so 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 under 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 connec-
tion with Lichens are presented in § 194. 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 lielotism, 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) MycorrJiiza. — 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. 149. 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 (e), outermost cells of the cortex (p) filled with
hyphal threads, which are sending branches into the adjacent cortical cells (a, i).
—After FUANK.

FIG. 150. Mycorrhiza: A, rootlets of white poplar forming mycorrhiza; S, enlarged
section of single rootlets, showing the hyphae penetrating the cells.— After
KERNEB.

THE NUTRITION OF PLANTS

161

oaks and their allies, etc. (Figs. 149, 150). 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.
151). 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-

FIG. 151. Root-tubercles on
Vicia Faba.—Mter NOLL.

162

PLANT STUDIES

nary crops have exhausted the soil of its nitrogen-contain-
ing salts, and it has become 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 Algae which they harbor with-
in their bodies (Fig. 152). 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
Myrmecopliytes, 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. 153). 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. 152. 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).^GOLDBERGER.

THE NUTRITION OF PLANTS

163

latter are used by the flowers as agents of pollination. An
account of this relationship, with illustrations, was given in

Fio. 153. An ant plant ( ffydnopkytum) from South Java, in which an excrescent
growth provides a habitation for ants. — After SCHIMPEB.

Chapter VII, but it should be associated with other illustra-
tions of symbiosis.

164

PLANT STUDIES

This association of insects and flowers is sometimes so
intimate that they have come to depend absolutely upon
one another. Especially among the orchids is it true that
special flowers and insects are adapted so exactly to one

another, that if one dis-
appears the other be-
comes extinct also.

122. " Carnivorous "
plants.— This name has
been given to plants
which have developed
the curious habit of
capturing insects and
using them for food,
and perhaps they had
better be called " insec-
tivorous plants." They
are green plants and,
therefore, can manu-
facture carbohydrates.
But they live in soil
poor in nitrogen com-
pounds, and hence pro-
teid formation is inter-
fered with. The bodies
of captured insects sup-
plement the proteid
supply, and the plants
have come to depend
upon them. Many, if
not all, of these car-
nivorous plants secrete
a digestive substance
which acts upon the

bodies of the captured insects very much as the diges-
tive substances of the alimentary canal act upon proteids

FIG. 154. The Californian pitcher plant (Dar-
lingtoniti), showing twisted and winged pitch-
er, the overarching hood with translucent
spots, and the fish-tail appendage to the hood
which is attractive to flying insects.— After
KEENER.

THE NUTRITION OF PLANTS

165

swallowed by animals. Some common illustrations are as
follows :

(1) Pitcher plants. — In these plants the leaves form
tubes, or urns, of various forms, which contain water, and
to which insects are attracted and drowned (see Fig. 146).
A pitcher plant common throughout the Southern States
may be taken as a type (see Fig. 147). The leaves are
shaped like slender, hollow cones, and rise in a tuft from

the swampy ground.
The mouth of this
conical urn is over-
arched and shaded
by a hood, in which
are translucent spots,
like small windows.
Around the mouth
of the urn are
glands, which se-
crete a sweet liquid
(nectar), and nectar
drops form a trail
down the outside of
the urn. Inside, just
below the rim of the
urn, is a glazed zone,
so smooth that insects
cannot walk upon it.
Below the glazed zone
is another zone,
thickly set with stiff,

downward-pointing hairs, and below this is the liquid in
the bottom of the urn.

If a fly is attracted by the nectar drops upon this curious
leaf, it naturally follows the trail up to the rim of the urn,
where the nectar is abundant. If it attempts to descend
within the urn, it slips on the glazed zone, and falls into

FIG. 155.

A sun-dew, showing rosette habit of
the insect-catching leaves.

166

PLANT STUDIES

the water, and if it attempts to escape by crawling up the
sides of the urn, the thicket of downward-pointing hairs
prevents. If it seeks to fly away from the rim, it flies
towards the translucent spots in the hood, which look like
the way of escape, as the direction of entrance is in the
shadow of the hood. Pounding against the hood, the fly
falls into the tube. This Southern pitcher plant is known

FIG. 156. Two leaves of a sun-dew. The one to the right has its glandular hairs
fully expanded ; the one to the left shows half of the hairs bending inward, in the
position assumed when an insect has been captured. — After KEENER.

as a great fly-catcher, and the urns are often well supplied
with the decaying bodies of these insects.

A much larger Californian pitcher plant has still more
elaborate contrivances for attracting insects (see Fig. 154).

(2) Drosera. — The droseras are commonly known as
" sun-dews," and grow in swampy regions, the leaves form-
ing small rosettes on the ground (see Fig. 155). In one
form the leaf blade is round, and the margin is beset by
prominent bristle-like hairs, each with a globular gland at
its tip (see Fig. 156). Shorter gland-bearing hairs are

THE NUTRITION OF PLANTS

scattered also over the inner surface of the blade. These
glands excrete a clear, sticky fluid, which hangs to them in
drops like dew-drops. If a small insect becomes entangled

FIG. 157. Plants of Dioncea, showing the rosette habit of the leaves with terminal
traps, and the erect flowering stem.— After KEBNEK.

in the sticky drop, the hair begins to curve inward, and
presently presses its victim down upon the surface of the
blade. In the case of larger insects, several of the marginal
hairs may join together in holding it, or the whole blade
may become more or less rolled inward.
12

168

PLANT STUDIES

(3) Dioncea. — This is one of the most famous and re-
markable of fly-catching plants (see Fig. 157). It is found
only in swamps near Wilmington, Xorth Carolina. The
leaf blade is constructed like a steel trap, the two halves
snapping together, and the marginal bristles interlocking
like the teeth of a trap (see Fig. 158). A few sensitive
hairs, like feelers, are
developed on the leaf
surface, and when one
of these is touched by
a small flying or hover-
ing insect, the trap
snaps shut and the in-
sect is caught. Only
after digestion does the
trap open again.

There are certain
green plants, not called
carnivorous plants,
which show the same
general habit of sup-
plementing their food
supply, and so reduc-
ing the necessity of

food manufacture. FIG. 158. Three leaves of Dioncea, showing

The mistletoe is a the details of the traP in the leaves to right

and left, and the central trap in the act of
green plant, growing capturing an insect.

upon certain trees, from

which it obtains some food, supplementing that which it

is able to manufacture.

In rich soil, the organized products of the decaying
bodies of plants and animals are often absorbed by ordinary
green plants, and so a certain amount of ready-made food
is obtained.

CHAPTER XI

PLANT SOCIETIES : ECOLOGICAL FACTORS

123. Definition of plant society, — From the previous
chapters it has been learned that every complex plant is
a combination of organs, and that each organ is related in
some special way to its environment. It follows, therefore,
that the whole plant, made up of organs, holds a very com-
plex relation with its environment. The stem demands
certain things, the root other things, and the leaves still
others. To satisfy all of these demands, so far as possible,
the whole plant is delicately adjusted.

The earth's surface presents very diverse conditions in ref-
erence to plant life, and as plants are grouped according to
these conditions, this leads to definite associations of plants,
those adapted to the same general conditions being apt to
live together. Such an association of plants living together
in similar conditions is a plant society, the conditions for-
bidding other plants. It must not be understood that all
plants affecting the same conditions will be found living
together. For example, a meadow of a certain type will not
contain all the kinds of grasses associated with that type.
Certain grasses will be found in one meadow, and other
grasses will be found in other meadows of the same type.

Very closely related plants generally do not live in the
same society, as their rivalry is apt to be intense. Closely
related plants are likely to occur, however, in different
societies of the same type. A plant society, therefore, may
contain a wide representation of the plant kingdom, from

plants of low rank to those of high rank.

169

PLANT STUDIES

Before considering some of the common societies, it is
necessary to note some of the conditions which determine
plant societies. Those things in the environment of the
plant which influence the organization of a society are
known as ecological factors.

124. Water, — Water is certainly one of the most im-
portant conditions in the environment of a plant, and has
great influence in determining the organization of societies.
If all plants are considered, it will be noted that the amount
of water to which they are exposed is exceedingly variable.
At one extreme are those plants which are completely
submerged; at the other extreme are those plants of arid
regions which can obtain very little water ; and between
these extremes there is every gradation in the amount of
available water. Among the most striking adaptations of
plants are those for living in the presence of a great amount
of water, and those for guarding against its lack.

One of the first things to consider in connection with
any plant society is the amount of water supply. It is not
merely a question of its total annual amount, but of its
distribution through the year. Is it supplied somewhat
uniformly, or is there alternating flood and drought ? The
nature of the water supply is also important. Are there
surface channels or subterranean channels, or does the
whole supply come in the form of rain and snow which
fall upon the area ?

Another important fact to consider in connection with
the water supply has to do with the structure of the soil.
There is what may be called a water level in soils, and it is
important to note the depth of this level beneath the sur-
face. In some soils it is very near the surface ; in others,
such as sandy soils, it may be some distance beneath the
surface.

Not only do the amount of water and the depth of the
water level help to determine plant societies, but also the
substances which the water contains. Two areas may have

PLANT SOCIETIES: ECOLOGICAL FACTORS

the same amount of water and the same water level, but
if the substances dissolved in the water differ in certain
particulars, two entirely distinct societies may result.

125. Heat. — The general temperature of an area is im-
portant to consider, but it is evident that differences of
temperature are not so local as differences in the water
supply, and therefore this factor is not so important in the
organization of the local associations of plants, called socie-
ties, as is the water factor. In the distribution of plants
over the surface of the earth, however, the heat factor is
probably more important than the water factor. The range
of temperature which the plant kingdom, as a whole, can
endure during active work may be stated in a general way
as from 0° to 50° C. ; that is, from the freezing point of
water to 122° Fahr. There are certain plants which can
work at higher temperatures, notably certain algae growing
in hot springs, but they may be regarded as exceptions. It
must be remembered that the range of temperature given
is for plants actively at work, and does not include the tem-
perature which many plants are able to endure in a specially
protected but very inactive condition. For example, many
plants of the temperate regions endure a winter tempera-
ture which is frequently lower than the freezing point of
water, but it is a question of endurance and not of work.

It must not be supposed that all plants can work equally
well throughout the whole range of temperature given, for
they differ widely in this regard. Tropical plants, for in-
stance, accustomed to a certain limited range of high tem-
perature, cannot work continuously at the lower tempera-
tures. For each kind of plant there is what may be called
a zero point, below which it is not in the habit of working.

AVhile it is important to note the general temperature
of an area throughout the year, it is also necessary to note
its distribution. Two regions may have presumably the
same amount of heat through the year, but if in the one case
jt is uniformly distributed, and in the other great extremes

172

PLANT STUDIES

of temperature occur, the same plants will not be found in
both. It is, perhaps, most important to note the tempera-
ture during certain critical periods in the life of plants,
such as the flowering period of seed-plants.

Although the temperature problem may be compara-
tively uniform over any given area, the eifect of it may be
noted in the succession of plants through the growing sea-
son. In our temperate regions the spring plants and summer
plants and autumn plants differ decidedly from one another.
It is evident that the spring plants can endure greater
cold than the summer plants, and the succession of flowers
will indicate somewhat these relations of temperature.

It should be remarked, also, that not only is the tem-
perature of the air to be noted, but also that of the soil.
These two temperatures may differ by several degrees, and
the soil temperature especially affects root activity, and
hence is a very important factor to discover.

At this point it is possible to call attention to the effect
of the combination of ecological factors. For instance, in
reference to the occurrence of plants in any society, the
water factor and the heat factor cannot be considered each
by itself, but must be taken in combination. For example,
if in a given area there is a combination of maximum heat
and minimum water, the result will be a desert, and only
certain specially adapted plants can exist. It is evident
that the great heat increases the transpiration, and tran-
spiration when the supply of water is very meager is pe-
culiarly dangerous. Plants which exist in such conditions,
therefore, must be specially adapted for controlling tran-
spiration. On the other hand, if in any area the combina-
tion is maximum heat and maximum water, the result will
be the most luxuriant vegetation on the earth, such as grows
in the rainy tropics. It is evident that the possible com-
binations of the water and heat factors may be very numer-
ous, and that it is the combination which chiefly affects
plant societies.

PLANT SOCIETIES: ECOLOGICAL FACTORS

126. Soil — The soil factor is not merely important to
consider in connection with those plants directly related
to the soil, but is a factor for all plants, as it determines
the substances which the water contains. There are two
things to be considered in connection with the soil, namely,
its chemical composition and its physical properties. Per-
haps the physical properties are more important from the
standpoint of soil-related plants than the chemical com-
position, although both the chemical and physical nature
of the soil are so bound up together that they need not be
considered separately here. The physical properties of the
soil, which are important to plants, are chiefly those which
relate to the water supply. It is always important to de-
termine how receptive a soil is. Does it take in water
easily or not ? It is also necessary to determine how re-
tentive it is ; it may receive water readily, but it may not
retain it.

For convenience in ordinary field work with plants,
soils may be divided roughly into six classes : (1) rock,
which means solid uncrumbled rock, upon which certain
plants are able to grow ; (2} sand, which has small water
capacity, that is, it may receive water readily enough, but
does not retain it ; (3) lime soil ; (4) clay, which has great
water capacity ; (5) humus, which is rich in the products
of plant and animal decay ; (6) salt soil, in which the water
contains various salts, and is generally spoken of as alka-
line. These divisions in a rough way indicate both the
structure of the soil and its chemical composition. Not
only should the kinds of soil on an area be determined,
but their depth is an important consideration. It is
very common to find one of these soils overlying another
one, and this relation between the two will have a very
important effect. For instance, if a sand soil is found
lying over a clay soil, the result will be that the sand soil
will retain far more water than it would alone. If a humus
soil in one area overlies a sand soil, and in another area

174 PLANT STUDIES

overlies a clay soil, the humus will differ very much in the
two cases in reference to water.

The soil cover should also be considered. The common
soil covers are snow, fallen leaves, and living plants. It
will be noticed that all these covers tend to diminish the
loss of heat from the soil, as well as the access of heat to
the soil. In other words, a good soil cover will very much
diminish the extremes of temperature. All this tends to
increase the retention of water.

127. Light, — It is known that light is essential for the
peculiar work of green plants. However, all green plants
cannot have an equal amount of light, and some have
learned to live with a less amount than others. While
no sharp line can be drawn between green plants which
use intense light, and those which use less intense light,
we still recognize in a general way what are called light
plants and shade plants. We know that certain plants
are chiefly found in situations where they can be exposed
freely to light, and that other plants, as a rule, are found
in shady situations.

Starting with this idea, we find that plants grow in
strata. In a forest society, for example, the tall trees rep-
resent the highest stratum ; below this there may be a
stratum of shrubs, then tall herbs, then low herbs, then
forms like mosses and lichens growing close to the ground.
In any plant society it is important to note the number of
these strata. It may be that the highest stratum shades
so densely that many of the other strata are not represented
at all. An illustration of this can be obtained from a
dense beech forest.

128. Wind. — It is generally known that wind has a dry-
ing effect, and, therefore, it increases the transpiration of
plants and tends to impoverish them in water. This factor
is especially conspicuous in regions where there are pre-
vailing winds, such as near the sea-coast, around the great
lakes, and on the prairies and plains. In all such regions

PLANT SOCIETIES: ECOLOGICAL FACTORS

the plants have been compelled to adapt themselves to this
loss of water ; and in some regions the prevailing winds are
so constant and violent that the force of the wind itself has
influenced the appearance of the vegetation, giving what is
called a characteristic physiognomy to the area.

These five factors have been selected from a much larger
number that might be enumerated, but they may be re-
garded as among the most important ones. It will be
noticed that these factors may be combined in all sorts
of ways, so that an almost endless series of combinations
seems to be possible. This will give some idea as to the
possible number of plant societies, for they may be as
numerous as are the combinations of these factors.

129. The great groups of societies. — It is possible to re-
duce the very numerous societies to three or four great
groups. For convenience, the water factor is chiefly used
for this classification. It results in a convenient classifica-
tion, but one that is probably more or less artificial. The
selection of any one factor from among the many for the
purpose of classification never results in a very natural
classification when the combination of factors determines
the group. However, for general purposes, the usual
classification on the basis of water supply will be used.
On this basis there are three great groups of societies,
as follows :

(1) Hydrophytes. — The name means " water plants," and
suggests that such societies are at that extreme of the water
supply where it is very abundant. Such plants may grow
in the water, or in very wet soil, but in any event they are
exposed to a large amount of water.

(2) Xerophytes. — The name means " drought plants,"
and suggests the other extreme of the water supply. True
xerophytes are exposed to dry soil and dry atmosphere.

(3) Mesophytes. — Between the two extremes of the water
supply there is a great middle region of medium water
supply, and plants which occupy it are known as meso-

176 PLANT STUDIES

phytes, the plants of the middle region. It is evident that
mesophytes gradually pass into hydrophytes on the one
side, and into xerophytes on the other ; but it is also evi-
dent that mesophyte societies have the greatest range of
water supply, extending from a large amount of water to
a very small amount.

It should be understood that these three groups of socie-
ties, which are distinguished from one another by the amount
of the water supply, are artificial groups rather than natural
ones, for they bring together unrelated societies, and often
separate those that are closely related. For example, a
swampy meadow is put among hydrophyte societies by this
classification ; and it may shade into an ordinary meadow,
which belongs among the mesophytes. Probably the largest
fact which may be used in grouping plant societies is that
certain societies are so situated that they seek for the most
part to reduce transpiration, and that others are so situated
that they seek for the most part to increase transpiration.

