iiXIlOOKpF BOTANY

ALLENiND GILBERT

UNIVERSITY OF CALIFORNIA
AT LOS ANGELES

GIFT OF

Arthur IT. Johnson

C. LINNAEUS
(Carl von Linne)

Born at Rashult, Sweden, 1707; died at Upsala, 1778.
Brought together in a systematic form all the available
descriptions of plants, added immensely from the results of
his own observation, and so established on a firm basis the
study of the classification of plants. His great work was the
Species Plantarum (1753).

TEXTBOOK OF BOTANY

BY

CHARLES E. ALLEN

PROFESSOR OF BOTANY AT-THE UNIVERSITY
OF WISCONSIN

AND

EDWARD M. GILBERT

ASSOCIATE PROFESSOR OF "BOTANY AT THE UNIVERSITY

'OF WISCONSIN; FORMERLY PROFESSOR OF BIOLOGY AT
THE STATE NORMAL SCHOOL, SUPERIOR, WISCONSIN

D. C. HEATH & CO., PUBLISHERS

BOSTON NEW YORK CHICAGO

COPYRIGHT, 1917,
BY D. C. HEATH & Co.

U7

QK47

PREFACE

THERE are such wide differences of opinion regarding the proper
content of an elementary course in botany that no teacher would
venture to put forth a particular selection of facts and principles
as the only one wisely to be made from the great body of knowledge
concerning plants. The present writers are quite uninclined to
adopt such an attitude toward their own choice; still less would
they insist upon the precise order in which the materials they
have selected should be presented.

We are convinced, however, that an introductory course can best
I '^ntered about a fairly intensive study of a small number of
pL.^0, and that an attempt at a more desultory treatment of the
subject must prove unsatisfactory. The plants used as types
should be easily available ; and so far as possible they should be
selected from among those that already have definite meanings to
the pupil, either because of their familiarity or because of their util-
ity. In addition, the predominance and the practical significance
of the seed plants may be recognized by devoting some time to a
V^ study of their divers forms and uses ; and in this study, too, illus-
W trations should be drawn chiefly from those plants of which the
• pupil sees or hears most in his everyday life. At whatever point
>L in the course this latter work is done, it should have been preceded

Yby an intensive study of the life of at least one particular seed
plant.

The present book offers a sufficient amount of work for a year's
course. Probably all teachers will agree that a secondary school
.-A ^course in botany should not occupy less time than this, although,
i" unfortunately, the ideal is often impossible of attainment. The
order of presentation here adopted is that which will probably, in
general, be most satisfactory in schools that begin the study of
botany in the fall. It involves, first, a short study of a familiar
seed plant (Chapter I) ; this is followed by the examination of a

442893

iv PREFACE

series of plant types (Chapters II-XIII), arranged in an ascending
series; then follows (Chapters XIV-XVIII) a discussion of the
varied forms and uses of the conspicuous organs of seed plants
and (Chapter XIX) of the classification of angiosperms ; and
finally (Chapters XX-XXIV) there is a brief consideration of
some of the more important practical aspects and applications of
botany.

If the course in botany occupies less than a year, or if it begins
at midyear or in the spring, it is plain that the work here outlined
will require abridgment, or modification in the order of topics, or
both. The teacher should, therefore, feel free to select from and
to rearrange the material given in the textbook. There are other
reasons why the teacher should not be too closely bound by the
arrangement of matter in the text ; local needs and conditions must
be carefully considered if the greatest possible effectiveness is to
be attained. For courses which begin at other times than in the
fall, or for which less than a year is allowed, the following modifi-
cations are suggested :

For a year beginning in February, Chapter I may be studied first,
with the substitution if necessary of the flowers of some of the
plants suggested in the laboratory directions (page 391) ; this may
be followed by Chapters XIV to XIX, then by Chapters II to
XIII, and these in turn by Chapters XX to XXIV.

For a course of two terms only, beginning in the spring ("spring
and fall botany"), the outline given in the preceding paragraph
may be followed, with the omission of Chapters III, VII (or VIII),
XIII, and XX to XXIV.

For a half-year's course beginning in the fall, we recommend
the following order: Chapters I, II, IV, V, VI, IX, X, XI (§§139-
153), XII, XIV to XVIII (abbreviating the laboratory work out-
lined in connection with the latter five chapters).

For a half-year's course starting in February, we recommend
beginning with Chapter I, substituting the flowers of other plants
for those of the cucumber; this may be followed by Chapters
XIV to XVIII, abbreviating the laboratory work suggested in
connection with these chapters, then by Chapters II, IV, V, VI,
IX, X, XI (§§ 139-153), and XII.

Special emphasis should be laid upon the importance of laboratory

PREFACE V

work. Directions for laboratory study, if included at al! in a
textbook, are necessarily so placed as unfortunately to suggest the
relative unimportance of the laboratory. Secondary school work
in a natural science should invariably have laboratory study as its
central feature, and the textbook should be considered an accessory
which helps to elaborate and to tie together the knowledge obtained
from the study of the objects themselves. Ample time should be
allowed for laboratory work, and whenever possible double periods
should be arranged for this purpose. In general, too, the labora-
tory study of a topic should precede the textbook study and recita-
tion upon that particular topic ; but this rule cannot always be
rigidly insisted upon, and here as elsewhere the judgment of the
teacher must play an important role. The laboratory directions
given in the present book (Appendix I) are intended to be only
suggestive. It may well be that in places the teacher will find it
advisable to abbreviate. In many more places it will be necessary
to supplement by additional directions and by the demonstration
of structures which cannot well be studied, or of experiments which
cannot well be carried on, by the pupils individually. Much the
greater part of the work outlined can be done with very simple
apparatus, including hand lenses or dissecting microscopes, of
which there should be one for each student. Some of the study
necessarily involves the use of a compound microscope. We do
not feel, however, that the secondary school student should spend
any considerable part of his time with the compound microscope,
and in general we recommend that this instrument be used only
for demonstrations arranged by the teacher. If the school is suf-
ficiently equipped, there are certain points, for example in the
study of bacteria, at which individual study with the aid of the
compound microscope is helpful. Even in the study of bacteria,
however, this individual work may be omitted and yet with the aid
of a few demonstrations the student may obtain a very satisfactory
conception of the nature and activities of the organisms in question.
A word may be added regarding work out-of-doors. There is
no way in which an enthusiastic teacher can more successfully
impart his enthusiasm to his pupils than by means of field work.
The successful teacher of botany is the one who induces his stu-
dents to explore the world of plants for themselves. Field work,

vi PREFACE

however, meets certain practical difficulties. In the crowded
condition of the average curriculum it is difficult to find time for
trips long enough for real accomplishment ; moreover, climatic
conditions in large portions of the country make field work pos-
sible only for a limited period at the beginning and the end of the
year. However, within the limits set by these practical conditions,
field work is to be encouraged ; and, assuming that the teacher is
gifted with enthusiasm of the right sort, even voluntary excursions
at out-of-class periods will be productive of valuable results. Es-
pecially in connection with the work at the beginning of the year
there should be some trips, which may also be utilized by the
teacher in collecting material for later study. But the mistake
must not be made of substituting, in any large measure, field work
for laboratory work. Nothing can replace the individual study of
plants in the laboratory under careful direction and supervision.
So far as possible, this laboratory study should be of live plants.
There is perhaps no way in which a teacher can add more to the
interest and consequently to the value of a course in botany than
by the actual growing of plants in the schoolroom.

If the course extends throughout the year, some time may well
be devoted in the spring and early summer to the collection and
identification of wild plants. The exact amount of work of this
nature must be left to the discretion of the teacher ; it will neces-
sarily depend upon much the same factors that govern field work
in general. If circumstances allow, the ability to identify unknown
plants by means of a manual is an accomplishment to the attain-
ment of which a reasonable amount of time may profitably be
devoted.

The interest and value of laboratory and textbook study may
be greatly enhanced by carefully selected supplementary reading.
Lists of references are given in Appendix II for each of the more
important topics to be studied, and a fair proportion of the books
cited in these lists should be in the school library. Large use may
profitably be made of the bulletins and circulars issued by the
United States Department of Agriculture and by the experiment
stations of the various states. We have included references to
many of these publications which will be helpful to the teacher
of botany, but the list is by no means complete. They may be

PREFACE vii

obtained in most cases from the respective experiment stations or
from the Superintendent of Documents at Washington, either
gratis or at a nominal price.

It is a pleasure to the authors to acknowledge their indebtedness
to Professor R. A. Harper, now of Columbia University. Whatever
value this book may have is due in large measure to the stimulus
that came through their years of association with him and to the
inspiration furnished by his discussions of the problems of botanical
teaching, and by his example as a teacher. Of the many others
to whom the authors are indebted for assistance, special mention
should be made of Dr. C. A. Fuller, now of Providence, Rhode Is-
land, whose valuable suggestions aided in the preparation of Chapter
II ; Professor E. T. Harper, of Geneseo, Illinois, upon whose col-
lection of photographs of the fleshy fungi we have freely drawn;
Mr. F. B. Moody of the Wisconsin State Conservation Commis-
sion, who furnished several of the photographs used in illustrating
Chapter XXII ; President V. E. McCaskill of the Superior State
Normal School, who has read and criticized several of the chapters ;
Professors L. R. Jones, G. W. Keitt, and A. G. Johnson, of the
Department of Plant Pathology of the University of Wisconsin,
for assistance especially in the preparation of Chapter XXIV;
Professor' Alban Stewart of the Florida College for Women ; and
to the various members of the Department of Botany of the Uni-
versity of Wisconsin, especially Professors J. B. Overton, R. H.
Denniston, E. T. Bartholomew, and G. M. Smith, Dr. W. N. Steil,
Dr. G. S. Bryan, and Mrs. P. M. Smith, for assistance and sug-
gestions in connection with all parts of the work.

MADISON, WISCONSIN.
May, 1917.

CONTENTS

CHAPTER
I.

A BRIEF STUDY OF A FAMILIAR PLANT

PAGE
I

The Squash, Pumpkin, or Cucumber

II.

BACTERIA

II

III.

PROTOCOCCUS

• 30

IV.

YEASTS '

• 33

V.

A POND SCUM

• 39

VI.

THE BREAD MOLD

• 53

VII.

THE WHEAT RUST

. 60

VIII.

A MUSHROOM

• 74

IX.

A Moss ~ .

. 86

X.

THE BRACKEN FERN

• 97

XI.
XII.

THE PINE
THE BEAN

• H3

• 137

XIII.

THE INDIAN CORN

. 156

XIV.

ROOTS AND THEIR USES ....

. 169

XV.

STEMS AND BRANCHES AND THEIR USES

. 1 86

XVI.

LEAVES AND THEIR USES

. 228

XVII.

FLOWERS AND THEIR USES ....

• 258

XVIII.

FRUITS AND SEEDS AND THEIR USES .

. 283

XIX.

SOME IMPORTANT FAMILIES OF ANGIOSPERMS

• 295

XX.

SOME USEFUL PLANTS AND PLANT PRODUCTS

• 313

XXI.

WEEDS AND POISONOUS PLANTS .

. 328

XXII.
XXIIJ.

FORESTRY AND FOREST MANAGEMENT .
PLANT BREEDING

• 342

358

XXIV.

PLANT DISEASES

• 373

CONTENTS

APPENDIX I.

— Directions for Laboratory and Field Work

PAGE
391

APPENDIX II.

— Reference Books

426

APPENDIX III.

— The State and Territorial Agricultural Ex-
periment Stations ....

438

APPENDIX IV.

— Botanical Supplies

440

Glossary
Index

443
4.SI

A TEXTBOOK OF BOTANY

CHAPTER I
A BRIEF STUDY OF A FAMILIAR PLANT

THE SQUASH, PUMPKIN, OR CUCUMBER l

1. The Squash Seed (Fig. i). — This is a hard, flat, white
object, rounded at one end and more or less pointed at the
other. At the pointed end is a scar marking the part of the
seed by which it was attached to the inside of the fruit (which
we commonly call the " squash ")• In this scar and a little
to one side of the point is a conspicuous depression or hole,
the micropyle. If a seed has first been soaked overnight,
it is easier to remove the outer hard covering, the seed coat.
Just inside this is a thin, greenish, skin-like layer, the en-
dosperm. Within this is the embryo, or young plant, which
makes up the larger part of the seed. One end of the embryo
is rather pointed and is called the radicle; this is turned
toward the micropyle. The greater part of the embryo is
made up of two thick seed leaves, in which food is stored that
is to be used by the embryo when the seed germinates. The
seed leaves are attached to the radicle, and between the seed
leaves, at the point where they join the radicle, is a small
swelling, the plumule. The plumule bears two very small
secondary leaves, which, however, can hardly be made out by

1 Although any one of the three plants mentioned may be used for the work of
the present chapter, the cucumber will usually be found most convenient because
of its smaller size. But the cucumber seed is not so favorable for study as is the
larger seed of the squash or pumpkin. Specific reference is made, therefore, to the
seed and seedling of the squash, and to the mature plant, flowers, and fruit of the
cucumber.

I

TEXTBOOK OF BOTANY

the use of an ordinary lens. The important fact for us to
notice is that the seed consists of a small plant (the embryo)
which is ready to continue its growth as soon as conditions

FIG. i. — A, side view of a squash seed ; B, a lengthwise section through
the middle of a squash seed ; a, scar, showing the place at which the seed
was attached; b, seed coat; c, endosperm; d, seed leaves; e, plumule;
/, radicle.

are favorable ; and also of some surrounding layers which
protect the embryo.

2. Germination of the Seed. — If some squash seeds are
placed in moist sand or sawdust and are examined from time
to time, it will be found that they gradually swell. This is
because water is taken in both by the seed coat and by the
embryo. After a few days the seed coat begins to crack;
the crack starts at the micropyle and extends down the two
edges of the coat. Then the end of the radicle begins to push
out through the opening in the seed coat (Fig. 2, A). This
is because all parts of the embryo, and especially the radicle,
are beginning to grow, and there is no longer room for the
whole embryo within the seed coat. As soon as the end of
the radicle is well outside the seed, it turns downward and
grows in that direction. This downward growth pushes the
tip of the radicle farther into the soil. From the radicle,
therefore, is developed the primary root of the young plant,

STUDY OF A FAMILIAR PLANT 3

as well as a short part of the very base of the stem. Before
the young root has grown very far, branch roots begin to grow
from it (Fig. 2, B). At this time we can see that the seed
leaves and the part of the radicle still within the seed coat
are also swelling, and that just within the edge of the splitting
seed coat there is a flat projection (a peg) which has grown
out of one side of the radicle. Now the upper portion of the

C ' D

FIG. 2. — A, a germinating squash seed; B, C, and D, stages in the
development of the seedling. Notice how the "peg" and the lengthening
upper part of the radicle help to free the seed leaves from the seed coat.

radicle grows still more and bends so as to push out of the
seed. This lengthening of the radicle finally pulls the seed
leaves out of the seed coat, the latter being held firmly in
place by the peg (Fig. 2, C). The seed coat has now been
thrown off entirely, and the radicle straightens so that the
end bearing the seed leaves and the plumule is turned upward.
3. Growth of the Seedling. — The young plant just be-
ginning to grow is called a seedling. When the growth of the
radicle has pushed the seed leaves well above the surface
of the soil, they spread apart, grow, and become green like
ordinary leaves (Fig. 2, D), although they are different in

4 TEXTBOOK OF BOTANY

shape and not so large as the leaves formed later. The plu-
mule, which has already begun to grow, now grows more
rapidly ; the two secondary leaves which it bears, and which
were already formed within the seed, spread out and become
large and green ; they are shaped much like the later leaves
of the plant. By the further growth of the plumule into a
long stem and by the production of more leaves upon the
stem, the above-ground portion of the seedling develops into
that of the mature plant at the same time that the root and its
branches are growing and pushing into the soil.

4. The Mature Cucumber Plant : Roots. — The primary
root is developed from the lower end of the radicle, which
continues to grow farther and farther into the soil. After
a time, however, the primary root grows more slowly, and
some of the branch roots grow fast enough so that they come
to be fully as long as the primary root. These branch roots
occasionally branch also, so that the root system of an older
plant is made up of a great many slender roots. It is by
means of this system of roots that the plant is firmly an-
chored in the soil. The roots also take up from the soil
large amounts of water as well as some other substances that
the plant needs, and these are carried through the roots to
the stem and thence to all parts of the plant above ground.
The water and other materials are not taken in from the soil
by all parts of the roots, but only through very short, slender
root hairs (see Fig. 2). These root hairs are borne in large
numbers, but only on the youngest parts of the root system —
that is, close to the growing ends of the primary root and of
each branch root.

5. The Stem. — We have seen that the plumule grows into
the stem of the mature plant. The stem branches, like the
primary root, though less frequently, and each branch of the
stem may branch again. The stem and its branches, like
the primary root and its branches, may continue to grow in
length as long as the plant lives. The stem at first grows

STUDY OF A FAMILIAR PLANT

upward . But it is not very strong, and when it is a few inches
in length its weight and that of the leaves make it bend over ;
from this time on, unless care is taken to train it upward on
a trellis or other support, the stem sprawls on the surface of
the ground.

6. Leaves. — The secondary leaves (a name given to all
the leaves that are formed after the two seed leaves) are pro-
duced at intervals along the stem. They are alternately
arranged — that is, at one point on the stem only one leaf
arises, and the leaf
next above will be
not on the same side
but on a different side
of the stem. Each
leaf has two parts,
the leaf-stalk and the
blade (Fig. 3). The
blade is the large, flat
portion of the leaf.
It has a lobed outline,
the three or five lobes
being pointed, and
the edge of each lobe
irregularly toothed.
There are many hairs growing on both the upper and lower
surfaces of the leaf, as well as on the leaf -stalk and on the
stem and branches of the plant. If the leaf be held up
between the eye and a window, one can see in the blade
many light green lines, the veins. Five large veins spread out
from the point where the blade is attached to the leaf -stalk ;
as these main veins spread out in the blade they give off
branches, the branches branch, and so on until the whole
system of veins looks like a network. It is in the leaf that
much of the food is manufactured which is to be used in the
growth of the plant, and the veins are useful in two ways :

FIG. 3. — Portion of a cucumber stem bearing
a leaf and a tendril.

6 TEXTBOOK OF BOTANY

first, they carry to all parts of the leaf the water and other
substances that have been brought up from the roots ; and
second, they carry from all parts of the blade to the leaf-
stalk and so finally to other parts of the plant the food that
has been manufactured in the leaf.

7. Tendrils. — Here and there, growing from the same
level on the stem as one of the leaves, is a slender structure
that looks like a branch, but is more or less curved or coiled
(Fig. 3). If the end portion of a young tendril is gently
stroked on one side with the finger or with a pencil, it will
often begin to bend toward the object that is stroking it. It
is in this way that tendrils coil about the objects that they
touch. Some of the relatives of the cucumber climb by
means of their tendrils. But the tendrils of the cucumber
are not numerous enough or strong enough to support the
weight of any large part of the plant ; for this reason the
plant usually sprawls on the ground, although sometimes
the ends of branches clamber up a short distance on neighbor-
ing objects. However, with a little assistance, a cucumber
plant can be induced to climb.

8. Terminal Buds. — The tip of the stem is covered by
young leaves which have not yet unfolded. The stem tip
and the young leaves that cover it are together called a bud.
This bud includes not only the few leaves that one sees on the
outside ; for if these are stripped off, several smaller leaves
will be found within. As the part of the stem inclosed within
the bud grows, the distance between the older leaves of the
bud increases, and these older leaves unfold, leaving the next
younger leaves as the outer covering of the bud; at the
same time new leaves are being formed within the bud as
minute swellings upon the stem, just back of its very end.
It is by means of these changes within the bud that the stem
grows in length and that new leaves are formed. A part of
the stem for a short distance back of the bud is also growing
longer, but the older parts do not grow in length. There

STUDY OF A FAMILIAR PLANT 7

is a bud at the end of each branch like that at the end of the
stem, and each branch grows in the way that has just been
described for the stem.

9. Axillary Buds. — In the axil of each leaf — that is, in
the angle where the leaf joins the stem or branch — there is
also a small bud. Now and then one of these buds grows out
into a branch. This explains why a branch always grows
from the axil of a leaf. As a rule most of the axillary buds
remain very small, and only here and there one grows farther.
But if the bud at the end of the stem or of a branch is killed
or removed, the axillary buds are stimulated to grow, and
several or even all of them for some distance back from the
end may grow into branches. This fact is often taken ad-
vantage of by gardeners, because by pinching off the terminal
buds one can stimulate the growth of branches and so in the
end induce the plant to bear more fruit than it otherwise
would.

10. Flower Buds and Flowers. — As the plant grows
older, we find on examination that in many cases an axillary
bud contains not only the growing point of a branch and sev-
eral young leaves, but the beginnings of flowers as well.
Such a bud is called a flower bud; one that contains only a
growing point and young leaves is a leaf bud. When the
flowers open (Fig. 4), we see that they are of two kinds. In
some, below the yellow part of the flower there is a swollen,
spiny region which seems to be a part of the flower-stalk $
but which really belongs to the flower; flowers with this
swollen portion are pistillate flowers. Others have no such
swollen part ; they are staminate flowers. Both kinds grow
from' axillary buds. The pistillate flowers are usually single,
the staminate flowers usually in clusters.

11. A Pistillate Flower (Fig. 4, A). — The outermost part
of the flower consists of five hairy, greenish-yellow, leaf -like
structures called sepals, which are grown together except
at their tips. Next within comes another series of five leaf-

8 TEXTBOOK OF BOTANY

like structures, the yellow petals, which are the largest and
most conspicuous parts of the flower ; they are attached be-
low to the sepals and are grown together with each other
about half-way up, their outer ends being free and spreading.
In the very center of the flower is the pistil. The upper end
of the pistil is the stigma, composed of three lobes having a
very rough surface ; each lobe is two-parted. Below the
stigma is the style, a short stalk that connects the stigma
with the green, swollen, spiny lower part of the pistil, the
ovary. The ovary seems to be below the petals and sepals,

FIG. 4. — A , a pistillate flower of the cucumber ; a, sepal ; b, petal ;
c, stigma ; d, style ; e, ovary. B, a staminate flower ; /, filament ; g, anther.

as though these parts of the flower were growing out of its
top, but really the lower parts of the sepals and petals have
grown closely together with the wall of the ovary. Below
the ovary is the short flower-stalk. A section cut across the
ovary shows that it is divided by cracks, usually three in
number, each of which begins at the center of the ovary and,
as it approaches the outer wall, divides into two branches
that curve inward toward the center. In the branch cracks
are found a number of small rounded swellings, the ovules.
The way in which the ovules are attached to the solid flesh
of the ovary cannot well be made out except in thin, specially
colored sections.

STUDY OF A FAMILIAR PLANT 9

12. A Staminate Flower (Fig. 4, S). — This looks much
like the pistillate flower, and like it has sepals and petals.
But within the petals, instead of a pistil are three stamens,
which are attached near the base of the petals. Each stamen
has a short stalk or filament, and a larger head or anther.
Growing out from the upper end of each anther is a forked
leaf -like projection. When the anthers are ripe, they open
by long, curved slits and allow the dust-like pollen to escape.
This pollen is made up of small round grains. Some of the
pollen grains must fall upon the stigma of a pistillate flower
if seeds are to be formed.1 The history of the germination
of the pollen grain on the stigma and of the growth of the
pollen tube from the pollen grain is a difficult one to follow
and will be taken up more fully in a later chapter. At the
center of the staminate flower is a whitish, three-lobed swell-

' ing that looks like a- small stigma. This really is a rudimen-
tary pistil, which is quite useless in the
staminate flower. In the same way, the
pistillate flower has a circle of rudimentary
stamens, which are very small and easily
overlooked.

13. The Fruit (Fig. 5). — The fruit of
the cucumber is the part of the plant that
is of use to us, and so it is with the fruit

that we are likely to be most familiar. It JTIG 5- — Portion
is developed from the ovary of the pistillate of a cucumber fruit,
flower. As this part of the flower grows
rapidly, the other parts (sepals and petals,
style and stigma) wither away and may be seen for some time
as little dried-up structures at the outer end of the fruit.
Ordinarily the fruit is picked for use while it is still green.
But if it is allowed to remain on the vines it becomes yellow

» As a rule, plants will not form seeds or fruits unless pollen grains land upon
their stigmas. Cucumbers of some varieties are exceptions to this rule, for they
may form fruits (but fruits without seeds) though their stigmas receive no pollen.

10 TEXTBOOK OF BOTANY

and, as we say, ripe. The spines that were noticed on the
surface of the ovary remain hard and sharp while the fruit is
growing, but many or all of them (in most varieties of cucum-
ber) dry and fall or are rubbed off before it is ripe. A cross
section of the ripe fruit shows about the same structure as one
through the ovary, except that all the parts are much larger.
The ovary wall has become thicker and hard ; it is now the
fruit coat or rind. The tissues that made up the inside of the
ovary have become soft and juicy, and the ovules have grown
into seeds, whose structure we have studied. The fruit of
the cucumber, unlike many other fruits, has no means of
opening or of scattering its seeds. Therefore, unless the
fruit is broken open in some way, the seeds remain inside,
protected by the fruit coat until the latter decays ; then they
fall upon the ground and are in a position to germinate.

14. Length of Life. — The whole history that we have'
followed is passed through in one season. The cucumber is
an annual; that is, no part of the plant lives through the
winter, but new plants must be raised from seed each year.

15. Relatives of the Cucumber. — The cucumber is a representative
of the genus Cucumis. The botanical name of the species is Cucumis
sativus. Another species of the same genus is Cucumis melo, the musk-
melon. These plants belong to the gourd family, which includes about
700 species, the greater part of them natives of the tropics. The pumg-
kin and the summer squash (both forms of Cucurbita pepo) are mem-
bers of the same family ; so are the Hubbard squash (Cucurbita maxima),
the winter crookneck squash (Cucurbita moschata}, the watermelon
(Citrullus vulgaris), and gourds of various forms (Lagenaria vulgaris).

16. Historical Note. — The cucumber is thought to have been
originally a native of East India. It has been cultivated from the
earliest times, and is said to have been introduced into China about
200 B. c. Many different varieties have been produced. The pumpkin
is probably a native either of Central or of South America. Pumpkins
were under cultivation by North American Indians when the continent
was discovered by white men ; but the pumpkins then grown seem to
have been more like the gourd pumpkins than like the field pumpkins
of the present day. The origin of the different squashes is uncertain.

CHAPTER II

BACTERIA

17. A Hay Infusion. — If we place some hay in water and
allow the mixture to stand in a warm place, after two or three
days we shall find on examination that it contains a great
number of small living
organisms. Some of
these swim actively ;
others are quiet except
as they are carried about
by currents in the liquid.
Among the most numer-
ous forms are likely to
be rod-shaped bodies,
some of them single,
others joined end to end

in chain-like rows. Some

FIG. 6. — Bacillus subtilis. A, in the
motile condition; B, in the resting con-
of the single bodies as dition, the vibrating threads having been
lost; C, in the spore condition. After
Brefeld.

well as some of the rows
of bodies are in active
motion ; others are quiet. The rod-shaped bodies belong to
the group of bacteria. Even among the rod-shaped bacteria
in the infusion there may be two or three different kinds ;
but the differences between them are slight, and we may con-
sider them under the name of what will probably be the most
abundant species, Bacillus subtilis (Fig. 6).

18. The Structure of a Bacillus. — Each rod-shaped body
is a cell ; Bacillus subtilis is a plant composed of a single cell.

12 TEXTBOOK OF BOTANY

A living bacillus seems under a microscope even of the high-
est power to be merely a colorless body, two or three times as
long as wide, with rounded ends. If two or more cells are
attached, the ends by which they join one another are flat-
tened rather than rounded.

Something more of the structure of the cell may be made out if it
is killed and stained by the use of suitable dyes. The process of stain-
ing is a delicate one and can be carried on successfully only after con-
siderable experience. A cell prepared in this way (Fig. 6, A) is seen
to be surrounded by a thin wall; within the wall is the protoplasm,
through which are scattered a few dark granules. Extending outward
from the wall are a number of long threads. These threads were part
of the living matter of the cell when it was alive, and it was by means
of the rapid vibration of the threads that the cell moved about in the
water.

19. Food. — This bacillus is commonly found in solutions
which, like the hay infusion, contain dead and more or less
decaying organic matter — that is, matter which has been a
part of the bodies of plants or animals. From this fact we
may infer that the bacillus needs ready-made organic food
just as animals do, and this is the case. We shall see later
that green plants can build up their living matter out of very
simple materials ; but this is not true of bacteria. Many
bacteria live, like Bacillus subtilis, on the dead substances
of animals and plants. Bacteria and other plants which use
dead food are spoken of as saprophytes. Other bacteria,
which live upon or in the living tissues of plants or animals,
are parasites.

20. How the Bacillus Obtains Food. — The wall of the
bacillus cell is firm and rigid, and has no opening through
which food materials can be taken into the cell. Therefore
it is necessary that anything which the cell is to take in as
food must first be dissolved, since water and many substances
dissolved in water can pass through the cell wall. Such a
substance as the hay with which we started is, of course, not
soluble in water ; so the bacillus must change some or all of

BACTERIA 13

the material of the hay into a soluble form before it can use
it. This is one of the things that bacteria do on a large
scale. They are able to change many organic materials
with which they come in contact into a soluble form — or,
as we commonly say, the materials are digested — and then
the bacteria absorb such parts of the solution as they
can use.

If we keep the hay infusion supplied with water so that
it does not dry out, the solid substance of the hay will gradu-
ally disappear, and finally there will remain only a slimy
solution with a disagreeable smell. The same thing would
happen to bread or meat or to a potato that was left in water
under similar conditions. The organisms that would be at
work in the digestion of meat would not be altogether the
same as those we find in the hay infusion ; but the most
numerous and active among them would be bacteria, although
Bacillus subtilis might not be one of them. Bacteria digest
solid foods like hay or meat by means of special substances
which they form within their cells and pass out through the
walls, just as the cells that line the human stomach form the
gastric juice which digests meat and other foods within the
stomach. Such substances, formed inside living cells, which
can produce changes in the chemical nature of other sub-
stances, are called enzyms. We shall learn that very many
different enzyms are produced by plant and animal cells,
and that each kind of enzym can cause one particular
kind of chemical change.

21. Respiration. — Like ourselves, the bacillus must
respire; that is, it must have oxygen if it is to remain active,
and this oxygen it takes in from the air. The oxygen is used,
not in building up, but in tearing down the substances
within the cell wall. This tearing down is just as necessary
as the building up ; it supplies the energy that the cell must
have in order to do work. One form of the energy so obtained
is heat.

14 TEXTBOOK OF BOTANY

22. Growth. — In the hay infusion we find bacillus cells of
different lengths. This is because a cell does not remain
the same size, but if it is supplied with food, and if other
conditions, such as moisture and temperature, are favorable,
it grows. Growth goes on because the cell builds up into
living matter some of the food that it takes in, and this be-
comes a part of the cell body, just as the food that we eat is in
part built up into the substance of our own bodies. It is true,
as we have just seen, that the opposite process also goes on ;
that is, the living matter is at the same time being broken
down into simpler substances by respiration, and these sim-
pler substances are given off to the outside through the cell wall
as waste matter. If the building up and tearing down should
just balance each other, the cell might remain of the same size.
But if food is abundant, as it is in a hay infusion, the
building up goes on more rapidly than the tearing down, and
the cell grows.

23. Reproduction. — The growth of a cell does not go on
indefinitely. When it reaches a certain size (which is always
about the same for any particular species so long as the condi-
tions remain unchanged) it can grow no longer, but divides.
The division of the cell is always crosswise, so that the two
smaller cells thus formed are attached end to end. These
may remain attached, and each one then grows to full size
and divides, and by this alternate growth and division rows
or colonies of cells are formed. The cells, however, are easily
broken apart, so that in an infusion we always find single
cells as well as colonies of various lengths. It is by division
that the bacillus reproduces, and cell division is the only kind
of reproduction that is found among bacteria. Many bac-
teria are able to grow and divide very rapidly ; some kinds
have been observed to divide about every half-hour. In
such a case a single cell might give rise in the course of ten
hours to 1,048,576 cells; and in the course of twenty-four
hours, if the food supply were abundant and all other con-

BACTERIA 15

ditions remained favorable, to an almost inconceivable
number.

It is not surprising, therefore, that bacteria are as numerous
as they are and that they are found practically everywhere ;
nor that, although each one is so extremely small, they are
able to accomplish tremendous results. The " scum " that
rises to the surface of the hay infusion contains great num-
bers of separate cells and rows of cells in a quiescent condi-
tion held together by a sticky, slimy substance which is
secreted by the bacteria. Although the cells in this scum are
not moving (because they have lost their vibrating threads),
they may still be actively dividing (Fig. 6, B).

24. Spore Formation. — If the liquid in which the bac-
teria live is allowed to dry up slowly, or if we keep it from dry-
ing up until the supply of food for the bacteria is exhausted,
a change takes place in the appearance of many of the cells.
The protoplasm of each cell shrinks away from the wall and
rounds up into a body much smaller than the original cell
(Fig. 6, Q, which lies at the center or toward one side or
one end of the old cell cavity and is closely surrounded by a
thick new wall. This shrinkage is at least partly due to the
loss of water, and the spore so formed is much less easily af-
fected by unfavorable conditions, such as dryness, heat, and
cold, than is the ordinary cell. Many kinds of bacteria
(though by no means all) are able to pass into the form of
spores, in which condition they may remain unaffected by
surrounding conditions for a long time. In this form they
may be blown about in the air, and when they land in a place
where conditions are favorable they can return to their origi-
nal form and then grow and multiply as before. This abil-
ity to change from one form to another is of great advantage
to bacteria, since it enables them to adapt themselves to
great changes in their surroundings.

25. Distribution and Forms of Bacteria. — More than two thousand
kinds or species of bacteria have been recognized, and new species are

i6

TEXTBOOK OF BOTANY

discovered every year. The majority of them are saprophytes, like
the one we have studied. They are found in every conceivable situa-
tion— in the air, in both salt and fresh water,
\ \ and in the soil. They live in the food we eat, in

TL \ the water we drink, and upon and within many

\ \ parts of our own bodies, as well as of the bodies

V». of lower animals and plants. Three classes of

JTIG ~ A pus- bacteria are distinguished which differ from one

forming bacterium, another in the general shape of their cells ; but
Streptococcus pyog- within each class there is considerable variety.
enes. Those of one class are nearly or quite globular.

They form colonies of different kinds, depending
upon whether the divisions take place all in the same direction or in
different directions. Some of the globular species form chains, as for

FIG. 8. — Disease-producing bacteria. A , the bacillus of Asiatic cholera ;
B, the bacillus of chicken cholera; C, the bacillus of splenic fever; D, the
spirillum of recurrent fever. After Gunther.

BACTERIA 17

example Streptococcus pyogenes (Fig. 7), one of the pus-forming bac-
teria ; others form plates or masses of cells. Another class includes
the rod-shaped bacteria, many of which form chain-like colonies ;
Bacillus subtilis is a type of this group. Those of the third class are
spiral or corkscrew-shaped. The spiral may be very short, as in the
" comma bacillus " that causes Asiatic cholera (Fig. 8, A) ; or it may
be composed of several coils, as in the species of Spirillum, one of which
(Fig. 8, D) is the germ of recurrent fever. Bacterial cells differ in size
as well as in form, although they are all very small ; in general they are
the smallest known living organisms. One of the smallest is y^rWrf
inch long and ^^V^ inch wide. One of the largest is ^5$ to -5^ inch
long and ^^ to ^^^ inch wide. It is estimated that it would require
16,800,000,000,000 bacilli of average size to weigh an ounce.

26. The Activities of Bacteria. — We have seen that in the
process of obtaining food for their own use, bacteria by means
of enzyms change the nature of organic substances such as
meat and hay and make them soluble. One of the most
striking, and from our point of view one of the most important,
characteristics of bacteria is their power of thus changing
the chemical nature of substances with which they come in
contact. All such changes are, of course, of direct benefit to
the bacteria ; but they are also in many cases of great conse-
quence to other plants and to animals. If, as is very com-
monly the case, the change is a breaking down of organic
substances — that is, of materials which have once been
parts of the living bodies of plants or animals — the process
is called decay. Not all forms of decay are due to bacteria ;
but bacteria are more largely concerned in decay and produce
more kinds than all other sorts of organisms taken together.
If in the process of decay bubbles of gas are formed, we often
speak of the process as fermentation; if an unpleasant odor
arises, we call it ptitref action.

Bacteria are often thought of as a group of useless and
harmful creatures ; as a matter of fact, only a small number
of species are injurious to man, and a much greater propor-
tion are useful in one way or another. Processes of decay,
due largely to bacteria, are constantly destroying the dead

1 8 TEXTBOOK OP BOTANY

bodies of plants and animals and returning the elements of
which they are made to the soil, water, and air to be used
again in building up the bodies of living animals and plants.
If it were not for decay, the surface of the earth would long
ago have been covered with dead organic matter, and the life
of the higher plants and animals, including man, would now
be impossible.

Most bacteria, including many that cause decay, like
Bacillus subtilis, can obtain the oxygen that they need for
respiration only from the air. For this reason, the decay of a
substance can often be stopped or prevented if air is entirely
excluded from it. This is one reason why fruits and vege-
tables are preserved in air-tight cans and jars. On the other
hand, some bacteria cannot grow in the presence of air ; so
they thrive only in places, for example deep in the soil, to
which air does not reach. Such bacteria need oxygen for
respiration just as all living organisms do ; but they obtain
it from the organic substances that they decompose, and not
directly from the air. An example of this class is Bacillus
tetanus (Fig. 9, D), which causes lockjaw. Since this bacillus
cannot multiply in the presence of air, it is important not to
allow wounds into which the lockjaw germ may have entered
to heal over too soon upon the surface, and not to keep them
covered so tightly as to keep out the air. There is a third
group of bacteria that can take their oxygen from the air,
but which, if they are shut away from the air, can obtain it
by the breaking down of organic materials.

27. Soil Bacteria. — Great numbers of bacteria are found
in the soil, especially in the upper layers to a depth of six
inches or a foot. Various countings of bacteria in the surface
layers of different kinds of soil have shown from 15,000,000 to
300,000,000 bacteria per ounce of soil. At greater depths the
numbers are smaller, and relatively few are found more than
five or six feet below the surface. Among those in the deeper
soil layers are many kinds that cause decay and putrefaction.

BACTERIA 19

Another group of soil bacteria that are of great importance,
particularly to the farmer, are' the nitrifying bacteria. The
decay-producing bacteria, as we have seen, decompose the
remains of plants and animals into simpler substances, but
not for the most part into materials which higher plants, like
the squash and the cucumber, can use for food. Among
the substances formed by decay are compounds containing
ammonia. The nitrifying bacteria change these ammonia
compounds first into a class of compounds called nitrites,
and then into nitrates, and the nitrates are substances which
the cucumber and other garden and farm plants can absorb
through their root hairs and can use in the building up of their
own bodies. It is not sufficient, therefore, that the soil be
fertilized by the addition of organic substances, such as
manures ; it must contain also both the decay-producing and
the nitrifying bacteria to change these substances into a form
suitable for plant food.

28. Bacteria in Milk. — One of the means used to measure
the cleanliness of milk is to count the bacteria contained in a
certain amount. The number of bacteria present varies
enormously with the care taken to secure clean milk and to
prevent the entrance of bacteria while handling and trans-
porting it. If extreme care is taken, the number may be kept
down to a few hundred per cubic centimeter. In certified
milk the number of bacteria is frequently limited to 10,000
per cubic centimeter, and in some cities milk cannot be sold
that contains more than 250,000 bacteria per cubic centi-
meter. On the other hand, the bacterial content of dirty
milk offered for sale has been found to run in some cases to
more than 15,000,000 per cubic centimeter. Of the many
kinds of bacteria found in milk, some are harmless and pro-
duce no particular effect ; some cause disease in persons who
drink the milk, and these, of course, are the forms that it is
especially important to keep out ; and some produce fermen-
tations of various kinds, most of which make the milk unfit

20 TEXTBOOK OF BOTANY

for use. Of the forms producing fermentation, the lactic
acid bacteria are of most interest. These grow and multiply
rapidly in milk at ordinary temperatures, so that if only a
few get in they will cause the milk to sour in a short time.
However, lactic acid bacteria multiply very slowly at lower
temperatures (4o°-5o° F.), and this is the reason why milk
remains sweet longer if it is kept cool. While lactic acid fer-
mentation spoils milk for most purposes, it is necessary in
order to prepare the milk for butter-making.

29. Sterilization and Pasteurization. — Milk as well as
other liquids may be sterilized by heating it three or four
times on successive days to the boiling point (2 12° F.). This
kills all bacteria whether in the active or the spore condition,
but it also produces changes in the chemical make-up of the
milk which render it less desirable for some purposes. By
heating the milk to about 155° F.1 for twenty minutes and
then cooling it, the great majority of the bacteria in the active
condition (but not those in the spore condition) are killed
and little change is caused in the milk itself. This process
is called pasteurization, and properly pasteurized milk, kept
in a cool place, should remain sweet for several days. In
time, however, some of the bacteria which were not killed
will grow, divide, and become numerous, and the milk will
sour or change in other ways, depending upon the kinds of
bacteria that it contains.

30. Other Saprophytic Bacteria. — Among the many sap-
rophytic bacteria that occur in milk are those which are con-
cerned in the ' ' ripening ' ' of cheese. The characteristic flavors
of many different kinds of cheese are due to substances produced
in the cheese by the action of particular species of bacteria.
To make one of these cheeses, therefore, it is necessary not
only to treat the materials in the proper way, but also to make
sure that the right kinds of bacteria are present. Another

1 The temperature actually used in the pasteurization of milk varies considerably,
but is usually between 140° F. and 160° F.

BACTERIA 21

familiar process due to bacteria is the fermentation that
produces vinegar.

31. Ptomains. — We have seen that bacteria decompose
organic substances into a great number of simpler compounds.
Some of these simpler compounds are useful to the bacteria
as food ; but many of them are merely by-products. Among
the latter are a class of substances called ptomains. Some
of the ptomains, produced for example in decaying meat,
cheese, or milk, are extremely poisonous to human beings.
Many deaths are caused by eating partly spoiled foods,
especially canned meats, in which ptomains have been formed
by the action of bacteria.

32. Disease -producing Bacteria. — Although only a small
proportion of the known species of bacteria are parasitic, the

A c

FIG. 9. — Disease-producing bacteria. A, the tuberculosis bacterium;
B, the diphtheria bacterium; C, the bacillus of typhoid fever; D, the
bacillus that causes lockjaw ; some of the cells are forming spores.

parasitic forms include those that cause most of the con-
tagious and infectious diseases of man and animals. Bac-
teria are not responsible for all these diseases ; some, such as
malaria and the African sleeping sickness, are produced by
one-celled animals ; and the organisms which cause some
common diseases (for example, smallpox) are unknown.
Many important plant diseases, too, are' due to bacteria,
though the number of such diseases thus far known is smaller
than the number of bacterial diseases in animals. Some

22 TEXTBOOK OF BOTANY

of the most important bacterial plant diseases will be dis-
cussed in Chapter XXIV.

33. Tuberculosis. — This name is given to diseased con-
ditions which are caused in various parts of the body by
Bacterium tuberculosis (Fig. g, A}. The most frequent form
is tuberculosis of the lungs, often called consumption. This
is the most serious and widespread disease that attacks the
human race. Each year about 150,000 persons are killed by
tuberculosis in the United States, and about 1,500,000 in
the world. Although the fight now being waged against
tuberculosis is reducing the death rate from year to year, it
is still true that of the persons now living in the United States
more than 5,000,000 will die of tuberculosis unless more
successful methods than are now known are found for treat-
ing the disease.

34. How Tuberculosis is Caused. — The lung cells that
are attacked by the bacteria are destroyed. Then there is a
growth of new cells around the diseased region, forming a
tubercle, which gave the disease its name. By the de-
composition of the lung tissues, the bacteria produce, among
other substances, one which passes into solution in the blood
of the patient and there acts as a poison. This is one of a
class of poisons, or toxins, which many parasitic bacteria
produce. The toxin of the tubercle bacteria is responsible
for many of the serious features of the disease. Eventually,
if the disease is not in some way checked,' the tissues of the
lungs are largely destroyed. In many cases, however, in
otherwise healthy and vigorous persons, the disease does
not progress far. This is because the white corpuscles of
the blood attack and kill the bacteria. The patient then
recovers.

The possibility of a cure of tuberculosis in its early stages
shows the importance of keeping in good general health as a
precaution against the disease ; and also the necessity of be-
ginning the treatment of tuberculosis at the earliest possible

BACTERIA 23

moment. Thus, it is said that about 90 per cent of all adult
Europeans have at one time or another been afflicted with
tuberculosis, although only 15 per cent die of the disease.
There is no doubt that every one of us has many times taken
the tubercle bacteria into his throat and lungs ; but if they
were not too numerous, and if we were in vigorous health,
the bacteria were quickly killed and no harm resulted. Al-
though tuberculosis most commonly affects the lungs, it oc-
curs also in the skin, in the spinal column, the hip joint, the
glands of the neck, the intestines, and the brain.

35. Tuberculosis in Cattle. — Tuberculosis is a disease of
some of the lower animals, including cattle, as well as of man.
The bacteria pass into the milk of diseased cows, and it has
been shown that tuberculosis may be conveyed to babies by
such milk. This is one reason for the adoption of laws by
various states requiring the testing of cattle for tuberculosis
and the killing of those found to be diseased. There is also
a possibility of getting the disease by eating the flesh of
affected cattle, but since most of the bacteria are killed in the
cooking of the meat, this danger is not so serious as is that
from milk.

36. How Tuberculosis is Spread. — The bacteria enter the
body by being breathed into the lungs, or by being taken into
the stomach with food, or through a wound. The first method
is probably by far the most common. The disease germs are
distributed in the sputum of diseased persons. If, therefore,
all the sputum were destroyed, the spread of the disease would
be very largely checked, and the immediate destruction of
the sputum is one of the most important means to be used in
combating tuberculosis. If it is not destroyed but is allowed
to dry, the bacterial cells also become dry and are carried
about like dust in currents of air (see Fig. 10). In this dried
condition the germs can live for a long time. They are
killed, however, by prolonged exposure to sunlight, and they
live longer in bad air, as in close, poorly ventilated rooms,

24

TEXTBOOK OF BOTANY

than in fresh air. Plenty of fresh air and sunshine are there-
fore very important, and especially so in the house where a
tuberculous person lives or has
lived. It is in crowded, unventi-
lated, and poorly lighted tene-
ments that a large proportion of
cases of tuberculosis occur, both
because conditions there are more
favorable for the bacteria, and
because persons living under such
conditions are less healthy and
so less able to throw off the
disease.

37. Diphtheria. — This is caused
by a bacterium that finds lodg-
ment in the throat (Fig. 9, B).
Living and multiplying here, the
bacterium gives off a toxin which
is carried by the blood to other

parts of the body and there produces the serious symptoms
of the disease. The presence of the toxin in the blood of
the sufferer causes the blood to form an antitoxin — a sub-
stance which counteracts the poisonous effects of the toxin.
If the antitoxin is formed in large enough quantity, the
most serious effects of the disease do not appear ; the
patient finally gets rid of the bacteria that are producing
the poison and recovers. If the antitoxin is not formed
rapidly enough, the disease grows worse and the patient
dies. Fortunately it has been found that a horse 'or mule
inoculated with diphtheria toxin produces a large amount of
antitoxin, and that this antitoxin, taken from the animal
and injected under the skin of the human sufferer, has the
same effect as the human antitoxin.

To be effective in curing diphtheria, the antitoxin must
be given early in the course of the disease ; so it is most im-

FIG. 10. — Photograph show-
ing the growth of bacterial
colonies on an agar plate that
had been exposed for a short
time to the air. The bacteria
floating about in the air settled
upon the plate and there grew
and multiplied.

BACTERIA 25

portant that diphtheria be recognized and treated at the
earliest possible moment. The use of this antitoxin has
greatly reduced the proportion of deaths from diphtheria.
For instance, in New York the average annual death rate
from diphtheria fell from 15.19 in each 10,000 of the popu-
lation before the introduction of antitoxin to 6.62 in 10,000
after its introduction ; and in Vienna it fell from 8.14 to 2.95
in 10,000. If a person recovers from an attack of diphtheria,
he will not as a rule have the disease again, no matter how
often he may be exposed ; he is immune. Exceptions to this
rule, however, occur. Similar immunity is known in the
case of many other diseases, such as measles, smallpox, and
yellow fever.

38. Typhoid Fever. — This is due to a bacillus which
seems to be taken in only with food or drink (Fig. 9, C). The
bacillus lives and multiplies chiefly in the small intestine,
but also in other parts of the body, as the blood and the
marrow of the bones. As in the case of the diphtheria bac-
terium, its evil effects are due to a toxin which is absorbed by
the blood. This toxin, however, is not given off by the living
typhoid bacilli, but is a part of their living matter, and it
passes into the blood of the human victim only after the
bacilli have died. The most common source of typhoid in-
fection is impure water, and the purity of the water supply of
a city can be quite accurately judged by the number of cases
of typhoid in that city. Flies, which breed and seek their
food in filthy places, carry the typhoid germs about upon
their bodies and deposit them in milk, cream, or other food
that they touch. Flies carry many other germs besides that
of typhoid, and they are now well recognized as dangerous
distributors of disease.

Persons who have been cured of typhoid fever may still
carry large numbers of actively multiplying typhoid bacteria
in their intestines or bile ducts ; this condition often lasts for
several months, and in some cases for years. Such carriers,

26 TEXTBOOK OF BOTANY

as they are called, as well as persons who are suffering from
a light attack which is not recognized as typhoid, are a source
of danger to others, especially if they are careless or un-
cleanly in their habits. One case of a typhoid carrier that
has been carefully studied was that of a cook; in several
families in which she worked for a term of years typhoid cases
occurred, and she was the cause of a number of deaths. An
outbreak of typhoid fever involving forty-one cases and three
deaths occurred at Madison, Wisconsin, in the fall of 1908,
among those who lived or ate at a certain boarding house.
The source was found to be a student who was employed in
cleaning and wiping dishes and who had returned to Madison
in the fall in the early stages of typhoid fever. Sufferers
from typhoid are not immune to the disease after recovering
from it ; they may be repeatedly attacked. However, an
artificial immunity can be produced by vaccination with
typhoid bacilli that have been killed by heat or other means ;
and the use of this method of vaccination has practically
eliminated typhoid from the armies of many nations.

39. Lockjaw. — The germ of lockjaw or tetanus (Fig. 9,
-D), is a bacillus that lives in the soil and is found practically
everywhere. The disease, like diphtheria, is caused by a
toxin which is given off by the bacillus and is taken up by the
blood. Infection occurs from soil that gets into cuts and
wounds. It follows that a cut should always be thoroughly
cleaned and then treated with an antiseptic, such as iodine,
which will check the growth and reproduction of any bacteria
that may be present. We have already seen that the wound
should not be so tightly covered as to prevent the entrance
of air, because it is in the absence of air that the tetanus
bacillus thrives.

40. Anthrax-. — This is a serious disease of cattle and
sheep. It is highly contagious and difficult to combat,
partly because the spores of the anthrax bacillus are very
resistant to drying and can live in the soil for many years.

BACTERIA 27

For this reason, anthrax sometimes appears suddenly and
without any apparent cause when cattle are turned into a
pasture where diseased animals had fed years before. The
disease is largely due to the rapid multiplication of the
bacteria in the blood vessels so that the circulation is stopped.
A toxin is also produced. Animals are made immune to
anthrax for about a year by vaccinating them with a culture
of anthrax bacilli that have been weakened by exposure to
air at a rather high temperature.

41. Nitrogen-fixing Bacteria (Fig. n). — Disease-produc-
ing bacteria live within the tissues of the host and are

FIG. ii. — Nitrogen-fixing bacteria. A, roots of a leguminous plant
(such as clover), bearing many small swellings. B, the method of entrance
of the bacteria through a root-hair, and their progress through the tissues
of the clover. C, a single cell of a clover root containing many bacteria,
which appear as small dark dots. D, single bacteria as they appear in' an
artificial culture. E, as they appear in a cell of the clover.

injurious to it. A quite different relation exists between
clover, alfalfa, beans, peas, and other plants of the same
family, and the bacteria which live within their roots. If
we pull up a clover plant we find many small swellings on all
parts of the roots. The swellings are outgrowths of the root

28 TEXTBOOK OF BOTANY

tissues and contain immense numbers of a particular sort
of bacillus. These bacilli can use nitrogen, which makes up
about four-fifths of the air, in manufacturing complex sub-
stances and ultimately in building up the living matter of
their own cells. The power of using the nitrogen of the air
in this way is possessed by some other bacteria and possibly
by some fungi, but not by green plants.

Now, nitrogen is necessary to the building up of all living
matter, and green plants as a rule obtain it from the soil in
the form of the compounds called nitrates. A soil that
contains too small an amount of nitrates will raise only
poor crops of grain or potatoes or of almost any useful plant.
But in the case of clover and related plants, when the bac-
teria in their root swellings die, as they do in large numbers,
the nitrogen-containing compounds in the bodies of the
bacteria are taken up by the host plant and are used by it as
food. Thus clover and alfalfa are able with the help of the
bacteria in their roots to use the nitrogen of the air, and this
is the reason why crops of these plants can be raised in soil
that is poor in nitrates. It also explains why soil is enriched
by growing clover or alfalfa upon it, especially if the crop is
plowed under, because then the nitrogen-containing sub-
stances of the plant are broken down by the soil bacteria
into nitrates which can be used by other plants. The root
bacteria of clover and alfalfa are not parasites, but are in a
sort of partnership with the host plant ; the host supplies
a moist place for development and also probably some forms
of food for the bacteria, and the bacteria supply nitrogen -
containing compounds for the host plant.

42. Historical Note. — Perhaps the first observation of bacteria
was in 1659 by Kirchner, who saw " minute living worms " in putrefy-
ing meat and other foods. Leeuwenhoek first described and figured
bacteria in a letter to the Royal Society of London in 1683. The
modern study of bacteria began with the work of Cohn, published
chiefly between the years 1853 and 1872. Pasteur in 1857 found
that the souring of milk is due to bacterial action, and he showed the

BACTERIA 29

practical importance of bacteria in producing fermentations of various
sorts. A paper by Koch in 1876 on anthrax was the first thorough
study of the production of a disease by bacteria, although the anthrax
bacillus had been suspected as early as 1863 of being the cause of the
disease, and Pasteur in 1870 had shown that a disease of silkworms
is due to bacteria. Koch devised ways of isolating and cultivating
bacteria and of staining them with anilin dyes, and by means of his
staining methods he discovered the- tuberculosis bacterium in 1882.

CHAPTER III
PROTOCOCCUS

43. General Appearance. — On the sides of fences or of
old buildings, especially in spots that are shaded much of
the time, we often see a layer of a dark-green, powdery sub-
stance which becomes bright green when moist. A similar
green layer is found on many
other objects, such as flower-
pots, trees, rocks, and stone
walls. If we examine a small
bit of this green coating under
the microscope, we shall prob-
ably find in it several different
kinds of minute plants, but the
one that is likely to be most
abundant appears in the form
of single green cells or of two,
four, or more cells joined to-
gether. This little plant is
Protococcus viridis.

44 . Structure . — A single cell
of Protococcus (Fig. 12, A) re-
minds us of a bacterial cell; but it is green and is larger
than most bacteria. The average diameter of a Protococcus
cell is said to be about -g-jnnr inch. It is surrounded by a wall
that is thicker than that of a bacterium. Its green color
is due to a substance called chlorophyl; this is the same
substance that gives the green color to the cucumber and to
other familiar plants. It is never present in bacteria.
3°

c D

FIG. 12. — Protococcus. A, a
single cell; B, a dividing cell;
C, the division completed, the two
daughter cells being still within
the wall of the mother cell ; D, a
colony of three cells.

PROTOCOCCUS 31

Sometimes the chlorophyl seems to be scattered all through the
protoplasm of Protococcus, but usually it is seen only in a part of the
cell ; in the latter case it is located in a body called a chloroplast, which
is a special, rather firm part of the protoplasm. The chlorophyl is
used by the plant in manufacturing certain complex foods (especially
sugars) out of very simple substances (water and carbon dioxid) which
are taken in from the outside. All green plants have this power of
building complex foods out of simple ones. Plants that have no
chlorophyl, such as the bacteria, cannot do this ; which explains why
bacteria must obtain their food ready-made and so are dependent
upon other organisms. Each cell of Protococcus also contains a very
small nucleus, which cannot be clearly seen except after a special treat-
ment of the cell.

45. Conditions of Life. — In the situations in which it
lives, Protococcus must be able to endure dry weather as well
as extreme heat and cold. When it has a supply of water,
such as may be caught during a rain in the crevices of the
bark of a tree on which it lives, it makes sugars and other com-
plex foods, as well as new living matter, and grows and
divides rapidly. When the water dries up or drains away,
the plant ceases to grow, and rests until another supply of
water comes to it. It is thought, however, that Protococcus
may take in some of the water that it needs from moist air.
The carbon dioxid that is necessary is taken from the air;
in the water that the cells absorb from the bark or stone or
other surface on which they live, there are small amounts
of the nitrates and other substances that are needed in build-
ing up living matter.

46. Reproduction. — Like the bacteria, Protococcus re-
produces only by a division of the cell, when it has grown
to a certain size, into two (Fig. 12, B, C). If the daughter
cells separate, each rounds up into a globular form ; but often
they remain together, flattened on the sides which touch,
thus forming a colony of two cells. By further divisions,
colonies of three, four, or sometimes more, cells are produced
(Fig. 12, D}. The divisions of Protococcus are not all in
the same direction, as is the case in the bacillus that we

32 TEXTBOOK OF BOTANY

studied, but they take place in three directions at right angles
to each other ; consequently, a colony of four cells forms a
plate, and one of more than four usually forms a group of two
or more cell layers.

47. Resting Cells. — Sometimes, under very unfavorable circum-
stances, the cells of Protococcus stop growing and dividing, and pass
into a condition somewhat like that of the spores of bacteria. The cell
contents do not shrink away from the wall, but the wall becomes
thicker and oil drops appear in the protoplasm. Such cells can return
to the ordinary condition when circumstances are once more favorable
for growth.

48. Distribution and Relationships. — Protococcus is found in
practically all parts of the world. There are also many other widely
spread species of one-celled green plants different from Protococcus
but probably related to it. These and many other plants containing
chlorophyi are grouped under the name of alga (singular, alga). Al-
though, as we shall see, many of the algse are larger and more complex
than Protococcus, they are all much simpler than the higher green
plants, such as the cucumber, wheat and other grains, and the trees.
Protococcus and its relatives are of special interest because all the
higher plants are undoubtedly descended from one-celled green algag
which were something like Protococcus, although probably not exactly
like any alga now living. The relationship of the bacteria to the algas
is not clear. Probably the bacteria or most of them are degenerate
descendants from algae even simpler in structure than Protococcus.

CHAPTER IV
YEASTS

49. A Yeast Culture. — If a portion of a cake of com-
pressed yeast or of dried yeast is put into a solution of mo-
lasses and the mixture is left in a warm place, in the course
of twenty-four hours the liquid is likely to become cloudy

E

FIG. 13. — A yeast. A, a single cell, killed and stained so as to show
its parts ; a, vacuole; b, nucleus; c, d, reserve food. B, the division of the
cell by budding. C, D, chains or colonies, formed by the remaining to-
gether of the daughter cells after division. E, spores inside the wall of the
mother cell.

and full of small bubbles that rise slowly to the surface.
Examining a drop of the liquid, we shall find that it contains
great numbers of rounded cells, some single and others in
chains of *two, three, or more. These cells are yeast plants.
A yeast cell (Fig. 13, A) is larger than the bacillus that we
have studied (it is about -j-^-j inch in diameter), but re-
sembles the bacillus in being colorless. It is either globular
or, more commonly, a little longer in one direction. It is
surrounded by a wall.

33

34 TEXTBOOK OF BOTANY

The protoplasm contains many small bodies or granules, some of
which often are yellowish in color ; these latter are drops of oil. There
is commonly also a large, round, clear space ; this is a vacuole — a
part of the protoplasm which contains chiefly water with small amounts
of various substances dissolved in it, and which because of its watery
nature is clearer and more transparent than the rest of the protoplasm.
Sometimes, instead of a single large vacuole, a cell contains two or more
smaller ones. There is also a nucleus, which cannot be seen in the living
cell, but which can be made visible by careful staining of a killed cell.

50. Food. — From the fact that the yeast reproduces so
rapidly in the molasses solution, we may conclude that it finds
there the substances necessary for its food. Since it has no
chlorophyl, it cannot make use of as simple food materials
as can Protococcus. We have seen that Protococcus can
build up sugars out of carbon dioxid and water. The yeast
cannot do this, so must obtain sugar or some similar food
ready-made. Sugar, of course, it finds in the molasses solu-
tion. But sugars contain no nitrogen, nor do they contain
certain other elements (especially sulphur and phosphorus)
that are needed in building up living matter. For this reason
the yeast could not long continue to live and grow in a pure
sugar solution — that is, in one that contained only sugar and
water. But in reality our molasses solution is not pure ; it
contains small amounts of substances other than sugars, and
these other substances supply the additional elements that the
yeast must have.

51. Respiration. — Like all other living organisms, the
yeast requires oxygen, which plays its part in breaking down
the living matter and other substances within the cell and so
in furnishing a supply of energy. Like Protococcus and
most other organisms, excepting some bacteria, -the yeast
must obtain oxygen from the air. It can, however, get along
for a time if air is excluded, and in this respect it resembles
those bacteria that can do without oxygen from the air ;
but the yeast must have access to the air from time to time
if it is to continue to thrive.

YEASTS 35

52. Fermentation. — What makes the yeast of so great
practical importance to us is its power of carrying on alcoholic
fermentation. This consists in breaking down a sugar into
carbon dioxid and alcohol. The carbon dioxid is the gas,
bubbles of which are so plentiful in a vigorous yeast culture.
This fermentation has nothing to do with the use of sugar by
the yeast as food. Neither the carbon dioxid nor the alcohol
produced by fermentation is of any use to the yeast ; in fact,
alcohol in any considerable quantity is a poison to it, and so
when the alcohol accumulates in the solution to a strength of
about 12 per cent the activity of the yeast is checked ; 14 per
cent of alcohol entirely stops its action, and more than 14 per
cent kills the yeast. The sugar that is used by the yeast as
food is taken directly into the cell, and is not fermented.

The usefulness of fermentation seems to be that it sets
free large amounts of energy which the yeast can use in
somewhat the same way that most plants and animals use
the energy set free in the process of respiration. The ability
to obtain energy through fermentation probably explains why
the yeast can get along for 'a time without oxygen from the
air — that is, fermentation in part replaces respiration in the
life of the yeast. This notion is supported by the fact that
fermentation is most rapid when the supply of oxygen is small
and when, therefore, respiration is slow. Yeast is used in
bread-making because by fermentation it produces carbon
dioxid; this gas makes its way throughout the dough,
forming minute cavities and, as we say, making the bread
light. The alcohol which is also produced is driven off by
the heat used in baking the bread, and the size of the cavi-
ties in the dough is increased because the gas expands when it
is heated. In the manufacture of fermented beverages, such
as beers and wines, the alcohol is the important product of
fermentation and the carbon dioxid is of less consequence.

53. Enzyms. — The yeasts, like bacteria and all other
organisms, produce enzyms which bring about chemical

36 TEXTBOOK OF BOTANY

changes both inside and outside the cell. Since the changes
produced by yeasts are of such great practical importance,
their enzyms have been much studied. The fermentation of
sugar is due to one of these enzyms. This is shown by the
fact that the yeast cells can be killed and the enzym ex-
tracted and filtered, and the substance so obtained will pro-
duce exactly the same change in sugar that ^oes on in the pres-
ence of living yeast. This particular enzym will not fer-
ment all sugars, but only certain comparatively simple ones,
and especially those of the class to which glucose belongs.
If the yeast is placed in a solution containing cane sugar (or
beet sugar, which is chemically the same thing) , it first changes
the cane sugar into a simpler sugar by means of a sugar-
changing enzym, and then this simpler sugar is fermented.

54. Reproduction by Division. — The yeast cells reproduce, like
those of bacteria and Protococcus, by division, but the method of
division is somewhat different. The first indication that it is to occur
is the appearance of a small swelling like a bud at one side or one end
of the cell (Fig. 13, B). This is caused by the pushing out of the
protoplasm and the cell wall at that point. The bud grows rather
rapidly. The nucleus of the cell divides into two, and one of the
daughter nuclei moves out into the bud. When the bud has reached
a certain size it is cut off by a wall, so that there are now two cells, of
which one (the former bud) is smaller than the other. The smaller
cell grows to full size. Both cells may then form new buds. The
cells may remain attached after a division, so forming a colony of two
cells ; but sooner or later they are likely to be separated. If growth
and division are going on rapidly, we frequently see not merely two
cells but a row of several cells (Fig. 13, C, D), and sometimes even
branched rows due to the formation of buds on two or more sides of a
particular cell.

55. Reproduction by Spore Formation. — Some yeasts under un-
favorable conditions, as when they are starved or when the liquid in
which they live dries up, form two, three, or four thick-walled cells
within the original cell wall (Fig. 13, £). These thick- walled cells
are called spores, and like the spores of bacteria they are able to endure
heat, cold, and dryness better than the ordinary yeast cells. Spore-
formation in yeasts, however, is quite different from spore-formation
in bacteria, because it results from cell division and is therefore a

LOUIS PASTEUR

Born at D61e, France, 1822; died at St. Cloud (near Paris),
1895. Added greatly to our knowledge of yeasts and bacteria
and diseases produced by bacteria. Devised the method of
cultivation of minute organisms in pure cultures, which is now
universally used by bacteriologists.

YEASTS 37

method of reproduction. In the bacteria, as we know, the spore is
formed by a shrinking of the cell contents without any division.

56. Species of Yeasts. — The yeasts belong to the genus
Saccharomyces. There are many species and varieties,
which are not easily distinguished from one another. Com-
mercial yeast used in bread-making is ordinarily a mixture
of several species. The yeasts used in beer-making are of
two distinct sorts which are very different in form and size.
" Bottom " yeast, used in brewing most German and Ameri-
can beers, is found in the lower part of the malt solution, and
produces fermentation at low temperatures. " Top " yeast,
used for English ale, stout, and porter, lives at the top of the
liquid, and its fermentation goes on at relatively high tem-
peratures. The yeasts that ferment grape juice are of differ-
ent varieties, and the characteristic flavors of the many
different wines are due in large part to the different yeasts
which produce them and which cause, in addition to the ordi-
nary alcoholic fermentation, the formation of other sub-
stances that modify the flavor of the wine.

Besides beers and wines, there are many other fermented
beverages due to the action of yeasts, such as kumiss and
pulque. Distilled liquors, like brandy and whisky, and
commercial alcohol itself, are also the result of a fermentation
by yeasts, followed by distillation. The beer yeasts and the
bread yeasts are known only in cultivation. The wine
yeasts live on the soil of vineyards and are carried to the skins
of the grapes in the dust that is blown about. They are
" wild " yeasts, and different varieties occur in different lo-
calities. In the same way, a wild yeast that lives on the soil
under apple trees causes the fermentation of cider ; and
many other wild yeasts produce a variety of fermentations.

57. Relationships. — The yeasts belong to the great group of fungi
(singular, fungus), which includes the relatively simple plants that are
without chlorophyl. In the broadest sense of the term, the fungi
include the bacteria also. The relation of yeasts to other fungi is not

442893

38 TEXTBOOK OF BOTANY

clear. There is some reason to think that they may be descendants
of more complex fungi which have degenerated in the course of evolu-
tion ; but this is by no means certain.

58. Historical Note. — In 1680, Leeuwenhoek noticed that yeast
seen under the microscope consists of small, rounded particles. About
1838 it was discovered by several observers that the particles which
Leeuwenhoek had seen are really plant cells, and it was concluded
that these living cells in some way produce the chemical changes that
go on only when they are present. Nearly twenty years later, Pasteur
took up the study of yeasts at the request of German brewers, who
were greatly troubled by impure yeasts. In 1856, Pasteur found a
method of securing " pure cultures " — that is, cultures which con-
tain only one variety of yeast and no other organism whatever. By
this method he studied many different forms of yeast ; he not only
succeeded in revolutionizing the brewing industry, but his method of
pure cultures was the starting-point of the modern study of bacteria
as well.

CHAPTER V
A POND SCUM

59. Pond Scums. — The appearance of a green layer on
the surface of pools, ponds, and lakes is a familiar one, es-
pecially during the warm months of the year. This scum is
made up of green plants which belong, like Protococcus, to
the group of algas. Of the many species that may be found
in such a green layer, some, like Protococcus, are one-celled, or
are made up of small groups of cells ; others have the form of
long threads, and one of the commonest of these thread-
shaped scum-forming algae is Spirogyra. Sometimes we find
several species of algae growing together on the surface
of a pond; sometimes the scum is composed largely or
wholly of one species. Spirogyra may be distinguished from
most of the other thread -shaped algae found in similar places
by the slippery feeling of a mass of the long, unbranched
threads.

60. The Spirogyra Plant. — The simple plants that we
have studied thus far (bacteria, Protococcus, and yeasts)
are sometimes found in colonies of various sizes ; but often
their cells are separate, and the single cells seem to get along
just as well as do those that are parts of colonies. Under
certain special conditions and at particular stages, the cells
of Spirogyra may occur singly ; but practically we always
find the plant in the form of a row of cells firmly attached to
one another. That is, the colony habit has become firmly
fixed in Spirogyra, whereas in the cases of the simpler plants
that we have studied a colony was a temporary and a more or
less accidental arrangement.

39

TEXTBOOK OF BOTANY

61. The Cell (Fig. 14). — A cell of Spirogyra is longer than it is
wide, and cylindrical, like a length of stovepipe. The cells are joined
end to end, and the whole plant is surrounded by a continuous, rather
thick wall, which is made up of several layers. The outermost layer,
which is very transparent and therefore not easily seen, is composed
of a slimy substance, and it is this layer that gives to the plant its
slippery feeling. There are cross walls also between adjacent cells.
The most noticeable part of the cell is the green chloroplast. Each
chloroplast winds about spirally, within and close to the wall. There
are about one hundred known species of Spirogyra, and one of the
points of difference between species is the number of chloroplasts in

each cell. Some species
have only one chloroplast,
some two, and some have
much larger numbers. Often
we find two or three species
mixed together, and it is
best to select for study a
form with one or two, or as
small a number of chloro-

be cd

FIG. 14. — A single cell of a Spirogyra
plant ; a, wall ; b, outer layer of slimy cyto-
plasm ; c, chloroplast, containing (d) pyre-
noids; e, nucleus, imbedded in a central
mass of slimy cytoplasm which is connected
by strands of the same substance with the
outer cytoplasmic layer.

plasts as can be found.

The body of the chloro-
plast itself is distinct from
the coloring matter (the
Morophyl) which makes it
appear green. This is shown
by the fact that the green

color can be dissolved out of the chloroplast by placing the plant in
alcohol. Scattered along the middle line of the chloroplast are a num-
ber of colorless pyrenoids. At just about the center of the cell is a
rather large, colorless, rounded nucleus. The nucleus is often hidden
by a coil of the chloroplast, but in some of the cells of a plant it can
usually be seen quite plainly if the microscope is carefully focused upon
the interior of the cell. In the nucleus there is a rounded body that
looks brighter than the rest of the nucleus ; this body is the nucleate.

By careful study, one can see a thin layer of granular substance just
within the cell wall ; sometimes the layer is in active movement, as is
shown by the streaming of the granules that it contains. This layer
of granular material is a part of the slimy cytoplasm.1 Another layer

1 Sometimes this slimy portion of the living matter of the cell is spoken of simply
as cytoplasm, or even as protoplasm. These terms are often confused ; but in the
usage of the most careful modern writers, protoplasm refers to all the substances

A POND SCUM 41

of slimy cytoplasm (also difficult to see) surrounds the nucleus, and
strands of the same material connect the layer about the nucleus with
the layer next the wall. Thus all parts of the slimy cytoplasm are
connected with one another, and the nucleus and chloroplast are im-
bedded in it.

The rest of the space inside the wall that is not occupied by the
slimy cytoplasm, chloroplast, and nucleus is the central vacuole. From
the description that has been given it is plain that this vacuole is of
very irregular shape. It contains a clear liquid (cell sap), composed
of water containing a weak solution of salts, sugars, acids, and other
substances.

62. The Food of Spirogyra. — The word food may be ap-
plied to any substance that is used by a living cell in any
stage of the building up of living matter. This building-up
process is one of many steps. Therefore there is a long series
of substances that may be used by plants, beginning with very
simple things (water and carbon dioxid), and ending with
certain very complex ones (proteins), which represent the last
steps previous to the formation of living matter itself. In
taking in food substances from outside, and in using these
substances within its own body, Spirogyra behaves very much
as does Protococcus and as do the higher green plants (such
as the cucumber) with which we are more familiar. In the
higher green plants, the work of absorbing and of manufac-
turing food is divided between many different kinds of cells ;
but in Spirogyra, as in Protococcus, each cell does practi-
cally all this work for itself. Spirogyra, like all other plants,
can take in materials from the outside only in a dissolved
condition ; everything that is to be absorbed, therefore, must
be dissolved in water before it can pass through the cell wall.

63. Manufacture of Carbohydrates. — It is true of all
green plants that they take in from the outside world only a
few very simple substances and that they build up these sub-
within the cell wall, and cytoplasm to all of the protoplasm excepting the nucleus.
Using the terms in this way, the chloroplasts, vacuoles, and some other parts of the
cell are parts of the cytoplasm, as is also the slimy, viscous material here called the
slimy cytoplasm.

42 TEXTBOOK OF BOTANY .

stances within their own bodies into more complex foods.
In this respect the green plants have a great advantage over
plants without chlorophyl (like the bacteria and the yeasts),
and over the animals (including ourselves) as well. Green
plants can live and thrive on a food supply that would be
quite useless to an organism without chlorophyl. Among
the simple substances absorbed by Spirogyra are water (which
is made up of hydrogen and oxygen), and carbon dioxid
(composed of carbon and oxygen). Carbon dioxid is a gas
which makes up about three-hundred ths of one per cent of the
air ; it is also present in solution in the water in which Spi-
rogyra lives. Cells containing chlorophyl can manufacture
out of carbon dioxid and water certain substances known as
carbohydrates (composed of carbon, hydrogen, and oxygen).
Starch and sugars are among the commonest carbohydrates.
Probably the first carbohydrate formed in the Spirogyra cell
is glucose or a similar sugar. When a sugar is built up out
of carbon dioxid and water, some of the oxygen which these
substances contain is given off. This oxygen appears as
bubbles of gas in the water, and if we examine a mass of
vigorous Spirogyra that is floating on the surface of a pond
on a bright day, we shall find many of these bubbles tangled
among the Spirogyra threads. Carbohydrates are manufac-
tured only by cells that contain chlorophyl, and only in the
presence of sunlight.

64. Starch. — The first carbohydrates manufactured by
the Spirogyra cell, as we have seen, are probably sugars.
They are at once dissolved in the cell sap. As time goes on,
the sap contains more and more sugar. But when the sugar
in the sap reaches a certain proportion, some of the sugar
is changed into another carbohydrate called starch. Starch
is a solid, insoluble substance and, being compact, it is a con-
venient form in which to store carbohydrates when more are
manufactured than can be used at once. The pyrenoids are
the parts of the cell that actually do the work of changing

A POND SCUM 43

sugars into starch. If we place a drop of iodine solution
upon a cell of Spirogyra, each pyrenoid seems to turn blue
or blue-black. Careful examination, however, shows that it
is not the pyrenoid itself that is colored by the iodine, but a
layer, or sometimes two or more layers, of small bodies sur-
rounding the pyrenoid. These small bodies are grains of
starch. Iodine is a valuable test for starch ; any substance
which turns blue or blue-black when in contact with iodine,
we may be sure is made of starch or contains starch.1

65. Digestion of Starch. — As we have seen, sugar is made
only in the sunlight, and when it is manufactured rapidly
(as on a bright day) much of it is changed into starch. Dur-
ing the night no sugar is made. The cell needs about as much
food at night as it does during the day, and so some of the
starch that has been stored up during the day is used for food
at night. Since the starch itself is not soluble, it must be
changed into a soluble form before it can be used — that is,
it must be digested. Spirogyra digests starch by means of
certain enzyms which it produces and which change the
starch back into a sugar.

66. Other Food Substances. — Carbohydrates are made
up of carbon, hydrogen, and oxygen. In addition to these
elements, living matter contains nitrogen, sulphur, and phos-
phorus, as well as smaller amounts of several other elements.
The elements that are not present in carbohydrates are ob-
tained by the plant in the form of simple salts — largely ni-
trates, sulphates, and phosphates — which are present in small
quantities in the water in which Spirogyra lives. Out of car-
bohydrates and some of these absorbed salts, the cell builds
up a class of very complex compounds known as proteins. Pro-
teins are always present in living cells, and up to the present
time they have never been made outside of living cells.

1 Some other substances, very similar in chemical composition to starch, are
also turned blue or violet by iodine ; but starch is the only substance so affected
that we are likely to meet in everyday life.

44 TEXTBOOK OF BOTANY

67. Living Matter. — Proteins, complex as they are, are not
themselves living matter, but living matter is built up in turn
out of proteins and some other food substances that the cell
has either taken in or made for itself. The living matter of
the Spirogyra cell is found in the slimy cytoplasm, in the
chloroplasts, and in the nucleus. It is a very unstable sub-
stance ; and just as it is being continually built up, so it is
being constantly torn down. This continual change that
living matter is undergoing is one of the most striking things
about it. We must think of a living cell as something like a
chemical laboratory in which there are going on at the same
time one long series of changes that lead from the simple
substances that come in from the outside, through the car-
bohydrates and proteins, to living matter itself ; and another
equally long series of changes that lead from living matter
downward again to very simple substances (including carbon
dioxid and water) , which in turn may be given off by the cell
as waste materials, or may be used once more in rebuilding
living matter. Even in the living parts of the cell there is a
good deal of water ; the cell wall is thoroughly water-soaked ;
and since the cell sap is mostly water, it follows that water
makes up a very large proportion of the whole bulk of the
Spirogyra cell.

68. Respiration. — Like the yeasts and other plants that
have been studied, Spirogyra must respire — that is, it must
take in oxygen, which like carbon dioxid is present in solu-
tion in the water in which the plant lives. Oxygen is not a
food as carbon dioxid is, because it is not used in building
up new substances. Its use is rather to assist in the tearing
down which, as we have seen, goes on side by side with the
building-up process. In this tearing down, energy is lib-
erated which the cell uses in various ways — for instance, in
growth, as well as in other activities that are continually
going on in the plant. Thus respiration is a source of
energy to the cell. One substance that is formed in large

A POND SCUM 45

quantities as a result of the tearing-down process of respira-
tion is carbon dioxid. In respiring, therefore, Spirogyra,
like nearly all plants and animals, takes in oxygen and gives
off carbon dioxid ; at the same time it may be taking in car-
bon dioxid as a food and giving off oxygen as a waste product
of carbohydrate formation. The net result of these two
opposite processes upon the supply of oxygen and carbon
dioxid in the water and the air about the plant depends
upon which process goes on more rapidly. During the day,
carbohydrate formation ordinarily goes on so actively that
much more carbon dioxid is taken in for this purpose than is
given off in respiration, and much more oxygen is given off
than is absorbed. At night, respiration continues but carbo-
hydrate formation is stopped, and so only oxygen is taken in
and only carbon dioxid is given off.

69. Reproduction by Division. — As in the other plants that we
have studied, the number of cells of Spirogyra is increased by the

division of one cell into two,

each of these into two, and so
on. The cells are so much
larger than those of the bac-
teria, Protococcus, or yeasts
that the method of division
can be more easily studied.
Unfortunately, division al-
most always goes on in Spiro- FIG. 15. —A stage in the division of
gyra during the night. The a Spirogyra cell (as seen in a lengthwise
first step in preparation for section). After Strasburger.
the division of the cell is a

division of the nucleus into two. This division of the nucleus is brought
about by a long and complicated process. The two daughter nuclei
then move apart toward the ends of the cell, and about halfway be-
tween them the outer layer of the cytoplasm (just within the wall)
becomes furrowed inward (Fig. 15), much as though some one had
wound a thread about the middle of the cytoplasm and then had begun
to tighten the thread. The furrow, which extends entirely around
the cell, becomes deeper and deeper, until the cell is cut into two cells,
the chloroplast also being cut in two in the middle. As the furrow
cuts inward, a new wall is formed within the furrow, connected with

46

TEXTBOOK OF BOTANY

the outer wall of the cell ; finally, when the new wall has grown clear
across the cell, the two daughter cells are fully formed, each having
all the parts that the mother cell had, but being only half as large.

In examining a Spirogyra plant, one always finds that the cells are
of different lengths ; and often there are two short cells side by side,
each about half the length of the longer cells of the thread. Such a
pair of short cells is the result of a receat division, probably one that
occurred during the previous night. After a division the daughter
cells grow, and when they have reached their full size each of them
again divides. It is by a series of alternate periods of growth and
division that the number of cells in a thread increases, and that the
thread as a whole grows longer.

Cell division is a method of reproduction because it increases the
number of cells; it does not, however, at least directly, increase the
number of plants. Sometimes a plant is accidentally broken into
two or more ; and the plants of some species of Spirogyra have a definite
method of breaking up at times into single cells or groups of cells.
Such a process of breaking up is also one of reproduction which in-
creases the number of plants, but not the number of cells.

70. Conjugation. — After the Spirogyra plants have been growing
for a time, their cells cease to divide and prepare instead for a very

FIG. 16. — Conjugation in Spirogyra. A, the commoner
method, by which gametes from different plants unite to form
a zygote ; B, the conjugation of gametes produced by the same
plant.

different process, in which two cells are to unite and form a single
cell. The first step in preparation for this conjugation is an arrange-
ment of the plants so that two lie parallel and near together. Then
many or all of the cells of each plant put out projections, one from
each cell (Fig. 16, A), which grow toward the cells of the neighboring
plant. Usually a cell in one plant is opposite a cell in the other ; the
projections from two opposite cells grow toward each other, come in

A POND SCUM

47

contact, and the wall of each projection is dissolved at the point of
contact ; the two cells, one in each plant, are now joined by a con-
jugation tube. The two plants are thus connected by a series of tubes.
Occasionally, of course, since the cells are not all of the same length,
a cell in one plant fails to find a mate in the other ; but the majority
of the cells are connected in pairs. While the conjugation tubes are
being formed, the contents of each cell shrinks away from the wall
and rounds up ; and of the two cells of a pair (one in each plant) , one
begins to round up a little earlier than the other. We shall speak of
the one that rounds up first as the male cell, or male gamete, and of
the other as the female cell or female gamete. After the conjugation
tube has been formed, the male cell (of course without its wall) moves
through the tube into the cavity occupied by the female cell. The
two cells now lie close together inside the same wall. They gradually
unite to form a single rounded cell, the zygote (Fig. 17, C), which builds
a new thick wall about itself. In the union of the male and female
cells, the cytoplasms of the two flow together, and their nuclei unite
to form a single nucleus (Fig. 17, A, B) ; the chloroplast of the male
cell disappears, and that of the female cell becomes the chloroplast
of the zygote. When conjugation takes place by the method just
described, all the gametes produced in one plant are usually of the
same sex ; in such a case we may speak of male plants and female plants.

71. Lateral Conjugation (Fig. 16, B). — In some species of Spirogyra,
conjugation takes place between two cells which lie next each other in
the same plant — that is, one plant bears both male and female gametes.
Each gamete puts out a short

projection close to the cross
wall that separates them, and
these projections unite to form
a short conjugation tube. In
other respects, this method of
conjugation is the same as that
already described.

72. Germination of the
Zygote. — The zygote is a
resting cell which can endure
unfavorable conditions (as the
spores of bacteria and yeasts
can) and can remain dormant
for a long time. Ordinarily
the zygote is formed by con-

FIG. 17. — A, a section of a zygote of
Spirogyra, showing the nuclei from the
two gametes. B, the union of the nuclei
completed. C, a mature zygote. D, a
germinating zygote. A and B after

jugation in the late spring or Trondle; C and D after Strasburger.

48 TEXTBOOK OF BOTANY

summer, or in some species of Spirogyra in the fall ; it sinks to the bottom
of the body of water in which the plants live and remains there until the
next spring, when it germinates. If the plants live in a small pond
that dries up during the summer, the zygote remains alive in the dried
mud and germinates when the pond again fills with water the next
spring. The old cell walls, within which the zygotes were formed,
decay and largely or entirely disappear. In germination, the zygote
simply grows in one direction (Fig. 17, D), becoming a long cell and
breaking through its outer wall at one side or end. Then it divides and
a cross wall is formed ; the zygote has now become a two-celled plant.
One of the two cells (the one that is not surrounded by the outer wall
of the zygote) divides, its daughter cells divide, and by a series of re-
peated divisions a long, thread-like plant is again formed.

73. Nature of Sexual Reproduction. — A union of two sexual cells
(gametes) to form a zygote is commonly called sexual reproduction.
Conjugation — that is, the union of two gametes that are nearly or
quite alike, as those of Spirogyra are — is one form of sexual reproduc-
tion. Strictly speaking, a union of gametes is not reproduction, be-
cause reproduction means an increase in numbers, and when two cells
unite to form one there are fewer cells than there were before. How-
ever, each of the many zygotes formed by the gametes from two Spiro-
gyra plants may grow into a new plant ; in this way the number of
plants is increased, and so it is true that indirectly the union of gametes
results in a reproduction of the plant. A similar union of gametes
occurs at some stage in the life, not only of many other green algae
more or less like Spirogyra, but also in that of most of the higher plants.
The same is true of the higher animals. The gametes of Spirogyra
are very much alike in size and appearance ; they differ in behavior
in that one (the male gamete) is more active than the other (the female).
In most of the plants that we are to study, we shall find a great differ-
ence in size and appearance as well as in behavior between the male
and the female gametes.

74. Distribution and Relationships. — The various species of
Spirogyra occur in bodies of fresh water in all parts of the world. Spiro-
gyra is a representative of the higher green algae, others of which differ
from Spirogyra in many respects, but most of which resemble it
in being thread-like. Some of them are unbranched threads like
Spirogyra ; others are branched. A common branched form is Cladoph-
ora (Fig. 18, A), dense masses of which are found in the same sort
of places as those in which Spirogyra grows. Vaucheria (Fig. 18, B),
which forms a dark-green felt on damp soil and greenhouse benches
or is attached to rocks and other objects in streams, is a branched alga,

A POND SCUM

49

FIG. 18. — Branched green algae :
A, Cladophora; B, Vaucheria.

composed, like the
bread mold to be
described in the
next chapter, of a
single large cell con-
taining many nuclei.
Most of the thread-
like green algae have
some form of sexual
reproduction, some
of them by means
of gametes nearly or
quite alike, as are
those of Spirogyra ;

others by means of large, passive female gametes and small, active
male gametes.

