reproduction would hardly have been developed unless it had been of
some benefit to the plants in which it occurs. The chief advantage
seems to be in more rapid multiplication and consequently better
chance to propagate the species, as compared with the slow process
of sexual reproduction were the plant confined to that method alone.
Only one plant is produced by each oöspore, and if this were a
gametophyte with its limited number of archegonia, multiplication
would be slow; but the sporophyte with its millions of spores,
each capable of producing a new individual, enables the species
to multiply indefinitely. At the same time the interposition of a
gametophyte, or sexual generation, secures the introduction of a new
strain with effects analogous to those of cross fertilization.
[Illustration: FIG. 509.—Part of the fruiting stem of a scouring
rush, _Equisetum limosum_, showing the cone-like spore cluster.
(_After_ GRAY.)]
=411. Classification of pteridophytes.=—In our study of this group,
the ferns have been taken as the type because they are the most
familiar and most widely distributed of all the vascular cryptogams.
But while they exceed in numbers, both of individuals and species,
all the other orders combined, they form only one division of three
great groups that make up the class Pteridophyta. These groups are:
(1) ferns, under which are included, besides the true ferns, two
widely differing orders, with the grape ferns and adder’s-tongue in
one, and the water ferns in the other; (2) the club mosses, embracing
the two subdivisions of _Lycopodium_ and _Selaginella_; (3) the
horsetail family, including horsetails and scouring rushes. Orders
(2) and (3) are grouped together as cone-bearing (strobilaceous)
pteridophytes, because their sporangia are clustered in oblong heads,
or _strobiles_ (Fig. 509), somewhat like the cones of the pine. The
orders of pteridophytes differ greatly among themselves, but agree
in possessing certain characteristics that point to their derivation
from a common ancestry.
=412. Distinction between pteridophytes and bryophytes.=—In passing
from the Thallophytes and Bryophytes to the vascular cryptogams, we
cross the widest chasm in the vegetable kingdom—a gap relatively as
great as that between vertebrates and invertebrates among animals.
The most important modifications that discriminate the two groups
are: (1) the presence in Pteridophytes of a highly organized vascular
system accompanied by a well-marked differentiation of the plant body
into root and stem; (2) increased importance and complexity of the
sporophyte with proportionate diminution of the gametophyte.
While vessels for conducting water occur in some of the bryophytes
(403), a well-defined vascular system and true roots are met with
first in the Pteridophytes. The change in the relative importance
of sporophyte and gametophyte is so marked that in Selaginella, the
genus which approaches nearest in structure to the seed-bearing
plants, the suppression of the gametophyte has proceeded so far that
it never leads an independent existence at all and is difficult even
to recognize as a distinct individual.
Practical Questions
1. Have ferns any economic use—that is, are they good for food,
medicines, etc.?
2. What is their chief value?
3. Under what ecological conditions do they grow?
4. Are they often attacked by insects, or by blights and disease of
any kind?
5. Of what advantage is it to ferns to have their stems
underground, in the form of rootstocks? (321.)
6. What causes the young frond of ferns to unroll? (54, 98.)
7. Name the ferns indigenous to your neighborhood.
8. Which of these are most ornamental, and to what peculiarities of
structure do they owe that quality?
9. Are cultivated ferns usually raised from the spores or in some
other way? Why?
10. After the great eruption of Krakatoa in 1883, by which the
vegetation of the island was completely destroyed, ferns were the
first plants to reappear. Explain why. (19; Exp. 17.)
VIII. THE RELATION BETWEEN CRYPTOGAMS AND SEED PLANTS
=413. No break in the chain of life.=—The great gap that was once
supposed to exist between the cryptogams and phanerogams has been
bridged over by the discovery of analogies in the reproductive
processes of the two groups that connect them together as successive
links in one continuous chain of vegetable life. It is therefore very
important to have a clear understanding of the nature and meaning of
these processes, for the chief turning points in the life history of
the different groups of plants are connected with them, their natural
relationships to each other, and their distribution according to
their respective places in the evolutionary scale, being determined
largely by a comparison of their modes of continuing the life of the
group.
=414. Alternation of generations in seed plants.=—This process, so
conspicuous among Bryophytes and Pteridophytes, and not unknown
among Thallophytes, is universal among seed plants (Spermatophytes)
also, though in so masked a form that it is not easy to recognize
without a more detailed study than would be practicable within the
limits of a book like this. Briefly, we may say that the stamens of
spermatophytes, and the pistils, or rather the carpels, which we
have seen to be transformed leaves (298), represent the sporophylls
(406) of the higher pteridophytes. The pollen sacs and ovules are
sporangia, bearing microspores and megaspores (409), represented
respectively by the pollen grains in the anther and the embryo sac
in the ovule. These go through a series of microscopic changes in
the body of the ovule analogous to the production of the oöspore
in the archegonia of ferns and liverworts, but the process is so
obscure that to an ordinary observer the pollen grains and the ovule
appear to be the real gametes, and were long supposed to be such.
The fertilized germ cell in the embryo sac (251) corresponds to
an oöspore; the embryo sac with the endosperm found in all seeds
(previous to its absorption by the cotyledons) is a rudimentary
gametophyte; and the embryo in the matured seed is the undeveloped
sporophyte, destined, after germination and further growth, to
produce a new generation with its recurrent cycle of alternating
phases.
[Illustration: FIG. 510.—Diagrammatic section through the ovule of a
gymnosperm belonging to the spruce family: _i_, integument covering
the ovule; _e_, endosperm (corresponding to female gametophyte),
which fills the embryo sac, containing two archegonia, _a_; _o_, egg
cell; _p_, pollen grains; _t_, pollen tubes entering the neck, _c_,
of the archegonia.]