However, the factors which determine societies are so
numerous that they cannot be presented in an elementary
book, and the simpler artificial grouping given above will
serve to introduce the societies to observation.

Upon a different basis another great group of societies
has been suggested as follows :

(4) Halophytes. — The word means " salt plants." The
basis of classification here depends not so much upon the
water supply as upon the fact that the water contains
certain, salts which make it impossible for most plants to
live. Such societies may be found near the sea-coast,
around salt springs, on alkaline flats, or wherever the soil
contains these characteristic salts.

CHAPTER XII

HYDROPHYTE SOCIETIES

130. General character. — Hydrophytes are related to
abundant water, either throughout their whole structure
or in part of their structure. It is a well-known fact that
hydrophytes are among the most cosmopolitan of plants,
and hydrophyte societies in one part of the world look
very much like hydrophyte societies in any other region.
It is probable that the abundant water makes the condi-
tions more uniform.

It is evident that for those plants, or plant parts, which
are submerged, the water affects the heat factor by dimin-
ishing the extremes. It also affects the light factor, in so
far as the light must pass through the water to reach the
chlorophyll-containing parts, as light is diminished in
intensity by passing through the water. Before consider-
ing a few hydrophyte societies, it is necessary to note the
prominent hydrophyte adaptations.

131. Adaptations. — In order that the illustration may be
as simple as possible, a complex plant completely exposed
to water is selected, for it is evident that the relations of a
swamp plant, with its roots in water and its stem and leaves
exposed to air, are complicated. A number of adaptations
may be noted in connection with the submerged or floating
plant.

(1) Thin-walled epidermis. — In the case of the soil-re-
lated plants, the water supply comes mainly from the soil,
and the root system is constructed to absorb it. In the
case of the water plant under consideration, however, the

177

178

PLANT STUDIES

whole plant body is exposed to the water supply, and there-
fore absorption may take place through the whole surface
rather than at any particular region such as the root. In
order that this may be done, however, it is necessary for
the epidermis to have thin walls, which is usually not the
case in epidermis exposed
to the air, where a certain
amount of protection is
needed in the way of
thickening.

(2) Roots much reduced
or wanting. — It must be
evident that if water is
being absorbed by the
whole free surface of the
plant, there is not so
much need for a special
root region for absorp-
tion. Therefore, in such
water plants the root sys-
tem may be much re-
duced, or may even disap-
pear entirely. It is often
retained, however, to act
as a holdfast, rather than
as an absorbent organ, for
most water plants anchor
themselves to some sup-
port.

(3) Reduction of water-conducting tissues. — In the ordi-
nary soil-related plants, not only is an absorbing root sys-
tem necessary, but also a conducting system, to carry the
water absorbed from the roots to the leaves and elsewhere.
It has already been noted that this conducting system takes
the form of woody strands. It is evident that if water
is being absorbed by the whole surface of the plant, the

FIG. 159. Fragment of a common seaweed
(Fucus), showing the body with forking
branching and bladder-like air cavities. —
After LUERSSEN.

HYDROPHYTE SOCIETIES 179

work of conduction is not so extensive or definite, and
therefore in such water plants the woody bundles are not
so prominently developed as in land plants.

(4) Reduction of mechanical tissues. — In the case of
ordinary land plants, certain firm tissues are developed so

FIG. 100. Gulfweed (Sargassum), showing the thallus differentiated into stem-like and
leaf -like portions, and also the bladder-like floats. — After BENNETT and MURRAY.

that the plant may maintain its form. These supporting
tissues reach their culmination in such forms as trees,
where massive bodies are able to stand upright. It is evi-
dent that in the water there is no such need for rigid sup-
porting tissues, as the buoyant power of water helps to
support the plant. This fact may be illustrated by taking

180

PLANT STUDIES

out of water submerged plants which seem to be upright,
with all their parts properly spread out. "When removed they
collapse, not being able to support themselves in any way.
(5) Development of air cavities. — The presence of air in
the bodies of water plants is necessary for two reasons: (1),

FIG. 161. Bladderwort, showing the numerous bladders which float the plant, the
finely divided water leaves, and the erect flowering stems. The bladders are also
effective "insect traps,'1 Utriculana being one of the "carnivorous plants."
—After KERNEB.

to aerate the plant ; (2), to increase its buoyancy. In most
complex water plants there must be some arrangement for
the distribution of air containing oxygen. This usually
takes the form of air chambers and passageways in the
body of the plant (see Figs. 87, 88, 89, 90). Of course
such air chambers increase the buoyancy of the body.
Sometimes, however, a special buoyancy is provided for
by the development of regular floats, which are bladder-

HYDEOPHYTE SOCIETIES

181

like bodies (see Figs. 159, 160). These floats are very com-
mon among certain of the seaweeds, and are found among
higher plants, as the utricularias or bladderworts, which

FIG. 162. A group of marine seaweeds (Laminarias). Note the various habits of the
plant body and the root-like holdfasts.— After KERNER.

have received their name from the numerous bladders
developed in connection with their bodies (see Fig. 161),
and which are also put to additional uses.

182 PLANT STUDIES

132. Societies. — Conspicuous among hydrophyte societies
may be mentioned the following : (1) Free-swimming soci-
eties, in which the plants are entirely sustained by water,
and are free to move either by locomotion or by water cur-
rents. 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 societies," 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 (Fig. 163). 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. 164, 167), 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. 163) ; " swamp-thickets," consist-
ing of willows, alders, birches, etc. ; "sphagnum-moors," in
which sphagnum moss predominates, and is accompanied by
numerous peculiar orchids, heaths, carnivorous plants, etc. ;
" swamp-forests," which are largely coniferous, tamarack
(larch), pine, hemlock, etc., prevailing.

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FIG. 165. A group of pondweede. The stems are sustained in an erect position by
the water, and the narrow leaves are exposed to a light whose intensity is dimin-
ished by passing through the water,— After KBKNEK.

FIG. 166. Eel grass (Vallisneria), a common pondweed plant. The plants are
anchored and the foliage is submerged. The carpel-bearing flowers are carried to
the surface on long stalks which allow a variable depth of water. The stamen-
bearing flowers remain submerged, as indicated near the lower left corner, the
flowers breaking away and rising to the surface, where they float and effect pollina-
tion.—After KEKNER.

FIG. 167. A reed swamp, fringing the low shore of a lake or a sluggish stream. The
plants are tall and wand-like, and all are monocotyls. Three types are prominent,
the reed grasses (the tallest), the cat-tails (at the right), and the bulrushes (a group
standing out in deeper water near the middle of the fringing growth). The plant
in the foreground at the extreme right is the arrow-leaf (Sagittaria), recognized
by its characteristic leaves.— After KEKNER.

CHAPTER XIII

XEBOPHYTE SOCIETIES

133. General character. — Strongly contrasted with the
hydrophytes are the xerophytes, which are adapted to dry
air and soil. The xerophytic conditions may be regarded
in general as drouth conditions. It is not necessary for
the air and soil to be dry throughout the year to develop
xerophytic conditions. These conditions may be put under
three heads : (1) possible drouth, in which a season of
drouth may occur at irregular intervals, or in some seasons
may not occur at all ; (2) periodic drouth, in which there
is a drouth period as definite as the winter period in cer-
tain regions ; (3) perennial drouth, in which the dry con-
ditions are constant, and the region is distinctly an arid
or desert region.

However xerophytic conditions may occur, the problem
of the plant is always one of water supply, and many strik-
ing structures have been developed to answer it Plants
in such conditions must provide, therefore, for two things :
(1) collection and retention of water, and (2) prevention of
its loss. It is evident that in these drouth conditions the
loss of water through transpiration (see §26) tends to be
much increased. This tendency in the presence of a very
meager water supply is a menace to the life of the plant.
It is impracticable to stop transpiration entirely, for it
must take place in connection with a necessary life-process.
The adaptations on the part of the plant, therefore, are
directed towards the regulation of transpiration, that it
188

XEKOPHYTE SOCIETIES 189

may occur sufficiently for the life-processes, but that it
may not be wasteful.

The regulation of transpiration may be accomplished
in two general ways. It will be remembered that the
amount of transpiration holds some relation to the
amount of leaf exposure or exposure of green tissue.
Therefore, if the amount of leaf exposure be diminished,
the total amount of transpiration will be reduced. Another
general way for regulating transpiration is to protect
the exposed surface in some way so that the water does
not escape so easily. In a word, therefore, the general
method is to reduce the extent of exposed surface or to
protect it. It must be understood that plants do not differ
from each other in adopting one or the other of these
methods, for both are very commonly used by the same
plant.

Adaptations

134. Complete desiccation. — Some plants have a very re-
markable power of completely drying up during the drouth
period, and then reviving upon the return of moisture.
This power is strikingly illustrated among the lichens and
mosses, some of which can become so dry that they may be
crumbled into powder, but revive when moisture reaches
them. A group of club mosses, popularly known as " res-
urrection plants," illustrates this same power. The dried
up nest-like bodies of these plants are common in the
markets, and when they are placed in a bowl of water they
expand and may renew their activity. In such cases it can
hardly be said that there is any special effort on the part of
the plant to resist drouth, for it seems to yield completely
to the dry conditions and loses its moisture. The power
of reviving, after being completely dried out, is an offset,
however, for protective structures.

135. Periodic reduction of surface. — In regions of periodic

190

PLANT STUDIES

drouth it is very com-
mon for plants to
diminish the exposed
surface in a very de-
cided way. In such
cases there is what
may be called a peri-
odic surface decrease.
For example, annual
plants remarkably
diminish their ex-
posed surface at the
period of drouth by
being represented
only by well-pro-
tected seeds. The
whole exposed sur-
face of the plant,
root, stem, and leaves,
has disappeared, and
the seed preserves the
plant through the
drouth.

Little less remark-
able is the so-called
geophilous habit. In
this case the whole of
the plant surface ex-
posed to the air dis-
appears, and only
underground parts,
such as bulbs, tubers,
etc., persist (see Figs-
45, 46, 66, 67, 68,
69, 70, 75, 144, 168,
169). At the re-

FIG. 168. The bloodroot (Sanguinaria), showing
the subterranean rootstock sending leaves and
flower above the surface. — After ATKINSON.

XEKOPHYTE SOCIETIES

191

FIG. 169. The spring «- W \- v
beauty (Claytonia), |

showing subterranean

tuber-like stem sending leaf and flower-bearing
stem above the surface.— After ATKINSON.

turn of the moist season
these underground parts
develop new exposed
surfaces. In such cases
it may be said that at
the coming of the drouth
the plant seeks a sub-
terranean retreat.

A little less decrease
of exposed surface is
shown by the deciduous
habit. It is known that
certain trees and shrubs,
whose bodies remain
exposed to the drouth,
shed their leaves and
thus very greatly reduce
the amount of exposure ;
with the return of mois-
ture, new leaves are put
forth. It will be re-
marked, in this connec-
tion, that the same
habits serve just as well
to bridge over a period
of cold as a period of
drouth, and perhaps
they are more familiar
in connection with the
cold period than in con-
nection with the drouth
period.

136. Temporary reduc-
tion of surface. — While
the habits above have to
do with regular drouth

192 PLANT STUDIES

periods, there are other habits by which a temporary re-
duction of surface may be secured. For instance, at the
approach of a period of drouth, it is very easy to observe
certain leaves rolling up in various ways. As a leaf be-
comes rolled up, it is evident that its exposed surface is
reduced. The behavior of grass leaves, under such cir-
cumstances, is very easily noted. A comparison of the grass
blades upon a well-watered lawn with those upon a dried-up
lawn will show that in the former case the leaves are flat,
and in the latter more or less rolled up. The same habit
is also very easily observed in connection with the larger-
leaved mosses, which are very apt to encounter drouth
periods.

137. Fixed light position. — In general, when leaves have
reached maturity, they are unable to change their position
in reference to light, having obtained what is known as a
fixed light position. During the growth of the leaf, how-
ever, there may be changes in direction so that the fixed
light position will depend upon the light direction during
growth. The position finally attained is an expression of
the attempt to secure sufficient, but not too much light
(see §13). The most noteworthy fixed positions of leaves
are those which have been developed in intense light.
A very common position in such cases is the profile posi-
tion, in which the leaf apex or margin is directed upwards,
and the two surfaces are more freely exposed to the morn-
ing and evening rays — that is, the rays of low intensity —
than to those of midday.

Illustrations of leaves with one edge directed upwards
can be obtained from the so-called compass plants. Prob-
ably most common among these are the rosin-weed of the
prairie region, and the prickly lettuce, which is an intro-
duced plant very common in waste ground (see Fig. 170).
Such plants received their popular name from the fact that
many of the leaves, when edgewise, point approximately
north and south, but this direction is very indefinite. It is

XEKOPHYTE SOCIETIES

193

evident that such a position avoids exposure of the leaf
surface to the noon rays, but obtains for these same sur-
faces the morning and evening rays. If these plants are
developed in the shade, the "compass" habit does not

FIG. 170. Two compass plants. The two figures to the left represent the same plant
(Silphium) viewed from the east and from the south. The two figures to the right
represent the same relative positions of the leaves of Lactuca. — After KERNER.

appear (see §15). The profile position is a very common
one for the leaves of Australian plants, a fact which gives
much of the vegetation a peculiar appearance. All these
positions are serviceable in diminishing the loss of water,
which would occur with exposure to more intense light.
138. Motile leaves, — Although in most plants the mature

194

PLANT STUDIES

leaves are in a fixed position, there are certain ones whose
leaves are able to perform movements according to the need.
Mention has been made already of such forms as Oxalis
(see §14), whose leaves change their position readily in
reference to light. Motile leaves have been developed most
extensively among the Leguminosce, the family to which

FIG. 171. Two twigs of a sensitive plant. The one to the left shows the numerous
small leaflets in their expanded position ; the one to the right shows the greatly
reduced surface, the leaflets folded together, the main leaf branches having
approached one another, and the main leaf-stalk having bent sharply downwards.
— After STRASBURGER.

belong peas, etc. In this family are the so-called " sen-
sitive plants," which have received their popular name
from their sensitive response to light as well as to other
influences (see Fig. 171). The acacia and mimosa forms
are the most notable sensitive plants, and are especially
developed in arid regions. The leaves are usually very
large, but are so much branched that each leaf is com-
posed of very numerous small leaflets. Each leaflet has

XEROPHYTE SOCIETIES

195

the power of independent motion, or the whole leaf may
move. If there is danger from exposure to drouth, some
of the leaflets will be observed to fold together ; in case

FIG. 172. A heath plant (Erica), showing low, bushy growth and small leaves.

the danger is prolonged, more leaflets will fold together ;
and if the danger persists, the surface of exposure will be
still further reduced, until the whole plant may have its
leaves completely folded up. In this way the amount of

196 PLANT STUDIES

reduction of the exposed surface may be accurately regu-
lated to suit the need (see §38).

139. Reduced leaves. — In regions that are rather per-
manently dry, it is observed that the plants in general pro-
duce smaller leaves than in other regions (see Fig. 173).
That this holds a direct relation to the dry conditions is

FIG. 173. Leaves from the common basswood ( Tilia), showing the effect of environ-
ment ; those at the right being from a tree growing in a river bottom (mesophyte
conditions) ; those at the left being from a tree growing upon a dune, where it is
exposed to intense light, heat, cold, and wind. Not only are the former larger,
but they are much thinner. The leaves from the dune tree are strikingly smaller,
much thicker, and more compact. — After COWLES.

evident from the fact that the same plant often produces
smaller leaves in xerophytic conditions than in moist con-
ditions. One of the most striking features of an arid
region is the absence of large, showy leaves (see Fig. 172).
These reduced leaves are of various forms, such as the
needle leaves of pines, or the thread-like leaves of certain
sedges and grasses, or the narrow leaves with inrolled
margins such as is common in many heath plants. The

XEEOPHYTE SOCIETIES

197

FIG. 174. Two species of Achillea on different soils. The one to the left was grown
in drier conditions and shows an abundant development of hairs. — After
SCHIMPER.

extreme of leaf reduction has been reached by the cactus
plants, whose leaves, so far as foliage is concerned, have
disappeared entirely, and the leaf work is done by the

198

PLANT STUDIES

surface of the globular, cylindrical, or flattened stems (see
§36).

140. Hairy coverings. — A covering of hairs is an effective
sun screen, and it is very common to find plants of xerophyte
regions character-
istically hairy (see

§35). The hairs
are dead struc-
tures, and within
them there is air.
This causes them
to reflect the light,
and hence to ap-
pear white or
nearly so. This
reflection of light
by the hairs dimin-
ishes the amount
which reaches the
working region of
the plant (see Fig.
174).

141. Body habit.
— Besides the va-
rious devices for
diminishing ex-
posure or leaf sur-
face, and hence
loss of water,
enumerated above,
the whole habit of
the plant may em-
phasize the same purpose. In dry regions it is to be observed
that dwarf growths prevail, so that the plant as a whole
does not present such an exposure to the dry air as in
regions of greater moisture (see Fig. 175). Also the pros-

FIG. 115. Two plants of a common scouring rush (Equi-
setum}, showing the effect of environment ; the long,
unbranched one having grown in normal mesophyte
conditions ; the short, bushy branching, more slender
form having grown on the dunes (xerophyte condi-
tions).— After COWLES.