75. Algae of Water Supplies. — The drinking water of
cities, whatever its source, is sure to contain some algae,
especially if it is stored in reservoirs. Certain kinds of
algae, of which Spirogyra is one, sometimes multiply very
rapidly in reservoirs of city water. This leads to unpleasant
results, partly because the mains or pipes may become
clogged, but chiefly because when the algae die they decay and
give an unpleasant taste and odor to the water. It has been
found that the growth of algae in drinking water can be
checked by the use of small amounts of copper sulphate, a
solution of which will kill the algae even though it is much too
weak to be poisonous to human beings.

76. Marine Algae. — The salt waters of seas and oceans,
like fresh waters, contain an abundance of plant life. Among
the inhabitants of salt water are a good many green algae,
not, however, including any of the species of Spirogyra.
But the most characteristic marine plants (" seaweeds ")
belong to the groups of brown and red algae — so-called be-
cause their cells contain a coloring matter, brown in the one
case and red in the other, masking the green color of the
chlorophyl which is also present. The brown algae include

TEXTBOOK OF BOTANY

the large seaweeds known as kelps, one of which is the very
common rockweed (Fig. 19). A close
relative of the rockweed is Sargassum,
which is torn by storms from the places
where it grows along the American
coast, and is carried out into the ocean
by currents, especially by the Gulf
Stream. Great numbers of the plants
come to rest in that part of the north
Atlantic which is most free from cur-
rents — the so-called "Sargasso Sea."
Certain kelps grow to be several
hundred feet in length; they are
therefore among the longest of living
plants, although of course the bulk of
such a plant is not equal to that of
a large tree. Kelps have been used
for many years as soil fertilizers on
the coasts of the Scandinavian coun-
tries, the British Isles, France, and
New England. Their value for this
purpose is due chiefly to the large
proportion of potash salts that they
contain. Immense beds of kelps exist

FIG. 19. — The rock-

weed (Fucus), a brown , , „ .,, ,. , TT . ,

alga. At the bottom is alonS the Pacific coast of the United
an irregularly flattened States and Canada, and it is thought
tjiat j^ey will prove a most valuable
r> /• .-> i_

Some of the brown

part that attaches the

plant to the rock or other L

object on which it grows. source of potash.

At various places on the algae supply iodine on a commercial
scale . gome are sources of mannite.
. • • ., r f *

Many brown algae are used for food

in China and Japan, on the Pacific

jsian(js and in the Arctic regions.
... T ' , , ,

None of the red alg^ Srow to be so
large as the great kelps, but many of

branches are bladder-like
swellings which help to
buoy the plant in the
water. In the • swollen
portions at the ends of
the branches, the repro-
ductive structures are
produced.

A POND SCUM 51

them are good-sized plants ; some of them are also used for
food in various parts of the world.

77. The Plankton. — The surface layers of any body of
water, salt or fresh, contain vast numbers of small organisms.
All of these floating plants and animals are spoken of together

FIG. 20. — One of the giant kelps (N ereocystis) .

as the plankton. The number of minute living organisms
present in and near the surface of a lake or river, and the
rapidity with which such organisms grow and multiply, are
almost inconceivable to one who has not made a microscopic
study of such waters. It has been estimated, for example,
that more than 149,000,000 pounds of small plankton organ-
isms are produced each year in the Illinois River; this is

TEXTBOOK OF BOTANY

about fifteen times the weight of all the fish hatched in the
same river in the course of a year. The plankton includes
various one-celled algae more or less like Protococcus, as

well as many species
that form small colo-
nies. Algse as large
as Spirogyra are not
ordinarily thought of
as belonging to the
plankton ; the use of
the term is commonly
limited to organisms
that are microscopic
or but Httle larger.
The plankton algae,
building up their
bodies as we have
seen that Spirogyra
does out of the simple
substances that are
dissolved in the river,
lake, or sea water,
themselves serve as
food for the many
kinds of minute ani-
mals in the plankton.
Both the plankton
algae and the plank-
ton animals in turn are used as food by the larger water
animals, especially the fish, and the latter in their turn are
an important item of human food. We are ourselves con-
cerned, therefore, with anything that affects the number and
the growth of the plankton organisms.

FIG. 21. — A red alga (Dasya elegans).

CHAPTER VI
THE BREAD MOLD

78. Molds. — We know that bread, if allowed to stand for
a time, becomes moldy. Spots, at first small and white or
gray, appear upon its surface. Many of these spots are
covered with a fluffy substance. Under a hand lens, the
fluffy substance is found to be made up of many white or
grayish branching threads. The spots grow rather rapidly,
and in time they may cover the whole surface of the bread ;
their color changes to black, pink, red, blue, or green, and they
take on a powdery rather than a fluffy appearance. The
bread now has a characteristic " moldy " smell, and it grad-
ually loses its firm consistency, changing to a slimy mass.
Some of the changes in the bread are due to the action of
bacteria, which may be present in immense numbers ; but
the fluffy spots consist of fungi of various kinds that are
commonly called molds; they are much larger and more
highly developed than the bacteria and yeasts, and they
live upon the bread, using it as food. Similar mold spots
appear on exposed surfaces of cake, fruits, preserves, damp
leather, or in fact of almost any moist organic substance.

One of the commonest of the molds is Rhizopus nigricans,
often called the bread mold, because it occurs so commonly on
bread, although it appears also on many other substances and
is said to cause a rot of sweet potatoes and of strawberries.
The fluffy mass that we first see on the bread is the body of the
fungus, and the powdery appearance as it grows older is caused
by the presence of its very numerous spores. The older
spots produced on the bread by this mold are black.
53

54

TEXTBOOK OF BOTANY

79. A Mold Plant (Fig. 22). — We can see with the aid of
a hand lens that the body of the bread mold is made up of
threads, somewhat like those of Spirogyra, but branching
abundantly, light-colored when young and darker or almost
black when old. If we pick off a piece of a young mold
plant and examine it under the. microscope, we find that the

FIG. 22. — Part of a bread mold plant; a, downward-growing branches
which obtain food for the plant; b, a horizontal branch; c, young spore
sacs, borne at the ends of upright branches ; d, an older spore sac contain-
ing ripe spores; e and /, broken spore sacs from which the spores have
escaped ; in /, the internal dome-shaped wall has collapsed.

threads are not divided by cross walls. In fact, the whole
plant — making, with all its branches, a large, interlacing struc-
ture — is, at least while it is comparatively young and
growing rapidly, a single cell. This cell is much larger as well
as more complex in form than any cell we have yet studied.
The branches of the plant are of two kinds : horizontal ones
(Fig. 22,6) which grow upon or near the surface of the bread,
and others that grow in groups from the horizontal branches
downward into the substance of the bread (Fig. 22, a).

THE BREAD MOLD 55

Each group of downward branches is connected by horizontal
branches with neighboring groups.

Within the cell wall which covers the plant is a colorless protoplasm
that includes many vacuoles of different sizes, and often also yellowish
fat drops, similar, except for their color, to the vacuoles. Frequently
the protoplasm is seen to be in motion. Scattered through it also
are many nuclei ; but they are too small to be seen in the living plant.
The presence of many nuclei in a single cell is another important differ-
ence between the bread mold and any of the plants previously studied.
As the mold plant grows older, and especially when it is forming spores,
cross walls appear here and there in various places, dividing the plant
into several or many cells, each of which still commonly contains
many nuclei. The same sort of cell division may occur earlier in the
life of the plant if the supply of water becomes insufficient, or if for
any reason conditions are unfavorable for growth.

80. Food. — Since it has no chloroplast and no chlorophyl,
the bread mold cannot use carbon dioxid and water to build
up carbohydrates, and, like the bacteria and the yeasts, it
must obtain its carbohydrate food ready made. Like the
yeast, the bread mold is a saprophyte — that is, it lives upon
dead organic materials. The carbohydrate food present in
bread is chiefly starch ; there is also some cellulose and there
are probably traces of sugar. The starch, as well as the pro-
teins which are present in the bread, must be digested —
that is, must be changed by enzyms into simpler substances
that can be dissolved and so taken in by the mold through its
wall. The bread also supplies water, of which the mold
requires a great deal, and probably small amounts of other
food substances as well. When more carbohydrate food is
taken in than the plant can use at once, the surplus is trans-
formed into fat. Fat is a very common reserve food in fungi,
taking the place of the starch that is so abundant in most
green plants.

81. Spore Formation. — After the mold has been growing
for some time and has reached a considerable size, branches
of a third kind begin to appear. These are stouter than the

56 TEXTBOOK OF BOTANY

branches we have already studied ; they start from the hori-
zontal branches at about the same places at which the groups of
downward branches start, but they grow upward into the air.
After one of these upright branches has grown for a time, its
upper end begins to swell, forming a globular body that will
become a spore sac (Fig. 22, c). When the spore sac has
reached nearly its full size, a dome-shaped wall is formed in
it, dividing it into a central portion and an outer portion.
The protoplasm (including cytoplasm and nuclei) which fills
the outer portion of the spore sac now cuts itself up into a
large number of small cells (Fig. 22, d). When the spores
are ripe, the outer wall of the spore sac breaks (Fig. 22, e, /),
and the spores are scattered. If. a spore falls upon moist
bread or some other substance on which the mold can live,
it begins to grow into a new plant. The spores are so light
that they are easily carried
about by currents of air. Like
the spores of bacteria and of
yeasts, they are present in the
air practically everywhere that
human beings live, and this is
why Rhizopus nearly always
appears on moist bread that is
exposed to the air.

82. Germination of the
Spores. — A mold spore can

7)P!»

live for some time in a dry

place without germinating.

FIG. 23. — A, a ripe spore of But if it falls in a place

the bread mold, much enlarged, favorable for growth, it SOOn

B, C, D, stages in the development •, , • , •,

of spores into young plants. develops into a new^ plant.

Germination begins with the

appearance of a swelling at one side of the spore (Fig. 23, B) ;
this swelling grows longer and begins to look like a branch
of a mature plant. Sometimes two or more outgrowths

THE BREAD MOLD 57

appear on different sides of the spore, and each grows into a
part of the new plant. Soon branches appear upon these
outgrowths (Fig. 23, C, D), and by continued growth and
repeated branching the condition of the mature plant is
reached.

83. Asexual Reproduction. — We have seen that the cells of Spiro-
gyra reproduce by division, but that cell division does not result, at
least directly, in a reproduction of the Spirogyra plant. Spore forma-
tion in the bread mold is brought about by cell division which, like
cell division in Spirogyra, increases the number of cells; but the spores
of the mold are a special sort of cells, each of which grows as soon as
possible into a new plant. Thus this particular kind of cell division
by which the mold spores are formed is a means of reproduction of the
plant as well as of the individual cells. Reproduction by means of
spores is commonly called asexual reproduction, to distinguish it from
the union of gametes, which is called sexual reproduction. We see
that the essential thing in asexual reproduction is a cell division; but
that in sexual reproduction the essential thing is a cell union.

84. Sexual Reproduction. — The bread mold has also a method
of sexual reproduction similar in some respects to that of Spirogyra.

FIG. 24. — The development of the gametes of the bread mold and
their union to form a zygote.

The two gametes that unite are always borne on two separate plants
which belong to two different races or strains, spoken of as plus and
minus strains. As a rule, when we find Rhizopus growing on bread
all the plants belong to one strain. Two plants of the same strain
growing together will not form gametes, and this is why we do not
often see the sexually produced zygotes. But when two plants, one
of a plus and one of a minus strain, grow so close together that a branch
of one comes in contact with a branch of the other, on each of these
branches a projection appears.

TEXTBOOK OF BOTANY

0

These two projections (which are themselves really short branches)
grow in length, their ends being in contact all the time (Fig. 24, A, B);
they look much like the projections which form the conjugation tube
of Spirogyra. Next, the end of each projection becomes a separate
cell cut off by a wall from the rest of the projection (Fig. 24, C). The
two short end cells thus formed are the gametes. The walls of the
two gametes are now dissolved where they touch each other, and the
gametes unite to form a single cell — the zygote. The zygote becomes
a large, spherical cell with a thick wall, still attached by short branches
to both the parent plants (Fig. 24, D). Of
the branches which bear the gametes, one is
somewhat smaller than the other, and the
smaller branch usually bears a smaller
gamete than the larger one.

85. Germination of the Zygote (Fig. 25).
— The zygote of Rhizopus, like that of
Spirogyra, is a resting cell ; that is, it may
remain for a long time without apparent
change and still be able to germinate when
conditions become favorable for the growth
of the plant. When the zygote germinates,
a swelling appears on one side, much as in
the germination of a spore; this swelling
grows, not into a large, much-branched plant
like the one we have studied, but into a short
stalk, which, like the upright branches of the
ordinary mold plant, bears a spore sac. The
spores produced in this spore sac germinate
in turn into branched plants exactly like the
plant that we studied first. Thus, instead
of developing a single ordinary plant from each zygote, as Spirogyra
does, the mold forms many spores almost at once, and so a great many
mold plants result from the germination of a single zygote.

86. Advantages of Spore Formation. It is plain that this
method of quickly multiplying its numbers after a zygote
germinates is very useful to the mold, especially as the zygotes
are scattered- about and subjected to all kinds of unfavorable
conditions, and it is probable that only a small proportion of
them ever germinate. The same sort of advantage to the
plant results from the production of spores throughout its

FIG. 25. — Germination
of a zygote of Rhizopus.
After Brefeld.

THE BREAD MOLD 59

life. Saprophytic plants like the mold, and parasitic ones
like many of the other fungi, are likely to produce great
numbers of spores. This habit enables them to multiply
their numbers quickly when food of the sort that they need is
plentiful ; and it gives them a much better chance of living
over the unfavorable periods that are bound to come to such
plants, when the food that they need is not to be had. On
the other hand, plants which, like Spirogyra, live under
conditions that are likely always to be much the same, at
least at the same season of the year, have much less need of
a means of rapid multiplication at special times. This is
why Spirogyra succeeds as well as it does without producing
any cells that correspond to the spores of the mold.

87. Relatives of the Bread Mold. — Rhizopus is one of a group of
fungi which are commonly called the black molds. Other members of
this group are Mucor, whose species are common, especially on soil ;
Pilobolus, which grows on dung ; Phycomyces, living on old bones and
other oily organic matter ; and Sporodinia, found on decaying mush-
rooms. All the black molds are characterized by a one-celled body
made up of branching threads and by a method of sexual reproduction
closely similar in each case to that of Rhizopus. In most of the black
molds the two gametes of a pair are of the same size, instead of being
different in size as are those of Rhizopus. In Sporodinia and in some
other forms, both gametes are borne on branches of the same plant ;
but in most species they are borne, as in the bread mold, on separate
plants belonging to two different strains. All the black molds pro-
duce large numbers of asexual spores, but these spores are produced
in very different ways in different species. Most of the black molds
are saprophytes, but a few are parasitic upon other fungi.

CHAPTER VII

THE WHEAT RUST

88. The Rusts. — There is a very large group of par-
asitic fungi which cause great damage to the plants on
which they live. Growing inside the tissues of its host plant, a

rust forms masses
of spores which
break through the
epidermis of the
host. But in-
stead of forming
only one kind of
spore, as the
bread mold does,
a single species of
ru st may bear four
different kinds of
spores ; although

not all the rusts
FIG. 26. — A, the upper surface of a barberry

leaf, showing the diseased areas caused by the rust ; actually do bear

the dark dots represent the openings into the cavities SO many. Many

in which spermatia are formed. B, the lower sur- rug^g require two

face of a leaf, showing infected areas and the cluster t

cups hosts, in each of

which a part of

the life history of the parasite is passed. The common
wheat rust, which we are to study, is one that lives for part
of the year upon one host, and then transfers its activities
to a second victim.

60

THE WHEAT RUST 61

89. Spring Stage of the Wheat Rust. — The first plant
attacked by this rust is not the wheat, but the barberry.
The branching threads of the fungus live in the leaves, young
stems, and fruits of the barberry. The threads, made up of
rather short cells attached end to end, grow for the most
part in the spaces between the cells of the host ; but they
give off, here and there, short branches which make their way
by means of a cell-wall-dissolving enzym into the cells of
the barberry. These short branches digest and absorb the
food materials of the host. Sometimes, though not usually,
they kill and absorb the living matter of the host cells them-
selves. More often the growth and division of the host
cells are abnormally stimulated, so that an infected leaf is
swollen, especially on the under side (Fig. 27, A), in the
regions in which the rust threads are most abundant. How-
ever, although such parts become unusually large, the bar-
berry plant as a whole is deprived of much of its food, and
so is more or less weakened. After the rust has become well
established in the barberry tissues, it proceeds to form spores.

90. Spring Spores. — These spores are formed in small
cup-shaped structures. The cups appear most commonly
on the under sides of the leaves of the barberry (Fig. 26, B),
projecting from the surface and just visible to the naked eye ;
but sometimes they grow on the upper sides of the leaves, on
the fruits, or on the young twigs. The cups are formed in
groups, and so are called cluster cups. The part of the leaf
on which a cluster of cups is borne is usually yellowish for a
short distance about the cluster; and the leaf tissues in
this yellow spot die early.

The formation of the cups and of the spores can best be studied
in a cross section of a leaf. At the place where a cup is to appear, a
cushion, composed of fungous threads packed closely together, is
formed beneath the epidermis of the leaf. Then the ends of the threads
turn directly toward the epidermis and grow so as to make a basal
layer of rather large vertical cells (Fig. 27, B), The pressure caused
by the growth of this layer and of the cushion of threads beneath it

62

TEXTBOOK OF BOTANY

finally breaks the epidermis of the leaf. Each cell of the basal layer,
like each of the other cells of the fungus up to this time, contains a
single nucleus. These basal cells become joined in twos by a dis-
solving of part of the walls between each pair of adjoining cells (Fig. 27,
D, a); the two cells of each pair have now become a single cell of ir-

FIG. 27. — A, a section through a portion of an infected barberry leaf
bearing spring spores on the lower surface and spermatia on the upper sur-
face. B, a section through a cluster cup, showing the spring spores. C, a
section through a cavity in which spermatia are being formed. D, the
formation of spring spores : a, the union of two gametes in the basal layer
of the cluster cup; b, the two nuclei of the zygote have divided; c, the
zygote has cut off a two-nucleate cell ; d, the zygote has formed a chain of
spring spores (e) alternating with small cells (/) which will soon disappear.
D after Christman.

regular shape, containing two nuclei. The two nuclei of each such
irregular cell now divide, one of each pair of daughter nuclei passes
to the upper end of the cell, and this end is cut off as a small two-
nucleate cell (Fig. 27, D, b and c). Then the two nuclei left in the
large lower cell divide again, and another small two-nucleate cell is
produced just below the first one.

The process of division is repeated again and again, so that a long
chain of two-nucleate spring spores is formed (Fig. 27, D, d).1 From

1 Really each cell of the chain in turn divides into two cells, of which one (the
upper) becomes a spore ; the lower one remains small and very soon breaks down

THE WHEAT RUST 63

each of the large irregular cells in the basal layer a chain of spores is
produced in the way just described, excepting that the chains of cells
at the very outside of the group remain connected with one another,
and form, not spores, but the outer wall of the cup. The cell unions
that take place at the base of the cluster cup are to be compared with
the sexual unions which we have studied in Spirogyra and in the bread
mold. The cells of the basal layer, therefore, before they unite in
pairs, are gametes, and the irregular cells formed by their union are
zygotes. An important difference, however, lies in the fact that a
zygote of Spirogyra is produced by a cell union and a nuclear union,
but a zygote of the rust results from a cell union only. The rust zygote
proceeds at once to the formation of many spores, and so the chances
for the survival and increase of the plant are greatly improved.

91. Spermatia. — As we have seen, the -cluster cups con-
taining spring spores are borne for the most part on the under
surface of the barberry leaf. On the upper surface of the leaf,
and usually just opposite a group of cluster cups, there
appears a yellowish spot in the midst of which are a number
of small dark dots (Fig. 26, A}. One can see in a cross
section of the leaf (Fig. 27., A, C) that each dot corresponds
to an opening in the upper epidermis of the leaf. Before
this opening was made, the fungous threads formed a cushion
below the epidermis, such as was formed before the appear-
ance of the cluster cup. Then the ends of the threads grew
upward, making a layer of slender, vertical cells whose
growth finally broke the epidermis. Some of the slender
cells grow out through the opening so made ; but most of
them end within the cavity produced by the pushing up
and breaking of the epidermis, and from their ends small
rounded cells (spermatia) are cut off one after the other.
The spermatia look like spores, excepting that they are
much smaller; but they never, so far as has been dis-
covered, develop into new plants ; and they seem to be
quite useless.

and disappears. These disappearing cells are to be seen only between the younger
spores (that is, the lower ones in each row), and even there they are often hard to
find.

64 TEXTBOOK OF BOTANY

92. Infection of the Wheat. — For some reason the spring
spores produced on the barberry cannot infect a barberry
plant, but they can infect wheat. If one of these spores,
carried by the wind or other agency (sometimes, perhaps, by
an insect), falls upon a young wheat plant, the conditions of
temperature and moisture being favorable, it swells and
pushes out a projection (a germ tube). The germ tube grows
into a thread which makes its way along the surface of the
wheat leaf or stem until it reaches an air-pore. The thread
swells at a point just above the pore ; from the swelling a
new branch grows down through the pore, and in the spaces
between the cells of the host it develops into a branching
plant body which may infeet a large area of the wheat plant.
Short branches of the fungus grow into the cells of the wheat,
whose food supply is used by the parasite in the same way
as was that of the barberry, cells. The portion of the rust on
the outer surface of the host (the germ tube and swelling)
soon withers and disappears.

93. Summer Spores. — As soon as the fungus is well
established in the wheat tissues, it proceeds to form spores

of a second kind.
Here also the first
step toward spore
formation is the
appearance of a
cushion of fun-
gous threads be-
neath the epider-
FIG. 28. — Section through a sorus on the wheat, . ,. , ,
in which both one-celled summer spores and two- 1
celled winter spores are being formed. then the threads

grow outward to

form a layer of rather broad parallel basal cells, which push
directly against the epidermis of the wheat and finally
break it. The break in the epidermis is irregular in shape
and often large ; it is called a sorus. From the outer end

THE WHEAT RUST

of each basal cell now grows a slender stalk; the end of
this stalk is cut off by a wall, swells, and becomes an. egg-
shaped summer spore (Fig. 28). When the summer spore is
ripe, it is easily broken away.

After the first summer spore has begun to develop, a second,
and sometimes a third and a fourth, each with its stalk, may
be formed from the same basal
cell. Thus a single sorus, con-
taining many basal cells, con-
tinues for some time to produce
new summer spores. The sum-
mer spores seen separately have
a yellowish color ; the sorus con-
taining a mass of them appears
orange, and it is for this reason
that the appearance of the sori
on the wheat is spoken of as
the "red rust." The summer
spores, if carried to other wheat
plants, may germinate (Fig. 29,
A), causing new infections in the
same way that the first infection
of the wheat was caused by the
spring spores. Thus the summer
spores carry the infection from
one wheat plant to another. If
the season is favorable to the
growth of the rust, the disease

may spread in the course of the summer from a few plants
that were infected by the spring spores throughout a whole
field of wheat.

94. Winter Spores. — As the end of the growing season
approaches, the rust produces spores of still another sort.
These are borne in' the same kind of sori as are the summer
spores, and indeed some of the earliest winter spores often

FIG. 29. — A, a germinated
summer spore ; the young plant
growing from it may infect a
wheat plant. B, a germinated
winter spore; the small plant
which has grown from it is
bearing sporidia.

66 TEXTBOOK OF BOTANY

appear mixed with summer spores in the same sorus (Fig. 28).
But in the sori that are formed later, only winter spores are
produced. Each winter spore has a slender stalk and con-
sists of two cells whose walls are thicker and darker than
those of the spring and summer spores. A sorus containing
only winter spores is black, and so the appearance of these
sori is spoken of as the " black rust." Thus the " red rust "
and the " black rust " are different stages in the history of
the same disease.

Each cell of a young winter spore contains two nuclei (as does the
summer spore) ; but as the spore ripens, the two nuclei in each cell
unite, so that the mature spore consists of two one-nucleate cells.
Since the two nuclei which are present at first in each cell of the winter
spore are direct descendants of the two nuclei of the spring spore, the
union of nuclei in the winter spore is really the completion of the sexual
process which began with the union of cells at the base of the cluster
cup just before the formation of spring spores. Whereas in Spirogyra
nuclear union follows closely upon the cell union which produces .the
zygote, cell union and nuclear union in the rust are separated by a
whole generation of the rust plant — that generation, namely, which
lives in the tissues of the wheat.

95. Germination of Winter Spores; Sporidia (Fig. 29, E).
— The winter spores are adapted by their thick walls and
probably by the comparatively dry condition of their pro-
toplasm to endure unfavorable conditions. They represent
a stage, therefore, in which the rust may live through the
winter. They remain upon the ground or the stubble, or are
scattered widely in the harvesting and threshing of the grain.
In order to produce new plants, they do not require, as the
spring and summer spores do, a particular host upon which to
grow. On the contrary, they germinate wherever they may
be when warm weather returns in the spring, provided
sufficient moisture is present. Each cell of the winter spore
can put out a germ tube and develop a new plant, so that the
" winter spore " is practically two spores that have remained
together. The plant that grows from each cell of the winter

THE WHEAT RUST 67

spore is small, consisting of (usually) four cells. From
each cell of this small plant a short branch grows ; the outer
end of the branch swells, is cut off by a wall, and becomes
a spore of a fourth kind which is called a sporidium. A rust
sporidium, carried to a leaf, young stem, or flower of a bar-
berry, may germinate there. The germ tube makes its way
directly through a surface cell (not as a rule, at least, through
an air-pore) and so infects the barberry.

96. Outline of the History of the Wheat Rust. — We see
that the complete life story of the wheat rust includes three
different plants, which are really so many distinct generations.
These three plants produce four different kinds of spores
(or, if we include the spermatia, five spore-like structures).
The plant living on the barberry bears spring spores (and
spermatia) ; the plant living on the wheat bears summer
spores and winter spores ; and the small • plant developed
from a winter spore bears sporidia.

97. Damage Done by the Wheat Rust. — The wheat plant
is weakened because the food stored in its cells for its own use
is taken by the rust. An infected plant does not grow to its
normal size, its grains are small and shriveled, and so the
wheat crop is injured both in quality and in quantity. The
rust occurs in all parts of the world where wheat is grown,
and in some regions the cultivation of wheat has been given
up because of the prevalence of the disease. It is worst in
damp regions and in years when there is much rain. The
loss in the United States in a single year from wheat rust alone
has been estimated at $67,000,000.

98. Prevention of Wheat Rust. — Although this disease
has been known and studied for years, it is still most difficult
to deal with. No practicable method has been found for the
direct treatment of infected wheat plants. The disease can
be partly checked by removing all barberries from the neigh-
borhood of wheat fields. Since the young wheat plant is
infected by spores from the barberry, and since neither winter

68 TEXTBOOK OF BOTANY

spores nor sporidia can infect the wheat, it would seem that
the removal of all the barberries within a considerable dis-
tance would make the infection of the wheat impossible.
But, as a matter of fact, serious epidemics of wheat rust occur
year after year in various parts of the world — for example,
in Australia and in some of the northwestern United States
— in which barberries are very rare or even unknown. So
it would seem that the rust is able to survive the winter in
some other form than in that of the winter spore. The most
probable explanation of this fact seems to be that some of
the summer spores live through the winter and infect the
young wheat plants in the spring. .The summer spores
are thin-walled, and apparently most of them are short-
lived and easily killed ; but a few are longer-lived and
remain able to cause infection for some months after their
production.

Another explanation for the survival and reappearance of
the rust in some cases is found in the fact that in warm regions
it can live and continue to form summer spores during the
winter. So, when new wheat plants appear in the spring,
there are fresh spores ready to infect them. The spread
of the rust from warmer to colder regions during the growing
season of the wheat may be brought about by the wind ; for
it has been shown that summer spores can be carried by the
wind to great distances. The most promising method of
combating the wheat rust seems to be the raising of varieties
of wheat that are rust-resistant — that is, are little or not at
all affected by the rust. The varieties of durum or macaroni
wheat, which are much -cultivated in Mediterranean countries,
are very resistant to rust, and they are being raised with some
success in certain American states. Attempts are also
being made, by crossing these with American varieties which
are susceptible to rust but are valuable in other respects,
to secure new resistant forms ; and already some very
promising results have been attained.

THE WHEAT RUST

69

99. Other Rusts of Cereal Grains. — As a group, the rusts have

been remarkably successful in adapting themselves to a parasitic life

— partly, no doubt, because of ^___

the number and variety of

spores that they produce. So

successful have tney been that

most of the species of seed-
bearing plants are attacked

each by one or more species of

rust. Some rusts seem to have

become so specialized as to be

able to live upon only one or a

very few hosts ; in other in-
stances, a single rust may

attack a considerable number

of hosts.1 Besides the common

wheat rust which has been

described in this chapter and

which is called Puccinia grami-

nis, there are at least two

other rusts that infect the

wheat. All the other cereal

grains, too, are attacked by

FIG. 30. — A branch of the red cedar
bearing two "cedar apples" — swellings
caused by the presence of a rust — in
the winter condition. After Jones and
Bartholomew.

rusts, some of which cause large

losses. The known grain rusts,

in addition to Puccinia grami-

nis are : the crown rust, one

of whose races or varieties

causes a serious disease of oats ;

the yellow rust, races of which attack wheat, barley, and rye ; the brown

rust of rye ; the brown rust of wheat ; the dwarf rust of barley ; and

1 A word of caution should accompany this statement. In some cases the rusts
appearing upon two or more hosts seem to be exactly alike, but the spores produced
by the rust upon one host will not infect the other host, and vice versa. Thus, there
are rusts on rye, oats, barley, and several common grasses which appear to be the
same as that upon the wheat and which are called by the same name (Puccinia
graminis). But the summer spores of the wheat rust will not infect the oat at all,
or only with great difficulty, and in the same way summer spores from Puccinia
graminis on oats will not infect the wheat, although both the rust on wheat .and
that on oats pass their spring stage upon the barberry. These facts have given
rise to the notion of specialized races of parasitic fungi. Two such races may seem
to have exactly the same structure, but they differ in that they have adapted them-
selves in some way to life upon different hosts.

TEXTBOOK OF BOTANY

the Indian corn rust. In the case of each of these -rusts, the summer
stage is passed upon a cereal grain, and the spring stage, where one
has been found, is passed upon an entirely different plant. For ex-
ample, the crown rust of the oat has its spring stage on the buckthorn,
and the spring stage of the corn rust is found on the wood sorrel.

100. Apple Rust. — The fungus that causes this disease
produces its winter spores upon the red cedar (jumper),

FIG. 31. — A " cedar apple " in the spring ; the finger-
like projections are masses of jelly in which the winter
spores germinate. After Jones and Bartholomew.

where it causes the swellings of the twigs and small branches
that are called " cedar apples " (Fig. 30). The cedar tree
is weakened if it is seriously affected, and sometimes it is

THE WHEAT RUST

killed. The winter spores of the rust are formed within the

cedar apple. In the spring the inner part of the cedar apple

becomes soft and sends out finger-like masses of jelly in

which the winter spores germinate (Fig. 31). The small

plants that grow from the winter spores bear sporidia within

and on the surface of the jelly. The sporidia are distributed

by the wind. If they fall upon leaves, flowers, young fruits,

or twigs of the apple, »

they produce an infec- \^

tibn. In a few weeks,

cluster cups begin to

appear, mostly on the

leaves but sometimes on

the fruits or twigs of the

apple (Fig. 32) ; the

spores formed in these

cups, often as late as

August, which correspond

to the spring spores of the

wheat rust, may then

cause a new infection of

the red cedar. No spores

are produced by this rust

that correspond to the

summer spores of the

wheat rust. If the apple

tree is badly diseased, its fruit crop is greatly damaged.

Not only does the .fruit that is directly attacked fail to

develop normally, but the diseased condition of the leaves

affects the nutrition of the tree as a whole, and so indirectly

checks the growth of the fruit.

The disease of the apple trees may be absolutely prevented
by the removal of red cedars from the neighborhood of the
apple orchard. Apparently the fungus has no way of sur-
viving the winter except within the tissues of the red cedar.

FIG. 32. — An apple infected by the
spores produced as a result of the germina-
tion of the winter spores. The spring
spores produced in the little cup-like
structures will infect the red cedar, caus-
ing the formation of "cedar apples."
After Jones and Bartholomew.

72 TEXTBOOK OF BOTANY

If the removal of cedars is out of the question, the disease
can be greatly checked by spraying the apple trees at the
proper times with Bordeaux mixture. It may be largely
avoided also by planting resistant varieties of apple ; but un-
fortunately some of the most valuable varieties are very
susceptible to the rust.

101. Some Other Rusts. — The blister rust of the pine, until re-
cently known only in Europe, passes its summer stage and forms
summer and winter spores upon currants and gooseberries, sometimes
seriously injuring these hosts ; its spring stage causes a very destruc-
tive disease of the white pine. This rust has lately been found in
North America, and it is not unlikely that it will greatly interfere with
the future raising, of white pine for forestry purposes. The fungus
may live for years in the bark of the pine. Its winter spores differ
from those of the wheat rust in being only one-celled. The rose rusts,
differently from the rusts so far mentioned, pass their whole life upon
a single host plant. Their spring spores are borne in irregular son
rather than in cups, and each winter spore consists of a row of several
cells. Some varieties of roses are badly injured by these rusts. The
common orange leaf rust of raspberries and blackberries produces
both spring and winter spores upon the same host ; it has no summer
spores. The asparagus rust also has no summer spores ; it forms its
spring and winter spores on the asparagus. The life cycle of the rust
of mallows and hollyhocks is very short. It has nothing that corre-
sponds to the spring stage of the wheat rust, and no spring spores,
spermatia, or summer spores. Spores are formed that correspond to
the winter spores of the wheat rust. Some rusts, living from year to
year in the tissues of certain trees, stimulate the host plant to the
very rapid production of branches in the infected part, and so cause
the formation of a " witches' broom." Such " brooms " are produced
on the red cedar by relatives of the apple rust.

102. Historical Note. — The notion that the presence of barberries
is in some way harmful to growing wheat was prevalent in Europe as
early as the middle of the seventeenth century. It is said that the
parliament of Rouen in 1660 ordered the destruction of barberries.
Similar laws were adopted in Massachusetts in 1755, in Lippe in 1805,
and in Bremen in 1815. Experiments carried on in the latter part of
the eighteenth century and the early part of the nineteenth in England,
Denmark, and Germany indicated that barberries are in some way
responsible for the occurrence of the wheat disease which was then

THE WHEAT RUST 73

variously called ".blight," "mildew," or "rust." In 1864, De Bary
proved that the rust on the barberry and that on the wheat are differ-
ent stages in the life history of a single fungus. This was the first
case in which two hosts were shown to be necessary to complete the
life history of a fungous parasite. De Bary's results were announced
in January, 1865. In June of the same year, Oersted showed the
connection between the rust on red cedars and that on pear trees.
Since De Bary's discovery, the planting of barberries in grain-raising
regions has been forbidden by law in England and other European
countries, as well as in some American states. Meyen suggested in
1841 that the structures in which the spermatia and the spring spores
are borne are respectively male and female organs. This notion re-
ceived much support. But in 1904, Blackman and Christman dis-
covered the cell unions that occur at the base of the cluster cups, and
so showed that the spermatia do not now act as male cells, whatever
may have been the case in the past. Beginning with De Bary and
his contemporaries, a great amount of study has been devoted to rusts.
Up to 1888, 1225 species of rusts had been described, of which 455
belonged to Puccinia, the genus to which the wheat rust belongs.
In 1897, about 1700 rusts were known, of which over 700 were species
of Puccinia; and in 1904, the number of species of Puccinia alone
had risen to 1226 — as many as the total number of rusts known
sixteen years before.

CHAPTER VIII
A MUSHROOM

103. The Field Mushroom : Vegetative Body. — Among
the largest and best-known fungi are those which are called
mushrooms or toadstools. They are most abundant in damp,

FIG. 33. — TThe field mushroom ; threads and strands of the vegetative
body living in the soil, and various stages in the development of the fruiting
bodies. At the right is a half-grown fruiting body cut lengthwise through
the middle, showing how the veil attaches the margin of the cap to the stalk
and covers the cavity in which the gills are being formed.

shady woods, though some, like the common field mushroom,
live in open woods, fields, pastures, or gardens. Many of
them are saprophytes, obtaining their food from decaying
leaves, wood, manure, and the like ; but some live as para-
74

A MUSHROOM 75

sites on the roots or other parts of living trees. What we
ordinarily call a " mushroom " is merely the part of the
fungus that grows above ground and bears the spores ; it is
the fruiting body of the plant. The vegetative body, like that of
the bread mold or the rust, consists of colorless or whitish
branching threads which live for the most part underground.
Some of them are combined into thicker strands, but these
strands, as well as the separate threads, are delicate and
easily broken when the soil is disturbed. For this reason
we usually see little or nothing of the vegetative body of the
mushroom, excepting some fragments that remain attached
to the fruiting body when- the latter is pulled from the soil
(Fig. 33). The threads, like those of smuts and rusts, are
made up of rather short cells joined end to end. They attach
themselves to particles of dead organic matter with which
they come in contact in their growth through the soil, and
digest such parts of these substances as they can use for food.

104. Fruiting Body. — In the summer or fall, after the
plant has been growing for some time, small knots appear
upon it here and there, near the surface of the soil. These
knots are composed of some of the branches of the fungus
which are beginning to pack themselves more closely together.
Each knot is the beginning of a fruiting body. The threads
composing the knot grow and branch, and so the knot de-
velops into a firm, rounded " button." By further growth
this button develops into the fruiting body of the mushroom
(Fig. 34). It becomes divided into an upper part which is
to form the cap, and a lower portion, the stalk. The margin
of the cap is at first attached to the stalk by a thin membrane,
the veil, which hides the lower side of the cap where vertical
folds or gills are being formed.

When the fruiting body reaches nearly its full size, the
margin of the cap, which until now has been curved down-
ward and inward, begins to spread outward ; this makes the
cap flatter on top, and causes a pull on the veil ; the veil is

TEXTBOOK OF BOTANY

torn irregularly, part of it going with the margin of the cap
but the greater part remaining attached to the stalk in the
form of a ring. The breaking of the veil leaves the gills on
the lower side of the cap uncovered. The gills hang down-
ward; they extend, somewhat like the spokes of a wheel,

FIG. 34. — The fully developed fruiting body of Psalliota arvensis,
closely related and very similar to the common field mushroom.

from the central part, where the cap is attached to the stalk,
to the outer margin of the cap ; there are also short gills,
between the longer ones, which reach to the outer margin of
the cap but not to its center. The cap varies in breadth
from two to six inches ; its top is white, cream -colored, or
brownish ; it bears many fine, silky hairs, and often some
small brownish scales. The flesh of the cap is white, turning

A MUSHROOM

77

pink if broken. The gills are at first flesh-colored or pink,
gradually changing, as the fruiting body grows older, to dark
brown or black. The stalk is white, and from two to four
inches high.

105. Structure of the Fruiting Body. — In a thin section of the
stalk, examined under a low power of the microscope, one sees many
cells of different shapes. From the way in which the fruiting body
has been developed, we know that

these are the cells of the separate
threads that make up the fruiting
body, cut across in various ways.
Such a structure as this, composed
of threads closely packed together, is
sometimes called a false tissue, to dis-
tinguish it from the true tissues which
make up the bodies of the higher
plants. The cap of the mushroom is
composed likewise of a false tissue.
A section through the cap which cuts
a gill crosswise shows how the spores
are formed (Fig. 35). Each surface
of the gill is made up of a layer of
rather long cells that are perpendicu-
lar to the surface. Some of the cells
of this layer are rather slender ;
others, when they reach their full

size, are much broader. Each of the way in which spores are formed,
broad cells of the surface layer is a

basidium. From the end of each basidium four slender projections
grow out ; the outer end of each projection swells and is cut off by a
wall, so becoming a spore.1

106. Distribution and Germination of Spores. — When the
spores are ripe they are shot off from the short stalks on which
they were borne. This shooting seems to be caused by a
sudden bulging of the wall at the end of each stalk. By
this means the spores are thrown far enough so that they may
fall without touching any of the neighboring basidia. Being

1 In some cultivated varieties (perhaps all) of the field mushroom, and occasion-
ally in wild races, each basidium forms only two projections and two spores.

FIG. 35. — A, section through
a gill, showing the arrangement
of threads and basidia. B, a
group of basidia of different ages,
showing their attachment to the
threads of the fungus, and the

78 TEXTBOOK OF BOTANY

very light, they are caught by currents of air as soon as they
have fallen below the lower surface of the cap in which they
were borne, and are scattered, often probably to great dis-
tances. The spores of some kinds of mushrooms are dis-
tributed by flies and other insects, which, attracted by the
odor of the decaying mushrooms, carry away great numbers
of spores upon their bodies. If a spore falls in a favorable
place it soon germinates, developing into a branching thread
in much the same way as does a mold spore, excepting that
cell divisions occur so that the thread and its branches are
made up of short cells.

107. Length of Life. — Although the fruiting body lasts
but a few days, the vegetative body of the mushroom may
live within the soil for a long time — even for many years —
each branch growing at its fonvard end while the older parts
of the plant die away. Perhaps it is because it can live
undisturbed from year to year within the soil that it has not
been necessary for the mushroom to form so many kinds of
spores as the wheat rust, for example, has developed. At any
rate, the mushroom certainly finds in a single kind of spores
a very successful means of reproduction and distribution.

108. Use and Culture of the Field Mushroom. — This
mushroom, which botanists call Psalliota campestris (or
Agaricus campestris), has been known for centuries. Its
usefulness as an article of food was referred to by Horace
(65-8 B.C.), and it was described by Pliny (about 23-79
A.D.). It is still much more widely used as food throughout
the civilized world than any other fungus, and is the only one
that is cultivated on a large scale. Numerous varieties are in
cultivation. Mushroom beds are usually prepared in dark
places and require soil that is rich in organic substances.
The beds are started by means of what is called " spawn,"
which consists simply of masses of rich soil or manure in
which many of the fungous threads are growing. Small
portions of the spawn are distributed through the soil of the

A MUSHROOM

79

new bed, which, if the culture is successful, soon becomes
penetrated in all parts by the growing threads. The fruiting
bodies are gathered when the margin of the cap begins to
break away from the ring.

109. Some Other Mushrooms. — There are many species
that are like the field mushroom in their general characters,
but are distinguished from it and from one another by the

FIG. 36. — The honey mushroom (Armillaria mellea).

color, size, and structure of different parts of the fruiting body.
Often it is very difficult to distinguish related species. The
common honey mushroom (Fig. 36), which is considered one
of the best of the edible forms, produces its fruiting bodies
in clusters, especially about old tree stumps, in late summer'
and fall. The fruiting bodies are somewhat larger than those
of the field mushroom ; they are yellow or yellowish brown,
usually with darker patches on the top of the cap, with a ring,
white to rusty-brown gills and stalk, and white spores. The

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cap is hemispherical at first, later flattened but with a slightly
bulging center. The vegetative threads penetrate the bark
of the roots of living trees, especially of some of the cone-
bearing trees, and between the bark and the wood they mass
together into flat strands that grow upward into the trunk
as well as through the roots. From these strands, separate

ABC

FIG. 37. — Poisonous mushrooms: A, Amanila uerna; the main portion
of the fruiting body emerging from the egg-shaped structure which com-
pletely enclosed it at an earlier stage; a part of this enclosing structure
remains in the form of a cup at the base of the stalk. B, a mature fruiting
body of Amanila pantherina. C, a somewhat younger fruiting body of the
latter species cut lengthwise, showing the ring still attached to the edge of
the cap. Photographs by E. T. Harper.

threads grow into the bark and wood, whose cells are de-
stroyed (rotted) by the fungus ; in time the tree is killed.
'By means of other strands which penetrate the soil -for long
distances, the fungus spreads from tree to tree. The strands
can also live saprophytically in the soil or in the dead wood
at the bases of stumps. Thus the honey mushroom is a widely
spread saprophyte as well as one of the most dangerous

A MUSHROOM

81

parasites of forest trees. Its fruiting bodies grow from the
underground strands as well as directly out of the bark of
killed trees. Another common edible mushroom of summer
and fall is the " shaggy mane " or " inky cap," found on
roadsides and in gar-
dens. Its fruiting
body is white, with
a narrow, thimble-
shaped cap one to
two inches, long, bear-
ing ragged brownish
or yellowish scales
on its upper surface.
The ring is thin ; the
gills are at first white,
but blacken rather
quickly ; after a few
days the whole fruit-
ing body dissolves
into an inky-black
liquid in which the
black spores are im-
mersed.

Some of the most FIG 38 _The fly mushroom
poisonous mushrooms muscaria). One of the most poisonous mush-
belong to the genus rooms known. Photograph by E. T. Harper.
Amanita (Figs. 37 and

38). Amanita phalloides is the "deadly Amanita" or
"death cup" which appears in summer and fall in rich
woods. Its cap and stalk are usually white, sometimes
brownish ; the gills and spores are white. At the base of
the stalk is a cup out of which the stalk seems to grow.
Sometimes, however, the cup is not easy to recognize. A
long, delicate ring is attached about the middle of the stalk
and hangs downward.

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TEXTBOOK OF BOTANY

A related species is the fly mushroom (Fig. 38), which also
has a hanging ring, a cup, and white gills and spores ; but
its cap is red on top with some scattered white scales.
This mushroom grows alone or in groups, in woods of the
most varied sorts. Both of these latter species are so poison-
ous that 50 grams (less than two ounces) of their flesh is a
fatal dose.

Only one who is thoroughly familiar with mushrooms can
be sure of distinguishing the edible from the poisonous
species. The only safe plan, if one is to eat mushrooms at
all, is to become acquainted with a few forms that cannot be
mistaken, and to eat no others except upon the advice of an

expert. The food
value of mushrooms
is small at best, and
it is not worth while
to run the slightest
risk of what may
prove a serious mis-
take. No fungus
should ever be eaten
unless it is young and
fresh and shows no
traces of being de-
cayed or worm-eaten.
110. "Fairy Rings."
— These more or less
regular circles of fruit-
ing bodies, growing in
lawns or pastures, are
produced by certain
species of mushrooms.

The ring-like arrangement of the fruiting bodies results from
the growth of the vegetative threads within the soil year
after year. At first a small area of the soil is penetrated

FIG. 39. — An edible mushroom (Hygrophorus
virgineus). Photograph by E. T. Harper.

A MUSHROOM 83

by the threads, and a small group of fruiting bodies is
formed. As the available food in this part of the soil is
used up, the older threads die and the younger branches
push out into the surrounding soil, where they produce a
new crop of fruiting bodies in a ring about the place where
the first ones grew. The growth outward from the original
center continues from year to year, and each successive ring
of fruiting bodies is a little wider than the preceding ring.

111. Relationships of Mushrooms. — The mushrooms, with some
related forms, are classed as basidium fungi. The rusts are also often
classed among the basidium fungi, because their winter spores, together
with the small, few-celled plants to which the winter spores give rise,
are thought to be comparable with the basidia of mushrooms and with
the projections growing from the basidia that bear the spores. If
this notion is correct, the sporidia of a rust would correspond to the
spores of a mushroom. Aside from the rusts (and the smuts, which
are probably related to the rusts), there are about 12,000 known species
of basidium fungi.

FIG. 40. — Specimens of a bracket fungus (Fomes applanatus). At the left
is shown one with its under surface exposed. Photograph .by E. T. Harper.

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TEXTBOOK OF BOTANY

112. Bracket Fungi. — A rather large class of basidium
fungi, closely related to the mushrooms, includes those that
produce the familiar " brackets " upon the sides of trees,
especially dead trees. A common member of this class is
Fomes applanatus (Fig. 40), whose brackets are flat, rather
thin, and sometimes very broad. The lower surface is white

FIG. 41. — A bracket fungus (Fomes applanatus). A, a fruiting body
cut so as to show the layers of which it is composed, each the growth of a
single year. B, a portion of the lower surface of a fruiting body enlarged,
showing the pores inside which spores are formed.

when fresh, but turns brown if bruised. The tendency to
turn brown is sometimes made use of in sketching by means
of scratches upon the white surface. The brackets are the
fruiting bodies of the fungus. They have no:gills; but the
flesh of their lower surfaces is penetrated by many very fine
pores (Fig. 41). The inner surface of each pore is lined with
a layer of basidia, each of which as a rule, like the basidia

A MUvSHROOM

of most of the mushrooms, bears four spores. The fruiting
body of Fomes lives and grows from year to year, forming hew
spores each year. But the fruiting bodies of some other
bracket fungi, such as the sulphur mushroom, a large, yellow,
quickly growing form that is soft and edible when young,
die after bearing one crop of spores. The branching threads
that make up the vegetative body of a bracket fungus live
in the tissues of the trees upon which the fruiting body
appears. Many species of bracket fungi live on dead trees ;
they are saprophytic. But
others are parasitic ; they
enter the host tree through
wounds, cause a decay of
the wood, and finally kill
the tree. .

113. Puffballs(Fig.42).
— These are still another
class of basidium fungi
whose basidia are entirely
enclosed within a rounded
mass of tissue which either
lies close to the ground or

is raised upon a short stalk. The largest of the group is
the " giant puff ball," specimens of which sometimes reach a
diameter of one and one-half or two feet. When young,
the flesh of this puff ball is firm and white, and it is then
edible. As it grows older, the inner part becomes darker
because of the formation and ripening of the spores. Finally
the interior consists of a mass of dark-brown or black spores
which escape through cracks in the wall of the puffball.

FIG. 42. — A puffball (Scleroderma

vulgar e) .

CHAPTER IX
A MOSS

114. Mosses. — Although none of them are large plants,
some of the mosses grow in such great numbers that they are
rather conspicuous features of the earth's vegetation. On the
whole, they have not been so successful in the struggle for

FIG. 43. — A, Funaria hygrometrica : a, the sexual plant; b, the asexual
or spore-bearing plant, attached to the sexual plant. B, a single leaf of
Funaria. C, upper end of a male plant, showing how the sex organs are
borne. C after Sachs.

existence as. have the seed-bearing plants ; and perhaps this
is the reason why mosses have adapted themselves to condi-
tions that are not favorable for larger and more highly de-
veloped plants. Thus we find mosses in very cold regions
86

A MOSS 87

where otherwise only a few much simpler plants can live ; on
the faces of rocks, where food material is scanty ; on decay-
ing wood, and the trunks of living trees ; on the soil of deeply-
shaded forests ; in shallow water, and in bogs and marshes.
Some mosses, like the one we are to study, can endure long
dry spells and can resume growth upon the return of moisture.
Not all mosses are adapted to all of these different condi-
tions ; but each sort of location has its characteristic species.

One of the commonest mosses is Funaria hygrometrica
(Fig. 43, A), which is selected for the present study. It
grows on dry or well-drained soil, on roadsides, in open
fields, gardens, and waste places. When it is fruiting it may
be recognized by its very numerous, reddish, curved, pear-
shaped spore sacs, which are borne on slender, twisted, red
stalks.

115. The Moss Plant. — What is commonly thought of as
a moss plant has an upright stem which bears green leaves and
colorless or brownish, hair-like rhizoids. A great difference
between the moss and any of the fungi or algas is in the fact
that its body is divided into stem and leaves. This upright
plant is especially well adapted to secure light, carbon dioxid,
and oxygen. The stem, supports the leaves in a position
favorable for their work, and conducts food substances from
place to place within the plant. For these purposes, the stem
has become a compact, cylindrical structure. It is more or
less green because its outer cells contain some chlorophyl,
but for the most part the manufacture of carbohydrates is
carried on in the leaves, and only a small part of this work
is done in the stem. Besides leaves and rhizoids, the stem
bears, usually near its base, occasional branches. A leaf
(Fig. 43, B) is the part of the plant that is chiefly concerned
with the manufacture of food substances, particularly of
carbohydrates. It has a midrib, made up of long, slender
cells. The rest of the leaf, to right and left of the midrib, is
composed of a single layer of green cells.

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TEXTBOOK OF BOTANY

The rhizoids are outgrowths from sarface cells of the stem,
chiefly from its lower part. Each rhizoid is a branching row
of cells. For the most part, the rhizoids grow downward into
the soil, anchoring the plant and absorbing from the soil the
water and other substances which the plant can use as food.
For the moss, as well as for most ferns and seed plants, the
soil is the source of supply of practically all the food that is
received from outside, excepting the carbon dioxid which
comes directly from the air.

116. Sex Organs. — The sex organs of mosses are borne
in groups, in the midst of a cluster of leaves at the end either of

the main stem or of
a branch. In some
mosses, male organs
(antherids) and fe-
male organs (arche-
gones) occur in the
same group ; in
other mosses they
are separate, but
groups of antherids
and groups of arche-
gones are borne on
different branches
of the same plant ;
and in still other
cases the separate
groups are produced
on different plants.
In Funaria the gen-
eral rule seems to
be that a group of
antherids appears at the end of the main stem (Fig. 43, C}.
and a group of archegones at the end of a side branch ; but
sometimes the female branch is separated and becomes a

FIG. 44. — A , an archegone of Funaria ; e, the
egg. B, an antherid. C, one of the hair-like
structures growing among the antherids.

A MOSS 89

small independent plant. Between the antherids are short,
hair-like rows of cells (Fig. 44, C), the end cell of each row
being larger than the others. Similar structures are found
also in the clusters of archegones, but the end cells of these
sterile hairs are no larger than the other cells.

117. Formation of Gametes. — An archegone (Fig. 44, A) is a
long, many-celled organ in whose basal part is a single female gamete,
here called an egg. Above the egg is a long narrow neck, surrounding
a canal filled with a thick, sticky liquid, which leads from the egg to
the open end of the neck. An antherid (Fig. 44, B) has the shape of
a rather slender sac. Its outer part is composed of a layer of flat

FIG. 45. — A, an antherozoid just escaped from the antherid. B, a swim-
ming antherozoid, freed from the surrounding sticky substance.

cells ; inside are produced many hundreds, perhaps thousands, of
antherozoids (Fig. 45), which are very small male gametes, each with
a slender body and two long vibrating hairs. If a drop of water is
placed upon a male head, the antherids that contain mature anthero-
zoids burst, and the mass of antherozoids oozes out into the water.
Each one can be seen moving about within a drop of a clear liquid
which is enclosed in a denser, sticky substance. In time this sticky
substance is dissolved, and the antherozoids swim about freely in the
water.

118. Union of the Gametes. — Since an antherid bursts only when
it is moistened, the antherozoids are most likely to escape at the time
of a rain, or possibly of a heavy dew. There must be water about
the archegone also if an antherozoid is to swim to the archegone and
enter its neck. When, as in Funaria, eggs and antherozoids are pro-
duced on distinct branches, some outside agency must carry the an-
therozoids to the female head. Probably they are carried often by
the splashing of raindrops from branch to branch or from plant to

go TEXTBOOK OF BOTANY

plant ; sometimes they may be carried by insects. In some way,
at any rate, antherozoids reach the female head ; and, swimming
about here, some of them come into the neighborhood of an archegone
and immediately swim to the opening of the neck. They do this
because a substance is given off from the archegone which serves as
a stimulus to the antherozoids ; they swim toward the point from
which the stimulating substance comes, and many antherozoids thus
attracted may swarm about the mouth of the archegone. Some of
them enter it and swim down the canal, through the liquid which
fills it, and finally one antherozoid unites with the egg. Since this
union of antherozoid and egg occurs inside the archegone, from which
the egg (and the zygote as well) cannot escape, it follows that the new
plant which is to grow from the zygote must begin to develop within
the archegone.

119. Germination of the Zygote. — Germination occurs
very soon after fertilization. As a result of the growth of
the zygote and of a series of cell divisions, a long, slender
embryo is formed. The lower end of the embryo grows down
through the base of the archegone into the tissues of the stem
of the parent plant. The growth of the new plant inside the
archegone seems to stimulate some of the cells of the latter
to renewed growth and division, and for a time the lower part
of the archegone grows rapidly enough to keep pace with the
development of the embryo. But after a time the growth
of the embryo becomes more rapid than that of the arche-
gone ; the latter is now broken, and the greater part of it is
carried up on the top of the embryo (Fig. 46, A}. This cap, •
formed from the archegone, remains for a time, but sooner
or later it falls off. The lower end of the embryo remains
imbedded in the tissues of the parent plant.

120. The Spore-bearing Plant (Fig. 43, A, b). — As the
new plant continues to grow, its upper portion becomes
thicker and develops into a spore sac ; this is supported on a
long, slender stalk. It is by means of the lower end of the
stalk, which' is imbedded in the tissues of the parent plant,
that the new plant absorbs water and other food substances
from the parent. The upper end of the stalk, where it is

A MOSS 91

attached to the spore sac, is somewhat enlarged ; many of
the cells of this part contain chlorophyl, and so can make
carbohydrate food.

The spore sac (Fig. 46, B) has a rather complex structure, but the
important thing for us to note is that the spore-bearing part is in the
form of a hollow cylinder, and that inside and outside this spore-bear-

FIG. 46. — A , the upper end of the spore-bearing (asexual) plant of
Funaria, still carrying the cap (c) which was formed from the archegone.
B, a spore sac (as seen in lengthwise section) from which the cap has fallen;
/, the part of the sac which will form the lid; sp, spore-bearing region;
st, enlarged upper end of the stalk. C, two teeth from the upper end of the
spore sac. B after Sachs.

ing region are various layers and groups of cells which make and store
food, and which have nothing directly to do with spore formation.
Many of these food-making cells, like those in the upper enlarged part
of the stalk, contain chlorophyl. Since so many cells in the spore sac
and in the stalk can manufacture food, this spore-bearing plant is not
wholly dependent upon the parent plant to which it is attached. How-
ever, since it is not directly connected with the soil, the spore-bearing
plant must take from the parent its whole supply of water and of the
other food substances that come from the soil ; to this extent, there-
fore, it is parasitic upon the parent plant. The spore sac is curved ;
the upper part of the stalk also bends as the sac becomes mature, so

TEXTBOOK OF BOTANY

that the upper, broader end of the spore sac is turned downward. This
upper end forms a lid which drops off when the spores are ripe. But
the falling of the lid does not leave entirely uncovered the cavity in
which the spores lie ; for attached to the margin of this cavity are
two circles of teeth (Fig. 46, Q.

In moist weather the teeth bend inward, closing the mouth of the
cavity and so preventing the escape of the spores as well as the entrance
of water into the spore sac. In dry weather the teeth curve outward,
and through the open spaces between them the spores may sift out.
Because of the presence of the teeth and of their changes in position,
the spores are scattered a few at a time ; thus, the chances are increased
that some spores at least will land in a convenient place and under
conditions favorable for germination. The spores are much like those
of fungi excepting that they contain chloroplasts.

121. The Protonema. — A moss spore, falling upon moist
soil or upon a moist stone, brick, or piece of wood, germinates

by pushing out
a projection that
grows in length
and is soon di-
vided by a cross
wall. As the
young plant con-
tinues to grow,

c / : . '•r^~r7r^:/?^>^"^-%/ more cross walls

are formed ; the
plant now con-
sists of a row of
cells arranged
end to end (Fig.
47, B). A sec-
ond projection
often grows out
from the oppo-
site side of the
spore and develops into a part of the same plant. The plant
branches freely and looks much like a branching green alga

FIG. 47. — A, spores of Funaria. B, a young plant
developed from a germinating spore ; this plant grows
into the protonema (C) ; b, a bud of the protonema
which will develop into an upright leafy branch (or
"moss plant").

A MOSS 93

(Fig. 47, C). This alga-like plant is called a protonema.
Some short green branches of the protonema grow upright,
instead of creeping as the longer branches do. Other
branches, losing their chlorophyl, push downward into the
soil or into the crevices of the substance on which the
protonema is growing ; these colorless or brownish branches
are rhizoids. The protonema grows and branches in this
way for some time ; but sooner or later a bud appears which
develops, not into a thread-like branch, but into a rounded
group of cells ; and this group of cells grows into an upright
branch or stem that bears leaves and rhizoids. This upright
branch is in fact exactly like the plant with which we began
the study of the life of the moss. Since a single protonema
may bear several of these leafy branches, it might be more
accurate to consider the protonema together with all the
upright branches growing from it as a single plant ; but as
the protonema dies sooner or later, each leafy branch comes
to be actually a separate plant, and so it is most convenient
to speak of it in that way.

122. The Two Generations of the Moss. — The whole life
of the moss divides itself naturally into two parts. The first,
beginning with the spore, includes the protonema and the
leafy branches or plants which grow from it ; in this part of
the life cycle the gametes (egg and antherozoid) are formed.
The second part of the history consists of the small plant
which grows from the zygote, and which in turn bears spores.
As we have seen, this spore-bearing plant is parasitic upon
the larger one which bore the egg, but it is none the less a
distinct plant. These two divisions of the life of the moss
are two distinct generations; the longer-lived one, in which
gametes are produced, is the sexual generation; the shorter-
lived one, in which spores are produced, is the asexual genera-
tion. In tracing the history of the moss, we must follow
through these two generations in order to return to the point
at which we started ; so this history may be represented, as

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TEXTBOOK OF BOTANY

in Figure 48, by a circle with two main divisions. The
formation of spores by the asexual generation of the moss
results in a rapid increase in the number of plants as well as

in a wide distribu-
tion of the species.
Something of this
sort seems to be
necessary, for the
moss can produce
only a small num-
ber of eggs, which
are confined within
the archegones and
whose fertilization is
not at all certain.
So, if the moss de-
pended entirely upon
sexual reproduction,
the chances for its
continued existence

would be comparatively slight. The occurrence of two very
different generations in the life of the moss is not unlike
what happens in the case of the bread mold, whose zygote
develops into a small plant quite different from the one that
produced the gametes ; and this small plant in turn bears
spores, each of which may grow into a plant that produces
gametes.

123. Other Mosses. — There are about eleven thousand known
species of mosses, most of them very similar in their life histories to
the one that we have studied. Among our common and larger mosses
are the bird's wheat or pigeon wheat, mosses and the tree moss. A very
important family is that of the peat mosses which grow in great num-
bers in peat bogs. Peat mosses live through the winter by means
of branches that start near the upper end of each plant ; these
branches live and grow the next year, while the older parts die. In
this way the plants live and grow, it may be for centuries, the older

FIG. 48. — Diagram illustrating the life
cycle of a moss.

A MOSS 95

parts dying each year and being pressed and packed down by the
weight of the younger growing branches above. The dead parts of
the moss plants, together with plants of other species growing among
them, and fallen leaves, twigs, bark, and the like, undergo changes
which result in the formation of beds of peat. Further changes in the
peat may in the course of ages lead to the formation of certain kinds
of coal. Such peat bogs, whose material is steadily heaped up, play a
large part in the filling in of swamps as well as of small ponds and
lakes. Many lakes in the northern United States are thus being
gradually filled by the ingrowth of beds of peat mosses from about
their borders. In some locations, for example on cliffs and rocky
hillsides, clumps of mosses of various kinds catch and hold soil-making
materials such as dust and fragments of animal and plant bodies.
As parts of the moss plants die and decay, their own substance is
added to the collection ; in this way, mosses, aided by the decay-
producing bacteria, prepare a soil in which larger and more highly
developed plants can in time establish themselves.

124. Relationships of the Mosses. — Most closely related
to the mosses are the liverworts. Some of these are leafy

FIG. 49. — A, a liverwort (Marchantia). B, part of a liverwort plant,
showing the upright branches (6) which bear sex organs (in the case shown,
archegones).

plants quite similar to the mosses ; others are flat, creeping
plants which grow on damp earth and rocks (Fig. 49) . Liver-
worts also have distinct sexual and asexual generations, but
the asexual generation of a liverwort is smaller and much

p6 TEXTBOOK OF BOTANY

simpler than that of a moss. In all probability, liverworts
and mosses are descended from green algae more or less like
Spirogyra, which originally lived in the water but which in
some long past period were forced to adapt themselves to
life on land. But no plants are now known, living or fossil,
that illustrate the steps by which such algae developed into
the present-day liverworts and mosses.

CHAPTER X
THE BRACKEN FERN

125. The Fern Plant (Fig. 50). — Many of the ferns are
known for the beauty of their leaves, which are the only
parts of most ferns that appear above ground. In the tropics
there are some tree ferns, which have an upright trunk with a
crown of leaves at the top. Of all the ferns, one of the best
known is that which is called the brake, the bracken fern, or the
eagle fern. Its botanical name is Pteris aquilina. It occurs
in open woods and in clear spaces, sometimes growing very
abundantly and covering large areas, especially in sandy soil.
Its long, slender stem grows horizontally, from a few inches
to a foot or more below the surface of the ground. It con-
tinues to live and grow slowly for many years. In some
parts of the world, this stem is ground and used as food.

The stem grows at the forward end, which, covered and
protected by scales, pushes its way through the soil. The
older part of the stem dies as the younger part grows. Now
and then the growing point divides ; two buds are so produced,
each enclosing one of the two new growing points, and thus
the stem branches by forking. Occasionally, also, a bud
arises at the base of a very young leaf and grows into a
branch of the stem. When the dying region of the stem
reaches a point at which branching has occurred, the two forks
(or main stem and branch) of course become independent
plants. Thus the number of plants is increased. From the
upper side of the stem, leaves grow upward ; one or more
leaves of the present year are to be found attached near
the growing end of the stem as well as near that of each

97

98

TEXTBOOK OF BOTANY

branch ; and farther back, on the older parts of the stem, are
the bases of the leaves of previous years. Ahead of this year's
leaves — that is, nearer the growing point of the stem —
are young leaves, still very small and protected by scales,

which will push
above ground
next year or the
year after.
Growing from
the lower side of
the stem, here
and there, are
roots.

126. Structure
of the Stem. —
New cells are be-
ing continually
formed at the
growing point ;
as these new cells
become older
they grow and
develop in vari-
ous ways to form
the different tis-
sues of the stem.
A cross section
through an older
part of the stem

(Fig. 51) shows

FIG. 50. — General appearance of a plant of the , . .

bracken fern, showing a portion of the underground us some^

stem, roots, and leaves. The youngest leaves (those the way in which

nearest the growing point of the stem) are still very ^jiese tissues are

small and do not show in the figure; back of this T

year's leaf are the bases of the dead leaves of previ- arranged,

ous years. such a section

THE BRACKEN FERN

99

we may notice especially a number of rounded groups of
cells of different sizes ; these groups are the vascular bundles
(Fig. 51, c). It must be remembered that in a cross section
we see the breadth and the thickness but not the length
of cells ; some of the cells of the vascular bundles are
many times as long as they are broad. If we follow the
course of the vascular bundles in the stem, we find that they

FIG. 51. — Cross section of the stem of the bracken fern; a, epidermis;

b, groups of very thick-walled cells which help to strengthen the stem;

c, a vascular bundle.

do not run parallel with one another throughout their length ;
here and there two bundles unite, and at other places they
give off branches, so that the whole system of bundles forms
a network. Of the branch bundles that pass off from the
bundles of the stem, some run into the leaves and others into
the roots, so that all parts of the plant are connected with one
another by means of the network of bundles. The long cells
in the vascular bundles supply a path for the passage of food
materials from one part of the plant to another. In a plant
so large as the fern this work of conduction is an important

loo TEXTBOOK OF BOTANY

one ; and it is not surprising that a large amount of special
tissue has been developed for the purpose.

127. Roots. — Now and then a root arises a short distance
back of the growing point of the stem ; other roots grow from
the bases of the leaf -stalks. The roots are short and slender ;
occasionally they branch. A short portion of each root, just
back of its end, bears many root hairs. Each root hair is a
surface cell of the root which has grown out beyond its
neighbors. These hairs come into very close contact with
the particles of soil, and take in some of the water which is
always present between and about the soil particles. With
the water the root hairs absorb salts and other substances
which are dissolved in the soil water and which the fern can
use as food. Thus all the materials which come from the
soil, including the plant's supply of water, are taken in by the
root hairs ; these materials are passed on to the inner cells
of the root, finally reaching the vascular bundles whose cells
conduct the materials through the root and thence to the stem
and leaves.

128. Leaves. — A leaf begins as a small swelling upon the
growing point of a stem or branch. The life of a single leaf
covers the greater part of three years. It passes the first
two years below ground ; in the spring of the third year it
pushes above the surface and unrolls from the base, growing
at the tip as it unrolls, until it has reached its full size ; in
the fall of the same year it dies, and finally it withers, is
broken, and the parts above ground decay. Under ordinary
conditions, the leaves grow to be from two to four feet high ;
but they may become much larger, and in some countries they
reach a height of twelve or fourteen feet. A leaf consists of
a slender stalk and a much-divided blade. The central axis
of the blade is a continuation of the leaf -stalk and corre-
sponds to the midrib of an undivided leaf like that of an oak ;
borne upon this central axis are two rows of leaflets. The two
lower leaflets are often much larger than the upper ones, and

THE BRACKEN FERN

are themselves divided into smaller divisions, the lower ones
of which are again divided. The upper leaflets of the leaf
are less divided than the lower ones, and the uppermost
leaflets are very small and not divided at all. Several vascu-
lar bundles, branches of some of the bundles in the stem,
pass up the leaf -stalk into the central axis of the blade, from
which, in turn, bundles pass off into the midribs of the leaflets.
The bundles in each leaflet again separate and branch, and
their branches
divide still fur-
ther, so that
finally vascular
bundles pass
into all parts of
each division of
the leaf-blade.
These branching
bundles are the
veins of the leaf.
They look like
fine, light-green
lines when the
leaf is held be-
tween the eye

and the light. On the under surface of the leaf are many
small air -pores (Fig. 52), which lead into spaces between the
cells in the interior of the leaf ; thus the inner cells can obtain
carbon dioxid from the air for the manufacture of carbo-
hydrates, as well as oxygen for respiration.

129. Formation and Germination of Spores. — The spores
of the bracken fern are borne in small spore sacs, great
numbers of which grow in a line on the under surface of a
leaf and close to its outer edge. Not all the leaves, however,
bear spore sacs. The sacs are protected by the margin of
the leaf, which folds under so as to cover the sacs while they

FIG. 52. — A, small part of a cross section through
a fern leaflet, showing spaces between the cells which
open to the outside through air-pores (a) in the
lower surface. B, an air-pore from the under
surface of the leaf ; it is a narrow opening between
two curved guard cells which are surrounded by
larger cells of very irregular shape.

TEXTBOOK OF BOTANY

are growing (Fig. 53, A), and which withers when the spores
are ripe.

Each spore sac (Fig. 53, B) has a slender stalk and a wall which is
composed of a layer of cells. The wall cells of one row, forming a

FIG. 53. — A, a leaflet of the bracken fern, seen from below; the margin
is folded over so as to cover the spore sacs, which are borne near the edge.
B, a spore sac; a, cells with specially thickened walls, which will bring
about the opening of the sac ; b, place at which the sac will open.

partial ring that runs from the base of the sac up one side, over the
end, and part way down the other side, have very thick walls and
project beyond the neighboring cells. When the spores are ripe, this
ring of cells straightens suddenly, tearing the sac open and throwing
out the spores.

The spores germinate in moist places, commonly on damp
soil. A spore develops at first into a row of cells, usually not

FIG. 54. — A, fern spores. B, C, early stages in the development of
sexual plant from a spore ; a, wall of the spore ; b, rhizoids.

THE BRACKEN FERN

103

more than three or four in number (Fig. 54, B). Later cell
divisions are in different directions (Fig. 54, C), so that the
young plant comes to consist not of a row but of a triangular
plate of cells, which as it grows becomes broader at the end
farthest from the old spore wall. As this small plant, which
is the sexual generation of the fern, continues to grow, a
notch appears in the forward (broader) end.

130. The Sexual Generation. — An older sexual plant, if
it has not been crowded while growing, has typically the heart

FIG. 55. — A, the sexual plant of a fern seen from below ; a, notch at the
forward end (the growing point) ; b, archegones ; c, antherids ; d, rhizoids.
B, a section through the sexual plant, showing an archegone borne on the
thickened part (just behind the growing point), and antherids and rhizoids
on the older, thinner parts.

shape shown in Figure 55, A. This plant grows very slowly
and remains so small that it is likely not to be noticed unless
we are specially looking for it. A plant a half-inch in diam-
eter is a large one. Its growth continues for some months,
and under certain conditions a plant may grow for a year
or more. It consists of one or two layers of green cells,

104 TEXTBOOK OF BOTANY

excepting that a small part just back of the growing point
(the notch) is several cells thick. This thicker part is not
found in smaller and younger plants, but only in those that
have been growing for some time. From the lower surface
of the plant rhizoids grow downward into the soil, serving
the same purposes as the rhizoids of a moss. Each rhizoid
is a long cell. The rhizoids are borne mostly on the older
part of the plant — that is, on the narrower portion farthest
from the growing point.

The sexual plant of the fern, like that of the moss, bears
sex organs. Both archegones and antherids are borne on
the same plant; as a rule they grow, like the rhizoids, from the
lower surface. Most of the antherids are formed on the older
parts of the plant — in the same general region, therefore,
as the rhizoids. But antherids sometimes appear also on
the younger portions of the plant. The archegones are
borne, in smaller numbers than the antherids, on the thicker
part of the plant near the growing point. They develop in
general later than the antherids ; consequently one is likely
to find many young plants, as well as older ones whose growth
was checked in some way while they were still small, which
bear antherids but no archegones.

131. Sex Organs, Gametes, and Fertilization. — The archegone of
a fern (Fig. 56, A) is shorter than that of a moss. It has no stalk
and its base is embedded, as though it had been pressed down among
the vegetative cells. The neck is short and is curved backward toward

the part of the plant
where antherids are
borne. The antherid
of a fern (Fig. 56, B)
is also smaller and
simpler than that of
a moss, and it pro-
^^ duces a much smaller
>«/ number of anthero-
FIG. 56. — Sex organs of a fern : A, an archegone; zoids (Fig. 57). Al-
B, an antherid. though both kinds of

THE BRACKEN FERN 105

gametes are borne close together on the same plant, it is probable that
as a rule self-fertilization — the union of an egg with an antherozoid
produced by the same plant — does not occur in the fern. That it
does not is suggested by the fact that the antherids usually ripen and
discharge their antherozoids before the
archegones on the same plant are
mature. This would seem to make
cross-fertilization necessary — that is,
the union of an egg and an antherozoid
borne by different plants. On the other
hand, young antherids are sometimes
found on the same plants with well-
developed archegones, and it is quite
possible that self-fertilization occurs
now and then. Cross-fertilization is

made easier by the fact that sexual FIG. 57. — A fern anthero-
plants commonly grow in groups, be- zoid. From a preparation by
cause many spores were dropped and Dr. W. N. Steil.
germinated near one another. Since

these little plants grow in moist places, there is enough water present
much of the time on their lower surfaces so that the antherids can open
and the antherozoids can swim to the mouths of the archegones either
on the same or on neighboring plants.

132. Development of the Asexual Plant. — Doubtless it
often happens that more than one egg is fertilized and so that
more than one zygote is formed in the archegones of a single
plant ; but we seldom find that more than one zygote has
developed into a plant of the next generation. This is prob-
ably because the new plant growing from the zygote receives
food for some time from the sexual plant that bore the egg ;
since the sexual plant is small and can supply only a limited
amount of food, only that one embryo develops which has an
advantage because of its greater vigor or its better location ;
the less fortunate embryos are starved and cease to grow.

The zygote, like the zygote of the moss, germinates in the arche-
gone. Very early the embryo (the young asexual plant, Figure 58) de-
velops four parts : one of these, the foot, remains small and imbedded
in the tissues of the sexual plant, from which it absorbs food for the
use of the embryo. Two other parts of the embryo, the primary root

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TEXTBOOK OF BOTANY

and the primary leaf, push their way out through the surrounding
tissues. First to break out, usually, is the root. As soon as its tip
is free, it turns downward and grows into the soil. Next the primary
leaf pushes out its tip ; it grows forward beneath the parent plant until
it reaches the .notch at the growing point ; then it turns upward and
forms a flat green blade, which is much simpler in outline than are
the blades of the leaves formed later.

Thus far the embryo has remained connected with the parent plant
by means of the foot, and dependent upon the parent for food ; but

FIG. 58. — A, the young asexual plant of a fern still attached to the
sexual plant ; the primary leaf and the primary root are both fully formed.
B, a portion of the young asexual plant, removed from the sexual plant
and considerably enlarged; a, the foot, by which the asexual plant is at-
tached to the sexual plant ; b, the young stem ; c, the base of the primary
leaf ; d, the upper part of the primary root.

now, having a root pushing into the soil and a leaf exposed to the air
the young plant can obtain or manufacture all its food. The sexual
plant by this time has given up most of its available food ; it withers
and dies, but what is left of it remains for a time attached to the young
asexual plant.- The stem of the asexual plant is the last of the four
embryonic parts to develop. For some time it is merely a bud-like
swelling at the base of the leaf; but after the primary root and the
primary leaf have begun to supply food for the plant, this bud grows

THE BRACKEN FERN

107

slowly into a horizontal underground stem. In time, new leaves grow
from the upper side of this stem and new roots from the lower side.
After the first of these new leaves and roots have appeared, the primary
leaf and primary root, which up to now have supplied food for the
plant, die and disappear. Now the asexual plant has reached the
condition at which we began to study it.

133. Outline of the Life of the Fern. — The fern, like the
moss, has a sexual generation which develops from a spore
and bears gametes,

and an asexual gener- ,•*'' *"*»x

ation which develops
from a zygote and * gametes

bears spores. In
both moss and fern,
a spore can develop
only into a sexual
plant, and a zygote
can develop only into
an asexual plant.
The great difference
between the moss
and the fern is that
the sexual plant of
the moss is large and
long-lived, and its
asexual plant small and short-lived ; but in the fern the con-
ditions are just the opposite, the sexual plant being small
and relatively short-lived, and the asexual plant large and
long-lived. Thus what is commonly known as the moss
plant is the sexual generation; what is commonly known as
the fern plant is the asexual generation.

There seems to be little doubt that the fern is descended
from some plant (perhaps a liverwort) which like the moss
had a long-lived sexual generation and a short-lived asexual
generation. In the evolution of the fern from this ancestor

sexual

generation asexual

generation

spores

FIG. 59. — Diagram illustrating the life
cycle of a fern.

io8 TEXTBOOK OF BOTANY

most of the work of food-making and food-storage was trans-
ferred from the sexual to the asexual generation. This
transfer of work could not take place in a plant like the moss,
whose asexual generation has no direct connection with the
soil and so must receive water and other substances from
the sexual generation. Before the asexual generation can
become independent, it must find a way of reaching the soil ;
and this some ancestor of the fern did by the development of
a root. Nothing at all like a root was ever developed, so
far as we know, by a sexual plant ; and the possession by the
asexual generation of this new organ, which can draw upon
the resources of the soil and can firmly anchor the plant, is
one reason why the asexual generation of the fern (and of
seed plants as well) has come to be so large and complex.
The sexual generation 'of the fern, on the contrary, having
little need of food-making and food-storing tissues, has be-
come very small. The history of the life of the fern may be
represented by a diagram (Fig. 59) which is like that used for
the moss (Fig. 48) except for the relative length of the lines
representing the sexual and asexual generations.

134. Other Ferns. — A comparatively small number of
species of ferns live in temperate regions, where they do not
as a rule grow in large numbers. But in tropical and sub-
tropical countries we find many more species, and in such
countries ferns often form conspicuous features of the land-
scape. Most of the ferns bear spore sacs in groups on the
under surface of the leaf, and not in a line near the margin
as those of the bracken fern are borne. Among the common
species in the United States and Canada are the lady fern,
the rock fern, and the maidenhair fern. Others of interest,
but not so common, are the royal fern, our largest species ;
the ostrich fern, the cinnamon fern, and the walking fern.
Among those of the tropics are the various species of tree
ferns already mentioned. Some small tropical ferns live on
the trunks of trees high above the ground.

THE BRACKEN FERN

109

135. Relatives of the Ferns : Water Ferns. — With the
true ferns, of which about four thousand species are known,
and which include the brake and the others that have been
mentioned, are grouped about eight hundred other species
of 'plants whose relationship to

the ferns is more or less close.
All of these plants resemble true
ferns in the fact that their asexual
generation is a large, highly de-
veloped plant, their sexual gen-
eration being small and incon-
spicuous. The water ferns are a
small group, living either on mud
or on the surface of bodies of
water. Their spore sacs are
formed inside a hard, nut -like
structure. The spores are of two
kinds : one kind, which is small,
develops into a small male plant
that bears antherozoids ; and the

other kind, much larger, develops

FIG. 60. — Mamlea, one of

into a female plant that produces the water ferns. This plant
eggs. lives in very wet places, usually

136. Horse-tails. -These, like on mud the stem creeping along

the surface. Growing on the

the brake, have an underground iower part of the left-hand leaf
stem. The stem sends up erect are two nut-like bodies. It is
branches, whose appearance gives jjj^j^ SP°reS °f **
the plant its name. The leaves

are very small scales which grow in circles upon the branch ;
the branch is green, and its cells manufacture most of the
plant's carbohydrate food. The upright branches have a
hard, rough surface, and some of the larger species are
called "scouring rushes," from the use to which they were
formerly put. The spore sacs are borne on leaves of a
special form which are crowded together at the upper end

TEXTBOOK OF BOTANY

of the branch so as to form a structure much like a pine
cone.

137. Club-mosses. — These are small, mostly creeping
plants, looking more like mosses than ferns. The moss-like
plants, however, belong to the asexual generation, so that the

FIG. 61. — A club-moss (Lycopo-
dium) that bears but one kind of
spores, i, a portion of the plant
showing the branching stem, leaves,
and roots, the spore-bearing leaves
being arranged in cone-like struc-
tures at the ends of upright branches.
2, a spore-bearing leaf, with a spore
sac at its base, j and 4, spores.
After Wossidlo.

FIG. 62. — A club-moss
(Selaginella) that bears spores
of two different sizes ; a, special
branches which bear roots at
their ends; b, foliage leaves;
c, spore-bearing leaves.

likeness to mosses is only apparent. Some of the club-mosses
(Fig. 61) bear one kind of spore, like the true ferns ; others
(Fig. 62) have two kinds of spores, like the water ferns, and
their sexual generation consists of male and female plants
that are very different in size. The spore sacs are borne
singly either on ordinary leaves, or on special leaves which

THE BRACKEN FERN

ill

grow in a cone-like group as do the spore-bearing leaves of
the horse-tails.

138. Fossil Ferns. — The ferns and some of their relatives,
having hard, resistant structures, have been preserved in
large numbers in the rocks whose material was deposited in
past ages. This is not true of most of the plants simpler than
the ferns, whose tissues are soft and have been destroyed,

FIG. 63. — Plants of the ages when the coal beds were being formed.
In the foreground, on the left, relatives of the club- mosses; just back of
these, tree-like forms related to the horse-tails; on the right, tree ferns.
After Stevens.

except for occasional fragments, by the pressure, heat, and
chemical changes to which the rock layers have been sub-
jected. For this reason, much more is known about the past
history of the ferns than about that of mosses, for example,
or that of most of the algae or fungi. Our great beds of coal
were formed at a time when ferns and their relatives made up
a large part of the vegetation of the earth, and so it is espe-
cially in the coal measures that rich material is found for the
study of fossil ferns (Fig. 63). Among the ferns of the coal-
forming period were many true ferns evidently related to

112 TEXTBOOK OF BOTANY

certain species of the present day ; some of these grew to be
large trees. There were other tree-like forms, some related
to the horse-tails and some to the club-mosses. There were
also plants which had fern-like leaves but produced true seeds ;
and these fossil plants have taught us much of the way in
which some of the living seed plants have developed from the
ferns.

CHAPTER XI

THE PINE

139. The Pine Tree. — The pine tree, like the fern plant,
belongs to the asexual generation. We may expect, therefore,
to find that in some
way the tree pro-
duces spores. First,
however, we shall
study the vegetative
parts of the tree,
namely, the stem
(trunk) and its
branches, the leaves,
and the roots. The
trunk, because it con-
tains many thick-
walled cells, can
stand erect and sup-
port its own weight
as well as that of the
branches and leaves.
The trunk grows in

length by means of a

. FIG. 64. — A pine tree grown in the open,

terminal bud, which Photograph by L. S. Cheney,

includes, besides the

growing point of the stem, the very youngest and smallest

branches and leaves. By the formation of new cells at the

growing point, and by the growth of these cells, the trunk is

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TEXTBOOK OF BOTANY

lengthened and new branches and leaves are formed during
the growing season.

At the coming of winter, growth stops and scale leaves
covered with resin are formed that protect the bud. When
growth begins again in the spring, the scale leaves drop off ;
but their bases remain, forming a ring
that looks like a thickening of the
stem. By means of this ring one can
see where the growth of one year
ended and that of the next year began.
From the thickened ring grow one or
more branches, which have developed
from buds in the axils of the fallen
scale leaves. If the terminal bud is
destroyed or killed, the growth of the
trunk ceases ; but commonly, in such
a case, one of the branches near the
top of the tree bends and grows up-
ward, so that the tree continues to
become taller. The stem of the fern
grows only in length ; but that of
the pine grows both in length and in
thickness. The trunk is slenderest
at the top and gradually thicker
toward the base, because the base
is the oldest part and has been
growing in thickness for the longest
time.

140. Inner Structure of the Stem. — At the very tip of
the stem (Fig. 66) are many small cells, which, during the
growing season, are continually growing and dividing. In
this region, too, are some very small swellings ; these are the
beginnings of new leaves and branches. Below the tip the
cells are larger ; farther down they are still larger, and dif-
ferent groups of them are gradually taking on the forms that

FIG. 65. — A pine tree
that grew in a forest.
Photograph by L. S.
Cheney.

THE PINE

are peculiar to the different tissues of the trunk. These
tissues are well shown in a section of a stem cut some dis-
tance below the growing point
(Fig. 67). In the center of the
stem is the pith. Just outside
this is a ring of vascular bundles,
the spaces between which (look-
ing like dark lines in the figure)
contain cells much like those of
the pith. Each vascular bundle
is composed of wood and bast.

The wood is the part of the
bundle that is turned toward
the center of the stem ; the bast
is the part turned outward.
The wood carries the sap from
the roots to the upper parts of
the plant, and the bast carries
manufactured food from the
leaves to the other organs.
Most of the cells of the vascular
bundles, especially those of the
wood, have very thick walls ; and the strength and stiffness
of the stem are due mainly to the thick-walled cells of the
wood. Outside the ring of vascular bundles is the cortex,
and outside this is the epidermis, which is composed of a
single layer of cells. Here and there in the cortex, groups
of cells are breaking down to form resin passages — cavities
which extend for some distance up and down in the stem,
and which contain resin.

141. Growth in Thickness. — The way in which the stem
grows thicker is shown by a cross section of a part of the
stem that has been growing for several years (Fig. 68). After
the different tissues have reached the condition already de-
scribed, divisions begin to occur in each vascular bundle in

stem (winter bud) ; a, bud scales ;
b, a young spur branch; c, an
older spur branch, with the bases
of the foliage leaves that it bore.