In the gymnosperms,—pines, yews, cycads, etc.,—which represent the
most ancient and primitive type of existing seed-bearing plants,
the similarity of these processes to those of certain of the
pteridophytes is very striking, and it was through the study of
these that the sequences of the process were traced in the much
more obscure form in which they occur among the angiosperms. From
the endosperm in the seeds of gymnosperms archegonia were found to
be developed (Fig. 510) in much the same way as in Selaginella,
from the prothallium, thus showing the endosperm to be a modified
and greatly reduced gametophyte. In some cases, it has even been
found to protrude a little way out of the embryo sac and to take
on a slightly greenish tinge—another reminiscence of its origin.
Fertilization, too, takes place in precisely the same manner as in
the pteridophytes, except that in all but the ginkgo and the cycads,
the fertilizing cells in the pollen grains are non-motile, and find
their way to the ovule by growing down into the embryo sac with the
pollen tube, instead of swimming to it—an adaptation probably brought
about in response to changed condition during the course of evolution
from aquatic to terrestrial life.
The analogies between the sequence of alternations in the two classes
will be made clearer by a comparison of the accompanying diagrams.
The corresponding terms applied to the various organs stand in
the same vertical row. Diagram (1) shows the process as it takes
place in the more highly developed Pteridophytes; diagram (2) the
corresponding phases in angiosperms.
PTERIDOPHYTES
_mospl_→_mic_→_mo_→_anG_→_ant_→_mg_→
╱ ╲
(1) _S_ _öos_→_S_
╲ ╱
_Mospl_→_Mgc_→_Mo_→_arG_→_arc_→_fg_→
_mospl_, microsporophyll; _mic_, microsporangium; _mo_, microspores;
_anG_, male gametophyte; _ant_, antheridia; _mg_, antherozoids. The
letters in the lower line stand for the corresponding female organs.
SPERMATOPHYTES
_st_→_an_→_pol_→_fc_→ _not_ →_gc_→
╱ _developed_ ╲
(2) _S_ _öos_→_S_
╲ _developed_ ╱
_p_ →_ov_→_em_→_end_→ _only in_ →_ec_→
_gymnosperms_
_st_, stamen; _an_, anther; _pol_, pollen; _fc_, food cells in pollen
grain; _gc_, generative cell; _p_, pistil; _ov_, ovules; _em_, embryo
sac; _end_, endosperm; _ec_, egg cell.
=415. Disappearance of the gametophyte.=—The seed is a comparatively
recent development in plant evolution. It has no counterpart anywhere
among the cryptogams, but is strictly characteristic of the three
great orders of Spermophytes: Monocotyl, Dicotyl, and Gymnosperms,
which compose the greater part of the vegetation of the globe.
Structurally, it is a matured sporangium containing a rudimentary
sporophyte (the embryo), and a reduced gametophyte (the embryo sac),
which, under the form of endosperm, has dwindled to an insignificance
that makes it difficult to recognize it as a phase in an alternation
of generations.
=416. Significance of the sporophyte.=—The gametophyte is obviously a
more ancient and primitive structure than the sporophyte, which first
becomes prominent in the ferns and their allies. The sudden and
violent break in the succession of vegetable life that accompanies
the appearance of the pteridophytes (412) is probably to be explained
by the development of a land flora and the necessity of adaptation to
life in a new medium. The fact that no living cell, whether vegetable
or animal, can absorb nourishment except in a liquid form, seems to
point to an aquatic origin more or less remote for all life. This
inference is further strengthened, in the case of plants, by the
fact that even in so highly organized a group as the pteridophytes,
fertilization cannot take place except in water. Such a requirement
would manifestly be a great disadvantage to land plants, and one of
the first steps in response to the demands of a new habitat would be
to get rid, as far as possible, of the primitive gametophyte with
its outgrown adaptations to a liquid medium, and to transfer the
greater part of the work of reproduction to the asexual generation,
in which the problem of fertilization did not have to be directly
met, the asexual spores germinating without it. The greater the
number of these produced, the better the chance that at least some of
the gametes developed from them would meet the difficult conditions
of fertilization, and the survival of the species be assured. At the
same time, in order to meet the requirements of terrestrial life
successfully, and to provide for continuing the sexual generation,
correlative changes would have to take place in the gametophyte by
which the increasing uncertainty of fertilization due to structural
changes in the sporophyte, and the absence of a liquid medium for
the conveyance of free swimming antherozoids would be avoided. This
necessity has been met by the development of the pollen tube, which
bores its way to the egg cell, carrying with it the generative cells,
which in seed plants have taken the place of the more primitive
antherozoids. With the concomitant reduction of the gametophyte and
development of the seed habit, the adaptation to land conditions has
been made complete.
Roughly speaking, it may be said: (1) that Thallophytes are
predominantly aquatic; (2) Archegoniates (Bryophytes and
Pteridophytes), amphibious; (3) Spermophytes, terrestrial; (4) that
the seed habit is a response to terrestrial conditions; and (5)
that the increased development of the sporophyte was a necessary
adaptation to meet those conditions.
IX. THE COURSE OF PLANT EVOLUTION
=417. Plant genealogy.=—It has been shown by a study of existing
forms of plant life that there is no hard and fast line of division
anywhere between the different groups, but that they are all
connected by ties of kinship more or less defined, according to their
distance from a common ancestral stock. The geological record points
to the same conclusion, and our classification of them into families,
orders, and species is merely a very imperfect genealogical table
of their supposed pedigrees. This does not mean, however, that we
can assert positively that such and such a species is derived from
such or such another, but that both are descended from some common
intermediate form more or less remote. While we have reason to
believe that the flowering plants are derived through pteridophyte
and bryophyte types from some of the green algæ, no direct connection
has ever been traced between any particular kind of flowering
plant and any particular kind of alga,—or between a liverwort and
an alga, for that matter,—and probably never will be, because the
intermediate forms die out, or pass on by variation into other lines
of development. But while this is true, all the evidence we possess
does go to show that, since the beginning of life on the globe, there
has been a general progressive evolution from lower and simpler to
higher and more complex forms.