XEROPHYTE SOCIETIES

199

trate or creeping habit is a much less exposed one in such
regions than the erect habit. In the same manner, the very
characteristic rosette habit, with its cluster of overlapping
leaves close against the ground, tends to dimmish loss of
water through transpiration.

One of the most common results of xerophytic conditions
upon body habit is the development of thorns and spiny

FIG. 176. Young plants of Euphorbia splendens, showing a development of thorns
characteristic of the plants of dry regions.

processes. As a consequence, the vegetation of dry regions
is characteristically spiny. In many cases these spiny pro-
cesses can be made to develop into ordinary stems or leaves
in the presence of more favorable water conditions. It is
probable, therefore, that such structures represent reduc-
tions in the growth of certain regions, caused by the unfavor-
able conditions. Incidentally these thorns and spiny pro-
cesses are probably of great service as a protection to plants
in regions where vegetation is peculiarly exposed to the
14

200

PLANT STUDIES

ravages of animals (see §105). Examine Figs. 176, 177,
178, 179, 180, 181.

142. Anatomical adaptations. — It is in connection with
the xerophytes that some of the most striking anatomical
adaptations have been
developed. In such
conditions the epider-
mis is apt to be cov-
ered by layers of
cuticle,, which are de-
veloped by the walls
of the epidermal cells,
and being constantly
formed beneath the
cuticle, may become
very thick. This
forms a very efficient
protective covering,
and has a tendency to
diminish the loss of
water (see §35). It is
also to be observed
that among xerophyfces
there is a strong de-
velopment of palisade
tissue. The working
cells of the leaves next
to the exposed surface
are elongated, and are
directed endwise to

the surface. In this way only the ends of the elongated
cells are exposed, and as such cells stand very closely to-
gether, there is no drying air between them. In some
cases there may be more than one of these palisade rows
(see §32). It has been observed that the chloroplasts in
these palisade cells are able to assume various positions in

b a,

FIG. 177. Two plants of common gorse or furze
(Ulex), showing the effect of environment : b
is a plant grown in moist conditions ; a is a
plant grown in dry conditions, the leaves and
branches having been almost entirely developed
as thorns. — After LOTHELIER.

XEROPHYTE SOCIETIES

201

the cell, so that when
the light is very intense
they move to the more
shaded depths of the
cell, and when it be-
comes less intense they
move to the more exter-
nal regions of the cell
(see Fig. 182). The
stomata, or breathing
pores, which are devel-
oped in the epidermis,
are also great regulators
of transpiration, as has
been mentioned already
(see §31).

143. Water reservoirs.
— In xero-
phytes at-
t e n t i o n
must be
given not
only to the

regulation of transpiration, but also to the
storage of water, as it is received at rare inter-
vals. It is very common to find a certain re-
gion of the plant body given over to this work,
forming what is known as water tissue. In
many leaves this water tissue may be distin-
guished from the ordinary working cells by
being a group of colorless cells (see Fig. 183).
In plants of the drier regions leaves may
become thick and fleshy through acting as
water reservoirs, as in the case of the agave,
sedums, etc. Fleshy or " succulent " leaves
are regarded as adaptations of prime impor-

FIG. 178. A branch of Cytisus, showing the
reduced leaves and thorny branches.— After
KERNER.

179. A
leaf of traga-
canth, show-
ing the re-
duced leaf-
lets and the
thorn-like
tip.— After
KERNEB.

202

PLANT STUDIES

tance in xerophytic conditions. In
the cactus plants the peculiar stems
have become great reservoirs of
moisture. The globular body may
be taken to represent the most com-
plete answer to this general problem,
as it is the form of body by which
the least amount of surface may be
exposed and the greatest amount of
water storage secured. In the case
of fleshy leaves and fleshy bodies it
has long been noticed that they not
only contain water, but also have a
great power of re-

FIG. 181. Twig of com-
mon locust, showing
the thorns. — After
KEENER.

FIG. 180. A fragment of bar-
berry, showing the thorns.
— After KERNEK.

taining it. Plant

collectors have found great difficulty in
drying these fleshy forms, some of which
seem to be able to retain their moisture in-
definitely, even in the driest conditions.
144. Xerophytic structure. — The adap-
tations given above are generally found
in plants growing in drouth conditions,
and they all imply an effort to diminish
transpiration. It must not be supposed,
however, that only plants living in
drouth conditions show these adapta-
tions. Such adaptations result in what
is known as the xerophytic structure,
and such a structure may appear even
in plants growing in hydrophyte condi-
tions. For example, the bulrush grows
in shallow water, and is a prominent
member of one of the hydrophyte socie-
ties (see §132) ; and yet it has a remark-
ably xerophytic structure. This is prob-
ably due to the fact that although it

XEKOPHYTE SOCIETIES

203

stands in the water its stem is exposed
to a heat which is often intense.

The ordinary prairie (see §146) is
included among mesophyte societies
on account of the rich, well-watered
soil; and yet many of the plants are
very xerophytic in structure, probably
on account of the prevailing dry winds.
The ordinary sphagnum-bog (see
§132), or "peat-bog," is included
among hydrophyte societies. It has
an abundance of v/ater, and is not ex-
posed to blazing heat, as in the case
of the bulrushes, or to drying wind,
as in the case of prairie plants ; and
yet its plants show a xerophytic struc-
ture. This is found to be due, proba-
bly, to a lack of certain important soil
materials.

It is evident, therefore, that xero-
phytic structures are not necessarily
confined to xerophytic situations. It
is probably true that all societies which
show xerophytic structures belong to-
gether more naturally
than do the societies
which are grouped ac-
cording to the water
supply.

Societies

FIG. 182. Cells from the leaf
of a quill wort (Isoetes).
The light is striking the
cells from the direction of
one looking at the illus-
tration. If it be some-
what diffuse the chloro-
plasts distribute them-
selves through the shal-
low cell, as in the cell to
the left. If the light be
intense, the chloroplasts
move to the wall and as-
sume positions less ex-
posed, as in the cell to
the right.

No attempt will be
made to classify these
very numerous socie-
ties, but a few prom-

FIG .183. A section through a Begonia leaf, show-
ing the epidermis (ep) above and below, the
water-storage tissue (ws) above and below, and
the central chlorophyll region (as).

204 PLANT STUDIES

inent illustrations will be given. Some of the prominent
societies are as follows : " rock-societies," composed of
plants living upon exposed rock surfaces, walls, fences, etc.,
notably lichens and mosses ; " sand societies," including
beaches, dunes, and sandy fields ; " shrubby heaths," char-
acterized by heath plants ; " plains," the great areas with
dry air and wind developed in the interiors of continents ;
" cactus deserts," still more arid areas of the Mexican re-
gion, where the cactus, agave, yucca, etc., have learned to

FIG. 184. A rock covered with lichens.

live ; " tropical deserts," where xerophytic conditions reach
their extreme in the combination of maximum heat and
minimum water ; " xerophyte thickets," the most impene-
trable of all thicket-growths, represented by the " chapar-
ral " of the Southwest, and the " bush " and " scrub " of
Africa and Australia; "xerophyte forests," also notably
coniferous. (See Figs. 193, 194.)

FIG. 189. Two plants of the giant cactus. Note the fluted, clumsy branching, leaf-
less bodies growing from the rocky, sterile soil characteristic of cactus deserts.
Certain dry-ground grasses and low, shrubby plants with small leaves may be seen
iu the foreground,

FIG. 194. A xerophyte conifer forest in the mountains. The peculiar conifer habit
of body is recognized, the trees finding foothold in the crevices of rocks or in
areas of rock debris.

CHAPTER XIV

MESOPHYTE SOCIETIES

145. General characters. — Mesophytes make up the com-
mon vegetation of temperate regions,, the vegetation most
commonly met and studied. The conditions of moisture
are medium, precipitation is in general evenly distributed,
and the soil is rich in humus. The conditions are not ex-
treme, and therefore special adaptations, such as are neces-
sary for xerophyte or hydrophyte conditions, do not appear.
This may be regarded as the normal plant condition. It
is certainly the arable condition, and most adapted to the
plants which men seek to cultivate. When for purposes
of cultivation xerophyte areas are irrigated, or hydrophyte
areas are drained, it is simply to bring them into mesophyte
conditions.

In looking over a mesophyte area and contrasting it
with a xerophyte area, one of the first things evident is that
the former is far richer in leaf forms. It is in the meso-
phyte conditions that foliage leaves show their remarkable
diversity. In hydrophyte and xerophyte areas they are apt
to be more or less monotonous in form. Another contrast
is found in the dense growth over mesophyte areas, much
more so than in xerophyte regions, and even more dense
than in hydrophyte areas.

Among the mesophyte societies must be included not

merely the natural ones, but those new societies which

have been formed under the influence of man, and which

do not appear among xerophyte and hydrophyte societies.

214

MESOPHYTE SOCIETIES 215

These new societies have been formed by the introduction
of weeds and culture plants.

146. The two groups of societies, — Two very prominent
types of societies are included here under the mesophytes,
although they are probably as distinct from one another as
are the mesophyte and xerophyte societies. One group is
composed of low vegetation, notably the common grasses
and herbs ; the other is a higher woody vegetation, composed
of shrubs and trees. The most characteristic types under
each one of these divisions are noted as follows.

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. 195,
197, 198, 199.)

FIG. 195. Alpine vegetation, showing the low stature, dense growth, and conspicu-
ous flowers. — After KERNEK.

FIG. 196. Two plants of a rock-rose (Helianthemum), showing the effect of low
ground and alpine conditions. The low-ground plant (a) shows an open habit,
and elongated stems with comparatively large and well-separated leaves. The
same plant in alpine conditions is drawn to the same scale in ft, and magnified in
c, the very short and compact habit being in striking contrast with that of the low-
ground form.— After BONNIER.

CHAPTER XV

THE PLANT GROUPS

147. 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. For example,
a lichen, a moss, and an oak differ very much in form and
size, and also in complexity, and because of this last fact an
oak would be regarded as a plant of higher rank than either
a lichen or a moss. It must not be supposed that rank is
measured by size, for in the highest group there are many
small plants.

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.

148. 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 will be noticed that all the names have the

221

222 PLANT STUDIES

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 Algm 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. Not 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.

149. 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.,

THE PLANT GROUPS 223

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.

150. 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.

151. 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 XVI

THALLOPHYTES: ALGJE

152. 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. While 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.

153. Algae and Fungi.— It is convenient to separate Thallo-
phytes into two great divisions, known as Alga and Fungi.
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,
224

THALLOPHYTES: ALG^E 225

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

154. 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

226 PLANT STUDIES

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.

155. 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) Cyanophycece,
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) Chlorophycem, 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.

156. 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-

THALLOPI1YTES : ALG^E

227

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. 204), but if pressed upon by contiguous cells may be-
come variously modified in
form (Fig. 200). Bounding
it there is a thin, elastic
wall, composed of a sub-
stance called cellulose. The
cell wall, therefore, forms a
delicate sac, which contains
the living substance known
as protoplasm. This is the
substance which manifests
life, and is the only sub-
stance in .the plant which
is alive. It is the proto-
plasm which has organized
the cellulose wall about it-
self, and which does all the
plant work. It is a fluid
substance which varies much in its consistence, sometimes
being a thin viscous fluid, like the white of an egg, some-
times much more dense and compactly organized.

The protoplasm of the cell is organized into various
structures which are called organs of the cell, each organ
having one or more special functions. One of the most con-
spicuous organs of the living cell is the single nucleus, a com-
paratively compact and usually spherical protoplasmic body,
and generally centrally placed within the cell (Fig. 200).
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. 200. Cells from a moss leaf, showing
nucleus (B) in which there is a nucle-
olus, cytoplasm ((7), and chloroplasts
(A). — CALDWELL.

228 PLANT STUDIES

nucleus lies imbedded within it (Fig. 200). 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 plaztid. 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. 200). An ordinary alga-cell,
therefore, consists of a cell wall, within which the proto-
plasm 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. 202) ; in other forms
the cells in a row become more compacted and flattened,
forming a simple filament (Fig. 203) ; in still other forms
the original filament puts out branches like itself, produc-
ing a branching filament (Fig. 207). 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.

157. 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: ALG.E

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 (Fig. 204), 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. 205, 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

230 PLANT STUDIES

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. 206, 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. 205, 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 231

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.

At first the two gametes are alike in size and activity,
and such plants are said to be isogamous — that is, " with
similar gametes." In other plants the gametes become
very dissimilar, one being large and passive, and called the
egg ; the other being small and active, and called the
sperm ; and such plants are said to be heterogamous — that
is, "with dissimilar gametes." The gametangium which
produces the egg is called an oogonium; that which pro-
duces sperms is the antheridium.

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 diifer-
ent ways.

CHAPTEE XVII

THE GREAT GROUPS OP ALG-EJ

158. 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 Algae (Phaeophyceae), and Eed 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. CYANOPHYCE^ (Blue-green Algae)

159. Gloeocapsa, — 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 Gloeocapsa 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
Gloeocapsa individuals being formed, this method of vegeta-
tive multiplication being the only form of reproduction
(Fig. 201).

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
232

THE GREAT GROUPS OF ALG.E

233

together imbedded in the jelly-like matrix formed by the

wall material (Fig. 201). These imbedded groups of indi-

viduals 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 represents a very simple life his-

tory, in 'fact a simpler one could hard-

ly be imagined.

160. 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 Glmocapsa, but they

are strung together to form chains of

varying lengths (Fig. 202). The jelly in

which these chains are imbedded is the

same as that found in Glwocapsa, 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. 202, A),
which simply means
"other cells." It is
observed that when
the chain breaks up

into fragments each
fragment isCOmpOSed

of the cells between

FIG. 201. Glceocapsa, a
blue-green alga, show-
ing single cells, and
small groups which have
been formed by division
and are held together by
the enveloping muci-
lage.—CALDWELL.

FIG. 202. Nostoc, a blue-green alga, showing the
chain-like filaments, and the heterocysts (A)
which determine the breaking up of the chain.—

234

PLANT STUDIES

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."

161. 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. 203), 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 FIG. 203. OscWaria,auue-

. - , , T. _. green alga, showing a

free surface rounded. If a filament group Of filaments u>,
breaks, and a new cell surface ex- and a single filament

-i •! i n i more enlarged (B).—

posed, it at once becomes rounded. CALDWEM..

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

f±T B

THE GREAT GROUPS OF ALG^ 235

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.

162. 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

236

PLANT STUDIES

upon the return of favorable conditions. These may be
regarded as resting cells. 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 Alg&).

163. 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
Glceocapsa, 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. 204). Like Glceocapsa, a cell
divides and forms two new cells, the only reproduction

FIG. 204. Pleurococcus, a one-celled green alga : A, show-
ing the adult form with its nucleus ; B, C, D, E,
various stages of division (fission) in producing new
cells ; F, colonies of cells which have remained in
contact. — C ALDWELL.

THE GREAT GROUPS OF ALG^E 237

being of this simple kind. It is evident, therefore, that the
group Chlorophycese 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 Algae. 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.

164. TTlothrix. — This form is very common in fresh wa-
ters, being recognized easily by its simple filaments com-
posed of short squarish cells, each cell containing a single
conspicuous cylindrical chloroplast (Fig. 205).

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
reproductive cells are not distinctly differentiated, but that
the same cell may be nutritive at one time and reproductive
at another. This plant uses cell division to multiply the
cells of a filament, and to develop new filaments from frag-
ments 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 develop-
ment of a new plant. In the germination of the zygote
a new filament is not produced directly, but there are
formed within it zoospores, each of which produces a
new filament (Fig. 205, F, G). All three kinds of repro-
duction are represented, therefore, but the sexual method

238

PLANT STUDIES

is the low type called isogamy, the pairing gametes being
alike.

Ulothrix is taken as a representative of the Conferva
forms, the most characteristic group of Chlorophyceae. All

4\ *"

FIG. 205. 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 (b) 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 ; G,
zoospores produced by zygote.— CALDWELL, except F and G, which are after

DODEL-PORT.

the Conferva forms, however, are not isogamous, as will be
illustrated by the next example.

165. Edogonium. — This is a very common green alga,
found in fresh waters (Fig. 206). The filaments are long and
simple, the lowest cell acting as a holdfast, as in Ulothrix

FIG. 206. Edogonium nodosum, a Conferva form : A, portion of a filament showing a
vegetative cell with its nucleus (d), an oogonium (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 (6), each containing two sperms; B,
another filament showing antheridia (a) from wyhich two sperms (b) have escaped,
a vegetative cell with its nucleus, and an oogonium which a sperm (c) has entered
and is coming in contact with the egg whose nucleus (rf) 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; E, a further stage of development; F, the
four zoospores formed by the oospore when it germinates.— CALDWELL, except
C and F, which are after PRINGSHEIM.

PLANT STUDIES

(§ 164). The other cells are longer than in Ulothrix, 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 organiz-
ing 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. 206, 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. 206, J9, E).

Other cells of the filament become very different from
the ordinary cells, swelling out into globular form (Fig.
206, 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 dif-
ferentiated from the other cells of the body, is the oogo-
nium. 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.
206, -4,/, 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. 206, B, c). As a result of this act of fer-
tilization an oospore is formed, which organizes a firm wall

THE GREAT GROUPS OF A~LGM

241

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.
When 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 neAV filament, but the
contents become organized into four zoospores (Fig. 206, 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 UlotJirix
and Edogonium, but they are sometimes extensively branch-
ing filaments, as in Cladophora, a green alga very common

FIG. 207. 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
ccenocytic.— CALDWELL.