Ii6 TEXTBOOK OF BOTANY

a layer of cells lying between the wood and the bast. The
cells of this layer divide so as to form two layers, three layers,
and so on. Then some of the cells between the vascular
bundles begin to divide in the same way. Thus a continuous
zone of dividing cells, called the cambium (represented by a

FIG. 67. — A cross section through a portion of a pine stem in which the
different tissues have developed. The narrow dark zone is the cambium
layer, separating the wood (on the inner side of the cambium) from the
bast (on the outer side). At the center, inside the wood, is the pith.

narrow dark ring in Figure 67), is formed which cuts through
the middle of each vascular bundle ; outside this zone lie the
bast, cortex, and epidermis, and inside it are the wood and
pith. The formation of new layers of cells pushes the wood
and bast farther apart, and so makes the stem thicker.

Most of the new cells that are formed on the inner side of
the cambium zone develop into wood cells, and most of those
formed on the outer side of the cambium become b'ast cells.

THE PINE 117

But some rows of cells (called medullary rays} running from
the central part of the stem toward the outside remain thin-
walled, and, except that they grow somewhat larger, do not
become very different from the cambium cells themselves.
The medullary rays thus cut across both the wood and the
bast ; but except for these rays, the wood forms a continuous
zone of increasing thickness just within the cambium, and
the bast forms a continuous zone just outside the cambium.
Within the newly formed wood, resin passages develop like

FIG. 68. — Part of a cross section through a portion of a pine stem
which has been growing in thickness for several years. The small light
spots in the wood represent resin passages.

those in the cortex. Although the process of growth in thick-
ness can best be studied in thin sections of the stem, we. must
bear in mind that the zones of wood, cambium, and bast which
we see in such a section really represent cylinders running up
and down within the trunk.

142. Annual Rings. — The new wood cells formed from the
cambium in the spring grow large and remain thin-walled.
Later in the season, smaller, thicker- walled cells are formed,
and those produced at the close of the growing season (in
late summer or early fall) are smallest and thickest-walled of
all. No divisions occur in the cambium during the winter ;

n8 TEXTBOOK OP BOTANY

when it becomes active in the spring, it again forms large,
thin-walled cells. This new spring wood is next to the
summer wood of the year before ; and the sharp contrast be-
tween the dark summer wood and the lighter-colored spring
wood causes the familiar appearance of rings in a section of a
tree trunk. It is because these rings are formed as just de-
scribed that one can tell about how old a tree is by counting
the rings in a section near its base. The number of rings is
not a perfectly accurate measure of a tree's age, because the
development of new wood may have been changed or pre-
vented in places by pressure or by wounds, and because occa-
sionally in a year of exceptional weather, as when a long
summer drought is followed by heavy rains, two rings are pro-
duced instead of one. It is only in the outermost part of the
wood — much more than the present year's growth, however
— that the sap flows upward ; this outer wood — the sap-
wood — is soft and moist. In the cells and cell walls of the
older heartwood changes have taken place which prevent the
passage of water. The heartwood is therefore dryer and
harder than the sap wood.

143. Cork and Bark. — Another kind of thickening occurs
in the cortex of the trunk. This results from the division of
the cells of a layer a short distance within the epidermis,
called the cork cambium. The new cells formed on the outer
side of the cork cambium develop thick walls that contain
a fat-like substance called cork. Water will not pass through
the walls of these cork cells. Now, since the whole water
supply of the trunk comes from the roots and is carried up
inside the trunk in the sapwood, the cork cells and the cells
outside them are cut off by the corky walls from a supply
of water ; these cells therefore become dry and dead, cracks
appear in their walls, and so a hard, dry bark is formed.
Later (in some species of pine only ;n parts of the tree that
are eight to ten years old), a new layer of cork cambium ap-
pears a little way beneath the first layer, new layers of cork

THE PINE 119

cells and bark are formed, and the older layer of bark peels
off. Then a third layer of cork cambium appears within the
second, then a fourth, and so on, and in time the whole cortex
has been changed to bark. Later layers of cork cambium
therefore must be formed within the bast. So the outer part
of the bast is also gradually changed to bark and scaled off,
at the same time that new bast is being formed from within
by the division of the cambium cells. This change of the
outer layers of the bast into bark explains why the bast never
becomes thick, although new bast is formed each year ; and
why most of the thickness of an older tree is made up of rings
of wood.

144. Branches. — These, in the pine, are of two kinds :
long branches and spur branches. The long branches develop
chiefly from the buds borne in the axils of winter bud scales ;
but sometimes adventive buds, which appear in various places
— for example, upon wounded parts of a trunk or branch —
grow into long branches. A long branch has the same struc-
ture as the trunk ; it grows in length and in thickness ; it •
forms bark ; and from the axils of its winter bud scales new
long branches may grow. The spur branches are very short,
never more than a fraction of an inch in length. They grow
from the buds in the axils of the numerous scale leaves that
are formed during the growing season upon the trunk and the
long branches. A spur branch lives and grows very slowly
for several years, never .itself branching. At its end is a
cluster of green foliage -leaves.

145. Leaves. — We have seen that two kinds of leaves are
borne by the pine : scale leaves (which include the winter
bud scales) and foliage leaves. Scale leaves are protective
organs and are usually short-lived. Much more conspicuous
are the long, green foliage leaves — the " pine needles " —
which grow in clusters at the ends of the spur branches.
Each cluster is surrounded in the bud by a thin membrane,
which later is torn and partly or entirely disappears. The

120 TEXTBOOK OF BOTANY

foliage leaves of the pine are not borne directly on the trunk
or on long branches, except in the case of young seedlings.
The number of leaves in the cluster at the end of each spur
branch varies with the species ; for example, the red pine has
two needles in each cluster and the white pine has five. The
foliage leaves do not fall off at the end of their first season
as do the leaves of most of our common trees ; they live and
remain on the tree for more than one year. The leaves of

FIG. 69. — Cross section through a foliage leaf of the Scotch pine ; a, epi-
dermis; b, an air-pore; c, layers of thick- walled cells just within the epi-
dermis ; d, thin-walled cells between which are air-spaces ; e, resin passage ;
./, vascular bundles.

some pines are said to live for ten years, but the average is
probably much less than this. A pine tree, at any rate, is
never bare of leaves, although each year some of the older
leaves drop off. When the leaves of a cluster fall, the spur
branch that bore them dies ; therefore spur branches and
foliage leaves (as well as scale leaves) are found as a rule
only on the younger portions of the trunk and of each long
shoot.

A pine needle is not cylindrical, but has one or more flattened sur-
faces, depending upon whether it is one of a cluster of two, three, or
five which were pressed together in the bud. On both upper and

THE PINE 121

lower surfaces are air-pores, like those on the lower surface of the
fern leaf. In a cross section through a pine leaf (Fig. 69) we find a
variety of tissues, in general much like those of the stem. In the
central part of the section are two vascular bundles,1 each composed
of wood and bast ; the wood is that part of each bundle turned toward
the upper side, and the bast is the part toward the lower side of the
leaf.

146. Roots. — The long tap root of the pine is continuous
with the trunk ; it may grow downward for a great distance.
The tap root gives off branch roots, which in turn branch,
and both the tap root and the branch roots form bark and
grow in thickness in much the same way as the trunk does.
There is a marked difference between the way in which
branches start from the stem and that in which branch
roots start from the tap root. A branch of the stem begins
as a surface swelling at the growing point of the stem ; a
branch root begins its development within the tap root,
some distance back of the growing point and just outside the
ring of vascular bundles ; so the new root must break its way
through the outer tissues of the older root within which it
has begun to grow. Although we ordinarily see little of the
roots of the pine, we must remember that they really make
up a large system, comparable in size with the trunk and its
branches. The weight of the parts of a tree above ground,
and the great pressure exerted upon it by the winds, make
necessary an extensive root system that will anchor the tree
firmly in the soil.

A root of the pine, as of the fern, bears root hairs just back
of the growing point. New root hairs are constantly being
formed in this region, but they soon die and fall or are rubbed
off. For this reason the zone in which root hairs are borne is a
short one. Since it is only through the root hairs that water
and other substances are taken from the soil, this work of
absorption can go on in only a small part of the root system of

1 In some species, including the white pine, the leaf contains only one vascular
bundle.

TEXTBOOK OF BOTANY

a large tree, and that the youngest part. A root contains
the same tissues as does a stem or branch, although somewhat
differently arranged.

147. The Staminate Cone. — The pine bears two kinds
of cones. It is not easy at first to think of these as corre-
sponding to the stami-
nate and pistillate
flowers of the cucum-
ber. But the cones
really are very primi-
tive flowers. The
two kinds of cones'
differ in size, the
staminate cone being
much smaller than
the carpellate. Both
are borne on the same
tree. Staminate cones
(Fig. 70) grow in clusters ; carpellate cones grow singly. A
staminate cone has a large number of leaf -like or scale-like
parts, attached to a central stalk. As a matter of fact, the
central stalk of the cone is a branch, and the leaf -like struc-
tures that it bears are really leaves. These leaves are not
green and so cannot manufacture food, as foliage leaves do ;
their work is to produce spores, and so we call them spore leaves.

FIG. 70. — A cluster of staminate cones of
the pine. After Stevens.

FIG. 71. — A, a microspore leaf of the pine as seen from below, showing
the pollen sacs. B, the same, seen from the side. C, a pollen grain ; a, the
generative cell ; b, the nucleus of the large vegetative cell ; c, the bladder-
like expansion of the outer wall of the pollen grain.

THE PINE

123

We saw that the green leaf of the fern does two kinds of
work : it manufactures food and it bears spores. In the pine,
these two kinds of work are performed by two distinct kinds
of leaves — the foliage leaves and the spore leaves. The
spores borne on the spore
leaves of the staminate cone
are very small, and so are
called microstores; therefore
the leaves of the staminate
cone are micros pore leaves.
The under surface of each
microspore leaf (Fig. 71. A)
is nearly covered by two
microstore sacs (or pollen
sacs) ; within these sacs a
great many microstores or
pollen grains are produced.

148. The Carpellate Cone
(Fig. 72). — This, like the
staminate cone, is a branch
to which many spore leaves
are attached ; since these
leaves bear large spores
(macr os pores) , they are called
macros pore leaves.1 On the

FIG. 72. — Carpellate cones of the
pine : <z, a young cone ready for pol-
lination ; b, a cone one year older, the
which are nearly ready for

macrospore leaves have spread apart,
allowing the seeds to drop out.
After Stevens.

upper surface of each macro- fertilization; c, one still older, whose
spore leaf (Fig. 73, A} are
two small swellings ; these
are macrospore sacs or, as

they are more commonly called, ovules. Each sac is sur-
rounded by an integument, excepting that at one end, where
the integument projects in the form of two horns, there is a
narrow opening through the integument called a micropyle.

1 The organ that is here called a macrospore leaf is more complex than the micro-
spore leaf, and there is a question as to whether it is not really more than a leaf.

124

TEXTBOOK OF BOTANY

In the central part of the macrospore sac, four macrospores
are formed (Fig. 73, C) ; they are much larger than micro-
spores. All the spores that we have studied hitherto were
produced in such a way that when they were ripe they could
escape from the parent plant. But the macrospores of the

FIG. 73. — A, a macrospore leaf of the pine bearing two macrospore
sacs (ovules). B, a lengthwise section of a macrospore leaf ; i, integument ;
m, micropyle. C, part of a lengthwise section of an ovule on a larger scale,
showing the four macrospores.

pine are so tightly imbedded in the tissues of the spore sac
that they cannot escape, and so if they are to germinate
they must do so inside the spore sac. This imprisoning of
the macrospores is one thing that distinguishes the seed
plants, and it leads to some very important consequences.

149. Germination of the Macrospore. — Of the four
macrospores, only one germinates. It develops into a small,
rounded mass of tissue which, since it grows from the spore,
belongs to the sexual generation of the pine. This mass of
tissue is a female plant; but, because of the position of the
spore from which it has grown, this small plant remains inside
the macrospore sac (Fig. 74). At the end of the female
plant nearest the micropyle, archegones (one to nine in
different species) are formed. Each archegone consists of a
large egg and a very short canal that leads from the surface
of the female plant to the egg.

THE PINE 125

150. Germination of the Microspore. — We have seen that
many microspores (pollen grains) are formed in each pollen
sac (microspore sac) . The microspores also germinate in the
spore sac in which they were formed. But the male plant
that is formed from a microspore is not, like the female
plant, firmly held in the spore sac ; after it has developed for
a time within the sac, it becomes free. The germinating
microspore does not at first grow larger ; it merely divides
to form four cells, all lying inside the microspore wall (Fig.

Of the four cells which now make up the young plant, three are
small and lie in a group at one side, close to the spore wall. The two
small cells nearest the wall seem to be of no use, and they, break down
and almost entirely disappear soon after they are formed. The third
small cell remains alive ; it is the generative cell. The fourth, a large
vegetative cell, fills the greater part of the space within the spore wall.
At this stage the development of a microspore into a male plant stops ;
the spore sac splits open, and the pollen grains escape. Thus we see
that a pollen grain is a microspore when it is first formed ; but by the
time that it escapes from the spore sac, the pollen grain is no longer a
spore, but a young male plant. A pollen grain has two bladder-like
projections, one at either side ; these are cavities formed by the ex-
pansion of the outer layer of the wall of the pollen grain ; these projec-
tions, by increasing the surface area of the pollen grain, help in its
scattering by the wind.

151. Pollination. — Since the female plant remains inside
the spore sac, the male plant (the pollen grain) must in some
way be brought to its neighborhood before a union of gam-
etes can occur. The wind is the agent that carries the
pollen of the pine. Since the wind scatters the pollen in
every direction, so that only one grain in many thousands will
land in the right place, the pine must produce much more
pollen than can actually be used. At about the time that the
pollen is being shed, the carpellate cone grows rather rapidly
in length ; this growth separates the macrospore leaves, and
some of the pollen grains which fall upon the cone sift down
between the spore leaves and so come near the opening of a

126

TEXTBOOK OF BOTANY

micropyle. A sticky liquid is formed in the micropyle and
oozes from its mouth. The jarring of the cone by the wind
shakes the pollen grains about, and when they come in con-
tact with this liquid they are held by it. Then a drying oc-
curs within the micropyle and the drop of liquid is sucked
back, carrying the pollen grains to the bottom of the micro-
pyle. The pollen grains are now in contact with the macro-
spore sac, within which is the female plant. The set of proc-
esses which thus bring
i the pollen grain close to
the female plant is called
pollination. It is plain
that pollination must
take place before fer-
tilization can occur.

152. Fertilization. —
After the pollen grain
has reached the base of
the micropyle, its de-
velopment into a male
plant continues. The
vegetative cell of the
pollen grain pushes out
a long projection — the
pollen tube (Fig. 74, /).
This tube burrows into the tissues of the macrospore sac, grow-
ing very slowly, occasionally branching, and using for food
some of the cells of the spore sac. While the tube is growing,
the generative cell within the pollen grain divides, forming a
stalk cell and a body cell. The body cell next divides into two
male gametes, which move, following the vegetative, nucleus,
toward the .growing end of the pollen tube. The gametes
are simple cells consisting of nucleus and some cytoplasm,
and with no -vibrating hairs such as are borne by the male
gametes (antherozoids) of mosses and ferns.

FIG. 74. — A lengthwise section of an
ovule older than that shown in Fig. 73, C,
showing germinating pollen grains, pollen
tubes, t, and the upper part of the female
plant with three archegones; each arche-
gone contains a large egg, e; i, integument ;
«, an egg nucleus.

THE PINE

127

The male plant is now fully formed. It includes at most
six cells, of which two were small and have almost or quite
disappeared ; the four remaining are the stalk cell, the two
gametes, and the vegetative cell of which the tube is a part.
Finally, the end of the tube makes its way through the tissue
of the macrospore sac into the neck of an archegone, and
there comes in contact with the egg. Then the end of the
pollen tube bursts, and its contents, including the male
gametes, are forced into the egg. One male gamete unites
with the egg. The result of
this union is a zygote, which
very soon begins to develop into
a new asexual generation. The
second male gamete and the
other substances that pass from
the pollen tube into the egg
seem to have no further use,
unless it is to serve as food for
the egg.

153. The Seed (Fig. 75).—
The growth and division of the
zygote result in the formation
of a young asexual plant (the
embryo) which lies in the center
of the tissues of the female

plant, part of which the embryo P^ b> remains of th* bodv °*

, ., the ovule ; c, suspensor (a part of

has destroyed and used as food, the embryo that takes no part in

The embryo develops the same the development of the mature

parts that we found in the em- P.lant)= *• endosPerm; ^radicle;

/, inner seed coat; g, outer seed

bryo of the squash: a radicle Coat; h, plumule; i, seed leaves,
whose growing point is turned

toward the micropyle, several seed leaves, and a very small
plumule. When these parts have been developed, the
embryo ceases to grow for a time. This stopping of the
growth of the new plant at a very early age is another

FIG; 75. — A lengthwise section
through a pine seed; a, micro-

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TEXTBOOK OF BOTANY

thing that distinguishes the seed plants. The embryo
now lies within the tissues of its parent, the female plant ;
the latter lies within the macrospore sac, which in turn is
surrounded by the integument. All these parts together
make up the seed. Thus the seed is a complex structure,
whose different parts represent three generations. The in-
tegument and the macrospore sac belong to the same
generation as the tree, that is, to the old asexual generation.
The female plant belongs to the sexual generation; and the
embryo is the new asexual generation.

Changes take place in all these parts as the seed ripens.
The integument develops into two seed coats : an outer one

FIG. 76. — A, a mature macrospore leaf bearing seeds, seen from the lower
side. B, the same, seen from above. C, a single seed with its wing.

which is hard and resistant, and an inner one which is very
thin and papery. The tissues of the ovule (inside the integ-
ument) have been largely destroyed by the growth of the
female plant ; but something of them remains in the mature
seed in the form of a cap over the micropylar end of the
female plant. The female plant in turn has been partly used
as food for the embryo ; but much of its tissue remains, sur-
rounding the embryo except at the root end, its cells filled
with starch and other foods which the embryo will use later.
This food-containing tissue of the female plant is called en-
dosperm in the ripe seed. A seed usually contains but one

THE PINE 129

embryo, although very rarely two or more are found,
which have resulted from the fertilization of more than
one of the eggs of a female plant. When the seed sepa-
rates from the macrospore leaf on which it is borne, a thin
layer of the outer tissue of the leaf remains attached to it
(Fig. 76, Q. This wing helps in the carrying of the seed
by the wind.

154. Times of Pollination, Fertilization, and Seed Development. —

Small buds which will grow into staminate and carpellate cones are
formed in the summer or fall. The next spring (in the northern United
States, late in May or early in June), the pollen ripens and pollina-
tion occurs. At this time the carpellate cone, the macrospore leaf,
and the macrospore sac are still small, and the female plant has just
begun to develop from the macrospore. Fertilization of course cannot
occur until the female plant has formed its eggs. So the pollen tube,
after it begins to develop, grows slowly in the tissues of the macrospore
sac while the female plant also continues to grow. It is not untiljune~] '
or July of the following year, when the pollen tube has been growing
for about thirteen months, that the eggs are ripe and fertilization
occurs. In the summer following fertilization, the zygote develops /-..
into an embryo and the seed is ripened ; this seed is shed in the fall
or in the following spring. Thus the history of a single carpellate cone
covers parts of three years.

155. Germination of the Seed. — The seed may germinate
in the spring following its ripening, or, if conditions then are
not favorable, it may remain apparently unchanged, but still
alive and capable of germination, for some years. When
conditions are right, the embryo becomes larger, at first
because its cells take in water ; the endosperm also absorbs
water ; and the pressure caused by the swelling of the embryo
and of the endosperm breaks the seed coats, which have been
softened by the water that has soaked into and through them.
The growing embryo digests and uses the food stored in the
endosperm, which thus helps to start the embryo in its devel-
opment. The radicle is the first part of the embryo to push
out of the seed coats. It turns downward and develops into
the primary root, except that, as in the squash, the upper end

130 TEXTBOOK OF BOTANY

of the radicle, just below the point of attachment of the seed
leaves, forms the base of the stem.

As the radicle and the seed leaves grow, the latter, which
have already begun to form chlorophyl, are pushed above
the surface of the soil. The upper end of the radicle becomes
upright, the seed leaves spread out, and the plant, now pro-
vided with a root and leaves, is ready to make its own way in
the world. The old seed coats, with what is left of the en-
dosperm, are usually carried upward on the ends of the seed
leaves, and as the leaves grow and spread out, the seed coats
are thrown off. As the primary root grows into a long tap
root, branch roots are formed. The plumule forms all of the
stem excepting its very base. For a time, foliage leaves are
borne directly upon the stem and its long branches ; these
early leaves are comparatively short and flatter than the later
leaves. In the course of a few months, spur branches begin
to appear, which bear foliage leaves of the ordinary kind ;
and from this time on, all the new foliage leaves are borne on
spur branches.

156. Life Cycle of the Pine. — The course of events in the
life of the pine can be understood only by comparing it with
such plants as the moss and the fern. This comparison was
first clearly made by Hofmeister (1824-1877), who showed
in this way the real nature of the different parts of the pine
cones as well as that of the parts of an angiosperm flower.
The central fact in the life of the moss, the fern, or the pine
is the occurrence of two distinct generations — an asexual
generation that reproduces by means of spores, and a sexual
generation that reproduces by means of gametes. While
the fern and the pine are alike in this central fact of having
two generations, the pine is different from the fern in the
following respects :

a. In the formation of two kinds of spores, of which one
grows into a male plant and the other into a female
plant. However, this is not peculiar to seed plants (of

THE PINE 131

which the pine is one), for, as we have seen, some of the

relatives of the ferns have two kinds of spores.

In the keeping of the macrospore in the spore sac, which

compels the female plant also to pass its whole life

within the macrospore sac.

In the great reduction in size of the sexual generation —

a reduction which has gone further in the male plant

than in the female plant. This reduction had begun in

\
\

asexual
generation }

I

FIG. 77. — Diagram illustrating the life cycle
of the pine.

the fern, whose sexual plant was much smaller than its
asexual plant, but it has been carried much farther in
the pine. •

d. In the development of a pollen tube, which carries the
male gamete to the egg. This has made it unnecessary
for the male gamete to form special organs for moving
itself about.

e. In the formation of a seed, containing an embryo which
has stopped growing for a time. The distribution of
mosses and ferns is brought about by the scattering of

132 TEXTBOOK OF BOTANY

the spores ; but in the pine the time at which the species
is distributed has been shifted from the period of the
spore to that of the seed. The seed is much better
adapted to this purpose than the spore, because it can
live for a long time without germinating, and because
it contains much food for the new plant. Note that a
seed is not a means of reproduction of the plant, as a
spore is. It is itself a little plant, wrapped up in tissues
belonging to the two previous generations.
The life cycle of the pine may be represented by a diagram

(Fig. 77) not unlike those which have been used for the moss

and the fern.

157. Seed Plants : Gymnosperms. — Each member of
the most highly developed class of plants — the seed plants —
has a history much like that of the pine. The seed plants
as a group- have adapted themselves so well to present con-
ditions upon the earth that they have spread over much the
greater part of its land surface. It is because they are so
well fitted to the conditions of existence that the largest and
longest-lived plants are seed plants. Seed plants are divided
into two distinct groups, named according to the ways in
which they bear their seeds. In the smaller and more primi-
tive group, to which the pine belongs, the seeds are produced
on the surface of a leaf (although a leaf of very special form)
or on a short branch. The members of this group are called
gymno 'Sperms or naked-seeded plants. A much larger group
consists of those which, like the cucumber, form their seeds
within a closed structure that becomes a fruit. Plants whose
seeds are shut up in this way are called angiosperms or hidden-
seeded plants.

158. Different Kinds of Pines. — The pines include about
eighty species, which live almost entirely in the north tem-
perate zone.. Among them are some of the most valuable
timber trees. Of the species native to North America, the
best known is the white pine (Pinus strobus), forests of which

THE PINE 133

formerly covered great areas in Canada and the northern
United States. They have been largely destroyed because
of the demand for white pine timber, and the tree is now
being planted on a large scale by the national and state
governments. About the beginning of the eighteenth cen-
tury, the white pine was introduced into Europe, where it is
called the " Weymouth pine." It is frequently seen in
European parks, and is planted to some extent in forests.

Another common American species is the red pine, also
called the " Norway pine " (Pinus resinosd). This is an
important timber tree, though its wood is less valuable than
that of the white pine. Pinus lambertiana, the " sugar
pine " of the Pacific coast states, is the largest American
tree next to the California redwoods. Its resin is sweet-
tasting and edible. The Scotch pine, also called " Scotch
fir," " Nonvay fir," and " Dantzic fir," is the commonest
species in Europe, where it is a most important timber tree.
It is a common ornamental tree in the United States, as is
also the Austrian pine. Some pines have large, nut-like seeds
whose inner parts (endosperm and embryo) are eaten. One
of these nut-pines is found in northern California ; the nuts
of another, living in the Mediterranean countries, are largely
used in Europe.

Aside from its wood, the most valuable product of the
pine is its resin. By distillation, turpentine is obtained
from the resin, and from the more solid substances that are
left after distillation rosin is made. Tar is obtained by the
dry distillation of the wood, and pitch by boiling down the
tar. Most of the turpentine produced in the United States
comes from the long-leaved yellow pine and the Cuban (or
slash) pine of the southern states.

159. Other Conifers. — The pine is a member of the
largest order of gymnosperms, called conifers because the
seeds of most of them are borne on cones. The seed-bearing
structures of some members of the order, such as the red cedar

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TEXTBOOK OF BOTANY

and the ground hemlock, are not at all cone-like, but the other
characteristics of these plants show that they are related to the
cone-bearing forms. Most of the conifers are trees. A few
are low shrubs, like the ground hemlock, or even creeping
forms, like the creeping juniper. Other conifers are the

spruces ; the firs ; the larches
(one of which is the American
tamarack), whose foliage
leaves, differently from those
of most conifers, live for only
one season and are shed in
the fall.; the arbor vitae, or
white cedar ; the hemlocks ;
the giant redwood of Cali-
fornia, which reaches a
greater size than that of any
other living plant excepting
some Australian gumtrees ;
and the bald cypress of the
southern United States, re-
markable for its " knees,"
vertical outgrowths of the
roots which rise several feet
above the surface of the
ground and which seem to
be respiring organs. Many
of these other conifers, like
the pines, are valuable as
timber trees and as sources

of resin and of various special products such as Canada
balsam and spruce gum. The spruce is the most impor-
tant source of pulp for paper-making ; but as it is becom-
ing scarcer, the wood of some other trees, especially that of the
balsam fir, is being used for this purpose. Attempts are
being made also to find ways of using pulp obtained from

FIG. 78. — White spruce trees.
Photograph by L. S. Cheney.

THE PINE

135

the steins of . various smaller plants. The " berries " of
the juniper, which correspond to the ripe carpellate cones of
the pine, are used in medicine.

160. Other Gymnosperms. — Aside from the conifers, there are
comparatively few species of gymnosperms now living. The majority

FIG. 79. — A cycad (Cycas revoluta).

of these belong to the tropical and subtropical order of cycads, repre-
sented in the United States by two species of Zamia which grow in
Florida. The cycads have a thick stem, at the top of which is a crown
of divided leaves very much like those of some ferns. In general ap-
pearance, the cycads are palm-like; some of them are called " sago
palms " because a coarse sago is obtained from their pith. However,
their similarity to the palms is misleading, for in many ways the cycads
show themselves to be related to the ferns ; and the fossil history of
the order is sufficiently complete so that their descent can be traced

136 TEXTBOOK OF BOTANY

back to very ancient ferns that were related to some tropical ferns of
the present time. The modern cycads are the survivors of what was
once a much larger group. While there can be little doubt that the
conifers, including the pine, have also come from fern-like ancestors,
their descent is not yet so well known as is that of the cycads. Another
gymnosperm is Ginkgo, the " maidenhair tret " of China and Japan,
many specimens of which are to be found in Europe and America.
This also is a survivor of what was once a large group. The cycads
and Ginkgo differ from all other seed plants (including the conifers)
in the fact that their male gametes have vibrating hairs and so can
swim about like those of the fern and the moss. However, the cycads
and Ginkgo, like the pine, also have a pollen tube, which furnishes a
path for the antherozoids to reach the eggs.

CHAPTER XII

THE BEAN

161. Angiosperms : the Bean Plant. — The great majority
of seed plants, unlike the pine, are angiosperms; they produce
their ovules (macrospore sacs), and consequently their seeds,

inside a closed vessel which is called .

an ovary. When the ovules develop
into seeds, the ovary becomes a fruit.
Almost all our cultivated plants are
angiosperms ; so also are most forest
trees (apart from the cone-bearing
ones) and most other conspicuous
wild plants except the mosses and
ferns. In studying the cucumber we
have learned something of the struc-
ture and way of life of an angio-
sperm, and the bean is a convenient
plant to use for a fuller study. Any
of the numerous cultivated varieties
of bean will answer for this purpose.
Like the cucumber, the bean is an
annual ; that is, none of its parts live

through the winter and grow from year to year, as the trunk
and roots of the pine do. Some varieties are low or " bush "
beans ; some are climbing or " pole " beans. The stem of
a climbing bean coils about any slender object that it
touches, such as a pole, or the stem or branch of another
plant (Fig. 80). This coiling is due to an unequal growth
of the stem on its different sides, which causes the upper
13?

FIG. 80. — Portion of a
bean stem twining about
a support.

138

TEXTBOOK OF BOTANY

FIG. 8 1. — A small part of a cross sec-
tion through a young portion of the stem
of a bean ; a, epidermis ; b, cortex ; Stem. — For
c, bast ; d, cambium ; e, wood ; /, pith. may use a

end to swing about in a
way that will be ex-
plained more fully in
Chapter XV. In all va-
rieties the stem branches
freely, each branch begin-
ning as a bud in the axil
of a leaf, and practically
all that will be said about
the stem applies also to
the branches.

162. Inner Structure of the
this study we
cross section
through the younger part either

of the main stem or of a good-sized branch (Fig. 81) ; the section

should be cut between the

points of attachment of two

leaves. In such a section we

shall observe that the vascular

bundles are arranged, like the

bundles of the pine, in a hol-
low cylinder, which in the

cross section looks like a ring.

Between the wood and the

bast of each bundle are one or

two layers of cambium cells.

In a section through an older

part of the stem (Fig. 82), we

find that the cambium makes

a complete ring, and that its

cells have begun to divide so

as to form more wood on the

inside and more bast on the

outside of the ring. The bean FIG '82. -Part of a cross section
through an older portion of the bean

stem therefore grows in thick- stem> in which the division of the cam.

ness just as the pine stem bium cells has beguri and new bast and

does ; but since the bean plant wood are being formed ; a, epidermis ;

lives only one season, its stem b, cortex; c, bast; d, cambium; e, wood;

never grows to be very thick, /, pith.

THE BEAN 139

and since it never contains a large proportion of wood, it does not
become hard like the stems of trees and shrubs. The vascular bundles
in the stem branch from time to time, and the branch bundles run out
from the stem into the branches and leaves.

163. Foliage Leaves. — The bean has nothing that cor-
responds to the scale leaves of the pine. All the leaves that
are formed later than the two seed leaves are foliage leaves,
except, of course, the special leaves (sepals, petals, stamens,
and pistil) that constitute the flower, and except also some
very small green leaves
(bracts) borne in the
flower clusters. The
foliage leaves are alter-
nately arranged upon
the stem ; that is, only
one is borne at any par-
ticular level, and no two
successive leaves arise
from the same side of FIG. 83. — Part of a cross section of a leaf
the Stem. The blade (of the lily) ; a, upper epidermis ; 6, layer of
r i, 1 c /-cv o \ • closely packed cells ("palisade layer"); c, a
of each leaf (Fig. 84) is vasJJ bundle . d> anPair.pore.

divided into three leaf-
lets, each with a short stalk of its own. Two of the leaflets
are attached to the sides of the leaf -stalk, opposite each
other ; the third is borne at the end of the leaf -stalk.

At the point where the leaf-stalk joins the stem or branch,
there are two small structures that look like little leaves ;
they are called stipules and are really parts of the leaf to
whose stalk they are attached. At the base of the stalk of
each side leaflet, where it joins the leaf -stalk, there is also
an attachment like a stipule but smaller; and at the base
of the stalk of the terminal leaflet are two similar attach-
ments.

The blade of each leaflet has a midrib from either side of
which pass off branch veins (vascular bundles), some large

140

TEXTBOOK OF BOTANY

and some small. These branch veins in turn branch,
their branches branch and so on, thus forming a network of
veins like that in the cucumber leaf. The leaves as well
as the stems and branches of many varieties of beans bear
fine, short hairs. If we examine the leaves of a bean plant
in the evening or at night, we shall see that their position
is somewhat different from what it was during the day.
Each leaflet has drooped so as to bring the three leaflets
closer together, and the leaf as a whole stands more nearly

vertical and closer
to the stem or
branch. These
changes in posi-
tion are caused by
a bending of the
leaf-stalk and of
the stalk of each
separate leaflet.
The bending of
the leaf -stalk takes
place in a short,
thickened region
near its base. The
stalks of the leaf-
lets are so short that practically the whole of each stalk
takes part in the bending and so corresponds to the thicker
part of the leaf -stalk. In the morning the leaves and leaflets
move back to the position in which we are accustomed to
see them during the day. The changes in the position of
the leaves at night are often called sleep movements, although
they really have nothing to do with anything like a sleep of
the plant.

164. Roots. — The root system of the bean consists of
a rather short primary root with many slender branches
which themselves branch ; some of the branch roots may

FIG. 84. — A bean leaf in its night position.
After Sachs.

THE BEAN 141

become almost as thick as the primary root, and in many
cases they are longer. Some short adventive roots also
grow from the lower part of the stem. The root system of
a bean bears many small swellings, in which are great num-
bers of bacteria. Something was said in Chapter II about
the bacteria that live in these swellings on the roots of the
bean and of many of its relatives (see § 41 and Fig. n).
We have seen that these bacteria can use the nitrogen of
the air, and that they are of great value to the host plant
(in this case the bean) because they provide it with the
nitrogen-containing substances that it needs for food.

165. Flowers. — These are borne in clusters. The stalk
of the cluster (the peduncle) is in each case a branch or the
end portion of a branch (or occasionally the end of the main
stem) . Each flower has a short stalk of its own (a pedicel)
which grows from the axil of a very small leaf (a bract) that
is borne on the peduncle. Each pedicel, therefore, is also
a branch. The flower cluster of the bean is of the sort
known as a raceme. Each flower is so attached to the
peduncle that it stands out horizontally, or nearly so. For
this reason we can speak of the upper and lower sides of a
flower.

A bean flower (Fig. 85) seems at first sight entirely dif-
ferent from anything that we have seen in the pine or in
any of the lower plants. Really, however, the flower of the
bean corresponds very closely to the cones of the pine. One
difference lies in the fact that a single pine cone bears only
one kind of spore leaves, whereas the same bean flower con-
tains both microspore leaves (stamens) and a macrospore
leaf (which forms the pistil). Therefore-, while the pine
has two kinds of cones, the bean has only one kind of flower.1
The flower has probably developed from a structure not

1 Many angiosperms, however, like the cucumber, bear stamens and pistils in
separate flowers. In such cases the staminate and pistillate flowers correspond
respectively to the staminate and carpellate cones of the pine.

I42

TEXTBOOK OF BOTANY

unlike a pine cone by a shortening and flattening of its cen-
tral axis, so that the spore leaves are borne at nearly the
same level, instead of at different levels upon a long axis.
The number of spore leaves also is much reduced in the bean
flower.

Another thing that distinguishes it from the pine cone
is the presence, outside the spore leaves, of two sets of outer
leaves (sepals and petals) which have nothing directly to do

FIG. 85. — Three views of a bean flower : A, from the top ; B, from the
side; C, also from the side, after the removal of a wing and part of the
standard; s, sepals; st, standard; k, keel; w, wing. The stamens and
pistil are enclosed in the keel.

with spore production, but which are none the less impor-
tant organs of the flower. Thus a flower, like a cone, is
really the end of a stem or branch on which grow certain
special leaves, some or all of which bear spores.

166. Sepals and Petals. — These parts develop before
the stamens and pistil, so that the latter are covered and
protected in the bud while they are growing. When the
stamens and pistil are nearly or quite full grown, the bud
opens — that is, the sepals and petals spread out. The
five green sepals, which are the outermost parts of the flower,
are united for the greater part of their length into a tube,
their free ends projecting as short teeth from the edge of
the tube. The petals of some varieties of the bean are

THE BEAN

143

white ; those of other varieties are colored in various ways.
The uppermost petal (the standard) is broad and erect, ex-
cept that its lower part is bent so as to be horizontal and
to cover the lower parts of the other petals. At its upper
end the standard is two-lobed, so that it looks as though it
might be composed of two petals ; but this is not the case.
On the sides of the flower
and below the standard are
two other petals, called
wings; they are broad and
rounded, but each is much
narrowed at the base. Be-
low the wings are the two
remaining petals ; they are
narrow and are united, ex-
cept at their ends, into a
structure like a trough with
its opening upward ; this
trough-shaped structure is
the keel. Its outer end is
spirally twisted.

FIG. 86. — A, a pollen grain of the
bean, as seen from the outside. B, a
cross section of a pollen grain ; a, one

167. Stamens. — Just of the germ poreS) where th'e outer

within the petals are the layer of the wall is lacking, and where

stamens or micros pore leaves,
which here are not at all
like foliage leaves. Of the
ten stamens in the bean

the pollen tube, surrounded by the
inner layer of the wall, may push out
when the pollen grain germinates;
b, the vegetative cell; c, the genera-
tive cell. C, a pollen grain (of the
lily) which . has germinated ; d, the
flower, nine are united by two male gamete nudei. e> the pol]en

their filaments into a partial tube ; /, the nucleus of the vegetative

tube that is open on the cell> which has moved to the fnd of
. 1 _1 . . , the tube. B after a preparation by

upper side. This partial Miss Mabel Brown,
tube really forms a second

trough that lies inside the trough-shaped keel. When all
the parts of the flower are in their usual positions, the one
free stamen covers the open part of the trough made by the

144 TEXTBOOK OF BOTANY

union of the other nine. This trough collects and holds
the nectar, which is produced on the inner sides of the bases
of the stamens. Each stamen is composed of a long, slender
filament and a small anther. The anther contains two
pollen sacs (microspore sacs) in which the pollen grains are
borne.

The history of the pollen grains of the bean is much like
that of the pollen grains of the pine. Each of the many
microspores formed in the pollen sac is a young pollen grain ;
but the microspore germinates while still in the sac by di-
viding into two cells, so that when the pollen grain is shed
it is no longer a microspore but a young male plant, which
consists of a small generative cell and a large vegetative
cell (Fig. 86, B). The wall of the pollen grain is compara-
tively thick ; . its shape and color and the nature of its outer
surface differ in different species. When the grains are
ready to be shed, the sacs that
contain them split open length-
wise.

168. The Pistil. — In the cen-
tral part of the flower is a pistil,
which may be thought of as a
macrospore leaf that has been
folded over along its midrib until
its edges joined. As a result, the
lower, enlarged part of the pistil

FIG. 87. -T bean, ovule <the ovar^ contains a chamber
(macrospore sac) ; a, micropyle; within which the ovules (macro-
b, outer integument; c, inner spore sacs) are borne. The ovary
±TS Afl™I! Hes horizontally inside the trough
tion by Miss Mabel Brown. formed by the nine united sta-
mens ; it is rather long and is

the part which will develop later into a pod. The ovules,
usually not less than four nor more than ten in number,
are attached alternately to the two edges of the leaf.

THE BEAN 145

Since these edges touch each other, all the ovules lie nearly
in a straight line ; but if a pod is split open, we can see
that in reality some of the ovules are attached to one edge
and some to the other. Each ovule (Fig. 87) has a thick
stalk, which is bent in such a way that the body of the
ovule is turned part way backward and its free end (with
the micropyle) is near the wall to which the stalk of the ovule
is attached. Two integuments are formed about the ovule,
instead of only one as in the pine ; they leave a narrow open-
ing (the micropyle) at the free end of the ovule.

The long, slender part of the pistil above the ovary is the
style ; the style, which contains a slender canal that is con-
tinuous with the cavity of the ovary, bends near the ovary
and turns upward ; it lies inside the keel, and so its upper
part is coiled in the same way that the end of the keel is.
The upper end of the style is a little thickened, and on the
inner side of this thicker part is the stigma. The surface
of the stigma is rough, and when it is touched a sticky
liquid oozes from it. The ovary and the lower part of the
style are covered with many short hairs, and there is another
brush -like group of hairs on the inner side of the upper part
of the style, just below, and on the sides of, the stigma.

169. The Female Plant. — One cell within the ovule
grows to be much larger than any of the others ; this is the
macrospore mother cell (d, Fig. 87). It divides to form a
row of three macrospores (instead of four, as in the pine) ;
and one (the largest) of these, macrospores, as in the pine,
develops into a female plant (Figs. 88 and 89).

But the female plant of the bean is much smaller and simpler than
the female plant of the pine. It consists of only seven cells. Each
cell has one nucleus, except that the central cell, which is much the
largest, contains two nuclei (Fig. 89, /). At the end of the female
plant nearest the micropyle is a group of three cells ; one of these
three is the egg (Fig. 89, d). This little seven-celled plant remains
throughout its life, like the female plant of the pine, shut up inside the
ovule.

i46

TEXTBOOK OF BOTANY

170. Pollination. — The pollen of the bean is usually car-
ried from the stamen to the pistil by insects. Insect-pol-
lination is more economical and effective than the wind-
pollination which is depended upon by the pine, because in-
sects, flying directly from flower to flower, are likely to carry
more of the pollen to the exact place where it is needed. The
insects that pollinate the bean are, most commonly at least,
large bumble-bees. The pollen drops out of the pollen sacs
when it is ripe and is caught in the bottom of the keel. None
of it falls upon the stigma, because the style projects beyond

FIG. 88. — A , the three macrospores into which the macrospore mother
cell of the bean (d, Fig. 87) has divided. B and C, stages in the develop-
ment of the largest of the three macrospores into a female plant. After
Miss Mabel Brown.

the stamens. In the keel, the pollen is covered by the wings
and other parts of the flower. It cannot be blown or washed
away, and it is protected from moisture, which is harmful
to it as it is to the pollen of most plants.

When a bee alights upon one of the wings of the flower,
both the wings and the keel are pressed downward. This
allows the style to push out of the keel, and the hairs near

THE BEAN

147

its end brush out the pollen that has collected in the bottom
of the keel. The nine united stamens are pressed downward
with the keel, but the upper free
one is not. A space is thus left
between the free stamen and
the group of nine. To reach
the nectar, the bee must insert
its proboscis to one side of the
free stamen and into the trough
formed by the united stamens:
In doing this, the proboscis first
touches the stigma ; if there are
pollen grains on the proboscis
(which were collected on an
earlier visit of the bee to an-
other flower), they are brushed
off on to the stigma and are
held there by the sticky fluid
that begins to flow when the
stigma is touched. Next the
bee's proboscis touches the
brush of hairs on the style and
some of the pollen grains that
are held by the brush stick to
the proboscis. When the bee
leaves the flower, its proboscis
is prevented from again touch-
ing the stigma by the hairs on
the style, so that none of the
pollen from this flower is left on
its own stigma. The pollen
that is carried away on the
bee's proboscis may stick to the stigma of the next
flower that it visits. Thus the structure of the flower
favors cross-pollination — that is, the landing of pollen

FIG. 89. — The female plant
of the lily (with neighboring cells)
at the time of fertilization :
a, pollen tube; b, two cells of
the female plant lying beside the
egg; c, a male nucleus uniting
with the egg nucleus, d; e, an-
other male nucleus which will
unite with two nuclei of the
female plant at /; g, three cells
of the female plant lying at the
opposite end from the egg.

148 TEXTBOOK OF BOTANY

from the anthers of one flower upon the stigma of another
flower.

When pollen is thus carried by insects from one flower to
another, it does not necessarily follow that the second flower
will be on another plant. But this will certainly be true in a
large proportion of cases, especially since the different flowers
of a plant open in general at different times ; consequently
the stigma of an older flower is likely to have been pollinated
before a younger flower of the same plant opens. But it
appears that if insects do not visit a bean flower, seeds are
nevertheless sometimes formed. So it is evident that in
such cases the pollen in some way reaches the stigma of the
same flower — that is, self-pollination occurs. Just how this
comes about is not yet known. The place in which the pol-
len grains of the bean finally land is very different from that
which is reached by the pollen grains of the pine. This must
be so, because the ovules of the bean are shut up inside the
ovary, so that the pollen cannot, as in the pine, be carried
to the ovules themselves.

Since a pollen grain of the bean must germinate upon the
stigma far from any of the female plants (which are inside
the ovules), the pollen tube has a much greater distance
through which to grow than had that of the pine. The size
and colors of the sepals and petals of many flowers seem to
be of use in attracting the attention of insects to the places
where nectar is to be found.

In general it is true that those angiosperms which, like the
bean, have more or less showy flowers are insect-polli-
nated ; and that others, such as the grasses and most of the
forest trees, which have small, inconspicuous flowers, are
wind-pollinated. There are exceptions to the latter rule,
because some insects seem to be attracted by the odors of
the flowers as well as by their size and color, and so they
may visit small flowers, such as the mignonette, that are
fragrant.

THE BEAN

149

171. The Mature Male Plant ; Fertilization. — The pollen tube,
in the bean as in the pine, is an outgrowth of the vegetative cell of
the pollen grain (Fig. 86, C). Soon after the tube begins to grow, the
generative cell moves into the tube and there divides to form two male
gametes. The mature male plant of the bean consists therefore of
only three cells — the vegetative cell which includes the pollen tube,
and the two male gametes. The pollen tube grows from the stigma
down through the canal of the style, feeding as it grows on substances
produced by the cells lining the canal ; it pushes into the ovary, reaches
an ovule, grows through the micropyle and into the tissues of the
ovule, and finally its tip penetrates the female plant itself (Fig. 89).
The end of the pollen tube now bursts, so that its contents are forced
into the interior of the female plant. Of these contents, the vegetative
nucleus and apparently the cytoplasm (includ-
ing the cytoplasm of the male gametes) are of
no further use, except perhaps as food. The
nucleus of one male gamete unites with the egg
nucleus, and the result of this union is the
zygote which will develop into a new asexual
plant. The other male gamete nucleus passes
into the large central cell of the female plant
and there unites with the two nuclei already
present in this cell. >

172. Formation of the Seed. — The
central cell, containing the large nucleus
that has been formed by the union of
three, begins to develop into endosperm
before the zygote begins to grow into
an embryo; so that when the embryo is
formed a supply of food is ready for it
in the endosperm. The cells of the
female plant, other than the egg and the
large central cell, are crushed and dis-
appear. The embryo feeds upon the
endosperm ; but the endosperm also
continues to grow (Fig. 90), using the
surrounding tissue of the ovule for its
food. However, the developing endo-

FIG. 90. — A young
bean embryo, almost
surrounded by endo-
sperm cells which will
be used as food by the
embryo ; a, embryo ;
b, endosperm ; c, inner-
most layer of cells of
the body of the ovule.
After a preparation by
Miss Mabel Brown.

TEXTBOOK OF BOTANY

sperm is used as food for the embryo about as rapidly as
the endosperm itself develops ; and finally most of the food
that had been stored in the ovule is transferred to the two
seed leaves of the embryo. The ripe seed thus contains no
endosperm, and the thick seed leaves fill much the greater
part of the space inside the seed coats. In this respect the
bean seed is like the seed of the squash.

The body of the embryo (consisting of radicle and plumule)
is much smaller than the seed leaves. It lies between the

seed leaves close to the
edge by which the seed
was attached to the pod.
The end of the radicle
projects from between
the seed leaves and is
turned toward the micro-

D r]

pyle. The plumule is

A^V^&ilS: »™d ** b— tw°-

the scar by which the seed was attached, three very small second-
and, just above, the micropyle; C, with ary leaves. The food in
one-half of the seed coat and one seed leaf , , ., •, -, • a

removed, showing the plumule, radicle, the Seed leaves 1S chiefly
and remaining seed leaf. starch and proteins. The

bean, like some other

plants of the same family, such as the pea and the lentil,
stores a comparatively large proportion of proteins in its
seed leaves. This is one reason why the seeds of these
plants are so valuable to us as food. Little or nothing of
the body of the ovule is left in the ripe seed. The integu-
ments develop into thin, hard seed coats.

The parts of the bean seed thus correspond closely to those
of the pine seed, except that such endosperm as was formed,
although it resembled the endosperm of the pine seed, arose
in a quite different way and disappeared before the seed
was mature. In the ripe bean seed (Fig. 91) the scar that
marks the point at which the seed was attached to the pod

THE BEAN

is on one side — the side of the seed that is somewhat hol-
lowed. Near one end of this scar is a small hole — the
micropyle.

173. The Fruit (Fig. 92). — As the ovules grow into
seeds, the ovary that contains them develops into a fruit
(the pod). It grows rapidly. In the case of those varieties
whose young pods are eaten in the form of
" string beans," they are large enough for
use ten or twelve days after pollination.
The ovary is horizontal or nearly so, as
we have seen, when the flower opens.
But as it grows after fertilization, its
weight bends the pedicel, and it hangs
downward. The walls of the pod are
green or greenish at first but sooner or
later they change, usually to yellowish or
brownish, sometimes to other colors, and
become thin, dry, and hard. The pods of
some varieties are still green at the string
bean stage ; those of others are yellow at
this time. .

FIG. 92. — A bean
fryit with half of the

r^i , - , , . pod removed, show-

The base of the style remains as a fng the seeds and the

remains of the style ;
b, the sepals.

pointed projection at the end of the pod ; way in which they
the rest of the style and the stigma wither are attached; a, the
after pollination. A small amount of
tissue develops between the seeds, so that
each one lies in a separate cavity ; but as the fruit ripens
these partitions dry and shrivel away. A ripe pod shows
a bulge corresponding to the position of each seed. In a
cross section through the pod of many varieties of bean
(Fig. 93), one sees a group of vascular bundles, containing
many thick-walled cells, near one edge of the section, and
two similar but smaller groups near the opposite edge.
The inner layer of the pod also contains thick-walled
cells. The groups of bundles near the edges of the pod

152

TEXTBOOK OF BOTANY

are the "strings" that are familiar to
every one who has shelled or cut up
green beans. The strings and the inner
tough layer of the pod were present in
all the earlier varieties of beans ; but in
more recent years improved varieties
have been produced in which the thick-
walled cells are either lacking altogether
from the vascular bundles and the inner
^^^ the pod, or else are late in
developing.

174. Germination of the Seed (Fig.
94). — The conditions under which seeds
will germinate have been carefully
studied in connection with the bean
and some of its relatives. One neces-
sary condition is the presence of water,
a good deal of which is absorbed by the
seed coat and by the embryo. Bean seeds germinate more
quickly if they are first placed in cold water and left there
overnight. Another necessary condition is a suitable tem-
perature. Bean seeds will not
germinate, no matter how
well they are supplied with
water, below 32° F. nor above
about 122° F. Another con-
dition is the presence of oxy-
gen. Seeds will not germinate
in an atmosphere from which
the oxygen has been removed ;
nor will they germinate well
in soil which is so thoroughly

FIG. 93. — Cross sec-
tion through a young j Q£

bean fruit and a seed ;

a, groups of vascular
bundles (" strings ") ;

b, outer layer of the
pod; c, inner layer;

d, outer seed coat ;

e, inner seed coat;
/, seed leaf; g, stalk
by which the seed is
attached to the pod.

water-soaked that there is
little or no air in its pores.
Germination begins by the

FIG. 94. — Stages in the germina-
tion of a bean seed and the devel-
opment of the seedling.

THE BEAN 153

elongation of the radicle, which pushes out through the
micropyle, cracking the seed coat as it does so. If the
seed germinates below the surface of the ground, the proc-
ess is very similar to the germination of the squash seed
(see Chapter I, § 2, and Fig. 2), except that there is nothing
like the " peg " of the squash seed to help in pushing
off the seed coat. The radicle bends if necessary, so that
its tip grows downward and forms the primary root. The
upper part of the radicle now grows in such a way that
the seed leaves and plumule are pushed upward. The seed
leaves, and for a time the seed coat, protect the small sec-
ondary leaves and the tip of the plumule from injury by
hard objects. After the plumule and seed leaves have
reached the surface of the soil, the radicle, which has re-
mained bent until now, straightens, the seed leaves sep-
arate, and the small secondary leaves grow and become
green ; they are the first foliage leaves of the plant. The
large seed leaves become greenish but soon begin to shrivel
and finally fall off. The food that they contain is used in
the growth of the radicle and plumule.

In some varieties of bean and in the pea the seed leaves
remain within the seed coat below the surface of the soil,
and merely separate so that the plumule may push out and
up. In these cases, the plumule in its upward growth re-
mains bent and so protects its delicate tip as well as the
tender secondary leaves.

175. Life Cycle of the Bean. — Although their life his-
tories are very much alike, the bean shows an advance over
the pine in several respects. The chief points of difference
between pine and bean, which are the same points that dis-
tinguish gymnosperms and angiosperms in general, are the
following :

a. The spore leaves of the pine cone are borne at dif-
ferent levels upon a comparatively long axis ; in the
bean flower this axis is much shortened, so that all the

154 TEXTBOOK OF BOTANY

spore leaves (stamens and pistil), as well as the sepals
and petals, are borne at nearly the same level.

b. The seeds of the pine are borne on the exposed surfaces
of the macrospore leaves; those of the bean are en-
closed within the ovary, which has been formed by a
folding of the macrospore leaf.

c. The sexual generation, already much reduced in the
pine, is reduced still further in the bean. The female
plant now consists of only seven cells, the male plant
of only three.

d. The endosperm of the pine is formed before fertiliza-
tion ; it is the vegetative tissue of the female plant.
•That of the bean develops after fertilization from a cell
whose nucleus has been formed by the union of two
nuclei of the female plant with one nucleus of the male
plant ; it disappears before the seed is ripe ; but in
the seeds of the corn (see Chapter XIII) and in those of
many other angiosperms, the endosperm is still present
in the ripe seed, just as it is in the seed of the pine.
The life cycle of the bean may be represented by a dia-
gram substantially like that used for the pine (Fig. 77).

176. Species and Varieties. — The name " bean " is applied to
many very different plants. But nearly all the plants that are culti-
vated for food in the United States and Canada under this name are
varieties of two species of the genus Phaseolus. Most of the common
field beans and garden beans belong to the species Phaseolus vulgaris;
they are sometimes classed together as " kidney beans." A list of
145 distinct varieties of kidney beans grown in the United States was
prepared in 1907, and it is estimated that in all, throughout the world,
there are at least 500 varieties. Among the kidney beans are both
low and climbing forms, and they differ greatly from one another in
the color, shape, and size of their pods and seeds, as well as in various
other ways. P. lunatus includes the Lima beans, of which there are
perhaps fifty varieties, some low and some climbing. Lima beans
are not so much grown in other parts of the world as they are in the
United States. Several others of the 150 or more species of Phaseolus
are cultivated in various parts of the world. P. multiflorus includes

THE BEAN '155

the varieties known as " scarlet runner beans," that are raised both
for food and for ornament. Certain varieties of P. acutifolius, a species
native to the southwestern United States, have long been grown by
the Indians for food and are now coming into general cultivation
under the name of " tepary bean." P. radiatus, the " Adzuki bean,"
is much used in Japan and has been introduced into the United States.

177. Relatives of the Beans. — The beans belong to the pulse
family, which includes more than 12,000 species. With one exception
(the composite family) this is the largest family of living seed plants.
Among the members of the family are hundreds of species that are
useful to man. The seeds and fruits of many are used as food ; the
roots of some are eaten, and some supply substitutes for coffee and tea.
Some are used as food for domestic animals. The wood of some trees
belonging to this family is used in building, for cabinet work, or as a
source of dyes. The fibers of some are used in making ropes, in f weav-
ing, and in paper-making. Others are sources of gums and balsams,
starch, oils, and perfumes. A considerable number are drug-plants,
and many are cultivated for ornament. Vicia faba, the " broad
bean," is grown largely in Europe ; the seeds are- eaten, like those of
the kidney beans, and the plant serves as food for horses and sheep.
This is the plant to which the name bean was originally given. Other
well-known members of the family are the pea, the lentil, lupines,
vetches (which include Vicia faba), the asparagus bean, the cow-pea,
the soy-bean, the hyacinth bean, the peanut (whose flower-stalks turn
downward and grow after pollination, so that the fruits are pushed
into the soil and ripen there) ; the clovers, alfalfa, the sensitive plant,
the honey loeust, the black locust, the sweet-peas, laburnum, wistaria,
the tamarind, the acacias, the sunn hemp, and Indigofera (which supplies
indigo). The drug known as " senna " consists of the dried leaves of
Cassia; licorice is obtained from the roots of Glycyrrhiza.

178. Historical Note. — Phaseolus vulgaris, P. lunatus, and P.
multiflorus (kidney beans, Lima beans, and scarlet runner beans) are
natives of the American continent, but they are not now known in the
wild condition. All three (including many varieties of kidney beans)
were cultivated by the American Indians before the coming of Colum-
bus. Seeds of Lima beans and kidney beans are reported to have been
found in old Indian tombs in Peru. Kidney beans seem to have been
introduced into Europe about the middle of the sixteenth century ;
Lima beans and scarlet runner beans were taken over later. Broad
beans have been widely used in Europe for centuries ; they were grown
by the ancient Egyptians and by the lake-dwellers of Switzerland, and
their origin is unknown.

CHAPTER XIII

THE INDIAN CORN

179. The Stem. — The corn, like the bean, is an angio-
sperm ; but it differs from the bean, as we shall see, in several
rather important respects. The up-
right stem is grooved on one side ; at
each joint of the stem the position of
the groove changes from one side of
the stem to the opposite side. The
stem in most varieties of corn under
ordinary conditions forms no branches
except the special ones that bear
flowers. Like the stems of the cu-
cumber and the bean, it grows in
length by means of a terminal bud.
But its growth ceases when the
" tassel " is formed at the top ; so
that the corn stem has a more
definite limit of length than has the
bean stem. The length of the stem
is very different, however, in different
varieties of corn, ranging, so it is
said, from eighteen inches to thirty
feet or more. The flowers and fruit
are formed during the same year in
which the seed germinates. The corn,
therefore, like the bean, is an annual.
A cross section through the corn
stem (Fig. 96) looks very different
156

FIG. 95. — Indian corn
plants.

THE INDIAN CORN

157

from one through the bean
stem. The most striking
difference is in the arrange-
ment of the vascular bundles.
Instead of being in a cylinder
(a ring in cross section), the
bundles are scattered through
the stem. Another impor-
tant point of difference is that
there is no cambium: a vascu-
lar bundle of the corn con-
sists only of wood and bast.
There being no cambium, the

3K±

After Stevens.

FIG. 97. — Lower portion of a
corn stem, showing the cluster of
roots growing from the base, the
brace roots, and one (the third)
secondary leaf. The very small
blade of the first secondary leaf
has withered, and only a portion
remains of the blade of the second
secondary leaf.

stem cannot grow in thickness
after the cells of any particular
part are fully grown. This is
why the corn stem is of about
the same diameter throughout
its length, instead of being
thicker toward the base as the
bean stem is.

180. Foliage Leaves.— These
are alternately arranged, like
the leaves of the bean. A corn
leaf (Fig. 95) has no leaf-stalk.
The lower part of the leaf forms
a sheath that surrounds the
stem for some distance above
the joint where the leaf is at-
tached. The upper, outspread
part of the leaf is the blade.
On the inner side of the leaf, at
the place where the blade joins

158 TEXTBOOK OF BOTANY

the sheath, there is a short, thin outgrowth. The blade
is long, drooping at the tip, narrow in proportion to its
length, and has a long, slender point. Its edge bears many
very fine teeth. On its upper surface a shallow groove
runs lengthwise above the midrib. The arrangement of
the veins looks quite unlike that in the bean leaf. Many
veins start from the base and run nearly parallel with one
another to the upper end of the leaf. The middle vein
(midrib) is much the largest. The midrib and the veins
that run parallel with it do not seem to be branched, as are
the veins in the bean leaf. There really are many slender
branch veins, which form a network ; but these interlacing
branches are so delicate that they are not easily seen, and
therefore the leaf is said to be parallel-veined.

181. Roots. — The primary root does not become very
long. Early in the life of the young plant, other roots begin
to grow from the lower part of the stem (Fig. 103, C, D, E) ;
indeed, some of these roots were already present in the seed
as very small swellings upon the sides of the plumule. Both
the primary root and the roots that grow from the stem give
rise to fine branch roots. The mature corn plant, there-
fore, has a cluster of slender branching roots (Figs. 97, 98)

FIG. 98. — The root system of a corn plant at the time of flowering.

THE INDIAN CORN

159

all of much the same size, one of which is the primary root.

As the plant grows,

circles of new short

roots (brace roots) grow

from some of the lower

joints of the stem above

ground where the leaves

are attached. The lower

ones of these new roots

reach down into the

soil ; later they shorten

somewhat, so that the

plant is firmly anchored

to the soil.

182. Flower Clusters;
Pistillate Flowers. —
The flowers of the corn,
like those of the cucum-
ber, are of two kinds,
pistillate and stami-
nate. Both kinds are
borne in clusters. The
cluster of staminate
flowers is the " tassel."

FIG. 99. — 'A, a spikelet from a young
ear of Indian corn, bearing two pistillate
flowers, one fully developed and one rudi-

t IS borne at the Upper mentary; a, rough, hairy tip of stigma
("silk") ; b, lower, less hairy part of stigma ;

c, ovary; d, scale-like leaves (bracts or
"chaff"); e, the undeveloped flower. B, a
spikelet on a larger scale, with the bracts

is and the greater part of the silk removed ;
a, base of the stigma; b, style; c, ovary;

d, rudimentary stamens; e, pistil, and/, one
of the stamens, of the undeveloped flower of
the spikelet. C, tip of the stigma, which is
forked and bears many hairs. D and E, por-

. tions of the lower part of the stigma as seen

The ear or ears develop from Opposite sides. A after Schmeil;
ordinarily in the axils of B,C,D,E after Weatherwax.

end of the stem, de-
veloping from the ter-
minal bud. A cluster
of pistillate flowers
an " ear." It develops
from an axillary bud,
and so each ear is found
in the axil of a leaf.

i6o

TEXTBOOK OF BOTANY

some of the upper leaves. But if the ears that appear in the
axils of these are removed while still very small, new ones will
be formed in the axils of some of the lower leaves.

The cob of an ear of corn is really a branch that bears many
flowers, closely packed together. The husks that cover the
ear are leaves of a special form, which protect the flowers

and young fruits from
injury. Each cob bears
many spikelets (small
branches) , which are
arranged in rows run-
ning lengthwise of the
cob. Each spikelet
(Fig. 99, A, B) bears
two very small pistil-
late flowers. Of these
two, the lower flower
(that nearer the cob)

in most varieties of corn

FIG. ioo. — A, a lengthwise section
through a pistillate spikelet of Indian corn ;
a, base of stigma.; b, style, penetrated by a
narrow canal ; c, ovary ; d, ovule ; e, pistil,
and /, stamen, of the undeveloped flower.

B, a lengthwise section through an ovary; never develops fully and
a, outer integument; b, inner integument;
c, ovule ; d, outline of the female plant, devel-
oped from the macrospore; e, micropyle.
A after Weatherwax ; B after True.

never forms a kernel.
The upper, fully de-
veloped flower of the
spikelet has a single

pistil formed, like that of the bean, by a single macrospore
leaf ; there are also three rudimentary stamens, which are
hardly to be made out in a full-grown flower. Around
and between the flowers there are scale-like leaves which are
not parts of the flowers themselves but are probably to be
thought of as bracts. These bracts make up the chaff that
remains between the kernels after the ear is ripe.

The pistil consists of a rather large ovary containing a
single ovule ; a short projection, the style, at the outer
end of the ovule and on its upper side (that is, the side
turned toward the tip of the ear) ; and the " silk," which is

THE INDIAN CORN

161

— — ti

attached at one side of the style and which seems to be an
extremely long stigma. The silk projects beyond the husks ;
all along its surface are hairs, which are most numerous near
the tip. The cluster of stigmas or silks hanging from the
end of the ear thus
furnishes an excellent
means for catching and
holding the pollen
grains. The flowers at
the base of the ear are
the oldest and first to
mature, and therefore
the kernels in this part
of the ear develop first.
183. Staminate Flow-
ers. — The tassel is a
much-branched cluster
of staminate flowers.
The final branches of
the cluster are spikelets,
corresponding to the
spikelets of the ear.
Each spikelet of the
tassel (Fig. 101, A) also
bears two (or occasion-
ally more) flowers, as well as several chaffy bracts or scales.
A flower consists of three stamens, a rudimentary pistil,
and two small, swollen, leaf -like structures that perhaps
correspond to sepals. Each stamen is composed of a fila-
ment which in the mature flower is long and drooping,
and a long anther which has four pollen sacs. Since there
are many staminate flowers in a " tassel," the amount of
pollen is very great ; it has been estimated that as many
as 18,000,000 pollen grains may be produced by a single
corn plant.

FIG. 101. — A, a spikelet from the
"tassel" of the Indian corn, bearing two
staminate flowers; a, one of the bracts;
b, filament; c, anther. B, a lengthwise
section through an unopened staminate
flower; d and e, bracts; /, filament, now
short, but which will become much longer
when the flower opens ; g, the rudimentary
pistil; h, one of the two small sepal-like
parts. B after Weatherwax.

1 62 TEXTBOOK OF BOTANY

184. Pollination. — The history of the formation of the
pollen grain within the pollen sacs, that of the macrospores
within the ovule (macrospore sac), and that of the develop-
ment of the female plant from one macrospore are so nearly
the same in the corn and in the lily that it is not necessary
to repeat what was said on these subjects in the previous
chapter. Since pistils and stamens are borne (except in
rare cases) in different flowers, pollination in the corn must
be, strictly speaking, cross-pollination ; but the pollen that
falls upon a particular stigma may come from a staminate
flower either on the same or on a different plant. Polli-
nation may result from the mere falling of pollen from stam-
inate flowers upon the silk of the pistillate flowers of the same
plant ; but more commonly pollination is brought about by
the wind, just as it is in the pine, and this usually, though
not always, means that the pollen from the staminate flowers
of one plant is carried to the pistillate flowers of another.

185. Formation of Seed and Fruit. — The embryo and
endosperm begin their development in the ovule of • the
corn in much the same way that the corresponding processes
begin in the bean ovule. But the embryo of the corn re-
mains small ; the endosperm continues to grow, using up
most of the substance of the ovule as it does so, and finally
the endosperm makes up the greater part of the bulk of the
seed. As the seed grows, the embryo is pushed to one side ;
it lies at the base of the upper side of the ripe seed. The
endosperm is full of food which will be used by the embryo
when the seed germinates. One great difference between
the bean and the corn seed is in the place in which the food
is stored. Most of the food of the bean seed is in the seed
leaves ; most of that of the corn seed is in the endosperm.

The greater part of the endosperm formed in the bean
seed is used as food for the embryo before the seed ripens ;
but in the corn most of the endosperm is not used in this
way until the seed germinates. The body of the embryo con-

THE INDIAN CORN

163

sistsof a radicle, which is turned toward the base of the kernel,

and a plumule, which is turned upward. The plumule bears

several small secondary leaves. Wrapped about the radicle

and plumule is a single broad, thick seed leaf (instead of the

two seed leaves of the bean) ;

this seed leaf separates the

radicle and plumule on the inner

side from the endosperm, and

covers them on the outer side

also, except for a very narrow

strip. The wall of the ovary,

which becomes the fruit coat

(corresponding to the pod of the

bean), remains thin and comes

to be very closely united with

the seed coat. Thus the corn

kernel is a fruit containing a

single seed; but, because the

fruit coat and seed coat have

grown so closely together, it is

only by studying the way in

which the kernel has developed

from the ovary of the flower

that we can make sure that the

outer covering of the kernel is really something more than

a seed coat.

At or near the free end of the kernel and on its upper side
(that is, on the side turned toward the tip of the ear) is a
small, sharp projection. This is the style ; the stigma (silk)
dried and withered after pollination but still remains at-
tached to the style. The end of the kernel that is attached
to the ear corresponds, of course, to the base of the ovary.
Near this place are the micropyle and the point of attach-
ment of the ovule within the ovary. But since these points
are both covered by the fruit coat they cannot be seen from

FIG. 102. — A, a side view of
a kernel of Indian corn, with a
portion of the fruit coat and seed
coat removed so as to show the
position of the embryo. B, a
lengthwise section of a kernel, cut
through the embryo ; a, style ;
b, horny endosperm; c, starchy
endosperm ; d, plumule, with sec-
ondary leaves ; e, thick seed leaf,
wrapped about the rest of the
embryo; /, radicle; g, point at
which the kernel was attached to
the cob.

1 64 TEXTBOOK OF BOTANY

the outside ; indeed, it is very difficult to make them out at
all in the ripe kernel.

186. Kinds of Food in the Kernel. — Since the food stored
within the kernel is the part of the corn plant that is valuable
to us, it is worth while to learn something of its nature. The
kernel contains four different kinds of substances that will
be useful as food either to the young corn plant that may
grow from the seed, or to the man or the animal that may eat
it. These food substances are starch, which is present in
the form of minute grains within the endosperm; sugars,
also in the endosperm as well as to some extent in the
embryo ; fats, present in small amounts in the endosperm,
but much more largely in the embryo ; and proteins, present
in the living matter of the embryo and in that of the endo-
sperm as well, and especially in certain rounded bodies in
the outermost layer of the endosperm next the seed coat.
These four classes of food substances are exactly those of
which our diet, as well as that of the lower animals, is chiefly
made up, and it is the presence of these substances that makes
the kernels of Indian corn and other grains so useful to us.

The food value of corn, as of wheat and rye, lies mainly
in its starch. The other food substances (sugars, fats, and
especially proteins) are present in too small amounts, and
for these we must look mainly to other articles of food. Pro-
teins are present in larger amounts in meats, eggs, cheese,
and in some seeds such as beans and peas. The food sub-
stances mentioned are present in different proportions in
different varieties of corn. In flint corns, the part of the
endosperm next the embryo is closely packed with starch
and is called the starchy endosperm; the part outside this,
which contains somewhat less starch and somewhat more
protein, looks clear and transparent, and is called the horny
endosperm. The horny endosperm does not shrink when the
kernel ripens, so that a kernel of flint corn remains plump.
In dent corns, the starchy endosperm extends to the outer

THE INDIAN CORN

165

end of the kernel, the horny endosperm being present only
on the sides. The starchy endosperm loses water and
shrinks as the kernel ripens, so that the outer end of the
kernel is indented. The endosperm of a pop corn is entirely
or almost entirely horny. It is the expansion of water within
the horny endosperm when the kernel is heated that causes
an explosion or " popping " of the corn. The endosperm of
sweet corns contains a large proportion of sugar and relatively
little starch ; the kernels lose much water as they ripen, and
so become wrinkled.

187. Germination. — In most respects the germination of
the corn kernel is much like that of the squash seed. The
radicle breaks
through the seed
leaf, the seed coat,
and the fruit coat,
and then bends,
if necessary, so as
to grow down-
ward into the soil
(Pig. 103, A, B).
The plumule also
breaks its way
out and grows
upward. At this
time, the plumule
and the smaller
secondary leaves
are surrounded
by the first sec-
ondary leaf , which
is so wrapped
about the plumule as to make a pointed structure with a hard,
sharp point that pushes through the soil. In time the pro-
tecting secondary leaf unrolls slightly, so that the plumule with

FIG. 103. — A, B, two views of a germinating
kernel of Indian corn. C, D, E, stages in the de-
velopment of a corn seedling ; notice the points at
which secondary roots arise.

1 66 TEXTBOOK OF BOTANY

the later leaves can push on beyond it. This first secondary
leaf remains small and forms almost no blade (Fig. 103, E).
The next forms a small blade; and each later leaf, as it
grows and opens, becomes larger than the preceding one,
until finally the size of leaf is reached that is characteristic
of the mature plant. Meanwhile the plumule has grown into
an erect stem, on which the leaves are borne. The seed
leaf remains within the kernel. It absorbs the food that is
stored in the endosperm and passes this food on to the other
parts of the seedling (radicle, plumule, and secondary leaves) .
After the food supply of the endosperm is used up, the seed
leaf is no longer useful, and it soon dies. The seed leaf of
the corn, therefore, never becomes a green foliage leaf.

188. Varieties of Corn. — Many varieties of Indian corn are in
cultivation, but all of them seem to have been developed from a single
species, Zea Mays. In 1899, a list was made of 507 varieties, divided
among the following groups : pop corns, flint corns, dent corns, soft
corns, and sweet corns. The flint corns, the dent corns, and the few
varieties of soft corn that are cultivated are usually spoken of as
" field corn." In addition to the five classes above named, two others
are known. These are the pod corns, little grown except as curiosities,
each of whose kernels is enclosed in a separate pod formed by a growth
of some of the surrounding bracts ; and the starchy-sweet corns, which
are cultivated by certain Indian tribes.

189. Relatives of the Corn. — The Indian corn is a member of the
grass family, whose 3500 species include all the wild and cultivated
grasses, the bamboos, sugar cane, sorghum, broom corn, and the cereal
grains (including, besides Indian corn, rice, wheat, barley, rye, oats,
and millet). The closest known relative of Indian corn is teosinte.
This is a native of Mexico, but it is raised as a fodder plant in many
warm countries. It is much like Indian corn, excepting that its clusters
of pistillate flowers are smaller and simpler than corn ears. It is
thought by some that Indian corn may have originated long ago as a
variety of teosinte; and that this new variety was found valuable
by the Indians, who began to cultivate it.

190. Historical Note. — Indian corn is not now known to grow
anywhere as a wild plant, excepting that now and then it escapes from
cultivation and lives wild for a few generations. Its original home
was on the American continent, probably in Mexico. It was widely

THE INDIAN CORN 167

cultivated by the natives of both North and South America when
the continent was discovered by white men. The name " maize,"
commonly applied to Indian corn, is taken from a name that Columbus
found in use among the natives of Haiti. In the United States the
plant is usually known simply as " corn." In Great Britain, " corn "
is a general term for the cereal grains, and Zea Mays is called either
" Indian corn " or " maize." The cultivation of maize was introduced
into Europe very early, and it is now found in all the temperate regions
of the earth. In Italy, Austria-Hungary, Russia, and the Balkan
States, and in Northern China, as well as in North and South America,
it is an important agricultural crop. However, nearly 75 per cent
of the world's production is supplied by the United States, where corn
has for a long period stood first among field products. In 1915, some-
thing over 3,000,000,000 bushels of corn were produced in the United
States. Most of the varieties known up to the middle of the last
century were flint and dent corns, both of which were cultivated by
Indians before the coming of white men. The first certain record of
the cultivation of sweet corn is in 1779, when it was obtained from the
Indians of the Susquehanna Valley and introduced into the region
about Plymouth, Mass. As late as 1854, only two varieties of sweet
corn seem to have been known, so that its cultivation on a large scale
is a very modern development.

191. Monocotyledons and Dicotyledons. — These are the
two great groups into which angiosperms are divided. The
monocotyledons are so named because their embryos have
but one seed leaf (cotyledon); among them are the Indian
corn and other grasses, the lilies and their relatives, the
palms, and the orchids. The dicotyledons, whose embryos
have two seed leaves, are much the larger group ; they in-
clude most of our garden plants and common weeds and
nearly all the common trees and shrubs excepting evergreens.
The squash, pumpkin, and cucumber belong to one family
of dicotyledons ; the beans and their relatives belong to
another family. Following are some of the differences be-
tween the two groups :

a. The vascular bundles in the stem of a dicotyledon are
arranged in a cylinder; in this respect dicotyledons
resemble the pine. The bast and wood of each bundle

1 68 TEXTBOOK OF BOTANY

are separated by a cambium layer, the division of
whose cells leads to the growth of the stem in thick-
ness. The monocotyledons, as a rule, have the bun-
dles in their stems scattered like those of the corn,
and form no cambium layer. This is the reason why
nearly all monocotyledons have slender stems and
remain small plants. A few of them, however, includ-
ing some of the palms, have a method of growth in
thickness quite different from that of the dicotyledons,
which enables them to become good-sized trees.

b. The leaves of monocotyledons are usually not lobed or
divided into leaflets. They are nearly always parallel-
veined like corn or lily leaves. The leaves of dicotyle-
dons are very various in form, but many of them are
lobed like oak leaves, or divided like the leaves of peas
and beans. They are netted-veined ; that is, the veins
are much branched, as in the cucumber and bean leaves,
the branch veins interlacing so as to form a network.

c. The flowers of monocotyledons most commonly have
their parts in threes or multiples of three ; for instance,
a lily flower has three sepals, three petals, six stamens,
and but one pistil, which, however, is formed by the
union of three macrospore leaves ; a staminate corn
flower has three stamens ; a pistillate corn flower has
only one pistil, consisting of a single macrospore leaf.
Dicotyledons commonly have the parts of their flowers
in fours or fives, or multiples of these numbers. Thus
a cucumber flower has five sepals, five petals, and
either three macrospore leaves or three stamens ;
but the three stamens seem really to represent five, four
of which are united in pairs. The bean, another
dicotyledon, has five sepals, five petals, ten stamens,
and one 'macrospore leaf.

d. The embryo of a monocotyledon has one seed leaf;
that of a dicotyledon has two seed leaves.

CHAPTER XIV

ROOTS AND THEIR USES

192. Origin and Growth of Roots. — A root may originate
in any one of three different ways : as a primary root, which
develops from the radicle of the embryo and is continuous
with the stem of the plant ; as a
branch root, growing out from the
primary root or from an older branch
root ; or as an adventive root, starting
from some part of the plant other
than a root — usually from the stem
or from a branch. A branch root or
an adventive root nearly always be-
gins its growth deep within the
tissues of the organ (root, stem, or
branch) from which it starts. This
is one way in which a root usually
differs from a branch, which begins

as a swelling upon the surface of the section through a root tip
organ that bears it. A root differs of the Indian com; a, root
,. 111 1-1 cap; b, embryonic region;

from a branch also, as a rule, in the c> region of growth

arrangement of its tissues, in having

its growing point protected by a root-cap, and in not bear-
ing leaves. However, it is sometimes difficult to say
whether a particular structure is a root or a branch, just
as at other times we cannot be sure whether a certain
organ is a branch or a leaf. So we must think of stems,
branches, leaves, and roots as classes into which it is con-
venient to divide the organs of plants ; but these classes
169

FIG. 104. — Lengthwise

170

TEXTBOOK OF BOTANY

are not always sharply separated, and sometimes we find
an organ that will fit into one class about as well as into
another.

There are three general forms that a root system may take :
(i) The primary root may grow into a long tap root that
bears many branches ; this form is rather
common among gymnosperms and di-
cotyledons, particularly in those that
become trees ; (2) sometimes, as in the
cucumber, the bean, and many other
dicotyledons, the primary root remains
short and gives rise to a cluster of long
branches ; (3) in many monocotyledons
the root system consists largely or
entirely of a cluster of adventive roots
that grow from the lower part of the
stem ; the primary root may remain
short (as in the corn) or it may die (as
.in the lily). But while most root
systems fall into one or the other of
these general classes, roots of very many
FIG. 105. — A barley different kinds and forms have been
root, showing the re- developed to meet different needs. The
gion just back of the g^^h of a root in length goes on in a

tip in which root hairs , , , . ,

are formed, and the short zone Just back of the root tlP

region a little farther (c, Fig. 104). Back of the region of

back in which they die growth, and to some extent perhaps in

and drop off. After ° . '. . ,.

Stevens, this region itself, root hairs are borne.

A little farther back still, the root hairs
and the other cells of the epidermal layer have died and
disappeared ; these older parts of the root are commonly
protected against the loss of water by the formation of cork
in the outer walls of what are now the surface cells. Roots
of gymnosperms and dicotyledons, especially of those which
live for more than one year, grow in thickness and form

ROOTS AND THEIR USES

171

bark ; but the bark of roots does not grow so fast nor be-
come so thick as that of stems often does.

193. Occurrence of Adventive Roots. — Not a few plants,
like the Indian corn, produce adventive roots regularly and
in considerable numbers. A
potato shoot growing from
an eye of a tuber sends out
adventive roots from its
lower part. Plants with
long underground stems, like
the may-apple, as well as
many trailing plants, pro-
duce adventive roots from
time to time. As the older
parts of such a plant, in-
cluding its primary root,
die, its root system comes
to consist entirely of adven-
tive roots. Some climbing
plants form adventive roots
in large numbers ; but such
plants usually remain con-
nected with the soil by
means of a primary root,
and the adventive roots are

FIG. 106. — A leaf of Bryophyllum
which is producing new plants — a
case of vegetative multiplication.
This leaf was placed on moist sand,
and in a few days adventive buds and

adventive roots developed wherever
the veins extended to the edges of the
leaf.

useful chiefly to assist the
plants in climbing. Many
plants form adventive roots
in response to the stimulus of a wound. In some kinds
of trees, for example, girdling (see § 232) is followed at
first by the formation of adventive roots on the upper
edge of the wound, and in other kinds it is followed by the
formation of adventive buds (which may develop into
branches) on the lower edge of the wound. If a leaf of a
rex begonia .is cut into several pieces and these are stuck

172 TEXTBOOK OF BOTANY

into the soil, in a short time each piece may form adventive
roots and an adventive bud, and so give rise to a complete
new plant.

194. Vegetative Multiplication. — It is plain that the
power which the begonia leaf has of forming adventive
roots and buds is of great advantage to the plant because it
can thus produce new plants under unfavorable conditions.
Not many seed plants can develop new plants from a part
of a leaf alone ; but there are many cases in which a small
part of a plant, by forming adventive roots or adventive
roots and buds, can grow into a complete new plant. This
fact is taken advantage of by gardeners and foresters, who
grow new plants from cuttings more quickly and easily than
they could from seeds. Thus a short piece of a young wil-
low stem, stuck in the ground, forms adventive roots at its
lower end and adventive buds at its upper end and so
grows into a tree.

Many cultivated plants, such as grapes and currants, the
flowering " geranium " (which is really a Pelargonium),
coleus, and verbena, are propagated by means of cuttings.
A cutting usually consists of a short branch bearing one or
more leaves or buds. But a new plant of gloxinia, as of
begonia, can be obtained from a single leaf or even from a
piece of a leaf ; and the bulb-scales of some lilies are used
as cuttings. All these are cases of vegetative multiplication,
because new plants are produced without waiting for polli-
nation, fertilization, and the ripening of a seed. There are
other kinds of vegetative multiplication that depend partly
or entirely upon the development of adventive roots. One
of these is the production of new strawberry plants by means
of runners.

Layering, a method used by gardeners, is not unlike the
one that the strawberry uses. In layering, a branch (of a
blackberry or raspberry, for example) is bent over to the
ground and part of it is covered with soil. Then, from the

ROOTS AND THEIR USES

173

FIG. 107. — Vegeta-
tive multiplication by
layering. A portion of a
living stem was covered
with soil and adventive
roots have grown from
the covered portion.

buried part, adventive roots grow into the ground (Fig.

107), and when the connection with the parent plant is

broken, the new roots with the adjacent

bud or buds form a new plant. The

slender canes of the black raspberry, if

allowed to grow long, bend over to the

soil of their own weight and so perform

the operation of layering for themselves.
195. Work of Roots : Absorption. —

The different forms that roots take are

closely connected with the kind of work

that they have to do. The work of

roots is of various kinds ; it differs much

with the location, size, and habit of the

plant. Much has already been said of

the part that roots play in absorbing, usually from the soil,

water and certain other substances that the plant needs.

Since absorption goes on through the root hairs, and since

these are short-lived and are borne only on the younger
parts of each root, it is necessary that
the root should continue to grow so
that there shall always be a young
region supplied with root hairs.

If the plant lives and grows for
many years, the roots must continue
to grow and branch, so that, as the
parts of the plant above ground need
more and more water, the root hairs
may increase in number and may
come into contact with a larger area
of soil. The growth of the roots also
brings them into deeper layers of the

soil where there is likely to be a more steady supply of water.

These are among the reasons why long-lived plants need

much-branched root systems, composed of long but relatively

FIG. 108. — Root hairs
of the barley.

174 TEXTBOOK OF BOTANY

slender roots that often reach to a great depth. Thus it is
reported that old, well-grown trees may send their roots
to a depth of sixty feet, provided the soil is deep enough
and otherwise favorable for the growth of the roots.
Annuals and small perennials have much shorter roots ; still,
the root systems of barley and mustard reach a depth of
about three feet, those of clover and wheat a depth of six
feet, and those of alfalfa, it is said, may extend nine feet
below the surface of the ground. It is plain that, other
things being equal, the plant whose roots grow to the greatest
depth has the best chance of living through a dry season.

196. Conduction. — The water and other substances
taken in by the root hairs must be carried from the extremities
of the root system through the whole length of the branch
roots and of the main root to the point where the latter
joins the stem. All parts of the root system must also be
supplied with food that has been manufactured in the parts
of the plant above ground. The conduction of the sap and
of manufactured foods goes on through the vascular bundles.
Thus absorption and conduction in roots are closely related ;
the more extensive the root system becomes, the farther is
the younger, absorbing portion of each root from the stem,
and the farther therefore must sap and manufactured foods
be carried.

197. Attachment and Support. — There are some plants,
such as the duckweeds which float upon the surfaces of ponds
and lakes, whose roots are merely absorbing and conducting
organs. But as a rule plants depend upon their roots also
to attach them to the soil or to the other substances on which
they live. If the stem is above ground and erect, the roots
are also a means of supporting the plant in its erect position.
The larger the plant, naturally, the more important is the
work of attachment and support. It is least important in
plants whose stems, like that of the may-apple, are under-
ground. The extensive, much-branched root system, which is

ROOTS AND THEIR USES

175

best for the work of absorption, is also as a rule best for the
support of an upright stem. So the need of support is an
additional reason for pushing the roots of a tree deeply and
widely into the soil. The roots of many plants, like the brace
roots of the Indian corn, shorten after they have grown to
some length — apparently through a change in shape, of
some of their cells — and pull the plant closer to, or more
deeply into, the soil, thus attach-
ing it more firmly.

Not a few trees support them-
selves by roots of special sorts.
One form of supporting roots is
seen in the "screw pines" (Fig.
109), which are really not pines
at all, but are monocotyledons.
Some of them become good-sized
trees. Their trunks send out ad-
ventive roots at various heights
above the ground, which grow
downward on all sides into the
soil and become woody and firm.
The base of the stem and the
primary root often die, in which
case the body of the tree is sup- porting roots
ported entirely on the stilt-like

adventive roots. Mangroves (Fig. no) are trees that grow
on low, swampy coasts, where the soil is moist and soft ; often
they live within the strip that is covered during part of each
day by the tide. They support themselves by roots that grow
downward from all parts of the trunk and branches. The
famous banyan trees of India support their lower horizontal
branches by similar prop roots that push into the soil and
grow to be thick and strong. These prop roots produce
adventive branches and look like so many additional trunks.
By means of these new branches and of the new prop roots

FIG. 109. — A screw pine
(Pandanus), showing the sup-
After Kerner.

