SECTION II. PHANEROGAMIA
The Transition from the Cryptogams to the Phanerogams
475
Scheme of Alternation of Generations .
479
Morphology anu Okuology of the PnANEROGAMtc Flower and of its
Sexual Generation
480
The phanerogamic flower .
480
Inflorescences
489
Floral oecology
493
Development of the Sexual Gkneii ATlON in THI' Phanerogams
502
The seed
515
Distribution of seeds
520
Germination .
523
Arrangement of Classes, Orders, and Families
525
Gymnospermae .
528
Cycadinae .
528
Ginkgoiuae .
530
Coni ferae
531
Gnetiuae
540
Fossil Gymnosperms .
540
BOTANY Angiospeumae . Si'B-ClASS I. DiCOTYLAE Series I. Clioripotalae A. Monoclilamydeae Verticillatae Juglandiflorae Querciflorae Salicillorae Urticiuae Loranthiflorae Piperinae Hamamelidiuae Tricoccae Centrospermae B. Dialypetalae Polycarpicae Rhoeadiuae Cisti florae Columniferau Gruinales Sapiudinae Prauguliiiae Saxifraginae Rosiflorae Leguminosae Passifloriuae Thymelaijiuae Myrtiflorae Umbelliflorae Series II. Sympetalae A. Pentacyclicae Ericiuae Diotjpyrinae Primulinae B. Tctracyclicae Coutortae Tubi florae Personatae Rubiinae Canipanulinae Aggregatae Sub-Class II. Munocutylae Helobiae Gluniillorau
CONTENTS
XI
Spadiciflorae Enaiitioblastae LiliiHorae Scitamineae Gynandrae Fossil Anghosperms
PAGE 693 t)99 700 709 711 714
Index of Literature
717
....... Systematic Index of Official and Poisonous Plants Index
741 745
INTRODUCTION
It is customary to place all living beings in either the animal or vegetable kingdoms, but in reality a sharp boundary line between animals and plants first becomes possible when they exhibit a complicated structure. In those of more simple organisation all distinctions disappear, and it becomes difficult to define the exact limits of Botany and Zoology. This, in fact, could scarcely be otherwise, as all the processes of life, in both the animal and vegetaljle kingdoms, are dependent on the same substance, protoplasm. With more complicated organisation, the specific differences increase, and the characteristics distinguishing animal from vegetable life become more obvious. For the present, it must be confessed, the recognition of an organism, as an animal or a plant, is dependent upon its corresj^ondence with an abstract idea of what a plant or animal should be, based on A certain points of agreement between the members of each class.
satisfactory basis for the separation of all living organisms into the categories of animals or plants can only be obtained when it is shown that all organisms distinguished as animals are in reality genetically connected, and that a similar connection exists between all plants. The proof of this can only be arrived at through the THEORY OF
EVOLUTION.
From the study of the fossil remains and impressions of animals and plants, it has been established that in earlier epochs forms of life differing from those of the present age existed on the earth. It is also generally assumed that all living animals and plants have been derived by gradual modification from previously existing forms. This
leads to the further conclusion that those organisms possessing closely similar structure, which are united as species in a genus, are in reality related to one another. It is also probable that the union of corre-
sponding genera into one family and of families into higher groups serves to give expression to a real relationship existing between them. The presumable origin of a living organism from others previously existing has been distinguished by Haeckel (^) as its phylogeny. He termed the series of changes passed through by a living being in
1
B
BOTANY
attaining its mature condition, its ontogeny. The supposition, that the successive steps in the ontogenetic development of an organism
correspond to those of its phylogenetic development, and that the
ontogeny of an organism is accordingly a more or less complete
repetition
of
its
phylogeny,
was
asserted
by
Fritz
Muller (-),
Avho
based his conclusions on the results of comparative research.
The idea of the gradual evolution of higher organisms from lower
was familiar to the Greek philosophers, but a scientific basis was first
given to this hypothesis in the last century. Through the work of Charles Darwin ('') in particular, who accumulated evidence for a
reconsideration of the whole problem of organic evolution, the belief
in the immutability of species has been overturned. Darwin sought to explain the origin of species by natural causes,
laying chief weight on a process of selection. In drawing his con-
clusions, he proceeded from the variability of living organisms, as
shoMHi by the fact that the offspring neither exactly resemble their
parents nor each other. Further, he called attention to the constant
over-pioduction of offspring, the majority of which must inevitably
be destroyed. If this were not so, and all the young produced by
even a single pair attained their full development, they would, in a
few generations, completely cover the whole surface of the earth. On account of insufficient space for all, the different claimants are
engaged in an uninterrupted struggle, in which the victory is gained
by those that, for any reason, have an advantage. Through this " struggle for existence " a selective process goes on among the
characters appearing in individual variations, and those which under
the conditions of life are in any way advantageous tend to be preserved. In this manner Darwin arrived at the supposition of a process of natural selection, which is the essential of his theory. Newly developed peculiarities must be inherited in order to become
permanent characteristics of a later generation. Darwin sought in
the experience of breeders evidence that such characters are inherited.