=418. Retrogressive evolution.=—While the general course of evolution
has been upward and onward, the movement has not always followed
a straight line, but, like a mountain road, shows many windings
and deviations from the direct route. The monocotyls furnish a
conspicuous example of this departure from the general law of
progression. It was formerly supposed, on account of their greater
simplicity of structure, that they were a more ancient type than
dicotyls, but recent investigations point to the conclusion that
they are a later offshoot, derived from some primitive form of
aquatic dicotyl, and represent, not an ancient and primitive stock,
but a case of retrogressive evolution from a higher type. Strong
presumptions in favor of this view are: (1) that various species of
dicotyls show an unequal development of the seed leaves, amounting,
in the bryony, to complete abortion of one of them, while some
monocotyl seeds show morphological characters that can best be
explained as survivals, or inheritances, from a dicotyl ancestor;
(2) the structural resemblances between gymnosperms and dicotyls are
closer than between gymnosperms and monocotyls, which could hardly
be the case if the latter were the more ancient; (3) the geological
record does not show them to have appeared before dicotyls; (4) the
number of cotyledons furnishes no criterion as to the relative age
of any plant group, since all three types are represented among the
pteridophytes, where plants are found bearing one, two, or more
cotyledons.
The theory of their comparatively recent origin from an aquatic
ancestor is further borne out by the many points of similarity
between their internal structure and that of hydrophytes (318), and
also by the great proportion of aquatic plants among them, amounting
to thirty-three per cent, while in dicotyls the proportion is only
four per cent. Can you give any reasons, from your examination of
their internal structure (113, 114), for believing that the line of
development which they have followed is a less effective one for
meeting conditions now existing on the globe than that attained by
dicotyls?
We should remember, too, that while progressive evolution implies
successful adjustment to surroundings, it is possible to conceive of
a state, as our planet approaches the period of cosmic debility and
decay, when the conditions of existence may become progressively more
and more unfavorable. In this case the course of evolution would be
reversed, the higher types gradually dying out as the struggle for
life became more severe, and the tendency would be constantly toward
lower and simpler forms, until finally all life would become extinct
on our planet. We have no right, however, to assume that during such
a course of retrogressive evolution the same forms would be repeated
in reverse order as have already appeared, because there is no reason
to believe that the conditions brought about by planetary decline and
“old age” would be the same as those attending planetary birth and
adolescence.
[Illustration: FIG. 511.—Diagram showing the supposed course of plant
evolution.]
=419. Explanation of the diagram.=—An attempt to show the general
course of plant evolution up to the present time is made in the
accompanying diagram. The four great divisions, Thallophytes,
Bryophytes, Pteridophytes, and Spermatophytes, are represented by
spaces between four horizontal lines arranged one above the other in
the order of their succession in time and complexity of organization.
It should be borne in mind that these dividing lines are not sharply
defined in nature, but overlap or indent the territory between them
with varying degrees of irregularity, like the coast line on a
map. The relative positions of the different orders we have been
considering are represented by upright and diagonal lines, the
general course of which, as indicated by the arrows, is intended to
give an idea of the trend of evolutionary progress in the particular
group represented by each line. No one of these lines is made to
originate directly in any other, because, with the possible exception
of the monocotyls, we have no authority for asserting that any such
direct connection exists between plants as we know them, but only
that certain types give evidence of descent from a common ancestry.
This lack of certainty is expressed by placing the point of origin
for any given line in more or less close proximity to the one which
is supposed to be the nearest living representative of the common
ancestor. The line of ferns, for instance, is depicted as originating
in the region of the bryophytes, somewhere in the neighborhood of
the liverworts, but the two lines nowhere come in contact, because
there is no evidence that any fern, living or fossil, is directly
descended from any particular kind of liverwort known to us. With
these explanations, the diagram shows, in a rough way, the generally
accepted view of plant relationships as based on the evidence at
present before us. But in questions of this sort it is wise to keep
in mind the blunt remark of a famous old American statesman, that
“only fools and dead people never change their opinions.”
Field Work
1. If you live in the country, study the appearance of plants
affected with blights, smuts, rusts, and mildews, and learn to
recognize the different kinds of disease by their signs. Notice
which kinds are most prevalent in your neighborhood, and what
plants are most affected by them.
2. Notice the different kinds of mushrooms you find growing wild.
Observe the difference between those that grow on the ground and
those that grow on logs, stumps, and trees; between those found
in the woods and those in open ground. Find out how those on the
ground get their nourishment. Uncover the mycelium, and notice
the extent of its surface. Examine the soil and find out if it
contains anything upon which they could feed. Note the prevalence
of shelf fungi on trees. Examine the condition of the wood where
they grow, and decide in what ways they injure their hosts. Notice
whether they abound most on healthy or on decaying trunks and
boughs, and decide whether this is because the fungus prefers that
kind of host, or whether the injury it does causes the decay, or
whether both causes operate together. Notice what fungi grow on
different trees, and study their preferences in this respect.
3. Observe the different kinds of lichens found in your walks
and try to distinguish the three classes. Which kind are most
abundant in your neighborhood? Which least so? Note the situations
in which you find each kind growing, whether on stumps, trees,
rocks, or the ground. Consider how the algæ and fungi aid each
other in the different positions; could either, for instance, exist
independently on bald rocks? Notice on what kind of trees the
different lichens seem to thrive best and on which poorly or not at
all, and whether the character of the bark—rough, smooth, scaly—has
anything to do with their choice of a habitat.