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TEXTBOOK OF BOTANY

FIG. no. — A mangrove (Rhizophora
conjugata), showing the numerous prop
roots. After Kerner.

which they in turn pro-
duce, a single tree may
extend over a great area.
Stories are told of a
banyan tree that shel-
tered Alexander's army
of 7,000 men, and of an-
other in whose shade was
built a village of a hun-
dred huts.

198. Storage.— Thick-
ened roots that serve for
the storage of food are
likely to be useful to
man, and so it is that
many plants with storage
roots are cultivated.
Such plants are often

biennials, like the carrot, beet, turnip, and
parsnip. The plant manufactures food
during the first year of its life and stores
it in the thick tap (primary) root. The
work of absorption from the soil is done
chiefly by short branch roots. It is not
merely the root that lives over winter ;
there is a short, thick stem attached to
the top of the root and not sharply marked
off from it. During the plant's first year,
this short stem bears a cluster of root
leaves ; the next year it grows into a tall
flower-stalk, and much of the food stored
in the root is used in forming flowers, seeds,
and fruits.

But it is not only biennials that have
thick storage roots. Radishes, for ex-

FIG. in. — Root
of the radish, a
typical storage root.
The stem is the very
short portion at the
upper end of the
large root, to. which
the leaves are at-
tached.

ROOTS AND THEIR USES 177

ample, are usually annuals. A radish may form a com-
paratively large root in a few weeks; if it is left in the
ground, it goes on to produce flowers and seeds during the
same season. The horseradish and the dandelion, on the
other hand, are perennials, whose thick tap roots, containing
storage food, live and grow for many years. The reserve
food of the dahlia, another perennial, is stored, not in a tap
root, but in a cluster of thick branch roots. The lower part
of the stem with the roots attached is dug up and kept over
the winter. In the spring it may be divided into as many
parts as there are resting buds at the base of the stem, and
each bud will grow into an upright, flower-bearing shoot.
Roots like those of the dahlia are often called tuberous roots ;
of course they must be distinguished from true tubers like
those of the potato, which as we know are branches, not roots.
The sweet potato, very differently from the ordinary potato,
is a thickened branch root ; it is, therefore, much like one of
the tuberous roots of the dahlia. Tapioca is a starchy food
obtained from the tuberous roots of cassava. Many orchids
have rounded or branched tuberous roots, as well as other
slender absorbing roots. The tuberous root, with a single
bud attached, is the part of the orchid plant that lives over the
winter and develops into a new plant the next spring. Some
desert plants have thick roots which serve for the storage
of water.

199. Respiration. — We must not overlook the fact that
respiration goes on in roots as well as in all other parts of the
plant where there are living cells. Roots are usually not in
so good a position to obtain oxygen as are stems and leaves.
Porous soils, if they are not water-soaked, contain a great
deal of air in their crevices, and since oxygen makes up about
one-fifth of the volume of ordinary air, roots living in such
soils find enough oxygen. A hard, compact soil, or one that
is water-soaked, may contain far too little air to meet the
needs of roots. One important reason for the plowing and

178 TEXTBOOK OF BOTANY

cultivation of soil is that it is thus made more porous and that
a supply of air is carried down to a depth at which roots may
use it. The draining of swamps and marshes removes the
water which fills the crevices of the soil and at the same time
draws a supply of air from above to replace the water. In
this way, land that could not before be used for growing crops
is reclaimed. One often sees dead trees about the edges of a
lake which has been raised to an unusual height by a series of
very wet seasons or by a dam in the stream below. In such
a case, probably several reasons have contributed to the
death of the trees ; but one main reason is that their roots have
been cut off from an oxygen supply because the soil in which
they grow has been flooded with water. The roots died just
as we should die if our supply of oxygen were cut off.

Many plants that live in or partly in water, like the water-
lilies, provide for a supply of air to their stems and roots by
large passages filled with air that run lengthwise through their
stems or leaf -stalks. These air passages also help in making
the stems and leaf -stalks lighter, and so in buoying them up
in the water. The bald cypresses of the southern United
States and Mexico, which live in swamps, have a striking
means of obtaining air for their roots. The roots produce
pointed, woody projections that grow directly up, sometimes
to a height of two or three feet above the surface of the soil.
These " cypress knees," which are conspicuous features of
southern swamps, help to secure a supply of air for the roots.
As a result of the respiration of roots, carbon dioxid is given
off to the soil. When carbon dioxid is dissolved in water, it
combines with some of the water to form carbonic acid.
Thus the soil water about a respiring root contains a weak
solution of carbonic acid, and this acid solution seems to help
the plant by dissolving some of the soil substances which the
plant needs and which would not dissolve in pure water. As
we know, it is only dissolved substances that can be absorbed
by root hairs.

ROOTS AND THEIR USES 179

200. Roots of Climbing Plants. — Among the means used
by climbing plants to attach themselves to the objects upon
which they climb are various forms of adventive roots. Some
tropical plants support themselves by wrapping their roots
tightly about the trunks of trees. Some, like the vanilla,
form slender root-tendrils, that are much like branch- and
leaf -tendrils. The roots of a few climbing plants take
the form of spines. The trumpet creeper has much-branched
roots whose root hairs penetrate the fine crevices of the wall
or other supporting object and so obtain a firm hold.

201. Roots of Parasitic Plants. — We have learned that
many of the simpler plants that are without chlorophyl —
such as the rusts and some of the bacteria — obtain their food
directly from living plants or animals, upon or in whose bodies
they live. They are parasites. The great majority of the
seed plants have chlorophyl and manufacture most or all of
their own food. But even among the seed plants there are
not a few which obtain at least part of their food ready made,
and so are saved the trouble of making it for themselves.
Some of these are saprophytes — that is, they feed upon
dead organic substances, usually with the aid of fungi that
live in or upon their roots or stems. Others are parasitic
upon living plants. In plants whose habit of life is so unusual
we may expect to find marked peculiarities of structure.
These peculiarities appear largely in the roots, because it is
by means of roots that such a parasite takes its food from the
host.

The seedling of a dodder (Fig. 112) has a primary root
which pushes into the soil, and a stem which grows in length
rather rapidly and which may remain alive, if it does not
become attached to a host plant, only so long as the supply
of food in the seed holds out. If the stem comes in contact
with a plant upon which it can live — which may, in the case
of different species of dodder, be a plant of clover, hop, flax,
or any one of a rather long list — it sends out small roots, or

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TEXTBOOK OF BOTANY

suckers, which push into the tissues of the host. The
suckers grow until they reach the bast and wood of the host
plant. Then they are in a position to rob the host of its
manufactured food which is being transported in the bast, as

well as of the water and
dissolved substances
that have come up
through the wood from
the roots of the host.
The primary root which
attached the dodder to
the soil now dies, as
does also the lower part
of the stem. The upper
part of the stem grows
rapidly, twining about
the host plant, branch -

FIG. 112. — A, dodder growing upon a
hop vine and bearing a cluster of flowers.
B, a cross section of the hop vine, showing
how the roots of the dodder grow into the
host until they reach its bast and wood.
After Kerner.

ing, and producing many
suckers and great numbers of red flowers and fruits. But it
forms no leaves, has no chlorophyl, and is entirely dependent
upon the host for food. Some of the dodders are serious
enemies of the gardener and of the farmer because of their
attacks upon cultivated plants.

The mistletoes differ from the dodders in the fact that they
have green leaves and so are only partly dependent upon the
host plant. The European mistletoe is well known because
its greenish branches, white berries,, and evergreen leaves
are much used for holiday decorations. It lives high up
in the branches of trees, particularly of those trees which,
like the poplars, firs, and apples, have a thin, soft bark.
If a mistletoe seed germinates on a branch of such a tree, a
slender sucking branch root pushes into the tissue of the
host and grows until it reaches the wood. In the next year,
new branch roots grow which run upward and downward
within the bark of the host plant. From these branch roots

ROOTS AND THEIR USES 181

new suckers are formed from time to time, which, like the
sucker formed in the first season, grow inward through the
tissues of the host until they reach the wood. Thus, while
the suckers of the dodder take materials both from the bast
and from the wood, the suckers of the mistletoe make con-
nection only with the wood of the host, whence they absorb
water and simple salts. Having green leaves, the mistletoe
takes carbon dioxid from the air and manufactures for itself
the more complex foods which the dodder takes from the
host plant. The American mistletoes are similar to the
European form in their manner
of growth and of obtaining food,
but are smaller plants. One of
them is also used, though less ex-
tensively, for Christmas decora-
tions.

Among the most remarkable
parasitic plants are the Rafflesias
and their relatives (Fig. 113).
Their vegetative body consists FIG. 113. — One of the Raf-
only of a network of thread-like J™^ ^ToT'Se
rows of cells, very much like the roots of Cissus. After Kerner.
body of a fungus ; this network

lives and grows between the bark and the wood of prostrate
stems and roots. The only part of the parasite that appears
outside the tissues of the host is the large flower. That of
one species of Rafflesia, found in Sumatra, is said to be the
largest flower borne by any plant. When fully open, it has
a diameter of three feet.

202. Mycorhizas. — A curious relation exists between
many forest trees, including oaks, maples, poplars, and most
of the conifers, and certain fungi whose branching threads
are found living upon small branch roots of the trees. The
fungous threads form a thick felt over the surface of a root ;
separate threads grow in between the cells of the cortex, and

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TEXTBOOK OF BOTANY

in some cases the fungous threads penetrate the root cells.
It is thought by some who have studied these mycorhizas
that the fungi are not, strictly speaking, parasitic upon the
trees ; rather, there is a sort of part-
nership between a tree and the fungus
living in its roots. The fungus finds
a sheltered place in which to live,
and probably also uses as food some
of the substances in the root cells.
On the other hand, it is thought that
the fungous threads on the outside
of the root assist the root by absorb-
ing water and other substances, and
so take the place of root hairs ; it is
not unlikely too that the fungus digests
some of the organic substances, such
as dead parts of plants, that are in
the soil, and so changes them into a
form which the tree can use as food.
Thus, the tree seems to be indirectly
saprophytic ; with the aid of the
fungus, it uses food materials which
FIG. 114. — The Indian without such help would be quite
pipe (Monotropa); a plant uselegs to ft jt ig not Qnl trees
withoutchlorophyl, which . *

lives upon organic sub- that enter into this kind of partner-
stances in the soil with ship with fungi ; some herbaceous
the aid of fungi which j te do th game thi Among

form a mycorhiza with J
its roots. the latter are many members of the

orchid family.

203. Roots of Epiphytes. — Epiphytes are plants that live
above the ground on the surfaces of other plants, but
are not parasitic upon them. Protococcus, when it lives
on the trunks of trees, is an epiphytic alga. A good
many mosses live on the trunks of trees. Epiphytic ferns
and seed plants are found mostly on the trunks and branches

ROOTS AND THEIR USES 183

of trees in tropical forests, where the air is always moist.

Evidently there is not likely to be much sqil nor a large supply

of water in such places, although some water may accumulate

in the crotches of the trees and in the hollows of the bark.

Small amounts of dead material, such as leaves and parts of

branches, may be caught also among the branches and roots

of the epiphyte, and by decaying

there may supply on a small scale

the substances that other plants

obtain from the soil. Evidently the

great problem for an epiphyte is to

make the best possible use of such

water and other food materials as

may come to its roots. So we find

that the roots of many epiphytes

are especially well supplied with

absorbing root hairs. The roots of FJG IIS^An epiphytic

Some epiphytes, notably of tropical orchid growing on the bark

orchids, are surrounded by a special of a tropical tree; notice

tissue composed of several layers of °£

cells whose structure enables theni

to absorb rain water and dew very rapidly and in large

amounts and to pass the water on to the inner cells of the

roots.

204. Direction of Growth of Roots ; Influence of Gravity.
— If a young pea, bean, or corn seedling is removed from the
soil in which it has started to grow and laid upon its side, the
root soon begins to curve in such a way that finally its tip
is turned directly downward. The curvature takes place a
short distance back of the tip, in the region where the cells
of the root are growing in length. Growth is faster on the
side of the root turned upward than on the side turned down-
ward, and it continues so until the tip is vertical. Plainly
it is of advantage to a plant to have its root grow downward
into the soil. But the fact that the plant is helped by this

1 84 TEXTBOOK OF BOTANY

position of the roots does not explain how the roots come to
grow in this particular way. A plant cannot choose to do a
thing because that thing will help it. The direction in which
a root or stem or other part grows is determined by the effect
of outside influences upon the plant. An outside influence
which can thus affect the growth or any other activity of a
plant is called a stimulus. •

The stimulus that has most effect in determining the direc-
tion of growth of roots is gravity. Most primary roots and
adventive roots tend to respond to the stimulus of gravity
by growing directly or almost directly downward. But
branch roots coming from a vertical root do not as a rule
grow straight downward ; if they did, they would lie close
beside the main root. As a matter of fact, branch roots
grow downward but at an angle with the main root. Ex-
periment shows that this difference in the direction of
growth of branch roots is due to a different response on their
part to the stimulus of gravity. The exact angle at which
a branch root tends to grow varies with its position upon the
plant and differs also in different species of plants. As a
result of this tendency on the part of branch roots, they
spread out from the main root and from one another, and the
root system comes in contact with much more of the soil than
it would if all the roots grew straight downward ; the roots
are thus in a position to absorb more water and other foods
and the plant is more firmly anchored. However, if part of
the main root is cut or broken away, one or more of the
branch roots nearest the break will turn and grow straight
downward. That is, the removal of part of the main root
causes the branch roots to respond differently to the stimulus
of gravity from the way in which they otherwise would
respond.

205. Responses to Other Stimuli. — While gravity is the
stimulus chiefly concerned in most cases in determining
the direction in which roots are to grow, it is by no means the

ROOTS AND THEIR USES 185

only one. The actual position of a root is probably seldom
exactly what it would be if gravity were the only stimulus at
work. Most roots tend to grow away from the light. Most
of them tend also to grow toward a supply of water, and some
grow away from the air. Various substances in the soil may
serve as chemical stimuli to roots ; in some cases the roots
grow toward the substance in question ; in other cases they
grow away from it. The pressure caused by contact with a
solid object, such as a stone, serves as a stimulus ; the root
bends, not necessarily at the point where it touches the hard
body, but in the region in which its cells are growing ; and the
result of the bending often is that the root grows around an
object that is in its way. The roots of parasitic plants like
dodders and mistletoes, when they push into the tissues of
a host plant, respond to a set of stimuli quite different from
those which affect the growth of ordinary roots. Probably
some of these are chemical stimuli and some are contact
stimuli.

CHAPTER XV
STEMS AND BRANCHES AND THEIR USES

206. Growth of the Stems of Seed Plants. — We have seen
that, while new cells are being formed in the embryonic re-
gion at the tip of a stem, the older cells just back of the tip
are growing longer. We have seen too that at the tip of the
stem appear small swellings which are to grow into leaves
and branches. The place on the stem at which a leaf (or a
pair or circle of leaves) is attached is called a node; the part
of the stem between two successive nodes is an internode.
The swellings that will become leaves are at first very close
together. The growth of the cells back of the tip pushes
the young leaves somewhat farther apart and so lengthens the
internodes. Some stems have little or no growth in length
excepting this near the tip. Such a stem grows slowly and
its internodes remain comparatively short. The stems of
many palms grow in this way ; but some of them live long
enough and form enough short internodes so that they be-
come tall trees. But in the stems of most seed plants growth
continues for a time also in the older parts — that is, in the
parts below the terminal bud . This growth is usually in the
internodes, so that for some time the young leaves are pushed
farther and farther apart. Growth of this kind is seen in the
cucumber, the bean, the corn, and indeed in most of our
common plants.

The length to which the internodes grow varies greatly in

different plants ; it is much affected, too, by the nature of

the soil and by conditions of light, heat, and moisture. This

is why, of two plants of the same variety grown under differ-

186 '

STEMS AND BRANCHES AND THEIR USES . 187

ent conditions, one may be short and stocky, and the other
tall and slender. The stems of some plants remain short for
a time, because their internodes do not grow in length to any
extent ; then comes a period when the new internodes grow
rapidly, forming a long, slender part of the stem. An ex-
ample of this kind of growth is seen in the radish, whose
foliage leaves are borne close together on the short lower part
of the stem ; the long upper part, that grows much later,
bears the flowers. There are some plants whose nodes grow
in length instead of the internodes ; in the arbor vitas (white
cedar) the growth of the nodes stretches the bases of the
leaves out along the stem ; since the internodes remain short,
the leaves are close to one another.

207. Nutation. — In a stem whose internodes continue
to lengthen for some time, the rate of growth is not the same
on all sides. At any particular time, growth is most rapid
on one side of the stem and so the stem bends toward the
opposite side. At a later time the region of most rapid
growth is on a different side, and the stem is bent in another
direction. The point of most rapid growth moves, as it were,
more or less regularly about the stem. As a result, the
direction in which the stem is bent is continually changing,
and the tip of the stem swings around. Since the stem is
steadily growing longer and pushing its tip forward as well
as swinging it about, the movement of the tip is on the whole
a spiral one. This movement of the stem tip is called nuta-
tion. Usually each internode, as it becomes older and ceases
to grow, straightens so that the stem is not permanently
twisted. Nutation is especially marked in climbing plants
with twining stems, such as the bean and the morning glory.
It is partly because of its nutation l that a bean stem winds
about any slender object with which it comes in contact.
At first the coils of the stem are loose ; but as each internode

1 The stimulus of gravity also plays a part in bringing about the winding of a
bean or other twining stem.

1 88 TEXTBOOK OF BOTANY

in time ceases to grow and straightens itself as much as pos-
sible, it is brought close against the supporting object.
Therefore, the older parts of the stem are wound tightly about
the support, but the younger part, including the internodes
that are still growing, is loosely wound.

208. Stems of Different Forms. — There are many differ-
ent kinds or species of seed plants which differ greatly in their
ability to live and grow in different sorts of places. Some
plants, such as the dandelion, have spread into many re-
gions and many countries. But each kind of plant, never-
theless, can live only under a certain range of conditions, and
as a rule this range is rather narrow. A plant that naturally
grows on dry land will not usually live long if transplanted to
a swamp ; a tropical plant will not endure a cold climate.
This means that each species is adapted to certain conditions
of life ; and different plants are adapted to different conditions
by the different ways in which they are built up. Since
various seed plants live under so many varying conditions —
in warm climates and in cold, in wet regions and in dry,
on the soil, in the water, and perched high in the air upon other
plants — it is not surprising to find great differences in the
make-up of their stems as well as of their other parts. It is
impossible here to speak of all the different forms of stems
that seed plants possess ; but some of the more common ones
will be mentioned.

209. Herbaceous and Woody Stems. — Most of the
smaller seed plants, especially those that live through but one
growing season, have soft stems ; .this is because they contain
comparatively little wood or other thick-walled tissues.
Such plants are called kerbs. The stems of other plants, par-
ticularly of those that live longer and grow to a large size,
contain more wood and often a large proportion of other thick-
walled tissues as well. Such stems are comparatively hard,
and the plants to which they belong are called woody plants.
A woody plant with an upright main stem that grows to a

STEMS AND BRANCHES AND THEIR USES "189

considerable height is a tree. One whose main stem remains
short and gives rise near the ground to several branches is a
shrub. The distinction between herbs, shrubs, and trees is
an old and a convenient one, but it is purely artificial. One
cannot distinguish sharply between herbs and woody plants,
because practically all stems contain some wood and because
there are all possible transitions between very soft and very

FIG. 1 1 6. — A shrub — the pussy willow (Salix discolor). Photograph
by R. H. Denniston and G. Kemmerer.

hard stems. Likewise there is no hard and fast line between
trees and shrubs. Some plants may grow either into trees
or into shrubs, depending upon the conditions surrounding
them.

210. Branched and Unbranched Stems. — Indian corn
usually has no branches excepting the short ones that bear
flowers — that is, the ears and tassels. Most other mono-
cotyledons, like the corn, branch little or not at all above
ground, except in their flower-bearing parts ; although some,

I go TEXTBOOK OF BOTANY

such as the lily, may form branches underground. The
common greenhouse palnis are familiar examples of plants
whose stems ordinarily bear no vegetative branches. But
their large flower clusters show that these stems, too, may
branch. Indeed, it would be difficult to name a plant whose
stem never branches under any circumstances ; and it is only
for the purpose of making a convenient distinction that the
stems of most palms and of many other monocotyledons are
said to be unbranched. On the other hand, the stems <3f most
dicotyledons and gymnosperms branch abundantly. In its
inner structure, and in the various forms that it may take,
a branch of any plant is usually like the main stem, although
there are certain special forms of branches that will be referred
to later. It is often convenient to use the word shoot, mean-
ing by it either a stem or a branch, together with the leaves
and such other structures as it may bear.

211. Erect Stems. — The stems of a large proportion of
seed plants grow upright and, whether herbaceous or woody,
they form enough thick-walled tissue to support their own
weight and that of their branches, leaves, and flowers. The
great advantage to the plant of having an erect stem is that
its leaves are carried upward and are separated so as to
receive the greatest possible amount of light. We have
already seen why light is necessary to green plants ; and the
effect of a partial lack of light is seen in the scarcity of small
plants in a deeply shaded forest. An erect stem may be very
much branched, like that of a pine ; or, like that of a palm, it
may be unbranched except in connection with a special pur-
pose such as flower production. The shape of a plant with a
branching stem depends in part upon the comparative rate
of growth of the main stem and of the branches. In. some
trees the main stem grows more rapidly, and consequently
is always longer, than any of its branches. If all the branches
of such a tree grow at about the same rate, the lowest ones,
being the oldest, are also the longest, and each branch is

STEMS AND BRANCHES AND THEIR USES 191

shorter than the one just below. Such regular growth is
characteristic of most of the firs and spruces, and it gives to
the crowns of these trees a symmetrical cone shape. The
trunk of a pine likewise grows faster than its branches ; but
the branches do not grow at so even a rate, especially on an

FIG. 117. — The white elm (Ulmus americana).
Photograph by G. Kemmerer.

older tree, as do those of the firs and spruces. As a result, the
crown of a pine tree, though conical in youth, is likely to
become irregular in shape as it grows older. If the trunk
does not continue to the top of the tree, but is replaced part-
way up by several large branches, the tree has a rounded
crown such as is common in the oaks and maples.

IQ2 TEXTBOOK OF BOTANY

The form of a tree is also influenced by the angle at which
the branches grow out from the trunk. If they are nearly
horizontal like those of an oak, the tree has a broad crown ;
if they are nearly upright, as those of the Lombardy poplar

FIG. 1 1 8. — The swamp white oak (Quercus bicolor). Photograph by
R. H. Denniston and G. Kemmerer.

are, the crown is narrow and cylindrical. Thus each species
has a crown of characteristic form, which is determined by the
factors that have been mentioned and by others, such as the
number of the branches and their stiff or drooping habit.
The same principles, of course, apply also to smaller plants
with erect branching stems.

STEMS AND BRANCHES AND THEIR USES 193

212. Influence of Light. — One stimulus that affects the
direction of growth of the parts of a plant is light. The stem
of an erect plant responds to the stimulus of light by growing
toward the point from which the light comes. If house plants
stand near a window, their stems grow toward the window.
Plants growing out of doors, unless they are close to a building
or other large object, receive light from above and from all
sides, but not from below ; and as a result of the many-sided
illumination they grow straight or nearly straight upward.
But even an out-of-door plant does not at any particular mo-
ment receive the same amount of light from all sides. On
a bright day, especially, the strongest light comes from the
east in the forenoon, from near the zenith at noon, and from
the west in the afternoon. If the growing parts of the stem
react quickly to the stimulus of light, the position of the
younger — that is, of the upper — parts of the plant will vary
from hour to hour. The sunflower, whose head of flowers
follows the sun in its daily course across the sky, shows
plainly the tendency to grow in the direction of the brightest
illumination. The older parts of the sunflower stem, which
are no longer growing in length, are erect because in the long
run they have received about as much light from the east
as from the west, and about as much from the north as from
the south.

The far-reaching effect of light conditions upon the
growth of erect stems is seen in comparing the long, slender
trunks of trees growing close together in a forest where they
have been largely shaded by neighboring trees, with the
shorter, thicker, much-branched trunk of a tree of the same
species growing in an open field where it has been well
lighted from all sides (see Figs. 64 and 65). The form
of the forest tree has also been influenced by the early
death of its lower branches whose leaves received too little
light to enable them to make the food that the branches
needed.

194 TEXTBOOK OF BOTANY

213. Influence of Gravity and other Stimuli. — Stems that
normally grow erect are affected also by the stimulus of grav-
ity, but in a way opposite to that in which the same stimulus
affects roots. This is shown by stems growing in darkness,
like the shoots that grow from potato tubers which are stored
in a damp, dark cellar. Such a shoot, even if in absolute
darkness, still tends to grow upward, that is, in a direction
opposite to that of the force of gravity. But its upward growth
is often hindered by the fact that it is too slender and weak
to hold itself erect, and so it may be only the growing end
that turns upward. Ordinarily, the influence of light arid
that of gravity work in the same direction, and combine to
induce stems to grow erect. But sometimes, as in the case
of house plants standing near a window, these two influences
work in different directions. In such a case the influence
of light is usually stronger than that of gravity, and the plant
becomes one-sided. The stimuli of light and gravity are
not the only ones that affect the growth of erect stems and
branches. It is probable that many other stimuli, such as
moisture or dryness, air pressure, and changes of tempera-
ture, are of importance in connection with growth. Some of
them certainly affect the rate of growth. But the effects of
these and of other factors upon the direction of growth are
not easy to study, because their influence is small in com-
parison with that of light and gravity.

214. Direction of Growth of Branches. — As a rule, the
branches that come from an upright stem do not grow straight
up ; they grow either horizontally or more or less diagonally
upward. The branches, like the main stem, are influenced
in their growth by the stimuli of light and gravity. Probably
most branches tend to grow toward the light. But since a
branch is shaded more or less by the main stem and its leaves,
as well as perhaps by other branches and their leaves, the
stimulus of light alone would ordinarily cause it to grow, not
directly upward, but in that direction from which it receives

STEMS AND BRANCHES AND THEIR USES 195

most light. The result of this tendency is that the branches
are more or less spread out. If the upper part of the trunk
of a tree is cut off, one (or more) of the uppermost branches
turns and grows upward, because that is now the direction
from which it receives most light.

The effect of the stimulus of gravity upon a branch is usu-
ally quite different from its effect on the main stem. Instead
of tending to grow in a direction opposite to that of the force
of gravity, as the stem does, the branch tends to grow at a
right angle, or at some other definite angle, to the direction
of the force. Thus the stimulus of gravity is an important
factor in inducing branches to grow horizontally or diagonally.
The final shape of a branch results from the combined effects
of the stimuli of light and gravity (and in a measure doubtless
of some other stimuli as well). The influences of light and
gravity may have worked in the same direction, but oftener
they have been more or less opposed, and the actual direction
of growth of the branch is a compromise between the con-
flicting tendencies.

215. Hollow Upright Stems. — Many members of the grass
family, such as wheat, have upright stems which are cylindri-
cal and hollow except for a cross partition at each node.
The outer solid part of the stem is thin, but it contains a large
proportion of thick- walled cells. The stem is also supported
in part by the bases of the leaves, each of which forms a
sheath about the stem, extending for some distance upward
from the node to which the leaf is attached. The stem is
made still more stiff by silica, which is deposited in the walls
of its epidermal cells, and which makes the surface of the
stem feel hard and harsh. Some grass stems contain so much
silica that when one of them is burned a skeleton of silica re-
mains that has the exact form of the stem. Grasses gain a
great advantage from their hollow cylindrical stems, because
this form gives the greatest resistance to sidewise strains with
the use of the least material. The same mechanical principle

196 TEXTBOOK OF BOTANY

is used in the building of bicycle frames, and in many kinds
of machinery.

The largest grasses with hollow stems are the bamboos,
which are inhabitants for the most part of tropical and sub-
tropical countries, and some of which reach a height of 120
feet and a diameter of eight to twelve inches. Bamboo stems
are best known to us by the fishpoles that are made from
them. They also supply material for buildings, ropes, mats,
and kitchen utensils, and for a great variety of other uses.
The grasses are by no means the only plants with hollow
stems ; very many annual plants have them. But as a fam-
ily, the grasses have carried this principle of stem construction
farther than any other group. Some plants, of which the
sunflower is one, have the central part of their stems rilled
with a soft pith. This, so far as strength is concerned,
amounts to much the same thing as having the stem hollow.

216. Trailing Stems. — As we have seen, a plant with an
erect stem has the great advantage that its foliage leaves are
carried up into the air, where they receive an abundance of
light. There are localities, however, which are not suited to
plants with erect stems. Such are the sides and tops of cliffs
and of rocky hills, where the soil is too thin to allow of the
growth of long roots, and where such plants as do grow are
exposed to strong winds. Some plants with erect stems —
the red cedar, for example, and some shrubs and herbs —
do grow in such locations ; but they are likely to be small
and stunted and are usually few in number. In such situa-
tions we find other plants — such as the creeping juniper —
whose stems creep or trail along the surface of the ground.
Trailing plants are not so much affected by winds as are up-
right plants ; for this reason they do not need the support
of long roots that penetrate deeply into the soil ; and since,
in locations 'like those described, they are not shaded by
taller plants, their leaves receive the light that they need.
In bogs, too, and in very sandy places, such as beaches, where

STEMS AND BRANCHES AND THEIR USES 197

the soil is too soft or too poor to support tall plants, we find
many plants with trailing stems. The cranberry is a trailing
bog plant. Some trailing plants also live in open woods;
they are likely to form their flowers or their flowers and leaves
very early in the spring, so that they ripen their fruits and
even perhaps manufacture much of the year's supply of food
before the leaves of the trees grow large enough to reduce
their light. The trailing arbutus of the northern woods,
whose flowers often open under the snow, is a trailing plant
that has become adapted to life in forests.

Many trailing plants, as well as many erect plants, bear
alternate leaves ; but the stem of a trailing plant is likely
to be twisted, so that, although the leaves borne at successive
nodes really arise from different sides of the stem, the side
from which any leaf arises is turned upward at that particular
node. So, because of the twisting of the stem, all the leaves
are in the most favorable position with reference to light.
Usually the roots of a trailing plant grow in clusters at the
nodes, and if by accident the stem is broken or killed between
two nodes, the part on either side of the injured place becomes
a separate plant. The power of multiplying in this way is
important to a trailing plant, which because of its position is
especially liable to injury. The branches of a trailing plant
may also be separated and live as independent plants.

217. Climbing Stems. — Climbing plants, like trailing
plants, can grow to a considerable length and can produce
many leaves, flowers, and fruits without using a large amount
of substance to build up a thick stem. The special advan-
tage of climbing plants over trailing plants is that they can
grow in the same localities that erect plants grow in, and
so can compete with erect plants for access to sunlight —
a thing which trailing plants in general cannot do. Some
climbing plants, such as beans and peas, are soft-stemmed
annuals ; others are woody-stemmed perennials, like the grape
and the Virginia creeper. It is in tropical forests that woody

198

TEXTBOOK OF BOTANY

climbing plants are found in largest numbers and grow to
the greatest size. Running from tree to tree, they often form
an inextricable tangle that reaches to the tops of the tallest
trees. Many climbing plants, like the bean, have twining

stems. Most of them,
whether their stems twine
or not, also have special
organs that fasten them
to supporting objects.
Some, like the English
ivy, have short adventive
roots that grow into the
crevices of walls, fences,
or rocks . The adventive
roots of some tropical
climbers grow like tight
girdles about the trunks
of trees upon which the
plants are climbing.
Many climbing plants
have tendrils (Fig. 128)
similar to those of the
cucumber ; and others
are assisted in climbing by the possession of thorns or
prickles.

218. Horizontal Underground Stems. — Many seed plants
have underground woody stems. In some cases these stems
are long and slender and grow horizontally from year to year
like the stem of the bracken fern. The common may-apple
(mandrake) has a stem of this sort. The parts of the plant
that push above ground live for a single season, and the
underground stem is the only part of the plant that lives from
year to year. Adventive roots arise here and there upon the
lower side of the stem. This stem, like an erect stem, bears
leaves ; but they are small, dark-colored scales. In the axil

FIG. 119. — Climbing stem of a tropical
plant. The branches grow into union
where they touch one another, forming a
lattice-work about the supporting stem.
After Kerner.

STEMS AND BRANCHES AND THEIR USES 199

of each leaf a bud is formed, which may grow either into an
underground branch similar to the main stem, or into an erect
branch that will push above the surface of the ground in the
spring and bear leaves, flowers, and fruit. In the formation
of such erect branches, the may-apple and many other seed
plants with underground stems differ from the bracken
fern, which sends only leaves above the surface of the ground.
As in the case of the fern, the older part of the may-apple
stem dies as the younger part grows.

In many plants, as for example in the Solomon's seal (Fig.
120), it is not an axillary branch but the end of the stem
itself that turns
upward and
bears leaves and
flowers. The
erect part of the
stem dies in the
fall, but the for-
ward growth is
continued under-
ground by the
last -formed axil-
lary bud. This

bud grows into a short branch that appears to be an ex-
tension of the main stem ; the growing end of this branch
in turn the next spring pushes up above the ground. The
underground part of the plant, therefore, though it looks like
a continuous stem, is really made up of a series of short
branches. The large markings that give the name to the
Solomon's seal are the scars left, one each year, by the death
of the upright shoots. Many grasses and sedges are remark-
able for their long, branching, underground stems. That
of the quack-grass can be cut up into small pieces, each of
which may become an independent plant. This is why quack-
grass is so troublesome a weed. The formation of a sod by

FIG. 1 20. — Underground stem of the Solomon's
seal (Polygonatum), showing the joints that mark the
growth from year to year, and the scars ("seals")
left by the death of the upright shoots.

200

TEXTBOOK OP BOTANY

grasses is due to the interlacing of their underground stems
and roots. Certain sedges and grasses have been largely
planted on the dykes in Holland, and on sand dunes on the
French coast which formerly drifted and were blown about,
covering forests, houses, and even villages. The under-
ground stems, branches, and roots form a tangle that binds
the loose sand into a firm soil, in which trees may then be
planted. The underground stems that we have been con-
sidering evidently do not respond to the stimulus of gravity
in the same way that an erect stem does. On the contrary,
they tend to grow at right angles to the direction of the force
of gravity. But when an axillary branch or the end of the
stem grows upward, it is because that part of the plant
responds in the same way that the trunk of a tree does —
namely, by growing in a direction opposite to that of the
force of gravity.

219. Other Forms of Stems and Branches. — The stems
of most seed plants come within the classes that have been

described : erect stems,

trailing stems, climbing
stems, and horizontal un-
derground stems. But
now and then a stem or
a branch takes on a form
different from any of
these. Some of the less
common forms have al-
ready been mentioned.
They are always of such
nature as to meet a
special need of the plant.
Most stems contain tis-

"' sues in which food is
FIG. 121. — The cotton tree, whose . . ....

swollen stem serves for the storage of stored. This IS especially

reserve food. After Kerner. true of thick, fleshy stems

STEMS AND BRANCHES AND THEIR USES 2OI

(Fig. 121). But in some plants certain parts of the stem or
of the branches are set apart as storage organs, and several of
the special stem struc-
tures that we have to
consider are organs of
this kind. Others are
supporting organs, and
still others serve as
means of multiplication.
220. Bulbs and Corms.
— A bulb consists of a
short stem covered by
fleshy leaves ; the leaves
contain most of the FIG. I22.-J,a lily bulb. B, the bulb
of a hyacinth cut lengthwise through the
plant's reserve food, middle. A after Gray.
Some bulbs, like those

of the onion, tulip, and hyacinth (Fig. 122, B), have leaves
so large that the outer ones completely cover the inner
leaves. Others, including the bulbs of lilies (Fig. 122, A),
have smaller leaves that merely over-
lap one another like the scales of a
fish. " Multiplier " onions produce
many branch bulbs in the axils of
their bulb leaves. The crocus has
a globular underground stem that
sends up a flower-bearing shoot in
the spring just as the onion bulb
FIG. 123. — Gladiolus does. But this bulb-like body of
corms. Last year's corm, , . . , « , , , .

now dead and decaying, is the crocus 1S covered only by thtfi
in the center. On either scales ; nearly its whole thickness is
side is a branch corm which made up of the stenij an(J most of
is sending up a flowering ,, /• j • j • j.1

shoot this year ™e reserve food is stored in the

stem instead of in the leaves. A

body like this is a corm. The jack-in-the-pulpit (Indian
turnip) and the gladiolus (Fig. 123) also have corms.

202 TEXTBOOK OF BOTANY

221. Tubers. — A potato tuber is the thickened end of an
underground branch. Its "eyes" are buds, each of which
is in the axil of a small scale leaf that may, however, be
rubbed off unless the tuber is very carefully removed from the
soil. The " skin " of the tuber is a corky layer. Most of
the cells within the tuber contain many grains of starch,
which is the form in which the potato stores most of its re-
serve food. The " hilling " of a potato plant induces it to
form more underground branches and so to increase the
number of tubers. If, in hilling, a green branch that has been
growing above ground is covered, this branch may form a
tuber in the same way that a branch does which has been
underground from the start. Sometimes, in an unusually
cloudy, wet year, tubers are formed on the green branches
that are entirely above ground. So it appears that the
above-ground and underground branches are alike in being
able to form tubers, and that the stimuli of darkness and
moisture determine upon which branches tubers shall appear.
When the other parts of the plant die, the tubers remain alive.
They are therefore a means by which the plant lives over the
winter and by which the number of plants is increased. As
is well known, a whole tuber is not needed to produce a new
potato plant ; a tuber may be cut into several pieces, each of
which, if it contains an eye, may give rise to a plant. Each
bud grows out into a stem, which in turn produces leaves,
adventive roots, and branches. Many other plants, less
well known than the potato, bear tubers ; among these are
the Jerusalem artichoke and the groundnut. The tuber of
what is improperly called a " tuberous-rooted " begonia is
really the base of the stem.

222. Permanently Green Stems. — The. young parts of
the stems of nearly all seed plants are green, and usually many
of the outer cells retain some chlorophyl and manufacture
some food for a long time — in the case of annual stems,
often through practically the whole life of the plant. But

STEMS AND BRANCHES AND THEIR USES 203

as a rule, most of the chlorophyl is contained in the cells of
the leaves, which make much the greater part of the plant's
carbohydrate food, the work of the stem being mainly other
than that of food-making. There are plants, however, of
which the asparagus (Fig. 124) is a familiar example, whose

FIG. 124. — The
tip of an asparagus
shoot, showing the
scale leaves in
whose axils clusters
of slender green
branches will later
appear.

FIG. 125. — A shoot of Ruscus, with
flat, green, leaf-like branches. Notice
that these branches in turn may bear
leaves and flowers. After Kerner.

leaves are reduced to scales or similar small structures, and
whose stems and branches remain green and do most of the
work of carbohydrate manufacture. When the young
shoots of asparagus first push out of the ground, they bear
only scale-like leaves ; but if they are allowed to grow tall,
from the axils of these leaves there grow clusters of fine, short,
leafless green branches. Some plants, like the common
greenhouse " smilax," have green branches that are broad

204

TEXTBOOK OF BOTANY

and flat and look exactly
like leaves; one can tell
that they are branches only
by noticing that each one
grows from the axil of a
scale-like leaf.

The thick green stems of
the members of the cactus
family and of some other
plants living in very dry
regions take on remarkable
shapes. The leaves and
most of the branches of
nearly all cactuses are re-
duced to scales or spines.

The advantage of such an
FIG. 126. — A cactus (Opuntia), .„

whose stem is thick and green, and arrangement will appear m
whose leaves are merely spines. Connection with our Study

of leaves. The stems of

cactuses not only manufacture and store food; they are
organs for water storage as well, and are often an important
source of water for travelers in the desert where these plants
grow. The stem of
the "nail-keg cactus "
is said to yield some-
times as much as a
pint of water.

223. Runners. —
This name is given
to certain branches
(of the strawberry,
for example), which

sprawl on the surface

^ , • FIG. 127. — The strawberry geranium

Of the ground, have (Saxifraga-sarmentosa), which bears runners

long internodes, and much like those of a strawberry.

STEMS AND BRANCHES AND THEIR USES 205

bear small leaves. The large leaves that make most of the
plant's carbohydrate food are borne on shorter, more erect
branches. Each runner has a terminal bud which, under
favorable conditions, can grow into a leafy shoot ; and when
the rest of the runner dies, the new shoot with the adven-
tive roots that it bears is an independent plant. A new
plant may be formed in a similar way from an axillary bud
at any node of the runner. So the runner is a means of
multiplication, because it gives rise to one or more new
plants. A single strawberry plant may send out many
runners, and thus in time come to be surrounded by a
group of daughter plants. The white clover and some
violets also multiply by means of runners.

224. Tendrils and Thorns. — Some plants have branch
tendrils — that is, Tendrils that are really branches; the
greater number of ten-
drils, however, are leaf
tendrils. Sometimes, in
plants with branch ten-
drils, each tendril is a
single long internode.
This is true of the pas-
sion-flower. But in other
plants, such as the Vir-
ginia creeper (Fig. 128, " "A
A), a tendril consists of FIG. 128. — The Virginia creeper (A),

several nodes and inter- and the nearly related Japanese ivy (B),
j -j. ir -L. showing how tendrils may assist in climb-

nodes and may itself bear ing After Kemer.
very small leaves from

whose axils grow branches that are also tendrils. It is
not certain whether the tendrils of the cucumber and its
relatives are branches or leaves. The growing point of a
tendril, like that of a climbing stem, has a marked nutation.
In addition, when any part of the tendril comes in contact
with a solid object, the pressure acts as a stimulus that

206 TEXTBOOK OF BOTANY

causes the tendril to grow more slowly at that point.
Growth continues as before on the opposite side of the
tendril, and as a result the tendril curves toward the object
that it touches. As new points on the tendril come into
contact with the object about which it is twining, growth
is checked in the same way at those points, and so the
curling continues until the tendril ceases to grow. Then
the part of the tendril below the point at which it began to
curl about the supporting object coils like a spring. This
shortens the tendril and pulls the part of the plant from which
it grows tightly against the support.

In the Virginia creeper and in some other plants (Fig. 128),
when the end of a tendril touches a solid body it broadens
out into a disk that fits closely
into the cracks and uneven places
in the support and so helps to hold
the plant in place. These disks
enable the plant to climb up the

face of a wall or of a rock where
TIG. 129. — A branched thorn , . , . - , -

of the honey locust. tnere 1S no object slender enough

for the tendrils to coil about.

Thorns, like tendrils, are sometimes branches and some-
times leaves. They protect the plant from injury by
making it unpleasant for animals to brush against or to
eat it. Branch thorns are either simple like those of the
hawthorn, the pear, and the blackthorn, or branched like
those of the honey locust (Fig. 129). Many climbing plants,
especially in the tropics, are assisted in climbing by thorns
which are turned or curved backward and which catch in the
trunks of trees.

225. The Strength of Stems. — Every erect stem that
grows above ground is subject to strains that are severe in
relation to the size of the plant. These strains result partly
from the weight of the stem itself and of its branches, leaves,
and flowers, which in the case of large trees amounts to

STEMS AND BRANCHES AND THEIR USES 207

thousands of pounds. There are strains due also to the pres-
sure of the wind, to the occasional brushing of men and
animals against the plant, to the fall of other plants against
it, and the like. The strains brought to bear upon a stem are
largely sidewise strains, and it must be able to give way more
or less before a specially severe strain by bending without
breaking, and must be able to straighten itself after the strain
has passed.

Seed plants have met the need for this particular kind of
strength in their stems by developing thick-walled cells that
are longest in a vertical direction. The greater part of the
trunk of a tree is composed of wood, and the wood, as we have
seen in the pine, is made up largely of long, thick-walled
cells, which help in strengthening the trunk as well as in con-
ducting the sap. There are other long, thick-walled cells
in the wood of the oak and of many other angiosperms (but
not of gymnosperms) , called wood fibers ; as a rule these are
narrower and shorter than the conducting cells. The fibers
are strengthening cells but do not conduct sap. It is plain
that if the various long cells in the wood ran crosswise instead
of lengthwise of the trunk, the trunk would not be able to
withstand the pressure of the wind but would be broken across
by a relatively slight strain.

On the other hand, it is because these cells run lengthwise
that the wood of a tree is easily split in that direction. We
say that a split " follows the grain of the wood " — that is,
it runs between the long wood cells, and if their course is for
any reason twisted or wavy, the split surface is not smooth. A
" knot " is a place in the stem from which a branch grew. At
that point many of the wood cells of the stem ran diagonally
or crosswise to connect with those of the branch ; this cross-
wise course of many of the cells makes it difficult to split
through a knot. Strengthening fibers similar to wood fibers
occur also in the bast. In some plants these bast fibers are
very long, and they are important elements in the strength

208 TEXTBOOK OF BOTANY

of the stems of many herbaceous plants which, like hemp and
flax, contain but little wood. The bark of the basswood
(linden) likewise contains a large proportion of bast fibers.
In addition to the strengthening cells, in the wood and bast,
many plants have thick-walled cells in their cortex. The
runners of the strawberry, for example, have several layers
of thick- walled cells just within the epidermis. Similar
strengthening tissue is sometimes formed also in the pith.

226. Differences in Woods. — Everyone knows that the
woods of different kinds of trees differ from one another in
various ways. There are differences, for example, in hard-
ness. Generally speaking, the wood of the pine and of other
gymnosperms is comparatively soft ; that of many common
angiosperm trees, such as the oak, maple, walnut, and elm,
is hard. But there are great differences in hardness between
different angiosperm woods ; and some, like the basswood,
are as soft as the wood of most gymnosperms. Woods differ
also in weight and durability. Differences in hardness,
weight, and durability are to be found not only between woods
of different species, but also between the woods of two trees
of the same species that have grown under different condi-
tions. By examining the structure of various woods, we can
discover some of the causes of these differences in quality
and can see why each kind of wood is useful for certain
purposes and not for others.

227. Sapwood and Heartwood. — In most angiosperm
trees, as in the pine, the older wood changes to heartwood.
This is usually different from the sapwood in color, often
harder and heavier because of changes that have occurred
in its walls, and more durable because it is not so easily af-
fected by decay-producing fungi. It is these qualities that
make the heartwood valuable for building purposes. The
time at which the change of sapwood into heartwood begins
to occur varies greatly. The oak begins to form heartwood
early in life ; the ash begins much later. When the change

STEMS AND BRANCHES AND THEIR USES 209

does begin, the sapwood is not turned into heartwood one
ring each year as we might expect ; but the thickness of the
zone that is changed varies from year to year with the condi-
tions of growth and with the age of the tree. The older the
tree, the more rapidly the change takes place ; for this reason,
the zone of sapwood is narrower in old trees than in young

FIG. 130. — Part of a cross section of a three-year-old stem of basswood ;
a, spring wood formed during the past year; b, summer wood; c, bast.
The large openings in the spring wood of each annual ring are sections of
vessels.

ones. In some trees, as in the oak, the distinction between
heartwood and sapwood is very sharp. This is especially
true of the ebony, whose sapwood is white and its heartwood
black. In some, including the ash, although the heartwood
is harder and more solid than the sapwood, it remains of much
the same color. In others, like the birch and the poplar, no
material change of any kind takes place in the wood ; it re-
mains soft, light in weight, and unchanged in color.

228. Spring and Summer Wood. — Trees differ much in
the thickness of their annual rings. Even in the wood of a
single tree, some rings are much thicker than others. Differ-

210 TEXTBOOK OF BOTANY

ences in the thickness of the rings might not affect the quality
of the wood if the proportion of spring and summer wood in
each remained the same. But if a thicker ring should mean a
greater proportion of spring wood with its large, thin- walled
cells, then of course the thicker the ring, the lighter and
softer the wood as a whole will be. This is the case in the
pine and in other gymnosperms. In good soil, well supplied
with water, a pine tree grows rapidly ; each annual ring is
thicker than would otherwise be the case, and contains a
greater proportion of large cells ; consequently 'the wood is
comparatively soft and light. But if the tree grows in poor
or in dry soil, the annual rings are thinner, and since there are
fewer large, thin- walled cells, the wood is harder and heavier.
This rule, however, is modified by conditions of climate ;
thus pine trees grown in cold countries have thin rings, but
their wood is comparatively soft. In angiosperm trees the
effect of rapid growth is just the opposite of what it is in gym-
nosperms. The thicker the annual ring of an angiosperm,
the greater is its proportion of summer wood. Therefore, an
oak tree living under favorable conditions of soil, moisture, and
temperature grows more rapidly and produces heavier, more
solid wood than does a tree that grows under unfavorable
conditions. The age of a tree also affects the thickness of its
annual rings. The older the tree, the thinner are its rings.
For this reason, a gymnosperm tree forms harder wood in its
old age than in its youth ; in an angiosperm tree, the later-
formed wood is softer. In tropical countries, where the
changes of season are less marked than with us, many trees
(some Indian oaks, for example) continue to grow in thickness
throughout the whole year. In such trees there is no distinc-
tion between spring and summer wood, and so of course
there is nothing that corresponds to the rings that we find
in the wood of trees of temperate countries.

229. Vessels. — We have seen that the sap passes upward
in the pine trunk through certain long cells of the wood.

STEMS AND BRANCHES AND THEIR USES 211

The wood of angiosperms contains similar conducting cells,
and with very few exceptions it contains vessels in addition.
The wood of gymnosperms contains no vessels. A vessel
is formed by a row of long cells whose walls are thickened and
marked in the same ways as are those of the conducting cells
already described. The cross walls between the cells disap-
pear, and so the row of cells becomes a continuous tube. A

FIG. 131. — A lengthwise section (diagrammatic) of a woody stem;
a, epidermis ; b, cork ; c, cortex ; d, bast fibers ; e, sieve tube ; /, cambium ;
g, various types of wood cells; h, pith. After Kerner.

vessel is usually broader as well as much longer than a conduct-
ing cell. Both conducting cells and vessels die when they are
fully formed, and so in any case it is through dead cells that
sap passes from the roots to the leaves and flowers. The
pores that are seen so plainly in cross sections of some woods
are the vessels that have been cut across. Angiosperm woods
differ much from one another in the number, size, and dis-
tribution of their vessels, and upon these points of difference
the density and the strength of a wood very largely depend.
For instance, while the vessels in a cross section of oak wood

212 TEXTBOOK OF BOTANY

are visible to the naked eye, those in birch and willow are so
narrow that they can be seen only with the aid of a micro-
scope ; but there are many more vessels in the wood of a
willow than in the harder wood of an oak. The spring wood
of the oak is made up almost entirely of vessels, the summer
wood mostly of conducting cells and fibers. The vessels
of the beech are scattered through both spring and summer
wood. Those of the black walnut are in small groups ; so
are those of the ash, but here the groups are arranged in
straight lines.

230. Medullary Rays. — These also differ much in differ-
ent woods. Since they consist of thin-walled cells, the hard-
ness and firmness of the wood are affected by the varying
distances between successive rays, as well as by the thickness
of each ray. Sometimes, as is often the case in the pine, a ray
includes only one layer of cells. In other cases it is two, three,
or several cells thick. Oak wood has two distinct kinds of
rays, one very thin, the other thick. Rays also differ
greatly in the distance to which they extend upward and
downward in the trunk. In a board that is cut from a tree
lengthwise, in such a way as not to pass through the center
of the trunk, the medullary rays are cut more or less nearly
straight across. If the board is so cut that it takes in the
center of the trunk, the medullary rays are not cut crosswise
but are parallel, or nearly so, to the surface of the board. A
board cut in this latter way is quarter -sawed, and it is the
markings due to the medullary rays that make quarter-
sawed oak so beautiful a wood.

231. Milky Juices. — Some common plants, among them
the milkweeds and the spurges, produce a white, sticky juice
that runs out when a stem or a leaf is broken. This juice is
formed in certain long cells in the cortex of the stem and
leaves. The liquid is a mixture of many substances. The
milky juices of many plants, including the milkweeds, contain
rubber. A good many tropical and subtropical trees and

STEMS AND BRANCHES AND THEIR USES 213

shrubs produce rubber in this way in large quantities. More
than half the total supply of rubber comes from the Amazon
Valley ; the trees of that region whose juices yield " Para
rubber " belong to the spurge family. Gutta-percha, which
is used for the insulation of electrical wires, especially in un-
derground and submarine cables, as well as in the manufac-
ture of hose, belting for machinery, golf balls, and in a variety
of other ways, is obtained from the milky juices of some other
tropical trees. The similar juice of a tree that grows in
Mexico and Central America supplies chicle, the basis of most
chewing gums.

232. Bark. — Each kind of tree has a bark of characteristic
appearance. Think, in this connection, of the very different
barks of the oaks, the poplars, the shagbark hickory, and the
paper birch. The appearance of the bark of any tree depends
in part upon the distance between the successive layers of cork
cambium, and in part upon the planes in which these layers
lie with reference to one another. If they are parallel or
nearly so, broad bark layers are produced of even thickness,
as in the case of the paper birch, whose successive layers of
cork cambium are very near together. If the layers are not
parallel but intersect one another, as they do in the oaks, the
bark cracks into narrower pieces of various shapes. The
thickness of bark depends largely upon the rate at which the
cork cambium cells divide and upon the number of layers of
cork cells that they form.

In the cork oak of 'southwestern Europe, which supplies
the " cork " of commerce, a single layer of cork cambium
remains active for several years. The first cork cells formed
each year are natter and darker than the later-formed ones,
and so the whole thickness of cork tissue is marked off into
layers, each representing a year's growth. This division into
layers may be seen in large bottle corks.

Sometimes the true bark (that is, the layers of cork and
other cells lying outside the cork cambium) is called " dry

214 TEXTBOOK OF BOTANY

bark," and the layers of cortex and bast that lie between the
cork cambium and the cambium proper are called " green
bark." The dry bark protects the living tissues within from
injuries by insects and larger animals ; from infection by
parasitic fungi ; from the too rapid loss of water by evapora-
tion, and to some extent from the effects of extreme cold. A
wound that penetrates the bark and injures the tissues be-
neath is healed (provided it is not too extensive) by the growth
and division of the living cells of the various tissues (cortex,
bast, medullary rays, cambium, and wood) that are in con-
tact with the wound. Ultimately bark is formed over the
surface of the new wound tissue. " Girdling " consists in re-
moving a strip of the bark and inner tissues down to the wood.
If the girdling extends all the way around the trunk, the move-
ment of food through the bast from the upper part of the tree
to the roots is cut off ; in time the roots, being starved, will
die, and the tree will be killed.

The bark of many trees contains large amounts of tannin,
which is used in the curing or tanning of leather. The bark,
first stripped from the tree, is so treated as to obtain from it a
solution which contains the tannin as well as some other sub-
stances that affect the quality of the leather. Tanbark is
obtained in largest quantities from the hemlock and the
oaks ; but the barks of the larch, willows, and other trees
are also largely used, as well as various woods and other
parts of plants, each producing a leather of a particular qual-
ity or color. Another important bark product is quinin,
obtained from several species of trees belonging to the genus
Cinchona. They are natives of South America, for which
reason the bark is called " Peruvian bark " ; but there are
Cinchona plantations in other warm countries as well. The
drug cascara is obtained from the bark of a tree that grows
near the Pacific coast from California to British Columbia.

233. Lenticels. — The surface of the trunks of many young
trees, such as willows and poplars, is marked by small

STEMS AND BRANCHES AND THEIR USES 215

yellowish or brownish spots or ridges. If one of these spots

is examined, it is found to have been caused by a break in the

outer surface of the bark, through which a mass of the inner

tissue has pushed out. Such a break in the bark is called a

lenticel. It results from the formation by a cork cambium

layer of -a loose cushion of cells whose walls are not corky.

The pressure of this cushion bursts the outer layers of bark.

Through the opening so made, and through the spaces between

the cells of the cushion, the air

penetrates to the inner cells of

the cortex. If it were not for

lenticels, the bark would cut off

the living cells within, many of

which still contain chlorophyl,

from any supply of oxygen for

respiration or of carbon dioxid

for carbohydrate manufacture.

As the bark grows thicker and its

outer layers peel off, new lenticels

are not usually formed. But

some trees with thin, smooth

bark, like the paper birch (Fig.

132), continue to form lenticels

even on the older parts of the

trunk.

234. Buds. — We have already seen something of the
structure of buds. A bud always contains the growing end
of a stem or branch ; if in addition it includes only young
leaves and the small buds in their axils, it is a leaf bud; if it
includes a flower or flowers, whether or not it contains leaves
also, it is a flower bud. A flower bud, like a leaf bud, may be
terminal or axillary. Often a flower bud can be recognized
by its appearance ; for example, the leaf buds of the apple
tree are slender and pointed, the flower buds are thicker and
rounded. When a bud is torn apart, one is often surprised to

FIG. 132. — A piece of birch
bark; the horizontal dark
streaks are lenticels.

216

TEXTBOOK OF BOTANY

find how many different things have been wrapped up in so
small a space. Thus the flower bud of the lilac contains the
beginnings of many leaves and of a whole flower cluster, in-
cluding perhaps a hundred or more flowers.

As a rule, a single bud is borne in the axil of each of the
leaves on a stem or branch. There are exceptions to this
rule, such as the asparagus, which has a cluster of short
branches (each developed from a bud)
in the axil of each scale leaf. In
general, the upper axillary buds, that
is, those nearest the terminal bud of
the stem or branch, are larger and
more likely to develop than the lower
ones. The difference in size between
upper and lower buds is very marked
in the lilac. The buds of an annual
plant, like the cucumber, must develop
very soon after they are formed, if
they are to develop at all. Such buds
have no covering for the young leaves,
branches, and flowers that they con-
tain. But perennial plants in tem-
perate and cold countries form buds
which must rest through the winter,
and so require protection against the
cold. Such buds are covered by scale-like leaves that
never become foliage leaves but that usually fall off in the
spring when the buds open. The grape and some other
perennials form some naked axillary buds that develop at
once, and other scaly axillary buds that rest throughout the
remainder of the year in which they were formed and develop
the next spring. But many perennials, including the lilac,
the apple, and most trees, bear only scaly buds in their axils,
which rest without further growth until the next spring.
As a rule, the terminal buds of a perennial plant grow con-

FIG. 133. — A, portion
of a lilac stem, with a
terminal bud and the
four uppermost axillary
buds. B, portion of an
Ailanthus stem with ac-
cessory buds at a, only
one of which will de-
velop. Notice the con-
spicuous bundle traces in
the leaf scar at b.

STEMS AND BRANCHES AND THEIR USES 217

tinuously during warm weather, and are then naked ; but
when they stop growing, upon the approach of cold weather,
they form scales that cover and protect them until the next
spring. This, as we have already seen, is the history of the
terminal buds of the pine. By tearing apart a winter bud of
the horse-chestnut, one gains a very good notion of the struc-
ture of buds in general and of scaly buds in particular. On
the outside are thick scales that overlap and are held together
by a sticky, varnish-like substance that covers their surfaces.
The scales within the outer layer are thinner, and those far-
ther in are more and more like ordinary leaves ; in the center,
finally, are the small, delicate leaves that will spread out and
become green when the bud opens. In the spring the sticky
substance that holds the outer scales together becomes soft,
the scales separate and turn back, and the inner part of the
bud grows out into a leaf -bearing branch. The scales and
their varnish-like covering not only protect the young inner
parts of the bud against the cold, but also prevent the evap-
oration of water from the bud. This is important at a time
when, as in the winter months, the roots cannot obtain water
from the soil.

235. Induced Growth of Buds. — In most plants only a
very small proportion of the axillary buds actually develop
into branches. If the terminal bud of a stem or branch dies
or is destroyed, the axillary bud or buds just below the termi-
nal one commonly grow out into a long branch or branches.
This happens regularly in many shrubs. For example, all
the terminal buds of the lilac die each fall ; in the spring the
two uppermost axillary buds of each shoot — which are di-
rectly opposite each other — grow into upright branches.
If the end of the shoot, including its upper axillary buds, is
killed or cut off, some of the axillary buds below the killed
region will grow into branches. As has been said, gardeners
remove the tips of cucumber shoots to induce the plants to
branch more freely than they otherwise would, and so to pro-

218 TEXTBOOK OF BOTANY

duce more fruit. Apple and other fruit trees are pruned,
both to obtain more compact, better-shaped trees, and also
to cause the formation of less wood and more fruit.

In the cultivation of wheat it is especially important to
encourage the development of axillary buds. In the axils of its
lower leaves a wheat plant bears buds, each of which may
develop into a stalk that ends in a head of grain . If the axillary
buds do not develop, each plant has but one stalk and one head.
Winter wheat, which begins its growth in the fall, develops
slowly. Its axillary buds remain close to the damp soil, send
out adventive roots, and so, being supplied with food, grow
into fruitful stalks. But spring wheat, whose seed germi-
nates in the spring, grows more rapidly. Its axillary buds
are carried up quickly above the surface of the ground, and
so are less likely to form roots and to grow into stalks. How-
ever, if the wheat field is rolled soon after the seeds have
germinated, the young plants are buried more deeply ; their
axillary buds remain for a longer time in or close to the soil,
form roots and stalks, and so the number of grain-bearing
heads on each plant is increased.

Brussels sprouts are the axillary buds of a variety of cabbage
in which these buds develop instead of the terminal bud that
in other cabbage varieties grows into a single large head.
The development of the axillary sprouts is encouraged, not
in this case by destroying the terminal bud, but by removing
the leaves in whose axils the buds are borne. The tiger lily
bears bulb-like axillary buds, each of which may grow into a
new plant. The bulblets of " top onions " belong in the
same class.

236. Adventive Buds. — These may appear on practically
any part of the plant — on the stem or branch, on a leaf, or
on a root. Very often they develop in response to the stim-
ulus of a wound. Plants differ greatly in their ability to
produce adventive buds. It is plain that a plant which reacts
to a wound stimulus by forming many adventive buds has

STEMS AND BRANCHES AND THEIR USES 219

an excellent means of replacing lost parts and sometimes of
multiplying its numbers under unfavorable conditions. The
branch that grows from an adventive bud is an adventive
branch. 'New branches often appear upon the trunk of a tree
about the place from which a branch has been removed.
Often the new branches are adventive branches. But this is
not always the case ; for it has been found that the axillary
buds of many forest trees can remain alive under the bark
for a long time, in some cases even for years, without develop-
ing. Some of the new branches, therefore, that grow from
the neighborhood of wounds, may come from resting buds
that were originally formed in the axils of leaves.

When a branch is cut back, also, it often sends out several
or many side branches, some of which may come from adven-
tive buds and some from resting axillary buds. This tend-
ency of trees when cut back to form new side branches is taken
advantage of in the pruning of shade trees to secure a sym-
metrical top, in the production of dwarf trees and trees of
various unusual forms, and in the trimming of ornamental
shrubs and hedges. If the top of a willow is cut off, many
new branches appear just below the cut surface and grow
into a new compact head. What is called coppice growth
results from the cutting off of the trunks of good-sized trees
at the surface of the ground. The numerous adventive shoots
that start are allowed to grow to the desired height and are
then cut, to be used in basket-making, for small firewood,
and for many other purposes, varying with the kind of tree
from which they come. The removal of the first lot of shoots
is followed by the growth of a new lot, and so the same root
system serves for the rapid production of many crops. Vari-
ous kinds of injuries — those caused, for example, by bruises,
by biting and boring insects, and by the growth of the para-
sitic fungi that form "witches' brooms " — may furnish the
stimulus for the development of adventive buds and
branches.

220 TEXTBOOK OF BOTANY

237. Hairs and Similar Structures. — Hairs, which appear
upon many stems, are best studied in connection with
leaves, upon whose surfaces they grow in great number and
variety. Like root hairs, the hairs of stems and leaves, as
well as those that are often borne on sepals, petals, and other
flower parts, are outgrowths each of a single epidermal cell.
A hair sometimes remains single-celled ; sometimes it becomes
a row of cells; sometimes it is branched. When present
in large numbers, hairs form a felt over the surfaces of stems
and leaves that helps to check the evaporation of water.
Many plants which, like the mullein, grow in extremely dry
soil, have very hairy stems and leaves. Winter buds are
often protected by hairs as well as by scales. Sometimes
the hairs form a woolly outer covering for the bud ; some-
times they are inside the protecting scales. The prickles of
roses, raspberries, blackberries, and gooseberries are like
hairs in that they grow from the surface of the stem ; but
some of the cells below the epidermis, as well as the epidermal
cells themselves, take part in their formation. These
prickles protect the plant against injury by animals, and
also, by penetrating objects with which they come in contact,
help the stems of some plants, such as climbing roses and
the hop, in climbing. Prickles look like thorns and serve
much the same purpose ; but that they are different in origin
is shown by the fact that they come off with the bark when
the latter is peeled off, while thorns (being either leaves or
branches) do not.

238. Length of Life of Stems. — The stems of many
plants live only through the growing season of a single year.
Such short-lived plants are called annuals. The cereal
grains are all annuals. So are cucumbers, peas, beans, and
many other garden plants. But some garden plants, like
the cabbage, carrot, and beet, and many wild plants, have
stems that live for two seasons. Such plants are biennials.
A biennial bears no flowers during the first year of its life ;

STEMS AND BRANCHES AND THEIR USES 221

it grows and stores away food (in the carrot and beet this
is stored in large quantities in the root) ; in the second
year it sends up a flower-bearing shoot, forms seeds, and
then dies. There are some plants that live more than
two years, but which, like biennials, flower only once in their
life and then die. Bamboos belong to this class ; so does the
century plant, which is said to live from ten to fifty years
before it bears flowers. The plants of another large class live
for many years and bear many sets of flowers. These are
perennials.

The long life of a perennial is due to the fact that it con-
tinues to grow and produce new tissues as its older parts die.
It is not true that any one particular part of the plant lives
for many years ; the parts of an old plant that are now alive
may be only a small fraction of the tissues that the plant has
produced. In an old tree, for example, the heartwood, which
makes up a large part of the bulk of trunk, branches, and
roots, is dead. So are most of the full-grown cells of the
sapwood, as well as all the cells in the outer part of the bark.
In the case of a plant with a long underground stem, like the
may-apple, the older parts of the stem and of the branches
are steadily dying. Most annuals are herbaceous plants.
Most perennials are woody, or at least the parts that live
for more than a year are woody.

239. Limits of Life of Perennials. — A plant can live
only so long as food substances can be carried between the
absorbing root hairs (borne just back of the root tips) and
the living tissues of its stem, branches, and leaves. The
root tips of a tree or of a climbing plant are continually
pushing farther into the soil, and the younger parts of the
stem and branches which bear most of the growing buds and
leaves are growing farther upward and outward. So, as the
plant grows older, water must be carried farther, and it
becomes more and more difficult to supply water to the grow-
ing parts. In time the supply of water will fall off, and as a

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result the growth of buds and the formation of new leaves
will become slower ; and the plant, poorly supplied with
carbohydrate food because of its fewer leaves, will grow
weaker and finally die. Thus an erect or climbing plant
has a fairly definite limit of life, although the limit is very
different in different species.

It is otherwise in plants with creeping or underground
stems. The older parts of these stems with the roots at-

FIG. 134. — The base of one of the giant redwoods of California.
Photograph by Squires.

tached to them are constantly dying ; but the younger parts
grow steadily forward, sending out new roots as they grow.
So there seems to be no necessary limit to the life of plants
such as these ; so far as we know, a plant with a creeping or
underground stem might live indefinitely if the surrounding
conditions remained favorable. Practically, the lives of
most perennials are more or less shortened by injuries and
by disease, and few if any reach the extreme age or the extreme
size which would be possible if they remained perfectly healthy .
240. The Largest and Oldest Plants. — The tallest known
trees are the gum trees of Australia ; some of them reach a

STEMS AND BRANCHES AND THEIR USES

223

height of 500 feet. Next to these are the giant redwoods of
California, the tallest of which are over 460 feet high. These
figures, however, are exceeded by those of the length of some
of the woody climbing plants of tropical forests ; thus rotang
palms (from which rattan is obtained) are said sometimes to

FIG. 135. — The "dragon tree" of Teneriffe. A member of the lily
family, which, like a few other monocotyledons (including the palms), has
a special method of growth in thickness and so is capable of developing into
a tree. After Smalian.

grow to a length of nearly 1000 feet. The tallest trees are
not the thickest ones. The diameter of the largest redwoods
is not over thirty-five feet ; that of the Australian gum trees
does not exceed twenty-five feet. The European chestnut,
however, though much shorter, may grow, it is said, to a
diameter of over fifty feet. A famous bald cypress near
Oaxaca, Mexico, has a diameter of a little more than fifty

224 TEXTBOOK OF BOTANY

feet, six feet above the ground. Aside from conifers (includ-
ing the redwoods), probably the largest tree in the United
States is a sycamore at Worthington, Indiana, which is
about 150 feet high and 42 feet in circumference five feet
above the ground. The ages of various large trees have been
estimated at 4000 or 5000 years, and one famous tree, the
" dragon tree " growing on the island of Teneriffe (Fig. 135),
was said to be 6000 years old. Such estimates seem to be
much exaggerated. There is evidence that the giant red-
wood, the true cypress, and the yew may live about 3000
years, and that the chestnut, one of the oaks, and the cedar
of Lebanon may live 2000 years. Probably not much
greater ages have been reached by any plants now living.

241. The Smallest Seed Plants. — These are members of
the genus Wolffia. The common Wolffias of the United
States and Canada consist each of a rounded green body
which floats in ponds and lakes and is so small (at most not
more than a sixteenth of an inch in diameter) that it may
easily be taken for a minute seed. The rounded mass of
cells is a stem, which branches by forming another small
group of cells within a sort of pocket. The branch breaks
away and becomes an independent plant. There are no
leaves or roots, and each plant may bear two simple flowers,
one consisting of a single stamen, the other of a single pistil.

242. Grafting. — It has been known since very ancient
times that parts of two plants may be made to grow together
into what is practically a single plant. In most cases the
process of grafting consists in attaching a bud or small shoot
(called the scion) from one plant to a plant or to the lower
part of a plant of another sort, which is called the stock.
The advantage of grafting varies in different cases. Some-
times a cultivated plant bears no seeds or its seeds do not
germinate well, and it cannot easily be multiplied by other
vegetative means, such as by layerings or cuttings. Scions
of such a plant may be grafted upon stocks of less desirable

4
STEMS AND BRANCHES AND THEIR USES 225

varieties that are easily raised from seed. Sometimes a
valuable plant produces seeds abundantly, but its seeds do
not " come true." For instance, the seeds of our cultivated
apples are likely to grow into trees whose fruit is very unlike,
and usually poorer than, that of the parent tree. For this
reason, apple seedlings can be used only as stocks, upon
which may be grafted scions of the variety desired.

Sometimes grafting is used for a fruit that is not well
adapted to the conditions of the region where it is to be
raised. Thus, in the southern United States the plum is
grafted upon the peach, whose roots grow better in sandy
soil than do those of the plum ; and in Russia, apple scions
are grafted upon stocks of the Siberian crab-apple, which is
better adapted to a severe climate. Sometimes the habit of
growth of the scion is affected by the character of the stock.
Thus dwarf pear trees are obtained by grafting the pear
upon a quince stock. The quince has a small, slowly grow-
ing root system, which supplies soil materials slowly to the
scion ; as a result, the growth of the scion is slower than it
would be if it were growing upon its own roots. It is only
by some influence upon its food supply that the stock can
affect the growth of the scion. Stories are told of changes
of other sorts caused by the influence of the stock, for ex-
ample in the color or flavor of the fruit or in the shape of the
leaves of the scion ; but such stories seem to be unfounded.

No one can tell, except by trying, whether a plant of a
particular variety or species can be grafted upon one of
another variety or species. As a rule, a graft is more likely
to be successful the more closely the stock and scion are re-
lated. In some cases, grafting is possible only between two
closely related varieties ; in others, it may be carried on be-
tween two species of the same genus ; and some successful
grafts have been made between members of different genera.
Grafting is usually practiced with woody plants, especially
with trees. Many herbaceous plants can be grafted, how-

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ever, and it is sometimes done, as for example with chrys-
anthemums, in order to have two or more kinds of flowers
on the same plant. With a few exceptions, monocotyledons
have not been grafted successfully. .

243. Methods of Grafting (Figs. 136, 137). — The im-
portant fact in the actual work of grafting is that only like
tissues will grow into union with one another ; that is, bast
will unite with bast, wood with wood, and cambium with

FIG. 136. — Various methods of grafting : A and B, two forms of
cleft grafts; C, a whip graft. After Gaucher.

cambium. So, in making a graft, one must match the tissues
of the scion with the corresponding tissues of the stock.
Especially must cambium be matched with cambium. It is
also important that a close joint be made and that the place
of union of stock and scion be protected, usually by grafting-
wax, until the wounded tissues have healed. Of the many
methods of grafting that have been devised, only a few of
the commoner ones will be mentioned. In a cleft graft the
stock is split, and the scion, trimmed to a wedge shape, is
inserted in the split. This method is largely used in the
grafting of fruit trees, when the graft is made some distance

STEMS AND BRANCHES AND THEIR USES 227

above the surface of the soil. Bark grafting is similar,
excepting that the split is made between the bark and the
wood of the stock ; it is used especially in grafting to rather
large stems or branches. In a whip graft, used with small
stocks in nurseries, both graft and scion are trimmed only
from one side to a wedge shape (a split or tongue being
left in the middle) and are fastened together with the cut
surfaces in contact. This method is used also when the scion
is attached directly to the root of the stock, as is often done
with apples in the western United States. In a veneer graft,

FIG. 137. — Various methods of grafting: A, budding; B, a contact
graft ; C, a form of saddle graft. After Gaucher.

the stock and scion are trimmed off slightly on one side, and
the cut surfaces are placed together. This method is used
largely with ornamental greenhouse plants. Sometimes
branches of two plants are attached, first being trimmed off
slightly at the point of contact and allowed to unite while
each is still growing upon its own roots. When the union
is complete, the scion is separated from its root. This method
is called inarching. Budding is practiced with small stocks,
usually not more than a year old ; the scion, a bud with a
small strip of bark attached, is inserted into a slit in the
bark of the stock. Apples, cherries, and other fruits are
largely multiplied in nurseries by budding.

CHAPTER XVI
LEAVES AND THEIR USES

244. Growth of Leaves. — As a general rule, a leaf differs
from a branch in the fact that it can grow to about a certain
size and no larger. While a leaf is enclosed in the bud, the
cells divide but the leaf remains small, growing very slowly.
Long before the leaf unfolds, its cells have ceased to divide ;
the leaf has all the cells that it ever will have. Thus the
leaf remains with no further perceptible change until warm
weather comes in the spring, when its cells begin to grow
again, chiefly by the taking in of water; little new living
matter is manufactured. The absorption of water can go
on rapidly, and this is why leaves unfold and grow so quickly
in the spring.

Each leaf is capable of growing to about a certain size.
The exact size that a particular leaf will reach depends upon
a good many factors, among them the amount of food and
water that the plant can supply to it. So it happens that
the different leaves on a single plant may be very different
in size ; the leaves of a plant growing in dry soil may be
smaller than those of a plant of the same sort living in a
moist place ; and the leaves of a young tree are sometimes
much larger than those of an old tree of the same kind.
.But in spite of all such differences, it is none the less true
that the size to which a leaf may grow is limited by the num-
ber of cells that it formed while it was shut up in the bud ;
although conditions may prevent it from reaching the full
size to which it might have grown, nothing can make it
grow beyond the limit set by the number of its cells.
228

LEAVES AND THEIR USES

2294

245. Parts of a Leaf (Fig. 138). — Most foliage leaves,
like those of the cucumber, are more or less clearly divided
into a leaf -stalk and a blade. Sometimes, as in the case of
the dandelion, the blade narrows gradually into the stalk, so
that we cannot say just where one ends and the other begins.
Some leaves, like those of most lilies, have no stalk at all ;
the blade is attached directly to the stem or branch of the
plant. We have seen that the lower
part of the leaf of the Indian corn
forms a sheath that surrounds the stem
for some distance. Such sheathing
leaves are characteristic of the mem-
bers of the grass family ; but they are
found in many plants of other families
as well.

Many leaves have stipules. Some
stipules, like those of the bean, are
small ; but some, as in the pansy and
the pea, are so large that they may
easily be taken for separate leaves. In
any case, the stipules are really parts
of the leaf to which they are attached.
Compound leaves, like those of the
bean, sometimes also have small stipule-
like attachments at the base of the
stalk of each leaflet in addition to the
stipules at the base of the leaf -stalk.

Usually both the leaf-stalk and the shoot (stem or branch)
are thickened slightly at or near the point where the leaf-
stalk is attached to the shoot. These two thickenings often
run together so that we cannot distinguish just where the
leaf -stalk ends and the tissues of the shoot begin. In many
of the plants of the pulse family (including peas, beans, and
clover) the thickening of the base of the leaf -stalk is especially
marked.

FIG. 138. — The leaf
of a rose — a pinnately
divided leaf with stip-
ules. The leaflets are
toothed.

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246. Hairs (Fig. 139). — Hairs are usually most numerous
on leaves, especially on their under surfaces ; but they are
borne also, and sometimes very abundantly, on stems and
branches, on various parts of flowers, and on fruits. The
downy appearance of the peach is due to a covering of soft,
short hairs. Hairs are outgrowths each from a single surface
cell, or in some cases from a small group of cells. Often a
hair is a single long cell not unlike a root hair. One-celled
hairs are sometimes bent so as to lie nearly parallel with the

surface of the leaf
that bears them ;
in such a case, if
they are numer-
ous, they give a
silky appearance
to the leaf. In
other cases the

ge-

A

FIG. 139. — Hairs: A, of the common
ranium (Pelargonium) ; B, of Correa speciosa;
C, of wormwood; D, of mullein. B, C, and D
after Kerner.

hair is composed
of a row of cells,
or even of several
rows side by side.
Sometimes it is
branched, like the
hairs of the mullein ; sometimes instead of a hair a plate
of cells is formed, like the chaffy scales of many ferns. In
general, hairs are useful to plants because they prevent the
too rapid evaporation of water.

Many plants living in very dry places, which can ill afford
'to give off much water to the air, have especially hairy leaves
and stems. Thus the branched hairs of the mullein form a
woolly coating which largely prevents currents of air from
reaching the. surface of the leaves and stem, and so prevents
the rapid carrying away of moisture. The woolly coatings
of some winter buds are useful in the same way, because
during winter the roots cannot supply any considerable

LEAVES AND THEIR USES 231

amount of water, and even a slight evaporation might cause
the wilting and death of the buds. Some plants (such as
many of the grasses and sedges) have stiff, sharp-pointed
hairs which, like thorns and spines, protect the plant from
destruction by hungry animals.

Some hairs are organs in which special substances are
produced. Such hairs are glandular hairs ; they are usually
swollen at or near the end, and in this swollen part of the
hair the substance it produces is stored. The glandular
hairs of the nettle have made a forcible impression upon
most of us ; it is a slightly poisonous liquid formed in them
that causes the unpleasant sting. The hairs of some tropical
.nettles produce still more poisonous substances whose effects
are said to last for days. Nettles and plants with similar
glandular hairs are carefully avoided by grazing animals.
But the substances formed in the glandular hairs are by no
means always poisonous. The varnish -like substance which
covers the winter buds of the horse-chestnut is produced by
glandular hairs borne on the bud scales. The bracts and
ovaries of the pistillate flowers of the hop bear scale-like
glandular structures that produce the bitter substance
which makes hops valuable for medicinal purposes as well
as in the manufacture of beer.

247. Shapes of Leaves. — One way in which species of
seed plants differ greatly from one another is in the shape
of their leaf -blades. These differences in shape are closely
connected with differences in the course of the veins in the
leaf. The leaves of most monocotyledons, like those of
corn, are parallel -veined. In such a leaf, there is one vein
running close to, and parallel with, each edge of the leaf.
Parallel-veined leaves usually have entire margins — that is,
margins that are not indented. Some monocotyledons and
most dicotyledons have netted- veined leaves, many of whose
veins run out toward the edge and there end abruptly. It
is possible for the edge of the leaf to be indented or cut-in

232 TEXTBOOK OF BOTANY

between the ends of two such veins, and this is why many
dicotyledons (though by no means all) have leaves with more
or less irregular outlines. If the indentations of the margin
are shallow, the leaf is toothed. The cherry, apple, and elm
have toothed leaves. If the indentations are deeper, as in
the leaves of the common maples and the grape, the leaf is
lobed. Sometimes the teeth, as in some grasses and sedges,
or the lobes, as in holly and thistle leaves, are stiff and sharp-
pointed ; they serve the same protective purpose as do sharp-
pointed hairs and spines. If the indentations cut down to
the midrib, as in the pea, or to the base of the leaf, as in the
horse-chestnut, the leaf is divided, and its parts are called
leaflets.

Divided leaves are of two kinds with reference to the
arrangement of the leaflets, and this arrangement is connected
with the course of the veins. In many netted-veined leaves
there is a single midrib, which gives off branch veins on
both sides ; these branch veins branch in turn, and so on.
The cherry leaf has this arrangement. If a leaf with the
veins so arranged is divided, the divisions cut down from
either side to the midrib ; the leaflets then are attached on
both sides of the midrib as the divisions of a feather are
attached to the quill. The leaf is pinnately divided. The
bracken fern has pinnately divided leaves ; so have roses
(Fig. 138) and peas. Some netted-veined leaves, instead of
a single midrib, have several large veins that start from a
common point at the base of the blade and run out in differ-
ent directions toward the edges of the leaf. This arrange-
ment is seen in maple and grape leaves. If such a leaf is
divided, the divisions cut down to the base of the leaf, and
the leaflets are all attached to one another at their bases,
somewhat like the fingers of a hand. Such a leaf, for exam-
ple that of the horse-chestnut or of the clover, is palmately
divided. The leaflets of a divided leaf, whether pinnately
or palmately divided, may themselves be toothed, lobed,

LEAVES AND THEIR USES 233

or divided. So leaves may be twice divided, like those of the
bracken fern and the sensitive plant. Some ferns have
leaves three times divided, and the common meadow-rue has
a four-times-divided leaf. «

There are many other points of difference in the shape of
leaves ; some are circular in outline, some are heart-shaped,
some oval, some long and slender, and so on. These differ-
ences are important in the classification of seed plants, and
for this reason each particular form of leaf has been given a
special name.

248. Leaves of Different Shapes on the Same Plant. —
Not only are leaves of different shapes found on different
plants ; there are also differences in shape between leaves
borne on the same plant. Strictly speaking, perhaps, no
two leaves, even on the same plant, are ever of exactly the
same shape. But the differences in most cases are com-
paratively small, and the foliage leaves of a particular plant
usually follow the same general pattern. But there are
exceptions to this rule. The leaves of the common mul-
berry vary in shape to an unusual extent, even on the same
tree, some being deeply lobed, others heart-shaped and quite
without lobing. There are not a few cases in which different
parts of the same plant bear two very different kinds of
foliage leaves. One class of such cases is seen in some plants
the early internodes of -whose stem remain very short. The
result is the production of a cluster of leaves close together and
close to the surface of the ground. These are commonly,
but not properly, called " root leaves." Later the stem
forms long internodes, so that a tall, upright shoot is pro-
duced bearing scattered leaves.

The root leaves and the upper leaves of the plant are often
decidedly different in shape, although if a complete series of
leaves is studied in the order of their age, a fairly gradual
change will usually be found from the form of the lowest
leaves to that of the uppermost ones. The common hare-

234 TEXTBOOK OF BOTANY

bell, for example, has root leaves with rounded, almost
circular blades, but its upper leaves are long and very narrow.
There are some water plants that bear leaves of one sort
under water and leaves, of a very different form in the air ;
this is true, for example, of the yellow water crowfoot and
of some of the pondweeds.

249. Special Kinds of Leaves : Seed Leaves. — Leaves,
like stems and branches, adapt themselves to particular
kinds of usefulness by taking on special forms, some of
which are very different from the forms of ordinary foliage
leaves. Most of the special kinds of leaves have already
been mentioned in one connection or another. We know,
for example, that the sepals, petals, and stamens of a flower
are leaves adapted to special purposes, and that the pistil is
either one leaf or else composed of two or more leaves united.
But in this chapter we shall consider only those leaves that
help in some of the vegetative work of the plant.

Seed leaves are usually different, sometimes very different,
from the later-formed foliage leaves of the same 'plant. If
the later leaves are divided, the seed leaves are likely to be
simpler in outline ; very frequently they are undivided, with
entire margins, as is the case in the bean. Some seed leaves
become green and for a time do the work of foliage leaves ;
this is true of the seed leaves of the squash. On the other
hand, the single seed leaf of grasses, including the corn, is an
absorbing organ which never gets outside the seed coat and
never serves as a foliage leaf. In many seeds, such as those
of the squash, the oak, and the bean, most of the reserve
food is stored in the seed leaves, which therefore in such
cases are very thick. Thus seed leaves serve a variety of
different purposes in different cases.

250. Scale Leaves and Bracts. — We have found that
scale leaves are borne by many plants — covering winter
buds, growing on underground stems, bulbs, and tubers,
or on ordinary shoots, such as those of the pine and the

LEAVES AND THEIR USES 235

asparagus. Most commonly they are protective structures.
But bulb scales, like those of the lily and the onion, serve for
the storage of food ; and some scale leaves (for example,
those of the asparagus) contain chlorophyl and manufacture
a small amount of food. Scale leaves, except for their smaller
size, are usually similar to the blades of foliage leaves ; as a
rule they have no stalks. Most flowers are borne at the
ends of short branches, each of which grows from the axil of
a leaf. This leaf may be an ordinary foliage leaf. But if
a plant bears many flowers, and especially if the flowers are
close together in a cluster, the leaves from whose axils the
flower-bearing branches grow are likely to be smaller than
the ordinary foliage leaves. Small leaves, so located, are
called bracts. In some lilies that bear large numbers of
flowers, the lower flowers grow from the axils of foliage
leaves of about the ordinary size. The higher flowers are
in the axils of smaller and smaller leaves, and the uppermost
leaves are merely bracts. In such a case no sharp distinc-
tion can be made between foliage leaves and bracts. When
many flowers are borne very close together, as in the spike
of the mullein or the head of the red clover, each individual
flower grows from the axil of a very small, scale-like bract.
The chaffy scales of the corn tassel and ear, and those of the
heads of wheat, oats, and other grasses, are also bracts.

251. Thorns and Tendrils. — We have seen that some
thorns are branches of a special
form ; others, though very similar
in appearance, are really leaves
or parts of leaves, or sometimes
even roots. Many of the spines
of cactuses seem to be leaves ;
others are probably reduced

branches. The thorns of the
, fiG. 140. — Simple and
barberry (Fig. 140) are leaves; branched thorns of the corn-
some of them are simple, some mon barberry.