242

PLANT STUDIES

in rivers and lakes (Fig. 207). 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.

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

FIG. 208. 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 (E)
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 coenocytic body (E\— CALDWELL.

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 (Fig. 208). 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 GROUPS OF ALG^E 243

plasm organized about it is a cell, whether it has a wall or
not. Therefore the body of Vaucheria 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 ccenocyte, or it is said to be cwnocytic. Vaucheria
represents a great group of Chlorophyceae whose members
have coenocytic bodies, and on this account they are called
the Siphon forms.

Vaucheria 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. 208, 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. 208, C'), swims about for a time, and finally
develops another Vaucheria body (Figs. 208, E\
209). 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. 209. 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, §165.

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,

244

PLANT STUDIES

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

FIG. 210. Vaucheria sessilis, a Siphon form,
showing a portion of the ccenocytic body, an
antheridial branch (A) with an empty anthe-
ridium (a) at its tip ; and an oogonium (B)
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. 210, B). The an-
theridium is a much smaller cell,
within which numerous very small
sperms are formed (Fig. 210, A, 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. 211).

167. 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. 211. Botrydium, one of
the Siphon forms of green
algae, the whole body con-
taining one continuous cav-
ity, with a bulbous, chloro-
phyll - containing portion,
and root - like branches
which penetrate the mud
in which the plant grows.

—CALDWELL.

THE GREAT GROUPS OF ALGJE

245

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

FIR. 212. 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.—
CALDWBLL.

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

FIG. 213. 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.

246

PLANT STUDIES

be solitary or several in a cell, and form very striking and
conspicuous objects (Figs. 212, 213).

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. 214. 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. 213, 214). 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 GEOCJPS OF ALG^E

247

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. 215, A), and some-
times zygotes are formed without
conjugation (Fig. 215, 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. 216).

168. 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
17

FIG. 215. Two Conjugate forms :
A (Mougeotia), showing for-
mation of zygote in conjuga-
ting tube ; B, C ( Gonatone-
ma), showing formation of
zygote without conjugation.
— After WITTROCK.

248

PLANT STUDIES

by walls, or they are coenocytic, 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. 216. A group of Desmids, one-celled Conjugate forms, showing various pat-
terns, and the cells organized into distinct halves.— After KERNEB.

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)

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

THE GREAT GROUPS OF ALG^E

249

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.

170. The plant
body. — There is very
great diversity in the
structure of the
plant body. Some
of them, as Ectocar-
pus (Fig. 217), 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. 217. 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.— CALDWELL.

C if:

FIG. 218. A group of brown seaweeds (Laminarias). Note the various habits of
the plant body with its leaf-like thallus and root-like holdfasts.— After KEENER.

THE GREAT GROUPS OF ALGJ2

251

feet long, whose stalk develops root-like holdfasts (Fig. 218).
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. 219). 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. 220), 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. 219. Fragment of a common brown
alga (Fucus), showing the body with
dichotomous branching and bladder-like
air-bladders.— After LUERSSEN.

252 PLANT STUDIES

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

FIG. 220. A portion of a brown alga (Sargassum), showing the thallus differentiated
into stem-like and leaf-Jike portions, and also the bladder-like floats. — After BEN-
NETT and MURRAY.

171. Reproduction. — The two main groups of Brown
Algae differ from each other in their reproduction. One,
represented by the Laminarias and a majority of the forms,
produces zoospores and is isogamous (Fig. 217). The zoo-
spores and gametes are peculiar in having the two cilia
attached at one side rather than at an end ; and they re-
semble each other very closely, except that the gametes
fuse in pairs and form zygotes.

FIG. 221. 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 (E), antheridium containing sperms (C), the discharged lat-
erally biciliate sperms (£), and eggs surrounded by swarming sperms (F, H).—
After SINGER.

254

PLANT STUDIES

The other group, represented by Fucus (Fig. 221), pro-
duces no asexual spores, but is heterogamous. A single
oogonium usually forms eight eggs (Fig. 221, A), which are
discharged and float freely in the water (Fig. 221, E). The
antheridia (Fig. 221, (7) produce numerous minute laterally
biciliate sperms, which are discharged (Fig. 221, 6r), swim
in great numbers about the large eggs (Fig. 221, F, H),
and finally one fuses with an egg, and an oospore is formed.
As the sperms swarm very actively about the egg and im-
pinge against it they often set it rotating. Both antheridia
and oogonia are formed in cavities of the thallus.

4. KHODOPHYCE^; (Red Algce)

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

marine forms, and are
anchored by holdfasts

M 7'^ff ofvariouskinds- They

5g?i«?C

belong to the deepest
waters in which Algae

gr°W' and [t is Probable

that the red coloring

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

173. The plant body.
-The Eed Algas, 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. 222. A red alga (Gigartlrta}, showing
branching habit, and "fruit bodies."—
After SCHENCK.

FIG. 224.

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

CALDWELJj.

FIG. 225. A red alga (Rabdvnid), showing holdfasts and branching thallus body.

CALDWELL.

FIG. 226.

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

THE GEEAT GKOUPS OF ALG^E

259

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. 222, 223, 224:, 225, 226). The differen-
tiation of the thallus into root and stem and leaf-like struc-
tures is also common, as in the Brown Algae.

174. 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-

FIG. 227. A red alga ( Callithamniori), show-
ing sporangium (A), and the tetraspores
discharged (£).— After THURET.

FIG. 228. A red alga (Nemaliori) ; A,
sexual branches, showing antheri-
dia (a), oogonium (0) with its trich-
ogyne (t), to which are attached two
spermatia (s) ; B, beginning of a
cystocarp (o), the trichogyne (t) still
showing ; O, an almost mature cys-
tocarp (0), with the disorganizing
trichogyne (t). — After KNY.

rangium always produces just
four, they have been called
tetraspores (Fig. 227).

Eed 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. 228, A, a) develop sperms which, like the
tetraspores, have no cilia and no power of motion. To dis-

260

PLANT STUDIES

tinguish them from the ciliated sperms, or spermatozoids,
which have the power of locomotion, these motionless male
gametes of the Eed Algae are usually called spermatia
(singular, spermatium) (Fig. 228, 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. 228, A,
o, t). Within the bulbous part
the egg, or its equivalent, is
organized ; a spermatium at-
taches itself to the trichogyne
(Fig. 228, 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
represents the very simplest
conditions of the process of
fertilization 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 de-
velops a conspicuous structure
called the cystocarp (Figs. 228, 229), 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. 229. A branch of Polysiphonia,
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).— CALDWELL.

THE GKEAT GROUPS OF ALG.E

261

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

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

FIG. 230. 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; A, a colony; i, a colony, the top and side view shown at k. — After KERNER.

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. 230).

262

PLANT STUDIES

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 different from
other forms, however, that it seems
best to keep them separate from all
other Algae.

176. Characeae. — These are common-
ly called " stoneworts," and are often
included as a group of Green Algae,
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. 231. A common Chara,
showing tip of main axis.
— After STRASBURGER.

THE GEEAT GROUPS OF ALG^E £63

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. 231).

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.

CHAPTER XVIII

THALLOPHYTES : FUNGI

177. 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 r but others
264

THALLOPHYTES: FUNGI

265

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.

178. 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. 232). A set of colorless branching

FIG. 232. A diagrammatic representation of Mucor, 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 hyphce (singular,
JiypJia) or hyplial threads. The mycelium is in contact with
its source of food supply, which is called the substratum.

266 PLANT STUDIES

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 hyphce 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.

179. 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) Pliycomycetes ("Alga-Fungi"), referring to the fact
that the forms plainly resemble the Algae ; (2) Ascomycetes
("Ascus-Fungi"); (3) ^cidiomycetes ("^Ecidium-Fungi ") ;
(4) Basidiomycetes (" Basidium-Fungi "). Just what the
prefixes ascus, cecidium, and lasidium 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 267

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)

180. Saprolegnia, — This is a group of "water-moulds,"
with aquatic habit like the Algae. They live upon the dead
bodies of water plants and animals (Fig. 233), and some-
times attack living fish, one kind being very destructive
to young fish in hatcheries. The hyphae composing the
mycelium are ccenocytes, 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. 233, B). The tip becomes
more or less swollen, and within it are formed numerous
biciliate zoospores, which are discharged into the water
(Fig. 233, (7), swim about for a short time, and rapidly form
new mycelia. The process is very suggestive of Cladophora
and VaucJieria. Oogonia and antheridia are also formed
at the ends of the branches (Fig. 233, F), much as in Vau-
cJieria. The oogonia are spherical, and form one and some-
times many eggs (Fig. 233, Z>, E). The antheridia are
formed on branches near the oogonia. An antheridium
conies in contact with an oogonium, and sends out a deli-
cate tube which pierces the oogonium wall (Fig. 233, 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 STUDIES

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

FIG. 233. 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.

181. 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. 234).

THALLOPHYTES: FUNGI

269

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. 235,

FIG. 234. Diagram showing mycelium and sporophores of a common Mucor.—
MOORE.

236). The sporangium wall bursts (Fig. 237), the light spores
are scattered by the wind, and, falling upon a suitable sub-
stratum, germinate and
form new mycelia.
evident that these

It is
asex-
ual spores are not zoo-
spores, for there is no
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. 235. Forming sporangia of Mucor, show-
ing the swollen tip of the sporophore (A),
and a later stage (B), in which a wall is
formed separating the sporangium from
the rest of the body.— MOORE.

270

PLANT STUDIES

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-

Fio. 236. Mature sporangium of Mucor, showing
the wall (A), the numerous spores (C), and
the coluraella (B)— that is, the partition wall
pushed up into the cavity of the sporangium.
— MOORE.

FIG. 237. Bursted sporangium of
Mucor, the ruptured wall not
being shown, and the loose
spores adhering to the colu-
mella.— MOORE.

tion of sporophores (Fig. 238). Two contiguous branches
come in contact by their tips (Fig. 238, A), the tips are cut
off from the main ccenocytic body by partition walls (Fig.
238, 5), the walls in contact disorganize, the contents of
the two tip cells fuse, and a heavy-walled sexual spore is
the result (Fig. 238, C). It is evident that the process is
conjugation, suggesting the Conjugate forms among the

THALLOPHYTES: FUNGI

271

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 gametangia. Mucor, therefore, is isogamous.

FIG. 238. Sexual reproduction of Mucor, showing tips of sex branches meeting (A),
the two gametangia cut off by partition walls (£), and the heavy-walled zygote
(C). — CALDWELL.

182. 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
coenocytic and entirely internal, ramifying among the tis-
sues within the leaf, and piercing the living cells with haus-
toria which rapidly absorb their contents (Fig. 239). The
presence of the parasite is made known by discolored and

272

PLANT STUDIES

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.

FIG. 239. A branch of Peronospora in contact with
two cells of a host plant, and sending into them
its large haustoria. — After DEBARY.

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. 240. Peronospora, one of the Phycomycetes, showing 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. 240). The oogonium is of
the usual spherical form, organizing a single egg. The an-

THALLOPHYTES : FUNGI 273

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 antheridium 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.

183. Conclusions. — The coenocytic 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)

184. 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-

274

PLANT STUDIES

dew, Microsphcera, grows on lilac leaves, which nearly al-
ways show the whitish covering after maturity (Fig. 241).
The branching hyphae show numerous partition walls, and
are not cosnocytic 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 abstraction, and the
spores formed in this way
are called conidia, or conidi-
ospores (Fig. 243, 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. 241. Lilac leaf covered with mil-
dew (Microsphcera), the shaded re-
gions representing the mycelium,
and the black dots the ascocarps.—
S. M. COULTER.

THALLOPHYTES : FUNGI

275

a little sphere, which suggested the name Microsplicera
(Fig. 241). The heavy wall of the ascocarp bears beauti-
ful branching hair-like appendages (Fig. 242).

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.
242). The ascocarp, there-
fore, is a spore case, just as
is the cystocarp of the Red
Algae (§ 174). 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 distin-
guished from other asexual
spores by the name asco-
spore.

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 produces 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.

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

FIG. 242. Ascocarp of the lilac mildew,
showing branching appendages and
two asci protruding from the ruptured
wall and containing ascospores.— S.
M. COULTER.

2T6

PLANT STUDIES

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. 243) ; the truffle-fungi, upon whose subter-

FIG. 243. Penicillium, a common mould : A, mycelium with numerous branching
sporophores bearing conidia ; S, 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. 244), 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. 245, 246), and the edible morels (Fig. 247).

THALLOFHYTES : FUNGI

277

FIG. 245. Two species of cup-fungus
(Pezlza).— After LINDAU.

FIG. 244. Head of rye attacked by " er-
got" (a), peculiar grain-like masses
replacing the grains of rye ; also a
mass of "ergot" germinating to
form spores (6). — After TULASNE.

FIG. 246. 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.

278

PLANT STUDIES

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

FIG. 247. 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. 248. Yeast cells, repro-
ducing by budding, and
forming chains.— LAND.

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. ^ECIDIOMYCETES (^Ecidium-Fungi)

186. 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 279

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 very 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.

187. 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. 249. Wheat rest, showing sporophores breaking through the tissues of the host
and bearing summer spores (uredospores). — After H. MARSHALL WARD.

rophores, each bearing at its apex a reddish spore (Fig. 249).
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
19

280

PLANT STUDIES

disease with great rapidity (Fig. 250). 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. 250. Wheat rust, showing a young hypha forcing its way from the surface of a
leaf down among the nutritive cells.— After H. MARSHALL WARD.

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

FIG. 251. 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. 251). It is two-celled, with a very heavy black

THALLOPHYTES : FUNGI

281

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. 252).
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. 253). These
chains of conidia are closely packed in cup-like receptacles,
and these reddish-yellow cup-like masses are often called

FIG. 252. 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.

282

PLANT STUDIES

"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 secidia which
give name to the group,
and ^Ecidiomycetes are
those Fungi in whose
life history aecidia 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

283

appear : (1) sporidia^ which develop the stage on the barber-
ry ; (2) cecidiosporesi which develop the stage on the wheat ;
(3) uredospores, which repeat the mycelium on the wheat ; (4)
teleutospores, which 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. 254. Two species of " cedar apple " ( Gymnosjwrancfivm), both on the common
juniper (Juniperus Virginiana).—A after FARLOW, E after ENGLER and PRANTL.

188. 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-

284

PLANT STUDIES

nected together, so that a mycelium bearing uredospores is
called a Uredo, one bearing teleutospores a Puccinia, and
one bearing secidia an ^Ecidiuin ; but what forms of Uredo,
Puccinia, and ^cidium 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. 254). 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).

189. 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

•V pp^ 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 ^Ecidiomycetes,

FIG. 255. The common edible mushroom,

Agaricus campestris.— After GIBSON. HO SCXUal prOCCSS has

THALLOPHYTES : FUNGI

285

"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-
cus] will serve as an illustration of the group (Fig. 255).

190. A common
mushroom. — The Jjffl , I

. ^aSOTlUUll/flkts^ LA, /» «. /TS /?*. /fJ

mycelium, 01 wmte
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
organized together
to form a single
complex spore-
bearing structure.
The mushroom

FIG. 256. A common Agaricus : A, section through one
side of pileus, showing sections of the pendent gills;
B, section of a gill more enlarged, showing the cen-
tral tissue, and the broad border formed by the ba-
sidia : C, still more enlarged section of one side of
a gill, showing the club-shaped basidia standing at
right angles to the surface, and sending out a pair
of small branches, each of which bears a single ba-
sidiospore.— After SACHS.

M 3

THALLOPHYTES: FUNGI

287

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 pileus. From the
under surface of the pileus there hang thin radiating plates,
or gills (Fig. 255), 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. 256). These end

FIG. 260. A bracket fungus (Polyporus) growing on the trunk of a red oak.—
CALDWELL.

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 braiiches arise, each bearing a minute
spore, very much as the sporidia appear in the wheat rust.

288

PLANT STUDIES

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.

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

FIG. 261. A toadstool of the bracket form which has grown about blades of grass
without interfering with their activity.— CALDWELL.

(Figs. 257, 258, 259). The " pore-fungi " have pore-like de-
pressions for their spores, instead of gills, as in the very
common " bracket-fungus " (Polyporus), which forms hard
shell-like outgrowths on tree-trunks and stumps (Figs. 260,

FIG. 262. The common edible Boletus (B. edu- FIG. 263. Another edible Boletus (B. stro-
lls), in which the gills are replaced by bUaceus).— After GIBSON.
pores.— After GIBSON.

FIG. 264. The common edibie "coral fun-
gus" (Clavaria).— After GIBSON.

FIG. 265. Hydmim repandum, in which gills
are replaced by spinous processes ; edi-
ble.—After GIBSON.

290

PLANT STUDIES

261), and the mushroom-like Boleti (Figs. 262, 263). The
" ear-fungi " form gelatinous, dark-brown, shell-shaped
masses, and the " coral fungi " resemble branching corals
(Fig. 264). The Hydnum forms have spinous processes

instead of gills (Fig.
265). The puffballs or-
ganize globular bodies
(Fig. 266), 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.