APPENDIX
SYSTEMATIC BOTANY
=Taxonomy, or systematic botany=, deals with the family relationships
of plants in the order of their nearness or remoteness with regard
to a common line of descent. Its chief value is the insight it
gives into the course of plant evolution and into the nature of
the modifications that differentiate each group from the ancestral
type. While it is not advisable to spend too much time in the mere
identification of species, a sufficient number should be examined
and described to familiarize the student with the distinctive
characteristics of the principal botanical orders.
=Principles of classification.=—All the known plants in the world,
numbering not less than one hundred and twenty thousand species
of the seed-bearing kind alone, are ranged according to certain
resemblances of structure, into a number of great groups known as
families or orders. The names of these families are distinguished by
the ending _aceæ_; the rose family, for instance, are the _Rosaceæ_;
the pink family, _Caryophyllaceæ_; the walnut family, _Juglandaceæ_,
etc. Each of these families is divided into lesser groups called
_genera_ (singular, _genus_), characterized by similarities showing
a still greater degree of affinity than that which marks the larger
groups or orders; and finally, when the differences between the
individual plants of a kind are so small as to be disregarded, they
are considered to form one species; all the common morning-glories,
for instance, of whatever shade or color, belong to the species
_Ipomea purpurea_. The small differences that arise within a species
as to the color and size of flowers, and other minor points,
constitute mere varieties, and have no special names applied to them.
The line between varieties and species is not clearly defined, and
in the nature of things can never be, since progressive development,
through unceasing change, is the law of all life.
In botanical descriptions, the name both of the species and the genus
is given, just as in designating a person, like Mary Jones or John
Robinson, we give both the surname and the Christian name. The genus,
or generic name, answers to the surname, and that of the species to
the Christian name—except that in botanical nomenclature the order
is reversed, the generic, or surname, coming first, and the specific
or individual name last; for example, _Ipomea_ is the generic, or
surname, of the morning-glories, and _purpurea_ the specific one.
=How to use the key.=—Any good manual will answer the purpose. Gray’s
“School and Field Book” is, perhaps, the best available at present
for the states east of the Mississippi. Reference to the floral
analyses in sections =I-IV= of Chapter VII will make its use clear.
Suppose, for instance, we want to find out to what botanical species
the morning-glory or the sweet potato belongs. Turning to the key,
we find the sub-kingdom of Phænerogams—flowering or seed-bearing
plants—divided into two great classes, Angiosperms and Gymnosperms,
as explained in 18. A glance will show that our specimen belongs
to the former class. Angiosperms, again, are divided into the two
subclasses of Dicotyledons and Monocotyledons (18, 171). We at
once recognize our plant, by its net-veined leaves and pentamerous
flowers, as a dicotyledon (171, 229), and turning again to the key,
we find this subclass divided into three great groups: Sympetalous
(211), called also Monopetalous and Gamopetalous; Apopetalous, or
Polypetalous (211), and Apetalous—having no petals or corolla. A
glance will refer our blossom to the sympetalous or monopetalous
group, which we find divided into two sections, characterized by
the superior or inferior ovary (218, 225). Further examination will
show that the morning-glory belongs to the former class, which is
in turn divided into two sections, according as the corolla is
_regular_, or _more or less irregular_. We see at once that we must
look for our specimen in the group having regular corollas. This we
find again subdivided into four sections, according to the number and
position of the stamens, and we find that the morning-glory falls
under the last of these,—“Stamens as many as the lobes or parts of
the corolla and alternate with them.” A very little further search
brings us to the family _Convolvulaceæ_, and turning to that title
in the descriptive analysis, we find under the genus, _Ipomea_, a
full description of the common morning-glory, in the species _Ipomea
purpurea_, and of the sweet potato in the species _Ipomea batatas_.
=Making collections.=—Mere labeled aggregations of species are not
recommended, but the collection of examples illustrating special
points in morphology and plant variation may be made with profit;
such, for instance, as the adaptations observed in tendrils and
stipular appendages, the various modifications of leaves and stems
to serve other than their normal purposes, or the different forms
of leaves and flowers on the same stem, or on different plants of
the same species. A collection made with some specific object in
view would also be instructive, and might prove of great value; for
instance, to get together examples of all the troublesome weeds of
a locality for the purpose of studying their habits and devising
means for their eradication; or of all the native useful plants, with
detailed analyses of their economic properties, and observations on
their habits and the practicability of further developing them. In
short, wherever collecting is carried on, it should be done with some
object other than the mere identification of species, which often
results in greater detriment to the wild plants of a neighborhood
than profit to the collector.
WEIGHTS, MEASURES, AND TEMPERATURES
As the metric system of weights and measures and the Centigrade
appraisement of temperatures are universally employed in scientific
works, the following tables showing the equivalents in our common
English standards of those in most frequent use, are given for the
convenience of students who have not already familiarized themselves
with the subject. The values given are approximate only, but will
answer for all practical purposes, except in cases where very
great exactitude is required. The micron, or micrometer, is used
principally by scientific investigators for measuring extremely
minute objects seen under the microscope.
MEASURES OF LENGTH
================================+=====================================
METRIC | ENGLISH EQUIVALENTS
-----------------+--------------+-------------------------------------
Kilometer | km. | ⅔ of a mile.
-----------------+--------------+-------------------------------------
Meter | m. | 39 inches.
-----------------+--------------+-------------------------------------
Decimeter | dm. | 4 inches.
-----------------+--------------+-------------------------------------
Centimeter | cm. | ⅖ of an inch.
-----------------+--------------+-------------------------------------
Millimeter | mm. | ¹⁄₂₅ of an inch.