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branched. The thorns of the black locust are merely
stipules ; and similar thorns are borne by various acacias
and euphorbias (Fig. 141), especially by species that live
in warm, dry regions. A tendril, too, may be a branch, a
root, a leaf, or part of a leaf. Sometimes, as in some rela-
tives of the sweet pea, a whole leaf develops into a tendril.
More commonly, as in the peas, sweet pea, and vetches,
the tendrils are merely some of
the last leaflets, the lower parts
of each leaf being of the ordinary
form. In some Indian grasses,
the midrib grows out beyond the
blade in the form of a tendril.
Sometimes stipules become ten-
drils, as in various species of
Smilax. Sometimes, as in Clema-
tis and in climbing varieties of
Tropaeolum (the common "nas-
turtium "), the leaf -stalk acts as
a tendril, still bearing at its
outer end a blade of the usual
form.

252. Insect-Catching Leaves.
— The leaves of a few plants
have taken on very odd forms
that make them traps for in-
sects. These plants, although they have chlorophyl and
can manufacture carbohydrates for themselves, use the softer
parts of the insects' bodies for food. Such use of animal
food is possible to but few green plants, most of which, as
we have seen, can use the materials of animals' bodies only
after they have been broken down, mainly by the action of
bacteria, into much simpler substances.

Among the best known of the insect-catching plants is the
" pitcher plant " of Canada and the eastern United States

FIG. 141. — Euphorbia splen-
dens, a plant whose stipules
take the form of thorns.

LEAVES AND THEIR USES

237

(Fig. 142). • Each leaf -blade of this
plant is curved into the shape of a
pitcher which catches and holds rain
water. Insects, attracted by nectar
that is produced about the mouth of
the pitcher, crawl into it. They are
prevented from crawling back by
strong, pointed hairs inside, which
are turned downward. Finally the
insects are drowned in the liquid in
the pitcher. This liquid contains
enzyms, produced by some of the
cells that line the pitcher. The
enzyms digest (that is, change to a
soluble form) such parts of the dead

insects' bodies as the plant can use FIG I42 _^ an m.
for food, and the leaf cells absorb sect-catching leaf of the
this dissolved food from the water, common pitcher plant
Pitcher plants of other species are
found in the southern United States, Of the leaf,
on the Pacific coast, and in the
tropical parts of
the eastern hemi-
sphere.

The "sun-
dews " catch in-
sects in a very
different way.
The edges and
the upper surface
of each leaf bear
thick glandular
hairs (Fie i/n) ^IG- I4^' — Leaves of a sundew (Drosera rotundi-

;" folia) : A, after the leaf has been stimulated by
Un the swollen the touch of an insect . 5> a leaf in the unstimu.

end of each hair lated condition. After Kerner,

238 TEXTBOOK OF BOTANY

is always a drop of thick liquid that glistens in the sun like
dew. If an insect alights on the upper surface of the leaf,
touching some of the hairs, it is caught in this sticky liquid.
The touch of the insect serves as a stimulus to the leaf, which
becomes curved, and the hairs bend over from all sides upon
the insect. The soft parts of the insect's body are then
digested by enzyms contained in the sticky secretion.

" Venus' fly-trap " (Fig. 144) has a leaf -blade of two parts,
separated by the midrib ; the two parts fold together upon

A

FIG. 144. — Venus' fly-trap (Dionaa muscipula). A, a plant, some of
whose leaves are open and some closed as the result of stimulation by an
insect ; B, a single leaf ; C, a cross section of the upper part of a leaf, closed.
After Kerner.

an insect that has touched any of the sensitive hairs on the
upper surface of the leaf.

253. Arrangement of Leaves. — A plant like the lilac
or the horse-chestnut, whose leaves are borne in pairs at
the nodes of the stem or branch, is said to have opposite
leaves. In such plants, very commonly, though not always,
the leaves of one pair grow in a direction at right angles to
that of the next pair above or below ; this is the case in the
horse-chestnut. Some plants, for example some lilies
(Fig. 145), have their leaves in circles of three, four, or more
at each node, instead of in pairs. Very many plants, how-
ever, like the bean and the cucumber, have only one leaf at
each node ; their leaves are alternate. In an alternate-

LEAVES AND THEIR USES

239

leaved plant, if one leaf
is on the north side of
the stem, the leaf next
above may be on the
south side, the next on
the north, and so on.
The leaves then are all
in two vertical rows,
and each leaf is directly
above the second leaf
below. Other alternate-
leaved- plants have each
leaf directly above the
third leaf below ; the
leaves are then in three
vertical rows. Still
others have their leaves
in five, eight, or more
vertical rows.

Whether the leaves are
opposite, in circles, or
alternate, we usually find

FIG. 146. — The leaf mosaic of
a primrose.

FIG. 145. — A plant of the wild yellow
lily (Lilium canadense), whose leaves are
borne in circles (whorls) of four or more.

that the result of their arrange-
ment is that they overlap one
another as little as possible.
If we look down on a plant
from above, we shall probably
find that the leaves are so
arranged that each fits in, as
it were, to a space left be-
tween the leaves above (Fig.
146), so that each receives the
greatest possible amount of
light. The appearance is
much like that of a mosaic
floor, in which each angular

240 TEXTBOOK OF BOTANY

piece of stone fits closely between the neighboring pieces.
This is why such an arrangement of leaves is spoken of as
a leaf mosaic. If the light comes chiefly from one side rather
than from above, as in the case of a grape vine growing
against a wall, the leaf mosaic is turned toward the side
from which the light comes, and not upward.

254. Responses of Leaves to Light Stimuli. — The mosaic
arrangement just described results partly from the fact that
the leaves are attached to different sides of the stem. But
no method of attachment of the leaves to the stem would of
itself prevent overlapping ; in particular, it could not provide
for the fullest possible illumination of the leaves when the
light comes from one side. The leaves of many plants,
especially of plants growing in shady places, can adjust their
own position so that the upper surface of their blades will
receive the greatest amount of direct light. This adjustment
is' brought about partly by the greater or less growth in
length of the leaf-stalk ; sometimes the leaves on the same
plant have stalks that differ greatly in length. The adjust-
ment of the leaf to light is also helped by a twisting of the leaf-
stalk, and sometimes too by a curving of the leaf-blade.
Most of these changes are responses to the stimulus of light,
although the stimulus of gravity plays a part also in deter-
mining the direction of growth and the position of the leaf.
These responses are more complex and more difficult to study
than the changes which occur in the direction of growth of
stems and branches in response to stimuli.

There are some plants whose leaves do not so place them-
selves as to receive the greatest amount of light. These are
especially plants that live in exposed places where the light
is so intense, particularly in the middle of the day, that it
might injure the leaves. The prickly lettuce is a fairly good
illustration. Its leaves are nearly vertical instead of hori-
zontal ; some of. them point toward the north, others toward
the south. In this position the surfaces of the leaves receive

LEAVES AND THEIR USES 241

the greatest possible amount of light in the early morning
and late afternoon when the light is least bright, and the
smallest possible amount at midday when it is most intense.
This and other plants with similarly vertical leaves are
sometimes called " compass plants."

255. Evaporation of Water. — Leaves are the parts of the
plant from which water is chiefly lost -by 'evaporation.
When we consider the total area of the surfaces of the leaves
of an ordinary plant and remember that water is continually
evaporating from all these surfaces, we can see that a large
amount of water must be lost. It has been calculated that
a single oat plant in the course of its life gives off about 14
pounds of water ; and that a birch tree with 200,000 leaves
loses about two barrels of water per day. The water thus
lost by the leaf cells that are in contact with the air is re-
placed by water that comes from the cells deeper within the
leaf ; these in turn draw upon the water in the wood cells of
the veins and leaf -stalk ; these take water from the wood
cells (and vessels) of the branch or stem, these from the
wood cells of the roots, these from the cells of the cortex,
and these from the root hairs, which finally, as we know,
absorb water from the soil. Thus there is what amounts to
a steady stream of water passing from the soil through vari-
ous tissues of the plant, but most of the way through the
wood, to the outer cells of the leaves and thence into the air.
The comparison of this current of water to a stream must not
be pushed too far. The water really passes through a long
series of cells and vessels, going from each cell or vessel to
the next through the wall which separates them.

It is because of this continual passage of water upward and
outward that the roots of a tree must penetrate to the deeper
layers of the soil where a steady supply of water is to be had.
It is because of the great need for water that the roots of a
tree must branch abundantly, so that there shall be many
growing root-tips, each with its zone of absorbing hairs.

242 TEXTBOOK OF BOTANY

It is because of the steady evaporation of water from its
leaves that a garden plant whose roots do not reach far into
the soil wilts in dry weather ; the cells of its stem and leaves
lose so much water that they are no longer full and plump.
This explains why, to keep the plant alive at such times, we
must supply water to the soil ; and it shows us one reason.
why the ground about the plant must be cultivated, so that
the upper layers of the soil shall be broken up and loosened
and thus prevented from giving off to the air the water which
the plant so badly needs.

256. Necessity for the Water Current. — We know that
in seed plants the leaves ordinarily contain most of the
chlorophyl and manufacture most of the carbohydrates.
The water which the leaves use in carbohydrate manufacture
comes from the roots, and this is one reason why the plant
must have a continuous series of conducting tissues leading
from the younger parts of the roots (where water is taken in)
to all parts of the leaves. The evaporation of water seems
to be important on warm days also in helping to cool the
leaves, which otherwise might be scorched by the sun's rays.
In this respect, the evaporation of water from leaves is useful
to the plant in the same way that the evaporation of perspira-
tion from our own bbdies is useful to us.

257. Dangers of too Rapid Evaporation. — The reasons
just given explain why there must be a constant supply of
water coming up from the roots ; still, in most cases the
amount of water that is necessary for these purposes is
probably small in comparison with the amount that actually
evaporates from the leaves. Not only is energy wasted in
thus bringing up to the leaves more water than is needed
for actual use ; but also the evaporation is a source of real
danger, because if the roots should not be able to supply
enough water to make up for what is lost from the leaves,
the leaves and stem would wilt. Such a loss that cannot
be made up is a serious matter ; water constitutes a large

LEAVES AND THEIR USES 243

part of the living matter itself as well as nearly all of the cell
sap, and too great a loss of water stops the activities of living
matter and finally kills it. This is what goes on in both
wild and cultivated plants in a dry summer. Even large
trees sometimes die after a series of dry seasons.

Much of the evaporation from leaves, although it is use-
less and even dangerous to the plant, is unavoidable, because
leaves must expose a large surface to the air in order to
absorb enough carbon dioxid, and also in order to receive
sufficient light for carbohydrate manufacture. The exposure
of a large leaf surface for these purposes means that much
water will be lost by evaporation ; and so the needs of the
leaf for light and carbon dioxid seem to explain why the
plant must do so much apparently unnecessary work in
pumping up water from the soil.

258. How Evaporation is Checked. — So serious is the
danger of too great a loss of water that many peculiarities
in the structure of leaves are to be explained by the need of
keeping the rate of evaporation as low as possible. Chief
among the devices for checking evaporation are the minute
air-pores which are present in great numbers on the surfaces
of leaves (see Fig. 52). The pores lead into intercellular
spaces within the leaves. Experiment has shown that the
gases of the air (including carbon dioxid) pass into and out
of these pores and come into contact with the inner cells of
the leaf about as readily as though these cells were not
covered by the epidermis, while the evaporation of water
from the inner cells is slower than it would be if the epidermis
were not there. The practical effect, then, of the presence
of air-pores and intercellular spaces is that the area of leaf-
cells which can absorb carbon dioxid is greatly increased
without a corresponding increase in the amount of water
evaporated. This result is helped also by the fact that as a
rule the air-pores are found (especially in plants living in
dry places) on the lower surface of the leaf, which is shaded

244

TEXTBOOK OF BOTANY

from the direct rays of the sun and which therefore, being
cooler, loses water less rapidly by evaporation than would the
upper surface if it were similarly provided with air -pores.
There are other ways, too, in wliich evaporation from leaves
is checked. One of these, as we have seen, is by the produc-
tion of hairs. Another is by the
formation of cutin, a substance some-
what like cork, with which the outer
walls of the epidermal cells are per-
meated and which sometimes forms a
thin layer on the outer surface of the
epidermis that can be separated and
peeled off. Wax, which is sometimes
formed on the outer surface of the
epidermis, also helps to check evapora-
tion. The wax may be in a uniform
layer, causing the shiny appearance
that is characteristic of the leaves of
some willows and grasses, and of the
surfaces of many fruits. Sometimes
the wax takes the form of mealy par-
ticles; this is the "bloom" of plums
FIG. 147. — An aloe, and grapes, and of the leaves of the
whose thick leaves serve cabbage and the tulip. Cutin and

surfaces of leaves, hairs on the lower

surfaces.

Another tendency often noticed in the plants of dry
localities is to reduce in various ways the area of their leaf
surfaces. Generally speaking, plants that live in moist, shady
places where evaporation is slow, or in lands with mild, .moist
climates where the water supply is ample, have large, thin,
and often divided leaves. The leaves of the plants of deserts
and other very dry regions are seldom divided, for a divided
leaf exposes more surface to the air than would an un-

LEAVES AND THEIR USES 245

divided leaf of the same bulk. Plants living in dry localities
also are likely to have especially thick leaves. The century
plant, the bases of whose leaves are very thick, is an exam-
ple. A thick leaf not only exposes less surface in proportion
to its bulk and so reduces the danger of evaporation ; its
thick tissues also serve for the storage of water. The
juices of the thick leaves of some relatives of the century
plant are extracted by the Mexicans in great quantities and
are used in preparing the drink called " pulque." An ex-
treme reduction in size of leaves is seen in the various cac-
tuses, in nearly all of which the leaves are merely small
spines, and all the green, food-making tissue is contained in
the stem and branches. The branches of the prickly-pear
cactus not only do the work of leaves ; they actually look
like broad, thick leaves.

In the case of plants of temperate regions with evergreen
leaves which remain alive for more than one year, the leaves
have much the same characteristics as have those of the
plants of dry regions. This is because much of the water in
the soil is frozen during the cold months, and so the water
supply of the roots is greatly reduced. Under such condi-
tions, if evaporation were to go on freely from the leaves,
they, and the plant as well, would die. This explains the
advantage of the thick cutin layer and the waxy coating of
such leaves as those of the evergreen hollies, the box, and
the European mistletoe. It explains, too, the advantage of
the small, needle-shaped leaves, well provided with cutin
and in some cases with wax, of the pines and spruces. These
latter are inhabitants for the most part of regions where the
winters are long and cold, and where there is great need to
guard against too rapid evaporation.

259. Manufacture of Food in Leaves. — Chlorophyl-
containing cells differ from all the other cells of living plants
and animals in their ability to manufacture carbohydrates
out of water and carbon dioxid. In most seed plants the

246 TEXTBOOK OF BOTANY

chlorophyl-containing cells are found chiefly in the leaves ;
the leaves are, therefore, among other things, the car-
bohydrate-making organs of the plant. They obtain carbon
dioxid directly from the air, or from water if they live in
water ; the water that is needed is brought to them from the
soil by means of -the root hairs and the conducting tissues of
the root and stem. The first form which the newly-made
carbohydrates take is probably that of some of the simpler
sugars such as glucose. It is in the making of sugars out of
carbon dioxid and water that the work of the chlorophyl is
done. Much of the sugar, as we shall see, is changed to
starch, but with this change the chlorophyl has nothing to do.

The sugar, once formed, may be handled by the plant in
any one of several ways. It may be used at once, in com-
bination with some of the substances that the plant receives
from the soil, in building up more complex materials, such
as proteins and finally living matter. It may be broken
down in the process of respiration, either in the cell in which
it was formed or in another cell to which it has been passed
on, so giving up its store of energy for use in doing some of the
work of the plant. Or if, as is likely to be the case on a bright
day, sugar is made more rapidly than it can be used, it may
be stored away for later use. The carbohydrate food is
usually not stored in the form of sugar, at least in the cell in
which it was manufactured. Sugar, being soluble in the cell
sap, would make the sap more and more dense and sirupy as
its manufacture goes on. This would interfere with the
movement of materials within the cell and possibly with
other forms of activity of the living matter. For these and
perhaps for other reasons, sugar is not usually a convenient
form for the storage of large amounts of food.

As a rule, when the solution of sugar in the cell sap has
reached a certain strength, some of it is changed into starch
and stored in the form of small grains inside the chloroplasts.
Starch is a compact form of food, and being insoluble it does

LEAVES AND THEIR USES 247

not increase the density of the cell sap. So it is that during
a bright day starch gradually accumulates in the green cells
of a leaf. The change of sugar into starch is not brought
about by the chlorophyl. Very likely this work is done by
means of an enzym, but of this we are not certain. Toward
night the manufacture of sugar and starch comes to a stop.
During the night the starch that has been stored in the leaf-
cells during the day is gradually changed back, by the action
of a diastase, into a sugar, and this sugar, being soluble,
passes slowly through the cell walls into neighboring cells,
thence into the bast cells of the veins, and through them to
the bast cells of the branch or stem, which in turn conduct
it to all parts of the stem, branches, leaves, flowers, fruits,
and roots. In each of these parts, some of the sugar is used
in the building up of other substances and finally of living
matter ; some is destroyed in the process of respiration ;
and some may be stored for future use.

Stored food, in greater or less amounts, may be found in
almost any part of the plant ; but it occurs in largest quantity
in organs that are specially adapted for permanent storage,
such as thick stems and roots, bulbs, tubers, and seeds.
The stored food may be in the form of glucose, as in the grape ;
it may be changed into a more complex sugar, as in the sugar
beet and the sugar cane ; more commonly it is changed into
starch, as in the potato tuber and in the kernels of corn and
of other grains ; it may be changed into a fat, as in walnuts
and hickory nuts ; or it may be combined with other sub-
stances to form proteins, such as are found in considerable
amounts in the seeds of peas and beans. Thus, during the
night the cells of the leaf are relieved of most of the starch
which they have accumulated during the day, though
usually their supply is not quite exhausted by morning. The
next day, if conditions are favorable, the work of sugar- and
starch-making is resumed, and in the following night most
of the starch is again removed. Carbohydrate-making is

248 TEXTBOOK OF BOTANY

thus the special work of the leaf-cells. They also take an
important part in the building up of higher compounds,
including proteins and living matter, out of the carbohy-
drates and the food substances derived from the soil. But
this latter work is not peculiar to the cells of the leaf ; it is
probably going on more or less actively all the time in all
the living cells of the plant.

260. Storage of Food in Leaves. — In general, the busi-
ness of leaves is the manufacture of food ; surplus food which
is to be kept for a long time is usually stored in other organs
of the plant. Nevertheless, there are not a few plants
whose leaves are important storage organs. Leaves in
which any considerable amount of food is stored are likely
to be thicker than those which merely manufacture food and
pass it on to other organs. The very thick leaves of the
century plant, as we have seen, serve for the storage of water ;
they contain also other food substances, some of which are
dissolved in the water. The bulb scales of lilies and onions
are examples of underground leaves that ajre important
storage organs ; in the case of the onions, we profit by the
provision which the plant has made for its own future needs.

261. Respiration. — This is another kind of work in
which leaves play a large part, although it goes on in all parts
of the plant where there are living cells. The importance
of leaves in this process results from the fact that they expose
a larger surface to the air and so can take in the oxygen that
is needed for respiration more rapidly than can the other
organs of the plant. The oxygen that is taken in by the
living cells of a plant, whether it comes directly from the
air as in the case of most seed plants, or from the water in
case the plant is submerged, must pass through the cell
walls in solution in water, just as do all other substances
solid, liquid, or gaseous (excepting water itself), that enter or
pass out of cells. Not all the oxygen is necessarily used in
the cell that first takes it in ; it may be passed on to cells

LEAVES AND THEIR USES 249

farther within the tissues. In respiration, the substances
already in the cells, including carbohydrates, fats, proteins,
and possibly some of the living matter itself, are broken
down into simpler substances, and the energy which was
stored in them is set free. Part of the energy so set free
shows itself in the form of heat ; the temperature of an active
part of the plant is. therefore always a little above that of the
surrounding air. Other portions of energy set free in respira-
tion are used in building up complex food substances and
living matter, in growth, in the movement of materials within
the plant (such as sap that is pumped up from the roots to
the leaves), and in the movements of leaves and other
parts of the plant.

Of the simple substances formed in the breaking-down
processes of respiration, the most abundant are water and
carbon dioxid. The water remains within the cell where it is
formed or passes to a neighboring cell. The carbon dioxid
passes off through the cell wall into the air, unless it can be
immediately used again in the building up of new carbohy-
drates. Therefore it is that the effect of respiration upon the
atmosphere about the plant is just the opposite of that of
carbohydrate manufacture. Respiration takes oxygen from
the air and gives carbon dioxid to the air ; carbohydrate
manufacture takes carbon dioxid from the air and gives
oxygen to the air. So long as a plant is growing and increas-
ing in weight, it is making carbohydrates on the whole more
rapidly than it is respiring ; the net result of its activities
upon the atmosphere is to decrease the amount of carbon
dioxid and to increase the amount of oxygen.

The net result of the activities of colorless plants and of
animals, which respire but do not make carbohydrates,
is to decrease the amount of oxygen in the air and to increase
the amount of carbon dioxid. Thus these two groups of
living beings, green plants on the one hand and colorless
plants and animals on the other, neutralize each other's

250 TEXTBOOK OF BOTANY

influence upon the air, and the members of each group supply
the particular gas that the members of the other group need.
During a bright day, green plants give off more oxygen to
the air than they take in, because carbohydrate manufacture
goes on then much more rapidly than respiration. During
the night, green plants respire, but do not make carbo-
hydrates ; therefore, they take oxygen from the air and give
off carbon dioxid.

262. Movements of Leaves : The Sensitive Plant. — If
we turn a leaf until its lower surface is upward and its upper

A

FIG. 148. — A , a sensitive plant whose leaves are in the ordinary expanded
condition. B, the same plant, after its leaves and leaflets have responded
to the stimulus of a blow.

surface downward, and fasten it in the new position, we shall
find that in the course of some hours it has turned (usually
by a twisting of the leaf -stalk) until the leaf -blade faces in the
same direction as before. This is one of the ways in .which
leaves can adjust their position in relation to light. A differ-
ent and more rapid sort of leaf movement is seen in certain
plants, one of which is the familiar " sensitive plant." This
plant, like the bean, is a member of the pulse family ; it is a

LEAVES AND THEIR USES 251

native of South America. A leaf of the sensitive plant has
four leaflets, each of which bears several pairs of secondary
leaflets. If the tip of a secondary leaflet is very gently
touched, that leaflet and the opposite one fold together ; the
bending takes place at the base of each leaflet. If instead of
merely touching the leaflet we stroke it slightly, not only the
one pair but all the pairs of secondary leaflets belonging to
the same primary leaflet fold together. But they do not
fold at the same time ; first the leaflet touched and its mate
fold, then the next pair, then the next, and so on, and finally a
bending occurs at the base of the primary leaflet so that it
droops. That is, the stimulus is conducted through the cen-
tral axis of the primary leaflet. This conduction through
the cells of the leaf is similar to the conduction of a stimulus
by means of nerves from one part of the human body to
another part. But the conduction is much slower in the case
of the plant. It seems to be through the cells of the vascular
bundles that the stimulus is chiefly conducted, and these
cells cannot be compared with nerves because their chief
business is not, like that of nerves, the conduction of stimuli.
If the leaflet is struck more violently, not only the parts
of one primary leaflet, but all the parts of the leaf, will be
affected, and we can follow the conduction of the stimulus to
the base of the first primary leaflet, and then from the bases
to the tips of the other primary leaflets. In this case, each
primary leaflet droops when the stimulus reaches its base,
and finally the whole leaf droops because of a bending at
the base of its stalk. The stimulus of a still more violent
stroke may be carried still farther, so as to affect other
leaves and even perhaps all the leaves of the plant. These
movements of the leaflets and of the whole leaf take place,
not only in response to the stimulus of a touch or a blow ;
they occur in the same way if a leaflet is stimulated by a
weak electric current, by a slight cut or other wound, or by
an irritating chemical substance such as hydrochloric acid.

252 TEXTBOOK OP BOTANY

A change from light to darkness is also a stimulus. If the
room or box in which a sensitive plant stands is darkened,
the leaflets of the plant fold and its leaves droop, just as
though some or all of the leaflets had been struck. If light
is now admitted, the leaves gradually straighten up and the
leaflets unfold ; that is, the plant recovers from its stimulated
condition. If a sensitive plant is placed for some minutes
in an atmosphere saturated with chloroform, it loses the
power to respond to stimuli of any sort, just as an animal
does when it is chloroformed. Like the animal, the plant
may return in time to its normal condition if the chloroform
is removed ; but if the plant is exposed to chloroform too
long, it will die.

We have seen that a leaf -stalk is usually somewhat thick-
ened at its base ; the thickening or cushion is especially
marked in the leaves of members of the pulse family, to which
the sensitive plant belongs. The cushion is usually lighter
green in color than the rest of the leaf-stalk. There is a
similar, though smaller, cushion at the base of each primary
leaflet, and a small one also at the base of each secondary
leaflet. When we touch a secondary leaflet, we may ob-
serve that the upward movement which brings this leaflet
face to face with the one opposite is due to a bending in the
cushion at its base ; and the drooping of the whole leaf is
brought about by a bending in the cushion at the base of the
leaf -stalk. These cushions, then, act somewhat like hinges ;
and the movements of the different parts of the leaf result
from changes that occur in the cushions when the leaf or
one of its parts is stimulated. The change that takes place
in one of these cushions at such a time results from a change
in the amount of water present in some of its cells.

263. " Sleep Movements." — Although other plants of
the pulse family have similar cushions at the bases of their
leaflets and of their leaves, very few of them respond to
stimuli by such rapid movements. However, many plants

LEAVES AND THEIR USES 253

of this family, as well as some of other families, including
various species of Oxalis, do respond to the stimulus of a
change from light to darkness by changing the positions
of their leaflets. The night positions of bean leaves have
been referred to, and those of clover leaves are very similar.
Upon the return of daylight the leaves and leaflets spread
out again in the position with which we are more familiar.

264. Formation of Habits. — It has just been said that
the night movements of leaflets and leaves are responses to
the stimulus of a change from light to darkness. Another
factor also may play a part in these movements. If a good-
sized bean plant or sensitive plant is placed in a dark room,
the leaves, as we should expect, take their night position.
But if the plant is kept in the dark room, we find that after
about twelve hours the leaves spread out into something
like the position that they ordinarily occupy in the daytime,
though they do not open so fully as they would if they were
exposed to bright daylight. At the end of another twelve
hours they fold ; after twelve hours more they open ; and
so on for some days. If the plant is exposed to continuous
light instead of continuous darkness, the same thing hap-
pens. These results mean that, having been exposed al-
ternately to light and darkness at intervals of about twelve
hours during its life, the plant has formed the habit of
changing the position of its leaves at those intervals, and
that now, even if there is no change from light to darkness
or vice versa, it goes on with its leaf movements in the
way that it has formed the habit of doing.

A young plant which has been kept in continuous light all
its life has not formed the habit of changing the position of
its leaves each morning and evening. But as soon as it is
placed under ordinary conditions of light and darkness, its
leaflets begin to fold up each night and to spread out again
each morning, and in time the habit becomes fixed upon the
plant. The formation of a -habit such as this by a' plant is

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fundamentally the same thing as the formation of a habit by
ourselves. It results from the fact that when living matter
has done a certain thing once in response to a stimulus, some
change takes place in it which makes it easier to do the same
thing a second time ; the third time it is easier than the
second ; and after many repeti-
tions the act may become so
easy that it is done without any
external stimulus at all.

265. Fall of Leaves. — In the
autumn the leaves of most of
our trees and other common
plants die and fall. If we ex-
amine a fallen leaf, we find that
the surface where it has broken
away from the stem or branch is
as smooth as though it had been
cut with a knife. The scar left
on the stem or branch by the
fall of the leaf is also smooth.
This means that the leaf has not
been to™ roughly from its place

the leaves and leaflets fall. At of attachment, but that changes
a, two leaflets have fallen; at have taken place in the leaf-
stalk which resulted in its sepa-
ration from the shoot. As the
end of the growing season ap-
proaches, a change takes place
in the walls of a layer of cells
extending across the leaf-stalk

just where it is attached to the stem or branch. These walls
become softened, so that a shaking by the wind, or sometimes
a touch, is all that is necessary to break them and so to send
the leaf to the ground. The walls of the layer of cells on
either side of the softened region become permeated with cork.

b, all the leaflets have fallen,
and only the petiole remains;
at c, the petiole also has gone,
and the leaf scar is shown with
traces of the five vascular bundles
that ran from the branch into
the leaf.

LEAVES AND THEIR USES 255

Not only are whole leaves separated in this way from the
plant that bears them ; in the case of some divided leaves
like those of the Virginia creeper or the horse-chestnut
(Fig. 149), each individual leaflet is separated in the same
way from the main stalk of the leaf. The fall of leaves may
occur not only in the autumn, but at any time of the year
when for some reason, such as lack of water, a part of the
plant dies. So the dropping of leaves may be observed at
almost any time on many common house and garden plants.
The leaves of the pine, which live for several years, are cut
off in the same way when they finally die. This method of
bringing about leaf -fall is found, generally speaking, only in
dicotyledons and gymnosperms. The leaves of most mono-
cotyledons (such as the Indian corn and the lily), and of
some dicotyledons like the oak, do not form a separation
layer. As a result, although they may die and wither,
they do not fall at once, but remain attached until they
decay or are torn away.

266. How Do the Death and Fall of Leaves Help the
Plant ? — The answer to this question, as to so many others,
lies in the plant's relation to water. We know that plants
in those regions which have cold winters can obtain com-
paratively little water from the soil during the winter. There-
fore, unless the area from which evaporation may take place
is greatly reduced, the plant will be injured or killed by the
too rapid loss of water which it cannot replace. Most of the
plants of temperate regions that live over the winter (that
is, biennials and perennials) avoid this danger by shedding
their leaves, from which evaporation chiefly occurs, in the
way we have just observed. The cork layer which covers
the scar left on the stem or branch by the falling of the leaf
serves to prevent evaporation at that point ; it is also a
protection against infection by the spores of parasitic fungi.
Since most of the monocotyledons of temperate countries
are either annuals, or perennials whose above-ground parts

256 TEXTBOOK OF BOTANY

die each year, they have no need to go to the trouble of cut-
ting off their leaves in order to prevent evaporation in the
winter. There are plants, to be sure, even in cold regions,
whose leaves do not drop in the fall. Conspicuous examples
of this sort are the pines and other cone-bearing trees,
which, however, are especially well protected against the rapid'
loss of water by the small area of their leaves, and by thick
layers of cutin or wax. In warmer countries, on the other
hand, where the ground is never frozen and there is always a
supply of water for the roots, a much larger proportion of
plants have leaves that remain alive and green throughout
the year.

267. Autumn Colors. — The leaves of many common
plants undergo changes of color in the autumn before they
die. The autumn tints of leaves are chiefly yellows, reds,
and browns, and combinations of these colors. These dif-
ferent colors arise in different ways. As the activities of the
leaf lessen at the approach of autumn, its cells cease to make
chlorophyl, and the chlorophyl that is present in the chlo-
roplasts gradually disappears. The chloroplasts always
contain more or less of a yellow coloring matter in addition
to the chlorophyl. This yellow substance does -not disap-
pear as rapidly as the chlorophyl does, and so when the
green color of the chlorophyl fades out, the yellow color
remains. The red colors of autumn leaves are due to sub-
stances which were not present earlier, but which are formed
in the cell sap (not in the chloroplasts) as the chlorophyl
disappears. These substances are similar to those which
give a reddish color to the young shoots of many plants in
the spring ; they are also like those found in the red leaves
of the copper beech and other plants, in many red flowers
and fruits, and in the root of the beet. The formation of
red coloring matters is favored by cold weather and by the
presence of sugars in the cells ; indeed, it seems probable
that sugars are used in their formation.

LEAVES AND THEIR USES 257

When cork layers begin to be formed across the leaf -stalk
in preparation for the fall of the leaf, the movement of sugar
out of the leaf is checked ; the leaf cells now contain more
sugar than usual, and the conditions are favorable for the
formation of red coloring matters. Bright sunlight also
favors the formation of these red substances. The brown
color of autumn leaves seems to be present, at least to a
large extent, in the cell walls, which turn brown as they die.

268. Some Practical Uses of Leaves. — Although we use
the leaves of many plants for food, their actual food value
is in most cases rather small. Most of the more solid and
really important articles of our diet, so far as they are sup-
plied directly by plants, come from the stems, roots, seeds,
and fruits in which plants store most of their reserve food.
The value of the leaves that we eat lies rather in their stimu-
lating and appetizing qualities. One may think in this
'connection of the leaves of onions, cabbage, lettuce, endive,
spinach, celery, parsley, spearmint, sage, and of others that
are used for salads, for flavoring, and in similar ways. Among
the leaves that are important for their stimulating properties
are those of tea and tobacco. The leaves of many plants,
such as arnica, boneset, spearmint, digitalis, horehound,
and witch hazel, contain substances that make them useful
in medicine. Those of not a few tropical plants, among
them some of the palms, supply fibers that are used in a
variety of ways. Many leaves, especially those of the
grasses, are also an important part of the food of many of
the lower animals which we in turn use for food, as beasts
of burden, and in other ways ; and in this indirect way leaves
are of very great value to man.

CHAPTER XVII
FLOWERS AND THEIR USES

269. Flowers and the Relationships of Plants. — Every
one knows that there are many kinds of flowers, differing
from one another in size and color, in the shape and arrange-
ment of their parts, and in the way in which they are borne
upon the plant. One reason why much study has been de-
voted to flowers is that the structure of a flower tells us more
about the relationships of the plant that bears it than does
the structure of any of the vegetative parts — stem, leaves,
or roots. This is because the vegetative parts change oftener
and more rapidly in the course of the evolution of plants
than flowers do.

The conditions under which plants live are continually
though slowly changing, and they have been changing for
-ages. If a region that has been low and wet becomes high
and dry, the species of seed plants that live in that region
must either die out or undergo changes in their roots and
leaves that will adapt them to the new conditions. The
same is true if land that has been high and dry becomes low
and swampy ; or if the formation of a new mountain range
affects the direction of the winds and the amount of rainfall
in the country on either side. Changes such as these in
the earth's surface have compelled the greatest variety of
changes in the vegetative parts of plants, and so have re-
sulted in the development of many new species. But a
change in the conditions surrounding a plant is not so likely
to make changes necessary in its flowers, which are not so
258

FLOWERS AND THEIR USES 259

directly concerned as are the stem, leaves, and roots in the
plant's relations with the world outside.

Flowers, to be sure, have undergone changes during the
millions of years that seed plants have existed ; if this were
not true, there would not be the great variety of flowers that
we now find. But these changes have gone on much more
slowly than have the changes in vegetative organs, and so
all the members of a family may have kept very much the
same flower structure, although in other ways they have
come to be very different from one another. This is why
the structure of flowers is so useful in fixing relationships.
For example, the apple, the raspberry, the strawberry, and
the rose are members of the same family. Their relation-
ship is shown by the structure of their flowers ; but one would
hardly suspect it from an examination of their other parts.

270. Staminate, Pistillate, and Perfect Flowers. — In
classifying angiosperms, we try to determine which of the
many kinds of flowers are most
primitive — that is, are most like
the flowers of the original ancestor
or ancestors of the angiosperms —

and which have departed farthest l..^!^^^- — d
from the original condition. In a

general way, it appears that the /- /

original angiosperm flowers were ^ ^ _A lengthwise
much like the cones of a pine, and section through the flower of
that in the course of time advances an apple (a perfect flower) ;
have been made from this condi- J^-; ^ "j^J
tion in several different directions, with ovules; /, flower-stalk.
For example, angiosperm flowers

seem to have been at first of two distinct sorts — staminate
and pistillate. Many angiosperms of the present day, like
the cucumber and the Indian corn, still have separate stami-
nate and pistillate flowers. In this respect, the cucumber
flower is more primitive than a flower which, like that of the

260

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b

bean, contains both stamens and pistil. A flower that con-
tains both stamens and pistil is often called a perfect flower.
This is a convenient term, but one that is likely to give a
wrong impression. For the work that they have to do, the
separate staminate and pistillate flowers of the cucumber
are just as perfect as is the " perfect" flower of the bean.
In the case of plants with separate
pistillate and staminate flowers, the
two kinds may be borne on two dis-
tinct plants. This is the case in the
willows, the poplars, and the hop.
But many plants with separate stami-
nate and pistillate flowers, among
them the corn, the cucumber, and
the oak, bear both kinds of flowers
on the same plant.

271. Sepals and Petals. — The
primitive angiosperm flowers prob-
ably, much like the pine cone, had
only stamens or pistils, and nothing
FIG. 151.— The floral that corresponded to sepals or petals,
structure of the Jack-in- There are still many angiosperms
the-pulpit; a, the s bathe, a .., « Ljn o i, r

large leaf which encloses ™th SUch naked flowers' Sudl> f°r
the flower cluster; b, the instance, is the Jack-in-the-pulpit
spadix or stalk which bears (pjg- x 5 x) whose flowers are crowded

j.1. _ flowprs *

it r r>u. together on a common stalk. The
pistillate flowers of the birch are also
naked. From the primitive condi-
tion of naked flowers there are several steps in advance.
Some flowers have sepals only ; these may be green or
greenish as in the flowers of the oak and the elm, or white
as in the common anemone, or colored as in the hepatica.
Some flowers, like the lily (Fig. 153), have sepals and
petals that are almost exactly alike; but most showy
flowers — such as the violet, the bean, the sweet pea, and

the numerous
staminate flowers at c, pis-
tillate flowers at d.

FLOWERS AND THEIR USES

261

the rose — have small green or greenish sepals and larger
white or colored petals.

272. Number and Arrangement of the Parts of Flowers.
— In some flowers, some or all of the parts are present in
large numbers. For example, the white water lily has a
large and indefinite number of petals and stamens; the

strawberry flower has a large
number of stamens and pis-
tils. On the other hand,
many flowers, like that of
the bean, have a compara-
tively small and fixed num-

FIG. 152. — The floral struc-
tures of Anthurhnn andreanum,
a plant belonging to the same
family (Araceae) as the Jack-in-
the-pulpit. The large, heart-
shaped spathe is gorgeously col-
ored, serving to attract insects.

FIG. 153. — A lily flower, cut in
half lengthwise ; a, sepal ; b, petal ;
c, anther; d, filament; e, stigma;
/, style ; g, ovary.

ber of each kind of parts. The flowers with large numbers
of parts are in that respect more primitive ; their parts are
usually arranged in a spiral. Notice, in this connection,
the arrangement of the petals of the white water lily.
From this condition of a large, indefinite .number of parts,
spirally arranged, the advance has been in the direction
of a smaller and fixed number of parts, which are usually

262 TEXTBOOK OF BOTANY

arranged, not spirally, but in a definite number of circles.
Thus the lily has one circle of sepals, one of petals, two
circles of stamens, and one circle of macrospore leaves which
have united to form a single pistil.

In the more advanced monocotyledons, the number of
each sort of part has usually become three or six ; in the more
advanced dicotyledons, it is most commonly four or five or
a multiple of four or five. In a particular flower, some of
the parts may remain numerous although the other parts
have become few and fixed in number; thus, the apple
flower has five sepals, five petals, and usually five macrospore
leaves, but many stamens. In other flowers, as in those of
the bean and lily, all the parts are few and fixed in
number.

273. Union of the Parts of a Flower. — In the more primi-
tive flowers, all the parts are separate from one another ;
the sepals are attached to the flower-stalk below the other
parts; the petals (if there are any) are next above the
sepals, the stamens are next, and the attachment of the
pistil or pistils is at the end or top of the stalk. This is the
arrangement in a buttercup. But many flowers have de-
parted from this condition, because some of their parts have
grown together more or less. Often the petals are united
into a tube for part of their length, as in the cucumber
flower, or for their whole length, as in the morning-glory
and the petunia. In flowers with united petals, the sepals
are usually also united with one another in the same way ;
this is the case in the cucumber flower. Sometimes, as in
the Roman hyacinth, both sepals and petals unite to form
a single tube.

Often some or all of the stamens are connected with one
another. For instance, in the flower of the sweet pea, as
in that of the bean, nine of the ten stamens are grown to-
gether by their filaments. All of the many stamens of the
hollyhock or of the cotton are united by their filaments into

FLOWERS AND THEIR USES

263

1

a tube. In the flowers of the sunflower, the dandelion, and
others of the composite family, the five stamens are united
by their anthers, the filaments being separate. The stamens
of some flowers are joined to the petals, or to the sepals, or
to both. The Roman hyacinth has a stamen opposite,
and partly united with,
each sepal and each
petal.

A pistil may be com-
posed of a single macro-
spore leaf, as in the bean
which has but one pistil,

or il! i !:• -I-::'.''

which has many. But
in many flowers the
pistil is a compound
structure formed by the
union of two or more
macrospore leaves. The
pistil of the sunflower or
of the dandelion is com- FIG. 154. — Cross section through the
posed of two macrospore ovary of a lily, showing how it is formed
leaves ; that of the lily ^ the ™™ °f three macrospore leaves.
J Six ovules appear in the section — two in

or the hyacinth of three ; each of the three cavities of the ovary,
and that of the apple

usually of five. These compound pistils are less primitive
than the simple pistil of the bean or of the corn. Still
another form of union of parts is seen in the pistillate
flower of the cucumber. There the sepals and petals are
grown together with the wall of the ovary. As a result,
instead of being attached to the flower-bearing branch
below the ovary, as in the lily flower for example, the
sepals and petals seem to grow out of the top of the ovary.
In the sunflower, sepals, petals, and stamens are united
in the same way with the ovary wall. In this respect,

264 TEXTBOOK OF BOTANY

the primitive condition is that found in the lily, whose
sepals, petals, and stamens are all separate from the ovary
wall.

274. Regular and Irregular Flowers. — The more primi-
tive flowers are regular; that is, they can be cut in many
ways into two like halves ; a flower is irregular if there is
only one direction in which it can be cut into two parts that
are alike. An irregular flower can be said to have a right side
and a left side ; a regular flower is alike on all sides. Ex-
amples of regular flowers are those of the lily and the rose.
The bean, pea, violet, and lady's slipper (Fig. 159) have
irregular flowers. From what has now been said about the
different forms of flowers, we see that the same flower may
be primitive in some respects and advanced in others. For
instance, the lily is primitive in having its parts all separate
and in being regular in shape ; it is advanced beyond the
primitive condition in having both stamens and pistil in
the same flower, in having sepals and petals, in having its
parts few and arranged in circles, and in having a compound
pistil. The bean flower is more primitive than that of the
lily in having a simple pistil ; it is more advanced in its
irregular form, and in the union of its sepals, that of two of
its petals, and that of all but one of its stamens.

275. Arrangement of Flowers. — A flower is always borne
at the end of a stem or branch. If a plant bears more than
one flower, then plainly all the flowers, or all but one, must
be borne on branches. Sometimes the flower-bearing branches
start here and there along the main stem in the axils of or-
dinary foliage leaves. But as a rule, if a plant has many
flowers, its flower-bearing branches are short and are borne
close together in the axils of small bracts. In this way a
flower cluster is formed. The stalk of each individual flower
in the cluster is called a pedicel; the stalk of the whole
cluster, which may be the end of the main stem or may
be itself a branch, is called a peduncle. Both peduncle and

FLOWERS AND THEIR USES 265

pedicels may vary much in length, and these variations re-
sult in flower clusters of different forms.

One of the simplest kinds of clusters is the raceme, in which
both the peduncle and the pedicels are fairly long and all
the pedicels are of about the same length. The lily-of-the-
valley, the bean, and the currant have their flowers in
racemes. In a spike, such as that of the plantain or of the
mullein, the pedicels are so short that the flowers are very
close to the peduncle, and the peduncle is shortened enough
to bring the separate flowers close together. A catkin is
much like a spike, excepting that it droops. The flower
clusters of willows and of a good many other trees and
shrubs are catkins. In a corymb, like that of a hawthorn,
the peduncle is shortened ; the pedicels are of unequal
length, so that all the flowers are borne at about the same
level and the cluster is more or less flat-topped. In a corymb
the flowers that come from the lower part of the peduncle
are the first to open. A cyme is like a corymb, excepting
that the flower at the end of the peduncle (the central flower
of the cluster) opens first, and those borne lower down on
the peduncle open later. The flower clusters of pears and
apples are small cymes. In an umbel, such as that of the
cherry, the peduncle is so much shortened that all the pedi-
cels arise at the same level. They are also of' about the
same length, so that an umbel, like a corymb, is flat-topped.

In a head, both peduncle and pedicels are much short-
ened, so that all the flowers are at about the same level and
are very closely packed together. The heads of the red
clover are familiar. So are those of the members of the
composite family, including the sunflower, the dandelion,
and the thistle. The flowers of composites are so closely
packed together that the head is thought of by most people
as a single flower. This notion is helped by the fact that
the outer flowers of the head are often (as in the sunflower
and the daisy) different from the inner ones and look like

266

TEXTBOOK OF BOTANY

petals; and by the further fact that just below the head
are many bracts that look like sepals. Really, however,
a single head of a sunflower, a daisy, or a dandelion contains
many separate small flowers.

276. Compound Flower Clusters. — The kinds of clusters
so far mentioned are simple; they have, in each case, a
peduncle whose branches are the pedicels. But the branches
of the peduncle may themselves branch, and so the pedicels
may be branches of the third or fourth order. Such repeated
branching gives rise to a compound flower cluster. A com-
mon form of compound cluster is the panicle, a compound
raceme. The tassel of the Indian corn is a panicle. The
flowers of the elder and of the mountain ash are borne in
compound cymes. Compound umbels are common ; they
i* *&« are borne by many mem-
bers of the parsley family,
including the parsley, the
carrot, and the parsnip.

277. Pollination: How It
is Brought About. — By pol-
lination is meant the carry-
ing of the pollen grains
from the anther that pro-
duced them to a stigma of
the same or of another
flower. The pollen of the
great majority of angio-
sperms is carried to the
stigmas either by the wind,
FIG. 155. — Tape-grass (Vallisneria as m ^g corn and Other
spiralis). The plant on the left bears
staminate flowers which, still unopened,
are breaking away and rising to the
surface of the water. The plant on

grasses ; or by insects, as
in the bean. Some agents
other than the wind and

the right bears a pistillate flower on a . , . ,

long stalk which reaches to the surface. msects brmS about

After Kemer.

tion in certain cases. Thus,

FLOWERS AND THEIR USES

267

there are some plants living in the water, such as the com-
mon tape-grass (also known as " eel -grass '•' and "wild
celery," Figs. 155 and 156), which depend upon currents
of water to carry the
pollen to the stigma.
It is not the pollen
alone of the tape-
grass that is carried,
however, but the
whole staminate
flower. This floats
about, as the illus-
tration shows, until
it comes in contact
with a pistillate
flower. There are

some plants whose
_ llj ^IG- *&• — Staminate and pistillate flowers

flowers are pom- of the tape-grass. The staminate flowers are

nated by humming caught in a slight depression in the surface of

birds and Other the water about a pistillate flower, and the

. pollen of some of the stamens is thus brought

birds, others are pol- into contact with the pistil After Wylie

linated by snails and

slugs, and a few in the tropics are pollinated by bats.

278. Pollination by the Wind. — It has already been
pointed out that pollination by the wind is an extravagant
method, because the pollen is scattered in a haphazard way
and only an occasional grain can land upon a stigma. Never-
theless, many angiosperms, as well as all gymnosperms,
depend upon the wind for pollination, and yet are very suc-
cessful in forming seeds and in multiplying their numbers.
Wind-pollinated angiosperms are chiefly plants that grow
in locations where the wind may well serve their purpose.
If they are small, like the grasses and sedges, great numbers
of plants of the same species commonly grow close to one
another in places like meadows and marshes where the wind

268 TEXTBOOK OF BOTANY

has full sweep. Under such circumstances each stigma has
a good chance of receiving pollen. Many shrubs and trees,
such as the hazel, alder, elm, oak, and poplar, are wind-
pollinated. Their flowers are high up above the ground,
where they are reached by winds from all directions. Wind-
pollinated plants necessarily produce much more pollen than
is actually needed for pollination. Their pollen grains are
usually small, smooth, and dry, so that they may be blown
about easily and carried long distances. Their stigmas are
often large, and branched or covered with projections in a

FIG. 157. — Types of pollen grains : a, pollen of one of the pinks (Dian-
thus); b, of the pumpkin; c, of Marina persica; d, of the enchanter's
nightshade (Circaa alpind) ; e, of a passion-flower (Passiflora kermensina) ;
f, of a pine (Pinus pumilio) ; g, of Cobcea scandens. After Kerner.

brush-like or feather-like fashion ; this increases the chance
that some of the pollen grains will be caught and held. As
a rule, the flowers of wind-pollinated plants are small and
have no bright-colored parts, no odor, and no nectar.

279. Pollination by Insects. — There are many more
species of insect-pollinated than of wind-pollinated plants.
As a rule, insect-pollinated plants produce less pollen than
do wind-pollinated plants ; on the other hand, their pollen
grains are sometimes (though by no means always) com-
paratively large. Pollen grains which are to be carried by
insects are often covered with a sticky substance, and as a
rule their outer surfaces are rough or provided with small

FLOWERS AND THEIR USES

269

spines or warts ; thus they are likely to stick to insects'
bodies and so to be carried about. The stigmas, too, are
commonly rough and sticky. Insect-pollinated plants have
various ways of advertising their presence to the insects
whose assistance is needed. Many of them have large,
brightly colored or white flowers. The plants that we raise
for the beauty of their flowers are insect -pollinated ; the size

FIG. 158. — Salvia glutinosa, showing how cross-pollination is assured.
A, a stamen ; the short upright column (/) is the filament ; c, c, the long
connective, bearing the anther at its upper end. B, a lengthwise section
of a young flower, showing the anther in its natural position. C, the same,
the anther having been pushed down by a bee pressing on the lower part
of the connective. D, a bee visiting a young flower ; the anthers have been
pushed down and are touching the bee's back. E, a bee visiting an older
flower whose pollen has been shed ; the style has now grown long and hangs
down so as to touch the bee's back at the same place at which it was touched
by the anthers of the younger flower. After Kerner.

and color of the flowers have come about, not because they
are beautiful, but because such flowers attract insects and
in this way are useful to the plant. We have selected the
plants for cultivation because the same things that make
their flowers attractive to insects are also pleasing to us.

However, the flowers of many cultivated plants have
been made much larger and more showy by breeding than
they originally were. Our large double roses and carnations,

270 TEXTBOOK OF BOTANY

for instance, are very different from the single wild flowers
from which they have been developed. The odors of flowers,
too, are a means of letting insects know of their presence.
Most of the odors that are attractive to insects are also,
fortunately, pleasant to us. The odors of certain flowers
are another reason why we have chosen for cultivation the
plants that bear them. Some flowers, like carnations, are
conspicuous to both sight and smell. Other plants, like
mignonette, have small, inconspicuous flowers which attract
insects chiefly by their odor. The pleasant-smelling sub-
stances contained in many flowers, such as roses, violets,
jasmine, and lavender, are extracted and used in the manu-
facture of perfumes. Occasionally, however, odors that
attract insects are very unpleasant to us ; examples of this
sort are the skunk cabbage and the carrion-flower.

280. Nectar. — Although it is true that flowers attract
the attention 'of insects by their size, color, and odor, the
insects do not visit flowers simply because they are beau-
tiful or sweet-smelling. An insect flies or crawls to a par-
ticular flower because that flower may be useful to it in some
way. Insects find different flowers useful in different ways.
Most often the flowers supply them with a special sweet
food called nectar. Nectar is produced in various parts
of a flower, and in some cases even outside the flower ; but
usually it is found in such a place that when an insect visits
a flower in search of nectar, some part of its body touches
one or more anthers and so brushes off and carries away some
of the pollen. The nectar of the horse-chestnut, for ex-
ample, is formed at the bottom of the sepals ; that of the
cucumber and the pumpkin, in a cup formed by a union of
the lower parts of the sepals and petals. The buttercups
and lilies produce nectar on the lower part of each petal ;
that of the columbine is formed in the lower spur-like end
of each petal ; and that of the strawberry in the bottom of
the flower, between the stamens and the pistils. Many of

FLOWERS AND THEIR USES 271

the features in which angiosperm flowers differ from one
another — including the shape and color of sepals and petals,
and the position of stamens, pistils, and nectaries — have
developed with reference to insect-pollination.

The relation of their flowers to insects, therefore, has been
a very important factor in the evolution of angiosperms ; and
one reason why the angiosperms as a group have been so
successful in the struggle for existence is the fact that so
many of them have secured the help of insects in pollination.
The relations of insects to flowers have likewise been an im-
portant factor in the evolution of insects. Thus, butter-
flies and moths live entirely or chiefly upon nectar; they
have a long, flexible, sucking proboscis, which can be pushed
deep into the parts of flowers where nectar is to be found.
The proboscis is of different length in different butterflies
and moths, and each species seeks the flowers to which the
length of its proboscis best adapts it. Bees not only feed
upon nectar themselves, but they gather and store it up in
the form of honey for the use of their young — a habit which
makes the honey-bee and the nectar that it gathers of great
practical interest to us. The mouth-parts of bees are
especially adapted to the work of biting and sucking, which
enables them to obtain nectar ; and some of them, includ-
ing the honey-bee, have a special apparatus on their hind
legs, consisting of a mass of rough, stiff hairs to which
pollen grains cling in great numbers.

281. Pollination of the Lady's-Slipper. — The lady's-
slipper offers a very good illustration of the way in which
a flower may be adapted to pollination by particular in-
sects. The flower of the lady's-slipper has the form of a
hollow sac with an opening at the top ; this opening is partly
closed by a flap. The edges of the opening in front of the
flap are curved inward, so that insects of various sizes can
get into the sac but cannot well get out at the same place.
Inside, at the bottom of the sac, are juicy hairs that are

272

TEXTBOOK OF BOTANY

eaten by insects ; these hairs perhaps bear also small drops
of nectar. If the insect is of the right size and strong enough,
it can push its way out through the opening at either side
of the flap ; certain bees, for example, can do this ; smaller
insects, such as flies, cannot, but remain inside the sac and
die there. On the under side of the flap (the side toward
the inside of the sac) is the stigma ; and on either side of

the stigma is an anther, whose
pollen is held together in a
sticky mass. As a bee pushes
out beside the flap, its shoul-
der brushes against an anther
and carries away the mass of
pollen. Then, when the bee
enters another flower, its
shoulder brushes against the
stigma of that flower and
there deposits the pollen.

As a rule, a flower of any
particular species may be

FIG. 159. — A lengthwise section
through the flower of a wild lady's-
slipper (Cypripedium acaule) ; a, one
of the three sepals ; b, a petal ; c, the

anther of a fertile stamen; <Z, a sterile Pollinated by any one of a
stamen ; e, the stigma ; /, hairs at number of different kinds of
the bottom of the sac, g, which is
composed of a single petal; h, the

ovary.

insects ; but sometimes, as in
the case of the lady's-slipper,
the flower is so formed that
it can be pollinated only by an insect of about a certain
size ; and often, as in the columbine and in flowers like the
petunia, whose petals are united into a tube, the nectar can
be reached only by an insect with a proboscis of at least a
certain length. There are flowers that are adapted to
pollination by only one particular kind of insect (see §§ 283
and 284 below).

282. Pollen as Food for Insects. — There are flowers —
including the common anemone, the roses, and the hepaticas
— '• which depend upon insects for pollination, but which form

FLOWERS AND THEIR USES

273

no nectar, or practically none. The insects that visit such
flowers eat the pollen instead of nectar ; and the flowers
produce so large an amount of pollen
that, although a good deal is eaten by
an insect visitor, enough clings to its
body so that it is sure to carry some
pollen to the next flower that it visits.
This method of providing food for in-
sects is by no means economical of
pollen ; but it is probably less extrava-
gant, after all, than wind-pollination.

283. Insects that Lay their Eggs in
Flowers : the Yucca Moth. — In some
cases, an insect visits a flower, not to
obtain food for itself, but to lay its eggs
in a place where its young, when the
eggs hatchj may find
food, or shelter, or
both. The Yuccas, liv-
ing in the southern United States and
Mexico, are members of the lily family,
with sword-like leaves and a tall stalk that
bears many white flowers (Fig. 160). The
flowers of various species of Yucca open
at twilight and are visited by a certain
night-flying moth. The female moth
alights first on an anther. There she
scrapes up a mass of the sticky pollen
grains and rolls them into a ball. After
FIG. 1 6 1. — The the pollen is gathered, the ball is tightly
held by a special long, flexible organ.
Then the moth visits a pistil (usually of
another flower) , and by means of a sharp-
pointed organ she pierces the ovary wall and deposits her
eggs in the ovary among the ovules. Finally she visits the

FIG. 160. — Yucca glo-
riosa. After Kerner.

Yucca moth gather-
ing pollen from an
anther. After Riley.

274

TEXTBOOK OF BOTANY

stigma of the same pistil and pushes the ball of pollen down
into the hollow style — just as though she intended to make
sure of the- pollination of that particular flower. When the
eggs hatch in the ovary of the flower, the young grubs eat '
some of the seeds into which the ovules have developed ;
after a time, the grubs escape through holes that they make
in the ovary wall.

The ovules, of course, would not have grown into seeds
if the flower had not been pollinated ; therefore, the pol-
lination by the mother moth insured
a supply of food for her young. But
the grubs eat only part of the many
seeds that the ovary contains. So
the plant secures a supply of seeds,
and in this way it also is benefited
by the visit of the moth. The
pollen of Yucca is not carried by
the wind ; and if the moth for any
reason does not visit the plant, no
seeds are formed. The same thing
is true if it is grown where the moth
does not live, as for example in
European gardens.

284. Pollination of the Fig. — The fig that we eat is not
a fruit, but the hollow end of a peduncle inside which was
borne a cluster of flowers. The arrangement of the flowers
is shown in Figure 163. It is the tissues of the hollow end
of the peduncle that become soft and juicy. In eating a fig
we bite many small, hard bodies ; these are the real fruits.
The flowers of the fig are of three kinds : staminate flowers,
pistillate flowers with long styles, and pistillate flowers with
short styles. Certain trees bear figs which when young con-
tain only long-styled pistillate flowers; the figs borne on
other trees contain staminate flowers near the openings of
their sac-like cavities and short-styled pistillate flowers in

FIG. 162. — A Yucca
flower ; the moth is forcing
a mass of pollen into the
cavity of the style. After
Kerner.

FLOWERS AND THEIR USES 275

the lower part of each sac. Figs of both kinds are visited
by the females of a certain kind of wasp.

Suppose that a wasp enters a fig which contains staminate
flowers and short-styled pistillate flowers. She inserts her
egg-depositing organ into a style and lays an egg in the
ovary. After this egg hatches, the young insect grows
rather rapidly and the tissues of the ovary wall surrounding
it also grow, forming a gall.
The young insect feeds on the
cells of this gall. When it is
fully grown, it breaks out of
the gall. The female insects
(but not the males) finally
make their way out of the
cavity of the fig. But in
doing so an insect brushes
against the anthers of the
male flowers which are near
the opening of the cavity and
collects pollen on all parts of
her body. The wasps which FIG. 163. — 4, a fig, showing how
. .... . ., ,, the flowers are borne inside the hoi-

escape in this way visit other low end of the pedunde 5> a

figs in order to find a place staminate flower of the fig. C, a

to lay their eggs. Some visit long-styled pistillate flower. D, a

r. , . . ' . , short-styled pistillate flower. After

figs containing staminate and Kerner

short-styled pistillate flowers

and repeat the history that we have just followed. Others
visit figs of the other sort, which contain only long-styled
pistillate flowers.

Coming in contact with these flowers, a wasp deposits on
the stigmas some of the pollen with which her body is cov-
ered, and so pollination is brought about. But when she
attempts to lay an egg in the ovary of one of these flowers,
her egg-depositing organ is not long enough to reach to the
base of the style. So the egg is laid, not in the ovary, but in

276 TEXTBOOK OF BOTANY

the style. Here conditions are not favorable for its further
development ; the egg dies, and no gall is formed. Instead,
in the ovary of this flower a seed is produced, and the ovary
develops into a small, hard fruit. The short-styled flowers
of the fig seem to be of no direct use to the plant. Indirectly
they are useful, because they supply a place in which the
eggs of the wasp can hatch, and so the species of insect
which pollinates the plant is kept alive. The figs that con-
tain only long-styled pistillate flowers, and in which there-
fore fruits may be formed, are the ones that develop into
edible figs. Most of the figs that contain staminate and
short-styled pistillate flowers dry and fall early and so are
useless. It is customary among fig-raisers to plant an oc-
casional tree bearing figs of this latter sort, and branches of
this tree on which figs are growing are hung on the branches
of the trees that bear edible figs. This insures the polli-
nation of the long-styled flowers in the edible figs and the
development of seeds.

The figs of some varieties will ripen in a perfectly normal
way even if none of their pistillate flowers are pollinated,
although of course they contain no fruits or seeds. The
figs of other varieties, however — including those which
supply the dried figs of commerce — will fall from the tree
before they are fully grown, unless their flowers have been
pollinated.

285. Cross-Pollination and Self -Pollination. — Cross-
pollination means the carrying of pollen from the anthers of
one flower to the stigma of another flower which may be on
the same or on a different plant. Self-pollination means the
carrying or dropping of pollen from the anthers of one flower
to the stigma of the same flower. There are peculiarities
in the structure of many flowers, both those of wind-polli-
nated and those of insect-pollinated plants, which make
self-pollination either impossible or much more difficult
than cross-pollination. The study of these peculiarities has

CHARLES DARWIN

Born at Shrewsbury, England, 1809; died at Down, 1882.
First established on a basis of scientific observation and
experiment the doctrine of the origin of new species of plants
and animals through descent from older species — a doctrine
first fully presented in 1859 in the Origin of Species. His
work has been of revolutionary importance, not only in
botany and zoology, but also in the other sciences as well
as in history and philosophy.

FLOWERS AND THEIR USES 277

led many observers to conclude that cross-pollination is of
greater benefit to plants than self-pollination. Darwin
found that in many plants, though by no means in all that
he studied, cross-pollination results in more vigorous and
more productive offspring than self-pollination. Especially
is this the case if the pollen and stigma are borne in flowers
on different plants. The results of cross-pollination between
flowers on the same plant are more like those of self-pollination,
although even this kind of cross-pollination is sometimes
more favorable than self-pollination.

The difference between the effects of cross-pollination be-
tween flowers on the same plant and those of cross-pollination
between flowers on different plants is shown by some recent
experiments. It is found that if the silk of Indian corn is
dusted with pollen from the tassels of another plant and is
kept free from the pollen of the same plant, the offspring is
as a rule more vigorous, grows to a larger size, and bears
more fruit, than that which results if the silk is dusted with
pollen from the same plant. On the other hand, self-pol-
lination often occurs in nature, and there are many kinds
of plants in which it is the regular method and which do
not seem to suffer from lack of self-pollination. However,
in varieties of tobacco that are ordinarily self -pollinated, it
is found that sometimes (though not always) plants of greater
vigor result from cross-pollination.

286. Arrangements that Favor Cross-Pollination. — One
of the simplest ways of securing cross-pollination between
flowers on different plants is followed when the staminate
and pistillate flowers are separate and borne on different
plants. This is the case in the willows, the poplars, and the
hop. The disadvantage of this arrangement is that both
kinds of plant (that is, those with staminate and those with
pistillate flowers) must grow near each other. If one sort
of plant is missing in a certain locality, or if plants of the
two kinds are too far apart, pollination does not occur and

278 TEXTBOOK OF BOTANY

no seeds are formed. If, as in the cucumber and the Indian
corn, staminate and pistillate flowers are separate but
borne on the same plant, only cross-pollination can occur,
but it may be between flowers on the same plant. However,
under such conditions some pollen is quite certain to be
carried from one plant to another.

Cross-pollination between flowers on different plants is
sometimes made more likely by the fact that the flowers of
the two sorts on a particular plant ripen at different times ;
either the staminate flowers ripen and shed their pollen be-
fore the pistillate flowers are ready for pollination ; or else,
as in the oaks and the walnuts, the pistillate flowers ripen
and are pollinated before the staminate flowers are ripe.
Among plants with perfect flowers (flowers containing both
stamens and pistils) there are also many conditions that favor
cross-pollination. One of the commonest, something like
what we have just seen in plants with separate staminate
and pistillate flowers, is the habit of ripening the stamens
and the pistil of the same flower at different times. Some-
times, as in the onion, the gladiolus, and the members of the
composite family, the stamens ripen first ; in other cases,
as in the horse-chestnut and in some varieties of tobacco, the
pistil ripens before the stamens.

In those flowers whose stamens and pistil ripen at nearly
the same time, the parts of the flower are often so arranged
that pollen falling from the anthers is not likely to land
upon the stigma. An arrangement of this sort has been
described in the bean, and the same result is brought about
in different flowers in a great variety of ways.

A peculiar arrangement that favors cross-pollination be-
tween flowers on different plants is seen in many species of
primroses (Fig. 164). These have perfect flowers, but
they are of two different kinds, which are borne on different
plants. The flowers of some plants have high stamens (that
is, stamens set high up on the petals) and low (short) pistils:

FLOWERS AND THEIR USES

279

the flowers of other plants have low stamens (of about the
height of the pistils of the first plant) and high pistils. An
insect that visits a flower of the first kind receives pollen on
the part of its body that touches an anther ; when it visits
a flower of the second kind, the part of its body that touched
the anther of the first flower touches the stigma of the
second and deposits pollen upon it. Another part of the
insect's body touches the anther of the second flower, and
when it visits a flower of the first
kind it is that part of the body which
touches the stigma.

Some plants even have stamens
and pistils of three different lengths,
and consequently three different kinds
of flowers. There is still another way

in which cross-pollination is some-

. -, m n /• FIG. 164. — Primrose

times favored. The pollen of some flowers. A> one ^ low

plants will not germinate on the stamens and high pistil;

stigma of the flower which produced B> one ***** hish stamens
. , . . and low pistil. After

it, nor even on the stigma of another Ejcnier and Prantl

flower of the same plant. In other

cases, a pollen grain may germinate on the stigma of the
same flower, but the pollen tube does not grow so rapidly
nor become so long as it would if the pollen came from
another flower, especially a flower borne on another plant.
This is the condition in the rye, the pear, the carnation, and
the American chestnut. In such cases, no seeds, or but
few seeds, result from self-pollination, but many seeds are
formed if cross-pollination occurs.

In other plants, however, pollen from the same flower is
as effective, so far as seed production goes, as pollen from
a different flower. This is true of oats, beans, peas, and
many varieties of wheat. But although many seeds may re-
sult from self-pollination in these cases, it does not always
follow that the plants that grow from these seeds will be as

280 TEXTBOOK OF BOTANY

vigorous as though the seeds had been produced by cross-
pollination.

287. Self -Pollination. — This is by no means rare, in
spite of the fact that so many features in the structure of
flowers seem to favor cross-pollination. Even in species
that are usually cross-pollinated, self-pollination is often
provided for in case cross-pollination should fail. An in-
stance of this kind is seen in the tiger lily, whose style, if
pollen is not brought in from another flower, bends so as to
bring its stigma into contact with an anther. There are
also not a few plants in which self-pollination is the rule,
and in which cross-pollination, if it happens at all, does so
only rarely and accidentally. This is true, for example, of
wheat, of most varieties of peas, and of some varieties of
barley.

Some other plants produce small flowers that never open
and in which therefore cross-pollination is quite impossible.
Illustrations of this sort are the hog-peanut and some of
our common violets. In the spring the violets bear the
familiar flowers which open and which may be cross-polli-
nated. After these spring flowers disappear, and from time
to time during the summer, small, green, bud-like structures
appear at the ends of short stalks. These bud-like bodies
are really flowers that never open. When the pollen-grains
of these, flowers are ripe, they germinate in the pollen sacs;
the pollen tubes grow out through the walls of the sacs,
find -the stigma of the pistil, and grow through the style into
the ovary. Thus, by means of these flowers the violet is
independent of the visit of insects and is sure to produce
seed ; indeed, some of the violets form most of their seeds in
the ovaries of these little closed flowers.

288. Hybrids. — Hybrids or crosses are plants produced
by the union of gametes that belong to different species or
varieties. In seed plants, such a union of different gametes
of course results from the pollination of a flower by pollen

FLOWERS AND THEIR USES 281

from a flower of a different variety or species. It is plain
that such a thing may happen in the case of wind-pollinated
plants whose pollen is blown about in all directions ; it hap-
pens also in insect-pollinated plants, because as a rule a
particular insect visits several or many kinds of flowers.
However, a hybrid does not always result when strange
pollen lands upon the stigma of a flower ; for often the
pollen of one species will not germinate upon a stigma of
another species ; and even if the pollen grain does germinate,
the pollen tube that grows from it may not reach the ovary,
or if it does, the unlike gametes may not be able to unite.
So hybrids are not so frequent as one might expect from
the lavish way in which flowers produce and distribute their
pollen.

Generally speaking, a hybrid is more likely to be formed
the more nearly related the plants are to which the gametes
belong. Thus there are many hybrids known between
varieties of the same species. Many common garden
varieties of roses, carnations, strawberries, peas, corn, and
other cultivated plants are descended from hybrids of this
sort. There are fewer, but still a good many, hybrids known
between distinct species ; and occasionally one is formed
between plants of different genera. Hybrids may be pro-
duced by artificial pollination — that is, the pollen may be
transferred by hand from a flower of one variety to the
stigma of a flower of another variety. When this is done,
care must be taken that the same stigma is not also dusted
with pollen of a flower of its own kind. For this reason, the
flower that is artificially pollinated is kept covered from a
time when it is quite young until after it has set seed and
its stigma and style have withered. If it is a perfect flower,
its stamens must be removed before they are ripe, so that
none of their pollen can possibly reach the stigma. A hy-
brid usually combines in a new way some of the qualities of
one parent with some of the qualities of the other parent.

282 TEXTBOOK OF BOTANY

Sometimes this new combination of qualities is a very valu-
able one. The production of hybrids is one of the means
used to secure new varieties of plants, and some of the
results that have been accomplished in this way will be
discussed in Chapter XXIII.

289. Some Practical Uses of Flowers. — Apart from their
value for ornamental purposes, the only practical uses to
which flowers are put on a large scale are the manufacture
of perfumes and drugs. They do not ordinarily contain
food substances in large enough quantities to make them
useful as articles of diet. The flowers of the cauliflower,
however, are an exception to this rule. The head of the
cauliflower is a thickened flower cluster which has been
much changed during the centuries that it has been culti-
vated. We eat the flower buds, the flower-stalks, and the
bracts. If the plant is kept alive through the winter and set
out again the next spring, it sends up a tall flower-stalk that
bears ordinary flowers, and that produces fruits and seeds.

The artichoke (or " French artichoke," so called to dis-
tinguish it from the " Jerusalem artichoke " whose tubers
are eaten) is a member of the composite family. We eat
the bracts which are attached just below the head of flowers,
and the soft, thick end of the flower-bearing branch. The
flowers themselves are not eaten. Cloves are the dried un-
opened flower buds of a tropical tree. The tree seems to
be a native of the Molucca Islands, but it is now cultivated
in various tropical countries. The dried buds contain about
eighteen per cent of the oil known as oil of cloves. Among
the flowers used for medicinal purposes are those of the
arnica, calendula, camomile, hemp, saffron, henbane, hore-
hound, and peppermint. Pyrethrum or insect powder is
made from the dried flowers of certain plants of the com-
posite family.

CHAPTER XVIII

FRUITS AND SEEDS AND THEIR USES

290. True Fruits and False Fruits. — We have seen that
the fruit of an angiosperm consists of a fruit coat which
encloses one or more seeds ; often also there is more or less
tissue between the seeds. The fruits of many angiosperms,
like those of the cucumber and the bean, contain more than
one seed each ; the fruits of many others are one-seeded.
All the members of the grass family, for example, to which
the corn belongs, have one-
seeded fruits ; so have the
members of the composite
family, which includes dan-
delions and thistles. In the
composites and in most
grasses, as in the corn, the
fruit coat is thin and fits so
closely about the seed that strawberry. B, a lengthwise section

the whole fruit looks much of *he, safe; a> ™0"en en<?, °[ thf
pedicel; b, one of the small, hard,
like a seed. Our common true fruits ; c, the sepals.
nuts, too, are one-seeded

fruits. The shell of a hazel nut, a walnut, a hickory nut,
a chestnut, or an acorn is the fruit coat ; the part inside,
which we eat, is the seed.

A fruit which, like all those mentioned so far, has been
formed from the ovary alone (with its enclosed seed or seeds) ,
is spoken of as a true fruit, because the word fruit is some-
times applied to a thing that is more than a true fruit. An
example of the latter sort is the red " fruit " that we call a
283 •

FlG. l65.-A, the false fruit of the

284

TEXTBOOK OF BOTANY

strawberry (Fig. 165). The soft, juicy part of a strawberry
is really the thickened end of the pedicel to which sepals,
petals, stamens, and pistils were attached ; the little hard
bodies that are borne in pits on the surface of the berry are
one-seeded true fruits. Each true fruit has been formed
from the ovary of one of the many pistils of the strawberry
flower. A structure which, like a strawberry, is more than
a true fruit (because it has been developed from something
more than -an ovary) is called a false fruit. This is not a
very fortunate name, because there
is nothing false about a strawberry ;
but it is a name that is rather
widely used.

The fleshy part of an apple is
formed by a thickening of the end
of the pedicel and of the lower parts
of the sepals, and only the core is
developed from the ovary. The
apple, therefore, like the pear and
the quince, which resemble it in this
respect, is a false fruit. The fleshy
part of the fig, another false fruit,
is, as we have seen, the sac-shaped
end of a peduncle ; inside it are the
small, seed-like true fruits. A pine-
apple is formed by the thickening of a whole flower cluster,
including the separate flowers, the bracts, and the peduncle.
A raspberry or a mulberry might be called a compound
fruit, because each little division of the berry is a separate
fruit, containing a seed ; as a matter of fact, each division of
the mulberry is a false fruit because the juicy part is developed
from the sepals. A blackberry is like a raspberry, excepting
that the end of the pedicel also becomes soft and juicy and
forms part of the berry that we eat. It is plain that fruits,
whether true or false, can be borne only by angiosperms.

FIG. 1 66. — A lengthwise
section through an apple;
a, tips of the sepals ; b, the
part developed from the
ovary (the "core"); c, a
seed; d, line showing the
course of a vascular bundle ;
e, the pedicel.

FRUITS AND SEEDS AND THEIR USES 285

because angiosperms are the only plants that produce seeds
within an ovary. However, the word fruit is often also ap-
plied to things that are neither true nor false fruits ; as, for
example, to the pine cone. We must be cautious not to be-
come confused by this and other careless uses of the word.
In the present chapter, only the fruits and seeds of angio-
sperms will be considered.

291. How Fruits are Useful to Plants: Protection of
Seeds. — No doubt the angiosperms have been greatly
helped by the fact that their seeds are enclosed in fruits.
But the advantages of this arrangement are by no means the
same in all cases ; various angiosperms produce very different
kinds of fruits that are useful in different ways. In general,
fruits are of use to the plants that bear them either because
they protect the seeds, especially while the seeds are young and
growing, or because they help in the scattering of the seeds.
Some, like the fruits of the gooseberry and the orange, are
useful in both these ways.

Many seeds have hard or tough seed coats which cover
the softer parts inside ; such seeds need little or no further
protection, unless perhaps while they are quite young.
But many seeds do need additional protection either from
being eaten by animals, or from injury by extreme heat or
cold or dryness. It is from dangers such as these that fruit
coats protect the seeds of many plants. If a fruit coat is very
hard, like that of a nut, the seed coat within is likely to be
thin and tender. The fruits of most members of the gourd
family, to which the cucumber and squash belong, have
fruit coats that are firm but not so hard as those of nuts ;
the seeds of this family are also protected by tough seed
coats.

The lemon, the orange, and their immediate relatives have
leathery fruit coats ; their seed coats, too, are hard and
firm. In stone fruits, like the cherry, plum, and peach, the
inner part of the ovary wall becomes the hard wall of the

286 TEXTBOOK OF BOTANY

stone ; the soft part inside the stone is the seed, and the seed
coat is thin and soft. Some fruit coats, like those of the
chestnut and the gooseberry, bear spines that protect them,
especially while they are young and growing, from the
attacks of animals.

292. How Fruits Help in the Scattering of Seeds. — A
great many of the structures of both seeds and fruits are help-
ful to the plant because they bring about, in one way or
another, a scattering of its seeds. Plainly it is a good thing
for a species to have its seeds scattered so that it may spread
over a wider area, provided enough seeds are formed. The
more widely the seeds are scattered, the more there are
that will fall in places where that particular kind of plant
cannot grow ; and unless a great many seeds are pro-
duced, so that a goodly number may still fall in favorable
places, a wide distribution may be bad rather than good for
the species. There are plants, such as the oak, the walnut,
and the hickory, that have no particular means for distribut-
ing their seeds. The fruits or seeds of such plants simply
fall to the ground under the plant that -bore them ; they are
not scattered, except as they may be accidentally blown or
rolled or knocked about for short distances. Of the plants
whose seeds are more widely scattered, a good many depend
upon the wind for this purpose. Sometimes the seeds alone
are carried by the wind ; but often the whole fruit is blown
about. Fruits that are distributed in this way are nearly
always small and light, and being small they are usually one-
seeded fruits. Some, like the fruits of the maple and the elm,
have wing-like attachments that increase their chances of
being blown about. Many of the fruits of the composite
family, such as those of the thistle and the dandelion, bear
what looks like a tuft of hairs or bristles ; these bristles are
really the sepals of the flower, which have remained attached
to the fruit.

Currents of water also play a large part in the scattering of

FRUITS AND SEEDS AND THEIR USES 287

FIG. 167. — Various devices for the scattering of fruits and seeds.
The following are carried by the wind : the seed of a Bignonia (a) ; the
fruit of A ilanthus (d) ; the seed of a willow (e) ; the fruit of the avens (g) ;
the fruits of the basswood (z), whose peduncle is united for a distance with
a bract-like leaf ; the fruits of the dandelion (7) ; and maple fruits (n) .
The fruits of the Spanish needles (c), of Hedysarum (h, /), and of the cockle-
bur (m) attach themselves to passing animals. The sepals of Salvia glu-
tinosa, surrounding the ripe fruits (/), bear sticky glandular hairs which
adhere to objects that they touch, as shown at k. When the germander
plant (b) is shaken, the fruits are discharged by a mechanism composed of
the sepals and the elastic pedicel. The fruits of Mgilops (d) and of Crupina
(/>) creep by means of the hygroscopic movements of hairs and other parts.
After Kerner,

288 TEXTBOOK OF BOTANY

fruits and seeds. Their effect is seen in the distribution of
species of plants, sometimes through long distances, along the
shores of rivers and lakes, as well as along sea-coasts and from
island to island in the seas and oceans. The coconut palm
grows on tropical coasts, especially on coral islands, and its
distribution depends very largely upon the carrying of its
fruits from place to place by ocean currents.

Many different means are resorted to by plants to secure
the scattering of their seeds by animals. The fruits of a
good many common weeds.have hook-like or barb-like attach-
ments by means of which they cling to the
coats of animals or to the clothing of
human beings that brush against the
plants on which they are borne. Some of
these hook-like attachments, such as those
of stick-tights and beggar-ticks, are out-
growths from the fruit coat ; those of bur-
dock burs and cockle-burs develop from
FIG. 168. — Ripe bracts just below the flower cluster. The
fruit of a lily be- wide distribution of the seeds of many
ginning to split at
the top. plants is due to the fact that their fruits

or parts of their fruits are edible. An
animal that eats such a fruit is of course likely to swallow
the seeds also ; but the latter are usually (though not
always) protected by their seed coats from the digestive
juices of the animal, and so pass uninjured through its
alimentary tract and may be deposited a long way from
the place where they were produced. While they are
growing, and the seed coats are still soft and thin, the fruits
that are later to be edible are usually hard and sour or bitter ;
it is only when they are ripe and the seed coats are fully
formed that they are pleasant to eat. These edible fruits are
of special interest to us. Among them are the stone fruits
(cherries, plums, apricots, and peaches), gourd fruits (such
as the pumpkin, squash, cucumber, and melons) , citrus fruits

FRUITS AND SEEDS AND THEIR USES

289

(including the orange, lemon, and grapefruit), berries (cur-
rants, gooseberries, blueberries, cranberries, tomatoes, grapes,
etc.), and the false fruits
and compound fruits that
have already been men-
tioned. Many of the edible
fruits, as we have them
now, have been greatly en-
larged and improved by
breeding.

The coats of a good many

fruits (for example, those of

, ,11 j -1 FIG. 169. — The discharge of the

the pea, the bean, and the seedfi of £e cranesbill by the sudden

morning glory) crack open opening of the fruit coat and the

when they are ripe, and so curling of the Parts into which it:

t1 ,, j r 11 splits. After Kerner.

allow the seeds to fall or

to be shaken out. Some fruit coats open in an explosive

way so as to throw out the seeds, sometimes to a consider-
able distance. The common
touch-me-not of the gardens
(known also as " balsam ")
is an instance of this kind ;
others are the cranesbills
(Fig. 169), the violets, whose
seeds are pinched or squeezed
out by a contraction of the
divisions into which the fruit
coat splits, and the " squirt-
ing cucumber " (Fig. 170),
whose seeds, with the juicy
pulp surrounding them, are
squeezed out through an
FIG. 170. — A branch of the squirt- opening in the end of the

ing cucumber showing a fruit falling f . R t th majority of

from its stalk and discharging its

seeds. After Kerner. fruits do not Split when they

2 go TEXTBOOK OF BOTANY

are ripe. Their seeds become free only when the fruit is
eaten or broken open, or when its coat decays ; or, as is the
case with the fruits of the corn, the thistle, and the oak, the
seed germinates within the fruit coat, which, like the seed
coat, is broken by the growth of the embryo.

293. Nature and Importance of Seeds. — We know that
the seed contains a small plant (the embryo) whose growth
has been stopped for a time. We know, too, that the embryo
can begin to grow again when conditions become favorable ;
and that the seed also contains a good deal of food that the
young plant may use in its growth. The habit of stopping
the growth of the embryo at a certain point, and of shutting
it up with a supply of food inside the seed coat, marks one
great difference between the seed plants and all other plants.
This habit is of great advantage, because the young plant so
protected may be carried in one way or another to a long
distance from the parent, may remain unchanged until condi-
tions about it are favorable, and may then grow rapidly, using
the food that was stored in the seed.

Just as different seed plants bear very different sorts of
flowers and fruits, so they produce many different kinds of
seeds. Every one knows that seeds vary greatly in size.
In some plants (some orchids, for example) the embryo is still
very small when the seed is ripe, sometimes consisting of only
a few cells ; in others (such as the bean and the Indian corn)
it has a small root and stem (the radicle) , a terminal bud (the
plumule), and several leaves. Often, as in the corn, the food
is nearly all stored in the endosperm ; but some seeds, like
those of the squash and the bean, contain little or no endo-
sperm when they are ripe, and most of their food is stored in
the seed leaves. Most seeds have a hard, tough seed coat ;
in the horse-chestnut and the Brazil nut the hard seed coat
seems much like the fruit coat of a true nut, such as the walnut
or acorn. Some seeds, on the other hand, like those of the
true nuts and of stone fruits, have s.oft, thin seed coats ; but

FRUITS AND SEEDS AND THEIR USES 291

in such cases the seed is usually protected by a specially hard
layer that belongs to the fruit coat.

294. Kinds of Food Found in Seeds. — Many seeds are
valuable to us because the food stored in them for the use
of their embryos is in a form that we can easily use. The
foods upon which the human race most largely depends are
obtained from the seeds of three of the cereal grains — wheat,
Indian corn, and rice. Many other seeds, too, such as those
of other cereals, nuts, beans, peas, and lentils, though used
to a less extent, are nevertheless very important sources of
human food. Starch is by far the commonest form in which
food is stored, both in seeds and in other parts of plants.
It is starch that is present in largest amount in the seeds of the
cereal grains, with the exception of the sweet corns. Starch
is a convenient form of storage food because it is dry and
compact, so that much can be stored in a comparatively small
space, and because, although it will not itself dissolve in
water, it may be easily and quickly changed to a substance
(a sugar) which dissolves readily. Starch is a carbohydrate.
Some other carbohydrate foods are found in seeds ; especially
some of the sugars (as in sweet corns) and cellulose, the sub-
stance of which cell walls are largely made. The cells of the
endosperm of some seeds (for example, those of the date,
the onion, and asparagus) have thick walls, and when the
seeds germinate some of the cellulose of the endosperm cell
walls is changed by means of an enzym to sugar, which is
then used by the growing embryo.

Besides carbohydrates, the most important classes of food
substances found in seeds are fats and proteins. Fats are
present in small quantities in the seeds of corn and of many
other plants. Some seeds contain large amounts of fats ;
examples are the walnut, the hickory nut, and the peanut,
the seeds of the flax, from which linseed oil is made, those of
the cotton, and those of the castor-oil bean. Proteins are
present in small amounts in all seeds. Some seeds, especially

2Q2

TEXTBOOK OF BOTANY

those of the bean, the pea, and their relatives, contain large
proportions of protein food. In the wheat kernel, as in that
of the corn, proteins are stored chiefly in the form of little
rounded bodies in the cells of the outer layer of the endosperm.
This layer is mostly or entirely removed in making white
flour, which thus contains much starch and only a very small
proportion of proteins. The outer layer of the endosperm is
kept, however, in the making of " whole wheat " flour, which
therefore contains a larger proportion of proteins than white
flour does.

295. Distribution of Seeds. — We have seen that the fruits
of many plants are scattered in various ways. But in the case

of other plants
whose fruit coats
split open, either
while the fruits
are still attached
to the plant that
bore them or
soon after their
separation from
the plant, it is
the seeds alone
that must be
scattered so far
as they are to be
scattered at all.
Such seeds are
distributed by
means much like
those that bring about the distribution of fruits. Many seeds
are extremely small and light and may be carried by the wind
to great distances. The blowing about of seeds is sometimes
helped by the presence of wing-like outgrowths of the seed
coat, such as those of the catalpa seed, or of tufts of hair like

FIG. 171. — A seed pod of the milkweed and
escaping seeds. After Stevens.

FRUITS AND SEEDS AND THEIR USES 293

those on the seeds of milkweeds (Fig. 171). The hairs
attached to the seed coat of the cotton are used in making
cotton thread and cotton cloth, and it is the presence of these
hairs that makes the cotton plant so valuable. Some seeds,
as well as fruits, are distributed by currents of water. Many
others lodge in the fur or on the bodies of animals. By means
of the mud that sticks to their feet, water birds are said to be
important carriers of the seeds of water and marsh plants.