OTHER THALLOPHYTES
WITHOUT CHLOROPHYLL

192. 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 plas-
modium, 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 amoebas. So suggestive
of certain low animals is this body and food habit that
slime-moulds have also been called Mycetozoa or "fungus-
animals,"

FIG. 266. Puffballs, in which the basidia and
spores are inclosed ; edible. — After GIBSON.

THALLOPHYTES : FUNGI

291

In certain conditions, however, these slimy bodies come
to rest and organize most elaborate and often very beau-
tiful sporangia, full of spores (Fig. 267). These varied
and easily preserved sporangia are used to classify the

FIG. 267. Three common slime moulds (Myxomycetes) on decaying wood : to the
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 plasmodium at base ;
below, groups ,of sporangia of Hemiarcyria, with a plasmodium mass at upper
left hand.— GOLDBKRGER.

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

193. 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 Cyanophycese, or " Fission-
Algae," so closely that they are often associated with them
in classification (see § 162).

FIG. 268. 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. subtilis), 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; H, Micro-
spira ; J, K, L, M, species of Spirillum.— After ENGLER and PRANTL.

THALLOPHYTES : FUNGI 293

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^^o in.). They are of various forms
(Fig. 268), 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

194. 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. 269, 270, 271). 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

THALLOPHYTES : FUNGI

295

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

FIG. 270. A common lichen (Physcia) growing on bark, showing the spreading thallus
and the numerous dark disks (apothecia) bearing the asci.— GOLDBERGER.

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

FIG. 271. A common foliose lichen (Pai^melid) growing upon a board, and showing

apothecia.— GOLDBERGER.
20

296

PLANT STUDIES

If a Lichen be sectioned, the relation between the sym-
bionts will be seen (Fig. 272). 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. 272. Section through thallns of a lichen (Stictd), showing holdfasts (r), lower (u)
and upper (o) surfaces, fungus hyphse (m), and enmeshed algae (g).— 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-

THALLOPHYTES : FUNGI

297

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 Algae. 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. 270,
271). 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. 273, 274). These sacs
are evidently asci, the apothecia correspond to ascocarps,
and the Lichen fungus proves to be an Ascomycete.

FIG. 273. Section through an apothecium of Anaptychia, showing stalk of the cup
(m), masses of algal cells (g), outer margin of cup (?•), overlapping edge (t, t), layer
of asci (/t), and massing of hyphse 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) Crustaceous Lichens, in which the thallus resem-

298

PLANT STUDIES

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

FIG. 274. Much enlarged section of a portion of the apothecium of Anaptychia, show-
ing the fungus mycelium (m), which is massed above (y), just beneath the layer of
asci (1, 2, 3, It), in which spores in various stages of development are shown.—
After SACHS.

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

CHAPTEE XIX

BRYOPHYTES (MOSS PLANTS)

195. 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

299

300 PLANT STUDIES

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

(5) AlgcB 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.

196. General characters of Bryophytes. — The name given
to the group means "moss plants," and the Mosses maybe
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.

197. 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. 275). It is prostrate, and is a regu-

BRYOPHYTES

301

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. 275, b). A bud develops into an erect

FIG. 275. 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 (£>) of leafy branches (gametophores).— After
MULLER and THUKGAU.

stalk upon which are numerous small leaves (Figs. 276, 290).
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

302

PLANT STUDIES

.rh

FIG. 276. A common
(Polytrichum commune),
showing the leafy gameto-
phore with rhizoids (rh),
and two sporophytes (sporo-
gonia), with seta (s), calyp-
tra (c), and operculnm (d),
the calyptra having been re-
moved.—After SCHENCK.

plant from which it came. This new
leafless body consists of a slender
stalk bearing at its summit an urn-
like case in which are developed nu-
merous asexual spores (Figs. 276, 292).
This whole structure is often called
the "spore fruit," 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-

BEYOPHYTES 303

duces only sexual spores (oospores), arid therefore produces
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."

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 :

Gz:g>o— S— o— G:z:8>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.

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.

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
common 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 gametopliore (" 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 imbedded in the gametophore is the foot, and the
urn-like spore-case is the capsule.

304

PLANT STUDIES

198. 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

FIG. 277. 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 (b), 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 archegonia (a), and paraphyses and leaf sections (b), and also a
single archegonium (B), with venter (b) containing egg and ventral canal cell, and
neck (K) containing the disorganizing axial row (neck canal cells). — After 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

BRYOPHYTES

305

globular body (Figs. 277, 278). 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 compact mass of small

cubical (square in section) cells, within

each one of which there is formed a

single sperm (Fig. 278). The sperm is

a very small cell with two long cilia

(Fig. 277). These small biciliate sperms

are one of the distinguishing marks

of the Bryophytes. When the mature

antheridia are wet they are ruptured at

the apex and discharge their contents

(Fig. 277), and the sperms escaping

swim actively about.

199. The archegonium. — This name
is given to the female sex organ, which
is a many-celled structure, shaped like
a flask (Figs. 277, 287). The neck of
the flask is more or less elongated, and

within the bulbous base (venter] the single egg is organized.
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.

200. 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. 279, 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. 279, 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

FIG. 278. Antheridium of
a liverwort in section,
showing single layer
of wall cells surround-
ing the mass of moth-
er cells.— After STRAS-

BURGER.

306

PLANT STUDIES

of the capsule like a loose cap or hood, known as the
calyptra (Fig. 276, c), 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.

201. The sporogoni-
um. — In its fullest de-
velopment the sporogo-
nium is differentiated
into the three regions,
foot, seta, and capsule
(Fig. 276) ; but in some
forms the seta may be
lacking, and in others
the foot also, the sporo-
gonium 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."

FIG. 279. Sporogonium of Funaria : A, an em-
bryo sporogonium (/,/')> developing within
the venter (£, b) of an archegonium ; B, C,

gonia, pushing up calyptra (c) and archego-
nium neck (h), and sending the foot down
into the apex of the gametophore. — After
GOEBEL.

BRYOPHYTES

307

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 sporogenous
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. In other cases, certain
mother cells become much modified in form, being organ-
ized into elongated, spirally-banded cells called elaters (Fig.
286), 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 sporogonium is a very important structure from
the standpoint of evolution, for it represents the conspicu-
ous part of the higher plants. The " fern plant," and
the herbs, shrubs, and trees among " flowering plants,"
correspond to the sporogonium of Bryophytes, and not to
the leafy branch (gametophore) or " moss plant."

CHAPTEK XX

THE GREAT GROUPS OF BRYOPHYTES

HEPATIC^E (Liverworts)

202. 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 :

THE GREAT GROUPS OF BRYOPHYTES

309

203. Marchantia 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. 280-282). 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. 283). 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. 280. A very small species of Riccia,
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 STKASBUBGEB.

FIG. 281. Rictiocarpus, 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." — GOLDBERGER.

FIG. 282. Two common liverworts : to the left is Conocephalus, a Marchantia form,
showing rhizoids, dichotomous branching, and the conspicuous rhombic areas
(areolae) on the dorsal surface; to the right is Ant/toceros, with its simple thallus
and pod-like sporogonia.— GOLDBERGER.

FIG. 283. 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 (eld) organized
into chambers by partitions (o); J?, 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 (s) and containing short,
often branching filaments whose cells contain chloroplasts (c/il), overarching
upper epidermis (0) pierced by a large chimney-like air-pore (sp).— After GOEBEL.

FIG. 284. Section through cupule of Marchantia, showing wall in which are chloro-
phyll-bearing air-chambers with air-pores, and gemmae (a) in various stages of
development.— After DODEL-PORT.

FIG. 285. Marchantia polymorpha : the lower figure represents a gametophyte bear-
ing a mature antheridial 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 within the antheridial cavities (a, b, c, d, e,f).— After KNY.
21

312

PLANT STUDIES

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. 286. Marchantia polymorpha, a common liverwort : 1, thallus, with rhizoids,
bearing a mature archegonial branch (/) and several younger ones (a, b, c, d, e);
3 and 3, dorsal and ventral views of archegonial disk; U and 5, young sporophyte
(sporogonium) embryos; 6. more mature sporogonium still within enlarged venter
of archegonium; 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. 283, B).

THE GREAT GROUPS OF BRYOPHYTES

313

The air chambers are outlined on the surface as small

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

Peculiar reproductive bodies are also developed upon

the dorsal surface of Marchantia for vegetative multiplica-

FIG. 287. Marchantia polymorpha : 1, partial section through archegonial disk, show-
ing archegonia with long necks, and venters containing eggs; 9, young archego-
nitim 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 KNT.

tion. Little cups (cupules) appear, and in them are numer-
ous short-stalked bodies (gemma), which are round and
flat (biscuit-shaped) and many-celled (Figs. 284, 285). The

314

PLANT STUDIES

gemmae fall off and develop new thallus bodies, making
rapid multiplication possible. Marchantia also possess re-
markably prominent gametophores, or " sexual branches "
as they are often called. In this case the gametophores are
differentiated, one bearing only antheridia (Fig. 285), and
known as the " antheridial branch," the other bearing only
archegonia (Figs. 286, 287), and known as the "archegonial
branch." The scalloped antheridial disk and the star-
shaped archegonial disk, each borne up by the stalk-like
gametophore, are seen in the illustrations.

204. Jungermannia 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

FIG. 288. Two liverworts, both Jnngermannia forms: to the left is Blasia, which
retains the thallus forms but has lobed margins ; to the right is Scapania, with
distinct leaves and sporogonia (A).— GOLDBERGER.

situations on rocks, ground, or tree-trunks ; or in the tropics
also on the leaves of forest plants. They are generally deli-
cate plants, and resemble small Mosses, many of them doubt-
less being commonly mistaken for Mosses (Fig. 288).

Instead of a flat thallus with even outline, the body is

THE GREAT GROUPS OF BRYOPHYTES

315

organized into a central stem-like axis bearing two rows
of small, often crowded leaves. In consequence of this
the Jungermannia forms
are usually called " leafy
liverworts," to distin-
guish them from the
other Liverworts, which
are " thallose." They are
also often called "scale
mosses," on account of
their moss-like appear-
ance and their small
scale-like leaves.

205. Anthoceros forms.
— This line contains com-
paratively few forms, but
they are of great interest,
as they are supposed to
represent forms which
have given rise to the
Mosses, and possibly to
the Pteridophytes also.

The thallus is very Sim- FIG. 289. Anthoceros gradlis: A, several
pie, being differentiated gametophytes, on which sporogonia have

neither in structure nor
form, as in the two other
lines ; but the special de-
velopment has been in
connection with the spo-
rogonium (Figs. 282, 289). This complex sporogonium
(sporophyte) has a large bulbous foot imbedded in the
simple thallus, while above there arises a long pod-like
capsule.

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

developed ; B, an enlarged sporogonium,
showing its elongated character and de-
hiscence by two valves leaving exposed
the slender columella on the surface of
which are the spores ; C, D, E, F, ela-
ters of various forms ; G, spores. — After

SCHIFFNER.

316 PLANT STUDIES

gametophyte ; the Jungermannia line has differentiated
the form of the gametophyte ; the Anthoceros 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)

206. 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 shuts off the lower strata of moss from complete
disorganization, and they become modified into a coaly
substance called peat, which may accumulate to consid-
erable thickness by the continued upward growth of the
mass of moss.

The gametophyte body is differentiated into two very
distinct regions : (1) the prostrate dorsi ventral thallus,
which is called protonema in this group, and which may
be either a broad flat thallus or a set of branching fila-
ments (Figs. 275, 290) ; (2) the erect leafy branch or
gametophore (Fig. 276). This erect branch is said to be

THE GREAT GROUPS OF BRYOPHYTES

317

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.

The leafy branch
of the Mosses usually
becomes independent
of the thallus by put-
ting out rhizoids at its
base (Fig. 290), the
thallus part dying.
Sometimes, however,
the filamentous proto-
nema is very persist-
ent, and gives rise to a
perennial succession of
leafy branches.

At the summit of
the leafy gametophore,
either upon the main
axis or upon a lateral
branch, the antheridia and archegonia are borne (Fig. 277).
Often the leaves at the summit become modified in form
and arranged to form 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 (Fig. 277), or it may

FIG. 290. A moss (Bryuiri), showing base of a
leafy branch (gametophore) attached to the
protonema, and having sent out rhizoids. On
the protonemal filament to the right and be-
low is the young bud of another leafy branch.
— MULLER.

318

PLANT STUDIES

contain both kinds, for Mosses are both dioecious and monoe-
cious. The two principal groups are as follows :

207. Sphagnum forms.— These are large and pallid bog
mosses, found abundantly in marshy ground, especially of
temperate and arctic regions, and are conspicuous peat-

B C D i E r A

FIG. 291. Sphagnum : A, a leafy branch (gametophore) bearing four mature sporo-
gonia ; J5, archegonium in whose venter a yonng embryo sporophyte (em) is de-
veloping ; C, section of a young sporogonium (sporophyte), showing the bulbous
foot (spf) imbedded in the apex of the pseudopoditim (ps}, the capsule (k), the
columella (cd) capped by the dome-shaped archesporium (spo), a portion of the
calyptra (cd), and the old archegonium neck (ah) ; />, branch bearing mature
sporogonium and showing pseudopodium (ps), capsule (k), and operculum (d) ;
E, antheridium discharging sperms ; F, a single sperm, showing coiled body and
two cilia.— After SCHIMPER.

formers (Fig. 291). The leaves and gametophore axis are
of peculiar structure to enable them to suck up and hold a
large amount of water. This abundant water-storage tissue
and the comparatively poor display of chlorophyll-contain-
ing cells gives the peculiar pallid appearance.

208. True Mosses. — This immense and most highly organ-
ized Bryophyte group contains the great majority of the

THE GKEAT GEOUPS OF BRYOPHYTES

319

Mosses, which are sometimes called the Bryum forms, to
distinguish them from the Sphagnum forms. They are
the representative Bryophytes, the only group vying with
them being the leafy
Liverworts, or Junger-
mannia forms. They
grow in all conditions
of moisture, from actual
submergence in water to
dry rocks, and they also
form extensive peat de-
posits in bogs.

The sporogonium has

a foot and Usually a long FlG< 292- Sporogonia of Grimmia, from all of

which the operculum has fallen, displaying

Slender Seta, but the Cap- the peristome teeth: A, position of the teeth

SUle is especiallv COm- when dry ; s> Position when moist.— After

KERNER

plex. When the lid-like

operculum falls off, the capsule is left like an urn full of
spores, and at the mouth of the urn there is usually dis-
played a set of slender, often very beautiful teeth (Fig.
292), radiating from the circumference to the center, and
called the peristome, meaning " about the mouth." These
teeth by bending inward and outward help to discharge the
spores.

CHAPTER XXI

PTERIDOPHYTES (FERN PLANTS)

209. 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 thallus 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.

320

PTEKIDOPHYTES

321

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

210. 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 Algae. 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.

211. 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. 293, A). Upon this thallus antheridia

322

PLANT STUDIES

and archegonia appear, so that it is evidently a gameto-
phyte. 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. 293. Prothallium of a common fern (Aspidmm): 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 SCHENCK.

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. 293, 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

323

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

In contrasting this life history with that of Bryophytes
several important diiferences 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.

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

FIG. 294. Archegonium of Pteris at the time of fertilization, showing tissue of gam-
etophyte (A), the cells forming the neck (B), the passageway formed by the dis-
organization of the canal cells (C), and the egg (D) lying exposed in the venter.
— CALDWELL.

rhizoids from its ventral surface (Fig. 293). It is so thin
that all the cells contain chlorophyll, and it is usually short-
lived.

324

PLANT STUDIES

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 archegonia are usually developed on
the under surface of the prothallium (Fig. 293, A), and dif-
fer from those of all Bryophytes, except the Anthoceros
forms, in being sunk in the tissue of the prothallium and
opening on the surface, more or less of the neck of the
archegonium projecting (Fig. 294). The eggs are not dif-
ferent from those formed within the archegonia of Bryo-

FIG. 295. Antheridium of Pteris (B\ showing wall cells (a), opening for escape of
sperm mother cells (<?), escaped mother cells (c), sperms free from mother cells
(5), showing spiral and multiciliate character.— CALD WELL.

phytes, but the sperms are very different. The Bryophyte
sperm has a small body and two long cilia, while the Pteri-
dophyte sperm has a long spirally coiled body, blunt behind
and tapering to a point in front, where numerous cilia are
developed (Fig. 295). It is, therefore, a large, spirally coiled,
multiciliate sperm, and is quite characteristic of all Pterido-
phytes excepting the Club-mosses.

When the prothallia are developing the antheridia begin

PTERIDOPHYTES 325

to appear very early, and later the archegonia. If the pro-
thallium is poorly nourished, only antheridia appear; it
needs to be well developed and nourished to develop arche-
gonia. There seems to be a very definite relation, there-
fore, between nutrition and the development of the two sex
organs, a fact which must be remembered in connection
with certain later developments.

213. The sporophyte,— This complex body is differ-
entiated into root, stem, and leaf, and is more highly
organized than any plant body heretofore mentioned (Fig.
296).