The breeder selects individuals presenting any desired characters for
the purpose of breeding, and has thus formed the races of domesticated
animals and cultivated plants. These have often departed so widely from their wild ancestral forms that the latter are not certainly known. Natural selection will work in the same way as this artificial selection
and, by repeated choice of individual peculiarities, which can be
inherited and thus combined with the pre-existing characters, can give
rise to new forms ;
these ultimately may depart widely from
the
ancestral form. By the continued operation of natural selection, organisms must result, which are, in the highest degree, fitted and
adapted to their environment. In this way the theory of selection seeks to explain as due to natural causes that adaptability to the environment which is such a striking characteristic of organic life. That the transitional forms in this process of phylogenetic development
INTRODUCTION"
no longer exist, is accounted for in the theory of natural selection by the assumption that the struggle for existence must necessarily have been most severe between similar organisms. For similar organisms have similar needs, and the new and better-equipped forms must ultimately prevail over the original less specialised organisms and exterminate them.
Since the publication of Darwin's works many investigators have laboured to advance and make clear our views on phylogeny.
Difficulties in applying the results of artificial selection to the natural
process became evident, for one main condition of successful artificial
selection, the isolation of the organisms from which breeding is taking
place, is not fulfilled under natural conditions. It might be expected
that the new form would disappear by crossing with other individuals,
A but recent work on heredity has minimised this difficulty.
newly
acquired character reappears in a portion of the descendants even
after crossing, and can thus, if advantageous, be selected. Hugo DE
Vries has endeavoured to obtain an insight into the laws of phylo-
genetic development by systematic cultivation of particular plants.
It would appear from such cultures {*) that the starting-point for the
origin
of
new species
is not
afforded
by the
" fluctuating variations,"
which continually occur, but by more marked variations which have
been
termed
" mutations " ;
these
mutations
appear suddenly and
are
inherited, reappearing according to special laws of heredity in the progeny. De Vries tended to assume the existence of a development
of the organic world due to original innate capabilities of the living substance, and not dependent on selection. The origin of the large subdivisions of the animal and vegetable kingdoms, the "archetypes," would be due to this sort of evolution {^). The organisms have been,
and are still, continually influenced by the environment, and by their
reaction to external conditions have become more or less directly adapted. In this way striking resemblances in external form have
arisen between organisms living under similar conditions although
belonging to different archetypes (''). Natural selection exercises a
constant influence on the process and tends to render species distinct
by removing the less advantageous valuations.
If the higher organisms have been evolved from the lower, a
sharp distinction between plants and animals is excluded. For the
characters which are distinctive of animals and plants have appeared
in the course of the phylogenetic development of organisms, and were
at first wanting. The simplest organisms which now exist are in
all probability similar to those which formed the starting-point of this development. The walls which surround the cells composing the plant body, and the green chromatophores within the latter,
are important indications of the vegetable character of an organism. Surrounded by firm walls, the living substance becomes more
isolated, and, consequently, independence of action in plants, as
BOTANY
compared with animals, is diminished. By means of the green colouring matter, plants have the power of producing their own nutritive substances from certain constituents of the air and water,
and from the salts contained in the soil, and are thus able to exist
independently ; while animals are dependent, directly or indirectly, for their nourishment, and so for their very existence, on plants.