296. Germinating Power of Seeds. — The seeds of dif-
ferent plants differ greatly in the length of time that they
remain able to germinate. As a rule, it is found that seeds
germinate best the season after they were produced ; that is,
at this time the largest proportion of seeds begin to germinate,
the growth of the embryos goes on most rapidly, and they are
most likely to grow into full-sized plants. After the first
season the germinating power usually diminishes, but at
very different rates in different cases. Some seeds will not
germinate at all if they are more than a year old ; some
remain able to germinate for two or three years, and some for
a much longer period. There is no doubt that some kinds of
seeds can still germinate when they are sixty or seventy years
old, and a few have been found to keep the power of germinat-
ing for as long as eighty-five years. There is probably no
well-established case in which seeds have germinated at a
much greater age than this ; although stories, quite without
foundation, are told of seeds that germinated after being
buried in the ground for centuries, or after lying for thousands
of years in Egyptian tombs.

The conditions under which seeds have been kept have
much to do with their germinating power. For example,
they must be kept dry ; for if they become moist they are
likely to begin to germinate, and then, qpnditions not being
favorable for the completion of germination, the embryos
die. The germinating power of most seeds is destroyed by
exposure to extreme heat or cold. But to this rule there are

294 TEXTBOOK OF BOTANY

exceptions ; for certain seeds, if dry, may be exposed for some
days to a temperature of about 480 degrees below zero
Fahrenheit without destroying their power of germination.

" Seed-testing " consists in placing a considerable number
of seeds, taken as a sample from a large lot, under conditions
favorable for germination — for example, between sheets of
blotting paper, in a germinating box, or in soil — and noting
the percentage of the whole number that germinate success-
fully. It is important for the farmer or the gardener to be
sure that the great majority of the seeds that he sows are
likely to germinate, and for this reason various methods of
practical seed-testing have been devised.

297. Development of Seeds or Fruits without Fertiliza-
tion ; Seedless Fruits. — In nearly all seed plants, no embryo,
and therefore no seed or fruit, can be formed unless the egg is
fertilized by a male nucleus. Some exceptions to this rule,
however, are known to occult The eggs of a few plants,
among them the common dandelion, can develop into
embryos without fertilization. Such plants, therefore, can
form seeds and fruits without a previous fertilization and
even without pollination. Certain other plants, including at
least some varieties of cucumbers, produce fruits without
pollination or fertilization ; but a cucumber fruit so produced
contains no developed seeds. A considerable number of
plants, including apples, pears, and lemons, bear occasional
seedless fruits ; but in most such instances, differently from
the case of the cucumber, it is probable that pollination and
fertilization actually occur, but that the seeds for some reason
fail to develop. By selection, species of seedless oranges and
other fruits have been developed which are much better for
eating than fruits with seeds. Seedless varieties, of course,
can be propagated ^nly by vegetative means, as by cuttings or
grafts. The common banana has been seedless for centuries.

CHAPTER XIX
SOME IMPORTANT FAMILIES OF ANGIOSPERMS

298. Classification of Plants. — So far as possible, plants
are classified according to their relationships, so that a system
of classification is much like a genealogical tree. Plants
which are very like one another, are said to be members of the
same species; for instance, our common apple trees belong
to the species known as Pyrus mains. Some species are com-
posed of plants that are different enough from one another
to be distinguished as varieties, but not different enough to
constitute separate species. Thus there are many varieties
of apples, some of which may have developed in the wild
state, but most of which are the result of breeding. Species
that are nearly related to one another are placed in the same
genus. For example, the common apple (Pyrus malus),
the Siberian crab-apple (Pyrus baccata) , and the pear (Pyrus
communis) belong to the genus Pyrus. Several or many
genera make up a family, and several families, in turn, are
grouped together to form an order. The genus Pyrus
belongs to the rose family (or Rosaces;} ; this family and some
others make up the order Ro sales. Since something new is
constantly being learned about the relationships of plants,
changes are made from time to time in their classification.
New species are found, and the arrangement of species into
genera, families, and orders must be changed to fit the newly
discovered facts. However, the seed plants have been
studied so long and so much is now known about them that
the general outlines of their classification may be con-
295

296 TEXTBOOK OF BOTANY

sidered fairly well settled ; although it is true that many new
species, even of seed plants, are described each year.

299. Families of Angiosperms. — Something was said in
Chapter XVII about the reasons why flowers are helpful in
determining the relationships of angiosperms. For the most
part, it is the structure of their flowers and fruits that is used
in arranging angiosperms in orders, families, and genera ;
species are distinguished from one another about as much by
the peculiarities of their vegetative parts (stems, roots, and
leaves) as by those of their flowers and fruits. As we already
know, angiosperms are divided first of all into the two great
groups of monocotyledons and dicotyledons. The mono-
cotyledons include eleven orders, which are divided into
forty-five families ; these in turn include a total of about
24,000 species. In the group of dicotyledons there are forty
orders, 240 families, and about 109,000 species. In the
present chapter only a few of the families of monocotyledons
and dicotyledons will be mentioned. These families are
selected either because of the large number of species that
belong to them, or because they include some of the plants
that are of greatest practical value to us.

MONOCOTYLEDONS

300. The Grass Family. — This family contains about
4000 species, among which are the Indian corn and the other
cereal grains. The grasses have small, simple flowers with
chaffy bracts, all much like the flowers of the corn excepting
that they are usually perfect. The fruits, with the exception
of a few that are nut-like or berry-like, are kernels, similar
to those of corn and wheat. Each kernel contains a single
seed ; the embryo lies at one side of the seed, surrounded
by the seed leaf, and the endosperm makes up the greater
part of the seed. The grasses have jointed, commonly
hollow, stems, and alternate sheathing leaves arranged in
two vertical rows. With the exception of the bamboos, they

SOME IMPORTANT FAMILIES OF ANGIOSPERMS 297

are all herbaceous plants. Besides the cereal grains and the
sugar cane, sorghum, and broom corn, the grasses of most
practical interest to us are the numerous species which, like
timothy and blue grass, are used as forage plants, either for
pasturage or for hay. The value of grasses for forage pur-
poses depends largely upon the fact that the individual plants
grow together in large numbers, so that a single species, or
two or more species growing together, may cover large areas.
Some, such as the common quack-grass, are annoying weeds.
An oil obtained from the roots of vetiver (cuscus grass) is
used in making perfumes. The tall, tree-like bamboos
(see § 215) have more or less woody stems.

301. The Sedge Family. — The sedges are much like
grasses in general appearance and in most of their char-
acteristics. Their fruits are nut-like, each containing a
single seed ; the embryo lies at the base of the seed, instead
of at one side as in a grass seed, and is entirely surrounded
by endosperm. The stems are usually three-sided and solid,
and the leaves are arranged in three rows. Among the
members of the family are some of the " rushes," the orna-
mental " umbrella plant," and the papyrus, whose pith was
used in ancient times in the manufacture of paper.

302. The Palm Family. — The palms differ from the great
majority of monocotyledons in the fact that the stems of
most of them become woody. Most members of the family
are trees, each bearing a crown of large leaves at its top.
Some, like the rattan palms, are woody climbing plants. The
fruits of palms are either stone fruits (like the coconut) or
berries (like the date). The endosperm is often hard and
horn -like ; the endosperm of the coconut, however, consists
of most of the edible " meat " and the milk. The hard part
of the fruit of the date palm is endosperm, and " vegetable
ivory " is made from the endosperm of another palm.
Many of the palms are of great practical value to the inhabi-
tants of the warm countries in which they live. The pith

298 TEXTBOOK OF BOTANY

of some supplies sago. Palm oil comes from the fruits of
certain palms that grow in western Africa and eastern South
America. The betel nut is the fruit of another palm, and the
fruits of various species, such as the date and the coconut, are
edible. • Copra, an important commercial product, is the
dried meat of the coconut, which is used in the manufacture
of coconut oil. Other products of various palms are wines,
soap, wax (from the surface of the stem), fibers of various
sorts (among them the coarse fibers from the leaf -stalks of
the raffia palm), and building materials.

303. The Arum Family. — The members of this family have
very simple flowers ; usually many flowers are borne in a
crowded spike which is partly surrounded and more or less
covered by a large bract. Well-known examples of this
floral arrangement are the Jack-in-the-pulpit (or " Indian
turnip ") and the calla lily. Others of the family are the
skunk cabbage and Acorus calamus, the " sweet flag," whose
fleshy creeping or underground stems are used in medicine
under the name of calamus. Not a few arums are cultivated
as house and greenhouse plants because of the beauty or the
oddity of their flower clusters and of the surrounding bracts.
Some members of the family have corms, like that of the Indian
turnip ; the corms of a number of species are eaten after being
cooked.

304. The Lily Family. — The flowers of this family are in
general similar to those of the familiar cultivated lilies ; the
sepals are usually showy and similar to the petals ; the flowers
are nearly always perfect and regular, with six stamens and a
single compound pistil ; the fruit is either a pod or a berry.
The family includes about 200 genera and about 2600 known
species. The true lilies are members of the genus Lilium.
Some of them, such as the tiger lily, the Easter lily, the gold-
banded lily, and the Turk's cap lily, have been cultivated for
centuries because of the beauty of their flowers. Other
members of the family cultivated for a similar reason are the

SOME IMPORTANT FAMILIES OF ANGIOSPERMS 299

tulips, the hyacinths, the lily-of -the- valley, and the yellow and
orange day lilies. Aspidistra and Sansevieria are much
raised in greenhouses because of their ornamental foliage.
Among the food plants of the family are the onions, leeks,
garlic, and chives, all members of the genus Allium, and the
asparagus. Besides the species of asparagus that is culti-
vated for its edible shoots, several are grown for ornamental
purposes. The " smilax " of florists (which is not a Smilax
but a Myrsiphyllum) is a near relative of the asparagus.
Some members of the family living in tropical countries are
important fiber plants ; one of them furnishes " bowstring
hemp." Of several drug plants that belong to this family,
the most important commercially are some of the Aloes.
The juice of their leaves supplies the drug known as " bitter
aloes," as well as certain valuable coloring materials. Some
species of Aloe are much used in warmer countries as orna-
mental plants, and in colder climates they are common in
greenhouses. Among the familiar wild flowers of the United
States and Canada are the bell wort, the dogtooth violets
(which are not violets at all), Solomon's seal, false Solomon's
seal, and the Trilliums. The Yuccas are conspicuous plants
of the southern United States, Mexico, and Central America.
The stems of one species of Yucca and of a few other members
of the lily family have a method of growth in thickness
which, though quite different from that which we have studied
in the pine, results in some species in the development of
trees. One of these is the " dragon tree," found in the
Canary Islands, which grows to a height of fifty to sixty feet.
A famous tree of this species on the island of Teneriffe was
seventy feet high when it was destroyed by a storm in 1878
(see Fig. 135).

305. The Amaryllis Family. — This is very nearly related
to the lily family; the members of the two differ in small
details in the structure of the flowers and fruits. In the
amaryllis family, the sepals, petals, and stamens are attached

300 TEXTBOOK OF BOTANY

above the ovary, whereas in the lily family they are nearly
always attached below. The present family also includes
a good many plants that are cultivated for their flowers.
Among the best-known are the amaryllis, narcissus, daffodil,
jonquil, and tuberose. The agaves are plants of tropical
America and the southwestern United States. The bases of
their leaves are much thickened and serve for water storage.
One of the agaves is that which we know as the " century
plant " ; the juice extracted from other agaves makes the
Mexican drink pulque ; and certain agaves and other mem-
bers of the amaryllis family supply a substitute for soap.
Sisal hemp is made from the fibers of some of the agaves.

306. The Iris Family. — This is closely related to the lily
and amaryllis families. The members of the iris family
have only three stamens instead of the six that are nearly
always present in the two preceding families. The stamens
and perianth leaves are inserted above the ovary, as in the
amaryllis family. To the iris family belong also a number of
plants that are cultivated for their showy flowers ; among
them the crocus, several species of iris (fleur-de-lis), and the
gladiolus. The drug and dyestuff known as saffron is ob-
tained from the dried stigmas of a species of crocus. The
blue flag, whose underground stem and roots are used in
medicine, is an American species of iris. " Orris root " is
the fragrant underground stem of a European iris.

307. The Banana Family. — This should be mentioned
because of the importance of the fruit of the cultivated
species of banana. Another species of the same genus is the
tropical plant which bears the edible fruit known as the plan-
tain; still another species growing in the Philippines supplies
manila hemp.

308. The Orchid Family. — The members of this family
are characterized by their irregular flowers, which are often
of an extremely odd and striking appearance. The flower
of the lady's-slipper (Fig. 159) may be taken as an example,

SOME IMPORTANT FAMILIES OF ANGIOSPERMS 301

although the flowers of orchids take on a great variety of
forms. The orchid family is the largest among the mono-
cotyledons, having over 7000 species, but few of the species
are plentiful and some are extremely rare. The oddity and
rarity of many orchids have made them favorite objects
of cultivation, and by long breeding some wonderfully beau-
tiful varieties have been developed. The lady's-slipper is
among the best-known of the orchids that grow wild in
temperate countries. The underground stems and roots of
many (if not all) orchids are inhabited by fungi that are in
partnership with the orchid plant and that assist it in securing
food. In some cases it is found that a seed cannot develop
into a plant unless it is infected by one of these fungi. Some
orchids, like the coral-roots, have no chlorophyl and live a
completely saprophytic life with the help of the fungi in their
tissiies. Many of the tropical orchids are epiphytes. The
flavoring extract known as vanilla is obtained from the fruit
of a tropical American orchid that is much cultivated in
tropical countries ; salep, used both as a food and as a drug,
consists of the dried tubers of various European and East
Indian orchids. Not many members of the family, however,
have been found useful for other than ornamental purposes.

DICOTYLEDONS

309. Forest Trees. — Certain small families, which are
among the more primitive of the dicotyledons, include some
of the common trees and shrubs. Thus the poplars and wil-
lows belong to the willow family ; the walnuts, butternut,
pecan, and hickory to the walnut family ; the birches, iron-
wood, hop-hornbeam, hazels, and alders to the birch
family ; and the beeches, chestnuts, and oaks to the beech
family.

310. The Nettle Family. — This large family also includes
many trees, among them the elms and the hackberries. Its
members have small flowers, simple in structure ; the stamens

302 TEXTBOOK OF BOTANY

and pistils are usually borne in separate flowers ; in some
species the two kinds of flowers grow on different plants, in
others on the same plant. The fruits are one-seeded, and
are often nuts or stone fruits. The nettles, which give the
family its name, are unpleasantly familiar weeds. The white
mulberry is important because its leaves are used as food for
silkworms. Its berries, like those of other mulberries, are
edible. It is a native of China and has been cultivated in
Mediterranean countries since the twelfth century. The
white, black, and red mulberries are used also as shade trees.
The osage orange, much used for hedges, is a close relative
of the mulberries. The six hundred species of the genus
Ficus are mostly tropical ; Ficus elastica is the india-rubber
tree, the most important source of rubber in the eastern
hemisphere. " Rubber plants," common house plants in
colder climates, are small specimens of this tree. The banyan
tree belongs to the same genus, as does also the cultivated
fig tree. The hop and the hemp are important members of
the nettle family ; the hemp is widely cultivated for its
bast fibers which are used in making ropes and cloth. The
hemp also supplies birdseed ; the drug known as hashish is
made from its flowers and leaves, and the drug cannabis
from the dried flowering tops of the pistillate plants. The
Asian plant that furnishes the fiber known as " ramie " or
" China grass " is a member of the family. Another is the
breadfruit tree, and another the upas tree of the East Indies,
whose juice is used by the natives for the poisoning of arrows,
and in regard to whose poisonous influence many extravagant
tales used to be told. Several tropical members of the
family besides Ficus elastica are sources of rubber.

311. The Goosefoot Family. — This is a small family
whose members are mostly herbs living in prairies or waste
places, many of them with fleshy leaves. The flowers are
small and inconspicuous and are borne in large numbers in
branched, spike-like clusters. The common edible beet, the

SOME IMPORTANT FAMILIES OF ANGIOSPERMS 303

sugar beet, and spinach are the important cultivated plants
of the family. American wormseed is a drug plant of some
importance. Several members of the family are well-known
weeds ; one of the commonest in the United States and
Canada is the plant known as " lamb's quarters " or " pig-
weed " ; another pernicious weed is the Russian thistle.

312. The Pink Family. — The families of dicotyledons so
far mentioned have, for the most part, small, inconspicuous
flowers. Many of the pink family, however, have com-
paratively large and showy, and some of them very fragrant,
flowers. The flowers are regular, usually with five (some-
times only four) sepals, the same number of petals if any
(petals are sometimes lacking), and not more than twice as
many stamens as sepals. The plants are mostly herbs with
opposite, undivided leaves. Of the plants of this family
that are grown for their flowers, the best known are the
carnations, which are descended from a European species
that has been in cultivation for many centuries. The com-
mon pinks and sweet williams are members of the same genus
as the carnations. A good many common wild plants also
belong to the pink family ; among these are various chick-
weeds, the campions, the catch-flies, the corn cockle, and the
bouncing bet.

313. The Crowfoot Family. — This is composed of herbs
of temperate and cold countries, whose regular flowers have
either sepals and petals, or sepals alone that resemble petals,
usually numerous stamens, and one or many simple pistils.
The family includes many common wild plants ; the butter-
cups, hepaticas, meadow-rues, anemones, marsh-marigolds,
baneberries, clematis, and columbine are among them.
The peony, some of the larkspurs, and species of columbine
and clematis are cultivated for their flowers. The drugs
known as black hellebore, golden seal, and aconite are sup-
plied by members of this family ; larkspur seed is also used
medicinally.

304 TEXTBOOK OF BOTANY

314. The Mustard Family. — The plants of this family are
nearly all herbs, many of them with sharp-tasting substances
in their stems, roots, or seeds. The flowers are regular, with
four sepals, four petals, two short and four long stamens,
and one two-parted pistil. The fruit is usually a pod-like
structure whose wall when it is ripe splits into two parts
that separate from a central partition to which the seeds are
attached. Among the many cultivated or useful plants
that belong to the mustard family are the radish, turnip,
rutabaga, rape, cabbage, cauliflower, Brussels sprouts, kohl
rabi, the mustard, horseradish, garden cress, and water cress.
Sweet alyssum, the candytufts, and the stocks or gilliflowers
are raised for their flowers. Among the common weeds of
the family are various mustards and the shepherd 's purse.

315. The Saxifrage Family. — This family and the next
are closely related. Most of the members of both have
regular flowers, with five sepals and five petals. Most of the
plants of the saxifrage family have not more than ten stamens
and fewer macrospore leaves than sepals ; often the macro-
spore leaves are united to form a compound pistil. The most
important members in cultivation are the currants and goose-
berries. Among those grown for ornamental purposes are
the mock-orange (commonly called " syringa "), the hydran-
geas and hortensia, and deutzia.

316. The Rose Family. — The members of this family
differ from those of the preceding one as a rule in having more
numerous — sometimes very numerous — stamens, and more
than one pistil — usually at least as many pistils as sepals.
The pistils are simple. The seeds are usually without endo-
sperm, whereas the seeds of the saxifrage family .contain
endosperm. The rose family includes the great majority
of -plants that are cultivated for their fruits, at least in tem-
perate countries, as well as many ornamental plants. One
division of the family includes Spir&a, some of whose species
are ornamental shrubs. The members of another division

SOME IMPORTANT FAMILIES OF ANGIOSPERMS 305

have false fruits in whose formation the calyx takes part ; to
this division belong the quince, pear, apple, and crab-apple,
the thorn-apple or hawthorn, the mountain ash, and the
service berry. Another division includes the strawberry,
the cinquefoil, and the avens ; to another belong the
brambles, the raspberry, blackberry, and some related plants
with edible fruits ; another includes the many species and
varieties of roses ; and to still another division, whose mem-
bers have stone fruits, belong the cherry, plum, apricot,
peach, and almond. The almond, as we buy it, corresponds
to the stone of a plum or a peach ; the outer layer of the fruit,
corresponding to the fleshy part of a peach, has dried and
split off.

317. The Pulse Family. — With one exception, this, with
over 12,000 species, is the largest family of seed plants.
The bean may be taken as a type. Most of the members
have flowers and fruits constructed much like those of the
bean, although not a few have regular or nearly regular
flowers. Some of the more important plants of the pulse
family were mentioned in Chapter XII.

318. The Flax Family. — This is very small, and is men-
tioned here only because of one important member, the flax
plant. Flax has been cultivated for its strong bast fibers,
which are used in making linen thread, in the countries about
the eastern end of the Mediterranean for four or five thousand
years. It is now raised chiefly in Europe, the United States,
and India, both for the fibers and for linseed oil, which is
made from its seeds.

319. The Rue Family. — This family is of practical interest
because of one tropical and subtropical genus (Citrus}, to
which belong the orange, lemon, citron, and lime, all of
which probably originated in southern Asia, and the grarje-
fruit, a native of the Malayan and Polynesian islands.

320. The Spurge Family. — This is a large family, whose
flowers, usually clustered, vary greatly in structure. Most

306 TEXTBOOK OF BOTANY

of them have a three-parted pistil whose ovary splits into
three parts in the ripe fruit. In the spurges themselves
(belonging to the genus Euphorbia) each small cluster of
flowers is surrounded by white or colored bracts that look
like petals ; the cluster thus is likely to be taken for a single
flower, but it really contains a pistillate flower consisting
only of a pistil, and a number of staminate flowers each with
one stamen and no sepals or petals. The plant known as
" Poinsettia " is a Euphorbia ; its showy, red, petal-like leaves
are bracts. Some other Euphorbias are also grown for
ornamental purposes. Most of the plants of this family
have a milky juice, from which, in the case of several species,
rubber is obtained. Most important is the " Para rubber "
furnished by two species of Hevea. The milky juice of a
Moroccan Euphorbia is the source of a resinous gum ; and
the juices of certain members of the family are poisonous.
Tapioca, obtained from the roots of the cassava, is an im-
portant food product of the tropics. Another member of the
spurge family is the castor-oil plant.

321. The Vine Family. — Grapes are said to have been in
cultivation longer than any other fruit. Those cultivated
in Asia and Europe belong to the species Vitis vinifera.
Varieties of this species are raised also in California ; some
are used in making wine, some for raisins, and some as table
grapes. Most of the grapes cultivated in other parts of the
United States belong to varieties that have been developed
from several North American species ; they are used mainly
as table grapes. The small fruits of a variety of Vitis vinifera
are dried and sold as " Greek currants." It was to these
fruits that the name currant was first given (from the
name of the Greek city of Corinth), and later it was ap-
plied to the fruits that we now more commonly know
as currants. The Virginia creeper (or woodbine), the
Japanese ivy, and some other climbing plants also belong
to this family.

SOME IMPORTANT FAMILIES OF ANGIOSPERMS 307

322. The Mallow Family. — This is characterized by
flowers with five sepals, five petals, and usually many stamens
of different lengths which are united by their filaments into
a tube that surrounds several pistils whose ovaries are united
into a ring or a compound pod. The genus of greatest prac-
tical interest is Gossypium, to which the cottons, the most
important of fiber plants, belong. Somewhat more than
half the world's supply of cotton is raised in the southern
United States ; outside the United States, the largest amounts
are furnished by India, Egypt, and China. Okra (gumbo) is
a close relative of the cotton. Another useful plant of this
family is the marshmallow. Among the ornamental culti-
vated members are the abutilon, hibiscus, and hollyhock.
The common mallow is a familiar weed.

323. The Violet Family. — Here only the violets will be
mentioned. Among them are some of our best-known wild
flowers. The violets raised by florists are descended from a
wild European species, and the many varieties of pansies
have been derived from crosses between two or more other
European species.

324. The Cactus Family. — The characteristic feature of
this family is the thick, fleshy stem, which takes on a variety
of forms. In some species, such as the night-blooming cereus,
the stem is tall and cylindrical ; in some it is nearly or quite
globular ; in others, as in the prickly pears, it is jointed,
each division being flat and more or less leaf -like. The leaves
of most members of the family are represented only by small
scales or spines, or both. Most of them are natives of the
drier regions and deserts of the new world. Some of the
prickly pears, of American origin, are cultivated for their
fruit in Mediterranean countries, where they sometimes go
by the name of " Indian fig."

325. The Parsley Family. — The botanical name of this
family ( Umbelliferd) refers to the arrangement of the flowers
of nearly all its members in simple or compound umbels.

3o8 TEXTBOOK OF BOTANY

An individual flower is small, with five sepals (which are
sometimes very small), five petals, five stamens, and a pistil
composed of two macrospore leaves with separate styles.
The sepals, petals, and stamens are " inserted above the
ovary " — that is, their lower parts are really grown together
with the wall of the ovary so that they seem to grow from
above it. The fruit is two-parted, each part containing a
single seed. To the parsley family belong a number of plants,
such as dill, coriander, parsley, fennel, caraway, angelica,
anise, lovage, and celery, whose leaves, fruits, and other parts
are eaten or used in the preparation of food because of their
aromatic flavor. To it also belong the parsnip and the
carrot, whose thickened roots are eaten. Several members
— for example, asafetida, caraway, coriander, anise, and fen-
nel — are sources of drugs ; some, including the poison hem-
lock (also medicinal) and the water hemlock, are poisonous ;
and others, like the wild carrot, are familiar weeds.

326. The Heath Family. — The name comes from the
heaths or heathers, which cover great areas in the Old World,
living in waste places, on hillsides, and in sandy forests.
Most of the members of this family are shrubs, with thick,
shiny leaves, which are often densely covered with hairs on
the lower surface. They are found for the most part either
in comparatively dry locations or in swampy places. The
flowers have four or five sepals, the same number of petals
generally more or less united, as many or twice as many
stamens, and a single compound pistil. Among the useful
members of the family are the blueberries, cranberries, huckle-
berries, and wintergreen. The rhododendrons, azaleas, and
kalmias are valued for their showy flowers. The " trailing
arbutus " is one of the American representatives of the family.
Another is the " Indian pipe," which has no chlorophyl but
which lives as a saprophyte, being helped in securing its food
from decaying matter in the soil by a fungus whose threads
form a thick felt over the surfaces of its roots.

SOME IMPORTANT FAMILIES OF ANGIOSPERMS 309

327. The Convolvulus Family. — This, as well as all the
other families to be mentioned later, is composed of plants
whose petals, and generally the sepals as well, are united
into tube- or bell-shaped structures. There are usually
five sepals, the same number of petals and of stamens, and
a single two-parted pistil. Many members of the family
are climbing plants. The genus Ipomosa includes the morn-
ing-glories, a number of which are in cultivation, and the
sweet potato, whose thickened roots we eat. The bindweeds
belong to the genus Convolvulus ; some of them are trouble-
some weeds. The parasitic dodders were described in
Chapter XIV.

328. The Mint Family. — The 3000 species of this family
are chiefly herbs with four-sided stems and opposite leaves.
Most of them have irregular, two-lipped flowers, with five
sepals and five petals, four stamens, two of which are longer
than the other two, and a two-parted pistil. The ripe fruit
separates into four (occasionally fewer) parts, each containing
a single seed. Many species contain aromatic substances
that make them valuable for flavoring purposes, or as
sources of perfumes and drugs. Well-known useful plants
are the peppermint and spearmint, pennyroyal, horehound,
rosemary, lavender, sage, balm, savory, and thyme. Coleus
is widely raised for ornamental purposes because of its
variegated leaves, and some tropical species of Salvia (the
sage) are cultivated for their showy flowers. The catnip, the
horsemint, and some of the true mints (species of Mentha)
are common weeds.

329. The Nightshade Family. — This includes chiefly
round-stemmed herbs, whose flowers are usually regular,
with five sepals, five petals, five stamens, and a two-parted
pistil. The fruit is a many-seeded capsule or berry. The
potato and the eggplant are members of the genus Solanum,
to which the nightshades and the horse nettle, a troublesome
weed, also belong. Tobacco, the tomato, the red peppers,

310 TEXTBOOK OF BOTANY

the ground cherry (or " husk tomato "), and the petunia
belong to the same family. Among the drugs obtained from
members of this family are belladonna, hyoscyamus, and
stramonium.

330. The Gourd Family. — The cucumber may be taken
as a type of this family. The most important cultivated
members were mentioned in Chapter I.

331. The Composite Family. — This is the most highly
developed and the largest family of angiosperms. It includes
about 13,000 species. Not only is the number of species
large, but some of the species, such as the thistles and the
dandelions, are represented by immense numbers of indi-
vidual plants, and are so persistent and so successful in their
methods of reproduction that they can be killed out only
with the greatest difficulty. The members of the family are
called composites because their separate flowers are so closely
grouped together in a head that most persons think of the
head as a single flower, especially since, just below it, there
are green bracts that look like sepals. The flower of a com-
posite has five sepals which take the form of a group of hairs,
bristles, or scales ; five petals united into a tube that is often
(as in the dandelion) prolonged on one side into a strap- or
tongue-shaped structure ; five stamens united by their
anthers into a tube; and a pistil apparently composed of
two macrospore leaves. Sepals, petals, and stamens are
inserted above the ovary. The fruit is small, dry, and seed-
like, containing a single seed ; the calyx remains attached to
the fruit, sometimes, as in the thistle, forming a means by
which the fruit may be blown about. Considering the size
of the family, not many of its members have been found
useful for human food ; among those that are so used are the
chicory, endive, lettuce, dandelion, salsify (or vegetable
oyster), the artichoke, and the Jerusalem artichoke. Many
are grown as ornamental plants, among them the sunflower,
daisy, dahlia, chrysanthemum, China aster, and ageratum.

ASA GRAY

Born at Sauquoit, N.Y., 1810; died at Cambridge, Mass.,
1888. The first great American botanist, and one of the
greatest botanists of his time in any country. His Manual
of Botany (several times revised) has been for many years
the leading authority in the identification of the seed plants
and ferns of the northern and eastern United States and
of Canada.

SOME IMPORTANT FAMILIES OF ANGIOSPERMS 311

Drugs are obtained from the boneset, burdock, camomile,
dandelion, calendula, arnica, echinacea, elecampane, tansy,
and wormwood. Pyre thrum or insect powder is made from
the dried flower heads of several composites. Wormwood is
used in the preparation of the alcoholic drinks known as
absinth and vermouth. The milky juice of a shrub known as
guayule, which grows abundantly in certain parts of Mexico,
is a source of rubber. Some of our commonest wild plants
and weeds belonging to the composite family are the golden-
rods, asters, wild sunflowers, coneflowers, ragweeds, and
thistles, the hawkweeds, the beggar ticks, the dandelion,
the yarrow, the may-weed, the cocklebur, the burdock, the
wild lettuce, sagebrush, tansy, and chicory.

312 TEXTBOOK OF BOTANY

THE PLANT KINGDOM

The following is a brief outline of the classification of plants.
In each group only those plants are mentioned that have
been especially discussed in this book.

I. Thallophytes (comparatively simple plants).

1. Algae (with chlorophyl).

a. Blue-green Algse (very simple forms, much like bacteria

except in color).

b. Green Algas : Protococcus, Spirogyra.

c. Brown Algae 1 e

j n j AI ( Seaweeds.

d. Red Algas J

2. Fungi (without chlorophyl).

a. Bacteria.

b. Slime Molds.

c. Alga-like Fungi : Bread Mold.

d. Sac Fungi : Yeasts.

e. Basidium Fungi : Wheat Rust, Mushrooms.
/. Imperfect Fungi.

3. Lichens (fungi which have formed a sort of partnership with

simple algas).
II. Bryophytes (moss-like plants).

1. Liverworts.

2. Mosses: Funaria.

III. Pteridophytes (fern-like plants).

1 . True Ferns : Bracken Fern.

2. Water Ferns.

3. Horse-tails.

4. Club-mosses.

IV. Seed Plants (or flowering plants).

1. Gymnosperms : Pine.

2. Angiosperms.

a. Monocotyledons : Indian Corn.

b. Dicotyledons : Squash, Pumpkin, Cucumber, Bean.

CHAPTER XX
SOME USEFUL PLANTS AND PLANT PRODUCTS

332. Cereal Grains. — Much has been said in previous
pages (see especially Chapter XIII) of the cereal grains —
wheat, Indian corn, rye, oats, barley, rice, and millet. All
the cereals supply food to a greater or less extent both for
man and for domestic animals. Food for man is obtained
from the fruit of the plant (the kernel or grain), in the form
of flour or meal, the extracted starch, and a great variety of
" cereal foods " or " breakfast foods " ; domestic animals eat
the kernels (especially of oats and corn), and also the leaves
and stalks — the latter in the form of straw or " fodder."
As a group the cereal grains are by far the most important
source of food, and the progress of civilization has been in
large measure dependent upon the increase of the areas
within which they are cultivated. Of this group of plants,
wheat is most valuable because it contains the best propor-
tions of different food substances — especially starch and
proteins. In most parts of the world that are occupied by the
white race, wheat is the chief vegetable food. Rice, however,
which contains a larger proportion of starch than any of the
other cereals, is actually depended upon by a larger number of
people than is wheat. Rice is said to be the principal food of
from one-third to one-half the population of the earth. Rye
largely takes the place of wheat in the colder or less fertile
regions of Europe. Oats are used most widely as food for
horses, and barley is most important as a source of malt for
the brewing of beer. Millet is used chiefly as food for ani-
mals, although it is used as food for man also in some parts
313

314

TEXTBOOK OF BOTANY

of the world. The straw of wheat, rye, and rice is used in
hat-making, for mats and ropes, for thatching, and in a
variety of other ways. With the cereals should be men-
tioned the sorghums, numerous varieties of which have been
under cultivation for many centuries. The kernels of sor-
ghum are used as food for man and for animals ; the stalks
are used as fodder ; and the sweet juice of some varieties is

FIG. 172. — A field of rice.

a source of sirup and sugar. Broom corn, whose stem-ends
and branched flower-stalks are used in the United States
for brushes and brooms, is a variety of sorghum.

333. Other Starch-producing Plants. — Aside from the
cereal grains, the most important starchy food is the tuber
of the potato. The potato plant is a native of America,
probably of South America, but is now cultivated throughout
a large part of the civilized world. Starch is extracted on a
large scale from many plants by grinding the part of the
plant which contains it and then washing with water. The

SOME USEFUL PLANTS AND PLANT PRODUCTS 315

greater part of the starch thus prepared is from potatoes and
corn ; but it is also obtained from other cereals (especially
rice), from beans, and from the arrowroot plant. Tapioca
is the starch extracted from the roots of the cassava, and sago
is the starch obtained from the pith of certain palms. Dex-
trin, a gum-like substance, is made by treating starch with
hot dilute acids. It is used for giving a smooth finish to
paper, for stiffening cotton cloth, in making mucilage, and
for other purposes.

334. Sugar-producing Plants. — By far the greater part
of the sugar in the market is obtained from the stalk of the

FIG. 173. — Harvesting sugar cane in Louisiana. •

sugar cane and from the root of the beet. The sugar from
both sources is alike, and in either case it is called cane sugar.
The juice of the beet or sugar cane is pressed out and evapo-
rated ; the sugar which then appears in the form of crystals
is separated from the remaining liquid (the molasses), and
after being refined and recrystallized is sold in the form of
granulated sugar, pulverized sugar, or loaf sugar. Sugar is
also made on a comparatively small scale from the juice of
some palm trees, from that of the sorghum (although this is

316 TEXTBOOK OF BOTANY

more largely used in making sirup), and from the sap of the
hard maple. Dextrose, otherwise known as glucose or grape
sugar, occurs in grapes and many other fruits, and in honey.
In nature it is usually associated with levulose (a sugar very
similar to dextrose) and sometimes also with cane sugar.
Dextrose is made commercially on a large scale by treating
starch with sulphuric acid. It is only about three-fifths as
sweet as cane sugar, and is correspondingly less valuable.
It is largely used in brewing and in the making of sirups and
candies.

335. Foods for Animals. — Besides the cereal grains, which
are .relatively as important for domestic animals as they are
for man, there are many forage plants —
that is, those which animals eat, either
fresh as they are growing, or dried in
the form of hay. The most extensively
used forage plants are various grasses,
some of them wild and some cultivated.
Some of the sedge family are also useful
in the same way, being commonly known
also as "grasses." In addition, certain
"""" _^h • members of the pulse family are very
son clover. important forage plants ; their value for

this purpose is due in large part to their
ability to use the free nitrogen of the air with the help of
the bacteria that live in their roots. It is for this reason
that the clovers, alfalfa, the cow pea, and the soy bean
can be raised successfully on nitrogen-poor soils and are
valuable, especially if the crop is plowed under, in increas-
ing the proportion of nitrogen-containing substances in the
soil. Of several clovers used as forage plants, the most widely
cultivated, especially in the northern United States, is the
red clover. Crimson clover, a species of European origin,
is raised to a considerable extent in the southeastern United
States. Alfalfa has long been grown in Europe, and more

SOME USEFUL PLANTS AND PLANT PRODUCTS 317

recently has been extensively
cultivated in the western
United States ; its cultiva-
tion is being extended east-
ward. The cow pea, which
is closely related to the com-
mon bean, is grown most
extensively in the southern
United States. The soy
bean, a native of China and
Japan, is also being increas-
ingly grown in the United
States as a forage plant. The
hyacinth bean, a native of
India, is recommended as a
forage plant and has been
cultivated for this purpose to

FIG. 175. — An alfalfa plant.

some extent ; but its chief use thus far, especially in tropical
and subtropical countries, has been as food for man. The

common pea is also largely
grown in some parts of the
United States as a forage
crop.

Various seeds, especially
those rich in oil, supply
valuable foods for animals.
Thus, cotton seeds are used
as food for cattle, and cot-
tonseed meal is made from
what remains of the kernels
after the oil has been pressed
out. Oil cake is similarly
made from the embryos of
corn grains from which the
FIG. 176. — The soy bean. oil has been extracted ; En-

318 TEXTBOOK OF BOTANY

seed oil cake is produced in the same way from flax seeds,
and coconut oil cake from the inner part of the coconut.

336. Beverages. — Aside from water (which is the basis
of all liquids suitable for drinking) and milk, practically all
of the great variety of beverages used in different parts of the
world are derived from plants, either directly by extracting
the juices, or by fermenting or fermenting and distilling.
Comparatively few of the beverages so obtained are entirely
lacking in stimulating qualities ; among the non-stimulating
ones are coconut milk, fresh grape juice, and fresh cider.
Trees of two Brazilian species (as well as other sorts in other
regions) are known as " cow trees " because of their milk-like
juice, which is used for food. With the non-stimulating
beverages must be included various coffee substitutes made
by roasting or otherwise treating some of the cereal grains ;
and chicory, whose roasted and ground roots are largely
employed as a substitute and adulterant for coffee.

Much more extensively used than any thus far mentioned
are those mildly stimulating beverages whose effect is due to a
substance produced by the plant from which they are made.
Of this class, tea and coffee are best known. Tea is made
from the young leaves of a plant that is grown in Japan, China,
India, Ceylon, and Java, and to a small extent in South
Carolina and some other localities. Coffee is made from the
bean-like seeds of a shrub or small tree. More than three-
fourths of the world's supply of coffee comes from Brazil ;
smaller amounts are produced in Mexico, Central America,
the West Indies, Venezuela, and Java. The stimulating
substance (caffein or thein) is the same in both tea and
coffee. Chocolate and cocoa come from the seeds of the
cacao tree. Chocolate is made by roasting, crushing, and
grinding the seeds into a fine paste ; it contains about fifty
per cent of oil. If part of the oil is removed, the substance
remaining is cocoa. The extracted oil is cocoa butter.
Chocolate and cocoa contain a small proportion of a stimu-

SOME USEFUL PLANTS AND PLANT PRODUCTS 319

lating substance, similar to caffein, called theobromin.
Brazil or Paraguay tea, prepared from the dried leaves of a
member of the holly family, is used in some of the countries
of South America. It also contains caffein.

Alcoholic beverages of one sort or another are used in
all parts of the world. Most important of the fermented
beverages, produced by the action of yeasts, are wines (made
mostly from grapes) and beers (made from barley malt to
which hops have been added). There are many other
fermented drinks used in particular countries or localities ;
for example, pulque, made in Mexico from the juice of some
of the agaves ; sake", a Japanese drink made from rice ; and
toddy, made in various tropical countries from the sap
of the coconut palm and from other materials. By distilling
fermented beverages, liquors containing a larger proportion
of alcohol are obtained. Whisky is made in this way from
the fermented juices of rye, corn, or sometimes of other
grains. Gin is distilled from rye or other grain and flavored
'with juniper berries ; vodka is distilled from rye or potatoes ;
and rum from the juice of the sugar cane. Brandy is dis-
tilled from wine, mescal from pulque, and arrack from toddy.
Absinth is made by steeping wormwood in alcohol or in a
strong liquor.

337. Other Stimulants and Narcotics. — Aside from the
stimulating beverages already mentioned, plants supply a
number of substances that are used for their stimulating or
narcotic effects in other than liquid form. Of these the best
known is tobacco. The tobacco plant was originally a
native of America, but its cultivation and use now extend
to almost all parts of the world. Many other substances,
most of them more powerful than tobacco, are used both for
their narcotic effect and in medicine. Opium is made by
drying the juice which exudes from cuts in the unripe fruits
of the white poppy. It is extensively used, especially in
Asiatic countries. Morphin and laudanum are prepared

320 TEXTBOOK OF BOTANY

from opium. Cocain is obtained from the leaves of the
coca tree. The leaves themselves are chewed by the people
of Bolivia and other South American countries. Cola nuts
are chewed by the natives of Africa. The tree that bears
them grows in western Africa, the West Indies, and Brazil.

FIG. 177. — A field of tobacco.

The nuts contain a large proportion of caff ein and some theo-
bromin. Areca nuts (or betel nuts), the seeds of a palm,
are chewed in India and other Asiatic countries. Hashish,
prepared from the dried leaves of the hemp, is used for
smoking and also in the preparation of a beverage.

338. Oils. — The oils which are stored in fruits, seeds, and
other parts of plants belong to the class known as fatty oils.
A fatty oil is- characterized by the fact that on treatment with
a dilute alkali, such as caustic soda or potash, it forms a soap
and glycerin. The fats of animal bodies belong to this
same class of fatty oils. Various vegetable oils are used in

SOME USEFUL PLANTS AND PLANT PRODUCTS 321

making soaps as well as in numerous other ways. Olive
oil, obtained by pressing the ripe fruit of the olive tree, is the
most valuable for food purposes. It is largely adulterated
with other oils of vegetable origin, such as cottonseed oil,
obtained by grinding and pressing the kernels of cotton seeds,
and peanut oil, pressed from peanuts. Peanut butter is
made by grinding but not pressing the peanuts. The plant
from whose seeds castor oil is made belongs to the spurge
family. The oil is used in making soaps and lubricants, in
medicine, and in the
manufacture of oilcloth,
artificial leather, and cel-
luloid. Treated with
sulphuric acid, castor oil,
as well as olive oil or
cottonseed oil, forms
what is known as " tur-
key red oil," which is
largely used in treating
cotton fabrics so that
they can be colored with
certain coal tar dyes.
Linseed oil, made from
flax seed, has the prop-
erty of drying quickly if exposed to the air, leaving a
varnish-like residue ; this property makes it valuable in
paints and varnishes. Linseed oil enters into the manu-
facture of linoleum, and, when thickened by long boiling,
it forms the basis of printer's ink. Corn oil, made from
the embryos of corn kernels, is used as a substitute for
linseed oil in paints; it is also used in making soaps
and lubricants. Corn oil, as well as linseed oil, can be
vulcanized by heating with sulphur, so forming a substitute
for rubber. An oil pressed from hemp seeds is also used, like
linseed oil, in paints and in soap-making. The kernel of the

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ripe coconut, broken up and dried in the sun, is called copra,
and is one of the most important commercial products of the
islands of the south Pacific. It is from copra that coconut
oil is pressed. This oil is used in southern Asia and the East
Indies as a cooking and illuminating oil, and in other parts
of the world for cooking and in making candles and soap.
Among the numerous other vegetable oils that are put to
practical uses are those obtained from the sunflower, soy bean,
walnut, poppy seed, and almond.

339. Waxes. — The waxy coating on the surfaces of leaves
and fruits is in some cases removed and used in various ways.
Thus the wax from the fruit of myrtle bushes, known as
myrtleberry or bayberry wax, is mixed with beeswax for use
in candle-making. Japan wax, from the fruit of some
Japanese sumachs, is used in a similar way, as well as in
making furniture polish, wax matches, and waxed paper.
The wax from the leaves of some palms is also of commercial
importance.

340. Gums and Resins. — These are obtained by drying
or otherwise treating the juices of plants. Gum arabic
comes from trees of acacia species growing in Egypt, Arabia,
and neighboring countries ; gum Senegal from an acacia
that grows in northwestern Africa ; and other gums from
acacia trees in different parts of the world. Gum tragacanth
is from the stems of species of Astragalus. By boiling certain
seaweeds (marine algas) gelatine is obtained. Agar-agar
is a seaweed gelatine, much used in bacteriological cultures
and for similar purposes, as well as medicinally ; it comes
from eastern and southeastern Asia and the neighboring
islands. " Irish moss " is a gelatinous seaweed.

Certain hard resins, used in making varnishes, are called
copals. There are many copals, usually named for the
locality from which they come. One of the best is Zanzibar
copal. It is obtained in part from living trees, but the best
is found in fossil form in the ground. The name gum dammar

SOME USEFUL PLANTS AND PLANT PRODUCTS 323

is given to several resins obtained from southeastern Asia,
which are also used in making varnishes. Other much-used or
well-known resins are myrrh, frankincense, asafetida, benzoin,
mastic, Japanese lacquer (from the sap of one of the sumachs
that supply Japan wax), balsam of Peru, and gamboge.

341. Spices. — The substances that are used as spices
come from different parts of plants, most often from the fruits
and seeds. Mustard consists of the ground seeds of several
species of Brassica. Pepper is the fruit of a vine, a species
of Piper. White pepper and black pepper are the same in
origin ; the difference between them results from the way
in which the fruit is treated. Red pepper or Cayenne pepper
is the ground pods of species of Capsicum, belonging to the
same family as the potato. The red pepper of our gardens
is also a Capsicum. Allspice is the dried unripe fruit of the
pimento tree, a native of the West Indies but cultivated
chiefly in Jamaica. Nutmegs are the kernels of the fruit of
a tree (Myristica) that is grown in various warm countries ;
the dried seed coats, removed from the kernels, are mace.
Caraway seeds are used to some extent in both the Old
World and the New. Cloves are the dried flower buds of a
tropical tree. Ginger is the dried underground stem of a
plant that is raised in various tropical countries. Turmeric
conies from the underground stems of another member of the
ginger family. Its most familiar use is in curry powder, in
which it is combined with other spices ; it is also used as a
yellow dye and in other ways. Cinnamon is the dried bark
of a tree that grows in Ceylon, and cassia bark and cassia
buds come from a similar tree of China and northern India.

342. Flavors and Perfumes. — These are usually in the
fonn of extracts from flowers, fruits, leaves, or other parts of
plants. Very commonly the extract is obtained by distilling
the plant parts with water. Some, such as orange and lemon
oils, are simply pressed — in these cases from the rind of the
fruit. Some flower extracts are obtained by a process of

324 TEXTBOOK OF BOTANY

absorption in lard or other fat. Since spices are used for
flavoring, and since many flavoring extracts are made from
spices, the line between spices and flavors is not a sharp one.
Most of the substances which largely or entirely make up
flavoring extracts and perfumes and give them their character-
istic properties, belong to the class known as volatile oils or
essential oils — a distinct class from the fatty oils already
spoken of. Mustard oil and clove oil are well-known examples
of this class. Vanilla extract is obtained from the unripe
fruit of a Mexican orchid. Other essential oils much used in
flavors, perfumes, or both, are those from roses (" attar of
roses "), lavender, bergamot, violet, wintergreen, peppermint,
rosemary, coriander, bay, and cinnamon. Many of the
essential oils are now made in the laboratory more cheaply
than they can be obtained from plants. It is for this reason
that some of the perfumes and flavors now largely used are
not actually derived from the plants whose names they bear.

343. Medicines. — The number of plants whose parts,—
bark, seeds, dried leaves, flowers, etc., — or extracts from
whose parts, are or have been used in medicine, is very large.
Some of these plants have been referred to in previous chap-
ters. In many cases the medicinal properties reside in the
essential oils, and the extracted oils themselves are much used
in medicine. Some of the plant products that have been
spoken 'of on a previous page as used for their stimulating
or narcotic properties are also useful medicinally. This is
especially true of opium, from which morphin and laudanum
are obtained, and of coca leaves, which are the source of
cocain. A number of drug plants are being increasingly
grown on a commercial scale in the United States.

344. Fiber Plants. — With the exception of silk, wool, and
asbestos, all the important fibrous materials used in the
weaving of fabrics and in the making of twine, rope, and the
like, are derived from plants. Of fiber plants, the most
important is cotton, which has been cultivated from very

SOME USEFUL PLANTS AND PLANT PRODUCTS 325

ancient times. At present, more than- half of the world's
supply is raised in the southern United States. The cotton

FIG. 179. — A field of cotton.

fiber is a long, single-celled hair borne on the seed. The

fibers are separated from the seeds by the machine known as

a cotton gin. Cotton yarns are

used in the weaving of cambric,

muslin, cheesecloth, duck, and

other fabrics. Cotton threads

are largely used with silk or wool

in the weaving of mixed goods.

Cotton treated with a solution of

caustic soda is " mercerized " ;

the fibers are much changed and

take on a silky appearance.

Linen is made from the bast
fibers of the stem of the flax
plant. The varieties of flax that FlG l8o _ Cotton seeds
are raised primarily for seed (from with fibers attached.

326 TEXTBOOK OF BOTANY

which linseed oil is obtained) are different from those that
supply a high-grade fiber. On the other hand, " fiber flax "
yields a considerable quantity of seed, though less than can be
obtained from the varieties of " seed flax." About four-fifths
of the world's supply of fiber flax is raised in Russia, though
the best fiber comes from Belgium. About one-third of the
total manufacture of linen is carried on in Ireland. Very
little fiber flax is raised in the United States (less than 2000
acres), but about 3,000,000 acres are devoted to the growth
of seed flax. The plants that are to furnish the fibers are
pulled from the ground before most of the seeds are fully ripe.

Hemp is made from the bast fibers of the hemp plant, of
which also Russia is the largest producer. The fibers are
longer and coarser than those of flax, but not so strong ; they
cannot be bleached white. They are used for twine, rope,
and coarse fabrics. Jute, used also for twine and rope, as
well as in carpets, burlap, and gunny cloth, is made from the
bast fibers of plants that grow in India. Sisal hemp, used
especially in making binding twine, is obtained from the fibers
of the leaves of an agave, which is raised chiefly in Yucatan.
Manila hemp comes from the leaf -stalks of a tree related to
the banana which grows in the Philippines. While those just
mentioned are the most important commercially, the fibers
or fibrous stems of many other plants are used in similar
ways in different countries. . Among them may .be mentioned
New Zealand flax, Tampico hemp, sunn hemp, bowstring
hemp, ramie, coconut fiber (from the outer husk of the nut),
raffia, rattan, and bamboo.

345. Dyestuffs. — Most of the coloring substances used for
dyeing fabrics, in giving color to paints and stains and the like,
were formerly derived from plants. But in the last fifty or
sixty years the manufacture of aniline dyes out of substances
derived from coal tar has become a very important industry.
The coal tar dyes can be made so cheaply, and in such a vast
variety of shades suitable for different purposes, that they

SOME USEFUL PLANTS AND PLANT PRODUCTS 327

have very largely displaced vegetable dyes. However, some
.dyestuffs obtained from plants are still important commer-
cially.

Indigo is one of the vegetable dyes that has been largely
replaced, though it is still used to some extent — as for
example in " bluing . " 1 1 is obtained from the j uices of several
tropical plants, mostly species of Indigofera. Logwood
extract is a red substance derived from the wood of -a tree
growing in Central America and the West Indies. It can be
used only in connection with a mordant, which causes the
fabric or other substance that is to be dyed to take and hold
the color. The color obtained is usually black, but it may
be violet, blue, or gray, depending upon the mordant used.
Madder is a red dye produced by powdering the dried roots
of a plant grown in central Europe and southern Asia.
Arnotto, a yellow dye used in coloring butter and cheese, is
made from the pulp of the fruit of a shrub of Central and
South America and the West Indies. Safflower, a red color-
ing matter used as a flavoring, in face rouge, and in making a
dye for silk, is the dried flowers of a plant of the composite
family. Other vegetable dyes are fustic, quercitron, saffron,
henna, litmus, and turmeric.

CHAPTER XXI
WEEDS AND POISONOUS PLANTS

346. Weeds. — A weed has been defined as a " wild plant
that has the habit of intruding where not wanted." It does
not follow that weeds are necessarily useless or harmful ;
indeed, many of them may at times be useful ; and some
annoying weeds belong to species which are or have been
cultivated but which make a nuisance of themselves when
they grow in the wrong place. Some plants that are not
particularly troublesome in their original home grow so
rankly as to be very annoying weeds when introduced into a
new country. Practically all our weeds are herbaceous ; they
may therefore be either annuals, growing rapidly from seed
and dying at the end of the season, or biennials or perennials
whose above-ground parts die each fall. To be successful
as a weed, a plant must have some very efficient method
of increasing its numbers ; and for this purpose it depends
usually either upon the production of a great number of seeds,
which are often specially well provided with devices for dis-
tribution, or upon multiplication by means of long, branch-
ing underground stems.

347. Injury Caused by Weeds. — As a general thing, the
greatest objection to weeds is that they reduce the crop of the
cultivated plants among which they grow. They do this
by crowding the useful plants and so reducing their supply
of light, moisture, and the food substances that the plants
must take from the soil. It has been suggested, too, that
weeds give off to the soil substances that may be poisonous
to other plants. The presence of such a weed as the Canada

328

WEEDS AND POISONOUS PLANTS

329

thistle interferes with the harvesting and handling of a crop,
and may greatly reduce its value. Thus a forage crop, such
as hay, is much less valuable if it contains a large proportion
of weeds that domestic animals will not eat or that, if eaten,
may injure them. The presence of weed seeds in a crop of
wheat or oats may greatly reduce the market value of the
grain. Sometimes parasitic fungi or insects live on weeds and
pass from the weeds to related useful
plants. Some weeds are poisonous
to man or to domestic animals ;
these will be discussed on a later
page.

348. Some Ways in which Weeds
May be Useful. — When land is
allowed to lie fallow — that is,
when it is not cultivated for one
or more years — it becomes covered
by a growth of grasses and weeds.
When these die, their substance
helps to enrich the soil by adding
to its supply of organic materials.
In this way a soil that has become
poor may be considerably improved
by the growth of weeds. However,
as a general thing the same or
greater good can be accomplished

more quickly by a proper rotation which includes at reason-
able intervals a crop of alfalfa or some other member of the
pulse family. Weeds also help, during the time of the year
when crop plants are not being grown, in holding the soil to-
gether by means of their root systems, thus checking erosion,
and also preventing the washing away of the nitrogen-con-
taining substances that are so important to soil fertility.

349. Annual Weeds. — A large proportion of common
weeds are annuals. Being annuals, they must depend upon

FIG. 181. — Pigeon grass.
After Weed.

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TEXTBOOK OF BOTANY

an abundant production of seeds to insure their perpetuation
and spread ; and some of our annual weeds are remarkable
for the vast numbers of flowers, fruits, and
seeds that they bear. A striking example of
this sort is the common ragweed, abundant
along roadsides and in neglected fields. The
ragweed is a composite. Other weeds of the
sanie family which likewise bear seeds in great
abundance are the mayweed, cocklebur, horse-
weed, and prickly lettuce. The grass family,
too, contributes a number of troublesome
annual weeds, among them chess, wild oats,
squirrel-tail grass, pigeon grass, crab grass, and
bur grass. The dodders and the wild morning-
glory are representatives of the convolvulus
family ; the buffalo bur and the jimson weed
of the nightshade family ; the lamb's quarters
and the Russian thistle of the goosefoot family ;
and the wild mustard and French-weed (penny
cress) of the cress family. The pigweed, purs-
lane, smartweed, and chickweed are also
common and widespread.

350. Biennial Weeds.—
This group is a compara-
tively small one. It is
plain that, like annuals,
biennials must depend
chiefly upon seeds for their
perpetuation and increase. The com-
posite family, whose members have such
effective means of producing and scatter-
ing their seeds, contributes a few im-
portant weeds to the biennial group.
Among them are the common thistle (bull thistle) and some
of its immediate relatives ; the burdock, skeleton weed, and

FIG. 182.—
Squirrel-tail
grass. After
Weed.

FIG. 183. — Lamb's
quarters. After Weed.

WEEDS AND POISONOUS PLANTS

331

FIG. 184. — The
After

black-eyed Susan. The wild carrot and the wild parsnip,
both members of the parsley family, are biennials ; and so
are the mulleins, the blue weed, the hound's
tongue, and the wild teasel.

351. Perennial Weeds. — The weeds of
this group multiply by means of seeds, but
the fact that parts of them live from year
to year makes it possible for them to in-
crease their numbers in other ways as well.
Many of them, such as the Canada thistle
and the horse-radish, spread very readily
by means of the growth and branching of
their underground parts.
Indeed, the horse-radish in
the United States depends
almost entirely upon this
vegetative method of propa-
gation and forms seeds but
rarely. The composite family, to which so
many annual and biennial weeds belong,
contributes also a goodly
number of perennial weeds ;
the list includes the Canada
thistle, the field sow thistle,
the iron weed, the dandelion,
and the marguerite or ox-
eye daisy. Among the
grasses that cause trouble
as weeds are the well-
known quack grass, the

Johnson grass, and Ber-
FIG. 185. — The Canada thistle. J

After Weed. muda grass. Other peren-

nial weeds are the bind-
weeds, horse nettle, milkweeds, plantains, field garlic, Indian
hemp, field sorrel, and yellow dock. The brake is one of

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TEXTBOOK OF BOTANY

FIG. 186. — The quack grass.

the few ferns that make themselves troublesome in this
way.
352. How Weeds are Introduced and Spread. — As we

have seen, most of our weeds, whether annual, biennial, or
perennial, produce great numbers
of seeds, and depend largely or
entirely upon seeds for their dis-
tribution. The most successful
weed, therefore, is the one that
has the most effective means of
scattering its seeds or fruits. An
excellent example of a very suc-
cessful weed is the dandelion,

whose plumed fruits are so easily carried to great distances

by the wind. Something was said in Chapter XVIII about

the various ways in which seeds and fruits are scattered,

and most of the means of distribution mentioned in that

chapter are employed by some of the common weeds.

That so many of the composite

family are weeds is due to the

excellent means of fruit distribu-

tion — especially distribution by

the wind — that the members of

that family have developed. Be-

sides composite weeds — includ-

ing the dandelion, thistles, and

wild lettuce — a good many

members of other families de-

pend likewise upon the wind ;

examples are the milkweeds,

FIG. rSy.- The Johnson grass.

with tufts of hairs attached to their seeds, and many of the
grasses and sedges, whose fruits are very small and light.
Among the weeds whose fruits attach themselves to the
bodies of animals, some composites, too, — such as the cockle-
bur and the burdock, — are conspicuous.

WEEDS AND POISONOUS PLANTS

333

But besides these methods of seed and fruit distribution
which are common to many plants, there are a number of
others that are peculiar to weeds and must be specially
guarded against. For instance, weed fruits and seeds are
often carried into new regions by railway trains ; and one
often finds newly introduced weeds and other plants growing

FIG. 188. — A mixture of seeds commonly found in low-grade alsike
clover seed: a, alsike clover; b, white clover; c, red clover; d, yellow
trefoil ; e, Canada thistle ; /, dock ; g, sorrel ; h, buckthorn ; i, rat-tail plan-
tain; k, lamb's quarters; /, shepherd's purse; m, mayweed; n, scentless
camomile ; o, white campion ; p, night-flowering catch-fly; q, ox-eye daisy;
r, small-fruited false flax; s, cinquefoil ; t, two kinds of peppergrass;
u, catnip ; v, timothy ; x, chickweed ; y, Canada bluegrass ; z, clover
dodder; i, mouse-ear chickweed; 2, knot-grass; j, tumbling amaranth;
4, rough amaranth ; 5, heal-all; 6, lady's thumb. After Hillman.

beside railway tracks, and perhaps spreading gradually from
there into neighboring fields. When weeds grow undis-
turbed among cultivated plants, their seeds are likely to be
harvested with the crop ; as a result, the weed seeds are
distributed with those of the harvested crop, as chess seed
with wheat, wild oats with cultivated oats, and dodder with
clover or alfalfa seed ; or the seeds, like those of many

334 TEXTBOOK OF BOTANY

undesirable grasses, are distributed with hay or straw. Weed
seeds are carried too by harrows and other implements used
in tillage ; by threshing machines ; in many stock feeds ; and
very extensively in fresh manures. Some plants, spoken of
as " tumble weeds," which have short roots, are easily torn
from the soil when they are dead, and are blown or rolled
by the wind from place to place, scattering seeds as they go.
This class'of plants includes the buffalo bur, the horse nettle,
the pigweed, the ragweed, ^and the Russian thistle.

It has already been said that perennial weeds, while they
may depend largely upon seeds for their distribution (consider
the dandelion, for example) also have the possibility of mul-
tiplying their numbers by vegetative means. The common-
est of these means is that used by the Canada thistle,
namely, the branching of an underground" stem, the branches
becoming separate plants by the death of the older parts of the
stem. Some of the grasses, notably quack grass, spread in
the same way ; and many other weeds spread by means of a
rapid growth of underground stems and roots. Runners, like
those of the strawberry, are produced by some of the hawk-
weeds. Tubers are formed by a few weeds ; nut grass (a
member of the sedge family) is a tuber-bearing weed, and the
Jerusalem artichoke, though not usually growing so abun-
dantly as to be troublesome, may be placed in the same class.
The field garlic is an illustration of a weed whose perennial
underground part is a bulb instead of an elongated stem.

353. The Control and Destruction of Weeds. — What has
just been said regarding the ways in which weeds spread may
suggest methods by which they are to be controlled. So far
as concerns annual and biennial weeds, and indeed many per-
ennial weeds also, it is plain that they will be eliminated if
they can be prevented from forming seeds. This can be done
by cultivation, which kills the weeds before they have "gone
to seed," or even by cutting off their tops early and frequently
enough. This is why many of the weeds that appear in

WEEDS AND POISONOUS PLANTS 335

lawns disappear in a comparatively short time if the lawns
are regularly mowed ; and it is a reason for the mowing of
fence rows and for the cutting of weeds that appear in pas-
tures. Sometimes it is helpful to burn weeds, especially if
they have begun to form their seeds when they are cut.
When such precautions as these are taken, and the original
weed plants die or are destroyed, there is no chance for the
species to appear in the following year. But unfortunately
these simple methods are not finally effective against weeds
whose seeds are carried long distances by the wind. No
matter how carefully thistles may be eliminated from a field,
or dandelions from a lawn, the owner is at the mercy of his
neighbor ; and if the neighbor persists in raising a good crop
of thistles or dandelions each year, only a continuous warfare
will keep them from making serious trouble on another's
premises. This is the reason that lies back of the enforce-
ment of laws against noxious weeds ; one person cannot
make much headway in the fight without help from the
community.

Each of the different ways in which weed seeds may be
introduced requires to be guarded against by special pre-
cautions. It is important to use in every case only the clean-
est seed that can be obtained — seed, that is, which is free
from weed seeds. It is commonly advised that a hay crop
be cut early ; one advantage of this practice is that weeds
growing among the crop are prevented from going to seed and
thus having their seeds distributed with the hay. Most
of the weed seeds in a manure pile rot rather quickly ; the
danger from manure can, therefore, be largely met by allow-
ing it to rot thoroughly. Of the tumbleweeds, probably the
worst is the Russian thistle, which is one of the most danger-
ous weeds in the prairie region of the western United States.
Its migration is stopped whenever it meets a good fence ;
fences, therefore, offer a means of combating the spread of this
and similar weeds. Tumbleweeds are of comparatively little

336 TEXTBOOK OF BOTANY

importance in a country where trees are plentiful, because
there are many obstacles to their travels about the country.
Those perennial weeds which spread by means of underground
stems and roots offer a set of special problems. Usually such
weeds must be dealt with by thorough cultivation ; the exact
methods to be adopted will depend upon the nature of the
weeds that are making the trouble and upon the character
of the crop that is being raised on the same land. Even
though cultivation does not directly reach all the underground
parts of the weeds, it may nevertheless be successful in kill-
ing them by keeping down their top growth, because the
roots and underground stems are dependent upon the food
that is manufactured by the leaves, and will die in time if
this source of food is shut off.

A proper rotation of crops, in addition to its other advan-
tages, offers means of dealing with weeds ; for instance, weeds
that become established in a field of wheat can be destroyed
the following year if cultivated crops be raised in the same
field; or they may be largely overcome by a forage crop,
such as grass or alfalfa, which interferes with the growth of
weeds by shading them, and is cut for hay before most of
the weeds have ripened their seeds. It is found that some
weeds, especially those with rather broad leaves, such as the
wild mustard, horse nettle, dandelion, and Canada thistle,
growing in pastures or grain fields, can be killed by the use
of poisonous sprays. The grasses and grains have narrow
leaves which do not catch and hold much of the poisonous
solution, whereas the larger leaves of the weeds hold enough
of the poison to injure or kill them. The substances most
used in these sprays are iron sulphate, copper sulphate, and
common salt. Directions for weed spraying are given in the
bulletins of various state experiment stations. Sometimes
it is found advisable to smother weeds that occupy as yet but
a small patch by covering them with building paper, or with
straw or manure ; and many other special methods have been

WEEDS AND POISONOUS PLANTS

337

FIG. 189. — The jimson weed.
After Weed.

devised for dealing with the prob-
lems raised by the growth of
particular weeds.

354. Plants Poisonous When
Eaten. — A rather large number of
plants contain substances that
render them poisonous in greater
or less degree when eaten by
human beings. Fortunately, the
number of poisonous plants to be found in any one locality
is ordinarily comparatively small, and it is easy to become
acquainted with all the dangerous ones that are likely to
be met. The poisonous plants most commonly confused
with harmless ones are perhaps some of the mushrooms
(see Chapter VIII, § 109). Another poisonous fungus of
considerable importance is the ergot, which is parasitic upon
rye and other grains and upon some wild grasses. Of the
much more numerous poisonous
seed plants, it is true in many cases
that the same substance which
gives the plant its harmful char-
acter also makes it valuable, when
properly used, as a medicine. To
the class of poisonous medicinal
plants belong aconite, belladonna,
conium (poison hemlock), helle-
bore, American false hellebore,
henbane, lobelia, pokeweed, and
stramonium ("jimson weed").

Conium seems to have been the
source of the extract which, under
the name of "hemlock," was used
by the Greeks and Romans for
FIG. 190. —The poison hem- the punishment of criminals. The
lock (conium). After Weed, water hemlocks, belonging to the

338 TEXTBOOK OF BOTANY

genus Cicuta, are closely related to coniurn and are likewise
extremely poisonous. Several human deaths are caused
each year by the eating of the parts, especially the roots, of
the water hemlock and poison hemlock. The similarity of
these plants to the cultivated parsnip seems to have been
the foundation of the widespread though incorrect notion
that the parsnip becomes poisonous if allowed to grow wild.
Sometimes the seeds of conium have been mistaken for those
of anise, and the leaves for those of parsley, with fatal results.

Corn cockle, a rather common weed in grain fields, is poi-
sonous. The chief danger from it seems to arise from the
mixing of the seeds with wheat or other grains. Flour made
from wheat containing cockle seeds has been known to pro-
duce serious, sometimes fatal, effects.

The juices of various spurges are poisonous. Two culti-
vated species which sometimes cause trouble are caper spurge
and " snow-on-the-mountain." The seeds of the former, if
eaten in too large numbers, cause illness and even death ;
and the poison of snow-on-the-mountain is Carried by honey
made from the nectar of the flowers. Honey obtained from
the broad-leaf laurel also is said sometimes to be poisonous ;
and children are reported to have been poisoned by eating
the young shoots of this plant which they mistook for winter-
green. The narrow-leaf laurel and the great laurel are like-
wise poisonous.

There has been much discussion as to the poisonous nature
of the black nightshade. The ripe fruits are said to have
been eaten in considerable quantities without bad effects ;
on the other hand, cases have been reported of the poisoning
of domestic animals by the eating of the leaves, and experi-
ments seem to show that the berries are sometimes poisonous.
The berries and leaves of the bittersweet, which, like the
nightshade, belongs to the same genus as the potato, have
been found to be somewhat poisonous.

There are some plants which are regularly used for fo6d in

WEEDS AND POISONOUS PLANTS 339

spite of the fact that they are poisonous in the condition in
which they are gathered. Thus, the fresh shoots of the
pokeweed are used like asparagus ; but the water in which
the shoots are first boiled must be discarded because of the
poisonous substance dissolved in it ; and it is important that
no part of the root be eaten. The fruits of the horse-chestnut
and its relatives, the buckeyes, are poisonous ; but those of
the California buckeye are said to be used by Indians after
the poisonous substance is removed by proper treatment.
The fruits of the horse-chestnut are fed to cattle in England,
the poison being first removed. The root of cassava, from
which tapioca is obtained, is another illustration. The
tapioca is the starch of the root ; to obtain it the root is
ground up and thoroughly washed to remove the poisonous
substance that it contains. Other plants that have been
found to be more or less poisonous are the lily-of -the- valley,
stagger bush, branch ivy, and false jessamine.

355. Plants Especially Dangerous to Animals. — Impor-
tant members of this class are numerous species of larkspur.
Some European larkspurs have long been considered poison-
ous to stock ; and serious losses of cattle and horses occur in
the mountainous grazing regions of the western United States,
caused by the eating of the native larkspurs. Curiously
enough, experiments seem to show that sheep are not poisoned
by these plants, although there are differences of opinion upon
this point. Serious damage is caused to horses, cattle, and
sheep in the western United States by certain plants, poison-
ing by which at first causes a sort of hallucination or insanity,
for which reason the plants causing the trouble are called
" loco weeds." The disease ends after some months in the
death of the poisoned animal. The woolly loco w^ed, found
from South Dakota and Wyoming to Texas and New Mexico,
is an Astragalus ; the stemless loco weed, which ranges from
British America to Mexico, is an Oxytropis ; both are mem-
bers of the pulse family. Some species of lupine, belonging

340

TEXTBOOK OF BOTANY

to the same family, have also been found to be poisonous to
livestock if eaten in sufficient quantities. Another poisonous
member of the pulse family is the rattlebox. Still another
western poisonous plant that causes important losses, espe-
cially of sheep, is the death camas (Zygadenus).

The leaves of the black cherry are poisonous when partially
wilted, and cattle are sometimes killed by eating the leaves
from cut branches. Some deaths have been reported, too, of
children who ate the kernels of black cherry seeds, or who
swallowed the fruits whole. The partially wilted leaves of
some other cherries and the kernels of many, perhaps of all,
cherries and plums, are poisonous. The sneezeweed, a com-
posite, which when powdered is used medicinally to produce
sneezing, has been known to kill sheep, cattle, and horses
which, unfamiliar with the plant, have eaten it. As a rule,
however, animals avoid the plant. Corn cockle, American
false hellebore, the buckeyes and the horse-chestnut, water
hemlock, poison hemlock, and the
broad-leaf laurel, already referred
to as poisonous to human beings,
are also dangerous to animals.

356. Plants Poisonous to the
Touch. — Well-known representa-
tives of this class are poison ivy,
poison oak, and the poison sumach
(poison elder). All these belong
to the same genus (Rhus) as the
common sumachs. Their irritat-
ing effects upon the skin are due
to an oil which is found in all
parts of the plant ; it is soluble

in alcohol and is destroyed by an alcoholic solution of sugar
of lead. Some of the primroses produce a somewhat similar
irritation of the skin in many persons. The milky juices of
the caper spurge, snow-on-the-mountain, and other spurges

FIG. 191. — The poison ivy.
After Weed.

WEEDS AND POISONOUS PLANTS

341

cause a serious irritation of the skin ; and some species of
lady's-slipper are reported to have an effect upon some
persons very like that of poison ivy.

357. Hay Fever. — Just as some sub-
stances produced by plants cause irritation
of the skin, others give rise to serious diffi-
culties because they are poisonous to the
mucous membranes of the nasal passages,
eyes, and throat. The irritated condition
that gives rise to " hay fever " and " rose
fever " is due to the poisonous action of
the pollen of certain plants. The plant
that seems to cause most trouble in this
way is the common ragweed which grows
abundantly along roadsides and on waste
land. Some cases of hay fever are apparently caused by
the pollen of certain grasses.

FIG. 192. — The
After

CHAPTER XXII
FORESTRY AND FOREST MANAGEMENT

358. Meaning of Forestry. — A generation ago "for-
estry " would have been considered, by people of the Western
Hemisphere at least, as synonymous with lumbering, which
concerns itself with the problem of how best to get the
products of the forest into the market in the form of lumber.
During recent years, however, forestry has come to be
thought of as primarily concerned with the ways and means
of raising repeated crops of forest trees on land that may not
be suitable for the growing of ordinary farm crops ; and, as
we shall learn, there are many problems other than that of
the mere growing of timber which must be considered in con-
nection with forestry.

359. History of Forestry. — Switzerland and Germany
were the first countries that seriously undertook to control
the cutting and replanting of forest areas. The city of
Zurich, as early as the year 853, took over the supervision of a
forest area, and since the middle of the fourteenth century
this area has been cut and the products have been handled
by a city commission. Large tracts in Germany have been
well cared for by cities and provinces since the thirteenth
century, and in that country schools of forestry were early
established. During the French Revolution there was a
ruthless destruction of forests covering the more elevated
regions throughout France ; as a result, not only was there
soon a lack 'of timber, but the floods carried sand and gravel
from the exposed slopes on to the farm lands below. The
replanting of mountain slopes was undertaken by local com-

342

FORESTRY AND FOREST MANAGEMENT 343

munities and cities and by national commissions, which have
done such excellent work that many of the forest areas com-
pare favorably with those of Germany. Not only were the
old areas replanted, but extensive tracts of land along the
sea coast, where the sands shifted and at times covered
entire farms, were taken over and planted with forest trees.
Other European and Asiatic countries have definite forest

FIG. 193. — A natural coniferous forest. Photograph from the
Wisconsin State Conservation Commission.

policies, and Japan ranks with Germany and France in the
results obtained from her forests.

It was not until about 1875 that a serious interest in for-
estry began to develop in the United States and Canada.
Up to this time it had seemed as though the forests were
inexhaustible. Sporadic efforts had been made in earlier
years by cities and by a few states to control in part the
cutting of timber. Some of the early settlements in New
England made laws regulating the cutting and sale of timber
products. William Penn in 1682 declared that one acre must
be kept in forest for each five acres cleared. It is unfortunate
that with this precedent the state of Pennsylvania should at
present be in worse condition than any other eastern state

344 TEXTBOOK OF BOTANY

because of the reckless use of her forests. Timber was in
great demand as the Pennsylvania coal mines were developed,
and the forests were cut but no effort was made to reforest the
cutover areas.

A forest agent was appointed in the United States Depart-
ment of Agriculture in 1876 ; this agency became a division
in 1886, and in 1897 the work had grown to such an extent
that a separate Bureau of Forestry was established. In 1891
laws were passed making it possible for the President to set
aside, from the national domain, forest lands as public reser-
vations.

360. National Forests in the United States. — President
Harrison set aside the first forest areas, and before the end
of his administration more than 13,000,000 acres were es-
tablished as forest reserves. President Cleveland added
22,000,000 acres of valuable forests. Some land was added
during President McKinley's term, but it remained for Presi-
dent Roosevelt to establish a definite forest policy. The
western part of the United States was carefully studied, and
wherever possible forest lands were set aside. These with-
drawals were so extensive that at the end of the Roosevelt
administration the national forests included almost 195,000,-
ooo acres under the control of a body of men trained in most
part for forest service. Since 1909 this area has been some-
what diminished because of the opening for settlement of the
better agricultural lands within the reserves, and at present
the national forest areas in the United States, Alaska, and
Porto Rico comprise about 185,000,000 acres, including about
one-fifth of the national timber supply, and divided into
more than 160 national forests. These forests are now open
for the widest possible use. The old timber is sold, trees are
continually being planted, roads are being built, grass lands
within their -boundaries are leased and furnish food for about
one-sixth of the meat-supplying animals of the country ;
homesteads are found wherever the land is best suited for

FORESTRY AND FOREST MANAGEMENT 345

FIG. 194. — A virgin forest of mixed hardwoods. Photograph from
the Wisconsin State Conservation Commission.

346 TEXTBOOK OF BOTANY

farming ; many mines are located within the forests, and the
immense water power available in them is being gradually
developed.

361. State and Private Forests. — Fourteen states have
established forest areas for timber supply and for the purpose
of protection against floods. These areas comprise at pres-

FIG. 195. — The results of a fire due to improper lumbering methods.

ent almost 4,000,000 acres. Railway companies are planting
large tracts which will in time supply ties and poles. Within
the past ten years more than a million acres of forests have
been planted by private individuals, and many states are en-
couraging the planting of woodlots on the poorer farm lands,
which will not only furnish a steady supply of fuel but will also
yield good returns as an investment. Many states have
established nurseries which supply young plants for the refor-
estration of cutover areas as well as trees for private forests
and woodlots.

FORESTRY AND FOREST MANAGEMENT

347

362. Canadian Forests. — Canada is more fortunate than
the United States in the fact that many of her largest forests
are still intact and under the supervision of the national and
provincial governments. The fact that the population of the
Dominion of Canada is much smaller than that of the
United States had resulted in the Canadian forests being al-
most untouched at the time when a demand arose for a defi-
nite forest policy. Very stringent national laws were passed

FIG. 196. — A portion of the state forest nursery at Trout Lake, Wisconsin.
Photograph from the Wisconsin State Conservation Commission.

determining the policy of the various provinces, as well as
regulating in a general way the forests which had passed into
the possession of some of the larger railways and the immense
tracts owned by the Hudson Bay Company. So, although
her forests have been at times carelessly handled, and al-
though, as a result, disastrous fires have destroyed large
quantities of timber, Canada has at present the richest
forests in the world ; they are rivaled only by some of the
tropical forests and by the extensive forested areas in Russia
and Siberia.

348

TEXTBOOK OF BOTANY

363. Need for Government Management. — The early
settlers in most regions of the United States and Canada found
the timber so abundant that no effort was made to conserve it.
Indeed, all the trees over large areas were girdled and al-
lowed to die and fall in order that fire might then aid in
clearing the land. This method was not only wasteful of
timber because the fires destroyed the dead trees, but the heat

FIG. 197. — Seven-year-old white pines in the state forest nursery at
Trout Lake. Photograph from the Wisconsin State Conservation Com-

was often so intense that all the decaying plant material in
the upper layers of the soil was also destroyed.

Lumbermen did not believe there would ever be a short-
age in the timber supply ; consequently they took only the
best trees and left the smaller ones and much waste material
which later furnished fuel for violent fires that devastated
vast tracts and destroyed the living as well as the dead timber,
in many cases with loss of life as well. Under the care of the
national and state forest services, and in many cases with the
help of private concerns, the fire losses are gradually decreas-

FORESTRY AND FOREST MANAGEMENT 349

ing, although even within recent years the losses from fire
in some states have exceeded the entire season's cutting.
During 1916 very considerable damage was caused by fires
in the national forests of the United States, and a total
of almost 300,000 acres were burned over. The actual loss
per acre is now comparatively small because steps are at once
taken to dispose of the remaining timber before it has begun
to decay. During the same year two very serious forest fires
occurred in Canada : one, on the eastern slope of the Rocky

FIG. 198. — A 56-year-old plantation of white pine at Sharon, Massachu-
setts. Photograph from the Wisconsin State Conservation Commission.

Mountains, did damage to the extent of several million dol-
lars ; the other, more serious in that it resulted in the loss
of many lives, burned over large areas in the province of
Ontario.

The forests of the United States have been so decreased by
this prodigal use of lumber that at present it is being cut
more than three times as fast as it is renewed by growth. It
has been estimated that at the present rate of cutting all the
virgin forests outside the national reserves will have disap-
peared by 1950. There has likewise been reckless cutting of
the timber for which the demand was greatest, so that cer-
tain kinds are almost gone. This condition of affairs is

350 TEXTBOOK OF BOTANY

coupled with the fact that the disappearance of the forests
has been followed in many localities by serious floods which
have caused great damage to property, at the same time
carrying sand and gravel from the head waters of streams
and depositing it upon the good farms of the lowlands. The
damage caused in this latter way is estimated at more than
$2,000,000 a year in the state of Wisconsin alone.

364. Improvement of Methods. — The use of lumber per
capita is much greater in the United States than in any other
country of the world, being more than twenty times that re-
ported for England and more than six times that in Germany.
The methods of lumbering used in the New World, although
much improved in recent years, are still much less economical
than European methods. The proportion of waste in these
operations in France and Germany is about four or five per
cent, but throughout the United States and Canada over
sixty per cent of the timber is wasted.

Although the better mills are making use of a large part of
the materials obtained from trees, many are still as wasteful
as ever. Each year, however, means of handling the refuse
are being introduced, and although the European record
may never be equaled under American conditions, millions of
dollars worth of timber products that are now wasted annually
will be saved. Closer cutting in the forest, saving the
branches and tops of trees for pulp wood or for distillation,
greater care in handling the logs as they pass through 'the mill,
and a variety of other means are being used to reduce the
waste. State, national, and provincial foresters are teach-
ing the protection of the standing timber against the ravages
of insects and disease ; laws are being passed to protect the
forests from destructive fires, as well as to encourage the re-
planting of cutover areas. These are some of the methods
by which it is hoped that our timber supply may be con-
served.

Many lumber companies have lately taken another impor-

FORESTRY AND FOREST MANAGEMENT

351

tant step in this direction. Tree cutting is being so planned
that the more mature timber may be cut each year and re-
newed by the growth of the uncut trees. When this is prop-
erly done, the same amount of timber may be cut each year
and thus a definite supply can be permanently relied upon.
Some states have endeavored to encourage this sort of con-

FIG. 199. — A well-managed forest; brush piled to prevent fire.

servative lumbering by regulating the taxes on timber lands
according to the proportion of trees cut.

365. Forest Regions of the United States. — The northern
forests include those of the New England states, New York,
the portions of other states covered by the Allegheny Moun-
tains, and the states of Michigan, Wisconsin, and Minnesota.
This region has been until recently the home of the pine
industry. The forests of northern New York and Maine are
still an important source of spruce for paper pulp, although
large amounts of pulp wood are now imported into the

352 TEXTBOOK OF BOTANY

United States from Canada. The white and Norway pines
were at their best in the three lake states, and some valuable
tracts of these trees still remain ; but nowhere else in the
world, perhaps, has lumbering been carried on in so wasteful
a fashion.

There is a mixture of hardwoods throughout this region,
hard maple, birch, and beech being abundant in the north-
ern part ; covering some of the mountain slopes of the south-
ern part are forests of chestnut, basswood, chestnut oak, and
yellow poplar ; and white, black, and red oak are abundant
in places. The forests of Michigan, Wisconsin, and Minne-
sota, because of the soil and water conditions, were made up
mainly of coniferous woods, including white and Norway
pines, hemlock, white and black spruce, balsam and cedar ;
abundant stretches of larch covered the more swampy areas.
Hardwoods, such as elm, maple, basswood, and birch, are
found in considerable quantity. The jack pine is found on
sandy areas at the edges of the heavier growths of timber.

The South Atlantic and Gulf states are covered in part
by immense forests of the long-leaved yellow pine (Pinus
palustris), which furnishes at present about one-third of the
annual lumber cut of the country. The forests, except in
the lowlands, are composed almost entirely of pine, and
conditions are such that it is easily handled. The long-
leaved and Cuban pines of these forests are the chief sources
of turpentine, and the turpentining methods used have as
a rule made the trees almost worthless for timber. Cypress,
the most enduring of woods, cottonwood, ash, sycamore, red
gum, elm, hickory, and many species of oaks are found in
the lowlands and along streams ; the cypress is at its best
in the more swampy regions.

A region comprising a considerable portion of the eastern
and southern slopes of the Alleghenies and extending north
and west into the central states east of the Mississippi is
known as the hardwood belt . Here are found beech , hickory,

FORESTRY AND FOREST MANAGEMENT 353

white ash, maples, cotton wood, walnut,, and white, black, and
red oaks. The forests, however, are not continuous, and all
are mixed. As most of these forests were on land that is
valuable for farming, large parts of them have already dis-
appeared, and in many localities they are now represented
only by woodlots in the pasture lands.

The forests of the Rocky Mountains are characterized by
the presence of the western yellow pine with the Douglas fir
and some spruce, and, in the southern half, the pifion pine.
The most heavily wooded region of the United States is found
in the Pacific Coast forests, where are found also the largest
trees in the world. The principal timbers are Douglas fir,
western yellow pine, redwood, red cedar, hemlock, and Sitka
spruce.

366. The Forests of Alaska, Porto Rico, and Hawaii. —
The Alaskan forests are quite extensive and are made up
mostly of fir, spruce, and hemlock. Those of Porto Rico con-
tain many valuable cabinet woods, as do also the more exten-
sive forests of the Philippines where some of the most valu-
able woods are found. Little attention has yet been paid to
these forests because of the many difficulties connected with
lumbering operations. The importation of live stock into
Hawaii completely destroyed the tropical forests because
grazing exposed the roots and the trees soon died. As a re-
sult, the heavy floods soon carried lava, ashes, and debris
into the sugar plantations of the lowlands, and the problem
became so serious that a careful study was made of the situa-
tion. Cattle were restricted to definite areas, and trees
which would grow very rapidly were planted on all slopes to
protect the lands from further floods. Gradually these trees
have been replaced by commercial timber, and the forests
will soon be yielding an income.

367. Forest Regions of Canada. — Extending from the
Atlantic Coast to the slopes of the Rocky Mountains are vast
forests similar to those of the northern United States. They

354

TEXTBOOK OF BOTANY

are most extensive in the provinces of New Brunswick,
Quebec, and Ontario, but extend into Labrador and around
the southern shores of Hudson Bay to the Alaskan boundary.

The greatest spruce for-
ests in the world are
found here, as well as
rich areas of white pine
and hemlock. • The for-
ests of Alberta and
British Columbia are
very much like those al-
ready described for the
northern Rocky Moun-
tains and the Pacific
Coast. The giant red-
wood is not found here,
nor are the other trees as
large as some of those
found in the western
United States, but the
forests cover so great an
area as to compare favor-
ably in productive power
with the richest forests
of the world.

368. Lumbering. — Un-
der this term are included
all the operations through
which a log goes from the

FIG. 200. — A lookout tower, 75 feet
high, on an elevation in a forest. By
means of such towers watch is kept over
large tracts of forest, and if a fire breaks
out it may quickly be located. Photo-
graph from the Wisconsin State Con-

servation Commission. time that a tree is felled

in the forest until it is in

final shape for one of the many wood-using industries. A
tree is felled j usually by means of a crosscut saw, cut into
suitable lengths (generally sixteen feet, although in the West
and South they are often sixty or more feet long) ; then

FORESTRY AND FOREST MANAGEMENT 355

hauled or skidded to the place from which it may be trans-
ported to the saw mill. Formerly, logs were floated down
streams to saw mills, but this has been found so wasteful that
now they are nearly all hauled by rail ; this is especially
true of the hardwoods, which soon become water-logged and
sink. In many of the Eastern and Northern forests the
methods are not greatly improved over those of fifty years
ago ; but in the Western forests, where logs of great size
must be handled, machinery is largely used in all lumbering
operations.