In most of the Ferns the stem is subterranean and dor-
si ventral (Fig. 296), but in the " tree ferns " of the tropics
it forms an erect, aerial shaft bearing a crown of leaves
(Fig. 297). In the other groups of Pteridophytes there are
also aerial stems, both erect and prostrate. The stem is
complex in structure, the cells being organized into differ-
ent " tissue systems," prominent among which is the vascu-
lar system-
One of the peculiarities of ordinary fern leaves is that
the vein system of the leaves branches dichotomously, the
forking veins being very conspicuous (Fig. 298). 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 centre of the roll
(Fig. 296). 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 said to have circinate vernation.
The combination of dichotomous venation and circinate
vernation is very characteristic of Ferns.

214. Sporangia. — 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 defi-
nite form known as sori. A sorus may be round or elon-

FIG. 296. A fern (Aspidiurri), 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 3 represents the under sur-
face of a portion of the leaf, showing seven sori with shield-like indusia; at 5 is
represented a section through a sorus, showing the sporangia attached and pro-
tected by the indusium; while at 6 is represented a single sporangium opening
and discharging its spores, the heavy annulus extending along the back and over
the top. — After WOSSIDLO.

"**&-'

FIG. 297. A group of tropical plants. To the left of the center is a tree fern, with its
Blender columnar stem and crown of large leaves. The large-leaved plants to the
right are bananas (monocotyledons).

328

PLANT STUDIES

gated, and is usually covered by a delicate flap (indusium)
which arises from the epidermis (Fig. 296). Occasionally
the sori are extended along the under surface of the mar-
gin of the leaf, as in maidenhair fern (Adiantum), and the
common brake (Pteris), in which case they are protected
by the inrolled margin (Fig. 298), which may be called a
" false indusium."

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 divide
the work. Certain leaves, or
certain leaf-branches, produce
spores and do no chlorophyll
work, while others do chloro-
phyll work and produce no
spores. This differentiation in
the leaves or leaf-regions is in-
dicated by appropriate names.
Those leaves which produce
only spores are called sporo-
pliylls, meaning " spore leaves,"
while the leaf branches thus
set apart are called sporophyll
branches. Those leaves which
only do chlorophyll work are
called foliage leaves ; and such
branches 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 differ-
entiation may be seen in the ostrich fern and sensitive
fern (Onoclea) (Fig. 299), the climbing fern (Lygodium),
the royal fern (Osmunda), the moon wort (Botrychium)
(Fig. 300), and the adder's tongue ( Ophioglossum).

Fro. 298. Leaflets of two common
ferns : A, the common brake
(Pteris) ; B, maidenhair (Adian-
tum) ; both showing sori borne
at the margin and protected by
the infolded margin, which thus
forms a false indusium. — CALD-
WELL.

FIG. 299. The sensitive fern (Onoclea sensibilis), showing differentiation of foliage
leaves and sporophylls. — Prom " Field, Forest, and Wayside Flowers."

330

PLANT STUDIES

An ordinary fern sporangium consists of a slender stalk
and a bulbous top which is the spore case (Fig. 296, 6).
This case has a delicate wall formed of
a single layer of cells, and extending
around it from the stalk and nearly to
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 be-
comes yielding the spring straightens
violently, the wall is torn, and the spores
are discharged with considerable force
(Fig. 301). This discharge 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.

215. 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 represents 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 heter-
ospory. 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.

FIG. ,300. A moonwort
(Botrychiwri), show-
ing the leaf differenti-
ated into foliage and
sporophyll branches.
—After STRASBUK-

GEB.

PTEKIDOPHYTES

331

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.

In some Pteridophytes, however, there is a decided dif-
ference in the size of the spores, some being quite small and

FIG. 301. 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.

others relatively large, the small ones producing male game-
tophytes (prothallia with antheridia), and the large ones
female gametophytes (prothallia with archegonia). When
asexual spores differ thus permanently in size, and give rise

332 PLANT STUDIES

to gametophytes of different sexes, we have the condition
called heterospory (" spores different "), and such plants are
called heterosporous (Fig. 307). In contrast with hetero-
sporous plants, those in which the asexual spores appear
alike are called homosporous, or sometimes isosporous, both
terms meaning " spores similar." The corresponding noun
form is homospory or isospory. Bryophytes and most Pteri-
dophytes are homosporous, while some Pteridophytes and
all Spermatophytes are heterosporous.

It is convenient to distinguish by suitable names the
two kinds of asexual spores produced by the sporangia of
heterosporous plants (Fig. 307). 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. 307). 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.

A formula may indicate the life history of a hetero-
sporous plant. The formula of homosporous plants with
alternation of generations (Bryophytes and most Pterido-
phytes) was given as follows (§ 197) :

G=g>o— S— o— G=ig>o— S— o— G—^>o— S, etc.

In the case of heterosporous plants (some Pterido-
phytes and all Spermatophytes) it would be modified as
follows :

PTERIDOPHYTES 333

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.

CHAPTER XXII

THE GREAT GROUPS OF PTERIDOPHYTES

216. 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 (Ferns)

217. 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. 297).

334

336 PLANT STUDIES

There are also epiphytic forms (air plants) — that is,
those which perch "upon other plants" but derive no
nourishment from them (Fig. 95). 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. 302),
although a number grow in comparatively dry and exposed
situations, sometimes covering extensive areas, as the com-
mon brake (Pteris).

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. 299, 300), but even this is excep-
tional. Another distinction is that the stems are un-
branched.

218. 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. 296, 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.

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.
303). 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 spreading wedge-shaped leaflets like a

THE GREAT GROUPS OF PTERIDOPHYTES

337

" four-leaved clover." The dichotomous venation and cir-
cinate vernation at once suggest the fern alliance. From
near the base of the petiole another
leaf branch arises, in which the blade
is modified as a sporophyll. In this
case the sporophyll incloses the spo-
rangia and becomes hard and nut-
like. Another common form is the

FIG. 303. A water-fern (Marsilia),
showing horizontal stem, with
descending roots, and ascend-
ing leaves ; a, a young leaf
showing circinate vernation ;
s,s. sporophyll branches ("spo-
rocarps ").— After BISCHOFF.

FIG. 304. One of the floating water-ferns (Sal-
vinid), 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. — After BISCHOFF.

floating Salvinia (Fig. 304). The chief interest lies in the
fact that the water-ferns are heterosporous. As they are
leptosporangiate they are thought to have been derived from
the ordinary leptosporangiate Ferns, which are homosporous.

EQUISETALES (Horsetails or Scouring rushes)

219. General characters. — The twenty-five forms now rep-
resenting this great group belong to a single genus (Equise-

338 PLANT STUDIES

turn, 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. 305).

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
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 aerial stem (really a branch) is either
simple or profusely branched (Fig. 305). In the species
illustrated the early aerial branches are simple, usually not
green, and bear the strobili ; while the later branches are
sterile, profusely branched, and green.

220. The strobilus. — One of the distinguishing charac-
ters of the group is that chlorophyll-work and spore-forma-
tion are completely differentiated. Although the foliage
leaves are reduced to scales, and the chlorophyll-work is
done by the stem, there are well-organized sporophylls.
The sporophylls 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 clus-
ter of sporophylls resembles (Fig. 305).

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

FIG. 305. 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.

340 PLANT STUDIES

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 dioe-
cious gametophytes.

LYCOPODIALES ( Club-mosses)

221. General characters, — This group is now represented
by about five hundred species, most of which belong to
the two genera Lycopodium and Selaginella, 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 ap-
pearance (Figs. 306, 307). 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 some-
times 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. 277) ; that is, it con-
sists 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. 306). This is in marked
contrast with the Filicales, whose leaves bear very numer-
ous sporangia, and with the Equisetales, whose sporophylls
bear several sporangia.

FIG. 306. A common club-moss (Lycopodvim davatum): 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.

A—--

FIG. 307. Selaginella Martensii: A, branch bearing strobili; B, a microsporophyll
with a microsporanginm, showing microspores through a rupture in the wall; C,
a megasporophyll with a megasporangium ; D, megaspores : E, microspores.—
GOLPBEKGBB.

CHAPTER XXIII

SPERMATOPHYTES : GYMNOSPERMS

222. 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 lieterospory 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.

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

23 343

344

PLANT STUDIES

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) TJiallopliytes. — Thallus body, but no archegonia.

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

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

(4) Spermatophytes. — Seeds.

224. 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 Anthophytes, 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 : GYMNOSPEEMS 345

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 coming 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.

GYMNOSPERMS

225. 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.

34:6 PLANT STUDIES

226. 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.

227. 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.

228. Microsporophylls. — In the pines the strobilus com-
posed of microsporophylls is comparatively small (Figs.
308, d, 309). 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. 309).

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. 308. 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; 6, 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 etaminate cones. — CALDWELL.

348

PLANT STUDIES

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. 309. Staminate cone (strobilus) of pine (Pinus): A, section of cone, showing
microsporophylls (stamens) bearing microsporangia; B, longitudinal section of a
single stamen, showing the large sporangium beneath ; C, cross-section of a sta-
men, showing the two sporangia; Z>, 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 STRASBUBGER.

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

SPERM ATOPH YTES : GYMKOSPEEMS

349

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

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

f-M

FIG. 310. Pinus sylvestris, showing mature cone partly sectioned, and showing car-
pels (sq, sql, «g2) with seeds in their axils (g), in which the embryos (em} may be
distinguished ; A, a young carpel with two megasporangia ; B, an old carpel with
mature seeds (ch), the micropyle being below (M).— After BESSEY.

the well-known cones so characteristic of pines and their
allies (Fig. 308, «, #, c). Each sporophyll is somewhat
leaf-like, and at its base upon the upper side are two
megasporangia (Fig. 310). It is these sporangia which are
peculiar in each producing and retaining a solitary large
megaspore. This megaspore resembles a sac-like cavity in

350

PLANT STUDIES

the body of the sporangium (Fig. 311, 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. 310, 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.
311, c, 312, nc) ; this sends out from
near its base an outer membrane
(integument) which is distinct above
(Figs. 311, b, 312, i), covering the main
part of the nucellus and projecting
beyond its apex as a prominent neck,
the passage through which to the apex
of the nucellus is called the micropyle
("little gate") (Fig. 311, a}. Cen-
trally placed within the body of the
nucellus is the conspicuous cavity
called the embryo-sac (Fig. 311, d),
in reality the retained megaspore.
The relations between integument, micropyle, nucellus,
and embryo-sac should be kept clearly in mind. In the

PIG. 311. Diagram of the
carpel structures of pine,
showing the heavy scale
(A) which bears the
ovule (B), in which are
seen the micropyle (a),
integument (6), nucellus
(c), embryo-sac or mega-
spore (d). — MOORE.

SPERMATOPHYTES : GYMNOSPERMS

351

nc-

pine the micropyle is directed downward, toward the base
of the sporophyll.

230. The gametophytes. — The male and female gameto-
phytes are so small that they develop entirely within the
spores (pollen-grain and

embryo-sac), and there-
fore can only be observed
by the microscope.

The female gameto-
phyte (often called " en-
dosperm ") fills up the
large embryo-sac, and on
its surface toward the
micropyle develops regu-
lar flask-shaped arche-
gonia (Fig. 312).

The male gameto-
phyte is still more re-
duced, and is represented
by a very few small cells
which appear within the
pollen - grain, two of
which are sperm -cells.
These sperm-cells must
reach the archegonia,
and accordingly the pol- FIG 312
len-grain sends out a tube
(pollen-tube), into which
the sperm-cells enter, and
are thus brought to the
archegonia (Fig. 110).

231. Fertilization. —

Diagrammatic section through ovule
(megasporangium) of spruce (Picea), showing
integument (i), nucellus (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 (o), and position of ger-
minating pollen-grains or microspores (p)
whose tubes (t) penetrate the nucellus tissue
and reach the archegonia. — After SCHIMPEK.

Before fertilization can

take place the pollen-grains (microspores) must be brought
as near as possible to the female gametophyte with its arche-
gonia. The spores are formed in very great abundance,

352

PLANT STUDIES

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. 309, />), so that they are well organized for
wind distribution. This transfer of pollen is called pol-
lination, 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 little drift at the
bottom of each carpel, where the
ovules are found (Fig. 310, A, B).
The flaring lips of the micropyle
roll inward and outward as they
are dry or moist, and by this mo-
tion 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.

232. The embryo.— By the act of
fertilization, an oospore is formed
within the archegonium. As it is on the surface of its food
supply (the endosperm), it first develops a long cylindrical
process (suspensor), which penetrates the endosperm and
develops the embryo at its tip. In this way the embryo lies
imbedded in the midst of its food supply (Fig. 313).

233. 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

Jia

FIG. 313. Embryos of pine : A,
very young embryos (ka) at the
tips of long and contorted sus-
pensors («) ; J5, older embryo,
showing attachment to suspen-
sor (s), the extensive root sheath
(wh), root tip (ws), stem tip
(#), and cotyledons (c). — After
STRASBURGER.

SPERMATOPHYTES: GYMNOSPERMS

353

transforms the integument into a hard bony covering,

known as the seed coat, or testa (Fig.

314). The development of this testa

hermetically seals the structures within,

further development and activity are

checked, and the living cells pass into

the resting condition. This protected structure with its

dormant cells is the seed.

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

FIG. 314. Pine seed.

FIG. 315. Pine seedlings, showing the long hypocotyl and the numerous cotyledons,
with the old seed case still attached.— After ATKINSON.

354 PLANT STUDIES

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 liv-
ing plant.

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 em-
bryo, which stops growing for a time, and then resumes it.
This resumption of growth is not germination, but is what
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 coats (Fig. 315).

234. The great groups of Gynmosperms.— There are at
least four living groups of Gymnosperms, and two or three
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 needle-like, broad,
or " fern-like." For our purpose it will be only necessary
to define the two most prominent groups.

235. Cycads. — Cycads are tropical, fern-like forms, with
large branched (compound) leaves. The stem is either a
columnar shaft crowned with a rosette of great branching
leaves, writh the general habit of tree-ferns and palms (Figs.
16, 316) ; or they are like great tubers, crowned in the
same way. In ancient times (the Mesozoic) they were very
abundant, forming a conspicuous feature of the vegeta-
tion, but now they are represented only by about eighty
forms scattered through both the oriental and occidental
tropics.

o 2

356 PLANT STUDIES

236. 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. 57),
while some are now very much restricted, although for-
merly very widely distrib-
uted, as the gigantic red-
woods (Sequoia) of the
Pacific slope. The habit of
the body is quite charac-
teristic, a central shaft ex-
tending continuously to the
very top, while the lateral
branches spread horizontal-
ly, with diminishing length
to the top, forming a coni-
cal outline (Figs. 56, 57).
This habit of firs, pines,
etc., gives them an appear-
ance very distinct from that
of other trees.

Another peculiar feature
is furnished by the char-
acteristic " needle-leaves,"
which seem to be poorly
adapted for foliage. These
leaves have small spread of
surface and very heavy pro-

FIG. 317. Arbor-vitae (Thuja), showing a * J -F

branch with scaly overlapping leaves, tecting WallS,and Showadap-

and some carpeiiate cones (strobiii).- tation for enduring hard

After EICHLER. ... . ,__.

conditions (Fig. 308). 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
the case of the common larch or tamarack, which sheds its
leaves every season (Fig. 56).

FIG. 31^. The common juniper (Juniperus commitni(f)\ the branch to the left bearing
staminate strobili; that to the right bearing staminate strobili above and carpel-
late strobili below, which latter have matured into the fleshy, berry-like fruit.
— After BERG and SCHMIDT.

CHAPTEK XXIV

SPERMATOPHYTES: ANGIOSPEEMS

237. 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.

238. 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
358

SPERMATOPHYTES : ANGIOSPERMS

359

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.

239. 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
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-
iar to Angiosperms, making the true
flower, and being associated with en-
tomophily.

240. Microsporophylls,— The micro-
sporophyll of Angiosperms is more
definitely known as a " stamen " than

FIG. 319. Stamens of hen-
bane (Hyoscyamus) : A,
front view, showing fila-
ment (/) and anther (p);
J5, back view, showing
the connective (c) be-
tween the pollen-sacs.
—After SCHIMPEB.
24

360

PLANT STUDIES

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. 319, 321, A).

FIG. 320. 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

FIG. 321. 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); S, 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 LUERSSEN.

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

SPERMATOPHYTES : ANGIOSPERMS

361

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. 320, 321). When they reach
maturity, the paired sporangia on each side usually merge to-
gether, forming two spore-containing cavities (Fig. 321, 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. 322. Various forms of stamens : A, from Solanum, showing dehiscence by
terminal pores; B, from Arbutus, showing anthers with terminal pores and
"horns"; C, from Herberts; 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 ENGLEB
and PRANTL.

362

PLANT STUDIES

FIG. 323. Cross - section of
anther of a li]y (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 deMscence, which means " a
splitting open," and the methods of
dehiscence are various (Fig. 322).
By far the most common method
is for the wall of each sac to split
lengthwise (Fig. 323), which is
called longitudinal deliiscence ; an-
other is for each sac to open by a
terminal pore (Fig. 322), in which
case it may be prolonged above into
a tube.

241. 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. 324, J), 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. 324. 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
^ ' ^ a coraP°und Pistil (syncarpous), showing
ovary (f), single style (g), and stigma (n).— After
BERG and SCHMIDT.