-----------------+--------------+-------------------------------------
Micron | µ | ¹⁄₂₅₀₀₀ of an inch.
-----------------+--------------+-------------------------------------
CAPACITY
-----------------+---------+------------------------------------------
Liter | l. | 61 cubic inches, or 1 quart, U.S. measure
-----------------+---------+------------------------------------------
Cubic centimeter | cc. | ¹⁄₁₆ of a cubic inch.
-----------------+---------+------------------------------------------
WEIGHT
-----------------+---------------+------------------------------------
Kilogram | kg., or kilo. | 2⅕ pounds.
-----------------+---------------+------------------------------------
Gram | gm. | 15½ grains avoirdupois.
| | ¹⁄₂₈ of an ounce avoirdupois.
=================+===============+====================================
METRIC AND ENGLISH SCALES
[Illustration: 10 CENTIMETERS = 1 DECIMETER
100 MILLIMETERS
4 INCHES]
TEMPERATURE EQUIVALENTS
The next table gives the Fahrenheit equivalent, in round numbers, for
every tenth degree Centigrade from absolute zero to the boiling point
of water. To find the corresponding F. for any degree C., multiply
the given C. temperature by nine, divide by five, and add thirty-two.
Conversely, to change F. to C. equivalent, subtract thirty-two,
multiply by five, and divide by nine.
Cent. Fahr.
----------------
100 212
90 194
80 176
70 158
60 140
50 122
40 104
30 86
20 68
10 50
0 32
−10 14
−20 −4
−30 −22
−40 −40
−50 −58
−100 −148
————————————————
Absolute zero.
-273 -459
FOOTNOTES:
[1] Vines, “Lectures on the Physiology of Plants,” p. 282. See also
Sachs, “Physiology of Plants.”
[2] Marshall Ward, “The Oak.”
INDEX
(The numbers, unless otherwise designated, refer to paragraphs.)
Aborted, 220, 291.
Absorption, 58, 71, 72; Exp. 39.
selective, 60.
Accessory buds, 158.
Accessory fruits, 302.
Adaptation, 206, 237.
Adhesive fruits, 20; Exp. 20.
Adjustment of leaves, 196-202.
Adnate, 374.
Adventitious buds, 65, 158.
Adventitious roots, 37, 83.
Æcidium, 362.
Aëration, 319.
Aërial roots, 88.
Aggregate fruits, 301, 303.
Air space, 114, 116, 184.
Akene, 234, 296, 302, 305.
Albumin, 3.
Albuminous, 56.
Albuminous seed, _i.e._, containing endosperm;
Field work, p. 28.
Aleurone, 3.
Algæ, 333, 336-342.
Alternate leaves, 168.
Alternation of generations, 395, 400, 409, 414.
Analogous, 108.
Anatropous, Fig. 26.
Angiosperms, 15, 18; Fig. 511.
Annuals, 91.
Annulus, 372, 405.
Anther, 213, 235; Figs. 270-274.
Antheridia, 389, 394, 398, 407.
Antheridial, 388.
Antherozoids, 389, 392, 395, 416.
Antisepsis, 355.
Arch of the hypocotyl, 42, 44.
Archegonia, 390, 394, 407, 408.
Archegonial, 388.
Archegoniates, 408, 416.
Archegonium, 391, 394, 398.
Asexual generation, 395, 399, 409, 416.
Asexual reproduction, 394, 395.
Asexual spore, 395, 407, 409, 410, 416.
Assurgent, 95.
Axial placenta, 216, 300.
Axil, 100, 166.
Axillary buds, 145.
Axis, 64, 65, 79, 152, 156, 159, 161.
Bacillus, 348, 349.
Bacteria, 333, 345, 347-353.
Bark, 118, 119, 122, p. 128, (3).
Basidia, 375.
Bast, 116, 119, 122.
Berry, 291.
Biennial, 92.
Bilabiate, 237, 243.
Bilateral regularity, 219.
Bilateral zonation, 326.
Black rust, 360.
Blade of leaf, 165.
Biogenetic law, 253.
Biological factors, 309.
Bordered pits, 114, 117; Fig. 123.
Boreal, 329.
Bract, 161.
Bryophytes, 334, 385-401.
Bud scales, 147-149.
Buds, 145, 155-158.
Bulb, 107.
Button (of mushroom), 370.
Calyptra, 399.
Calyx, 211.
Cambium, 115, 116, 120, 123.
Cap, 372, 373.
Capillarity, 136; Exp. 53.
Capitate, 220.
Caprification, 279, 305.
Caprifig, 279.
Capsule, 298.
Carbon, 27, 28, 62.
Carbon dioxide, 29, 63, 185, 186, 187, 189; Exps. 23, 25.
Carpels, 216, 288.
Caruncle, 13.
Catkin, 161.
Caulicle, 46.
Cedar apples, Fig. 456.
Cell, 6, 7.
collecting, 184.
companion, 114.
Cell sap, 7, 110.
Cell wall, 7, 183.
Central cylinder, 67.
Central placenta, 216, 300.
Chalaza, 13.
Chlorophyll, 186, 341, 366.
Chlorophyll bodies, 184, 186, 382.
Cion, 65.
Classification, 90, 252, 283, 343, 384, 411, 417.
Cleistogamic flowers, 272.
Climatic zones, 329.
Climbing stems, 96-98.
Clipped seed, p. 12 (material).
Closed bundle, 114.
Close-fertilized, 272.
Cluster cups, 362.
Coccus (pl. cocci), 339, 348.
Coiled inflorescence, 162.
Collective fruits, 304.
Colony, 316, 337, 357.
Color of flowers, 276.
Compass plants, 199.
Complete flower, 219.
Composite, 235, 381.
Composite flower, 236.
Compound leaf, 178.
Conduplicate, Figs. 159, 160.