The first saw mill in the New World was erected at Ber-
wick, Maine, in 1631. It was a very simple affair, compar-
able as to size with the small portable mills now in use that
are capable of cutting from 2000 to 4000 board feet a day.
Many of the larger modern saw mills can cut more than a half
million board feet in the same time, all the operations being
performed by intricate machinery. The log is carried into
one of these mills by an endless chain and is then placed on a
" carriage " which carries it past the saw so that pieces of
varying thickness may be cut off. The sawyer controls these
operations by means of levers and determines in a general
way what type of lumber shall be cut from each individual
log. All the earlier saw mills used /heavy circular saws, many
of which wasted almost a half inch each time a piece was cut
off; these are now almost entirely replaced by the " band
saw " in the shape of a continuous steel band which is more
economical with material and which will cut through much
larger logs. From this saw the main part of the log and the
pieces that have been cut from it go to other saws which cut
them into their final forms, such as heavy timbers, planks, or
boards ; the smaller pieces are cut into laths or shingles, or
are used in making matches and excelsior, or are distilled in
order to obtain various by-products. The lumber taken from
the mill is piled in open piles to allow it to dry ; after drying
it is taken to the planing mill where it is finished for market.

356

TEXTBOOK OF BOTANY

369. Various Uses of Wood. — The chief wood products
are lumber, firewood, railway ties, posts and poles, mine
timber, pulp wood, and tanbark. Lumber makes up about
half of the total amount of these products, and firewood

about one third of the
total. About 30 per cent
of the lumber is made
into finished building ma-
terial such as flooring,
sash, doors, and siding ;
about 2 5 per cent is used
as rough lumber; 10 per
cent is used in the mak-
ing of boxes and crates;
5 per cent in the manu-
facture of cars ; 3 per
cent for furniture ; about
7 per cent is exported;
and the remainder is used
in various other ways.
Spruce, poplar, and larch
have been most used for
wood pulp, but now
many other of the softer
woods are being used.
Oak and hemlock bark
and chestnut wood are
used in tanning leather ;
over a million cords of
bark and two hundred
thousand tons of wood are used in this way each year.

370. Wood Distillation. — The production of turpentine
and rosin has been for many years an important industry in
the southern states. Almost 30,000,000 gallons of turpen-
tine and more than 3,000,000 barrels of rosin are produced

FIG. 20 1 . — A grove of mature red
pines (" Norway " pines) at Trout Lake,
Wisconsin. Photograph from the Wis-
consin State Conservation Commission.

FORESTRY AND FOREST MANAGEMENT 357

annually. The waste material from many saw mills is now
distilled by various processes, producing great quantities of
wood alcohol, turpentine, formaldehyde, tar, creosote, and a
variety of other products. The gases given off in some of
these processes are used as fuel, and the charcoal which'
remains is valuable. A cord of long-leaved pine will produce
in this way twenty-four gallons of turpentine, thirty-three
gallons of pyroligneous acid, used in making vinegar, explo-
sives, and, when united with other substances, many pig-
ments ; one hundred and twenty gallons of tarry and oil
products, which may again be distilled ; and there remain
fifty-six bushels of very good charcoal.

371. Other Wood Products. — The making of veneers
(thin slices or sheets of wood) has become an important
industry in late years. Formerly only the expensive woods
were used in this way, and the veneers of these woods were
put over cheaper woods in the manufacture of furniture;
but now many of the cheaper woods are cut into veneers,
from which boards can be built up that are lighter and
stronger than if they were made of a single piece, and are less
likely to warp. Excelsior, made by shredding the wood with
sharp spurs or knives, is used in great quantities in making
mattresses, in upholstering, and in packing glassware, furni-
ture, and metals, as well as in a number of other ways. The
making of maple sugar and sirup is an important industry
in Vermont, New Hampshire, and New York ; and maple
sugar is made to some extent in all the north central states.
Most of this work is done between the middle of March and
the middle of April. A single tree may produce in a season
about two pounds of sugar or a quart of sirup.

CHAPTER XXIII
PLANT BREEDING

372. What Plant Breeding Is. — As we have seen, the
varieties of Indian corn are numbered by hundreds ; and
there are many varieties of potatoes, apples, roses, and indeed
of most of our cultivated plants. Most of these varieties have
arisen since the plants in question have been in cultivation.
All the varieties of Indian corn, for example, are probably
descended from a single wild species, and the great majority
of them have appeared since corn began to be cultivated by
white men. All the varieties of potatoes probably came
from a single species, and all the apples (including the crabs)
from three species. Some varieties of cultivated plants
originated without anyone's knowing exactly when they ap-
peared or where they came from ; but most of them have de-
veloped because some of the men who were growing plants
tried to obtain varieties that would better serve their needs.
The improvement of old sorts of plants or the development
of new sorts is plant breeding. The few varieties of corn that
were cultivated by the American Indians when white men
first came to the continent had probably developed and been
preserved quite accidentally ; but most of the varieties that
have appeared since have been the result of more or less
systematic breeding.

The development of varieties of cultivated plants is similar
in many respects to the development of varieties and species
among plants that are growing wild. Just as the many cul-
tivated varieties of potatoes are descended from a single
wild species of Solanum, so that and all the other species of the
358

PLANT BREEDING

359

same genus (including the eggplant and the nightshades)
came in turn from a single still older species. But one
difference is worth noting between the varieties that have
developed among wild plants and
those that have been produced by
breeding. No variety can exist for
any length of time in the wild state
unless it is particularly well fitted to
the conditions about it, and especially
unless it has very effective means of
reproduction. But there are many
varieties of cultivated plants which
would be quite unable to live, or to
reproduce, or both, if they were not
carefully cultivated and propagated
by artificial means. We do not
know, for example, what the original
ancestor of the Indian corn may
have been ; but none of its present-
day varieties thrives except in culti-
vation. If some corn plants do
spring up in a wild state, their de-
scendants die out in the course of
two or three generations at most,
largely because they have no way of
distributing their heavy fruits.

The wild ancestors of our culti-
vated plants were in almost all cases
much less useful or attractive to man
than their cultivated descendants
are. The original plants must, how-
ever, have had some valuable qualities, or men would not have
begun to cultivate them. After the cultivation of a particu-
lar species began, it was noticed that some individual plants
of the species were better adapted than others to the purpose

FIG. 202. — The result
of seven years of breeding.
The head of barley on the
right is one of a variety
developed from one repre-
sented by the head at the
left.

360 TEXTBOOK OP BOTANY

for which they were grown. Long ago — no one can say just
when — men learned that the seeds of large plants are more
likely to produce large plants than the seeds of small ones
are, and that the seeds of a plant with large fruits are, on the
whole, most likely to produce plants with large fruits. So,
here and there, growers began to pick out and to sow the
seeds of those particular plants which seemed to them most
valuable. This kind of selection was the beginning of plant
breeding, which therefore goes back a long way. But it is
only in rather recent times that breeding has been carried on
according to definite plans and on a large scale.

373. What Plant Breeders Try to Do. — One of the most
important things to be considered in the breeding of a variety
of plants is its yield of fruits, seeds, flowers, or other useful
parts. Sometimes breeders aim at a high yield for each in-
dividual plant — each apple tree, or rose bush, for example.
But often it is more important to consider the yield of all the
plants that can be raised in an acre or in some other limited
area ; for a greater yield may often be obtained from a large
number of small plants, each one yielding comparatively
little, than from the smaller number of large plants that
might be raised on the same piece of land.

Closely related to the question of yield is that of the length
of the season during which the plant produces flowers or
fruits. As a rule, a particular sort of plant has a short
bearing season, ranging from a few days to a few weeks.
Sometimes this period may be lengthened by breeding ; thus,
rose varieties have been developed that bloom at intervals
throughout the whole summer. But more commonly the
same end is reached by breeding different varieties which
bear at different times ; and so we have early and late cher-
ries, early and late apples, and early and late ' potatoes.
Early varieties are likely to be especially valuable ; the
highest prices are paid for the first strawberries or the first
peaches that appear in the market ; and so it is well worth

PLANT BREEDING 361

while to produce a new form that will be a little earlier than
any existing variety.

Another quality of great importance is the plant's ability
to resist diseases. Much attention is being paid by plant
breeders to the development of disease-resistant varieties —

FIG. 203. — Breeding for disease resistance. Seeds were obtained from
a single plant which remained healthy in a field of cabbages otherwise
badly affected by a disease known as "yellows." The seeds were planted
with those of other varieties in a diseased field, and the result is here shown.
Only the plants in the row grown from the selected seed were normal. After
Jones and Oilman.

varieties, that is, that are not attacked or are attacked only
to a small extent by a particular disease. For some time it
has been known that certain apple varieties are little affected
by rust ; durum wheat also resists rust ; and varieties of
cotton, watermelon, and flax have been obtained that are
resistant to a class of very destructive diseases known as
wilts. Other characteristics of plants that may be influenced

362

TEXTBOOK OF BOTANY

by breeding. are the size, shape, color, taste, and keeping
quality of fruits and other edible parts, and the size, color,
and odor of flowers.

All these qualities and many others that might be named
are of a more or less general nature ; a single variety of apple
or of potato or of rose might conceivably be bred which would
combine in itself all the desirable general qualities, excepting
perhaps that of a long bearing season. In addition, how-
ever, there are local and special conditions to be met, which

FIG. 204. — Breeding for disease-resistance. A crop of healthy plants
grown from the seed of those shown in Figure 203. This seed was sown
in a field in which other varieties had been a complete failure because of
yellows. The selected variety gave 95 per cent of a normal yield. After
Jones and Oilman.

make it necessary to develop many different varieties of the
same species. Most important, perhaps, of the local condi-
tions are those of climate. Varieties that are adapted to a
locality where the growing season is long and where rain is
abundant are not likely to thrive where the summers are short
and there is little rain. In the great grain-raising 'Countries
much work has been and is being done to produce different
varieties of wheat, oats, barley, and rye that will grow well
and yield good crops under different conditions of climate.
The whole world is benefited whenever a variety is obtained

PLANT BREEDING 363

that may profitably be raised in a region where the cultiva-
tion of that kind of crop has hitherto been impossible. This
is especially true if the new variety is suited to dry regions,
such as the arid and semi-arid parts of the western United
States. Soil conditions, too, differ greatly ; some varieties
of plants grow best in sandy soil, others in clay ; some in soils
that are rich in organic matter, and others in soils that are
comparatively poor.

Sometimes varieties must be bred to meet local tastes and
fashions. In some localities there is almost no market for
apples unless they are large and highly colored, while in other
places at the same time dull-colored apples of ordinary size
but of good flavor sell readily. It is often true, too, that dif-
ferent varieties of the same or of related species must be bred
for different purposes. Thus there are table grapes, raisin
grapes, and wine grapes ; apples th'at must be used soon after
they are picked, and apples that can be kept in good con-
dition for winter use.

374. Selection. — No two plants of the same variety are
exactly alike. In an ordinary field of wheat, some plants
have larger heads than others. The grains from the plants
with larger heads are likely on the average to produce larger-
headed plants than will the grains from plants with smaller
heads. Therefore, if we wish to obtain a race of wheat with
large heads, we may select our seed grain from those plants
which come nearest to being what we desire, and on the whole
we shall improve the variety of wheat in this particular re-
spect. In the same way we may select seed grain with ref-
erence to the number of heads per plant, the size of individ-
ual grains, the strength of stem, the ability of the plant to
endure drought, its resistance to rust, or with reference to a
combination of any two or more of these qualities. Such
a selection of the seeds of the most desirable plants has played
a very large part in the breeding of cultivated varieties.

Until quite recent years seed selection has usually consisted

364 TEXTBOOK OF BOTANY

simply in choosing the seeds of a good many plants in a patch
or in a field that were above the average with respect to the
desired qualities, and in repeating the same process year
after year. But the results of this method of selection have
not always been satisfactory. Although the average of the
variety can usually be raised in the direction wished, the

FIG. 205. — The improvement of corn by selection. The well-formed,
well-filled ears at the left belong to a variety that was developed from one
represented by the ears on the right.

improvement is sometimes small ; moreover, many plants in
each generation are below the average, and if the practical
growers do not continue to select their seed carefully each
year, the seed of the inferior plants will be mixed with that
of the better ones and the variety will deteriorate rapidly.
To a certain extent these disadvantages are avoided by an-
other method of selection which is now largely used.

The newer method is based on the fact that the inherited
qualities of a plant cannot always be judged from Us appearance.

PLANT BREEDING

365

This is true because the size of the plant, the number and
size of its flowers and fruits, and many of its other character-
istics depend both upon the qualities that it inherits from its
parents and upon the conditions under which it grows.
Thus a wheat plant that under favorable conditions would
bear large heads may bear small ones in a bad season, or if
it grows in poor soil or in a dry place ; and a plant whose heads
would ordinarily be small may under unusually favorable

FIG. 206. — Breeding plots at the Wisconsin Experiment Station. These
plots are so small th'at it is possible to give attention to individual plants.

conditions bear fairly large ones. Now, an ordinary variety
of wheat is a mixture of many races; some of which inherit a
tendency to produce large, some a tendency to produce me-
dium, and some a tendency to produce small, heads. So,
when we select a number of plants with large heads, it is quite
likely that some or even most of them belong to really large-
headed races ; but some may belong to small- or medium-
headed races and only happen, because of specially favorable
circumstances, to bear large heads. The grains from the
plants of the large-headed races will produce plants whose

366 TEXTBOOK OF BOTANY

heads on the average are large, though there will be differ-
ences in size due to external conditions ; but the grains from
the plants of other races will not, on the average, produce
large-headed plants. So, although the average size of head
may have been increased by selection, the variety is still
mixed because it contains both large-headed and small-
headed races. If a new selection of the same sort is made
each year, the average of the variety may slowly be raised
for a number of seasons, and afterward kept up by continued
selection ; but we are not likely to produce in this way a pure
large-headed variety.

A pure variety may be obtained, however, by using the
more modern method of selection. This consists in select-
ing, as before, the grains of several or many large-headed
plants, but in sowing those from each plant in a separate plot.
The offspring of each original plant are kept separate, and by
studying the offspring for one, two, or more generations it
is possible to determine which of the plants that were first
selected really belonged to large-headed races and which did
not. Then, by breeding from the descendants of that origi-
nal plant which passed on in the highest degree the tendency
to bear large heads, a variety is established which consists
of a single race ; it is a thoroughbred variety and has the same
advantages that a thoroughbred variety of- horses or cattle
has. When such a variety is obtained, it is less likely to
deteriorate than a variety obtained by the older method,
which is almost certain to be mixed. However, as we shall
see, selection cannot be entirely neglected even after a pure
variety has been established.1

'Strictly speaking, a "pure variety," in the sense in which the expression is
used here, is possible only in the case of a plant which, like many of the wheats, is
regularly self-pollinated. In species or varieties that are ordinarily cross-pollinated,
any plant is sure to combine within itself qualities derived from various races, and
with each generation new qualities are likely to be introduced. However, even
in cross-pollinated species, it is possible to obtain by close inbreeding between nearly
related or carefully selected plants races that are approximately pure, at least with

PLANT BREEDING

367

375. Mutations. — If a variety selected as just described
would never change — .that is, if its seeds grew year after
year into plants which, on the average, when raised under
similar conditions, were like the plants that bore the seeds —
then the work of selection for any particular quality might be
done once for all. But as a matter of
fact, varieties, no matter how pure they
may be at the start, do not remain un-
changed. In each generation, the indi-
vidual plants of a variety differ from one
another in many ways. Most of the
differences result from differences in the
conditions under which the plants grow ;
such differences are not passed on through
the seeds to the offspring, and so do not
affect the purity of the variety. But
now and then a plant differs from its
parents or from any of its immediate
ancestors in a way that is not caused,
at least directly, by external conditions.
Such a mutation, as a difference of this
kind is called, is due to causes that we
do not understand ; unlike the differ-
ences that result from external condi-
tions, it is likely to be passed on to the
offspring. A mutation may therefore be
the starting point of a new race. By the
appearance of new races in this way, a pure variety in the
course of time becomes a mixed variety. Some of the races
resulting from mutations are sure to be undesirable. There
may occur, for instance, in a large-headed variety of wheat a
plant that not only itself bears small heads, but which, if

reference to certain important qualities. Such a race, while not strictly speaking
pure, is thoroughbred in the same sense that a closely inbred race of cattle or horses
is thoroughbred.

FIG. 207. — A stool
of rye grown at the
Wisconsin Experi-
ment Station from a
single seed of an im-
proved variety.

368 TEXTBOOK OF BOTANY

its grains are planted, will give rise to a small-headed race.
To prevent a lowering of the average of the variety, the new
small-headed race must be weeded out by selection. This
explains why selection must be continued, even after a valu-
able pure variety has been established.

On the other hand, mutations sometimes give rise to races
that are improvements on the variety from which they come.
Among the members of a large-headed variety a plant with
heads larger than the average may appear, which will pass
on to its offspring a tendency to bear especially large heads.
By selecting the grains of such a plant and of its offspring,
we may obtain from the large-headed race that was first se-
lected a new race with still larger heads. Thus, by taking
advantage of mutations that lead in the right direction, a
variety may be improved step by step. However, the
amount of improvement that can be made in any particular
direction is limited. We could hardly hope by selection, no
matter how long continued, to produce wheat twenty feet
high, or with heads a foot long. When an attempt is made
to breed for a particular quality, by either the older or the
newer method of selection, improvement may be rapid for a
few. generations ; but then it becomes slower and slower, and
finally a point is reached beyond which no perceptible ad-
vance can be made. After this time, about all that selection
can do is to remove undesirable mutations when they appear
in order to keep the variety at the level it has reached.

As a rule, a mutation results in only a small difference
between parent and offspring ; but now and then the dif-
ference is great enough to be conspicuous, as when a double
flower appears on a plant belonging to a race with single
flowers. A plant that shows such a striking mutation is
often called a sport. Sometimes a sport gives rise to a valu-
able new variety. The double-flowered varieties of roses,
carnations, violets, and many other cultivated plants, and
the seedless varieties of oranges and other fruits have been

PLANT BREEDING

369

developed from sports. Very likely the same, thing is true
of the cabbage. At any rate, the plant which is thought to
have been the original of the cultivated cabbage, and which
still grows wild
on the seaside
cliffs of western
and southern
Europe, has no
head, but in-
stead a cluster
of root leaves.

376. Hybrid-
ization.— Some-
thing was said in
Chapter XVII
(§ 288) about
the production
of crosses or
hybrids when the
stigma of a
flower is dusted
with pollen from
a flower of an-
other variety or
of another spe-
cies. A hybrid FlG 2og _ The ^ Brassica Oieracea (A), from
usually pos- which the cultivated plants shown are believed to
Sesses some of have been derived; B, kohlrabi; C, cauliflower;

nolifi^c nf D> cabbage; £> Welsh or Sav°y cabbage; F, Brussels
the qualities of sprouts Mt£T Smalian-

one parent com-
bined with some of the qualities of the other parent. Hybrids
frequently result from the carrying of pollen from flower to
flower by the wind or by insects. Such accidental hybrids
are sometimes troublesome in plant breeding, because they
introduce impurities into varieties that it is desired to keep

370 TEXTBOOK OF BOTANY

pure. . Accidental hybridization may be prevented by plant-
ing each variety at a distance from any other that might be
crossed with it ; or by covering the flowers with sacs of gauze
or of oiled paper during the time that their stigmas are able
to receive pollen. But occasionally the new combination of
qualities that appears in a hybrid makes it a more useful plant
than either of its parents. Plant breeders produce hybrids,
when they wish them, by artificial cross-pollination — that is,
they deposit the pollen from a flower of one variety by means
of suitable instruments upon the stigma of a flower of another
variety. In such a case, the stigma must be protected from
pollen of its own kind. 'This is done by bagging the flower,
and, if it contains both stamens and pistil, by removing the
anthers before their pollen is ripe.

The exact combination of qualities that appears in a hy-
brid is not as a rule permanent, because the seeds of a
hybrid commonly grow into plants that differ from one an-
other. It is sometimes said that the offspring of a hybrid
" split up " into different sorts of plants. These offspring
combine in themselves in various ways different qualities
of the original parents of the hybrid, including qualities
that did not appear in the hybrid as well as qualities that
did. Suppose now that a hybrid combines the qualities of
its parents in such a way as to make it a useful new sort of
plant. We cannot as a rule hope to obtain a crop of plants
like the hybrid by planting its seeds, because it is likely that
many of the plants that grow from these seeds will be differ-
ent from the hybrid. But we can make the hybrid the start-
ing-point of a new variety of plants like itself if it can be
multiplied in vegetative ways — for example, by buds, cuttings,
or grafts — because a plant produced by vegetative multi-
plication is, with very rare exceptions, like its parent. Since
apple trees are multiplied by grafts and cuttings, a new
apple variety may be propagated from a hybrid. Many of
our most valuable varieties of apples have in fact been

PLANT BREEDING 371

propagated from accidental hybrids, and a seed of such an
apple is for this reason likely to grow into a tree very differ-
ent from the parent. Many varieties of potatoes, which
are multiplied by cuttings from the tubers, are also hybrids.
When a hybrid forms seeds as a result of self-pollination
or of pollination between flowers of the same plant, its off-
spring commonly " splits up " in accordance with certain
fairly definite rules.1 Some (but by no means all) of these
offspring, differently from the original hybrid, breed true
— that is, their seeds grow into plants like themselves, the
seeds of this next generation into similar plants, and so on.
It is possible, then, to obtain from some of the offspring of
a hybrid new races that can be propagated by means of
seeds. Plant breeders may therefore combine hybridization
with a selection among the descendants of the hybrid. It is
only in quite recent years that the possibility of producing
new races in this way has been at all well understood, and
even yet we have much to learn about the laws that govern
the splitting up of the offspring of hybrids. Still, many
valuable varieties have been produced in the past by breeders
who selected in a more or less haphazard way the most
promising among the descendants of a hybrid that they had
obtained either accidentally or intentionally. Now breeders
know much better than they did even ten or fifteen years ago
what to expect when they produce a hybrid. They may
hope to secure from among its offspring a new race that will
combine in itself the desirable qualities of both parents of
the hybrid. But to secure just the combination of qualities
that is wished, it is often necessary to raise the hybrid plants
and their offspring in great numbers ; sometimes tens of
thousands or even hundreds of thousands of plants must be
grown before the exact combination appears.

1 Discussions of these rules (the "Mendelian laws"), with their modifications and
their applications to the production of new varieties, will be found in any modern
book on plant or animal breeding.

372 TEXTBOOK OF BOTANY

377. The Breeders of Plants. — Until about the middle
of the last century, plant breeding was done almost entirely
by private persons and firms — especially by seed raisers,
nurserymen, and florists. Here and there an individual
farmer, gardener, or amateur flower grower interested him-
self in the production of new varieties. It was men of
these types who developed most of our present varieties,
and they are still doing extremely valuable work. Perhaps
the best known of the private breeders of the present time is
Luther Burbank, among whose productions are varieties
of potatoes, raspberries, and walnuts, the stoneless plums,
and the Shasta daisy. But much of the most thorough and
important breeding work is done nowadays under the direc-
tion of national, state, and provincial governments. Most
of the European countries have departments that devote
much attention to the improvement of cultivated plants.
In North America, the United States and Canadian De-
partments of Agriculture have many plant breeders at work
on experimental farms which are so located as to test va-
rieties of plants under all possible conditions. In addition,
each state of the United States and each province of Canada
has an experiment station, and in nearly every one of these
stations the same sort of work is being carried on. The
departments of agriculture and the experiment stations
are also doing much, through their bulletins and by other
means, to spread a knowledge of the methods of plant
breeding, and especially of seed selection, among the men who
actually raise plants on farms, in orchards, greenhouses,
and market gardens. New varieties are developed and
tested at experimental farms ; but they may be kept up to
a high standard and even improved by careful selection of
seed each year, and this work of seed selection can in many
cases be done as well by practical growers as by professional
breeders.

CHAPTER XXIV
PLANT DISEASES

378. Disease-producing Fungi. — From previous chap-
ters a knowledge has been gained of the importance of bac-
teria, rusts, and mushrooms, and of the damage that some
of the members of these groups of fungi do by producing
diseased conditions in other plants. There are, however,
many fungi beside those that we have specially studied which
are responsible for diseases that, in the case of cultivated
plants, result in losses amounting to many millions of dol-
lars each year. Every plant of economic importance is
attacked by one or more parasitic fungi, and a simple enu-
meration of the diseases that they cause would occupy more
space than can be given to this chapter. So only a com-
paratively few diseases, which are well known and are of
great practical importance, will be briefly described. The
fungi that produce plant diseases belong to the following
groups :

a. Bacteria. These were discussed in Chapter II. Some
of the diseases that they cause are described in §§ 379
and 380 below.

b. Slime Molds. Each of these very simple plants con-
sists of a single cell which is sometimes quite large,
containing many nuclei but possessing no cell wall.
When it is mature, the whole cell divides into many
small spores. Each spore may become a free-swim-
ming cell which later develops into a mature plant.
(See § 381.)

373

374

TEXTBOOK OF BOTANY

c. Alga-like Fungi. These possess many characteristics in
growth and reproduction which indicate that they may
have arisen from the algae. The bread mold and its
relatives are among the members of this group. Some
of the parasitic forms are discussed in §§ 382-384.

d. Sac Fungi. These produce usually at least two types
of spores ; those of one type are produced on thread-
like projections from the plant body ; spores of a
second sort are borne in small sac-like structures which
most commonly contain eight spores, but in some
species contain more or fewer than eight. The sacs
are in most cases partly or entirely surrounded by in-
terlacing branches of the fungus, which form a fruiting
body of characteristic form. (See §§ 385-389.)

e. Basidium Fungi. The mushroom and its relatives
belong to this group, in which the rusts and the smuts
(§ 390) are usually included.

/. Imperfect Fungi. To this group belong a large num-
ber of disease-producing fungi. They are called " im-
perfect " because it is believed by most students of
fungi that we do not know their entire life history.
Many formerly listed in this group have been found,
when their whole history was worked out, to be sac
fungi ; others have been referred to the basidium fungi.
(See §§ 3QI-393-)

379. Pear Blight. — This disease, known also as " fire
blight " and " twig blight," is probably the most important
bacterial disease affecting cultivated plants. It attacks the
apple, crab-apple, pear, quince, and some related plants.
The ravages of the disease are so serious that the growing of
pears and apples has been almost entirely given up in some
regions of the United States. The bacteria that cause it
live in the 'inner tissues of the twigs and branches. The
first symptom that is likely to be noted is a withering of the
leaves, flowers, and younger branches in from two to four

PLANT DISEASES

375

weeks after flowering. The branches are at first slightly
swollen, then they turn dark brown, and soon the tissues
shrink and wilt conspicuously (Fig. 209). If it is not
checked at this time, the disease will extend into adjacent
tissues, and may readily be carried by insects to other
branches and to neighboring
trees. It is especially likely to
be spread by insects just after a
rain, because at such times a
gummy substance is excreted on
the surfaces of diseased branches,
in which substance are countless
living bacteria. The bacteria
live through the winter in the
diseased tissues, and in the fol-
lowing spring when the tree
resumes its growth they may
infect the living tissues of the
tree or may be carried by insects
to still other plants. The bac-
teria also live in cankers on vari-
ous parts of apple trees, and
these cankers are prolific sources
of new infections.

The only means known for
controlling the disease is the
cutting out and burning of dis-
eased branches as soon as they

are discovered. An infected branch must be cut at some
distance below the place where the disease is evident, be-
cause some of the bacteria are usually present below the
darkened portions. Great care must also be taken to see
that the pruning knife or saw does not come into, contact
with the diseased tissues, for in that case the cutting tool
itself will carry the disease from tree to tree.

FIG. 209. — A branch of an
apple tree attacked by the fire
blight. Notice the character-
istic appearance of the younger
portions, which look as though
they had been scorched.

376

TEXTBOOK OF BOTANY

Some varieties of apples and pears are apparently more
resistant to the disease than others, but their resistance
seems to be dependent at least in part upon climatic
conditions. A variety which is fairly resistant in one
locality sometimes proves to be very susceptible in another
region.

380. Other Bacterial Diseases. — Crown gall, which causes
peculiar enlargements of stems and roots at the surface of
the soil, is becoming a serious
menace in regions where apples
are grown. It also attacks vari-
ous other plants, such as rasp-"
berries, grapes, walnuts, and
willows. It can be eliminated
only by planting such nursery
stock as is absolutely free from
the disease and by destroying
any plant found affected. The
black rot of cabbage has entirely
ruined the cabbage industry in
many localities. The bacteria
enter through the air-pores and
water-pores of the leaves. The
leaves turn to a yellowish color,
the veins become black, and as
the disease spreads to other parts
of the plant the leaves fall off
and soon the plant withers and
dies. A rotation of crops and

clean seed beds have so far been the only means of
control, although it seems possible that in the near future
resistant varieties may be developed. The bacteria that
cause the wilts of the cucumbers and melons live in the
wood cells and vessels, which thus become clogged up.
The parts of the plant above ground therefore do not

FIG. 2io.-The crown gall
of the apple. Soft, spongy
swellings are formed at or just
below the surface of the soil.
This disease is likely to be found
on grafted nursery stock.

PLANT DISEASES

377

receive their necessary supply of water, and so wilt
and die. The bean blight is another important bacterial
disease.

381. Club Root of Cabbage. — This disease, also known
as " club foot," has long been a serious menace to the cab-
bage industry in Europe. The
estimated damage in Russia alone
for a year is over $5,000,000.
The disease is likewise found in
almost all regions in the United
States where cabbages are grown
extensively. Young plants are
stunted and many die at this
stage ; others continue to live but
never form a head that is market-
able. The roots are stimulated
to excessive growth, and swell-
ings (Fig. 211) are caused; these
swellings are often only slight
enlargements on the sides of the
roots, but in other cases they
reach a considerable size. The
parasite, which is usually consid-
ered to be one of the slime molds,
is known to attack the cabbage,
turnip, cauliflower, radish, ruta-
baga, and Brussels sprouts, and
has been found on the mustards
and other weeds. The thick -walled spores of the fungus
live through the winter in the soil and in diseased tissues.
In the spring the spores germinate and infection takes place
in the roots of young plants. No means has yet been dis-
covered for the control of this disease, but rotation of crops
and care in planting only healthy individuals may consider-
ably check the loss.

FIG. 211. — The club root
of cabbage. The younger roots
and the lower portions of the
stem become greatly swollen;
the plants are weakened and
often killed.

378

TEXTBOOK OF BOTANY

382. Damping off. — Much loss is occasioned in green-
houses, seed beds, and often in fields by fungi which attack
young plants at the surface of the soil. An infected plant
at first appears slightly water-soaked ; soon it wilts, and
then, as the shoot falls to the soil, the fungus spreads to all
its parts and in a short time kills the plant. The fungus

which most commonly
causes this trouble lives
as a saprophyte in the
upper layers of rich,
moist soils. The plant
body of the fungus is
made up of delicate
threads much like those
of the bread mold; it
reproduces by means of
spores, each of which,
when it becomes free, di-
vides into several small
cells that can swim
about in water by means
of delicate vibrating
threads. Gametes are
also produced which
unite to form thick-
walled zygotes (Fig.

FIG. 212. — The zygote of one of the
" damping off " fungi ; a, wall of the
oogone, an organ in which the egg was
formed ; b, outer wall, c, middle, and d, in-
ner walls of the zygote ; e, fat body ; /, a
tube through which the antherozoid passed
to unite with the egg ; g, antherid ; h, zygote
nucleus; i, a vacuole in the cytoplasm of
the zygote ; j, the branch of the fungus on

which the antherid was borne. 212) ; it is probably by

means of these zygotes

that the fungus lives through the winter. Similar troubles
are also caused by several quite different fungi, among them
some of the black molds and some of the imperfect forms.
Damping off can be partially prevented by sterilizing the
soil either by heating it or by the use of formaldehyde ; it
can be checked, too, by careful cultivation so that the fungi
are not allowed to grow on the refuse that may be present.

PLANT DISEASES

379

No plants should be used which come from seed beds or
greenhouses in which damping off is known to have
occurred.

383. Downy Mildew of the Grape. — This disease appears
on young branches and leaves of both wild and cultivated
grapes and is not uncommon wherever
grapes are grown. It may at times
cause considerable damage, especially
to slow-growing varieties. The disease
was introduced into Europe from the
United States, and in a short time it
almost ruined the grape-growing in-
dustry over extensive areas. An af-
fected leaf shows irregular yellowish
areas on the upper surface, and at the
same time spore-bearing branches ap-
pear on the lower surface of the leaf
immediately below the discolored spots.
Irregular dark areas appear also on the

stem, and at times the fungus is so . Fl.G" 2I*-~ sfpor,e"
7 ° bearing branch of the

abundant on the young fruit as to give downy mildew of the
it a downy appearance, whence the grape, making its ap-
name "downy mildew." It is only pearance through an air
J J pore on the under side

when the fruit is diseased that any Of the leaf; o, a portion
considerable loss is caused in the United of the branch with spores
States. The fun^s lives between the ^VitacLe^
cells of the host, sending short, rounded sp0re; c, a spore, much
branches into the living host cells and enlarged,
thus robbing them of their food. The
spores are borne on peculiarly branched structures that
project beyond the surface of the host (Fig. 213) and
produce free-swimming cells like those of the damping-off
fungus, which in turn germinate and produce the new
growth upon the grape. The large thick -walled zygotes
are not very commonly found, although they do occur.

380

TEXTBOOK OF BOTANY

FIG. 214. — A potato leaf at-
tacked by the late blight.

This fungus can be fairly well
controlled by spraying the grape
plants with the well-known Bor-
deaux mixture.1

384. Late Blight and Rot of
Potato. — This, commonly called
the " potato disease," is at times
very destructive and has been
responsible for the " potato
famines " of history. Because
of its destructiveness it has been
extensively studied and was one
of the first plant diseases against
which governments waged a real

warfare. The fungus that causes the disease is very com-
mon in some of the northern United States, and its spread

may at any time when conditions are favorable become a

serious problem. It seems to prefer the

colder climates and wet, heavy soil.

The fungus first attacks the potato

leaves, causing spots which are purplish

in color when wet, but brown when dry.

The disease may be confined to the leaf ;

but it may spread to the stem and finally

to the tubers, causing a dry rot of the

latter if they are growing in dry soil or

a wet rot if the soil is heavy and wet.

The diseased tubers are very likely to

decay in storage because many of their

1 Bordeaux mixture. This is probably the most im-
portant and most commonly used of fungicides. The
formula usually regarded as standard is the following,
known as the "5 — 5 — 50" formula:

Copper sulphate, 5 pounds.

Stone lime, 5 pounds.

Water, 50 gallons.

FIG. 215. — A few
cells of a potato leaf on
which spores of the late
blight fungus have
landed; a, a. spore; b, a
germinating spore ; c, a
germinated spore, the
germ tube from which
is entering an air-pore
of the leaf. After Weed.

PLANT DISEASES

outer cells have been killed by the fungus so that it is easy
for decay-producing fungi to enter. The fungous body is
very much like that of the downy mildew fungus, excepting
that the short branches that enter the host cells are also
thread-like and much more delicate than the main branches.
The spores also are very much like those of the downy mil-
dew fungus, and the large, thick- walled zygotes are very
rarely found. The disease may be kept under control by
the use of the Bordeaux mixture, making from three to five
applications at intervals of about two weeks. Some varieties
of potato seem to be more
resistant than others, but
their resistance appears
to depend partly upon
conditions in the locality
in which they are grown,
because potatoes de-
scribed as resistant in
one region may prove
very susceptible in an-
other.

385. Brown Rot. —
This disease attacks the
peach, plum, cherry,
apricot, and related
plants. The damage
done by the brown rot
fungus (one of the sac
fungi) is enormous, a con-
servative estimate plac-
ing the annual loss in past

years at over $5,000,000. It usually attacks the fruit, but
may cause damage to flowers, leaves, and small branches.
On the fruit, the disease first appears as a small, dark, decayed
spot which gradually enlarges until it covers perhaps the

FIG. 216. — A branch bearing peaches
affected by the brown rot.

382 TEXTBOOK OF BOTANY

entire fruit. The fruit now decays, and in the meantime
the fungus produces an abundance of spores, which may
be scattered by the wind or may remain on the stems and
leaves to spread the disease the following year. The fruit
finally becomes hard, shriveled, and wrinkled (Fig. 216) ;
in this condition it either remains on the stem or falls to
the ground. The next spring the plant
body of the fungus, which has remained
dormant in the decayed fruit, develops
a saucer-shaped fruiting body on a short
stalk. Within this saucer are borne an
immense number of small sacs in each
of which eight spores are produced. In
order to check the ravages of this fungus
it is necessary to remove the diseased
portions of the plant as soon as they are
FIG. 217.— Spores of discovered. These, with the decayed
the brown rot fungus fmits from the tree and ground, should
^ once be burned, because the spores
may be carried to a considerable distance
by the wind. Spraying also helps to check the growth of
the fungus. For this purpose, modifications of the ordinary
Bordeaux mixture and a lime-sulphur wash are probably
the best.1

386. Powdery Mildews. — More than sixteen hundred
species of seed plants are known to be attacked by one or
another of these parasitic fungi. Although strict parasites,

1 Lime-sulphur wash. This can be obtained in prepared form, or it may be made
according to the following formula :

Flowers of sulphur, 10 pounds.
Stone lime, 10 pounds.

Water, 50 gallons.

The lime is poured into a barrel, three to five gallons of water are added, then the
sulphur is sifted in and the whole mixture is stirred while the lime is being slaked.
More water is added as the mixture becomes heated. When the lime is entirely
slaked the rest of the water may be added.

PLANT DISEASES 383

they do very little harm to many of the plants upon which
they live ; on the other hand, if conditions are favorable for
their growth they may cause much damage. Powdery
mildews are found from the tropics to Greenland. The
leaves of the host plant are usually the parts affected, but
the mildew may appear on the young branches and on the
fruit as well. The plant body of the fungus, composed of a
tangled mass of delicate light-colored threads, is found on
the surface of the host ; projecting from these threads into
the host cells are variously shaped short branches which
absorb food. On upright branches spores are borne, which
spread the fungus during the growing season. Later there
usually appear little dark spherical fruiting bodies with
peculiar projections from their lower portions. Within the
fruiting bodies one or more sacs are formed, which contain
usually eight spores each. One of these mildews sometimes
causes considerable damage to young peach trees ; another
attacks the gooseberry. The apple and strawberry are also
affected, and the powdery mildew that attacks grapes has at
times caused immense losses both in the United States and
in Europe.

387. Black Knot. — This disease affects plums and cherries
and is so vigorous in its attacks that it has entirely ruined
the plum and cherry orchards in various parts of New York
and of some of the other Atlantic states. In the eastern
portions of the United States the fungus thrives well both
on wild and cultivated forms ; but in some regions farther
west it is found only on wild varieties, and cultivated plums
and cherries are often not affected, even though growing near
diseased trees of related wild species. The knot appears
in early spring as a conspicuous swelling, usually on one of
the smaller branches of the tree (Fig. 218). The bark cracks
and breaks off and the exposed tissues turn to a deep olive-
green color. At this time abundant spores are formed from
short threads arising from the surface of the knot. These

TEXTBOOK OF BOTANY

spores continue to be produced for three or four months.
In the meantime the knot has been growing in size and
has turned almost black, and small rounded swellings have
appeared on the surface ; these swellings contain a second
type of spore. During the late
summer another set of rounded
bodies appear on the knot; these
remain over the winter, and in the
spring they are found to contain
many small sacs, in each of which
are eight spores. The only known
means of controlling this disease is
to cut out and destroy the knots.
This means is successful only if
there is cooperation on the part of
growers, not only in cleaning out
their orchards but also in carefully
watching the wild varieties for the
appearance of knots.
388. Black Rot of Grapes.— This

FIG. 218. — Portions of ,.

tWo branches of the choke- disease causes great damage to the

cherry attacked by the black grape crop if weather conditions are

knot. The fungus grows in favorable. It is most serious if the

the tissues of the host, pro- , , . , j .,

ducing large, irregular swell- days are warm and moist> and lts

ings which will eventually ravages are greatly checked by a

encircle the stem and kill short spell of cool; dear days> A1_

though the greater harm comes from
the injury to the fruit, the disease is
found on the leaves, and from these, under favorable con-
ditions, it may soon spread to the fruit. On the leaves
small brown spots appear, which rapidly grow in size and
number, giving the leaf a wrinkled appearance. Upon the
fruit a small spot, purplish in color, is first noticed. This
grows, and finally the whole fruit decays and shrivels.
Spores are produced in abundance upon the affected parts,

all beyond
portion.

the diseased

PLANT DISEASES 385

and by their means the disease spreads rapidly. The
shriveled fruits lie on the ground, and the next spring portions
of the fungous body which have remained within them begin
to grow again and produce the spore sacs. Until a few years
ago this fungus was known only in North America, but now
it is reported as doing considerable damage to grapes in
southern Europe. Cleanliness in the orchard, the removal
of all diseased portions of the plants, and spraying with the
Bordeaux mixture, will almost eliminate the disease.

389. Chestnut Blight, or Bark Disease of the Chestnut. —
This disease has been known for only a few years, but it
threatens to destroy every chestnut tree in the United
States. The damage already done is estimated at from
$60,000,000 to $75,000,000, and no remedy so far tried has
been of any avail. The government authorities, with aid
from various states, are making efforts to eradicate the dis-
ease, but it has obtained such a start in some regions that all
hope of saving the forests has been given up. The fungus
grows in the outer layers of twigs, stems, and trunks, and
gradually kills the tissues around the part affected ; this
causes the death of all the parts of the tree above the dis-
eased region. The diseased parts show a characteristic light
brown color, but before long all the affected tissues shrivel.
Through the cracks thus produced, as well as through the
natural openings in the bark, short branches of the fungus
grow outward and produce spores which spread the disease.
Spores produced in sacs appear during the autumn ; but the
spore sacs may continue to be formed for a long time, some
having been obtained from tissues eighteen months after
the diseased condition was first noticed. A Japanese chest-
nut seems to be immune to the disease, and efforts are being
made to secure hybrid forms which may also be immune.

390. Smuts. — These very common diseases produce
black, powdery masses upon the Indian corn and upon
various other grains and grasses. The swellings, caused by

386

TEXTBOOK OF BOTANY

corn. Notice the immense size
of the diseased kernels. The
dark portion of the figure repre-
sents masses of escaping spores.

the corn smut are sometimes as
large as a man's fist ; they occur
on the stem, leaves, or roots, in
the ears or in the tassels. A
large part of an ear, or even a
whole ear, may be replaced by
the black masses. The fungus
that causes the disease is made
up of branching threads which

FIG. 219. -A smutted ear of grow between the cells of the
host plant and send branches
into the cells to obtain food.
The fungus does not kill the
host cells at once ; on the con-
trary, it stimulates many of them to rapid growth and
division, thus causing the appearance
of a swelling. The host cells are finally
killed, and then the fungous threads
divide into very short cells which be-
come dark, thick-walled winter spores.
These spores may germinate in any
moist place, producing a short, thread-
like plant of four or five cells, each of
which in turn may give rise to small
thin-walled spores (sporidia), which
when they are carried to a corn plant

cause a new infection. The corn smut

~. , . , FIG. 220. — .-

affects only the tissues in the neighbor- nated winter spore of the

hood of its place of entrance. The corn smut, the short plant
only method known for -controlling ™hi_ch f ™s ^rom the
this disease is to remove and destroy
all the swellings before the winter this plant bears,
spores are 'formed. *"& sporidium. C a

_, . spondium which is bud-

The common loose smut of oats can ding to form a new sporid-
infect the oat plant only when it is a ium.

and the small
(sporidia) which
B, a

PLANT DISEASES

387

very young seedling. The fungus grows with the growth of
the host, forming its spores in the young oat kernels ; finally
the kernels and the chaffy scales enclosing them are largely
replaced by masses of the winter spores. The oat smut can
be controlled by treating the seed grain in such a way (for
example, with formaldehyde or hot water) as to kill the
spores that adhere to the grain, without killing the grain
itself. The stinking smut of wheat, so called because of
its disagreeable odor, like
the oat smut forms its
spores in the kernel, but
it does not entirely de-
stroy the kernel or the
surrounding chaff.

The damage done by the
corn smut in the United
States has been estimated
at $50,000,000 per year.
The oat smut causes an
estimated yearly loss in
the United States of
about $35,000,000. The
stinking smut formerly
destroyed from one-half
to three-fourths of the
wheat crop. The loss
has been greatly decreased by treating the seed grain, but is
still considerable in parts of the United States and Canada.

391. Common Scab of Potato. — This disease is found
wherever the potato is grown. It produces rough, scabby
spots on the surface of the potato, which are often deepened
by larvae and insects. The fungus may live in the soil
for years, and the tubers may become diseased at any time
during the growing season. For these reasons it is neces-
sary to practice long rotations and to plow under green

FIG. 221. — .4, the head of a healthy
oat plant. B, the head of an oat plant
attacked by the loose smut.

388

TEXTBOOK OF BOTANY

crops in order to eliminate the disease. It has been found
that lime, ashes, and horse manure tend to increase the
growth of the fungus. Care must be taken to use only dis-
infected potatoes for planting.

392. Peach Scab. — This is a common and well-known
disease, found on almost all second- and third-grade peaches

FIG. 222. — A potato leaf at-
tacked by the early blight.

FIG. 223. — A bean plant inoculated
with the imperfect fungus which causes
anthracnose — a disease which is at times
very serious, attacking the younger parts
of the stem, the leaves, and the pods.

and apricots. It causes small, circular, dirty spots over
the greater portion of the fruit. If the spots are very nu-
merous, the skin of the fruit is likely to crack, making pos-
sible the entrance of decay-producing fungi. This disease
is often associated with the brown rot of the peach and some-
times causes equal loss to the grower. Leaves and twigs
may also become infected ; the fungus may continue to live
in the twigs for several years and so be a continual source of
spread of the disease. The means of control suggested for

PLANT DISEASES 389

the brown rot are also successful with the scab, and the im-
mense losses of past years are not apt to occur in the future.
393. Early Blight of the Potato. — This disease may at
times cause almost as much damage as the more dreaded late
blight already described. It causes brownish spots on the
leaves, around which appear concentric lighter rings. When
the spots become enlarged the leaf dies, and thus, since the
food supply is reduced, the tubers produced are usually
small. The same fungus also attacks the tomato, causing
a smaller crop of this fruit. Spraying will check the disease
except under very unfavorable conditions. The peach leaf
curl, stem rot of the clover, root rot of tobacco, canker of
currant and gooseberry, ergot of rye and timothy, leaf spot
of the strawberry, apple scab, bitter rot of the apple, blight of
ginseng, dry rot of the potato, flax wilt, and the anthracnose
of the bean are other plant diseases of considerable economic
importance.

APPENDIX I
DIRECTIONS FOR LABORATORY AND FIELD WORK

Many plants will grow readily in the classroom, adding to its
attractiveness, and at the same time furnishing material for study
and experiment. They may be grown either in pots or in window
boxes ; the latter can be bought or easily made. Good loamy
soil with plenty of humus should be used. The following plants
are quite hardy and should be tried before an attempt is made to
grow others which may prove much more difficult : Geranium,
Pelargonium, Begonia, umbrella plant, ferns, Vinca, wandering
Jew (Tradescantia) , rubber plant (Ficus), century plant, and
various cacti.

Methods of making simple aquaria for the cultivation of algae
and other water plants are described in Hodge's Nature Study and
Life.

CHAPTER I

See the footnote on page i . Should the flowers of squash, pumpkin,
or cucumber not be available at the time this chapter is taken up, some
other reasonably simple flower may be used — such, for example,
as the buttercup, anemone, crocus, hyacinth, lily, strawberry, morning-
glory, petunia, or tomato. In case such a substitution is made, it
will be necessary for the teacher to modify the directions here given so
far as they apply to the flowers.

1. Put some squash or pumpkin seeds into lukewarm water and
leave them in the water over night. Examine these soaked seeds
and compare them with unsoaked ones.

2. Notice the scar at the pointed end of a seed. What caused
it ? In one end of the scar and a little to one side of the point of
the seed, find a deep hole or depression, the micropyle. If there
is more than one depression, the micropyle is the deepest. How
far into the seed does the opening of the micropyle go?

392 TEXTBOOK OF BOTANY

3. Remove the seed coat. Can you see that it is composed of
more than one layer? Just within is the thin, green, papery en-
dosperm. Remove this. All that now remains belongs to the
embryo.

4. Carefully cut away one of the thick seed leaves of the embryo.
There remains the second seed leaf, and attached to it are the radicle
and plumule. Which of these two is larger? Which is turned
toward the micropyle?

6. Examine the plumule with a hand lens. It can be studied
better in seeds that have been soaked for two or three days. How
many small leaves does it bear ?

6. Cut another seed lengthwise in such a way that each seed
leaf will be cut through the middle. Draw one of the cut surfaces,
showing the seed coat, endosperm, seed leaves, plumule, and
radicle.

7. Plant some seeds, which have been soaked over night in cold
water, an inch below the surface of moist sand or sawdust. After
the first two or three days pull up a seed or two each day and study
the way in which they germinate.

8. Where does the seed coat crack when the seed germinates?
Which part of the embryo pushes out first? Which way does it
turn ? Study the growth of the embryo into a seedling ; what
changes take place in each part of the embryo? Study the way
in which the seed coat is finally pushed off.

9. Draw in outline three young seedlings at different stages in
their development.

10. Sow some cucumber seeds in moist sand. After a seedling
has developed one or two secondary leaves, wash off the sand or
sawdust very carefully from the root system. To what parts of the
roots does the sand or sawdust stick most closely? Why? Can
you tell by examination where the stem ends and the root begins ?

11. Can you distinguish the primary root from the branch roots ?
Do the latter also branch? Lay the plant down, spread out the
roots as flat as possible, and sketch the root system.

12. Study the root hairs of a very young seedling from a seed
germinated between pieces of moist filter paper or blotting paper.
Can you see the hairs with the naked eye ? Examine them with a
hand lens. On what part of the root do they grow?

LABORATORY AND FIELD WORK 393

13. Examine a full-grown leaf from an older plant. What is
its shape? What are the parts of the leaf? What differences do
you find between the upper and lower surfaces? Study the veins
and the way in which they branch. Notice that they form a fine
network. Study the hairs with a hand lens. On what parts of
the leaf do you find them? On what parts are they most numer-
ous ? Where are the largest hairs borne ?

14. What is the shape of the stem ? Is it solid or hollow ? How
are the leaves arranged on it ? Can you find a bud in the axil of
each leaf ? Where are the branches attached to the stem ? Where
are the tendrils attached?

15. Draw a portion of the stem and two successive leaves at-
tached to it, with the axillary buds. Show the veins in one leaf.

16. Examine the bud at the end of the main stem or of a branch.
Tear it apart carefully. Of what parts do you find it composed?
How many young leaves do you find in it?

17. Remove the parts, one by one, from a pistillate flower ; from
a staminate flower. Draw the circle of sepals so removed, cut in
one place and spread out flat ; draw the circle of petals in the
same way ; a pistil, naming the parts ; a stamen, naming the parts.

18. Follow from day to day the development of the ovary into
a fruit. Cut a ripe or nearly ripe fruit crosswise and draw one
of the cut surfaces, naming the parts.

19. Make a list of the different varieties of cucumber and of
squash grown in your locality. What are the important points of
difference between them?1 What particular advantage has each
variety, and for what special uses is it best suited ?

CHAPTER II

1. Place some hay in a dish of lukewarm water, cover it, and
put it in a warm place. After two or three days examine a very
small drop of the water under the high power of the microscope.
It will be found to contain a great many organisms of different
sorts, among them some having the shape of short rods with rounded
ends. Most of these are probably cells of Bacillus subtil is. Are
they colored? Some are swimming actively, others are quiet.
Describe their movement.

394 TEXTBOOK OF BOTANY

2. Examine a rod that is not moving. Little can be seen of
its structure because of its small size. You will observe that it
does not change its shape, being kept rigid by the cell wall. Does
the protoplasm appear granular? Draw a cell.

3. Study the rows or chains of cells. How are the chains formed ?
Are the ends of individual cells rounded or flattened? Draw a
chain in outline, showing the cell boundaries.

4. Examine a bit of the scum that forms on the surface of the
infusion after a few days. In it will be found many bacteria held
together by a sticky substance. Are the cells moving or quiet?
Are they single or in colonies ?

6. Look for bacteria of other forms in the infusion. They are
more likely to appear after some days. Draw in outline such
forms as you find, on the same scale as your previous drawings.

6. In the scum from an old infusion, look for chains of cells in
which spores are being formed. Draw such a colony if you find
one.

7. What causes the unpleasant odor that the infusion gives off?

8. Boil a good-sized potato with its skin on for fifteen or twenty
minutes. Then, with a clean, sharp knife that has been sterilized
in a flame, cut the potato into thin slices, being careful not to touch
the cut surface with the fingers. Seven petri dishes and covers
must be prepared in advance. Each should be carefully washed
and then boiled in clean water while the potato is boiling. When
the potato is ready to slice, remove the petri dishes from the water
one at a time, pour out the water and place in the bottom a piece
of perfectly clean filter paper which, if possible, has been sterilized
by heat in a dry oven for a half -hour. Dip the paper into the
water in which the petri dishes are boiled. Handle dishes and
paper with stout fofceps which have also been sterilized in a flame.
Place a slice of potato in each petri dish on the filter paper and
cover at once. All this work must be done as quickly as possible.

9. Leave one dish covered. Uncover a second one and leave
it exposed to the air of the room for a half hour, then cover it again.
Uncover a third one long enough to make a scratch on the surface
of the potato with a needle that was first sterilized, then dipped
into a hay infusion. The fourth potato slice should be inoculated
in the same way with material from the floor of the room.

LABORATORY AND FIELD WORK 395

10. The four dishes now accounted for should be numbered and
kept on a shelf or other convenient place in the room, not in the
direct sunlight, where they may be examined from day to day.

11. Inoculate the three remaining slices from some fresh milk.
Place one of these in a window where it will receive as much direct
sunlight as possible, one in a dark closet or other dark room, and
the third in an icebox.

12. Examine all the cultures carefully, without removing the
covers, once a day for a week; make a full record of all that you
observe in each culture with respect to the following points :

a. The appearance of spots (bacterial colonies) on the surface of the

potato. Compare with Figure 10, page 24.

b. The color of the spots.

c. Their shape, and growth from day to day. Some of the spots

may develop a fuzzy appearance. Examine these with a hand
lens. If a spot contains fine threads, it is not composed of
bacteria, but of a mold, belonging to a higher order of plants.

d. Changes in the appearance of the potato due to the action of the

bacteria.

13. What do you conclude from these experiments as to :

a. The presence of bacteria in the air ? In the dust on the floor ?

In milk ?

b. The rate of multiplication of bacteria ?

c. The effect of sunlight on the development of bacteria? Of

darkness ? Of heat ? Of cold ?

14. Examine under the microscope bacteria from your different
cultures. Note the different shapes and sizes that you find.

15. Why are the care and inspection of city water supplies ex-
tremely important?

16. What serious disease is especially likely to be carried by
impure drinking water?

17. How may impure water be treated to make it safe for drink-
ing?

18. Why should living and sleeping rooms have abundant sun-
light and fresh air?

19. Why are tuberculous patients kept in the open air as much
as possible?

396 TEXTBOOK OF BOTANY

20. What kinds of floor coverings (carpets, rugs, linoleum, cork,
or simply hardwood flooring) are best for rooms used by large num-
bers of people ? Why ?

21. Why do many cities and some states require the testing of
cattle for tuberculosis ?

22. Why should the surface of a wound be kept open^for a time
instead of being allowed to heal over as soon as possible ?

23. Why do teeth that are not kept clean decay?

24. What substances are used as " antiseptics "? How are they
used?

26. Why are milk, meat, and other foods kept in refrigerators
in warm weather?

26. Why are fruits and vegetables heated or boiled before being
canned ?

27. Why must the cans in which they are placed be tightly
sealed?

28. Why do preserves containing a large proportion of sugar
keep well without being tightly sealed?

CHAPTER III

1. Observe the greenish patches on the bark of 'trees or on the
shaded parts of a stone wall. How is the green substance dis-
tributed? Is it a thin or a thick layer? Is it more abundant on
one side of a tree than on another? Why? Can you scrape it
off in sheets? Remove some of the material, bring it into the
laboratory and place it in a damp place or sprinkle it with water.
What changes take place in its appearance?

2. Mount a small portion of the green material in water, tear it
apart carefully and examine it under the microscope. Look for
small green cells which are alone or in twos or fours. These are
cells of Protococcus. Do you ever find more than four cells in a
colony ? If so, are they all in one layer ?

3. Can you see that each cell is surrounded by a transparent
wall ? This appears most • clearly on the sides where two cells are
attached to each other.

4. Is the green color scattered all through the cell? If not,
can you see that it is contained in a body (the chloroplast) with a
definite outline?

LABORATORY AND FIELD WORK 397

5. Draw a single cell, showing all the parts that you can see.

6. Draw in outline colonies of two and of four or more cells.

CHAPTER IV

Baker's yeast or any of the various yeast cakes or fresh compressed
yeast may be used for this study. Brewer's yeast, if it is to be had, is
preferable, and especially " top " yeast, which has rather large cells.
In many places, however, top yeast is not readily obtainable.

1. Into a battery jar or other convenient glass jar containing
molasses solution (one part of molasses to ten parts of water), drop
a cake of compressed yeast or a similar amount of whatever yeast
is used. Cover the jar, set it in a warm place, and observe it as
often as possible for two or three days.

2. Soon, probably within a few hours, bubbles of gas will be
seen rising to the surface of the liquid. What changes take place
in the appearance of the liquid? Does it remain clear? Does a
scum form on the surface ?

3. Notice the odor of the liquid after a day or two. To what is
it due ?

4. When the bubbles are rising freely, mount a drop of the liquid
and examine it under the microscope. It will be found to contain
yeast cells, some single, some in chains.

5. Study a single cell. What is its shape? Compare it as to
size with the bacillus and Protococcus already studied. Is it
colored? Has it a wall? What is the appearance of the proto-
plasm? Are any bodies visible in the protoplasm? Have any of
them a noticeable color? There may be one large, clear space (a
vacuole), or perhaps two or three small vacuoles.

6. Draw a cell on a large scale, showing all the parts that you
can see.

7. Find a cell that has a small projection (a bud) at one end.
Find others, showing buds of different ages. What does a bud
finally become? How, if at all, is it separated from the larger cell
with which it was at first connected?

8. Draw in outline three stages in the development of buds.

9. Do you ever find more than two cells connected? Draw in
outline the largest colony you find.

3Q8 TEXTBOOK OF BOTANY

10. Immerse a funnel in a battery jar containing an active
yeast culture, the upper (small) end of the funnel being just below
the surface of the liquid. Insert a test tube filled with the same
solution over the open end of the funnel, so that the open end of
the tube is below the surface of the liquid in the jar. If this is
carefully done, the tube remains filled with the liquid. Fasten it
in this position. Bubbles of gas will rise in the tube and displace
the liquid. When most of the liquid is displaced, turn the tube
containing the gas right side up. Light a splinter and insert it
into the tube. What happens to the light? Why? What is
the gas in the tube ?

11. Place another active yeast culture in a wide-mouthed bottle.
Cork the bottle. Through the cork pass a bent tube, one end of
which is above the surface of the yeast culture, and the other end
of which dips into some lime-water in a tumbler. The gas formed
by the yeast will pass into the lime-water. What changes take
place in the appearance of the lime-water? Why?

12. Prepare three jars with molasses solution and yeast. Cover
one with dark paper so as to shut out all the light and keep it be-
side your first culture (described in § i).

13. Place a second in a cool place — in an ice box if one is
available.

14. The third jar should be washed thoroughly in boiling water,
and the solution for this jar should be boiled for five minutes after
the yeast is added but before placing it in the jar. After the solu-
tion is placed in the jar, cover it tightly and place it beside the first
culture.

15. Watch the different cultures and make careful notes of the
results, comparing them with the first culture. What do you con-
clude as to the following points :

a. Does darkness or light affect the activity of the yeast ?

b. Does cold affect it ?

c. What happens to the yeast when it is heated to the boiling point ?

Compare with bacteria in this respect.

16. Place some yeast in molasses to which no water has been
added. Keep it in a warm place. Does fermentation take place ?
Why?

LABORATORY AND FIELD WORK 399

CHAPTER V

1. Examine a mass of Spirogyra growing on the surface of a jar
of water in bright sunlight. How do the plants feel to the touch ?
What is their color? Notice the bubbles of gas tangled among
the plants.

2. Compare a similar culture which has been kept in the dark
for at least twelve hours. Are the plants on the surface of the
water, or at the bottom ? Why ? Do the plants differ in appear-
ance in any way from those that have stood in the light ?

3. Disentangle from the mass a single thread-like plant or as
large a part of one as possible. How long is the thread? Is it
branched ?

4. Examine a plant under the microscope. Notice that it is
made up of cells joined end to end. Are the cells alike in length ?
In thickness ? What is the shape of a cell ?

6. Study a single cell, noting the parts mentioned below. Some
of these parts can be seen more clearly if the plant is placed for a
short time in a weak solution of iodine in potassium iodid. This
kills the living materials of the cell and stains them yellowish-
brown. However, the cell should first be studied while alive, and
everything possible observed in the living condition.

a. The outer wall.

b. The cross wall between two adjoining cells ; compare this with the

outer wall.

c. The layer of slimy cytoplasm, containing granules. Is it in

motion ?

d. The green chloroplast or chloroplasts. What is the shape of one ?

Can you trace it from one end of the cell to the other ? Where
does it lie with reference to the wall ? Where does it lie with
reference to the slimy cytoplasm ?

e. Colorless bodies (pyrenoids) imbedded in the chloroplast. In the

iodine solution a blue or blue-black color will appear just outside
each pyrenoid ; if the iodine acts long enough, the color may
become so dense that the pyrenoid itself appears to be stained.
What is the meaning of this blue color ?

/. The nucleus, a rather dense spherical or ellipsoidal body at or
near the center of the cell ; it contains a globular, somewhat
brighter body, the nucleole.

400 TEXTBOOK OF BOTANY

g. A thin film of slimy cytoplasm just outside the nucleus.

h. Strands of slimy cytoplasm running in all directions from the layer

about the nucleus to the layer just within the wall.
i. The central vacuole. What is its shape ? What does it contain ?
j. Draw very carefully a single cell, naming all the parts.

6. Place a number of plants in alcohol in a test tube. Close the
end of the tube with a cork and set it away. Examine it the next
day. Is the alcohol colored? Lift the plants out of the alcohol.
Are they still green ?

7. Examine one of these plants under the microscope. Are the
chloroplasts still present in the cells? What is the relation of the
chloroplasts to the green coloring matter (chlorophyl) ? What has
happened to the chlorophyl ?

8. In a large glass jar that stands in a sunny place and contains
a vigorous culture of Spirogyra in water, completely immerse an
inverted funnel, so that all the plants are held within or below
the larger end of the funnel. Invert a test tube full of water so
that its open end fits over the neck of the funnel, and fasten the
tube in this position. The bubbles of gas formed by the plant
will rise and replace the water in the test tube. When the tube is
filled with gas, remove it and insert into it a glowing match or
splinter. If the experiment is successful, the glowing end of the
match or splinter will burst into flame. What does this show as
to the nature of the gas in the test tube ? How was this gas pro-
duced by the plant ?

9. Determine by a similar experiment whether or not the same
gas is produced by plants kept in darkness.

10. If living plants in process of conjugation are available, they
should be used for the following study. Otherwise, material pre-
served in alcohol or formalin may be used. Notice that two plants
place themselves parallel for part or all of their length. Study the
following steps in the process of conjugation :

a. The appearance of a swelling on the side of each cell which is

turned toward the other plant.

b. The growth of these swellings from two cells, one in each plant,

until they touch each other.

c. The disappearance of the walls of the swellings at the point where

they meet ; the two swellings now form a continuous conjuga-
tion tube.

LABORATORY AND FIELD WORK 401

d. The gradual contraction and rounding up of the respective cells

(gametes). What parts of the cells take part in this rounding
up ? Do the two gametes begin to contract at the same time ?

e. The passage of one (the male) gamete through the tube into the

cavity occupied by the other (the female).
/. The union of the two gametes into a single rounded cell (the

zygote).
g. The formation of a thick wall about the zygote. Notice that the

zygote occupies less space than was filled originally by either of

the two gametes that have united to form it.

11. Should the material at hand show the lateral method of
conjugation — which is less common than the method above de-
scribed — the conjugation tube will be seen to be formed between
two adjacent cells of the same plant instead of between cells of two
different plants.

CHAPTER VI

1. Place a slice of moist bread (not wet enough to be soggy) in
an evaporating dish; leave the dish uncovered for a half -hour;
then cover it and let it stand in a moderately warm place. If the
surface of the bread seems to be drying out at any time, add a little
water. In the course of one or two days fluffy spots will appear
on the surface of the bread ; in a day or two more, the molds which
cause these spots begin to form spores, and the spots take on a
more powdery appearance. Among these molds Rhfeopus is almost
sure to be one ; it can be recognized by the presence of stout upright
branches at the top of each of which is a globular spore sac.

2. If Rhizopus is overgrown by other molds, as sometimes
happens, it will be best to prepare a practically pure culture. This
can be done by transferring from the first culture, by means of
sterile forceps, a small amount of the mold bearing spore sacs
to a slice of bread that has been freshly cut with a sterile knife,
moistened with boiled water, and placed in a sterilized evaporating
dish which is kept covered.

3. Study the young spots on the bread with a hand lens. Notice
that each spot consists of a tangle of branched threads, white or
grayish while young. There are two kinds of branches — some
that grow horizontally along the surface, and some that grow
downward into the bread.

402 TEXTBOOK OF BOTANY

4. Describe the arrangement of the branches and the relation
of the two kinds to each other. Do the branches differ in size?
Is a single branch of the same diameter throughout its length?
Which kiryi digests and absorbs food from the bread? By means
of which kind of branches does the plant spread over the bread ?

5. Somewhat later, upright branches appear. Where do they
grow from? What do they bear at the upper end? Of what use
are they to the plant? What is the advantage of their upright
growth ? ,

6. As the mold grows older, what changes take place in its
appearance? What changes occur in the bread? What has
happened to the starch and other solid substances in the bread ?

7. Mount in water a small part of a young mold plant. Ex-
amine a branch under the compound microscope. Is it made up
of small cells like a thread of Spirogyra ? Find the following parts,
comparing each with the corresponding part of a Spirogyra cell :

a. The cell wall.

b. The granular protoplasm. What is its color?

c. Vacuoles. Are they of the same or of different sizes ?

d. Oil drops, similar to the smaller vacuoles, but yellowish in color.

8. Compare, - with reference to all the parts named above, a
branch from an older mold plant.

9. Draw on a large scale a small portion of a branch of a young
plant, naming all the parts.

10. Sketch different stages in the growth of an upright branch
and in the formation of the spore sac at its upper end.

11. Crush under the cover glass a mature spore sac. Note :

a. The outer wall, which breaks under a very slight pressure.

b. The numerous spores which have been enclosed within the wall of

the sac. Are they all of the same shape ? Of the same size ?

c. The dome-shaped central portion of the spore sac, surrounded by

a wall that is attached to the remaining basal part of the wall
of the sac.

12. Study a single spore under the high power. What can you see
as to the structure of its wall ? Of its protoplasm ? Draw a spore.

13. Spores may be germinated in the course of a day or two in a
good-sized drop of water on a slide. The slide should be kept on

LABORATORY AND FIELD WORK 403

moist filter or blotting paper under a battery jar or in a covered
evaporating dish, so that the water on the slide will not evaporate.
In such a culture find spores and young plants showing different
stages in germination and growth.

14. Notice that germination begins by a swelling of the spore;
next there appears a projection (or sometimes two or three pro-
jections) on the surface of the spore. Follow the growth of a
projection. Into what does it develop? How long is it before
the first branch appears ?

15. Make outline drawings of three stages in the germination of
the spore.

16. If spores from plus and minus strains of Rhizopus l are
mixed and sown upon bread, gametes and zygotes will be formed
at the places where branches from plants of the two strains come in
contact. Or if a culture of Sporodinia (the mushroom mold) can
be obtained, it will be found to produce gametes and zygotes, be-
cause in this mold conjugation occurs between gametes formed
on different branches of a single plant.

17. Notice the outgrowth of swellings from two neighboring
branches. The swellings grow into short branches whose ends
are in contact. Look for the following stages :

a. Cell division, resulting in the formation of a gamete at the end

of each short branch.

b. The disappearance of the walls of the gametes where they touch

each other.

c. The union of the gametes into a single cell — the zygote.

d. The growth and rounding up of the zygote.

e. The formation of a thick wall about the zygote. Is this wall

smooth ? What is its color ?

18. Are the short branches which bear the gametes alike?
Are the gametes themselves alike ?

19. Compare conjugation in the bread mold> and in Spirogyra.

20. Draw a ripe zygote with the short branches which hold it,
showing the attachment of the latter to the longer branches of the
parent plant or plants.

1 Cultures of the separate strains may be obtained from some of the companies
that supply plant materials for class use.

404 TEXTBOOK OF BOTANY

CHAPTER VII

Barberry leaves should be collected when the cluster cups are at
their best — in ordinary seasons in April or May. The leaves may be
pressed and dried for class use. Collect rusted wheat and other grains
during the summer and fall. Cedar apples may be gathered during
the fall and winter ; the infected leaves of apple, crab, and hawthorn
in the early summer months.

1. Study infected barberry leaves and note the position and size
of the diseased areas. What is their color ? Are the leaves swollen ?
With a hand lens study carefully the diseased spots. What differ-
ences do you find between the spots on the upper and those on the
lower surface of a leaf ? Draw a portion of the upper and a portion
of the lower surface, showing the spots.

2. Under the microscope study a cross section of a barberry leaf.
On the lower surface find a cluster cup. What is its boundary?
How are the spores (spring spores) borne in the cup? What is
the shape of a spore ? Draw a spore.

3. In the upper surface of the leaf do you find cavities in which
small spore-like cells (spermatia) are produced? (The spermatia
themselves, being very small, will probably not be seen.)

4. Study rusted wheat stems and leaves. What is the shape and
size of the patches (sori) in which the rust spores are borne ? Com-
pare a sorus with a cluster cup. Do the sori differ in color? If
so, how? Draw a sorus.

6. Extract a portion of a light-colored sorus and examine it in a
drop of water under the microscope. Study the summer spores ;
if possible, find one still attached to its stalk. Draw a spore on
the same scale as your drawing of the spring spore.

6. Examine in the same way some winter spores obtained from
a dark-colored sorus. Compare a winter spore with a spring spore
and a summer spore as to size, shape, color, and thickness of wall.
Draw a winter spore on the same scale as your drawings of the
other spores.

7. Compare the rust of some other grain with the wheat rust.
Are the sori similar in all respects? Do you find summer spores
and winter spores ? Are they different in any way from the corre-
sponding spores of the wheat rust ?

LABORATORY AND FIELD WORK 405

8. Soak a cedar apple in water for a few minutes, then place
it on moist filter paper or blotting paper and cover it' with a tumbler.
Examine it after a few hours ; note the finger-like projections that
it has pushed out. Mount a small bit of one of these projections
in water and study it under a microscope. It will be found to
contain spores. Which kind of spores of the wheat rust do those
in the cedar apple resemble ?

9. Compare the cluster cups of the rust on the apple (or of the
very similar rusts on the crab-apple or hawthorn) with those of the
rust on the barberry. What differences do you find?

CHAPTER VIII

It is not necessary, though preferable, to study in the laboratory the
same species of mushroom that is described in the text. Mushrooms
of various kinds may be gathered at any time during the summer or
fall, and are readily preserved in 70 per cent alcohol. Be certain
to obtain portions of the vegetative threads. Fresh horse- or cow-
dung, placed in a battery jar and covered, will produce a good crop
of mushrooms for class study in from ten to fourteen days. Mush-
room spawn, readily obtained from dealers, may be' planted and will
give abundant material for study, if the necessary conditions for its
cultivation are at hand. Directions for planting and for the care of
a mushroom bed are given with the spawn purchased. Atkinson's
Mushrooms, Edible, Poisonous, etc. has an interesting chapter on the
cultivation of mushrooms.

1. Examine material that shows various stages in the develop-
ment of fruiting bodies. Notice the thread-like underground
vegetative portions of the plant. Find also swellings ("buttons")
of different sizes.

2. Cut one of the larger buttons in half from top to bottom ;
what structures do you find inside ?

3. Study the way in which the buttons develop into fruiting
bodies. By means of sections made as above described, follow
the development of stalk, cap, and gills. Sketch sections showing
two stages in development.

4. Study a full-grown fruiting body. Notice :

a. The shape, size, and color of the cap. Does it bear scales ? What
is the color of the flesh when it is freshly broken ? Does the
color change after it is broken ?

406 TEXTBOOK OF BOTANY

b. The shape and arrangement of the gills; their color. Does the

color change as the fruiting body grows older ? If so, can you
find what causes the change ?

c. The shape, size, and color of the stalk. Is it smooth or scaly?

Is it solid or hollow? How is the cap attached to the stalk?
Is the stalk always perfectly vertical ? If not, is the cap hori-
zontal or tilted ? Of what advantage is it to have the cap
carried up above the ground ?

d. Is there a ring ? A cup ?
6. Sketch a fruiting body.

6. Place a small portion of a gill in water, crush it slightly, and
examine it under the microscope. Notice that it is made up of
delicate branching threads. Look for swellings (basidia) at the
outer ends of some of the threads. Do you find spores? What
can you make out as to their formation? Draw a portion of a
branching thread ; a basidium (if seen) ; a spore.

7. Cut off the stalk of a full-grown living mushroom ; place the
cap gill-side downward on a sheet of smooth paper and cover it
with a tumbler or battery jar. After a few hours examine the spore
print. What is the color of the spores? How are they arranged
on the paper? What is the cause of this arrangement? (It will
be well to use both light-colored and dark paper unless one is sure
in advance of the color of the spores.)

8. Observe mushrooms growing in a dung culture. Compare
them in all respects with the mushroom already studied. Can you
determine what special means any of them have to secure the dis-
tribution of their spores?

9. Compare any other mushrooms that you can obtain with
those already studied. If possible, examine one of the poisonous
Amanitas ; notice the ring near the top and the cup-like swelling
at the base of the stalk.

10. Study the manner of growth of the fruiting body of a bracket
fungus. Notice especially the structure of the lower surface.
How and where are the spores borne ?

11. Make a list of the mushrooms and other basidium fungi that
you find growing.

CHAPTER IX

Any common species of moss will do almost equally well for this
study ; different species may be used, if it is found more convenient,

LABORATORY AND FIELD WORK 407

for the study of different organs and different portions of the life history.
It should be noted, however, that any other moss will differ in details
from the one described in the text. Moss spores can be germinated
without much trouble on moist bricks or tiles. Germination is slow
and may require several weeks.

1. Examine a "moss plant." Of what parts is it composed?
In .what position does it grow ? Does the stem branch ?

2. How are the leaves arranged? What is the form of a leaf,
as seen under a hand lens ? Can you see veins ? Are there differ-
ences between the leaves borne on different parts of the plant?
Draw a leaf in outline.

3. What differences do you find between male and female heads
— that is, the ends of stems or branches on which antherids and
archegones are borne? Tear apart a head of each sort. How are
the sex organs arranged? What other structures do you find in
the heads? Sketch an antherid and an archegone. How many
gametes are borne in each ?

4. Examine different stages in the development of the asexual
plant. How does it secure its food? How is it attached to the
sexual plant ? What is the origin of the cap that is carried for a
time on the top of the asexual plant ? How do the spores escape
when they are ripe ? Draw a sexual plant to which an asexual
plant is attached, naming all the parts of each.

5. Press out the spores from a ripe spore sac and examine them
under a microscope. What is their shape? Their color?

6. If material is available, study and draw a portion of the pro-
tonema, which has grown from a germinated spore. This is the
first stage in the history of the sexual plant. Can you discover
how the leafy branches (commonly known as "moss plants") arise
from the protonema ?

7. Find as many different kinds of mosses growing out of doors
as possible. In what sort of places does each kind grow?

CHAPTER X

For this, as for some of the preceding studies, it is not necessary to
use the species described in the text, though this is preferable. The
bracken fern is to be found growing almost everywhere. The leaves
and stems may be dried ; it will be well also to preserve parts of spore-

4'08 TEXTBOOK OF BOTANY

bearing leaves in 70 per cent alcohol or in 4 per cent formalin for the
study of the spore sacs and spores. The sexual plants may be obtained
by sowing spores in late summer or fall upon damp soil, sand, peat, or
sphagnum, which should first be sterilized by heating in an oven, if
possible, and after the sowing kept moist (but not wet). It is best to
sow the spores of several species, since there are great differences in
germinating power. Germination may require several weeks, or in the
case of some species several months. Sexual plants can also be ob-
tained from dealers in botanical supplies.

1. What are the parts of a fern plant? What is their relation
to one another ? Which are the longer-lived parts ? How does
the stem branch ? Are all parts of the stem alive ?

2. Can you find the growing end of the stem or of a branch?
What parts do you find at or near the growing end ?

3. Cut across a stem between the points where two leaves
are given off. Study the cut surface of the stem with a hand
lens and sketch it. What different tissues can you make out?
How many vascular bundles are present ? Are they of the same
size?

4. Where are the roots borne? Where are the youngest roots?
What is the shape of a root ? Its length ? Does it branch ?

5. Where are the younger leaves to be found? What is the
appearance of the youngest leaf you can find ? How do the leaves
change as they grow older? Are there portions of dead leaves still
attached to the stem?

6. What are the parts of a full-grown leaf? Does it bear hairs
or scales? If so, where? Describe the structure of the leaf -blade.
Draw one of the smallest divisions of a leaf, showing the arrange-
ment of the veins.

7. Peel off a portion of the epidermis (outer layer of cells) from
the lower surface of the leaf and examine it under the microscope.
Do you find air-pores? Are they few or many? Do the guard
cells differ from the other cells of the epidermis in shape, size, or
color ? Draw an air-pore with a few of the neighboring cells.

8. Where .are the spore sacs borne? Are they single or in
groups? How are they protected? Examine and draw a spore
sac. What are its parts? By alternately moistening and drying
a ripe spore sac, try to induce it to open under a microscope and to

LABORATORY AND FIELD WORK 409

observe how the spores are thrown out. Examine some of the
spores. How do they compare with the spores of a moss ?

9. Study the sexual plant of a fern. What is its shape? How
large is it ? Which is its oldest part ? Its youngest part ? Where
are the rhizoids ? What is their work ?

10. Where are the antherids? The archegones? Are there
few or many of each? Draw a sexual plant as seen from the
under side, showing the positions of the rhizoids, antherids, and
archegones. Look for moving antherozoids ; they will break out
of the ripe antherids if the sexual plant is placed in water.

11. If material is to .be had, study a young asexual plant still
attached to the sexual plant. Can you find the primary leaf,
primary root, young stem, and foot? How does the primary leaf
compare with the leaves that are formed later ?

12. Collect and make a list of the different kinds of ferns that you
find growing. In what kinds of places do the different species live ?

13. Make another list of such relatives of the ferns as you find —
water ferns, horse-tails, and club-mosses.

CHAPTER XI

1. Examine branches of a pine tree. Can you distinguish be-
tween long branches and spur branches? Do both kinds grow
longer from year to year? Do both grow thicker from year to
year?

2. Find scale leaves and foliage leaves. Where is each borne?
How do they differ in size, shape, and color ? Draw a twig, show-
ing both kinds of branches and both kinds of leaves.

3. Can you determine by examining a long branch how much of
it has grown during the present year, and how much during each
previous year? What marks the end of each year's growth?
Where do new long branches start ? New spur branches ?

4. Study a cross section cut through a long branch not far back
of the terminal bud. Can you distinguish epidermis, cortex, vas-
cular bundles, and pith? How are the vascular bundles arranged?
What are the parts of a vascular bundle? In which part of a
bundle do you find the largest cells ? Draw a large enough portion
of the section to show the different tissues.

4io TEXTBOOK OF BOTANY

6. Study a cross section through a part of a branch that is three
or more years old. Compare it with the section previously studied.
What changes have taken place in the wood ? In the bast ? Where
are the new cells being formed which add to the thickness of the
branch? What kinds of cells do you find in the medullary rays?
Can you distinguish between spring and summer wood ? Why can
we tell the approximate age of a tree or of a branch by counting
the annual rings? Is bark being formed? If so, can you make
out in the section how its formation goes on? In what parts of
the stem do you find resin passages? Draw a portion of this
section.

6. Where and how are the small staminate cones of the pine
borne ? What are the parts of a cone ?

7. Examine a single microspore leaf torn from a staminate cone.
Do you find pollen sacs ? How many ? Where are they borne ?
Draw a microspore leaf showing the pollen sacs.

8. Break open a pollen sac and examine with a compound
microscope the pollen grains that escape. Draw a single pollen
grain.

9. Compare a young carpellate cone with a staminate cone. Is
it made up of similar parts ? How are the carpellate cones borne-?
On what part of a branch do you find the youngest cones? The
year -old cones ? The ripe cones ?

10. On what part of a macrospore leaf are the macrospore sacs
(ovules) borne? How many macrospore sacs on a leaf? What
parts can you make out in 'a sac? Draw a macrospore leaf, show-
ing the sacs.

11. Compare a year-old cone with the young cone just studied.
What changes have taken place in the macrospore leaves ? In the
macrospore sacs ?

12. Study a still older cone, bearing mature seeds. From what
has each seed developed ? What is the wing-like structure attached
to a seed ? How do the seeds escape from the cone ?

13. "Nut pine" seeds are best for the study of the structure of
the seed. On the outside is a hard coat ; from what did it develop ?
Crack open this coat ; is there an inner seed coat ? Inside find the
endosperm and the embryo. Of what parts is the embryo com-

LABORATORY AND FIELD WORK 411

14. Make a list of the kinds of pines and other gymnosperms
that you find growing in your locality. Which of them are native
plants? Which have been introduced from other parts of the
world ?

CHAPTER XII

1. Watch the growth of the stem of a climbing bean from day
to day and observe how it climbs. Compare this with th'e way in
which tall peas and sweet peas support themselves in an upright
position.

2. Where are branches borne? Do they twine like the main
stem ? Do the branches themselves branch ?

3. How does the blade of a bean leaf compare with that of a
leaf of a cucumber or squash ? What is the arrangement of the
veins in a leaflet ? Draw a leaf and a portion of the stem or branch
to which it is attached, naming the parts of the leaf. Is there a
bud in the axil of the leaf ?

4. Observe the position of the leaves and leaflets after dark.
Compare it with their position during the day. Can you find
other plants growing either in- or out-of-d'oors that show such
differences in the positions of their leases by day and by
night ?

6. What is the form of the root system of the bean ? Can you
recognize the primary root ? Do the roots branch ? Notice es-
pecially the small swellings that are likely to occur at various
places on the roots. What organisms live in the swellings? How
are these organisms important to the bean plant? Draw a small
portion of the root system, showing some of the swellings.

6. In a cross section of the stem can you make out epidermis,
cortex, vascular bundles, and pith? Compare the arrangement
of the vascular bundles with their arrangement in the pine stem.
In what part of each bundle is the wood? The bast? Draw a
portion of the section.

7. Study a cross section of a leaf. Notice the upper and the
lower epidermis. Are the cells of the layer just below the upper
epidermis different in any way from the other cells of the leaf?
What kind of cells make up most of the thickness of the leaf?
Are there spaces between the cells ? In what cells do you find the

4I2 TEXTBOOK OF BOTANY

greater number of chloroplasts ? Where are the vascular bundles ?
How do they compare with the bundles in the stem ?

8. Where are flowers borne? How many flowers does one plant
produce ? Do all the flowers of a plant open at the same time ?

9. Remove, one by one, the parts of a flower. How many sepals
are there? How many petals? How many stamens? What
striking peculiarities do you note in the sepals? In the petals?
In the arrangement of the stamens? Cut away the sepals and
petals from the right or left half of another flower ; draw the re-
mainder of the flower as seen from the cut surface. What are the
parts of the pistil ? Can you find the ovules (macrospore sacs) ?
If so, how many are there ? How are they borne ? Dissect and
draw the pistil.

10. What changes take place in the ovary as it develops into a
fruit? What changes take place in other parts of the flower?
What is the form of the fruit ? How are the seeds borne inside
the fruit? How are they set free? From what did each seed
develop? Draw a fruit from which one-half the fruit coat has
been removed, allowing the seeds to be seen.

11. Put some bean seeds into lukewarm water and leave them
over night. Examine them the next morning and compare them
with unsoaked seeds. On what part of a seed is the scar by which
it was attached ? Where is the micropyle ?

12. Remove the seed coat. Is it composed of more than one
layer? All within the seed coat is the embryo. Why is there
no endosperm? What is the largest part of the embryo? Why?

13. Remove one of the seed leaves and find the plumule and the
radicle. In what direction is each of these parts turned? How
many secondary leaves are borne on the plumule? Draw an em-
bryo from which a seed leaf has been removed.

14. Study the germination of the seed and the development of
the seedling, following §§ 7-9 of the laboratory directions for
Chapter I.

15. Make a list of the varieties of beans that you find in culti-
vation. Which are pole beans and which bush beans? In what
other respects do the varieties differ ?

16. List the other cultivated and wild plants that you find
belonging to the pulse family.

LABORATORY AND FIELD WORK 413

CHAPTER XIII

1. Examine a leaf of the Indian corn. How is it attached to
the stem ? What are the parts of a leaf ? Compare in this respect
with a bean leaf. -How are the leaves arranged on the stem?
How do the upper and lower surfaces of a leaf -blade differ from
each other? What is the arrangement of the veins in a leaf?
Can you find teeth on the edges of the blades ? Draw a leaf show-
ing its attachment to the stem, and the veins.

2. What is the shape of the stem after all parts of the leaves
have been removed? Is the stem thicker below than above?
Compare in this respect with the bean stem. Is it swollen at
any point ? Is it solid or hollow ? Does it branch ?

3. Study the bud at the end of the stem. Tear it apart. How
many and what parts do you find in it ?

4. In a cross section of the stem, see if you can make out the
parts mentioned in § 6 of the directions for the study of the bean.
What differences do you find between the corn and bean stems?
Draw a portion of the section.

6. Compare the root system of the corn with that of the bean.
Do the roots branch? Are any roots produced above the surface
of the ground ? If so, from what points on the stem do they grow ?
How do they help the plant ?