SPERMATOPHYTES: ANGIOSPERMS

363

gether form a common ovary, while the styles may also
combine to form one style (Fig. 324, (7), or they may remain
more or less distinct (Fig. 324, B). Such an ovary may
contain a single chamber, as if the carpels had united edge
to edge (Fig. 325, ^4) ; or it may contain as many chambers
as there are constituent carpels (Fig. 325, 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,

A 3 C

FIG. 325. 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 showing ovulea
attached to free axis (free central).— After SCHIMPER.

therefore, may have one loculus or several loculi. Where
there are several loculi each one usually represents a con-
stitutent carpel (Fig. 325, B) ; where there is one loculus
the ovary may comprise one carpel (Fig. 324, A), or several
(Fig. 325, A).

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. 324, A), or it may be several carpels or-
ganized together (Fig. 324, B, (7), the former case being a
simple pistil, the latter a compound pistil. In other words,

364

PLANT STUDIES

any organization of carpels which appears as a single organ
with one ovary is a pistil.

The ovules (megasporangia) are developed within the
ovary (Fig. 325) either from the carpel wall, when they are
foliar, or from the stem axis which ends
within the ovary, when they are canline
(see § 89). They are similar in struc-
ture to those of Gymnosperms, with in-
tegument and micropyle, nucellus, and
embryo-sac (megaspore), except that
there are often two integuments, an
outer and an inner (Fig. 326).

242. Modifications of the flower,— In
general, the flower may be regarded as
a modified branch bearing sporophylls
and usually floral leaves. Its repre-
sentative among the Pteridophytes and
Gymnosperms is the strobilus, which
has sporophylls but not floral leaves.
In Angiosperms it begins in a simple and somewhat indefi-
nite way, gradually becomes more complex, until finally it
appears as an elaborate and very efficient structure.

The evolution of the flower has proceeded along many
lines, and has resulted in great diversity of structure. These
diversities are largely used in the classification of Angio-
sperms, as it is supposed that near relatives are indicated
by similar floral structures, as well as by other features.
Some of the lines of evolution may be indicated as fol-
lows :

1. From naked flowers to those ivith distinct calyx and
corolla. — In the simplest flowers floral leaves do not appear,
and the flower is represented only by the sporophylls.
When the floral leaves first appear they are inconspicuous,
scale-like bodies. In higher forms they become more promi-
nent, but are still all alike. At last the floral leaves become
differentiated, the outer set (calyx) remaining scale-like or

FIG. 326. A diagrammatic
section of an ovule of
Angiosperms, showing
outer integument (ai),
inner integument (ii),
micropyle (»i), nucellus
(yfc), and embryo-sac or
megaspore (em).— After
SACHS.

SPERMATOPHYTES : ANGIOSPERMS

like small foliage leaves, and the inner set (corolla) becom-
ing more delicate in texture, larger, and generally brightly
colored (Fig. 71).

2. From 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. As this axis is elongated and capable of continued
growth, an indefinite number of each floral organ may ap-
pear. The spiral arrangement and indefinite numbers,
therefore, are regarded as primitive characters.

In higher forms the axis becomes shorter, the spiral
closer, until finally the sets of organs seem to be thrown
into rosettes or cycles. These cycles may not appear in all
the organs of a flower, but finally, in the highest forms, all
the floral organs are in definite cycles. All through this
evolution from the spiral to the cyclic arrangement there
is constantly appearing a tendency to " settle down " to
certain definite numbers, and when the complete cyclic
arrangement is finally established these numbers are estab-
lished, and they become characteristic of great groups.
For example, in the cyclic Monocotyledons there are nearly
always just three organs in each cycle, while in the cyclic
Dicotyledons the number five prevails.

3. From hypogynous to epigynous flowers. — In the sim-
pler flowers the sepals, petals, and stamens arise from be-
neath the ovary or ovaries (Fig. 72, ./), and as in such cases
the ovary may be seen distinctly above the origin (inser-
tion) of the other parts, such a flower is often said to have
a " superior ovary," or to be hypogynous, meaning in effect
" under the ovary," referring to the fact that the insertion
of the other parts is under the ovary.

There is a distinct tendency, however, for the insertion
of the outer parts to be carried higher up, until finally it is
above the ovary, and sepals, petals, and stamens seem to
arise from the top of the ovary (Fig. 72, 5), such a flower
being epigynous. In such cases the ovary does not appear

366 PLANT STUDIES

within the flower, but below it (Fig. 132), and the flower
is often said to have an " inferior ovary."

4. From apocarpous to syncarpous flowers. — In the
simpler flowers the carpels are entirely distinct, each car-
pel organizing a simple pistil, a single flower containing as
many pistils as there are carpels (Fig. 324, A). Such a
flower is said to be apocarpous, meaning " carpels separate."
There is a very strong tendency, however, for the carpels of
a flower to organize together and to form a single com-
pound pistil (Fig. 324, B, C), such a flower being called
syncarpous, meaning " carpels together. "

5. From polypetalous to sympetalous flowers. — While the
petals are entirely distinct from one another in the lower
forms, a condition described as polypetalous, in the highest
Angiosperms they are coalescent, the corolla thus becoming
a more or less tubular organ (Figs. 73, 74). Such flowers
are said to be sympetalous, meaning " petals united."

6. From regular to irregular flowers. — In the simplest
flowers all the members of one set are alike, and the flower
is said to be regular (Fig. 74, a, I)}. In certain lines of
advance, however, there is a tendency for some of the mem-
bers of a single set, particularly the petal set, to become
unlike. For example, in the common violet one of the
petals develops a spur ; while in the sweet pea the petals
are remarkably unlike. Such flowers are said to be irregu-
lar (Fig. 74, c, d, e), and as a rule irregularity is associated
with adaptations for insect pollination.

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, with indefinite numbers, hypogynous, and apocar-
pous, it would rank very low ; but if it has a calyx and
corolla, is completely cyclic, epigynous, syncarpous, sym-
petalous, and irregular, it would rank very high.

243. The gametophytes,— As in the case of the Gymno-
sperms, the gametophytes of Angiosperms are exceedingly

SPERMATOPHYTES : ANGIOSPERMS

367

simple, being developed entirely within the spores which
produce them.

The male gametophyte is represented by a few cells which
appear within the pollen grain, two of which are male cells.

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 penetrates
through the stigmatic
surface, enters among
the tissues of the style,
which is sometimes
very long, slowly or
rapidly traverses the
length of the style sup-
plied with food by its

Cells but not penetrat- FlG- 327- Diagram of a longitudinal section through

. , a carpel, to illustrate fertilization with all parts

ing them, enters the

in piace : ,, gtigma ; ff, style ; o, ovary ; ai, ii,
outer and inner integuments ; n, base of nucel-
lus ; /, funiculus ; b, antipodal cells ; c, endo-

8perm nucleug . k egg and one 8ynergid ; Pt poi-

len-tnbe, having grown from stigma and passed

" micr°pyle (m) to the egg-After

Cavity Of the OVary,
, -i -, . -,

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. 327).

368

PLANT STUDIES

The female gametophyte develops within the embryo-
sac, and consists at first of seven independent cells, one
of which is the egg, no archegonium being formed. The

n 1

FIG. 328. Development of embryo of shepherd's purse (Capsetta), a Dicotyledon;
beginning with 7, the youngest stage, and following the sequence to VI, the old-
est stage, v represents the suspensor, 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.

egg is in the end of the sac nearest the micropyle, in
the most convenient position for the entering tube.
After fertilization has been accomplished and an oospore
formed, one of the free cells within the embryo-sac be-
gins to divide and to form the endosperm, embryo and
endosperm thus developing together until the seed is com-
pleted.

SPERMATOPHYTES : ANGIOSPERMS

369

244. The embryo, — When the oospore germinates, a more
or less distinct suspensor is usually formed, but never so
prominent as in Gymnosperms ; and at the end of the sus-
pensor the embryo is developed, which, when completed, is
more or less surrounded by nourishing endosperm, or has
stored up within itself an abundant food supply.

The two groups of Angiosperms differ widely in the
structure of the embryo. In Monocotyledons the axis of
the embryo develops the root-tip at one end and the " seed-
leaf" (cotyledon) at the other, the
stem-tip arising from the side of the
axis as a lateral member (Fig. 329).
Naturally there can be but one coty-
ledon under such circumstances, and
the group has been named Monocoty-
ledons.

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) appear-
ing as a pair of opposite lateral mem-
bers on either side of the stem-tip
(Fig. 328). As the cotyledons are
lateral members their number may
vary. In Gymnosperms, whose em-

, j, , , . , , P. FIG. 329. Young embryo of

bryos are of this type, there are often water plantain (Alisma^ a

several cotyledons in a cycle (Fig.

315) ; and in Dicotyledons 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. 143, 315, 331), which
means " under the cotyledon/' a region which shows pecul-
iar activity in connection with the escape of the embryo

Monocotyledon, the root
being organized at one
end (next the suspensor),
the single cotyledon ((7)
at the other, and the stem-
tip arising from a lateral
notch (v). — After HAN-
STEIN.

3YO PLANT STUDIES

from the seed. Formerly it was called either caulicle or
radicle. In Dicotyledons the stem-tip between the coty-
ledons often organizes the rudiments of subsequent leaves,
forming a little bud which is called the plumule.

Embryos differ much as to completeness of their devel-
opment within the seed. In some plants, especially those
which are parasitic or saprophytic, the embryo is merely a
small mass of cells, without any organization of root, stem,
or leaf. In many cases the embryo becomes highly devel-
oped, the endosperm being used up and the cotyledons
stuffed with food material, the plumule containing several
well-organized young leaves, and the embryo completely
filling the seed cavity. The common bean is a good illus-
tration of this last case, the whole seed within the integu-
ment consisting of the two large, fleshy cotyledons, between
which lie the hypocotyl and a plumule of several leaves.

245. The seed. — As in Gymnosperms, while the processes
above described are taking place within the ovule, the in-
tegument or integuments are becoming transformed into
the testa (Fig. 330). When this hard coat is fully devel-

FIG. 330. 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 (pc\ seed testa (sc), nucellus tissue (p), endosperm (en), and
embryo (em).— After ATKINSON.

oped, the activities within cease, and the whole structure
passes into that condition of suspended animation which is
so little understood, and which may continue for a long
time.

SPERMATOPHYTES : ANGIOSPERMS

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. 115), or the tufts of
hair on the seeds of milkweed, cotton, or fireweed.

246. 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.
122). In case there is but one seed, the modified ovary
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. 116, 117), or by animals
(Fig. 129).

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 organizes two layers, the inner being very hard, form-
ing the " stone," the outer being pulpy, or variously modi-
fied (Fig. 330). 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 fertilization in changing
structure is felt beyond the ovary. In the apple, pear,
quince, and such fruits, the pulpy part is the modified
calyx (one of the floral leaves), the ovary and its contained

PLANT STUDIES

seeds being represented by the " core." In other cases, the
end of the stem bearing the ovaries (receptacle) becomes
enlarged and pulpy, as in the strawberry. This effect
sometimes involves even more than the parts of a single
flower, a whole flower-cluster, with its axis and bracts, be-
coming an enlarged pulpy mass, as in the pineapple.

The term " fruit," therefore, is a very indefinite one, so
far as the structures it includes are concerned.

247. The germination of the seed.— It is wrong to apply
the term " germination " to the renewal of activity by the
young plantlet within the seed, as has been shown before
(page 354), but in the absence of a better word it will be
used. This " awakening of the seed " is a phenomenon so
easily observed that it can hardly escape the attention of
any one.

Just how long different seeds may retain their vitality —
that is, live in a state of suspended animation — is not very
definitely known. Some seeds have germinated after hav-
ing remained in a dried-up condition for many years, but
such stories as that wheat taken from the wrappings of
Egyptian mummies has been made to germinate are myths.

If the structures of the seed are normal, its germination
will follow its exposure to certain conditions, prominent
among which are water, heat, and oxygen. Seeds vary in
the amount of water and heat absolutely needed, but for
terrestrial plants all the suitable conditions are supplied
by burial in loose, moist soil, at the temperatures which
prevail during the growing season.

This so-called germination is merely a renewal of the
growth of the embryo, which results in freeing it from the
seed coats, and in enabling it to establish itself for inde-
pendent living. All the conditions for growth are present,
namely, food material, stored within the seed, most com-
monly as starch or oil ; oxygen, to be used in respiration ;
water, to put the cells in proper condition for work, and
to act as an agent of transfer; and a suitable tempera-

SPERM ATOPHYTES: ANGIOSPEKMS 373

ture, necessary for the chemical changes about to be
made.

The first conspicuous change noted in the seed after the
absorption of water is the softening of the contents, the
solid and insoluble starch, if that be the form of the food
storage, being converted by a process of digestion into
soluble sugar, ready for transfer. The digestive substance
is known as enzyme, and the most abundant enzyme in
seeds is diastase, which has the power of transforming
starch into a sugar. Accompanying these changes there is
to be noted a marked evolution of heat, so that if a large
mass of seeds is set to germinating, as in the process
known as malting, the amount of heat generated may be
very great.

The first part of the embryo to protrude from the seed
is the tip of the hypocotyl, thrust out by the rapid elonga-
tion of the upper part of the hypocotyl (Fig. 143, B). This
protruding and rapidly elongating tip, which is to develop
the root, now rapidly elongates and is very sensitive to the
influence of gravity, responding by developing any curva-
ture necessary to reach the soil. Penetrating the soil, and
beginning to put out lateral branches, it secures the grip
necessary for the extrication of other regions of the em-
bryo.

After some anchorage has thus been obtained, the upper
part of the hypocotyl again begins a period of rapid elonga-
tion, which results in the development of a curvature known
as the " hypocotyl arch " (Figs. 143, C, and 143, a). In
the case of the germinating bean this arch is the first struc-
ture to appear above ground, and its pull upon the seed
is very apt to bring it to the surface.

Finally, the arch, in its effort to straighten, pulls the
cotyledons out of the seed-coats and with them the stem
tip, the axis of the plant straightens up (Fig. 143, «), the
seed-leaves and sometimes other leaves expand, and ger-
mination is over ; for with roots in the soil, and green

374

PLANT STUDIES

leaves expanded to the air and sunlight, the plantlet has

become independent (Fig. 331).

It must not be supposed that all of the details just

given apply to the germination of all seeds, for there are
certain notable variations. For ex-
ample, in the pea and acorn the
cotyledons, so gorged with food as
to have lost all power of acting as
leaves, are never extricated from
the seed-coats, but the stem tip,
which lies between the cotyledons,
is pushed out by the elongation of
the cotyledons at base into short or
sometimes long stalks. In the ce-
reals, as corn, wheat, etc., the em-
bryo lies close against one side of
the seed, so that it is completely
exposed by the splitting of the thin
skin which covers it. In such a
case the cotyledon is never un-
folded, but remains as an absorbing
organ, while the root extends in
one direction, and the stem, with
its succession of unsheathing leaves,
develops in the other.

248. Summary from Angiosperms.
— At the beginning of this chapter

FIG. 331. seedling of hornbeam (§ 237) the characters of the Gym-
(Carpinus), showing pri- nosperms were summarized which

mary root (Jiw) bearing root- * . .

lets (gw) upon which are distinguished them irom Angio-
numerous root hairs (r), hy- Sperms, whose contrasting charac-

pocotyl (h), cotyledons (c), , , „ ,,

young stem («>, and tot (/> ters may be stated as follows :

and second (f) true leaves. (1) The Hlicrospore (pollen-

-After SCHIMPEB. grain), chiefly by insect pollination,

is brought into contact with the stigma, which is a recep-
tive region on the surface of the carpel, and there de-

SPERMATOPHYTES: ANGIOSPERMS 375

velops the pollen-tube, which penetrates the style to reach
the ovary cavity which contains the ovules (megasporangia).
The impossibility of contact 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.

CHAPTER XXV

MONOCOTYLEDONS AND DICOTYLEDONS

249. Contrasting characters. — The two great groups of
Angiosperms are quite distinct, and 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. 332). 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. 333, 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
376

FIG. 332. 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 377

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. 333. 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. 334, w). This means an annual increase in the diam-

3Y8

PLANT STUDIES

FIG. 334. Section across a young twig of
box elder, showing the four stem regions:
€, epidermis, represented by the heavy
bounding line; c, cortex; w, vascular cyl-
inder; p, pith.— From "Plant Relations."

eter of woody stems (Fig.
335, w), and a possible
increase of the branch
system and foliage dis-
play each year.

(3) Leaf veins form-
ing an open system (Fig.
333, 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

may remain entire, it ^^^^^^^^^^^

very commonly be- S&^\ ^^^/ff

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 (Fig. 336),
and such a leaf is said

FIG. 335. Section across a twig of box elder
three years old, showing three annual rings,
or growth rings, in the vascular cylinder; the
radiating lines (rri) 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

379

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. 336). Such
a leaf is palmate or palmately veined, and inclines to broad
forms.

(4) Cyclic flowers pentamerous or tetramerous. The
flowers "in fives" are greatly in the majority, but some

FIG. 336. 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.

380 PLANT STUDIES

It is the combination of characters which determines a
group.

250. Monocotyledons. — In the Monocotyledons about forty
families are recognized, containing numerous genera, and
among these genera the twenty thousand species are dis-
tributed. It is evident that it will be impossible to con-
sider such a vast array of forms, even the families being too
numerous to mention.