Confluent, 404.
Conifers, 117, 327.
Conjugation, 342, 394.
Corolla, 211.
Cortex, 64, 115, 122.
Corymb, 161.
Cotyledon, 11, 12, 18.
Cross cut, 133.
Cross fertilization, 255.
Cross pollination, 255.
Crustaceous lichen, 384.
Cryptogam, 332.
Crystalloids, 60.
Culture medium, 347; p. 306 (material).
Cycle, 217, 219, 229.
Cycle of growth, 50.
Cyme, 162.
Cymose inflorescence, 162.
Cypress knees, 319.
Deciduous, 203.
Declined, 95.
Decurrent, 374.
Definite annual growth, 153.
Definite inflorescence, 160, 162.
Dehiscent fruits, 283, 298.
Deliquescent, 144.
Determinate growth, 153.
Determinate inflorescence, 160, 162.
Diadelphous, 239.
Diastase, 9.
Dichogamy, 269.
Dichotomous, 152; Fig. 155.
Dicotyl, 42, 115, 116, 171, 220.
Dicotyledonous, 12.
Differentiate, 245, 345, 409.
Diffusion, 9, 57.
Digestion, 9.
Dimorphic, 270.
Dimorphism, 270.
Dimorphous, 270.
Diœcious, 268.
Disinfection, 355.
Disk flower, 233.
Dispersal of seed, 19-25.
Dominant, 257, 258.
Dormant buds, 157.
Dorsal; Figs. 390, 391.
Drupe, 292.
Dry fruits, 283, 293-300.
Duct, 67, 111, 114.
Ecological factors, 310.
Ecology, 266, 308, 310.
Edgings, 134.
Egg cell, 251, 391.
Elators, 393.
Embryo, 11.
Embryology, 253.
Embryo sac, 251.
Endodermis, 67 (b).
Endosperm, 11, 13, 14, 16, 17, 414.
Epicotyl, 45, 46, 47.
Epidermis, 64, 115, 122, 183.
Epigynous, 225, 230.
Epiphyte, 87, 394.
Essential constituents, 62.
Essential organs, 212.
Evolution, 242, 245, 265, 334, 335, 401, 414, 415, 417, 418, 419.
Evolutionary, 253, 413.
Excentric attachment, 372.
Excurrent, 144, 154.
Factors, 54, 265, 310.
Fall of the leaf, 203.
Fascicled roots, 80, 81.
Fats, 1, 3, 4.
Feather-veined, 172.
Ferments, 9, 356.
Fertile, 404.
Fertile flower, 267.
Fertilization, 247, 251, 252, 392, 408, 416.
Fibrous roots, 37, 78, 80, 81.
Fibrovascular bundle, 67, 114, 116, 176, 288.
Fig wasp, 279.
Filament of the stamen, 213;
a hairlike appendage, 341, 361, 369, 393, 396.
Filamentous algæ, 340, 341.
Fission, 338, 394.
Fleshy fruits, 283, 288-292.
Floral envelopes, 211.
Foliaceous lichen, 379, 384.
Follicle, 298.
Forestry, 139-142.
Forked stems, 152.
Formation, 316.
Free, 218, 374.
Free central placenta, 216.
Free gills, 374.
Free ovary, 218.
Free veining, 402.
Freezing, 33.
Frog’s spit, 340.
Frond, 402.
Fruit, 282.
Fruticose lichen, 384.
Function, 41.
Fungi, 333, 343, 344, 345, 346, 378.
Fungus, 86, 364.
Gametes, 394.
Gametophyte, 394, 395, 396, 406, 407, 410, 412, 414, 415, 416.
Gemmæ, 387.
Generative cell, 249, 416.
Geophilous, 321.
Geotropism, 51, 52, 53.
Germ, 2, 11.
Germ cell, 251, 414.
Germination, 32, 35; Exps. 25, 26-29.
Germs, 352, 355.
Gills (of mushroom), 374.
Girdling, 131.
Glutin, 3.
Gourd, 14, 290.
Grain, 11, 297.
Grain of timber, 133, 134, 135.
Gravity, 52.
Growth, 48-52, 179.
Guard cell, 183.
Gymnosperms, 15, 18, 117, 414.
Gymnosporangium, Fig. 456.
Halophyte, 317, 323.
Haustoria, 85.
Hay bacillus, 348, 349.
Head, 161.
Heartwood, 131.
Heliotropic, 200.
Heliotropism, 198.
Herbaceous, 90, 94, 115, 116.
Heredity, 264, 265.
Hilum, 12, 13, 14.
Homologous, 108.
Host plant, 85.
Humus, 75, 86.
Hybrid, 256.
Hybridization, 256, 257, 263.
Hydrophytes, 317, 318, 319.
Hymenium, 375.
Hymenomycetes, 375.
Hyphæ (sing. hypha), 369, 380.
Hypocotyl, 11, 12, 14, 46.
arched, 42, 44.
straight, 44.
Hypogynous, 218, 225.
Imbibition, 136.
Imperfect flower, 219, 231, 267.
Impure hybrid, 258, 259.
In-breeding, 254.
Incomplete flower, 219.
Incubation, 354.
Indefinite annual growth, 153.
Indefinite inflorescence, 160, 161.
Indefinite number of parts, 229.
Indehiscent fruit, 283, 294.
Indeterminate growth, 153.
Indeterminate inflorescence, 160, 161.
Indusium, 404.
Inferior ovary, 221, 225.
Inflorescence, 159.
Insectivorous plants, 208-210.
Internode, 46, 110; Exp. 35.
Invasion, 328.
Inverted seed, 14.
Involucre, 161, 232.
Involute, 373; Fig. 251.
Iodine solution, Exp. 3.
Irregular flower, 219, 237.