6. The pistillate flowers are borne on the ear. Just where is the
ear produced ? How many ears on each plant ? What is the cob ?
What are the husks? How are the flowers arranged on the cob?
How many pistils in a flower? What are the parts of a pistil?
What is the silk? Can you find any parts in the flower other
than the pistil? Notice the scales or "chaff" surrounding and
between the flowers. Draw a complete pistil.

7. Examine a tassel, which bears the staminate flowers. Can
you see how the flowers are arranged? How many stamens
in each flower? What are the parts of a stamen? Where is
pollen formed ? Can you find other parts of the flower than the
stamens? Notice the scales that surround the flower. Draw a
stamen.

8. Compare the ovary of a young flower with one that has begun
to develop into a fruit (or kernel), and also with a full-grown kernel.

414 TEXTBOOK OF BOTANY

How does the ovary change as it grows into a fruit ? What changes
take place in the cob ? In the husks ?

9. What is the shape of a ripe corn kernel? What differences
do you notice between its two broad sides? Can you find where
the silk was attached ?

10. Place kernels in lukewarm water and leave them over night.
How have they been changed by the soaking? Peel off the seed
coat and the fruit coat, which have grown together. Inside find
the endosperm and the embryo. Which makes up the larger part
of the kernel ? On which side of the kernel is the embryo located ?
Separate the embryo from the endosperm. Notice that the embryo
is surrounded by the thick seed leaf.

11. With a sharp knife split another soaked kernel lengthwise
so as to cut through the middle of the embryo. With the aid of a
hand lens, find the following parts of the embryo : seed leaf, radicle,
plumule, secondary leaves. Draw the cut surface so as to show
these parts as well as the endosperm and the outer coat of the
kernel,

12. Study the germination of the corn seed as directed in §§ 7
and 8 of the directions for the study of the squash or pumpkin seed.
Notice especially what happens to the seed leaf, the first secondary
leaf, and the later leaves ; also how, after the primary root has
begun to grow, other roots start. Where do they grow from?
Draw in outline three seedlings of different ages.

13. After a seedling has developed one or two ordinary leaves,
pull it up and wash its roots very carefully. To what parts of the
root system does the sand or sawdust stick most closely? Why?
Is the kernel still attached to the young plant ? If so, what holds
it in pla'ce ?

14. Compare ears of flint, dent, sweet, and pop corn. How do
they differ ? How do their kernels differ ?

15. Make a list of the varieties of corn that are grown in your
neighborhood. How do they differ? To what class (flint, dent,
sweet, or pop) does each variety belong? What advantages does
each variety have ?

16. Compare varieties of corn whose kernels are of different
colors (yellow, red, black, etc.). In what part of the kernel is the
color located ?

LABORATORY AND FIELD WORK 415

17. Make a list of the uses to which the different parts of the
corn plant are put — kernels, cobs, husks, stems, and leaves.

18. Why is so large a part of the world's corn crop produced in
the United States ? Which states in the ' United States produce
the most corn ? Why are these states best suited to corn growing ?

19. Further suggestions for practical study may be found in
Farmers' Bulletins 409 and 617, published by the United States
Department of Agriculture.

CHAPTER XIV

1. Study the root systems of as many as possible of the follow-
ing : dandelion, clover, sweet potato, radish, beet, dahlia, some of
the grasses or grains, and some small trees and shrubs. Which
of those studied have large primary roots? Which have branch-
ing primary roots? Which have clustered roots? Which have
fibrous roots?

2. With a hand lens examine cross sections of roots of corn, of pea,
and of some woody plant. Find the epidermis, cortex, vascular
bundles, and pith. How does the arrangement of these tissues
compare with their arrangement in the stems that you have studied ?
Sketch a section. Look for the beginnings of secondary roots.
Where do they start?

3. Study the roots of an onion or other plant growing in water.
Notice the cap-like mass of cells (root cap) covering the tip of the
root. What is the function of the root cap ?

4. Study a prepared longitudinal section of a root tip under
the compound microscope. Can you recognize the root cap?
The region of embryonic cells? How do the cells in the older
parts of the section differ from the embryonic cells ?

5. Mark with India ink an actively growing bean root, prefer-
ably one not more than two inches long, at intervals of one-fourth
inch. Place the plant in a moist chamber and examine it from
day to day. In what part does most of the growth in length take
place ?

6. By means of pins, fasten bean seedlings with roots about an
inch in length to a block of wood so that the roots point in various
directions. Place the block in a moist chamber and observe the
seedlings after twenty-four hours. In which direction do the roots

416 TEXTBOOK OF BOTANY

now point? If they have bent, in what part of each root did the
bending take place?

7. Sprout seeds of radish, barley, and corn in sand or sawdust,
and when the roots are an inch or more long pull up some of the
plants. Note how the sand or sawdust sticks to the roots. What
holds it in place? What does this suggest as to the proper care
to be taken of the roots in transplanting young cabbage or tomato
plants ?

8. Test such roots as those of beets, carrots, and sweet potatoes
for (a) starch, (6) sugar, and (c) proteins.1

9. Fasten a root of sweet potato or carrot in a bottle or tumbler
which contains water enough to cover the lower part of the root.
Observe the vigorous growth of the leaves which soon appear.
What is the source of food supply for the growth of the leaves ?

CHAPTER XV

1. Study with a hand lens a cross section of a basswood stem
several years old. Can you tell the age of the stem ? What differ-
ences do you find between spring and summer wood ?

2. Study an underground stem of quack grass, iris, or Solomon's
seal. How old is it? How can you tell? What is the extent of
each year's growth ?

3. Examine a potato tuber. What structures indicate that it is
really a stem ? Put a potato into a tumbler partly filled with water
and examine after a few days. What changes have taken place ?

4. Cut a thin section across a potato tuber and hold it toward
.the light. Can you find regions that correspond to those found
in stems that you have previously studied?

6. Cut off the lower end of a potato tuber and place the cut end
in a dish containing red ink. After some time cut across the tuber

1 (a) Treatment with iodine, which turns starch blue, is the ordinary test for
starch, (b) Boil small portions of the root to be tested, and while the liquid is
still warm add slowly a few drops of Fehling's solution. If sugar is present, the
liquid will take ,on a yellowish color, and soon a yellowish or reddish precipitate
will appear at the bottom of the test tube, (c) Gently heat in water portions of
the roots to be tested, then add a few drops of nitric acid. If proteins are present,
a yellow color will appear, which turns to a deep orange if some drops of ammonia
are added and the whole is again gently heated.

LABORATORY AND FIELD WORK 417

and note the path through which the liquid has been con-
ducted. Can you detect vessels with the hand lens? Perform
the same experiment with stems of other plants and compare the
results.

6. Place a young potted bean plant, preferably one five or six
inches high, upright in a dark box which has a small opening in
one end. Examine it after twenty-four hours, and again after
forty -eight hours. What changes do you observe ?

7. Place a similar plant on its side in a perfectly dark box.
Examine it after two days. What changes have taken place?
What do you conclude from this and the preceding experi-
ment as to the responses of a stem to the stimuli of light and
gravity ?

8. Mark a young bean stem at intervals of one-fourth inch with
India ink; after twenty -four hours note where growth has taken
place. Compare this result with that of your similar study of the
bean root.

9. Secure portions of stems of alder, cherry, willow, maple, lilac,
and other plants. Note the positions of buds. What is their
relation to leaves or leaf scars? Note especially the buds of the
lilac. Do you observe anything characteristic of them which ex-
plains the shape of a lilac bush ?

10. Place portions of various woody stems in a dish containing
water, and if possible cover the whole with a larger jar. Examine
the stems from day to day for a week or more. Do you find that
growth has taken place at regions where no buds were present?
What happens when a willow tree has the greater number of its
branches removed?

11. Tear apart a fairly large bud, such as the winter bud of a
lilac or of a horse-chestnut. What covers the bud on the outside?
What structures do you find inside? How many leaves does it
contain ? What is at the center of the bud ?

12. Study thorns of various types. Which of them seem to be
branches?

13. If an orchard containing young trees is available, it may be
possible to make a study of various types of grafting, budding,
and layering. Compare the methods used with those described
in the text. If possible, some work in actual budding or grafting

4i8 TEXTBOOK OF BOTANY

should also be done, using the figures and descriptions in the text
as guides.1

14. Name the principal timber trees found in your neighborhood.

16. Is there any difference in texture between the wood of rapidly
growing and that of slowly growing trees? Which makes the better
timber ?

16. Which is better for timber, a tree grown in the open or one
grown in a forest ? Why ?

17. What are the objects to be gained in pruning timber trees?
Orchard trees? Ornamental trees and shrubs?

18. Where are the principal timber areas of your state ?

19. W,hat is meant by quarter-sawed lumber? What timbers
are cut in this way? Consult a carpenter as to methods.

20. What are the relations of the sugar, rubber, and turpentine
industries to your stem studies?

CHAPTER XVI

1. Bring in leaf -bearing portions of several common plants —
for instance, the clover, strawberry, apple, and cherry — and
compare the leaves with those that you have already studied in
the following respects :

a. Their arrangement on the stem.

b. Their division into stalk and blade.

c. The presence of stipules, and their comparative size. Do you

find leaves without stipules ?

2. What leaves do you find with parallel veins? With pinnate
veins ? With palmate veins ?

3. What leaves do you find that are simple? What that are
pinnately divided? What that are palmately divided?

4. Compare the leaves of a young oak, basswood, or grape with
those of an older plant of the same kind. What differences have
appeared in the leaves as the plant grew older?

1 Grafting wax may be made by first heating and then thoroughly mixing equal
parts of beeswax, tallow, and linseed oil. Soft cotton twine or strips of cheese-
cloth saturated with this mixture should be used in binding the parts. The wax
should cover all cuts and cracks in order to prevent evaporation and to keep out
fungi and insects. It may readily be kneaded into shape if slightly warmed in the
hand, or it may be softened by the addition of more oil.

LABORATORY AND FIELD WORK 419

5. Find as many as possible of the following special leaf struc-
tures and determine the special use of each to the plant :

a. . Hairs or scales.

b. Layers of cutin or wax.

c. Disagreeably smelling, or poisonous, substances.

d. Sharp teeth, or cutting edges.

e. Small, thick leaves.

6. Find as many leaves as possible that have taken on some of
the following special forms : thorns or spines ; tendrils ; bracts ;
scales ; forms adapted to catch insects.

7. Study and draw a cross section of a leaf of English ivy, nas-
turtium, or sunflower, noticing the following tissues :

a. Upper epidermis; how many layers of cells? Are air-pores

present ?

b. One or more layers of closely packed cells just below the upper

epidermis. What is their shape ?

c. The spongy part of the leaf, containing air spaces. What are the

shapes of the cells ?

d. Veins. To what structures in the stem do they correspond ?

e. The lower epidermis. Compare with the upper epidermis.

8. Boil some freshly picked nasturtium leaves for a few minutes,
then soak them in hot alcohol for half an hour. What happens to
the chlorophyl? Now place them for a few minutes in a solution
of iodine. What color do the leaves take on? What does this
color change teach you?

9. Pin two small pill boxes or circular disks of cork on opposite
sides of a leaf so as to exclude the light from part of the leaf (the
leaf being still attached to the plant) ; leave the plant in bright
light for a day or two. Then cut off the leaf and treat it as you
did the leaves in the previous experiment. Compare the results
of the two experiments. How do you explain the difference?

10. Obtain a begonia or some other plant whose leaves have air-
pores only on their under surfaces. Coat the under surfaces of
some of the leaves with vaseline and leave the plant in bright light
for a day or two. Then remove the vaseline with benzine and
treat the leaves as in the two preceding experiments. Explain
your results.

420 TEXTBOOK OF BOTANY

11. Place a young, vigorously growing plant in a battery jar
containing a little water. Tie a piece of cloth over the top of the
jar and around the plant, so that only the leaves are exposed.
Coat the cloth well with paraffin or vaseline so that no water can
evaporate from the battery jar or from the stem of the plant.
Weigh the whole carefully, then place it in the light. After twenty-
four hours, weigh it again. Explain your results.

12. Arrange cut leaves of various plants with the lower ends of
their stalks in red ink. After a short time remove them and ex-
amine for the paths taken by the ink through the leaves.

CHAPTER XVII

1. Study several common flowers ; compare them with the
flowers you have already studied as to :

a. Numbers of sepals, petals, stamens, and pistils.

b. Whether or not any of the parts are grown together.

c. Whether the ovary is inferior or superior.

d. Whether the pistils are simple or compound (that is, composed of

one or more than one macrospore leaf).

e. Whether the flower is regular or irregular.
/. Shape, size, and structure of the ovary.

g. Length and shape of the style.

h. Adaptation of the stigma for catching and holding pollen.

2. What common plants have their flowers in racemes? In
umbels? In spikes? In heads? In panicles?

3. Study with a hand lens the anthers of several common flowers.
Notice the number and shapes of the anther sacs ; the way in which
they open to let the pollen escape ; whether the pollen is sticky or
dry and powdery. Examine pollen grains of two or three different
flowers under the compound microscope ; draw the grains.

4. Shake the pollen of various plants into dishes containing
respectively five per cent, ten per cent, and fifteen per cent cane
sugar solutions. Cover the dishes. After twenty-four hours
examine to see which grains have germinated arid how germina-
tion came about. Draw a germinated pollen grain.

5. Find as many as possible of the following adaptations : flowers
that bloorri at night only ; flowers that bloom by day and close in
the evening; nectar-producing structures; "guides" which seem

LABORATORY AND FIELD WORK 421

to point the way to the places where nectar is produced ; peculiar
shapes of flowers which adapt them to pollination by particular
insects; structures which keep out some insects. Of what ad-
vantage is each of these adaptations to the plant?

6. If possible, study some of the common wild violets in bloom.
Notice the showy flowers, and then look for other much less con-
spicuous flowers that never open. (Not all species of violets have
these inconspicuous flowers.) What parts do the flowers of the
latter sort have? In what way do they differ from the showy
flowers? Of what use to the plant are the inconspicuous flowers?

CHAPTER XVIII

1. Obtain such common fruits as are available. Determine
from what structure present in the flower each part of the fruit
has been developed. What changes has each structure undergone ?

2. Note the number of seeds present in each fruit. How are
•the seeds protected?

3. Collect the fruits of several of our common weeds. Do you
find any special means in each case for the scattering of the fruits
or seeds ?

4. Make a list of common seeds with, and of those without,
endosperm.

5. Soak the seeds of several common plants in cold water for
twenty-four hours ; place some of each sort under different condi-
tions of temperature, keeping them between pieces of moist filter
paper or blotting paper. Note the percentage of germination in
each case. What differences do you find between different kinds
of seeds in their power of germination? What influence does
temperature have upon germination ?

6. Germinate soaked seeds in darkness and in light. Which is
the more favorable for germination? Are all seeds alike in this
respect ?

7. Place some soaked seeds in a bottle filled with water which
has been boiled to drive out the air. Seal the bottle or cover the
water with a layer of oil and observe from day to day. Do the
seeds germinate? Explain.

8. Sprout seeds of corn, peas, and beans. When the stems are
a half-inch long, remove one or both cotyledons of the beans and

422 TEXTBOOK OF BOTANY

peas and cut away the endosperm of the corn. Compare the
further growth with that of normal seedlings.

9. Take seeds of several plants, such as beans, peas, radish, and
corn ; divide those of each sort into three groups : large, medium,
and small. Plant each lot under as nearly as possible the same
conditions and observe the germinating seeds and seedlings from
time to time. Do you find that there is any relation between the
size of a seed and the size and vigor of the plant that grows from
it ? If so, which size of seed gives the best results ?

10. If possible, secure some seeds that were gathered before they
were ripe, some of the same sort gathered when they were just ripe,
and others that remained on the plant for some time after ripening.
Plant them and observe to determine the length of time needed for
germination and the rate of growth of the plants that grow from
each lot.

CHAPTER XIX

In connection with the study of this chapter, if time allows, the
class may well be given practice in identifying some of the common
wild plants. In this work, the pupil learns not only the names of
particular plants and their reference to the appropriate families,
orders, and classes ; he also learns — what is perhaps more im-
portant — how to identify unknown plants by means of a manual.
A list of some of the leading manuals available for the identification
of the seed plants and ferns in various parts of the United States
and Canada will be found in Appendix II.

CHAPTER XX

1. Make a list of twenty of the more important plants raised
in your neighborhood which supply food for man. What part of
the plant is used in each case? What changes does the plant
undergo to make it suitable for use ?

2. Name ten foods derived from plants which are imported from
other parts of the world.

3. What -cultivated plants growing in your neighborhood are
used as food for animals ? What wild plants ?

4. What plants have you seen growing that supply fibers ? For
what purposes are their fibers used? What other sorts of plant

LABORATORY AND FIELD WORK 423

fibers are used in making the different kinds of cord, binding
twine, rope, sacking, etc. that you may find in various shops
and stores?

5. What plants growing in your locality are used in any of the
following ways : as medicines, for stimulants, for beverages, as
sources of oils, waxes, resins, perfumes, or dyestuffs ?

6. If possible, a visit should be made to a museum in which
economic plants and their products are exhibited. Notes may be
taken of the different plants observed, of the regions in which
they grow, and of the ways in which they are treated to make them
of use.

7. A visit may also be paid to a convenient flour mill, beet sugar
factory, or other factory in which plant products are manufactured.
Each of the processes concerned in the transformation of the raw
material into its final form should be carefully observed.

8. Materials for study may often be obtained from large con-
cerns manufacturing starch, sugar, cocoa, and other food products,
cotton seed products, or cotton cloth and other fabrics, showing the
stages that the plant materials have passed through in the process
of manufacture.

CHAPTER XXI

Students should bring in some of the common weeds of the
locality and become familiar with their general appearance. Es-
pecial attention should be paid in this study to the poisonous
weeds. If a small plot of weedy ground is available for the pur-
pose, the experiment may be tried of spraying it two or three times
at intervals of a week with a twenty per cent solution of iron sul-
phate. Compare the effects of this treatment on the grasses and
on the broad-leaved weeds.

CHAPTER XXII

1. The class should visit a neighboring forest or wood lot to
observe the different species of trees and their arrangement. Are
the various kinds of trees irregularly scattered or are those of each
sort in a group by themselves? How do the trees growing in a
forest differ from those of the same kind grown in the open ? What
is meant by " self -pruning " ? How does it come about?

424 TEXTBOOK OF BOTANY

2. If timber is being cut, make a study of the various processes
concerned. Is there much waste ? What might be done with the
parts of the trees that are not used? How are the logs handled
after the trees are cut down ?

3. A study may also be made of shade and ornamental trees,
special attention being paid to those which are of economic im-
portance.

4. A saw mill should be visited if possible. Even a portable mill
is well worth visiting. Follow the log from the time it enters until
it leaves the mill. What is meant by straight cut lumber ? Quarter-
sawed lumber ?

5. A visit to a lumber yard should be made. Note what kinds
of wood are found. What names are given to the various kinds of
lumber? For what are the different kinds used? A furniture
store or a cabinet maker's shop will show some of the more valuable
woods. Where are they obtained ? For what are they used ?

6. Visit if possible some wood-using industry such as a chair
or furniture factory, box factory, wagon works, or pulp mill ; ob-
serve the woods used and the processes employed in the making
of the finished product.

CHAPTER XXIII

If there is opportunity to do so, the class should visit a greenhouse
or other place where plant-breeding is being done. Notice whether
or not all new plants are grown from seeds. If not, what methods
of multiplication are used? Do all the seeds of any plant grow
into plants exactly like the parent? What methods are used in
crossing plants ? What is the object of crossing ? What methods
of selection are in use? If new races produced by selection are
available, compare them with the parent races. What improve-
ment has been brought about by selection ? Lists may be made by
pupils of such varieties as they find in cultivation of the wheat, pea,
tomato, potato, or other common plant. What are the advantages
of each variety? Why is it worth while to have more than one
variety of a particular species ? What can you find out about the
history of common cultivated varieties? Have full records gener-
ally been kept in the past of plant-breeding work ?

LABORATORY AND FIELD WORK 425

CHAPTER XXIV

It will not be feasible in most schools to do any formal work in
connection with the subject of this chapter. Students should be
on the lookout for plants attacked by parasitic fungi, and, with
the aid of the teacher, should learn to place in their appropriate
groups the more important disease-producing fungi such as smuts,
rusts, powdery mildews, downy mildews, damping-off fungi, and
those which cause leaf- and fruit -spots. Lists may also be made
of the plant diseases that are most troublesome in the immediate
locality, and the students should become familiar with the means
by which these particular diseases may best be checked. Help
may always be had from the nearest agricultural experiment
station in the identification of parasitic fungi.

APPENDIX II
REFERENCE BOOKS

The following is a list of books which may be used to supplement
the text. An attempt has been made to select a comparatively small
number of works which will prove most helpful, copies of some or many
of which are likely to be in the school library. With a few exceptions,
references to secondary school textbooks have not been included.
Copies of various textbooks are sure to be accessible and should be
freely used by the teacher ; but their inclusion in any considerable
number would have made the present list too long. The same may
be said of the bulletins of the United States Department of Agricul-
ture and of the various state experiment stations ; a list of the latter
is given in Appendix III. Lists of bulletins and circulars may be
had from the Superintendent of Documents at Washington and from
the directors of the experiment stations. The interest of pupils in
the study of particular plants, and in such general topics as lumber-
ing, forestry, grafting, plant breeding, and plant diseases, may be
greatly stimulated by giving them access to these official publica-
tions. Some bulletins which are likely to prove especially helpful have
been listed, but they are an inconsiderable fraction of the number that
may be used to advantage.

CHAPTER I

Bailey : The Standard Cyclopedia of Horticulture, 26. edition, vol. ii, pp.

905-910. The Macmillan Company.

Bergen : Essentials of Botany, pp. 4, 5, 23, 24. Ginn and Company.
Corbett : Cucumbers. Farmers' Bulletin 254, U. S. Department of

Agriculture.

CHAPTER II

Abel : Care of 'Food in the Home. Farmers' Bulletin 375, U. S. Depart-
ment of Agriculture.

Bennett and Murray : A Handbook of Cryptogamic Botany, pp. 449-456.
Longmans, Green and Company.
426

REFERENCE BOOKS 427

Conn : Bacteria, Yeasts, and Molds in the Home. Ginn and Com-
pany.

Duggar : Fungous Diseases of Plants, chap. ix. Ginn and Com-
pany.

Jordan: A Textbook of General Bacteriology. W. B. Saunders and
Company.

Lipman : Bacteria in Relation to Country Life. The Macmillan Com-
pany.

Rogers : Bacteria in Milk. Farmers' Bulletin 490, U. S. Department
of Agriculture.

Rogers : Home Pasteurization of Milk. Circular 152, Bureau of Animal
Industry, U. S. Department of Agriculture.

Sedgwick and Wilson: An Introduction to General Biology, chaps, xvi,
xvii. Henry Holt and Company.

Stevens: Introduction to Botany, pp. 254-261. D. C. Heath and
Company.

CHAPTER III

Coulter: A Textbook of Botany, pp. 102-104. D. Appleton and

Company.
Curtis: Nature and Development of Plants, 3d edition, pp. 182-183.

Henry Holt and Company.
Gager: Fundamentals of Botany, pp. 252-255. P. Blakiston's Son and

Company.
Sedgwick and Wilson: An Introduction to General Biology, chap. xiv.

.Henry Holt and Company.

CHAPTER IV

Atwater : Bread and Breadmaking. Farmers' Bulletin 389, U. S.
Department of Agriculture.

Conn : Bacteria, Yeasts, and Molds in the Home. Ginn and Com-
pany.

Coulter, Barnes, and Cowles : A Textbook of Botany, vol. i, pp. 70-71,
409-410. American Book Company.

Curtis : Nature and Development of Plants, 3d edition, pp. 248-250.
Henry Holt and Company.

Sedgwick and Wilson : An Introduction to General Biology, chap. xv.
Henry Holt and Company.

Stevens : Introduction to Botany, pp. 256, 261-263. D. C. Heath and
Company.

428 TEXTBOOK OF BOTANY

CHAPTER V

Bennett and Murray : A Handbook of Cryptogamic Botany, pp. 264-267.
Longmans, Green and Company.

Coulter, Barnes, and Cowles: A Textbook of Botany, vol. I, pp. 38-41.
American Book Company.

Strasburger, Jost, Schenck, and Karsten : A Textbook of Botany, 4th
English edition, pp. 348-349. The Macmillan Company.

Vines : Elementary Textbook of Botany, p. 256. The Macmillan Com-
pany.

CHAPTER VI

Bennett and Murray : A Handbook of Cryptogamic Botany, pp. 335-341.

Longmans, Green, and Company.
Bergen and Davis : Principles of Botany, pp. 239-242. Ginn and

Company.

Conn : Bacteria, Yeasts, and Molds in the Home. Ginn and Company.
Curtis : Nature and Development of Plants, 3d edition, pp. 224-227.

Henry Holt and Company.
Gager: Fundamentals of Botany, pp. 256-267. P. Blakiston's Son and

Company.

CHAPTER VII

Bennett and Murray : A Handbook of Cryptogamic Botany, pp. 383-387.

Longmans, Green, and Company.
Bergen and Davis : Principles of Botany, pp. 260-264. Ginn and

Company.
Carleton : Cereal Rusts of the United States. Bulletin 16, Division of

Vegetable Pathology, U. S. Department of Agriculture.
Curtis: Nature and Development of Plants, 3d edition, pp. 251-257.

Henry Holt and Company.

Duggar : Fungous Diseases of Plants, chap. xiv. Ginn and Company.
Freeman: Minnesota Plant Diseases, pp. 159-164, 282-293. University

of Minnesota.
Gager : Fundamentals of Botany, pp. 272-276. P. Blakiston's Son and

Company.
Jones and Bartholomew: Apple Rust and its Control in Wisconsin.

Bulletin 257, Wisconsin Agricultural Experiment Station.
Milburn and Bessey : Fungoid Diseases of Farm and Garden Crops,

pp. 48-55. Longmans, Green and Company.
Olive: Rusts of Cereals and other Plants. Bulletin 109, South Dakota

Agricultural Experiment Station.

REFERENCE BOOKS 429

Strasburger, Jost, Schenck, and Karsten : A Textbook of Botany, 4th
English edition, pp. 405-409. The Macmillan Company.

CHAPTER VIII

Atkinson: Mushrooms, Edible, Poisonous, etc. Henry Holt and

Company.
Atkinson and Shore: Mushroom Growing for Amateurs. Bulletin 227,

Cornell University Agricultural Experiment Station.
Clements : Minnesota Mushrooms. University of Minnesota.
Duggar : The Cultivation of Mushrooms. Farmers' Bulletin 204, U. S.

Department of Agriculture.
Gager : Fundamentals of Botany, pp. 276-284. P. Blakiston's Son and

Company.
Long: The Death of Chestnuts and Oaks Due to Armillaria mellea.

Bulletin 89, U. S. Department of Agriculture.
Patterson: Mushrooms and Other Common Fungi. Bulletin 175,

Bureau of Plant Industry, U. S. Department of Agriculture.

CHAPTER IX

Barnes and Heald : A nalytic Keys to the Genera and Species of North

American Mosses. University of Wisconsin.
Bennett and Murray : A Handbook of Cryptogamic Botany, pp. 136-149.

Longmans, Green and Company.

Bergen and Davis : Principles of Botany, chap. xxiv. Ginn and Com-
pany.
Campbell : The Structure and Development of Mosses and Ferns. The

Macmillan Company.
Coulter, Barnes, and Cowles : A Textbook of Botany, vol. I, pp. 115-121.

American Book Company.
Curtis : Nature and Development of Plants, 3d edition, chap. vii. Henry

Holt and Company.
Grout: Mosses with a Hand-Lens. A. J. Grout, 360 Lenox Road,

Brooklyn, New York.

Grout : Mosses with Hand Lens and Microscope. A. J. Grout.
Strasburger, Jost, Schenck, and Karsten : A Textbook of Botany, 4th

English edition, pp. 436-442. The Macmillan Company.

CHAPTER X

Bennett and Murray : A Handbook of Cryptogamic Botany, pp. 64-82.
Longmans, Green and Company.

430 TEXTBOOK OF BOTANY

Campbell : The Structure and Development of Mosses and Ferns. The

Macmillan Company.

Clute : Our Ferns in Their Haunts. Frederick A. Stokes Company.
Coulter, Barnes, and Cowles : A Textbook of Botany, vol. i, pp. 155-170.

American Book Company.
Cox : Eradication of Ferns from Pasture Lands in the Eastern United

States. Farmers' Bulletin 687, U. S. Department of Agriculture.
Curtis : Nature and Development of Plants, 3d edition, chap. viii. Henry

Holt and Company.
Gager : Fundamentals of Botany, chaps, xii-xiii. P. Blakiston's Son and

Company.
Sedgwick and Wilson: An Introduction to General Biology, chaps.

viii-x. Henry Holt and Company.
Strasburger, Jost, Schenck, and Karsten : A Textbook of Botany, 4th

English edition, pp. 442-446, 449-454. The Macmillan Company.
Underwood : Our Native Ferns and their Allies. Henry Holt and

Company.
Wright : Flowers and Ferns in their Haunts. The Macmillan Company.

CHAPTER XI

Coulter and Chamberlain : Morphology of Gymnosperms. D. Appleton
and Company.

Gager : Fundamentals of Botany, chap. xxvi. P. Blakiston's Son and
Company.

Gray : New Manual of Botany, 7th edition. American Book Com-
pany. (Contains a list and descriptions of the gymnosperms
growing wild in the central and northeastern United States and
the adjacent parts of Canada.)

Hall and Maxwell : Uses of Commercial Woods : Pines. Bulletin 99,
Forest Service, U. S. Department of Agriculture.

Mohr: Timber Pines of the United States. Bulletin 13, -Forest Service,
U. S. Department of Agriculture.

Penhallow : A Manual of the North American Gymnosperms. Ginn and
Company.

Schorger and Betts : The Naval Stores Industry. Bulletin 229, U. S.
Department of Agriculture.

CHAPTER XII

Bailey : The Standard Cyclopedia of Horticulture, 2d edition, vol. i ,
pp. 458-463. The Macmillan Company.

REFERENCE BOOKS 431

Corbett: The School Garden. Farmers' Bulletin 218, U. S. Department
of Agriculture.

Corbett : Beans. Farmers' Bulletin 289, U. S. Department of Agri-
culture.

Fluharty : Bean Growing. Fanners' Bulletin 561, U. S. Department of
Agriculture.

Tracy: American Varieties of Garden Beans. Bulletin 109, Bureau
of Plant Industry, U. S. Department of Agriculture.

CHAPTER XIII

Bowman and Crossley : Corn. Bowman and Crossley, Ames, Iowa. *
Halligan : Fundamentals of Agriculture, pp. 83-104. D. C. Heath and

Company.
Hartley : The Production of Good Seed Corn. Farmers' Bulletin 229,

U. S. Department of Agriculture.
Hopkins : The Structure of the Corn Kernel and the Composition of its

Different Parts. Bulletin 87, Illinois Agricultural Experiment

Station.

Hunt: Cereals in America, chaps, ix-xviii. Orange Judd Company.
Myrick : The Book of Corn, chaps, ii-iv. Orange Judd Company.
Sargent : Corn Plants, chaps, i-iv, xi-xviii. Houghton, Mifflin and

Company.

Shamel : Manual of Corn Judging. Orange Judd Company.
Shoesmith : The Study of Corn, chap. i. Orange Judd Company.
Sturtevant : Varieties of Corn. Bulletin 57, Office of Experiment

Stations, U. S. Department of Agriculture.

CHAPTER XIV

Curtis : Nature and Development of Plants, 3d edition, chap. ii. Henry
Holt and Company.

Duggar : Plant Physiology. The Macmillan Company.

Ganong : A Textbook of Botany for Colleges, chap. v. The Macmillan
Company.

Kerner and Oliver : The Natural History of Plants. Henry Holt and
Company.

King: Physics of Agriculture, chaps, i, iv. Mrs. F. H. King, Madison,
Wisconsin.

Osterhout : Experiments -with Plants, chap. iii. The Macmillan Com-
pany.

Stevens : Plant Anatomy, 3d edition, chap. vi. P. Blakiston's Son and
Company.

432 TEXTBOOK OF BOTANY

CHAPTER XV

Coulter, Barnes, and Cowles : A Textbook of Botany, vol. I, pp. 239-
247. American Book Company.

Ganong : A Textbook of Botany for Colleges, chap. iv. The Macmillan
Company.

Jones : How the Maple Lives and Works. Bulletin 103, Vermont Agri-
cultural Experiment Station.

Osterhout : Experiments with Plants, chap. v. The Macmillan Com-
pany.

Peirce : A Textbook of Plant Physiology, chaps, iii-v. Henry Holt and
Company.

Stevens : Plant Anatomy, 3d edition, chaps, ii, iii, vii, x. P. Blakiston's
Son and Company.

Ward : The Oak. D. Appleton and Company.

CHAPTER XVI

Bergen and Davis : Principles of Botany, chaps, x-xii. Ginn and

Company.
Coulter, Barnes, and Cowles: A Textbook of Botany, vol. i, pp. 318-

331 ; vol. 2, pp. 521-644. American Book Company.
Curtis : Nature and Development of Plants, 3d edition, chap. i. Henry

Holt and Company.

Duggar : Plant Physiology. The Macmillan Company.
Ganong : A Textbook of Botany for Colleges, chap. iii. The Macmillan

Company.
Kerner and Oliver : The Natural History of Plants. Henry Holt and

Company.
MacDougal : Practical Textbook of Plant Physiology. Longmans,

Green, and Company.
Stevens : Introduction to Botany, chap. v. D. C. Heath and Company.

CHAPTER XVII

Bergen and Davis : Principles of Botany, chaps, xiii-xv, xxxii. Ginn

and Company.

Coulter: Plant Structures, chap. xiii. D. Appleton and Company.
Coulter, Barnes, and Cowles: A Textbook of Botany, vol. 2; chap. v.

American-Book Company.
Darwin : The Effects of Cross- and Self- Fertilisation in the A nimal

Kingdom. D. Appleton and Company.
Gray : Lessons in Botany, pp. 72-117. American Book Company.

REFERENCE BOOKS 433

Kerner and Oliver: The Natural History of Plants, vol. 2. Henry

Holt and Company.
Knuth : Pollination of Flowers. 3 volumes. Henry Frowde, Amen

Corner, E. C., London, England.
Stevens : Introduction to Botany, chap. viii. D. C. Heath and Company.

CHAPTER XVIII

Beal : Seeds of Michigan Weeds. Bulletin 260, Michigan Agricultural

Experiment Station.
Bergen and Davis : Principles of Botany, chaps, i, ii, xvi, xxxiii. Ginn

and Company.
Coulter, Barnes, and Cowles : A Textbook of Botany, vol. 2, chap. v.

American Book Company.
Curtis: Nature and Development of Plants, 3d edition, pp. 127—136.

Henry Holt and Company.
Kerner and Oliver: The Natural History of Plants, vol. 4. Henry

Holt and Company.
Peirce : A Textbook of Plant Physiology, chap. vii. Henry Holt and

Company.
Stevens : Introduction to Botany, chap. ix. D. C. Heath and Company.

CHAPTER XIX

To the following may be added an indefinite number of state and

local lists and manuals, each of which will be useful to schools within

the area that it covers.

Apgar : Ornamental Shrubs of the United States. American Book Com-
pany.

Apgar : Trees of the Northern United States. American Book Company.

Armstrong and Thornber : Field Book of Western Wild Flowers. G. P.
Putnam's Sons.

Blakeslee and Jarvis : Trees in Winter. The Macmillan Company.

Britton : Manual of the Flora of the Northern States and Canada. Henry
Holt and Company.

Britton : North American Trees. Henry Holt and Company.

Britton and Brown: An Illustrated Flora of the Northern United States,
Canada, and the British Possessions. 3 volumes. Charles Scrib-
ner's Sons.

Chapman : Flora of the Southern United States. American Book Com-
pany.

Coulter and Nelson : New Manual of the Botany of the Central Rocky
Mountains. American Book Company.

434 TEXTBOOK OP BOTANY

Cowles and Coulter: A Spring Flora for High Schools. American
Book Company. (For the north central and eastern United
States.)

Dame and Brooks : Handbook of the Trees of New England. Ginn and
Company.

Frye and Rigg : Elementary Flora of the Northwest. American Book
Company.

Gray: New Manual of Botany, 7th edition. American Book Com-
pany. (For the central and northeastern United States and the
adjacent parts of Canada.)

Gray and Bailey : Field, Forest, and Garden Botany. American Book
Company.

Hough : Handbook of the Trees of the Northern States and Canada, East
of the Rocky Mountains. R. B. Hough, Lowville, New York.

Howell : Flora of the Northwest. J. K. Gill and Company, Portland,
Oregon.

Keeler: Our Native Trees. Charles Scribner's Sons.

Keeler: Our Northern Shrubs and How to Identify Them. Charles
Scribner's Sons.

Lounsberry : A Guide to the Trees. Frederick A. Stokes Company.

Mathews : Field Book of American Wild Flowers. G. P. Putnam's Sons.

Nelson : An A nalytical Key to some of the Common Flowering Plants of
the Rocky Mountain Region. D. Appleton and Company.

Nelson : Spring Flora of the Intermountain States. Ginn and Company.

Piper and Beattie : Flora of Northwest Coast. New Era Printing Com-
pany.

Sargent : Manual of the Trees of North A merica (exclusive of Mexico) .
Houghton, Mifflin and Company.

Schaffner : Field Manual of Trees. Adams Company, Columbus, Ohio.

Small : Flora of the Southeastern United States. John K. Small, Perry
Ave. and 2O7th St., Bedford Park, New York City.

Tracy : Flora of the Southeastern States. Ginn and Company.

Wright : Flowers and Ferns in their Haunts. The Macmillan Company.

CHAPTER XX

Bailey : Cyclopedia of American Agriculture. 4 volumes. The Mac-
millan Company.

Bailey : The . Standard Cyclopedia of Horticulture. 6 volumes. The
Macmillan Company.

Burkett and Poe : Cotton. Doubleday, Page and Company.

Fraser: The Potato. Orange Judd Company.

REFERENCE BOOKS 435

Halligan : Fundamentals of Agriculture, chap. iv. D. C. Heath and
Company.

Hunt: Cereals in America. Orange Judd Company.

Hunt : Forage and Fiber Crops in America. Orange Judd Company.

Sargent : Plants and their Uses. Henry Holt and Company.

Spillman : Farm Grasses in the United States. Orange Judd Com-
pany.

Stockberger : Drug Plants under Cultivation. Farmers' Bulletin 663,
U. S. Department of Agriculture.

Stubbs and Purse: Sugar Cane. D. G. Purse, Savannah, Georgia.

Toothaker: Commercial Raw Materials. Ginn and Company.

CHAPTER XXI

Beal : Michigan Weeds. Bulletin 267, Michigan Agricultural Experi-
ment Station.

Blatchley : The Indiana Weed Book. The Nature Publishing Company,
Indianapolis, Indiana.

Chesnut : Principal Poisonous Plants of the United States. U. S. De-
partment of Agriculture, Division of Botany, Bulletin 20.

Chesnut : Thirty Poisonous Plants of the United States. Farmers'
Bulletin 86, U. S. Department of Agriculture.

Clark and Fletcher : Farm Weeds of Canada. Government Printing
Bureau, Ottawa, Ontario.

Cox: Weeds: How to Control Them. Farmers' Bulletin 660, U. S.
Department of Agriculture.

Georgia : A Manual of Weeds. The Macmillan Company.

Henkel: Weeds Used in Medicine. Farmers' Bulletin 188, U. S. De-
partment of Agriculture.

Pammel : Manual of Poisonous Plants. L. H. Pammel, Ames, Iowa.

Pammel : Weeds of Farm and Garden. Orange Judd Company.

Shaw : Weeds and How to Eradicate Them. Webb Publishing Company.

Weed: Farm Friends and Farm Foes. D. C. Heath and Company.

CHAPTER XXII

Bryant : Logging. John Wiley and Sons.

Collins: Practical Tree Surgery. Year Book, U. S. Department of

Agriculture, 1913.
Defebaugh : History of the Lumber Industry in America. The American

Thresherman, Chicago.

436 TEXTBOOK OF BOTANY

Fernow : Care of Trees in Street, Lawn, and Park. Henry Holt and

Company.
Graves: Principles of Handling Wood Lots. Bulletin 42, Forest

Service, U. S. Department of Agriculture.
Kellogg : The Timber Supply of the United States. Circular 166,

Forest Service, U. S. Department of Agriculture.
Kellogg and Hale : Forest Products of the United States. Bulletin 74,

Forest Service, U. S. Department of Agriculture.
Moon and Brown: Elements of Forestry. John Wiley and Sons.
Peck : Opportunity in Forest Planting for Farmers. Year Book, U. S.

Department of Agriculture, 1909.
Pinchot : Forestry and Lumber Supply. Circular 25, Forest Service,

U. S. Department of Agriculture.
Pinchot: Primer of Forestry. Farmers' Bulletins 173 and 358, U. S.

Department of Agriculture.
Price, Kellogg, and Cox: Forests of the United States. Bulletin 171,

Forest Service, U. S. Department of Agriculture.
Roth : A First Book of Forestry. Ginn and Company.
Stone: Shade Trees, Characteristics, Adaptation, Diseases, and Care.

Bulletin 170, Massachusetts Agricultural Experiment Station.
Weiss: The Preservative Treatment of Fence Posts. Circular 117,

Forest Service, U. S. Department of Agriculture.
Winkenwerder : Forestry in the Public Schools. Circular 130, Forest

Service, U. S. Department of Agriculture.

CHAPTER XXIII

Bailey and Gilbert : Plant Breeding. The Macmillan Company.

Cook: Wild Wheat in Palestine. Bulletin 274, Bureau of Plant In-
dustry, U. S. Department of Agriculture.

Fraser : The Potato. Orange Judd Company.

Harwood : New Creations in Plant Life. The Macmillan Company.

Hunt : The Cereals in America. Orange Judd Company.

Hunt: The Forage and Fiber Crops in America. Orange Judd Company.

Montgomery : Experiments in Wheat Breeding. Bulletin 269, Bureau
of Plant Industry, U. S. Department of Agriculture.

Sargent : Corn Plants. Hough ton, Mifflin and Company.

Stuart : Group Classifications and Varietal Descriptions of Some A merican
Potatoes. • Farmers' Bulletin 176, U. S. Department of Agricul-
ture.

Wight: The Varieties of Plums Derived from Native American Species.
Farmers' Bulletin 172, U. S. Department of Agriculture.

REFERENCE BOOKS 437

CHAPTER XXIV

Arthur and Stuart : Corn Smut. I2th Annual Report, Indiana Agri-
cultural Experiment Station, pp. 84-135.

Duggar : Fungous Diseases of Plants. Ginn and Company.

Freeman : Minnesota Plant Diseases. University of Minnesota.

Halligan : Fundamentals of Agriculture, chap. vi. D. C. Heath and
Company.

Jones and Oilman : Control of Cabbage Yellows. Research Bulletin 38,
Wisconsin Agricultural Experiment Station.

Massee : A Textbook of Fungi. The Macmillan Company.

Milburn and Bessey : Fungoid Diseases of Farm and Garden Crops.
Longmans, Green and Company.

Moore: Oat Smut and its Prevention. Bulletin in, Wisconsin Agri-
cultural Experiment Station.

Swingle : The Prevention of Stinking Smut of Wheat and the Loose Smut
of Oats. Farmers' Bulletin 250, U. S. Department of Agriculture.

Weed : Farm Friends and Farm Foes. D. C. Heath and Company.

APPENDIX III

THE STATE AND TERRITORIAL AGRICULTURAL
EXPERIMENT STATIONS

Alabama —

College Station : A uburn
Canebrake Station : Uniontown
Tuskegee Station : Tuskegee In-
stitute

Alaska — Sitka

Arizona — Tucson

Arkansas — Fayettevitte

California — Berkeley
Colorado — Fort Collins
Connecticut —

State Station : New Haven

Storrs Station : Starrs

Delaware — Newark
Florida — Gainesville

Georgia — Experiment
Guam — Island of Guam

Hawaii — Honolulu

Idaho — Moscow
Illinois — Urbana
Indiana — Lafayette
Iowa — Ames

Kansas — Manhattan
Kentucky — Lexington

Louisiana —

State Station : Baton Rouge
Sugar Station : A udubon Park,

New Orleans
North Louisiana Station : Cal-

houn

Maine — Orono

Maryland — College Park

Massachusetts — A mherst

Michigan — East Lansing

Minnesota — University Farm,
St. Paul

Mississippi — Agricultural College

Missouri —

College Station : Columbia
Fruit Station : Mountain Grove

Montana — Bozeman

Nebraska — Lincoln
Nevada — Reno
New Hampshire — Durham
New Jersey — New Brunswick
New Mexico — State College
New York —

State Station : Geneva

Cornell Station : Ithaca
North Carolina —

College Station : West Raleigh

State Station : Raleigh
North Dakota — Agricultural
College

438

AGRICULTURAL EXPERIMENT STATIONS 439

Ohio — Wooster Tennessee — Knoxville

Oklahoma — Still-water Texas — College Station

Oregon — Coruallis

Utah — Logan
Pennsylvania — Stale College

Porto Rico — Vermont — Burlington

Federal Station : Mayaguez Virginia — Blacksburg

Insular Station : Rio Piedras

Washington — Pullman
Rhode Island — Kingston West Virginia — Morgantown

Wisconsin — Madison

South Carolina — Clemson College Wyoming — Laramie
South Dakota — Brookings

APPENDIX IV
BOTANICAL SUPPLIES

Following is a brief list of the addresses of persons and firms who
supply materials of various sorts that may be needed for laboratory
work in botany. This list makes no pretension of being complete.

Seeds, Plants, and Bulbs

W. Atlee Burpee and Company, Burpee Buildings, Philadelphia.
Currie Brothers Company, 384 East Water St., Milwaukee.
Henry A. Dreer, 714 Chestnut St., Philadelphia.
Peter Henderson and Company, 35-37 Cortlandt St., New York.
J. M. Thorburn and Company, 53 Barclay St., New York.
Utah Rare Plant Company, Salt Lake City, Utah.
Vaughan's Seed Store, 43 Barclay St., New York; 84-86 Randolph St.,
Chicago.

Plants and Plant Parts, Living, Dried, and Preserved in Alcohol
or Formalin; Herbarium Supplies, Microscopic Preparations

Biological Supply Company, 106 Edgerton St., Rochester, New York.
Cambridge Botanical Supply Company, Waverley, Massachusetts.
Marine Biological Laboratory, Supply Department, Woods Hole,

Massachusetts.

Professor M. S. Markle, Earlham College, Earlham, Indiana.
The Plant Study Company, P. O. Box 15, Cambridge, Massachusetts.
St. Louis Biological Laboratory, University Heights, St. Louis, Missouri.
Dr. W. N. Steil, Biology Building, Madison, Wisconsin.

Microscopes, Projection Lanterns, Glassware, and other Laboratory
Equipment

Bausch & Lomb Optical Company, Rochester, New York.
Cambridge Botanical Supply Company, Waverley, Massachusetts.
Central Scientific Company, 412-420 Orleans St., Chicago.
Chicago Apparatus Company, 557-559 West Quincy St., Chicago.
440

BOTANICAL SUPPLIES ' 441

The Chicago Laboratory Supply and Scale Company, 39 West Randolph

St., Chicago.

Columbia School Supply Company, Indianapolis.
Conrad Slide and Projection Company, 4028 Jackson Blvd., Chicago.
Goder-Heimann Company, 87 East Lake St., Chicago.
E. Leitz, 30 East i8th St., New York.

E. H. Sargent and Company, 125-127 West Lake St., Chicago.
Spencer Lens Company, Buffalo, New York.

GLOSSARY

Adventive. A term applied to roots, buds, or branches borne in any

other than the usual place.
Alga. A comparatively simple plant (simpler than a moss or liverwort)

which contains chlorophyl.
Alternate leaves. Those of which only one is borne at a particular

node on a stem or branch ; the leaves at two successive nodes are

on different sides.

Annual. A plant which completes its entire life cycle in a single season.
Anther. The head, or upper part, of a stamen, in which the pollen

grains are borne.
Antherid. The organ of a moss, liverwort, or higher plant in which

male gametes are produced.
Antherozoid. A motile male gamete.
Archegone. The egg-producing organ of a moss, liverwort, or higher

plant.
Axil. The upper angle between a leaf and the stem or branch on which

it is borne.
Axillary. Borne in, or growing from, an axil ; as axillary buds, or

axillary flowers.

Bark. The dry portion of a stem or root lying outside the cork cam-
bium. The tissues between the cork cambium and the cambium
proper are sometimes called green bark, to distinguish them from
the true or dry bark.

Basal. Referring to that part of a structure or organ nearest its base
or point of attachment.

Basidium. A large cell bdrne on the surface of one of the gills of a
mushroom, or on the corresponding surface of any of the related
fungi, at whose end the spores are produced.

Bast. The part of a vascular bundle through which manufactured
food is conducted ; also called the phloem.

Biennial. A plant which requires two years in which to complete its
life cycle, usually storing food the first year and bearing flowers
and fruit the second.

Bract. A small leaf from whose axil a flower grows.

Bulb. A short shoot covered with thick, fleshy leaves, as in the onion or
lily.

443

444 TEXTBOOK OF BOTANY

Cambium. A layer between bast and wood by the division of whose

cells the stem or root grows in thickness.
Carbohydrate. A substance composed of carbon, hydrogen, and oxygen,

and belonging to the class which includes starch and the sugars.
Carpel. One of the parts of a compound pistil ; a macrospore leaf.
Carpellate. Referring to a cone which bears carpels (macrospore

leaves). Also used in the same sense as pistillate.
Catkin. A more or less dense, scaly flower cluster like that of the poplar,

alder, or willow.
Cell. A unit of living matter. A plant or an animal may be a single

cell, or may be composed of several or many cells.
Chlorophyl. The green coloring matter found in the cells of many plants.
Chloroplast. A small chlorophyl-containing body found in the cells of

green plants.
Conjugation. The union of like gametes, such as those of Spirogyra or

of the bread mold.
Cork. A substance (also called suberin) which permeates the walls of

certain cells, especially of those formed from the cork cambium ;

the term cork is also applied to the cells themselves whose walls

contain suberin.

Conn. A solid bulb-like structure not covered by thick leaves.
Cortex. The part of the stem lying between the epidermis and the

region in which the vascular bundles are contained.
Corymb. A flat-topped or convex flower cluster whose outermost

flowers are the oldest.
Cotyledon. A seed leaf.
Cross-pollination. The falling or depositing of pollen from the anther

of one flower upon the stigma of another flower.
Cutin. A secreted waxy layer on the outer surface of the epidermis,

especially of leaves or fruits.
Cutting. A severed portion of a plant from which a whole new plant

may be developed.
Cyme. A flat-topped or convex flower cluster in which the central

flower is the first to open.
Cytoplasm. All the substance of a cell contained within the cell wall,

except the nucleus.

Digest. To change an insoluble substance into a form in which it
may be dissolved.

Egg. A female gamete.

Embryo. The young resting plant contained in a seed.

GLOSSARY 445

Endosperm. 'The food-containing tissue lying outside the embryo and

within the seed coat.
Enzym. A substance produced in a living cell which causes or hastens

particular chemical changes in other substances.

Epidermis. The outer layer of cells of leaves, stems, roots, or fruits.
Epiphyte. A plant which grows, usually at some distance above the

ground, upon another plant but not parasitic upon it.

Family. A group of related genera.

Fermentation. Any one of many chemical changes produced by simple

organisms such as yeasts or bacteria ; especially, but not exclusively,

those in which bubbles of gas are given off.
Fertilization. The union of unlike male and female gametes.
Fiber. An elongated, usually slender cell with firm walls; as bast

fibers or wood fibers.

Filament. The stalk-like part of a stamen below the anther.
Fruit. A ripened ovary with the seed or seeds inclosed within it.
Fungus. A comparatively simple organism which contains no chlo-

rophyl.

Gamete. A cell which may unite with another cell, thus forming a
zygote.

Genus. A group of related species.

Germinate. To begin to grow, usually after being for some time in a
resting or dormant condition ; applied to spores, zygotes, and seeds.

Gill. One of the vertical flaps on the under side of the cap of a mush-
room, on whose surface spores are borne.

Glandular. Applied to a structure whose function is the secretion of
some special substance.

Grafting. The attachment of the parts of two plants in such a way that
they will grow together.

Head. A dense cluster of flowers on a very short axis.

Heartwood. The hard inner layers of the wood of the trunk and larger

branches of a tree or shrub. Distinguished from sapwood.
Host. An organism (plant or animal) on or in whose tissues a parasitic

organism lives.
Hybrid. A plant produced by the crossing of two species or varieties.

Imperfect. Applied to a flower having either stamens and no pistil,

or a pistil (or pistils) and no stamens.
Infection. The establishment of a parasite in or upon the tissues of a

host.

446 TEXTBOOK OF BOTANY

Integument. The layer, or one of the layers, of tissue surrounding the

ovule, which develops into the seed coat or coats.
Internode. The parts of a stem or branch between two successive

joints or nodes.

Keel. The two lower (usually united) petals of 'the flowers of most of
the members of the pulse family.

Lenticel. An opening in the bark of a woody plant, through which the
gases of the air may reach the inner tissues.

Macrospore. The larger kind of spore of a plant which produces

spores of two kinds.
Macrospore sac. A structure in which macrospores are produced ; in

seed plants, the same as the ovule.
Medullary rays. Radial rows or layers of thin-walled cells, cutting

through the wood or bast of a gymnosperm or dicotyledon.
Micropyle. An opening through the integument or seed coat.
Microspore. The smaller kind of spore of a plant which produces two

kinds ; in seed plants, the young pollen grain.
Microspore sac. A cavity in which microspores are produced. In

seed plants, the same as a pollen sac.

Nectar. A fluid, commonly sweet, secreted usually in some part of

the flower for the attraction of insects.
Node. One of the joints of a stem or branch, at which a leaf or leaves

arise.

Nucleole. A small, usually rounded body lying within a nucleus.
Nucleus. A definite portion or organ of a living cell bounded by a

membrane; distinguished from the cytoplasm.
Nutation. . The movement in a more or less nearly spiral direction of the

end of a stem or branch, due to unequal rates of growth on different

sides.

Opposite leaves. Those of which two are borne, opposite each other, at

the same node of a stem or branch.
Order. A group of related families.
Organic. Belonging to, or produced by, an organism.
Organism. A living being — plant or animal.
. Ovary. The lower part of a pistil, containing one or more cavities in

which an ovule (macrospore sac) or ovules are borne.
Ovule. The macrospore sac of a seed plant ; a small body which may

develop into a seed.

GLOSSARY 447

Palmate. Arranged like the fingers of a hand ; contrasted with pinnate,
Panicle. An open or loose flower cluster; a compound raceme.
Parasite. An organism which lives in or upon another organism (the

host), and obtains some or all of its food from the host.
Pedicel. The stalk of each individual flower in a cluster.
Peduncle. A flower stalk; used to designate either the stalk of .a

solitary flower or the common stalk of a cluster.
Perennial. A plant which remains alive for more than two years.
Perfect. Applied to a flower having both stamens and pistil or pistils.
Petal. One of the leaf-like parts of a flower next within the sepals.

Some flowers have no petals ; if present, they are usually the most

conspicuous parts of the flower.
Pinnate. Arranged like the parts of a feather ; applied to the veins or

divisions of a leaf.
Pistil. A structure borne in the central part of a flower, consisting of

one or more carpels.

Pistillate. Applied to a flower having a pistil or pistils but no stamens,
Plumule. The part of an embryo which is above the cotyledons.
Pollen. The small bodies (pollen grains) produced in an anther.
Pollen sac. A chamber in which pollen grains are formed ; the same as

a microspore sac; also called an anther sac.
Pollen tube. An outgrowth from the germinating pollen grain, by

means of which the male gametes of a seed plant are 'carried to the

neighborhood of the egg.
Pollination. The falling or depositing of pollen from the anther upon

the stigma.
Primary leaf . The first leaf, or one of the first leaves, formed by an

embryo ; in seed plants, the same as a seed leaf.
Primary root. The first root ; in a seed plant, the primary root develops

from the lower end of the radicle.
Protein. One of a class of very complex substances produced in living

cells. Proteins are important constituents of all living matter.
Protonema. The thread-like vegetative growth produced by the

germinating spore of a moss.
Protoplasm. The total liquid and semi-liquid constituents of a cell;

everything inside the cell wall.

Ptomain. One of a class of substances produced by the action of bac-
teria in the decomposition of organic substances. Some of the

ptomains are extremely poisonous.

Putrefaction. The decay of organic substances, by the action of bac-
teria and other minute organisms. The term is especially applied

to those forms of decay in which offensive, odors are given off.

448 TEXTBOOK OF BOTANY

Pyrenoid. A small body found in the cells of green algae, whose func-
tion is the manufacture of starch. It is very commonly imbedded
in a chloroplast.

Race. A group of plants or animals, very similar and closely related.
Raceme. An elongated flower cluster, with many short pedicels borne

at different levels upon the peduncle.

Radicle. That part of an embryo below the seed leaf or leaves.
Respiration. The breaking down of living substance and food in a

living organism, as a result of which energy is set free for the use

of the organism. Commonly respiration involves the taking in

of oxygen and the giving off of carbon dioxid.
Response. The change produced in a cell or organism as the result of a

stimulus ; also called a reaction.
Rhizoid. An elongated cell or row of cells by means of which a plant

absorbs food materials from the soil or water.

Root cap. The protective cap-like mass of cells covering a root tip.
Rudimentary. Not fully developed.

Sap. The liquids of a plant, especially those found in the vascular
bundles. The water and dissolved substances transported through
the wood constitute the crude sap; the manufactured foods trans-
ported in the bast are the elaborated sap.

Saprophyte. A plant which obtains its food from dead or decaying
organic materials.

Sapwood: The moist, usually comparatively soft, outer layers of the
wood of the trunk and larger branches of a tree or shrub.

Scion. The shoot or bud which is grafted upon a stock.

Secondary leaf. Any leaf formed later than the primary leaf or leaves.

Secondary root. Any root formed later than the primary root.

Seed. A structure developed from an ovule ; it consists of a small
plant (the embryo), surrounded by nutritive and protective layers.

Seed leaf. The first-formed leaf, or one of the first-formed leaves, of an
embryo.

Seedling. A young plant just beginning to grow from a germinated
seed.

Selection. The choice of plants (or animals) having certain' desirable
qualities, 'to be used as the parents for the next generation ; a
method used in the production of improved strains and breeds.

Self-pollination. The falling or depositing of the pollen from an anther
upon a stigma of the same flower.

GLOSSARY 449

Sepal. One of the outer circle of leaf-like parts of a flower. Most

commonly the sepals are comparatively small and green ; but in

some flowers they are large and white or brightly colored.
Sheath. The basal portion of a leaf which more or less surrounds the

stem, as in the members of the grass family.
Sorus. A spot or region in which spores are formed.
Species. A name applied to a group of plants so nearly alike that they

may be referred to by the same name.
Spermatium. A small spore-like cell produced in great numbers by

the wheat rust and many other rusts. The spermatia seem to be

entirely functionless.
Spike. A dense, elongated flower cluster in which the individual

pedicels are very short.
Spikelet. A small or secondary spike ; used in connection with the

flower clusters of members of the grass family.
Spore. A reproductive cell that can develop into a new plant. In

some of the bacteria, the name is applied to a specially resistant

condition into which an ordinary cell may pass 4
Spore sac. A structure in which spores are borne.
Sporidium. One of the kinds of spores produced by rusts. It is borne

on a very small plant which grows from the germinating winter

spore.
Spring spore. One of the spores of the wheat rust produced on the

barberry, or the corresponding spore of any other rust ; also called

an (zciospore or acidiospore.
Stamen. One of the parts of a flower which bears pollen ; a microspore

leaf.

Staminate. Applied to a flower having stamens but no pistil.
Standard. The large upper petal of the flowers of many of the pulse

family.

Stigma. The upper part of a pistil, on which the pollen grains land.
Stimulus. A change outside a cell or organism which causes a change

in the processes going on within the cell or organism.
Stipule. A leaf-like appendage at the base of a leaf-stalk.
Stock. The basal part of a plant (root, or stem and root) upon which a

graft is made.
Strain. A race or breed of plants or animals. Especially applied to two

sorts (plus and minus strains) to which the plants of the bread mold

and some of its relatives belong. The difference between plus and

minus strains is probably a sexual difference.
Style. The slender, often hollow, portion of a pistil between the stigma

and the ovary.

450 TEXTBOOK OF BOTANY

Summer spore. A spore produced by the rust on the wheat during the
summer, or the corresponding spore of other rusts ; also called a
urediniospore or uredospore.

Tap root. A primary root which persists as the plant grows and which

pushes directly downward.
Tendril. A slender outgrowth, especially of climbing plants, by means

of which the plant may attach itself to neighboring objects.
Terminal. Referring to that part of a structure or organ farthest from

its place of attachment.
Toxin. One of a class of poisonous substances produced by parasitic

bacteria.
Tuber. A thickened portion of an underground stem or branch.

Umbel. A flower cluster in which all the pedicels arise from the peduncle
at about the same level.

Vacuole. A portion of the protoplasm of a cell, surrounded by a mem-
brane, and containing a watery solution of various foods and other
substances.

Variety. A group of plants that are very similar; a sub-division of a
species.

Vascular bundle. A group of conducting cells, consisting either of
wood, bast, or both wood and bast.

Veil. A membrane which for a time attaches the cap of a mushroom
to its stalk, and so covers the gills.

Vein. One of the vascular bundles of a leaf, usually appearing as a
light green line.

Vessel. A long tube produced by the breaking down' of the cross walls
in a row of cells.

Whorl. A circle of three or more leaves borne at the same node.

Wing. One of the lateral petals of the flowers of many of the pulse
family.

Winter spore. A two-celled spore produced by the rust on the wheat,
or the corresponding spore (not in all cases two-celled) of other
rusts; also called teliospore or teleutospore.

Wood. The part of a vascular bundle through which water and dis-
solved substances (usually obtained from the soil) are transported ;
also called xylem,

Zygote. A cell produced by the union of. two gametes.

INDEX

Absorption by roots, 173

Agar-agar, 322

Agaricus campestris, 78

Ailanthus, buds, 216

Air, influence on growth, 185

Air-pores, 101, 120, 139, 243

Alcoholic fermentation, 35-37, 319

Alfalfa, 27, 317

Algae, 32, 39, 312; brown, 49, 50,

51; green, 48, 49; of water sup-
plies, 49; red, 49, 50, 52
Aloes, 244, 299
Amanita muscaria, 81
Amanita panthcrina, 80
Amanita phalloides, 81
Amanita verna, 80
Amaryllis family, 299
Angiosperms, 132, 137, 153, 312;

families of, 295-311
Annual plants, 10, 137, 156, 220, 329
Annual rings, 117, 209, 210
Antherids of fern, 103, 104; of

moss, 86, 88, 89
Antherozoids, of fern, 104, 105 ;

of moss, 89, 90
Anthracnose of bean, 388
Anthrax, 26, 29

Anthurium andreanum, flower, 261
Antitoxin, diphtheria, 24
Apple, crown gall, 376; fire blight,

374, 375; flower, 259; fruit, 284;

rust, 70-72
Arbor vitas, 187
Archegones, of fern, 103, 104, . 105 ;

of moss, 88, 89; of pine, 124,

126, 127

Armillaria mellea, 79
Arum family, 298

Asexual generation, of fern, 105-108 ;
of moss, 86, 90, 91, 93, 107; of
pine, 113, 127, 128, 130, 131

Asexual reproduction, 57

Asparagus, 203

Asparagus rust, 72

Attachment of plants by roots, 174

Autumn colors of leaves, 256

Bacillus, of anthrax, 26; of Asiatic
cholera, 16, 17 ; of chicken cholera,
16; of lockjaw, 18, 21, 26; of
splenic fever, 16; of typhoid fever,
21,25

Bacillus subtilis, 11-15

Bacteria, 11-29, 34, 38, 53, 373~377

Bacterium, of diphtheria, 21, 24;
of tuberculosis, 21, 22-24, 29

Bamboos, 196

Banana family, 300

Banyan trees, 175

Barberry, rust, 60-63

Bark, 118, 171, 213

Barley, root, 170; root hairs, 170,
173; rusts, 69

Basswood, stem, 209

Bast, 115, 116, 117, 138, 209

Bast fibers, 207, 211

Bean, anthracnose, 388; blight,
377; stem, 187

Beans, 137-155

Beech family, 301

Begonia, vegetative multiplication,
171

Beverages, 318

Biennial plants, 176, 220, 330

Birch bark, 215

451

452

INDEX

Birch family, 301

Bittersweet, 338

Blackberry, rust, 72

Black knot, 383, 384

Black molds, 59

Black rot, of cabbage, 376 ; of grapes,
384

Blight of bean, 377

Bordeaux mixture, 72, 380, 381, 382,
385

Brace roots, 157, 159, 175

Bracken fern, 97-108

Bracts, 141, 159, 160, 161, 235

Branches, 186-227; comparison with
roots, 169; of bean, 138; of cu-
cumber, 4, 7 ; of fern, 97 ; of moss,
87, 94; of moss protonema, 92,
93; of pine, 114, 115, 119

Brassica oleracea, 369

Bread mold, 53-59, 94

Breeding of plants, 358-372

Broom corn, 314

Brown rot, 381, 382

Brugmansia, 181

Brussels sprouts, 218, 369

Bryophyllum, vegetative multiplica-
tion, 171

Bryophytes, 312

Buckthorn, rust, 70

Bud scales, 114, 115, 119, 216

Buds, 215-219; adventive, 119, 171,
172, 218; axillary, 7, 216-218;
flower, 7, 215; leaf, 7, 215; of
fern stem, 97 ; of moss protonema,
93; terminal, 6, 113, 114, 115, 156,
216

Bulbs, 201

Burdock, 331

Cabbage, 361, 362, 369; black rot,

376; club root, 377
Cactus family, 307
Cactuses, 204, 245
Cambium, 116, 117, 138, 211; cork,

118, 213

Canada thistle, 328, 331, 334

Cankers, 375

Carbohydrate manufacture, 41, 43,

45, 87, 245-248
Carbohydrates, 42, 43, 55, 291
Catkin, 265
Cauliflower, 282, 369
Cedar, red, rust, 69, 70, 71, 73
Cell, division, 14, 30, 31, 33, 36, 45,

55 ; sap, 41 ; walls, 12, 30, 40
Cereal grains, 313; rusts, 69
Cherry, black knot, 383
Chestnut blight, 385
Chlorophyl, 30, 40, 42, 256
Chloroplasts, 31, 40, 47
Chocolate, 318
Cinchona, 214
Citrullus vulgaris, 10
Cladophora, 48, 49
Classification of plants, 295, 312
Climbing plants, 179, 197, 198
Clover, 27; crimson, 316
Cloves, 282
Club-mosses, no
Club root, 377
Cob of Indian corn, 160
Cocoa, 318
Coffee, 318
Compass plants, 241
Composite family, 155, 310
Conduction, of foods, 99, 174; of

stimuli, 251

Cones of pine, 122, 126, 129, 141
Conifers, 133-135
Conium, 337
Conjugation, in Spirogyra, 46-48;

in wheat rust, 62
Convolvulus family, 309
Coppice growth, 219
Copra, 322

Cork, 112, 170, 211, 213
Cork cambium, 118, 213
Corms, 201
Corn, 156-168; pollination of, 277;

root tip, 169; rust, 70; smut, 385-

387

INDEX

453

Cortex, 115, 118, 138, 208, 211

Corymb, 265

Cotton, 307, 324

Cotton tree, 200

Cranesbill, seed discharge, 289

Cress family, 330

Crocus, corm, 201

Cross-fertilization, 105

Cross-pollination, 147, 276—280, 370

Crowfoot family, 303

Crown gall, 376

Cucumber, 4-10, 294; squirting, 289

Cucumis melo, 10

Cucumis satimis, 10

Cucurbita maxima, 10

Cucurbita moschata, 10

Cucurbita pepo, 10

Currant rust, 72

Cutin, 244

Cuttings, 172, 370

Cycads, 135

Cycas revoluta, 135

Cyme, 265

Cypress knees, 134, 178

Cytoplasm, 40

Damping off fungi, 378

Dasya elegans, 52

Decay, 17

Dicotyledons, 167, 312 ; comparison
with monocotyledons, 168; fami-
lies, 301-311

Digestion, 13, 55

Dioncca muscipida, 238

Diphtheria, 24

Diseases of plants, 373-389

Disease-resistant varieties, 361, 362

Distillation of wood, 356

Division of cells, 14, 30, 31, 33, 36,
45, 55

Dodders, 179, 180

Downy mildew, 379

Dragon tree, 223, 224, 299

Drosera rotundifolia, 237

Dyestuffs, 326

Egg, of bean, 145; of lily, 147;

of fern, 104, 105; of moss, 88, 89;

of pine, 124, 126
Elm, white, 191
Embryo, of bean, 149, 150, 152; of

fern, 105, 106 ; of Indian corn, 162,

163; of moss, 90; of pine, 127,

129; of squash, i, 2
Endosperm, i, 2, 127, 128, 149, 162,

163, 164

Enzyms, 13, 35, 43
Epidermis, 99, 115, 120, 138, 139,, 211
Epiphytes, 182, 183
Euphorbia splendens, 236

Fairy rings, 82

Fall of leaves, 254-256

Families of angiosperms, 295-311

Fats, 55, 164, 320

Female plant, of bean, 145, 146; of
lily, 147 ; of pine, 124, 126, 128

Fermentation, 17, 19, 35, 319

Fern, comparison with pine, 130—132

Ferns, 97-112

Fertilization, in bean, 149 ; in fern,
105; in moss, 90; in pine, 126,
129

Fiber plants, 324-326

Fig, pollination of, 274-276

Fire blight, 374, 375

Flavors, 323

Flax, 305, 325

Flax family, 305

Floral parts, arrangement, 261 ; num-
ber, 261 ; union, 262

Flower clusters, 141, 264-266

Flowers, 258-282 ; of bean, 141-145 ;
of cucumber, 7-9 ; of Indian corn,
159-162

Fames applanatus, 83, 84

Food, in Indian corn kernel, 164;
in seeds, 291 ; manufacture by
plants, 31, 41-43, 245-248; of
bacteria, 12; of bread mold, 55;
of yeasts, 34 ; storage of, 248

454

INDEX

Forage plants, 316

Forestry, 342-357

Forests, Alaskan, 353 ; Canadian,
347,3535 Hawaiian, 353 ; national,
344; of the United States, 344-
346, 351-353; Porto Rican, 353;
private, 346; state, 346

Fruit coat, 10, 163

Fruit, of bean, 151, 152; of cucum-
ber, 9; of Indian corn, 163-165;
of lily, 288

Fruits, 132, 137, 283-290

Fucus, 50

Funaria hygrometrica, 86, 87

Fungi, 37, 312, 373; alga-like, 374;
basidium, 83-85, 374;. bracket,
83, 84; disease-producing, 373;
imperfect, 374; sac, 374

Gametes, male, of bean, 149; of

pine, 126
Gametes, of bread mold, 57; of

fern, 104, 105 ; of moss, 88, 89 ;

of rust, 62, 63 ; of Spirogyra, 46, 47
Germ tube, 64, 67
Ginkgo, 136
Girdling, 214
Gladiolus, corm, 201
Glandular hairs, 231
Gooseberry, rust, 72
Goosefoot family, 302
Gossypium, 307
Gourd family, 10, 310
Gourds, 10
Grafting, 224-227

Grape, black rot, 384 ; downy mil-
dew, 379
Grapes, 306

Grass family, 166, 195, 296
Gravity, influence on growth, 183,

194, 195, 200
Ground hemlock, 134
Growth, of leaves, 228; of roots,

183-185; of stems in length, 186;

of stems in thickness, 115-118,

138, 2.99

Gums, 322
Gutta-percha, 213
Gymnosperms, 132, 153, 312

Habits, formation of, 253

Hairs, 5, 220, 230, 244; glandular,

231

Hay fever, 341
Head, 265

Heartwood, 118, 208
Heath family, 308
Hemp, 326
Herbs, 1 88
Hollyhocks, rust, 72
Honey locust, thorn, 206
Horse-chestnut, fall of leaves, 254;

winter buds, 217
Horse-tails, 109
Husks of Indian corn, 160
Hyacinth, bulb, 201
Hybrids, 280-284, 369-371
Hygrophonis virgineus, 82

Immunity, 25, 26

Indian corn, 156-168; pollination

of, 277; root tip, 169; rust, 70;

smut, 385-387
Indian pipe, 182

Insect pollination, 146-148, 268-270
Integuments, 123, 124, 126, 128,

144, 145, 160
Internodes, 186
Iris family, 300

Jack-in- the-pulpit, flower, 260
Japanese ivy, 205
Jimson weed, 337
Johnson grass, 332
Junipers, rust, 69, 70-72

Kelps, 50, 51

Kernel of Indian corn, 163-165 ;

germination of, 165
Kohl rabi, 369

INDEX

455

Lady's-slipper, pollination of, 271,
272

Lagenaria vulgaris, 10

Lamb's quarters, 330

Larkspur, 339

Late blight of potato, 380

Layering, 172, 173

Leaf mosaic, 239

Leaf, of lily, 139; primary, of fern,
106

Leaves, 5, 228-257; night position
of, 140, 252; of bean, 139, 140,
153; of cucumber, 5 ; of fern,
97, 98, 100, 101, 102, 107; of
Indian corn, 156, 157 ; of moss, 86,
87; of pine, 114, 119, 120, 123,
130; secondary, i, 4, 5, 150, 153;
seed, 1-3, 127, 130, 150, 152, 163,
234

Lenticels, 214, 215

Lettuce, prickly, 240

Light, influence of, on growth, 185,
193, 195, 240

Lilac, buds, 216, 217

Lillum canadense, 239

Lily, bulb, 201 ; family, 298 ; flower,
261; fruit, 288; leaf, 139; ovary,
263 ; wild yellow, 239

Lime-sulphur wash, 382

Liverworts, 95

Living matter, 44

Lockjaw, 26

Loco weeds, 339

Lumber, 356

Lumbering, 354

Lycopodium, no

Macrospore leaves, 123, 124, 128, 144
Macrospore sacs, 124, 126, 144
Macrospores, 123, 124, 145, 146;

germination of, 124
Maidenhair tree, 136
Male plant, of bean, 144, 149; of

pine, 125—127
Mallow family, 307

Mallows, rust, 72

Mandrake, 198

Mangroves, 175, 176

Marchantia, 95

Marsilea, 109

May-apple, 198

Medicines, 324

Medullary rays, 117, 212

Melons, 10

Mendelian laws, 371

Micropyle, i, 123, 126, 127, 144, 150,
160

Microspore leaves, 122, 123, 143

Microspore sacs, 122, 123, 144

Microspores, 123, 125, 144; germina-
tion of, 125, 144

Mildew, downy, 379; powdery, 382

Milkweed, 292

Milky juices, 212

Millet, 313

Mint family, 309

Mistletoe, 180

Mold, bread, 53-59, 94

Molds, 53 ; black, 59

Monocotyledons, 167, 312; com-
parison with dicotyledons, 168;
families of, 296-301

Monotropa, 182

Mosaic, leaf, 239

Moss, comparison with pine, 130-132

Mosses, 86-96

Movements of leaves, 250-252

Mucor, 59

Multiplication, vegetative, 171, 172,
iQ7, 37°

Mushrooms, 74-85

Mustard family, 304

Mutations, 367-369

Mycorhizas, 181

Narcotics, 319

Nectar, 144, 147, 270

Nereocystis, 51

Nettle family, 301

Nightshade, black, 338 ; family, 309

456

INDEX

Nodes, 1 86

Nuclei, 31, 33, 34, 40, 55, 62, 66

Nutation, 187.

Oak, swamp white, 192

Oat, rusts, 69 ; smut, 386, 387

Odors of flowers, 361

Oils, essential, 324; fatty, 320-322;

volatile, 324
Opuntia, 204
Orange, 285
Orchid family, 300
Orchids, epiphytic, 183
Ovary, 8, 9, 137, 144, 159, 160
Ovules, 8, 123, 124, 126, 128, 144,

145, 160

Palisade layer, 139
Palm family, 297
Pandanus, 175
Panicle, 266
Parasitic bacteria, 12
Parasitic fungi, 60, 80, 85
Parasitic seed plants, 179-181
Parsley family, 307
Pasteurization of milk, 20
Peach scab, 388
Pear blight, 374
Pear rust, 73
Peas, 27, 153
Peat mosses, 94
Pedicels, 141, 264
Peduncles, 141, 264
Pepper, 323

Perennial plants, 177, 221, 331
Perfumes, 323
Petals, 8, 9, 142, 148, 260
Phaseolus acutifolius, 155
Phaseolus lunatus, 154, 155
Phaseolus multijlorus, 154, 155
Phaseolus radiatus, 155
Phaseolus vulgaris, 154, 155
Phycomyces, 59
Pigeon grass, 329
Pilobolus, 59

Pine, blister rust, 72; comparison
with bean, 153; long-leaved yel-
low, 352; red (Norway), 352,
356; white, 348, 349, 352

Pineapple, 284

Pines, 113-136

Pink family, 303

Pinus Lambertiana, 133

Pinus palustris, 352

Pinus resinosa, 133

Pinus strobus, 132

Pistils, 8, 141, 144, 159, 160, 263;
rudimentary, 9, 160, 161

Pitcher plants, 236, 237

Pith, 115, 116, 138, 196, 211

Plankton, 51

Plant breeding, 358-372.

Plant diseases, 373-389

Plant products, 313-327

Plum black knot, 383

Pod of bean, 144, 151, 152

Poison hemlock, 337

Poison ivy, 340

Poison oak, 340

Poisonous plants, 80, 81, 337-341

Pollen, 9, 268; as food for insects,
272; of bean, 143, 144, 148; of
cucumber, 9; of Indian corn, 161 ;
of lily, germination, 143 ; of pine,
122, 123; of pine, germination,
125; sacs, 122, 123, 161; tube,
9, 126, 129, 143, 147, 148, 149

Pollination, 266-280; of bean, 146-
148; of Indian corn, 162 ; of pine,
125, 126, 129

Polygonatum, 199

Pond scums, 39

Potato, 314, 358; early blight, 388,
389; late blight, 380; rot, 380;
scab, 387; tubers, 202

Powdery mildews, 382

Pressure, influence on growth, 185

Prickles, 220

Prickly lettuce, 240

Primrose, flowers, 278, 279; leaf
mosaic, 239

INDEX

457

Prop roots, 175, 176
Protection of seeds, 285
Proteins, 41, 43, 150, 164, 291
Protococcus, 30-32, 182
Protonema, 92

Protoplasm, 12, 15, 34, 40, 55
Psalliota arvcnsis, 76
Psalliota campestris, 78
Pteridophytes, 312
Pteris aquilina, 97
Ptomains, 21
Puccinia, 73
Puccinia graminis, 69
Puffballs, 85

Pulse family, 155, 229, 305
Pumpkin, 10
Pure varieties, 366
Putrefaction, 17
Pyrenoids, 40, 42

Quack grass, 332
Quercus bicolor, 192
Quinin, 214

Raceme, 141, 265

Races, specialized, 69

Radish, 176, 187

Rafflesias, 181

Ragweed, 341

Raspberry, 284; rust, 72

Redwoods, 134, 222, 223

Reproduction, asexual, 57; of bac-
teria, 14; of bread mold, 57-59;
of Protococcus, 31; of Spirogyra,
45-48; of yeasts, 33, 36; saxual,
48, 57, 63, 66

Resin of pine, 114, 115, 133

Resin passages, 115, 117, 120

Resins, 322

Respiration, 13, 18, 34, 44, 177, 248-
250

Rhizoids, of fern, 102, 103, 104;
of moss, 87, 88, 93

Rhizophora conjugata, 176

Rhizopus nigricans, 53-59

| Rice, 313, 314
I Rockweed, 50

Root hairs, 3, 4, 100, 121, 170, 173

Roots, 4, 160-185; of bean, 140;
of climbing plants, 179, 198;
of cucumber, 4; of epiphytes,
183; of fern, 98, 100, 106, 107,
108; of Indian corn, 157, 158,
175; of parasitic plants, 179, 185;
of pine, 121, 130; of squash, 2, 3

Rose family, 304

Rose, leaf, 229; rusts, 72

Rotation of crops, 336, 376, 387

Rubber, 212

Rue family, 305

Runners, 204, 334

Ruscus, 203

Rusts, 60-73, 83

Rye, 313; rusts, 69

Saccharomyces, 37

Salix discolor, 189

Salvia glutinosa, pollination of, 269

Saprophytic bacteria, 12, 1 6

Saprophytic fungi, 55, 59, 80, 85

Saprophytic seed plants, 179, 182, 301

Sap wood, 1 1 8, 208

Sargassum, 50

Saxifrage family, 304

Scale leaves, 114, 115, 119, 216, 234

Scales of ferns, 97, 98

Sderoderma vulgare, 85

Screw pines, 1 75

Seaweeds, 49

Sedge family, 297

Seed coats, i, 2, 127, 128, 152, 163

Seed leaves, 1-3, 127, 150, 152, 163,
234

Seed, of bean, 149-152; of bean,
germination, 152; of cucumber,
10 ; of Indian corn, 162-164;
of Indian corn, germination, 165;
of pine, 127-129; of pine, germi-
nation, 129; of squash, i, 2; of
squash, germination, 2, 3

458

INDEX

Seed plants, 132, 137, 312

Seed testing, 294

Seedless fruits, 9, 294

Seedling, of bean, 152; of Indian
corn, 165 ; of squash, 3

Seeds, 281-294, 333

Selaginella, no

Selection, 360, 363-366, 371

Self-fertilization, 105

Self-pollination, 148, 276, 280

Sensitive plant, 250-252

Sepals, 7-9, 142, 148, 151, 260

Sex organs, of fern, 103, 104; of
moss, 86, 88

Sexual generation, of fern, 102, 103,
107 ; of moss, 85-89, 93 , of pine,
124, 125, 128

Sexual reproduction, 48, 57, 63, 66

Shaggy mane (mushroom), 81

Shrubs, 189

Silk of Indian corn, 159, 161, 163

Sleep movements, 140, 252

Slime molds, 373, 377

"Smilax," 203

Smuts, 83, 385-387

Solomon's seal, 199

Soy bean, 317

Spawn, mushroom, 78

Specialized races, 69

Spermatia, 60, 62, 63, 73

Spices, 323

Spike, 265

Spikelets of Indian corn, 159-161

Spirillum, 17

Spirillum of recurrent fever, 16, 17

Spirogyra, 39-49, 57, 59

Spore formation, advantages, 58

Spore leaves, 122, 142

Spore sacs, of bread mold, 54, 56,
58; of fern, 101, 102; of moss,
87, 90-92

Spores, of bacteria, n, 15, 20, 21,
36; of bread mold, 55-58; of
bread mold, germination, 56; of
fern, 101, 102; of fern, germina-
tion, 102 ; of moss, 92 ; of moss,

germination, 92 ; of mushrooms,
77, 79, 81-83; of mushrooms,
distribution, 77; of mushrooms,
germination, 78; of rusts, 60-68,
70-72, 83; of rusts, germination,
64-66, 71 ; of yeasts, 36

Sporodinia, 59

Sports, 368

Spring wood, 117, 209

Spruce, white, 134

Spurge family, 305

Spurges, 338

Squashes, 1-4, 10

Squirrel-tail grass, 330

Stamens, 8, 9, 141, 143, 161 ; rudi-
mentary, 9, 159, 160

Starch, 42, 164, 246, 247

Stem, of bean, 137, 138, 187; of
cucumber, 4; of fern, 97, 98, 99,
106; of Indian corn, 156, 157;
of moss, 87; (trunk) of pine, 113-
119

Stems, 186-227

Sterilization of milk, 20

Stimulants, 319

Stimuli, 183-185, 218, 240

Stipules, 139, 229

Storage in roots, 176

Strains, plus and minus, 57

Strawberry, 283

Streptococcus pyo genes, 16

Sugar beet, 315

Sugar cane, 315

Sugar-producing plants, 315

Sugars, 36, 42, 164, 246, 247, 315

Summer wood, 117, 209

Sundews, 237

Sunflower, 193

Support of plants by roots, 174-176

Tap roots, 121, 130

Tape-grass, 266, 267

Tassel of Indian corn, 159, 161

Tea, 318

Tendrils, 5, 6, 205, 236

INDEX

459

Teosinte, 166

Tetanus, 26

Thallophytes, 312

Thistle, Canada, 328, 331, 334

Thorns, 206, 235, 236

Tissue, false, 77

Tissues, of bean leaf, 139; of bean

stem, 138; of fern stem, 98, 99;

of Indian corn stem, 157; of pine

leaf, 120; of pine stem, 114— 1 18
Tobacco, 319, 320
Toxins, bacterial, 22, 24-27
Trailing stems, 196
Trees, 189; ages of, 224; forest,

301 ; forms of, 190-192 ; size of,

222-224

Trunk of pine, 113-119
Tuberculosis, 22-24
Tuberous roots, 177
Tubers, 202, 334
Tumble weeds, 334
Turpentine, 133, 352, 356
Twig blight, 374
Typhoid fever, 25

Ulmus americana, 191
Umbel, 265

Vacuoles, 33, 34, 41, 55
Vallisneria spiralis, 266, 267
Vascular bundles, of bean, 138, 139,

151, 152; of fern, 99-101; of

Indian corn, 157; of pine, 115,

116, 120, 121
Vaucheria, 48, 49
Vegetative multiplication, 171, 172,

iQ7, 37°

Veins, 5, 101, 139, 158
Veneers, 357
Venus' fly-trap, 238
Vessels, 210-212
Vicia fabd, 155

Vine family, 306
Violet family, 307
Virginia creeper, 205, 206

Walnut family, 301

Water current, 241, 242

Water, evaporation from leaves,
241-245; influence on growth,
185

Water ferns, 109

Water hemlock, 337

Wax, 244, 245

Waxes, 322

Weeds, 328-341

Wheat, axillary buds, 218; durum,
68, 361; macaroni, 68; rusts,
60-68, 73; smut, 387

Willow family, 301

Willow, pussy, 189 ; vegetative mul-
tiplication of, 172

Wilts, 376

Wind pollination, 125, 148, 162, 267

Witches' brooms, 72, 219

Wolffia, 224

Wood, 115-117, 121, 138, 207,
21 1 ; distillation, 356; durability,
208; fibers, 207; hardness, 208;
products, 356, 357; uses, 356;
weight, 208

Yeasts, 33-38

Yucca gloriosa, 273

Yucca, pollination of, 273, 274

Zamia, 135

Zea Mays, 166, 167

Zygote, of bean, 149; of bread
mold, 57, 58; of damping off
fungus, 378; of fern, 105; of
moss, 90; of pine, 127; of rust,
62, 63 ; of Spirogyra, 46, 47

UNIVERSITY OF CALIFORNIA, LOS ANGELES

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