Almost all the other differences which distinguish plants from animals may be traced to the structure of plants, or to the manner in which they obtain their food. Another characteristic of plants is the unlimited duration of their ontogenetic development, which is continuous, at the growing points during their whole life. That none of these criteria are alone sufficient for distinguishing plants from animals is
evident from the fact that all the Fungi are devoid of green pigment,
and, like animals are dependent on substances produced by green plants for their nourishment. On the borderland of the two kingdoms, where all other distinctions are wanting, phylogenetic re-
semblances, according as they may indicate a probable relationship
with plants or animals, serve as a guide in determining the position of
an organism. While it is thus impossible to distinguish sharply the two great groups of living organisms from one another, a distinction between them and lifeless bodies is readily recognised. Living organisms are
endowed Avith the quality of irritability, in which all lifeless bodies
are deficient. External or internal stimuli influence living organisms
to an activity, which is manifested in accordance with the requirements and conditions of their internal structure. Even in the
smallest and simplest known organisms the manifestations of life are
occasioned by a similar sensitiveness to external or internal stimuli. It is, therefore, probable that the lowest living beings must have possessed essentiall}'^ simpler properties than any organisms now known, which would enable lis to connect them with non-living substances. The substance Avhich serves as a basis for all development must be supposed to have had an inorganic origin. So far as is actually known, however, all living organisms have arisen only from similar organisms. So far as experience has shown, spontaneous generation is unknown. In the olden times it was a common sup- position, which Aristotle himself held, that even highly organised animals and plants could originate from sand and mud. In the same degree that knowledge of the actual development of living organisms was extended, the previously accepted cases of spontaneous generation became more and more restricted, and were finally limited to intestinal worms which could not otherwise, it Avas thought, be accounted for, and to microscopic organisms, the origin of which also was not understood. Now, for such organisms the possibility of a spontaneous generation has been disproved by more modern investiga-
tions ;
the history of
the
development of
intestinal Avorms
is
knoAvn,
INTRODUCTION and the germs of minute organisms have been found to exist every- where. Schwann and Pasteur have been pioneers in this work, and have shown that it is possible to hinder the development of the lower organisms, in places where it is customary to find them, by destroying all existing germs and at the same time preventing the entrance of new ones. It is due to the results obtained by these men in their investigations on spontaneous generation that we are now able to preserve food in a scientific manner. The germs previously existing in the substance to be conserved are destroyed by heat, while, by a proper mode of sealing, the entrance of new germs is rendered impossible, and the decomposition, which their presence wovdd occasion, is accordingly prevented. All known living organisms have been derived from other living organisms. But the idea of the origin of living from dead substances on the other hand derives important su^iport from the progress of chemical research. In the early decades of the last century it was customary to draw a distinct line of separation between organic and inorganic chemistry, and to assume that the substances dealt with by organic chemistry could only be produced by the vital action of organisms. The laws governing inorganic chemistry appeared to have no reference to organic chemistry, the formation of organic substance being due to a special force, the "vital force." In 1828 WOhler obtained urea from ammonium cyanate, and thus for the first time produced an organic compound from an inorganic substance. In 1845 KoLBE completely synthesised trichloracetic acid, and in 1850 Berthelot synthesised alcohol and formic acid. The former substance had been synthetically prepared by Hennel in 1828, but Berthelot was the first to recognise its identity w^ith the substance formed in alcoholic fermentation. By these results the former distinction between organic and inorganic chemistry was destroyed. Organic chemistry has become the chemistry of carbon compounds. Recently Emil Fischer has synthesised sugars, and attacked the problem of the synthesis of albuminous substances. In some such way it is possible that living matter originated from non-living at some period in the evolution of the earth when the conditions for its formation existed. In order that the organic Avorld should have developed from the first living matter, one of the original properties of the latter must have been a capability of continued existence among its surroundings. It must have been capable of variation and of retaining the new characters appearing in this way, of growth, i.e. the increase of itself at the cost of foreign substances, and of reproduction, ie. multiplication by separation into a number of parts. Some observers have recently described the origin of microscopic structures, which behave similarly to living beings, in bouillon and other organic culture media when exposed to the action of radium ("). i
BOTANY
Botany, or the science of plants, may be divided into a general
and a special part. In the general part, the structure and functions
of
plants
as
such will
be
considered ;
in the
special part,
their parti-
cular structure and functions in the separate divisions of the
vegetable kingdom will be discussed.
The study of
the
structure of
plants is called
MORPHOLOGY ;
that
of the causes of the vital phenomena of plants Physiology. To
these may be added the study of the vital economy of plants, their
OecoloGY.(^) Physiology attempts to explain the processes of life causally. The teleological point of view is, on the other hand, adopted by oecology, which is mainly concerned with the relation of organisms to their environment.
In the general part of this text-book, the morphology and physiology of plants will be considered in relation to examples selected from the vegetable kingdom. In the special part, the various families of plants, with their special morphology, physiology, and oecology, will be
described in order.
PAET I GENERAL BOTANY SECTION I MORPHOLOGY
GENERAL BOTANY