Irritability, 201.
Joint, 110, 113.
Keel, 238.
Knots, 137.
Lamina, 209.
Laminæ, 368, 374.
Lateral, 372, 398.
Lateral buds, 145.
Leaf attachment, 167.
Leaf cups, 202.
Leaf scars, 146.
Leaf traces, 146.
Legume, 299.
Lenticels, 106, 118, 288.
Lichen, 379.
Life cycle, 359, 364.
Loam, 75.
Lobing, 177; Figs. 210-212.
Locule, 216.
Loment, Fig. 394.
Lyrate, Fig. 197.
Medulla, 119, 122.
Medullary rays, 64, 116, 121, 122, 134, 135.
Megasporangia, 409.
Megaspore, 409, 414.
Mendel’s law, 258.
Mesophyte, 317, 324.
Metabolism, 193.
Microbe, 351, 355.
Micrococcus, 339.
Micropyle, 12, 13, 14, 15, 45.
Microsporangia, 409.
Microspore, 409, 414.
Midrib, 172.
Mixed forest, 139, 324.
Modification, 100-108, 206, 207, 289.
Molecule, 136.
Monadelphous, 239.
Monocotyl, 110, 112, 171, 217, 221, 418.
Monocotyledonous, 11.
Monœcious, 268.
Monopetalous, 211.
Monosepalous, 211.
Morphology, 108.
of the flower, 244.
Mosaic (leaf), 197.
Mosses, 334, 396-401.
Muck, 75.
Multiple fruit, 304, 305.
Mushroom, 333, 367.
Mutation, 264.
Mycelium, 343, 359, 369.
Mychorrhiza, 86.
Neck canal, 391.
Net-veined, 171.
Neuter, 267.
Neutral flower, 231, 267.
Nitrogen, 62, 63, 188.
Nitrogenous food, 188.
Node, 46, 65, 110, 113.
Nucleus, 7, 341.
Numerical plan, 217, 229.
Nut, 295.
Nutriment, 3, 186.
Nutrition, 50, 54, 179, 193.
Nyctitropic, 200.
Obsolete, 220.
Oil, 1, 3, 8.
Oöspore, 393, 394, 395.
Open bundle, 116.
Operculum, 399.
Opposite leaves, 168.
Organ, 41.
Organic foods, 4.
Organs of reproduction, 40.
of vegetation, 40.
Osmosis, 56, 57.
Ovary, 214, 216, 223.
Ovule, 216.
Oxidation, 27; Exps. 21, 22.
Oxygen, 62, 63, 186, 187; Exps. 22, 66.
Palisade cells, 184.
Palmate veining, 172.
Panicle, Fig. 171.
Papilionaceous, 237, 238.
Pappus, 234.
Parallel veining, 171.
Paraphyses, 375, 398.
Parasitic, 5, 345, 364.
Parasitic plants, 85, 343, 382.
Parenchyma, 110, 114, 115.
Parietal, 216.
Pathogenic, 352, 353.
Pedicel, 159.
Peduncle, 159, 288.
Pentamerous, 229.
Pepo, 290.
Perennial, 93.
Perfect flower, 219.
Perianth, 211.
Pericarp, 288.
Perigynous, Figs. 301, 302.
Persistent, 166.
Petals, 211.
Petiole, 165.
Phanerogams, 331, 332.
Phloem, 114, 116.
Photosynthesis, 186, 192, 193.
Phototropism, 195.
Phyllotaxy, 168, 169.
Pileus, 373.
Pinna, 402.
Pinnate veining, 172.
Pinnule, 402.
Pioneer plant, 316, 319, 320.
Pistil, 212, 214, 223, 228, 240.
Pistillate, 267.
Pitcher plant, 209.
Pith, 110, 115, 116, 119, 121, 122.
Pitted ducts, 114.
Placenta, 216, 288, 298, 300.
Plant society, 316.
Plasmolysis, 59.
Pleurococcus, 337.
Plicate, 155.
Plumule, 11, 12, 14, 45, 46.
Pod, 298.
Pollen, 213.
Pollen grains, 213.
Pollen sac, 213.
Pollen tubes, 249, 250.
Pollination, 215, 247.
Polycotyledons, 15, 45.
Polymorphic, 365.
Polymorphism, 365.
Polypetalous, 211.
Polysepalous, 211.
Pome, 288.
Prefoliation, 155.
Primary, 396.
Primary root, 42, 79.
Pronuba, 278.
Prostate, 95.
Protection, 199, 204, 207, 280, 287.
Proteins, 3, 8, 33, 188, 204.
Prothallium, 407.
Protonema, 396.
Protoplasm, 6, 7, 57, 58, 67, 110, 116.
Pteridophytes, 335, 411, 412.
Puccinia, 360.
Pure dominant, 258, 259.
Pure forest, 139, 324.
Pure recessive, 258, 259.
Pycnidia, 363.
Quartered cut, 135.
Raceme, 161.
Rhachis, 178.
Radial section, 132, 135.
Radicle, 46.
Rhaphe, 13.
Ray, 161, 391.
Ray flowers, 231.
Receptacle, 211, 288, 289, 388, 390, 398.
Recessive, 257, 258.
Red rust, 359.
Regular flower, 219.
Reproduction, 338, 351, 358, 383.
Respiration, 30, 31, 191, 192.
Resting spore, 338, 342, 358, 394.
Reticulation, 172, 402.
Retrogressive evolution, 418.
Revolute, 373, 404.
Rhizoids, 379, 386.
Rhizome, 105.
Ringing, 127.
Rings of growth, 122, 123, 134, 135.
Rogue, 260.
Root cap, 39.
Root hairs, 38, 67.
Root pressure, Exp. 49.
Root pull, 69.