Prominent among the families are the aquatic pond-
weeds of various kinds, the marshy ground cat-tails, the
grasses and sedges, the tropical palms, the aroids, the lilies,
and the orchids. Of these, the grasses form one of the
largest and one of the most useful groups of plants. It is
world-wide in its distribution, and is remarkable 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 Monocotyle-
dons. Here belong the various cereals, sugar-canes, bam-
boos, and pasture grasses, all of them immensely useful
plants.

The palms and the aroids each number about one thou-
sand species, and are conspicuous members of tropical vege-
tation.

In temperate regions, however, the lilies and their allies
stand as the best representatives of Monocotyledons, with
their usually conspicuous and well-organized flowers.

In number of species the orchids form the greatest
family among the Monocotyledons, the species being vari-
ously estimated from six thousand to ten thousand. In
display of individuals, however, the orchids are not to be
compared with the grasses, or even with the lilies, for in
general they are what are called "rare plants." Orchids
are the most highly developed of Monocotyledons, and their
brilliant coloration and bizarre forms are associated with
marvellous adaptations for insect visitation.

MONOCOTYLEDONS AND DICOTYLEDONS 381

251. Dicotyledons, — 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
Arcliiclilamydem 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
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 Archichlamydeae
contain about one hundred and sixty families, and the
Sympetalae about fifty.

(1) ArcMcJilamydecB. — In this great division of Dicoty-
ledons are such groups as the great tree alliance which
includes poplars, oaks, hickories, elms, willows, etc. ; the
buttercup alliance, which includes buttercups, water-lilies,
poppies, mustards, etc. ; the rose family, one of the best
known and most useful groups of the temperate regions ;
the pea family, by far the greatest family of the Archi-
chlamydeae, containing about seven thousand species ; the
parsley family, or umbellifers, containing numerous useful
forms, and being the most highly organized family of the
Archichlamydeae.

(2) Sympetalce. — 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
Archichlamydeae. The flowers are constantly cyclic, the
number five or four is established, and the corolla is

382 PLANT STUDIES

sympetalous, the stamens usually being borne upon its
tube.

Among the numerous families the following are promi-
nent : the heaths, mostly shrubs of temperate and arctic or
alpine regions ; the convolvulus alliance, with corolla in the
form of conspicuous tubes, funnels, trumpets, etc. ; the
aromatic mint family, with more than ten thousand species,
and its allies the nightshades, the figworts, and the ver-
benas ; and, last and highest, the family of composites, the
greatest and ranking family of Angiosperms, estimated to
contain at least twelve thousand species, more than one
seventh of all known Dicotyledons, and more than one
tenth of all Seed-plants. Not only is it the greatest family,
but it is the youngest. Composites are distributed every-
where, but are most numerous in temperate regions, and
are mostly herbs.

GLOS SARY

[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.]

AKENE : a one-seeded fruit which ripens dry and seed-like.

ALTERNATION OF GENERATIONS: the alternation of gametophyte and
sporophyte in a life history.

ANEMOPHILOUS : applied to flowers or plants which use the wind as agent
of pollination.

ANTHER: the sporangium-bearing part of a stamen.

ANTHERIDIUM : the male organ, producing sperms.

APETALOUS : applied to a flower with no petals.

APOCARPOUS : applied to a flower whose carpels are free from one an-
other.

ARCHEGONIUM : the female, egg-producing organ of Bryophytes, Pteri-
dophytes, and Gymnosperms.

ASCOCARP : a special case containing asci.

ASCOSPORE : a spore formed within an ascus.

Ascus : a delicate sac (mother-cell) within which ascospores develop.

ASEXUAL SPORE : one produced usually by cell-division, at least not by
cell-union.

CALYX : the outer set of floral leaves.

CAPSULE: in Bryophytes the spore-vessel ; in Angiosperms a dry fruit

which opens to discharge its seeds.
CARPEL : the megasporophyll of Spermatophytes.
CHLOROPHYLL : the green coloring matter of plants.
CHLOROPLAST : the protoplasmic body within the cell which is stained

green by chlorophyll.

CONJUGATION : the union of similar gametes.
COROLLA : the inner set of floral leaves.

384 PLANT STUDIES

COTYLEDON : the first leaf developed by an embryo sporophyte.

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.

DEHISCENCE: the opening of an organ to discharge its contents, as in
sporangia, pollen -sacs, capsules, etc.

DICHOTOMOUS : applied to a style of branching in which the tip of the
axis forks.

DIOECIOUS : applied to plants in which the two sex-organs are upon dif-
ferent individuals.

DORSIVENTRAL : applied to a body whose two surfaces are differently
exposed, as an ordinary thallus or loaf.

EGG : the female gamete.

EMBRYO: a plant in the earliest stages of its development from the

spore.
EMBRYO-SAC : the megaspore of Spermatophytes, which later contains

the embryo.
ENDOSPERM: the nourishing tissue developed within the embryo-sac,

and thought to represent the female gametophyte.
ENTOMOPHILOUS : applied to flowers or plants which use insects as agents

of pollination.
EPIGYNOUS : applied to a flower whose outer parts appear to arise from

the top of the ovary.

FERTILIZATION : the union of sperm and egg.

FILAMENT: the stalk-like part of a stamen.

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.

GAMETANGIUM : the organ within which gametes are produced.
GAMETE : a sexual cell, which by union with another produces a sexual

spore.
GAMETOPHYTE: in alternation of generations, the generation which

bears the sex organs.

HETEROGAMOUS : applied to plants whose pairing gametes are unlike.

HETEROSPOROUS : applied to those higher plants whose sporophyte pro-
duces two forms of asexual spores.

HOMOSPOROUS : applied to those plants whose sporophyte produces simi-
lar asexual spores.

GLOSSARY 385

HOST : a plant or animal attacked by a parasite.

HYPHA : an individual filament of a mycelium.

HYPOCOTYL : the axis of the embryo sporophyte between the root-tip

and the cotyledons.
HYPOGYNOUS : applied to a flower whose outer parts arise from beneath

the ovary.

INFLORESCENCE : a flower-cluster.

INTEGUMENT : in Spermatophytes a membrane investing the nucellus.

ISOGAMOUS: applied to plants whose pairing gametes are similar.

MALE CELL : in Spermatophytes the fertilizing cell conducted by the

pollen-tube to the egg.

MEGASPORANGIUM : a sporangium which produces only megaspores.
MEGASPORE : in heterosporous plants the large spore which produces a

female gametophyte.

MEGASPOROPHYLL : a sporophyll which produces only megasporangia.
MESOPHYLL : the tissue of a leaf between the two epidermal layers which

usually contains chloroplasts.

MICROSPORANGIUM : a sporangium which produces only microspores.
MICROSPORE : in heterosporous plants the small spore which produces a

male gametophyte.

MICROSPOROPHYLL : a sporophyll which produces only microsporangia.
MICROPYLE : the passageway to the nucellus left by the integument.
MONCECIOUS : applied to plants in which the two sex organs are upon

the same individual.
MYCELIUM : the mat of filaments which composes the working body of

a fungus.

NAKED FLOWER : one with no floral leaves.
NUCELLUS : the main body of the ovule.

OOGONIUM: the female, egg-producing organ of Thallophytes.

OOSPHERE : the female gamete, or egg.

OOSPORE : the sexual spore resulting from fertilization.

OVARY : in Angiosperms the bulbous part of the pistil, which contains

the ovules.
OVULE : the megasporangium of Spermatophytes.

PARASITE : a plant which obtains food by attacking living plants or

animals.
PERIANTH : the set of floral leaves when not differentiated into calyx

and corolla.

PLANT STUDIES

PETAL : one of the floral leaves which make up the corolla.

PHOTOSYNTHESIS : the process by which chloroplasts, aided by light,
manufacture carbohydrates from carbon dioxide and water.

PISTIL : the central organ of the flower, composed of one or more car-
pels.

PISTILLATE : applied to flowers with carpels but no stamens.

POLLEN : the microspores of Spermatophytes.

POLLEN-TUBE : the tube developed from the wall of the pollen grain
which penetrates to the egg and conducts the male cells.

POLLINATION : the transfer of pollen from anther to ovule (in Gymno-
sperms) or stigma (in Angiosperms).

POLYPETALOUS : applied to flowers whose petals are free from one an-
other.

PROTHALLIUM : the gametophyte of Ferns.

PROTONEMA : the thallus portion of the gametophyte of Mosses.

RECEPTACLE : in Angiosperms that part of the stem which is more or
less modified to support the parts of the flower.

RHIZOID : a hair-like process developed by the lower plants and by in-
dependent gametophytes to act as a holdfast or absorbing organ,
or both.

SAPROPHYTE : a plant which obtains food from the dead bodies or body
products of plants or animals.

SCALE : a leaf without chlorophyll, and usually reduced in size.

SEPAL : one of the floral leaves which make up the calyx.

SEXUAL SPORE : one produced by the union of gametes.

SPERM : the male gamete.

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.

SPORANGIUM: the organ within which asexual spores are produced
(except in Bryophytes).

SPORE : a cell set apart for reproduction.

SPOROGONIUM : the leafless sporophyte of Bryophytes.

SPOROPHORE : a special branch bearing asexual spores.

SPOROPHYLL : a leaf set apart to produce sporangia.

SPOROPHYTE : in alternation of generations, the generation which pro-
duces the asexual spores.

STAMEN : the microsporophyll of Spermatophytes.

STAMINATE : applied to a flower with stamens but no carpels.

STIGMA : in Angiosperms that portion of the carpel (usually of the style)
prepared to receive pollen.

GLOSSARY 387

STOMA (pi. STOMATA) : an epidermal organ for regulating the communi-
cation between green tissue and the air.

STROBILUS : a cone-like cluster of sporophylls.

STYLE: the stalk-like prolongation from the ovary which bears the
stigma.

SYMBIONT : an organism which enters into the condition of symbiosis.

SYMBIOSIS : usually applied to the condition in which two different
organisms live together in intimate and mutually helpful relations.

SYMPETALOUS : applied to a flower whose petals have coalesced.

SYNCARPOUS : applied to a flower whose carpels have coalesced.

ZOOSPORE : a motile asexual spore.

ZYGOTE : the sexual spore resulting from conjugation.

INDEX

Adaptation, 147.

^cidiomycetes, 278.

Alga), 224, 225.

Alternation of generations, 300,

321.

Anemophilous, 352.
Angiosperms, 358, 370.
Animals, 145.
Anther, 360.
Antheridium, 231, 304.
Anthoceros, 315.
Ant plants, 162.
Araucaria, 74.
Archegonium, 305.
Ascocarp, 274.
Ascoraycetes, 273.
Ascospore, 275.
ASCIIS, 275.
Asexual spore, 229.
Assimilation, 154.

Bacteria, 291.
Banyan, 105.
Basidiomycetes, 284.
Begonia, 25.
Birch, 71.
Blade, 35.
Body, 2, 222, 226.
Botrychium, 244.
Branched leaves, 19.
Bryophytes, 222, 299, 320, 344.

Bud, 73, 141.
Bulb, 75.
Burdock, 121.

Calyx, 79.
Capsule, 303.
Carbohydrate, 153.
Carnivorous plants, 164.
Carpel, 79, 350, 362.
Carrot, 120.
Cell, 226.
Characeae, 262.
Chlorophycese, 236.
Chlorophyll, 149.
Chloroplast, 39, 152, 228.
Chrysanthemum, 23.
Cilia, 230.
Cladophora, 241.
Cleistogamy, 130.
Club-mosses, 340.
Cocklebur, 120.
Compass plant, 10, 48, 193.
Compound leaves, 19.
Conifer, 83, 356.
Conjugation, 237.
Corolla, 79.
Cortex, 83.
Cotton wood, 70.
Cotyledon, 51, 73, 369.
Cyanophyceae, 232.
Cycad, 22, 354.

390

PLANT STUDIES

Cyclic, 365, 366, 377, 379.
Cypress, 96.
Cytoplasm, 227.

Dandelion, 114.
Desmids, 248.
Diatoms, 261.
Dichotomous, 251.
Dicotyledon, 83, 365, 376.
Digestion, 154.
Dionaea, 168.
Dodder, 106.
Drosera, 166.

Ecological factors, 170.
Ecology, 4.
Edogonium, 238.
Egg, 110, 231.
Elm, 67, 68.
Embryo, 111, 352, 369.
Embryo-sac, 350.
Endosperm, 351.
Entomophilous, 359.
Epidermis, 37, 83.
Epigynous, 365.
Equisetum, 337.
Evolution, 223.

Fern, 55, 56, 85, 334.

Fertilization, 351.

Filament, 360.

Flower, 76, 140, 364 ; and insects,

123, 162.

Foliage, 6, 28, 35.
Foot, 303.
Fruit, 368.
Fucus, 251.
Fungi, 224, 264.

Gametangium, 231.
Gamete, 230.
Grametophore, 303,

Gametophyte, 303, 323, 351, 366,

367, 375.
Germination, 111, 138; of seed,

369.

Geotropism, 69, 91, 138.
Glceocapsa, 232.
Gymnosperms, 345, 358.

Hair, 136, 198.
Halophytes, 176.
Haustoria, 266.
Heliotropism, 12, 68, 139.
Heterogamous, 231.
Heterospory, 330.
Homospory, 332.
Horsetails, 337.
Host, 264.

Hydrophytes, 175, 177.
Hydrotropism, 91, 138.
Hyphae, 265.
Hypogynous, 365.

Insects and flowers, 123, 162.
Integument, 350.
Isogamous, 231.

Jungermannia, 314.

Lady-slipper, 132-136.
Laminaria, 249.
Latex, 136.
Leaves, 28, 35, 139.
Lichens, 159, 293.
Life-relations, 4.
Light, 143, 174.
Light-relations, 8.
Linden, 116.
Liverworts, 308.
Lycopodium, 340.

Maple, 26, 115.
Marchantia, 107, 309.

INDEX

391

Megasporangia, 332.
Megaspore, 332.
Megasporophyll, 349, 362.
Mesophyll, 39.
Mesophytes, 175, 214.
Micropyle, 350.
Microsporangia, 332.
Microspores, 332.
Microsporophyll, 346, 859.
Migration, 147.
Mildews. 273.
Monocotyledon, 85, 365.
Mosaic, 24.
Mosses, 316.
Motile leaves, 10, 193.
Moulds, 276.
Mucor, 268.
Mushroom, 285.
Mycelium, 265.
Mycorhiza, 159.

Naked flower, 364
Nectar, 123.
Nostoc, 233.
Nucellus, 350.
Nucleus, 227.
Nutrition, 3, 149, 223.

Oak, 69.
Oogonium, 231.
Oospore, 240.
Orchid, 98.
Organ, 3.
Oscillaria, 234.
Ovary, 125, 362.
Ovule, 350.

Palm, 86.

Parasite, 106, 150, 157.

Peronspora, 271.

Petal, 79.

Petiole, 35.

Phaeophyceae, 248.

Photosynthesis, 28, 150.

Phycomycetes, 267.

Physiology, 149.

Pine, 65, 66.

Pistil, 77, 350, 363.

Pitcher plants, 165.

Pith, 83.

Plastid, 228.

Pleurococcus, 236.

Pollen, 77, 346 ; tube, 351.

Pollination, 77, 121, 123.

Potato, 76.

Protandry, 128.

Protection, 41, 137, 189.

Proteid, 153.

Prothallium, 322.

Protogyny, 128.

Protonema, 303.

Protoplasm, 227.

Pteridophytes, 222, 320, 343, 344.

Rain, 51.
Raspberry, 91.
Receptacle, 81.
Redbud, 10.

Reproduction, 3, 109, 223, 228.
Respiration, 32, 154.
Rhizoids, 308.
Rhodophyceaa, 254.
Rivalry, 146.
Root, 89, 107, 138.
Rootstock, 75.
Root tubercles, 161.
Rosette habit, 17, 47.
Rubber tree, 104.

Saprolegnia, 267.
Saprophyte, 150, 157.
Sargassum, 251.

Seed, 352 ; distribution, 79, 112.
Selaginella, 340.

392

PLANT STUDIES

Sensitive plants, 11, 50.

Sepal, 79.

Seta, 303.

Sexual spore, 230.

Shoot, 53.

Slime moulds. 290.

Smilax, 61.

Societies, 1, 169.

Soil, 90, 145, 173.

Sperm, 231.

Spermatophytes, 222, 343, 344.

Sphagnum, 318.

Spiral, 365.

Spirogyra, 244.

Sporangium, 230, 325.

Spore, 110, 229.

Sporogonium, 303, 306.

Sporophore, 266.

Sporophyll, 346.

Sporophyte, 303, 325.

Stamen, 79, 346, 359.

Stem, 54, 83, 139.

Stigma, 125, 362.

Stipules, 35.

Stomata, 38.

Strobilus, 338.

Struggle for existence, 142.

Style, 125, 362.

Symbionts, 158, 295.

Symbiosis, 158, 295.

Temperature, 145, 171.
Thallophytes, 222, 224, 299, 344.
Transpiration, 31, 154.
Tuber, 74.
Tumble weed, 117.

Ulothrix, 237.

Vascular system, 83.

Vaucheria, 242.

Vegetative multiplication, 109,

229.

Veins, 36, 40.
Violet, 117.

Water, 142, 151, 170; reservoirs,

201.

Water ferns, 336.
Wheat rust, 279.
Wind, 174.
Witch hazel, 118.
Woodbine, 63.

Xerophytes, 175, 188.

Yeast, 278.
Yucca, 131.

Zoospore, 230.
Zygotes, 237.

THE END

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