Rootstock, 105.
Root system, 89.
Root tubercles, 63, 300.
Rosette, 197.
Rotation of crops, 24, 327.
Runner, 95.
Samara, 296.
Sap movement, 125, 126, 128, 129.
Saprophyte, 86.
Sapwood, 131.
Scale leaves, 101, 106, 107, 147-149, 207.
Scape, 107, 159.
Scorpioid inflorescence, 162; Figs. 173-176.
Screenings, 20; p. 28, Qn. 22.
Secondary roots, 37, 42, 79.
Seed, 11-18, 332, 415.
Seed coat, 12, 14, 15, 43.
Seedless fruits, 285, 286.
Seedlings, 36, 42, 43, 45.
Seed plants, 331, 414.
Seed vessel, 282.
Selection, 260, 265, 286.
artificial, 262.
natural, 261.
Self-fertilization, 254, 271.
Sepals, 211.
Sessile, 167, 214.
Seta, 399.
Sexual generation, 395, 396, 406, 410, 416.
Sexual reproduction, 394, 395, 410.
Sheath, 67, 116.
Shrinking of timber, 136.
Sieve tube, 114.
Slabs, 134.
Sleep movements, 200.
Soils, 75, 77.
Sori, 404.
Spathe, 221.
Specialization, 237.
Spermatophytes, 331, 335, 394, 414.
Spermatozoid, 389.
Spermogonia, 363.
Spike, 161.
Spirillum, 348.
Spirogyra, 341.
Sporangia, 390, 405.
Spore, 332, 349, 350, 377, 406, 410.
Spore case, 390, 393, 405.
Spore print, 376.
Sporidium, 361.
Sporogonium, 393, 399.
Sporophyll, 406, 414.
Sporophyte, 393-395, 399, 406, 410, 412, 414, 416.
Sport, 264.
Stamen, 212, 213.
Staminate, 267, 268.
Staminodia, 244.
Standard, 238.
Starch, 3, 4, 187, 204, 288; Exps. 69, 70.
Stems, 90-99.
Sterile flower, 267.
Sterilization, 354.
Stigma, 214.
Stigmatic surface, 223.
Stimulus, 98, 186, 201.
Stipe, 240, 372, 402.
Stipule, 149, 165, 166.
Stolon, 95.
Stoma, 181, 182, 183.
Stomata, 181, 182.
Stone fruit, 292.
Storage of food, 2, 3, 4, 17, 70, 103, 104-107, 287.
Strangling fig, 88.
Strobile, 411.
Strobiliaceous, 411.
Style, 214.
Succession, 327.
Sugars, 3, 4, 204, 288.
Summer spores, 360.
Sundew, 210.
Superior ovary, 218, 221, 225.
Supernumerary buds, 158.
Suppressed, 220.
Survival of the fittest, 261.
Suture, 216, 298, 299.
Swarm spore, 349.
Swelling of timber, 136.
Symbiosis, 309, 382.
Symmetrical flower, 219.
Sympetalous, 211.
Syncarpous, 300.
Synsepalous, 211.
Systematic botany, _see_ Appendix.
Tangential cut, 132, 134.
Tap root, 79.
Teleutospore, 360.
Tendril, 96, 97.
Terminal bud, 145, 154.
Testa, 14.
Thallophytes, 333.
Thallus, 333, 341, 343, 379, 380, 381, 385.
Tillage, 76.
Tissue, 60, 61.
Toadstools, 367.
Toxins, 345.
Tracheids, 114, 117.
Trailing, 95.
Trama, 375.
Transpiration, 179, 180.
Trifoliolate, Figs. 215, 216.
Trimerous, 217.
Trimorphic, 270.
Tuber, 106.
Tumbleweeds, 23.
Turgidity, 7.
Turgor, 179.
Twining, cause of, 98; Exp. 55.
Twining stems, 96; Exp. 54.
Type, 18, 260, 263, 265, 336, 411.
Umbel, 161.
Umbonate, 373.
Underground stems, 104-107.
Unicellular, 337.
Unisexual, 267.
Uredo, 359.
Uredospore, 359, 360.
Variation, 263, 264, 265.
Vascular bundles, 111.
Vascular cryptogams, 403, 411, 412.
Vascular cylinder, 64.
Vascular system, 111, 113, 335.
Vegetative reproduction, 358.
Veil, 371.
Veins, 173-176.
Venter, 391.
Ventral, Figs. 390, 391.
Vernation, 155.
Vessels, 111.
Vexillum, 238, 239.
Vibrio, 348.
Vitality of seeds, 34; Exp. 30.
Volva, 371.
Water roots, 39, 84.
Whorled leaves, 168.
Wind pollination, 274, 275.
Wings, 238.
Winter spores, 360.
Xerophyte, 317.
Xerophyte societies, 317, 320-322.
Xylem, 114, 116.
Yeast, 356.
Yeast colony, 357.
Yellow trumpets, 209.
Yucca, 278.
Yucca moth, 278.
Zonation, 325, 327.
bilateral, 326.
concentric, 326.
horizontal, 326.
vertical, 326.
Zones of vegetation, 325.
TRANSCRIBER’S NOTE
Obvious typographical errors and punctuation errors have been
corrected after careful comparison with other occurrences within
the text and consultation of external sources.
Some hyphens in words have been silently removed, some added,
when a predominant preference was found in the original book.
Except for those changes noted below, all misspellings in the text,
and inconsistent or archaic usage, have been retained.
p. 45: ‘many of them has’ amended to ‘many of them have’
p. 281: ‘are adpated’ amended to ‘are adapted’
p. 291: ‘and as it can, moveover’ amended to ‘and as it can, moreover’
p. 354: ‘eruption of Krakatao’ amended to ‘eruption of Krakatoa’